Large-scale treatment of high-salt, high-pH wastewater for {sup 137}Cs and {sup 90}Sr removal, using crystalline silicotitanate resin

A full-scale demonstration of cesium removal technology has been conducted at Oak Ridge National Laboratory (ORNL). This demonstration utilized a modular, mobile ion-exchange system and existing facilities for the off-gas system, secondary containment, and utilities. The ion-exchange material, crystalline silicotitanate (CST), was selected on the basis of its effectiveness in laboratory tests. The CST, which was developed through a Cooperative Research and Development Agreement between DOE and private industry, is highly selective for removing cesium from solutions containing high concentrations of other contaminants, such as sodium and potassium. Approximately 116,000 liters of supernate was processed during the demonstration with {approximately} 1,142 Ci of {sup 137}Cs removed from the supernate and loaded onto 266 liters of the CST sorbent. The supernate processed had a high salt content, about 4 M NaNO{sub 3} and a pH of 12 to 13. The CST also loaded Ba, Pb, Sr, U and Zn. Analysis of the spent sorbent has shown that it is not hazardous under the Resource Conservation and Recovery Act (RCRA). The cesium breakthrough curves for the lab and full-scale columns agreed very well, suggesting that lab-scale tests can be used to predict the performance of larger systems. The cesium breakthrough curves for runs at different flowrates show that film diffusion is significant in controlling the mass transfer process. Operational factors that increase the effect of film diffusion include the small size and high porosity of the CST sorbent, and the relatively low liquid velocity through the sorbent