A ROBUST ALKALINE-SIDE CSEX SOLVENT SUITABLE FOR REMOVING CESIUM FROM SAVANNAH RIVER HIGH LEVEL WASTE#

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Abstract
A robust solvent suitable for extracting cesium from alkaline nitrate media like that of the high-level liquid waste stored at the U.S. Department of Energy Savannah River Site has been developed. The solvent is composed of the cesium extractant calix[4]arene-bis-(tert-octylbenzo-crown-6) (“BOBCalixC6”) at 0.01 M, the modifier l-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol (“Cs-7SBT”) at 0.50 M, trioctylamine (“TOA”) at 0.001 M, and the aliphatic diluent Isopar® L. The solvent holds up exceptionally well under various stresses, such as sustained contact with waste simulant and dilute nitric acid; repeated extraction, scrubbing, and stripping cycles; and excessive loading. The behavior of the solvent in batch-equilibrium flowsheet tests conducted at 15, 25, and 45 °C is presented. Flowsheet calculations show that the Savannah River Site requirements for a decontamination factor of 40,000 and a cesium concentration factor of 12 could be met in a 22-stage bank of 25-cm centrifugal contactors at 25 °C with conservative assumptions regarding hydrodynamics and stage efficiency. Exploiting the temperature dependence of extraction and stripping could reduce the number of stages to 18.