Adsorption and diffusion of cesium ions in zirconium(IV) iodomolybdate exchanger

Abstract

Tetravalent metal acid (TMA) salt zirconium(IV) iodomolybdate ion exchanger was chemically synthesized under different conditions and subjected into batch reactor for cesium removal investigation. The properties of synthesized exchangers were characterized using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Data revealed that the prepared beads are amorphous in nature and thermally stable up to 350°C. The influences of contact time, pH, ionic strength, and organic acids were investigated. Results illustrated that cesium uptake reached equilibrium within 2h and it is strongly dependent on ionic strength and nearly independent of pH values. Speciation of cesium ions and their ability to form ternary complexes less adhered to the applied exchangers predominate their adsorption behavior. The prepared exchangers had a good ion-exchange capacity ranged from 7.94 to 9.62mmolg−1.Several kinetic models were used to evaluate the experimental data and to determine the mechanism controlling cesium adsorption process. In addition, a number of one- and two-resistance diffusion models were applied to explore the rate determining step in cesium diffusion behavior. The numerical values of the different rate constants, correlation coefficients and effective diffusion coefficients as well as activation energy were determined.Data clarified that pseudo-second-order model and homogeneous particle diffusion model (HPDM) best correlated the diffusion of cesium through ZIM particles. The magnitudes of the effective particle diffusion coefficient were in range of 10−12m2s−1 indicating a chemisorption nature for cesium adsorption. Moreover, the values of the activation energy confirmed cesium adsorption to be diffusion controlled and suggested that ion-exchange was the main uptake mechanism.