ADSORPTION BEHAVIOR OF CADMIUM IN RESPONSE TO SOIL SURFACE CHARGE

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Abstract
The adsorption behavior of Cd, both as Cd2+ and complexed as CdEDTA2-, on 4 soils was investigated. Christiana silt loam (Typic Paleudult), Lima loam (Typic Hapludalf), and Vergennes silt loam (Glossaquic Hapludalf) all exhibited low zero points of charge (ZPC .simeq. 2) and thus were negatively charged over the entire pH range typical of soil systems. Dothan clay (Plinthic Paleudult), in contrast, had a ZPC around pH 6.0, indicating an electropositive surface at its field pH (4.7). The pH-dependent adsorption of Cd2+ was nearly identical for the 4 soils. When complexed as Cd-EDTA2-, Cd was absorbed by the positively charged Dothan soil, suggesting that strong chelation does not necessarily preclude substantial metal absorption. In soils with high ZPC, complexed heavy metals may be less mobile and available than their unbound counterparts.