WO2020232505A1

WO2020232505A1 - Production of manganese sulphate

Info

Publication number: WO2020232505A1
Application number: PCT/AU2020/050499
Authority: WO
Inventors: Yatendra Sharma
Original assignee: Mn Energy Limited
Priority date: 2019-05-21
Filing date: 2020-05-21
Publication date: 2020-11-26

Abstract

A process (10) for the production of manganese sulphate, the process comprising the steps of: (i) Passing a manganese containing ore (12) to a reduction step (14); (ii) Passing a product of the reduction step to a wash (26) in dilute acid (24) whereby potassium is removed therefrom; (iii) Passing the product of step (ii) to a sulphuric acid leach step (30) whereby a manganese sulphate containing pregnant leach solution is produced; and (iv) Passing the pregnant leach solution of step (iii) to one or more impurity removal steps (36, 42, 48), whereby a purified manganese sulphate containing solution (58) is obtained.

Description

“Production of Manganese Sulphate”

Field of the Invention

[0001 ] The present invention relates to a process for the production of manganese sulphate. More particularly, the process of the present invention is intended in one advantageous form to allow the production of manganese sulphate from cryptomelane manganese ore.

[0002] In one highly preferred form, the process of the present invention facilitates the production of battery grade manganese sulphate monohydrate from

cryptomelane manganese ore.

[0003] In another form, the process of the present invention facilitates the production of electrolytic manganese dioxide from cryptomelane manganese ore.

Background Art

[0004] Traditionally, electrolytic manganese dioxide (EMD) is produced from manganese dioxide pyrolusite ore containing a maximum 1.0% K₂O. The traditional process route for the production of battery grade manganese sulphate monohydrate (hereinafter“BGMSMH”) and electrolytic manganese dioxide (hereinafter“EMD”) requires firstly the pyro-metallurgical reduction of a high manganese dioxide pyrolusite ore, typically with a manganese dioxide content of over 35% by weight, to produce a mono-oxide of manganese, MnO. The MnO is then leached in sulphuric acid to produce a liquor, or pregnant leach solution (PLS) containing MnSO₄. Impurities from this PLS are then removed from this liquor. Potassium (K) is removed by jarositing, iron (Fe) and aluminium (Al) are removed by goethiting and heavy metal impurities are removed by a sulphiding process. To achieve BGMSMH, this PLS is concentrated and crystallised. EMD is deposited on titanium anodes by way of an electrochemical process, for example electrowinning, and the deposited EMD is then scraped, neutralised, milled and dried. [0005] As noted above, BGMSMH and/or EMD are produced from manganese dioxide pyrolusite ore containing a maximum 1.0% K₂O. Cryptomelane

manganese ore contains up to 4% K₂O. This ore cannot be processed to prepare BGMSMH and/or electrolytic manganese dioxide using the conventional route as the potassium content is too high to remove economically by the traditional jarositing process. Potassium impurity in a pregnant leach solution (PLS) at >20 ppm is very problematic for BGMSMH production and for EMD deposition, and need to be removed to an acceptable level.

[0006] The process of the present invention has as one object thereof to overcome substantially one or more of the above mentioned problems associated with prior art processes, or to at least provide a useful alternative thereto.

[0007] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an

acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0008] Throughout the specification and claims, unless the context requires otherwise, the word“comprise” or variations such as“comprises” or“comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0009] The term battery grade manganese sulphate mono-hydrate is to be understood to refer to, unless the context requires or suggests otherwise, a material containing in excess of 31 % manganese by weight. Impurities present in battery grade manganese sulphate mono-hydrate are to be understood to individually not be present in amounts of more than about 50 ppm, and preferably individually not more than 20 ppm.

[0010] Percentage values referenced herein will be understood to be references to % by weight, unless the context requires or suggests otherwise. Disclosure of the Invention

[0011 ] In accordance with the present invention there is provided a process for the production of manganese sulphate, the process comprising the steps of: a. Passing a manganese containing ore to a reduction step; b. Passing a product of the reduction step to a wash in dilute acid whereby potassium is removed therefrom; c. Passing the product of step (ii) to a sulphuric acid leach step whereby a manganese sulphate containing pregnant leach solution is produced; d. Passing the pregnant leach solution of step (iii) to one or more impurity removal steps, whereby a purified manganese sulphate containing solution is obtained.

[0012] Preferably, the manganese containing ore is a cryptomelane ore. The cryptomelane ore preferably contains £ 4% potassium.

[0013] Still preferably, the reduction step (i) produces a reduced manganese product amenable to acid leaching.

[0014] In one form, the reduction step (i) is a calcination step. Preferably, the calcination step is an air calcination step.

[0015] The dilute acid of the dilute acid wash step (ii) is preferably less than or equal to about 2% acid. The wash step (ii) preferably utilises H₂SO₄ in a stoichiometric ratio with potassium present.

[0016] The dilute acid wash step (ii) is preferably conducted at about 70°C. The residence time of the dilute acid wash step (ii) is preferably between about 30 to 60 minutes.

[0017] The dilute acid wash step preferably removes at least: a. 70% of potassium present in the reduced manganese ore of step (i); or b. 80% of potassium present in the reduced manganese ore of step (i).

[0018] The leach step (iii) preferably utilises 25% H₂SO₄. Preferably, the H₂SO₄ is present in at least a stoichiometric ratio with manganese and other acid soluble impurities present. Still preferably, the H₂SO₄ is present in a stoichiometric excess of about 5 to 10% with manganese and other acid soluble impurities present.

[0019] The leach step (iii) still preferably operates at atmospheric or ambient pressure, and at a temperature of about 90°C.

[0020] Preferably, the impurity removal steps comprise one or more precipitation steps. The precipitation steps may preferably comprise one or more of a jarositing step, a goethiting step, and a sulphiding step, whereby a purified manganese sulphate solution is obtained.

[0021 ] In one form of the present invention, the precipitation steps comprise each of a jarositing step, a goethiting step, and a sulphiding step, whereby a purified manganese sulphate solution is obtained.

[0022] Preferably, the purified manganese sulphate solution is passed to a concentration step. In the concentration step the manganese sulphate solution is preferably concentrated to: a. near saturation point; or b. about 500 - 700 g/L.

[0023] In one form of the present invention, the concentrated manganese sulphate solution is passed to a crystallisation step whereby manganese sulphate mono- hydrate is produced. Preferably the manganese sulphate mono-hydrate produced is of battery grade. [0024] In a further form of the present invention, the concentrated manganese sulphate solution may be passed to an electrowinning step, whereby electrolytic manganese dioxide is deposited. Preferably, the pH of the solution passed to the electrowinning step is about pH 1.

[0025] Preferably, a spent liquor from the electrowinning step is recycled to the sulphuric acid leach step (iii).

Brief Description of the Drawings

[0026] The process of the present invention will now be described, by way of example only, with reference to two embodiments thereof and the accompanying drawings, in which:-

Figure 1 is a schematic flow-sheet depicting a process for the production of a manganese sulphate solution in accordance with the present invention, further showing a process whereby a battery grade manganese sulphate mono-hydrate is produced; and

Figure 2 is a schematic flow-sheet depicting a process for the production of electrolytic manganese dioxide from a manganese sulphate solution produced by way of the process of Figure 1.

Best Mode(s) for Carrying Out the Invention

[0027] The present invention provides a process for the production of a process for the production of manganese sulphate, the process comprising the steps of: a. Passing a manganese containing ore to a reduction step; b. Passing a product of the reduction step to a wash in dilute acid whereby potassium is removed therefrom; c. Passing the product of step (ii) to a sulphuric acid leach step whereby a manganese sulphate containing pregnant leach solution is produced; and d. Passing the pregnant leach solution of step (iii) to one or more impurity removal steps, whereby a purified manganese sulphate containing solution is obtained.

[0028] In a preferred form, the manganese containing ore is a cryptomelane ore. The cryptomelane ore contains £ 4% potassium, present as a potassium complex of other elements, for example as K₂O. Further, it is envisaged that the

manganese ore will contain between about 1 and 4% potassium.

[0029] The reduction step (i) produces a reduced manganese product amenable to acid leaching. In one form, the reduction step (i) is a calcination step for example an air calcination step. The dilute acid of the dilute acid wash step (ii) is less than or equal to about 2% acid. The wash step (ii) utilises H₂SO₄ in a stoichiometric ratio with potassium present.

[0030] The dilute acid wash step (ii) is conducted at about 70°C. The residence time of the dilute acid wash step (ii) is between about 30 to 60 minutes. The dilute acid wash step removes at least 70%, for example at least 80%, of potassium present in the reduced manganese ore of step (i).

[0031 ] The leach step (iii) utilises 25% H₂SO₄. The H₂SO₄ is present in at least a stoichiometric ratio with manganese and other acid soluble impurities present.

For example, the H₂SO₄ is present in a stoichiometric excess of about 5 to 10% with manganese and other acid soluble impurities present. The leach step (iii) operates at atmospheric or ambient pressure, and at a temperature of about 90°C.

[0032] The impurity removal steps comprise one or more precipitation steps. For example, the precipitation steps comprise one or more of a jarositing step, a goethiting step, and a sulphiding step, whereby a purified manganese sulphate solution is obtained.

[0033] In one form of the present invention, the precipitation steps comprise each of a jarositing step, a goethiting step, and a sulphiding step, whereby a purified manganese sulphate solution is obtained. [0034] The purified manganese sulphate solution is passed to a concentration step. In the concentration step the manganese sulphate solution is concentrated to: a. near saturation point; or b. about 500 - 700 g/L.

[0035] In one form of the present invention, the concentrated manganese sulphate solution is passed to a crystallisation step whereby manganese sulphate mono- hydrate is produced. The manganese sulphate mono-hydrate produced is of battery grade.

[0036] In a further form of the present invention, the concentrated manganese sulphate solution is passed to an electrowinning step, whereby electrolytic manganese dioxide is deposited. The pH of the solution passed to the

electrowinning step is about pH 1. A spent liquor from the electrowinning step is recycled to the sulphuric acid leach step (iii).

[0037] In Figure 1 there is shown a process 10 for the production of manganese sulphate in accordance with one preferred embodiment of the present invention.

In the specific embodiment of Figure 1 the process is employed in the production of a BGMSMH.

[0038] A Mn Cryptomelane ore 12, containing between 1 to 4% potassium, is passed to a calcination or reduction step 14, conducted for example in a reduction furnace or kiln 16 which in one form may utilise natural gas or coal as the reductant. The ore and reductant are heated at about 950°C in the reduction furnace 16 for a nominal residence time of about two hours (at temperature) to reduce the Mn^lV+ and Mn^lll+ to Mn^ll+. The reduction of cryptomelane Mn ore to MnO improves the amenability of the cryptomelane Mn ore to leaching in sulphuric acid.

[0039] The converted product of the reduction furnace 16 is passed to a calcine cooler 18. Off-gases 20 from the reduction furnace 16 are cleaned in an electrostatic precipitator (not shown). Recovered solids from the off-gases are conveyed to a cooler (not shown).

[0040] The cooled product from the calcine cooler 18 is then milled in a closed- circuit wet grinding mill 22 to reduce the material to Pso 212 mm and the mill product is then pneumatically conveyed to a storage silo (not shown). A fine size range is preferred to ensure high Mn recoveries in the subsequent process steps.

[0041 ] The reactions taking place during calcination, when conducted using natural gas or coal as the reductant, are as follows:

[0042] At the same time the reduction of Fe contained in the ore occurs as follows:

[0043] A dilute acid wash using 2% H₂SO₄ is carried out on the reduced

cryptomelane Mn ore as described below to remove a large proportion of any potassium and sodium present.

[0044] The cooled calcined product is treated, at atmospheric pressure, with a dilute solution (2% strength) of H₂SO₄ acid 24 at 90°C for about 30 to 60 minutes in a reaction vessel 26 to remove a proportion of the potassium present from the ore. The dilute H₂SO₄ is provided in a stoichiometric ratio of K in the ore. This process removes at least 70%, for example at least 80%, of K present in the calcined cryptomelane Mn ore. [0045] The calcination step 14 of cryptomelane Mn ore appears to have fixed K as a potassium manganate (foMnCU) and potassium manganite (hQMnCU). Where HCI is utilised as the dilute acid, using a 1 % HCI solution, these compounds are found to decompose in HCI acid at temperature (90°C). The reactions are expected to be as following:

[0046] As KCI is soluble in water and rest of the calcined cryptomelane Mn ore is not, this provides partial separation of K.

[0047] The product from the dilute acid wash is leached with sulphuric acid 28 at a strength of about 25% in a leach step 30. The sulphuric acid is provided in at least a stoichiometric ratio relative to Mn and other acid soluble impurities in the ore.

For example, the sulphuric acid is provided in a 5 to 10% excess to the

stoichiometric ratio relative to Mn and other acid soluble impurities in the ore.

[0048] The leach step 30 is conducted in leach tanks 32 operating at ambient pressure and a temperature of about 90°C (±5°C) with a nominal tank residence time of about 2 hours.

[0049] The reactions taking place during sulfuric acid leach, where the prior reduction step utilises either natural gas or coal as described above, are understood to be as follows:

[0050] The Mn sulphate liquor and residue slurry exiting the leach tanks 32 are pumped to a pressure filtration unit for solid-liquid separation 34. This is followed by a jarositing step 36, in which ferric sulphate, if necessary, is added to the PLS in jarositing tanks 38 for remaining K impurity removal. The addition of ferric sulphate is understood to be necessary only if levels of iron in the PLS are considered low, as a K:Fe molar ratio of at least 1 :12 is desired for the jarositing step 36. The preferable K:Fe ratio is 1 :16 for the jarositing step 36. It is believed that potassium ions form an insoluble complex with iron.

[0051 ] The product of the jarositing step 30 is passed to a filter 40 from which the jarositing precipitates are separated from the PLS. The PLS is then passed to a second precipitation or goethiting step 42, in which hydrated lime is added in a vessel 44, to remove at least Fe and Al.

[0052] The second precipitation stage, the goethiting step 42, removes Al and Fe as noted above. This is achieved by increasing the pH of the manganese sulphate liquor to in the range of 5.5 to 7.0, for example about 6.5, by adding hydrated lime slurry. The following reactions are understood to take place:

[0053] A third precipitation stage, for example a sulphiding step 48, receives clear PLS from a solid liquid separation step, for example a filter 46, after the goethiting step 42. The sulphiding step 48 removes metal impurities such as, inter alia, Ni, Co, Cu, and Zn by sulphiding the manganese sulphate liquor after the goethiting step 42. The manganese sulphate liquor is treated with a sulphide such as BaS, NH4S or H2S to precipitate these metal impurities as sulphides.

[0054] A resulting liquor 54 is then solid liquid separated, for example by way of a filter 50, the pH of a filtrate 52 being adjusted to pH 3.5, and then passed through high vacuum low temperature multiple effect concentrators 54, in which the PLS is concentrated to near saturation point of manganese sulphate. This assists in precipitating dissolved Ca in the PLS due to the solubility factor. Once the saturation point of manganese sulphate in the PLS is reached, it is cooled and filtered 56 to produce a purified liquor 58. [0055] The purified liquor 58 is crystallised 60 using standard evaporation crystallisation technology, thereby providing a BGMSMH product 62.

[0056] The impurity removal circuit, incorporating the jarositing, the goethiting, and the sulphiding steps, is designed to remove remaining potassium, sodium, iron, aluminium, calcium and the like impurities from the manganese sulphate solution, the PLS, and provide a clear, battery grade manganese sulphate liquor for either BGMSMH or EMD electrowinning.

[0057] The purified liquor 58 may also be passed to an EMD electro-deposition process 64 to deposit EMD on titanium anodes, as shown in Figure 2.

[0058] The EMD deposition process 64 from the purified manganese sulphate liquor 58 takes place in an electrowinning step 66 on titanium anodes (using copper cathodes) in cell houses. The manganese sulphate liquor 58 containing about 500 to 700 g/L manganese, is pumped to an electrochemical cell house with a sufficient amount of sulphuric acid to maintain pH at about 1. The electro deposition of EMD takes place at about 95°C with current density of about 60 Amp/m².

[0059] The following reaction is understood to take place at the anode:

[0060] The EMD deposited on titanium anodes is scrapped off the anodes in a scraping step 68. The EMD is neutralised using caustic soda/ soda ash solution 82 in a first neutralisation step 70, then wet ball milled 72, then passed to a second neutralisation step 74, and again wet ball milled 76, to the desired customer specifications, dried 78 and packaged 80.

[0061 ] A spent liquor from the electrowinning step 66 is passed to a spent liquor tank 84 before being fed back to the leach step 32, either directly or via the wet grinding mill 22. [0062] The processes for the production of BGMSMH 62 and electrolytic manganese dioxide 64 of the present invention may be better understood with reference to the following non-limiting example.

Example

[0063] A cryptomelane manganese ore feed has a composition set out in Table 1 below:

Table 1

STEP 1 : PYROMETALLURGY

Reduction of Cryptomelane Mn Ore

Experimental

[0064] Prepare a sample of the provided particle size <(-1 mm) and mix with coal or natural gas to a stoichiometric ratio at 1 :1 .3, ore to carbon. [0065] Run this sample at 950°C temperature and residence time of 2 hours in a furnace/ kiln to calcine the ore.

STEP 2: HYDROMETALLURGY

Milling of Reduced Cryptomelane Mn Ore

Experimental

[0066] Wet ball milling of the sample after reduction particle size to P₈₀ 212mm.

Dilute Acid Wash of the Milled Calcined Ore

Experimental

[0067] The calcined cryptomelane Mn ore and dilute acid in stoichiometric ratio to K present in the ore is charged into a vessel equipped with a stirrer. The process was carried out at a temperature of 900°C under agitation for half an hour.

Thereafter the treated ore was separated by filtering and washed with Dl water, whereby there was obtained an ore containing a decreased amount of potassium to ³70% based on the dry ore.

Leaching of the Calcined and Water Leached Mn Ore and Impurity Removals

Experimental

[0068] Leach each sample separately with spent sulphuric acid at 90°C (±5°C) for a residence time of 2 hour.

[0069] After leaching, pressure filtration was used to remove solids. The PLS is a clear solution.

[0070] To the filtrate (PLS) add H₂O₂ to oxidize any Fe II into Fe III and carry out jarositing step at 90°C (±5°C) for an hour. [0071 ] Filter the PLS to remove double salt of K-Fe complex formed as a result of jarositing.

[0072] To the PLS filtrate of jarositing, add hydrated lime to increase the pH to 6.5 for the goethiting step to remove Fe and Al from the PLS. Stir the PLS with solids to provide a slurry. Heat the slurry to 90°C (±5°C) for two hours. Remove the solids formed during goethiting by filtration.

[0073] Clear PLS after goethiting is treated with a sulphide such as BaS or NH4S or H₂S to remove other metal impurities, including Co, Cu, Ni, and Zn. A stoichiometric ratio of the amount of a sulphide to these metal impurities is required to precipitate heavy metal impurities from the assay results of the PLS as above.

[0074] Heat the PLS at 90°C (±5°C). Add stoichiometrically calculated sulphide to the PLS. Continue to stir and heat at 90°C (±5°C) for an hour. Cool the PLS and filter to remove sulphides.

[0075] Store the PLS for electrometallurgy treatment if desired. Expected Mn²⁺ concentration is 80g/L if to be progressed to EMD production.

STEP 3 REMOVAL OF DISSOLVED CALCIUM FROM PLS

Experimental

[0076] Adjust the pH of PLS after sulphiding step to 3.5 by H₂SO₄ addition.

Concentrate this PLS to near saturation point of manganese sulphate using high vacuum low temperature multiple effect concentrator technology. After near saturation of manganese sulphate is obtained, cool the PLS and filter to remove precipitated Ca, largely as calcium sulphate. STEP 4 CRYSTALLISATION OF MANGANESE SULPHATE LIQUOR TO PRODUCE BGMSMH

Experimental

[0077] Crystallise the purified MnSO₄ liquor from Step 3 using evaporative crystallisation technology.

STEP 5 ELECTROMETALLURGY FOR EMD PRODUCTION

(i) Adjust Mn²⁺ concentration of PLS to approximately 65 g/L (±5) Mn.

(ii) Add 45 g/L sulphuric acid 98% to the above.

(iii) Heat the above solution to 90°C (±5°C). Referred to here as electrolyte.

(iv) Subject the above electrolyte for electrodeposition of MnO₂ on Titanium anodes and Cu cathodes for a period of 10 to 14 days (subject to the laboratory condition of the lab). Keep temperature of cell house at 90°C (±5°C), current density at 60 Amp/m², and average voltage at 3.2 to 3.6V.

(v) It is made sure that the concentration of Mn²⁺ in the electrolyte in the cell house does not fall below 45 g/L.

(vi) After the completion of the deposition cycle, the Ti electrode are removed and washed with deionised water.

(vii) Scrape the EMD from the Ti electrodes.

(viii) Wet mill first to D₅₀ 35 mm and neutralise using 10% caustic

soda/soda ash solution.

(ix) Wash 3 times with 15% w/w water of EMD slurry to clear slurry with any excess caustic soda/ soda ash, and/ or sodium sulphate.

(x) Wet mill EMD now to D₅₀ 2mm. (xi) Again neutralise wet slurry of EMD by caustic soda 10% solution. Expected pH is 6.5.

(xii) Wash 3 times with 15% w/w water of EMD slurry to clear slurry with any excess caustic soda and/ or sodium sulphate.

(xiii) Dry and weigh the EMD powder.

(xiv) Determine electrochemical activity of EMD powder for alkaline

batteries.

[0078] It is envisaged that the reduction step (i) is preferably provided as a calcination step, and that the calcination step is preferably an air calcination step. It is understood that the reactions described herein as occurring during calcination are those relevant for calcination using natural gas or coal and that the reactions occurring should air calcination be utilised will differ therefrom.

[0079] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

1. A process for the production of manganese sulphate, the process comprising the steps of: a. Passing a manganese containing ore to a reduction step; b. Passing a product of the reduction step to a wash in dilute acid whereby potassium is removed therefrom; c. Passing the product of step (ii) to a sulphuric acid leach step whereby a manganese sulphate containing pregnant leach solution is produced; and d. Passing the pregnant leach solution of step (iii) to one or more impurity removal steps, whereby a purified manganese sulphate containing solution is obtained.

2. The process of claim 1 , wherein the manganese containing ore is a

cryptomelane ore.

3. The process of claim 2, wherein the cryptomelane ore contains: a. £ 4% potassium; or b. between 1 and 4% potassium.

4. The process of any one of claims 1 to 3, wherein the reduction step (i)

produces a reduced manganese product amenable to acid leaching.

5. The process of any one of the preceding claims, wherein the reduction step (i) is: a. a calcination step; or b. an air calcination step.

6. The process of any one of the preceding claims, wherein the dilute acid of the dilute acid wash step (ii) is less than or equal to about 2% acid.

7. The process of any one of the preceding claims, wherein the dilute acid of the wash step is dilute H₂SO₄

8. The process of claim 7, wherein the dilute H₂SO₄ is provided in a

stoichiometric ratio with any potassium present.

9. The process of any one of the preceding claims, wherein the dilute acid wash step (ii) is conducted at about 70°C.

10. The process of any one of the preceding claims, wherein the residence time of the dilute acid wash step (ii) is between about 30 to 60 minutes.

1 1.The process of any one of the preceding claims, wherein the dilute acid wash step removes: a. at least 70% of any potassium present in the reduced manganese ore of step (i); or b. at least 80% of any potassium present in the reduced manganese ore of step (i).

12. The process of any one of the preceding claims, wherein the leach step (iii) utilises 25% H₂SO₄.

13. The process of any one of the preceding claims, wherein the H₂SO₄ of the leach step (iii) is present in at least a stoichiometric ratio with manganese and other acid soluble impurities present.

14. The process of claim 13, wherein the H₂SO₄ is present in a stoichiometric excess of about 5 to 10% with manganese and other acid soluble impurities present.

15. The process of any one of the preceding claims, wherein the leach step (iii) operates at atmospheric or ambient pressure, and at a temperature of about 90°C.

16. The process of any one of the preceding claims, wherein the impurity removal step (iv) comprises one or more precipitation steps.

17. The process of claim 16, wherein the one or more precipitation steps

comprise: a. one or more of a jarositing step, a goethiting step, and a sulphiding step, whereby a purified manganese sulphate solution is obtained; or b. each of a jarositing step, a goethiting step, and a sulphiding step,

whereby a purified manganese sulphate solution is obtained.

18. The process of any one of the preceding claims, wherein the purified

manganese sulphate solution is passed to a concentration step, in which the manganese sulphate solution is concentrated to: a. near saturation point; or b. about 500 - 700 g/L.

19. The process of any one of the preceding claims, wherein the concentrated manganese sulphate solution is passed to a crystallisation step whereby: a. manganese sulphate mono-hydrate is produced; b. battery grade manganese sulphate mono-hydrate is produced.

20. The process of claim 18 or 19, wherein the concentrated manganese sulphate solution is passed to an electrowinning step, whereby electrolytic manganese dioxide is deposited.

21.The process of claim 20, wherein the pH of the solution passed to the electrowinning step is about pH 1 .

22. The process of any one of claims 18 to 21 , wherein a spent liquor from the electrowinning step is recycled to the sulphuric acid leach step (iii).

23. A process for the production of electrolytic manganese dioxide, wherein a purified manganese sulphate containing solution is obtained by way of the process of any one of claims 1 to 17, and wherein the concentrated manganese sulphate solution is passed to an electrowinning step, whereby electrolytic manganese dioxide is deposited.

24. The process of claim 23, wherein the pH of the solution passed to the

electrowinning step is about pH 1.

25. The process of claim 23 or 24, wherein a spent liquor from the electrowinning step is recycled to the sulphuric acid leach step (iii) of the process for the production of a purified manganese sulphate containing solution.