Patent Application
20080226528
The invention relates to the use of a molten alkali metal metalate phase. The invention further relates to the use of a molten silica glass phase in combination with the metalate phase in a number of specific applications. The invention relates to methods of obtaining an alkali metal metalate that can be processed into a purified metal from a metal source. Metal sources include native ores, recycled metal, metal alloys, impure metal stock, recycle materials, etc. The invention further relates to a method of using a molten alkali metal metalate as a process medium or solvent in purifying or extracting high value metal or metal oxides from metal sources. The invention further relates to processes for vitrification such that the silicate glass phase can be prepared as is or can be prepared with a particulate phase distributed throughout the silica glass phase and encapsulated and fixed within the continuous glass phase.
The invention further relates to methods of obtaining tungsten metal from an alkali metal tungstate, typically finely divided tungsten metal powder from a variety of tungsten sources including recycled tungsten scrap, tungsten carbide scrap, low grade tungsten ore typically comprising tungsten oxide or other form of tungsten in a variety of oxidation states.
In the typical prior art process for metal winning, often a first step involves the combination of a caustic reagent such as sodium hydroxide in a high temperature digestion (e.g., autoclave) to solubilize valuable components of a metal source. Such sodium hydroxide processing causes problems related to the difficulty in separating metal species and problems relating to the nature of metal silicate materials produced during the solubilization process.
Since all metals are solubilized in the reaction into a typically sodium metalate form, different metals can be difficult to separate due to the fact that many valuable metals in the transition metal groupings having similar properties are difficult to separate efficiently. Further, the water soluble silicates formed in the processes may form polymeric silica gels, which can substantially inhibit the processability of the solubilized metalate. Additionally, ion exchange columns used in downstream processing can be irreparably harmed by silica that can bind to the resin irreversibly. As a result, sodium hydroxide solubilization processes require substantial intermediate purification to separate valuable metal species from other species in the mixture and to remove silicates from the reaction mixture prior to downstream processing.
Still further, the sodium solubilization metalate processes of the prior art do not lend themselves to winning metal from low grade sources. It is not a commercially viable process to produce tungsten or other transition metals from low grade sources since the concentration of the metal is so low and the resulting by-products from the sodium hydroxide digestion interfere with downstream processing, so that the overall cost of processing does not justify the use of low grade sources.
Downey et al., U.S. Pat. No. 5,882,620, suggest a direct pyrometallurgical process for forming tungsten carbide. While such direct high temperature processes can have some applicability to purification of tungsten, they are difficult to carry out with low grade ore. Further, the process does not work with many metals well enough to realize substantial commercially viable success.
Sodium tungstate is often formed in metal winning processes. However, the use of sodium tungstate or sodium metalates in high temperature fusion chemistry is not known.
In prior art processes for producing sodium tungstate, traditional sources of tungsten, typically tungsten ore, are crushed, milled and sized to a useful size. Often a sulfide float is used to remove copper and bismuth from the raw ore. The crushed ore is separated into a −40 mesh portion that is 70% tungsten oxide which can be further refined. The larger size material is then magnetically separated to remove iron and other ferromagnetic materials leaving a 72% tungsten ore. That ore is then typically combined with a strong base such as NaOH to form a sodium tungstate solution which is then filtered. Silicates are precipitated from solution. The filtrate is solvent extracted with an ammonium reagent to form ammonium paratungstate which is then crystallized and then ultimately reduced with hydrogen. Hydrogen reduction forms tungsten metal by contacting tungsten with hydrogen at high temperature.
While this traditional process produces tungsten metal, a significant problem exists at the stage where the tungsten oxide intermediate product is contacted with a strong base. That strong base tends to dissolve all of the metal containing input material leaving a sodium tungstate solution containing a variety of calcium, magnesium and other impurities that are brought forward in the process sequence. While silicates and some other materials are precipitated, the material remains somewhat impure.
A substantial need exists to obtain a tungsten purification system that obtains a substantially purified sodium tungstate that can be further processed into tungsten metal. Further, substantial need exists in learning to use molten sodium metalate phases as solvents or processable liquid materials. Finally, a substantial need exists in using fusion processes to form vitreous structures wherein particulate material, such as radioactive waste products, can be encapsulated and held within the vitreous structure.
The process of the invention for refining a source of metal into a useful metal uses an aqueous metalate salt and a process for converting the impure metalate salt into a relatively pure metalate. The process involves combining a source of metal with an alkali metal salt and a source of silicon dioxide to form a mixture. The mixture is heated to a temperature to allow microcorrosion with the tungsten species by the alkali metal salt to form a melt flux. The components of the flux microcorrode, and as it reacts within the flux, the alkali metal salt reacts with metal sources in the melt to form an alkali metal metalate in the melt flux. As this reaction proceeds, the alkali metal metalate product phases out of the reaction mixture creating a soda glass fraction and a heavier metalate fraction. The separated alkali metal metalate phase is substantially purified metalate salt. The novel process of the invention involves a high temperature melt/flux separation step that results in the formation of a highly purified metalate salt substantially free of calcium, with an increased oxidation state and as the reaction proceeds a phase separation occurs. The sodium metalate precipitates from the flux into a metalate phase leaving a separated flux phase containing a silica glass. Such a glass phase includes the large majority of impurities that can be separated in a heated state or liberated by crushing the mixture and then be dissolved in water to an appropriate concentration and further processed for purification into metal.
The process of the invention employs, as a second aspect of the invention, a unique reactor system that is adapted to an input of a metal source, an alkali metal salt and silica. The reactor is shaped and configured to accept the charge, heat the charge to a temperature that can form a molten glass phase and a molten alkali metalate phase within the reactor vessel. The density and viscosity of the molten phases are controlled by reactor dimensions, power input, temperature and mix ratios. As such, the reactor can act as a substantially continuous reactor. As additional charge is added to the top of the reactor, the charge is driven by gravity through the intake portion of the reactor into a reaction zone wherein the reactor heating causes the charge to react and form a silicate glass phase and a sodium metalate phase. The density of the molten phases causes the phases to be directed to the base of the reactor where the phases can either be separated and removed from the reactor or removed from the reactor simultaneously for further processing.
The reactor is an inductively heated conductive container and/or an inductive reactor core. We have found that the power output from an induction coil directed to the conductive container and/or core can be matched to the geometry of the core and container such that the power is converted to heat which can form the fused glass and molten metalate phases in the reactor space. The induction coil or solenoid cooperates with the conductive container and a conductive reactor core to create conditions such that the particulate input can be heated, fused, reacted and converted to a useful by-product, and then withdrawn through the bottom of the reactor vessel. The reactor core is shaped and configured such that it optimizes the heating of the charge, the heat causing the positive reaction to occur and then providing a path such that the molten or fused liquid can flow through the core structure to an exit from the vessel. The input power, the internal volume of the reactor vessel, the configuration of the reactor core, all cooperate in combination with the input charge to rapidly heat and fuse, thereby promoting a rapid corrosion reaction to form the product alkali metal metalate.
The material of construction for the shell and core of the reactor is chosen to provide maximum electrical heating efficiency by induction, good thermal durability, and resistance to chemical attack from the flux and the product. The shape of the reactor core with respect to the reactor shell is driven by the chemical and physical response of the reaction mixture to temperature and power draw. The starting material, usually a powder blend with moderate bulk density, reacts upon heating, increasing in density, and corroding nearby components, which in turn increases the density, enhances corrosion and thereby reaction rate.
Flow of material through the reactor is optimized by shaping the reactor core to match the rate of reaction. As the materials melt and react, the density of the reaction mixture increases, air is excluded, and byproduct gases are released. By matching the cross-sectional area of the reactor core to the density of the reaction mixture at each point in time, maximum heat and power transfer is achieved. To maintain temperature, power draw is adjusted by changing the wall thickness of the reactor core and the lateral position within the induction coil. The length of time the materials stay at the target temperature is controlled by adjusting the path for material flow, resulting in a change in hold up volume.
Heating occurs in the reactor core and shell through eddy current losses. The magnetic field around the current carrying core and shell results in a temperature rise based on the resistance of the material of construction, the frequency of the applied magnetic field, the cross-sectional area of the susceptor, and the location in the coil. If the reactor shell is conductive then there is a limitation of the heating of the reactor to the wall and if the wall is too large compared to its reference depth, there will not be a strong enough field inside to power the core. In general the reactor shell wall must be less than about 10% of the outside diameter to provide enough field to power the core.
The process for refining an ore source into tungsten metal uses an aqueous tungstate salt. The process for converting an impure tungstate salt into a relatively pure alkali metal or sodium tungstate involves combining a tungsten source with an alkali metal or sodium salt and a source of silicon dioxide to form a mixture. The mixture is heated to a temperature forming a melt flux. Within the flux, the alkali metal or sodium source reacts with the tungsten in the tungsten source forming heavy alkali metal or sodium tungstate in the melt flux. As the reaction produces an alkali metal or sodium tungstate, a phase change occurs such that the sodium tungstate phase separates from the flux phase. The heavy sodium tungstate phase is substantially pure sodium tungstate. The lighter soda glass phase floats on the heavy tungstate. The flux phase contains a silicate glass and the major proportion of impurities separated from the tungsten source.
These phases can be separated and the metalate phase is dissolved in water for further purification. The improved melt flux process converts tungsten to sodium tungstate that can be easily dissolved into water to form a processable sodium tungstate solution for further purification. The silicate glass phase is insoluble and after phase separation includes the vast majority of impurities including calcium, iron, sulfur, manganese, cobalt and other such compounds. The recovery of tungsten as measured by the amount of tungsten added to the flux compared to the amount of tungsten recovered from the flux exceeds 90% recovery. The purity of tungsten as sodium tungstate in solution is substantially greater than 90% and approaches 99% pure.
The tungsten metal of the invention can be formed in a small particle form having a particle size that ranges from about 1 micron and higher to facilitate the microcorrosion reaction. Typically, the particle size of the material can be from about 10 microns to about 300 microns, can be about 50 microns to about 500 microns or can be about 70 microns to 500 microns or higher. The metal particulates of the invention are particularly suitable for forming a metal polymer composite using metals of high density. The metal particulates, particularly bismuth, tungsten and other high density metals are particularly useful for forming very high density metal polymer composite materials by blending an appropriate selection of metal particle sizes with appropriate amounts of polymers under the right conditions to obtain close packing and high composite densities. A fast productive method for forming a highly pure metal particulate is particularly useful in an overall process for forming the metal polymer composites. Overall, the process begins with a source tungsten ore and ends with a fully compounded metal polymer composite material. In the process, the tungsten ore is purified to a substantially pure sodium tungstate, the sodium tungstate is converted into a tungstate anion absorbed onto an ion exchange resin which can be eluded from the resin under appropriate conditions to form an ammonium or amine tungstate salt, preferably ammonium paratungstate which can be crystallized into a crystal form. The crystallized ammonium paratungstate is then calcined to a tungsten oxide, which can be directly reduced in a hydrogen furnace to tungsten particulate. The tungsten particulate, under appropriate conditions, can be combined and compounded with an appropriate polymer to form the compounded composite which is then pelletized or formed into a final product.
For the purpose of this invention, the term “source of metal” includes a source of a metal from the Groups IVB, VB, VIB, VIIB, VIII, IVA and VA. In the reaction between the alkali metal salt and the source of metal in the melt flux, the metal needs to react in the melt flux to form a metalate salt.
The term “source of metal” includes metal or metal scrap, metal alloy, tailings from the manufacture or processing of metal ores or high grade ores. The term “source of metal” can include virtually any metal containing composition that can react with the alkali metal salt at melt flux temperatures. The term “source of tungsten” includes any tungsten containing composition that will react with an alkali metal or sodium salt at flux temperatures to form the alkali metal or sodium tungstate product in the melt reaction.
The term “source of tungsten” includes tungsten scrap, tungsten carbide that can be scrap, recycle or synthetic tungsten carbide, tailings from the manufacture of high grade sodium tungstate or can include sodium tungstate native ore. High grade ore from natural sources typically contains 30-72% tungsten on a tungsten oxide basis. Substantially complete tungsten recoveries from such ores are possible. Tungsten source characterizes hard scrap, typically comprising 80-95 wt % as tungsten oxide can also be used beneficially. Relatively low grade tungsten ores, typically not usable in traditional processing can be used. These ores typically contain 10-40 wt % as tungsten oxide.
The term “alkali metal salt” typically refers to alkali metals in Group IA of the Periodic Chart. Alkali metals typically include lithium, sodium and potassium salts that can be used in the flux reaction of the invention. Preferred salts in this regard include lithium oxide, sodium oxide, potassium oxide, lithium carbonate, sodium carbonate or potassium carbonate. Typically, any basic alkali metal salt of these metals can be used such that the salt will form an effective amount of the alkali metal oxide in the flux to react with the source of metal to form the alkali metal metalate salt for that in the melt initiates the phase separation. In the context of this invention, an alkali metal does not include any of the metals that can be purified to form the product of the invention.
The term “alkali metal metalate” typically refers to alkali metal salts (typically lithium, sodium, potassium salts) of metalate anions. Typically, the metalate anion is made from Group IIIB, IVB, VB, VIB, VIIB, VIII, 1B metals. Preferably, the metals include yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, platinum, palladium, silver, gold, iridium, osmium, rhenium, tungsten, tantalum, hafnium, lanthanum and mixtures thereof.
The process of the invention involves selecting a source of a metal, combining the source of metal with an alkali metal salt in silicon dioxide to form a mixture, heating the mixture to form a melt flux. At the melt temperature, the alkali metal salt reacts with the source of metal to form an alkali metal metalate, which in turn causes a phase separation into a soda glass fraction and a sodium metalate fraction. At this temperature, the soda glass fraction floats on the heavier metalate fraction permitting ease of separation or processed as a mixture which the metalate is liberated by crushing. The sodium metalate fraction is highly pure and can be readily processed to give the pure metal in a variety of metal forms.
One important value of the process of the invention is the removal of virtually all soluble sulfur leaving little detectable soluble sulfur in the final purified metal product. From low grade ores, metal recoveries can be achieved up to 96-98 wt %. Another advantage of the refining process of this invention involves the ability to mix a variety of metal sources. Hard scrap, carbides, oxide tailings, and high grade ore can be used in varying proportions without substantial detriment and can all be processed, adding to the utility of the method.
The melt flux process of the invention can convert all available metal from the metal source or mixtures of metal sources into a soluble metal salt which can then be directed to an ion exchange resin for further purification.
The process by which the impurities in the native metal ore are removed, leaving the purified alkali metal metalate, involves combining a source of silica and an alkali metal salt, typically sodium or potassium carbonate or sodium or potassium oxide with a tungsten oxide source. When heated, this mixture forms a melt flux. As the alkali salt decomposes into an alkali metal oxide, typically sodium oxide (Na2O), potassium oxide (K2O) or lithium oxide (Li2O), it becomes molten. The molten phase including the alkali metal oxide reactant reacts with or “corrodes” the source metal in the mixture including high grade or low grade ore, carbide, or other recycle materials. Virtually all the metal in the melt flux is converted to a metalate salt (MOn)−2 while the excess alkali metal oxide combines with silicon dioxide to create a soda glass. This soda glass (can be considered a slag) contains virtually all oxides and other impurities from the source of metal and impurities formed in the melt process. Impurities remain within the soda glass as the pure metalate separates into a phase that is more dense than the glass and separates by gravity from the glass slag to form a lower fraction or liberated in a crushing phase.
Depending on the source of metal used, the process can use different ratios of silica, alkali metal salt and source of metal. The data shown below explore the usable and preferred ratios of materials to form the melt flux leading to metalate separation.
In the overall process utilizing tungsten, a tungsten ore selected from scheelite or wolframite is combined with a flux forming blend that such that the combination reacts and then separates or microseparates under conditions of high temperature into a slag phase and a high density alkali metal or sodium tungstate phase. In one embodiment of the invention, the slag forming materials comprise about 10 to 55 wt % of an alkali metal salt, such as sodium carbonate, and about 30 to 50 wt % of silica. About 15 to 65 wt % tungsten ore is added to these slag forming materials. The material is then comminuted and processed to form a particulate blend having a particle size of typically about 10-500 mesh or less, typically 200 mesh. The particulate material is then heated in a furnace (O2 atmosphere) to a temperature greater than about 1050° C. At this temperature, the flux material becomes molten and impurities from the ore become dissolved or suspended into the flux.
Over a period of time that can range from about 3 to 600 minutes, the molten material separates into a low density upper phase and a high density lower phase. The high density lower phase comprises alkali tungstate, such as sodium tungstate, of substantial purity. The substantial majority of any impurities, most typically calcium oxide, magnesium salts, boron compounds, aluminum compounds, silicon compounds and other trace metals in the ore are dissolved in the flux forming compounds and remain in the low density upper phase after phase separation is complete.
The molten mass can be visually inspected to ensure full phase separation and the slag portion can be removed from the top or the sodium tungstate can be removed from the bottom. Preferably, the slag is removed from the top by eluting the liquid leaving the high density sodium tungstate phase in the bottom of the process equipment. This process can be conducted either in a batchwise or continuous fashion, relying on the high density sodium tungstate phase to readily separate from the slag forming components of the flux material. This can also be done continuously and liberated in a crushing phase to allow dissolution of the metalate into the aqueous phase.
After the material is cooled to a temperature less than about 675° C., the purified sodium tungstate can then be placed in a ball mill or other comminuting structure to reduce the particle size of the sodium tungstate to less than about 1 mm (less than or equal to 200 mesh). Once the particle size is reduced to a size effective for dissolution, the sodium tungstate is then dissolved in deionized water, the percentage based on the mass of sodium tungstate in the dissolution step. Once the sodium tungstate is fully dissolved, sodium tungstate is filtered and the particulate is removed, leaving a concentrated solution of sodium tungstate typically comprising about 10 to about 500 grams of sodium tungstate per liter of solution.
The filtered sodium tungstate solution can then be applied to an ion exchange resin. Preferably, the ion exchange resin is an anion resin with a strong anion such as chloride anion. The resin binds with the tungstate anion displacing the chloride anion from the resin, thus extracting tungsten from the concentrated aqueous solution. A preferable anion exchange resin comprises Rohm & Haas IRA 4400Cl resin with a chloride anion species. Once the anion exchange resin is loaded with tungstate, the tungstate is eluted from the resin using an aqueous ammonium hydroxide, ammonium chloride solution at a concentration of about 1 normal. The chloride ion being in excess displaces the tungsten oxide and regenerates the ion exchange column. The ammonium cation elutes as the tungstate counterion yielding ammonium paratungstate. The ammonium paratungstate is crystallized and then placed in a reducing atmosphere at a temperature of about 300° to about 1000° C. to convert the ammonium paratungstate to tungsten blue oxide while the ammonia can be recovered. The tungsten blue oxide is then placed in a hydrogen reduction furnace to convert the tungsten oxide to tungsten particulate. Typically, the atmosphere comprises about 10 to 30% hydrogen, the balance being nitrogen or other inert gases.
After reduction and sizing, the preferred tungsten metal particulate may be combined with a polymer to form a polymer composite as describe above. Polymers or other agents may be added to the tungsten metal at about 0.01 to about 5 wt % of polymer based on the weight of the modified particulate metal. One value of the overall process is the substantial separation of alkali metal ions from the tungsten during the process. The concentration of the alkali metal ions arising in the initial phase separation is reduced from about 70 grams per liters to less than about 27 milligrams per liter in the aqueous solution prior to ion exchange. Prior the ion exchange step, the raw aqueous alkali metal tungstate solution contains a variety of anions including WO4−2, MoO4−2, HSO4−1, HPO4−2, SiO−1 and OH−1. By using a strong basic ion exchange resin, these anions can be separated from the tungsten material which is eluted and substantially purified. Prior to contact with a column, the alkali metal tungstate solution must be adjusted to an optimal concentration that ranges from about 10 to 50 grams of sodium tungstate per liter of aqueous solution. As the concentration of alkali metal tungstate increases, the binding capacity of the resin is substantially reduced.
In the crystallization step, solution from the ion exchange step is evaporated, the ammonia and water are volatilized forming ammonium paratungstate NH4[(H2W12O42]10, a low solubility salt. This salt readily crystallizes substantially increasing the purity. Upon heating the ammonium paratungstate crystal to calcining temperatures, ammonia and water are driven from the salt resulting in the formation of tungsten oxide, typically the blue tungsten oxide crystal form.
An experiment was conducted to determine the utility of the invention in converting a variety of metal sources to metal showing that the process can be used with high grade or low grade ore and alloy components. In the conduct of the experiment, the metal source, sodium carbonate and silicon dioxide were mixed in a mixing cup in the amounts shown in the following tables. The formulation was mixed and charged to a Coors crucible of an appropriate size. The crucible was heated in the muffle furnace from ambient at a heating rate of 10° C. per minute until reaching a maximum temperature of 1200° C. The crucibles were maintained at that temperature for at least 180 minutes. The crucibles were removed from the muffle furnace after the termination of the heating period and cooled. The crucibles were broken apart, the separated silica glass phase was removed and the precipitated metalate fraction was placed into appropriately sized glass beakers with deionized water for dissolution of the sodium metalate. Once fully dissolved, the metalate solutions were filtered using a vacuum pump and then diluted to a constant volume of 250 milliliters. The aqueous samples were analyzed for soluble metalate or tungstate salt using an Asoma XRF Elemental Analyzer (from the Asoma Instruments Company of Austin, Tex.). The following tables show that the results of the experiments using a source of tungsten comprising a combination of a 56.3 wt % WO3 source, an 86.6 wt % WO3 source, and a 31 wt % WO3 source. In all cases, the metal source provides substantial recoveries of tungsten from the flux process.
The following experiment reproduces the method used to obtain the data from the previous tables. However, in this experiment, a mixture of tungsten carbide and tungsten oxide WO3 were obtained and combined with sodium carbonate and silicon dioxide in the flux process described above. The mixing of tungsten oxide sources with other metal sources can provide flexibility in costs and raw material supplies for producing the tungsten metal. This experiment shows that different sources of tungsten can be mixed in the same mixture for melt processing and the resulting process will result in a high quality product and the silica glass fraction would be able to accommodate the impurities from any tungsten source or combinations of sources.
Mixing two high-recovery formulations of each independent WO3 source produced a hybrid charge with a high recovery, resembling an average of the two formulations.
In an example of how a reactor of the invention, specifically the reactor shown in
Further, in
Referring again to
The material of construction for the reactor vessel 72 and core 74 is chosen to maximize electrical heating efficiency by electrical induction, good thermal stability, resistance to chemical attack and oxidation of the materials. The chemical charge and the result in reaction products should also not substantially modify the materials of the vessel 72 and the core 74. The shape of the reactor core with respect to the vessel 72 is driven by the chemical and physical response of the reaction mixture to the temperature of the core and the power draw from the solenoid. In the beginning, the charge material, usually a powder blend with moderate bulk density, reacts upon heating and contact with the reactor core 74 and vessel 72. As the material begins to react, it increases in density and causes a microcorrosion reaction with nearby components in the charge. As the reaction continues and the temperature rises, the materials fuse and melt. The fluidity, viscosity and density of the material causes the fluid to flow by force of gravity to the bottom of the vessel. The molten material then flows through a plurality of apertures 104 at the base of the core into the bottom of the reactor and accumulate in the bottom of the reactor until they reach the height of the stand pipe 73 and then are permitted to exit the reactive vessel. The time during which the molten materials react within the reactor 70 is set by the depth of the stand pipe 73. The materials will be substantially complete in their reaction after a period of time at which the reaction will tend to slow in an accumulated mass in the bottom of the vessel 72.
Typical induction solenoid or coils can be obtained that operate at a power output of about 10 to about 300 KW at a power frequency of about 1 to about 10 kilohertz. The magnetic field formed by the solenoid flows around the solenoid to form a substantially parallel field within the reactive vessel. The field strength interacts with the conductive portion of the vessel and the reactor core to produce heating. The internal diameter of the induction solenoid is typically about 0.3 to about 1 meter. The height of the solenoid is typically about 0.3 to about 1.5 meter and is substantially circular in cross-section.
The reactor vessels 52, 62 and 72 of
The typical charge to the reactor includes silica, an alkali metal salt and a source of metal. The configuration of the reactor must be such that the reactor reaches a temperature sufficient to fuse the silica, alkali metal salt and source of metal. Such a temperature is typically at least 800° C. and typically ranges from about 950° C. to about 1400° C. At a temperature of about 1050° C. to about 1300° C., the reactive vessel of the invention can typically process sufficient reactor charge such that the reactor will produce about 60 to about 200 kilograms per hour of total reaction product including silica glass and alkali metal metalate.
The reactor vessels of
Alternatively, the molten material flowing from the reactor either in a batch mode or a continuous mode can be separated into a silica glass phase and a metalate phase upon exiting the reactor. The molten material can be introduced into a crucible wherein it forms a separate glass and metalate phase. The materials can be removed from the crucible after cooling and can be easily mechanically separated. One mode of mechanical separation involves crushing the materials into relatively small but manageable particulates. The highly dense metalate can then be separated due to substantial differences in density to a metalate portion and a silica portion.
The molten material can also be separated using a porous separation plate. We have found that a graphite plate having a random array of apertures can act as a separating surface. The glass phase tends to not wet the graphite portion and tends to be retained on the surface of the circular portion. The metalate material tends to wet the graphite portion and then rapidly passes through the perforate portions of the plate effecting a clean and substantial separation of the glass phase from the metalate phase.
The reactor of the invention can be used in three types of reaction schemes. In one embodiment of the invention, the reaction scheme is a vitrification process in which material particulate can be fused within a glass to isolate the particulate contents from the environment. In such a reaction, the reactor is used primarily to fuse silica into a glass and cause the particulate, in a reacted or unreacted state, to form within the vitrified glass, encapsulating the particulate within the glass structure isolating the particulate from the environment. This process is primarily thermal.
In another embodiment of the invention we have found that one component of the reaction product is a calcium metalate due to the presence of calcium salts in most metal sources. We have found that as the water extracts the soluble sodium metalate salts from the particulate grind, that the substantially insoluble calcium metalate forms a fine precipitate that is removed with the sodium metalate solution and can be then collected and returned to the reactive vessel for further processing in order to recycle all metalate into the reactor for the purpose of ensuring that all metalate is ultimately converted into soluble sodium or other alkali metal salts.
In another embodiment of the invention, we have found that the sodium metalate tends to act as a solvent for any other metalate salt for purification purposes, thereby broadening the utility of the invention to include other metals that may be purified using this embodiment of the invention. In yet another embodiment of the invention, sodium metalate may be used as a reaction medium. In a process for the purpose of removing high value material from a low grade source, the sodium metalate material of the invention can act as a reaction medium or solvent. If the source has a reactive metal component, the sodium metalate can be contacted with the source and can cause a reaction within the metal source to form a second metalate species that can be absorbed into and carried with the reaction medium. Alternatively, the alkali metal metalate material of the invention can act as a solvent material. High value materials within a source can be contacted with the sodium metalate material. High value materials within the source can then become solubilized in and carried with the metalate material as a solvent and, once removed from the source, can then be further purified into high value materials.
In an example of the above embodiments, we have found that by using the sodium metalate product of the invention, noble metals such as gold, silver, platinum and iridium can be extracted from a low value source by contacting the source with the metalate. Any substantial quantity of noble metal that is unoxidized in the reaction mixture will be soluble in, and will be separated with, the melt from the source material. Once removed, the metalate can be easily processed to remove the noble metal species from the metalate.
One substantial advantage of the processes of this invention is that winning of metal from low value sources for the production of metals such as tungsten, tantalum, niobium, palladium and other similar metals can commercially be obtained using the reaction or extraction mode using sodium metalate of the invention. Since we have found that after the reaction is complete, the silica glass phase can be separated from the metalate phase and that the reaction of the invention can rapidly concentrate, even a low concentration of metal in a low quality ore metal source results in the efficient formation of substantially pure metalate phase. As a result, even tailings from ore production mining or metal winning can be a valuable source of metal for further processing when employing the methods of the invention.
The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/873,735, filed Dec. 8, 2006, which application is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60873735 | Dec 2006 | US |
