Microbial formation of crystalline scoro

Scorodite (FeAsO4·2H2O) is a thermodynamically stable mineral with advantages as an arsenic disposal compound. With an aim to immobilize highly toxic As(III) contained in the copper refinery process solution, eventually in the form of crystalline scorodite, the use of thermo-acidophilic iron-oxidizing archaeon, Acidianus brierley, was investigated. The extent of As(III) oxidation by A. brierley became greater at elevated cubic As(III) concentrations, especially in the presence of excess ferrous (Fe(II)) on cell surface. Microbial growth on yeast extract was also implied to facilitate As(III) oxidation by Fe(II) on cell surface. When the initial Fe(II)/As(III) ratio was set 1.4 in the presence of yeast extract, both ions were readily oxidized and 86–100% of As was precipitated as crystalline scorodite. The molar ratio of microbially-oxidized Fe(II) and As(III) was an important factor to determine the type of the secondary mineral formed. Phosphate concentration was another critical factor for scorodite biomineralization. Biogenic scorodite was crystallized with an almond-shaped polyhedron habit of 1 μm in size. This study provides insights into the potential utilization of microbial techniques for the treatment of As(III)-bearing copper refinery process solution by producing scorodite.