Thermodynamic and kinetic studies on Cs⁺- and Sr²⁺-exchange in natural zeolite from Akita, Japan

Abstract

Thermodynamic and kinetic studies on the adsorption of Cs⁺ and Sr²⁺ by Na-exchanged clinoptilolite-rich zeolite rock from Akita (Northern Japan) were performed for the purpose of nuclear waste treatment. The thermodynamic parameters such as selectivity coefficient, thermodynamic equilibrium constant, and standard free energy of exchange were evaluated. These values indicated that the selectivity order was determined as Cs⁺ > Na⁺ > Sr²⁺. In order to discuss the adsorption mechanism of Cs⁺ and Sr²⁺ onto Na-exchanged clinoptilolite, the effective diffusion coefficients were calculated and two kinetic models, pseudo-first-order and pseudo-second-order kinetic model, were tested. For all systems studied, chemisorption seems significant in the rate-controlling step, and the pseudo-second-order kinetic model provided the best correlation of the experimental data.

Keywords:

• ion exchange
• radioactive fission products
• clinoptilolite
• thermodynamics
• kinetics

Acknowledgment

The authors are grateful to Mr M. Kubo for experimental assistance.