Bioleaching of heavy metals from spent household batteries using Acidithiobacillus ferrooxidans: Statistical evaluation and optimization

In this study, spent batteries were selected from municipal waste for bioleaching and extraction of their heavy metals. The bioleaching of nickel, cadmium, and cobalt from Ni-Cd and NiMH batteries was done using Acidithiobacillus ferrooxidans, a resistant strain used for bioleaching. The adaptation process was successful and the solid-to-liquid ratio reached 10 g/L (battery powder weight/volume of medium). A Box-Behnken design of response surface methodology (RSM) was used to investigate the effects of initial pH, powder size, and initial Fe3+ concentration on the percentage of metals recovered. The proposed statistical method was used to accurately evaluate the interactions of the factors and their effects on the recovery efficiency of nickel, cadmium and cobalt during bioleaching. Under the specified conditions, up to 99% recovery was observed for each metal, confirming that A. ferrooxidans is an effective toxin resistant microorganism for bio-recovery of heavy metals. Decreasing the initial pH and particle size and increasing the initial Fe3+ concentration led to maximum recovery for nickel and cobalt; while the optimum condition for cadmium was different for Ni and Co. To maximize simultaneous extraction of three metals, the optimum value for initial pH, particle size and initial Fe3+ concentration were obtained 1, 62 mu m and 9.7 g/L, respectively. Under these conditions, the recoveries predicted by the software (Design Expert version 7.1.4) were 85.6% for Ni, 66.1% for Cd, and 90.6% for Co. These results were confirmed using a verification experiment at optimum condition, which calculated 87%, 67%, and 93.7% for Ni, Cd and Co, respectively. Due to the distinct chemical characteristics of Cd in contrast with Ni and Co, its recovery in the optimal condition for simultaneous recovery was decreased; in the other words; Cd recovery was higher when it was the sole target for extraction. (C) 2014 Elsevier B.V. All rights reserved.