Abstract
Removal efficiencies of Pb and Cd from artificially contaminated clay soils with chelating agents such as ethylenediaminetetraacetic acid (EDTA) have been investigated. Retention characteristics of Pb in bentonite and kaolinite are dependent on pH. At high pH, precipitation mechanisms (e.g., precipitating as hydroxide/oxide or carbonate) dominate. As pH decreases, exchangeable form becomes dominant. The amounts of Pb retained in bentonite increase up to pH 5, but conversely decrease thereafter. This result corresponds to the change of the forms of Pb retained in bentonite. The amounts of Pb retained in kaolinite increase with an increase in pH. Removal efficiency of Pb retained as hydroxide/oxide or carbonate with chelating agents increases with an increase in pH of leach liquor. Pb retained as exchangeable form is removed by reaction with chelating agents and cation exchange with H+. Meanwhile, retention characteristics of Cd in bentonite and kaolinite are not dependent on pH and exchangeable form is dominant. The amounts of Cd retained in bentonite increase up to pH 5 and remain nearly constant thereafter. Meanwhile, the amounts of Cd retained in kaolinite increase with an increase in pH. Removal efficiency of Cd retained as exchangeable form increases with an increase in acidity of leach liquor. Also, removal efficiencies of Pb and Cd retained as exchangeable forms are enhanced by addition of Na salts.
