Recovery of manganese and zinc from spent Zn-C cell powder: Experimental design of leaching by sulfuric acid solution containing glucose

The spent Zn-C cell powder, containing ZnMn2O4, ZnO, MnO(OH) and possibly Mn2O3 and Mn3O4, can be leached by a sulfuric acid solution mixed with some glucose. The leaching is found to be dependent on solid to liquid (S/L) ratio, amount of glucose, concentration of sulfuric acid solution, time and pulp agitation speed. For 5 g powder (S), 1 h leaching time and 300 rpm pulp agitation speed, two-level four-factor (24) experimental designs have been carried out to derive models for extraction of both Mn(II) and Zn(II). Amount of glucose (G, g), concentration of H2SO4 solution (C, mol/L), volume of H2SO4 solution as leachant (L, mL) and leaching temperature (T, °C) are considered as factors (variables). The model in both cases consists of mean, factor effects and interaction effects. The four-factor interaction effect is observed in neither of the cases. Some two-factor and three-factor effects are found to have produced positive or negative contributions to dissolution percentage in both cases. The models are examined for comparison with experimental results with good fits and also used for optimization of factors. At optimized condition (G = 0.50 g, C = 2 mol/L, L = 250 mL and T = 100 °C), an aliquot of 5 g powder in 1 h and at 300 rpm produces a solution containing (7.08 ± 0.10) g/L Mn(II) and (2.20 ± 0.06) g/L Zn(II) corresponding to almost 100% extraction of both metal ions.