Anomalous effect of presence of Na ions on the removal of Sr-90 from solutions by using various zeolites

The removal of Sr-90 from high salt-loaded, alkaline, simulated wastes by i on-exchange, using four indigenously available synthetic zeolites in their Na-form viz., 13X, 4A, AR-1 (mordenite) and ZSM-5, was studied. In batch te sts, the zeolites were contacted under stirred and unstirred conditions, wi th solutions containing varying concentrations of Na ions (present as NaNO3 + NaOH solutions) and trace amount of Sr-90. Under stirred contact, the up take of Sr declined with increasing concentrations of Na ions in the range 0 mM to 110 mM, but at very high concentrations (1.1 M and 4 M Na), the rem oval improved slightly. In contrast, under unstirred contact, the removal o f Sr was high at moderate concentrations of Na ions (0 mM to 110 mM), while at higher concentrations (1.1 M and 4 M Na), the removal declined. In colu mn trials using zeolite 4A bed, the removal of Sr showed a minimum at low c oncentration of Na ions (2.2 mM) but improved gradually with increasing con centration (up to 110 mM Na), an observation not comparable with either sti rred or unstirred contact conditions.