Claims:We Claim:
1. A method (100) to determine optimum specific SO2 required for a leaching process (200) of sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn>90%, the process (200) comprising:
pulverizing low-grade ferruginous Mn ore (Mn 17 – 27%) to obtain pulverized ore of predetermined size of 150 microns;
mixing the said pulverized ore with water in at least one reactor to obtain a reaction slurry to maintain a desired pulp density which will be in the range of 25-40%;
stirring the reaction slurry at least 400 RPM speed and simultaneously purging SO2 gas at a flow rate of 0.01-0.02 LPM per gram Mn in leach slurry to obtain a mixture of Mn leach liquor and leach residue.
filtering the mixture of Mn leach liquor and leach residue to separate Mn leach liquor;
purifying the Mn leach liquor to obtain purified filtrate, wherein the purifying is carried out by sequentially adding H2O2 having concentration 0.2-0. 3% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 - 6.5 followed by filtering, and Na2S of concentration 0.01-0.02% w/v followed by filtering to obtain purified filtrate; and
processing the said purified filtrate to produce various Mn derivatives product which have Mn in the range of 32-99.9%;
wherein the method (100) comprises:
conducting a number of experimental runs of said process (200) each using a selected distinct set of values for said process parameters;
measuring values of the Mn% in the obtained product; and
determining the optimum specific SO2 required to obtain the product having Mn>90%.
2. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the stirring and purging is carried out for 60 - 90 minutes.
3. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 2, wherein the optimum specific SO2 requirement was determined to be 0.014 LPM per gram Mn in the leach slurry to treat the sub grade manganese ore (Mn: 17% - 27%) with >90% Mn recovery at 25% pulp density and 60 minutes leaching duration, wherein at the optimum specific SO2 requirement value the utilization efficiency of the SO2 during leaching process (200) is maximized.
4. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the more than one leaching reactor is used to ensure near 100% SO2 utilization in recovering Mn from the ore.
5. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the vacuum pressure filter was used to separate the leach liquor and residue.
6. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the reaction slurry is stirred at speeds ranging from 400-1000 RPM.
7. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the SO2 gas used for purging is can be pure SO2 gas or a mixture of SO2 gas + N2 gas.
8. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the product can be any one of manganese derivatives including MnSO4, MnCO3, pure Mn metal (EMM) and pure Mn oxides including MnO2 (EMD), Mn2O3, Mn3O4 and MnO.
9. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 4, wherein the at least one reactor includes a first reactor, and a second reactor connected in series with the first reactor, wherein the reaction slurry is prepared in both the first reactor and the second reactor.
10. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 4, wherein a third reactor is connected in series with the first two leaching reactors to scrub the SO2 going out of them, wherein the third reactor is filled with Na2CO3 solution.
11. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the purifying is carried out by sequentially adding H2O2 having concentration 0.2% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 followed by filtering, and Na2S of concentration 0.015-0.02% w/v by filtering to obtain purified filtrate.
12. The method (100) to determine optimum specific SO2 required for the leaching process (200) as claimed in the claim 1, wherein the product having Mn is electrolytic manganese dioxide with purity >90%.

Dated this 10th day of March 2022

Signature:
Name: Sridhar R
To, Of K&S Partners, Bangalore
The Controller of Patents Agent for the Applicant
The Patent Office, at Kolkata IN/PA-2598
, Description:FIELD OF INVENTION
[0001] The present invention relates to a method to determine optimum specific SO2 requirement to improve SO2 utilization efficiency during leaching process of sub grade manganese ore, and more particularly, to the method to determine optimum specific SO2 required during SO2 leaching process of sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn>90%, and to improve SO2 utilization efficiency.

BACKGROUND
[0002] Over the past few decades, manganese (Mn) in both pure form and alloy form (for e.g., silicomanganese (SiMn), ferromanganese (FeMn)) have played a very important role in the steel manufacturing. Apart from the pure Mn metal, SiMn and FeMn alloys which are mainly used in 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 industries such as fertilizer, food, pharma, and battery etc. The starting material to produce different derivatives of Mn is high grade Mn ore. However, the worldwide availability of high-grade ores is limited. Further in countries such as India Mn ores have iron impurities in the form of hematite and goethite.
[0003] Due to the increased mining for prolonged periods, high-grade ores got depleted simultaneously generating huge amounts of low-grade ores and other waste overburden. Utilization of these low-grade ores is crucial to meet the increased demand for various manganese derivates and, also from the sustainability perspective. Currently they are not being fully utilized as there is no commercially viable process either for their upgradation or direct use. Upgradation through beneficiation route is challenging due to the similar mineralogical characteristics of Mn and Fe oxides. However, upgradation of ferruginous manganese ores with Mn>30% can achieved through roasting and magnetic separation process. But the same can’t be used for processing the ore ores with Mn<30% as the process turns out to be non-economical. Reduction roasting-magnetic separation process is cost intensive process.
[0004] In this regard, hydrometallurgical process like leaching can be effective in treating the low-grade ferruginous Mn ores with Mn<30%. Mn is in its +4-oxidation state in manganese dioxide which can’t be dissolvable in aqueous solutions. Hence, to enable dissolution of Mn ores in aqueous solutions it needs to be reduced to +2 state. This can be achieved either through the roasting of ore prior to its leaching or by employing a reductant directly during its leaching. The former approach is commercially non-viable due to the higher cost of roasting whereas, the later approach results in simultaneous recovery of Fe along with Mn in case if the reducing agent used is non-selective towards Mn recovery. Higher selectivity towards Mn recovery over the Fe is an important factor to consider while selecting the reducing agents for the leaching of manganiferrous iron ores. Reducing agents that selectively leaches Mn eliminates the additional purification step required for iron removal from the leach liquor hence play a significant role in deciding the commercial viability of the process.
[0005] Reductive leaching of Mn ores using SO2 gas bubbling is well reported in the literature. In ores with iron as major impurity, SO2 selectively recovers Mn into the leach liquor leaving behind the iron oxide as is. Also, the kinetics of MnO2 dissolution by using SO2 gas are very fast. Some of the prior art on the leaching of Mn ores with Sulphur dioxide gas are disclosed in US20050103163A1, CN1161936A, JPH02248327A.
[0006] Developing a process that makes use of the manganiferrous iron ores to completely convert it into MnSO4 and iron rich residue without generating any waste could be beneficial from the perspective of value generation from waste and the environmental pollution.
OBJECTIVE OF INVENTION
[0007] It is an object of the invention to solve the aforementioned problems of the prior art and to provide a SO2 leaching process with specific attention to the use of sub grade and low-grade Mn ores to generate MnSO4.
[0008] Another objective of the present invention is to optimize the leaching process parameters that corresponds to maximum SO2 utilization efficiency and Mn recovery.
[0009] Another objective of the present invention is objective of this invention is to purify the MnSO4 leach liquor and carry out its electrolysis to produce electrolytic manganese dioxide (EMD).
SUMMARY OF INVENTION
[0010] This summary is provided to introduce concepts related to a method to determine optimum SO2 required during leaching process to recover Mn metal from a sub grade manganese ore and to improve the SO2 efficiency. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0011] In one aspect of the present invention, a method to determine optimum specific SO2 required for a leaching process of sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn>90% is provided. The process comprising pulverizing low-grade ferruginous Mn ore (Mn 17 – 27%) to obtain pulverized ore of predetermined size of 150 microns. The process also comprises mixing the said pulverized ore with water in at least one reactor to obtain a reaction slurry to maintain a desired pulp density which will be in the range of 25-40%. The process further comprises stirring the reaction slurry at least 400 RPM speed and simultaneously purging SO2 gas at a flow rate in the range of 0.1 LPM - 0.3 LPM into the reaction slurry to obtain a mixture of leach residue and Mn leach liquor. The process comprises filtering the mixture of Mn leach liquor and leach residue to separate Mn leach liquor. The process further comprises purifying the Mn leach liquor to obtain purified filtrate, wherein the purifying is carried out by sequentially adding H2O2 having concentration 0.2-0. 3% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 - 6.5 followed by filtering, and Na2S of concentration 0.01-0.02% w/v followed by filtering to obtain purified filtrate. The process also comprises processing the said purified filtrate to produce various Mn derivatives which have Mn in the range of 32-99.9%. The method comprises conducting a number of experimental runs of said process each using a selected distinct set of values for said process parameters. The method also comprises measuring values of the Mn% in the obtained product. The method further comprises determining the optimum specific SO2 required to obtain the product having Mn>90%.
[0012] In an embodiment, the stirring and purging is carried out for 60 - 90 minutes.
[0013] In an embodiment, the optimum specific SO2 requirement was determined to be 0.014 LPM per gram Mn in the leach slurry to treat the sub grade manganese ore (Mn: 17% - 27%) with >90% Mn recovery at 25% pulp density and 60 minutes leaching duration.
[0014] In an embodiment, more than one leaching reactor is used to ensure near 100% SO2 utilization in recovering Mn from the ore.
[0015] In an embodiment, the vacuum pressure filter was used to separate the leach liquor and residue.
[0016] In an embodiment, the reaction slurry is stirred at speeds ranging from 400-1000 RPM.
[0017] In an embodiment, the SO2 gas used for purging is can be pure SO2 gas or a mixture of SO2 gas + N2 gas.
[0018] In an embodiment, the product can be any one of manganese derivatives including MnSO4, MnCO3, pure Mn metal (EMM) and pure Mn oxides including MnO2 (EMD), Mn2O3, Mn3O4 and MnO.
[0019] In an embodiment, the at least one reactor includes a first reactor, and a second reactor connected in series with the first reactor, wherein the reaction slurry is prepared in both the first reactor and the second reactor.
[0020] In an embodiment, a third reactor is connected in series with the second reactor, wherein the third reactor is filled with Na2CO3 solution.
[0021] In an embodiment, the purifying is carried out by sequentially adding H2O2 having concentration 0.2% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 followed by filtering, and Na2S of concentration 0.015-0.02% w/v by filtering to obtain purified filtrate.
[0022] In an embodiment, the product having Mn is electrolytic manganese dioxide with purity >90%.
[0023] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 is a flowchart which illustrates a leaching process of sub grade manganese ore, according to an embodiment of the present invention.
[0025] Figure 2 is a flowchart which illustrates a method to determine optimum specific SO2 required for the leaching process of sub grade manganese ore
[0026] Figure 3 illustrates an X-Ray diffractogram of sub grade Mn ore, according to embodiment of the present invention.
[0027] Figure 4 illustrates a SEM- Elemental mapping of sub grade Mn ore showing distribution of Mn and Fe oxides, according to an embodiment of the present invention.
[0028] Figure 5 illustrates Chemical analysis of various particles of sub grade Mn ore, according to an embodiment of the present invention.
[0029] Figure 6 illustrates a graph depicting the effect of SO2 flow rate on manganese and iron recovery, according to an embodiment of the present invention.
[0030] Figure 7 illustrates a graph depicting the effect of leaching duration on manganese and iron recovery, according to an embodiment of the present invention.
[0031] Figure 8 illustrates a graph depicting the effect of leaching duration at different SO2 flow rates and pulp density on the leach slurry temperature, according to an embodiment of the present invention.
[0032] Figure 9 illustrates an XRD of EMD, according to an embodiment of the present invention.
[0033] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.

DETAILED DESCRIPTION
[0034] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0035] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0037] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0038] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0039] Referring to Figure 1, an exemplary process (200) for leaching a sub grade manganese ore (Mn: 17% - 27%) is provided. The process (200) for leaching of the sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn (32%-99.9%) begins at step (202). At step (202), the process (200) comprises pulverizing low-grade ferruginous Mn ore (Mn 17 – 27%) (as received from the mines are used as fines) to obtain pulverized ore of predetermined size of 150 microns. In preferred embodiment, the sub grade manganese ore (Mn: 17% - 27%) is a sub-grade ferruginous Mn ore with 17.1% Manganese. In another embodiment, the sub grade manganese ore (Mn: 17% - 27%) is a low-grade ferruginous Mn ore with 26.29% Manganese.
[0040] At step (204), the process (100) comprises mixing the said pulverized ore with water in at least one reactor to obtain a reaction slurry to maintain a desired pulp density in the range of 25-40%. In the preferred embodiment, more than one leaching reactor is used to ensure near 100% SO2 utilization in recovering Mn from the ore. In one example, the at least one reactor includes a first reactor, and a second reactor connected in series with the first reactor. The reaction slurry is prepared in both the first reactor and the second reactor. A third reactor is connected in series with the first two leaching reactors to scrub the SO2 going out of them. In an example, the third reactor is filled with Na2CO3 solution.
[0041] At step (206), the process (200) comprises stirring the reaction slurry at 400 - 1000 RPM speed and simultaneously purging SO2 gas at a flow rate calculated at 0.01-0.02 LPM per gram Mn in leach slurry. In the preferred embodiment, the stirring and purging is carried out for 60 - 90 minutes. The SO2 gas used for purging can be pure SO2 gas or a mixture of SO2 gas + N2 gas.
[0042] At step (208), the process (200) comprises filtering the mixture of Mn leach liquor and leach residue to separate Mn leach liquor. In the preferred embodiment, the vacuum pressure filter was used to separate the leach liquor and leach residue.
[0043] At step (210), the process (200) comprises purifying the Mn leach liquor to obtain purified filtrate, wherein the purifying is carried out by sequentially adding H2O2 having concentration 0.2-0. 3% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 - 6.5 followed by filtering, and Na2S of concentration 0.01-0.02% w/v followed by filtering to obtain purified filtrate. In preferred example, the purifying is carried out by sequentially adding H2O2 having concentration 0.2% (v/v), hydrated lime to maintain the pH of the Mn leach liquor at 6.0 followed by filtering, and Na2S of concentration 0.015-0.02% w/v by filtering to obtain purified filtrate.
[0044] At step (212), the process (200) comprises processing the said purified filtrate to produce various Mn derivatives which have Mn in the range of 32-99.9%. The product can be any one of manganese derivatives including MnSO4, MnCO3, pure Mn metal (EMM) and pure Mn oxides including MnO2 (EMD), Mn2O3, Mn3O4 and MnO. In an example, the product derived is MnSO4 and electrolysis of purified MnSO4 leach liquor lead to electrolytic manganese dioxide with 88% purity. The EMD produced is used in alkaline battery applications. The battery made of produced EMD has a current efficiency of 89.1%, voltage of 2.2V, and specific energy consumption of 1.56 kWh/Kg MnO2 realized.
[0045] Referring to Figure 2, an exemplary method (100) to determine the optimum specific SO2 required for the leaching process (200) of sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn>90% is depicted. At step (102), the method (100) comprises conducting a number of experimental runs of said process (200) each using a selected distinct set of values for said process parameters.
[0046] At step (104), the method (100) comprises measuring values of the Mn% in the obtained product. At step (106), the method (100) comprises determining the optimum specific SO2 required to obtain the product having Mn>90%.
[0047] From the above method (100) and the process (200), the optimum specific SO2 was determined to be 0.014 LPM per gram Mn in the leach slurry to treat the sub grade manganese ore (Mn: 17% - 27%) with >90% Mn recovery at 25% pulp density and 60 minutes leaching duration.
[0048] Experiments:
[0049] The chemical analysis of the pulverized ores which may be used are shown in Table 1 below:

Table 1: Chemical composition of sub grade and low-grade ferruginous Mn ore
[0050] For purposes of experiments only sub grade Mn ore available in its as is from the ore was used.
[0051] Referring to Figure 3, XRD results of the sub grade ferruginous Mn Ore are illustrated. Referring to Figure 4, SEM analysis of the sub grade ferruginous Mn ore is illustrated. Ore in the as received condition was used for scanning electron microscope analysis. Figure 4 shows mapping results for different elements in the ores and Iron and manganese oxides are the major phases in the ore. No interlocking between the iron and manganese oxides was observed and they exist in the ore as separate phases. Mapping results of the ore also reveals the presence of silica and alumina and their particle size is relatively small compared to the Fe and Mn oxides. They are present in the ore as aggregate of small particles and, also surrounding the Mn and Fe oxides. A simple washing of ore can take out the Alumina and silica present on the surface of ore particles.
[0052] Point EDS analysis of different particles of the rock as shown in Figure 5 is mentioned in Table-2. These results are also in agreement with the chemical analysis, XRD and mapping results. Fe and Mn in the ore exists as oxides and, as separate particles. Pure white particle in the Figure 4 corresponds to manganese dioxide whereas the light grey particles are iron oxide particles. The grey colored aggregate with small white particles inside are the aggregate of silica, alumina, and other gangue oxides.
Element/ wt.% Mn Fe O Si Al
1 76.28 22.92 0.8
2 77.73 22.27
3 70.03 25.07 2.56 2.35
4 74.75 23.46 1.8
5 77.45 22.55
6 5.65 72.06 22.29
7 75.12 23.31 1.57
8 42.93 34.64 22.43
9 75.24 23.19 0.92 0.65
10 5.04 63.3 25.63 2.66 3.37
11 72.43 5.04 22.54
12 73.41 23.86 1.6 1.13
13 77.73 22.27
14 77.45 22.55
15 72.1 4 22.14
16 3.25 71.57 23.34 0.98 0.87
Table 2: Point EDS analysis for points corresponding to Figure 5
[0053] Thus, the characterization results for the manganiferrous iron ore indicate that the rock mainly contains 17.16% Mn as MnO2, 41.17% Fe(T) as Fe2O3. Both the iron and manganese oxide phases exist as separate phases.
[0054] Leaching experiments were carried out by varying SO2 gas flow rate, pulp density, stirring speed and leaching time. Leaching results indicated that, SO2 is highly selective towards dissolution Manganese alone. Due to that, the residue remaining after leaching was found to contain iron enriched to as high as about 57%. From the results, it was observed that the SO2 gas flow rate and leaching time have significant effect on %Mn recovered from the ore.
[0055] The effect of variation in SO2 flow rate on the manganese and iron recovery is shown in Figure 6. It can be observed from the results that with increasing the SO2 flow rate from 0.1 to 0.3 LPM, there is an improvement in both the manganese and iron recovery. The manganese recovery values increased from 53.5% at 0.1 l/min SO2 flow rate to 93.2% at 0.3 LPM. About 40% improvement in the %Mn recovered indicates the significant influence of SO2 flow rate on the Mn recovery. At the same time, the relative improvement in the average %Fe recovered was about 10%. At the highest SO2 flow rate of 0.3 LPM, the %Fe recovered was only 13.1% while 93.2% of the Mn present in the ore was recovered. This proves the selectivity of SO2 towards leaching of Mn over the Fe.
[0056] Effect of leaching time on the manganese and iron recovered from the ore is shown in Figure 7. It is observed from the Figure 7 that with the increase in the leaching duration the manganese recovered from the ore enhanced from 62.2% to 86% with an increase in the leaching time from 20 to 80 min. It is also observed that beyond 60 min., the duration of leaching has a negligible effect on the manganese recovery. On the contrary, the average iron recovery started to reduce from about 20% to 8% as the leaching duration increases. Reason for the same can be attributed to the reduction in iron content to the oxidative hydrolysis of the soluble Fe2+ complex, Fe (HSO3)2.
[0057] Based on the leaching results obtained, optimum conditions to treat the subgrade Mn ore with about 17% Mn are 0.3 LPM SO2, 60 min. leaching duration, 25% pulp density, and 800 RPM stirring speed. Leaching under these optimized conditions has resulted in 97.9% Mn recovery and the leftover residue has Fe enriched to 53%. Thus, under these optimized conditions the specific SO2 requirement is calculated to be 0.014 LPM per gram Mn in slurry. The derived specific SO2 requirement value can be used to calculate the optimum SO2 flow rate required to treat a different grade of Mn ore with Mn as low as 17% under the condition of 25% pulp density and 60 minutes leaching with Mn recovery efficiency as high as 97%.
[0058] To validate the calculated specific SO2 requirement value, a low-grade ferruginous Mn ore with 26.2% Mn was chosen. Based on its Mn content, for a 25% pulp density SO2 flow rate required to treat the ore in 60 minutes duration was calculated to 0.45 LPM SO2. Leaching under these conditions resulted in 94.1% Mn recovery. Hence, the specific SO2 requirement value of 0.014 LPM per gram Mn in slurry can be used to calculate the SO2 flow rate required to process the ore at a chosen pulp density in 60 minutes leaching duration and with a Mn recovery>90%.
[0059] Even at the optimum SO2 flow rate calculated using the derived specific SO2 requirement, 100% SO2 utilization in recovering the Mn could not be achieved. Figure 8 shows the effect of leaching time on leach slurry temperature at different SO2 pulp density and pulp density combinations. It can be observed that the slurry temperature raises as the leaching proceeds which is due to the exothermic nature of SO2 and MnO2 reaction. Thus, during the SO2 leaching of Mn ore the slurry temperature raises which is associated with the decrease in the SO2 solubility in the leach slurry. This leads to efficiency loss through SO2 loss to scrubber and thus jeopardizing the scalability of the process.
[0060] In this regard, placing an additional reactor in series next to the leaching reactor can help not only to make use of the leaked SO2 from leaching reactor but also to treat additional Manganese ore in the additional reactor. A third reactor in series to the first two could help in scrubbing the SO2 that leaves the additional reactor. Owing to the higher reactivity of SO2 towards Na2CO3, aqueous Na2CO3 solution was used in the third reactor. At the SO2 flow rate calculated using the specific SO2 requirement to treat low grade ferruginous ore with 26.2% Mn, it was observed that pH of the sodium carbonate solution in the scrubber was changed from 9.93 to 9.71 indicating the leakage of SO2 from the leaching reactor to the scrubber. However, the change in the pH was insignificant (decrease of 0.03) when an additional leaching reactor containing Mn ore at 10% pulp density was placed between the first leaching reactor and the scrubber. This indicates that no SO2 is going to the scrubber and thus the SO2 purged was almost completely utilized in the leaching of the ore.
[0061] The SO2 coming out of the leaching reactor was consumed in the additional leaching reactor where an additional 42% of the Mn in the ore (5% pulp density) present second reactor was recovered.
[0062] The leach liquor obtained after leaching using sub grade Mn ore was purified to take out the impurities. Purification involves addition of H2O2 followed by the addition of hydrated lime till a pH of 6-6.5 is achieved. The former step helps to improve the iron removal efficiency whereas the later step involves removal of Fe and Al as hydroxide precipitates. After that, the last step involves addition of Na2S to the partially purified liquor to take out heavy metal impurities as sulphide precipitates. All these purification steps were carried out at room temperature under mild stirring conditions. The impurity free MnSO4 liquor which was at a pH of about 6.5 was used as a starting material to produce electrolytic manganese dioxide.
[0063] As there was no replenishment of electrolyte during the electrowinning, to maintain sufficiently high Mn concentration purified leach liquor obtained through processing of sub grade ore and containing with 55 g/l Mn was used as electrolyte. Distilled water was added to the electrolysis cell at regular intervals to make up for the electrolyte losses associated with vapors formation. After completion of electrowinning, the MnO2 deposit from the anode was collected, washed (using water followed by NaOH), dried and pulverized. As per the Indian standard IS11153:1996 (Reaffirmed in 2003), for the EMD to be suitable for use in alkaline battery applications it should meet the specification as per Indian standard IS11153:1996 (Reaffirmed in 2003) apart from having ? structure. Chemical analysis of EMD produced in comparison to the standard is given in Table 3.
Species Weight (%) as per Indian Standard IS11153:1996 (Reaffirmed in 2003) EMD produced in current work
MnO2 =90 88.01
Fe = 0.1 0.021
Cu = 0.002 0.0004
Ni = 0.003 0.0006
Ti = 0.003 0.008
Sulphate as SO4 = 1.5 2.91
Table 3: Chemical analysis of EMD produced using MnSO4 from sub grade ores
[0064] XRD of the produced EMD is shown in Figure 9 which indicates that the MnO2 in the EMD has ? structure. Crystal structure of EMD is closely related to the ß, ? and e MnO2. Among them ? form of EMD is relatively more active chemically and electrochemically due to which it is preferred for use in battery applications.
[0065] Examples
Example-1
[0066] Pulverized sub grade Mn ore with 17.1 wt.% Mn was used as starting material for leaching. To maintain a pulp density of 10% (w/w), 50 grams of ore was added to 450 grams of water. SO2 flow rate of 0.25 litres per minute was used. A stirring speed of 1000 rpm was used. Leaching was carried out for 60 minutes. After leaching, the mother leach liquor and undissolved residue was separated. The undissolved residue mainly contains iron (Fe[T]- 54.12), silica- 5.57 and alumina-4.82. Iron in the residue was enriched to 54.12% compared to that of 41.17% present in the ore. 13.94% of the iron in the ore leached into the solution. Under the tested conditions, a Manganese leaching efficiency of 98.13% was observed.
Example-2
[0067] Pulverized sub grade Mn ore with 17.1 wt.% Mn was used as starting material for leaching. To maintain a pulp density of 20% (w/w), 100 grams of ore was added to 400 grams of water. SO2 flow rate of 0.1 liters per minute was used. A stirring speed of 800 rpm was used. Leaching was carried out for 60 minutes. After leaching, the mother leach liquor and undissolved residue was separated. The undissolved residue contains iron (Fe[T]- 46.73%), silica- 4.25% and alumina-5%. Apart from them, leach residue also contains 8.52% Mn indicating the incomplete dissolution of MnO2 present in the ore. Only 56.4% of the Mn present in the ore got leached into the solution.
Example-4
[0068] Pulverized sub grade Mn ore with 17.1 wt.% Mn was used as starting material in leaching. A SO2 flow rate of 0.3LPM, 25% pulp density, 60 minutes leaching, and 800 RPM was used. After the leaching, the undissolved leach residue contains 53% Fe(T) and a Mn leaching efficiency of 97.9% was realized. Under these optimized conditions, the specific SO2 requirement was calculated to be 0.014 LPM per gram Mn present in the leach slurry.
Example-5
[0069] Pulverized low grade ore with 26.2 wt.% Mn was used as starting material for leaching. The specific SO2 requirement derived in example-4 was used to calculate the optimum SO2 flow rate required to treat the low-grade ore at 25% PD and in 60 minutes leaching duration. The SO2 flow rate was calculated to be 0.45 LPM. Under this condition, a Mn recovery of 94.1% was realized and the leach residue was found to contain 55.3% Fe. Also, as observed from the change in the pH of Na2CO3 solution in the scrubber from 9.93 to 9.71 it was understood that a small fraction of SO2 being purged is going out of leaching reactor to the scrubber.
Example-6
[0070] Pulverized low grade ore with 26.2 wt.% Mn was used as starting material for leaching. The specific SO2 requirement derived in example-4 was used to calculate the optimum SO2 flow rate required to treat the low-grade ore at 25% PD and in 60 minutes leaching duration. The SO2 flow rate was calculated to be 0.45 LPM. To utilize the SO2 leaving the leaching reactor to scrubber (as highlighted in example 5) an additional reactor was placed between the leaching reactor and scrubber. It contains the low-grade ore at 5% PD. Leaching results indicated that, apart from the 94% Mn recovery in leaching reactor, a 42% Mn recovery was realized in the additional reactor. It was also observed that the change in the pH of Na2CO3 solution in the scrubber is insignificant (decrease by 0.03) indicating the near 100% use of SO2 in recovering Mn from the ore.
Example-7
[0071] Purified leach liquor obtained under the conditions mentioned in example-4 was used as electrolyte to produce electrolytic manganese dioxide. Two graphite cathodes and one titanium anode were used as electrodes. Electrowinning was carried out in the electrolyte maintained at 90 °C throughout the 4 h. electrowinning duration. A total current of 1A was applied to the anode with surface area of 135 cm2 i.e., a current density of 7.4 mA/cm2. Based on the weight of the deposit current efficiency was calculated to be 89.1%. The voltage of the electrowinning cell was 2.2V which was almost constant during the 4 hours electrowinning. By using the deposit weight, cell voltage and current, specific energy of the cell was calculated to be 1.56 kWh/Kg MnO2. EMD produced has a purity of 88% and with ? structure.
[0072] The present invention relates to the method (100) to determine optimum specific SO2 required for a leaching process (200) of sub grade manganese ore (Mn: 17% - 27%) to obtain a product having Mn>90%. The determined optimum specific SO2 requirement can be used to extrapolate the requirement of SO2 flow rate to treat any for other grades of manganese ore with 17-27% Mn. The method (100) also optimizes the leaching process parameters that corresponds to maximum SO2 utilization efficiency and Mn recovery. Thus, the developed method (100) not only helps process any low-grade ferruginous Mn ore with Mn (17-27%) but also with near 100% SO2 utilization and Mn recovery.
[0073] Furthermore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0074] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0075] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.