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Heavy Metal Release from Contaminated Soils

Comparison of Column Leaching and Batch Extraction Results

Institute of Terrestrial Ecology, Swiss Federal Institute of Technology, Grabenstrasse 3, CH-8952 Schlieren, Switzerland

View larger version (22K): [in a new window]   Fig. 1. Column effluent composition of Soil 1. (a) Preconditioning with 10-5 M CaCl2 and leaching of Ca-exchangeable metals with 10-2 M CaCl2 solution (pH 6). An effluent volume of 1 mL/g corresponds to approximately 2.6 pore volumes. (b) Leaching with 10-2 M CaCl2 adjusted to pH 3.0. An effluent volume of 1 mL/g corresponds to approximately 2.1 pore volumes. The first 100 mL/g corresponded to the same leaching sequence as in (a).

View larger version (23K): [in a new window]   Fig. 2. Column effluent composition of Soil 2. (a) Preconditioning with 10-5 M CaCl2 and leaching of Ca-exchangeable metals with 10-2 M CaCl2 solution (pH 6). An effluent volume of 1 mL/g corresponds to approximately 1.7 pore volumes. (b) Leaching with 10-2 M CaCl2 adjusted to pH 3.0. An effluent volume of 1 mL/g corresponds to approximately 1.5 pore volumes. The first 100 mL/g corresponded to the same leaching sequence as in (a).

View larger version (24K): [in a new window]   Fig. 3. Column effluent composition of Soil 3. (a) Preconditioning with 10-5 M CaCl2 and leaching of Ca-exchangeable metals with 10-2 M CaCl2 solution (pH 6). An effluent volume of 1 mL/g corresponds to approximately 1.9 pore volumes. (b) Leaching with 10-2 M CaCl2 adjusted to pH 3.0. An effluent volume of 1 mL/g corresponds to approximately 1.7 pore volumes. The first 100 mL/g corresponded to the same leaching sequence as in (a).

View larger version (25K): [in a new window]   Fig. 4. Column effluent composition of Soil 4. (a) Preconditioning with 10-5 M CaCl2 and leaching of Ca-exchangeable metals with 10-2 M CaCl2 solution (pH 6). An effluent volume of 1 mL/g corresponds to approximately 1.6 pore volumes. (b) Leaching with 10-2 M CaCl2 adjusted to pH 3.0. An effluent volume of 1 mL/g corresponds to approximately 1.1 pore volumes. The first 100 mL/g corresponded to the same leaching sequence as in (a).

View larger version (26K): [in a new window]   Fig. 5. Column effluent composition of Soil 3 during leaching with CaCl2 solutions adjusted to pH 3. (a) Experiment with a low Ca influent concentration of 10-5 M (an effluent volume of 1 mL/g corresponds to approximately 1.9 pore volumes). (b) Experiment at low flow rate of 0.05 mL/min (an effluent volume of 1 mL/g corresponds to approximately 1.7 pore volumes).

View larger version (27K): [in a new window]   Fig. 6. Column effluent composition of Soil 4 during leaching with CaCl2 solutions adjusted to pH 3. (a) Experiment with a low Ca influent concentration of 10-5 M (an effluent volume of 1 mL/g corresponds to approximately 1.5 pore volumes). (b) Experiment at low flow rate of 0.05 mL/min (an effluent volume of 1 mL/g corresponds to approximately 1.2 pore volumes).

View larger version (58K): [in a new window]   Fig. 7. Amounts of Cd, Zn, Pb, and Cu extracted in column leaching experiments, single batch extraction with 1 M CaCl2 solution at a solution to soil ratio (SSR) = 100 mL/g, and sequential batch extractions. All results are given in percent of the respective total metal concentrations (Table 1). The arrows on top of bars for column experiments indicate that the respective pools were not depleted at the end of the leaching period.