SEPARATION OF ZINC FROM MANGANESE BY SOLVENT EXTRACTION FROM ACIDIC LEACHATES OF SPENT ZINC-MnO<sub>2</sub> DRY CELLS USING NEUTRAL ORGANOPHOSPHORUS EXTRACTANTS

This paper describes a route for recovering manganese and zinc from spent zinc-MnO₂ dry cells via acid leaching using sulfuric or hydrochloric acids as leachants. Hydrogen peroxide was added as reductant. Experiments were run at 25-40 °C for 1-3 h. Under the best optimal conditions, over 97.5 wt.% of zinc and manganese were leached by both acids. Zn(II) was best extracted at high free acidity (≥ 1 mol L^-1) with tributylphosphate (TBP) or trialkylphosphine oxides (Cyanex 923) diluted in n-heptane. Cyanex 923 was a better extractant than TBP, and the extraction was better performed in hydrochloric leachates. Mn(II) was more co-extracted from hydrochloric leachates and when Cyanex 923 was the extractant, but was easily scrubbed with dilute leachant (~1-2 mol L^-1). Zn(II) striping was possible using 5 mol L^-1 HCl or H₂SO₄. Manganese was precipitated as oxalate (MnC₂O₄.2H₂O), free of leached contaminants. High-purity sodium salts of the anions of the leachants were recovered after slow evaporation of the final solution.

Keywords:
Zinc-MnO₂ dry cells; acid leaching; zinc extraction; neutral organophosphorus extractants; manganese oxalate; sodium salts

Authorship

Vinício Francisco Ibiapina

Departamento de Química Analítica, Instituto de Química, Universidade Federal do Rio de Janeiro, 21941-909 Rio de Janeiro - RJ, BrasilUniversidade Federal do Rio de JaneiroBrasilRio de Janeiro, RJ, BrasilDepartamento de Química Analítica, Instituto de Química, Universidade Federal do Rio de Janeiro, 21941-909 Rio de Janeiro - RJ, Brasil

Júlio Carlos Afonso ^**e-mail: julio@iq.ufrj.br

Rubens Souza da Silva

Departamento de Química e Materiais Nucleares, Instituto de Engenharia Nuclear, 21941-906 Rio de Janeiro - RJ, BrasilInstituto de Engenharia NuclearBrasilRio de Janeiro, RJ, BrasilDepartamento de Química e Materiais Nucleares, Instituto de Engenharia Nuclear, 21941-906 Rio de Janeiro - RJ, Brasil

Cláudio Augusto Vianna

José Luiz Mantovano

*e-mail: julio@iq.ufrj.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables | Formulas

Figures (7)
Tables (7)
Formulas (14)

Leachant	Time (h)	Zn	Mn	Ba + Ca	Pb	Fe	Al
H₂SO₄ + H₂O₂	1	99.5	92.4	negligible	negligible	26.0	74.1
	2	99.8	96.3	negligible	negligible	34.1	77.1
	3	> 99.9	97.3	negligible	negligible	35.9	78.0
HCl + H₂O₂	1	> 99.9	98.0	97.1	93.6	90.1	97.8
HCl + H₂O₂	2	> 99.9	> 99.9	99.5	> 99.9	93.8	99.5

Leachant	Mn(II) (g L^-1)	Zn(II) (g L^-1)	Fe(III) (mg L^-1)	Al(III) (mg L^-1)	Pb(II) (mg L^-1)	Ba(II) + Ca(II) (mg L^-1)
H₂SO₄ + H₂O₂	3.3	2.6	4.0	5.1	negligible	< 0.1
HCl + H₂O₂	6.5	5.0	20.0	12.2	0.6	16.1

Leachant	Time (h)	Before calcining (mg)	After calcining (mg)	Difference (mg)
H₂SO₄ + H₂O₂	1	142	56	86
	2	147	57	90
	3	109	25	84
HCl + H₂O₂	1	95	9	86
HCl + H₂O₂	2	92	10	82

Leachant	Time (h)	ZnO	MnO	SiO₂	PbO	Fe₂O₃	Al₂O₃	BaO + CaO
H₂SO₄ + H₂O₂	1	1.7	69.9	22.6	0.2	0.8	1.9	2.6
	2	1.6	49.6	45.8	0.1	0.6	0.6	1.6
	3	1.4	48.6	44.9	0.1	0.6	0.4	3.8
HCl + H₂O₂	1	3.0	4.0	89.5	< 0.1	2.2	0.2	0.8
HCl + H₂O₂	2	2.8	3.4	92.5	< 0.1	0.2	< 0.1	0.8

Acidic solution	Scrubbed Mn(II) (wt.%)	Stripped Zn(II) (wt.%)
H₂SO₄ 1 mol L^-1	99.5	< 0.1
H₂SO₄ 2 mol L^-1	> 99.5	< 0.1
H₂SO₄ 3 mol L^-1	-	10
H₂SO₄ 4 mol L^-1	-	90
H₂SO₄ 5 mol L^-1	-	> 99.5
HCl 1 mol L^-1	> 99.5	< 0.1
HCl 2 mol L^-1	> 99.5	< 0.1
HCl 3 mol L^-1	-	15
HCl 4 mol L^-1	-	94
HCl 5 mol L^-1	-	> 99.5

Acid leachant	Salt	Expected mass (kg)	Recovered mass (kg)	%
H₂SO₄	Na₂SO₄	33.50	33.27	99.3
HCl	NaCl	10.82	10.71	99.0

Item	H₂SO₄	HCl
Acid	5 L (US$ 50)	5 L (US$ 190)
H₂O₂	5 L (US$ 1750)	5 L (US$ 1750)
Energy consumption^1 1 Stirring/heating;	10 kWh^-1 (US$ 3)	10 kWh^-1 (US$ 3)
Adjust free acidity at 1 mol L^-1	0.850 L (US$ 12.75)	0,640 L (US$ 57.60)
Washing insoluble matter	8.0 L (US$ 0.04)	4.0 L (US$ 0.02)
n-heptane	17.77 L (US$ 610.30)	13.72 L (US$ 437.17)
Cyanex 923	1.13 L (US$ 565.95)	0.88 L (US$ 391.07)
Mn(II) scrubbing^2 2 9 mol L-1 H2SO4 + water to prepare a 2 mol L-1 solution;	18.9 L (US$ 43.95)	14.6 L (US$ 33.95)
Zn(II) stripping^3 3 9 mol L-1 H2SO4 + water to prepare a 5 mol L-1 solution;	18.9 L (US$ 111.36)	14.6 L (US$ 86.03)
6 mol L^-1 NaOH^4 4 Adjust pH to precipitate Mn(II);	6.3 L (US$ 314.33)	4.9 L (US$243.33)
1 mol L^-1 Na₂C₂O₄^5 5 Mn(II) precipitation;	5.3 L (US$ 63.60)	5.3 L (US$ 63.60)
6 mol L^-1 NaOH^6 6 Adjust pH to neutralize the final aqueous solution;	0.001 L (US$ 0.05)	0.001 L (US$ 0.05)
Washing MnC₂O₄.H₂O	2.5 L (US$ 0.013)	2.5 L (US$ 0.013)
Energy consumption^7 7 Evaporation;	50 kWh^-1 (US$ 15)	40 kWh^-1 (US$ 12.0)
Total estimated costs	US$ 3,540.34	US$ 3,267.83
ZnO	260 g (US$ 26)	260 g (US$ 26)
MnC₂O₄.2 H₂O	440 g (US$ 88)	450 g (US$ 90)
Sodium salts^8 8 See Table 6	31.27 kg (US$ 5,040)	9.02 kg (US$ 676.50)
Total value products	US$ 5,154.00	US$ 792.50

Brasil

Brasil

SEPARATION OF ZINC FROM MANGANESE BY SOLVENT EXTRACTION FROM ACIDIC LEACHATES OF SPENT ZINC-MnO2 DRY CELLS USING NEUTRAL ORGANOPHOSPHORUS EXTRACTANTS

SEPARATION OF ZINC FROM MANGANESE BY SOLVENT EXTRACTION FROM ACIDIC LEACHATES OF SPENT ZINC-MnO₂ DRY CELLS USING NEUTRAL ORGANOPHOSPHORUS EXTRACTANTS