FRACTIONATION AND OXIDATION OF CHROMIUM IN TANNERY WASTE AND SEWAGE SLUDGE-AMENDED SOILS

Clay, sand and peat soils were mixed with tannery waste so that the fi nal concentrations of total chromium were between 1500 and 2000 mu g g (-1) and with sewage sludge where the final concentrations of total ch romium ranged from 170 to 200 mu g g(-1). The experiment was carried o ut for 2 years under atmospheric conditions. Fractionation of chromium was studied in these soils employing a sequential extraction procedur e and oxidation of chromium by measurement of chromium(VI) in the wate r-soluble fraction. The results of fractionation studies in tannery wa ste-amended soils indicated that 5 months after the start of the exper iment up to 1.1% of total added chromium was oxidized in clay, 0.45% i n sand, and only 0.03% in peat soil. The concentration of the water-so luble chromium and chromium(VI) decreased in further continuation of t he experiment since chromium was redistributed to more sparingly solub le fractions of soils. The process of chromium oxidation was not obser ved in sewage sludge-amended soils.