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To investigate the aging process and reduction of Cr(VI) in two soils. The adsorption behavior of the soils demonstrated that the paddy soil had higher adsorption capacity for Cr(VI), but the capacity was lower for Cr(III), which contrasted the results for fluro-aquic soil. The mobilizable Cr was assessed using EDTA extraction. The results suggested that the reduction of Cr(VI) to Cr(III) and the aging process occurred simultaneously. A simplified kinetic model was established and the rate constants of the reduction and aging processes were obtained. The aging process and reduction of Cr(VI) were faster in the paddy soil, due to a higher adsorption capacity and stronger reducing ability, as indicated by the organic matter and amorphous Fe oxides. The Cr(III) aging was faster in the fluro-aquic soil due to the low solubility of Cr(III) at a high pH. The modeling study provides a fundamental understanding of the dynamics of Cr mobility in a complicated soil system.

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