Bioleaching of zinc and manganese from spent Zn–Mn batteries and mechanism exploration

In this work, bioleaching was used to extract valuable Zn and Mn from spent Zn–Mn batteries. The results showed that 96% of Zn extraction was achieved within 24 h regardless of energy source types and bioleaching bacteria species. However, initial pH had a remarkable influence on Zn release, extraction dose sharply decreased from 2200 to 500 mg/l when the initial pH value increased from 1.5 to 3.0 or higher. In contrast to Zn, all the tested factors evidently affected Mn extraction; the maximum released dose of 3020 mg/l was obtained under the optimum conditions. The acidic dissolution by biogenic H2SO4 by the non-contact mechanism was responsible for Zn extraction, while Mn extraction was owed to both contact/biological and non-contact mechanisms. The combined action of acidic dissolution of soluble Mn2+ by biogenic H2SO4 and reductive dissolution of insoluble Mn4+ by Fe2+ resulted in 60% of Mn extraction, while contact of microbial cells with the spent battery material and incubation for more than 7 days was required to achieve the maximum extraction of Mn.