Experimental Verficiation of Caustic-Side Solvent Extraction for Removal of Cesium from Tank Waste

摘要

A caustic-side solvent extraction (CSSX) process was developed to remove Cs from Savannah River Site (SRS) high-level waste. The CSSX process was verified in a series of flowsheet tests at Argonne National Laboratory (ANL) in a minicontactor (2-cm centrifugal contactor) simulant. The CSSX solvent, which was developed at Oak Ridge National Laboratory (ORNL), conists of a calixarene-crown ether as the extractant, an alkyl aryl polyester as the modifier, trioctylamine as the supressant, and Isopar~RL as the diluent. For Cs removal from the SRS tank waste, the key process goals are that: (1) Cs is removed from the waste with a decontamination factor greater than 40,000 and (2) the recovered Cs is concentrated by a factor of 15 in dilute nitric acid. In the flowsheet verification tests, the objectives were to: (1) prove that these process goals could be met; (2) demonstrate that they could be maintained over a period of several days as the CSSX solvent is recycled; (3) verify that the process goals could still be met after the solvent composition was adjusted. The change in composition eliminated the possibplity that the calixarene-crown ether could preciitate from the solvent. The process goals were met for each of the verification tests. The results of these tests, which are summarized here, show the CSSX process is a very effective way to remove Cs from caustic-side waste.