Patent Application
20180282837
The technical field relevant to apply the developed invention is mining and metallurgy, since it allows extracting ferrous and non-ferrous metals from sulphurated minerals bearing them by applying an improved direct reduction process, with no emissions of sulphur dioxide and without producing slag, which is commonly produced by conventional pyrometallurgical plants, thus minimizing environmental pollution. In addition, through the proposed regeneration and recycling of iron as reducing agent and sodium carbonate as flux, the operating costs of the process are substantially reduced.
According to Aranguren F & Mallol A. (1), several metallurgical reduction processes were known and applied for some time in metal extraction activities. Among them, the reduction of iron oxide minerals (mainly, hematite and magnetite) stands out for its relevance, since it allows to obtain pig iron or direct-reduced iron, metallurgical products from which steel can be obtained, depending on the technique applied. In these cases, coal or metallurgical coke and/or carbon monoxide and/or hydrogen gas and/or natural gas are required as reducing agents; limestone and dolomite are required as alkaline fluxes, where, at the same time as the main process occurs, the reduction of other elements takes place in the same reactor, elements such as silicon, titanium, manganese, chromium, vanadium, among others, always from its oxidized compounds. The following are established as essential chemical reactions in the reduction process applied to oxidized iron minerals:
3 Fe2O3+CO→2 Fe3O4+CO2
Fe3O4+CO→3 FeO+CO2
FeO+CO→Fe+CO2
Similarly, as indicated by Aranguren & Mallol (2), in 1620 the first furnace for iron minerals processing was built in the United States of America. Later, during several centuries and until the creation of comprehensive plants, which included the production of pig iron and metallurgical coke, the iron and steel industry commonly used producer gas as fuel, which performed a dual function, both as heating agent and reducing agent. Producer gas was produced by total gasification of a solid fuel, such as bituminous coal, anthracite, lignite, or the same coke, being able to produce the gasification with air alone, air and water vapor, or also with oxygen and water vapor. The fundamental reactions that occur in a gas-powered reactor are shown below:
C+O2→CO2
C+CO2→2 CO
C+H2O→CO+H2
C+2 H2O→CO2+2 H2
CO+H2O→CO2+H2
2 C+2 H2O→CH4+2 CO
Improving the already known reduction process of iron minerals and using carbon monoxide as reducing agent, in 1918 Wieber (3) proposed that gases resulting from iron minerals reduction, mainly carbon dioxide with residual carbon monoxide used as reducing agent, to be conducted to another reactor where coal combustion shall occur. This would generate more carbon monoxide from the same recycled carbon dioxide and from coal, reducing the consumption of the latter.
Given that the above-mentioned improved process requires the use, to a noticeable extent, of hydrogen gas as a reducing agent due to its greater heating power, the presence of hydrogen gas in the percentage composition of reducing gases should correspond to a range between 20% and 35%, which can be achieved if natural gas is used in a complementary manner, with a reaction to water vapor at high temperatures of:
CH4+H2O→3 H2+CO
being feasible to reduce iron oxide minerals with hydrogen gas using the following fundamental reactions:
3 Fe2O3+H2→2 Fe3O4+H2O
Fe3O4+H2→3 FeO+H2O
FeO+H2→Fe+H2O
On the other hand, the conventional techniques currently used to extract non-ferrous common metals (lead, copper, zinc, antimony, etc.) from their sulphurated minerals consist of toasting them to obtain oxidized compounds of the above-mentioned metals to, subsequently, apply pyrometallurgical processes to extract lead, copper, zinc, antimony, etc.; or, alternatively, hydro-electrometallurgical processes, as in the case of zinc extraction, being the following reactions fundamental in the pyrometallurgical extraction of non-ferrous common metals (4):
2 PbS+3 O2⇄2 PbO+2 SO2
2 PbO+C⇄2 Pb+CO2
2 Cu2S+3 O2⇄2 Cu2O+2 SO2
2 Cu2O+C⇄4 Cu+CO2
2 ZnS+3 O2⇄2 ZnO+2 SO2
2 ZnO+C⇄2 Zn+CO2
2 Sb2S3+9 O2⇄2 Sb2O3+6 SO2
2 Sb2O3+Sb2S3⇄6 Sb+3 SO2
One of the characteristics of the plants implementing these latest processes is the large amount of emissions of sulphur dioxide they generate, forcing them to install expensive sulphuric acid manufacturing plants to minimize environmental pollution, as well as great amounts of slag, which are stockpiled near the metallurgical plants, polluting the environment in the area of influence.
In the same way, it is also known that coal gas (by-product of blast-furnace coke furnaces) contains hydrogen sulphide gas, which is one of the components that should be removed before its usage. An alternative is to pass the hydrogen sulphide gas through a mass of hydrated iron oxide to obtain the following reaction (5):
Fe2(OH)6+3 H2S⇄Fe2S3+6 H2O
therefore, when the mass of hydrated iron oxide is saturated with sulphur, the compounds generated are aerated, obtaining not only elemental sulphur (S), but also the regeneration of hydrated iron oxide due to the following reaction caused by the presence of oxygen and water:
Fe2S3+3 H2O+3/2O2⇄Fe2(OH)6+3 S
It is known that only in 1823 the first plant of sodium carbonate production on an industrial scale was established in England, applying the process conceived by Nicolas Leblanc (6), which was used up to 1885, approximately. The following are the main chemical reactions of the above-mentioned process:
NaCl+H2SO4→NaHSO4+HCl
NaCl+NaHSO4→Na2SO4+HCl
Na2SO4+2 C→Na2S+2 CO2
Na2S+CaCO3→Na2CO3+CaS
In 1861, Ernest Solvay (7) developed the process named after him, which quickly became the leading process to produce sodium carbonate worldwide. The first industrial plant that applied this process was settled in Belgium in 1865. Later, in 1874, another plant was established in England and, in 1882, the largest plant at the time was implemented in the United States of America, which continues to operate nowadays. Then, in 1988, the world largest sodium carbonate industrial production plant was settled in France and used the Solvay Process, which has the following main chemical reactions:
CaCO3→CaO+CO2
CaO+H2O→Ca(OH)2
NH3+CO2+H2O+NaCl→NaHCO3+NH4Cl
2 NaHCO3→Na2CO3+H2O+CO2
Ca(OH)2+2 NH4Cl→2 H2O+CaCl2+2 NH3
In Peru, since 1955 (8), studies analyzing the possibility of implementing a sodium carbonate plant were carried out. However, it was in 1978 (9) that the implementation of a sodium carbonate plant was envisaged, and then became effective and started to operate in 1988 (10); this technology was known as the Soda—Carbon Dioxide Gas Process, which is based on the following chemical reaction:
2 NaOH+CO2→Na2CO3+H2O
The technological innovation developed allows extracting, in addition to iron, metals such as, but not limited to, lead, silver, zinc, copper, molybdenum, antimony, arsenic, with or without associated iron, and with gold that could be hosted as inclusion in certain cases, from sulphurated minerals containing them. For this purpose, an improved direct reduction process is applied to the metals to be extracted, which is achieved without sulphur dioxide emissions nor producing slags commonly generated by conventional pyrometallurgical plants, thus minimizing environmental pollution. In addition, through the proposed regeneration and recycling of iron as reducing agent and sodium carbonate as flux, the operating costs of the process are substantially reduced.
This technology can be also applied to the remediation of tailings deposits containing various ferrous and non-ferrous metal sulphides. Currently, the metallurgical mining matrix worldwide states that concentration plants only recover, through a selective flotation process, metallic sulphides with commercial value, such as argentiferous galena: PbS bearing Ag, chalcopyrite: CuFeS2 bearing Au, and sphalerite: ZnS, leaving great amounts of iron sulphides in the tailings, such as pyrite, pyrrhotite, and arsenopyrite, which are depressed in flotation cells together with non-metallic minerals extracted from mine, mainly quartz (SiO2) and other silicates, which are stockpiled in tailings deposits under inadequate conditions in most cases. This is one of the main reasons the abovementioned tailings deposits are very likely to generate pollutants such as arsenical and acidic water in rainy seasons, due to the high amount of arsenic and iron sulphides they contain.
The remediation of the tailings of these concentration plants registered as mining environmental liabilities would only be feasible if we take economic advantage of most mineral species existing in said tailings, trying to mainly recover the metallic mineral species disposed, such as pyrite, pyrrhotite, and arsenopyrite, not only because these minerals, part of the main pollutant species, can have important values of gold and silver, but also because they can serve as raw material for obtaining metallic iron by using this low-cost technological innovation with minimal environmental impact; thus, iron becomes a metallurgical product with significant commercial value from which steel can be obtained for the construction and metal-mechanic industries.
In addition, other residual metallic sulphides of commercial value might be also recovered through selective flotation, provided that these are contained in the tailings deposits. It is important to take them into account, not only because that would help to increase the income from the sale of non-ferrous metals to be obtained, which would be extracted from sulphurated minerals bearing them through the technological innovation developed, but also because the application of this invention would finally allow to obtain truly clean solid waste that might be used in the construction industry as an aggregate (fine sand) or raw material for white bricks manufacturing.
In the smelting furnace considered for this process, the concentrated sulphurated minerals, bearing the metal or metals to be extracted, are smelted, as the case may be. For this purpose, iron is used as reducing agent and sodium carbonate as flux, resulting in smelted or powdered metal or metals, depending on their physical properties, a slag of controlled composition formed by ferrous oxide and sodium sulphide, and gaseous emissions of carbon dioxide. In order to have an effective control of the slag composition, which is essential to regenerate and recycling the reducing agent and flux, general reactions are established for the cases below, considering the following general definitions:
MxSy+y Fe+y Na2CO3→x M+y Na2S+y FeO+y CO2
MxFeySz+(z−y)Fe+z Na2CO3→x M+z Na2S+z FeO+z CO2
MxFeySz+(Au,Ag)m+n Pb+(z−y)Fe+z Na2CO3→→x M+m(Au,Ag)+n Pb+z Na2S+z FeO+z CO2
[(M1)aFebSc+(c−b)Fe+c Na2CO3]+[(M2)xFeySz+(z−y)Fe+z Na2CO3]→→a (M1)+x (M2)+(c+z)Na2S+(c+z)FeO+(c+z) CO2
(M1)aFebSc+(M2)xFeySz+[(c−b)+(z−y)]Fe+(c+z) Na2CO3→→a (M1)+x (M2)+(c+z)Na2S+(c+z)FeO+(c+z)CO2
(M1)a(M2)bFeySz+(z−y)Fe+z Na2CO3→a(M1) b(M2)+z Na2S+z FeO+z CO2
[(M1)a(M2)bFecSd+(M3)w(M4)xFeySz+[(d−c)+(z−y)]Fe+(d+z)Na2CO3]→→a (M1)+b (M2)+w (M3) x (M4)+(d+z)Na2S+(d+z)FeO+(d+z)CO2
It should be noted that the above-mentioned stoichiometric formulation is valid even when some (or all) of the following cases occur:
In this sense, the simultaneous presence of both cases mentioned above, would have the following stoichiometric formulation, where M4=M2, and y=0:
[(M1)a(M2)bFecSd+(M3)w(M2)xSz+[(d−c)+(z)]Fe+(d+z)Na2CO3]→→a (M1)+(b+x) (M2)+w (M3)+(d+z) Na2S+(d+z)FeO+(d+z) CO2
The present invention includes a new technological process of seven stages, which are schematized in detail in the following diagrams.
Preferred examples of the real applicability of the Technological Innovation described in the previous points:
The extraction of Copper, Gold as an inclusion, and other metals from the sulphurated minerals that contain them (Chalcopyrite (CuFeS2)), Chalcocite: Cu2S, Bornite: Cu5FeS4, Enargite: Cu3AsS4, Carrotite: CuCo2S4 and Tenantite: Cu12As4S13) to which they can be associated, is based on using appropriate amounts of both the reducing agent Iron (Fe), as well as the flux Sodium Carbonate (Na2CO3), and the products of the chemical reaction that occurs between the aforementioned reactants are the following: Metallic Copper (Cu) melted with Gold, if it was an inclusion, a slag constituted by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), and gaseous emissions of Carbon Dioxide (CO2).
In the case of the Chalcopyrite, the chemical formula established for this sulphurated mineral is used: CuFeS2, from which the Copper (Cu) is extracted, specifying that the smelting of the concentrates of this sulphurated mineral together with Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux should be carried out considering the appropriate stoichiometric quantities, not only for the direct reduction of Copper (Cu), but also to control the composition of the slag to be produced, so that the regeneration and recycling of both the reducing agent Iron (Fe) and the flux of Sodium Carbonate (Na2CO3) is possible in the following sub-processes, which implies that the slag of the direct reduction process of Copper (Cu) should not be composed of three or more compounds, but only two, and it is necessary that one of them is soluble in Water, that is, it must be composed by the insoluble compound Ferrous Oxide (FeO) and by the highly soluble compound Sodium Sulphide (Na2S), so that the products of the chemical reaction in the reactor are high density molten Copper (Cu), containing Gold if it was an inclusion, an alkaline and low density fluid slag, and the gaseous effluent Carbon Dioxide (CO2), according to the following reaction:
CuFeS2+Au+Fe+2 Na2CO3→Cu+Au+2 Na2S+2 FeO+2 CO2
It is specified that the amount of flux that must be added to the reactor should be appropriate so that Ferrous Sulphide (FeS) does not appear in the slag. According to chemical thermodynamics, the reaction begins to occur from 1100° C., and should preferably be completed at 1350° C.
Due to the reaction mechanisms involved in the process of direct reduction of Copper from the sulphur minerals that contain it (Chalcopyrite, Chalcocite, Bornite, Enargite, Carrotite and Tenantite), the number of gram-atoms of Iron (Fe), or its equivalent in weight, which will have to be considered as a reducing agent reactant in the aforementioned process, is directly related to the number of Sulphur (S) atoms contained in the sulphide copper mineral, and the gram-atoms of Iron, or its equivalent in weight, that are contained in the copper sulphurated minerals such as Chalcopyrite and Bornite must be reduced to the resulting amount, if applicable. On the other hand, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which must be considered as a reactant flux in the aforementioned process, is also directly related to the amount of Sulphur atoms existing in the chemical formula of Chalcopyrite or other copper-containing sulphurated minerals such as Chalcocite, Bornite, Enargite, Carrotite and Tenantite, according to the corresponding chemical reactions specified that follow:
Cu2S+Fe+Na2CO3→2 Cu+FeO+Na2S+CO2
Cu5FeS4+3 Fe+4 Na2CO3→5 Cu+4 FeO+4 Na2S+4 CO2
Cu3AsS4+4 Fe+4 Na2CO3→3 Cu+As+4 FeO+4 Na2S+4 CO2
CuCo2S4+4 Fe+4 Na2CO3→Cu+2 Co+4 FeO +4 Na2S+4 CO2
Cu12As4S13+13 Fe+13 12 Cu+4 As+13 FeO+13 Na2S+13 Na2CO3→CO2
In this process, the extraction of the lead metal from the Galena (PbS), or from the sulphurated mineral that contains it, is based on the appropriate use of both Iron (Fe) as a reducing agent as well as Sodium Carbonate (Na2CO3) as flux, and the products of the chemical reaction that occurs between the aforementioned reactants are the following: Cast metal lead, a slag formed by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), and gaseous emissions of Carbon Dioxide (CO2). In order to have an effective control during the formation of the slag, since it is critical step, the chemical formula established for the Galena or Lead Sulphide is used: PbS, a sulphurated mineral from which metal lead is to be extracted. It should be considered that the application of the improved direct reduction process involves the use of the reducing agent and the flux in the appropriate stoichiometric proportions, so that the regeneration and recycling of the referred metallurgical inputs are feasible in the following processes. For this purpose, it is indispensable for the slag, at the end, to be formed not by three or more compounds, but only by two, and one of them should be soluble in Water. In this regard, it should be pursued that the slag obtained from the metal lead extraction in smelting furnace only consists of the insoluble compound Ferrous Oxide (FeO) and the water-soluble compound Sodium Sulphide (Na2S), which requires full control of the formation of Ferrous Sulphide (FeS) in the slag, and can be achieved if the main reaction of the direct reduction process using Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux is the following:
PbS+Fe+Na2CO3→Pb+Na2S+FeO+CO2
According to chemical thermodynamics, the aforementioned reaction begins to occur at 950° C. and should preferably be completed by 1400° C.
Likewise, while extracting Silver from the sulphurated minerals that contain it, such as, without limitation, Acanthite or Ag2S (Argentite at temperatures greater than 177° C.), proper use of both Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux should be applied, and the products of the chemical reaction between the aforementioned reactants are the following: cast metal silver, a slag formed by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), and gaseous emissions of Carbon Dioxide (CO2). Regarding the slag, the same criteria and technical foundations for its conformation are applied, so it is necessary for the chemical reaction occurring inside the furnace, where the sulphurated minerals concentrates are cast, to be the following:
Ag2S+Fe+Na2CO3→2 Ag+Na2S+FeO+CO2
According to chemical thermodynamics, the aforementioned reaction begins to occur at 775° C. and should preferably be completed by 1425° C.
However, in general, Galena (PbS) is associated with various sulphide Silver minerals such as Acanthite (Ag2S), so that the reactants must be handled in the smelting furnace in order to carry out the following chemical reaction:
PbS+Ag2S+2 Fe+2Na2CO3→Pb+2Ag+2Na2S+2FeO+2CO2
It should be noted that Acanthite or Ag2S contributes one more atom of Sulphur (S) to the reactants, which should be reflected in the amounts of the reducing agent Iron and the flux Sodium Carbonate that must be added. According to chemical thermodynamics, the aforementioned reaction begins at 950° C. and should preferably be completed by 1150° C., although it was experimentally verified that the reaction occurs completely at 950° C.
In view of the above, it is concluded that, during the process of direct reduction of Lead from the sulphurated mineral containing it, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which should be considered as a reactant flux in the process, is directly related to the sulphur atoms existing in the chemical formula of Galena or Lead Sulphide (PbS), a mineralogical compound that contains the metal Lead to be extracted. Likewise, the number of gram-atoms of Iron (Fe), or its equivalent in weight, that will need to be considered as a reactive reducing agent in the process is directly related to the number of gram-moles of Ferrous Oxide (FeO) that will be obtained and, as it depends on the number of gram-moles of Oxygen (O2) released as such in the chemical reaction, it is inferred that the required amount of gram-atoms of Iron (Fe) atoms will depend on the number of moles of Sodium Carbonate (Na2CO3) considered as a flux and also on the number of Sulphur atoms (S) contained in the Galena or Lead Sulphide (PbS).
In this process, the extraction of Zinc metal from the Sphalerite (ZnS) or the sulphurated mineral that contains is done by applying the improved direct reduction process, which is based on the proper use of both Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux, and the products of the chemical reaction between the reactants are the following: metal gaseous Zinc (later liquefied by condensation), a light and fluid slag formed by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), and gaseous emissions of Carbon Dioxide (CO2). Given its importance, it is also necessary to have an effective control during the formation of the slag during the direct reduction process. To do this, once the smelting furnace is charged with the concentrated minerals of Sphalerite, the Iron (Fe) is added as a reducing agent and Sodium Carbonate (Na2CO3) as a flux, specifying that the use of these metallurgical inputs must be done in stoichiometric proportions, so that the regeneration and recycling of both the reducing agent and the flux is possible from the products obtained from the chemical reaction. This can be achieved if the slag is mainly formed not by three or more compounds, but only by two, and one of them should be soluble in Water. In this regard, it should be pursued that the slag obtained from the metal Zinc extraction in the smelting furnace consists only of the insoluble compound Ferrous Oxide (FeO) and the water-soluble compound Sodium Sulphide (Na2S), which implies full control of the non-formation of Ferrous Sulphide (FeS) in the slag, for which it is necessary that the chemical reaction of the process complies with the following:
ZnS+Fe+Na2CO3→Zn+Na2S+FeO+CO2
According to chemical thermodynamics, the reaction begins at 1000° C. and is preferably completed at 1850° C.
In this sense, if Sphalerite (ZnS) is associated with sulphurated Silver minerals such as Acanthite (Ag2S), then, the chemical reaction that will occur in the smelting furnace is the following:
ZnS+Ag2S+2 Fe+2Na2CO3→Zn+2Ag+2Na2S+2FeO+2CO2
It should be noted that Silver, when presented in association with the zinc sulphides in the form of Acanthite or Ag2S, contributes one more Sulphur (S) atom to the reactants, which will affect the quantities required from the reducing agent Iron and the flux Sodium Carbonate. According to chemical thermodynamics, the reaction begins at 950° C. and should preferably be completed at 1150° C.
In view of the above, it is concluded that, during the process of direct reduction of Zinc from the sulphurated mineral containing it, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which should be considered as a reactant flux during the process, is directly related to the existing sulphur atoms in the chemical formula of Sphalerite (ZnS), a mineralogical compound containing the zinc metal to be extracted. Likewise, the number of gram-atoms of Iron (Fe), or its equivalent in weight, which must be considered as a reactive reducing agent in the process, is directly related to the number of gram-moles of Ferrous Oxide (FeO) obtained as a product and, as it depends on the number of gram-moles of Oxygen (O2) released as such in the chemical reaction, it is inferred that the required gram-atoms of Iron (Fe) will depend on the number of moles of Sodium Carbonate (Na2CO3) considered as a flux and also on the number of Sulphur atoms (S) contained in the Sphalerite (ZnS).
In this process, the extraction of Gold (Au), Silver (Ag) and Iron (Fe) contained in the sulphurated minerals of the latter, such as Pyrite (FeS2), Pyrrhotite (FeS), Marcasite (FeS2), is carried out by applying the improved direct reduction, using the Sodium Carbonate flux in an appropriate way and the Iron in a complementary way as a facilitator of the atomic exchange, which depends on the mineralogical species. In the case of mono-sulphurated iron minerals (pyrrhotite), the iron content in these is sufficient to cause the chemical reactions between the reactants that allow the extraction of Gold and Silver. In the case of the bi-sulphurated iron minerals, given that there is twice the sulphur atoms in the reactants, it will always be necessary to add the stoichiometrically necessary amount of iron as a reactant so that it acts efficiently as a facilitator of the atomic exchange in the chemical reaction. However, for an effective extraction of this precious metals, Gold and Silver, it is necessary to introduce not only the iron sulphurated concentrates in the smelting furnace together with the additional Sodium Carbonate and Iron flux if necessary, but also metal Lead, so that it together with the precious metals Gold and Silver form a high density cast metal product that can be sieved and that, in turn, is easily separable from the other product called slag, which will be of low density and low viscosity because it will be mainly composed of Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), which gives gaseous emissions of Carbon Dioxide (CO2) as a third product.
Also, it is important to specify that the metal Lead, the same one that is added to the smelting furnace together with the reactants, is obtained as a cast metal product carrying the metals Gold and Silver, which are also cast. On the other hand, in order to have an effective control during the formation the slag, it is necessary that the iron sulphide concentrate smelting, as in the case of the gold pyrites, which is introduced in the furnace together with the additional Iron (Fe) required and the indispensable Sodium Carbonate (Na2CO3) as a flux, is made considering the appropriate stoichiometric amounts of these metallurgical inputs, not only to obtain the maximum recoveries of Gold and Silver, but also to meet the need to have a controlled composition of the slag to be produced, so that the regeneration and recycling of both the reducing agent Iron (Fe) and the flux of Sodium Carbonate (Na2CO3) is possible in the subsequent processes. This implies that care must be taken so that the slag from the Gold extraction process (Au) is formed not by three or more compounds, but only by two, and one of them should be soluble in Water, so that the three products of the chemical reaction happening in the smelting furnace are, first of all, the high-density cast metal product consisting of Gold, Silver and Lead, secondly, a low density fluid slag formed by Ferrous Oxide and Sodium Sulphide (FeO and Na2S) and, finally, the gaseous effluent Carbon Dioxide (CO2), according to the following reaction:
Au+Ag2S+Pb+FeS2+2 Fe+3Na2CO3→Au+2Ag+Pb+3Na2S+3FeO+3CO2
According to chemical thermodynamics and considering the energy costs involved, the temperature range in which the reaction preferentially occurs is between 775° C.-950° C. The above chemical reaction is merely an example, since it is known that the mineralogical species contained in Silver appear in much lower quantities (Ounces/Ton) than the percentage amounts contained in Pyrite.
It should be noted that Silver is associated with iron sulphides in the form of Acanthite Ag2S (Argentite above 177° C.) and, therefore, contributes one more atom of Sulphur (S) to the reactants, which will affect the quantities required of the reducing agent Iron and the flux Sodium Carbonate. Likewise, the amount of flux that must be added to the reactor must be correct so that Ferrous Sulphide does not form in the slag (FeS).
In view of the above, it can be inferred that, in case no silver sulphurated mineral is associated with Pyrite (FeS2), and if the latter is only gold pyrite, then the following chemical reaction will take place in the smelting furnace:
Au+Pb+FeS2+Fe+2Na2CO3→Au+Pb+2Na2S+2FeO+2CO2
In accordance with chemical thermodynamics and considering the energy costs, the temperature range in which the reaction preferentially occurs is between 750° C.-950° C., and it should be specified that the gold extraction process from gold pyrite or Iron disulphide (FeS2) is characterized by, on the one hand, the number of gram-atoms of iron (Fe), or its equivalent in weight, which will need to be considered as a reactive reducing agent in the process, is directly related to the number of atoms of Sulphur (S) contained in the Pyrite or Iron disulphide (FeS2), exceptionally the gram-atoms of Iron or its equivalent in weight that are contained in the gold pyrite must be deducted in this calculation. And, on the other hand, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, that should be considered as a reactant flux in the Gold extraction process is also directly related to the amount of existing Sulphur atoms in the chemical formula of Pyrite or Iron Disulphide (FeS2).
It should be noted that, by means of complementary metallurgical processes such as the dissolution of part of the slag (of the soluble Sodium Sulphide or Na2S), the filtering of the solid waste (FeO), the agglomeration and sintering of the Ferrous Oxide (FeO) pellets and the reduction of Iron from the FeO pellets using reducing gases (Carbon Monoxide and Hydrogen), the metal iron is finally obtained.
In this process, the extraction of the Antimony metal from the sulphurated mineral that contains it is done by applying the direct reduction improved with regeneration and recycling of the metallurgical inputs involved, which is based on the proper use of both Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux, and the products of the chemical reaction between the reagents are the following: metal Antimony, a slag formed mainly by the insoluble compound Ferrous Oxide (FeO) and by the water-soluble compound Sodium Sulphide (Na2S), and, gaseous emissions formed mainly by Carbon Dioxide (CO2). In order to effectively control the formation of the slag, the concentrated minerals Stibnite or Antimony Trisulphide (Sb2S3), which is a sulphurated mineral extracted from metal Antimony, should be inside the smelting furnace. Then, the reducing agent Iron (Fe) and the flux Sodium Carbonate (Na2CO3) are added to the reactor in stoichiometric proportions that allow the regeneration and recycling of the mentioned metallurgical inputs in the subsequent processes; for such purpose, the formation of the slag should be controlled, taking care that the latter is constituted not by three or more compounds, but only by two, and one of them should be soluble in Water. In this regard, it should be pursued that the slag obtained from the smelting furnace during the metallic antimony extraction is only composed of Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), which implies that the formation of Ferrous Sulphide (FeS) in the slag must be controlled, for which it is necessary for the reaction of the direct reduction process using Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux to be the following:
Sb2S3+3 Fe+3 Na2CO3→2Sb+3 Na2S+3FeO+3 CO2
In this case, chemical thermodynamics state that the reaction begins at 300° C. and should preferably be completed at 625° C.
In view of the above, it is concluded that, in the direct reduction process of Antimony from the sulphurated mineral that contains it, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which must be considered as a reactant flux in the process, is directly related to the sulphur atoms existing in the chemical formula of Stibnite or Antimony Trisulphide (Sb2S3), a mineralogical compound containing the metal Antimony to be extracted. Likewise, the number of gram-atoms of iron (Fe), or its equivalent in weight, which will need to be considered as a reactive reducing agent in the process, is directly related to the number of gram-moles of Ferrous Oxide (FeO) to be obtained as product and, since it depends on the number of gram-moles of Oxygen (O2) released as such in the chemical reaction, it is concluded that the required gram-atoms of Iron (Fe) atoms will depend on the number of moles of Sodium Carbonate (Na2CO3) considered as a flux and also on the number of Sulphur atoms (S) contained in the concentrated mineral of Stibnite or Antimony Trisulphide (Sb2S3).
Regarding the extraction of Silver and Antimony from Stefanite (Ag5SbS4), the established procedure for non-ferrous sulphurated minerals from two polyatomic metals is applied:
Ag5SbS4+4 Fe+4 Na2CO3→5 Ag+Sb+4 Na2S+4 FeO+4 CO2
Regarding the extraction of Antimony and Silver from the argentiferous Tetrahedrite (Ag3SbS3+x(Fe, Zn)6Sb2S9), considering for this case that x=1 and that silver has replaced copper in the sulphosalt, the established procedure for combinations of ferrous and non-ferrous bimetallic sulphurated minerals:
[Ag3SbS3+(Fe, Zn)6Sb2S9]+6 Fe+12 Na2CO3→→3 Ag+3 Sb++6 Zn+12 Na2S+12 FeO+12 CO2
In this process, the extraction of molybdenum metal from the sulphurated mineral that contains it (Molybdenite or MoS2) is carried out by applying the improved direct reduction process, which is based on the appropriate use of both iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux, and the products of the chemical reaction between the reactants are the following: Powdered metallic molybdenum due to its high smelting point, a light and fluid slag formed by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), and gaseous emissions of Carbon Dioxide (CO2). Given its importance, during the aforementioned process of improved direct reduction, it is also necessary that there is an effective control of the formation of the slag. For this purpose, once the concentrated minerals of Molybdenite are inside the smelting furnace, Iron (Fe) as a reducing agent and Sodium Carbonate (Na2CO3) as a flux are added, stating that the use of these metallurgical inputs must be done in proper stoichiometric proportions, so that the regeneration and recycling of both the reducing agent and the flux is possible from the products obtained from the chemical reaction. This can be achieved if the slag is mainly formed not by three or more compounds, but only by two, and one of them should be soluble in Water. In this sense, it should be pursued that the slag obtained from the molybdenum metal extraction in the smelting furnace is only composed of the insoluble compound Ferrous Oxide (FeO) and the water-soluble compound Sodium Sulphide (Na2S), which implies that the non-formation of Ferrous Sulphide (FeS) in the slag must be controlled at the same time, for which the following chemical reaction is necessary in the main process:
MoS2+2 Fe+2 Na2CO3→Mo+2 Na2S+2 FeO+2 CO2
In accordance with chemical thermodynamics, considering the energy costs involved, the reaction begins at 1175° C. and should preferably be completed at 1375° C.
From the above, it is concluded that, during the process of direct reduction of molybdenum from the sulphurated mineral that contains it, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which must be considered as a reactant flux, is directly related to the sulphur atoms in the chemical formula of molybdenite or molybdenum disulphide (MoS2). Likewise, the number of gram-atoms of Iron (Fe), or its equivalent in weight, which will need to be considered as a reactive reducing agent in the process, is directly related to the number of gram-moles of Ferrous Oxide (FeO) that will be obtained as a product and, since it depends on the number of gram-moles of Oxygen (O2) released as such in the chemical reaction, it is inferred that the required gram-atoms of Iron (Fe) will depend on the number of moles of Sodium Carbonate (Na2CO3) considered as flux, and also on the number of Sulphur atoms (S) contained in the concentrated mineral Molybdenite or Molybdenite Bisulphide (MoS2).
During the extraction process of the Arsenic (As) and Gold (Au) metals contained in the Gold Arsenopyrite (AsFeS with Au), we have the following chemical reaction:
AsFeS+Au+Na2CO3→As+Au+Na2S+FeO+CO2
According to chemical thermodynamics, the previous reaction begins at 825° C., and the reaction must be completed preferably at 1325° C., considering reasonable energy costs.
When Gold Arsenopyrite is associated with Pyrite (FeS2), the above chemical reaction must be restated as follows:
AsFeS+Au+FeS2+Fe+3 Na2CO3→As+Au+3 Na2S+3 FeO+3 CO2
According to chemical thermodynamics and considering the energy costs, the previous reaction begins at 770° C., and the reaction must be completed preferably at 900° C.
Given that in certain cases the Gold Arsenopyrite is not only associated with Pyrite (FeS2) but also with Chalcopyrite (CuFeS2), the corresponding chemical reaction is the following:
AsFeS+Au+FeS2+CuFeS2+2 Fe+5 Na2CO3→→As+Au+Cu+5 Na2S+5 FeO+5 CO2
According to chemical thermodynamics, the above reaction begins at 875° C., and it must be completed preferably at 975° C. considering reasonable energy costs. It must have been verified that it is possible to extract all the Arsenic contained in the aforementioned gold Arsenopyrite concentrate at the most appropriate stoichiometric conditions and at a temperature of 1000° C.
Regarding the recovery of Gold, due to the relatively low boiling point of the metal Arsenic, it is essential to consider the use of the metal Lead as an additional reactant in the previous reactions, so that it can be at the end the carrier of the Gold in the products of the reaction, not only because of the affinity that exists between the two metals, but also because, together with Lead and Gold, they form a cast metal product of high specific weight, which is easily separated from the slag constituted by sodium sulphide and ferrous oxide in order to obtain a proper casting.
Likewise, as in the previous preferred examples, in order to effectively control the formation of the slag, the chemical formulas established for Arsenopyrite (AsFeS), Pyrite (FeS2) and Chalcopyrite (CuFeS2) are used, specifying that the smelting of the concentrates of these ferrous sulphurated minerals together with the reducing agent Iron (Fe) and with the flux Carbonate of Sodium (Na2CO3) should be carried out considering the appropriate stoichiometric amounts of the latter, not only so as to obtain a high recovery of Arsenic (As), Gold (Au) and Copper (Cu), as applicable, but also to be able to reduce and recycle the reducing agent Iron (Fe) and the flux Sodium Carbonate (Na2CO3) the subsequent processes, which implies that the slag from the extraction process of Arsenic (As) and Gold (Au) and/or Copper (Cu) should not be composed by three or more compounds, but only by two, by Ferrous Oxide (FeO) and water-soluble Sodium Sulphide (Na2S), avoiding Ferrous Sulphide (FeS) as a component of the slag at all times. The third product of the above chemical reactions is the gaseous effluents of Carbon Dioxide in the corresponding stoichiometric amounts.
For the extraction process of the metals Arsenic (As) and Silver (Ag) contained in Proustite (AgAsS3), the general referential chemical reaction established for the non-ferrous sulphurated minerals of two polyatomic metals is applied and, in this sense, the referred process has the following chemical reaction:
Ag3AsS3+3 Fe+3 Na2CO3→3 Ag+As+3 Na2S+3 FeO+3 CO2
the technical criteria discussed above prevail for all purposes.
During this extraction process of Iron (Fe) contained in sulphurated minerals such as, without limitation, Pyrrhotite (FeS), Pyrite and Marcasite (both FeS2), we use in an appropriate way both Iron (Fe) as facilitator of the atomic exchange, if the stoichiometric balance of the chemical reaction requires it, as well as Sodium Carbonate (Na2CO3) as a flux, so that a slag that can be cast is obtained as a product of the process, which must have low density and low viscosity because it will be formed by Ferrous Oxide (FeO) and Sodium Sulphide (Na2S), giving also the respective gaseous emissions formed by Carbon Dioxide (CO2) as a second product. Likewise, in order to effectively control the formation of the slag, the chemical formulas established for iron sulphurated minerals are used, such as Fe2S in the case of Pyrites, specifying that the smelting of one gram-mole of Pyrite with a gram-atom of Iron (Fe) and one gram of the Sodium Carbonate (Na2CO3) flux must be made considering the appropriate stoichiometric quantities in order to fully control the composition of the slag to be produced, so that the reduction and recycling of both the sodium carbonate (Na2CO3) and the iron (Fe) flux that should be added, in the case of having iron disulphides as reactant, is possible in the subsequent processes. This implies that care must be taken so that the slag from the Iron (Fe) extraction process is formed mainly not by three or more compounds, but only by two, one of them should be soluble in Water (Sodium Sulphide), but not the other one (Ferrous Oxide), and also the formation of Ferrous Sulphide (FeS) in the slag should be avoided with the following reaction:
FeS2+Fe+2 Na2CO3 FeO+2 Na2S+2 CO2
According to chemical thermodynamics, the above reaction occurs at 750° C., and should preferably be completed at 950° C., considering reasonable energy costs.
The control over the composition of the slag allows to take advantage of the high solubility of Sodium Sulphide (Na2S) in Water (H2O) and, for the purposes of having the Ferrous Oxide (FeO) compound as the only solid residue, it is indispensable that the slag, which is obtained in the smelting furnace for iron sulphide concentrates, is mixed in the Solution reactor with the amount of liquid water necessary, considering the solubility of Sodium Sulphide (Na2S), so that the following electrochemical dissociation reaction occurs:
Na2S+H2O⇄2 Na++HS−+OH−
Then, the resulting solution is filtered, and only solid waste formed by Ferrous Oxide (FeO) is separated. Next, the agglomeration and subsequent sintering of the solid waste is carried out in the respective furnace, at a controlled temperature, so that the agglomerated Ferrous Oxide (FeO) products, appropriately sintered and converted into “pellets”, acquire the mechanical property of compressive resistance required inside the Iron Reduction Furnace, where the FeO “pellets” will be finally sent. In order to achieve the reduction of the iron contained in Ferrous Oxide “pellets”, it is necessary to have coal, metallurgical coke or natural gas fuel available in the combustion furnace, where the reducing gases (carbon monoxide and hydrogen) will be generated, and insufflate them both with air and/or water vapor required as the case may be, such as the gaseous effluents Carbon Dioxide (residual CO2) and Carbon Monoxide (remaining CO) recycled from the Iron Reduction Furnace, which result in the following chemical reactions at a temperature between 900° C. and 1000° C., as applicable:
C+CO2→CO2
C+CO2→2 CO
C+H2O→CO+H2
C+2 H2O→CO2+2 H2
CO+H2O→CO2+H2
CH4+H2O→3 H2+CO
The sintered “pellets” are introduced and accumulated in the Iron Reduction Furnace in order to be subjected, for the necessary period, to the appropriate flow of the Carbon Monoxide (CO) and Hydrogen (H2) reducing gases from the combustion furnace, which causes the oxidation state +2 of Iron to be reduced to zero, thus making possible the extraction of metal iron (Fe) using the following chemical reactions:
FeO+CO→Fe+CO2
FeO+H2→Fe+H2O
From the above, it is concluded that, in a process of Iron extraction from Pyrite and Marcasite (both Iron Bisulphides: FeS2), Pyrrhotite (Iron Sulphide: FeS) or other Iron
Sulphides, the number of gram-atoms of iron (Fe), or its equivalent in weight, which will have to be considered as a reactant in the process, is directly related to the number of atoms of sulphur (S) contained in Pyrite and/or Marcasite (FeS2), with the exception that the gram-atoms of Iron, or its equivalent in weight, that are contained in the Pyrite and/or Marcasite to be cast must be deducted in this calculation. And, on the other hand, the number of moles of Sodium Carbonate (Na2CO3), or its equivalent in weight, which must be considered as a reactant flux in the Iron extraction process, is also directly related to the amount of Sulphur atoms existing in the chemical formula of Pyrite and/or Marcasite (Iron Bisulphides: FeS2). It is specified that, in the case that the cast of one mole gram of Pirotite (FeS) is desired, only one mole gram of sodium carbonate will be required as a flux. It is necessary to consider the previous indications so as to have control over the composition of the slag, which must be composed of Ferrous Oxide (FeO) and Sodium Sulphide (Na2S). Gaseous emissions of Carbon Dioxide (CO2) will be obtained as an additional product in these cases. As previously mentioned, an adequate control over the composition of the slag makes it possible to take advantage of the high solubility of Sodium Sulphide in Water, which, in turn, makes it possible to obtain Ferrous Oxide (FeO) as the only solid residue after the corresponding filtering, which will then be agglomerated and sintered to obtain “pellets” of Ferrous Oxide. The metal Iron, which was to be extracted from the Iron sulphurated minerals, is obtained from this pellets.
| Number | Date | Country | Kind |
|---|---|---|---|
| 002185-2015/DIN | Oct 2015 | PE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/PE2016/000014 | 8/15/2016 | WO | 00 |
