Leaching Studies of Spent Zinc-Manganese Alkaline Batteries with Sulphuric Acid

Abstract:

The hydrometallurgical processing of metal bearing residues is one of the established routes envisaging metals recovery. In these processes, the leaching operation plays a central role as allows the solubilization of metals for further separation and recovery as pure products. This route can be applied to spent domestic batteries recycling, which studies on sulphuric acid leaching of spent alkaline batteries are reported in this paper. Material samples used in the trials were prepared concerning the real proportion of the most common sizes and shapes of batteries found in the usual stream of this type of wastes. The research involved the evaluation of some factors which affect leaching yields namely temperature, reaction time and stirring speed, through a two-level factorial design methodology and analysis of variance. In this study, other factors related with leachant concentration and stoichiometry were maintained constant. Zinc leaching yields were generally high and even near 100% when the high levels of the variables were used, meaning that zinc oxides present in the electrodes are very reactive to acid leachant. The variables had all positive effects being temperature the most significant factor (confidence level 99%) while the other factors were less significant (98.8% for time and 95% for stirring speed). Concerning manganese, leaching yields obtained were more dependent from the factors, being also positive and varying from 11% (for low levels of factors combination) to 89% (for high levels of factors combination). Temperature and time were highly significant (confidence levels above 99.9%) while stirring speed was less significant (97%). Contamination of leach liquors with iron was also evaluated since it is an impurity which requires special attention during the process development. For the higher levels of the factors (t = 1 h, T=80°C and ω=400 rpm) the final solution contained 10 g/L Zn, 15 g/L Mn and 3.2 g/L Fe. The removal of the iron from the solution is a necessary step prior to the separation and recovery of zinc and manganese.