Claims:We Claim:
1. A method for processing manganese ore comprising:
leaching a slurry comprising manganese ore and recycled leach liquor with sulphur dioxide gas in a reactor to obtain a leach solution;

subjecting the leach solution to solid liquid separation resulting in wash liquor and leach liquor;

recycling a portion of the leach liquor; and

purifying remaining portion of the leach liquor to remove manganese dithionate, iron, aluminium, heavy metal, impurities, or any combination thereof, and extracting manganese,

wherein iron concentration and manganese dithionate concentration during the method is maintained at a level below 1 g/L, and wherein the recycled leach liquor comprises manganese dithionate and manganese sulphate.

2. The method as claimed in claim 1, wherein the slurry is prepared by a process comprising:
a) crushing the manganese ore and preparing slurry with process water and the recycled leach liquor of pulp density of at least about 10% w/v; or
b) crushing the manganese ore, pulverizing the crushed manganese ore with the recycled leach liquor of pulp density of at least about 10% w/v to obtain a slurry mixture, and gravity separation of the slurry particles of the mixture based on desired particle size.

3. The method as claimed in claim 1, wherein purifying the remaining portion of leach liquor comprises:
adding an oxide additive, acid additive, or a combination thereof to the remaining leach liquor to maintain manganese dithionate levels below 0.1 g/L;
removing iron by adding hydrated lime slurry and increasing pH of the leach liquor to obtain pregnant leach solution (PLS);
removing heavy metals from the PLS by precipitating the heavy metals by sulphidation; and
extracting manganese as manganese salt.

4. The method as claimed in any of the preceding claims, wherein the portion of leach liquor is recycled to slurry preparation process as defined in claim 2.

5. The method as claimed in any of the preceding claims, wherein the portion of leach liquor recycled ranges from about 20% to 30%.

6. The method as claimed in any of the preceding claims, wherein the recycled leach liquor comprises manganese dithionate at a concentration greater than 5 g/L, manganese (Mn) at a concentration greater than 70 g/L, and iron (Fe) at a concentration less than 5 g/L.

7. The method as claimed in any of the preceding claims, wherein the recycled leach liquor has a pH of about 1.8 to 7.0.

8. The method as claimed in any of the preceding claims, wherein the oxide additive is selected from manganese containing material, manganese ore, roasted manganese ore, or any combination thereof; and the acid additive is selected from sulfuric acid, peroxydisulfuric acid, peroxymonosulfuric acid, or any combination thereof.

9. The method as claimed in any of the preceding claims, wherein the oxide additive, acid additive, or a combination thereof is added to the remaining leach liquor and the resulting solution is stabilized for about 10 minutes to 6 hours for decomposition of manganese dithionate and lowering the manganese dithionate concentration to below 0.1 g/L.

10. The method as claimed in claim 1, wherein the sulphur dioxide gas is passed through sparger for dispersion and mixing in the reactor.

11. The method as claimed in claim 1, wherein the leaching is carried out at a pH below 4.0, preferably below 2.0.

12. The method as claimed in claim 1, wherein the leaching is carried out in reactors configured in series mode.

13. The method as claimed in claim 1, wherein the solid liquid separation comprises filtration and involves washing of manganese values from cake formed during reductive leaching of the slurry.

14. The method as claimed in claim 1, wherein the wash liquor is recycled for next batch of leaching.

15. The method as claimed in claim 1 or claim 3, wherein the remaining portion of leach liquor is purified for removing dissolved iron and heavy metallic ions by precipitation.

16. The method as claimed in claim 15, wherein the removal of dissolved iron is carried out by oxidation of Fe(II) to Fe(III) by addition of oxidizing agent followed by its precipitation by addition of hydrated lime slurry.

17. The method as claimed in claim 16, wherein the oxidizing agent is selected from a group comprising hydrogen peroxide, sodium perchlorate, oxygen gas, manganous oxide, potassium permanganate and combinations thereof.

18. The method as claimed in claim 16, wherein the addition of hydrated lime slurry precipitates Fe as its hydroxide along with the precipitation of aluminium (Al).

19. The method as claimed in claim 1 or claim 3, wherein the heavy metal is selected from a group comprising zinc (Zn), copper (Cu), nickel (Ni), cobalt (Co), arsenic (As), antimony (Sb) and combinations thereof.

20. The method as claimed in claim 3, wherein the sulphidation is carried out using sodium hydrogen sulphide, sodium sulphide, or a combination thereof.

21. The method as claimed in claim 3, wherein the pH is increased between 4.5 to 6.0 to obtain the PLS, preferably to about 6.0.

22. The method as claimed in any of the preceding claims, wherein the manganese is extracted as manganese sulphate solution or manganese sulphate crystals.

23. The method as claimed in claim 1, wherein the iron concentration is maintained at a level below 1 g/L by providing and controlling oxidation reduction potential (ORP) below 550 mV and by providing an excess or residual amount of manganese ions in the slurry.

24. The method as claimed in any of the preceding claims, wherein the manganese ore is selected from a group comprising high iron containing low grade manganese ore, high iron containing medium grade manganese ore, high iron containing high grade manganese ore, partially reduced manganese ore, and combinations thereof.

25. A method of controlling manganese dithionate concentration in leach liquor obtained by leaching of a manganese ore, said method comprising:
a) recycling a portion of the leach liquor to the leaching process, wherein said recycled leach liquor is employed as a dithionate based reductant in the leaching process; and
b) purifying remaining portion of the leach liquor by adding an oxide additive, acid additive or a combination thereof,
wherein the manganese dithionate in the method is controlled at a concentration below 1 g/L.

26. Manganese obtained by the method as claimed in claim 1.
, Description:TECHNICAL FIELD
The present disclosure relates to the field of hydrometallurgy. The disclosure relates to a method for processing manganese ore, and particularly on controlling manganese dithionate concentrations during leaching of the manganese ore.

BACKGROUND OF THE DISCLOSURE
During the process of leaching manganese (Mn) bearing resources using sulphur dioxide or sulphuric acid as reductant, manganese sulphate, manganese dithionate and iron sulphate (in case of high iron bearing manganese resources) are generated forming a part of the leach solution. Reaction for said leaching process can be described as:
MnO2 + SO2 = MnSO4
MnO2 + 2SO2 = MnS2O6

Due to presence of manganese dithionate (MnS2O6) in the leach solution, efficiency of subsequent Mn extraction or electrowinning decreases and hence there is requirement to decompose/lower the dithionate from the manganese sulphate solution (leach liquor solution) before it is sent for Mn electrowinning cell.

Several methods exist for recovering highly pure manganese sulphate from the leach liquor solution comprising manganese sulphate (MnSO4), manganese dithionate (MnS2O6) and other metals/impurities. However, the existing methods of recovering manganese sulphate in the leach liquor generated from leaching of low grade manganese ores require in-situ decomposition of manganese dithionate (MnS2O6). The primary drawbacks of existing methods are:
1. Decomposition of manganese dithionate in presence of manganese sulphate under conditions which favour undesirable manganous sulphate precipitation i.e. high temperature and high pressure required to move the reaction forward. Further, there is in-situ generation of sulfuric acid during such reaction/process of dithionate decomposition which increases corrosion of the reactor system.
2. To destroy/decompose manganese dithionate, expensive crystallization techniques are employed which require energy in the form of electricity and steam. Also, the method generates toxic SO2.
3. pH of about 1.0 to 1.5 is usually employed to control the formation of manganese dithionate during low grade manganese ore processing. However, said approach fails to control undesirable impurities generated during leaching from ore bodies because of their dissolution behavior and higher kinetics due to rise in temperature.

Overall, manganese extraction/manganese sulphate production via. leaching of low grade manganese ore using sulphur dioxide (reductant) leads to generation of manganese dithionate, wherein control or decomposition of said dithionate in-situ has not been explored without addition of additives and/or employing unfavourable process conditions.

Thus, there is a need in the art to develop an alternate, simple, more efficient and cost-effective method for selective leaching of manganese from manganese ore overcoming the drawbacks/disadvantages discussed above. The present disclosure attempts to address said need.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to a method for processing manganese ore comprising:
leaching a slurry comprising manganese ore and recycled leach liquor with sulphur dioxide gas in a reactor to obtain a leach solution;
subjecting the leach solution to solid liquid separation resulting in wash liquor and leach liquor;
recycling a portion of the leach liquor; and
purifying remaining portion of the leach liquor to remove dithionate, iron, aluminium, heavy metal, impurities, or any combination thereof, and extracting manganese,
wherein iron concentration and dithionate concentration during the method is maintained at a level below 1 g/L, and wherein the recycled leach liquor comprises manganese dithionate and manganese sulphate.

The present disclosure also relates to a method of controlling manganese dithionate concentration in leach liquor obtained by leaching of a manganese ore, said method comprising:
a) recycling a portion of the leach liquor to the leaching process, wherein said recycled leach liquor is employed as a dithionate based reductant in the leaching process; and
b) purifying remaining portion of the leach liquor by adding an oxide additive, acid additive or a combination thereof,
wherein the manganese dithionate in the method is controlled at a concentration below 1 g/L.

The present disclosure further provides manganese obtained by the method of manganese ore processing as described above.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 illustrates an exemplary method for manganese ore processing and control of manganese dithionate according to the present disclosure.

Figure 2 illustrates another exemplary embodiment of the method of processing manganese ore and control of manganese dithionate according to the present disclosure.

Figure 3 shows the effect of recycle ratio (recycled leach liquor) on manganese recovery and free SO2 after leaching [SO2 flow rate = 0.5 litres per minute (lpm)].

Figure 4 (a, b and c) shows the multiphase configuration of reactors for extraction of manganese from ore using SO2 + N2 mixture in leaching section.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

As used herein, the phrase ‘high iron containing low grade manganese ore’ or ‘low grade high iron manganese ore’ refers to any ore having < 30% Mn. Exemplary example includes pyrolusite.

As used herein, the phrase ‘high iron containing medium grade manganese ore’ refers to any ore with Mn/Fe ratio less than 1.

A primary object of the present disclosure is to design a hydrometallurgical process for treating manganese bearing material/ore for selective leaching of manganese, wherein the formed manganese dithionate during the leaching process is controlled or utilized efficiently.

An object of the present disclosure is to develop a process for treating manganese bearing material/ore for selective leaching of manganese, wherein an alternate or additional reductant is employed with or without employing sulphur dioxide as the reductant.

Another object of the present disclosure is to develop a process for treating manganese bearing material/ore for selective leaching of manganese, wherein the operation of leaching process is carried out below pH 4.0, and more preferably below pH 2.0.

To meet the above objectives and to address/obviate the drawbacks associated with existing manganese ore processing methods, the present disclosure provides a method for processing manganese ore to leach or extract manganese, said method comprising recycling the in-situ generated manganese dithionate as a reductant. In an embodiment, said recycling comprises recycling a portion of the manganese dithionate containing leach liquor obtained during the manganese ore processing method.

The present disclosure further provides a method of controlling manganese dithionate concentration in leach liquor solution obtained during leaching of a manganese ore, said method comprising recycling a portion of said leach liquor back to the leaching process/step, wherein said recycled leach liquor is employed as a dithionate based reductant in the leaching process.

More particularly, the present disclosure provides a method for processing manganese ore comprising:
leaching a slurry comprising manganese ore and recycled leach liquor with sulphur dioxide gas in a reactor to obtain a leach solution;
subjecting the leach solution to solid liquid separation resulting in wash liquor and leach liquor;
recycling a portion of the leach liquor; and
purifying remaining portion of the leach liquor to remove manganese dithionate, iron, aluminium, heavy metal, impurities, or any combination thereof, and extracting manganese,
wherein iron concentration and manganese dithionate concentration during the method is maintained at a level below 1 g/L, and wherein the recycled leach liquor comprises manganese dithionate and manganese sulphate.

In an embodiment of the above described method, the slurry comprising manganese ore and recycled leach liquor is prepared by crushing the manganese ore and preparing slurry with process water and the recycled leach liquor of pulp density of at least about 10% w/v. In an embodiment, said slurry preparation is carried out in the crushing and grinding section as shown in Figure 1.

In an embodiment of the above described method, the slurry comprising manganese ore and recycled leach liquor is prepared by:
- crushing the manganese ore,
- pulverizing the crushed manganese ore with the recycled leach liquor of pulp density of at least about 10% w/v to obtain a slurry mixture, and
- gravity separation of the slurry particles of the mixture based on desired particle size.

In an embodiment, the above described slurry preparation is carried out in crushing, grinding and hydrocyclone (gravity separation) sections as shown in Figure 2.

In an embodiment of the above described method, the portion of leach liquor is recycled to the slurry preparation process as described above.

In an embodiment of the above described method, the portion of leach liquor recycled ranges from about 20% to 30% including values and ranges therefrom. In an embodiment, the portion of leach liquor recycled is about 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

In an embodiment of the above described method, the recycled leach liquor comprises manganese dithionate at a concentration greater than 5 g/L, manganese (Mn) at a concentration greater than 70 g/L, and iron (Fe) at a concentration less than 5 g/L.

In some embodiments, the recycled leach liquor comprises manganese (Mn) as manganese dithionate at a concentration ranging from 5 g/L to 15 g/L, manganese (Mn) as manganese sulphate at a concentration ranging from 70 g/L to 90 g/L, iron (Fe) at a concentration ranging from 3 g/L to 5 g/L, and other metallic impurities greater than R% dissolved in the leach liquor, where R is recycle ratio. The ranges recited herein include all the individual values and narrower ranges/sub-ranges.

In some embodiments, the recycled leach liquor comprises 5, 8, 10 or 15 g/L of Mn as manganese dithionate, greater than 70, 72, 75, 78, 80, 85 or 90 g/L of Mn as manganese sulphate, iron at a concentration between 3, 4 or 5 g/L, and other metallic impurities greater than R% dissolved in the leach liquor, where R is recycle ratio.

In an embodiment of the above described method, the recycled leach liquor has a pH of about 1.8 to 7.0.

In an embodiment of the above described method, the portion of recycled leach liquor acts as a reductant along sulphur dioxide gas during the leaching process.

In an embodiment of the above described method, while a portion of the leach liquor is recycled back to the slurry preparation process and subsequently employed in the leaching process, the remaining portion of leach liquor is purified by:
adding an oxide additive, acid additive, or a combination thereof to the remaining leach liquor to maintain dithionate levels below 0.1 g/L;
removing iron by adding hydrated lime slurry and increasing pH of the leach liquor to obtain pregnant leach solution (PLS);
removing heavy metals from the PLS by precipitating the heavy metals by sulphidation; and
extracting manganese as manganese salt.

In an embodiment of the above described method, the remaining portion of leach liquor ranges from about 70% to 80% including values and ranges therefrom. In an embodiment, the remaining portion of leach liquor is about 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79% or 80%.

In an embodiment of the above described method, the oxide additive is selected from manganese containing material, manganese ore, roasted manganese ore, or any combination thereof.

In an embodiment of the above described method, the acid additive is selected from sulfuric acid, peroxydisulfuric acid, peroxymonosulfuric acid, or any combination thereof.

In an embodiment of the above described method, oxide additive and acid additive is added to the remaining portion of leach liquor to maintain dithionate levels below 0.1 g/L.

In an embodiment of the above described method, oxide additive or acid additive is added to the remaining portion of leach liquor and the resulting solution is stabilized for about 10 minutes to 6 hours for decomposition of manganese dithionate and lowering the manganese dithionate concentration to below 0.1 g/L.

In an embodiment of the above described method, oxide additive and acid additive is added to the remaining portion of leach liquor and the resulting solution is stabilized for about 10 minutes to 6 hours for decomposition of manganese dithionate and lowering the manganese dithionate concentration to below 0.1 g/L.

In an embodiment of the above described method, the sulphur dioxide gas (reductant) is passed through sparger for dispersion and mixing in the reactor.

In an embodiment of the above described method, the leaching is carried out at a pH below 4.0.

In an embodiment of the above described method, the leaching is carried out at a pH below 2.0.

In an embodiment of the above described method, the leaching is carried out in reactors configured in series cocurrent mode, distributed cocurrent mode or counter current mode as shown in Figure 4.

In an embodiment, the leaching is carried out in reactor configured in series cocurrent mode as illustrated in Figure 4(a) viz. (a) series configuration with co-current flow of slurry and distributed gas distribution. Under this reactor configuration in leaching, a co-current flow of slurry of gas can be observed. The SO2/SO2-N2 mixture gas coming from source is compressed using Compressor (C-1) from 1 atm to pressure of 2.5 atm. This pressure is required to overcome the pressure inherited from the water column in reactor vessel. The following gas is measured and control using a PID loop for the gas distribution in three reactor systems. The distribution ratio depends on total residence time and eventually depends on Mn recovery. Part of gas mixture (SO2-N2) mixture is passed to leach reactor (LR1). Manganese slurry is passed to leach reactor LR1 to LR3 using gravity method. Part of unreacted slurry S1 is pumped to LR2 and eventually part of manganese slurry S3 is pumped to LR3. The gas mixture is distributed as SO2-LR1 to LR1. Unreacted gas LR1-SO2 along with fresh gas SO2-LR2 is passed to LR2. In LR2, part of SO2 mixture (SO2-LR2) along with LR1-SO2 is passed to LR2. In Leach reactor (LR3), part of SO2 mixture (SO2-LR3) along with LR2-SO2 is passed to LR3. Reacted manganese in the solution is measured in the pregnant leach solution (PLS). Manganese content in the solution is measured and accordingly using ‘P control loop’ the SO2 mixture flow rate can be varied to meet the desired manganese recovery.

In an embodiment, the leaching is carried out in reactor configured in distributed cocurrent mode as illustrated in Figure 4(b) viz. (b) parallel configuration with counter current flow of slurry and gas. Under this reactor configuration in leaching, a counter current scheme for gas flow and manganese slurry is presented. The SO2/ SO2-N2 mixture gas coming from source is compressed using Compressor (C-1) from 1 atm to pressure of 2.5 atm. This pressure is required to overcome the pressure inherited from the water column in reactor vessel. The gas input to the LR3 is designated as SO2-IN. In leach reactor (LR3), fresh gas is reacting with partly reacted manganese slurry, in this reactor maximum conversion is available. Part of unreacted gas (SO2-1) is passed to LR2 which can react with coming manganese slurry from LR1- LR2. Unreacted SO2-2 from LR2 is sent to LR1 where it is reacted with fresh manganese slurry in LR1. Finally, unreacted SO2 gas SO2-F is sent to scrubber.

In an embodiment, the leaching is carried out in reactor configured in counter current mode as illustrated in Figure 4(c) viz. c) series configuration with co-current flow of slurry and gas flow
This configuration is like configuration under Figure 4(b), where the gas flow and manganese flow are co-current scheme. Other parts are similar to said configuration (b).

In an embodiment of the above described method, the solid liquid separation comprises filtration and involves washing of manganese values from cake formed during leaching of the slurry.

In an embodiment of the above described method, the wash liquor obtained after leaching is recycled for next batch of leaching.

In an embodiment of the above described method, the purification of the remaining portion of leach liquor comprises removing dissolved iron and heavy metallic ions by precipitation.

In an embodiment of the above described method, the removal of dissolved iron is carried out by oxidation of Fe(II) to Fe(III) by addition of oxidizing agent followed by its precipitation by adding lime slurry. In an embodiment, the lime slurry is hydrated lime slurry.

In an embodiment of the above described method, the oxidizing agent is selected from a group comprising hydrogen peroxide, sodium perchlorate, oxygen gas, manganous oxide, potassium permanganate and combinations thereof. In an embodiment, the oxidizing agent is hydrogen peroxide (H2O2).

In an embodiment of the above described method, the addition of lime slurry or hydrated lime slurry precipitates Fe as its hydroxide along with the precipitation of aluminium (Al).

In an embodiment of the above described method, the heavy metal purified from the pregnant leach solution (PLS) is selected from a group comprising zinc (Zn), copper (Cu), nickel (Ni), cobalt (Co), arsenic (As), antimony (Sb) and combinations thereof.

In an embodiment of the above described method, the sulphidation process to purify/remove the heavy metal is carried out using sodium hydrogen sulphide, sodium sulphide, or a combination thereof. In an embodiment, the sulphidation is carried out using sodium hydrogen sulphide.

In an embodiment of the above described method, during purification of the remaining portion of leach liquor, the pH is increased between 4.5 to 6.0 to obtain the PLS. In an embodiment, the pH is increased to about 6.0.

In an embodiment of the above described method, the manganese is extracted as pure manganese salt.

In an embodiment of the above described method, the manganese is extracted as manganese sulphate solution.

In an embodiment of the above described method, the manganese is extracted as manganese sulphate crystals.

In an embodiment of the above described method, manganese dithionate concentration during the method is maintained at a level below 0.1 g/L.

In an embodiment of the above described method, the iron concentration is maintained at a level below 1 g/L by providing and controlling oxidation reduction potential (ORP) below 550 mV and by providing an excess or residual amount of manganese ions in the slurry.

In an embodiment of the above described method, the manganese bearing material or the manganese ore is selected from a group comprising high iron containing low grade manganese ore, high iron containing medium grade manganese ore, high iron containing high grade manganese ore, partially reduced manganese ore, and combinations thereof. In an embodiment, the manganese ore is high iron containing low grade manganese ore. In an embodiment, the manganese ore is pyrolusite.

In some embodiments, removing impurities while purifying remaining portion of the leach liquor comprises separating/removing impurities which come from the ore.

As described above, the present disclosure also relates to a method of controlling manganese dithionate concentration in leach liquor obtained during leaching of a manganese ore.

In an embodiment, said method of controlling manganese dithionate concentration in leach liquor obtained by leaching of a manganese ore comprises:
a) recycling a portion of the leach liquor to the leaching process, wherein said recycled leach liquor is employed as a dithionate based reductant in the leaching process; and
b) purifying remaining portion of the leach liquor by adding an oxide additive, acid additive or a combination thereof,
wherein the manganese dithionate in said method is controlled at a concentration below 1 g/L.

In an embodiment of the method of controlling manganese dithionate concentration in leach liquor obtained by leaching of a manganese ore, the manganese dithionate is controlled at a concentration below 0.1 g/L.

The present disclosure further provides manganese extracted by the manganese ore processing method described above.

Thus, the present disclosure relates to an alternate, simple and cost-effective method for processing/controlling manganese dithionate generated during leaching of manganese ore. The method involves treating manganese ores, such as the low grade high iron bearing pyrolusite ore for selective leaching of manganese, wherein said method controls the disadvantageous manganese dithionate in leach liquor generated during leaching by efficiently recycling and utilizing said leach liquor as a reductant. The method additionally utilizes sulphur dioxide gas as reductant along with control of iron concentrations during the operation.

In embodiments of the present disclosure, the method of preparing high purity manganese salts from manganese ore as described herein particularly employs the features: (1) reductive leaching of manganese ore using combination of manganese dithionate and SO2 as reductant in lixiviant (water); (2) recovery of iron value as hydroxide cake; and (3) preparation of manganese end products from the purified manganese sulphate solution.

In embodiments of the present disclosure, the present method utilizes low grade high iron bearing manganese ore feedstock as primary source of raw material for production of highly pure manganese salts. The present method can operate either with run of mine ore sized to size fraction or with pre-reduced manganese ore as well. As described above, the method comprises selective reductive leaching of manganese ore using sulphur dioxide as reductant and recycled manganese dithionate containing leach liquor as the additional reductant. The present method utilizes the recycled manganese dithionate as a reductant for reduction of manganese ore and eventually the generated manganese dithionate by leaching is decomposed which leads to the control of manganese dithionate ion levels below 1 g/L in the final solution during and after leaching process.

As exemplary method of the present disclosure is described below:

Manganese ore is fed to crushing and grinding circuit wherein the ore material is initially screened to get minus 30 mm fraction. This fraction is fed to a primary crusher like jaw crusher followed by grinding in pulveriser circuit with separation occurring through air classifier circuit. The required size fraction of manganese feedstock was employed for slurry preparation using fresh water, recycle water from previous wash as well as recycled leach liquor comprising manganese sulphate and manganese dithionate (manganese dithionate concentration equal to or greater than >10 g/L), and was subject to leaching. During the process of leaching, the prepared manganese feedstock slurry comprises more than 10 wt% solids, less than about 120 g/L of manganese sulphate in solution, about 10-80 g/L of manganese dithionate, and the leaching process is carried out at a temperature of less than 100oC and operating pH between 1.1 to 3.0. Post leaching, the obtained leach solution preferably has an initial soluble iron concentration of less than 0.2 g/L. The iron concentration in the final leach solution i.e. pregnant leach solution (PLS) is preferably maintained at a level below 0.2 g/L by controlling the oxidation reduction potential (ORP) below 550 mV (vs Ag/AgCl reference electrode) and by providing an excess or residual amount of manganese ions in the slurry.

In an embodiment, leaching reaction can be operated in series mode with banks of reactors attached with flow of material flowing from first reactor to last one with being total gas divided in a specific ratio. Total leaching time varies from about 2 to 4 hours depending on input manganese concentration, concentration of sulphur dioxide in the input gas and residence time for each reactor. With said arrangement, up to 80% of manganese is dissolved. Conditions can be optimized based on series of experiments for different samples of feed material. Quantity and rate of addition of sulphur dioxide is controlled as per target pH and Eh (oxidation reduction potential or redox potential) to achieve said 80% dissolution of manganese. Iron dissolution during leaching reaction is almost nil or negligible. During the leaching process, a part of the manganese dithionate contained in the generated leach liquor (about 70 to 80%) is decomposed in-situ while another part of the leach liquor containing manganese dithionate (about 70 to 80%) is recycled back which will decompose and act as a reducing agent to leach fresh MnO2 in the manganese ore slurry.

The chemical reactions involving decomposition of manganese dithionate is as follows:
MnO2 + SO2 = MnSO4 .…... [Reaction 1]
2Fe2O3 + 4SO2 = 4FeSO4 ….…[Reaction 2]
MnO2 + 2SO2 = MnS2O6 …….[Reaction 3]
MnO2 + MnS2O6 = 2MnSO4 ……..[Reaction 4]

The parameters of leach solution like Eh (oxidation reduction potential), pH, Mn concentration during leaching in presence of recycled manganese dithionate is controlled such that final pH of the leach solution is about 1.9 with Eh 500 mV (vs Ag/AgCl reference electrode). To control the final parameters, the recycle ratio of [S2O6]2-/[SO2]2- is retained greater than 0.5 in the leach reactor during the leaching. The residue loaded leach solution obtained post leaching is filtered to separate the unreacted residue using filtration unit operation. Thereafter, the filtered part i.e. leach liquor required in desired ratio (after determining the MnS2O6 as free SO2) is recycled back for slurry preparation/next leaching operation cycle. Subsequently, remaining leach liquor is further treated with an oxidizing agent such as hydrogen peroxide to convert ferrous iron to ferric which is then precipitated as ferric hydroxide by adjusting the pH using lime slurry. During this stage, dissolved aluminium is also precipitated as aluminium hydroxide. The resulting solution is called PLS which is further purified to remove heavy metals and other impurities. Particularly, filtration is performed to filter solid content from the PLS. Heavy metals in the leach solution especially zinc-nickel-cobalt is removed from PLS by treatment with sodium sulphide (Na2S) or sodium hydrogen sulphide (NaHS) at a pH between 5.5-7.0. Preferably, after whole treatment process with purification steps, the manganese in the solution is present as manganese sulphate with pH of the purified solution between 6.0-7.0 which can be further processed to obtain manganese sulphate solution or manganese sulphate crystals, or can be sent to electrolyser to produce electrolytic manganese metal (EMM).

Another exemplary method of the present disclosure is described below:

Low grade manganese ore with Mn < 30% and Mn/Fe: 0.9-1.0 is subject to crushing in primary crusher like jaw crusher and subsequently reduced size fraction from the primary crusher is fed into ball mill or roll pulveriser fitted with hydrocyclone and pulse jet filter for further size reduction to make the material amenable for leaching. In this process, the manganese ore is subjected to slurry preparation using recycled process water, mother liquor from manganese sulphate crystallization and recycled manganese dithionate containing leach liquor. The slurry is mixed properly with residence time of approximately 60 minutes and the process parameters of the slurry is controlled such that the pH should not be below 4.0. Sulphur dioxide gas is used as reductant during the leaching process which is sparged into the leach slurry. The sulphur dioxide gas is generated by either burning sulphur flakes through sulphur burning step or by passing SO2 gas from the tonner. The solids percentage in the leach slurry is more than 10 wt%. Due to reaction of sulphur dioxide with manganese dioxide (ore), heat gets liberated due to exothermic nature of the reaction and therefore the temperature of slurry is increased to a maximum of 100oC. The concentration of manganese in the leach solution is <120 g/L and the temperature of leach solution is maintained less than 90oC with pH of the solution maintained below 2.0. During the process of leaching, process parameters are controlled in such a way that total dissolved iron value after subsequent leaching is less than 0.2 g/L and most iron value is present in the form of ferrous sulphate (FeSO4). Leaching is carried out in continuous arrangement following counter current containing fresh leach liquor with exhausted SO2 gas from another reactor and vice versa. This approach provides better control over manganese dissolution with higher productivity. After completion of leaching process, the slurry mass is filtered. The filtrate obtained after filtration contains most of the iron from the ore used for leaching. Iron removal is carried out by adding hydrated lime slurry and pH of the solution is increased. The resulting solution leach liquor is called as PLS (Pregnant Leach Solution). Consumption and volume of sulphur dioxide during leaching is governed by three factors: a) concentration of free SO2 in the recycled leach liquor containing manganese dithionate; b) total iron in the PLS shall be less than 0.2 g/L; and c) final PLS should contain dithionate ion less than 1 g/L. During the leaching process, the pH of the solution and hence the ORP is precisely controlled by changing the gas flow rate and recycle ratio of manganese dithionate concentration (ratio of [S2O6]2-/[SO2]2-). Reactions taking place during leaching is already explained under Reaction 1 to Reaction 4 above. It is predominant that while the method of the present disclosure ensures production of manganese sulphate, there is formation of dithionate which eventually depends on SO3-. The production of dithionate follows to proceed as a free radical combination reaction as shown below:
SO3- + SO3- = S2O6 2-
Dithionate generated or recycled back are consumed as free SO2 which reacts with manganese dioxide to generate manganese sulphate with subsequent oxidation of sulphur in S2O62- radical as also explained under reaction Reaction 4 above. With said reaction conditions, approximately 75-80% manganese is usually recovered into the PLS. However, due to the addition of recycle leach liquor containing manganese dithionate radicals, said manganese recovery increases to 85-88%. Figure 3 provides understanding with respect to effect of manganese dithionate addition on the manganese recovery at constant flow rate of SO2.

On completion of leaching, filtration of slurry is carried out using standard filtration equipment. After filtration, solution obtained is taken for purification where an additive in the form of oxide and acid is added and pH of the leach liquor solution is controlled to a desired value between 0.2-1.5. The residence time for the stabilization reaction is about 0.1-1.5 hours and during the reaction Eh of the solution is controlled between 100-300 mV (vs Ag/AgCl reference electrode). With addition of oxide and acid, the dithionate concentration is brought below 0.2 g/L in the solution. The iron value in the leach liquor which is present as ferrous (Fe2+) is converted to ferric (Fe3+) by adding oxidizing agent such as hydrogen peroxide and eventually the iron is precipitated as hydroxide and the level is reduced to <1 ppm in solution through addition of hydrated limestone slurry. Thereafter, a standard filtration setup with filtration media with less than 5-micron pore size is employed for filtration with double filtration under pressure. During the filtration, iron hydroxide cake which was generated in-situ was filtrated from the clear pink liquid. Solids obtained is washed thoroughly to reclaim any residual manganese value and stored for subsequent processing for recovery of iron. Purified iron-free PLS solution is passed to sulphidizing process for removal of heavy metals including nickel, zinc, cobalt and copper as their respective sulphides. Following the sulphidizing step, the heavy metal precipitates are removed by fine cartridge filtration and subsequently the purified manganese sulphate solution is stored for preparation of manganese salts or EMM. Following reactions happen during the purification of leach liquor:
MnO2 + MnS2O6 = 2MnSO4
Fe2(SO4)3 + 3Ca(OH)2 = 3CaSO4 + 2Fe(OH)3
Al2(SO4)3 + 3Ca(OH)2 = 3CaSO4 + 2 Al(OH)3
CuSO4 + Ca(OH)2 = CaSO4 + Cu(OH)2
CoSO4 + 2NaHS = CoS + Na2SO4 + H2S
NiSO4 + 2NaHS = NiS + Na2SO4 + H2S
ZnSO4 + 2NaHS = ZnS + Na2SO4 + H2S

After purification of PLS, for preparation of manganese sulphate, the solution is subjected to evaporation and crystallization. Evaporation is carried out in normal single effect thin film evaporator with standard cooling circuit followed by drying to obtain manganese sulphate monohydrate crystals.

Thus, it is understood from the above discussion and embodiments that one of the objects of the present disclosure is to provide a cost efficient way to control the dithionate contamination which inherently occurs during sulphur dioxide based leaching. Another object is the direct utilization of low grade ores of manganese for preparing high purity manganese salts or EMM from the leach liquor. The same is achieved by utilizing sulphur dioxide and recycled leach liquor solution containing manganese dithionate (> 10 g/L) as reductants. During the process, another by-product obtained is iron hydroxide cake and also achieving beneficiation enrichment without any high temperature reduction. Thus, the proposed method of the present disclosure achieves clean and environmental friendly waste water recycle with minimal discharge of off-gas and water to the green belt.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

INCORPORATION BY REFERENCE
All references, articles, publications, patents, patent publications, and patent applications (if any) cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

EXAMPLES

Example 1: Method for processing manganese ore and controlling manganese dithionate levels according to present disclosure

EXAMPLE 1A:
The method for processing manganese ore according to the present disclosure is described in Figure 1. Said method was performed as follows:
1. Low grade manganese ore lumps with Mn:Fe of 1.5 (detailed chemical analysis shown in Table 1) was crushed to size distribution below <1 mm using jaw crusher and pulveriser based system. The oversized particles were sent back to screen again for crushing.
2. Crushed and pulverized manganese ore was made slurry with process water and recycled manganese dithionate containing leach liquor of desired pulp density of 25 wt% and eventually the slurry was transferred to the leaching reactor for reductive leaching with sulphur dioxide as the reducing agent along with free SO2 from recycled manganese dithionate containing leach liquor. About 0.1-10 litre per minute (LPM) of gas was passed through sparger to make bubble size of below <1 mm for better dispersion and mixing. Eh and pH of the leaching slurry was continuously monitored and after achieving a pH value of below 2.0, the leaching was stopped. During the leaching, intermittent liquid solutions were tested for Mn (II), Fe(II) and free SO2 dissolved in the solution. Once the desired value was achieved, the gas to the leaching reactor was slowly stopped and allowed to stabilize.
3. The leach solution was taken to filter press for solid liquid separation and cake washing was carried out to wash out manganese values from the solid cake. The wash liquor was stored separately and recycled to next batch.
4. The dithionate bearing leach liquor solution which has free SO2 concentration was subjected to recycling such that about 20% was recycled back for slurry preparation and further leaching.
5. The remaining leach liquor (about 80%) was taken for purification to remove iron, aluminium, heavy metals, other impurities etc. in the leach liquor. The leach cake obtained after filtration was stored for further utilization. A recovery value of >70% manganese was obtained after purification along with < 0.5 g/L Fe, <8 g/L dithionate ions and >99% removal of impurities.

Particularly, the above mentioned purification process comprised subjecting the obtained leach liquor to purification for elimination of dissolved iron and other heavy metallic ions by subsequent precipitation. An additive mixture of oxide and acidic nature chemical was first added and the solution was stabilized for about 1-2 hours which resulted in decomposition of dithionate and control of dithionate levels below 1 g/L. Iron which is generally present as Fe(II) had to be oxidized to Fe(III) and was carried out by addition of hydrogen peroxide of about 30-40 wt% into the leach liquor solution. Hydrated lime slurry of about 20 wt% was added into the leach solution and subsequently pH of the leach solution was increased to 6.0 with precipitation of iron (Fe) and aluminium (Al) as hydroxide cake. The iron cake was removed from the leach liquor solution by filtration using filter press. The obtained leach liquor solution was PLS and further purification of the PLS was carried out to remove heavy metals such as Zn, Cu, Ni, Co, traces of As etc. using sulphidation by addition of sodium hydrosulphide of about 30 wt% concentration with continuous monitoring of Eh and pH for about 1-4 hours. The final PLS obtained was stored for further processing to produce manganese salts (purified manganese sulphate solution).

Table 1. Chemical analysis at different stages of manganese ore processing according to Example 1A
Chemical Analysis of Manganese Ore (wt %)
Mn (%) Fe (%) Cu (%) Ni (%) Co (%) Al (%) Free SO2 (%)
26.54 28.17 0.014 0.003 0.021 2.89 NA
Chemical Analysis of Recycled Solution
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (g/L)
12.43 158 3.9 9.0 45.6 1.8 4
Pregnant Leach Solution (PLS):
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (g/L)
83.56 320 4.1 9.02 48.9 3.2 8
Solution after Iron and Dithionate Removal:
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (ppm)
83.9 <1 0.25 3.7 48.9 <1 1.5
Solution after Sulphide Precipitation:
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (ppm)
84.01 <1 <1 1.7 17 <1 <1.5

EXAMPLE 1B:
Another exemplary method for processing manganese ore according to the present disclosure is described in Figure 2. Said method was performed as follows:
1. Low grade manganese ore lumps with Mn:Fe: 1.5 (detailed chemical analysis shown in Table 2) was crushed to size distribution between 3-5 mm using jaw crusher and was screened. The oversized particles were returned back for crushing.
2. The crushed ore was sent to pulverizer/ball mill along with recycled leach liquor containing manganese dithionate to prepare a slurry of specified pulp density of 70%. The conditioned slurry was fed to ball mill circuit for grinding. Discharge of the ball mill was sent to dilution tank to adjust the pulp density before sending to hydrocyclone (gravity separation).
3. In the hydrocyclone, the overflow containing desired particle size was sent downstream for leaching and underflow of the hydrocyclone was recycled back to ball mill along with fresh feed of leach liquor and ore slurry.
4. The overflow from the hydrocyclone was sent to liquor preparation tank of desired pulp density of 25% along with wash water from filtration circuit.
5. The leach liquor of desired pulp density of 25 wt% and eventually the slurry was transferred to the leaching reactor for reductive leaching with sulphur dioxide as a reducing agent which was obtained by burning sulphur in the sulphur melter to generate SO2 gas. Eh and pH of the leaching slurry was continuously monitored and after achieving a pH value of below 2.0, the leaching was stopped. During the leaching, intermittent liquid solutions were tested for Mn (II), Fe(II) and free SO2 dissolved in the solution. Once the desired value was achieved, the gas to the leaching reactor was slowly stopped and allowed to stabilize.
6. The leach solution was taken to filter press for solid liquid separation and cake washing was carried out to wash out manganese values from the solid cake. The wash liquor was stored separately and recycled to next batch.
7. The dithionate bearing leach liquor which has free SO2 concentration was subjected to recycling such that about 20% was recycled back for slurry preparation and further leaching.
8. The remaining leach liquor (about 80%) obtained was taken for purification to remove iron, aluminium, heavy metals, other impurities etc. in the leach liquor. The leach cake obtained after filtration was stored for further utilization. A recovery value of 80-82% manganese was obtained along with < 0.5 g/L Fe, <1 g/L dithionate ions, and >99% removal of impurities.

Particularly, the above mentioned purification process comprised subjecting the obtained leach liquor to purification for elimination of dissolved iron and other heavy metallic ions by subsequent precipitation. An additive mixture of oxide and acidic nature chemical was first added and the solution was stabilized for about 1-2 hours which resulted in decomposition of dithionate and control of dithionate levels below 1 g/L. Iron which is generally present as Fe(II) had to be oxidized to Fe(III) and was carried out by addition of hydrogen peroxide of about 30-40 wt% into the leach liquor solution. Hydrated lime slurry of about 20 wt% was added into the leach solution and subsequently pH of the leach solution was increased to 6.0 with precipitation of iron (Fe) and aluminium (Al) as hydroxide cake. The iron cake was removed from the leach liquor solution by filtration using filter press. The obtained leach liquor solution was PLS and further purification of the PLS was carried out to remove heavy metals such as Zn, Cu, Ni, Co, traces of As etc. using sulphidation by addition of sodium hydrosulphide of about 30 wt% concentration with continuous monitoring of Eh and pH for about 1-4 hours. The final PLS obtained was stored for further processing to produce manganese salts (purified manganese sulphate solution).
9. The produced manganese sulphate solution was sent to multi-effect evaporator where evaporation of the water was carried out by supplying steam and resulted in formation of crystals of manganese sulphate along with liquor which is cooled to desired temperature. The concentrated liquor along with manganese sulphate crystals were sent to centrifuge to separate mother liquor which was further sent to leaching section. The crystals of manganese sulphate were dried to get manganese sulphate monohydrate crystals with Mn >31.8%.

Table 2: Chemical analysis at different stages of manganese ore processing according to Example 1B
Chemical Analysis of Manganese Ore (wt %)
Mn (%) Fe (%) Cu (%) Ni (%) Co (%) Al (%) Free SO2 (%)
26.54 28.17 0.014 0.003 0.021 2.89 NA
Chemical Analysis of Recycled Solution
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (g/L)
21.67 950 12 2.2 18.5 1.8 8
Pregnant Leach Solution (PLS)
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (g/L)
84.22 980 16.1 11.22 70.3 5.02 6
Solution after Iron and Dithionate Removal
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (ppm)
83.9 <1 0.25 3.7 48.9 <1 1.5
Solution after Sulphide Precipitation
Mn (g/L) Fe (ppm) Cu (ppm) Ni (ppm) Co (ppm) Al (g/L) Free SO2 (ppm)
84.01 <1 <1 1.7 17 <1 <1.5

The above examples/results describing the present method clearly shows that the manganese dithionate levels generated by leaching of manganese bearing raw materials/ores (MnO2) can be controlled by an alternate approach viz. employing ‘recycled leach liquor solution’ (comprising manganese dithionate and manganese sulphate) as an additional reductant along with the primary reductant (SO2 gas) for leaching of the ore. Recycling a portion of said dithionate containing leach liquor solution is advantageous as it also results in reduction/decomposition of the in-situ generated manganese dithionate, apart from said dithionate containing leach liquor being utilized as a supplementary reductant. The remaining portion of the leach liquor can be further purified to remove additional dithionate, iron, aluminium, heavy metals and other impurities, to extract pure manganese as manganese salt (eg. MnSO4). Particularly, during said purification of the remaining portion of leach liquor, additives (oxide based and/or acid based) are employed to remove/decompose the disadvantageous manganese dithionate levels so that the overall dithionate concentration is maintained below 1 g/L, preferably below 0.1 g/L during the process. The present method improves the overall efficiency and cost-effectiveness of manganese extraction along with effectively getting rid of the undesired manganese dithionate levels in an alternate and environmental friendly manner.