Kinetic analysis of the exchange processes between sodium ions from zeolite A and cadmium, copper and nickel ions from solutions

Kinetics of exchange processes between the sodium ions from zeolite A and cadmium, copper and nickel ions from solutions were determined by measuring the changes in the concentrations of Me2+ (Me2+ = Cd2+, Cu2+ and Ni2+) and sodium ions in both zeolite and the liquid phase during the exchange processes. The exchange kinetics were analyzed in accordance with the existing models, namely that diffusion and chemical reaction may be the rate-determining steps. Analyses have shown that chemical exchange is possible rate-determining step of the exchange process. Hence, the exchange kinetics were additionally analyzed in accordance with the kinetic model derived on the basis of the second order forward reaction between the Me2+ ions from solution and sodium ions from zeolite A, and the second order backward reaction between sodium ions from solution and Me2+ ions from zeolite A. Satisfactory agreement between the measured exchange kinetics and the exchange kinetics calculated by numerical solutions of the model equations, show that the exchange process takes place in accordance with the proposed model, i.e. by the second order forward and backward chemical reactions. (C) 2003 Elsevier B.V. All rights reserved.