Optimization of bioleaching conditions for metal removal from spent zinc‐manganese batteries using response surface methodology

Abstract

AbstractBACKGROUNDAs a special residue containing zinc and manganese, spent Zn–Mn batteries cause a serious concern due to their toxicity, abundance and permanence in the environment, and biotechnological recovery of Zn and Mn is one method of recycling this waste. In this study identification of the optimum values of the effective parameters in biotechnological processes was investigated using response surface methodology.RESULTSThe released dose of Zn and Mn was highly dependent on many parameters. Non‐linear equations were formulated to describe the relationship between bioleaching efficiency of Zn and Mn and four important parameters. The optimum parameter values were determined as follows: dose of mixed energy substrates, exogenous‐acid pH adjustment, incubating temperature and pulp density of 28 g L−1, 1.9, 33 °C, 9.7%, respectively, for Zn release and 29 g L−1, 1.8, 36.7 °C, 8%, respectively, for Mn mobilization. The maximum predictive extraction efficiency of Zn and Mn was 52.5% and 52.4%, respectively.CONCLUSIONThe maximum efficiency of extraction of both Zn and Mn reached 50% under optimum conditions after 9 days of bioleaching. Additionally, XRD analyses suggested that Zn and Mn existed mainly as Hetaerolite (ZnMn2O4) in the spent Zn–Mn batteries, which gradually disappeared and released Zn2+ and Mn2+ into solution during bioleaching process. © 2014 Society of Chemical Industry