Role of clay minerals on reduction of Cr(VI)

•Fe(II) released from clay mineral reduced Cr(VI) fast.•Fe(II) adsorbed on the surface of clay mineral reduced Cr(VI) slowly.•Clay minerals are sources of Fe(II) to reduce Cr(VI).

Clay minerals could reduce Cr(VI) to Cr(III) in the soil, but the mechanisms and influential factors for the reduction reaction have not been clearly reported. In this study, it was hypothesized that the Fe(II) released from the clay minerals or adsorbed on the clay surface plays a crucial role in the reduction of Cr(VI). The Fe(II) released from clay minerals reduced Cr(VI) rapidly in the aqueous phase at the initial stage, and the amount of Fe(II) in the aqueous phase was directly proportional to the amount of Cr(VI) reduced. Cr(VI) was then reduced gradually by the Fe(II) adsorbed on the clay minerals. XPS analysis confirmed the change of Fe speciation on the surface of the clay minerals. Therefore, we concluded that the reduction in Cr(VI) by the clay minerals was due to the Fe in the clay minerals.

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