Application of commercial zeolite-13X in the treatment of simulated and actual radioactive effluent containing caesium

Abstract

The removal of Cs⁺ ions from aqueous solution and radioactive effluent, by ion-exchange with Na ions of indigenously available synthetic zeolite-13X, has been studied. The zeolite has been characterized with respect to chemical composition, stability to acid, XRD and IR spectral patterns. Batch studies on the kinetics of the Cs-Na exchange process indicate that at higher Cs concentrations in solution, such as 50<i>m</i>M and 100m<i>M</i> Cs, 'particle diffusion' is the controlling factor,as inferred from the observed linearity in the Bt-t plots. The linearity is absent in case of lower concentrations where the process may be controlled by 'film diffusion'. The K_d value are of the order of a few thousands to a few tens of ml/g, depending on the initial concentration of the Cs ions. Agitation affected the kinetics in such a way that the time required for attainment of equilibrium is reduced from about 48h in an unstirred solution to 2h in a thoroughly stirred solution. Equilibrium studies, carried out under isonormal solution conditions at two different total (Cs + Na) ionic concentrations, 0.025 <i>N</i> and 0.1 <i>N</i>, resulted into ‘adsorption isotherms' showing replacement of 35% and 50% of the exchangeable Na⁺ ions for the two cases, respectively. The column studies, conducted with a pure solution of ¹³⁷Cs in ordinary water and a 2g (= 3 ml) column of the zeolite, led to a removal of as high as 99.9% ¹³⁷CS.When an actual radioactive waste solution, received from the Madras Atomic Power Station, Kalpakkam, and containing predominantly ¹³⁷Cs,is passed through a 1g (= 1.5 ml) bedofzeolite-13X, the per cent breakthrough is found to be less than 4% (96% removal) till the passage of 1000 bed volumes.