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 24h 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 500mg/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 3020mg/l was obtained under the optimum conditions. The acidic dissolution by biogenic H ₂SO ₄ 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 Mn ²⁺ by biogenic H ₂SO ₄ and reductive dissolution of insoluble Mn ⁴⁺ by Fe ²⁺ resulted in 60% of Mn extraction, while contact of microbial cells with the spent battery material and incubation for more than 7days was required to achieve the maximum extraction of Mn.