ABSTRACT
Different types of microorganisms play important roles in the bioleaching process. Bacteria and archaea commonly used in bioleaching processes are able to oxidize iron and/or inorganic sulfur compounds, acidophiles, many times autotrophic, and they can tolerate elevated concentrations of metals. Bioleaching has been considered to be a key technology for the recovery of metals such as Al, Ni, Zn, Cu, Cd, and Cr from fly ashes, electronic scraps, spent batteries, waste slag, and spent petroleum catalysis. The most important species of fungi capable of bioleaching are Aspergillus niger and Penicillium simplicissimum because of their ability to excrete abundant amounts of organic acids such as oxalic acid, citric acid, and maleic acid that selectively dissolve some metals. Bioleaching and biosorption are promising routes because they offer an ecological alternative in an economically feasible manner. Bioleaching has been used for the recovery of metals from ores for many years.
