ANAEROBIC MICROBIAL REMOBILIZATION OF TOXIC METALS COPRECIPITATED WITH IRON-OXIDE

An anaerobic N2-fixing Clostridium sp. solubilized Cd, Cr, Ni, Pb, and Zn coprecipitated with goethite (α-FeOOH) by (i) direct action due to enzymatic reduction of ferric iron and the release of metals associated with iron and (ii) indirect action due to metabolic products. The extent of dissolution depended upon the nature of the association of the metals with goethite. Substantial amounts of Cd and Zn, which were closely associated with iron, were released due to direct action. Nickel was solubilized by direct and indirect actions, while a small amount of Cr was solubilized only by direct action. The nature of association of Pb in the coprecipitate was not affected by the presence of other cations and it was solubilized by indirect action. In the presence of bacteria, the concentration of soluble Pb decreased due to biosorption. These results show that there could be significant remobilization of toxic metals coprecipitated with iron oxides in wastes, contaminated soils, and sediments due to microbial iron reduction. © 1990, American Chemical Society. All rights reserved.