Adsorption of Copper, Zinc, and Cadmium by a Forest Soil

Abstract

Time‐dependent batch equilibrium studies for Cu, Zn, and Cd were conducted to determine the sorbing properties for these metals on the upper 30 cm of a forest soil. Major cations were added to equilibrating solutions in an attempt to match to cationic matrix of a sewage sludge. Essentially all of the Cu was adsorbed by the soil in the first 0.3 hour of equilibration. Copper adsorption data fit the Freundlich isotherm better than the Langmuir isotherm. Adsorption of Zn and Cd was more time dependent than Cu, especially for the 0–7.5 cm depth of soil, and was described with some success by the empirical kinetic equation, ∂ S /∂ t = aC b S c , where S is µ g metal absorbed per g soil, C is concentration of metal in final equilibrating solution, t is time, and a, b , and c are constants. Batch data taken at 3 hours of equilibration for Zn and Cd also fit the Freundlich isotherm better than the Langmuir isotherm. For Cu, Zn, and Cd adsorption, Freundlich constants ( K ) were higher for the 0–7.5 cm depth than for the 7.5–15 cm depth, indicating the binding effects of the higher level of organic matter in the surface 7.5 cm of forest soil.