ANALYSIS OF BREAKTHROUGH PROFILES BASED ON GAMMA-RAY EMISSION ALONG LOADED PACKED BED COLUMNS: COMPARATIVE EVALUATION OF IONSIV® IE-911 AND CHABAZITE ZEOLITE FOR THE REMOVAL OF RADIOSTRONTIUM AND CESIUM FROM GROUNDWATER

Abstract

A gamma counting system has been assembled that can profile the breakthrough fronts of gamma-emitting radioisotopes longitudinally along a loaded column. This profiling technique has been particularly useful in column studies such as those performed with IONSIV® IE-911, a crystalline silicotitanate (CST) manufactured by UOP, in which long operating times are required to observe cesium effluent breakthrough at the low inlet (10−4 ppm) concentrations studied here. The length of the mass transfer zone and extent of column saturation can be detected by viewing the relative emission of gamma emitters along the length of the column. In this study, gamma scans were used to analyze loaded CST and zeolite columns used in the treatment of process wastewater simulant and actual groundwater. The longitudinal gamma scans for both 90Sr and 137Cs conformed with breakthrough results based on column effluent activity. Although not obvious from data obtained by monitoring effluent activity, the gamma scans indicated that both cesium and strontium in the saturated zone of the CST column are slowly displaced by the higher levels of groundwater cations and are then resorbed further down the column. This displacement phenomenon identified by gamma scans was also noted for the zeolite column, in which both the gamma scan and column effluent data exhibited radionuclide displacement. The gamma emission intensities from the CST column runs are used to quantitate and compare the distribution coefficient and loading capacity of 137Cs on CST versus zeolite. Managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract DE-AC05-96OR22464.