Optimization of bioleaching conditions for metal removal fromspent zinc-manganese batteries using response surface methodology.

BACKGROUND: As 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 thiswaste. In this study identification of the optimum values of the effective parameters in biotechnological processes was investigated using response surfacemethodology. RESULTS: The released dose of Zn andMnwas highly dependent on many parameters. Non-linear equationswere formulated to describe the relationship between bioleaching efficiency of Zn andMn 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. Themaximum predictive extraction efficiency of Zn andMn was 52.5% and 52.4%, respectively. CONCLUSION: The maximum efficiency of extraction of both Zn andMn reached 50% under optimum conditions after 9 days of bioleaching. Additionally, XRD analyses suggested that Zn andMn existed mainly as Hetaerolite (ZnMn₂O₄) in the spent Zn-Mn batteries, which gradually disappeared and released Zn²⁺ and Mn²⁺ into solution during bioleaching process. [ABSTRACT FROM AUTHOR]