Journal of AUoys and Compounds, 185 (1992) 151-162 151 JALCOM 213 Contribution to the knowledge of the electrochemical properties of actinides in non-aqueous media II: The reduction of hexavalent uranium in various organic solvents L. Martinot*, D. Laeckmann, L. Lopes**, T. Materne and V. Muller Laboratory of Analytical Chemistry and Radiochemistry, B6, University of Liege, Sart-Tilman, B-4000 Liege (Belgium) (Received December 18, 1991) Abstract The electrochemical behaviour of hexavalent uranium is reported in various organic solvents at room temperature and also in hexamethylphosphoramide, dimethylsulphone, sulpholane between 310 and 400 K. The reduction of UO22÷ proceeds in two steps, leading to tetravalent uranium. Depending on the solvent acidity, the tetravalent species is either soluble or precipitates as UO2(cr). Numerous additional kinetic phenomena are evidenced in all the reactions. Special attention is paid to the deposition of UO2(cr) in macroscopic quantities. 1. Introduction In a previous paper in this journal [ 1 ], we reported numerous experimental investigations on the electrochemical reduction of tetravalent uranium in different organic liquids -- at both 298 and 400 K -- and it appeared that a great deal of information was gained by electrochemical transient techniques. In the present paper, we similarly describe the properties of hexavalent uranium while giving special attention to the electrochemical deposition of uranium dioxide on solid electrodes. 2. Experimental details Cs2UO2CI 4 is used as the feed material in all the solvents; the purification of organic liquids and the measurements of the water content together with the facilities have been described previously [1 ]. Tetramethylenesulphone (TMSO2) (sulpholane) (purity, 98%; Janssen Pharmaceutica) was distilled under reduced pressure (about 1 mmHg; N2 atmosphere) in the presence *Present address: Inter-University Institute for Nuclear Sciences, Brussels, Belgium. **Present address: University of Aveiro, Aveiro, Portugal. 0925-8388/92/$5.00 © 1992- Elsevier Sequoia. All rights reserved