Reduction and oxidation processes of chromium in soils

The kinetics of reduction and oxidation of soluble chromium in various soil s (peat, clay, sand, and luvi-chromic cambisols) were studied at constant s oil moisture and constant temperature. A total of 1500 g of each soil was i ncubated with different concentrations of aqueous solutions of K2Cr2O7 or C rCl3 [1-1000 mu g (g of dry soil)(-1)]. The total exchangeable chromium and Cr(VI) were analyzed in soil extra cts over a period of up to 10 days. The parameters influencing the reduction and oxidation of soluble chromium wer e studied. Reduction of soluble chromium was observed in all the soils exam ined. It depends mostly on the content of organic matter, on the concentrat ion of the added chromium, and on the pH of the soil. Up to 3 days of the e xperiment, the reaction was found to he first-order with respect to. Cr(VI) . Oxidation of soluble chromium was observed especially in soils high in ma nganese(IV) oxides and low in organic matter. The oxidation of added solubl e chromium did not occur in peat soil. The results indicate that the oxidat ion and reduction of soluble chromium added to soils depends on the soil st ructure and on the reduction/oxidation conditions in the particular soil.