Bioleaching of V, Ni, and Cu from residual produced in oil fired furnaces using Acidithiobacillus ferrooxidans

This study presents bioleaching of metals from a vanadium-rich oil-fired ash (OFA) sample using adapted Acidithiobacillus ferrooxidans. OFA is a major by-product of thermal power plants that contains metals such as V, Ni and Cu. The adaptation of bacteria to the ash sample was carried up to 4% (w/v), then three factors affecting metals recovery including initial pH, initial Fe2+ concentration and inoculum percentage were selected to be optimized. Initial pH of 1, inoculum of 1% and initial Fe2+ concentration of 1 g/l were determined as optimal condition. Under optimum condition after 10 days the maximum recovery for V, Ni and Cu was obtained 82%, 86%, and 87%, respectively. Results showed that in comparison with chemical leaching, bioleaching recovery of V, Ni and Cu were improved 20%, 16% and 8%, respectively. To determine the rate limiting step of the process, modified shrinking core model was used and result showed that diffusion step controlled the overall dissolution. The morphology and crystallinity of the samples before and after bioleaching were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. Risk assessments of OFA before and after bioleaching by the toxicity characteristic leaching procedure (TCLP) were done and results indicated the bioleaching process detoxified OFA and the bioleached residue was well within the regulatory limits. (C) 2015 Elsevier B.V. All rights reserved.