ADSORPTION-DESORPTION CHARACTERISTICS OF HIGH-LEVELS OF COPPER IN SOIL CLAY FRACTIONS

Copper adsorption and desorption under acid conditions by soil clay fr actions separated from Vertisol, Planosol and Gleyic Acrisol has been studied in 0.01 M Ca(NO3)(2). A Freundlich equation was appropriate to describe Cu adsorption. Within the range of 150 to 2600 mg of copper per kg of soil clay fraction the proportions of Cu not displaced durin g 5 successive 48-hour desorptions with 0.01 M Ca(NO3)(2) decreased wi th increasing adsorption density and at the lower pHs. The proportions ranged from as high as 0.98 in the case of the Vertisol clay (pH 5.3) to as low as 0.12 (88% desorption) in the Planosol clay (pH 4.5). Mea surement of separation factors (alpha Cu/Ca) showed that the preferenc e of the clay surface for Cu over Ca decreased in the order: Gleyic Ac risol > Planosol > Vertisol. A considerable amount of sorbed copper co uld be solubilized by decreasing pH values to 4 when in the Planosol c lay 39% was desorbed and 45% was desorbed in the Gleyic Acrisol clay.