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

► Bioleaching was used to extract Zn and Mn from spent Zn–Mn batteries for the first time. ► The almost complete release of both Zn and Mn showed great potential of bioleaching in the recovery of the spent batteries. ► The acidic dissolution by biogenic H 2SO 4 as non-contact mechanism was responsible for Zn extraction. ► Mn extraction was due to both contact and non-contact mechanism. ► Acidic dissolution by H 2SO 4 and reduction dissolution by Fe 2+ as non-contact mechanism contributed 60% of Mn extraction. 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 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 7 days was required to achieve the maximum extraction of Mn.