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Ion-exchange performance of crystalline silico-titanates for cesium removal from Hanford Tank Waste Simulants
A new class of inorganic ion exchangers, called crystalline silicotitanates (CSTs), has been prepared at Sandia National Laboratories and Texas A&M University. CSTs have been determined to have high selectivity for the adsorption of Cs and Sr, and several other radionuclides from highly alkaline, high-sodium supernate solutions such as those found at Westinghouse Hanford (WHC). An extensive program has been conducted to assess the applicability of CSTs for treating Hanford wastes. Continuous flow, ion-exchange columns are expected to be used to remove Cs and other radionuclides from the Hanford tank supernate. The proposed application for the CST would be Cs removal from highly alkaline salt solutions in a single pass process with interim storage of the Cs loaded CST until the glass vitrification plant is operational. This paper presents test results which address the important chemical, physical, and radiological properties which are expected to be relevant for Hanford radwaste processing. Results indicate that CSTs have a large distribution coefficient (K{sub d}>2000 mL/g in NCAW simulants) for adsorbing ppm concentrations of Cs. These wastes are highly alkaline (>O.6M OH{sup {minus}}) with high sodium (>5M Na{sup +}) concentrations. CSTs exhibit very high K, values (>20,000 mL/g) for Cs in neutral solutions and K, values of >2,000 mL/g in solutions containing 2M HNO{sub 3}. Presented are results from initial experimental efforts that describe the potential performance of the CSTs in laboratory-scale ion-exchange columns. Included are results showing the stability of the CST material in basic solutions and in radiation doses up to 10{sup 9} rads (Si). The status on the commercialization of the CST powder and engineered-form is discussed. Sufficient material for expanded testing and evaluation is expected to become available during 1994.