A process for manganese purification

Abstract

The invention provides a process for manganese purification, the process comprising: providing an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); and extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase, and wherein the ratio of Mn to Ca in the Mn-rich extractant phase is greater than the ratio of Mn to Ca in the aqueous solution.

Description

[0001] A process for manganese purification

[0002] Technical Field

[0003]

[0001] The invention relates to a process for manganese purification comprising extracting manganese from an aqueous solution comprising manganese (Mn), calcium (Ca) and magnesium (Mg) into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof. The invention further relates to a process for purifying manganese present in an organic extractant phase, comprising extracting calcium and magnesium from a manganese-rich extractant phase comprising an organophosphorus extractant, manganese, calcium and magnesium into an aqueous scrubbing solution comprising manganese ions.

[0004] Background of Invention

[0005] [2] High purity manganese sulphate monohydrate (HPMSM) is a critical precursor component in the formation of lithium battery cathodes of Nickel-Cobalt- Manganese (NCM) and lithium manganese oxide (LMO) batteries. There is a trend to use manganese to replace part of the cobalt content in NCM batteries to reduce manufacturing costs. HPMSM is also a promising component for lithium manganese iron phosphate, e.g. LiMno.6Feo.4PO4, (LMFP) with combined features of the high safety of LiFePO4 and the high energy density of LiMnPO4, and reduced material costs.

[0006] [3] HPMSM for battery applications must have a minimum manganese concentration of >32% by weight. Impurities such as alkaline earth metals (Ca and Mg) and alkali metals (Na and K) have negative impacts on high-temperature morphology and cycling performance of lithium-ion batteries. Industry specifications for battery grade manganese sulphate call for Ca and Mg concentrations each below 100 ppm.

[0007] [4] Historically, manganese extracted in hydrometallurgical mineral processing operations has been purified by electrowinning technology, thus producing electrolytic manganese metal (EMM) and electrolytic manganese dioxide (EMD). The flowsheet to produce EMM and EMD typically comprises (i) separation of K / Na by jarosite [(K, Na, NH4+) Fe3(SO4)2(OH)6] precipitation, (ii) Fe / AI removal by hydroxide precipitation, and (iii) heavy metals (Zn, Cu, Ni, Co) removal by sulphide precipitation or ionexchange. After the above purification steps, the impurities of Ca and Mg remain in solution with Mn, and are only controlled to a limited extent in the EMM and EMD process, e.g. via bleed treatment using precipitation to recover Mn, as a carbonate or by other methods such as low temperature crystallisation to remove Mg sulfate. More effective processes for separation of Ca and Mg are required to meet industry specifications for battery grade HPMSM.

[0008] [5] A known method for Mn purification involves precipitation of Ca and Mg as CaF2 and MgF2 using large amounts of highly toxic, polluting fluoride. The method suffers from difficulty in filtration due to the formation of gel-like CaF2 and MgF2 precipitate and costly removal of excess fluoride and waste treatment to meet environmental regulations.

[0009] [6] Various solvent extraction (SX) processes have also been reported for separation of Mn from Ca and Mg, using bis(2,4,4-trimethylpentyl)phosphinic acid extractant (e.g. Cyanex 272) or synergistic SX extractant systems, e.g. consisting of di- (2-ethylhexyl) phosphoric acid (D2EHPA) and the synergist alkyl-4-pyridinecarboxylate ester (4PC). However, these solvent extraction systems are expensive and may have drawbacks of low loading capacity.

[0010] [7] D2EHPA is a much cheaper extractant than bis(2,4,4- trimethylpentyl)phosphinic acid, but the affinity preference for metals is reported to be in the order of Ca > Mn > Mg (in the absence of a synergist), with the affinity difference between Mn and Ca being very small. Therefore, it is commonly accepted that a solvent extraction process for Mn purification using D2EHPA or other organophosphoric acid extractants would require two solvent extraction circuits and many stages to separate Ca from Mn in one circuit (due to the small extraction affinity difference) and then to separate Mn from Mg in the other. See for example Wang et al, Hydrometallurgy 185 (2019) 55-60. The phosphonic acid extractant 2-ethylhexyl phosphonic acid mono-2- ethylhexyl ester (EHEHPA) is reported to have a very similar affinity for both Mn and Ca, so that EHEHPA and other organophosphonic acid extractants have previously been considered unsuited for purifying Mn when present together with Ca and Mg. See for example Dreisinger et al, Hydrometallurgy, 12 (1984) 1 -20. [8] There is therefore an ongoing need for new methods of purifying manganese, which at least partially address one or more of the above-mentioned shortcomings, or provide a useful alternative.

[0011] [9] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0012] Summary of Invention

[0013]

[0010] The present invention is based on the discovery that preferential extraction of manganese, relative to both calcium and magnesium, can be achieved with an organophosphorus acid extractant, such as an organophosphoric acid, in the absence of a synergist, by careful control of one or more process conditions in the extraction step. In particular, a high loading of multivalent metal ions, relative to the theoretical loading capacity of the organic extractant phase, is required to reverse the usual affinity preference for Mn and Ca to an order of Mn > Ca > Mg, and to achieve a significant selectivity for Mn extraction while rejecting substantial amounts of Ca and Mg. Elevated extraction temperatures are also preferred to enhance the affinity preference for Mn vs Ca. Typically, the pH should also be carefully controlled within a target range to facilitate a high loading of multivalent metal ions into the extractant and enhanced Mn extraction selectivity.

[0014]

[0011] Similar principles can be applied to the operation of a subsequent scrubbing step, in which an aqueous scrubbing solution containing Mn ions is used to scrub coextracted Ca and Mg from the Mn-rich organic extractant phase. A high loading of multivalent metal ions relative to the theoretical loading capacity of the organic extractant phase, and the presence of Mn ions in the aqueous scrubbing solution, provide highly selective and efficient scrubbing of Ca and Mg from the organic phase, being replaced by Mn. With a sufficiently high Mn concentration in the aqueous scrubbing solution, net Mn transfer from the organic extractant phase to the scrubbing solution can be avoided or acceptably limited, and in some embodiments the Mn concentration in the organic phase is actually increased due to a net transfer of Mn from the aqueous scrubbing solution to the organic extractant phase, thus facilitating the displacement of Ca and Mg. The resultant scrubbed organic extractant phase may therefore have exceptional Mn purity, with Mn / Ca and Mn / Mg ratios approaching or exceeding the specifications required for battery grade manganese salts.

[0015]

[0012] By combining such extraction and scrubbing steps, the inventors have developed an overall flow scheme for purifying manganese present initially in an aqueous solution together with Mn, Ca, Mg and optionally also other cations, using a single solvent extraction circuit to produce high purity manganese salts such as HPMSM. Advantageously, only a single solvent extraction circuit is needed to extract Mn in high yield while rejecting substantial proportions of both Ca and Mg to the Mn- lean aqueous raffinate. As a consequence, the subsequent scrubbing step can be operated efficiently, e.g. at an acceptably low ratio of aqueous scrubbing solution to organic extractant phase (A / O ratio), to achieve desired Mn purity levels. Each unit operation in the flow scheme (extraction, scrubbing and stripping) may include an acceptably small number of stages, and the aqueous scrubbing solution may be provided by an internal recycle within the process.

[0016]

[0013] In accordance with a first aspect the invention provides a process for manganese purification, the process comprising: providing an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); and extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof , thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate.

[0017]

[0014] In one set of embodiments, the process for manganese purification comprises: providing an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); and extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase, and wherein the ratio of Mn to Ca in the Mn-rich extractant phase is greater than the ratio of Mn to Ca in the aqueous solution.

[0018]

[0015] In some embodiments, the organophosphorus extractant is an organophosphoric acid.

[0019]

[0016] In some embodiments, the aqueous solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5, or in the range of 2.5 to 4.5, or in the range of 3 to 4, during the extracting. When the organophosphorus extractant is an organophosphoric acid, the pH range may be in the range of 3.2 to 3.7 during the extracting.

[0020]

[0017] In some embodiments, the organic extractant phase has a temperature of above 30°C during the extracting. In some embodiments, the organic extractant phase has a temperature of above 40°C, or above 45°C, or above 50°C, such as in the range of 50 to 80°C, during the extracting.

[0021]

[0018] In some embodiments, the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. In some embodiments, the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 75%, or at least 80%, such as at least 85%, or between 70% and 90%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

[0022]

[0019] In some embodiments, the Mn-rich extractant phase comprises an amount of Mn corresponding to at least 50%, or at least 60%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, such as at least 90%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

[0023]

[0020] In some embodiments, the ratio of Mn to Ca in the Mn-rich extractant phase is at least 1.5 times the ratio of Mn to Ca in the aqueous solution, optionally at least double the ratio of Mn to Ca in the aqueous solution.

[0024]

[0021] In some embodiments, the organophosphoric acid has the formula (RO)2PO2H, wherein each R is independently an organyl group. In some embodiments, each R is independently selected from optionally substituted branched, straight chained or cyclic alkyl, alkenyl or alkynyl groups. In some embodiments, each R is independently selected from C4+ alkyl or cycloalkyl groups. In some embodiments, each R is independently selected from n-octyl, cyclooctyl and 2-ethylhexyl. In some embodiments, the organophosphoric acid is D2EHPA.

[0025]

[0022] In some embodiments, the process comprises extracting Mn from the aqueous solution into the organic extractant phase in two or more extraction stages, optionally wherein: the aqueous solution flows sequentially through the extraction stages from a first extraction stage to a final extraction stage; and the organic extractant phase flows counter-current to the aqueous solution through the extraction stages from the final extraction stage to the first extraction stage. In some embodiments, the process comprises two or three extraction stages.

[0026]

[0023] In some embodiments, at least 95%, or at least 98%, of the Mn is extracted from the aqueous solution after the final extraction stage.

[0027]

[0024] The process is preferably conducted with a single solvent extraction circuit. Therefore, in some embodiments, the process further comprises extracting Mn present in the Mn-rich extractant phase into an aqueous liquid; and recovering Mn present in the aqueous liquid to produce a manganese salt product without contacting the aqueous liquid with an organic extraction phase comprising Mn ions. Mn present in the aqueous liquid may be recovered, to produce the manganese salt product, without extracting Ca or Mg from the aqueous liquid into an organic extraction phase.

[0028]

[0025] In some embodiments, the process comprises a first solvent extraction circuit in which (i) Mn is extracted from the aqueous solution into the organic extractant phase to produce the Mn-rich extractant phase, (ii) Mn present in the Mn-rich extractant phase is extracted into an aqueous liquid, thereby producing a Mn-lean extractant phase, and (iii) a least a portion of the Mn-lean extractant phase is recycled to form at least a portion of the organic extractant phase, wherein Mn present in the aqueous liquid is recovered from the aqueous liquid as a manganese salt product without purification in a second solvent extraction circuit. The aqueous liquid may be an acid stripping solution, such as an aqueous solution comprising H2SO4.

[0029]

[0026] In some embodiments, the process further comprises: contacting the Mn- rich extractant phase with an aqueous scrubbing solution comprising Mn ions; and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution.

[0030]

[0027] The presence of Mn ions in the aqueous scrubbing solution may prevent or acceptably limit the net transfer of Mn ions from the Mn-rich extractant phase to the aqueous scrubbing solution. In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase. In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a zero or positive net transfer of Mn from the aqueous scrubbing solution to the Mn-rich extractant phase.

[0031]

[0028] In some embodiments, at least 50%, or at least 70%, or at least 80%, or at least 85%, or at least 90%, such as at least 95%, of the Ca in the Mn-rich extractant phase is extracted into the aqueous scrubbing solution.

[0032]

[0029] In some embodiments, the Ca-lean extractant phase comprises an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0033]

[0030] In some embodiments, the Ca-lean extractant phase comprises an amount of Mn corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0034]

[0031] In some embodiments, the Mn-rich extractant phase has a temperature of above 30°C, or above 40°C, or above 45°C, or above 50°C, such as in the range of 50 to 80°C, when extracting Ca and Mg into the aqueous scrubbing solution.

[0035]

[0032] In some embodiments, the aqueous scrubbing solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5.0, or in the range of 2.5 to 4.5, or in the range of 3 to 4, when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution. When the organophosphorus extractant is an organophosphoric acid, the pH range may be in the range of 3.2 to 3.7 when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution.

[0033] In some embodiments, the process comprises extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution in two or more scrubbing stages, optionally wherein: the Mn-rich extractant phase flows sequentially through the scrubbing stages from a first scrubbing stage to a final scrubbing stage; and the aqueous scrubbing solution flows counter-current to the Mn-rich extractant phase through the scrubbing stages from the final scrubbing stage to the first scrubbing stage.

[0036]

[0034] In some embodiments, in at least one scrubbing stage, and optionally in each scrubbing stage: (i) the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase; (ii) the Mn-rich extractant phase comprises an amount of Mn corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase; (iii) the Mn- rich extractant phase has a temperature of above 30°C, or above 40°C, or above 45°C, or above 50°C, such as in the range of 50 to 80°C, when extracting Ca and Mg into the aqueous scrubbing solution; and / or (iv) the organophosphorus extractant is an organophosphoric acid and the aqueous scrubbing solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5.0, or in the range of 2.5 to 4.5, or in the range of 3 to 4, when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution. When the organophosphorus extractant is an organophosphoric acid, the pH range may be in the range of 3.2 to 3.7 when extracting Ca and Mg into the aqueous scrubbing solution.

[0037]

[0035] In some embodiments, the Ca-lean extractant phase has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, preferably less than or equal to 1 .5 x 10’4, more preferably less than or equal to 7.5 x 10’5.

[0038]

[0036] In some embodiments, the process further comprises extracting Mn from the Ca-lean extractant phase into an acid stripping solution in one or more stripping stages, thereby producing an Mn-lean extractant phase and a Mn-rich strip solution.

[0037] In some embodiments, the process further comprises precipitating or crystallising a manganese salt, such as manganese sulfate monohydrate, from the Mn- rich strip solution. The manganese salt may have a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, or less than or equal to 1 .5 x 10’4, such as less than or equal to 7.5 x 10’5.

[0039]

[0038] In some embodiments, the process further comprises recycling a portion of Mn-rich strip solution or a crystallisation product liquor remaining after manganese precipitation or crystallisation to form the aqueous scrubbing solution comprising Mn ions.

[0040]

[0039] In one set of embodiments, the process for manganese purification comprises:

[0041] • providing an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg);

[0042] • extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase, and wherein the ratio of Mn to Ca in the Mn-rich extractant phase is greater than the ratio of Mn to Ca in the aqueous solution;

[0043] • contacting the Mn-rich extractant phase with an aqueous scrubbing solution comprising Mn ions; and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution, wherein the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase;

[0044] • extracting Mn from the Ca-lean extractant phase into an acid stripping solution, thereby producing an Mn-lean extractant phase and a Mn-rich strip solution; and

[0045] • recovering Mn present in the Mn-rich strip solution as a manganese product salt.

[0040] In such embodiments, one or more of the following may optionally apply:

[0046] • the organophosphorus extractant is present in an amount of at least 70 mol%, or at least 80 mol%, or at least 90 mol%, or at least 95%, such as substantially 100 mol% of the total organophosphorus and organonitrogen components in the organic extractant phase;

[0047] • the organophosphorus extractant is an organophosphoric acid;

[0048] • the organic extractant phase is substantially free of an organonitrogen synergist;

[0049] • the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 70% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase;

[0050] • the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a zero or positive net transfer of Mn from the aqueous scrubbing solution to the Mn-rich extractant phase;

[0051] • the Mn-rich strip solution is not further purified by solvent extraction;

[0052] • the Ca-lean extractant phase and the Mn-rich strip solution both have a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, or less than or equal to 1 .5 x 10’4, such as less than or equal to 7.5 x 10’5.

[0053] • the manganese product salt has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, or less than or equal to 1 .5 x 10’4, such as less than or equal to 7.5 x 10’5.

[0054]

[0041] In accordance with a second aspect the invention provides a process for purifying manganese (Mn) present in an organic extractant phase, the process comprising: providing a Mn-rich extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, and a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); and extracting Ca and Mg from the Mn-rich extractant phase into an aqueous scrubbing solution comprising Mn ions, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution.

[0055]

[0042] In one set of embodiments, the process for purifying manganese (Mn) present in an organic extractant phase comprises providing a Mn-rich extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, and a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); contacting the Mn- rich extractant phase with an aqueous scrubbing solution comprising Mn ions; and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution, wherein the Ca-lean extractant phase comprises an amount of multivalent metal ions corresponding to at least 60% of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0056]

[0043] In some embodiments, the organophosphorus extractant is an organophosphoric acid.

[0057]

[0044] In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase. In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a zero or positive net transfer of Mn from the aqueous scrubbing solution to the Mn-rich extractant phase.

[0058]

[0045] In some embodiments, the Ca-lean extractant phase comprises an amount of multivalent metal ions corresponding to at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0059]

[0046] In some embodiments, the Ca-lean extractant phase comprises an amount of Mn corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0060]

[0047] In some embodiments, the Mn-rich extractant phase has a temperature of above 30°C, or above 40°C, or above 45°C, or above 50°C, such as in the range of 50 to 80°C, when extracting Ca and Mg into the aqueous scrubbing solution.

[0061]

[0048] In some embodiments, the aqueous scrubbing solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5.0, or in the range of 2.5 to 4.5, or in the range of 3 to 4 when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution. When the organophosphorus extractant is an organophosphoric acid, the pH range may be in the range of 3.2 to 3.7 when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution.

[0062]

[0049] In some embodiments, the process comprises extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution in two or more scrubbing stages, optionally wherein: the Mn-rich extractant phase flows sequentially through the scrubbing stages from a first scrubbing stage to a final scrubbing stage; and the aqueous scrubbing solution flows counter-current to the Mn-rich extractant phase through the scrubbing stages from the final scrubbing stage to the first scrubbing stage.

[0063]

[0050] In some embodiments, in at least one scrubbing stage, and optionally in each scrubbing stage: (i) the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase; (ii) the Mn-rich extractant phase comprises an amount of Mn corresponding to at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase; (iii) the Mn- rich extractant phase has a temperature of above 30°C, or above 40°C, or above 45°C, or above 50°C, such as in the range of 50 to 80°C, when extracting Ca and Mg into the aqueous scrubbing solution; and / or (iv) the organophosphorus extractant is an organophosphoric acid and the aqueous scrubbing solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5, or in the range of 2.5 to 4.5, or in the range of 3 to 4, such as in the range of 3.2 to 3.7, when extracting Ca and Mg into the aqueous scrubbing solution.

[0064]

[0051] In some embodiments, the Ca-lean extractant phase has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, preferably less than or equal to 1 .5 x 10’4, more preferably less than or equal to 7.5 x 10’5.

[0065]

[0052] In some embodiments, the organophosphoric acid has the formula (RO)2PO2H, wherein each R is independently an organyl group. In some embodiments, each R is independently selected from optionally substituted branched, straight chained or cyclic alkyl, alkenyl or alkynyl groups. In some embodiments, each R is independently selected from C4+ alkyl or cycloalkyl groups. In some embodiments, each R is independently selected from n-octyl, cyclooctyl and 2-ethylhexyl. In some embodiments, the organophosphoric acid is D2EHPA.

[0066]

[0053] In some embodiments, the process further comprises extracting Mn from the Ca-lean extractant phase into an acid stripping solution in one or more stripping stages, thereby producing an Mn-lean extractant phase and a Mn-rich strip solution.

[0067]

[0054] In some embodiments, the process further comprises precipitating or crystallising a manganese salt, such as manganese sulfate monohydrate, from the Mn- rich strip solution.

[0068]

[0055] In some embodiments, the process further comprises recycling a portion of Mn-rich strip solution or a crystallisation product liquor remaining after manganese precipitation or crystallisation to form the aqueous scrubbing solution comprising Mn ions.

[0069]

[0056] Unless the context dictates otherwise, where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0070]

[0057] Further aspects of the invention appear below in the detailed description of the invention.

[0071] Brief Description of Drawings

[0072]

[0058] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0073]

[0059] Figure 1 is a block flow diagram depicting a process for manganese purification according to embodiments of the disclosure.

[0074]

[0060] Figure 2 is a graph showing the % Mn extraction as a function of extraction pH and temperature, as determined in Example 1 .

[0061] Figure 3 is a graph showing the % Ca extraction as a function of extraction pH and temperature, as determined in Example 1 .

[0075]

[0062] Figure 4 is a graph showing the % Mg extraction as a function of extraction pH and temperature, as determined in Example 1 .

[0076]

[0063] Figure 5 is a graph showing the extracted Mn / Ca ratio as a function of extraction pH and temperature, as determined in Example 1.

[0077]

[0064] Figure 6 is a graph showing the extracted Mn / Mg ratio as a function of extraction pH and temperature, as determined in Example 1.

[0078]

[0065] Figure 7 is a graph showing the extracted Mn / Ca ratio as a function of total loaded capacity of the extractant, as determined in Example 1 .

[0079]

[0066] Figure 8 is a graph showing an Mn extraction distribution isotherm, together with constructed McCabe-Thiele diagram for an operating A / O ratio of 1 :2.5, as determined in Example 2.

[0080]

[0067] Figure 9 is a graph showing a Ca extraction distribution isotherm, together with constructed McCabe-Thiele diagram for an operating A / O ratio of 1 :2.5, as determined in Example 2.

[0081]

[0068] Figure 10 is a graph showing an Mg extraction distribution isotherm, together with constructed McCabe-Thiele diagram for an operating A / O ratio of 1 :2.5, as determined in Example 2.

[0082]

[0069] Figure 1 1 is a graph showing the % metal extraction for Mn, Mg and Ca, and the Mn / Ca and Mn / Mg ratios (wt / wt) in the loaded extractant, as a function of the % loading relative to the theoretical total loading capacity of the extractant, as determined in Example 2.

[0083]

[0070] Figure 12 is a graph showing extracted Mn / Ca ratios as a function of the concentration of multivalent metal ions in the extractant after equilibration, as determined in Examples 2 and 3.

[0071] Figure 13 is a graph showing extracted Mn / Ca ratios as a function of the % loading relative to the theoretical total loading capacity of the extractant, as determined in Examples 2 and 3.

[0084]

[0072] Figure 14 is a graph showing scrubbing efficiencies (% removal) for Mn, Ca and Mg as a function of pH when scrubbing a Mn-rich extractant phase with deionised water at 50°C, as determined in Example 4.

[0085]

[0073] Figure 15 is a graph showing scrubbing efficiencies (% removal) for Mn, Ca and Mg as a function of pH when scrubbing a Mn-rich extractant phase with a 15 g / L Mn scrubbing solution at 50°C, as determined in Example 4.

[0086]

[0074] Figure 16 is a graph showing scrubbing efficiencies (% removal) for Mn, Ca and Mg as a function of pH when scrubbing a Mn-rich extractant phase with a 30 g / L Mn scrubbing solution at 50°C, as determined in Example 4.

[0087]

[0075] Figure 17 is a graph showing scrubbing efficiencies (% removal) for Mn, Ca and Mg as a function of pH when scrubbing a Mn-rich extractant phase with a 45 g / L Mn scrubbing solution at 50°C, as determined in Example 4.

[0088]

[0076] Figure 18 is a graph showing the Mn stripping distribution isotherm together with constructed McCabe-Thiele diagram for an operating A / O ratio of 1 :3.5, as determined in Example 7.

[0089]

[0077] Figure 19 is a graph showing the % Mn, Ca and Mg extraction, as a function of extraction pH, as determined in Example 8.

[0090]

[0078] Figure 20 is a graph showing the extracted Mn / Ca and Mn / Mg ratios as a function of extraction pH, as determined in Example 8.

[0091]

[0079] Figure 21 is a graph showing the % Mn, Ca and Mg extraction, as a function of extraction pH, as determined in Example 9.

[0092]

[0080] Figure 22 is a graph showing the extracted Mn / Ca and Mn / Mg ratios as a function of extraction pH, as determined in Example 9. Detailed Description

[0093] Process for manganese purification

[0094]

[0081] The present invention relates to a process for manganese purification. The manganese is initially present in an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg). Mn is extracted from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate. The extraction process is operated such that the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% (and preferably higher amounts such as at least 75%) of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. At such high loading capacities, the ratio of Mn to Ca in the Mn-rich extractant phase may be greater than the ratio of Mn to Ca in the aqueous solution.

[0095] Aqueous solution comprising a plurality of metal ions

[0096]

[0082] The manganese to be purified is initially present in an aqueous solution comprising a plurality of metal ions, including at least Mn, Ca and Mg. In some embodiments, other divalent metal ions are also present, such as for example one or more of Zn, Cu, Cd, Co and Ni. In some embodiments, the aqueous solution further comprises one or more trivalent metal ions, such as for example Fe(lll) and / or Al(lll). In some embodiments, the aqueous solution further comprises monovalent cations, such as alkali metals (Na, K) and ammonium (NH4+). The aqueous solution also comprises anions, which in some embodiments include at least one selected from sulfate, chloride, and nitrate. In some embodiments, the aqueous solution comprises sulfate, typically as the predominant (e.g. >50 mol%, e.g. >80 mol%) anion, optionally with minor amounts of chloride and / or nitrate. Chloride may complex with metals in solution, including Mn, potentially affecting the extraction selectivity. In some embodiments, therefore, the aqueous solution is free of chloride or chloride is present in functionally insignificant amounts, such as an amount of less than 10 mol%, or less than 5 mol%, such as less than 2 mol%, of the total anions in the aqueous solution.

[0083] The aqueous solution may in principle be derived from any source, but in some embodiments the aqueous solution is a process stream in a hydrometallurgical process for recovering one or more metals from a metal source, for example a manganese-bearing ore or concentrate, or a waste product such as waste electronics or recycled batteries or battery components. In some embodiments, the aqueous solution is provided by leaching a metal source with an acid, such as H2SO4, to extract manganese and other metals, and subjecting the leachate to one or more preliminary purification steps such as i) K / Na removal by jarosite [(K, Na, NH4+) Fe3(SO4)2(OH)6] precipitation, (ii) Fe / AI removal by hydroxide precipitation, and / or (iii) heavy metal (Zn, Cu, Cd, Co, Ni) removal by sulphide precipitation or ion-exchange. In such scenarios, the aqueous solution may comprise (i) Mn as the most abundant metal, (ii) Ca and Mg as impurity metal ions, with (iii) other multivalent metal ions being absent or only present in trace amounts. It will be appreciated however that such steps are not required in all scenarios. For example, prior removal of monovalent ions may not be required in the present solvent extraction-based process, unlike in certain other Mn-recovery processes such as EMD where the presence of K during electrolysis promotes the formation of the a-MnO2 which is non-battery active. Prior removal of metals such as Co and Ni is also not essential since these could be separated from Mn in a later process step.

[0097]

[0084] The amounts of Mn, Ca and Mg in the aqueous solution can vary widely, depending on the source of the solution and any pretreatment steps. Mn may be present in amounts up to the saturated concentration, which is about 240 g / L in some conditions. The Ca in solution may be derived from the leaching, or from limestone / lime previously added for neutralisation, e.g. for Fe / AI hydroxide precipitation. The maximum Ca in solution may be limited to the saturated concentration of calcium sulfate (CaSCU), which may be in the range of 0.4 to 1 .0 g / L Ca depending on the conditions. In some embodiments, the Mg in solution is present in amounts of up to 50 g / L Mg, or in the range of 0.5 to 30 g / L Mg such as 0.5 to 20 g / L Mg, depending on factors such as the Mg content of the source ore and any pretreatment removal steps. Extraction

[0098]

[0085] The process comprises a step of extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof. In some embodiments, the organophosphorus extractant is an organophosphoric acid. In some embodiments, the organophosphorus extractant is an organophosphonic acid. The organophosphorus extractant is typically diluted with an organic liquid diluent.

[0099]

[0086] As used herein, an organophosphoric acid encompasses both the protonated and deprotonated forms of a molecule having the formula (RO)2PO2H (in protonated form), where each R is independently an organyl group. In some embodiments, each R comprises from 1 to 30 carbon atoms, such as from 2 to 18 carbon atoms. In some embodiments, each R is independently selected from optionally substituted branched, straight chain or cyclic alkyl, alkenyl or alkynyl groups. If substituted, suitable substituents may include -OH, C1-12 alkoxy, C1-10 aryl, nitrile, halogen and the like. In some embodiments, each R is independently selected from C4+ alkyl or cycloalkyl groups, such as C6-10 alkyl or cycloalkyl groups. In some embodiments, each R is independently selected from Cs alkyl or cycloalkyl groups, such as n-octyl, cyclooctyl and 2-ethylhexyl. In some embodiments, the organophosphoric acid is D2EHPA.

[0100]

[0087] As used herein, an organophosphonic acid encompasses both the protonated and deprotonated forms of a molecule having the formula (RO)R’PO2H (in protonated form), where R and R’ are independently an organyl group. In some embodiments, R and R’ each independently comprise from 1 to 30 carbon atoms, such as from 2 to 18 carbon atoms. In some embodiments, R and R’ are each independently selected from optionally substituted branched, straight chain or cyclic alkyl, alkenyl or alkynyl groups. If substituted, suitable substituents may include -OH, C1-12 alkoxy, Ci- 10 aryl, nitrile, halogen and the like. In some embodiments, R and R’ are each independently selected from C4+ alkyl or cycloalkyl groups, such as Ce-io alkyl or cycloalkyl groups. In some embodiments, R and R’ are each independently selected from Cs alkyl or cycloalkyl groups, such as n-octyl, cyclooctyl and 2-ethylhexyl. In some embodiments, the organophosphonic acid is EHEHPA.

[0088] The process does not rely on the presence, in the organic extractant phase, of (i) an organophosphinic acid, i.e. a molecule of formula (FQ2PO2H where each R is an organyl group, (ii) a synergist such as an alkyl-4-pyridinecarboxylate ester or other neutral ligand capable of coordinating to Mn and thus modifying its extractability by an organophosphoric or organophosphonic acid, (iii) a synergist such as a quaternary alkyl ammonium cation, or (iv) a neutral organophosphorus extractant such as tributyl phosphate (TBP) and the like.

[0101]

[0089] To significantly change the extraction selectivities of organophosphorous extractants (such as organophosphoric or organophosphonic acids), organophosphorous and organonitrogen synergists are typically used in a ratio of at least 1 :1 (mokmol) relative to the organophosphorus extractant. However, such synergists are not required and are typically not desirable in the methods disclosed herein. Accordingly, in some embodiments, the organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof is present in an amount of at least 70 mol%, or at least 80 mol%, or at least 90 mol%, or at least 95%, such as substantially 100 mol% of the total organophosphorus and organonitrogen components in the organic extractant phase.

[0102]

[0090] In some embodiments, the organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof is present in an amount of at least 90 wt.%, or at least 95 wt.%, of the total organophosphorus components in the organic extractant phase. In some embodiments, the organic extractant phase is substantially free of an organophosphinic acid. In some embodiments the organic extractant phase is substantially free of 4-pyridinecarboxylate ester. In some embodiments the organic extractant phase is substantially free of N- heteroaromatic compounds. In some embodiments, the organic extractant phase is substantially free of an organonitrogen synergist. In some embodiments, the organic extractant phase is substantially free of synergistic neutral ligands capable of coordinating to Mn. In some embodiments, the organic extractant phase is substantially free of a neutral organophosphorus extractant. In some embodiments where the organophosphorus extractant is an organophosphoric acid, the organic extractant phase is substantially free of an organophosphonic acid. By “substantially free” it is meant that such components are either entirely absent or present in functionally negligible amounts, for example less than 1 wt.%, or less than 0.1 wt.%, of the organic extractant phase.

[0103]

[0091] The organophosphorus extractant may be diluted with an organic liquid diluent such as a hydrocarbon liquid. The hydrocarbon liquid may be aliphatic or aromatic or a combination thereof. In some embodiments, the organic liquid diluent is an aliphatic hydrocarbon liquid, such as a saturated aliphatic hydrocarbon liquid and / or a C10-C16 aliphatic hydrocarbon liquid. As used herein, an aliphatic hydrocarbon liquid comprises predominantly aliphatic hydrocarbon molecules, although it is not excluded that aromatics and / or other components may be present in minor amounts.

[0104]

[0092] The organophosphorus extractant may be present in a suitable amount in the organic extractant phase to provide a high capacity for Mn extraction, with the organic liquid diluent optionally present to modify the concentration of the organophosphorus extractant, reduce the viscosity and adjust the specific gravity of the organic phase for improved dispersion I coalescence, faster phase separation, improved mass transfer and the extraction kinetics. In some embodiments, the organic extractant phase comprises the organophosphorus extractant in an amount of between 10% and 90% (v / v), such as between 30% and 85% (v / v), for example between 40% and 80% (v / v).

[0105]

[0093] During the extraction, the organophosphorus extractant should preferably be at least partially in its deprotonated form (i.e. (RO)2PO2‘ or (RO)R’PO2') to allow coordination with Mn ions. Optionally, the organic extractant phase may be preneutralised with a suitable base, such as NH4OH, NaOH, KOH, Na2CO3, NaHCOa, K2CO3 or KHCO3, so that the organophosphorus extractant is at least partially in its deprotonated form prior to contact with the aqueous solution. Alternatively, the organophosphorus extractant may be deprotonated by adjusting the pH of the aqueous solution during the extraction, i.e. after the organic extractant phase and aqueous solution are already in contact. The pH may be adjusted as required by adding a suitable base as described or an acid, e.g. H2SO4.

[0106]

[0094] The organic extractant phase, prior to contact with the aqueous solution, is typically barren of multivalent metals, particularly Ca and Mg which are undesirable after extraction in the Mn-rich extractant phase. Ca is particularly undesirable due to the inefficiency of exchange with Mn and the risk of exceeding the saturation concentration, thus precipitating gypsum, after extraction into the aqueous phase. In some embodiments, therefore, the organic extractant phase, prior to contact with the aqueous solution, comprises Ca in amounts of less than 10%, preferably less than 5%, or less than 2%, or less than 1 %, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

[0107]

[0095] The aqueous solution should have a suitable pH, during the extraction (specifically, once the system is equilibrated), to allow extraction of Mn, preferably with good selectivity in comparison to Ca and Mg. The optimum pH will depend on the pKa of the organophosphorus extractant. In some embodiments where the organophosphorus extractant is an organophosphoric acid, the aqueous solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5, or in the range of 2.5 to 4.5, such as in the range of 3.0 to 4.0, for example in the range of 3.2 to 3.7, during the extracting. The inventors have found by experiment that the highest Mn / Ca ratios of metal ions extracted into the organic extractant phase can be obtained at a pH of about 3.5 when using D2EHPA. Higher pH values of the aqueous solution may be preferred in embodiments where an organophosphonic acid extractant is used. It has been found by experiment that the highest Mn / Ca ratios of metal ions extracted into the organic extractant phase can be obtained at a pH of about 4.0 when using EHEHPA.

[0108]

[0096] In some embodiments, the extraction is performed at ambient temperature or higher. In some embodiments, the extraction is performed at a temperature of above 20°C. However, the inventors have surprisingly found that enhanced selectivities for Mn vs Ca extraction are obtained at elevated operating temperatures during extraction. In some preferred embodiments, therefore, the extractant phase has a temperature of above 30°C during the extracting. In some embodiments, the organic extractant phase has a temperature of above 40°C, or above 45°C, such as above 50°C, for example in the range of 40°C to 80°C or 50°C to 80°C, during the extracting. Higher temperatures may also reduce or avoid any difficulties in phase separation after extraction.

[0109]

[0097] The extraction process may be operated such that the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. In some embodiments, the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, or at least 75%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. As used herein, a multivalent metal cation has a valency of 2 or higher, and includes divalent and trivalent cations.

[0110]

[0098] The inventors have found that high ultimate loaded capacities of multivalent metal cations in the organic extractant phase, i.e. after extraction, are important to achieve a preferential extraction selectivity for Mn vs Ca, and that higher selectivities are typically obtained with higher loaded capacities. Without limitation by any theory, this is ascribed to a competitive extraction effect whereby increasing coordination of the organophosphoric or organophosphonic acid with multivalent metal ions allows Mn coordination to be preferred relative to Ca and Mg coordination since fewer vacant coordination sites are available. There may be a practical upper bound to the capacity utilisation imposed by increasing viscosity and / or precipitation in the organic extractant phase, so that in some embodiments the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to less than 100%, or less than 95%, such as about 90% or less, of the total loading capacity based on the amount of organophosphoric acid in the Mn-rich extractant phase.

[0111]

[0099] During solvent extraction processes, divalent metal ions coordinate with organophosphoric acid or organophosphonic acid extractants in a molar ratio of 1 :2. Therefore, the amount of divalent metal ions corresponding to 100% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase will be a molar amount equal to half of the molar amount of the organophosphorus extractant. Thus, as an example, an amount of divalent metal ions corresponding to 50% of the total loading capacity based on the amount of organophosphoric (and / or organophosphonic) acid in the Mn-rich extractant phase can be calculated as 50% of 50% (=25%) of the molar amount of organophosphoric (and / or organophosphonic) acid in the Mn-rich extractant phase. If any trivalent metal ions are present, these will strongly coordinate with organophosphoric or organophosphonic acid extractants in a molar ratio of 1 :3. This ratio can be used to calculate the corresponding percentage of the loading capacity based on the amount of any trivalent metal ions.

[0100] In general, the correspondence between total loading capacity based on the amount of organophosphorus extractant and the amount of divalent and trivalent metal ions may be calculated by equation (1 ): where X is the % of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase;

[0112] D is the molar amount of divalent metal ions in the Mn-rich extractant phase;

[0113] T is the molar amount of trivalent metal ions in the Mn-rich extractant phase; and P is the molar amount of organophosphorus acid extractant in the Mn-rich extractant phase.

[0114]

[0101] A target amount of multivalent metal ions in the Mn-rich extractant phase may be achieved by: (i) controlling the ratio of the aqueous solution to the organic extractant phase (i.e. the A / O ratio) and / or (ii) the concentration of organophosphorus extractant in the organic extractant phase, and / or (iii) by controlling the pH of the aqueous solution during the extraction. Higher A / O ratios and / or lower organophosphorus extractant concentration relative to the amount of Mn in the aqueous solution will tend to favour an increased loading capacity in Mn-rich extractant phase. pH control ensures that a sufficient proportion of the organophosphorus extractant is present in deprotonated form, and thus able to extract multivalent metal ions to high capacity utilisations.

[0115]

[0102] The aqueous solution may, in some embodiments, comprise multivalent metal ions other than Mn, Ca and Mg that are more preferentially extracted than Mn in the process disclosed herein, for example trivalent metal ions and / or zinc (Zn2+). These metals will then be co-extracted with Mn into the Mn-rich extractant phase, contributing to the total loaded capacity. Ca and Mg may therefore still be excluded according to the principles disclosed herein, thus achieving a desirable preference for Mn extraction vs Ca and Mg. It will be appreciated that the other multivalent metal ions may then be separated from Mn, if desired, in a downstream process.

[0116]

[0103] In some embodiments, therefore, the multivalent metal ions present in the Mn-rich extractant phase comprise Mn, Ca, Mg and one or more additional multivalent metal ions with a higher affinity for the organophosphorus extractant than Mn, with the total amount of these multivalent metal cations (the Mn, Ca, Mg and one or more additional multivalent metal ions with a higher affinity for the organophosphorus extractant than Mn) corresponding to at least 50%, or at least 60%, or at least 70%, or at least 75%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

[0117]

[0104] In some embodiments, Mn is the most preferentially extracted metal ion present in the aqueous solution, for example because other strongly extracted multivalent metal ions were already removed in one or more earlier purification steps. In these or other embodiments, Mn may be the most abundant extractable metal species present in the aqueous solution immediately prior to extraction, typically by a substantial margin. In such scenarios, the practically relevant consideration for Mn selectivity may be the total amount of Mn (or Mn + Ca + Mg) extracted into the organic phase. In some embodiments, the Mn-rich extractant phase comprises a combined amount of Mn, Ca and Mg corresponding to at least 50%, or at least 60%, or at least 70%, or at least 75%, such as at least 80%, for example at least 85% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. In some embodiments, the Mn-rich extractant phase comprises an amount of Mn corresponding to at least 50%, or at least 60%, or at least 70%, or at least 75%, such as at least 80%, for example at least 85% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

[0118]

[0105] The methods disclosed herein have surprisingly been found capable of preferentially extracting Mn relative to Ca. In some embodiments, therefore, the ratio of Mn to Ca in the Mn-rich extractant phase is greater than the ratio of Mn to Ca in the aqueous solution. For example, the ratio may be at least 1 .5 times greater, or doubled.

[0119]

[0106] The aqueous solution may comprise monovalent cations such as alkali metals, e.g. K, Na, and / or ammonium (NH4+). Organophosphoric acid and organophosphonic acid extractants generally have a poor affinity for such species under Mn extraction conditions and it is expected that they will remain predominantly in the Mn-lean aqueous raffinate following the extraction.

[0107] The extraction step may be performed using solvent extraction methods and apparatus, such as one or more mixer-settlers, known to those of skill in the art. In general, such methods involve contacting the aqueous solution with the organic extractant phase, mixing the two phases under conditions to allow transfer of multivalent metal ions into the extractant phase, preferably to the equilibrium compositions, and separating the organic and aqueous liquid phases to produce the Mn-rich extractant phase and the Mn-lean aqueous raffinate.

[0120]

[0108] In some embodiments, Mn is extracted from the aqueous solution into the organic extractant phase in two or more extraction stages, thus providing a suitably high total recovery of Mn from the aqueous solution. Each stage may be performed with conventional solvent-extraction apparatus such as a mixer-settler. In some such embodiments, the aqueous solution flows sequentially through the extraction stages from a first extraction stage to a final extraction stage, and the organic extractant phase flows counter-current to the aqueous solution through the extraction stages from the final extraction stage to the first extraction stage (“counter-current flow mode”). In each stage, the aqueous solution and organic extractant phase are contacted, mixed (preferably to equilibrium) and separated before moving to the next stage in sequence. The amount of multivalent metal ions present in the organic extractant phase increases in each stage through which it flows, with the highest concentration (equivalent to that of the Mn-rich extractant phase) thus obtained in the first stage of extraction.

[0121]

[0109] In some embodiments, at least one of the extraction stages, and optionally each of the extraction stages, has a pH and temperature in the preferred ranges previously disclosed herein. In some embodiments, most of the metal ion extraction takes place in the first extraction stage, and the conditions in the first extractant stage are particularly important in determining the overall selectivity of extraction. Thus, in some embodiments, at least the first extraction stage has a pH and temperature in the preferred ranges previously disclosed herein. For example, the first extraction stage may have a pH in the most preferred range (e.g. 3.2 to 3.7, such as about 3.5 for organophosphoric acids) to maximise Mn selectivity, whereas the final extraction stage may have a higher pH to maximise total Mn recovery. In some embodiments, the temperature may be similar in all stages.

[0110] In other embodiments, the aqueous solution flows sequentially through the extraction stages from a first extraction stage to a final extraction stage, but in one or more of the stages the aqueous solution is extracted with a fresh portion of organic extractant phase which passes only through a single stage (“cross-current flow mode”). Again, at least one of the extraction stages, and optionally each of the extraction stages, may have a pH and temperature in the preferred ranges previously disclosed herein.

[0122]

[0111] Combinations of the counter-current and cross-current flow modes are also envisaged. Thus, in some such embodiments, the aqueous solution flows sequentially through the extraction stages from a first extraction stage to a final extraction stage, and (i) at least one portion of the organic extractant phase flows counter-current to the aqueous solution through two or more of the extraction stages, and (ii) at least one portion of the organic extractant phase flows cross-current through a single extraction stage. Each portion of the organic extractant phase recovered after extraction may then be combined to produce the Mn-rich extractant phase, or the organic extractant phase recovered from cross-current extraction may be merged with the organic extractant phase passing through counter-current extraction at any location in the counter-current extraction sequence, with a single stream of Mn-rich extractant phase ultimately exiting the train of stages. Such combined extraction modes may assist to control the Ca concentration in the aqueous solution below its saturation concentration during extraction, thus limiting or avoiding the risk of gypsum precipitation.

[0123]

[0112] In some embodiments, the process comprises between one and five extraction stages, such as two or three. The required number of stages will be determined by the efficacy of Mn extraction in each stage and the required minimum Mn recovery. In some embodiments, at least 90%, or at least 95%, or at least 98%, of the Mn is extracted from the aqueous solution after the final extraction stage. The inventors have found that two or three extraction stages is sufficient to achieve such Mn recoveries while maintaining an effective preference for Mn recovery over Ca.

[0124]

[0113] However, it should be appreciated that high Mn extraction recoveries are not necessarily required in all scenarios. For example, an overall process for Mn recovery from an aqueous solution may comprise (i) a process for manganese purification using a solvent extraction step as disclosed herein, for producing a high purity manganese salt such as HPMSM, followed by (ii) a different manganese recovery process, such as EMM and / or EMD, for recovering residual Mn from the aqueous solution after solvent extraction.

[0125] Scrubbing

[0126]

[0114] Despite the preferential selectivity for Mn extraction relative to Ca and Mg in the extraction step, the Mn-rich extractant phase may still contain residual Ca and Mg in undesirably high amounts, for example to meet particular target Mn purity specifications. The process may thus further comprise contacting the Mn-rich extractant phase with an aqueous scrubbing solution comprising Mn ions, and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution to produce a Ca-lean extractant phase and a Ca-rich scrub solution.

[0127]

[0115] The aqueous scrubbing solution should have a suitable pH, during the scrubbing (specifically, once the system is equilibrated), to allow retention of Mn while favouring the partitioning of Ca and Mg to the Ca-rich scrub solution. In some embodiments, in particular where the organophosphorus extractant is an organophosphoric acid, the aqueous scrubbing solution has a pH in the range of 2.0 to 5.0, or in the range of 2.5 to 5, or in the range of 2.5 to 4.5, such as in the range of 3.0 to 4.0, for example in the range of 3.2 to 3.7, when extracting Ca and Mg from the Mn- rich extractant phase into the aqueous scrubbing solution. Again, higher optimum pH values may be preferred if using an organophosphonic acid extractant, for example about 0.5 pH units higher.

[0128]

[0116] In some embodiments, the scrubbing is performed at ambient temperature or higher. In some embodiments, the scrubbing is performed at a temperature of above 20°C. However, enhanced selectivities for Mn retention vs Ca scrubbing may be obtained at elevated operating temperatures during scrubbing. In some embodiments, the Mn-rich extractant phase has a temperature of above 30°C, or above 40°C, or above 45°C, such as above 50°C, for example in the range of 40°C to 80°C or 50°C to 80°C, when extracting Ca and Mg into the aqueous scrubbing solution. Higher temperatures may also reduce or avoid any difficulties in phase separation after scrubbing.

[0129]

[0117] The presence of Mn ions in the aqueous scrubbing solution prior to at least one stage of scrubbing is important to prevent or acceptably limit losses of Mn from the Mn-rich extractant phase, and to maintain a high Mn concentration in the organic phase so as to “crowd out” Ca and Mg, forcing these species to partition to the aqueous scrubbing solution. The presence of Ca and Mg is undesirable in the aqueous scrubbing solution, and in some embodiments the aqueous scrubbing solution is substantially free of Ca and Mg prior to scrubbing.

[0130]

[0118] In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase, or at least 95% of the concentration of Mn in the Mn-rich extractant phase. In other words, no more than 10%, or no more than 5%, of the extracted Mn is lost to the aqueous scrubbing solution. In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a zero or positive net transfer of Mn from the aqueous scrubbing solution to the Mn-rich extractant phase.

[0131]

[0119] It will be appreciated that the absolute amount of Mn ions required in the aqueous scrubbing solution to achieve a given loaded capacity or Mn purity in the Ca- lean extractant phase will depend on various implementation-specific factors, but may be determined by routine experiments with the benefit of this disclosure. In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration of at least 0.01 M, or at least 0.02 M, or at least 0.1 M, or at least 0.2M, or at least 0.5M, such as at least 0.7M.

[0132]

[0120] After the scrubbing, the Ca-lean extractant phase may comprise an amount of multivalent metal ions corresponding to at least 60%, or at least 70%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase. By the same principles already disclosed in relation to the extraction step, a high loading of multivalent metal ions in the organic phase achieved during scrubbing preferences Mn retention in the organic extractant phase and partitioning of Ca and Mg to the aqueous scrubbing solution.

[0133]

[0121] A target maximum amount of multivalent metal ions in the Ca-lean extractant phase may be achieved by: (i) operating the extraction step to produce a suitably high amount of multivalent metal ions in the Mn-rich extractant phase and / or (ii) using a sufficiently high concentration of Mn ions in the aqueous scrubbing solution and / or (iii) controlling the ratio of the aqueous scrubbing solution to the Mn-rich extractant phase (i.e. the A / O ratio) and / or (iv) controlling the pH of the aqueous scrubbing solution during the scrubbing, and / or (v) controlling the temperature of the Mn-rich extractant phase during the scrubbing. Higher A / O ratios will tend to favour an increased loading capacity in the Ca-lean extractant phase. pH and temperature control, as described above, will also favour high loading capacity and efficient scrubbing.

[0134]

[0122] In some embodiments (for example when Mn is the most preferentially retained metal ion present in the Mn-rich extractant) the Ca-lean extractant phase comprises an amount of Mn ions corresponding to at least 60%, or at least 70%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0135]

[0123] The methods disclosed herein have surprisingly been found capable of achieving very high manganese purities with respect to Ca and Mg contaminants. In some embodiments, at least 80%, or at least 85%, such as at least 90%, for example at least 95%, of the Ca in the Mn-rich extractant phase is extracted into the aqueous scrubbing solution. In some embodiments, the Ca-lean extractant phase has a Ca:Mn ratio (wt / wt) and / or a Mg:Mn ratio (wt / wt) which are less than or equal to 3.1 x 10’4, or less than or equal to 1.5 x 10’4, such as less than or equal to 7.5 x 10’5, which ratios may be suitable to meet various industry specifications for high purity grades of manganese products, such as HPMSM.

[0136]

[0124] In practice, the Mn present in the Ca-lean extractant phase may be further purified during Mn recovery from the Mn-rich strip solution, e.g. in a crystallisation step, as described further below. Thus, a Ca:Mn ratio (wt / wt) and / or a Mg:Mn ratio (wt / wt) in the Ca-lean extractant phase that is somewhat higher than specified for the ultimate Mn product may be acceptable, provided that the purity specifications are met after Mn recovery (e.g. in crystallisation).

[0137]

[0125] The scrubbing step may be performed using solvent extraction methods and apparatus, such as one or more mixer-settlers, known to those of skill in the art. In general, such methods involve contacting the Mn-rich extractant phase with the aqueous scrubbing solution, mixing the two phases under conditions to allow transfer of multivalent metal ions between the phases, preferably to the equilibrium compositions, and separating the two liquid phases to produce the Ca-lean extractant phase and the Ca-rich scrub solution.

[0138]

[0126] In some embodiments, Ca and Mg are extracted from the Mn-rich extractant phase into the aqueous scrubbing solution in two or more scrubbing stages, thus providing a suitably high total removal of these species. Each stage may be performed with conventional solvent-extraction apparatus such as a mixer-settler. In some such embodiments, the Mn-rich extractant phase flows sequentially through the scrubbing stages from a first scrubbing stage to a final scrubbing stage; and the aqueous scrubbing solution flows counter-current to the Mn-rich extractant phase through the scrubbing stages from the final scrubbing stage to the first scrubbing stage (“countercurrent flow mode”). In each stage, the organic extractant phase and the aqueous scrubbing solution are contacted, mixed (preferably to equilibrium) and separated before moving to the next stage in sequence. The amount of Ca and Mg ions present in the organic extractant phase decreases in each stage through which it flows, with the lowest concentration (equivalent to that of the Ca-lean extractant phase) obtained in the final stage. Thus, in some embodiments, at least the final extraction stage has a pH and temperature in the preferred ranges previously disclosed herein. Optionally, each extraction stage has a pH and temperature in these ranges.

[0139]

[0127] In other embodiments, the Mn-rich extractant phase flows sequentially through the scrubbing stages from a first scrubbing stage to a final scrubbing stage, but the organic phase is extracted in each stage with a fresh portion of aqueous scrubbing solution (“cross-current flow mode”). The post-extraction aqueous scrubbing solution removed from each scrubbing stage may then be combined to produce the Ca-rich scrub solution. Again, at least one of the scrubbing stages, and optionally each of the scrubbing stages, may have a pH and temperature in the preferred ranges previously disclosed herein. Combinations of the counter-current and cross-current flow modes are also envisaged.

[0140]

[0128] The required number of scrubbing stages will be determined by the efficacy of Ca and Mg scrubbing in each stage and the required purity of Mn to be produced. In some embodiments, the process comprises between one and seven extraction phases, or between three and six scrubbing stages, such as four or five scrubbing stages. In some embodiments, the Ca-lean extractant phase produced by the final scrubbing stage has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, or less than or equal to 1.5 x 10’4, for example less than or equal to 7.5 x 10’5, which ratios may be suitable to meet various industry specifications for high purity grades of manganese products, such as HPMSM.

[0141]

[0129] The aqueous scrubbing solution may be provided within the overall process by recycling an aqueous process stream or manganese product having a suitably high purity Mn composition, as will be explained further hereafter. In some embodiments, therefore, the aqueous scrubbing solution comprises Mn ions in a desired concentration prior to scrubbing.

[0142]

[0130] However, in multi-stage scrubbing embodiments, it should be appreciated that it is not essential that the initial aqueous scrubbing solution should contain Mn ions. For example, in a counter-current flow mode as described above, it is envisaged that an aqueous scrubbing solution which is substantially free of Mn, Ca and Mg ions may be flowed to the final scrubbing stage. In this stage, some proportion of the Mn present in the organic phase transfers into the aqueous scrubbing solution (e.g. less than 10%, or less than 5%). Therefore, the aqueous scrubbing solution comprises Mn ions when it moves to the subsequent stages in sequence. Thus, in at least the first scrubbing stage, the Mn-rich extractant phase is contacted with an aqueous scrubbing solution comprising Mn ions. It is expected that sufficient Mn ions can be transferred to the aqueous scrubbing solution, in this manner, to crowd out Ca and Mg from the Mn-rich extractant phase in the initial scrubbing stages. A pH profile across the stages may also be used to enhance overall selectivity while acceptably limiting the loss of Mn to the Ca-rich scrub solution.

[0143]

[0131] Following the scrubbing step, the Ca-rich scrub solution, which may contain substantial concentrations of Mn together with the scrubbed Ca and Mg, may be recycled back to the extraction step where the Mn content is re-extracted back into the organic extractant phase. Thus, Mn is not lost in the process by including Mn ions in the aqueous scrubbing solution. The separated Ca and Mg ultimately exits the process in the Mn-lean aqueous raffinate. Stripping and Mn recovery

[0144]

[0132] The process may include a step of recovering Mn from the Ca-lean extractant phase. In some embodiments, Mn is extracted from the Ca-lean extractant phase into an acid stripping solution in one or more stripping stages, thereby producing an Mn-lean extractant phase and a Mn-rich strip solution.

[0145]

[0133] The acid stripping solution may be an aqueous solution comprising a suitable mineral acid such as H2SO4. Due to the very low pH, the acid re-protonates the organophosphoric or organophosphonic acid in the organic extractant phase, thus releasing the multivalent metal ions (high purity Mn) into the aqueous phase.

[0146]

[0134] Manganese may then be recovered from the aqueous Mn-rich strip solution by conventional methods. In some embodiments, a manganese salt such as manganese sulfate monohydrate is precipitated or crystallised from the Mn-rich strip solution, separated from the crystallisation product liquor, and dried. For example, a manganese salt may be crystallised from the Mn-rich strip liquor by concentration, e.g. by evaporation under vacuum at a suitable temperature to ensure the required degree of hydration of the product salt. High purity manganese salts, particularly with respect to Ca and Mg content, may be obtained because of the effective extraction and scrubbing steps as disclosed herein.

[0147]

[0135] Because of the efficient purification procedures conducted in the extraction and scrubbing stages, as disclosed herein, the Mn in the Mn-rich strip solution may already be highly pure. Specifically, the Mn-rich strip solution may have a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) sufficiently low that, following Mn recovery from the strip solution, the Ca:Mn ratio (wt / wt) and the Mg:Mn ratio (wt / wt) in the recovered Mn product are less than or equal to 3.1 x 10’4, or less than or equal to 1.5 x 10’4, for example less than or equal to 7.5 x 10’5, which ratios may be suitable to meet various industry specifications for high purity grades of manganese products, such as HPMSM. In some embodiments, the Mn-rich strip solution itself has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4, or less than or equal to 1 .5 x 10’4, for example less than or equal to 7.5 x 10’5.

[0148]

[0136] Due to its high Mn purity, the Mn-rich strip solution may be sent directly for Mn recovery, e.g. precipitation or crystallisation. There is no need to subject the Mn- rich strip solution to a solvent extraction purification step, e.g. to preferentially extract Ca. Such a step is typically undesirable due to (i) the complexities and costs of adding a second solvent extraction circuit to the process, (ii) the inefficiency of preferential Ca extraction from the Mn-rich strip solution due to the small affinity difference between Ca and Mn even under optimised conditions, and (iii) the inability to preferentially extract Mg from the Mn-rich strip solution. Accordingly, in some embodiments, the Mn-rich strip solution is not contacted with an organic extractant phase comprising an organophosphorus extractant and Mn ions. In some embodiments, the Mn-rich strip solution is not contacted with an organic extractant phase comprising an organophosphorus extractant. In some embodiments, the Mn-rich strip solution is not purified by contact with an organic extractant phase solvent extraction purification step, prior to Mn recovery from the Mn-rich strip solution.

[0149]

[0137] In some embodiments, a portion of the Mn-rich strip solution or the crystallisation product liquor remaining after Mn crystallisation is recycled to form the aqueous scrubbing solution comprising Mn ions, as used in the scrubbing step. In principle, a portion of the manganese salt product could also be redissolved to provide the aqueous scrubbing solution.

[0150]

[0138] Following the stripping step, the Mn-lean extractant phase, now depleted of multivalent metal ions, may be recycled to the extraction step to form all or part of the organic extractant phase. Optionally, the Mn-lean extractant phase is first neutralised (saponified) with a suitable base before return to extraction.

[0151]

[0139] A process 100 according to embodiments of the invention will now be described with reference to Figure 1. Aqueous solution 102, comprising a plurality of metal ions including manganese (Mn), calcium (Ca) and magnesium (Mg), typically with a sulfate anion matrix, is provided for purification of the Mn therein. Aqueous solution 102 may also include monovalent cations e.g. alkali metals (Na, K) and ammonium (NH4+). Aqueous solution 102 is contacted with organic extractant phase 104 in extraction unit 106. Organic extractant phase 104 comprises an organophosphoric acid such as D2EHPA, typically diluted in a hydrocarbon diluent. Mn is thus extracted from aqueous solution 102 into organic extractant phase 104. After the extraction, the two phases are separated to produce Mn-rich extractant phase 108 and Mn-lean aqueous raffinate 110.

[0140] The extraction in extraction unit 106 is done under conditions to favour selective extraction of Mn in preference to both Ca and Mg. Thus, Mn-rich extractant phase 108 comprises an amount of multivalent metal ions (alternatively, an amount of Mn ions only) corresponding to at least 50%, and preferably at least 75%, of the total loading capacity based on the amount of organophosphoric acid in Mn-rich extractant phase 108. Moreover, organic extractant phase 104 preferably has a temperature of above 30°C during the extracting, or above 50°C, such as a temperature in the range to 50 to 80°C.

[0152]

[0141] A desirably high amount of multivalent metal ions in the Mn-rich extractant phase may be achieved by controlling the ratio of aqueous solution 102 to organic extractant phase 104 (i.e. the A / O ratio) and / or the concentration of organophosphoric acid in organic extractant phase 104, and / or by controlling the pH of aqueous solution 102 in the extraction. Higher A / O ratios and / or lower organophosphoric acid concentration relative to the amount of Mn in aqueous solution (102) will tend to favour an increased loaded capacity in Mn-rich extractant phase 108. pH values in the range of 2.0 to 5.0, preferably 2.5 to 4.5, more preferably 3.0 to 4.0, most preferably 3.2 to 3.7, will also favour high loading capacity and selective Mn extraction.

[0153]

[0142] Due to the preferential extraction of Mn, the ratio of Mn to Ca in Mn-rich extractant phase 108 is greater than the ratio of Mn to Ca in aqueous solution 102, and preferably substantially greater such as more than double.

[0154]

[0143] To achieve a high overall extraction of Mn, aqueous solution 102 may be subjected to two or more extraction stages in extraction unit 106. In some embodiments, two or three extraction stages is sufficient to achieve a high Mn recovery, such as at least 95%, preferably at least 98%, extraction of Mn from aqueous solution 102. Advantageously, substantially smaller fractions of the Ca and Mg in aqueous solution 102 may be co-extracted into Mn-rich extractant phase 108.

[0155]

[0144] Mn-rich extractant phase 108 is then sent to scrubbing unit 1 12, where it is contacted with aqueous scrubbing solution 1 14 which comprises Mn ions, typically manganese sulfate, preferably in high purity. Ca and Mg ions are thus extracted from Mn-rich extractant phase 108 into aqueous scrubbing solution 1 14. After separation of the phases, Ca-lean extractant phase 1 16 and Ca-rich scrub solution 1 18 are thus produced. In some embodiments, the concentration of Mn ions in aqueous scrubbing solution 1 14 is sufficiently high to produce a zero or positive net transfer of Mn from aqueous scrubbing solution 1 14 to Mn-rich extractant phase 108.

[0156]

[0145] After the scrubbing step, Ca-lean extractant phase 1 16 preferably comprises an amount of multivalent metal ions (alternatively, an amount of Mn ions only) corresponding to at least 60%, or at least 70%, such as at least 85%, of the total loading capacity based on the amount of organophosphoric acid in this phase. This may be achieved by using a sufficiently high concentration of Mn ions in aqueous scrubbing solution 1 14, by controlling the ratio of aqueous scrubbing solution 1 14 to Mn-rich extractant phase 108 (i.e. the A / O ratio), by controlling the pH of aqueous scrubbing solution 1 14, and / or by controlling the temperature of Mn-rich extractant phase 108 during the scrubbing. Higher A / O ratios will tend to favour increased loading capacity in Ca-lean extractant phase 1 16. pH values in the range of 2.0 to 5.0, preferably 2.5 to 4.5, more preferably 3 to 4, most preferably 3.2 to 3.7, and temperatures of above 30°C, preferably in the range of 50 to 80°C, will also favour high loading capacity and efficient scrubbing.

[0157]

[0146] As a result of the Mn ions in aqueous scrubbing solution 1 14 and the resultant high loaded capacity of Ca-lean extractant phase 1 16, Ca and Mg are very efficiently scrubbed from Mn-rich extractant phase 108, whereas the Mn concentration of Ca-lean extractant phase 116 may be the same or even greater than in Mn-rich extractant phase 108.

[0158]

[0147] To achieve a high overall removal of Ca and Mg, Mn-rich extractant phase 108 may be subjected to two or more scrubbing stages. In some embodiments, two to six, such as four or five, scrubbing stages are sufficient to achieve adequate removal of Ca and Mg even for ultrahigh purity manganese specifications. Ca-lean extractant phase 1 16 after the final scrubbing stage may thus have a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) which are both less than or equal to 3.1 x 10’4, preferably less than or equal to 1 .5 x 10’4, more preferably less than or equal to 7.5 x 10’5.

[0159]

[0148] Ca-rich scrub solution 1 18, containing substantial concentrations of Mn together with the scrubbed Ca and Mg, is recycled back to extraction unit 106, where the Mn content is extracted back into organic extractant phase 104 and thus returns to scrubbing unit 1 12 in Mn-rich extractant phase 108. All Ca and Mg circulating between extraction unit 106 and scrubbing unit 1 12 ultimately exits the process in raffinate 1 10.

[0160]

[0149] Advantageously, the efficiency of the scrubbing step may be improved, or the necessary number of stages reduced, as a result of the selective extraction of Mn achieved in extraction unit 106. The scrubbing step should ideally be operated with the lowest practically possible amounts of aqueous scrubbing solution 1 14 (i.e. lower A / O ratio) so as to minimise the amount of Ca-rich scrub solution 118 recycled to extraction unit 106. However, the amount of aqueous scrubbing solution 1 14 used must be sufficient to deplete Ca to the required levels in the organic phase and to subsequently maintain the scrubbed Ca in solution in Ca-rich scrub solution 1 18. In some embodiments, the saturation solubility of Ca in Ca-rich scrub solution 1 18 is in the range of 0.5-0.8 g / L, depending on factors such as the temperature, pH and Mn concentration. At Ca concentrations close to or above the saturation solubility, there is a risk of gypsum precipitation and associated operation problems in the process. More selective extraction of Mn in extraction unit 106, as provided by the methods disclosed herein, reduces the amount of Ca to be scrubbed in scrubbing unit 1 12, thus providing a more efficient scrubbing process, for example via operation at lower A / O ratios without exceeding the solubility limitation of Ca.

[0161]

[0150] Ca-lean extractant phase 1 16 is then sent to stripping unit 120, where it is contacted with acid stripping solution 122, such as concentrated H2SO4. Mn is extracted from Ca-lean extractant phase 1 16 into acid stripping solution 122. After separating the organic and aqueous phases, Mn-lean extractant phase 124 and Mn- rich strip solution 126 are produced. Ca-lean extractant phase 1 16 may be subjected to two or more stripping stages to enhance the overall Mn recovery. In some embodiments, two or three stripping stages is sufficient to achieve near-quantitative recovery of Mn.

[0162]

[0151] Mn-rich strip solution 126 is then sent to crystallisation unit 128 where manganese salt 130, typically manganese sulfate monohydrate, is crystallised, separated from crystallisation product liquor 129, and recovered by conventional methods. Due to the highly efficient purification of Mn in extraction unit 106 and scrubbing unit 1 12, manganese salt 130 may meet specifications set for applications where high purity Mn is required, such as battery applications.

[0152] Aqueous scrubbing solution 114 may be provided within the process either by diluting and recycling a portion of Mn-rich strip solution 126 (not shown) or by recycling a portion of crystallisation product liquor 129.

[0163]

[0153] Mn-lean extractant phase 124, now substantially depleted of Ca and Mg (in scrubbing unit 1 12) and Mn (in stripping unit 120) is recycled to extraction unit 106 to form all or part of organic extractant phase 104. Preferably, Mn-lean extractant phase 124 is first neutralised (saponified) with base 132 in pre-neutralisation unit 134. Base 132 may suitably be NH4OH, NaOH, KOH, Na2CO3, NaHCOs, K2CO3 or KHCO3. Alternatively, Mn-lean extractant phase 124 can be sent directly to extraction unit 106, with base 132 added to the extraction mixture therein while controlling the pH to a target value.

[0164]

[0154] As described above, process 100 uses an organophosphoric acid such as D2EHPA as the organophosphorus extractant. Alternatively, the organophosphorus extractant could be an organophosphonic acid such as EHEHPA. It will be appreciated that the preferred pH values in the extraction and scrubbing steps may be higher in such embodiments due to the different pKa value of the organophosphonic acid.

[0165] Process for purifying manganese (Mn) present in an organic extractant phase

[0166]

[0155] In a second aspect the invention relates to a process for purifying manganese (Mn) present in an organic extractant phase. The process comprises providing a Mn-rich extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, and a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg). The Mn-rich extractant phase is contacted with an aqueous scrubbing solution comprising Mn ions such that Ca and Mg is extracted from the Mn- rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution. The scrubbing process is operated such that the Ca-lean extractant phase comprises an amount of multivalent metal ions corresponding to at least 60% (and preferably higher amounts such as at least 75%) of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

[0156] The process of the second aspect is similar to the scrubbing step of the process for manganese purification already described herein, and the skilled person will appreciate that the principles and preferred features of that process generally remain applicable. However, the Mn-rich extractant phase in the second aspect is not limited to a Mn-extract phase as produced by the previously described process. For example, the Mn-rich extractant phase to be purified may in principle comprise any amount of multivalent metal ions, including an amount of multivalent metal ions corresponding to less than 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. At least some advantages of the scrubbing process described herein may be obtained regardless of the initial metal loading in the Mn-rich extractant phase.

[0167]

[0157] The Mn-rich extractant phase may comprise an organophosphorus extractant and organic liquid diluent of a composition and in amounts as previously described herein. The Mn-rich extractant phase may comprise an amount of multivalent metal ions (alternatively, an amount of Mn ions only) corresponding to at least 10%, or at least 20%, or at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, such as at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase. It is not excluded that the Mn-rich extractant phase comprises divalent metal ions other than Mn, Ca and Mg, trivalent metal ions, and / or monovalent ions.

[0168]

[0158] After the scrubbing, the Ca-lean extractant phase may comprise an amount of multivalent metal ions corresponding to at least 70%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase. In some embodiments (for example when Mn is the most preferentially retained metal ion present in the Mn- rich extractant) the Ca-lean extractant phase comprises an amount of Mn ions corresponding to at least 60%, or at least 70%, such as at least 80%, for example at least 85%, of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase. By the same principles already disclosed herein, a high loading of multivalent metal ions in the organic phase during scrubbing preferences Mn retention in the organic extractant phase and partitioning of Ca and Mg to the aqueous scrubbing solution.

[0159] The presence of Mn ions in the aqueous scrubbing solution prior to at least one stage of scrubbing is important to prevent or acceptably limit losses of Mn from the Mn-rich extractant phase, and to maintain or produce a high Mn concentration in the organic phase so as to “crowd out” Ca and Mg, forcing these species to partition to the aqueous scrubbing solution. In embodiments where the Mn-rich extractant phase initially contains low amounts of multivalent metal ions, suitably high concentrations of Mn can nevertheless be produced in the Ca-lean extractant phase due to Mn transfer from the aqueous scrubbing solution. The presence of Ca and Mg is undesirable in the aqueous scrubbing solution, and in some embodiments the aqueous scrubbing solution is substantially free of Ca and Mg.

[0169]

[0160] In some embodiments, the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a zero or positive net transfer of Mn from the aqueous scrubbing solution to the Mn-rich extractant phase.

[0170]

[0161] The aqueous scrubbing solution should have a suitable pH and temperature, during the scrubbing, to achieve effective removal of Ca and Mg. Preferred ranges are generally as already disclosed herein in relation to the scrubbing step of the process for manganese purification. Similarly, the scrubbing step may be conducted using solvent extraction methods and apparatus as already disclosed herein, for example Ca and Mg extraction from the Mn-rich extractant phase into the aqueous scrubbing solution in two or more scrubbing stages.

[0171]

[0162] The process may also include steps of recovering Mn and ultimately an Mn salt from the Ca-lean extractant phase as already disclosed herein. Optionally, the aqueous scrubbing solution comprising Mn ions, for use in the scrubbing step, is produced by recycling a high purity Mn stream from within the Mn recovery process. Following the scrubbing step, the Mn-lean extractant phase, now depleted of multivalent metal ions, may be recycled to an extraction step to form all or part of an organic extractant phase used therein to produce the Mn-rich extractant phase.

[0172] EXAMPLES

[0173]

[0163] The present invention is described with reference to the following examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein. Example 1.

[0174]

[0164] An aqueous feed solution containing 32 g / L Mn (0.58 M Mn), 0.4 g / L Ca (0.01 M Ca) and 2 g / L Mg (0.082 M Mg), adding up to a total metal molar concentration of 0.672 M, was prepared by dissolving the respective metal sulphate salts (AR grade) in deionised (DI) water at room temperature. No pH adjustment was made prior to the experiments, leaving the natural pH at about 3.8.

[0175]

[0165] An organic extractant phase was prepared by diluting D2EHPA (95% purity, as purchased) with Escaid 1 10, a low-aromatic hydrocarbon fluid (predominantly C12- Cu) available from ExxonMobil, to prepare a 50% (v / v) D2EHPA solution (1.435 M D2EHPA).

[0176]

[0166] The aqueous feed solution was then contacted with the organic extractant phase at 1 :1 A / O ratio (A / O = aqueous to organic, v / v) to equilibrium extraction at pH values in the range of 0.5 - 5.0 and at various temperatures in the range of 10 - 80 °C. For each investigated temperature, an experiment was conducted in a 0.5 L hexagonal glass jar, mixing by an overhead stirrer (bottom vaned impellers) at 600 rpm. Solution pH was adjusted by adding 12.5% NH3 solution and measured by a pH probe (lonode electrode model IJ44C HT). A sample of the mixture was taken at each equilibrium pH value, and the pH value was recorded for constructing the pH isotherms curves. The organic and aqueous mixture sample was separated through a Whatman 1 PS phase separation paper. The organic phase was stripped at 40 °C with 1 M HCL All the aqueous phase samples and the organic strip liquor samples were analysed by inductively coupled plasma-optical emission spectrometry (ICP-OES).

[0177]

[0167] A 1 .435 M D2EHPA solution has 0.72 M loading capacity for divalent metal ions (i.e. each mole of Me2+extracted requires 2 mole of D2EHPA). Therefore, the experiments were conducted at 93.7% of the theoretical maximum loading capacity (= 0.672M 1 0.72 x 100), assuming all metal ions are extracted.

[0178]

[0168] As seen in Figure 2, the extraction efficiency of Mn consistently increases with both pH and temperature in the investigated ranges. By contrast, as seen in Figure 3, the extraction efficiency of Ca decreases in the pH range of 2.5 - 4, and decreases with increasing temperature. As seen in Figure 4, Mg extraction efficiency increases with both pH and temperature, but remains low (< c.a. 50%) below pH 4 for all temperatures.

[0179]

[0169] The resulting effect on the selectivity of Mn vs Ca extraction can be seen in Figure 5, which shows the Mn / Ca ratio (mass / mass) in the extractant as a function of pH and temperature, with comparison against the Mn / Ca ratio of 80 in the aqueous feed. At pH values above 2.5-3.5, and temperatures of 20°C and higher, preferably above 30°C, Mn is selectively extracted in preference to Ca in these experiments, with the best results obtained at about pH of about 3.5 and temperatures of about 40-80°C.

[0180]

[0170] The corresponding Mn / Mg ratio is seen in Figure 6, with comparison against the Mn / Mg ratio of 16 in the aqueous feed. Mn is preferentially extracted vs Mg in all experiments, but with the best results obtained in the pH range of about 2-3.5.

[0181]

[0171] Overall, the results suggest that pH values in the range of 3-4 and elevated temperatures (e.g. 40°C or higher) are preferred to extract Mn with reduced extraction of Ca and minimal extraction of Mg, and an extraction selectivity preference of Mn > Ca > Mg.

[0182]

[0172] Figure 7 shows the Mn / Ca ratio (mass / mass) in the extractant as a function of total loading capacity of the extractant, calculated according to equation (2). total loading capacity = (moles of Mn + Ca + Mg) / (0.5 x total moles of D2EHPA) x100 (2)

[0183]

[0173] In this experiment, the total loading capacity is dominated by the pH- dependent extraction of Mn, and is thus correlated with pH. Nevertheless, the results show that Mn is preferentially extracted vs Ca at total loading capacities greater than about 40-50%, with high loading capacities leading to improves selectivities in the range of about 50% to 80%.

[0184] Example 2.

[0185]

[0174] An aqueous feed solution containing 122 g / L Mn (2.22 M Mn), 0.41 g / L Ca and (0.01 M Ca) 2 g / L Mg (0.082 M Mg), adding up to a total metal molar concentration of 2.313 M, was prepared as described for Example 1 .

[0175] An organic extractant phase was prepared by diluting D2EHPA (95% purity, as purchased) with Escaid 1 10 to prepare a 70% (v / v) D2EHPA solution (2.0 M). The fresh organic was pre-neutralised with 25% NH4OH solution by mixing for 30 minutes at room temperature and an A / O ratio of 1 :8.3 to obtain about 90% loaded capacity. The two phases, after mixing, formed one phase which was used for the experiments without phase separation.

[0186]

[0176] The aqueous feed solution was then contacted with the pre-neutralised organic extractant phase at pH values in the range of 3.8 - 4.0 and 50°C at various A / O ratios in the range of 1 :10 to 1 :1 , to equilibrium extraction. The experiments were otherwise conducted as described for Example 1 .

[0187]

[0177] Figure 8, Figure 9 and Figure 10 show the Mn, Ca and Mg extraction distribution isotherms respectively, together with constructed McCabe-Thiele diagrams for an operating A / O ratio of 1 :2.5, as obtained from these experiments.

[0188]

[0178] According to the McCabe-Thiele diagram shown in Figure 8, about 100% Mn would be extracted in 2 to 3 theoretical extraction stages at a 1 :2.5 A / O operating ratio with co-extraction of about 50% Ca (Figure 9) and 32% Mg (Figure 10).

[0189]

[0179] Figure 1 1 shows the % metal extraction for Mn, Mg and Ca, and the Mn / Ca and Mn / Mg ratios (wt / wt) in the loaded extractant, as a function of the % loading relative to the theoretical total loading capacity of the extractant. At the extremes of the investigated A / O ranges, the amount of divalent metal ions extracted into the organic phase was 89% of theoretical capacity with an A / O ratio of 1 :2, and only 24% of theoretical capacity with an A / O ratio of 1 :10. It can be seen that the % extraction of Mn remained high (>75%) in all experiments, but the Mn / Ca and Mn / Mg ratios increased as the % loading of the extractant increased. Significant selectivity towards Mn extraction vs Ca selectivity was only obtained at a % loading greater than 50%, with very significant enhancements obtained at a % loading greater than 75%, as can be seen by comparing the Mn / Ca ratio against that in the aqueous feed.

[0190] Example 3.

[0191]

[0180] An aqueous feed solution containing 32 g / L Mn (0.58 M Mn), 0.225 g / L Ca (0.006 M Ca) and 1.95 g / L Mg (0.080 M Mg), adding up to a total metal molar concentration of 0.668 M, was prepared as described for Example 1 . The same organic extractant phase as prepared in Example 1 were used in this example.

[0192]

[0181] The aqueous feed solution was then contacted with the organic extractant phase (50% v / v D2EHPA solution, 1 .44 M) at pH values in the range of 3.8 - 4.0 and 50°C at various different A / O ratios, to equilibrium extraction. The experiments were otherwise conducted as described for Example 1 .

[0193]

[0182] Figure 12 shows the Mn / Ca ratios in the loaded extractant, with comparison against the Example 2 results, as a function of the concentration of metal ions in the extractant after equilibration. It can be seen that the selectivity for Mn increases as the metal loading approaches half the D2EHPA concentration (i.e. 1 M and 0.77 respectively). Figure 13 shows the Mn / Ca ratios in the loaded extractant, with comparison against the Example 2 results, as a function of the % loading relative to the theoretical total loading capacity of the extractant. Significant selectivity towards Mn extraction vs Ca selectivity was obtained in both cases at % loading greater than about 70%, as can be seen by comparing the Mn / Ca ratio against that in the aqueous feeds. The best results were obtained at about 90% loading capacity.

[0194] Example 4.

[0195]

[0183] An aqueous feed solution containing 32 g / L Mn (0.58 M Mn), 0.35 g / L Ca (0.009 M Ca) and 2 g / L Mg 0.082 M Mg), adding up to a total metal molar concentration of 0.673 M, was prepared as described for Example 1 . The same organic extractant phase as prepared in Example 1 were used in this example (50% v / v D2EHPA solution, 1 .44 M, but pre-neutralised as in Example 2).

[0196]

[0184] The aqueous feed solution was then contacted with the pre-neutralised organic extractant phase at a pH of 3.85, 50°C and A / O ratios of 1 :1 , to equilibrium extraction. The experiment was otherwise conducted as described for Example 1 . This resulted in extraction of 83.7% of the Mn, 31 .5% of the Mg and 59.8% of the Ca into the organic extractant phase, at a loaded capacity of 70.5% relative to the theoretical loading capacity.

[0197]

[0185] The loaded organic extractant phase was then contacted with scrub solutions containing deionised (DI) water solely (0 g / L Mn) or manganese sulfate at concentrations of 15 g / L Mn (0.27 M), 30 g / L Mn (0.54 M) and 45 g / L Mn (0.82 M), respectively, at 1 :1 A / O, 50 °C in the pH range of 3 - 3.6 which was adjusted by addition of H2SO4 solution or NH4OH solution, to equilibrium scrubbing. The experiments were otherwise conducted using the apparatus and procedure described in Example 1 .

[0198]

[0186] The scrubbing efficiencies for Mn, Ca and Mg are shown in Figure 14 (DI water scrubbing solution), Figure 15 (15 g / L Mn scrubbing solution), Figure 16 (30 g / L Mn scrubbing solution) and Figure 17 (45 g / L Mn scrubbing solution). Here, the scrubbing efficiencies refer to the % removal of the metal ion from the organic extractant phase into the scrubbing solution.

[0199]

[0187] With the scrub solution containing DI water solely (0 g / L Mn), the scrubbing efficiency of Ca was very low, varying from 25% at pH 3 to 10% at pH 3.6. The scrubbing efficiency of Mg was also low, from 80% to 45% in the same pH range. Simultaneously, significant losses of Mn were evident: from 25% to about 20% in the same pH range. The poor results can be attributed to the low % loading of the organic extractant phase after the scrubbing, relative to the theoretical total loading capacity of the extractant, also shown in Figure 14. The % loading was in the range of 50% to 57% in the investigated pH range.

[0200]

[0188] In comparison, the scrubbing efficiency of Ca was significantly improved from about 70% with 15 g / L Mn scrub solution to about 80 - 85% with 30 g / L Mn scrub solution, and further to about 90% with 45 g / L Mn scrub solution. The scrubbing efficiency of Mg also increased together with Mn concentration in the scrub solution, with >95 % removal with the 45 g / L Mn scrub solution. The increased Ca and Mg scrubbing efficiencies were consistent with the increase in the % loading of the organic extractant phase after the scrubbing, relative to the theoretical total loading capacity of the extractant loaded capacities. The % loading increased together with Mn concentration in the scrub solution due to an extraction of Mn from the scrub solutions into the organic phase (seen as negative scrubbing efficiencies in Figures 15-17). The loading of Mn also increased with pH, so that the best scrubbing results were obtained at pH 3.4 and 3.6 when using the 45 g / L Mn scrub solution, where the organic extractant phase has a % loading of nearly 90% after scrubbing.

[0189] The results demonstrate that scrubbing with water or dilute acid solely cannot efficiently or completely remove the co-extracted Ca and Mg from the organic extractant phase in a single stage, due to the considerable concomitant losses of Mn, which releases more sites available for loading of Ca and Mg.

[0201]

[0190] The results further demonstrate that the scrub solution should contain a sufficient concentration of Mn such that the total loading capacity of the organic extractant phase is as high as possible after the scrubbing step. This greatly enhances the selectivity of scrubbing and the resultant purity of Mn present in the organic phase after scrubbing.

[0202] Example 5.

[0203]

[0191] An aqueous feed solution containing 134.5 g / L Mn (2.45 M), 0.39 g / L Ca (0.010 M) and 2 g / L Mg (0.082 M), adding up to a total metal molar concentration of 2.54 M, was prepared as described for Example 1 . The same organic extractant phase as prepared in Example 2 were used in this example (70% v / v D2EHPA solution, 2.0 M, pre-neutralised to pH 3.67).

[0204]

[0192] The aqueous feed solution was then contacted with the pre-neutralised organic extractant phase at a pH of 3.6-3.7, 50°C and A / O ratio of 1 :2.2, to equilibrium extraction. The extraction was otherwise conducted as described for Example 1 . This resulted in extraction of 70.0% of the Mn, 16.4% of the Mg and 28.9% of the Ca into the organic extractant phase, at a loaded capacity of 78.7% relative to the theoretical loading capacity.

[0205]

[0193] The loaded organic extractant phase was then contacted with scrub solutions containing manganese sulfate at a concentration of 52.5 g / L Mn (0.96 M), at 1 :10 A / O, 50 °C, pH 3.4, adjusted by addition of H2SO4 solution or NH4OH solution, to equilibrium scrubbing, and then separated from the scrubbing solution. The scrubbing experiment was otherwise conducted using the apparatus and procedure described in Example 1 . The organic extractant phase was subjected to a series of 5 sequential scrubbing steps using this methodology. The results are shown in Table 1 . Table 1.

[0206] * Negative %Mn scrubbing efficiencies mean the %Mn loaded from the scrub solution into the organic.

[0207]

[0194] After three scrubbings, the mass ratios of Ca / Mn and Mg / Mg decreased to 2.6 x 10’4and 2.9 x 10’4, respectively, which were below the mass ratios of Ca / Mn < 3.1 x 10’4and Mg / Mn < 3.1 x 10’4(equivalent to <100 ppm Ca and <100 ppm Mg normalised to > 32% Mn) specified for high purity manganese sulfate monohydrate (HPMSM).

[0208]

[0195] After four scrubbings, the Ca / Mn and Mg / Mn decreased to 1 .5 x 10’4and 1 .4 x 10’4(equivalent to <50 ppm Ca and <50 ppm Mg normalised to > 32% Mn), respectively, which are the specified levels for ultra purity manganese sulphate monohydrate (UPMSM).

[0209]

[0196] After five scrubbings, the Ca / Mn and Mg / Mn decreased to 7.5 x 10’5and 4.7 x 10’5(equivalent to <25 ppm Ca and <25 ppm Mg normalised to > 32% Mn), respectively, which was the levels for even purer UPMSM.

[0210]

[0197] This example demonstrates that a solvent extraction process as disclosed herein can separate Ca and Mg by simple extraction and scrubbing steps in one circuit to meet the battery grade standards of HPMSM. The process can separate Mn from Ca and Mg for UPMSM at <50 ppm Ca and Mg, respectively, and even purer at <25 ppm Ca and Mg, if desired. Example 6.

[0211]

[0198] An aqueous feed solution containing 119 g / L Mn (2.18 M), 0.4 g / L Ca (0.010 M) and 2 g / L Mg (0.082 M), adding up to a total metal molar concentration of 2.28 M, was prepared as described for Example 1 . The same organic extractant phase as prepared in Example 2 were used in this example (70% v / v D2EHPA solution, 2.0 M, pre-neutralised to pH 3.87).

[0212]

[0199] The aqueous feed solution was then contacted with the pre-neutralised organic extractant phase at a pH of 3.8, 50°C and A / O ratios of 1 :2.4, to equilibrium extraction. The extraction was otherwise conducted as described for Example 1 . This resulted in extraction of 95.2% of the Mn, 42.2% of the Mg and 51 .0% of the Ca into the organic extractant phase, at a loaded capacity of 87.6% relative to the theoretical loading capacity.

[0213]

[0200] The loaded organic extractant phase was then contacted with scrub solutions containing manganese sulfate at a concentration of 69.8 g / L Mn (1 .27 M), at 1 :10 A / O, 50 °C, pH 3.2-3.3, adjusted by addition of H2SO4 solution or NH4OH solution, to equilibrium scrubbing, and then separated from the scrubbing solution. The scrubbing experiment was otherwise conducted using the apparatus and procedure described in Example 1 . The organic extractant phase was subjected to a series of 4 sequential scrubbing steps using this methodology. The results are shown in Table 2.

[0214] Table 2.

[0215] * Negative %Mn scrubbing efficiencies mean the %Mn loaded from the scrub solution into the organic.

[0201] After four scrubbings, the mass ratios of Ca / Mn and Mg / Mg decreased to 7.9 x 10’5(equivalent to <25 ppm Ca and <25 ppm Mg normalised to > 32% Mn), respectively, which were the levels for even purer UPMSM.

[0216]

[0202] This example again demonstrates the solvent extraction process as disclosed herein can separate both Ca and Mg by simple extraction and scrubbing steps in one circuit to meet the battery grade standards, and can separate Mn from Ca and Mg to the levels for UPMSM at <50 ppm Ca and Mg, respectively, and even purer at <25 ppm Ca and Mg, if desired.

[0217] Example 7.

[0218]

[0203] The scrubbed organic extractant phase obtained after sequential scrubbing in Example 5 was then stripped using 3M H2SO4 at 50°C, at various different A / O ratios in the range of 1 :10 to 1 :1 , to equilibrium stripping. The stripping experiment was conducted using the apparatus and procedure described in Example 1 , without pH adjustment.

[0219]

[0204] The results are shown in Table 3, and Figure 18 shows the Mn stripping distribution isotherm. The McCabe Thiele diagram predicts two theoretical stripping stages at an operating A / O of 1 :3.5 for about 210 g / L Mn (sulphate) solution suitable for crystallisation of HPMSM.

[0220] Table 3.

[0221] Example 8.

[0222]

[0205] An aqueous feed solution containing 34.8 g / L Mn (0.62 M Mn), 0.30 g / L Ca (0.007 M Ca) and 1.98 g / L Mg (0.081 M Mg), adding up to a total metal molar concentration of 0.71 M, was prepared by dissolving the respective metal sulphate salts (AR grade) in deionised (DI) water at room temperature. No pH adjustment was made prior to the experiments, leaving the natural pH at about 3.8.

[0223]

[0206] An organic extractant phase was prepared by diluting EHEHPA (lonquest 801 , 96.5% purity, as purchased) with Escaid 1 10 to prepare a 50% (v / v) EHEPA solution (1.50 M EHEHPA).

[0224]

[0207] The aqueous feed solution was then contacted with the organic extractant phase at 1 :1 A / O ratio (A / O = aqueous to organic, v / v) to equilibrium extraction at pH values in the range of 1 - 5.0 at 50°C. The experiment was conducted by the same procedure as Example 1 . A 1 .50 M EHEHPA solution has 0.75 M loading capacity for divalent metal ions. Therefore, the experiment was conducted at 95% of the theoretical maximum loading capacity (= 0.71 10.75 x 100), assuming all metal ions are extracted.

[0225]

[0208] As seen in Figure 19, the extraction efficiency of Mn consistently increases with pH, whereas the extraction efficiency of Ca plateaus in the pH range of 2.5 - 4 and the Mg extraction efficiency remains low (< c.a. 20%) below pH 4. The resulting effect on the selectivity of Mn extraction vs Ca and Mg can be seen in Figure 20 which shows the Mn / Ca and Mn / Mg ratios (mass / mass) in the extractant as a function of pH, with comparison against the corresponding ratios in the aqueous feed. At pH values above 2, Mn is selectively extracted in preference to Ca in these experiments, with the best results obtained at a pH of about 4.0.

[0226] Example 9.

[0227]

[0209] The experiment of Example 8 was repeated, but with an aqueous feed solution containing 32.9 g / L Mn (0.60 M Mn), 0.41 g / L Ca (0.010 M Ca) and 2.02 g / L Mg (0.083 M Mg), and with an organic extractant phase prepared by diluting D2EHPA and EHEHPA (1 :1 v / v) with Escaid 1 10 to prepare a 25% (v / v) D2EHPA + 25 % (v / v) EHEHPA solution (1.47 M total organophosphorus extractant). The experiment was conducted at 96% of the theoretical maximum loading capacity, assuming all metal ions are extracted.

[0228]

[0210] As seen in Figure 21 , the extraction efficiency of Mn consistently increases with pH, whereas the extraction efficiency of Ca decreases slowly in the pH range of 2.5 - 4.5 and the Mg extraction efficiency increases with pH but remains low (< c.a. 20%) below pH 4. The resulting effect on the selectivity of Mn extraction vs Ca and Mg can be seen in Figure 22 which shows the Mn / Ca and Mn / Mg ratios (mass / mass) in the extractant as a function of pH, with comparison against the corresponding ratios in the aqueous feed. At pH values above 2.5, Mn is selectively extracted in preference to Ca in these experiments, with the best results obtained at about pH of about 4.0.

[0229]

[0211] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

Claims

Claims1 . A process for manganese purification, the process comprising: providing an aqueous solution comprising a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); and extracting Mn from the aqueous solution into an organic extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, thereby producing a Mn-rich extractant phase and a Mn-lean aqueous raffinate, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 50% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase, and wherein the ratio of Mn to Ca in the Mn-rich extractant phase is greater than the ratio of Mn to Ca in the aqueous solution.

2. The process according to claim 1 , wherein the organophosphorus extractant is an organophosphoric acid.

3. The process according to claim 1 or claim 2, wherein the aqueous solution has a pH in the range of 2.5 to 4.5 during the extracting.

4. The process according to any one of claims 1 to 3, wherein the organic extractant phase has a temperature of above 30°C during the extracting.

5. The process according to any one of claims 1 to 4, wherein the organic extractant phase has a temperature of above 50°C during the extracting.

6. The process according to any one of claims 1 to 5, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 70% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

7. The process according to any one of claims 1 to 5, wherein the Mn-rich extractant phase comprises an amount of multivalent metal ions corresponding to at least 80% of the total loading capacity based on the amount of organophosphorus extractant in the Mn-rich extractant phase.

8. The process according to any one of claims 1 to 7, wherein the ratio of Mn to Ca in the Mn-rich extractant phase is at least double the ratio of Mn to Ca in the aqueous solution.

9. The process according to any one of claims 1 to 8, further comprising: contacting the Mn-rich extractant phase with an aqueous scrubbing solution comprising Mn ions; and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution.

10. The process according to claim 9, wherein the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase.11 .The process according to claim 9 or claim 10, wherein the Ca-lean extractant phase comprises an amount of Mn corresponding to at least 70% of the total loading capacity based on the amount of organophosphorus extractant in the Ca- lean extractant phase.

12. The process according to any one of claims 9 to 11 , wherein the Mn-rich extractant phase has a temperature of above 30°C when extracting Ca and Mg into the aqueous scrubbing solution.

13. The process according to any one of claims 9 to 12, wherein the aqueous scrubbing solution has a pH in the range of 2.5 to 4.5 when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution.

14. The process according to any one of claims 9 to 13, wherein the Ca-lean extractant phase has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4.

15. The process according to any one of claims 9 to 14, further comprising extracting Mn from the Ca-lean extractant phase into an acid stripping solution in one or more stripping stages, thereby producing an Mn-lean extractant phase and a Mn- rich strip solution.

16. The process according to claim 15, further comprising precipitating or crystallising a manganese salt from the Mn-rich strip solution.

17. A process for purifying manganese (Mn) present in an organic extractant phase, the process comprising: providing a Mn-rich extractant phase comprising an organophosphorus extractant selected from an organophosphoric acid, an organophosphonic acid and combinations thereof, and a plurality of metal ions comprising manganese (Mn), calcium (Ca) and magnesium (Mg); contacting the Mn-rich extractant phase with an aqueous scrubbing solution comprising Mn ions; and extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution, thereby producing a Ca-lean extractant phase and a Ca-rich scrub solution, wherein the Ca-lean extractant phase comprises an amount of multivalent metal ions corresponding to at least 60% of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

18. The process according to claim 17, wherein the organophosphorus extractant is an organophosphoric acid.

19. The process according to claim 17 or claim 18, wherein the aqueous scrubbing solution comprises Mn ions at a concentration sufficient to produce a concentration of Mn in the Ca-lean extractant phase of at least 90% of the concentration of Mn in the Mn-rich extractant phase.

20. The process according to any one of claims 17 to 19, wherein the Ca-lean extractant phase comprises an amount of Mn corresponding to at least 80% of the total loading capacity based on the amount of organophosphorus extractant in the Ca-lean extractant phase.

21. The process according to any one of claims 17 to 20, wherein the Mn-rich extractant phase has a temperature of above 30°C when extracting Ca and Mg into the aqueous scrubbing solution.

22. The process according to any one of claims 17 to 21 , wherein the aqueous scrubbing solution has a pH in the range of 2.5 to 4.5 when extracting Ca and Mg from the Mn-rich extractant phase into the aqueous scrubbing solution.

23. The process according to any one of claims 17 to 22, wherein the Ca-lean extractant phase has a Ca:Mn ratio (wt / wt) and a Mg:Mn ratio (wt / wt) of less than or equal to 3.1 x 10’4.

24. The process according to any one of claims 17 to 23, further comprising extracting Mn from the Ca-lean extractant phase into an acid stripping solution in one or more stripping stages, thereby producing an Mn-lean extractant phase and a Mn- rich strip solution, and precipitating or crystallising a manganese salt from the Mn- rich strip solution.

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