Competitive effect of copper, zinc, cadmium and nickel on ion adsorption and desorption by soil clays

This study evaluated the effect of competing copper, zinc, cadmium and nick el ions in 0.01 M Ca(NO3)(2) on heavy metal sorption and desorption by soil clay fractions. Initial Cu addition levels varied from 99 mg kg(-1) to 900 mg kg(-1) and Zn, Cd and Ni levels were 94, 131 and 99 mg kg(-1), respecti vely. Sorption of Cu conformed to a Freundlich equation. The amounts of met als not displaced by successive 48 h desorption cycles with 0.01 M Ca(NO3)( 2) were considered 'specifically adsorbed'. Total sorption of Zn and Cd gen erally decreased in the order: Vertisol > Gleyic Acrisol > Planosol clay. M ore than 70% of the copper was specifically sorbed. Specific sorption of Zn was depressed by competition with Cu in the three clays investigated. At s urface coverages higher than 200 mg Cu per kg of soil clay, zinc sorption i n the Planosol and Gleyic Acrisol clays took place at low affinity sites. T he exchangeable component of sorbed cadmium accounted for > 60% of the sorp tion in the Vertisol clay, > 70% in the Gleyic Acrisol clay and was almost 100% in the Planosol clay. Nickel was not retained by the Planosol and Gley ic Acrisol clays and was ionexchangeably adsorbed by the Vertisol clay. At the conditions studied, Ni and Cd remain a ready source of pollution hazard .