STUDIES ON THE ION-EXCHANGE BEHAVIOR OF THORIUM IONS WITH ZEOLITES

Commercial, synthetic zeolites, have been evaluated for the removal of thorium ions from aqueous solution by ion-exchange. Kinetics of uptak e of thorium ions from solutions of various initial Th concentrations by four zeolites of different types viz., 13X, AR-1, ZSM-5 and 4A, was studied in batch experiments. The Th-Na exchange process is accompani ed by side reactions such as H-Na exchange and surface precipitation o f Th-hydroxide, making it difficult to derive any conclusive evidence about the nature of diffusion of thorium ions. Acidity of the solution , produced due to the hydrolysis of Th ions, has an adverse effect on the stability of the zeolites. X-ray diffraction and Infra red spectra l studies were used for the characterization of the zeolites with resp ect to crystallinity, surface precipitation of Th-hydroxide etc., befo re and after exchange. Stirring was observed to dramatically affect th e establishment of equilibrium requiring about 2 weeks for unstirred a nd just 4 hours for thoroughly stirred solutions. Adsorption isotherms obtained for Zeolite-13X, the one performing the best, with isonormal solutions of Th-nitrate at total ionic concentrations (Th + Na) of 0. 024 N in one case and 0.1 N in the other, displayed unique shapes attr ibutable to the accompanying side reactions. Distributions coefficient (K(d)) values varied from above 2000 ml/g at 0.1 mM Th to 15 ml/g at 10 mM Th concentration. In column experiments with 1 mM Th-nitrate sol ution and Zeolite-13X, percent breakthrough of 10, 50 and 96% were obt ained on passing 125, 350 and 700 bed volumes respectively. Exchange c apacity of 1.2 meq/g, corresponding to the passage of 300 bed volumes, was observed.