Biogenic scorodite crystallization by Acidianus sulfidivorans for arsenic removal

Scorodite is an arsenic mineral with the chemical formula FeAsO4·2H2O. It is the most common natural arsenate associated with arsenic-bearing ore deposits. In the present study we show that the thermoacidophilic iron-oxidizing archaeon Acidianus sulfidivorans is able to precipitate scorodite in the absence of any primary minerals or seed crystals, when grown on 0.7 g L-1 ferrous iron (Fe2+) at 80 °C and pH 1 in the presence of 1.9 g L-1 arsenate (H3AsO4). The simultaneous biologically induced crystallization of ferric iron (Fe3+) and arsenic to scorodite prevented accumulation of ferric iron. As a result, crystal growth was favored over primary nucleation which resulted in the formation of highly crystalline biogenic scorodite very similar to the mineral scorodite. Because mineral scorodite has a low water solubility and high chemical stability, scorodite crystallization may form the basis for a novel method for immobilization of arsenic from contaminated waters with high arsenic concentrations