CONTRIBUTION TO THE KNOWLEDGE OF THE ELECTROCHEMICAL PROPERTIES OF ACTINIDES IN NONAQUEOUS MEDIA .3. THE REDUCTION OF TETRAVALENT THORIUM AND TETRAVALENT NEPTUNIUM IN VARIOUS ORGANIC-SOLVENTS

The electrochemical behaviours of both Th(IV) and Np(IV) are investiga ted in different organic solvents at room temperature and at 400K in d imethylsulfone (DMSO(2)) and hexamethylphosphoramide. A four-electron transfer is the characteristic of tetravalent thorium reduction while the corresponding neptunium species is reduced to the metal in two ste ps where Np(III) is the transient species. The reactions are complicat ed by additional kinetic phenomena. Neptunium metal is gained with Cs2 NpCl6 as feed material by reduction on a Hg-pool cathode in acetonitil e (current yield, about 7%) while the yield drops to 0.4% in DMSO(2).