Adsorption of Zn2+ and Cd2+ Ions on Vermiculite in Buffered and Unbuffered Aqueous Solutions

Abstract

Studies of Zn2+ and Cd2+ ion adsorption onto vermiculite from buffered and unbuffered aqueous solutions were conducted in order to compare their ion adsorption behaviours in different systems. The use of buffer reagents had a strong and negative effect on the adsorption of the metal ions under study. The experimental data obtained from both the buffered and unbuffered solutions could not be described by a single traditional adsorption isotherm due to the effect of the adsorbent concentration (W). The equilibrium ion concentration in bulk solution (Z) and the equilibrium ion adsorption density (X/W ratio) decreased with increasing W in both buffered and unbuffered systems, indicating that the use of a buffer solution is not an effective measure for eliminating the effect of the adsorbent concentration. The addition of competitive ions (H+, Cd2+ and Zn2+) greatly reduced the adsorption of the target metal ion. Within the pH range tested (initial pH < 7), the competitive effect of H+ ions was equivalent to t...