Development of the SREX Process for the Treatment of ICPP Liquid Wastes

摘要

The removal of Sr-90 from actual and simulated wastes at the Idaho Chemical Processing Plant (ICPP) at the Idaho National Engineering and Environmental Laboratory (INEEL) has been demonstrated with the SREX process. This solvent extraction process employs the extractant 4',4' (5') de-(t-butylcyclohexano)-18- crown-6 in 1-octanol or a mixture of tributyl phosphate and a hydrocarbon diluent called Isopar L. This development work is based upon earlier work performed by Horwitz, et al. at Argonne National Laboratory. Process flowsheets have been designed for testing in countercurrent experiments with centrifugal contactors. The flowsheets have been designed using batch contact solvent extraction methods. The extraction of Sr as well as other interfering ions has been studied. The effect of various parameters including nitric acid dependence, extractant concentration dependence, Hydronium ion concentration, and interferent concentrations upon the extraction efficiency of the process has been evaluated. The radiolysis of the SREX solvent has also been investigated as a function of absorbed gamma radiation. The extraction efficiency of the solvent has been shown to be only slightly dependent upon absorbed dose in the range 0-1000 kGy. The decontamination of actual sodium-bearing waste and dissolved calcine solutions has been accomplished in batch contact flowsheets. Decontamination factors as high as 10E3 have been obtained with sequential batch contacts. Flowsheets have been developed to accomplish decontamination of the liquid wastes with respect to Sr-90, as well as the removal of Pb and Hg. Pb may be partitioned from the Sr fraction in a separate stripping procedure using ammonium citrate. This work has led to the formulation of countercurrent flowsheets which have been tested in centrifugal contactors with actual waste and reported in the document INEEL/EXT-97-00832.