Electrochemical assessment of water|ionic liquid biphasic systems towards cesium extraction from nuclear waste |
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Authors: | T. Jane Stockmann Jing Zhang Anne-Marie Montgomery Zhifeng Ding |
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Affiliation: | 1. Laboratoire d’Electrochimie Physique et Analytique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 6, Lausanne CH-1015, Switzerland;2. Department of Chemistry, The University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada |
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Abstract: | A room temperature ionic liquid (IL) composed of a quaternary alkylphosphonium (trihexyltetradecylphosphonium, P66614+) and tetrakis(pentafluorophenyl)borate anion (TB−) was employed within a water|P66614TB (w|P66614TB or w|IL) biphasic system to evaluate cesium ion extraction in comparison to that with a traditional water|organic solvent (w|o) combination. 137Cs is a major contributor to the radioactivity of spent nuclear fuel as it leaves the reactor, and its extraction efficiency is therefore of considerable importance. The extraction was facilitated by the ligand octyl(phenyl)-N,N′-diisobutylcarbamoylphosphine oxide (CMPO) used in TRans-Uranium EXtraction processes and investigated through well established liquid|liquid electrochemistry. This study gave access to the metal ion to ligand (1:n) stoichiometry and overall complexation constant, β, of the interfacial complexation reaction which were determined to be 1:3 and 1.6 × 1011 at the w|P66614TB interface while the study at w|o elicited an n equal to 1 with β equal to 86.5. Through a straightforward relationship, these complexation constant values were converted to distribution coefficients, δα, with the ligand concentrations studied for comparison to other studies present in the literature; the w|o and w|IL systems gave δα of 2 and 8.2 × 107, respectively, indicating a higher overall extraction efficiency for the latter. For the w|o system, the metal ion-ligand stoichiometries were confirmed through isotopic distribution analysis of mass spectra obtained by the direct injection of an emulsified water–organic solvent mixture into an electron spray ionization mass spectrometer. |
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Keywords: | CE, counter electrode CV, cyclic voltamogramms ESI-MS, electrospray ionization mass spectroscopy FIT, facilitated ion transfer IL, ionic liquid IT, ion transfer ACT, ligand transfer to the aqueous phase followed by complexation and transfer to the organic phase TOC, (metal) transfers to the organic phase with subsequent complexation micro-ITIES, micro-interface between two immiscible electrolytic solutions CMPO, octyl(phenyl)-N,N&prime -diisobutylcarbamoylphosphine oxide PPW, polarizable potential window RE, reference electrode SNF, spent nuclear fuel TB&minus , tetrakis(pentafluorophenyl) borate anion TATB, tetraphenylarsonium tetraphenylborate TIC, transfer through interfacial complexation TID, transfer through interfacial decomplexation TRUEX, TRans-Uranium EXtraction P66614+, trihexyltetradecylphosphonium w|DCE, water|1,2-dichloroethane w|o, water|organic solvent w|P66614TB or w|IL, water|P66614TB WE, working electrode |
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