EP4649056A1

EP4649056A1 - Process for preparing a high-purity manganese sulphate solution

Info

Publication number: EP4649056A1
Application number: EP24700031.8A
Authority: EP
Inventors: Joris ROOSEN; Jan Luyten; Werner VERDICKT
Original assignee: Umicore NV SA
Current assignee: Umicore NV SA
Priority date: 2023-01-10
Filing date: 2024-01-10
Publication date: 2025-11-19
Also published as: WO2024149809A1

Abstract

The present invention provides a process for preparing a high-purity manganese sulphate solution, comprising the steps of: i) providing an aqueous mixed metal ion solution comprising manganese, cobalt and calcium; ii) extracting manganese and calcium from said aqueous mixed metal ion solution using a first organic phase comprising an alkylphosphorus-based extractant (I) and a first diluent, thereby obtaining a first aqueous raffinate comprising cobalt, and a manganese-and calcium-rich organic phase; iii) stripping said manganese- and calcium-rich organic phase with a mineral acid, thereby obtaining an aqueous solution comprising manganese and calcium; iv) extracting manganese from said aqueous solution obtained in step iii) using a second organic phase comprising an alkylphosphinic acid-based extractant (II) and a second diluent, thereby obtaining a second aqueous raffinate comprising calcium, and a manganese-rich organic phase; and v) stripping said manganese-rich organic phase obtained in step iv) with sulphuric acid, thereby obtaining an aqueous solution comprising manganese sulphate.

Description

PROCESS FOR PREPARING A HIGH-PURITY MANGANESE SULPHATE SOLUTION

TECHNICAL FIELD

The present invention relates to a novel method for producing an aqueous high-purity manganese sulphate solution, which can be used as such for use in the electroless deposition of manganese metal layers or the production of battery materials, or which may be further processed in a crystallization unit for producing high-purity manganese sulphate crystals, having a purity sufficient for use in the electroless deposition of manganese metal layers or the production of battery materials.

INTRODUCTION

The development of lithium-ion batteries, and specifically the use of nickel-manga- nese-cobalt cathode materials has increased the demand for high-purity manganese sulphate, either as a solid or in solution. Indeed, impurities in the cathode materials strongly affect the performance of the batteries. New methods are developed for processing raw materials or battery recycling feed to recover high quantities of nickel and cobalt in high purity. Much less effort has been devoted to recovering manganese in sufficiently high purity for use as a feedstock for preparing nickel-manganese- cobalt cathode materials.

WO 2002/22898 describes a method of separating cobalt from impurity elements including manganese in an aqueous leach solution, the process including an organophosphoric acid solvent extraction stage including the steps of: (a) contacting the aqueous leach solution with an organic solution comprising an organophosphoric acid in an organic solvent to produce a loaded organic solution containing manganese and, to the extent that they are present, calcium, zinc and copper, and a some cobalt; and an aqueous raffinate solution containing most of the cobalt; (b) scrubbing the loaded organic solution with an aqueous scrub solution containing manganese and copper to produce a scrubbed organic solution containing less cobalt and a spent aqueous scrub solution containing some cobalt, as well as manganese; (c) recycling the spent aqueous scrub solution to step (a); (d) selectively stripping the scrubbed organic solution to remove a portion of the manganese and copper to form the aqueous scrub solution for use in step (b); and (e) recovering cobalt from the aqueous raffinate produced in step (a). However, said method does not allow to separate manganese from calcium, such that manganese cannot be recovered in sufficiently high purity. New methods are therefore required to achieve a straightforward and selective recovery of manganese with optimal use of materials and energy.

SUMMARY

The current invention provides in a solution for at least one of the above-mentioned problems by providing a process for preparing a high-purity manganese sulphate solution, as described in claim 1.

The present inventive process provides a straightforward and versatile method for obtaining high-purity manganese sulphate in an energy and materials efficient manner.

DESCRIPTION OF THE FIGURES

By means of further guidance, figures are included to better appreciate the teaching of the present invention. Said figures are intended to assist the description of the invention and are nowhere intended as a limitation of the presently disclosed invention. The figures and symbols contained therein have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Figure 1 shows schematically a process according to the first aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention. As used herein, the following terms have the following meanings:

"A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/- 20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

"Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows at least and do not exclude or preclude the presence of additional, non-recited components, features, elements, members or steps known in the art or disclosed therein.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints. All percentages are to be understood as percentage by weight, abbreviated as "wt.%" or as volume per cent, abbreviated as "vol.%" or as atomic per cent, abbreviated as "at.%", unless otherwise defined or unless a different meaning is obvious to the person skilled in the art from its use and in the context wherein it is used.

Regarding the organic phase following terms are used to identify its components or the whole: i. In the context of the present invention, the term "organic phase" is to be understood as synonymous for the term "solvent" or "solvent mixture" and designates a liquid composition comprising one or more extractants, diluents, and optionally one or more modifiers. ii. The "extractant" or extracting agent is the active component in the organic phase that extracts the metal species to the organic phase by chemically binding with it and forming a metal-extractant complex that is better soluble in the organic phase than it is in the aqueous phase. iii. The "diluent" is an organic molecule or usually a mixture of different organic molecules added to the organic phase to dilute the extractant and allow for dissolution of the metal complexes, improve the physical properties of the organic phase (especially phase-separation phenomena) and decrease its cost, given that diluents are usually cheaper than extractants. Diluents are frequently kerosene fractions and can be aliphatic or aromatic hydrocarbons, naphthenes, etc., or mixtures thereof. The diluent is preferably a kerosenebased petroleum fraction such as Escaid, Elixore, Shellsol, Isopar, etc. iv. The organic phase may also contain a "modifier". A modifier is sometimes added to improve solubility of metal complexes into the organic phase, to alter the physical properties of the solvent such to avoid crud formations or third- phase formation as these phenomena are unwanted in solvent extraction. A modifier can also be added to prevent chemical degradation of extractant or diluent. However, modifiers may impair the selectivity of the organic phase as these may participate in the complex formation of the metals with the extractant.

The "selectivity" S of an extractant for one metal over another metal can be expressed as the ratio of the distribution coefficients D for both metals:

SMg/Ni = D|v|g I D|\|i

The "distribution coefficient" of a metal is understood to be the ratio of the equilibrium concentrations of this metal in the organic phase and the same metal in the aqueous phase, respectively:

DM = [M]o / [M]A wherein M is a metal, such as nickel or magnesium, 0 refers to the organic phase and A refers to the aqueous phase. In the context of the present invention, the term "raw material feed" refers to one or more feedstocks that comprise any one or a combination of nickel, cobalt, manganese, or lithium. Said metals may be included as such or may be included as a compound of the aforementioned metals, or as a mixture of compounds. In some embodiments, said raw material feed may comprise any one or combination of raw materials and recycled materials. Examples of raw materials include, but are not limited to, mixed hydroxide precipitates (MHP), nickel sulphide concentrate, cobalt sulphide concentrate, nickel laterite, nickel matte, or ferronickel. Examples of recycled materials include, but are not limited to, spent cathode material, and material derived from recycled lithium-ion batteries or lithium-ion battery manufacturing scrap, collectively, referred to herein as 'black mass'.

In the context of the present invention, the term "MHP" is to be considered as an abbreviation of the term "mixed hydroxide precipitate." Mixed hydroxide precipitate (MHP) is an intermediate product of nickel metallurgy derived from processing laterite ores which contains primarily nickel and a minor amount of cobalt. MHP is a solid product which is typically prepared by extracting nickel and cobalt from laterite ores. Alternatively, or additionally, MHP may be obtained from nickel and/or cobalt containing materials produced as production waste during preparation of cathode materials or obtained from battery recycling processes.

In the context of the present invention, the term "CHIP" is to be considered as an abbreviation of the term "cobalt hydroxide intermediate precipitate." Cobalt hydroxide intermediate is comprised primarily of cobalt, and typically has a cobalt content of 25 wt.% to 40 wt.%, relative to the total weight of said intermediate product. Typically, said CHIP comprises a significant amount of nickel. CHIP'S are known to have a very low amount of impurities, which render them attractive for processes according to the present invention.

Said "raw material feed" may refer to a solid feed comprising an MHP product, a CHIP product, or a mixture of two or more MHP products, two or more CHIP products, or a mixture of one or more MHP products and one or more CHIP products. Preferably, said raw material feed comprises at least one nickel compound and at least one cobalt compound. Preferably, said nickel compound and said cobalt compound are comprised as a nickel(II) compound and as a cobalt(II) compound, respectively. Yet, said nickel compound and said cobalt compound may also be comprised in higher oxidation states such as 3+ or 4+, or said metal-containing feed may comprise a mixture of nickel and/or cobalt compounds in oxidation state 2+ and in oxidation state 3+ and/or 4+. In addition, said raw material feed may comprise alloys of nickel (0) and cobalt (0), and/or said raw material feed may comprise one or more ores comprising nickel and cobalt.

In the context of the present invention, the term "continuous process" is to be considered as a process in which the produced solution has a substantially constant outflow and composition. Specifically, a continuous process is a process in which the produced solution has a constant composition within the range of what are considered normal process variations. More specifically, the produced solution has a composition wherein the concentration of each ingredient is within the range of +/-20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/- 3% or less of its average concentration. In a preferred embodiment, the present invention provides a continuous process which operates under steady-state conditions.

In the context of the present invention, the term "aqueous medium" is used for a water-based solution. The aqueous medium facilitates the handling of the contents of the reactor, such as mixing or pumping. The aqueous medium may already contain some of the other ingredients taking part in the reaction, or those can be added later. Said aqueous medium may in particular contain the mineral acid.

In the context of the present invention, the term "cathode precursor material" is comprised of a mixed metal hydroxide, carbonate, oxyhydroxide and/or oxide, and comprises nickel and at least one metal selected from cobalt, manganese and aluminium. Preferably, said cathode precursor material comprises Ni in an amount of at least 30 mol.%, or even at least 50 mol.%, relative to the total content of nickel, cobalt, manganese and aluminium in said cathode precursor material, preferably in an amount of 60 mol.% to 95 mol.%, and all values there in between. Said cathode precursor material may further comprise one or more metals selected from Ba, Al, Ti, Zr, W, Fe, Cr, Mo, Nb, Mg and V, more preferably from Al, Ti, Zr, W and Mg. In one preferred embodiment, said cathode precursor material comprises Ni, Co and Al. In another preferred embodiment, said cathode precursor material comprises Ni, Co and Mn.

In a first aspect, the present invention provides a process for preparing a high-purity manganese sulphate solution, comprising the steps of: i. providing an aqueous mixed metal ion solution comprising manganese, cobalt and calcium; ii. extracting manganese and calcium from said aqueous mixed metal ion solution using a first organic phase comprising an alkylphosphorus-based extractant (I) and a first diluent, thereby obtaining a first aqueous raffinate comprising cobalt, and a manganese- and calcium-rich organic phase; iii. stripping said manganese- and calcium-rich organic phase with a mineral acid, thereby obtaining an aqueous solution comprising manganese and calcium; iv. extracting manganese from said aqueous solution obtained in step iii. using a second organic phase comprising an alkylphosphinic acid-based extractant (II) and a second diluent, thereby obtaining a second aqueous raffinate comprising calcium, and a manganese-rich organic phase; and v. stripping said manganese-rich organic phase obtained in step iv. with sulphuric acid, thereby obtaining an aqueous solution comprising manganese sulphate.

The inventive process provides a straightforward process for preparing manganese sulphate as a concentrated solution. Moreover, the process allows for obtaining a concentrated manganese solution directly from a process for leaching a raw material feed comprising manganese with a mineral acid different from sulphuric acid, such as hydrochloric acid. This can be especially advantageous in cases where an excess of hydrochloric acid is available as a waste product from another industrial process. Nevertheless, the leaching acid may advantageously be sulphuric acid as sulphuric acid leaching will provide an aqueous mixed metal sulphate solution having a low content of calcium ions. Another advantage of the present invention is provided by the fact that a high-quality alkylphosphinic acid-based extractant (II) can be used for extracting manganese in high purity, whereby the amount of the aqueous solution comprising calcium and manganese from which manganese and calcium are to be separated, is limited in volume, thereby reducing the amount of energy required to realize the sequestration of high-purity manganese sulphate. Advantageously, nickel present in the aqueous mixed metal ion solution provided in step i. is separated from manganese in step ii. since nickel remains in the first aqueous raffinate comprising also cobalt. Thus, cobalt values, as well as nickel and/or lithium values - if present, remain predominantly in the aqueous phase during the extraction in step ii. This means that more than 50%, relative to the total amount of said metal, preferably more than 70%, more than 80%, more than 90% or even more than 95% of said metal is distributed to the aqueous phase. Manganese and calcium are predominantly distributed to the organic phase. This means that more than 50%, relative to the total amount of said metal, respectively, preferably more than 70%, more than 80%, more than 90% or even more than 95% of said metal is distributed to the organic phase.

Preferably, said aqueous mixed metal ion solution provided in step i. is formed by reacting a raw material feed comprising manganese, cobalt, and calcium with a mineral acid in an aqueous medium. Preferably, said aqueous mixed metal ion solution is subjected to a preparation step for reducing the amount of impurities such as copper, zinc, and cadmium. Advantageously, an aqueous mixed metal ion solution comprising manganese, cobalt and/or calcium and at least one of copper, zinc and cadmium is subjected to a sulphidation step. Preferably, the amount of calcium in the aqueous mixed metal ion solution provided in step i. is below the precipitation point, according to: whereby [Ca²⁺][SO²“] < K_sp(7") and whereby K_sp (T) is the dissolution constant for CaSC at temperature T. Typically, the aqueous mixed metal ion solution provided in step i. has a content of calcium lower than 0.6 g per litre, preferably lower than 0.3 g per litre and more preferably lower than 0.2 g per litre, yet more than 1 mg per litre, typically more than 10 mg per litre.

The solvent extraction steps ii. and iv. can be performed in any device suitable and are not specifically limited. Solvent extraction equipment generally includes at least one or more devices consisting of a mixer-settler, a column contactor, a centrifugal contactor or any other type of contactor. Preferably, the extraction is performed in a counter-current configuration.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said aqueous mixed metal sulphate solution comprises at least manganese, cobalt and calcium, and further comprises one or more impurities selected from the group comprising nickel, magnesium, zinc, cadmium, iron, aluminium, and copper. Other impurities may be present as well. The present invention has the advantage that the elements cobalt and calcium, and if present nickel, magnesium, zinc, cadmium, iron, aluminium, and copper, are completely separated from manganese in one straightforward sequence of solvent extraction processes. It affords a high-purity aqueous manganese sulphate solution comprising manganese with a concentration between 40 and 200 g/L and calcium with a concentration of at most 50 mg/L. Furthermore, the aqueous phase comprising cobalt, and if present nickel, can be easily processed further using processes as described in PCT patent application PCT/EP2022/086839 filed on 20 December 2022 and European patent application 22191867.5 filed on 24 August 2022.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said aqueous mixed metal ion solution comprising manganese, cobalt and calcium which is provided in step i. is obtained from leaching a raw material comprising at least manganese, cobalt and calcium with a mineral acid, wherein said mineral acid is hydrochloric acid or sulphuric acid. The use of hydrochloric acid may be advantageous in situations where an amount of hydrochloric acid is available. Preferably, said mineral acid used to provide the aqueous mixed metal ion solution by leaching from a raw material in step i. is sulphuric acid. Using sulphuric acid as leaching agent in step i. is advantageous since the amount of calcium which will be co-leached with manganese will be limited by the limited solubility of calcium sulphate in water. This reduces the amount of extractant required in step iv. to separate manganese from calcium. Optionally, said raw material feed comprising manganese, cobalt and calcium is reacted with said mineral acid in an aqueous medium in presence of an oxidizing agent such as air, oxygen, or hydrogen peroxide. Alternatively, said raw material feed comprising manganese, cobalt and calcium is reacted with said mineral acid in an aqueous medium in presence of an reducing agent such as sulphur dioxide, metabisulphite, etc. to improve dissolution of manganese.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said mineral acid used in step iii. is hydrochloric acid. Using hydrochloric acid to strip calcium and manganese from the extractant used in step ii. allows to ensure complete removal of all calcium impurities from the extractant in the organic phase. As such, the organic phase can optimally be recycled to step ii.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said alkylphosphorus-based extractant (I) used in step ii. is an alkylphosphoric acid-based extractant (I), or a manganese salt thereof. Alkylphosphoric acid-based extractant and manganese salts thereof are preferably used to ensure a high recovery rate for the extraction of manganese from the mixed metal aqueous feed solution. At the same time, a high selectivity for manganese extraction can be realized, albeit with the co-extraction of minor amounts of calcium. Preferably, the present invention provides a process according to the first aspect of the invention, wherein said alkylphosphoric acid-based extractant (I) used in step ii. is di-(2-ethylhexyl)phosphoric acid, or a manganese salt thereof.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said first alkylphosphorus-based extractant

(I) used in step ii. is not an alkylphosphinic acid-based extractant (II).

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said alkylphosphinic acid-based extractant

(II) used in step iv. is bis(2,4,4-trimethylpentyl)phosphinic acid, or a manganese salt thereof.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said extraction in step ii. is performed at a temperature between 25°C and 55°C. Preferably, said extraction in step ii. is performed at a temperature between 30°C and 45°C. Preferably, said extraction in step ii. is performed at a pH between 2 and 7, preferably between 3 and 5 and most preferably between 3.0 and 4.0. Most preferably said pH is about 4.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said stripping in step iii. is performed at a temperature between 20°C and 60°C. Preferably, the mineral acid used in step iii. is hydrochloric acid, and said temperature is between 20°C and 40°C, more preferably between 25°C and 35°C. In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said extraction in step iv. is performed at a temperature between 40°C and 70°C. Preferably, said extraction in step iv. is performed at a temperature between 45°C and 60°C. Preferably, said extraction in step iv. is performed at a pH between 2 and 7, preferably between 3.0 and 6.0 and most preferably between 4.0 and 5.0. Most preferably said pH is about 4.5.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said stripping in step v. is performed at a temperature between 40°C and 60°C. Preferably, sulphuric acid is used as a stripping agent in step v.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said aqueous mixed metal ion solution formed or provided in step i. is subjected to a copper removal treatment, prior to step ii. Copper may be removed from said aqueous mixed metal solution via precipitation, sulphidation, cementation, solvent extraction, or ion exchange.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said aqueous mixed metal ion solution formed or provided in step i. is subjected to a zinc removal treatment, prior to step ii. Zinc may be removed from said aqueous mixed metal solution via sulphidation, solvent extraction, or ion exchange.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby zinc is removed from the aqueous mixed metal ion solution provided in step i. preferably through sulphidation and filtering of the zinc sulphide precipitate, prior to step ii. Sulphidation, in the context of the present invention, comprises contacting zinc ions dissolved in said aqueous phase with a sulphidizing agent. Said sulphidizing agent can be one or more selected from the group consisting of H2S and salts thereof such as but not limited to U2S, Na2S, K2S, and (NH4)2S. Even more preferably, the present invention provides a process according to the first aspect of the invention, whereby zinc is removed from the aqueous solution comprising manganese and calcium obtained from the stripping process of step iii. and preferably prior to step iv. Preferably, zinc is removed through sulphidation and filtering of the zinc sulphide precipitate.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said aqueous mixed metal ion solution formed or provided in step i. is subjected to an iron and/or aluminium removal treatment, prior to step ii.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, whereby said aqueous feed solution comprising manganese, cobalt and calcium is obtained by removing iron and/or aluminium from a pregnant leach solution comprising manganese, cobalt and calcium, and iron and/or aluminium, respectively. Said iron and/or aluminium can advantageously be removed by adding a basic reagent such as a hydroxide or other to said aqueous solution, thereby forming an iron and/or aluminium hydroxide precipitate. Potentially, addition of an oxidant, like for example oxygen or hydrogen peroxide, might be included in that iron and/or aluminium removal step. In a preferred embodiment, said iron and/or aluminium is removed by precipitation using a calcium base such as calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate or any other cal- cium-containing basic reagent. The use of a calcium base is advantageous since calcium forms calcium sulphate, also called gypsum, with low aqueous solubility in this step of the process. Hence, the use of excessive amounts of calcium base is not detrimental to the purity of the obtained manganese sulphate solution. Only a limited amount of calcium will remain in the manganese solution that is sent to the solvent extraction step iv. The latter process is designed to enable complete removal of calcium from the manganese solution. Furthermore, the formation of calcium sulphate during precipitation of iron and/or aluminium enhances the filterability of the iron and/or aluminium precipitate. Hence, it may be preferred that the calcium base is used in a stoichiometric excess relative to the amount of iron and/or aluminium impurities present in said aqueous feed solution. In another preferred embodiment, the employed base may be a hydroxide or carbonate of manganese or any other manganese-containing basic reagent, thereby introducing beneficial manganese ions in the manganese sulphate solution. Other preferred manganese bases are manganese bicarbonate and manganese hydroxy sulphate. In yet another preferred embodiment, impurities such as iron and/or aluminium may be separated by precipitation using a combination of two or more precipitation agents selected from calcium base and manganese base. Furthermore, impurities such as iron and/or aluminium may be removed by precipitation in two or more precipitation steps, whereby a different precipitating agent may be used in each precipitation step. In a preferred embodiment, a manganese base is used in a first precipitation step, and a calcium base is used in a subsequent precipitation step.

In another embodiment, calcium is already present into the nickel feed solution entering the solvent extraction step ii, because it was introduced by raw materials upfront or by using a calcium containing reagent, such as a calcium base as calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate or another calcium containing basic reagent before entering the solvent extraction step ii.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention wherein said aqueous mixed metal ion solution provided in step i. is obtained from leaching a raw material feed comprising nickel, lithium, iron and/or aluminium, and optionally further comprising one or more of zinc, copper and cadmium.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said aqueous mixed metal ion solution provided in step i. further comprises nickel.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said aqueous mixed metal ion solution provided in step i. further comprises lithium.

In a preferred embodiment, the present invention provides a process according to the first aspect of the invention, wherein said raw aqueous mixed metal ion solution provided in step i. further comprises one or more elements selected from the group zinc, copper, cadmium, iron and aluminium.

Claims

1. Process for preparing a high-purity manganese sulphate solution, comprising the steps of: i. providing an aqueous mixed metal ion solution comprising manganese, cobalt and calcium; ii. extracting manganese and calcium from said aqueous mixed metal ion solution using a first organic phase comprising an alkylphosphorus- based extractant (I) and a first diluent, thereby obtaining ii.(a) a first aqueous raffinate comprising cobalt and, if present in said aqueous mixed metal ion solution, nickel, and ii.(b) a manganese- and calcium- rich organic phase; iii. stripping said manganese- and calcium-rich organic phase ii.(b) with a mineral acid, thereby obtaining an aqueous solution comprising manganese and calcium; iv. extracting manganese from said aqueous solution obtained in step iii. using a second organic phase comprising an alkylphosphinic acid-based extractant (II) and a second diluent, thereby obtaining iv.(a) a second aqueous raffinate comprising calcium, and iv.(b) a manganese-rich organic phase; and v. stripping said manganese-rich organic phase iv.(b) obtained in step iv. with sulphuric acid, thereby obtaining an aqueous solution comprising manganese sulphate.

2. Process according to claim 1, wherein said an aqueous mixed metal ion solution provided in step i. is obtained by reacting a raw material feed comprising manganese, cobalt and calcium with a mineral acid in an aqueous medium, whereby said mineral acid is hydrochloric acid or sulphuric acid.

3. Process according to claim 1 or 2, wherein said mineral acid used in step iii. is hydrochloric acid.

4. Process according to claim 2 or 3, wherein said aqueous mixed metal ion solution comprising manganese, cobalt and calcium which is provided in step i. is obtained from leaching a raw material comprising at least manganese, cobalt and calcium with sulphuric acid, and wherein said mineral acid used in step iii. is hydrochloric acid.

5. Process according to any of claims 1 to 4, wherein said alkylphosphorus-based extractant (I) used in step ii. is an alkylphosphoric acid-based extractant (II).

6. Process according to claim 5, wherein said alkylphosphoric acid-based extractant (I) used in step ii. is di-(2-ethylhexyl)phosphoric acid.

7. Process according to any of claims 1 to 6, wherein said first alkylphosphorus- based extractant (I) used in step ii. is not an alkylphosphinic acid-based extractant (II).

8. Process according to any of claims 1 to 7, wherein said alkylphosphinic acidbased extractant (II) used in step iv. is bis(2,4,4-trimethylpentyl)phosphinic acid, or a manganese salt thereof.

9. Process according to any of claims 1 to 8, wherein said extraction in step ii. is performed at a temperature between 25°C and 55°C.

10. Process according to any of claims 1 to 9, whereby said stripping in step iii. is performed at a temperature between 20°C and 60°C.

11. Process according to any of claims 1 to 10, wherein said extraction in step iv. is performed at a temperature between 40°C and 70°C.

12. Process according to any of claims 1 to 11, whereby said stripping in step v. is performed at a temperature between 40°C and 60°C.

13. Process according to any of claims 1 to 12, whereby said aqueous mixed metal ion solution formed or provided in step i. is subjected to a zinc removal treatment, prior to the extraction of step ii.

14. Process according to any of claims 1 to 12, whereby said aqueous solution comprising manganese and calcium obtained from step iii. is subjected to a zinc removal treatment, prior to the extraction of step iv.

15. Process according to any of claims 1 to 14, wherein said aqueous mixed metal ion solution provided in step i. further comprises lithium.