Reductive leaching of manganese and zinc from spent alkaline and zinc–carbon batteries in acidic media

Abstract

The main purpose of this work was to investigate the effectiveness of oxalic acid as a reductant for the leaching of manganese and zinc from spent alkaline and zinc–carbon batteries in sulfuric acid or hydrochloric acid media. Three different types of battery powders were tested: zinc–carbon, alkaline and mixed (50% zinc–carbon, 50% alkaline). Kinetic tests were initially conducted with the mixed battery powder. Leaching experiments were carried out according to 2 4 full factorial design, and regression equations for the leaching of Mn and Zn were determined. Washing of the powders (neutral leaching) was effective on the removal of potassium and chloride. Increasing solid/liquid ratio from 1/5 to 1/10 in neutral leaching did not significantly change potassium and chloride removal. A leach duration of 3 h was found to be generally sufficient for the equilibrium to be reached for both Zn and Mn. Oxalic acid concentration had strongest negative effect on Zn leaching in both sulfuric and hydrochloric acid media, whereas the concentrations of sulfuric and hydrochloric acids exhibited strongest positive effect for both Mn extraction yield (MnEY) and Zn extraction yield (ZnEY). In the range of tested conditions, pulp density had no important effect on MnEY and ZnEY for both acids. Temperature had negative effect for both MnEY and ZnEY in sulfuric acid solution; however, such effect was less pronounced in hydrochloric acid solution. For the sulfuric acid solution, 91% MnEY and 112% ZnEY were achieved at 45 °C after 3 h of leaching by 10% pulp density, − 30% oxalic acid (30% less than the stoichiometric requirement), + 30% H 2SO 4. For the hydrochloric acid solution, about 86% MnEY and 95% ZnEY were obtained at 20% pulp density, − 30% oxalic acid, + 30% HCl, at 45 °C after 3 h of leaching.