Simulant flowsheet test with modified solvent for cesium removal using caustic-side solvent extraction.

Abstract

A modified solvent has been developed at Oak Ridge National laboratory (ORNL) for a caustic-side solvent extraction (CSSX) process that removes cesium (Cs) from Savannah River Site (SRS) tank waste. The modified solvent was evaluated using the same CSSX flowsheet, SRS simulant, and 33-stage minicontactor (2-cm centrifugal contactor) that had been used to test the previous CSSX solvent. As with the previous solvent, the key process goals were achieved: (1) the Cs was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered Cs was concentrated by a factor of 15 in dilute nitric acid. Thus, the modified CSSX solvent can be used in place of the previous solvent while maintaining satisfactory hydraulic performance and still achieving process requirements at the bench scale.

Demonstration of Caustic-Side Solvent Extraction with Optimized Solvent in the 2-cm Centrifugal Contactor Apparatus Using Dissolved Salt Cake from Tank 37H

“…The low solvent and strip flow rates used at the end of the 2-cm contactor test may have resulted in low fluid levels or erratic flow rates that can decrease the strip stage efficiencies. 16,19 However, measurements of the volume of the stage samples showed approximately 17 mL per strip stage, which is similar to previous tests showing higher efficiencies .…”

“…In addition, solvent DF values exceeded 100,000 in FY-2001 testing with the old solvent composition and averaged 400,000 in ANL testing with optimized solvent. 16 Solvent decontamination in the first 16-hour portion of the test showed a steady decline until about 8 hours. This corresponds to the time interval from the start of the test to the first timed volumetric collection of solvent.…”

“…The 90% efficiency found for the extraction stages agrees well with previously measured values. Leonard 16 obtained an efficiency of 85% using 2-cm contactors with the modified solvent and simulated waste. The strip efficiency of 80% is less than Leonard's value of 92%, but equals the process objective of 80%.…”

Cesium Removal from Savannah River Site Radioactive Waste using the Caustic-Side Solvent Extraction (CSSX) Process

“…1,2 This solvent consists of a calix [4]arene-crown-6 extractant (BOBCalix ® ) dissolved in an inert hydrocarbon matrix (Isopar ® L). An alkylphenoxy alcohol modifier (1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol, also known as Cs-7SB) added to the solvent enhances the extraction power of the calixarene and prevents the formation of a third phase.…”

“…The CSSX process for removal of cesium from alkaline solutions is the reference process for decontamination of high level waste (HLW) at the Savannah River Site (SRS). The solvent consists of a calix [4]arene-crown-6 extractant (BOBCalix), an alkylphenoxy alcohol modifier, and trioctylamine (TOA) dissolved in an inert hydrocarbon matrix (Isopar ® L). Previously, we demonstrated the solvent extraction process with actual SRS HLW supernatant solution using a non-optimized solvent formulation.…”