PNNL

Abstract

The treatment of Hanford tank waste is one of the most technically challenging environmental cleanup activities for the Department of Energy to date. To expedite the processing of liquid waste stored in underground tanks in southeastern Washington State it is necessary to remove the significant dose contributor, 137Cs. Crystalline silicotitanate (CST) ion exchanger is currently used to remove 137Cs from the aqueous phase of Hanford tank wastes in preparation for vitrification at the Waste Treatment and Immobilization Plant (WTP). Toward this effort, a series of batch contact tests that varied in [K] were conducted to look at the impact of K concentration on Cs distribution. Experimental distribution ratios (Kd) were compared to the distribution ratios predicted using the ZAM model. A significant underprediction of Cs capacity in the presence of K was seen with the existing model. A revision of the equilibrium constants was determined and provided a statistically better fit for determining the Cs Kd values in tank waste matrices. Improving the understanding of potassium impacts on ion exchange behavior will help in the operation of a critical component of one of the most complex waste treatment processes in the world today. Optimization of this process can result in significant cost savings and less waste production.