THE EFFECT OF PRESSURE, HUMIDITY, CAUSTIC PRETREATMENT, AND ORGANIC CONSTITUENTS ON THE CESIUM ION EXCHANGE PERFORMANCE OF IONSIV® IE-911

Abstract

We examined 137Cs exchange of crystalline silicotitanate (CST) in simulated waste solution. In particular, we focused on the effect of CST pretreatment on the kinetics and extent of cesium adsorption. We used IONSIV®IE-911 (UOP LLC, Molecular Sieves Division, Des Plaines, Ill), the engineered form of CST. Pretreatment steps examined include soaking IE-911 in 2 mol/L NaOH solution for 3 days, exposing IE-911 to 50% relative humidity for 1 week, and for 3 days, soaking IE-911 in organic-containing simulated salt solution or drying untreated IE-911 in air at 100°C. Some tests were conducted with the sample under 50 and 25 psig of argon. Pretreatment of IE-911 in 2 mol/L caustic solution for 72 hours yielded a slower approach to equilibrium cesium distribution in batch contact tests than the untreated IE-911 samples. Adsorbed carboxylates and carbonates likely affected the cesium transport by either increasing the path length or reducing mass transfer rate. However, the effect was completely removed when IE-911 was rinsed with deionized water. Heating IE-911, as received from the vendor, at 100°C for 72 hours significantly degraded its cesium-removal performance by a 40.7% reduction in capacity and a 43% reduction in sorption rate (relative to the untreated IE-911) over 1 week of testing. However, sodium conversion of these samples did not affect cesium sorption. The presence of organic chemicals (e.g., tri-n-butyl phosphate, dibutylphosphate, butanol, paraffin, and Dow Corning H-10 defoamer) in simulated salt solution did not affect cesium sorption on pretreated IE-911. Nearly identical (i.e., a difference of only 5.6%) distribution coefficients (K d) were found between lot no. 9990-9681-0004 and no. 9990-9881-0005. Increasing the atmospheric pressure from 0 to 50 psig had no effect on cesium sorption.