Claims:WE CLAIM:

1. A method for producing electrolytic manganese dioxide (MnO2) (EMD) from low grade ferruginous manganese ore comprising -
a. preparing manganese sulphate (MnSO4) leach liquor from the low-grade ferruginous manganese ore; and
b. subjecting the MnSO4 leach liquor to electrowinning to form the EMD; wherein the electrowinning is performed while maintaining an anode to cathode distance of about 3 cm to about 4.5 cm in the electrowinning cell.
2. The method as claimed in claim 1, wherein the low-grade ferruginous manganese ore comprises less than about 30% Manganese (Mn) and more than about 20% Iron (Fe).
3. The method as claimed in claim 1, wherein the MnSO4 leach liquor is prepared by reacting the low-grade ferruginous manganese ore with sulphur dioxide (SO2).
4. The method as claimed in claim 1, wherein the MnSO4 leach liquor is subjected to purification prior to electrowinning.
5. The method as claimed in claim 4, wherein the purification of the MnSO4 leach liquor comprises purification step(s) selected from a group comprising addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation, activated charcoal treatment or any combination thereof.
6. The method as claimed in claim 5, wherein the purification of the MnSO4 leach liquor comprises
a) adding oxidizing agent(s) to the MnSO4 leach liquor;
b) subjecting the MnSO4 leach liquor of step (a) to hydroxide precipitation;
c) subjecting the MnSO4 leach liquor of step (b) to sulphide precipitation; and
d) subjecting the MnSO4 leach liquor of step (c) to activated charcoal treatment;
wherein the oxidizing agent in step (a) is selected from hydrogen peroxide (H2O2), manganese dioxide (MnO2) powder, air and/or oxygen or any combination thereof; wherein the hydroxide precipitation is facilitated by adding an agent selected from a group comprising hydrated lime, sodium hydroxide (NaOH) and high-grade Mn oxide ore or any combination thereof; wherein the sulphide precipitation is facilitated by adding an agent selected from a group comprising sodium sulphide and ammonium sulphide or any combination thereof; and wherein steps (b), (c) and (d) are followed by filtration.
7. The method as claimed in claim 1, wherein pH of the MnSO4 leach liquor is adjusted to about 4.5 to about 6.5 prior to subjecting the MnSO4 leach liquor to the electrowinning.
8. The method as claimed in claim 7, wherein the pH adjustment is performed by addition of acid to the MnSO4 leach liquor; wherein the acid is selected from a group comprising sulphuric acid (H2SO4) and Ammonium sulphate ((NH4)2SO4) or a combination thereof.
9. The method as claimed in claim 1, wherein free acid concentration of the MnSO4 leach liquor prior to the electrowinning ranges about 10 g/L to about 25 g/L, preferably about 15 g/L to about 20 g/L.
10. The method as claimed in claim 1, wherein the free acid concentration of the MnSO4 leach liquor is maintained at less than about 20 g/L, preferably less than about 5 g/L during the electrowinning.
11. The method as claimed in claim 1, wherein the MnSO4 leach liquor has Mn concentration ranging from about 50 g/L to about 80 g/L, preferably about 50 g/L to about 60 g/L.
12. The method as claimed in claim 1, wherein the electrowinning is performed using titanium anode(s) and graphite cathode(s).
13. The method as claimed in claim 1, wherein the electrowinning is characterized by one or more of current density ranging from about 80 A/m2 to about 140 A/m2, temperature of the MnSO4 leach liquor ranging from about 80°C to about 95°C, and/or feed flow rate of the MnSO4 leach liquor into the electrowinning cell ranging from about 8 g/L to about 11 g/L.
14. The method as claimed in claim 1, wherein the electrowinning is performed for about 24 hours to about 96 hours.
15. The method as claimed in claim 1, wherein the EMD is deposited on the anode in the electrowinning cell.
16. The method as claimed in 15, wherein the EMD deposit from the anode is stripped to obtain the EMD.
17. The method as claimed in claim 1, wherein the EMD has purity ranging from about 91% to about 94%.
18. The method as claimed in claim 1, wherein the EMD is battery grade EMD.
19. The method as claimed in claim 1, wherein the method has current efficiency ranging from about 75% to about 99.5%.
20. The method as claimed in claim 1, wherein the method has specific energy consumption ranging from about 1.2 kWh/kg to about 2.5 kWh/kg.
, Description:FIELD OF INVENTION
[0001] The present disclosure relates to the fields of material science and metallurgy. Particularly, the present disclosure relates to a method for producing electrolytic manganese dioxide (EMD) through electrowinning. The present disclosure, further, analyses and reports the effect of different electrowinning parameters on the efficiency and scalability of the method.
BACKGROUND
[0002] Manganese is an abundant resource that is embedded in the Earth’s crust and has wide variety of applications. The most known application is in the steel and metal alloy making industries, in which manganese is used to improve the strength and properties of steel. More than 85% of all manganese consumed goes into steel as an alloying element and after steel, the second most important market for manganese is primary and rechargeable batteries.
[0003] Despite its ubiquity, manganese is rarely found in high enough concentrations to form an ore deposit. Of the hundreds of minerals containing manganese, only around 10 are of mining significance. Manganese ore can be classified into low-grade ore (Mn<35%), medium grade ore (Mn 35-45%), and high-grade ore (Mn>45%).
[0004] Manganese both in the pure form and as silicomanganese (SiMn) and ferromanganese (FeMn) alloys plays very important role in the making of steel. Demand for Mn primarily comes from the steel industry and hence, with growing demand for steel, the demand for manganese is also growing. Apart from pure Mn metal, SiMn and FeMn alloys which are mainly used in the steel industry, additional demand for Mn comes from its other derivatives like MnSO4, MnCO3, Mn (OH)2 and synthetic MnO2 etc. which are used in the fertilizer, food, pharma, and battery industry etc. Although electrolytic manganese dioxide (EMD) has steady demand coming from the alkaline battery industry, its demand in both primary and secondary Li ion batteries is on the rise. Not only in batteries, EMD is also being explored in catalysis applications. Conventionally, EMD is produced using high grade Mn ores which contain Mn either in the form of carbonate or oxide. Carbonate ores are majorly found in China which is a major exporter of EMD. Indian manganese ores are oxide type, majority of which are low grade ores with Fe as major impurity. Indian state Odisha alone contributes to around 50% of total Mn reserves in India. Utilization of these low-grade ores is crucial not only to meet the increased demand from various manganese derivates but also from the sustainability perspective.
The need of the hour, therefore, is to devise an economical and sustainable method to produce electrolytic manganese dioxide (EMD).

SUMMARY OF THE DISCLOSURE
[0005] Addressing the above identified need in the art, the present disclosure provides a method for producing electrolytic manganese dioxide (MnO2) (EMD) from low grade ferruginous manganese ore comprising -
a. preparing manganese sulphate (MnSO4) leach liquor from the low-grade ferruginous manganese ore; and
b. subjecting the MnSO4 leach liquor to electrowinning to form the EMD; wherein the electrowinning is performed while maintaining an anode to cathode distance of about 3 cm to about 4.5 cm in the electrowinning cell.
[0006] In some embodiments, the low-grade ferruginous manganese ore comprises less than about 30% Manganese (Mn) and more than about 20% Iron (Fe).
[0007] In some embodiments, the MnSO4 leach liquor is subjected to purification prior to electrowinning.
[0008] In some embodiments, the purification of the MnSO4 leach liquor comprises purification step(s) selected from a group comprising addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation, activated charcoal treatment or any combination thereof.
[0009] In some embodiments, free acid concentration of the MnSO4 leach liquor prior to the electrowinning ranges about 10 g/L to about 25 g/L, preferably about 15 g/L to about 20 g/L.
[0010] In some embodiments, the free acid concentration of the MnSO4 leach liquor is maintained at less than about 20 g/L, preferably less than about 5 g/L during the electrowinning.
[0011] In some embodiments, the MnSO4 leach liquor has Mn concentration ranging from about 50 g/L to about 80 g/L, preferably about 50 g/L to about 60 g/L.
[0012] In some embodiments, the electrowinning is performed using titanium anode(s) and graphite cathode(s).
[0013] In some embodiments, the electrowinning is characterized by one or more of current density ranging from about 80 A/m2 to about 140 A/m2, temperature of the MnSO4 leach liquor ranging from about 80°C to about 95°C, and/or feed flow rate of the MnSO4 leach liquor into the electrowinning cell ranging from about 8 g/L to about 11 g/L.
[0014] In some embodiments, the electrowinning is performed for about 24 hours to about 96 hours.
[0015] In some embodiments, the EMD is deposited on the anode in the electrowinning cell. Said EMD deposit from the anode, in some embodiments, is stripped to obtain the EMD.
[0016] In some embodiments, the EMD has purity ranging from about 91% to about 94%. In some embodiments, the EMD is battery grade EMD.
[0017] In some embodiments, the method has current efficiency ranging from about 75% to about 99.5%.
[0018] In some embodiments, the method has specific energy consumption ranging from about 1.2 kWh/kg to about 2.5 kWh/kg.

BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:
Figure 1 depicts the effect of current density on current efficiency and specific power consumption.
Figure 2 depicts the effect of electrolyte temperature on current efficiency and specific power consumption.
Figure 3 depicts the effect of anode to cathode distance on current efficiency and specific power consumption.
Figure 4 depicts the effect of initial electrolyte pH on current efficiency and specific energy consumption.
Figure 5 depicts variation in cell voltage and free acid concentration of electrolyte with respect to electrowinning time at initial electrolyte pH of 6 (left) and initial electrolyte pH of 0.5 (right).
Figure 6 depicts the effect of controlling and maintaining free acid concentration in the electrolyte in a fixed range.
Figure 7 depicts the XRD of the deposit produced with and without any control over the free acid concentration.
Figure 8 depicts the condition of a lead anode after use in the electrowinning step.

DETAILED DESCRIPTION
General definitions
[0020] As used herein, the term ‘purified leach liquor’, ‘purified MnSO4 leach liquor’, ‘feed’ and ‘electrolyte’ have been used interchangeably to refer to the MnSO4 leach liquor prepared from low grade ferruginous manganese ore that is subjected to processing or purification to remove impurities and that is fed to the electrowinning cell.
[0021] The term ‘electrowinning’ in the context of the present disclosure has the same meaning that is known by persons skilled in the art, referring to recovery of a metallic product from a solution by means of an electrolytic chemical reaction.
[0022] Reference to ‘anode-cathode distance’ or ‘anode to cathode distance’ and ‘ACD’ throughout the present disclosure, unless otherwise defined, refers to the center-to-center between anode and cathode of an electrolytic or electrowinning cell.
[0023] As used herein, the term ‘comprising’ when placed before the recitation of steps in a method means that the method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps. For example, a method comprising steps a, b, and c encompasses a method of steps a, b, x, and c, a method of steps a, b, c, and x, as well as a method of steps x, a, b, and c. Furthermore, the term ‘comprising’ when placed before the recitation of steps in a method does not (although it may) require sequential performance of the listed steps, unless the content clearly dictates otherwise. For example, a method comprising steps a, b, and c encompasses, for example, a method of performing steps in the order of steps a, c, and b, the order of steps c, b, and a, and the order of steps c, a, and b, etc.
[0024] 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 suffix ‘(s)’ at the end of any term in the present disclosure envisages in scope both the singular and plural forms of said term.
[0025] As used in this specification and the appended claims, the singular forms ‘a’, ‘an’ and ‘the’ includes both singular and plural references unless the content clearly dictates otherwise. 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. As such, the terms ‘a’ (or ‘an’), ‘one or more’, and ‘at least one’ can be used interchangeably herein.
[0026] Numerical ranges stated in the form ‘from x to y’ include the values mentioned and those values that lie within the range of the respective measurement accuracy as known to the skilled person. If several preferred numerical ranges are stated in this form, of course, all the ranges formed by a combination of the different end points are also included.
[0027] The terms ‘about’ or ‘approximately’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, are meant to encompass variations of and from the specified value, such as variations of +/-10% or less, +/-5% or less, +/-1% or less, and +/-0.1% or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier ‘about’ or ‘approximately’ refers is itself also specifically, and preferably, disclosed.
[0028] As used herein, the terms ‘include’, ‘have’, ‘comprise’, ‘contain’ etc. or any form said terms such as ‘having’, ‘including’, ‘containing’, ‘comprising’ or ‘comprises’ are inclusive and 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.
[0029] As regards the embodiments characterized in this specification, it is intended that each embodiment be read independently as well as in combination with another embodiment. For example, in case of an embodiment 1 reciting 3 alternatives A, B and C, an embodiment 2 reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is to be understood that the specification unambiguously discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned otherwise.
Disclosure
[0030] The present disclosure provides a method for production of MnSO4 allowing utilization of low-grade ores to produce valuable electrolytic manganese dioxide (EMD) through an energy and cost effective and thus sustainable route.
[0031] Particularly, the present disclosure provides a method for producing electrolytic manganese dioxide (MnO2) (EMD) from low grade ferruginous manganese ore comprising -
a. preparing manganese sulphate (MnSO4) leach liquor from the low-grade ferruginous manganese ore; and
b. subjecting the MnSO4 leach liquor to electrowinning to form the EMD; wherein the electrowinning is performed while maintaining an anode to cathode distance of about 3 cm to about 4.5 cm in the electrowinning cell.
[0032] The aforesaid method allows utilization of low-grade ferruginous manganese ore to produce EMD. This not only addresses the issues associated with the storage and utilization of low-grade ores but also generates a highly valuable product i.e., EMD from an otherwise low value starting material.
[0033] In some embodiments, the low-grade ferruginous manganese ore comprises less than about 30% Manganese (Mn) and more than about 20% Iron (Fe).
[0034] In some embodiments, the low-grade ferruginous manganese ore comprises about 17% to about 27% Mn and about 30% to about 41% Fe.
[0035] In some embodiments, the low-grade ferruginous manganese ore comprises about 3% to about 5 % SiO2, about 5% to about 7% Al2O3, about 0.4% to about 0.5% K2O, about 0 % to about 0.05% MgO, about 0 % to about 0.75 % CaO, and/or about 0% to about 0.05% Na2O.
[0036] In some embodiments, the MnSO4 leach liquor is prepared by reacting the low-grade ferruginous manganese ore with sulphur dioxide (SO2).
[0037] In a non-limiting embodiment, the leaching is performed in a reactor, wherein the reactor comprises a suspension of the low-grade ferruginous manganese ore in a suitable solvent such as but not limited to water and SO2 gas is purged into the reactor at the desired flow rate for a specified period of time to obtain the leach liquor. In some embodiments, after the said leaching process, the MnSO4 leach liquor and the undissolved residue are separated.
[0038] In some embodiments, the MnSO4 leach liquor is subjected to purification prior to electrowinning to yield a precursor for the electrowinning.
[0039] While the purification may be performed by any method well known in the art, in some embodiments, the purification of the MnSO4 leach liquor comprises purification step(s) selected from a group comprising addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation, activated charcoal treatment or any combination thereof.
[0040] In some embodiments, the purification of the MnSO4 leach liquor comprises two or more purification steps selected from a group comprising addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation and activated charcoal treatment.
[0041] In some embodiments, the purification of the MnSO4 leach liquor comprises the following purification steps - addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation and optionally, activated charcoal treatment.
[0042] In some embodiments, the purification of the MnSO4 leach liquor comprises the following purification steps - addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation and sulphide precipitation.
[0043] In some embodiments, the purification of the MnSO4 leach liquor comprises the following purification steps - addition of an oxidizing agent to the MnSO4 leach liquor, hydroxide precipitation, sulphide precipitation and activated charcoal treatment.
[0044] In some embodiments, the oxidizing agent is selected from a group comprising but not limited to hydrogen peroxide (H2O2), manganese dioxide (MnO2) powder, air and/or oxygen or a combination thereof. In some embodiments, addition of the oxidizing agent to the MnSO4 leach liquor leads to removal of impurities such as but not limited to one or more of iron, aluminum, and copper.
[0045] In some embodiments, the hydroxide precipitation is facilitated by adding an agent selected from a group comprising hydrated lime, sodium hydroxide (NaOH) and high-grade Mn oxide ore or any combination thereof, preferably high-grade Mn oxide ore to the MnSO4 leach liquor.
[0046] In some embodiments, the hydroxide precipitation facilitates removal of aluminium and iron from the MnSO4 leach liquor.
[0047] In some embodiments, the sulphide precipitation is facilitated by adding an agent selected from a group comprising sodium sulphide and ammonium sulphide or any combination thereof, preferably sodium sulphide. In some embodiments, the sulphide precipitation facilitates removal of heavy metals from the leach liquor.
[0048] In some embodiments, the activated charcoal treatment facilitates removal of residual sulphides and heavy metals from the leach liquor.
[0049] In a non-limiting embodiment, the purification of the MnSO4 leach liquor comprises
a) adding oxidizing agent(s) to the MnSO4 leach liquor;
b) subjecting the MnSO4 leach liquor of step (a) to hydroxide precipitation;
c) subjecting the MnSO4 leach liquor of step (b) to sulphide precipitation; and optionally,
d) subjecting the MnSO4 leach liquor of step (c) to activated charcoal treatment.
[0050] In a non-limiting embodiment, the pH of the leach liquor of step (b) is raised to about 5 to about 6, preferably about 5.5. Maintaining said pH, in some embodiments, the leach liquor is stirred for about 2 hours to about 4 hours, preferably about 3 hours.
[0051] In a non-limiting embodiment, the pH of the leach liquor is maintained at 6 to about 7 during the sulphide precipitation. Maintaining said pH, in some embodiments, the leach liquor is stirred for about 1 hour to about 3 hours, preferably about 2 hours.
[0052] In some embodiments, steps (b), (c) and (d) in the aforesaid purification protocol are followed by filtration, wherein the filtrate from step (b) is subjected to step (c), the filtrate from step (c) is subjected to step (d) and the filtrate from step (d) is the purified leach liquor that acts as a precursor or electrolyte for the electrowinning.
[0053] In some embodiments, the leach liquor, prior to the electrowinning, is conditioned for use as a precursor for the electrowinning.
[0054] In some embodiments, pH of the MnSO4 leach liquor is adjusted to about 4.5 to about 6.5 prior to subjecting the MnSO4 leach liquor to the electrowinning.
[0055] In a non-limiting embodiment, the pH adjustment is performed by addition of acid to the MnSO4 leach liquor; wherein the acid is selected from a group comprising sulphuric acid (H2SO4) and Ammonium sulfate ((NH4)2SO4) or a combination thereof.
[0056] In some embodiments, pH of the MnSO4 leach liquor is adjusted to about 4.5, about 5, about 6 or about 6.5 prior to subjecting the MnSO4 leach liquor to the electrowinning. Initial electrolyte pH plays a key role in determining the cycle time. Starting the electrowinning in a cell containing an acidic electrolyte tends to have a relatively shorter cycle time in comparison to that of the cell with basic electrolyte. During the electrowinning, formation of EMD and sulfuric acid in the cell are the two major reactions. Thus, as the electrowinning proceeds, the cell becomes more acidic. The free acid concentration of the cell keeps on increasing. Beyond certain value, it has negative impact main on the specific energy consumption and partly on the current efficiency. Rate of increase in the cell voltage as the electrowinning proceeds is relatively high when the free acid concentration in the electrolyte is high. This increase in cell voltage with electrowinning duration also limits the cycle time. Hence, maintaining the free acid concentration below certain value helps to control the increase in the voltage, thereby increasing cycle time.
[0057] In some embodiments, free acid concentration of the MnSO4 leach liquor prior to the electrowinning ranges about 10 g/L to about 25 g/L, preferably about 15 g/L to about 20 g/L.
[0058] In a non-limiting embodiment, free acid concentration of the MnSO4 leach liquor prior to the electrowinning is maintained at about 10 g/L, about 12 g/L, about 14 g/L, about 16 g/L, about 18 g/L, about 20 g/L, about 22 g/L, about 24 g/L or about 25 g/L.
[0059] In some embodiments, free acid concentration of the MnSO4 leach liquor is maintained at less than about 20 g/L, preferably less than about 5 g/L during the electrowinning.
[0060] In a non-limiting embodiment, free acid concentration of the MnSO4 leach liquor is maintained at about 1 g/L, about 2 g/L, about 3 g/L, about 4 g/L, about 5 g/L, about 6 g/L, about 7 g/L, about 8 g/L, about 9 g/L, about 10 g/L, about 11 g/L, about 12 g/L, about 13 g/L, about 14 g/L, about 15 g/L, about 16 g/L, about 17 g/L, about 18 g/L, about 19 g/L, or about 20 g/L during the electrowinning.
[0061] In some embodiments, the MnSO4 leach liquor subjected to the electrowinning has Mn concentration ranging from about 50 g/L to about 80 g/L, preferably about 50 g/L to about 60 g/L.
[0062] In a non-limiting embodiment, the MnSO4 leach liquor subjected to the electrowinning has Mn concentration of about 50 g/L, about 55 g/L, about 60 g/L, about 65 g/L, about 70 g/L, about 75 g/L or about 80 g/L.
[0063] In some embodiments, the electrowinning is performed using titanium anode and graphite cathode.
[0064] In some embodiments, the electrowinning is performed using a titanium anode and 2 graphite cathodes.
[0065] In some embodiments, the distance between the anode and the cathode is about 3cm to about 4.5cm. Said distance is maintained between the anode and each cathode.
[0066] In a non-limiting embodiment, the distance between the anode and the cathode is about 3cm, about 3.1cm, about 3.2cm, about 3.3cm, about 3.4cm, about 3.5cm, about 3.6cm, about 3.7 cm, about 3.8 cm, about 3.9cm, about 4cm, about 4.1cm, about 4.2cm, about 4.3cm, about 4.4cm or about 4.5cm.
[0067] Without intending to be limited by theory, in some embodiments, as the anode to cathode distance (ACD) increases, the resistance arising from the ion flow in the electrolyte also increases. Hence, it is beneficial to operate the cell at lower anode to cathode distance. However, the ACD should not be too low. Operating a cell at a very low ACD limits the cycle time. This is because, as the electrowinning proceeds the deposit thickness increases. Higher is the cycle time, thicker will be the final deposit. If the distance between anode-cathode is small, there is a possibility of anode and cathode touching each other, leading to shorting of the cell. Thus, it is beneficial to maintain ACD in the range of about 3cm to about 4.5cm.
[0068] In some embodiments, the electrowinning is performed at a current density ranging from about 80 A/m2 to about 140 A/m2.
[0069] In a non-limiting embodiment, the electrowinning is performed at a current density ranging of about 80 A/m2, about 85 A/m2, about 90 A/m2, about 95A/m2, about 100 A/m2, about 105 A/m2, about 110 A/m2, about 115 A/m2, about 120 A/m2, about 125 A/m2, about 130 A/m2, about 135 A/m2 or about 140 A/m2.
[0070] EMD layer conductivity is improved at higher temperatures. Therefore, it is preferred, in some embodiments, to conduct the electrowinning at elevated temperatures. In some embodiments, temperature of the MnSO4 leach liquor employed for the electrowinning ranges from about 80°C to about 95°C.
[0071] In a non-limiting embodiment, temperature of the MnSO4 leach liquor employed for the electrowinning is about 80°C, about 82°C, about 84°C, about 86°C, about 88°C, about 90°C, about 92°C, about 94°C or about 95°C. In some embodiments, electrowinning above 95°C may be challenging due to the boiling of aqueous electrolyte leading to evaporation of water in the electrolyte. Similarly, if the electrolyte temperature drops below 80°C, the efficiency of the cell may have a tendency to reduce while the specific power may simultaneously increase. This is due to the semiconductive nature of the EMD wherein, during electrowinning at low electrolyte temperatures the EMD layer on the anode acts as resistor thereby increasing the cell voltage leading to raise in the specific energy consumption. Apart from that, it also impacts cycle time of the electrowinning step. This is due to the side reactions that occur in the cell at increased cell voltages thereby making the bath unstable. In some embodiments, conducting the electrowinning at room temperature leads to electrolyte instability and a dirty bath leading to halt of electrowinning.
[0072] In exemplary embodiments, since higher current density and lower specific consumption is essential for the economical operation of an electrowinning cell a temperature of about 90 °C is employed for the electrowinning of EMD.
[0073] In some embodiments, feed flow rate of the MnSO4 leach liquor into the electrowinning cell ranges from about 5 g/L to about 15 g/L.
[0074] In a non-limiting embodiment, the feed flow rate is adjusted depending upon the feed Mn concentration. In some embodiments, as feed Mn concentration increases, feed flow rate is reduced.
[0075] In some embodiments, feed flow rate of the MnSO4 leach liquor into the electrowinning cell is about 5 g/L, about 6 g/L, about 7 g/L, about 8 g/L, about 9 g/L, about 10 g/L, about 11 g/L, about 12 g/L, about 13 g/L, about 14 g/L or about 15 g/L.
[0076] In some embodiments, the electrowinning is characterized by one or more of current density ranging from about 80 A/m2 to about 140 A/m2, temperature of the MnSO4 leach liquor ranging from about 80°C to about 95°C, and/or feed flow rate of the MnSO4 leach liquor into the electrowinning cell ranging from about 5 g/L to about 15 g/L.
[0077] In some embodiments, the electrowinning is performed for about 8 hours to about 96 hours.
[0078] In exemplary embodiments, the electrowinning is performed for about 24 hours to about 96 hours.
[0079] In further preferred embodiments, the electrowinning is performed for about 74 hours to about 96 hours.
[0080] In a non-limiting embodiment, the electrowinning is performed for about 8 hours, about 12 hours, about 18 hours, about 24 hours, about 30 hours, about 36 hours, about 42 hours, about 48 hours, about 54 hours, about 60 hours, about 66 hours, about 72 hours, about 78 hours, about 84 hours, about 90 hours or about 96 hours.
[0081] In some embodiments, the EMD is deposited on the anode in the electrowinning cell.
[0082] In a non-limiting embodiment, the EMD deposit from the anode is stripped to obtain the EMD.
[0083] In some embodiments, the stripped EMD is then washed to yield the final product. In some embodiments, pH of the stripped and washed EMD is adjusted to near-neutral or neutral pH.
[0084] In some embodiments, the washing is performed in water. In a non-limiting embodiment, the stripped EMD is washed alternatingly in hot water and by cold water, preferably hot water followed by cold water and final pH of the EMD is adjusted to about 6 to about 7. In another non-limiting embodiment, the pH adjustment is achieved by washing the washed EMD in sodium hydroxide (NaOH) and/or ammonia (NH3) solution.
[0085] In some embodiments, the EMD produced by the method of the present disclosure has purity ranging from about 91% to about 94%.
[0086] In a non-limiting embodiment, the EMD produced by the method of the present disclosure has a purity of about 91%, about 92%, about 93% or about 94%.
[0087] In a non-limiting embodiment, the EMD is battery grade EMD.
[0088] In some embodiments, the method has current efficiency ranging from about 75% to about 99.5%.
[0089] In exemplary embodiments, the method has current efficiency ranging from about 91% to about 98%.
[0090] In some embodiments, the method has current efficiency of about 75%, about 80%, about 85%, about 90%, about 94%, about 99% or about 99.5%.
[0091] In some embodiments, the method has specific energy consumption ranging from about 1.2 kWh/kg to about 2.5 kWh/kg.
[0092] In exemplary embodiments, the method has specific energy consumption ranging from about 1.2kWh/kg to about 1.5 kWh/kg.
[0093] In some embodiments, the method has specific energy consumption of about 1.2 kWh/kg, about 1.3kWh/kg, about 1.4kWh/kg, about 1.5kWh/kg, about 1.6kWh/kg, about 1.7kWh/kg, about 1.8kWh/kg, about 1.9kWh/kg, about 2kWh/kg, about 2.1kWh/kg, about 2.2kWh/kg, about 2.3kWh/kg, about 2.4kWh/kg or about 2.5 kWh/kg.
[0094] Overall, the process of the present disclosure provides an efficient method for effective utilization of low-grade ferruginous manganese ore resources to obtain higher grade EMD. Without being bound by theory, said process may have obvious variants such as but not limited to utilization of different quality manganese ore, employment of different leaching processes or different purification processes for the leach liquor, use of upgraded electrowinning equipment and different post processing steps for the obtained EMD. Taken together, the method of the present disclosure provides multiple advantages such as:
- Efficient utilization of low-grade ferruginous manganese ore resources to obtain higher grade EMD;
- Addressal of issues associated with the storage and utilization of low-grade ores;
- Identification of parameters that can influence the commercial viability of the process and thereby help in better selection of the operating parameters;
- High energy efficiency of the method; and
- Scalability of the method.
[0095] In an embodiment, the foregoing descriptive matter is illustrative of the disclosure and not a limitation. Providing working examples for all possible combinations of optional elements in the composition and process parameters is considered redundant.
[0096] 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.
EXAMPLES:
EXAMPLE 1: Characterization of starting material
[0097] Low grade ferruginous manganese ore comprising less than about 30% Mn and more than about 20% Fe was used as starting material to produce MnSO4 leach liquor. Table 1 shows the chemical analysis of the Mn ore used to generate the leach liquor.
Table. 1. Chemical analysis of ferruginous manganese ore
Component Mn Fe(T) SiO2 Al2O3 K2O MgO S CaO LOI Na2O
Mn ore 27.25 22.42 13.56 6.82 1.11 0.1 0.007 0.076 9.85 0.021
[0098] Leaching was performed by taking about 25%-40% of the ore in distilled water, which was subjected to intimate mixing to keep the mass in suspension. SO2 gas at a flow rate of about 0.014 lpm/gm Mn was purged into the reactor for about 2 hours. After the leaching, the MnSO4 leach liquor and the undissolved residue were separated.
[0099] The pregnant leach solution was subjected to purification. Initially iron, aluminum and copper present in the solution were precipitated as respective hydroxides by addition of high purity Mn oxide ore to the leach liquor till the slurry pH was raised to about 5.5. Said solution was stirred for about 3 hours at constant pH and then filtered. The filtrate was then subjected to sulphide precipitation by addition of about 0.01-0.02% of solution weight of sodium sulphide for removal of heavy metals present in the solution. During this step pH was maintained at about 6.75 for about 2 hours at room temperature and the slurry was filtered to obtain the electrolyte for electrowinning.
Table 2. As is and purified MnSO4 leach liquor chemical analysis
Element Cu Zn Fe Al Ni Co Mn Cd
Before purification (ppm) 5.18 21.11 30.52 ND 13.04 26.99 86538.46 0.73
After purification (ppm) 0.98 3.33 2.88 ND 7.55 11.26 86057.69 0.45

[00100] Purified MnSO4 leach liquor with the composition shown in Table 2 was used as a precursor for the EMD electrowinning.
[00101] Sulphuric acid (H2SO4) was added to the purified MnSO4 leach liquor to change its pH to about 6 prior to its use as electrolyte for EMD electrowinning. The purified MnSO4 leach liquor was diluted to an Mn concentration of about 50 g/L and temperature of the purified MnSO4 leach liquor was adjusted to about 90°C. Electrowinning was carried out in an electrowinning cell containing a titanium (Ti) anode placed between two graphite cathodes, maintaining an anode to cathode distance (ACD) of about 3 cm. As the electrowinning proceeded, fresh feed was provided to the cell at a feed flow rate of about 11 ml/min and at the same time, spent electrolyte was taken out of the cell.
[00102] After performing electrowinning for about 72 hours, EMD was found to be deposited on the anode. The EMD was stripped from the anode. The stripped EMD was washed in hot water followed by cold water. The EMD was then washed in dilute NaOH to adjust the final pH to about 6-7.
[00103] The above experiment was repeated to analyze the effect of the current density, electrolyte temperature, initial electrolyte pH in the cell and free acid concentration of the cell on the current efficiency and specific energy consumption of the method.
EXAMPLE 2: Analyzing the effect of current density during electrowinning
[00104] Purified MnSO4 generated through SO2 leaching as described in Example 1 was used as electrolyte. Electrowinning was carried out using Ti anode and graphite cathode. Electrolyte temperature of about 80°C, ACD of about 3 cm, initial electrolyte pH of about 6 and a feed Mn concentration and flow rate combination of about 80 g/L and about 8 g/L, respectively were employed for electrowinning. Electrowinning was carried out for about 8 hours.
[00105] Two sets of experiments were performed wherein the electrowinning was conducted at the above-mentioned parameters, one at a current density of about 90 A/m2, and the other at a current density of about 120 A/m2.
[00106] Figure 1 shows the effect of current density on the current efficiency and specific power consumption. A current efficiency of about 85.67% and specific energy consumption of about 1.43 kWh/ kg was realized when the current density was maintained at about 90 A/m2. A current efficiency of about 77.14% and specific energy consumption of about 2.34 kWh/ kg was realized when the current density was maintained at about 120 A/m2. Therefore, with an increase in the current density from 90A/m2 to 120A/m2 there was a reduction in the current efficiency and an increase in the specific energy consumption.
EXAMPLE 3: Analyzing the effect of feed temperature during electrowinning
[00107] Purified MnSO4 generated through SO2 leaching as described in Example 1 was used as electrolyte. Electrowinning was carried out using Ti anode and graphite cathode. ACD of about 3 cm, initial electrolyte pH of about 6 and a feed Mn concentration and flow rate combination of about 80 g/L and about 8 g/L, respectively were employed for electrowinning. Electrowinning was carried out for about 8 hours.
[00108] The effect of electrolyte temperature was studied at two different electrolyte temperatures, 80°C and 90°C under the above-mentioned parameters of electrowinning. Figure 2 shows the variation in the current efficiency and specific power consumption with respect to change in the eletrolyte temperature. With increase in electrolyte temperature there was an increase the current efficiancy while the specific power consumption decreased. This is due to the semiconductive nature of EMD wherein conductivity raises with temperature.
EXAMPLE 4: Analyzing the effect of anode to cathode distance during electrowinning
[00109] Purified MnSO4 generated through SO2 leaching as described in Example 1 was used as electrolyte. Electrowinning was carried out using Ti anode and graphite cathode. Electrolyte temperature of about 80°C, current density of about 90 A/m2, initial electrolyte pH of about 6 and a feed Mn concentration & flow rate combination of about 80 g/L and about 8 g/L, respectively were employed for electrowinning. Electrowinning was carried out for about 8 hours.
[00110] Two sets of experiments were performed wherein the electrowinning was conducted at the above-mentioned parameters, one at maintaining ACD at about 3cm, and the other maintaining ACD at about 4.5cm.
[00111] Figure 3 shows the effect of ACD on the current efficiency and specific power consumption. A current efficiency of about 93.27% and specific energy consumption of about 1.38 kWh/ kg was realized when the ACD was maintained at about 3cm. A current efficiency of about 89.84% and specific energy consumption of about 1.75 kWh/ kg was realized when the ACD was maintained at about 4.5 cm. Therefore, with an increase in the ACD from about 3cm to about 4.5cm there was a reduction in the current efficiency and an increase in the specific energy consumption.
EXAMPLE 5: Analyzing the effect of feed pH during electrowinning
[00112] Purified MnSO4 generated through SO2 leaching as described in Example 1 was used as electrolyte. Electrowinning was carried out using Ti anode and graphite cathode. Electrolyte temperature of about 90°C, ACD of about 3cm, current density of about 90 A/m2, and a feed Mn concentration & flow rate combination of about 80 g/L and about 8 g/L, respectively were employed for electrowinning.
[00113] Two sets of experiments were performed wherein the electrowinning was conducted using electrolytes having pH of about 0.5 and 6.
[00114] Electrowinning using the initial electrolyte pH of about 6 was carried out for about 40 hours continuously during which the cell voltage reached as high as about 3.9V by the end of 40 hours. Beyond 40 hours, the voltage started to fall mainly due to the shorting effect of the electrodes caused by the EMD flakes. Hence the test was terminated after 40 hours. Electrowinning using the electrolyte with an initial electrolyte pH of about 0.5 was carried out for about 24 hours. Even after a prolonged electrowinning duration of 40 hours the current efficiency of the cell was relatively better than the 24 hours electrowinning carried out at an initial electrolyte pH of 6. The specific power consumption in the latter case, however, was much higher than that of the former mainly due to the higher cell voltage.
[00115] When electrowinning was carried out using the electrolyte with an initial pH of about 0.5, a relatively higher cell voltage of about 2.35V was observed just after the starting of the electrowinning process. By the end of about 24 hours of electrowinning, the free acid concentration increased to about 37.26 g/L and at the same time the electrowinning cell voltage increased to about 5.52V. Electrowinning could not be continued beyond about 24 hours due to the significant rise in cell voltage which further contributed to the increase in specific energy consumption. Figure 5 depicts variation in cell voltage & free acid concentration of electrolyte with respect to electrowinning time at initial electrolyte pH of 6 (left) and initial electrolyte pH of 0.5 (right). Hence, on comparing the results of the electrowinning using the electrolyte that has initial pH of about 6 and about 0.5, it was understood that the initial free acid concentration has a significant effect on the cell voltage which further affects the specific energy consumption. Figure 4 depicts the effect of the initial electrolyte pH on current efficiency and specific energy consumption.
EXAMPLE 6: Analyzing the effect of free acid content in the feed during electrowinning
[00116] In continuation to Example 5, an additional experiment was carried out to study the effect of free acid concentration on the cell voltage.
[00117] Purified MnSO4 generated through SO2 leaching as described in Example 1 was used as electrolyte. Electrowinning was carried out using Ti anode and graphite cathode. Electrowinning was carried out for about 24 hours under conditions of a feed Mn concentration of about 50 g/L, initial free acid concentration in the feed of about 15 g/L, feed flow rate of about 11 g/L, ACD of about 3 cm, current density of about 90 A/m2 and an electrolyte temperature of about 90°C. Initial pH of the electrolyte was about 6. Electrowinning was carried out for 24 hours duration.
[00118] In the first experiment, free acid concentration in the electrolyte was maintained at about 15 g/L to about 20 g/L during the electrowinning by adding dilute ammonium hydroxide solution. Under these conditions, a current efficiency of about 93% and specific energy consumption of about 1.4 kWh/ kg was realized. Figure 6 shows the effect of maintaining free acid concentration fixed at about 15 g/L to about 20 g/L during the electrowinning on the current efficiency and specific energy consumption.
[00119] In a subsequent experiment, keeping other parameters constant, free acid concentration in the electrolyte was maintained at about 1.4 g/L during the electrowinning by adding dilute ammonium hydroxide solution. Under these conditions, a current efficiency of about 99% and specific energy consumption of about 1.25 kWh/ kg was realized. The EMD produced was found to have a purity of about 91.9%. Table 3 provides chemical analysis of the EMD deposit obtained at the conditions employed in this experiment.
Table 3: Chemical analysis of the EMD deposit
MnO2 Cu Zn Fe Al Cd Pb Co Ni SiO2
Weight % 91.9 0.017 0.003 0.007 ND 0.001 0.005 ND ND ND

[00120] It was therefore observed from the above experiments that free acid concentration had a significant effect on the current efficiency and specific energy consumption. However, even though the free acid concentration had a significant effect on the specific energy consumption, current efficiency, and the deposit purity, it was found to have no effect on the effect on the structure of the deposit. Figure 7 shows the XRD of the deposit produced with and without any control over the free acid concentration. In both the deposits, apart from the gamma phase no other phases could be observed. Thus, EMD with a purity of about 91.9% and gamma crystal structure was produced by using the MnSO4 generated through SO2 leaching of low-grade ferruginous manganese ores.
EXAMPLE 7: Analyzing the effect of the anode material on the efficiency of electrowinning
[00121] Example 1 was repeated using lead anode and graphite cathode.
[00122] The electrowinning led to formation of a white precipitate on the anode within about 5-10 minutes of operation, which was found to be lead sulphate (Figure 8). This led to a continuous rise in the voltage of the cell and darkening of the electrolyte. The white precipitate was eventually found to inhibit the MnO2 electrowinning process and thus, no MnO2 deposit was formed on the anode under such circumstances. Thus, change of the anode material had a detrimental impact on the process.