Removing heavy metals from contaminated clay soils by extraction with hydrochloric acid, edta or hypochlorite solutions

Abstract

Removal efficiencies of six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) from contaminated clay soils were measured In batchwise extractions. Between 80 and 9054 of Cd, Cu, Pb and Zn could be extracted by hydrochloric acid (HC1) treatment (repeated extractions with 0.1 N or a single one with 2 N). N1 extraction percentages varied between 45 and 8054. A concentration above 0.1 N HC1 will be necessary to clean the contaminated clay soils to maximum tolerable metal levels. This will cause severe damage to the original soil structure. A successful extraction with EDTA required a suspension pH below 4. Only Cd and Pb were removed to levels comparable with the HC1 treatments. Chromium could hardly be extracted by HC1 or EDTA. Treatment with a hot 0.46 M sodium hypochlorite solution at pH=8.5 gave the greatest chromium release compared to other, tested extractants: 70–8554 Cr removal.