Hydrometallurgical Production of Electrolytic Manganese Dioxide (EMD) from Furnace Fines

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Article Hydrometallurgical Production of Electrolytic Manganese Dioxide (EMD) from Furnace Fines

Mehmet Ali Recai Önal 1,*, Lopamudra Panda 2, Prasad Kopparthi 3, Veerendra Singh 3, Prakash Venkatesan 4 and Chenna Rao Borra 5

1 InsPyro N.V. Kapeldreef 60, 3001 Leuven, Belgium 2 Research & Development Group, Tata Steel Ltd., Kalinga Nagar 755026, India; [email protected] 3 Research and Development Division, Tata Steel Ltd., Jamshedpur 831001, India; [email protected] (P.K.); [email protected] (V.S.) 4 Department of Materials Engineering, Synthesis and Recycling (4MAT), Université Libre de Bruxelles, 50 Avenue FD Roosevelt, CP165/63, 1050 Brussels, Belgium; [email protected] 5 Department of Metallurgical and Materials Engineering, Indian Institute of Technology–Kharagpur, Kharagpur 721302, India; [email protected] * Correspondence: [email protected]; Tel.: +32-466-23-23-39

Abstract: The ferromanganese (FeMn) alloy is produced through the smelting-reduction of manganese ores in submerged arc furnaces. This process generates large amounts of furnace dust that is environmentally problematic for storage. Due to its ﬁneness and high volatile content, this furnace

dust cannot be recirculated through the process, either. Conventional MnO2 production requires the pre-reduction of low-grade ores at around 900 ◦C to convert the manganese oxides present in the ore into their respective acid-soluble forms; however, the furnace dust is a partly reduced by-product. In this study, a hydrometallurgical route is proposed to valorize the waste dust for the production of battery-grade MnO2. By using dextrin, a cheap organic reductant, the direct Citation: Önal, M.A.R.; Panda, L.; and complete dissolution of the manganese in the furnace dust is possible without any need for Kopparthi, P.; Singh, V.; Venkatesan, high-temperature pre-reduction. The leachate is then puriﬁed through pH adjustment followed by P.; Borra, C.R. Hydrometallurgical direct electrowinning for electrolytic manganese dioxide (EMD) production. An overall manganese Production of Electrolytic Manganese recovery rate of >90% is achieved. Dioxide (EMD) from Furnace Fines. Minerals 2021, 11, 712. https:// Keywords: manganese ore; furnace dust; leaching; dextrin; manganese dioxide; electrolytic man- doi.org/10.3390/min11070712 ganese dioxide (EMD)

Academic Editor: Jean-François Blais

Received: 13 May 2021 Accepted: 25 June 2021 1. Introduction Published: 1 July 2021 Manganese is an important raw material for steelmaking, batteries, fertilizers, catalysts, pigments, and non-ferrous alloys [1]. Manganese is the third most common constituent Publisher’s Note: MDPI stays neutral of steel, which is used as both a deoxidizer and an alloying agent. Typically, 7–10 kg of with regard to jurisdictional claims in manganese-based ferroalloys (FeMn alloys) are required per ton of steel production [2]. published maps and institutional afﬁl- Steelmaking, including its iron-making component, consumed more than 90% of mined iations. manganese ores in 2013 [3]. Manganese dioxide (MnO2) occurs in nature as the mineral pyrolusite, which is about 62–63% manganese. The most important use of MnO2 is in primary Leclanché (carbon–zinc) and alkaline batteries. This material is used in obtaining the spinel structure of the cathode Copyright: © 2021 by the authors. materials to be used in rechargeable Li-ion batteries (e.g., LiMn2O4)[4–6]. MnO2 needed Licensee MDPI, Basel, Switzerland. for the production of batteries must have high purity and high electrochemical activity. This article is an open access article Among its several allotropic forms, electrochemical activity is the highest for γ-MnO2. distributed under the terms and Hence, it is the best material for battery applications [7]. conditions of the Creative Commons Since the early 2000s, the steady growth in demand for manganese dioxides has Attribution (CC BY) license (https:// come from primary and secondary battery industries [8,9]. Three groups of manganese creativecommons.org/licenses/by/ dioxides are being used in energy storage devices—namely natural (NMD), chemical 4.0/).

Minerals 2021, 11, 712. https://doi.org/10.3390/min11070712 https://www.mdpi.com/journal/minerals Minerals 2021, 11, 712 2 of 14

(CMD), and electrolytic (EMD) manganese dioxide. The first type has been used in standard or Leclanché cells, whereas modern batteries, such as alkaline and lithium batteries, require the two synthetic forms with improved properties. In terms of alkaline batteries, the use of EMD within the industry has exceeded 230,000 metric tons per annum, with a growth rate of about 10% annually [7]. With increasing global demand for batteries, the annual growth rate is expected to rise in the future. An additional increase in the demand for EMD is expected from the secondary, or rechargeable, battery market. This is mainly because lithium manganese ion batteries that use EMD in their manufacturing are replacing cobalt-type batteries as the cheaper and greener alternative. Manganese is being considered as a potential replacement for cobalt in the cathode material of lithium-ion batteries since it can increase safety and reduce cost, and it is environmentally more benign [10]. Growth is also likely to come from the use of EMD in hybrid electric vehicles [11]. It is possible to use a manganese ore to directly manufacture batteries so long as it meets specific characteristics and composition. This type of manganese dioxide is known as natural manganese dioxide, or NMD [12]. However, the demand for this material cannot be fulfilled through fresh ore only. The minimum and maximum concentrations for an ore suitable for Leclanché battery production is roughly 75–85 wt.% for MnO2 with 3–5 wt.% H2O, 0.5–5 wt.% SiO2, 0.2–0.3 wt.% Fe, and 0.1–0.2 wt.% for other metal oxides [13]. However, in alkaline, lithium, and other modern batteries, synthetic manganese dioxide with improved purity and quality becomes a must; therefore, it is necessary to produce it through chemical (CMD) or electrochemical (EMD) processes. Conventionally, synthetic manganese dioxide is mainly produced from pyrolusite (MnO2) or rhodochrosite (MnCO3) ores. Pyrolusite ore has to be reduced before leaching, or it can be directly leached through a reductive leaching process [14]. After leaching and filtration, the leach liquor contains a variety of impurities, such as alkali metals, iron, nickel, and so on. Most of the iron present in the solution is removed through goethite precipitation by increasing the pH of the leachate to 2–3 with the addition of lime. Potassium and the rest of the iron are removed through further lime addition to maintain a pH level between 4–6 (i.e., jarosite precipitation). Mn does not precipitate until pH > 7 [15]. Ni, Cu, Mo, and other impurities that do not precipitate like Mn are removed through sulfide precipitation by adding Na2S or B2S[7]. After these purification steps, the manganese sulfate solution is forwarded to the electrochemical (for EMD) or chemical (for CMD) production step. The electrolysis process is more advantageous, as it produces MnO2 with better properties, regenerates acid, uses a smaller number of reagents, and generates fewer residues that may be harmful to the environment [7,12,16–18]. In EMD production, a purified leach solution containing around 150 g of MnSO4/L is used. Cell reactions are given in Equations (1)–(3) [19]. The voltammogram of EMD production exhibits an anodic current peak at about 1.3 V vs. SCE (MnO2 deposition), while a cathodic peak appears at 0.8 V vs. SCE. at anode: 2+ + - Mn + 2H2O = MnO2 + 4H + 2e (1) at cathode: + - 2H + 2e = H2 (2) overall: 2+ + Mn + 2H2O = MnO2 + 2H + H2 (3) Furnace dust is a problematic by-product of the ferromanganese (FeMn) and silicomanganese (SiMn) industries. Its storage is a long-term environmental concern, as it requires efficient technologies for its recycling [19]. The furnace dust contains high concentrations of manganese oxides, with up to 40% or more concentrate [20]. The recycling of the dust back into the ferroalloy furnaces would not only reduce that environmental liability but also decrease the fresh ore consumption. Unfortunately, this is not possible due to the high volatile content of furnace dust, along with its fineness. Many manganese ores contain substantial amounts of potassium (up to 2–3%). Much of this volatilizes and reports to Minerals 2021, 11, 712 3 of 14

the fume during the smelting operation [20]. The concern regarding the recycling of the fume is that volatile transition metals, such as zinc, can build up due to repeated recycling. One of Elkem’s submerged arc furnaces producing high carbon FeMn alloy had a severe eruption on December 9, 1992, due to an accumulation of volatiles which caused unstable structure formations in the furnace [21]. There is limited literature on the topic of recycling FeMn or SiMn furnace fines for manganese recovery, particularly through hydrometallurgical treatments. Nkosi et al. (2011) obtained a 49% Mn recovery rate from SiMn submerged arc furnace dust through direct atmospheric leaching using a diluted sulfuric acid solution [22]. de Arujo et al. (2006) studied the replacement of rhodochrosite ore by ferromanganese fines for the production of EMD [19]. The fines were directly digested in high concentrations of sulfuric acid, and the resultant solution was purified through pH adjustment first using NH3 (for iron removal) and then using a Na2S addition (for heavy metal removal). However, the study is mostly focused on the electrodeposition behavior of the purified digestion solution, with very little insight into the previous steps. Shen et al. (2007) and Hamano et al. (2008) proposed recycling routes for different dust samples generated by FeMn and SiMn production [23,24]. However, both studies only focus on the recovery of zinc that constitutes ≤1.5% of the dust. In this study, an alternative hydrometallurgical process is proposed for the utilization of FeMn furnace dust in the production of high purity electrolytic manganese dioxide (EMD). An experimental comparison is made between direct reductive leaching of the fines, using a novel, cheap, and green organic, and direct acid leaching. It should be noted that, unlike the ores, the furnace dust is already in fine sizes, thus rendering the costly particle size reduction steps unnecessary. Its use to replace rhodochrosite (MnCO3) and pyrolusite (MnO2) for EMD production has other advantages too. The concentrations of some undesirable impurities, such as Ni, Cu, and Mo, are smaller in the furnace dust than they are in the rhodochrosite ore. Although K and Na contents are significantly higher in the furnace dust, these elements do not affect the manganese dioxide electrodeposition. Furthermore, such fines do not generate CO2, which is formed through the reaction of carbonate present in the rhodochrosite ore. In comparison to the pyrolusite ore, the furnace dust is already partially reduced during its formation. This means direct reductive leaching of the furnace dust is more beneficial, as less of the reductant will be needed than is needed for the ore. Compared to their inorganic counterparts, organic reductants are more preferable due to their environmentally friendly nature. Soluble organic compounds are the most suitable, compared to insoluble organic compounds, due to their faster reactivity. Sugar and glucose were found to be the most promising reductants [25]. However, in this study, dextrin—a water-soluble, organic reductant—is investigated as the cheaper organic alternative over sugar or glucose. The produced leachate is then purified conventionally, and the subsequent solution is used for conventional EMD production.

2. Materials and Methods The furnace dust used in this study was obtained from the Ferro Alloy Plant (FAP) of Tata Steel in Joda, India. The entire sample was collected over a period of time in order to have an average chemical composition and phase distribution that might have varied by short-term differentiations in the furnace input materials. After sieved to −1 mm size, the entire sample was mixed thoroughly before preparing a representative sample. A part of the representative sample was taken for analyses using a coning and quartering technique. Chemical grade sulfuric acid, dextrin, and slaked lime (Ca(OH)2) were used in the present study. A particle size analysis was carried out with the help of the wet sieving method. The chemical analysis of the samples was performed using a Spectro Analytical Instruments, Ciros model, inductively coupled plasma-optical emission spectrometer (ICP-OES) (SPEC- TRO Analytical Instruments Inc., Clive, Germany). The mineral phases of the samples were Minerals 2021, 11, 712 4 of 14

identiﬁed using a Panalytical X’pert Pro X-ray diffractometer (XRD) (Malvern Panalytical Ltd., Malvern, UK). The experimental parameters for XRD analysis were: 20–90 2-theta de- gree; radiation of CuKα; acceleration voltage of 40 kV; acceleration current of 30 mA; with a step size of 0.020 degrees. The phases present in the samples were also examined using a JEOL (Tokyo, Japan), an 840A model scanning electron microscope (SEM), equipped with an energy-dispersive X-ray detector (EDX).

2.1. Leaching Experiments Leaching was performed in a conical flask on a magnetic stirrer that was fixed at 200 rpm throughout the study. 10 g of the dust sample was used in each experiment with a fixed solid: liquid ratio of 1:5 wt./vol. The acid amount was varied between 1M (8%) and 3M (24%). The dust sample was slowly added to the acidic solution with or without a reductive agent. The slow addition was due to the vigorous nature of the exothermic leaching reaction amplified by the fine particle size of the dust. To avoid material and heat loss, the flask was covered with aluminum foil or a watch glass throughout the leaching duration. The studied parameters and their ranges are summarized in Table1.

Table 1. Experimental parameters used in this study.

Acid Concentration Dextrin Amount Solid: Liquid Ratio Parameter Temperature (◦C) Time (min) (%) (wt.% of dust) (wt./vol) Range 30–90 15–240 8–24 2–10 1:5 (ﬁxed)

After the leaching duration was completed, the solution was allowed to cool down. The sludge was rather gelatinous and hard to filter, possibly due to the presence of or- thosilicic acid. The cooled solution was treated with lime addition to ease the filtration, which also helped neutralize the excess acid and remove the impurities. The lime-treated solution, with a pH of around 6, was quickly filtered with a funnel and filter paper. Since Mn precipitation does not occur up to pH 7–8, the loss of Mn to precipitation was minimal and was included in the overall Mn recovery rate [15]. The residue was washed 5 to 6 times to remove all the soluble manganese compounds. This final solution was used for electrolysis experiments.

2.2. Electrolysis Experiments The electrolysis experiments were carried out in a cell consisting of a 250 mL beaker on top of a heating plate, two counter electrodes, one anode, a thermometer, and a DC power supply. Graphite was used for both electrodes. The cathode dimensions were 5 cm length, 1 cm width, and 0.1 cm thickness. The anode dimensions were 5 cm length, 2 cm width, and 0.1 cm thickness. The electrolyte was prepared from purified leach solution and sulfuric acid. The solution temperature was maintained at 92 ◦C(±2 ◦C). The volume of the electrolyte was maintained through water addition during the experiment. The anode and counter electrodes were partially submerged in the electrolyte in order to maintain anode to cathode surface ratio of 2:1. After closing the cell, the synthesis of MnO2 was carried out with the help of a DC power supply. No external stirring was needed, as the hydrogen gas generated during the process created sufficient stirring in the solution. Electrolysis was carried out at different current densities and acid concentrations to op- timize the current efficiency. Different current densities (i.e., 0.5, 1, 1.5, 2, and 2.5 amp/dm2) were used with 0.5 mol of MnSO4 and 0.25 mol of acid-containing electrolytes. In the other set of experiments, different H2SO4 concentrations (from 0.05 to 0.45 M, with 0.1 intervals) were used. In all experiments, the electrolysis duration was fixed to 1 h. The weight of MnO2 deposited on the anode was noted after each experiment. Minerals 2021, 11, x FOR PEER REVIEW 5 of 14

Minerals 2021, 11, x FOR PEER REVIEW 5 of 14 0.1 intervals) were used. In all experiments, the electrolysis duration was fixed to 1 h. The weight of MnO2 deposited on the anode was noted after each experiment. 0.1 intervals) were used. In all experiments, the electrolysis duration was fixed to 1 h. The 3.weight Results of MnOand Discussions2 deposited on the anode was noted after each experiment. 3.1. Characterization of Furnace dust 3. Results and Discussions The chemical analysis of the furnace dust used in the present study is provided in Table3.1. Characterization 2, and shows of that Furnace the majordust constituents of the sample are Mn- and Si-based compounds.The The chemical XRD analysispattern ofof thethe furnacefurnace dustdust usedin Figure in the 1 presentshows threestudy mainis provided compounds— in Minerals 2021, 11, 712 5 of 14 namely,Table 2, andhausmannite shows that (Mn the major3O4), manganositeconstituents of (MnO), the sample and are silica Mn- (SiO and2 ).Si-based The SEM com- micro- graphpounds. of Thethe XRDfurnace pattern dust of sample the furnace in Figure dust in 2 Figure shows 1 thatshows most three of main the furnacecompounds— dust is less than3.namely, Results 10 microns. andhausmannite Discussions The spot(Mn3 Oand4), manganositearea analysis (MnO), indicated and thesilica presence (SiO2). Theof alkali SEM metals,micro- such 3.1.graph Characterization of the furnace of Furnace dust Dust sample in Figure 2 shows that most of the furnace dust is less as sodium, potassium, and barium. thanThe 10chemical microns. analysis The spot of the and furnace area dust analysis used inindicated the present the study presence is provided of alkali in metals, such Tableas sodium,2A, andcumulative shows potassium, that theparticle majorand barium. constituents size analysis of the sampleof the are sample Mn- and using Si-based the com- wet sieving method showedpounds.A Thecumulative that XRD >90% pattern ofparticle of the the furnacesample size analysis dust was in Figureless of than1the shows sample 37 three microns, mainusing compounds— andthe wetD80 ofsieving the sample method was 32 microns.namely, hausmannite This shows (Mn3O that4), manganosite the furnace (MnO), dust and silicasample (SiO2 ).was The SEMsuch micrograph a fine material that further ofshowed the furnace that dust >90% sample of the in Figuresample2 shows was less that mostthan of37 the microns, furnace dustand isD less80 of than the sample was 32 grinding10microns. microns. wouldThis The spotshows be and simply that area analysisthe redundant. furnace indicated dust the sa presencemple was of alkali such metals, a fine such material as that further sodium,grinding potassium, would andbe simply barium. redundant. Table 2. Chemical analysis of the furnace dust. Table 2. Chemical analysis of the furnace dust. Table 2. Chemical analysis of the furnace dust. Mn Fe(total) Al2O3 CaO MgO SiO2 Mn Fe(total) Al2O3 CaO MgO SiO2 Mn Fe(total) Al2O3 CaO MgO SiO2 wt.% 42.742.7 3.40 3.40 4.20 2.85 4.20 3.60 2.85 9.00 3.60 9.00 wt.% 42.7 3.40 4.20 2.85 3.60 9.00

FigureFigureFigure 1. 1.1.XRD XRD pattern patternpattern of the of of furnace the the furnace furnace dust (Quartz: dust dust (Quartz: JCPDS (Quartz: 46-1045, JCPDS JCPDS Hausmannite: 46-1045, 46-1045, Hausmannite: JCPDS Hausmannite: 24-0734, JCPDS JCPDS 24-0734, 24-0734, andand Manganosite: Manganosite: JCPDS JCPDS 72-1533). 72-1533). and Manganosite: JCPDS 72-1533).

FigureFigure 2. 2.SEM SEM micrograph micrograph of the of furnace the furnace dust sample dust (numbers sample indicate (numbers the position indicate of eachthe position of each spot/areaspot/area analysis). analysis). Figure 2. SEM micrograph of the furnace dust sample (numbers indicate the position of each spot/area analysis).

Minerals 2021, 11, x FOR PEER REVIEW 6 of 14

3.2. Leaching Experiments Without Reductant Addition (Direct Acid Leaching) In the first part of the experiments, leaching was conducted without a reductant, at different leaching temperatures and acid concentrations, for a 1 h duration. The obtained results are provided in Figure 3a. The Mn dissolution rate increases to about 50% when the acid concentration is increased to 12%; however, it becomes stagnant thereafter, with a <10% increase at the highest acid concentration studied (20%). Meanwhile, manganese dissolution slightly increases with an increase in the leaching temperature. This may be due to the faster reaction of Mn with acid. The initial drastic increase in the Mn dissolution rate is due to an increase in the availability of sulfuric acid. However, at higher acid concentrations, there is barely any soluble manganese form left. In all experiments, the Mn dissolution rate is less than 60%. This is due to the presence of Mn3O4 and MnO2 in the furnace dust sample. The Mn3O4 reaction with sulfuric acid is provided in Equation (4). From this reaction, it can be concluded that two parts of Mn3O4 present in the dust sample are soluble, and one part is insoluble. This Minerals 2021, 11, 712 6 of 14 is because the MnO2 present in the dust is completely insoluble in the sulfuric acid solution. This explains why the overall Mn recovery is less than 60%. A cumulative particle size analysis of the sample using the wet sieving method showed 3 4 2 4 4 2 2 that >90% of the sample was lessMn thanO 37 + microns,2H SO and = 2MnSO D80 of the sample+ MnO was+ 322H microns.O (4) This shows that the furnace dust sample was such a ﬁne material that further grinding wouldThe be simplyeffect redundant.of leaching duration on Mn dissolution was studied at different time inter-

vals3.2. from Leaching 15 Experiments to 60 min, Without a 12% Reductant acid concentration, Addition (Direct Acid and Leaching) a 30°C leaching temperature. Figure 3b showsIn the that, ﬁrst part after of the the experiments, first half leachingan hour, was the conducted dissolution without rate a reductant, of Mn atreaches a maximum ofdifferent about leaching48% and temperatures becomes and stable acid concentrations, despite the for very a 1 h duration.fine particle The obtained size of the sample that improvesresults are providedthe leaching in Figure kinetics.3a. The Mn The dissolution optimized rate increases conditions to about for 50% direct when leaching are then the acid concentration is increased to 12%; however, it becomes stagnant thereafter, with founda <10% at increase a 30°C at theleaching highest acid temperature, concentration a studied 12% (20%).acid concentration, Meanwhile, manganese and a 30 min leaching duration.dissolution slightly increases with an increase in the leaching temperature. This may be due to the faster reaction of Mn with acid.

Figure 3. (a) The effect of leaching temperature and acid concentration on Mn leaching, and (b) the Figureeffect of 3. time (a) on The leaching effect at of 30 ◦leachingC with a 12% temperature acid concentration. and acid concentration on Mn leaching, and (b) the effect of time on leaching at 30 °C with a 12% acid concentration. The initial drastic increase in the Mn dissolution rate is due to an increase in the availability of sulfuric acid. However, at higher acid concentrations, there is barely any solubleThe manganese XRD analysis form left. of Inthe all residue experiments, is provided the Mn dissolution in Figure rate 4. isOnly less than the silica and gypsum phases60%. This are is clearly due to the detectable. presence of MnThe3O 4calciumand MnO 2oxinide the furnacepresent dust in sample.the sample The reacted with the Mn O reaction with sulfuric acid is provided in Equation (4). From this reaction, it can be sulfuric3 4 acid to create insoluble gypsum. There is no clear indication of any Mn-based concluded that two parts of Mn3O4 present in the dust sample are soluble, and one part is insoluble. This is because the MnO2 present in the dust is completely insoluble in the sulfuric acid solution. This explains why the overall Mn recovery is less than 60%.

Mn3O4 + 2H2SO4 = 2MnSO4 + MnO2 + 2H2O (4) Minerals 2021, 11, 712 7 of 14

The effect of leaching duration on Mn dissolution was studied at different time intervals from 15 to 60 min, a 12% acid concentration, and a 30 ◦C leaching temperature. Figure3b shows that, after the first half an hour, the dissolution rate of Mn reaches a maximum of about 48% and becomes stable despite the very fine particle size of the sample that improves the leaching kinetics. The optimized conditions for direct leaching are then found at a 30 ◦C leaching temperature, a 12% acid concentration, and a 30 min leaching duration. Minerals 2021, 11, x FOR PEER REVIEW 7 of 14 The XRD analysis of the residue is provided in Figure4. Only the silica and gypsum phases are clearly detectable. The calcium oxide present in the sample reacted with the sulfuric acid to create insoluble gypsum. There is no clear indication of any Mn-based compoundscompounds (e.g.,(e.g., MnOMnO22)) inin thethe XRDXRD pattern.pattern. However,However, thethe freshfresh andand acid-insolubleacid-insoluble MnO MnO22 producedproduced throughthrough thethe partialpartial dissolutiondissolution ofof Mn Mn33OO44 duringduring leachingleaching cancan stillstill bebe presentpresent inin thethe residue.residue. Synthetic Synthetic MnO MnO2 typically2 typically has has low-intensity low-intensity and and broad broad characteristic characteristic peaks peaks [15]. Along[15]. Along with thewith fineness the fineness of the of furnace the furnace dust thatdust promotes that promotes the background the background noise, noise, it is very it is likelyvery likely that thethat amorphous the amorphous and weakand weak peaks peaks of MnO of MnO2 that2 that partly partly coincide coincide with with those those of gypsumof gypsum are are dwarfed dwarfed by by the the stronger stronger peaks peaks of theof the two two crystalline crystalline phases. phases.

FigureFigure 4.4. XRDXRD resultresult ofof the residue generatedgenerated after leaching without a reductant (Gypsum: JCPDS JCPDS 74-143374-1433 andand Quartz:Quartz: JCPDSJCPDS 39-1425).39-1425).

3.3.3.3. LeachingLeaching withwith ReductantReductant AdditionAddition (Direct(Direct ReductiveReductive Leaching)Leaching) ThroughThrough directdirect acidacid leachingleaching experiments,experiments, itit waswas foundfound thatthat maximummaximum recoveryrecovery ofof thethe manganesemanganese isis lessless thanthan 60%60% withoutwithout anyany additionaddition ofof aa reductant.reductant. ThisThis isis mostmost likelylikely duedue toto thethe involvementinvolvement of of MnO MnO2,2 which, which can can only only be be effectively effectively dissolved dissolved in sulfuricin sulfuric acid acid in ain reducing a reducing atmosphere. atmosphere. In the In secondthe second part ofpart the of leaching the leaching experiments, experiments, dextrin dextrin was added was asadded the reductant. as the reductant. The amount The ofamount dextrin of required dextrin for required the complete for the reduction complete of reduction manganese of dioxidemanganese was dioxide calculated was according calculated to according the reaction to the in Equationreaction in (5). Equation Around (5). 50% Around of the 50% Mn presentof the Mn in thepresent dust in sample the dust is soluble sample in is acidsolu withoutble in acid any without reductant. any Hence,reductant. the Hence, other half the requiresother half a reductant.requires a Then,reductant. the stoichiometric Then, the stoichiometric need for dextrin need wasfor dextrin calculated was as calculated 0.05 g/g ofas dust0.05 g/g (or of 5% dust dextrin). (or 5% However, dextrin). However, for the initial for the studies, initial 50% studies, excess 50% or excess 0.08 g/g or 0.08 of dust g/g (or 8% dextrin) was used to ensure sufﬁcient dextrin presence. It should be noted that the of dust (or 8% dextrin) was used to ensure sufficient dextrin presence. It should be noted reduction of MnO2 by dextrin (or the oxidation of dextrin by MnO2) is most likely not a that the reduction of MnO2 by dextrin (or the oxidation of dextrin by MnO2) is most likely single-step reaction. Previous studies showed that the acid leaching of the pyrolusite ore not a single-step reaction. Previous studies showed that the acid leaching of the pyrolusite (MnO2) in the presence of carbohydrates, such as glucose (C6H12O6), lactose (C12H22O11), ore (MnO2) in the presence of carbohydrates, such as glucose (C6H12O6), lactose and sucrose (C12H24O11), results in intermediate reactions that provide intermediate degra- (C12H22O11), and sucrose (C12H24O11), results in intermediate reactions that provide intermediate degradation products, such as HCOOH and HCHO [25–27]. Based on this information, it is very likely that the same is valid for the case of dextrin, another carbohydrate.

12MnO2 + C6H10O5 + 12H2SO4 = 12MnSO4 + 17H2O + 6CO2 (5)

Figure 5a shows the effect of the leaching temperature and acid concentration on Mn dissolution in the presence of dextrin. To ensure that the amount of acid is sufficient in the case of a possible complete Mn dissolution, these experiments were conducted at more than 12% acid concentration. The results show that, with an increase in the leaching temperature, Mn dissolution increases; however, the temperature effect is more prominent at higher acid concentrations. The manganese dissolution rate is the highest for all acid concentrations studied when the leaching temperature is increased to 90 °C. This is possibly due to the increase in the reaction rate between dextrin and MnO2 Leaching efficiency also

Minerals 2021, 11, 712 8 of 14

dation products, such as HCOOH and HCHO [25–27]. Based on this information, it is very likely that the same is valid for the case of dextrin, another carbohydrate.

12MnO + C H O + 12H SO = 12MnSO + 17H O + 6CO (5) Minerals 2021, 11, x FOR PEER REVIEW 2 6 10 5 2 4 4 2 2 8 of 14

Figure5a shows the effect of the leaching temperature and acid concentration on Mn dissolution in the presence of dextrin. To ensure that the amount of acid is sufficient in the case of a possible complete Mn dissolution, these experiments were conducted at more than increases12% acid concentration. with increasing The results showacid that, concentration. with an increase in theAt leaching low acid temperature, concentrations, this may be Mn dissolution increases; however, the temperature effect is more prominent at higher acid causedconcentrations. by the The unavailability manganese dissolution of the rate free is the highestacid that for all is acid consumed concentrations by both the direct and re- ductivestudied when leaching the leaching of manganese. temperature is increasedWith the to 90addition◦C. This is of possibly more due acid, to the this problem should have increase in the reaction rate between dextrin and MnO2 Leaching efficiency also increases beenwith increasingeliminated acid concentration.since, at 90 At°C low, the acid dissolution concentrations, of this Mn may almost be caused reaches by completion with 20% acidthe unavailability concentration of the and free acidis not that affected is consumed by by higher both the acid direct levels. and reductive Since acid concentrations of leaching of manganese. With the addition of more acid, this problem should have been >20%eliminated will since, only at 90consume◦C, the dissolution high amounts of Mn almost of reaches the neutralizing completion with 20%agent acid in the subsequent purifi- cationconcentration step, and the is notoptimum affected by conditions higher acid levels. for Since leaching acid concentrations become ofa >20%90 °C leaching temperature andwill onlya 20% consume acid high concentration. amounts of the neutralizing Under agentthese in theconditions, subsequent purification>95% of manganese can be dis- step, the optimum conditions for leaching become a 90 ◦C leaching temperature and a 20% solvedacid concentration. into the Undersolution. these conditions, >95% of manganese can be dissolved into the solution.

Figure 5. (a) The effect of temperature and acid concentration on leaching with a reductant Figure(8% dextrin) 5. (fora) aThe 1 h leachingeffect duration,of temperature and (b) the effectand of acid leaching concen durationtration at 70 ◦C on and leaching90 ◦C, a with a reductant (8% dextrin)20% acid concentration,for a 1 h leac andhing a 8% dextrin duration, addition. and (b) the effect of leaching duration at 70 °C and 90 °C, a 20% acidTo study concentration, the effect of leaching and duration,a 8% dextrin sets of experimentsaddition. were conducted at 70 and 90 ◦C with a 20% acid concentration and different time intervals. Leaching duration was To study the effect of leaching duration, sets of experiments were conducted at 70 and 90 °C with a 20% acid concentration and different time intervals. Leaching duration was varied from 15 min to 4 h, as shown in Figure 5b. With increasing leaching duration, Mn recovery drastically increases up to 1 h, and its effect becomes negligible with prolonged durations for both studied leaching temperatures. The time required for maximum Mn dissolution is higher for reductive leaching compared to direct leaching (i.e., with no reductant); this is due to the slower reaction between dextrin and MnO2. Lastly, to study the effect of the amount of reductant, experiments were conducted that varied the added dextrin amount at 90 °C for 1 h with a 20% acid concentration (Figure 6). With an increase in the concentration of dextrin, manganese dissolution increases; this is due to the increased availability of dextrin for MnO2 reduction. Maximum recovery of manganese (>95%) can be obtained with 8% dextrin addition (or 0.078 g/g dust). Hence, it is not possible to reduce the dextrin amount without losing Mn into the residue.

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varied from 15 min to 4 h, as shown in Figure5b. With increasing leaching duration, Mn recovery drastically increases up to 1 h, and its effect becomes negligible with prolonged durations for both studied leaching temperatures. The time required for maximum Mn dissolution is higher for reductive leaching compared to direct leaching (i.e., with no reductant); this is due to the slower reaction between dextrin and MnO2. Lastly, to study the effect of the amount of reductant, experiments were conducted that varied the added dextrin amount at 90 ◦C for 1 h with a 20% acid concentration (Figure6). With an increase in the concentration of dextrin, manganese dissolution increases; this is due to the increased Minerals 2021, 11, x FOR PEER REVIEWavailability of dextrin for MnO2 reduction. Maximum recovery of manganese (>95%) can 9 of 14 be obtained with 8% dextrin addition (or 0.078 g/g dust). Hence, it is not possible to reduce the dextrin amount without losing Mn into the residue.

FigureFigure 6. 6.Effect Effect of dextrinof dextrin amount amount on Mn leachingon Mn leaching at 90 ◦C, a at 20% 90 acid °C, concentration, a 20% acid concentration, and a 1 h and a 1 h leachingleaching duration. duration.

Sulfuric acid leaching of the furnace dust without a reductant can dissolve only <60% of manganeseSulfuric into acid the solution.leaching The of optimum the furnace conditions dust for without leaching a without reductant a reductant can dissolve only <60% areof manganese a 30 ◦C leaching into temperature, the solution. a 12% acidThe concentration, optimum conditions and a 30 min leachingfor leaching duration. without a reductant Manganeseare a 30 °C dissolution leaching can temperature, be improved through a 12% theacid addition concentration, of dextrin as and a reductant. a 30 min leaching dura- Mn dissolution of >95% can be obtained at 90 ◦C with a 20% acid concentration, a 1 h leachingtion. Manganese duration, and dissolution an 8% dextrin can addition. be improved through the addition of dextrin as a reductant. Mn dissolution of >95% can be obtained at 90 °C with a 20% acid concentration, a 1 h 3.4.leaching Electrolytic duration, MnO2 (EMD) and Productionan 8% dextrin addition. After almost complete leaching of manganese from the furnace dust, the manganese sulfate-rich solution can be used in the production of different end products. In this study, the3.4. leachate Electrolytic was used MnO in the2 (EMD) production Production of electrolytic manganese dioxide (EMD). However, furtherAfter studies almost can investigate complete the leaching use of furnace of manganese dust for chemical from manganese the furnace dioxide dust, the manganese (CMD)sulfate-rich or manganese solution sulfate can production. be used in The the latter produc is, fortion example, of different an important end sourceproducts. In this study, for the secondary battery industry. the Figureleachate7a shows was theused effect in of the current production density on of current electrolytic efﬁciency manganese in a 0.25 M H 2dioxideSO4 (EMD). How- containingever, further electrolyte. studies The can current investigate efﬁciency the (CE use) of theof furnace process is dust calculated for chemical based on manganese diox- Equationide (CMD) (6), where or manganeseW, n, F, M, I, and sulfatet refers production. to the weight of The MnO 2latterdeposited, is, thefor numberexample, an important of electrons, the Faraday constant (96500 coulombs), the molecular weight of MnO2, the currentsource in for amperes the secondary (amps), and battery time in seconds, industry. respectively. Figure 7a shows the effect of current density on current efficiency in a 0.25 M H2SO4 W ∗ n ∗ F containing electrolyte. The currentCE = efficiency (CE) of the process is (6)calculated based on M ∗ I ∗ t Equation (6), where W, n, F, M, I, and t refers to the weight of MnO2 deposited, the number of electrons, the Faraday constant (96500 coulombs), the molecular weight of MnO2, the current in amperes (amps), and time in seconds, respectively. 𝑊∗𝑛∗𝐹 𝐶𝐸 = (6) 𝑀∗𝐼∗𝑡 From Figure 7a it can be seen that current efficiency increases with an increase in the current density to some extent, and it decreases gradually thereafter. Maximum current efficiency was obtained at 1 amp/dm2, which is generally used in conventional EMD processes. At higher current densities, the rate of MnO2 deposition is faster compared to the transport of ions. Moreover, the evolution of oxygen takes place at the anode due to the water-splitting reaction, which dominates over the MnO2 deposition. The addition of sulfuric acid to the electrolyte is required in order to improve the conductivity of the solution. Figure 7b shows the effect of the concentration of sulfuric acid on the current efficiency of the process. The efficiency is slightly increased by increasing the acid concentration from 0.05 to 0.25 M. This is due to the sufficient availability of the ions, which improves current conductivity. Above that value, there is no effect of the amount of acid on the current efficiency.

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Figure 7. (a) The effect of current density, and (b) acid concentration on current efficiency. Figure 7. (a) The effect of current density, and (b) acid concentration on current efficiency. From Figure7a it can be seen that current efficiency increases with an increase in the current density to some extent, and it decreases gradually thereafter. Maximum current 2 efficiencyThe wasEMD obtained powder at 1 produced amp/dm2, which at 1 isamp/dm generally usedcurrent in conventional density is EMD shown in Figure 8a. In Figureprocesses. 8b, At the higher BSE current image densities, of the the sample rate of MnOshows2 deposition a rather is fastersmooth compared surface, to with some cracks inthe the transport sample of ions.that Moreover, developed the evolution during ofthe oxygen mech takesanical place removal at the anode of duethe todeposit from the an- the water-splitting reaction, which dominates over the MnO2 deposition. ode. The addition XRD pattern of sulfuric of acidthe toEMD the electrolyte powder is is required provided in order in Figure to improve 9. It the shows only the peaks ofconductivity gamma-MnO of the solution.2, which Figure is 7suitableb shows the for effect battery of the concentration applications. of sulfuric However, acid the bulk density measurementon the current efficiency of the of EMD the process. powder The efficiency is necessary is slightly in increasedorder to by fully increasing confirm the this statement. In acid concentration from 0.05 to 0.25 M. This is due to the sufficient availability of the ions, agreementwhich improves with current these conductivity. results, Abovethe chemical that value, an therealysis is no effectof the of powder the amount showed of that all of the impuritiesacid on the current were efficiency.less than 0.1 wt.%. TheEnergy EMD powderconsumption produced ( atEC 1) amp/dm during2 currentthe process density was is shown calculated in Figure8 a.based In on the formula in Figure8b, the BSE image of the sample shows a rather smooth surface, with some cracks in Equationthe sample (7), that developedwhere V, during I, t, and the mechanicalW refer to removal voltage of thein depositvolts, current from the anode. in amperes (amps), time inThe h,XRD and pattern the weight of the EMD of the powder MnO is2 provided deposited in Figure in kg,9. It respective shows only thely. peaksThe energy required for theof gamma-MnOproduction2, whichof EMD is suitable powder for batterywas found applications. to be However,in the range the bulk of density 1.4–2.0 kWh/kg of MnO2 measurement of the EMD powder is necessary in order to fully confirm this statement. In produced.agreement with these results, the chemical analysis of the powder showed that all of the impurities were less than 0.1 wt.%. kWh 𝑉∗𝐼∗𝑡 Energy consumption (EC) during the process𝐸𝐶 was calculated= based on the formula in (7) Equation (7), where V, I, t, and W refer to voltage in volts,kg current in𝑊 amperes (amps), time in h, and the weight of the MnO2 deposited in kg, respectively. The energy required for the production of EMD powder was found to be in the range of 1.4–2.0 kWh/kg of MnO2 produced. kWh V ∗ I ∗ t EC = (7) kg W The overall flow sheet of the process is provided in Figure 10 with a partial mass balance. Based on 100 g of furnace dust input with 42.7% Mn, about 61 g of electrolytic MnO2 can be produced, which corresponds to an overall Mn recovery rate of 90.3% from the dust sample.

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Figure 8. (a) An image of the electrolytic MnO2 (EMD) powder produced in this study, and (b) the FigureFigure 8. 8.(a )( Ana) An image image of the of electrolytic the electrolytic MnO2 (EMD) MnO powder2 (EMD) produced powder in produced this study, and in this (b) the study, and (b) the powder surface under BSE. powderpowder surface surface under under BSE. BSE.

Figure 9. XRD result of the FigureEMD produced. 9. XRD result of the EMD produced. Figure 9. XRD result of the EMD produced.

The overall flowThe sheet overall of the flow process sheet is ofpr theovided process in Figure is provided 10 with in a Figure partial 10 mass with a partial mass balance. Based onbalance. 100 g of Based furnace on 100dust g inpuof furnacet with 42.7%dust inpu Mn,t aboutwith 42.7% 61 g ofMn, electrolytic about 61 g of electrolytic MnO2 can be produced, which corresponds to an overall Mn recovery rate of 90.3% from MnO2 can be produced, which corresponds to an overall Mn recovery rate of 90.3% from the dust sample. the dust sample.

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FigureFigure 10. 10.Overall Overall ﬂow flow sheet sheet for the for production the production of EMD from of EM 100D g furnacefrom 100 dust g input:furnace gm, du gram;st input: gm, gram; Wt,Wt, weight. weight. 4. Conclusions 4. ConclusionsFerromanganese furnace dust is an environmentally problematic by-product of FeMn alloy production.Ferromanganese This study furnace shows thedust feasibility is an envi of battery-graderonmentally electrolytic problematic MnO2 by-product of productionFeMn alloy from production. a real furnace dustThis sample. study The shows main conclusionsthe feasibility of the studyof battery-grade are: electrolytic • The particle size of the dust (D ) was 32 microns. The XRD result of the furnace dust MnO2 production from a real80 furnace dust sample. The main conclusions of the study are: revealed that Mn O , MnO, and silica phases were present in the sample. Mn content • 3 4 wasThe 42.7%. particle size of the dust (D80) was 32 microns. The XRD result of the furnace dust • Therevealed leaching that of the Mn furnace3O4, dustMnO, without and silica a reductant phases resulted were in present <60% Mn in dissolution, the sample. Mn content ◦ withwas a 12%42.7%. acid concentration, a 30 C leaching temperature, and a 30 min leaching • duration.The leaching of the furnace dust without a reductant resulted in <60% Mn dissolu- • Dextrin, a green, cheap, and water-soluble organic reductant, was found suitable as a reductant.tion, with a 12% acid concentration, a 30 °C leaching temperature, and a 30 min leach- • 98.9%ing duration. Mn dissolution is obtained by the optimum leaching conditions of a 90 ◦C • leachingDextrin, temperature, a green, cheap, a 1 h leaching and water-soluble duration, a 20% organic acid concentration, reductant, was and anfound suitable as 8%a dextrinreductant. addition. • Optimized conditions for electrolytic manganese dioxide (EMD) production were: a • 98.9% Mn dissolution is obtained by the optimum leaching conditions of a 90 °C current density of 1 amp/dm2 and a sulfuric acid concentration of 0.25 M. The product obtainedleaching through temperature, the electrolysis a 1 h process leaching is a pure duration, gamma a MnO 20%2 phase. acid concentration, and an 8% • Adextrin total manganese addition. recovery of 90.3% from the furnace dust is possible with the • proposedOptimized ﬂow sheet.conditions for electrolytic manganese dioxide (EMD) production were: a current density of 1 amp/dm2 and a sulfuric acid concentration of 0.25 M. The product Author Contributions: Conceptualization, M.A.R.Ö. and C.R.B.; methodology, C.R.B.; software, 2 C.R.B.;obtained validation, M.A.R.Ö.,through C.R.B.,the electrolysis P.V., L.P., P.K., process V.S.; formal is a analysis, pure gamma C.R.B., L.P., MnO V.S.,phase. P.K.; • A total manganese recovery of 90.3% from the furnace dust is possible with the proposed flow sheet.

Author Contributions: Conceptualization, M.A.R.Ö. and C.R.B.; methodology, C.R.B.; software, C.R.B.; validation, M.A.R.Ö., C.R.B., P.V., L.P., P.K., V.S.; formal analysis, C.R.B., L.B., V.S., P.K.; investigation, L.P., P.K., V.S.; resources, L.P., P.K., V.S.; data curation, C.R.B.; writing—original draft preparation, M.A.R.Ö.; writing—review and editing, M.A.R.Ö., P.V., C.R.B.; visualization, M.A.R.Ö.; supervision, C.R.B.; project administration, C.R.B. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding.

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investigation, L.P., P.K., V.S.; resources, L.P., P.K., V.S.; data curation, C.R.B.; writing—original draft preparation, M.A.R.Ö.; writing—review and editing, M.A.R.Ö., P.V., C.R.B.; visualization, M.A.R.Ö.; supervision, C.R.B.; project administration, C.R.B. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: Investigators are thankful to M.B. Denys, (RD&T, India), and Rajeev Singhal, EIC (FAMD), for providing an opportunity to work on this project. Thanks are also due to V. Tathavadkar, Head (IFA Research Group); A.K. Lahiri; B.D. Nanda; and B.N. Rout, FAP Joda, for providing valuable inputs. Special thanks are also to Ranjeet Singh, R&D, for his help while conducting the test work. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References 1. Sharma, T. Physico-chemical processing of low grade manganese ore. Int. J. Miner. Process. 1992, 35, 191–203. [CrossRef] 2. Corathers, L.A. U.S. Geological Survey (USGS) Minerals Yearbook: Manganese; US Geological Survey: Reston, VA, USA, 2005. 3. Elliott, R.; Coley, K.; Mostaghel, S.; Barati, M. Review of Manganese Processing for Production of TRIP/TWIP Steels, Part 1: Current Practice and Processing Fundamentals. JOM J. Miner. Met. Mater. Soc. 2018, 70, 680–690. [CrossRef] 4. Kronenberg, M.L.; Blomgren, G.E. Primary Batteries—Lithium Batteries. In Comprehensive Treatise of Electrochemistry; Bockris, J.O., Conway, B.E., Yeager, E., White, R.E., Eds.; Springer: Boston, MA, USA, 1981; pp. 247–278. ISBN 9781461566892. 5. Sattar, R.; Ilyas, S.; Kousar, S.; Khalid, A.; Sajid, M.; Bukhari, S.I. Study on the reduction roasting of spent LiNixCoyMnzO2 lithium-ion battery cathode materials. Environ. Eng. Res. 2020, 25, 88–95. [CrossRef] 6. Munir, H.; Srivastava, R.R.; Kim, H.; Ilyas, S.; Khosa, M.K.; Yameen, B. Leaching of exhausted LNCM cathode batteries in ascorbic acid lixiviant: A green recycling approach, reaction kinetics and process mechanism. J. Chem. Technol. Biotechnol. 2020, 95, 2286–2294. [CrossRef] 7. Biswal, A.; Tripathy, B.C.; Sanjay, K.; Subbaiah, T.; Minakshi, M. Electrolytic manganese dioxide (EMD): A perspective on worldwide production, reserves and its role in electrochemistry. RSC Adv. 2015, 5, 58255–58283. [CrossRef] 8. Zhang, W.; Cheng, C. Manganese metallurgy review. Part I: Leaching of ores/secondary materials and recovery of electrolytic/chemical manganese dioxide. Hydrometallurgy 2007, 89, 137–159. [CrossRef] 9. Biswal, A.; Dash, B.; Tripathy, B.C.; Subbaiah, T.; Shin, S.M.; Sanjay, K.; Mishra, B.K. Inﬂuence of alternative alkali reagents on Fe removal during recovery of Mn as Electrolytic Manganese Dioxide (EMD) from Mn sludge. Hydrometallurgy 2013, 140, 151–162. [CrossRef] 10. Zhu, L.; Bao, C.; Xie, L.; Yang, X.; Cao, X. Review of synthesis and structural optimization of LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium-ion batteries applications. J. Alloys Compd. 2020, 831, 154864. [CrossRef] 11. Chow, N. Manganese ore for lithium batteries. Met. Powder Rep. 2012, 67, 34–36. [CrossRef] 12. Biswal, A.; Sanjay, K.; Ghosh, M.K.; Subbaiah, T.; Mishra, B.K. Preparation and characterization of EMD from manganese cake—A byproduct of manganese nodule processing. Hydrometallurgy 2011, 110, 44–49. [CrossRef] 13. Taucher, W.; Kordesch, K. Alkaline manganese dioxide-Zinc batterdes primary and rechargeable cells with and without mercury. Stud. Environ. Sci. 1994, 59, 163–202. [CrossRef] 14. Ghosh, S.; Mohanty, S.; Akcil, A.; Sukla, L.B.; Das, A.P. A greener approach for resource recycling: Manganese bioleaching. Chemosphere 2016, 154, 628–639. [CrossRef] 15. Önal, M.A.R.; Borra, C.R.; Guo, M.; Blanpain, B.; Van Gerven, T. Hydrometallurgical recycling of NdFeB magnets: Complete leaching, iron removal and electrolysis. J. Rare Earths 2017, 35, 574–584. [CrossRef] 16. Rodrigues, S.; Munichandraiah, N.; Shukla, A.K. A cyclic voltammetric study of the kinetics and mechanism of electrodeposition of manganese dioxide. J. Appl. Electrochem. 1998, 28, 1235–1241. [CrossRef] 17. Harris, M.; Meyer, D.M.; Auerswald, K. The production of electrolytic manganese in South Africa. S. African Inst. Min. Metall. 1977, 77, 137–142. 18. Banerjee, T.; Chakrabarti, H.K.; Kar, B.C.; Dhananjayan, N. Electrolytic Manganese & Manganese Dioxide from Low-grade Indian Ores. Indian Min. J. 1957, 69–75. 19. de Araujo, J.A.M.; de Castro, M.M.R.; Lins, V.F.C. Reuse of furnace ﬁnes of ferro alloy in the electrolytic manganese production. Hydrometallurgy 2006, 84, 204–210. [CrossRef] 20. Matricardi, L.R. Disposal of ferromanganese furnace fume. In Proceedings of the Electric Furnace Conference, Houston, TX, USA, 9–12 December 1975; pp. 73–75. 21. Lee, Y.E.; Kozak, D.S. The role of zinc in the eruption of high carbon FeMn smelting furnace. In Proceedings of the Electric Furnace Conference, Washington, DC, USA, 7–10 November 1993; pp. 145–150. 22. Nkosi, S.; Steenkamp, J.D.; Groot, D.R.; Gous, J.P. Hydrometallurgical process for the recovery of manganese from pelletized silicomanganese submerged arc furnace dust. In Proceedings of the Fray International Symposium, Cancun, Mexico, 4–7 December 2011; pp. 309–320. Minerals 2021, 11, 712 14 of 14

23. Hamano, T.; Zhang, G.; Brown, P.; Ostrovski, O. Manganese furnace dust: Drying and reduction of zinc oxide by tar. ISIJ Int. 2008, 48, 906–911. [CrossRef] 24. Shen, R.; Zhang, G.; Dell’Amico, M.; Brown, P.; Ostrovski, O. A feasibility study of recycling of manganese furnace dust. In Proceedings of the XI International Conference on Innovations in the Ferro Alloy Industry, Infacon XI, Maharashtra, India, 18–21 February 2007; pp. 507–519. 25. Trifoni, M.; Toro, L.; Vegliò, F. Reductive leaching of manganiferous ores by glucose and H2SO4: Effect of alcohols. Hydrometallurgy 2001, 59, 1–14. [CrossRef] 26. Furlani, G.; Pagnanelli, F.; Toro, L. Reductive acid leaching of manganese dioxide with glucose: Identiﬁcation of oxidation derivatives of glucose. Hydrometallurgy 2006, 81, 234–240. [CrossRef] 27. Adrover, A.; Velardo, A.; Giona, M.; Cerbelli, S.; Pagnanelli, F.; Toro, L. Structural modelling for the dissolution of non-porous ores: Dissolution with sporulation. Chem. Eng. J. 2004, 99, 89–104. [CrossRef]