Biosolubilisation of Metals and Metalloids

Abstract

The solubilisation of metals and metalloids is catalysed by a variety of microorganisms in natural and engineered environments. Biosolubilisation has a number of undesired implications, such as the generation of acid mine drainage and the formation of acid sulfate soils, which have harmful environmental impacts. Biosolubilisation also contributes to the corrosion of man-made structures causing significant economic losses. On the other hand biosolubilisation has been harnessed by the mining industry to recover valuable metals and uranium from low-grade ores and concentrates in large scale. This allows the utilisation of ores the processing of which would not be economically feasible through traditional mining methods. Biosolubilisation holds also potential for the recovery of resources from waste and clean-up of metal contaminated environments. This chapter reviews the role that microorganisms have in the solubilisation of various metals and metalloids, the mechanisms through which biosolubilisation occurs and microbial groups mediating the solubilisation. The environmental implications and industrial applications of biosolubilisation are also discussed. Microorganisms can catalyse biosolubilisation through oxidative and reductive dissolution, mediated by the oxidation and reduction of ferrous and ferric iron, respectively. Moreover, biosolubilisation can be achieved through the production of biogenic acids, alkali and ligands, such as cyanide, thiosulfate, organic acids and iodide. Mechanisms contributing to microbially influenced corrosion of metallic iron and steel include differential aeration cells, galvanic cells, attack by microbial oxidants, acids, sulfides and other metabolites, cathodic depolarisation and direct microbial extraction of electrons from steel. A wide range of microorganisms are able to facilitate solubilisation reactions, including bacteria, archaea and eukaryotes. Bioleaching has been explored for recovering metals from e.g. a variety of sulfide ores, metallurgical waste, electronic scrap, sludge from municipal and industrial wastewater treatment, municipal solid waste incineration fly ash and contaminated sites. Large-scale biosolubilisation has been mainly used for copper-, cobalt-, nickel-, zinc-, uranium- and gold-containing sulfidic ores through oxidative bioleaching, whereas reductive bioleaching is yet to be implemented at industrial scale.