Recovery of Manganese and Zinc from Waste Dry Cell Powder
Part I: Characterization and Leaching
Ranjit K. Biswas*, Aneek K. Karmakar, Sree L.
Kumar and Mohammad N. Hossain Dept. of Applied Chemistry & Chemical Engineering
Rajshahi University Rajshahi, Bangladesh [email protected]
Abstract— A large number of waste dry cells (Haque brand) were broken down and collected as powder. This powder was sun-dried, dry-ground and sieved down to 300 mesh size and stored. The sample was analysed and found to contain (35.4±0.2)% Mn, (11.0±0.1)% Zn and ~2.5% Fe as major metallic constituents. The phases, ZnMn2O4and Zn(ClO4)2.2H2O were identified in the sample. The material was found to be leached effectively by a glucose-containing 2 mol/L sulfuric acid (0.5 g/
250 mL) solution. However, the dissolution was dependent on the ratio of powder to volume of leachant; and the stage-wise leaching was not fruitful for Mn-dissolution. On leaching 5 g of powder with a 250 mL 2 mol/L sulfuric acid solution, containing 0.5 g glucose, at 100 oC and 300 rpm for 1 h, a solution containing (7.08±0.10) g/L Mn(II), (2.20±0.06) Zn(II) and ~0.40 g/L Fe(III) was recovered.
Index Terms — battery, waste, characterization, leaching, sulfuric acid, glucose
I. INTRODUCTION
A dry cell, once used, cannot be regenerated. A dry cell [1]
consists of a flat-bottomed cylinder of Zn acting as anode and a rod of porous C, carrying a brass cap, acting as cathode. Most of the interior of the cylinder is packed with bobbin (a mixture of 60% MnO2, 20% C black, 10% NH4Cl and 10% water).
Surrounding the central carbon electrode is placed an electrolyte (starch and flour gelled with 9% ZnCl2 and 26%
NH4Cl solution) in a muslin bag, acting as a diaphragm. During use, Zn anode is corroded as: Zn → Zn2+ + 2e. The released electron is conveyed to the bobbin via C cathode and electrolyte for the cathodic reaction: MnO2 + H2O + e → MnO(OH) + OH-. Moreover, due to some secondary reactions, ZnMn2O4, Zn(ClO4)2, Mn3O3, MnO2, [Zn(NH3)2]Cl, NH3 etc.
are formed. Consequently, waste dry cell powder may contain varieties of compounds of Zn and Mn, along with NH4Cl, carbon, starch and flour.
As Mn3+ and Mn4+ salts are insoluble, the leaching of MnO2 by an acid is difficult and the acid-leaching system must contain a reducing agent: e.g. SO2 [2-4], sucrose [5-7], methanol [8], lactose and whey [9, 10], glucose [11, 12], oxalic
acid [13], saw dust [14], cane molasses [15], molasses alcohol waste water [16], tender maize stem (cornstalk) [17], FeSO4 [18] etc. It is likely, therefore, that the leaching of MnO2, Mn2O3, Mn3O4 and ZnMn2O4 etc. present in the waste dry cell powder by a H2SO4 solution would also require a reducing agent. Moreover, the identification of oxidation derivatives of glucose as formic acid has been reported by Furlani et al. [19].
In this work, the waste dry cell powder will be subjected to (i) NH4Cl sublimation, (ii) TG (iii) XRD (iv) EDXRF and (v) chemical analyses for characterization; and the leaching behavior of the powder will be examined by H2SO4-glucose mixture.
II. EXPERIMENTAL A. Materials
Two hundred waste batteries of Haque brand were collected from a scrap shop, dismantled to collect the sticky mass on a large size polythene sheet. The material was sun- dried for 4 days (R.H = 40-80%) to eliminate stickiness. It was then dry-ground and sieved by a 300-mesh sieve to collect the undersized particles only. The powder mass was then stored in a large caped bottle. Analytical reagent grade chemicals of either E. Merck (Germany/India), or Loba Chemie (India) were used without further purifications.
B. Analytical
The [Zn2+] and [Mn2+] in solutions were estimated by AAS (Shimadzu AA-6800 Spectrophotometer). In concentrated solutions of Zn2+ and Mn2+, the total concentration was estimated by titration with standard EDTA solution as usual [20a]. The [Mn2+] alone was estimated by the HNO3-KIO4 oxidative method at 545 nm [20b]. The difference gave [Zn2+].
The thermogram of 20 mg of sample in a Pt-crucible, with alumina as reference, was taken by a Stanton Redcroft STA 781 TG apparatus, in air atm. (30 cm3/min) at a heating rate of 2 oC/min. The XRD patterns of samples in KBr-pellet forms were taken by a Philips PW 3040 X part PRO XRD using Cu
ISBN 978-984-33-8940-4
0 100 200 300 400 500 600 700 800 60
65 70 75 80 85 90 95 100
Zn(OH)2 + Mn2O3 ZnMn2O4 + H2O
6th plateau 5th plateau 4th plateau 3rd plateau 2nd plateau Absorbed H2O removal
1st plateau
NH4Cl removal by sublimation
Combined NH3 + H2O removal in charing of starch and flour
Carbon oxidation
Condensed water removal: 2 MnOOH Mn2O3 + H2O
Kα radiation (40 kV and 30 mA) and step-scanning procedure (2θ = 0.1o/min).
Metallic parts in sample were estimated by an EDX-3600B XRF spectrophotometer (Qualitest, USA) operated at 40 KV and 200 μA. An exactly-weighed 1 g sample was converted to pellets by applying pressure of 50 kg/cm2. The test time was 100 s. The X-ray was allowed to fall at 25 different places on the pellet surface. The contents at these places were averaged to report.
For chemical analysis, 1 g sample was tri-acid (12 mL 1:3 conc. HCl-HNO3 mixture followed by 5 mL conc. H2SO4) digested to create a 100 mL clear solution, using 1 mol/L sulfuric acid solution. Its [Mn(II)], [Zn(II)] and [Fe(III)] were determined by AAS.
C. Leaching Procedure
A definite amount of leaching agent was taken in a 500/250 mL quick-fit conical flask. A moist cloth wrapped set at flask mouth (1 m glass tube), acted as condenser. It was immersed in a large beaker containing thermostated water up to its neck; and the stirring of mass in flask was aided by a magnetic hot plate (300 rpm). When the solution in the flask reached the desired temperature, a weighed amount of powder was added; and the stirring at the desired temperature was continued for a certain time. After leaching, the slurry was filtered and the filtrate was subjected to analysis of its Mn2+
and Zn2+ contents.
D. Sublimation Procedure
An aliquot of 20 g sample was taken in a weighed Petri dish (10 cm dia), spread flat and covered by a weighed funnel, wrapped externally with moist cotton. The system was heated for 10 min at ~300oC. The system cooled to room temperature, funnel was taken out to weigh after drying its outer surface.
The weight of residual sample was also calculated.
III. RESULTS AND DISCUSSION A. Characterization
On sublimation, 1.10 g NH4Cl is obtained from 20 g powder and so, it contains 5.5% NH4Cl. Total weight loss is 10.50% (residue = 17.90 g). The nitrogen content in the sample, using the micro-Kjeldahl method, is 1.55% N2. The presence of 5.5% NH4Cl corresponds to 1.44% N2. The excess N2 (0.11%) correspond to complexed ammonia in the sample.
The thermogram of the powder is given in Fig. 1. There are six distinct plateau areas in the thermogram. 5% weight loss, within 110 oC, is assigned for the removal of absorbed water.
The weight loss of 5.50% between the 1st and 2nd plateaus is due to sublimation of NH4Cl within 220-250 oC. The weight loss within 320-350 oC is due to removals of combined NH3 and of H2O formed on charring of starch and flour ((C6H10O5)n
→ 6nC + 5nH2O). The major weight loss appearing between the 3rd and 4th plateaus (~16.5%) is attributed to the removal of carbon. The weight losses between the 4th and 5th plateaus, and also between the 5th and 6th plateaus (about 1% in each case), could be due to the elimination of condensed water formed by the following types of reactions:
Fig. 1. Thermogram for waste dry cell powder.
2MnOOH → Mn2O3 + H2O (1) Zn(OH)2 + Mn2O3 → ZnMn2O4 + H2O (2) Zn(OH)2 + 2MnOOH → ZnMn2O4 + 2 H2O (3) Thus, the thermogram of the waste dry cell indicates that it contains: i) 5% absorbed water, ii) 5.5% NH4Cl, iii) 5%
combined NH3 and condensable water from carbohydrate, iv) 16.5% C containing materials, and v) 66% metallic constituents in the form of oxides and mixed oxides.
The XRD pattern of the pasty material of the unused dry cell indicate that the material is semi-crystalline (one peak of 2θ = 44.588o, broad). The same, after hot water leaching (100
oC) for 1 h, is shown in Fig. 2a. It indicates that the residue after hot water leaching contains: Zn(ClO4)2.2H2O (Ref. Code Nos. 00-044-0217, score 25; and 00-033-1470, score 35), MnO2 (Ref. Code No. 00-012-0714, score 53) and synthetic MnO2 (Ref. Code No. 00-024-0735, score 43). During manufacture of the battery, ZnCl2 is used instead of zinc perchlorate. Zinc perchlorate is presumably formed by the following type of reaction, during storage or hot water leaching:
Fig. 2. XRD of (a) non-used dry-cell powder and (b) waste dry-cell powder after hot water leaching.
Temperature, oC
Percentage of material retained
1. MnO2 (00-012-0714) 2. MnO2 (00-024-0735) 3. Zn(ClO4)2.2H2O (00-044-0217) 4. Zn(ClO4)2.2H2O (00-033-1470)
(a) 1. MnO2 (00-012-0714)
2. MnO2 (00-024-0735) 3. Zn(ClO4)2.2H2O (00-044-0217) 4. Zn(ClO4)2.2H2O (00-033-1470)
(a) Position [o2 Theta]
Counts
1. ZnMn2O4 (00-001-0455) almost similar to 01-071-2899 and 01-001-0445
2. Zn(ClO4)2.2H2O (00-044-0217) 1. MnO2 (00-012-0714) 2. MnO2 (00-024-0735) 3. Zn(ClO4)2.2H2O (00-044-0217) 4. Zn(ClO4)2.2H2O (00-033-1470)
(a)
(b)
0 20 40 60 80 0
20 40 60 80 100
0 100 200 300 400
0 20 40 60 80 100 120
ZnCl2 + 16MnO2 → Zn(ClO4)2 + 8Mn2O3 (4) The XRD pattern of the waste dry cell powder also indicates its semi-crystalline nature (not depicted). However, the XRD pattern (Fig. 2b) of the residue left, after hot water leaching (100 oC, 1 h) of the waste dry cell powder, shows the presence of ZnMn2O4 (Ref. Code No. 00-001-0455, 01-071-2899 and 01-001-0445) and ZnClO4.2H2O (Ref. Code No. 00-044-0217).
The XRD pattern of the powder obtained on heating of the waste dry cell powder at 700 oC for 1 h (not presented) is very much similar to the pattern in Fig. 2b, excluding the peaks for ZnClO4.2H2O.
The EDXRF analysis shows the presence of (32±3)% Mn, (10.5±0.9)% Zn and (3±0.4)% Fe as major metallic constituents in the sun-dried sample. The minor components detected are (1.5±0.4)% Al, (3±0.5)% Si, ~0.4% K, 0.001% P, 0.001% S, 0.003% Ca, 0.005% V, 0.025% Cr, 0.003% Na, 0.02% As, 0.005% Sn and 0.004% Pb.
However, the chemical analysis indicates the presence of (35.4±0.2)% Mn, (11±0.1)% Zn and 2.5% Fe. These values are more or less comparable to those obtained from the EDXRF method. In the leaching studies, the latter set of percentages of metals in the sun-dried sample has been considered as the basis.
B. Leaching
The leached solution, obtained on leaching of 1 g powder by 100 mL water under reflux at 100 oC for 2 h, is found to contain (0.017±0.0002) g Zn(II) (15.5% dissolution) and no manganese. So the powder contains 15% water soluble Zn and no water-soluble Mn. Triplicate experiments, on leaching of 1 g powder with 100 mL 1 mol/L H2SO4 solution at 100oC for 2 h, have shown that leached solutions contain (0.042±0.004) g Zn(II) and (0.065±0.01) g Mn(II), corresponding to 38.2% Zn dissolution and 18.4% Mn dissolutions, respectively.
Therefore, H2SO4 alone is not a good leaching agent the powder.
The powder contains Zn(ClO4)2 and ZnMn2O4. In hot water leaching, only ZnCl2 is possibly dissolved. But in 1 mol/L H2SO4 medium, Zn(II) is dissolved, both from ZnCl2/Zn(ClO4)2 and ZnMn2O4. The dissolution of Zn(II) from ZnMn2O4 occurs via reaction: ZnMn2O4 + H2SO4 → ZnSO4 + Mn2O3 + H2O. A part of Mn2O3 is presumably dissolved by the following reaction:
Mn
2O
3+ H
2SO
4→ MnSO
4+ MnO
2+ H
2O (5)
MnO2, produced above and the free existing MnO2 (if any) in the powder, is not leached by 1 mol/L H2SO4 solution. It can be demonstrated that the complete leaching of Mn(II) and Zn(II) from the powder cannot be achieved, even with conc. H2SO4 at
~300oC. Based on the literature, [11, 12] it is thought that the powder can be leached effectively by a dilute H2SO4 solution, provided glucose is added to the system as a reducing agent.
Figure 3 shows the effect of leaching time on % dissolution of Zn2+ and Mn2+. It is seen that dissolution percentage of both metal ions increases with increasing leaching time. The maximum dissolution percentage is achieved within 40 min for both metal ions. On the other hand, Fig. 4 represents the effect of pulp-stirring speed on % dissolutions. It is seen that -
Fig. 3. Effect of time on dissolutions of Mn(II) and Zn(II) from the powder under reflux (100 oC) at 300 rpm. Powder = 5 g, glucose = 0.5 g, vol. of 2 mol/L H2SO4 = 250 mL.
maximum recoveries of both metal ions increase with increasing pulp agitation speed up to ~250 rpm. However, in subsequent experiments, leachings for 1 h at 300 rpm are allowed to ensure maximum recoveries in other parametric conditions.
The effect of glucose on dissolution of Mn(II) from the waste dry cell powder by sulphuric acid solution under reflux at 100 oC for 1 h and at 300 rpm for S/L of (1/100) g/mL is shown in Fig. 5. It is seen for both concentrations of sulphuric acid used, the optimal amount of glucose is 0.20 g per 100 mL leachant. On the other hand, Fig. 6 represents the variation of dissolution percentage of Mn(II) with sulphuric acid concentration. The dissolution percentage of Mn(II) increases with increasing acid concentration up to ~1.5 mol/L and then remains unchanged. It is, therefore, concluded that 2 mol/L H2SO4 solution containing requisite amount of glucose is required for quantitative dissolution.
Using 250 mL of 2 mol/L H2SO4 solution, containing 0.5 g glucose as leachant, under reflux at 100 oC for 1 h at 300 rpm,
% dissolutions of Zn2+ and Mn2+ for various amounts of powder are given in Fig. 7.It is seen that 100% dissolutions of both metal ions are achieved if the amount of powder is kept up
Fig. 4. Effect of pulp agitation speed on dissolutions of Mn(II) and Zn(II) from waste dry cell powder. Legends are as in Fig. 3.
Leaching time, min
% Dissolution
, Mn(II) at 100oC
, Mn(II) at 45oC
, Zn(II) at 100oC
, Zn(II) at 45oC
% Dissolution
Pulp agitation speed, rpm Pulp agitation speed, rpm
, Mn(II) at 100oC
, Mn(II) at 45oC
, Zn(II) at 100oC
, Zn(II) at 45oC
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0.0 0.5 1.0 1.5 2.0 2.5 0
20 40 60 80 100
0 10 20 30 40 50
0 20 40 60 80 100
0 10 20 30 40 50
0 1 2 3 4 5
20 40 60 80 100
0 10 20 30 40
Fig. 5. Effect of glucose on dissolution of Mn(II) from the powder by H2SO4
solution under reflux at 100oC for 1 h and at 300 rpm. Volume of H2SO4
solution = 100 mL, Solid to liquid ratio (S/L) = 1/100 g/mL.
to 5 g. With further increase in the amount of powder used in leaching, the % dissolution of both metal ions are decreased gradually to 54.50% for Mn(II) and 66.00% for Zn(II), on 50 g powder being used.
The [metal ions] in leached solutions, obtained in these experiments, are also depicted in Fig. 7, [metal ion] in leached solution (g/L) vs. amount of powder (g) plots. For both metal ions, it is seen that the concentration increases linearly up to 5 g powder. With further increase in amount of powder used, the slope of concentration increment is decreased gradually up to 12.5 g powder. With more powder in the system, concentration is again increased linearly up to a maximum of 50 g powder used in these experiments. The slopes for Mn(II) and Zn(II) are 1.42 and 0.44 L-1, respectively, initially. Above 12.5 g powder, respective slopes are 0.69 and 0.27 L-1. As it is seen that, at a solid-to-liquid ratio of 1/5 (50 g per 250 mL of 2 mol/L H2SO4 containing 0.5 g glucose), only 54.50% Mn(II) and 66.00%
Zn(II) are dissolved, a stage-wise leaching was carried out.
The residues obtained in the 1st, 2nd and 3rd stages were leached with fresh leaching agent under similar conditions. The stage-wise leaching results are shown in Fig. 8. It is seen that the 100% zinc extraction occurs at the 4th stage. Yet the
Fig. 6. Effect of [H2SO4] on dissolution of Mn(II) from powder during its leaching by H2SO4-glucose mixture under reflux at 100oC and at 300 rpm for 1 h. S/L = (1/100) g/mL.
Fig. 7. Effect of the amount of waste powder used in leaching. % dissolution vs. amount of powder and conc. of metal ion in leach solution vs. amount of powder plots. Temp. = 100oC, rpm = 300, [H2SO4] = 2 mol/L, Vol. of H2SO4 = 250 mL, Time = 1 h, glucose = 0.50 g.
cumulative manganese dissolution percentage is not so greatly increased through the stages (54.50% dissolution in the 1st stage is increased only to 68% in the 4th stage). Therefore, it is concluded that the advantage of stage-wise leaching at high S/L ratio provides no significant advantage for complete dissolution.
The behaviour of manganese in the stage-wise leaching is unexpected. Moreover, on stage-wise leaching, the combination of obtained leached solutions results in the decrease of cumulative concentration of metal ions. The [metal ion] in cumulated solution vs. stage number plots is also given in Fig. 8. It is seen that [Mn(II)] of 38.59 g/L in the 1st stage is decreased to 12.03 g/L in the cumulated solution. After the 4th stage, [Zn (II)] decreases to 5.5 g/L, compared to 14.52 g/L in the 1st stage.
It is, therefore, concluded that the Mn and Zn in the powder can be effectively leached by 2 mol/L sulfuric acid solution containing 2 g/L glucose, under reflux at 100 oC for 1 h at 300 rpm. However, the S/L ratio appears as critical for 100%
dissolution of both metals. It is, finally, concluded that stage- wise leaching at high S/L ratio is not effective for complete dissolution of manganese.
Fig. 8. Stage-wise leaching at high S/L; (wt, g/vol, mL) ratio. Temp = 100oC, vol. of 2 mol/L H2SO4 = 250 mL, powder = 50 g, pulp agitation speed = 300 rpm, glucose = 0.5 g. Residue after each stage is leached further by 250 mL 2 mol/L H2SO4 solution containing 0.5 g glucose.
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0 20 40 60 80 100
Wt. of glucose, g/100 mL
% Dissolution of Mn(II)
(), 2.0 mol/L H2SO4
(), 1.0 mol/L H2SO4
Concentration of H2SO4, mol/L
% Dissolution of Mn(II)
(), 0.30 g Glucose (), 0.05 g Glucose
Amount of powder, g
% Dissolution [Metal ion] in leach solution, g/L
, Mn(II)
, Zn(II)
% Dissolution [Metal ion] in cumulated solution, g/L
Stage number
, Mn(II)
, Zn(II)
IV. CONCLUSIONS
The powder portion of waste single brand dry cell was found to contain (35.4±0.2)% Mn, (11.0±0.1)% Zn and ~2.5%
Fe as major metallic constituents. The identified phases in the sample were ZnMn2O4 and Zn(ClO4)2.2H2O. The material could be leached by a 2 mol/L H2SO4 solution containing glucose. The dissolution was dependent on the S/L ratio. The stage-wise leaching was not fruitful for Mn-dissolution. An aliquot of 5 g powder could be dissolved completely by 250 mL 2 mol/L H2SO4 solution containing 0.50 g glucose under reflux (100 oC) for 1 h at 300 rpm. The resultant solution was found to contain (7.08±0.10) g/L Mn(II), (2.20±0.06) g/L Zn(II) and ~0.40 g/L Fe(II).
ACKNOWLWDGEMENT
The authors are grateful to the Faculty of Engineering Rajshahi University for financial support via a UGC-RU research grant.
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ISBN 978-984-33-8940-4
