Soil Chemistry Effect on Feasibility of Cr-decontamination by Acid-Washing

Soil washing with sample acid jas been proven to be effective for removal of cationic heavy metals from contaminated soils. Since the obsorption of anitonic heavy metals is enhanced in acidic medium, the efficiency of acid-washing may not be guaranteed for soils that are doubly contaminated with cationic and anitonic heavy metals. To evaluate the efficiensy of acid-washing, nine soils are artifically contaminated with chromate and chromium was extracted with hydrochrolic acid of 0.5 mmol L[-1] to 1mol L[-1]. A part of spiked chromate was reduced to trivalent chromium and the remaining chromate ions were almost quantitatively extracted witht the hydrochloric acid. However, increasing hydrochloric acid aoncentration was not effective for the extraction. Possible mechanisms underlying the observed low efficiency were considerated to be the enhanced reduction in acidic solution, complexation by humic substance and obserption via caution exchange reactions. We concluded that acid-washing satisfactorily works for chromate removal in non-allophanic soils but inefficient for removal of trivalent chromim particularly from soils having high effective cation exchange capacity and organic matter content