Patent Application
20240327732
More and more it is becoming difficult to dispose of solid waste products, not only from current ongoing operations (such as sewage treatment), but also stores of legacy waste products from past (and present) operations such as coal mining (waste products: “garbage” coal, fine refuse), coal burning (waste product: coal-ash or fly ash) and hardrock ore mining (waste product: mine tailings). Not only is the cost of treating these waste products becoming very high, but even finding a location where the waste products can be disposed of is becoming very difficult. Certain waste products (e.g., sewage sludge) can be heat treated in furnaces and the like to render them non-toxic, but this requires a significant amount of energy to do so. In general, treating solid waste products is an energy-intensive exercise. In some instances the waste product can be sequestered, such as by encapsulating it in Portland-cement based concrete. However, the inclusion of waste products into the Portland-cement based concrete mix almost inevitably results in compromising the strength of the concrete (unless very small portions of the waste product are added, which renders the practice impractical for disposing of large volumes of waste product).
In addition to the solid waste generated by the burning of coal (i.e., mostly fly ash), the mere process of mining coal generates significant volumes of solid waste. In fact, for every ton (2000 lb) of useful coal generated, it is estimated that an additional 800 lb of coal waste is produced. This coal waste (also known as coal refuse, coal tailings, and “gob”—short for “garbage of bitumen”) frequently includes low grade coal, coal fines, rock and soil, is generally unfit for use in most coal fired power plants. Consequently it is accumulated in tailings piles or soil tips. These piles of coal waste can have significant negative environmental consequences, including the leaching of metals into waterways and ground water. The coal waste piles can also create a fire hazard, with the potential to spontaneously ignite. It is therefore desirable to find a way to safely and economically dispose of these coal waste piles.
Biochar is the lightweight black residue, made of carbon and ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as “the solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment”. Biochar is a carbon-rich (65-90%) material that possesses a porous structure of char particles. A common biomass used to produce biochar is waste wood, such as from forestry and construction. Biochar has many potential uses, such as a soil supplement, a water filtration bed (such as a bioswale), and as a substitute for plastic fillers in carbon reinforced products. However, biochar is typically fragile (low compressive strength), and so tends to break apart during transit from the point of manufacture to the point of end use, resulting in fines which cannot be used and must be disposed of.
Disposing of these various waste products is a significant problem. Oftentimes the only apparent solution is merely to move the waste product from one location to another (such as a long-term impoundment), which does nothing to address the problem of actual disposal of the product. Other times the typical solution is to use energy and resource intensive processes (such as incineration) which are not only costly, but typically generate large amounts of gaseous waste products in the form of carbon dioxide. What is needed is an energy efficient way to actually dispose of the waste products. It is also desirable to find a means for extracting available energy from these waste products which is more efficient than traditional methods such as burning.
In light of the “Background” information provided above, it is desirable to find a way to dispose of solid waste products, such as coal waste, fly ash and sewage sludge. In my U.S. patent application Ser. Nos. 17/803,729 and 17/300,773 (referenced above) I describe novel metal-cement based concrete products and methods for making the same. I have now further developed methods for including selected solid waste products as part of the formulation for these metal-cement based concrete products. The resulting concrete product, which essentially sequesters the waste product, is generally a useable resource product (i.e., a product that can be used as a resource itself, such as a raw material resource, or an energy resource). The concrete product (which includes the waste material) can be provided in a unitized form (e.g., a brick, or a briquette). While in general these waste-product concrete products will have lower compressive strength than other metal-cement based concrete products provided for herein, in some instances they can be used for can be used for purposes where high compressive strength is not a consideration, such as for landscape retaining walls, edging strips, and walking path pavers. Further, in the curing process of the waste-containing concrete product, the waste product becomes chemically bound to the other concrete (and cement) components (or encapsulated by the other components), thus rending the waste product inert at environmental temperatures and pressures. I have also developed methods for including carbon-based energy containing materials into the metal-cement based concrete products, and which allows for the later efficient release of energy from these energy-containing materials. All of the foregoing will be described more fully below. However, before describing methods for making and using the solid waste containing metal-cement based concrete products, I will describe the metal-cement based concrete products which have high compressive strength and are thus useful for paving, building and other construction uses.
As indicated above, I have discovered new and useful methods for the manufacture of concrete products using metal-based cement as the cementing agent, as more specifically described below. More specifically, I have developed formulations and methods for chemically bonding metal-based cement with aggregate (as well as with reinforcing fibers and rods) at ambient temperatures in order to provide for the cast-in-place manufacture of metal-cement based concrete products. I have also developed formulations and methods for forming cast and/or extruded concrete building units using metal-based cements which can form the subject units at controlled elevated temperatures, but which are well below temperatures used in prior art for forming bricks and the like. Further, I have developed new and useful formulations and methods for using metal-based cement to manufacture unitized cast building units having porosity and permeability, and strength, beyond that achievable using Portland cement.
The basic formulation for my metal-based-cement concrete is: (i) a metal-based cementing agent; (ii) a cement reacting agent; and (iii) an aggregate defined by an exposed surface area having one or both of metallic and silicone aggregate linking elements thereon which can chemically bond with the metal-based cementing agent via the cement reacting agent. Further, the compressive strength of metal-based cements (about 30,000-50,000 psi) is much higher than the compressive strength of Portland cement (about 1500-14,000 psi), and is also much closer to the compressive strength of most aggregates (about 15,000-80,000 psi). Accordingly, a metal-cement-based concrete product will have a minimal compressive strength of about 15,000 psi (based on the minimal strength of the aggregate), as compared to a Portland-cement based concrete product which will have a maximum compressive strength of about 10,000 psi. Further, the stress/strain characteristics (as well as the coefficients of thermal expansion), of the cured cement, and the aggregate, in the metal-cement based concrete products provided for herein are much closer to one another than in Portland cement based concrete, thus reducing differential forces within the concrete during tensile loading (as well as thermal expansion/contraction).
Due to the wide variation of definitions of “cement” which are available, and in order to avoid confusion with those definitions for purposes of the following description, I will use herein the term “cement” to mean a solid product which is formed by the reaction of two or more chemical compounds, such chemical compounds to be identified herein as cement agents or “cementing agents”. Accordingly, the cement agents will chemically react with one another to form a cohesive solid—i.e., cement. The cement can be an end product useful by itself—i.e., a cement product. An example of a cement product can be a solidified covering applied over a surface in order to seal or join the surface. Many cements have the properties of adhering to surfaces to which they are applied. A typical desired property of any cement is that the resulting solid cement exhibits the property of high compressive strength (relative to the intended application). A secondary desired property of any cement is that it exhibits the property of high tensile strength (again, relative to the intended application). A correlation of these two desired properties is that the cement chemically bind the cement agents together with strong chemical bonds in order to produce strength (compressive and/or tensile) in the resulting cement. Further, the cement agents can be combined with a filler (i.e., an aggregate) in order to produce a concrete product. Accordingly, a desirable property of the cement agents is that when they combine to form cement, they can also attach chemically to an included aggregate (or another cementing agent, and/or a reinforcing member) in order to form a concrete product. As with a cement product, the primary desirable property of a concrete product is compressive strength, followed by tensile strength.
Beyond the strength considerations of cement described above, other desirable properties relate to the workability of the cement. That is, it is desirable that the cement (or cementing) agents be selected to allow the agents to be worked into the desired final form and density prior to solidification of the cementing agents. The primary consideration of workability of the cementing agents is the cure time—i.e., the time between mixing of the cementing agents and the solidification of the agents into cement. The cure time can be affected by a number of different factors, including: (i) the selection of the cementing agents; (ii) the temperature of the cementing agents during the curing reaction; and (iii) the conditions (other than temperature) under which the cementing agents are allowed to react. The third factor (i.e., non-thermal conditions under which the agents react) can be affected by the addition to the cementing agents of chemical accelerants or decelerants (i.e., to respectively accelerate or decelerate the chemical reaction of the cementing agents), as well as other factors such as the ambient atmosphere under which the reaction of the cementing agents is allowed to occur.
From the above discussion, it is apparent that an essential property of cementing agents is that they will cure (i.e., will chemically react with one another in order to form a solid product) when combined together under the desired conditions. I have thus developed metal-based cementing agent combinations which allow for the production of cement and concrete products at ambient temperatures, as well as the production of cement and concrete products at elevated temperatures (and which are below temperatures used in prior art processes to manufacture products such as bricks and the like). I will now proceed to describe these formulations and methods in detail. In the following discussion, unless otherwise indicated, the term “concrete product” is meant to refer to the metal-cement based concrete products provided for herein.
I will now discuss each of the three primary components (i.e., the metal-based cementing agent, the cement reacting agent, and the aggregate) of the metal-cement based concrete product of the present disclosure in detail, followed by examples. In general, the metal-cement based concrete product of the present disclosure results from chemical bonds according to the structure of “Z—X-M-X—Z”, wherein: (i) “Z” denotes a chemical element available on the aggregate which can bond with “X”; (ii) “X” denotes a chemical element which is present in the cement reacting agent; and (iii) “M” denotes a metal which is present in the metal-based cementing agent. (It will be observed that the “Z—X-M-X—Z” notation is a simplification for purposes of illustration, and does not include attached elements such as oxygen, hydrogen, etc. Further, while direct “Z—X” and “X-M” chemical bonds are preferable, some of the bonds formed may have intermediate oxygen bonds.) As but one non-limiting example (for purposes of illustration only), the metal-based cementing agent can be zinc oxide ((ZnO), wherein the metal “M” component is zinc (Zn)), the cement reacting agent can be phosphoric acid ((H3PO4, wherein the “X” component is phosphorous (P)), and the element “Z” can be aluminum (AI). In this example the “Z—X-M-X—Z” bonds are “Al—P—Zn—P—Al”. That is, the aluminum elements on the faces of the aggregate are covalently bonded to the metallic “M” element of the metal-based cementing agent by the “X” element of the cement reacting agent. Other examples of the “X” component can be sulfur and boron. It will be noted that the chemical reaction producing this result is an acid-base reaction resulting in strong covalent bonds (as distinguished from the hydration reaction which occurs in the manufacture of Portland cement concrete, and which produces relatively weak covalent bonds). Notably, in the hydration reaction for the curing of Portland cement, no bonding between the cement and the aggregate is necessary in order for the concrete formation process to occur. It will also be noted that in the formulation for forming concrete according to the present disclosure, there is no requirement for the addition of water to the mix materials. That is, while the addition of water is necessary in order for Portland cement to cure into a solid product, there is no requirement of water to be added to the mix components (metal-based cementing agent, cement reacting agent, and aggregate) of the present disclosure in order for them to chemically react to form a concrete product. While in the above discussion the metal-based cementing agent, the reacting agent, and the aggregate are indicated as being joined by the “Z—X-M-X—Z” elements, the chemical bonds between these elements can be either direct bonds, or bonds facilitated by other elements (notably oxygen, hydrogen and/or sulfur). Additionally, the “Z—X-M-X—Z” elements can be interspersed by hydrates, as described further below. It will further be appreciated that the “Z” element does not need to be the same element in all positions in the “Z—X-M-X—Z” chain. For example, the structure can be “Al—P—Zn—P—Cd”, where the “Z” element includes aluminum and cadmium. Additional “Z” elements can be included, depending on their availability in the aggregate, and their ability to form a bond with the “X” element in the cement reacting agent.
Metal-based cementing agent: The metal-based cementing agent provides a metal which forms a strong chemical bond (via the acid element “X”) with the aggregate, thus binding the aggregate particles together (via the metal-based cement) into a concrete product. Unlike a Portland-cement-based concrete product, in the metal-cement-based concrete of the present disclosure the chemical bonds between the cement and the aggregate are strong chemical bonds. The metal-based cementing agent can be a metal oxide, a metal peroxide, a metal hydroxide, a metal phosphate, a metal sulfide, a metal carbonate, a metal halide, and a metal organic. Metal sulfides, metal sulfates, metal nitrides and metal carbides are less preferred forms of the metal-based cementing agent, but can be used in selected formulations. Examples of metal oxides which can be used as the metal based cementing agent include iron oxide (preferably Fe2O3 and/or Fe3O4), zinc oxide (ZnO), palladium oxide (PdO), aluminum oxide (Al2O3), and silver oxide (Ag2O). Other metal oxides can also be used, such as peroxides (e.g., ZnO2). Examples of metal phosphates which can be used as the metal based cementing agent include zinc phosphate, magnesium phosphate, aluminum phosphate, and manganese phosphate. Other metal phosphates can also be used. Examples of metal carbonates which can be used as the metal based cementing agent include zinc carbonate (ZnCO3), palladium carbonate (PdCO3), and silver carbonate (Ag2CO3). Examples of metal halides which can be used as the metal based cementing agent include zinc chloride (ZnCl2)), palladium chloride (PdCl2), and aluminum chloride (AlCl3). Examples of metal sulfides which can be used as the metal based cementing agent include zinc sulfide, lead sulfide and palladium sulfide. An example of a metal sulfate that can be used is ZnSO4. Examples of metal organics include metal formates and metal acetates (e.g., lead formate and zinc acetate, respectively). Examples of metal hydroxides that can be used include magnesium hydroxide, aluminum hydroxide, zinc hydroxide and palladium hydroxide. The selection of any specific metal-based cementing agent will be primarily driven by the desired properties of the resulting concrete product, as described further below. While from the above it can be seen that many different metals can be used in different formulations in order to form the metal based cementing agent, certain metals are less desirable, such as iron, magnesium, lead and cadmium.
The metal-based cementing agent is preferably provided in a soluble form, such as zinc acetate (for example). The metal-based cementing agent can also be provided in a dry powder form, having a preferable size of about 100 nm or less. Ideally, the metal-based cementing agent is available for the reaction with the acid-based cement reacting agent on a molecular level (i.e., fully soluble) to maximize the number of bonds formed with the “X” element in the acid (indicated above)—i.e., the “M-X” bonds. By providing the metal-based cementing agent as a very fine powder, the acid can more easily dissolve the particles towards the molecular level.
Cement reacting agent. The cement reacting agent provides the “X” element (described above) for linking the metal “M” element in the metal-based cementing agent to the “Z” element on the face of the aggregate. The acid-based cement reacting agent provides an acid to electro-chemically reduce the bonding element (“Z”) on the faces of the aggregate, as well as the metal in the metal-based cementing agent, to enable chemical linking of aggregate particles to one another by way of the metal in the metal-based cementing agent. This linking is facilitated by the “X” element in the acid (indicated above). The acid-based cement reacting agent is of the form HnXOm, wherein “X” is preferably selected from group consisting of phosphorous, sulfur, carbon and boron, and “n” and “m” are selected to form an acid when in combination with “X” (as described more fully below). The acid-based cement reacting agent can be, for example, a phosphoric acid, a boric acid, a sulfuric acid, and a hydrochloric acid. Other forms for the cement reacting agent are described below. The acid-based cement reacting agent can also be a derivative of any of the aforementioned acids, such as sulfurous acid. In the example wherein the acid-based cement reacting agent is phosphoric acid (H3PO4), then following the general form indicated above (i.e., “HnXOm”), “X” is “P” (phosphorous), “n”=3, and “m”=4. Other derivative acids can be acids with less acidic cations, such as sodium, ammonium (NH4), and potassium, (generally of the form “Hn-1YlXOm”, wherein “Y” denotes an alkali (e.g., potassium, sodium), an amine group (e.g., NH4), or an organic group such as a methyl or ethyl group). The acid-based cement reacting agent can be provided in a dry form or in a liquid form. An example of a dry acid is P2O5 (diphosphorus pentoxide), which will form phosphoric acid when mixed with water. Another example of a dry acid is P4O10. The selection of the specific acid-based cement reacting agent to be used in the formulation of a concrete product is primarily driven by the ability of the “X” component in the acid to chemically bond with the “Z” component on a face of the aggregate, as well as to the metal “M” component in the metal-based cementing agent, as further discussed below. Acid-based cement reacting agents having higher pH values (e.g., a pH of 2 to 3) are generally preferable over lower pH acids (e.g., pH of 1 to 2), not only for reacting purposes but also for safety of handling during mixing of the concrete mix components.
As indicated above, the acid-based cement reacting agent can be either provided in a liquid (soluble, or anhydrous) form, or in a dry form. Using a liquid (or soluble) form will generally improve the completeness of the chemical reactions (i.e., with the cementing agent and the aggregate) when mixing the components together, due to the freer availability of the “X” element in a molecular solution. When the acid-based cement reacting agent is a liquid, it can be mixed with the aggregate first, and then the cementing agent can be added at the time when curing is desired. Preferably, a liquid acid-based cement reacting agent is added to a pre-mixture of all of the dry components (e.g., aggregate, cementing agent and any reinforcing fibers). However, by providing the acid-based cement reacting agent in a dry form, the curing reaction can be deferred until a desired time, at which point water (or another selected liquid) can be added to the mixture of materials in order to initiate the curing process. When the acid-based cement reacting agent is provided in a dry form, it is preferably provided as a powder, and with a size of preferably less than 100 nm. As with the metal-based cementing agent, the acid-based cement reacting agent is ideally provided on a molecular level to maximize the number of bonds formed with the “M” component of the metal-based cementing agent, and the “Z” component in the aggregate (i.e., the “M-X—Z” bonds).
In addition to providing the “X” element which links the metal molecule in the metal-based cementing agent to the aggregate, the acid-based cement reacting agent can also function to put the linking element on the face of the aggregate into a condition to bond with the “X” element (as described further below). Accordingly, it can be advantageous in certain mixtures to use a combination of a least two acid-based cement reacting agents-one to first prepare the aggregate for linking, and a second to provide the linking “X” component. Further, the term “acid-based cement reacting agent” should be understood to include not only acids, but also compounds that become acidic once combined with one or more of the metal-based cement concrete components. The term also includes Lewis acids, hydrogen peroxide, and metal peroxides.
Other examples of the cement reacting agent that can be used include sodium phosphate (Na3PO4), ammonium phosphate variants (e.g., (NH4)3PO4), (NH4)H2PO4), or (NH4)2HPO4)), triethyl phosphate ((C2H5)3PO4), and ethyl acetate (C4H8O2, or CH3COOC2H5) from reacting zinc acetate and triethyl phosphate. Exemplary metal-based cement agents which can be used with these cement reacting agents include zinc acetate and zinc formate. The byproducts of the cement agent and the cement reacting agent when using these variants can include ammonium carbonate and ammonium formate, which will typically form a solid at ambient temperatures (and can thus be extracted later by heating the concrete product to a temperature of between 136 F to 250 F). Of note, the byproducts using these formulations do not include water, and thus set times can be quicker (and concrete product formulation temperatures can be lower).
Aggregate: The aggregate used for the concrete products provided for herein is selected to have on the faces thereof one or more elements (designated by the letter “Z”) which, under the influence of the cement reacting agent, will form a strong chemical bond with the “X” component of the cement reacting agent. While mechanical interference with sheering forces resulting from the presence of the aggregate in formulations of concrete products according to the present disclosure is a desirable trait, the more desirable trait of aggregates used in the formulations provided for herein is the ability to chemically bond with the “X” component in the cement reacting agent. Preferably, aggregates which can be used in concrete formulations provided for herein have a metal element (which I will designate generically as “M2”), a silicon atom (Si), or a combination thereof, on the face of the aggregate. Preferable “M2” metals include aluminum and zinc. Generally, metals on the faces of the aggregate particles provide better bonding sites, but certain exceptions exist (as described more fully below). The “M2” metal element on the face of the aggregate, as well as the silicon atom, will typically be initially chemically inert. For example, any metal “M2” elements on the face of the aggregate may be in the form of an oxidized metal. Likewise, silicon atoms on the face of the aggregate may be present in the form of an oxide. However, when the faces of the aggregate are placed in contact with the cement reacting agent (or an etching acid), the metal-oxides (and silicon oxides, and the like) on the faces of the aggregate will become chemically active such that they can chemically bond with the “X” element in the reacting agent. The aggregate can be naturally sourced (e.g., from naturally occurring rock), as well as from rough-processed rock deposits (e.g., mine tailings) and highly-processed minerals (e.g., silica gel). When the aggregate contains a large amount of silicon on the particle faces, then the chemical bonding performance of the aggregate (i.e., bonding with the metal-based cement) can be enhanced by preparing (i.e., washing) the aggregate with an etchant, such as potassium hydroxide. As indicated earlier, while silicon is generally a less preferable aggregate bonding element, in the case of a synthesized aggregate (e.g., silica gel), or metal silicate molecules (such as zinc silicate) it can result in an extremity strong and chemical inert concrete product. Silica gel is an amorphous and porous form of silicon dioxide, and as such will allow the metal-based cement to penetrate into the aggregate particle, thus forming more bonds between the cement and the aggregate. When the aggregate is naturally occurring (e.g., gravel, rock, etc.), then some pre-processing (such as crushing, washing, etc., described more fully below) can be provided to enhance the performance of the aggregate in the final concrete product. The aggregate can also be a mixture of a naturally occurring aggregate, a rough-processed aggregate, and/or a synthetic aggregate. The aggregate can also be, or include, recycled metal-based cements, and metal-cement based concrete, assuming the final desired properties of the concrete product are not compromised (strength-wise, or otherwise) by the properties (size, strength, permeability, etc.) of the recycled cement and/or concrete used for (or as part of) the aggregate. Recycled Portland cement concretes should be avoided as a source of aggregate due to the reaction with, and consumption of, the acid-based metal cement reacting agent. Further, aggregates with significant carbonate content should be avoided for the same reason. Also, the aggregate can include up to 40% by weight of fly ash. In certain formulations provided for herein below, the aggregate can include heavy crude oil (i.e., crude oil having an API gravity of 22.5° API or lower), which can be mixed with a solid aggregate (such as fly ash).
A preferred source of the aggregate for use in forming concrete products according to the present disclosure is mine tailings. Mine tailings are typically rich in the “M2” metal elements which can chemically bond with the “X” element in the cement reacting agent. Further, a preferred particle size for the aggregate is between 50 and 200 mesh. More preferably, the aggregate includes particles of various sizes between the 50 and 200 mesh range. When mine tailings are used for the aggregate it is desirable to screen out particles larger than 50 mesh, and particles small than 200 mesh. Particles larger than about 50 mesh can be reduced in size to the desired range by crushing, grinding or other mechanical processes. However, when the cementing agent is provided in a soluble form, then it can be desirable that the aggregate is provided in size down to the molecular level (such as when silica gel is used for the aggregate).
The aggregate used in the formulation of metal-cement based concrete products provided for herein will typically be sourced from crustal rock (i.e., rock extracted from the crust of the Earth). Crustal rock is abundant in aluminum silicate, and thus the “M2” element in the aggregate will typically be aluminum. However, as indicated above, mine tailings can include additional “M2” metal elements, such as Au, Ag, Sn, Cd, Cu, Ni, Mn, Pb, Pt, Pd, Zn and Fe. The selection of the aggregate to be used in forming concrete products according to the present disclosure is driven primarily by the desired concrete product to be formed. As described further below, the desired concrete product drives the selection of the aggregate, which in turn drives the selection of the metal-based cementing agent and the cement reacting agent. As indicated above, certain metals in the aggregate (such as iron) do not form the strong chemical bonds which are an objective of the concrete provided for herein. However, the presence of these metals in an available aggregate cannot always be avoided, and so a certain amount can be tolerated so long as the desired physical properties (e.g., strength, chemical resistance, porosity, etc.) of the final concrete product are not compromised.
Liquids. While, as indicated above, the addition of water is not necessary in order to promote the chemical reaction between the three primary components (i.e., the metal-based cementing agent, the cement reacting agent, and the aggregate) in order to result in a concrete product according to the present disclosure, there can still be advantages to adding a liquid to the primary mix components for purposes of: (i) workability (i.e., being able to place the mix components into the desired final form prior to solidification); (ii) facilitating chemical contact of the mix components with one another in order to increase the efficiency of the chemical reactions (i.e., increase the percent of the mix components which will chemically react with one another); (iii) acting as a solvent to place certain soluble solid mix components into a liquid solution (e.g., dry acid to liquid acid); (iv) acting as a retardant to increase the working time of the mix components prior to solidification; and (v) increasing porosity (and/or permeability) of the resulting concrete product. One liquid which can be added to the mix components is water. Another liquid which can be added to the mix components is a solvent. Examples of solvents that can be used as additive liquids include alcohols, as well as other organic compounds (such as xylene, naphtha, acetone, dimethyl sulfoxide, etc.). The selection of the liquid which can be added to the mix components for the concrete product is based on the ability of the liquid to perform the desired function—e.g., workability, contact facilitation, retarding or accelerating solidification, and/or formation of porosity/permeability. When selecting the liquid (if any) to be added to the mix components, considerations such as vapor pressure, surface tension and chemical activity are to be taken into account. For example, if enabling contact between the mix components is a consideration, then a liquid having a low surface tension (such as an alcohol) is desirable. Likewise, if retarding the reaction rate of the cement bonding process is a consideration, then a liquid having a low vapor pressure and being generally non-reactive with the other mix components is desirable. In general, any liquid added to the mix components will be expelled from the mix components during the curing process (i.e., they will not chemically bond with the other mix components in order to form the resulting concrete product). However, certain liquids can evolve in a vapor form during the curing process, and can become entrapped in the resulting concrete product. These entrapped vapors (resulting from the addition of a liquid to the mix materials) can thus produce voids in the resulting concrete product (i.e., porosity), as well as channels in the resulting concrete product (i.e., permeability).
When the concrete products of the present disclosure are formed as unitized cast (or extruded) units, the formed units can be formed in a vacuum environment, and/or an elevated temperature environment, in order to encourage the removal of any added liquids. More specifically, any added liquid, and the vacuum/temperature of the curing environment, can be selected to achieve desired properties in the resulting concrete product. For example, if porosity (and/or permeability) is a desired property of the resulting concrete product, then any added liquid to the mix materials should be selected to evolve from the mix materials in a vapor form during the curing process in order to form the desired voids and channels in the final concrete product, or be forced out after curing by the use of vacuum or pressure. In general, any liquid added to the mix components should preferably be selected to not form substitute chemical bonds between the metal-based cementing agent, the cement reacting agent, and the aggregate, as this will tend to weaken the strength of the resulting concrete product. However, in some instances it can be desirable for any added liquid to react with one of more of the mix components—for example, ethyl alcohol added to form ethyl acetate, in conjunction with alcohol, which can then evaporate, thus removing excess acetate.
Selection of the concrete components. As indicated above, the metal-based cement concrete products provided for herein are formed at least from the combination of mix components of: (i) a metal-based cement agent; (ii) a cement reacting agent; and (iii) an aggregate. The selection of the mix components used to form a concrete product according to the present disclosure is primarily driven by the desired properties of the concrete product to be formed, and the conditions under which the concrete product is to be formed. The first criteria (i.e. the desired properties of concrete product to be formed) mostly includes the properties of strength, durability (chemical and mechanical), and porosity and permeability. The second criteria (i.e., the conditions under which the concrete product is to be formed) mostly includes the option of cast-in-place formation of the concrete product versus unitized casting, or extruding, of the concrete product. Additional considerations can include cure time and other tertiary factors. Once these criteria for the final concrete product to be formed have been determined, the selection of the mix components starts with the selection of the aggregate. The aggregate is primarily selected based on the availability of “M2” elements, or silicon elements, on the faces of the aggregate in order to form strong chemical bonds, and thus produce a concrete product having high mechanical strength. The process of selecting an aggregate can be performed by testing different aggregate candidates from among different sources. Each aggregate candidate can be tested for the presence of “M2” and/or silicon bonding elements in order to determine its potential to be used as an aggregate. Common testing techniques include x-ray diffraction, ICP (inductively coupled plasma atomic emission spectrometry) and titration. Once a suitable aggregate is identified (i.e., an aggregate having the desired “Z” element available on the face of the aggregate), then the next step is to select the cement reacting agent having an “X” element which can form a chemical bond with the “Z” element in the aggregate. In general, it is preferable to select a cement reacting agent which includes a “X” element which forms a strong insoluble chemical bond with the “M2” (or Si) “Z” element in the aggregate. Then, based on the selection of the cement reacting agent, a metal-based cementing agent is selected which preferably forms a strong chemical bond between the “M” metal element in the metal-based cementing agent and the “X” element in the cement reacting agent. Additionally, the “X” element can be chosen for a second purpose of making certain metal sulfides or aramides unreactive, thus rendering mine tailings more suitable as an aggregate source.
The first consideration when selecting the mix components for the metal-based cement concrete product is whether the concrete product will be cast-in-place (i.e., cast at the location, and in the position, where the final concrete product is desired), or whether the concrete product can be unit-cast, and then subsequently moved to the desired location where the final concrete product is desired. In the first instance (cast-in-place formation), the primary consideration is the available temperature. The typical cast-in-place scenario is casting in an outdoor environment, where temperatures can vary widely. For example, if the cast-in-place concrete product is a bridge support column, then ambient curing temperatures can vary from freezing (i.e., 32 F), or below, to over 100 F. Construction of cast-in-place concrete is frequently scheduled for favorable curing temperatures, even when using Portland-cement. Portland cement-based concrete products are rarely cast at temperatures below 40 F since the water in the mixture-essential for the hydration reaction-must remain liquid. Similarly, metal-based cements generally favor higher curing temperatures. However, I have developed formulations (discussed in more detail below) for metal-cement concrete products which can be cast-in-place at temperatures as low as 25 F, and even lower. The minimal cure temperature for metal-cement-based concrete products is driven primarily by avoiding freezing of the liquid acid component, as well as any added liquids and any liquids produced as a result of the cement forming and concrete forming reactions. For example, formulations which produce, as a byproduct, ethyl acetate or ammonium acetate (as discussed elsewhere herein) can be used at temperatures of at least as low as 32 F since the freezing point of these compounds is below the freezing point of water. It will be appreciated that formulations provided for herein for metal-cement-based concrete which is cast-in-place and cured at ambient temperature can also be used to produce unitized construction blocks and the like at ambient temperatures (i.e., not all unitized concrete products formed and cured according to the current methods need to be cured at elevated temperatures in order to achieve full strength). Cast-in-place construction of concrete using metal-based cements, as well a low-temperature casting of concrete products, is discussed more fully below.
As described above, it is desirable to select a metal-based cement which will react (i.e., bond with) the selected aggregate. For example, when the aggregate is silica based (such as sand), then a preferable metal-based cement can be a metal phosphate cement, since phosphate ions (freed during the reacting of the cement agents) will easily bond to the silica in the aggregate. As another example, when the aggregate is clay, then a preferred metal-based cement can be an aluminum hydroxide (AlH3O3) cement, thus creating metal-phospho-silicate bonds between the cement and the clay aggregate particles. Since creating the cement-to-aggregate bonds is essential to overall strength of the resulting concrete product, it is desirable to provide sufficient cementing agent to coat the faces of the aggregate. Accordingly, when calculating the percent of cement to be added to the aggregate, the surface area of a unit volume of aggregate can be estimated, and then the amount of cement needed to wet this surface area calculated based on tests to determine the wetting ability of the selected cement for the selected aggregate, especially considering how soluble the cementing agent is in the cement reacting agent and solvent combination used.
Regarding unitized casting of metal-cement based concrete products, this option allows the use of an oven (or kiln) to raise the curing temperature, thus facilitating a greater selection of the metal-based cement over cast-in-place options. Further, while prior-art formation of cast construction units (such as bricks and the like) require kilning at temperatures of around 1500 F and above (in order to sinter elements to one another), formulations of the metal-cement based concrete products provided for herein are heated to at most about 500 F in order to facilitate curing of the cement, as well as increasing the potential for making the “X” elements in the cement reacting agent bond with the “Z” element in the aggregate. Of note, while Portland-cement unitized concrete products can be cured at temperatures of between 70 F and 250 F, this does nothing to increase the resulting strength of the final concrete product, but only serves to reduce the curing time. On the other hand, for selected formulations of the metal-cement based concrete products provided for herein, providing a curing temperature of between 70 F and 250 F can greatly increase the strength of the final concrete product (i.e., over a Portland-cement cast concrete unit cured at the same temperature). Further, as discussed more fully below, the present disclosure allows for the formation of concrete products having high porosity, and high permeability, and these products are preferably formed as unitized cast units which are cured at temperatures of between 100 F and 500 F.
Formulations. In general, the concrete products provided for herein are formulated from the above described components in the following amounts. For the metal-based cement agent, typically between about 2% to about 25% by weight of the total mass of the mix components; for the cement reacting agent, the amount is based on achieving a stoichiometric ratio for bonding with the metal-based cementing agent; and for the aggregate, whatever is left to add up to 100% total weight of the mix components (typically between about 70% and 96% by weight of the total mass of the mix components). As indicated above, supplemental liquids can be added for various reasons, and this can amount to anywhere from between 0% and about 25% by weight of the total mass of the mix components.
Aggregate preparation: The metal-cement based concrete products provided for herein form their greatest strength when there is maximal bonding of the aggregate to the cement. Accordingly, it is desirable to provide the aggregate in small particles in order to increase the opportunity for the metal-based cement to bond with the aggregate. Preferably, the aggregate is of a mesh size of between 50 and 200 mesh. Aggregate particles of greater than a mesh size of 200 (about 74 microns) are typically not desirable because they increase the required amount of metal cement to an unacceptable level (based on economics—but, as indicated above, in certain instances it can be desirable, and economic, to provide the aggregate on a molecular-size level). That is, the cost of the metal cement will typically be about 10 times (or more) than the cost of the aggregate, and thus it is desirable to minimize the amount of metal-based cement used (and thus maximize the amount of aggregate used), while still achieving the desired mechanical properties (typically, compressive strength) of the resulting concrete product. Accordingly, when selecting the aggregate size, the primary considerations are: (i) the desired end strength of the resulting concrete product; (ii) the availability of a suitable aggregate; and (iii) the cost of forming the concrete product. (In some instances strength may be a secondary consideration, such as when porosity and/or permeability are more important, or when resistance to chemical degradation is more important.) Regarding the second consideration (i.e., availability of a suitable aggregate), this consideration links closely to the third consideration—i.e., cost, or more generally, economics. Aggregate economics include the cost of transporting the aggregate to the mix site, preparation costs (e.g., grinding, milling, etching, etc.), and the cost of compatible cementing agents.
As indicated above, a primary source for the aggregate can be mine tailings. Mine tailings are generally the discarded mineral ore after the desired minerals (typically metals as metal sulfides and metal oxides) have been extracted from the mineral ore by one or more processes (typically, extraction by flotation or acid leaching). Mineral ore is typically processed to extract one, or perhaps two or even three, selected metals (or other components) from the ore, thus leaving behind other elements which are not economically practical for extraction. Thus, mine tailings can be relatively rich in metallic components (i.e., the “Z” or “M2” element in the aggregate) for purposes of bonding to the “X” element in the cement reacting agent, but which are not present in sufficient quantity to economically justify extraction from the mineral ore. Mine tailings from different mines can be combined for use as the aggregate in order to increase the availability of different “Z” elements in forming the “Z—X-M-X—Z” concrete structure (described above). As indicated above, the “Z” element does not need to be the same element in all positions in this chain. When using mine tailings as a source for aggregate, certain considerations may need to be addressed. One consideration is in removing particles from the tailings which are over-sized or under-sized (according to the above discussion regarding aggregate particle size). A second consideration is that mine tailings (which are typically aggregated into a heap—i.e., a generally conical pile) can, over time, accumulate what is generally known as “slimes” between the tailing particles. These “slimes” can include viscous mud, as well as jarosite. Whatever the origin, these “slimes” in mine tailings can inhibit the chemical bonding between the cement reacting agent and the aggregate. Accordingly, when using mine tailings as an aggregate, it is desirable to remove these slimes” from mine tailings before using them as an aggregate. One method for removing “slimes” from mine-tailing sourced aggregate is to first wash the mine tailings with an acid (such as sulfuric acid or phosphoric acid). It will be noted that the washing of mine-tailing based aggregate with an acid (such as sulfuric acid or phosphoric acid) can replace, at least in part, the addition of an acid-based cement reacting agent when formulating a concrete product according to the present disclosure. For example, a mine tailing source (or combination) can be treated with sulfuric acid (H2SO4) having a pH of 1-2 for a period of 4-8 hours, and then rinsed with water before being used as the aggregate in order to form a concrete product according to the present disclosure.
Once an aggregate is selected, then the next step is to prepare the aggregate for use as a mix material in the metal-based cement concrete product to be formed. The preparation of the aggregate can include the following steps: (i) screening the aggregate to segregate the desired particle sized aggregate from over- and under-sized aggregate particles; (ii) crushing over-sized aggregate particles in order to produce desirable sized aggregate particles; (iii) washing the aggregate to remove undesirable fines which may be present in the aggregate; and (iv) washing the aggregate particles with an acid in order to expose chemically reactive metal elements on the faces of the aggregate which can then more freely react with the metal-based cementing agent. A fifth step of drying, or wetting, the aggregate in order to achieve a desired water/solvent content for desired aggregate moisture level can also be performed.
Mixing of Components: The present disclosure provides for two distinct methods for mixing the mix components in order to form a concrete product. The primary difference between the two methods is whether the cementing agent is added before the cement reacting agent, or the other way around. Basically, once the cement components are added together the cement starts to cure (unless both cement components are initially added in a dry form), so any aggregate or other additives need to be mixed before the reactive cementing components are added together (or before any liquid intended to initiate the reaction between the two agents is added). In the preferred embodiment the cement components are both provided (ultimately) in the form of a liquid, which maximizes contact between molecules of the cement agent and molecules of the cement reacting agent. While both the cement agent, and the cement reacting agent, can be added initially to the mixture of concrete components in a dry form, this is a less preferred arrangement because: (i) the components will not be as evenly distributed in combination as if they were both provided in a liquid form; and (ii) in some combinations when the cement reacting agent is provided in a dry form (e.g., P2O5), it can release a significant amount of energy when water or another solvent is added to the mixture of the components.
In a first embodiment of a method for mixing components for the formulation of a concrete product as provided for herein, the metal-based cementing agent is provided in a liquid soluble form, and is preferably placed in a liquid form (i.e., in solution) prior to the addition of the cement reacting agent. The liquid soluble cement agent can be placed in solution before being mixed with the aggregate, or afterwards. One example of a liquid soluble cement agent is zinc formate (C2H2O4Zn), which is a solid powder at ambient conditions, and is typically soluble in water at ambient temperatures. Next, the cementing agent is mixed with the aggregate. (Any preparation of the aggregate-such as grading, washing, etc.—is performed prior to mixing the aggregate with the cementing agent.) Once the cementing agent and the aggregate are mixed, then the cement reacting agent—preferably in a liquid form—is added to the mixture. The reasons for using a liquid cement reacting agent are: (i) better distribution of the cement reacting agent (versus a solid, which can clump); and (ii) less energy is released from an acid-based cementing agent when it is in a liquid form as opposed to a dry form (such as, for example, P2O5). Also, at this time, or prior to adding the cement reacting agent, additive components (such as accelerants, decelerants, etc.) can be added to the mixture of the cement agent and the aggregate.
As an alternative embodiment, the three primary components (cementing agent, cement reacting agent, and aggregate) can all be mixed together using dry components. It will be noted that this mixture is still a dry mixture, and free anions have not yet been provided in order to allow a dry acid (or base) cement reacting agent component to react with the metal-based cementing agent. Preferably the mixing of the three dry components (metal-based cementing agent, cement reacting agent, and aggregate) is performed in a dry atmosphere due to the generally hydroscopic nature of the cement reacting agent. (Note that the dry metal-based cementing agent and the dry cement reacting agent can be mixed together prior to being mixed with the aggregate, or all three components can be mixed together at the same time.) It is preferable to mix the aggregate with only one of the metal-based cementing agent or the cement reacting agent prior to adding the third component in order to decrease the potential for the metal-based-cementing agent and the cement reacting agent to react with one another in the presence of any incidental water, such as ambient humidity or the like. Assuming the metal-cement components are initially added in a dry form, then the third step is to add water (or another selected liquid) to the mixture, and then mix the four components well in order to initiate the chemical reaction between the metal cement components. Preferably the water (or other liquid) is added while the dry metal-based cementing agent, the dry cement reacting agent and the aggregate are being further mixed. The resulting combination produces a wet mixture which will solidify into a solid concrete product as the metal-based cementing agent, the cement reacting agent, and the aggregate react with one another and cure to form the end concrete product. Before allowing the cementing agents to cure, the wet concrete can be poured (i.e., cast-in-place), placed into a mold, or extruded, in order to produce the desired end concrete product. As indicated above, this alternative embodiment (i.e., of using dry metal-based cementing agents in the initial mix, versus using liquid formulations of these components) is less preferred due to the amount of energy which can be released by using a dry form of the cement reacting agent.
Accordingly, an exemplary embodiment for a method of mixing the components to form a metal-cement based concrete product is as follows:
As indicated, the above method is one example only. There are a number of variations that can be performed, all within the scope of mixing the three basic components in order to produce a concrete product. For example, another embodiment of mixing the components for the formulation of the concrete products provided for herein is to first mix the metal-based cementing agent in a dry form with the aggregate, and then to add (and mix) the cement reacting agent in an anhydrous form (i.e., a liquid form) to the dry mixture of the metal-based cementing agent and the aggregate (along with any other dry components, such as setting agents and accelerators (or decelerators)). In this second embodiment the anhydrous cement reacting agent will immediately begin the curing process, and so forming of the final concrete product preferably begins shortly following addition (and mixing) of the anhydrous cement reacting agent with the mixture of the metal-based cementing agent and the aggregate. For cast-in-place applications of the concrete product, the aggregate, metal cement agent (either in liquid or dry form), and any supplemental liquids can be pre-mixed at a plant, then transferred to the location where the casting is to take place, at which time the metal cement reacting agent (preferably in liquid form) can be added, and mixed with the other components, prior to casting the concrete.
The above example of mixing the components for the metal-cement based concrete can also include adding excess of the cement reacting agent, and/or adding hydrogen peroxide (H2O2) (to decrease pH of the mixture), thus dissolving the metal cement agent and preparing the faces of the aggregate (by acid etching). In this variation the excess acid is reacted with a curing agent (accelerator), as will be described in more detail below.
As further described herein, the general methods described above can include additional steps such as heating the mixture of components, placing the mixture of components in a vacuum (or in a pressure chamber) during curing, and washing (rinsing) the concrete product after curing to remove residual water soluble byproducts (such as acetates) to open up channels for permeability. As will be appreciated, formulations in controlled environments (typically, for unit-cast or extruded concrete product) allow for the recovery of gasses which can evolve during the curing process, such as vaporous hydrochloric acid.
Formation of Concrete Products: As indicated above, concrete products provided for herein using metal-based cements can be produced either as cast-in-place concrete products, or as unitized cast (or extruded) products. By their very definition, cast-in-place concrete structures are cast in the place of their final desired position or location. Examples of cast-in-place concrete structures include road surfaces, support columns, dams, and structural building foundations, and are typically 6 inches or more in thickness. By comparison, unitized cast structures are typically cast at a location remote from their final intended position, and are then subsequently transported to their final desired position or location following sufficient cure time to allow them to be put in place. As will be appreciated, cast-in-place formation of concrete products is typically dependent on ambient conditions (typically temperature and humidity) of the casting site to provide the conditions necessary for achieving the desired properties of the resulting concrete product. By contrast, unitized cast (and extruded) structures can be formed under controlled conditions (e.g., temperature and pressure) which are not available at the desired final locus of placement. While unitized cast concrete products can be formed at ambient temperatures, the use of a controlled environment for unitized cast or extruded concrete products allows for a greater range of metal-based cements and additives to be used, with increased assurance of the properties for the final concrete product. Accordingly, the following discussion is separated into two parts-casting in ambient conditions, and casting in controlled environment conditions.
Ambient-condition formation of concrete products. While ambient-condition casting of concrete products using metal-based cements will typically pertain to cast-in-place formation, the following discussion can also apply to unitized product formation. As described above, the primary considerations (beyond product strength) when selecting metal-based cements for cast-in-place concrete formulations include the freezing point of any liquids used in the formulation of, or derived during the curing of, the concrete product. Specifically, if the concrete product is to be cast at temperatures below about 40 F, then it is desirable that water not be used, or derived, in order to prevent the freezing thereof which can damage the concrete product. For most acid reactions (i.e., the reactions between an acid-based cement reacting agent and the metal-based cementing agent, as well as with the aggregate), water is a byproduct. For example, if the metal-base cementing agent is palladium carbonate (3PdCO3), and the acid based cementing agent is phosphoric acid (H3PO4), then in this instance the reaction is:
3PdCO3+2(H3PO4)->Pd3(PO4)2+3(CO2)+3(H2O).
In this example the carbon dioxide is released from the concrete product as a gas, and the water is released either as a gas or a liquid, or a combination thereof. In any event, if the temperature of the mix components falls below 32 F before the concrete product is cured, the water released by the reaction can freeze and cause fractures. However, one advantage of using metal-based cements in the production of concreted products is the quick cure time. Thus, if the mix components for a cast-in place formation are mixed in a heated plant to a temperature of 65 F (for example) prior to being transported to the casting location (where the temperature can be below 32 F), then the cement can be fully cured before the temperature of the mix components drops below 32 F due to ambient cooling. Of course, when relying on the temperature of the mix components to keep any generated water in a liquid form prior to curing of the cement, the ambient temperature needs to be considered, as well as: (i) the temperature of the mix components at the time of casting; and (ii) the cure time for the selected cement components. Rather than relying on making difficult thermodynamic calculations to allow for casting of water-containing metal-cement concrete products at temperatures below 32 F, safe-harbor is to limit the formation of such products to ambient temperatures above 32 F. However, special formulations can allow for formation of concrete products at temperatures below 32 F, as described in the next paragraph.
Low-temperature formulations. In order to allow metal-cement based concrete products to be formed (typically, cast-in-place) at temperatures below 32 F, certain formulations of the mix products can be used. A first technique is to add to the concrete mix components a supplemental liquid which will lower the freezing point of any water initially present within the mix components (or water generated as a result of the cement curing reaction). The supplemental liquid selected to lower the freezing point of the water should be selected so that it does not chemically bond with the metal-based cementing agent or the cement reacting agent, which would prevent the formation of the cement bonds. Examples of supplemental liquids which can be used to lower the freezing point for any water present in the concrete product mix components include ethylene glycol and ethyl alcohol. The quantity of supplemental liquid added to the mix components to lower the freezing point of any present water can be calculated based on the known amounts of water (both initially present and to be generated) in the mix components, and using freezing point data for combinations of the supplemental liquid and water. For example, a combination of 20% ethylene glycol and 80% water (by volume) will lower the freezing point of the solution to about 18 F. Using this first technique, it is possible to form cast concrete products using metal-based cements at temperatures of −20 F, or even lower. However, one drawback to this first technique is that the mixture of water and supplemental liquid will be retained in the final concrete product, thus reducing the strength of the concrete product. A second technique (similar to the first technique) is to select a metal-based cementing agent that will produce a salt which, when in solution with the water present in the mixture, will lower the freezing point of the water. For example, if the metal-based cementing agent is a sulfate (e.g., zinc sulfate), then the reaction with the acid reacting component can produce a sulfate salt, which in solution with water will lower the freezing point of the water. A third technique is to select the cementing components such that: (i) the cement reacting agent component is not provided in any anhydrous form; and (ii) the by-product of the reaction does not produce water. One example is the use of zinc formate (C2H2O4Zn) as the metal-based cementing agent. In this example an acid-based cement reacting agent can be phosphoric acid, and the byproduct of the cement curing reaction is not the formation of water, but rather the formation of formic acid. Another example is the use of zinc acetate as the cement agent, and ammonium phosphate or ethyl phosphate as the cement reacting agent.
Controlled environment formation of concrete products. As described above, when forming metal-cement concrete products, the use of a controlled environment in the formation process can allow for the production of concrete products having superior properties over prior art concrete products. The use of a controlled environment in the formation of concrete products is typically impracticable for cast-in-place concrete products, due to the difficulty of arranging for a controlled environment. That is, while a controlled environment for cast-in-place formation of concrete product can be achieved, the cost for doing so can outweigh the advantages. For example, a controlled environment for cast-in-place formation of a concrete product can be achieved by: (i) tenting an area where the casting is to be placed, and providing heating and perhaps vacuum control under the tented area; and (ii) placing heating elements into the volumetric area where the casting is to take place in advance of the casting. It will be appreciated that these measures will typically be cost prohibitive, but they can be provided if circumstances warrant the cost. Accordingly, the following discussion will pertain mostly to the formation of concrete produces by unitized casting and extrusion in a controlled environment.
A first technique for casting metal-cement based concrete products in a controlled environment is heating cast units (or extruded product) in an oven in order to drive off liquids and/or gasses from the concrete product mix during the cement curing process. Oven heating of the units can also be used to react excess cement reacting agent with hydroxide (OH−) agents, such as clay, aluminum hydroxide (Al(OH)3) or iron magnetite (Fe3O4). (By “excess” I here mean beyond a stoichiometric balance with the metal cement agent provided.) The primary objective here is to eliminate those liquid and gaseous components from the mix components, and reaction products, which can otherwise reduce the strength of the resulting concrete product if they remain in the final concrete product. (As described below, this technique can also be used to produce porosity and permeability in the final concrete product, and so the specific formulations used to form the concrete product, and the temperatures to which they are subjected in an oven, can produce different concrete products-everything from a very dense concrete product with high strength, to a less dense concrete product having lower strength.) When the objective is to remove water from the final concrete product, adding heat (by way of an oven) will cause the water in the outer portions of the concrete product to open up passageways such that water vapor from the inner portions of the concrete product can then move outward and be removed from the concrete product. Of course, it is desirable that the oven temperature be selected such that the outer portions of the concrete product do not cure (and close off water vapor passageways) before water vapor from the inner portions can be released from the concrete product. Accordingly, the oven temperature for forming concrete products can constitute a heating regimen, consisting of a first temperature (of about 220-250 F) to drive off water from the concrete products, and then a secondary higher temperature (of between about 300-500 F) in order to facilitate curing of the cement in the concrete product. The selection of the higher temperature for curing the metal-based cement in the concrete product will depend on the specific components selected for the metal-based cement used. In one variation the oven temperature for curing the concrete products can be between 150 degrees F. and 210 degrees F. This lower temperature range facilitates removal of water without boiling the water, which can potentially damage the concrete product before it is fully cured.
A second technique for casting metal-cement based concrete products in a controlled environment is placing cast units (or extruded product) in a vacuum controlled environment in order to extract liquids and gasses from the concrete product mix during the cement curing process. The primary difference between this second (vacuum) technique and the first (oven) technique is that the vacuum technique does not require the addition of heat in order to facilitate the remove of undesirable gasses and liquids from the concrete product mix. As will be appreciated, the reaction of the metal-based cementing agent and the acid-based cementing agent is accelerated by the addition of heat, and so providing a vacuum environment to the mix components does not provide an accelerating heat component. That is, providing a vacuum environment to the mix components facilitates in the removal of gasses and liquids which can compromise the strength of the final concrete product, while not accelerating the reaction rate for curing of the cement. Thus, the vacuum environment technique allows for more undesirable gasses and liquids to be removed from the final concrete product than does curing in an oven environment. As with the oven technique for curing metal-cement based concrete products, the selection of a vacuum to be provided during curing of the metal-based cement in the concrete product will depend on the specific components selected for the metal-based cement used. An exemplary range of for vacuum curing the concrete products is 1-2 psi below atmospheric pressure.
A third technique for casting metal-cement based concrete products in a controlled environment is placing cast units (or extruded units) of the concrete product in a combined vacuum and temperature controlled environment in order to extract undesirable liquids and gasses from the concrete product mix during the cement curing process, while at the same time controlling the rate of curing of the concrete product by controlling the temperature. This third technique provides a high degree of flexibility to achieve the desired properties of the final concrete product.
Alternative embodiment: In another alternative embodiment for forming concrete products using metal-based cements, the metal-based cementing agent is provided in the form of a metal formate, the cement reacting agent is one of phosphoric acid or sulfuric acid, and the aggregate is defined by an exposed surface area having metallic linking elements thereon in the form of metallic compounds (such as metal oxides and/or metal sulfates) which will react in the presence of the acid-based cement reacting agent to thereby bond with the “X” component of the acid-based cement reacting agent. When the acid-based cement reacting agent is phosphoric acid or sulfuric acid, then the “X” component is respectively phosphorous or sulfur. The metal formate can be, for example, zinc formate (C2H2O4Zn), lead formate (C2H2O4Pb), or formates of the metals cobalt, nickel and silver. Further, in this embodiment the bulk of the aggregate is preferably in the form of aluminosilicates (including metal silicates) which are generally insoluble in weak acids. More preferably, the aggregate includes about 5% (by weight) of metals, and between 50 to 90% (by weight) of metal silicates. Further, the metallic linking elements on the surfaces of the aggregate preferably include 50% or more (by weight) of aluminum, iron, zinc, lead, palladium, gold, copper, nickel, cobalt, palladium, or combinations thereof. A useful aggregate for this formulation is mine tailings, prepared to the size range described above. The metal-based cementing agent is provided in the range of between 2 to 25% of the total dry weight of components of the mixture, with the remainder of the dry weight components being mostly (or all) aggregate. The acid-based cement reacting agent is provided in a quantity to achieve stoichiometric balance with the available metals on the aggregate such that there is ideally little to no free (i.e., surplus) “X” component present in the formed concrete product. As indicated in the example below, the acid-based cement reacting agent can be provided in a dry form, and then an activating liquid can be added to the mixture of components to place the dry-form acid-based cement reacting agent into a reactive state so that acidification of the metallic compounds on the surfaces of the aggregate can take place. Examples of liquids that can be added to activate the dry-form acid-based cement reacting agent (i.e., activating liquids) include water, formic acid, acetic acid and hydrogen peroxide.
In one example of this embodiment the metal-based cementing agent is zinc formate, the acid-based cement reacting agent is phosphoric acid, and the aggregate is mine tailings having zinc and/or aluminum (generically, “M2”) as the metal in the metallic compounds on the surfaces thereof. The aggregate preferably includes about 20% by weight of the metallic compounds, and is graded to 100% passing 50 mesh, and 75% passing 150 mesh. The zinc formate is provided in the amount of between 2.5% and 25% of the total weight of the metallic compounds in the aggregate. The phosphoric acid is provided in the form P2O5 (phosphorus pentoxide), which is a dry form of the acid, and is provided in the amount of 2-20% of the aggregate weight. The zinc formate and aggregate are first blended together, and then the dry-form phosphoric acid (i.e., the phosphorus pentoxide) is added and mixed with the zinc formate and aggregate. In this example the activating liquid is 5-25% (by weight of the aggregate) of water, which is then blended into the mixture of components. The water not only places the dry phosphorus pentoxide into the form of liquid phosphoric acid, but also reacts with the formates (in the zinc formate) to produce formic acid. The formic acid reacts with the metallic compounds on the faces (surfaces) of the aggregate, placing them in a state to bond with the phosphorous from the phosphoric acid. It will also be noted that in forming the formic acid from the formate available from the zinc formate, the zinc is thus freed so that it also can also bond to the phosphorous. The bonding process then proceeds to bond the “M2” metal on surface of the aggregate to the zinc, thus forming a Zn—P-M2 cement bond, with the remainder of the aggregate (still bound to the M2 metals) forming a concrete product. More preferably, the metal-based cement components are first placed in a liquid form (using the dry-weight percentages indicated above) prior to being combined with one another, and the aggregate, in order to increase molecular contact, and to better manage control of exothermic reactions when combining the cement reacting agent with the other components.
In one variation, the metal-based cementing agent can further include a metal carbonate (e.g., zinc carbonate, ZnCO3). In this instance the by-products in forming the concrete product can include carbon dioxide, which can be useful in forming voids (and thus, porosity and permeability) in the resulting concrete product. Carbon dioxide can also be generated using metal formates alone (i.e., without the addition of a carbonate compound), but typically the mix components will need to be heated in order to cause the formates to form carbon dioxide.
In this embodiment, the reactions between the metal formate cementing agent, the phosphorus pentoxide, the water, and the metallic compounds on the surfaces of the aggregate produce by-products such as water and/or carbon dioxide, which are not chemically bound to the concrete product, and can thus be removed in order to form porosity and permeability in the resulting concrete product. For example, when the concrete product is cast-in-place, and the process is performed in temperatures above freezing (i.e., above 32 F), then excess water can gravity drain from the formed concrete product, thus leaving voids for porosity and permeability. By providing excess water, more voids can be created, but at the expense of compressive strength of the resulting concrete product (not just from the presence of voids, but also due to pH reduction, and thus reduced freeing of “M2” metals on the aggregate to bond with the “X” component of the acid component (i.e., cement reacting agent)). It will thus be appreciated that if it is an objective to form a concrete product having porosity and/or permeability, the ambient conditions for curing the cement in the concrete product will be a significant consideration. When the concrete product is to be formed as a cast-in-place unit, then ambient temperature is the primary driver when considering how to formulate the final concrete product in order to achieve porosity and permeability, and further in light of the desired strength to be obtained. In this instance it can be desirable to provide more components which result in the generation of CO2 as a by-product, as CO2 will remain in a gas state well below the freezing temperature of water, and thus can evolve from the forming concrete product, thus resulting in a concrete product having desired properties of porosity and permeability. However, when the concrete product is to be formed as unit-cast product in a controlled environment, then much more latitude is provided in the way of selecting how to formulate the final concrete product in order to achieve porosity and permeability. More specifically, a controlled environment allows excess water (and/or CO2) to be removed by heat and/or a partial vacuum, thus allowing greater permeability to be achieved with less reduction in compressive strength. In general, the degree of porosity and permeability that can be achieved when casting concrete product in ambient conditions, and without significantly compromising strength of the product, is limited by those conditions. On the other hand, when curing conditions can be controlled (e.g., conditions such as temperature and pressure), then the characteristics of the concrete product (e.g., porosity, strength) can be controlled to a much higher degree. The formulation for a concrete product manufactured according to the present disclosure will depend on: (i) the final desired compressive strength of the resulting concrete product; (ii) the desired porosity/permeability of the resulting concrete product; and (iii) the conditions under which the final concrete product is to be formed. It will be appreciated that these are competing considerations, and that the specific formulation should be derived in light of these competing considerations, within the limits of what can be achieved. As a general guide, the methods provided for herein allow for: (i) the production of cast-in-place concrete products having high compressive strength, but low porosity and permeability; and (ii) the production of unit-cast concrete products under controlled environmental conditions which result in both high compressive strength, as well as higher values (versus cast-in-place formulations) of porosity and permeability.
Further alternative embodiment: In yet a further embodiment, a metal-cement-based concrete product can be manufactured using mine tailings from metal ore mining as both the aggregate and the metal-based cementing agent. Such tailings typically have residual metals on the faces (exposed surfaces) of the particles, and which can act in essentially the same manner as the metal(s) in the metal-based cementing agent. That is, the metals in the mine tailings aggregate can act as the metal-cement base, at least in part. Typical residual metals found in metal ore mine tailings include zinc, aluminum and lead. Further, such mine tailings typically include a large quantity of silicates which are tightly chemically bonded to the residual metals. By first mixing the metal-containing mine tailings with formic acid (or another carboxylic acid such as acetic acid), and subsequently adding phosphoric acid (or alternately, sulfuric acid) as the acid-based cement reacting agent, a metal-phosphosilicate (or, in the case of sulfuric acid, a metal-sulfide-silicate) concrete is formed. Preferably, the acid-based cement reacting agent is provided to the mix in a liquid form, such as anhydrous phosphoric acid. More specifically, by first adding the carboxylic acid to the metal-containing mine tailings, a carbon atom will attach to the metal molecule on the surface of the mine tailing particle. This then allows the phosphoric acid to substitute a phosphorous atom for the carbon atom, creating the metal-phosphorous bond, and releasing the previously attached carbon atom in the form of CO2 (due to the presence of available oxygen from the phosphoric acid).
In one example of this embodiment, the aggregate is provided as mine tailings having the chemical and mechanical (i.e., size) properties as provided for in the alternative embodiment described above. That is, the aggregate comprises mine tailings having metallic compounds on the faces thereof, which can react with formic acid to place the metals (from the metallic compounds) in a state where they can then react with phosphoric acid, forming a strong chemical bond which results in a concrete product linking particles of the mine-tailing aggregate by a phosphorous atom. In this example the aggregate (mine tailings) are first mixed with phosphoric acid. Thereafter, formic acid (in a liquid form) is added to the mixture, and is blended to form a slurry which can then be cast (either in-place, or in a form). The liquid formic acid not only provides an activating agent to place the metal compounds on the faces of the aggregate into a state in which they can then bond with the phosphorous of the phosphoric acid, but also acts to free the phosphorous from the phosphoric acid. Further, the liquid formic acid provides a liquid which facilitates in the dry aggregate and liquid phosphoric acid pentoxide being placed into a workable form so that the combination of components (aggregate, phosphoric acid and formic acid) can be cast into the desired shape for the resulting concrete product. Further, to facilitate workability of the constituent components, additional supplemental liquids can be added to the mixture. Examples of such supplemental liquids can include water, as well as accelerants (such as methyl phosphate (CH3O4P−2) and/or ethyl phosphate (C6H15O4P), as described below with respect to accelerants which can be used to shorten curing times of the concrete products provided for herein). In one example the aggregate comprises at least 85% of metal silicate, with metallic linking elements on the exposed surface area of the aggregate in the form of metal oxides and/or metal silicates.
Porous/permeable concrete formulations. In addition to providing enhanced strength and resistance to strength deterioration over prior art formulations for cement and concrete products, the metal-based cement concrete products provided for herein also allow for engineered properties of porosity and permeability. It can be desirable to increase porosity of cement and concrete products for the purpose of reducing weight of the concrete product. It can also be desirable to increase the permeability of cement and concrete products for the purpose of allowing water to flow through the concrete product. Likewise, it can be desirable to decrease the permeability of cement and concrete products for the purpose of preventing the flow of water through the concrete product. To that end, I have developed methods and formulations for adjusting the porosity and permeability of metal-based cements and concrete products in order to achieve the desired associated properties. With respect to the formulations of metallic carbonate cements, porosity and permeability can be provided for in concrete products by providing excess of the metal-based cement agent (i.e., excess over the stoichiometric balance needed to bind the aggregate) so that excess carbon dioxide is released, thus causing voids (i.e., porosity) and, where the excess CO2 is allowed to be released from the curing concrete product, permeability. An example of this is the use of excess PdCO3 in the reaction with phosphoric acid according to the following equation:
3PdCO3+2(H3PO4)->Pd3(PO4)2+3(CO2)+3(H2O).
This method is preferable for forming cast-in-place concrete products where the curing of the concrete can be performed at ambient temperatures, but requires addition of more of the typically more expensive metal cementing agent.
A second method for creating porosity and permeability using a metal-carbonate cement is by using excess of the cement reacting agent. For example, according to the above equation, if excess phosphoric acid (H3PO4) is used, then this results in the formation of diphosphorus pentoxide (P2O5), which can then be sublimed from its solid form to a vapor which can produce the desired porosity/permeability in the resulting concrete product. However, to get the solid diphosphorus pentoxide to sublime the concrete product must be subject to higher-than-ambient temperatures (e.g., about 644 F), and thus this method is more suited to the formation of unitized concrete products (such as blocks and the like).
A further method of creating permeability in the concrete product using metal-based cements is by providing an anion which will vaporize (from a liquid) or sublime (from a solid) and thus create voids in the resulting concrete product. One example of this method is by using a metal chloride cement such that the chloride provides a free chlorine atom which can act as the ion. For example, using aluminum chloride as the metal-based cementing agent, and phosphoric acid as the cement reacting agent, the following reaction occurs:
AlCl3+H3PO4->AlPO4+3HCl.
In this instance the chlorine is released as gaseous hydrochloric acid (HCl), which can form voids in the resulting concrete product. For the specific reaction provided above, heat must be added (e.g., heating to a temperature of 70 F), and thus this method is better suited for the manufacture of unitized concrete products where the units can be heated if ambient temperatures are less than 70 F. Further, performing this method in an oven allows the gaseous hydrochloric acid to be recovered, versus being released to the atmosphere. By adjusting the amount of cementing agents, more or less HCl can be generated. When sufficient of the metal chloride cementing agents are added, then the released hydrochloric acid is sufficient to transpire from the forming concrete product, thus forming channels for permeability. This method is particularly well suited for the manufacture of drainage tiles designed to allow water to pass through the tile, rather than run off of the tile.
Another method for creating porosity/permeability in the concrete products provided for herein is available when the metal-based cement agent is provided as a formate or an acetate. In this case the reaction with the cement reacting agent can produce a solid byproduct within the concrete product, such as sodium acetate or ammonium acetate, for example. These organic byproducts are water soluble, and can then be removed from the final (cured) concrete product by flushing water (preferably warm water) through the concrete product. After the byproducts (organic and/or inorganic) are solubilized and rinsed from the concrete product, the remaining voids can provide porosity and permeability. The extent of the porosity/permeability achieved using this technique can be varied by adding more of the cement components to the concrete mixture, thus increasing the quantity of the byproducts generated.
One example of a metal carbonate which can be used in the cement is palladium carbonate (PdCO3), and an acid which can be used with this metal carbonate is phosphoric acid (H3PO4). In this instance the reaction is
3PdCO3+2(H3PO4)->Pd3(PO4)2+3(CO2)+3(H2O).
In this example the carbon dioxide is released from the cement as a gas, and the water is released either as a gas or a liquid, or a combination thereof. As described herein, by entrapping some of the released carbon dioxide within the solid cement product, porosity can be achieved within the end product. Further, by allowing some of the carbon dioxide to escape at a controlled rate, the end product can be configured to have a desired permeability. Methods for adjusting the release of the carbon dioxide to achieve porosity and/or permeability were described above regarding curing the concrete product under controlled conditions of temperature and/or vacuum.
Yet another method for achieving porosity and/or permeability in the metal cement-based concrete product provided for herein also provides for improved bonds between the aggregate and the metal-cement for improved strength. As described above, aggregates proposed for use herein can oftentimes be defined by two or more different types of metal being present on the faces of the aggregate, as well as silicon. As also described above, certain metals make better (stronger) bonds with the cement reacting agent than do other metals. By etching the faces of the aggregate prior to forming the bonds with the metal cement reacting agent, a selected (desired) metal element can be attached to the faces of the aggregate, thus creating a uniform metal environment over the surface of the aggregate. In general the method includes using a first acid to etch the aggregate, and a second acid to form the bonds between the etched aggregate and the metal component of the metal cement. The first acid decays into gaseous products which are preferably evolved from (i.e., removed from) the forming concrete product, which can produce porosity and permeability in the end product. The first acid is selected to slowly decay during the cement curing process, freeing up the selected (desired) metal in the metal cement to react with the second acid. This method can also be described as precoating the aggregate with the selected metal since the etched surfaces of the aggregate will bond with the provided metal from the metal-cement. This method typically employs the step of heating the concrete mix to elevated temperatures (well above atmospheric temperatures) and thus is more suited to fabricating cast concrete units such as blocks, pavers, beams, etc. I will now describe some specific examples of this method.
In a first example of the method described immediately above, the selected metal for making the bonds to (and between) the aggregate is zinc, the first acid is sulfuric acid (H2SO4), and the second acid is phosphoric acid (H3PO4). In this example the metal-based cementing agent is provided in two parts—the first part being a metal oxide, and the second part being a metal sulfate to provide the basis for the first acid (here, sulfuric acid). More specifically, the first part of the metal-based cementing agent is zinc oxide (ZnO), and the second part is an aqueous liquid solution of zinc sulfate (ZnSO4). The aggregate is preferably a metals-containing aggregate, such as from mine tailings (as described elsewhere herein). The following example provides quantities of mix components for a sample of concrete product, which can be scaled up accordingly for commercial quantities. In this example the mix components were as follows:
In one variation of the above example, the mix components can also include an oxidizer. One exemplary oxidizer is hydrogen peroxide (H2O2). The oxidizer produces an oxidizing agent which facilitates in the etching of the faces of the aggregate. When hydrogen peroxide is used as the oxidizer in example provided above, the reaction is:
6(ZnSO4)+nH2O2+4(H3PO4)->2Zn3(PO4)2+0.5nO2+nH2O+6(H2SO4),
where “n” (italicized) is selected to achieve initially mostly H2SO5 from H2SO4+H2O2. The addition of the oxidizer (here, hydrogen peroxide in this reaction) not only etches the faces of the aggregate, but also facilitates maintaining an acid condition of the phosphates until the sulfuric acid (H2SO4) is driven off (in the oven curing step). That is, the reaction of the zinc phosphate will occur in a slowly decaying acid environment, with H2SO5 (peroxymonosulfuric acid, also known Caro's acid) being formed and consumed as an intermediate reaction product. It will be noted that the reaction products include molecular oxygen (O2), which can either be evolved from the mix products at ambient temperature (i.e., prior to any oven drying of the cast concrete unit), or entrained, depending on the viscosity of the wet (i.e., pre-cured) concrete. In the event that the molecular oxygen is evolved, there will be very little porosity obtained as a result of the molecular oxygen. Further, as the sulfuric acid has a boiling point of 638 F, it tends to sublime at the lower oven curing temperature of 450 F, and thus as the sulfuric acid is released from the concrete mix components during curing, porosity and permeability in the end concrete product can be achieved. The mix components can further include a small amount (˜1% total mass of the concrete mix) of calcium hydroxide (Ca(OH)2) which can react out excess sulfuric acid from the curing concrete product.
As indicated, the method described above results in the generation of sulfuric acid (H2SO4) vapor, and since the method is typically practiced in a closed environment the off-gassing sulfuric acid can be recovered for later industrial use. One such use is in making sulfur-based plant fertilizers, such as ammonium sulfate. In this secondary process the recovered sulfuric acid can be infused into water to produce a wet acid product. This wet acid can then be neutralized (e.g., by the addition of ammonium hydroxide), and then treated with a carbonate salt (e.g., potassium carbonate—K2CO3) to produce potassium sulfate (K2SO4). The potassium sulfate can then be used in other industrial processes (e.g., as fertilizer).
I have observed that in certain instances the flow of water through the permeable concrete products described above is inhibited by surface tension of the water at the outer surface of the concrete product. This situation can be addressed by roughening the outer surface of the permeable concrete products. This roughening can be achieved in various ways, including: providing a mold into which the concrete product is cast with a roughened inner surface, thus imparting the roughened features to the concrete product; acid etching the concrete product; and grit blasting the concrete product. Preferably the roughening, and cleaning of particles from the cast product, is performed prior to any heating of the product (unless the roughening is performed by the mold into which the unit is cast).
Excess acid neutralization variation for creating porosity and permeability via dehydration reaction. A still further variation for creating porosity and permeability in metal-cement based concrete products is to provide excess acid, either as excess of the acid-based cement reacting agent or as another acid. Further, along with adding (or forming within the chemical reactions) excess acid, porosity and permeability are increased by the addition of an additive component which provides a hydroxide (OH) group (as described further below). Examples of this additive component include talc (i.e., hydrated magnesium silicate—Mg3Si4O12), EPK (Edgar Plastic Kaolin) clay (97% Kaolinite—Al2O3, 2SiO2, and 2H2O), feldspars (such as Custer feldspar), bauxite, aluminum oxide and magnetite (Fe3O4). The metal-based cementing agent is preferably provided as a metal oxide and/or a metal peroxide. The addition of excess acid (esp., excess acid-based cement reacting agent) serves at least two purposes: (i) it places the metal-based cementing agent into solution (i.e., a liquid form); and (ii) it acid etches the faces of the aggregate to expose more of the metal components in the aggregate for chemical reacting to bind with the metal cement agents. Putting the metal-based cementing agent in solution provides for: (i) increased contact between the metal cementing agent and the aggregate, (ii) ease of workability of the concrete mixture (e.g., placing the mixture into molds), and (iii) secondary cementing reactions with metals in the hydroxide-supplying additives (EPK clay and/or talc). An additional benefit of providing surplus acid in the mix components is that it raises the chemical reaction temperature of the hydroxide-supplying additives (EPK clay and/or talc) above ambient so that curing time of the concrete product can be more closely controlled in a temperature controlled environment (such as an oven). Of course, when excess acid is provided in the mix components, it is desirable to react the excess acid which, if left in the final concrete product, can degrade the product. The hydroxide-supplying additives (e.g., EPK clay, aluminosilicate and/or talc) can react with the excess acid in order to produce water, which facilitates in forming porosity and permeability in the concrete product. More specifically, the total water in the mix (including water generated as a result of the hydration reaction, water added directly to the mix, and water present in the aggregate) generally determine the porosity, and size of the pores, to provide interconnectedness of the pores, and thus permeability, to the end product. An additional benefit to using potassium-aluminum-silicate (i.e., Custer feldspar) as a hydroxide-supplying additive is that it removes excess water from the mix of materials (by reacting with the water to form carbonates and/or sulfates), leaving behind aluminum silicates. The Custer feldspar improves durability of the end concrete product, can act as a brightening agent, and allows for the use of less zinc-based metal cement agent. Other additives can also be used to react the excess acid, as described below. As indicated above, magnetite can be one such additive, which can also act as a setting agent (as described below). The use of magnetite as a setting agent results in the formation of hydrates in the concrete product. These hydrates (typically iron hydrates) can afterwards be removed from the cured concrete product by washing or heating, thus producing porosity and permeability in the concrete product. I will now provide an example of the excess acid variation, and will follow the example with a discussion specific to the example.
Example of excess-acid variation for producing porosity and permeability. In the following example (and indeed, as with all examples provided for herein) the quantities of the mix components are provided to produce a standardized cylindrical 2 inch (diameter) by 4 inch test specimen. These test specimens can be scaled up to commercial sized units by linear scaling of the quantities of mix components. In this example the mix components were as follows:
The test unit which was formed according to the above example achieved the following results: water flow of >10 inches water per hour (>25 in/hr with 50 g of water); and compressive strength of >8500 psi. (Water flow rates were determined using simulated increasing rainfall rates until water flowed across the top surface of the tested concrete block rather than through the block.) Further, notwithstanding the high water flow through the finished concrete product, the concrete product had a glazed-finish surface appearance due to the addition of the talc. (A similar result can be achieved by using K-feldspar instead of, or along with, talc—in both instances the glazed finish appearance is due to the presence of silica on the surface of the end product following curing.) Porosity for the concrete product was calculated to be 40%. During the curing process in the above example, carbon dioxide is released as a byproduct (the carbon being released from a metal carbonate—e.g., ZnCO3, talc, and/or feldspar), resulting in porosity in the concrete product. Further, during the reaction the OH− groups released from the EPK clay and talc bind with H+ released from the phosphoric acid (the acid-based cement reacting agent) to form water, which is released from the product during the drying and oven curing stage to form permeability connecting the porous spaces. The resulting concrete product thus not only can pass significant quantities of water (due to its high permeability), but can also be used to store large amounts of water (when sealed on the sides and bottom) due to its high porosity. Thus, the porous, permeable concrete product can be used as a water detention cell in the manner described below with respect to
In the example just described, the mold was a rectangular shaped mold with sides formed from wood and a concrete bottom (formed using Portland cement). The concrete bottom of the mold was prepared by spraying vegetable oil over the area which would be in contact with the poured concrete, and then applying fine silica sand to the vegetable oil (to act as a release agent). This approach was found to be preferable to using a metal mold since the wooden and prepared concrete mold did not chemically react with acid in the poured concrete.
Modifications to excess acid method. In the example provided above, the hydroxide-supplying additive is provided as equal parts EPK clay and talc. However, each of these components can be added in amounts ranging from none to 100%. Also, as an alternative to the EPK clay and/or talc, the hydroxide components can be provided by adding hydrogen peroxide (liquid) to the mix components, or using a metal peroxide (e.g., zinc peroxide (ZnO2)) instead of, or in addition to, the metal oxide used as the metal-based cementing agent. Also, alternative methods to consume the excess acid include the following: (a) add ethylene derivatives (such as ethylene glycol) to the mix components to produce tri-ethyl phosphate (which consumes surplus hydrogen and phosphorous); (b) add ethanol to the mix components to produce tri-ethyl phosphate; and (c) add brewer's yeast to the mix components and heat to 250-450 F, which will cause the yeast to react with the phosphorous and sublime off. In the case of alternative (b) (adding ethanol), the ethanol can also be produced as a byproduct within the reaction by adding yeast and sugar to the mix components, or yeast and ethylene glycol, which will produce ethanol. Further, an alternative formulation is as follows:
In addition to creating porosity and/or permeability in the end concrete product, it can also be desirable to produce concrete products having low (or nil) porosity or permeability. For example, lowering porosity will typically raise the compressive strength of the concrete product. Also, lowering permeability will reduce water intrusion into the concrete product, making the product more resistant to deterioration from freeze-thaw cycles. The method used to reduce porosity/permeability will depend in large part on the metal cement selected for use. In one example where the metal cement produces an anion as a by-product of the curing reaction, then porosity can be reduced by including a component which can scavenge the released ions and thus prevent them from being in a gaseous form. For example, if the anion is chlorine and the cement curing reaction results in the release of hydrochloric acid (gas), then by adding a metal oxide (or hydroxide), the chlorine is captured as a solid metal chloride. In another example, when the cement reacting agent is phosphoric acid, then a useful acid scavenger is potassium-feldspar (also known as K-feldspar, and Custer). In this instance the K-feldspar scavenges the phosphate ions, preventing them from becoming acidic. More specifically, the excess phosphoric acid will react with the K-feldspar, decomposing to silica and potassium-aluminum-phosphate (a metal hydrate). This is an exothermic reaction, which aids in driving the cementing reaction to completion and also raises the pH to near 7 (neutral). Thus, the K-feldspar drives the cementing reaction to completion by acid scavenging as well as heating.
Additional acid scavengers that can be used in the methods of fabricating the metal-cement based concretes provided for herein include sodium feldspar, sodium silicate, calcium silicate, magnesium silicate and potassium silicate. The indicated silicates can act not only as acid scavenging agents, but also as a metal-based cementing agent (more specifically, an alkali metal cementing agent). Further, when the formulation includes a hydroxide supplying agent (such as EPK clay, as described above), then the indicated silicates will form alkali aluminum silicates, which have the effect of accelerating the curing reaction of the cement in the concrete product. Further, metal-based cementing agents (such as zinc sulfate) can be replaced in the mixture in whole, or in part, by alkali metal cementing agents such as potassium sulfate or sodium sulfate. In this instance, when the mixture includes a hydroxide supplying agent (such as EPK clay) the alkali metal cementing agents will produce alkali aluminum silicate cement, and the sulfate ion will react with the setting agent (e.g., magnetite) to form an insoluble cement iron sulfate. When the metal-based cement agent is entirely an alkali metal cementing agent, the resulting cement will be an alkali aluminum silicate cement (versus for example, a metal phosphate cement). The alkali aluminum silicate cement behaves more like a ceramic than a metal cement, and can thus be used in applications where wear is a potential issue.
Accelerants and setting agents. In order to shorten curing time for the metal-cement based concrete products provided for herein, accelerants can be added to the mixture of materials. Beyond the advantage of allowing the concrete products to be placed in service sooner, the use of accelerants also has the advantage of allowing cast-in-place concrete to be formed at lower ambient temperatures (versus not using an accelerant). Further, as discussed above, concrete products having porosity and permeability can be formed using the methods provided for herein, however the use of an accelerant can tend to prevent the release of gasses (such as CO2 and water) which can form such features, and thus results in a concrete product having higher density, and consequently greater strength. In addition to accelerants, a setting agent can also be added to the mixture of components for the metal-cement based concrete. A setting agent allows the mixture of the metal-based cementing agent, the acid-based cement reacting agent, and the aggregate to form a solid concrete product which can then further cure to achieve its ultimate strength. That is, the setting agent allows the mixture of components to cure to a certain degree of hardness such that the concrete product can be handled, or temporarily used, until the desired end-strength of the concrete product is achieved. For example, a setting agent allows a unit-cast concrete product to be removed from a mold (or taken from an extrusion unit) prior to achieving its ultimate strength so that the unit-cast (or extruded) concrete product can be moved to a more convenient location for ultimate curing, thus freeing up the molds and/or extrusion units to form more concrete products. Likewise, for cast-in-place concrete products a setting agent allows the formed concrete product (such as a roadbed) to be used in limited duty to facilitate further construction of the final concrete structure. One example of an accelerant which can be used in the formation of the concrete products is methylated acid—i.e., the acid-based cement reacting agent used to react with the metal-based cementing agent can be provided in the form of a methylated acid, such as methyl phosphate (CH3PO4) or trimethyl phosphate ((CH3)3PO4). An example of an accelerant can thus be a metal formate or metal acetate, such as the magnesium based 3Mg(OAc), where “OAc” is a generic descriptor for the acetic acid or, in this case, an acetic acid compound. When the acid-based cement reacting agent includes phosphoric acid (H3PO4), then methyl phosphate is produced, which can act as the accelerant, freeing up the magnesium to react and form Mg3(PO4)2 (a metal cement bond), and releasing gaseous acetic acid (CH3OAc) as a byproduct. Further, if in this example the metal cement agent is a zinc formate or zinc acetate (generically, Zn+2(OAc)2), then an intermediate product of ethyl phosphate is formed, the zinc is freed to react with this intermediate product, and a final metal cement of zinc phosphate (Zn3(PO4)2)) is formed, with a gaseous by product of acetic acid. In this example the phosphoric acid bonds with metal “M” elements in the aggregate, as well as with the metals in the metal-cement component, as well as with the metal in the setting agent.
Additional examples of accelerants that can be used in forming concrete products according to the present disclosure include ammonium phosphates—specifically, diammonium phosphate (NH4)2HPO4, monoammonium salt (NH4)H2PO4, and triammonium phosphate. In addition to acting as an accelerant, formulations of methyl phosphates and ammonium phosphates can act as the cement reacting agent. Specifically, mono- and di-methyl phosphates have extra oxygen over trimethyl phosphate, and thus can act as a metal-cement reacting agent. Likewise, mono- and di-ammonium phosphates have extra protons (i.e., acidic) over triammonium phosphate, and thus can act as a metal-cement reacting agent.
Hydrate-forming setting agents. A principal effect of the reaction of the metal cement acid-based reacting agent with the metal cement agent and the aggregate is the release of liquid water. In order to speed the setting of the concrete product it is beneficial to remove this water, either by physically extracting it from the concrete (e.g., by evaporation) or by chemically binding it with other elements within the concrete—i.e., performing a dehydration process. I have found that metal oxides can be used to form metal hydrates within the concrete products provided for herein, thus fixing the excess water in the concrete and allowing faster setting times for the concrete. The metal-based setting agent is preferably a metal oxide which, when it bonds with the anion produced by the cement reacting agent (e.g., anions such as phosphates, sulfates, borates, etc.) will chemically produce a hydrate, and preferably a higher order hydrate (e.g., 2+ or higher). More specifically, the metal cement reacting agent will produce, depending on the agent used, a phosphate, sulfate or borate, which can combine with the metal in the metal-based setting agent, along with water in the concrete, to form a metal hydrate, which can also act as an insoluble cement. Typical metals in the metal-based setting agent are iron, manganese and magnesium. I have found that iron has a particularly beneficial effect in this regard, and more specifically, magnetite (Fe3O4) and/or iron peroxide (FeO2). For example, when magnetite is used as the metal-based setting agent, and the cement reacting agent is phosphoric acid, then the surplus water forms with the setting agent and the phosphates to produce iron phosphate hydrate. The amount of the metal-based setting agent to be added to the concrete mix is from about 0.5% to about 5% of the total dry weight of the mix components. Preferably the metal-based setting agent is provided as a fine powder (about 10 micron or less), and is added to the concrete mix components in a dry form, and prior to the addition of any liquid component. Also, when the concrete is to be cast-in-place (i.e., prepared at a plant and transported to a remote site for casting), then it can be desirable to add the metal-based setting agent at the location where the casting is to take place. In this instance the metal-based setting agent can be provided as a liquid emulsion by mixing the powdered form of the cementing agent with a liquid such as water, ethylene glycol, and/or alcohol. An additional benefit to adding the metal-based setting agent to the concrete is that it allows the metal in the metal cement agent to react more readily with the cement reacting agent. It is known that metal hydrates can act as fire insulation (since they hold a large quantity of water, and thus have very high heat capacities), and so a metal-cement based concrete formed using a metal-based setting agent will inherently have high resistance to fire (i.e., will retain strength, and will resist heat transfer).
As indicated above in the discussion on forming porous and permeable metal-cement based concrete products, the use of a metal-based setting agent can aid in this regard. Specifically, the hydrates formed by the use of the metal-based setting agent have typical sublimation and/or melting points of around 400 F (or even as low as 250 F). Accordingly, when the concrete product can be placed in an oven at this hydrate melting/sublimation temperature, the hydrates will tend to be driven off from the concrete product (more particularly, the water is released from the hydrates), leaving behind voids (porosity) and channels (permeability) in the concrete product. Alternately, the hydrates can be removed from the concrete product by water washing (wherein heated water under pressure tends to be more effective at removing the hydrates). It will be noted that the hydrates can be left in the concrete product with no ill effect, and removed at a later time if so desired. And, as indicated earlier, the hydrates can, when left in the concrete product, have a beneficial fireproofing effect.
When a metal-based setting agent is used in the formulation of the metal-cement based concretes, and particularly when the metal in the setting agent is iron, then the resulting concrete product will typically be dark grey to black. In some instances, for aesthetic purposes, it is desirable that the concrete product be a lighter color than black, and even that it be a near-white color so that is can later be stained to desired color. I have found that the addition of titanium dioxide (TiO2), along with the use of the iron metal setting agent, can produce lighter colored concrete product—even near white, depending on the amount of titanium dioxide used. That is, the titanium dioxide acts as a brightening agent. However, the addition of titanium dioxide tends to reduce the effectiveness of the iron-based setting agent. The amount of the brightening agent to be added to the concrete mix is from about 0.5% to about 2.5% of the total dry weight of the mix components. The ratio of the combined amounts of metal setting agent and brightening agent can be 25/75-75/25 (setting agent/brightening agent).
Following is an example of a formulation for a metal-cement based concrete product that includes a metal-based setting agent.
Thus far I have chiefly described the use of setting agents with respect to oven-cured concrete product. However, I have also developed a formulation using a setting agent that can be used for cast-in-place concrete products. In this formulation the metal-based cementing agent is zinc sulfate (ZnSO4). An exemplary formulation is thus as follows:
Plasticizers. I have observed that when using setting agents in the manufacture of the metal-cement based concrete (as described above), small surface cracks can be found on the cured and kilned (heated) concrete products. While not affecting performance of the concrete product (i.e., permeability and compressive strength are not appreciably affected), these surface cracks can be undesirable from an aesthetic standpoint. One method to reduce the formation of such surface cracks is to place the concrete products into an oven under conditions that reduce any drawdown of the oven temperature while the concrete product is being placed into the oven. One way to do this is to provide a heat sink in the oven which can help to return the oven to the desired temperature once the oven is sealed. In this way the outer surfaces of the concrete product have less time to dry out at temperatures below the desired curing (kilning) temperature. Further, the use of more of the metal-cement in the mix of materials can help to resist tension forces which result from the removal of the hydrates (and which thus cause surface cracking). Another method to reduce the formation of surface cracks is to provide the concrete product with a plasticizer either as part of the formulation, or as a surface treatment. The plasticizers can aid in lowering bubble formation on the surface of the concrete product, which in turn can lead to the cracking phenomenon mentioned above. One example of a plasticizer that can be used is tri-ethyl phosphate, which can be produced by adding ethylene glycol and phosphoric acid (H3PO4). In this instance it is desirable that the ethylene glycol and phosphoric acid be added in a stoichiometric ratio such that there is no (or very little) surplus ethylene glycol in the mix components (which could deprive the concrete mix of the phosphoric acid needed to form the metal cement). The ethylene glycol can be added in the amount of 1-2.5% of the total mix components. When the cement reacting agent is sulfuric acid, then a plasticizer that can be used is hydrogen peroxide. In addition to acting as a plasticizer, the hydrogen peroxide acts as a curing retardant (by making the hydrates more acidic), removes water from the curing product, entrains additional air in the curing product, and reduces the size of bubbles that form during the curing process (making for increased permeability and porosity, while preserving strength of the end product). The amount of hydrogen peroxide to be used is less than 0.5%, and preferably between 0.10 and 0.25%. The hydrogen peroxide works particularly well when zinc sulfate is used as the metal-based cementing agent, but does not cure quickly in cast-in-place applications, making it more useful for cast products that can be placed in an oven for curing. For cast-in-place applications, surface cracking can be reduced by heating the surface of the concrete with a heater (e.g., a propane heater) to a temperature of about 350 F.
Following is an example of a cast-in-place formulation using plasticizers.
Reinforcing materials. The metal-cement based concrete products produced by the methods provided for herein can be supplemented with enhanced strength and/or durability attributes by the addition of reinforcing materials. In the formation of concrete products using Portland cement, the traditional method for reinforcing the concrete product is by the use of steel bar material (commonly known as “rebar”). It is also known to use fibers (such as steel, glass and plastic) in order to reinforce concrete. All of these known means for reinforcing Portland-cement based concrete are equally applicable to the metal-cement based concrete products provided for herein, although the specific mechanisms for providing increased strength and durability to the final concrete product can vary. In the case where iron-based reinforcing bar material is used, the bar material can first be coated with a material which will bond with the metal-based cement such that iron in the iron-based reinforcing bar material will not be made available for future chemical reactions. One example of a coating which can be applied to iron-based rebar material is a polymeric coating such as nylon. However, when the cement reacting agent is phosphoric acid, then the iron reinforcing bar material will react with the phosphoric acid, generating an iron phosphate (FePO4) protective coating. It is noteworthy that glass fiber reinforcement (including spun basalt fiber) is oftentimes not used in Portland cement concrete products due to the alkaline nature of Portland cement, which can cause degradation of the fibers. This, however, is not a concern when glass reinforcing fibers (including spun basalt) are used in metal-cement based concrete products.
Additional Considerations. Aggregate: It is desirable that the aggregate be of a complimentary size to the size of the cementing agent particles. By this I mean that the sizes (i.e., diameters) of the aggregate particles are not more than an order of magnitude greater than the size of the granular cementing agent particles, and more preferably not more than three times the size. When the cementing agent is soluble (e.g., ZnO and Fe+2 and Fe+3 oxides), then it is desirable that the aggregate particles be as small as is commercially viable, and preferably less than 150 mesh (a typical size for mine tailings). The objective is to optimize use of low cost materials (in particular, the aggregate) in order to reduce the amount of higher cost components in the concrete product. By using small sized aggregate particles, the overall surface area of aggregate is increased, thus increasing the number of bonding sites that can be used to cement the aggregate particles to one another with the cementing agent.
Cement reacting agent: For the formulations provided for herein, the cement reacting agent will typically be phosphoric acid and water, and therefore the water to acid ratio is important to: (i) supply even distribution of the acid to the surfaces of the aggregate and the other granular components; (ii) provide workability of the concrete mix to allow the mixture to be well blended (i.e., near homogeneous) and capable of being placed into forms; and (iii) provide sufficient interstitial water to allow hydrates to form around the setting agent particles (and thus pull water from the acid-base reaction to allow the reaction to cure and reduce, to a high degree, interstitial un-hydrated water and unreacted acid).
Acid scavenging agent. With respect to the acid scavenging agent, the granular particle size (mean diameter) of this component is preferably less than the grain size of the aggregate and the metal-based cementing agent(s) used in the formulation. Further, the acid scavenging agent is preferably provided in such a concentration as to afford a theoretical overlap of the hydrate width formed around the setting agent particles, and the limited number of hydrates that will form around the acid scavenging agent particles as they are reacting with the acid (i.e., the cement reacting agent). More preferably, the size of the acid scavenging agent (e.g., 325 mesh) is less than the size of the aggregate (e.g., 0.25 mm), the cementing agent (e.g., 150 mesh) and the setting agent (e.g., 120 mesh). However, it is not desirable to provide all of the concrete mix components sized to a molecular level, for reasons of economics, chemistry (hydrate sizes are larger than molecular component sizes), and any desired permeability (molecular sized voids do not allow for water flow).
Setting agent. Generally, for a cast-in-place impermeable concrete product manufactured using the metal-cement formulations provided for herein, it is desirable that the setting agent be sized as small as is economically feasible, and that only as much be used as is needed to provide enough time to work the liquid concrete mix into a form or mold before the concrete sets. For formulations where the finished concrete product is to have permeability, then the setting agent can be of a larger grain size (e.g., between 40 and 150 mesh). Further, the selection of the setting agent used is important. For example, magnetite (Fe3O4), having +3 iron available, will cause the concrete to set slower, but also adds to the total amount of cementing agent, whereas FeO will only act to create a cemented agent with the large potential of hydrates around it, causing the mixture to set. Generally Fe2+ iron is a better setting agent than Fe3+ iron, and Fe2+ iron by itself (i.e., as FeO) is a better setting agent than Fe2+ iron as part of a mineral (e.g., magnetite, which has approximately one third Fe2+ iron and two thirds Fe3+ iron by weight). (Note: for purposes of the present disclosure, the nomenclature of “Fe3+” should be considered the same as Fe+3″, and likewise “Fe2+” and “Fe+2”.)
Exemplary formulations of metal-cement based concrete products. Following are exemplary formulations for three types of metal-cement based concrete products which can be manufactured according to the above description. The first exemplary formulation is for a cast-in-place concrete product; the second exemplary formulation is for a plant-cast concrete product (i.e., the product is cast in a controlled environment in a plant setting, versus the ambient conditions of the cast-in-place first example); and the third exemplary formulation is for a clay-brick type of concrete made using metal cements. For each exemplary formulation I will provide exemplary material types and ranges, as well as conditions under which the concrete product can be formed.
First exemplary formulation: cast-in-place metal-cement based concrete product. In the first exemplary formulation, the metal-cement based concrete product is formed as a cast-in-place unit. Examples of such cast-in-place concrete products can include road surfaces, foundations, and other concrete products which are more easily formed in-place versus being formed at a remote location, and then transported to the desired final location of the concrete product. The desired properties for this exemplary formulation are that the resulting concrete product exhibit: (i) high compressive strength; (ii) resistance to cyclical freeze-thaw thermal expansion; and (iii) low permeability to transmission of fluids through the concrete product. For this example, the mix components include:
Another example of a metal-cement based concrete that can be cast in place (or unit cast, if desired) is as follows:
In this formulation the metal-based cementing agent, the cement reacting agent, the aggregate, the setting agent and the acid scavenging agent are mixed together to form a liquid concrete mixture which is then placed in a form (e.g., a formed area) and allowed to cure into the final concrete product. In the above description for this formulation I have used the term “mean diameter”, by which I mean taking the diameter of a particle over three orthogonal axes, and then averaging the three diameters to arrive at a mean diameter. The porosity (and permeability) of the finished concrete product can be enhanced by using an amount of the acid scavenging agent near the low end of the range provided for, or less. Further, in addition to the listed components, additional water can be added to enhance workability of the concrete mix. When the concrete product is unit cast, then the method can include the additional step of heating the cast unit in an over to a temperature of between 170 C and 190 C for 1 hr per inch (25 mm) of thickness.
A specific example resulting in a high density (4 gm/cm3) concrete product mix is as follows (for a 445 gm block of concrete):
In this example the use of magnetite can reduce compressive strength of the concrete product, but results in the high density indicated.
Another example of a concrete mix using metal-based cement can be used to produce cast units which can be used as traffic lane separators (oftentimes known as “jersey barriers”). An exemplary formulation for a 355 gm cast unit is as follows:
The resulting concrete product had a compressive strength of greater than 3500 psi. A variation on the above formulation can also be used to produce a foundation for the traffic barriers, in which case the aggregate is increased by adding 200 gm of basalt chips, graded between 0.5 inch and 0.75 inch (12-18 mm). This foundation material can be cast in place. The compressive strength of the foundation material was greater than 2500 psi.
In the immediately above example the formulation can be varied to produce a brick which can be used in construction by reducing the amounts of pipe bedding material and magnetite used for the aggregate, and making up the difference with kaolinite clay. The amount of kaolinite clay which forms part of the aggregate can be between 5% and 25% (by weight) of the total aggregate. When kaolinite clay is added to the aggregate, then less cement reacting agent is needed, and more acid scavenging agent can be added to account for the properties of the added clay. Also, in the above examples the metal-based cement reacting agent can be augmented with soluble zinc oxide, but not in excess of the amount of iron oxide provided for the cementing agent. Further, in the above examples the hematite (Fe2O3) cementing agent can be augmented with magnetite (Fe3O4) to provide +3 iron to the mixture, which will slow the curing time of the concrete mix. This can be useful when transporting the cement mix from a mix site to a pour site and the set time must be greater than the transit time. It will be noted that in the examples just provided, an acid scavenging agent (also known as a scalping agent) was provided in order to improve longevity of the concrete product (i.e., resist deterioration due to the presence of excess acid in the concrete product).
Second exemplary formulation: plant-cast metal-cement based concrete product. In the secondary exemplary formulation, the metal-cement based concrete product is manufactured in a plant environment—i.e., a controlled environment, as opposed to the uncontrolled ambient environment under which the cast-in-place metal-concrete product is formed. The desired properties for this exemplary formulation are that the resulting concrete product exhibit: (i) high compressive strength; (ii) high porosity; and (iii) high permeability. (An exemplary use of this concrete product is as the water detention cells 206, described below with respect to
A specific example for casting permeable sidewalk slabs or pavers is as follows (for a 390 gm example unit):
In this example after the concrete mixture was placed into a form and cured until firm, the cast unit was removed from the form, placed in an oven and heated to 350 F (177 C) for 1 hr per inch (25 mm) of thickness. The resulting concrete product had a porosity of 30%, a compressive strength greater than 3000 psi, and passed 20 inches of water in an hour. In general flow channels were formed by linked hydrates around the resulting iron phosphates—i.e., the +2 and +3 iron phosphates each crystallize about 8 to 20 hydrates, so a large flow regime was produced. Note that in this example no acid scalping agents were used, as the potassium-aluminum-phosphate (K-feldspar) and magnesium-phosphate produce only about 1.5 to 4 hydrates around the phosphates. It is also noted that excess acid in this formulation is mitigated by the heating of the cast unit, so no acid scavenging agent is required.
Another example of a permeable unit-cast concrete product similar to the paver example just provided is for a subterranean water detention cell which can be placed in an underground vault as part of a stormwater collection system. For a 390 gm example unit:
In this example after the concrete mixture was placed into a form and cured until firm, the cast unit was removed from the form, placed in an oven and heated to 350 F (177 C) for 1 hr per inch (25 mm) of thickness. (Prior to heating, the cast concrete unit was surface roughened by acid etching to improve subsequent water flow through the final concrete product.) The resulting concrete product had a porosity of 35%, a compressive strength greater than 2500 psi, and passed 20 inches of water in an hour. As with the paver formulation described above, this formulation for a water detention cell results in large numbers of hydrates which are driven off by the heating process, thus opening up large flow channels. Again, no acid scavenging agents are needed here due to excess acid being driven off by the heat, and the fact that the scavenging agents tend to produce less hydrates.
Third exemplary formulation: plant-cast metal-cement based clay brick product. In the third exemplary formulation the objective is to form a brick using clay as the aggregate and metal-cement as the binder. In this example the mix components can include:
When the wet concrete uses clay as an aggregate, then the wet concrete can be extruded to manufacture units such as bricks. In this instance it can be helpful to provide a retardant to the wet concrete mixture to allow sufficient time to move the extruded units from the extruder to a drying rack. Further, when using clay as an aggregate to manufacture bricks and the like, the preferred method of mixing the components is using a dry powdered cement reacting agent such as diphosphorus pentoxide. The extruded units can be dried at a low temperature (about 200 F or below). After drying, the brick units can be placed in an oven at a selected temperature to allow unreacted portions of the dry acid component to sublime and form pores in the brick units. For example, when the dry acid component is diphosphorus pentoxide, the dried brick units can be kilned (heated) at a temperature of 644 F or below. At this temperature the diphosphorus pentoxide will sublime, but not the metal, and the vapor from the diphosphorus pentoxide will form voids in the brick units. Porosity can also be produced in the brick units when they are manufactured by adding wet acid and water to the dry metal-based cementing agent/aggregate mixture. In this example excess wet acid (e.g., H3PO4) is added to the mixture.
In a further exemplary formulation, the metal-based cementing agent is at least 85% anhydrous zinc acetate, the cement reacting agent is at least 70% ammonium phosphate and at least 20% phosphoric acid, and the accelerant is at least 85% anhydrous magnesium. In this example the ratio of the non-aggregate cementing agent components (excluding water) to the aggregate is 1:7. Further, the aggregate can be any of the types of aggregate provided for herein, such as sand, and preferably is sized such that at least 80% of the aggregate passes a 150 micron screen. To assist in workability of the concrete components, and aid in wetting the aggregate surfaces, water can be added in a ratio of 1.5 parts water to 1 part metal-cement components.
Biochar Aggregate. Biochar is a high-carbon, fine-grained residue produced via pyrolysis in the direct thermal decomposition of biomass in the absence of oxygen. Accordingly, the inclusion of biochar to the aggregate used in the metal-based concretes provided for herein is a successful way to sequester carbon. The inclusion of biochar in the aggregate also facilitates in increasing porosity in concrete formulations intended to have water permeable properties. The inclusion of biochar into aggregate for the metal-cement based concretes requires a two step process: first, the manufacture of the biochar aggregate as a separate product, and then using the manufactured biochar aggregate as part of the aggregate in the mix for the metal-based concrete products provided for herein. An exemplary formulation (for a 135 gm unit of biochar aggregate) is as follows:
In this example after the aggregate mixture was placed into a form and cured until firm, the cast unit was removed from the form, placed in an oven and heated to 350 F (177 C) for 1 hr per inch (25 mm) of thickness. The resulting aggregate product had a porosity of 40-45%, a compressive strength greater than 1500 psi, and passed 20 inches of water in an hour. It is noted that the ash in the biochar acts in-part as the metal-based cement reacting agent holding the biochar aggregate together. Once manufactured, the biochar aggregate can be crushed and otherwise sized and used to supplement the normal aggregate in the metal-cement based concrete products. However, due to the low compressive strength of the biochar aggregate, its use in forming metal-cement based concrete products can be limited. Specifically, the biochar aggregate can be used in applications where high compressive strength is not a requirement, such as the water detention cells described in one example provided above. Typically, for such uses, the biochar aggregate can supplement between 30% and 50% (by weight) of the normal aggregate.
One variation on the method just described for manufacturing biochar aggregate is to not heat the formed aggregate product. This will leave excess acid in the product, which can be used to offset the cement reacting agent used in formulating the metal-cement based concrete into which the biochar aggregate will be used. Further, the biochar aggregate can facilitate catalytic properties in permeable formulations of the metal-cement based concretes. Specifically, the biochar aggregate can represent a separate catalytic aggregate within a larger catalytic mix (as described below), and can enhance flow of liquid through the catalytic concrete unit. In addition to being used to supplement the aggregates in the metal-cement based concretes, the biochar aggregate can be used by itself for purposes such as a soil supplement or a catalytic unit.
Examples. I will now provide two specific examples of formed concrete products which were manufactured using metal-based cements according to the above disclosure. In both examples a cylinder of 2 inches in diameter by 4 inches in length was cast using the indicated components. Both examples included curing the cast units at an ambient temperature of 60 degrees F., and at standard atmospheric pressure. Weights are given in grams (g).
Example I: In a first example, a metal-cement based concrete product is formed using the following materials, and according to the indicated process:
Example II: In a second example, a metal-cement based concrete product is formed using the following materials, and according to the indicated process:
It will be appreciated that the exemplary formulations for metal-cement based concrete products provided above are exemplary only, and should not be considered as limiting the scope of formulations which can be provided according to the present disclosure.
In-situ application of metal-based cements to form concrete. A further example of a method of forming a metal-cement based concrete product is injection of a metal cement reacting agent into in-situ ground to form a solidified mass-essentially, a metal-cement based concrete product. More specifically, it can be desirable to consolidate ground or terrain to prevent erosion, landslides, and slumping, as well as to make the ground or terrain less permeable to water (for example, to reduce landslides due to rain). Since many ground compositions (soils, rocks, and combinations thereof) include metals and silicates, the ground can already thus possess materials which can act as a metal-based cementing agent, as well as an aggregate. In order to activate these in-situ components and get them to form a metal cement (or a metal-cement based concrete), a metal-cement reacting agent can be injected into the ground. Examples of the metal-cement reacting agents that can be used are as described above, and can include phosphates and borates. The metal-cement reacting agent can be injected into the ground under pressure and into injection holes drilled into the ground. Preferably, prior to injecting a metal-cement reacting agent, samples of the ground are analyzed to determine which metals are present, and in what percentages, to thus allow a preferred metal-cement reacting agent to be selected, and the injection quantities to be calculated. This method of in-situ forming of metal cement (and/or metal-cement based concrete) can be useful for increasing the durability of earthen dams, stabilizing tailings impoundments, stabilizing roadbeds and trails, and strengthening earthen foundations.
Use of porous, permeable metal-cement based concrete products as catalysts. The porous, permeable metal-cement based concrete products provided for herein can be used as catalysts in certain circumstances. Specifically, a fluid containing components that can be advantageously reacted to an end product can be flowed through the porous, permeable metal-cement based concrete product, and metals within the concrete product (particularly metals which are part of the aggregate) can act as a catalyst in order to encourage the advantageous reaction. Further, an aggregate can be selected which has two metals present—a first metal selected to react with the metal-cement reacting agent (in order to form the concrete product), and a second metal selected to act as the catalyst for the chemical reaction of the fluid being flowed through the porous, permeable concrete product. In addition to metals in the aggregate acting as a catalyst, metals in the metal-based cementing agent can also act as catalysts. Preferably the metal-cement based concrete includes at least one metal selected from the group of transition metals in the periodic table of the elements. Metals that can be used (preferably in the amount of between 20 to 50% of the metal in the metal cement, either singly or in combination) include gold, silver, copper, nickel, platinum, palladium and molybdenum. Depending on the intended use as a catalyst, alkali metals can also be included in the catalytic sieve. The porous, permeable metal-cement based concrete product are particularly useful to as catalytic sieves due to their high rate of flow of liquids through the product (20 inches of liquid water per hour at atmospheric pressure), their high interior surface area (calculated to be between 106 and 108 square meters per cubic meter of volume (m2/m3), small pore size (10-100 nm diameter), and high porosity (30-50% of volume). The catalytic sieve is particularly effective as a heterogeneous catalyst, as when the component to be catalyzed is a gas dissolved in a liquid such as water. In one specific example, when the metal-cement based concrete product includes zinc (as in either the metal cement and/or the aggregate), water bearing molecular nitrogen flowed through the concrete product resulted in dissociation of the molecular nitrogen into atomic nitrogen, after which it was able to combine with other components to produce products such as amines. Exemplary metals that can be used in the metal cement and/or the aggregate which have catalytic properties include zinc, copper, molybdenum, vanadium, palladium, gold, nickel, and, less desirably, iron. The aggregate used in the manufacture of these catalytic sieves can be low in metals (e.g., clay), and the amount of the metal-cement used can be increased to thus provide more of the selected catalytic metal in the concrete product. It will be appreciated that the manufacture of certain of the concrete products provided for herein can result in a catalytic sieve, even if that is not the intended goal. Accordingly, in order to prevent undesired catalytic action from occurring, the catalytic sites can be neutralized by the addition of a neutralizing agent, such as soluble silicates. An efficient way to accomplish this is by treating the surface of the concrete product with a sodium silicate stain, which can also provide the product with a desired color for aesthetic purposes. Likewise, in order to obtain catalytic action from a concrete product provided for herein which may be lacking in the desired catalytic metals is to surface treat the concrete product with a liquid solution having the catalytic metals therein, which will then adhere to the pore surfaces of the concrete product.
The catalytic sieves can be used to treat natural bodies of water (oceans, streams, lakes, etc.) which contain dissolved gasses, for the purpose of removing or neutralizing those gasses. For example, carbon dioxide can be removed from ocean water by using a catalytic sieve selected to react the carbon dioxide with calcium ions in the water to generate calcium carbonate, and thus capture the carbon. Likewise, nitrogen can be captured by the catalytic sieves provided for herein. The catalytic sieves, in the form of concrete blocks, can be placed in these natural bodies of water, and currents will move the water through the concrete block in order to generate the desired reaction products.
Coal waste energy brick. As described above, coal waste (i.e., the discarded portion of mined coal which is deemed not commercially useful as fuel) typically contains about 30% of coal, and 70% of non-coal materials such as rock, soil and other materials. The coal portion of the coal waste is deemed either too expensive to extract from the coal waste, or not useful as fuel due to being too fine or poor grade. The coal waste is discarded into tailings ponds or piles, and there is currently no way to dispose of this coal waste other than to move it from one location to another, which does nothing to address the underlying problem of the existence of the coal waste tailings. The methods described above for making metal-cement based concrete can be used to consolidate this coal waste into concrete (either bricks, or monolithic blocks using the in-situ process described above) with the coal waste forming at least part of the aggregate. However, the resulting concrete product is of relatively low compressive strength (about 3000 psi or less), rendering the concrete product useless for most commercial applications. Further, placing the coal waste into a concrete form does not address the problem of the existence of the coal waste—at most it merely makes it somewhat easier to transport the coal waste from one location to another. Realizing that coal waste still has energy content (from the approximately 30% coal content), I have developed a method for adding commercially useful coal (sometimes known as run-of-mine coal, or ROM coal) with coal waste and forming the combination into an energy brick (or a briquette) which can be subsequently processed (as described below) to extract significant portions of the coal energy from the brick, leaving a spent brick that can be used in other commercial applications (as also described below).
Forming of coal waste energy brick. Coal waste can be formed into an energy brick by using the coal waste as part of the aggregate, along with run-of mine coal, generally following the methods described above. A generic formula for the coal waste energy brick is as follows:
An exemplary coal waste energy brick was formed using the following formulation:
In this example the run-of-mine coal was sized to 0.25 inches (approx. 7 mm) or less. (The particle size of any aggregate component should preferably be between one-sixth and one-eighth of the minimum dimension of the resulting brick in order to ensure that the brick will have sufficient structural integrity to withstand later handling. Depending on the size of the resulting brick, coal particles of up to 0.5 inches can be used.) Also, the coal waste is preferably screened prior to use in the mixing of the concrete components to remove any large rocks (e.g., rocks greater than 0.5 inches in diameter). The working fluid (water) can be waste water from a coal waste retention pond, waste water from a coal fired power plant, or other waste water. The resulting brick was formed in a mold measuring 3.75 inches by 3.5 inches by 2 inches. After mixing the components and then placing them in the mold, the components cured into the coal waste brick after 15 to 120 minutes, after which they were extracted from the mold.
It will be appreciated that the coal waste will typically contain a certain amount of metal ions—the amount and type will vary depending on the source of the coal. These metal ions can act as part of the metal-based cementing agent. Certain coal wastes which are high in iron (such as coal from India) may contain sufficient iron that less additional metal-based cementing agent is required in order to form the waste coal brick. In order for the metal ions in the coal waste to be available, the coal waste is preferably ground to a size of −325 mesh (i.e., 325 mesh or less in size).
Processing of coal waste energy brick. In order to extract the latent energy from the coal waste energy brick (i.e., the energy which can be derived from the coal volatile portion within the brick), the energy brick can be subjected to a process such as pyrolysis. (Pyrolysis generally consists of heating a material within an enclosed vessel above decomposition temperature of the material, breaking chemical bonds in the material and generating newly formed products. In this instance the material in question is the coal volatiles within the coal waste energy brick. Pyrolysis is generally performed in a low or no oxygen environment, which thus distinguishes pyrolysis from burning, which is generally understood to mean oxidation of the material in order to release energy and transform the material into combustion products, such as ash and carbon dioxide.) Pyrolysis is usually performed in either a continuous feed rotary reactor, or in a static batch reactor. In either event, heat is typically either applied to the outside of the reactor, thus heating the material within the reactor, or by adding some oxygen or air to cause some thermal oxidation of gasses coming off the coal as (for example) syngas (i.e., CO, H2, CH4 and CO2). In one variation, a low oxygen heated gas can be passed through the reactor to perform the pyrolysis process. Examples of such a gas can include exhaust from natural gas oxidation, such as carbon dioxide and nitrogen. For pyrolysis of coal, the process typically takes place between 800 and 1400 degrees Fahrenheit (approx., 450° C.-760° C.), at standard (atmospheric) pressure. As the temperature of the energy brick passes 350° F. (approx. 177° C.) hydrates that are formed within the fuel brick will be released from the brick, in the manner described above in the section relating to the manufacture of permeable unit-cast concrete products. This will create porous permeable channels within the energy brick, thus allowing the products of pyrolysis of the coal within the brick to escape from the brick. The porous permeable channels also allow for later ingress of gasses (e.g., oxygen and carbon dioxide) into the energy brick (e.g., for further product synthesis and/or post-processing use of the energy brick.) The pyrolysis of coal into resulting products is a complex process of chemical decomposition and synthesis. The products of pyrolysis of coal are generally referred to as syngas (short for synthetic gas), and mostly include gaseous light hydrocarbons such as methane (CH4), molecular hydrogen (H2), carbon monoxide and carbon dioxide. Depending on the presence of other non-coal elements and compounds within the energy brick (e.g., organic compounds such as biomass), the pyrolysis of the energy brick can generate products such as nitrous oxides, carbon dioxide and ammonia. Further, the presence of certain metals, metal oxides and metal phosphates within the energy brick (such as iron, which can be present in the coal waste or as part of the metal-based cementing agent) are believed to produce certain catalytic reactions with the coal to produce other pyrolysis products, such as liquid hydrocarbons. In fact, the presence of metals and metallic compounds within the energy brick are believed to cause the energy brick to become a kind of Fischer-Tropsch reactor during the pyrolysis process. To that end, the energy brick can be manufactured to include certain specific metals in order to act as Fischer-Tropsch reaction catalysts to produce specific selected products derived from the energy brick during pyrolysis of the brick. These metals typically include iron, nickel and cobalt. The metals can be added to the energy brick formulation either in their elemental form, or as metals which are part of the aggregate. For example, certain coal waste piles can include rock which includes the desired catalytic metals. Also, mine tailings can be available which include the desired catalytic metals, and so those mine tailings can be used to supplement the aggregate in the formulation of the energy brick. It will be understood that at temperatures of between 550° C. and 700° C. complex hydrocarbons can also be evolved from the energy brick (as described below with respect to the catalytic fuel brick), and these hydrocarbons are generally believed to be inherent in the carbonaceous aggregate, versus being catalytically synthesized during heating of the fuel brick.
Energy brick as blast furnace feedstock. As indicated above, the energy bricks provided for herein can include coal, which acts as the primary energy source within the energy brick, and metals which can be part of the coal waste, of which can be added from other sources such as mine tailings and fly ash. When the energy brick includes sufficient iron (e.g., 15% to 45% by weight of the overall weight of the energy brick, which can be accounted for by magnetite in the metal-based cementing agent), then the energy brick can be used as feedstock in a blast furnace to produce pig iron. That is, the pyrolyzed coal (i.e., coal char) within the energy brick provides the fuel for the blast furnace, while the iron within the energy brick provides the iron ore content for the pig iron. (It will be appreciated that this use of the energy brick as blast furnace feedstock can be an alternative to the pyrolysis processing of the energy brick described above. It will also be appreciated that volatile compounds within the energy brick are first extracted from the energy brick prior to placing the energy brick into the blast furnace.)
Post processing of energy brick. Once the latent energy within the energy brick is extracted (either by pyrolysis, or other means, as described above), the spent energy brick can be used for other commercial purposes. As described herein, heating of the metal-cement based concretes (e.g., as in a furnace or oven) removes volatile components (such as hydrates) from within the concrete product, thus rendering the concrete product porous and permeable. Accordingly, after heating the energy brick to extract the volatile coal energy from the brick, the spent energy brick will be a porous, permeable carbon rich matrix, and can include metals which can act as catalytic sites. The pore sizes in the coal char portion of the spent energy brick are on the order of 1-10 μm, whereas pores resulting from the evolution of hydrates in the binders (described elsewhere above) are typically in the sub-micron range (e.g., 10-100 nm). This renders the spent energy brick as being useful for commercial applications such as an agricultural soil amendment, a petrochemical catalyst bed, and activated carbon water treatment (e.g., at ocean reefs to adjust acidity). The spent energy bricks can also be used for thermal insulation (due to their light weight and high porosity), filler materials where crush strength is not a primary consideration, and for the reduction of metals such as iron, nickel, copper and cobalt. Thus, the coal waste is transformed into an energy unit from which energy can be extracted, and then afterwards used in a commercial manner, thus essentially removing the coal waste from the waste stream altogether (versus merely moving the waste from one form and place to another).
With continued reference to
Returning to step 120 (or 122) of the process diagram 100 of
Catalytic fuel brick. As described above, certain formulations provided for herein for manufacturing unitized concrete products using metal-cement based concretes result in the formation of hydrates within the concrete which, once the concrete is heated to a temperature of about 350° F. (175° C.)) results in the hydrates evolving from the concrete, leaving behind a permeable matrix of pores. The pores (and the permeable channels connecting them) are small in size—on the order of 10-100 nm. I have now discovered that these pores and permeable channels allow the unitized concrete product to be used as a kind-of fixed bed catalytic reactor. More specifically, the metals within the metal-based cement, as well as metals in the aggregate, allow for chemical reactions to occur with compounds evolved from the aggregate during heating of the concrete product (i.e., following the evolution and release of the hydrates). This catalytic action is particularly noted when the aggregate (or aggregate components) contains a relatively large percent of carbon as a constituent element. Examples of such aggregate components include coal and biomass. (Examples of high-carbon aggregates will be discussed more fully below.) It is of significant note that when these high-carbon aggregate concrete units are heated (as described below), the products which evolve from the concrete unit are not merely compounds inherent in the aggregate prior to heating, but are new compounds formed within the concrete unit itself in a catalytic reaction during the heating process (specifically, by reacting on catalytic surfaces within the pores of the concrete unit), and which are then released from the concrete unit to be collected for later use. The most significant of these catalytic products are hydrocarbons which can be used as fuel (similar to refined petroleum products), as well as other commercially useful hydrocarbons. I have found that liquid distillates, in addition to syngas, are derived from this process (such as C1-C7 aromatics, alkanes and parafins). To generally describe these unitized concrete products with this catalytic property, I will use the term “catalytic fuel brick”, although it is understood that hydrocarbon (and other) useful products can be evolved from these bricks during heating. It is to be noted that the hydrocarbon products evolved from the catalytic fuel brick are different from products that would be evolved if the aggregate were merely heated in a reactor (such as a Fischer-Tropsch reactor) and not in the fuel-brick form described herein. Specifically, products evolved from direct pyrolysis of the aggregate tend to be syngas, and are typically not useful as end hydrocarbon products unless separate Fischer-Tropsch reactors are utilized. In the following discussion I will first describe formulation of the catalytic fuel bricks, then I will describe methods (and results) of extracting hydrocarbon products from the catalytic fuel bricks. I will then describe post-processing uses of the hydrocarbon depleted bricks.
Formulations of catalytic fuel bricks. The catalytic fuel brick is manufactured by providing a mixture of constituent components of the catalytic fuel brick, the constituent components of the catalytic fuel brick including:
High-Carbon Aggregate. The high-carbon content aggregate used in the catalytic fuel brick can be sourced from a number of sources. Examples include (without limitation): coal (both clean (“run-of-mine”) and coal waste); biomass, including wood biomass, grain biomass (e.g., corn, soy), and non-wood vegetation biomass (e.g., grasses, leaves, non-wood plants and municipal waste water solids); dried algae; plastic; heavy crude oil; and high-carbon fly ash. The primary consideration for determining whether or not a high-carbon aggregate can be used in the catalytic fuel brick is the ability for the carbon compounds to be freed from the aggregate at the temperatures of heating (between 450° C. and 1000° C.) of the catalytic fuel brick. The high-carbon content aggregate can be combined with other examples of aggregate provided for above (e.g., feldspar-aggregates I will term here as “low-carbon aggregates”), and particularly low-carbon aggregates high in typical catalytic metals (e.g., silver, platinum, palladium, copper, nickel). To this end, mine tailings can serve as useful low-carbon aggregate components for the catalytic fuel bricks. In two examples (described more fully below), the high-carbon content aggregate was 100% run-of-mine coal, and 100% cracked corn. The high-carbon aggregate can also include asphalt, asphalt roofing material and (as described further below) heavy crude oil.
Metal-based cementing agent. The preferred metal-based cementing agent for the catalytic fuel bricks is magnetite (Fe2+Fe23+O4), although this can be supplemented with, or replaced by, hematite, iron oxide, slag and/or mine tailings. As indicated above, the hematite is preferably provided in a granular form having a mean diameter of less than 100 microns. Other catalytic metal oxides and metal silicates can also be used for the metal-based cement (either alone or in combination), such as copper, nickel, etc.
Processing of catalytic fuel brick. After the catalytic fuel brick has been formed (as described above) it can then be processed to evolve and extract hydrocarbon products there from. As described above, the catalytic fuel brick is first heated to evolve the hydrates. This is done at a temperature of between 20° C. and 175° C., and for a period of time until the brick has reached this temperature throughout for a period of at least 2 hours. (Less time can be achieved at higher temperatures.) This initial heating can be performed as part of the latter high-temperature heating (described below), or as a separate step. For example, the catalytic fuel brick can be manufactured at a first location, and provided with the preliminary heating (hydrate removing) process at the first location (e.g., where there is low-cost drying equipment available), and then subsequently moved to a second location for further processing. This will decrease shipping weight of the fuel brick by about 5-15%, depending on the formulation. I described in an above section how fuel bricks can be heated in a pyrolysis unit (such as a retort) to extract useful products from the fuel brick. While this kind of heating can also be applied to the catalytic fuel brick, preferably the catalytic fuel brick is heated using inductive heating in an induction heater. Using an induction heater to heat the catalytic fuel brick has a number of advantages. First, the induction heater can be an airtight closed unit (example described below with respect to
In
Example of operation of catalytic fuel brick reactor. As indicated above, the catalytic fuel brick reactor 412 of
Examples of Catalytic Fuel Brick reactions and products. In a first example of subjecting a catalytic fuel brick of the present disclosure to an elevated temperature within a controlled oxygen environment, a catalytic fuel brick was manufactured as described above, using bituminous coal as the primary aggregate, magnetite as the metal-based cementing agent, and phosphoric acid as the cement reacting agent (with iron oxide as the setting agent). After driving off the hydrates at 150° C., the temperature was increased to 650° C. to evolve products from the fuel brick. The results (in units of weight) are shown in Table 1 (extending the weight amounts from the test fuel brick to one ton (2000 lb) of coal aggregate).
In Table 1 (above), “hydrocarbon oils” are distinguishable from other hydrocarbon products evolved from the catalytic fuel brick by the characteristic that they are liquid at standard temperature and pressure. Also, while I have referred above to the products evolved from the catalytic fuel brick during heating generically as “hydrocarbons”, it is noted that at least two of the products—water (H2O) and carbon dioxide (CO2) are not hydrocarbons. In Table 1 the “Other” compounds include the gasses shown in Table 3 below. The evolved water from the process will generally be discharged as water vapor, or condensed to liquid water and either used as part of a commercial process (e.g., as water for formulating the catalytic fuel brick), or discharged via a water treatment unit. The evolved carbon dioxide can be separated from other evolved gasses and used as a commercial gas (e.g., for cryogenic freezing, manufacturing, chemical synthesis, etc.).
The approximate liquid volume of the hydrocarbons in the products evolved from the catalytic fuel brick (and reported in Table 1) scales to 73 gallons per ton (2000 lb) of coal aggregate.
In a second example of subjecting a catalytic fuel brick of the present disclosure to an elevated temperature within a controlled oxygen environment, a catalytic fuel brick was manufactured as described above, using cracked corn as the primary aggregate, magnetite as the metal-based cementing agent, and phosphoric acid as the cement reacting agent (with iron oxide as the setting agent). After driving off the hydrates at 150° C., the temperature was increased to 550° C. to evolve products from the fuel brick. The results (in units of weight) are shown in Table 2 (extending the weight amounts from the test fuel brick to one ton (2000 lb) of cracked corn aggregate).
From Table 2 it can be seen that approximately 4000 lb of catalytic fuel brick, containing 1 ton (2000 lb) of cracked corn, 1,157 lb of bio-oils, 947 lb of water, and 160 lb of carbon monoxide and hydrogen are released during the controlled environment heating process. It is noted that the total amount evolved from one ton of corn exceeds 2000 lb. This is due to the fact that the catalytic fuel brick is approximately 50% corn (by weight), with the rest of the weight of the brick coming from the metal-based cement and other additives, some of which also evolve during the heating process (for example, water). The catalytic fuel bricks using cracked corn as the aggregate release larger quantities of bio-oils and water compared to hydrocarbons from catalytic fuel bricks wherein coal is the aggregate. This is because the amount of carbon in coal (˜85% by weight) far exceeds that in corn. Corn has more hydrogen and oxygen molecules; thus, when heated, corn-based catalytic fuel bricks release more liquids and gases than coal-based catalytic fuel bricks (on an equivalent aggregate mass basis).
Table 3 (below) shows the mass distribution of coal- and corn-based catalytic fuel bricks following heating in the controlled environment reactor.
In Table 3 the catalytic fuel bricks are referred to as “Energy Blocks”, and the aggregate (coal or corn) is referred to as “feedstock”.
Heavy crude oil as high-carbon aggregate. In addition to coal and biomass as the high-carbon aggregate in the catalytic fuel brick, I have also discovered that heavy crude oil (i.e., crude oil having an API gravity index of less than 22.3 degrees API, or 22.3° API) can also be used. More preferably, the crude oil has an API index of less than 20° API. The heavy crude oil of API index 20° API can constitute up to 30% by weight of the total mass of the catalytic fuel brick. A heavy crude oil of API index 15° API can constitute up to 35% by weight of the total mass of the catalytic fuel brick. The heavy crude will constitute at least 30% by weight of the total weight of the aggregate. The metal-based cementing agent used when heavy crude oil is the aggregate is magnetite, with phosphoric acid as the cement reacting agent and iron oxide, or elemental iron, as a setting agent. When heavy crude oil is used as the aggregate in a catalytic fuel brick, then as the hydrates are driven out of the brick at 150° C., then some light aromatic substances within the heavy crude oil will also be evolved. Any light aromatic substances which are evolved from the catalytic fuel brick during the hydrate extraction process can be separated from the hydrates by known oil refining processes, and especially oil/water separation processes. As indicated, crude oil as an aggregate (in the catalytic fuel bricks provided for herein) differs from coal, corn or other biomass as an aggregate in that crude oil contains many of the desirable products without the catalytic reforming process that occurs for say coal. Accordingly, the heating regime for crude-oil aggregate catalytic fuel bricks will differ from that for other aggregates notably, coal and corn). More specifically, most of the native petroleum products resident within the heavy crude oil will be released by heating the catalytic fuel brick to about 300° C. Thereafter, raising the temperature of the catalytic fuel brick (to between 450° C. and 550° C.) appears to catalytically reform asphaltenes and other remaining heavy oil residue from the heavy crude oil into lighter hydrocarbon compounds, notably C1-C7 gasses and aromatics. A generic formula for the heavy crude oil energy brick is as follows:
An exemplary heavy crude oil energy brick was formed using the following formulation:
In formulating the heavy crude oil based catalytic fuel brick, I have found that adding a bio oil (preferably, phenols) to the component mix in the ratio of about 1:5 (bio oils to heavy crude oil, weight ratio) increases the amount of crude oil that can be emulsified into the fuel brick, and act more hydrophilic. For example, an oil aggregate component of bio oil and crude oil comprising up to 35% by weight of the total weight of the mix components can set to a solid brick in under 2 hours at ambient temperature.
Results of extraction of fuel components from heavy-crude aggregate catalytic fuel bricks.
I have also determined that the faster a catalytic fuel brick (including coal based, biomass based and heavy crude oil based catalytic fuel bricks) can be brought up to the desired temperature for the desired conversion of hydrocarbons contained therein (i.e., by catalytic cracking and subsequent reforming), the more effective will be the conversion. The desired temperatures are 450° C. for heavy crude oil based catalytic fuel bricks, 500° C. for biomass based catalytic fuel bricks, and 650° C. for coal based catalytic fuel bricks. The induction heating process described above (for heating the catalytic fuel bricks to the desired temperatures for catalytic cracking and reforming of hydrocarbons contained therein) achieves the desired rapid heating over convective based heating methods. However, all three types of heating methods (conductive, inductive and retort) can be used, and all are effective in causing some catalytic cracking and reforming activity within the catalytic fuel brick. Also, larger catalytic fuel bricks can result in more catalytic hydrocarbon cracking and reforming versus smaller catalytic fuel bricks of the same composition due to residence time of the compounds within the catalytic structure of the brick. It can also be advantageous to seal off some of the outer surfaces of the catalytic fuel brick to increase residence time of the hydrocarbons within the fuel brick during the catalytic cracking and reforming process. This can be accomplished, for example, by applying a glaze to at least a portion of the outer surface to be sealed. For example, a cylindrical catalytic fuel brick can have the cylindrical sides sealed, leaving open the opposing ends for flow of gasses there through. By use of these techniques (faster, longer heating) solid-aggregate catalytic fuel bricks (e.g., using coal and/or biomass as the aggregate) can produce evolved hydrocarbon products similar to heavy crude oil based catalytic fuel bricks. Also, as described above, a passageway through the energy brick (see item 614,
Sequential processing of hydrocarbons in catalytic fuel bricks. As indicated above, carbonaceous materials ranging from biomass, coal and heavy crude oil can be used as aggregates in the catalytic fuel bricks provided for herein. In general, the heavier the carbon molecules are in the aggregate, the heavier will be the resulting evolved fuel products. For example, coal as a catalytic fuel brick aggregate will result in heavier products than will heavy crude. Consequently, one method for producing lighter end products from heavy-chain carbon aggregates (e.g., coal) is to form a first catalytic fuel brick using the heavy-chain carbon aggregate, extract volatile compounds from this first catalytic fuel brick using the methods provided for herein above, and then use those extracted volatile compounds to form a second catalytic fuel brick (e.g., in the method described above for using heavy crude oil as a catalytic fuel brick aggregate). Lighter compounds can then be extracted from the second catalytic fuel brick using the methods provided for herein.
Manufacture of iron and other metals from catalytic fuel bricks. As indicated above, once the various (and mostly) hydrocarbon products have been evolved from the catalytic fuel brick by heating at temperatures of up to 800° C., the residual catalytic fuel brick can be further heated (in a controlled environment) to reduce iron oxide, other metal oxides, and metal silicates within the fuel brick into direct reduced iron (or “DRI”) or other-metal reduction, with the coal char in the residual brick acting as the reduction agent. (For other metals, such as nickel in nickel silicates, hydrogen gas (H2) can be used as the reduction agent.) DRI, also known as sponge iron, is a steel scrap substitute for the production of steel. It is typically produced by reducing iron ore by introducing syngas, generated by heating coal at temperatures from 800° C. to 1,250° C., to the iron ore. My process of heating the residual catalytic fuel brick directly does not require the addition of syngas to perform the oxygen reduction process, but can require the addition of oxygen to the reactor if there is insufficient oxygen to complete the reduction process. The DRI produced from the residual catalytic fuel brick is not a direct replacement for typical DRI because, in addition to the reduced iron, the DRI in the residual catalytic fuel brick includes silica slag and variable levels of char (depending on the aggregate used to manufacture the original catalytic fuel brick). Accordingly, the DRI from the residual catalytic fuel brick is a high-carbon DRI, and can be used primarily in blast furnace applications for producing pig iron. Also, if the aggregate used is biomass, the production of the high-carbon DRI can achieve net zero carbon emissions.
While the above process for producing iron is described for spent catalytic fuel bricks (i.e., after the majority of volatile fuel components have been extracted from catalytic fuel bricks using coal, corn or other biomass as the aggregate), the same process can be applied to catalytic bricks that use high-carbon ash from coal fired power plants (or waste coal, or coal refuse) as the aggregate. This ash typically has insufficient volatile hydrocarbons and hydrogen to produce any commercially viable chemicals or fuels (in the manner described above), but the presence of the carbon in this ash, along with the iron in the ash and the catalytic brick cement component, allows the brick to be heated directly to the iron reduction stage (i.e., to a temperature of between 800° C.-1100° C.) after first removing the hydrates from the brick (by heating to 150° C.). The catalytic brick manufactured from this high-carbon ash can be heated using the same induction heating process described above, as well as by convective electric heating and gas retort heating.
Battery Cathodes and Anodes from Spent Heavy Crude Oil Catalytic Fuel Bricks. I have discovered that following extraction of hydrocarbon distillates from crude oil catalytic fuel bricks at temperatures up-to 650° C., and prior to extracting other compounds at higher temperatures, as described herein above, the remaining (or spent) brick can be used as a cathode, or an anode in lithium ferric phosphate batteries, (also known as LFP, or LiFePO4, batteries). The specific use of the spent catalytic fuel brick as either a cathode or an anode will depend on the voltage differential vis-à-vis the other electrode. This voltage differential (between cathode and anode) can be created using different chemistries for the composition of the heavy crude oil catalytic fuel bricks from which the cathode/anode is to be derived (as discussed further below). More specifically, the strong, durable, highly porous permeable spent catalytic fuel brick resulting from heating a catalytic fuel brick (and preferably, a heavy crude oil (or bio oil) based catalytic fuel brick) creates a metal phosphate based material with dendritic like carbon that completes an electrical circuit between the iron phosphate mineral which act as semi-conducting material. In this way, this spent brick material acts like a semi-conducting cathode (or anode) material for an LFG rechargeable battery. It is because of the dispersed molecular nature of oil (versus a solid carbonaceous material like coal or biomass) that enables the deposition of nanoscale dendritic carbon that interconnects the iron phosphate molecules. During pyrolysis of the hydrocarbon material within the fuel brick, the nanoscale pores created in the absence of hydrates originally arrayed around the iron phosphate molecules, and similar scale pores of where oil hydrocarbons were volatilized, created an electrical continuity of dendritic carbon conductor and semi conducting iron phosphate molecules. In order to increase electrical conductivity into the spent catalytic fuel brick, opposing faces of the spent fuel brick can be doped with a conductive metal, such as copper. In order to direct the spent crude oil catalytic fuel brick to use as an anode (versus a cathode), the formulation of the brick can include increasing the amount of iron (e.g., hematite) used as the metal-based cementing agent (or as an additive) to provide additional receptors for the lithium ions. Another method to shift the chemistry of the spent fuel brick to use as an anode is to add additional carbon (e.g., in the form of graphite) to the formulation, and/or reducing the amount of phosphoric acid (phosphate) used in the formulation.
Engineered catalytic fuel bricks. The metal-based cementing agent used in the manufacture of the catalytic fuel bricks described above was magnetite (Fe2+Fe23+O4), which contributes to the catalytic action produced by the brick on the aggregate when heated as described. However, other metal-based cementing agents described herein above can produce different beneficial catalytic reactions on the compounds evolved from the aggregate during heating. Metal-based cementing agents based on metals such as silver, copper, platinum, palladium, nickel, cobalt, chromium, manganese and silver, for example, can be used to achieve specific results based on uses with different aggregates. Additionally the metal can serve a second purpose when they are reduced from metal oxides and/or metal silicates.
Metal-cement based concrete units for making Portland cement. The manufacture of Portland cement involves the manufacture of Portland clinker, which is then ground into fine powder which is the Portland cement itself. Portland clinker generally consists of the calcium silicates alite (Ca3SiO5) and belite (Ca2SiO4), along with tricalcium aluminate (Ca3Al2O6) and calcium aluminoferrite (Ca2(Al,Fe)2O5). These components are produced by heating clays and limestone at high temperature (900° C. to 1450° C.). During the production of Portland clinker, the calcination process CaCO3->CaO+CO2 occurs. The calcium oxide (CaO, also called Lime) is used in the Portland clinker, and the carbon dioxide is typically released into the atmosphere. In addition to the carbon dioxide produced during the calcination process, the energy required to heat the starting components to these high temperatures (900° C. to 1450° C.) is usually provided by burning natural gas or fine coal, which also produces large quantities of carbon dioxide. Also, there can be various pozzalons, such as reactive shales and fly ash, which can be added to the Portland cement as part of the sintered clinker or more usually as an additive to the actual cement at a batch plant to reduce the amount of Portland cement needed. (Pozzalons can reduce the amount of Portland cement needed by as much as 30%.) These pozzalons, when the hydration lime reactions of the Portland cement are done, can combine with the leftover lime and form a cementitious material that increases the density, and thus the strength, of the Portland cement portion. I have developed a method for manufacturing lime, as well as Portland cement clinkers, using metal-cement based concrete, the method eliminating the need to heat the components using fossil fuels (such as coal, natural gas or oil).
Manufacturing Lime: In one example, the metal-cement based concrete unit used to manufacture lime includes, as mix components (and by weight percent of the overall mix), 15% magnetite as the metal-cement based cementing agent, 10-12% phosphoric acid as the metal-cement reacting agent, 5% iron oxide as a setting agent, 5% water, and 65% limestone primarily CaCO3) as the aggregate. The mix components are mixed, formed and cured in the manner provided hereinabove. The finished first precursor unit is then heated using the inductive heating method described above (see
Manufacturing Portland Cement: In general, this method includes making a metal-cement based concrete unit with preferably crushed and ground limestone (which reacts slower with phosphoric acid than lime) along with all the other components described above (e.g., calcium, silicates and such as the aggregate) in the mix, and using magnetite as the metal-based cementing agent, and using induction heating to react the components. In addition, some carbon is preferably added to the mix (e.g., such as high carbon fly ash or waste coal) to add a reduction agent for the iron. The temperature ranges this mixture goes through are about 600° C. to calcine the limestone, about 900° C. to reduce the excess iron oxides in the binder, up to 1250° C. to decompose and sublimate the phosphoric acid, and about 1450° C. to sinter the remaining mixture. The end product is Portland cement clinker which can then be ground for use as cement. Once ground the cement will need to be cleaned via magnets of any excess iron metal particles (to the extent that the final specification of the Portland cement allows for iron in the mixture). In one example, the metal-cement based concrete unit for making Portland cement includes, as mix components (and by weight percent of the overall mix), 15% magnetite as the metal-cement based cementing agent, 10-15% phosphoric acid as the metal-cement reacting agent, 5% iron oxide as a setting agent, 5% water, and 65% calcium silicate (Ca2SiO4) as the aggregate. The aggregate can be sourced from blast furnace slag, and typically has a composition of 40%-65% calcium silicate (by weight), and 25% to 35% Lime (by weight). The mix components are mixed, formed and cured in the manner provided hereinabove. The Portland cement precursor unit is then heated using the inductive heating method described above. More specifically, the second precursor unit is first heated to 600° C. to calcine the limestone into lime. The Portland cement precursor unit is then heated to 1000° C. to convert the magnetite into iron (in the manner described herein above), and then further heated to 1300° C. to drive off phosphorous compounds (also in the manner described herein above). The remaining Portland Cement precursor unit will then be mostly calcium silicate (Ca2SiO4), lime and iron (Fe), with some other minerals (particularly metals) inherent in the original aggregate (all together forming a Portland cement pre-clinker. This remaining Portland cement precursor unit can then be crushed, and the iron separated from the pre-clinker (e.g., by magnetic separation).
The preceding description has been presented only to illustrate and describe exemplary methods and apparatus of the present invention. It is not intended to be exhaustive or to limit the disclosure to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.
This application is a continuation-in-part of U.S. patent application Ser. No. 17/803,729, filed Oct. 31, 2022, which is in turn a continuation-in-part of U.S. patent application Ser. No. 17/300,773, filed Nov. 1, 2021, both of which are hereby incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17803729 | Oct 2022 | US |
| Child | 18445972 | US | |
| Parent | 17300773 | Nov 2021 | US |
| Child | 17803729 | US |
