Effects of Cr(VI)-reducing bacteria on the behaviour of Cr(VI) adsorption by goethite and haematite: speciation and distribution

Propose: In the soil environment, the existence of Cr(VI)-reducing microorganisms might affect the adsorption, desorption and reduction of Cr(VI) adsorbed on soil minerals (such as Fe oxides). The behaviour of Cr(VI)-reducing microorganisms might affect the adsorption and reduction of Cr(VI) by soil minerals. Materials and methods: Goethite and haematite with saturated adsorbed Cr(VI) were incubated with Microbacterium sp. QH-2, a Cr(VI)-reducing bacteria. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to detect the changes in goethite and haematite. X-ray absorption near-edge structure (XANES) was performed to detect the changes in Cr(III) and Cr(VI) on goethite and haematite. Results and discussion: Strain QH-2 adhered to the surfaces of goethite and haematite. No morphological changes in goethite and haematite were detected after incubation. No secondary Fe minerals formed. Cr(III) was the dominant species of Cr on goethite and haematite (78.5% for goethite and 96.7% for haematite) after incubation. Furthermore, the reduction rate of Cr(VI) by strain QH-2 in the liquid phase was faster than that of Cr(VI) adsorbed on goethite and haematite. Conclusions: The existence of strain QH-2 could promote the adsorption of Cr by goethite and haematite. Strain QH-2 could affect the morphological distribution and transformation of Cr in Fe oxides such as goethite and haematite.