Oxidation and Fate of Chromimn in Soils

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Land disposal of chromium-containing wastes constitutes an environmental risk where oxidation of Cr(III) to Cr(VI) may occur. The oxidation rate of Cr(III) to Cr(VI) and different forms of Cr(VI), labile (adsorbed and solution) and solid forms were determined, in 11 moist soil samples collected from four Texas soil series (Silawa, Boonville, Burleson, and Pledger soils). The Cr oxidation rate increased with increasing content of reactive manganese (Mn) oxides and decreasing pH of the soils as follows: Pledger > Silawa > Boonville ≌ Burleson. Concentration of labile Cr(VI) in the soils was apparently controlled by barium chromate (BaCrO_4) without barite (BaSO_4) or by Cr-substituted barite [Ba(S,Cr)O_4] in the presence of barite. The Boonville soil contained barite and a much lower concentration of labile Cr(VI) than the other soils. Based on the Cr oxidation rate and forms of Cr(VI), soils with a low content of reactive Mn oxide, high pH, and barite was recommended for field testing as safe land disposal sites of Cr-containing wastes to minimize Cr oxidation and mobility. Boonville soil was the best soil among the four soils for safe land disposal of wastes containing Cr.
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