|Budget Amount *help
¥6,400,000 (Direct Cost : ¥6,400,000)
Fiscal Year 1997 : ¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1996 : ¥5,300,000 (Direct Cost : ¥5,300,000)
Electropositive actinide metals have been prepared by metallothermic reduction of the haide, oxide and carbide and by electrolysis in a molten salt. It, however, is an enormous task to produce highly radioactive metals by these methods. The mercury electrode with a large hydrogen overpotential of ca. -1.5V in an aqueous solution is widely used to deposit elements belonging to the groups form VIa to IVb, such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga and Ge, whose reduction potentials are more positive than the overpotential. Radiopolarography is an interesting technique, in which the amalgamation of radioactive ions in aqueous solutions is measured by the radioactivity in the mercury drops and the waves are allowed to be observed even in the more negative potential than the hydrogen overpotential. These facts suggests the feasibility to prepare electropositive metals from the aqueous media by bulk electrolysis using a mercury pool electrode.
The electrochemical preparation of uranium, neptunium, lanthanum and cerium metals from the aqueous solution using a mercury pool electrode was investigated. The amalgamation rate of uranium was approximately regarded as a first-order chemical reaction. On the other hand, the reduction rates of lanthanum and cerium showed a different kinetics from uranium. The purity of uranium metals prepared by thermal decompositions of the amalgams were estimated to be 4N at least by the gaseous and metallic impurity analysis. The heating temperature of the neptunium amalgams was decided by the analysis of mercury in the lanthanum and cerium metals. The neptunium amalgams were synthesized from acetate buffer solutions and the bright metallic buttons of neptunium metals were obtained. As a result of this study, and the proposed method is shown to be much easier and simpler than the conventional preparation and the actinide metals are found to be excellent quality.