Redox Interactions Between Cr(VI) and Fe(II) in Bioreduced Biotite and Chlorite
2014
Contamination of the environment with Cr as chromate (Cr(VI)) from industrial activities is of significant concern as Cr(VI) is a known carcinogen, and is mobile in the subsurface. The capacity of Fe(II)-containing phyllosilicates including biotite and chlorite to alter the speciation, and thus the mobility, of redox-sensitive contaminants including Cr(VI) is of great interest since these minerals are common in soils and sediments. Here, the capacity of bacteria, ubiquitous in the surface and near-surface environment, to reduce Fe(III) in phyllosilicate minerals and, thus, alter their redox reactivity was investigated in two-step anaerobic batch experiments. The model Fe(III)-reducing bacterium Geobacter sulfurreducens was used to reduce Fe(III) in the minerals, leading to a significant transformation of structural Fe(III) to Fe(II) of 0.16 mmol/g (∼40%) in biotite and 0.15 mmol/g (∼20%) in chlorite. The unaltered minerals could not remove Cr(VI) from solution despite containing a larger excess of Fe(II) ...
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