ADSORPTION-DESORPTION BEHAVIORS OF PB AND CD IN LAKE CHAPALA, MEXICO

The adsorption-desorption behaviors of Cd and Pb in Lake Chapala sedim ents were studied through laboratory experiments and computer modellin g. Experiments were designed to study the effects of water quality var iations observed in the lake over two decades, on the sorption behavio rs of these metals. Both Cd and Pb formed outer-sphere complexes with the functional groups on the sediment surface. Overall equilibrium ads orption constants obtained at low ionic strength of experimental backg round electrolytes were used to simulate higher salinity conditions in the water-sediment system. Pb adsorbed forming stronger surface compl exes (pK = -2.0 and -3.5) than Cd (pK = 8.2), and the reaction of Pb w ith the sediment surface was almost irreversible when compared to Cd w hen electrolyte concentrations were increased. These observed behavior s have been explained by the different chemical properties of these me tals. (C) 1997 Elsevier Science Ltd.