Manganese Extraction Method

Abstract

The present invention relates to a method for recovering manganese from an acidic leach solution containing manganese ions, the method comprising the steps of: (i) subjecting the acidic leach solution to one or more preliminary impurity removal steps to remove a substantial proportion of the impurities of interest, thereby producing a purified leach solution containing manganese; (ii) subjecting the purified leach solution to a solvent extraction step comprising contacting the purified leach solution with an organic solution of a carboxylic acid to extract manganese ions into the organic solution, and separating the loaded organic solution from an aqueous raffinate; and (iii) subjecting the loaded organic solution to a stripping step comprising contacting the loaded organic solution with an acidic strip solution to produce a manganese strip solution.

Description

[Technical Field]

[0001] The present invention relates to a process for extracting manganese from an acidic leach solution. More particularly, the process of the present invention utilizes solvent extraction to selectively recover manganese from the acidic leach solution. [Background technology]

[0002] The following discussion of the background art is intended solely to facilitate an understanding of the present invention and is not intended to be an admission or acknowledgement that any material referred to is or was part of the common general knowledge at the priority date of this application. Summary of the Invention [Problem to be solved by the invention]

[0003] High-purity manganese products such as electrolytic manganese dioxide (EMD), electrolytic manganese metal (EMM), chemical manganese dioxide (CMD), manganese carbonate and manganese sulfate (MSM / HPMSM) are required for use in specialty metals and lithium-ion battery cathodes. Demand for high-purity manganese metal and high-purity manganese sulfate is expected to increase dramatically in the near future, driven by the rapid expansion of electric vehicle production and grid storage capacity, in addition to growth in traditional end-use markets.

[0004] Manganese can be recovered from several sources, including naturally occurring ores, marine nodules, and industrial wastes. Hydrometallurgical processing of such materials typically involves a manganese leaching step using an acidic solution. The manganese leaching step also leaches out many impurities, including K, Na, Ca, Mg, Se, Si, Ni, Co, Fe, and Al. Separating the manganese from these impurities is difficult. Instead, the acidic leach solution is typically first treated to remove such impurities before a high-purity manganese product is recovered from the solution.

[0005] Separating manganese from other impurities using solvent extraction techniques is technically challenging: common extractants used to extract impurities from acidic leach solutions, such as Cyanex 272 and DEHPA, have low selectivity for the impurities relative to manganese, resulting in co-extraction of manganese and product loss.

[0006] Throughout this specification, unless the context requires otherwise, the term "comprise" or variations such as "comprises" or "comprising" will be understood to mean the inclusion of a stated integer or group of integers, but is not intended to exclude any other integer or group of integers. [Means for solving the problem]

[0007] In a first aspect of the present invention, there is provided a method for recovering manganese from an acidic leach solution containing manganese ions, comprising the steps of: i. subjecting the acidic leach solution to one or more preliminary impurity removal steps to remove a substantial proportion of the target impurities, thereby producing a purified leach solution containing manganese; ii. subjecting the purified leach solution to a solvent extraction process comprising contacting the purified leach solution with an organic solution of a carboxylic acid to extract manganese ions into the organic solution, and separating the loaded organic solution from an aqueous raffinate; iii. subjecting the loaded organic solution to a stripping step, the stripping step comprising contacting the loaded organic solution with an acidic strip solution to produce a manganese strip solution; and A method is provided, comprising:

[0008] In one aspect of the invention, the target impurities do not include at least one of potassium, magnesium, calcium, and sodium. Preferably, the one or more preliminary impurity removal steps produce a purified leach solution that includes manganese and one or more of potassium, magnesium, calcium, and sodium.

[0009] The present inventors have discovered that manganese can be preferentially extracted from a solution containing potassium, magnesium, calcium, and sodium using an organic solution of carboxylic acid. A manganese strip solution having a reduced impurity content may then be produced. By reducing the impurity content of the resulting manganese strip solution, the further purification steps required to recover a high purity manganese product are minimized.

[0010] In one aspect of the invention, the acidic leach solution is a sulfate solution.

[0011] In one aspect of the invention, the purified leach solution is substantially free of metals not included in the group comprising manganese, potassium, magnesium, calcium and sodium. Preferably, the concentration of any metal not included in the group comprising manganese, potassium, magnesium, calcium and sodium is less than 100 ppm. More preferably, the concentration is less than 10 ppm. Even more preferably, the concentration is less than 5 ppm.

[0012] In one form of the invention, the one or more preliminary impurity removal steps are targeted at removing one or more of iron, aluminum, nickel, copper, zinc, cobalt, titanium, cadmium, mercury, lead, selenium, silica, arsenic, and chromium from the acidic leach solution. Preferably, the one or more preliminary impurity removal steps reduce the concentration of any of iron, aluminum, nickel, copper, zinc, cobalt, titanium, cadmium, mercury, lead, selenium, silica, arsenic, or chromium in the acidic leach solution to less than 100 ppm. More preferably, the concentration is less than 10 ppm. Even more preferably, the concentration is less than 5 ppm.

[0013] In one aspect of the present invention, the solvent extraction step is carried out at a pH of 5 to 7.5. Preferably, the solvent extraction step is carried out at a pH of 6 to 7. More preferably, the solvent extraction step is carried out at a pH of 6 to 6.5.

[0014] In one embodiment of the present invention, the solvent extraction step is carried out at a temperature of 30 to 50°C.

[0015] In a preferred embodiment of the invention, the solvent extraction step is repeated two or more times, preferably in countercurrent operation.

[0016] In one aspect of the invention, the loaded organic solution is subjected to a scrubbing process, which comprises contacting the loaded organic matter with a scrubbing solution to displace impurities in the loaded organic solution. Preferably, a portion of the manganese strip solution is used as the scrubbing solution.

[0017] In one form of the invention, the loaded organic solution is subjected to a washing step, which comprises contacting the loaded organic solution with an aqueous washing solution to remove water-soluble impurities in the loaded organic solution, preferably demineralized water.

[0018] In one aspect of the present invention, the carboxylic acid is a trialkylacetic acid. Preferably, the carboxylic acid is a C10 carboxylic acid. More preferably, the carboxylic acid is a C10 tertiary carboxylic acid.

[0019] In one aspect of the invention, the carboxylic acid is neodecanoic acid.

[0020] In one aspect of the invention, the organic solution does not contain other metal extractants. Preferably, the organic solution contains only carboxylic acids.

[0021] In one aspect of the invention, the strip solution comprises sulfuric acid or hydrochloric acid.

[0022] Further features of the present invention will be more fully described in the following description of several non-limiting embodiments. This description is included solely for purposes of illustrating the present invention and should not be understood as a limitation on the broad summary, disclosure, or description of the present invention set forth above. The following description makes reference to the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a flow chart of the method of the present invention. [Figure 2] 1 is a plot showing pH isotherms. [Figure 3] 1 is a plot of results from a solvent extraction test. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention relates generally to the recovery of manganese from acidic leach solutions using a solvent extraction process.

[0025] The acidic leach solution may be any acidic solution that contains manganese ions. Preferably, the acidic solution is a sulfate solution.

[0026] In one embodiment, the manganese concentration in the acidic leach solution is at least 50 g / L. In one embodiment, the manganese concentration in the acidic leach solution is at least 60 g / L. In one embodiment, the manganese concentration in the acidic leach solution is at least 70 g / L. In one embodiment, the manganese concentration in the acidic leach solution is at least 80 g / L. In one embodiment, the manganese concentration in the acidic leach solution is at least 90 g / L.

[0027] In one embodiment, the method of the present invention includes contacting a manganese-containing material with an acidic leach solution to produce an acidic leach solution. Preferably, the acidic leach solution is sulfuric acid. Methods for acid leaching materials are well known to those skilled in the art and include, for example, atmospheric leaching, pressure leaching, oxidation leaching, and reduction leaching. The most suitable leaching process often depends on the manganese material itself and the oxidation state of the manganese. Suitable manganese-containing materials include ores, marine nodules, and industrial wastes.

[0028] In addition, during the acid leaching step of the manganese material, impurity elements are leached into solution along with the manganese. The extractants used in the solvent extraction process of the present invention have been found to exhibit preferential extraction of manganese over potassium, magnesium, calcium, and sodium, although other metals have been found to co-extract with manganese. The acid leach solution is subjected to one or more impurity removal steps prior to the solvent extraction step to remove at least a substantial portion of the target impurities.

[0029] Throughout this specification, unless the context requires otherwise, the term "impurities of interest" is understood to refer to metal impurities in the acidic leach solution that are co-extracted with manganese in the solvent extraction process. Furthermore, potassium, magnesium, calcium and sodium are not recognized as falling within the scope of "impurities of interest."

[0030] Throughout this specification, unless the context requires otherwise, the term "removing a substantial portion" is understood to refer to reducing the concentration of a target impurity below a threshold concentration. The threshold concentration depends on the acceptable content of the impurity in the manganese product and the concentration of manganese in the acidic leach solution. As will be understood by those skilled in the art, the acceptable content of an impurity in a high-purity manganese product depends on the intended use of the product. For example, high-purity manganese for use in lithium-ion batteries must meet certain impurity specifications. The threshold concentration must be adjusted to meet the required specifications. In a preferred embodiment of the present invention, the threshold concentration of the target impurity is 100 ppm. It should also be understood that the threshold concentration depends on the concentration of manganese in the acidic leach solution. The factor from 100 g / L of Mn in the liquor is approximately 3, so a concentration of 3 ppm in the liquor would be approximately 10 ppm for 100 g / t of Mn.

[0031] The impurities present in the acidic leach solution will depend on the manganese-containing material being leached. Preferably, one or more impurity removal steps remove a substantial portion of any of the following from the acidic leach solution: iron, aluminum, nickel, copper, zinc, cobalt, titanium, cadmium, mercury, lead, selenium, silica, arsenic, and chromium.

[0032] It is contemplated that any means available to one of ordinary skill in the art may be used to remove the target impurity. It is contemplated that successive impurity removal steps may be used to remove different target impurities. It is further contemplated that successive impurity removal steps may be used to remove varying amounts of the target impurity. For example, a first impurity removal step may be used to remove a majority of the target impurity, and a second impurity removal step may be used to remove the remaining trace amounts. The choice of impurity removal means will depend on the particular impurities in the acidic leach solution.

[0033] In one embodiment of the present invention, the preliminary impurity removal step comprises a neutralization step. Preferably, the neutralization step comprises adding a neutralizing agent to raise the pH of the solution to a point where one or more target impurities precipitate. The neutralization step may further comprise the addition of a reducing agent or an oxidizing agent. The neutralizing agent is preferably K + , Mg 2+ , Ca 2+ , NH4 + , Mn 2+ or Na + The resulting slurry is subjected to solid / liquid separation and the precipitated solids are removed from the solution. Preferably, the neutralization step does not raise the pH of the acidic leach solution above 6.

[0034] In one embodiment of the present invention, the preliminary impurity removal step comprises a pressure precipitation step. The pressure precipitation step comprises subjecting the acidic leach solution to elevated temperature and pressure for a time sufficient to precipitate the target impurities from the acidic leach solution. Preferably, the pressure precipitation step is carried out in a pressure reactor. In one embodiment of the present invention, the pressure precipitation step is carried out at a pressure of at least 2 bar. In one embodiment of the present invention, the pressure precipitation step is carried out at a pressure between 2 and 10 bar. In one embodiment of the present invention, the pressure precipitation step is carried out at a temperature of at least 135°C. Preferably, the pressure precipitation step is carried out at a temperature of at least 150°C. More preferably, the pressure precipitation step is carried out at a temperature of at least 160°C. In one embodiment of the present invention, the pressure precipitation step is carried out at a temperature between 135°C and 200°C. Preferably, the pressure precipitation step is carried out at a temperature between 160°C and 180°C. In one embodiment of the present invention, the residence time of the pressure precipitation step is at least 30 minutes. Preferably, the residence time for the pressure precipitation step is 30 to 120 minutes. Such pressure precipitation steps produce an iron-rich precipitate. The resulting slurry is subjected to solid / liquid separation and the precipitated solids are removed from the solution.

[0035] In one embodiment of the present invention, the preliminary removal step comprises one or more solvent extraction steps, each comprising contacting the acidic leach solution with an organic solution of an extractant suitable for selectively extracting one or more target impurities from the acidic leach solution while substantially excluding manganese. Preferably, the one or more solvent extraction steps remove iron and / or aluminum from the acidic leach solution.

[0036] In one embodiment of the present invention, the preliminary removal step comprises one or more ion exchange steps. Each ion exchange step comprises contacting the acidic leach solution with a sorbent material to selectively extract one or more target impurities from the acidic leach solution while rejecting manganese. The sorbent used will depend on the impurities in the acidic leach solution, and those skilled in the art will recognize suitable sorbents for removing such impurities.

[0037] In one form of the invention, the preliminary removal step comprises one or more precipitation steps, which involve contacting the acidic leach solution with a precipitating agent. Any precipitating agent that results in the precipitation of one or more target impurities is suitable. In one embodiment, the precipitating agent is sodium dimethyldithiocarbamate, sodium trithiocarbonate, sodium polythiocarbonate, or a mixture thereof.

[0038] In one form of the invention, the preliminary removal process comprises a sulfiding process, which comprises contacting the acidic leach solution with a sulfiding agent. Contemplated sulfiding agents include Na2S, BaS, (NH4)HS, (NH4)2S, HS, and NaHS. The addition of the sulfiding agent results in the precipitation of the remaining target impurity metals as metal sulfides. The resulting slurry is subjected to solid / liquid separation, and the precipitated solids are removed from the solution.

[0039] In one form of the invention, the preliminary removal step comprises a fluorination step, which comprises contacting the acidic leach solution with a fluorination agent. The addition of the fluorination agent results in the precipitation of the remaining target impurity metals as metal fluorides. Suitable fluorination agents include NHF and BaF. The resulting slurry is subjected to solid / liquid separation, and the precipitated solids are removed from the solution.

[0040] The one or more impurity removal steps produce a purified leach solution. In one embodiment of the present invention, the purified solution is substantially free of any target impurities. As previously mentioned, any metal not included in the group of manganese, potassium, magnesium, calcium, and sodium should be considered a target impurity. The actual target impurities present in the acidic leach solution will depend on the manganese-containing material processed to form the acidic leach solution. Preferably, the purified solution is substantially free of iron, aluminum, nickel, copper, zinc, cobalt, titanium, cadmium, mercury, lead, selenium, silica, arsenic, and chromium.

[0041] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 1000 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Co: 0 to 1000 ppm Includes.

[0042] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 1000 ppm Ti: 0 to 100 ppm Cd: 0 to 100 ppm Hg: 0 to 100 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Pb: 0 to 100 ppm Co: 0 to 1000 ppm Cr: 0 to 100 ppm Includes.

[0043] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 100 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Co: 0 to 100 ppm Includes.

[0044] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 100 ppm Ti: 0 to 100 ppm Cd: 0 to 100 ppm Hg: 0 to 100 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Pb: 0 to 100 ppm Co: 0 to 100 ppm Cr: 0 to 100 ppm Includes.

[0045] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 5 ppm Al: 0 to 5 ppm Ni: 0 to 25 ppm Ti: 0 to 5 ppm Cd: 0-5 ppm Hg: 0-2 ppm Cu: 0-5 ppm Zn: 0 to 5 ppm Pb: 0 to 5 ppm Co: 0 to 25 ppm Cr: 0 to 5 ppm Includes.

[0046] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0-2 ppm Al: 0 to 2 ppm Ni: 0 to 2 ppm Ti: 0 to 2 ppm Cd: 0 to 1 ppm Hg: 0 to 1 ppm Cu: 0-2 ppm Zn: 0 to 2 ppm Pb: 0 to 1 ppm Co: 0 to 2 ppm Cr: 0 to 1 ppm Includes.

[0047] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 10 ppm Al: 0 to 10 ppm Ni: 0 to 25 ppm Ti: 0 to 100 ppm Cd: 0-5 ppm Hg: 0 to 100 ppm Cu: 0-5 ppm Zn: 0 to 10 ppm Pb: 0 to 100 ppm Co: 0 to 25 ppm Cr: 0 to 5 ppm Includes.

[0048] In one embodiment, the purified leach solution comprises: Mn: 50-150 g / L K: 0-100 g / L Mg: 0-100 g / L Ca: 0-100 g / L Sodium: 0-300 g / L Includes.

[0049] In one embodiment, the purified leach solution comprises: Mn: 90-150 g / L K: 0-100 g / L Mg: 0-50 g / L Ca: 0-50 g / L Sodium: 0-230 g / L Includes.

[0050] In a preferred embodiment of the present invention, the purified leach solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 1000 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Co: 0 to 1000 ppm Mn: 50-170 g / L K: 0-100 g / L Mg: 0-100 g / L Ca: 0-100 g / L Na: 0-300 g / L Includes.

[0051] In a preferred embodiment of the present invention, the purified leach solution comprises: Fe: 0 to 100 ppm Al: 0 to 100 ppm Ni: 0 to 100 ppm Cu: 0 to 100 ppm Zn: 0 to 100 ppm Co: 0 to 100 ppm Mn: 50-150 g / L K: 0-100 g / L Mg: 0-100 g / L Ca: 0-100 g / L Sodium: 0-300 g / L Includes.

[0052] In one embodiment of the present invention, the purified leachate solution comprises: Fe: 0 to 5 ppm Al: 0 to 5 ppm Ni: 0 to 25 ppm Cu: 0-5 ppm Zn: 0 to 5 ppm Co: 0 to 25 ppm Mn: 50-150 g / L K: 0-100 g / L Mg: 0-100 g / L Ca: 0-100 g / L Sodium: 0-300 g / L Includes.

[0053] The purified leach solution is then subjected to a solvent extraction process which comprises contacting the purified leach solution with an organic solution of a carboxylic acid to extract the manganese ions into the organic phase.

[0054] Throughout this specification, unless the context requires otherwise, the term "organic solution of carboxylic acid" will be understood to refer to an organic compound dissolved in an organic solvent (or diluent) where the carboxylic acid has available protons which can displace manganese ions from the acidic leach solution.

[0055] Throughout this specification, unless the context requires otherwise, the term "loaded organic solution" and similar variations will be understood to refer to an organic solution containing carboxylic acid enriched with manganese ions transferred from the acidic leach solution to the extractant.

[0056] Throughout this specification, unless the context requires otherwise, the term "scrubbing" is understood to refer to a purification step of the loaded extractant in which at least some undesirable elements are removed.

[0057] Throughout this specification, unless the context requires otherwise, the term "washing" is understood to refer to a purification step of the loaded extractant in which at least some undesirable elements are removed using an aqueous wash solution.

[0058] Throughout this specification, unless the context requires otherwise, the term "stripping" is understood to refer to the process of transferring the metal of interest from a loaded organic solution to an aqueous phase by the addition of a strip solution.

[0059] As previously mentioned, the solvent extraction process involves contacting the purified leach solution with an organic solution of a carboxylic acid.

[0060] Throughout this specification, unless the context requires otherwise, the term "carboxylic acid" is understood to refer to an organic compound having the general formula R-COOH, where R represents an optionally substituted aliphatic or aromatic group, or combination of these groups. Such groups include optionally substituted alkyl, alkenyl, alkynyl, aryl, or heteroaryl groups. The term "optionally substituted" should be understood to mean that the reactive group may or may not be further substituted with one or more groups.

[0061] Preferably, the carboxylic acid is a trialkylacetic acid. In this context, the term trialkylacetic acid refers to a carboxylic acid having three alkyl groups on the α-carbon. It should be understood that the term "alkyl" refers to linear, branched, monocyclic, or polycyclic alkyl.

[0062] Preferably, the carboxylic acid is a C10 carboxylic acid. More preferably, the carboxylic acid is a C10 tertiary carboxylic acid. Even more preferably, the carboxylic acid is represented by the formula:

[0063] [ka] where R1 and R2 are alkyl groups and R1+R2=7 carbons.

[0064] In one embodiment, the carboxylic acid is neodecanoic acid, which is commercially available under the trade name Versatic 10 (Hexion).

[0065] The organic solution may be any suitable organic solvent known in the art. In a preferred embodiment, the organic solution is an aliphatic hydrocarbon solution. Suitable organic solutions include Vivasol D80, Shellsol D80, and Exxsol D80.

[0066] The concentration of the carboxylic acid in the organic solution depends on the viscosity and concentration of manganese in the acidic leach solution. In one embodiment, the concentration of the carboxylic acid in the organic solution is between 30 and 60%.

[0067] In one embodiment, the pH of the acidic leach solution is between 5 and 7.5. In one embodiment, the pH of the acidic leach solution is between 6 and 7. In one embodiment, the pH of the acidic leach solution is between 6 and 6.5. The pH of the acidic leach solution is maintained within the range of 5 to 7.5 during the solvent extraction process. A suitable neutralizing agent may be added to each mixer-settler to maintain the pH within this range.

[0068] The solvent extraction step is carried out at a temperature of 30 to 50°C.

[0069] The aqueous to organic (O:A) ratio in the solvent extraction process is in the range of 1:10 to 10:1. Preferably, the O:A ratio in the solvent extraction process is 3.5 to 4:1. As will be appreciated by those skilled in the art, the organic to aqueous ratio in the extraction process will depend on the amount of manganese in the pregnant leach solution as well as the manganese loading on the organic. One method for calculating the equilibrium concentration of the extractant is to utilize a mass balance, i.e., it is equal to the difference between the total (analytical) concentration of the extractant and the sum of all solvated species in the solvent phase.

[0070] In the solvent extraction process, an organic solution is loaded with manganese ions. The loaded organic phase is then separated from the Mn-depleted aqueous phase. Contacting the acidic leach solution with the organic solution of carboxylic acid, and subsequent separation of the loaded organic phase, is carried out using a suitable solvent extraction mixer-settler.

[0071] In one embodiment of the present invention, two or more mixer-settlers are used in series. Preferably, three or more mixer-settlers are used in series. In embodiments where multiple mixer-settlers are used, the mixer-settlers are arranged in countercurrent operation. As will be appreciated by those skilled in the art, countercurrent operation is achieved by repeated single-stage contacting, with the aqueous and organic phases moving in opposite directions between stages. The inventors have found that the use of multiple mixer-settlers in countercurrent operation maximizes the extraction of manganese into the organic phase while minimizing co-extraction of other species.

[0072] In one embodiment, the loaded organic phase is subjected to a scrubbing step. The scrubbing step includes contacting the loaded organic phase with a scrubbing solution containing manganese ions. The scrubbing step is used to remove impurities loaded onto the carboxylic acid. During contact, the manganese ions in the scrubbing solution are preferentially loaded onto the carboxylic acid, displacing the impurity ions.

[0073] In one form of the invention, the scrubbing solution is a sulfate solution. In a preferred form of the invention, a portion of the manganese strip solution is used as the scrubbing solution.

[0074] In one embodiment, the ratio of loaded organic to scrub solution is 20:1 to 100:1 (organic:aqueous) by volume. Preferably, the ratio is between 25:1 and 50:1 (organic:aqueous) by volume. More preferably, the ratio is about 35:1 (organic:aqueous) by volume.

[0075] The scrubbing step is carried out using a suitable mixer-settler apparatus. In one embodiment, the scrubbing step is carried out in a single mixer-settler. In another embodiment, the scrubbing step is carried out in two or more mixer-settlers arranged in series.

[0076] In one embodiment of the present invention, the loaded organic solution is subjected to a washing step. The washing step includes contacting the loaded organic solution with an aqueous washing solution to remove water-soluble impurities in the loaded organic solution. Preferably, the aqueous washing solution is demineralized water. The washing step is used to remove calcium and other water-soluble impurities loaded on the carboxylic acid. During the contact, calcium ions in the loaded organic matter migrate to the aqueous phase due to their increased solubility in the aqueous phase. The aqueous phase can then be separated.

[0077] In one embodiment, the ratio of loaded organic to aqueous solution is between 20:1 and 100:1 (organic:aqueous) by volume.

[0078] The washing step is carried out using a suitable mixer-settler apparatus. In one embodiment, the washing step is carried out in a single mixer-settler. In another embodiment, the washing step is carried out in two or more mixer-settlers arranged in series.

[0079] The loaded organic matter obtained from the washing step is directed to the stripping step, and the aqueous phase obtained from the scrubbing phase is preferably returned to the solvent extraction step to prevent manganese loss.

[0080] The stripping step involves contacting the loaded organic material with an acidic strip solution to transfer most of the manganese ions from the loaded organic material into an aqueous phase to produce a manganese strip solution, which is recycled back to the solvent extraction step.

[0081] In a preferred embodiment, the acidic strip solution comprises sulfuric acid, hi one embodiment, the sulfuric acid concentration is at least 100 g / L.

[0082] Contacting the loaded organics with the acidic strip solution is carried out using a suitable solvent extraction mixer-settler apparatus. In one embodiment of the present invention, two or more mixer-settlers are used in series. Preferably, three or more mixer-settlers are used in series. In embodiments where multiple mixer-settlers are used, the mixer-settlers are arranged in counter-current flow.

[0083] The manganese strip solution produced has a high manganese purity. In embodiments where sulfuric acid is used as the strip solution, the manganese strip solution is a high purity manganese sulfate solution.

[0084] A manganese product may be recovered from the manganese strip solution.

[0085] In one embodiment, the manganese strip solution is directed to a crystallization process to recover manganese sulfate. In the crystallization process, water is removed from the manganese strip solution using evaporation, and manganese sulfate is crystallized. The resulting slurry is subjected to a solid-liquid separation process to recover the manganese sulfate. Preferably, the crystallization process is a partitioning process. As will be appreciated by those skilled in the art, the partitioning process does not completely remove all of the water from the manganese strip solution. This prevents any remaining impurities from crystallizing with the manganese sulfate. Preferably, about 90% of the water is removed.

[0086] It is contemplated that other means of manganese recovery may be incorporated into the process. In another embodiment, an electrowinning circuit may be used to recover EMM and / or EMD. Those skilled in the art will recognize that other means of manganese recovery may be implemented.

[0087] FIG. 1 shows a flow diagram of a method for recovering manganese from an acidic leach solution according to one embodiment of the present invention.

[0088] In the embodiment shown in FIG. 1, the manganese-containing material 12 is subjected to a leaching process 14 in which the manganese-containing material 12 is contacted with an acidic leaching agent 16 and the manganese is extracted into solution.

[0089] The resulting leach slurry 18 is directed to one or more impurity removal steps to remove target impurities from the solution. The leach slurry 18 may be directed to a solid-liquid separation step (not shown) to remove leach residues prior to further processing, as determined by the particular impurity removal step used.

[0090] In the embodiment shown in Figure 1, the leach slurry 18 is first conducted to a pressure precipitation process 20, which involves subjecting the leach slurry 18 to elevated temperatures and pressures for a time sufficient to precipitate dissolved impurities from the leach slurry 18. The resulting slurry 22 is conducted to a solid-liquid separation process 24, where precipitated species 30 are removed.

[0091] The resulting solution 32 is directed to a neutralization step 34, where it is contacted with a neutralizing agent 36, such as limestone, to raise the pH of the solution to between 3 and 6.5. The increase in pH of the solution leads to the precipitation of impurities in the solution without precipitating manganese. The primary precipitated species is calcium sulfate. The resulting slurry is subjected to solid / liquid separation, where precipitated solids 38 are removed from the recovered solution 40.

[0092] The resulting solution may be subjected to one or more additional impurity removal steps (not shown). One of the impurity removal steps may be a sulfiding step, which is envisioned to include adding a sulfiding agent to precipitate target impurities as solid sulfate salts. Suitable sulfiding agents may be selected from NaHS, NaS, HS, and BaS. Additionally or alternatively, one of the impurity removal steps may be an ion exchange step, in which small amounts of remaining target impurities, such as copper, cobalt, and nickel, are removed from the solution.

[0093] The one or more impurity removal steps produce a purified leach solution 40 that is substantially free of any target impurities.

[0094] The purified leach solution 40 is directed to a manganese solvent extraction circuit 42 to recover manganese. In the embodiment shown in Figure 1, the manganese solvent extraction circuit 42 includes an extraction stage 44, a scrubbing stage 46, and a stripping stage 48 to selectively recover manganese from the purified leach solution 40 in a manganese strip solution 50. A Mn-free raffinate 52 is directed to a holding tank for further processing.

[0095] In the extraction stage, the purified leach solution 40 is contacted with a carboxylic acid organic solution 54 to selectively extract manganese from the purified leach solution 40 into a loaded organic phase 55. The extraction stage 44 preferably includes multiple solvent extraction mixer-settlers arranged in series. The purified leach solution 40 and the carboxylic acid organic solution 54 are contacted in a countercurrent configuration to maximize extraction efficiency. A neutralizing agent 56 is dosed into each mixer-settler to maintain a target pH.

[0096] The loaded organic phase 54 is conducted to a scrubbing stage 46. In the scrubbing stage 46, the manganese-loaded extractant 54 is contacted with a portion of a scrubbing solution 58 containing manganese ions. In the extraction stage 44, the manganese ions in the scrubbing solution 58 are preferentially loaded onto the loaded extractant 54, displacing any impurity elements loaded onto the loaded extractant 54.

[0097] The aqueous phase from the scrubbing stage 46 is returned to the first extractor mixer settler. The loaded extractant 60 from the scrubbing stage 46 proceeds to the stripping stage 48.

[0098] In the stripping stage 48, the loaded extractant 60 is contacted with an acidic stripping solution 62, and most of the manganese ions on the organic matter are displaced into the aqueous phase, producing a manganese stripping solution 50.

[0099] The organic phase 64 discharged from the stripping stage 48 is recycled to the extraction stage 44 where it again contains manganese. In this way, the organic phase 64 is maintained in a closed circuit within the manganese solvent extraction circuit 42.

[0100] The manganese strip liquor 50 from the stripping stage 48 is directed to a manganese crystallization stage 66, which produces a slurry of manganese sulfate pentahydrate in a sulfuric acid liquor. The slurry is sent to a suitable solid-liquid separation process to separate the manganese sulfate solids 68.

[0101] Example 1 To investigate the effect of pH on the extraction of various chemical species from aqueous solutions, studies were conducted using organic extractants containing carboxylic acids. The organic used in the studies was 60% by volume of Versatic 10 in Vivasol D80. The studies were conducted at 30°C with a phase ratio (O / A) of 1.0.

[0102] The results of the tests were used to construct a pH isotherm, which is shown in Figure 2. The results show that the amount of manganese increases as the pH increases from 5.5 to 7.5. The results also show that the co-extraction of calcium and magnesium increases over this range. The results suggest that the preferred pH for manganese extraction with minimal co-extraction of calcium and magnesium is between 6 and 7. The maximum manganese to calcium / magnesium ratio occurs at a pH of approximately 6.5.

[0103] Example 2 Tests were conducted to determine whether manganese could be effectively recovered from acidic leach solutions containing calcium and magnesium. Solvent extraction was carried out using the following conditions: Aqueous solution: 90g / L Mn with Ca and Mg (synthetic) B137784, Organics: (60% by volume Versatic 10 in Vivasol D80, acid washed), Evaluated at equilibrium pH 6 and phase ratio (O / A) 1.

[0104] The results are shown in Table 1.

[0105] [Table 1] FIG. 3 shows the loading of each species over successive contacts.

[0106] The results show that manganese was loaded onto Versatic 10. It was also shown that under optimized conditions, the concentrations of co-extracted calcium and magnesium could be reduced by preferentially loading Mn onto Versatic 10 over multiple contacts. Those skilled in the art will understand that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variations and modifications. The invention also includes all of the steps, features, chemical formulas, and compounds referred to or shown in this specification, individually or collectively, and any and all combinations of steps or features, or any two or more of them.

Claims

1. 1. A method for recovering manganese from an acidic leach solution containing manganese ions, comprising: i. subjecting the acidic leach solution to one or more preliminary impurity removal steps to remove a substantial proportion of the target impurities, thereby producing a purified leach solution containing manganese; ii) subjecting the purified leach solution to a solvent extraction process comprising contacting the purified leach solution with an organic solution of a carboxylic acid to extract manganese ions into the organic solution, and separating the loaded organic solution from an aqueous raffinate; iii) subjecting the loaded organic solution to a stripping step, the stripping step comprising contacting the loaded organic solution with an acidic strip solution to produce a manganese strip solution; A method comprising:

2. 10. The method of claim 1, wherein the target impurities do not include at least one of potassium, magnesium, calcium, and sodium.

3. 3. The method of claim 1 or claim 2, wherein the one or more preliminary impurity removal steps produce a purified leach solution comprising manganese and one or more of potassium, magnesium, calcium, and sodium.

4. 10. The method of claim 1, wherein the acidic leach solution is a sulfate solution.

5. 10. The method of claim 1, wherein the purified leach solution is substantially free of any metal not included in the group comprising manganese, potassium, magnesium, calcium, and sodium.

6. 6. The method of claim 5, wherein the concentration of any metal not included in the group including manganese, potassium, magnesium, calcium, and sodium is less than 100 ppm.

7. 10. The method of claim 1, wherein the solvent extraction step is carried out at a pH of 5 to 7.

5.

8. 10. The method of claim 1, wherein the solvent extraction step is repeated two or more times.

9. 9. The method of claim 8, wherein the solvent extraction step is repeated in countercurrent operation.

10. 10. The method of claim 1, wherein the carboxylic acid is a trialkylacetic acid.

11. 2. The method of claim 1, wherein the carboxylic acid is a C10 carboxylic acid.

12. 12. The method of claim 11, wherein the carboxylic acid is a C10 tertiary carboxylic acid.

13. 12. The method of claim 11, wherein the carboxylic acid is neodecanoic acid.

14. 10. The method of claim 1, wherein the organic solution does not contain a separate metal extractant.

15. The method of claim 1 , wherein the strip solution comprises sulfuric acid or hydrochloric acid.

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