Chemistry of Cr in Some Swedish Soils

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Abstract
Retention and recovery of Cr(III) and Cr(VI) added to four mineral soils and their impact on pH and status of soluble Mn were investigated. Undried soil portions (≤4 mm) equal to 50 g dry matter were packed in glass columns and eluted with CrCl3 solution containing 6250 μg Cr(III) or K2Cr2O7 solution containing 1000 μg Cr(VI), displacing the retained Cr(III) and Cr(VI) with NH4Cl and KH2PO4 solutions respectively. Mn was measured in all effluents. Total Cr, Cr(III) and Mn were determined on an atomic absorption spectrometer with a graphite furnace and D2-background compensation and Cr(VI) on a photometer. Cr(III) strongly acidified and Cr(VI) weakly acidified the soils. The soils possessed a high affinity for retention of Cr(III) and a low one for retention of Cr(VI). Recovery of the retained Cr was very low and tended to be greater the lower the soil pH. Oxidation of Cr(III) was not detected. Reduction of Cr(VI) was substantial in the soils. It increased linearly with decreasing pH (R 2=0.71) and increasing humus content (R 2=0.72). While Cr(III) mobilized soluble Mn in all soils, Cr(VI) immobilized the Mn in two of the soils.

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