Treatment of radioactive liquid waste containing caesium by indigenously available synthetic zeolites: A comparative study

Indigenously available, commercial samples of synthetic zeolites 13X, AR-1, 4A and ZSM-5, have been characterized and evaluated for their performance towards the removal of caesium from pure aqueous solutions as well as from actual radioactive liquid wastes. The kinetics of the exchange process was studied in batch experiments with pure CsCl solutions spiked with radioactive 137Cs. The kinetic data were used to calculate the “diffusional time frequency”, B. The observed linearity of the Bt-t plots in the case of uptake of Cs by zeolite 13X, indicated that at higher Cs concentrations and under stirred conditions, the uptake was controlled by “intra-particle diffusion”. Kd values were found to be of the order of 103-101 ml g−1, depending on the initial concentration of Cs ions, and followed the order 13X> 4A> AR-1> ZSM-5. Equilibrium studies were carried out under stirred conditions, using various zeolites and isonormal solutions of Cs + Na, at a constant total ionic concentration of 0.1 N. The adsorption isotherms indicated a high selectivity of the zeolite AR-1 for Cs, which was further confirmed by drawing Kielland-type plots. In column trials, actual radioactive waste solutions received from the Madras Atomic Power Station (MAPS), Kalpakkam, were treated with these zeolites. Two waste streams, containing predominantly 137Cs and varying in dissolved solids content, were passed through 1 g (bed volume 1.5 ml) beds of 13X, AR-1 and 4A. The breakthrough curves indicated that AR-1 was the best zeolite for effluent that contained low dissolved solids, while none of the zeolites was found to be promising for the treatment of waste streams with high dissolved solids.