Studies of sorbent/ion-exchange materials for the removal of radioactive strontium from liquid radioactive waste and high hardness groundwaters

Different sorbents were studied in terms of their full-scale applicability for radioactive strontium removal in low-level liquid radioactive waste (LLRW) management. The following types of sorbent/ion-exchange materials were investigated: natural zeolite-clinoptilolite, modified natural clinoptilolite, synthetic zeolites, new synthetic crystalline materials selective to strontium, ion-exchange resins, and modified fiber sorbents. Simulated solutions for experimental tests were prepared according to the composition of one of the facilities at the Hanford nuclear site (Richland, WA, USA). The following experiments were performed at different concentrations of strontium and competing elements (calcium, on the first hand): batch tests for determination of strontium distribution coefficients, sorbent/ion-exchanger selectivity to strontium in time presence of calcium, and kinetic measurements of strontium uptake. Modifications of Amberlite and Duolite ion-exchange resins (Rohm and Haas, USA) and new synthetic crystalline materials - silicotitanate IE-911 (UOP, USA) and sodium titanate (Allied Signal, USA) - showed the highest distribution coefficients of strontium (K(d)similar to 2x10(4)-4x10(5) ml/g). For all materials, the K-d decreased significantly with increased calcium concentration. On the other hand, each of these sorbents showed poor selectivity to strontium in the presence of calcium. Newly developed sorbents (Institute of Chemistry, Vladivostok, Russia) based on a fiber matrix (FM and FP) showed the best relative selectivity to strontium followed by the natural zeolite (clinoptilolite extracted and produced in the USA). Synthetic zeolites (IE-96, TIE-96) had moderate values of both parameters (distribution coefficient and selectivity). Fiber sorption materials were also absolute leaders in kinetic measurements removing 40% to 60% of the strontium from solution within a few minutes. (C) 2000 Elsevier Science Ltd. All rights reserved.