Effect of ionic strength on cadmium adsorption onto kaolinite in single- and multi-element systems

摘要

Cadmium (Cd) adsorption on kaolinite was studied at three ionic strengths (I) viz., 0.01, 0.1 and 0.5 using mu NaNO_3 as a background electrolyte and at an equilibrium pH 6. Applied concentration of Cd ranged from 16.7 to 950.0 mu M in the single-element system, whereas, applied concentration of Cd and other metals (Cu, Pb and Zn) ranged from 4.2 to 237.5 mu M each in the multi-element system. Cd adsorption increased with increase in equilibrium concentration at any ionic strength and decreased with increase in ionic strength at any given equilibrium concentration in both single- and multi-element systems. At I= 0.5, the adsorption isotherm approached linearity, whereas, at I = 0.01, the adsorption isotherms reached a plateau at higher equilibriumconcentrations in both single- and multi-element systems. The difference between Cd adsorption I = 0.5 and I=0.1 was greater in the single element system than the multi-element system. A similar pattern was observed for difference between Cd adsorptionat I= 0.1 and I= 0.01, however the magnitude of the difference was much greater in the latter case.