Radiochemical studies of some transplutonium elements

Radiochemical studies of some transplutonium elements are reviewed. Radiocoulometric and radiopolarographic methods suitable for studies of elements at the tracer scale concentration level are briefly described. These two techniques have been recently used for studying the chemistry of mendelevium in aqueous solution. It was concluded that mendelevium is reduced at - 1.50 V/NHE in non complexing medium; effect of citrate, acetate and chloride ions indicates that its chemistry is very similar to that of divalent fermium. Preliminary experiments are described on diffusion coefficient measurements of some lanthanide and actinide ions in aqueous solution. The gas thermochromatographic method has been applied to the study of the tetravalent fluorides of Pu, Am, Cm, Bk, Cf and Es. Deposition temperature Tsub(c) has been measured for all the considered elements. The value obtained for einsteinium, Tsub(c) = 695 0C is consistent with the existence of the gaseous EsF4 compound. This is the first experimental indication of the existence of tetravalent einsteinium, which would be thermally less stable than that of the lighter actinides. Some thermodynamical consequences of these data are drawn. 3/0 redox potentials are estimated and stability of oxidation states (2 to 6) are compared in the actinide series. Enthalpy of hydration is also calculated with a semi empirical expression. (author)