Impact of microbial Fe-oxide reduction on the sorption of Co(II)EDTA by goethite and a subsurface sediment

The dissimilatory bacterial reduction of goethite and a goethite-containing natural subsurface material and its impact on the sorption and stability of Co(II)EDTA complexes were investigated. In the absence of bacterial reduction, Co(II)EDTA sorbed as an anion. However, some dissociation of the complex was observed below pH 6.0 as a result of Fe{sup 3+} and Al{sup 3+} liberated by the solids. The sorption behavior of Co(II)EDTA changed markedly during the course of bacterial reduction as a result of ferrous iron release. Evolved Fe{sup 2+} displaced Co{sup 2+} from the Co(II)EDTA complex and competed for surface sorption sites. Geochemical calculations show how the time variant concentrations of Fe{sup 2+} produced during the course of bacterial reduction impact both aqueous and surface speciation.