OA18868A

OA18868A - Sulfide recycling in manganese production

Info

Publication number: OA18868A
Application number: OA1201800333
Authority: OA
Inventors: Arash KASAAIAN
Original assignee: Arash KASAAIAN
Priority date: 2016-03-02
Filing date: 2017-03-02
Publication date: 2019-09-13

Abstract

A method of producing manganese metal or EMD by leaching a source of manganese with a solution comprising sulfuric acid to form a leach solution, adding one or more sulfides generated in a sulfide recycle stage to the leach solution in order to form sulfide precipitates comprising heavy metal sulfides, removing the sulfide precipitates from the leach solution, feeding the leach solution to one or more electrolytic cells, subjecting the purified leach solution to electrolysis so as to deposit manganese metal or EMD, reacting the sulfide precipitates with an acid to generate H2S, reacting the H2S with a hydroxide solution or an Mn2+ solution in order to produce one or more sulfides for recycle and precipitating heavy metal sulfides.

Description

SULFIDE RECYCLING IN MANGANESE PRODUCTION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application daims priority to U.S. Provisional Patent Application No. 62/302,648, filed Match 2, 2016, entitled Sulfide Recycling in Manganèse Production. The entire disclosure of the foregoing application is incorporated by référencé herein.

BACKGROUND

[0002] High purity manganèse and electrolytic manganèse dioxide (EMD) are typicatly produced by an electrolytic process (electrowinning, also known as electroextraction). For example, a manganesecontaining material is leached with a sulfuric acid solution to provide a manganèse sulfate (MnS04) solution. This leach solution is then subjected to electrolysis in an electrolytic cell, such that, depending on cell operating conditions, manganèse is deposited on the cathode or EMD is deposited on the anode. Typically, spent electrolyte solution comprising sulfuric acid, manganèse sulfate and ammonium sulfate ((NH4J2SCE) is withdrawn from the electrolytic cell, and provides most of the sulfuric acid solution for leaching. Afterthe spent electrolyte solution is combined with the manganèse ore (or other manganèse source), the resulting leach solution containing manganèse sulfate (as well as other sulfates, particularly (NH4)2S04)) is purified and thereafter returned to the electrolytic cell as the cell feed.

[0003] In the electrolytic production of high purity manganèse, the spent electrolyte solution used for leaching comprises anolyte withdrawn from the electrolytic cell, and the cell feed (i.e., the purified leach solution) is introduced into the cathode side of the cell (i.e., as the catholyte). Pure manganèse is deposited on the cathode(s) within the cathode chamber(s). For the electrolytic production of EMD (Mn02), spent electrolyte solution withdrawn from the cell (which is typically an undivided cell) is similarly used for leaching purposes, and the purified leach solution is used as the cell feed. Pure EMD is deposited on the anode(s) within the electrolytic cell.

[0004] The manganese-containing material is typically roasted prior to leaching in order to reduce higher oxides of manganèse (e.g., Mn02, Mn203 and Mn304) to manganèse oxide (ΜηΟ). Alternativeïy, and as described in U.S. Pat. No. 5,932,086, issued August 3, 1999, titled Process for Making Manganèse, and International (PCT) Pub. No. WO 99/14403, published March 25, 1999, titled Process for Making Manganèse (both of which are incorporated by référencé herein), the manganèse ore can be sintered in order to convert ΜηΟ2 to Μη3Ο4, and thereafter the Mn304 leached with a sulfuric acid solution along with a reducing agent (e.g., sulfur dioxide, activated carbon, hydrogen peroxide, hydrogen sulfide, reducing sugars and/or molasses) to provide a manganèse sulfate solution (i.e., the cell feed).

[0005] Purification of the leach solution is generally necessary prior to feeding the leach solution into the electrolytic cell (as the cell feed). In particular, the leach solution should hâve very low concentrations of Fe, Al, Si, Ni, Co, Cu, Ζη, Pb, Mo, etc. These impurities are deleterious to electrolysis operation, causing low current efficiency, and can also reduce the purity level of the manganèse or EMD product. Typically, iron, aluminum and silica are removed from the leach solution by increasing the pH of the leach solution from about 3 (or lower) to about 4 to 7 (e.g., 6 to 7) and adding an oxidizing agent. The pH is increased by adding a base such as ammonia gas and/or lime to the leach solution, and typical oxidizing agents used for this purpose include Mn02 and/or air. Iron, aluminum and silica (when présent) will precipitate from the leach solution and can be removed by filtration or other conventional means.

[0006] Sulfides are used to remove heavy metals such as Ni, Co, Cu, Ζη, Pb, and Mo as insoluble métal sulfides. In particular, after removal of Fe, Al and silica (and, in some instances, other impurities), one or more sulfides are added to the leach solution. Typically, the sulfides used for this purification step comprise one or more alkali métal or alkaline earth métal sulfides (e.g., NaHS and/or BaS) and/or ammonium sulfide, with about 5 to 10 times the stoichiometric amount of sulfide being necessary in order to reduce the heavy métal impurity level to below 1 mg/L (i.e., 1 ppm) in the leach solution/cell feed. Following the addition of the sulfide solution, the métal sulfide précipitâtes are removed from the leach solution, usually by filtration. However, not only are undesirable impurities such as Ni, Co, Cu and the like removed (as their insoluble sulfides), but also significant amounts of manganèse (as MnS). In fact, these mixed sulfide solids (e.g., removed as a filter cake) can contain up to 90% MnS. In addition, the mixed sulfide solids are considered a hazardous waste material, and therefore must be disposed of in a controlled manner. As used herein, the terms mixed sulfide solids (or mixed métal sulfide solids) and mixed métal sulfate refer to mixtures of two or more métal sulfides (e.g., MnS, NÎS, CoS) and mixtures of two or more métal sulfates (e.g., MnS04, NiSCE, C0SO4, etc.), respectively.

[0007] Thus, the above-described electrolytic production of high purity manganèse or EMD results in waste streams, particularly insoluble heavy métal sulfides of valuable metals such as Μη, Ni, Co, Cu and Mo, as well as sulfur (in the form of sulfides). In addition, many conventional processes for the electrolytic production of high purity manganèse and/or EMD employ materials that can be difficult (or impossible) to obtain in sufficient quantités (or even in any quantity) at locations where manganèse ore is typically processed. For example, ammonia, hydrogen sulfide and/or sodium sulfide are not always obtainable where manganèse ore is processed, and in some instances, liquid and gaseous reactants are not permitted to be brought on site.

[0008] While a variety of devices and techniques may exist for producing manganèse and EMD, it is believed that no one prior to the inventor(s) has made or used an invention as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] While the spécification concludes with daims particularly pointing out and distinctly claiming the invention, it is believed that the invention will be better understood from the detailed description of certain embodiments thereof when read in conjunction with the accompanying drawings. Unless the context indicates otherwise, like numerals are used in the drawings to identify similar éléments in the drawings. In addition, some of the figures may hâve been simplified by the omission of certain éléments in order to more clearly show other éléments. Such omissions are not necessarily indicative of the presence or absence of particular éléments in any of the exemplary embodiments, except as may be explicitly stated in the corresponding detailed description.

[0010] FIG. 1 depicts a schematic illustration of one embodiment of a manganèse production process.

[0011] FIG. 2 depicts a schematic illustration of another embodiment of a manganèse production process.

[0012] The drawings are intended to illustrate rather than limit the scope of the présent invention. Embodiments of the présent invention may be carried out in ways not necessarily depicted in the drawings. Thus, the drawings are intended to merely aid in the explanation of the invention. Thus, the présent invention is not limited to the précisé arrangements shown in the drawings.

DETAILED DESCRIPTION

[0013] The following detailed description describes examples of embodiments of the invention solely for the purpose of enabling one of ordinary skill in the relevant art to make and use the invention. As such, the detailed description and illustration of these embodiments are purely illustrative in nature and are in no way intended to limit the scope of the invention, or its protection, in any manner. It should also be understood that the drawings are not to scale and in certain instances details hâve been omitted, which are not necessary for an understanding of the présent invention.

[0014] Embodiments of the présent disclosure provide a method of recovering and recycling suifide from a heavy métal suifide waste, wherein the suifide is recovered as MnS that is then recycled back to a production process. A waste stream comprising a slurry of heavy métal sulfides is reacted with an acid in order to generate H2S. The H2S is then reacted with an Mn2+ solution to produce MnS that is recovered (e.g., by filtration) and then recycled back to a production process (e.g., a process for producing manganèse or EMD). By way of example, following H2S génération, the H2S is removed and absorbed in a solution containing Mn2+. In some instances, the heavy métal suifide waste stream is produced during the step of purifying a manganese-containing solution during the electrolytic production of manganèse or EMD, and the mrecovered MnS is recycled back for use in this same purification step. The manganese-containing solution being purified contains manganèse (e.g., MnS04) as well as a plurality of other heavy metals. The acid reacted with the slurry of heavy métal sulfides comprises, for example, sulfuric acid.

[0015] By way of one spécifie example, the heavy métal suifide waste stream is produced during the preelectrolysis purification of a leach solution in a process for the production of manganèse métal or EMD, and the Mn2+ solution reacted with the generated H2S comprises melectrolytic cell feed or electrolyte solution (e.g., catholyte) extracted from the electrolytic cell. By using cell feed or electrolyte solution extracted from the electrolytic cell, high purity MnS {>90%, >95%, >99%, >99.5%, >99.9%, >99.95%, >99.99%, or even >99.995% purity) can be produced and recycled back for use in purifying a manganese-containing solution. Applicant has discovered that the use of high purity recycled MnS for the pre-electrolysis purification of the leach solution (rather than adding conventionally used sulfides such as ammonium suifide, alkali métal suifide or alkaline earth métal suifide) in order to provide the cell feed significantly reduces the amount of Μη in the heavy métal suifide waste stream. In addition, this avoids the need to purchase other sulfides for purification (or significantly reduces the amount needed), and reduces the total amount of solid waste that is produced.

[0016] Other embodiments of the présent disclosure provide a method of recovering and recycling suifide from a heavy métal suifide waste stream, wherein the suifide is recovered as one or more alkali métal sulfides, alkaline earth métal sulfides and/or ammonium suifide that are recycled back to a production process. A waste stream comprising a slurry of heavy métal sulfides is reacted with an acid in order to generate H2S. The H2S is then reacted with a solution, suspension or slurry containing one or more alkali, alkaline earth, or ammonium hydroxides and/or ammonia gas in order to produce the corresponding sulfide(s). These sulfides are then recycled back to a production process (e.g., a process for producing manganèse or EMD). By way of example, following H2S génération, the H2S is removed and absorbed in a solution, suspension or slurry containing one or more alkali, alkaline earth, or ammonium hydroxides. In some instances, the heavy métal sulfide waste stream is produced during the step of purifying a manganese-containing solution (e.g., pre-electrolysis purification of a leach solution) during the production of manganèse or EMD, and the recovered sulfide is recycled back for use in this same purification step. The acid reacted with the slurry of heavy métal sulfides comprises, for example, sulfuric acid, and reaction of the slurry of heavy métal sulfides with H2S04 generates not only H2S but also a métal sulfate solution. In some embodiments, the hydroxide(s) in the absorption solution, suspension or slurry comprise one or more of LiOH, NaOH, and KOH. In other embodiments, the hydroxide(s) in the absorption solution, suspension or slurry comprise one or more of Mg(OH)2, Ca(OH}2, and Ba(OH)2. In still further embodiments, the H2S is absorbed into a solution containing ammonia or ammonium ion. By way of one spécifie example, the heavy métal sulfide waste stream is produced during the pre-electrolysis purification of a leach solution in a process for the production of manganèse métal or EMD.

[0017] In the above-described embodiments for the production of manganèse métal or EMD, when sulfuric acid is reacted with the slurry of heavy métal sulfides to generate the H2S, a mixed métal sulfate solution is also generated. In some embodiments sulfide is added to the mixed métal sulfate solution in order to convert at least a portion of the métal sulfates into their corresponding métal sulfides.

[0018] Embodiments described herein also include methods for electrolytically producing manganèse métal or EMD wherein sulfide removed from the leach solution prior to electrolysis (i.e., as mixed métal sulfides) is recovered and recycled back to the pre-electrolysis purification step rather than being discarded (e.g., as mixed sulfide solids filter cake). In addition, heavy metals such as Ni, Co, Cu, Ζη, Pb, Mo, Sb, As and Bi (hereinafter, Secondary Metals) can be recovered. It will be understood that not ali of these Secondary Metals are necessarily présent in the process, depending, in part, on the Mn-containing starting material.

[0019] The mixed métal sulfide solids removed from the leach solution in the preelectrolysis purification step are reacted with an acid (e.g., H2S04) to generate H2S on site. When the acid used is H2S04, the metals of the mixed sulfide solids (i.e., Μη and one or more of the Secondary Metals) form mixed métal sulfates that remain in solution, and the metals can be recovered therefrom in one or more subséquent steps (as further described herein). The H2S, generated by reacting the mixed métal sufides with acid is the vehicle used to recycle sulfide back to the pre-electrolysis purification step.

[0020] In particular, the generated H2S is reacted in order to generate sulfide(s) that is mrecyded back to the pre-electrolysis purification step. In some embodiments, the generated H2S is reacted with a solution containing Mn2+ ions (e.g., a solution containing MnS04) in order to generate MnS that is then recycled back to the pre-electrolysis purification step. In one particular embodiment, the Mn2+ containing solution reacted with the H2S comprises electrolysis cell feed and/or catholyte extracted from the electrolysis cell. Since cell feed and catholyte hâve been purified to remove Secondary Metals, relatively pure MnS can be generated in this manner. For example, the MnS recycled back to the pre-electrolysis purification step is generally pink/orange in color, indicating that minimal amounts of Secondary Métal sulfides are présent. Thus, the recycled sulfide in these embodiments is primarily MnS, with less than 10%, less than 5%, less than 1%, less than 0.5%, less than 0.1%, less than 0.05%, less than 0.01%, or even less than 0.005% by weight Secondary Métal sulfides (based on the total sulfide solids présent in the recycle stream).

[0021] In still further embodiments for electrolytically producing manganèse métal or EMD wherein sulfide removed from the leach solution prior to electrolysis, the generated H2S is reacted with one or more alkali, alkaline earth or ammonium hydroxides and/or ammonia gas in order to generate the corresponding alkali métal sulfide(s), alkaline earth métal sulfide(s) and/or ammonium sulfide. The sulfide(s) is then recycîed back to the pre-electrolysis purification step.

[0022] Yet another embodiment of the présent disclosure provides a method of purifying an MnSCri solution containing one or more heavy métal impurities chosen from the group consisting of Ni, Co, Cu, Ζη, Pb, Mo, Sb, As and Bi. This method comprises reacting the MnS04 solution with MnS, without adding any additional sulfîdes, such that the heavy métal impurities form their respective sulfide précipitâtes (NiS, CoS, etc.}. Applicant has discovered that by reacting the MnSCE solution with high purity MnS (>90%, >95%, >99%, >99.5%, >99.9%, m>99.95%, >99.99%, or even >99.995% purity), the heavy métal impurities are precipitated as their respective sulfides while the Μη remains in solution (as soluble MnS04). The MnS used to extract the heavy métal impurities comprises high purity MnS containing less than 10%, less than 5%, less than 1%, less than 0.5%, less than 0.1%, less than 0.05%, less than 0.01%, or less than 0.005% by weight of other métal sulfides (based on total sulfide solids).

[0023] FIGURES 1 and 2 and their discussion below describe the production of manganèse métal (or, alternatively, EMD) using a source of manganèse. By way of example, as is well-known to those skilled in the art, naturally-occurring manganese-containing material is réduction roasted prior to leaching in order to reduce higher oxides of manganèse (e.g., Μη02, Mn203 and Mn304) to manganèse oxide (ΜηΟ) (Le., reduced Μη ore). !t will be understood, however, that other sources of manganèse may be employed as feedstock, induding sources of ΜηΟ that do not require réduction, as well as Mn304-containing and/or manganèse carbonatecontaining materials. For example, the processes described in U.S. Pat. No. 5,932,086 and PCT Pub. No. WO 99/14403 * sinterrng manganèse ore in order to convert Mn02 to Mn304, then adding a reducing agent (e.g., sulfur dioxide, activated carbon, hydrogen peroxide, hydrogen sulfide, reducing sugars and/or molasses) to the leach solution - can be used to provide the manganese-containing material used in the processes described herein.

[0024] For producing manganèse, an MnS04 leach solution, following purification to remove certain impurities, is added to the cathode side of an electrolysis cell(s). One or more electrolytic cells are employed, each having an anolyte chamber and a catholyte chamber, typically separated by a membrane or diaphragm. While operating conditions can vary, cell température is typically around 30 to 40°C and the pH on the cathode side of the cell is typically about 7 to 9. Ammonium sulfate ((NH4)2S04) is also typically présent in the cell, and acts as a buffer on the cathode side for maintaining the proper pH. The membrane/diaphragm ensures that the catholyte pH is significantly higher than the acidic pH of the anolyte, since acid (H2S04) (along with water) is generated at the anode. When an electrical potential is applied between the cathode(s) and anode(s), pure manganèse métal is deposited onto the cathode(s), from which it can be recovered by conventional means known to those skilled in the art.

[0025] For producing EMD, a divided cell is not necessary since EMD is produced under acidic conditions. While operating conditions can once again vary, cell température for the production of EMD is typically around 90 to 100°C and the pH throughout the cell is highly acidic (e.g., less than 2). Ammonium sulfate is also not needed under these operating conditions. When an electrical potential is applied between the cathode(s) and anode(s), EMD is deposited onto the anode(s), from which it can be recovered by conventional means known to those skilled in the art. Acid is also generated at the anode.

[0026] FIGURE 1 is a schematic représentation of one embodiment of a process for producing manganèse according to the présent disclosure, wherein mixed métal sulfide solids (MnS + Secondary Métal sulfides) removed from the leach solution (e.g., by filtration) in a preelectrolysis purification step (14) are reacted with H2SO4 to generate H2S. The H2S is then reacted with one or more alkali hydroxides, alkaline earth hydroxides or ammonium hydroxide and/or ammonia gas to generate the corresponding alkali métal sulfide(s), alkaline earth métal sutfide(s) and/or ammonium sulfide that is returned (i.e., recycled) to the pre-electrolysis purification step. It will be understood that various conventional processing steps are not depicted in FIG. 1. In addition, the process of FIG. 1 can be modified in order to produced EMD mrather than manganèse, as described above.

[0027] In leaching step (10), a source of manganèse such as reduced manganèse ore, primarily comprising ΜηΟ, is leached with a sulfuric acid solution in order to convert the ΜηΟ (or other manganèse source) to manganèse (II) sulfate (MnS04). The sulfuric acid solution used for leaching comprises spent electrolyte solution, i.e., anolyte, withdrawn from the electrolysis cell(s). In addition to H2S04, the spent electrolyte solution also contains MnS04, and (NH4)2S04. (In the production of EMD, ammonium sulfate is not présent in the electrolyte solution withdrawn from the cell(s) for leaching.) The Μη ore and sulfuric acid solution are combined in a suitable vessel, such as an open stirred tank. Of course, other types of conventional equipment can be employed for this purpose. Additional sulfuric acid and (NH4)2S04 are periodically added to the process, as needed, typically by an addition to the leach tank.

[0028] The reduced Μη ore (or other feedstock) not only contains ΜηΟ (or other manganèse source), but also one or more impurities such as Fe, Al, Si, as well as some or ail of the Secondary Metals (Ni, Co, Cu, Ζη, Pb, Mo, Sb, As and Bi). These impurities are removed priorto electrolysis. First, iron, aluminum and silica are removed from the leach solution by increasing the pH of the leach solution and adding an oxidizing agent. For example, NH3, lime and/or ΜηΟ is added to the leach solution in order to increase the pH (from about 3 or less) to about 4 to 9, about 4 to 7, or about 6 to 7. Suitable oxidizing agents indude, for example, Mn02, oxygen (typically as air), 03 or H2O2. Μη02 and/or air are typically used for this purpose for cost savings. When used, air is bubbled into a vessel containing the leach solution. Following the pH adjustment and the addition of Mn02 and/or air as oxidizing agents, iron, aluminum and silica will precipitate from the leach solution and are removed by filtration in step (12) (or by other conventional means for removing solids).

[0029] Following removal of Fe, Al and Si in step 12, the leach solution is subjected to pre-electrolysis purification step (14) in order to remove heavy métal impurities, i.e., the Secondary Metals. In this step, one or more sulfides are added to the leach solution, causing the heavy metals to be converted into their respective insoluble sulfides. in particular, an aqueous sulfide solution comprising one or more alkali métal, alkaline earth métal and/or ammonium sulfides is added to the leach solution, wherein the sulfides are obtained from the sulfide recovery loop described below. Suitable sulfides include, for example, U2S, Na2S, NaHS, K2S, KHS, MgS, CaS, BaS and/or NH4HS, and their concentration in the sulfide solution used in step (14) preferably does not exceed their respective solubility limits (i.e., they are preferably in solution), The leach solution and sulfide solution are combined rn a suitable vessel, such as an open stirred tank; however, other types of conventional equipment can be employed for this purpose.

[0030] Following the addition of the sulfide solution, the heavy métal impurities are converted from their sulfates into their respective insoluble sulfides (e.g., NiS, CoS, etc.). A portion of the MnS04 is also converted into insoluble MnS. The resulting sulfide précipitâtes are removed from the leach solution by filtration step (16) (or by other conventional means for removing solids), resulting in mixed sulfide solids (MSX) comprising sulfides of Μη, as well as sulfîdes of some or ail of the Secondary Metals. (It will be understood that MSX is intended to refer generally to the various sulfides of these metals, rather than a précisé Chemical formula.) In general, the mixed sulfide solids resulting from step (16) in FIG. 1 comprise about 50 to about 95% MnS by weight (on a dry basis), along with varying amounts of other heavy métal sulfides depending on, among other things, the impurities présent in the Mn-containing feedstock.

[0031] Following removal of the mixed sulfide solids (e.g., as a slurry), the purified leach solution is the cell feed for electrolysis step (20). The level of impurities remaining in the cell feed will vary depending on the feedstock and the purification parameters (e.g., amount of sulfide solution added). For example, the level of heavy metals (Fe and the Secondary Metals) can be less than about 5 mg/L, or even less than about 1 mg/L. The cell feed is introduced into the cathode side of the electrolysis cell(s), thereby supplying Mn2+ to the catholyte (the solution on the cathode side of the electrolysis cell(s)). In some embodiments the cell feed will generally comprise less than 1 mg/L of heavy métal impurities (Fe and the Secondary Metals) and at least about 30 g/L Mn2+. One or more electrolytic cells are employed, each having an anolyte chamber (22) and a catholyte chamber (24), typically separated by a diaphragm or membrane such as a doth membrane. When an electrical potential is applied between the cathode(s) and anode(s), pure manganèse métal is deposited onto the cathode, from which it can be recovered by conventional means known to those skilled in the art.

[0032] The sulfide recovery loop in the embodiment of FIG. 1 comprises an H2S génération stage (30) and a sulfide recycle stage (32). In the H2S génération stage (30), the mixed sulfide solids (MSX) slurry recovered from the leach solution is reacted with an acid, e.g., an aqueous solution of FLS04. This reaction may be take place in any suitable vessel, such as an agitated tank. The mixed sulfide solids react with FLS04 according to the reaction:

MSX + H2S04 -> H2S + M(S04)x wherein M is Μη as well as some or ail of the Secondary Metals (i.e., Ni, Co, Cu, etc.), depending on the composition of the Mn-containing feedstock. The generated H2S is then stripped from the reaction solution using, for example, a packed column and air or other gas suitable for stripping H2S. Alternatively, the reaction vessel can be heated to boiling, with the steam carrying the H2S from the reaction vessel. Of course, a variety of apparatus can be employed for the H2S génération and removal, such as those commonly used for contacting a gas and a liquid. In addition, various other acids besides FLS04 can be used, including HCl and H3PO4.

[0033] In addition to stripping H2S from the reaction solution, the air, steam or other gas used in the H2S génération stage (30) facilitâtes the transfer of H2S from génération stage (30) to the sulfide recycle stage (32). The solution remaining in the H2S génération stage (30) comprises a solution of mixed métal sulfates (M(SC>4)x). As further described herein, the metals can be recovered therefrom in one or more subséquent steps.

[0034] In the sulfide recycle stage (32), the H2S from génération stage (30) is absorbed in (i.e., reacted with) a solution, suspension or slurry of one or more alkali métal, alkaline earth métal and/or ammonium hydroxides. In particular, the H2S is put through a column such as a tray column or packed column, or other device commonly used for contacting gas and liquid, along with an aqueous hydroxide solution such as a solution of NaOH. Alternatively, the H2S can be bubbled into an agitated tank containing an aqueous hydroxide solution/suspension/slurry. The H2S reacts with, for example, NaOH according to the reactions:

H2S + 2NaOH-> Na2S + 2H20

H2S + 2NaOH-> NaHS+H20

Other hydroxides react with H2S in a similar mannerto generate the corresponding sulfide(s). For example,

Ba(OH)2 + H2S -> BaS + 2H20

As yet another alternative, the H2S can be reacted with ammonia gas in order to generate NH4H5.

[0035] The resulting solution of sulfide solution (e.g., Na2S/NaHS, BaS, and/or other sulfides) is then returned to purification step (14) described above in order to convert heavy metals in the leach solution into their respective insoluble sulfides (which are thereafter removed from the leach solution prior to electrolysis). In general, particularly since the processes described herein are typically performed on a batch basis, more and more hydroxide is added in order to generate a higher concentration sulfide solution, thereby reducing storage costs and maintaining a better water balance in the circuit. In addition, for the pre-electroîysis purification step (14), a stoichiometric excess (e.g., 5χ to 10χ) is typically used in order to ensure nearly complété précipitation of the Secondary Metals (as their respective sulfides).

[0036] It will be understood that any alkali métal, alkaline earth métal and/or ammonium hydroxide can be used in sulfide recycle stage (32), including one or more of LiOH, NaOH, KOH, Mg(OH)2, Ca(OH)2, Ba(OH)2 and/or NH4OH. The use of alkali métal and/or alkaline earth métal hydroxides is advantageous at sites where ammonia cannot be obtained or utilized, whether because of logistical reasons or prohibitions on its use.

[0037] As a resuit of the above process, it is not necessary to continually add sulfide to the process, as the sulfide necessary for purification (i.e., the précipitation of the Secondary Metals) is recovered from the mixed métal sulfides and recycled back into the process. (Although it may be necessary to add additional sulfide from time to time in order to, for example, make up for lost sulfide.) In addition, the mixed métal sulfides (MSX) are converted into their sulfates (M(SC>4)x), and the resulting M(SC>4)x solution remaining after the H2S génération stage (30) can be readily processed to recover not only Μη (e.g., as MnSCL, which can be returned to the leaching step (10)), but also the Secondary Metals.

[0038] By way of example, when the MnSCL concentration in the M(SC>4)x solution generated in stage (30) reaches high levels (e.g., about 20 to 300 g/L), the impurity level will typically be about 0.1 to 10 g/L. At this point, the M(S04)x solution can be neutralized with an alkaline or alkaline earth hydroxide or ΜηΟ, and separated from any solids such as BaSCL and/or CaSCL. By way of further example, if Ba(OH)2 is added in the sulfide recycle stage (32), ,the mixed sulfide solids reacted with acid in the H2S génération stage (30) will contain insoluble BaS04. Next, sulfide (e.g., a stoichiometric amount of sulfide such as MnS, Na2S or

NaHS) is added to the neutralized M(S04)X solution, causing the Secondary Metals to precipitate as their respective sulfides. After filtering, the Secondary Métal sulfides can be, for example, sold for their métal value. The remaining liquid will mainly comprise an MnS04 solution, with small amounts of impurities, and can be returned to the leach solution where it will provide additional Mn2+ for subséquent electrolysis or sold.

[0039] FIG. 2 is a schematic représentation of an alternative embodiment of a process for producing manganèse according to the présent disclosure. As before, the process of FIG. 2 can be modified in order to produced EMD ratherthan manganèse, as previously described herein.

[0040] In the process of FIG. 2, like that of FIG. 1, mixed métal suifide solids removed from the leach solution following a pre-electrolysis purification step are reacted with an acid such as H2SO4 in order to generate H2S. In this embodiment, however, the H2S is then reacted with a solution containing Mn2+ ions in order to generate MnS that is recyded back to the preelectrotysis purification step (e.g., in the form of a slurry). When the Mn2+ solution reacted with the H2S contains low levels of Secondary Metals, high purity MnS is produced. In the example of FIG. 2, the Mn2+ solution reacted with the H2S comprises a portion of the electrolysis cell feed and/or catholyte extracted from the electrolysis cell(s). (In the case of producing EMD using the process of FIG. 2, cell feed is reacted with the H2S in step (132).)

[0041] The applicant has found that, when high purity MnS is recycled back to the preelectrolysis purification step, the MnS will react with the métal sulfates in the leach solution according to the following reaction: MnS + M'S04 -> MnS04 + M'SX wherein M' is one or more of the Secondary Metals. In other words, the recycled MnS is used as the suifide in the pre-electrolysis purification step.

[0042] Accordingly, in the leaching step (110) of the process depicted in FIG. 2, reduced manganèse ore (or other suitable manganese-containing feedstock) is leached with a sulfuric acid solution in order to convert the MqO (or other manganèse source) to manganèse (II) sulfate (MnS04). As before, the sulfuric acid solution used for leaching comprises anolyte (spent electrolyte) withdrawn from the electrolysis cell(s). Additional sulfuric acid and (NH4)2S04) may be added, as needed. By way of example, the Mn2+ concentration of the leach solution can be about 12 to 70 g/L, about 30 to 40 g/L, or about 32 g/L. These same Mn2+ concentrations in the leach solution are also suitable for the process of FIG. 1. The Mn2+ concentration of the cell feed is similar to that of the leach solution, as negligible amounts of Mn2+ is lost to the mixed suifide solids (as MnS) in step (116).

[0043] Iron, aluminum and silica, to the extent présent in the feedstock, are removed from the leach solution in the manner described previously with respect to FIG. 1, i.e., infiltration step (112) (or by other conventional means for removing solids). The leach solution is then subjected to pre-electrolysis purification step (114) in order to remove heavy métal impurities (i.e., the Secondary Metals). In this step, suifide solids or a suifide slurry primarily comprising high purity MnS is added to the leach solution, causing the Secondary Metals to be converted into their respective insoluble sulfides. As before, a stoichiometric excess (e.g., about 5χ to 10χ) is used. The high purity MnS solids/slurry is obtained from the suifide recovery loop described below.

[0044] Following the addition of the MnS solids/slurry, the Secondary Métal impurities are converted from sulfates into their respective insoluble sulfides (e.g., NiS, CoS, etc.). As in the previous embodiment, the resulting sulfide précipitâtes are removed from the leach solution by filtration step (116) (or by other conventional means for removing solids), resulting in mixed sulfide solids similar to those produced in the embodiment of FIG. 1.

[0045] As in the embodiment of FIG. 1, the purified leach solution following filtration step (116) is the cell feed for electrolysis step (120). Likewise, the sulfide recovery loop in the embodiment of FIG. 2, like that of FIG. 1, comprises an H2S génération stage (130) and a sulfide recycie stage (132). The H2S génération stage (130) is the same as that described previously for FIG. 1, with the generated H2S stripped from the reaction solution and supplied to the recycle stage (132). The M(S04)x solution generated in step (130) can be processed to recover Μη (e.g., as MnS04 for return to the leaching step (110)) and the Secondary Metals in the manner described previously.

[0046] In the sulfide recycle stage (132), the H2S from génération stage (130) is reacted with a solution containing Mn2+ ions in order to generate high purity MnS that is recyded back to the pre-electroiysis purification step (114), such as in the form of solids or a slurry. While other Mn2+ containing solutions can be used, the cell feed and/or catholyte provide a readily availabfe Mn2+ solution for this purpose, as each contains appréciable amounts of MnS04 in solution. Also, by using cell feed or catholyte to generate MnS for recycie back to the purification step (114), considérable cost savings can be achieved. For example, as compared to the process of FIG. 1, there is no need to purchase additional sulfide such as BaS for the preelectrolysis purification step (114). While it is necessary to add acid, such as H2S04 in the H2S génération step (130), H2S04 is aiready used in the process and can be inexpensively manufactured on site.

[0047] The H2S is reacted with cell feed and/or catholyte solution such that the H2S reacts with MnS04 according to the reaction:

H2S + MnS04 -> MnS + H2S04

This reaction is carried out, for example, in the manner described above with respect to FIG. 1, such as using a tray column or packed column, or other device commonly used for contacting gas and liquid, or by bubbling the H2S into an agitated tank containing the Mn2+ solution.

[0048] Assuming that sufficient MnS04 and H2S are available in sulfide recycle stage (132), the above reaction will proceed until the pH of the reaction solution reaches about 3 to 4— at which point H2S will no longer react with Mn2+ to produce MnS. Thus, the pH of the reaction solution should be maintained above 4, or above about 4.5 in order to prevent excessive odor (from unreacted H2S). Also, since the catholyte typically has a higher pH (about 8.5) than the cell feed (pH about 7), more MnS can be produced from catholyte before the lower pH limit is reached. In addition, base can be added to the reaction solution in recycle stage (132) in order to maintain the pH at about 6 to 7, while adding sufficient H2S to precipitate ail of the Μη (as MnS) in the reaction solution. Suitable bases include, for example, alkali, alkaline earth or ammonium hydroxides and/or ammonia gas, or even ΜηΟ.

[0049] The reaction product from the recycle stage (132) is filtered (or otherwise removed) in step (136) and the recovered high purity MnS (as a solid or slurry) is returned to purification step (114) described above in order to convert the Secondary Metals in the leach solution into their respective insoluble sulfides (which are thereafter removed from the leach solution prior to electrolysis). The high purity MnS returned to purification step (114) contains less than 10%, less than 5%, less than 1%, less than 0.5%, less than 0.1%, 10 less than 0.05%, less than 0.01%, or even less than 0.005% by weight of other métal sulfides (based on the total sulfide soiids). The filtrate remaining after filtration step (136) can be used, for example, as additional cell feed, particularly when an excess of cell feed or catholyte is used in recycle stage (132) such that the filtrate contains unreacted Mn2+.

[0050] Once again as a resuit of the process of FIG. 2, it is not necessary to continually add sulfide to the process, as the sulfide necessary for purification (Le., précipitation of heavy metals) is recovered from the mixed métal sulfides and recycled back into the process. In addition, the pure MnS used for purification purposes is safer and easier to store than the sulfides used in conventional processes, does not introduce additional water into the System, has very little odor (especially compared to ammonium sulfide/bisulfide), and does not add unwanted éléments such as Na to the cell feed. Furthermore, the cost of sulfides (e.g., NaHS, BaS, NH4HS, etc.) is nearly, if not entirely, eliminated, as are the safety hazards associated with the disposai of impurity sulfides. The process atso facilitâtes the recovery of Μη, Ni, Co, and other vaiuable metals, while also producing very little solid waste material.

[0051] While various embodiments hâve been described in detail above, it will be understood that the processes, components, features and configurations described herein are not limited to the spécifie embodiments described above. For example, the processes described herein can be used in the production of EMD. In the case of EMD production, spent electrolyte solution is used in the leaching step. In addition, when the process of FIG. 2 is used in conjunction with EMD production, the most convenient source of Mn2+ in the sulfide recycle stage (132) is either cell feed or electrolyte solution withdrawn from the electrolysis cell(s)

Claims

1. A method of producing manganèse métal or EMD, comprising:

(a) leaching a source of manganèse with a solution comprising sulfuric acid to form a leach solution;

(b) adding the one or more sulfides produced in step (g) to said leach solution to form sulfide précipitâtes comprising one or more heavy métal sulfides;

(c) removing said sulfide précipitâtes from said leach solution so as to provide a purified leach solution;

(d) feeding said purified leach solution to one or more electrolytic cells;

(e) subjecting the purified leach solution to electrolysis so as to deposit manganèse métal or EMD;

(f) reacting said sulfide précipitâtes with an acid to generate H₂S;

(g) producing one or more sulfides, the production comprising reacting said H₂S with a hydroxide solution or an Mn²* solution; and (g) recyding said one or more sulfides produced in step (f) to step (b).

2. The method of claim 1, wherein said sulfuric acid solution in step (a) comprises electrolyte solution removed from said one or more electrolytic cells.

3. The method of claim 2, wherein the method comprises the production of manganèse métal and said electrolyte solution comprises anolyte removed from said one or more electrolytic cells.

4. The method of any one of daims 1-3, wherein said one or more heavy métal sulfides comprise one or more sulfides of Ni, Co, Cu, Zn, Pb, Mo, 5b, As and Bi.

5. The method of any one of daims 1-4, wherein in step (f) the sulfide précipitâtes are reacted with H₂SO₄.

6. The method of any one of daims 1-5, wherein in step (g) the H₂S is reacted with an Mn²* solution in orderto produce MnS.

7. The method of any one of daims 1-5, wherein in step (g) the H₂S is reacted with a solution comprising one or more hydroxides chosen from the group consisting of alkali hydroxide, alkaline earth hydroxide and ammonium hydroxide, and the sulfide précipitâtes formed in step (b) further comprise MnS.

8. The method of any one of daims 1-5 and 7, wherein said one or more sulfides recycled in step (g) comprises ammonium sulfide.

9. The method of daim 7, wherein in step (g) the H₂5 is reacted with a solution comprising one or more of LiOH, NaOH, KOH, Mg(OH)₂, Ca(OH)₂ and Ba(OH)₂.

10. The method of daim 9, wherein in step (g) the H₂5 is reacted with a solution comprising Ca(OH)₂.

11. The method of any one of daims 1-10, wherein in step (f) the sulfide précipitâtes are reacted with acid in an aqueous reaction solution, further comprising the step of stripping said H₂S from the aqueous reaction solution with air or steam.

12. The method of any one of daims 1-11, wherein in step (g), reacting said H₂S with a hydroxide solution or an Mn²‘ solution comprises absorbing the H₂S in said hydroxide solution or said Mn^2t solution.

13. The method of any one of daims 1-12, wherein step (f) also generates a métal sulfate solution, and further comprising the steps of:

adding at least one of an alkaline métal hydroxide, an alkaline earth métal hydroxide or MnO to said métal sulfate solution;

-adding sulfide to the mixed métal sulfate solution in order to convert at least a portion of the métal sulfates into their corresponding métal sulfides; and

-removing the métal sulfides from the mixed métal sulfate solution

14. The method of daim 13, wherein the sulfide added to the mixed métal sulfate solution is chosen from the group consisting of MnS, Na₂S and NaHS.

15. A method of producing manganèse métal in accordance with any one of daims 1-5, 13 and 14, wherein:

-step (e) comprises subjecting the purified leach solution to electrolysis so as to deposit manganèse métal on one or more cathodes of said one or more electrolytic cells; and

-in step (g), reacting said H₂S with a hydroxide solution or an Mn^!* solution comprises reacting said H₂S with an Mn^h solution comprising at least one of:

-a portion of said purified leach solution; and

-catholyte withdrawn from said one or more electrolytic cells thereby producing métal sulfide solids for use in step (b) comprising greater than 95% by weight MnS based on the total métal sulfide solids,

16. The method of claim 15, wherein the métal sulfide solids produced in step (g) comprises greater than 99% by weight MnS based on the total sulfide solids.

17. The method of claim 15, wherein the métal sulfide solids produced in step (g) comprises greater than 99.9% by weight MnS based on the total sulfide solids.

18. The method of any one of claims 1-17, further comprising, prier to step (b), the steps of:

-increasing the pH of the leach solution to 4 to 7 and adding an oxidizing agent, whereby one or more of iron, aluminum and silica are precipitated from the leach solution; and

-removing said one or more of iron, aluminum and silica from the leach solution.

19. The method of any one of claims 1-18, wherein step (g) comprises contacting the H₂S gas and said hydroxide or Mn^J+ solution in a tray column or a packed column.

20. The method of any one of claims 1-19, wherein step (g) comprises bubbling the H₂S gas into an agitated tank containing said hydroxide or Mn²’ solution.