A COMPARATIVE-STUDY ON INDIGENOUSLY AVAILABLE SYNTHETIC ZEOLITES FOR REMOVAL OF STRONTIUM FROM SOLUTIONS BY ION-EXCHANGE

Removal of strontium ions from solutions by Sr-Na exchange, using indi genously available synthetic zeolites, has been studied. Batch tests i ndicated that the time required for equilibrium was 4 hours under stir red condition. The percent removal and the distribution coefficient (K -d) values for Sr were determined at different concentrations, ranging from traces of Sr (solution of Sr-90-nitrate) to 50 mM Sr-nitrate. Tw o zeolites viz., 4A and 13X, were observed to provide high removal of Sr, while the other two, AR-1 (a synthetic mordenite) and ZSM-5, were not as effective. The nature of diffusion of Sr ions. controlling the exchange reaction, was studied by drawing Bt-t plots (B, diffusional f requency and t, time). Linear plots, obtained for 13X and 4A, at 50 mM Sr(NO3)(2) concentration, indicated that the process tvas controlled by diffusion through the particles. At lower concentrations of Sr and for the other two zeolites. the plots were non-linear and the process might be controlled by film diffusion. The equilibrium studies, carrie d out using isonormal solutions of Sr and Na ions at a total Sr+Na con centration of 0.1 N, indicated a marginal selectivity for Sr, in case of 4A and 13X. The corrected selectivity coefficient (K-c) values were calculated and Kielland plots were drawn. Column trials with 1.5 ml b eds of the granular zeolites and a simulated waste solution containing Sr-90, indicated that 4A and 13X could remove about 90-92% of Sr, at a flow rate of 60 bed volumes per hour (BV/h). The removal increased t o 97%, when the flow rate was reduced to 12 BV/h. The third zeolite AR -1 provided lower removal of Sr in both the cases. When another simula ted alkaline waste solution, containing high salt content (3M NaNO3), in addition to Sr-90 and Cs-137, was treated using a mixed zeolite col umn (4A + AR-1), the removal of both the Sr and Cs isotopes was about 55-65%.