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

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

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

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

Distribution of six heavy metals in contaminated clay soils before and after extractive cleaning

A sequential extraction procedure according to Tessier et al. is carried out to compare the distribution of six metals (Cd, Cr, Cu, Ni, Pb and Zn) in contaminated clay soils before and after extractive cleaning. Extraction of metals from the ‘soil fractions’ with 0.1 N HC1 or 0.1 M EDTA becomes more difficult in the order: ‘Carbonate’ <‘Fe/Mn-Oxides’ <‘Organic/Sulfidic’ <‘Residual’ Extraction from the ‘residual’ fraction in particular is much harder than from the other three: 50% of the experiments shows a metal extraction efficiency less than 33% from this ‘soil fraction’. Removing the remaining pollution will be difficult without drastic destruction of soil components

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

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

Distribution of six heavy metals in contaminated clay soils before and after extractive cleaning

A sequential extraction procedure according to Tessier et al. is carried out to compare the distribution of six metals (Cd, Cr, Cu, Ni, Pb and Zn) in contaminated clay soils before and after extractive cleaning. Extraction of metals from the ‘soil fractions’ with 0.1 N HC1 or 0.1 M EDTA becomes more difficult in the order: ‘Carbonate’ <‘Fe/Mn-Oxides’ <‘Organic/Sulfidic’ <‘Residual’ Extraction from the ‘residual’ fraction in particular is much harder than from the other three: 50% of the experiments shows a metal extraction efficiency less than 33% from this ‘soil fraction’. Removing the remaining pollution will be difficult without drastic destruction of soil components

Continuous treatment of heavy metal contaminated clay soils by extraction in stirred tanks and in a countercurrent column

Extn. of metals from 2 contaminated waste site clay soils by 0.1-0.3 N HCl solns. was tested in 3 lab. scale, continuous processes: 2 stirred tank reactors (CSTR' s) in series; a countercurrent sieve-plate column fed with flocculated clay soil materials; and a combination of tank reactor and column. After extn. clay soil suspension and extractant were sepd. by means of flocculation and sedimentation. The countercurrent process gave greater efficiencies in removing the metal than the CSTR process but the difference was only small. The following type of cleaning process seemed to be promising: first an extn. in a stirred tank followed by a second extn. in a countercurrent column. Residence time in the CSTR could be short (15-30 min), but as long as possible in the column

Extraction kinetics of six heavy metals from contaminated clay soils

The rate of the extraction of four heavy metals (Cu, Nl, Pb and Zn) from artificially polluted and waste site clay soils is determined in a 0.1 N HCl solution. A two-reaction model is developed that describes the rate of extraction at a constant pH and at a constant temperature by two processes: a fast, irreversible reaction that is first-order in the metal concentration in the clay and a slow, reversible first-order reaction. The influence of the temperature on the extraction rate is measured over a range of 5 to 80°C for Ni extraction from an artificially polluted clay soil. Calculated values for the energy of activation suggest that the extraction process is rate-limited by a diffusion process in the porous soil particles, but chemical limitations seem probable in case of the older contaminations in the waste site soils