Electrochemical Behavior of the System of Uranium(VI) Extraction with CMPO-Ionic Liquid

Abstract

The electrochemical behavior of U(VI) extracted from an aqueous solution of uranyl nitrate by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in an ionic liquid was investigated. The hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C4mimNTf2) was used in this study. Using an equimolar series method, we found that CMPO and U(VI) formed a 3:1 molar complex during the extraction process. Cyclic voltammetry was used to investigate the electrochemical behavior of the U(VI)-CMPO complex in C4mimNTf2. The U(VI)-CMPO complex was found to be quasi-reversibly reduced to a U(V)-CMPO complex. The formal redox potential (E �� , vs Fc/Fc + ) for the U(VI)/ U(V) couple was determined to be (-0.885±0.008) V. Controlled-potential electrolysis of the extract gave a deposit on the surface of a platinum plate. X-ray photoelectron spectroscopy showed that the deposit contained only U(VI), U(IV), and oxygen, and the CMPO extractant and the ionic liquid were not trapped in the deposit.