Sorption and desorption of copper on soil clay components

Toxic effects have been reported due to the accumulation of Cu in soils receiving long-term applications of swine (Sus scrofa) manure, sewage, municipal composts, and mining waste. The objective of this study was to quantify sorption and desorption of Cu on various clay and clay-organic matter fractions separated from a Zook soil (fine, smectitic, mesic Cumulic Vertic Endoaquolls) located in central Iowa. The clay was separated into four particle-size fractions and portions of each fraction were treated with H2O2 and/or dithionite-citrate-bicarbonate (DCB) for removal of organic matter and free-iron compounds, respectively. A batch-equilibration technique was employed to evaluate sorption of Cu at pH 6.0 in the presence of 0.01 M CaCl2. The sorption isotherms show that Cu was preferentially sorbed on organic matter associated with the coarse clay fraction of the soil. After removal of organic matter, the fine clay (