Research on Physicochemical Properties of Electrolytes for Electrowinning of Rare-Earth Metals

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Recently, the rare earth elements have become indispensable industrially in the fields of magnetic, electronic and optical materials etc. Although they are used as the metals, oxides and other compounds, production of the metals is interested in this project. As rare earth metals are very active chemically, main method of the production is molten salt electrolysis.In this project, the physicochemical properties, for example, molar volume, electrical conductivity, viscosity, surface tension and electrode behavior etc,, of the molten salt containning rare earth compounds are investigated. The molten salts used are chlorides. Rare earth chlorides used are LaCl_3, CeCl_3 and SmCl_3. Density, electrical conductivity and viscosity of rare earth chlorides-alkali chloride binary melts were measured. Molar volumes calculated from the density of the binary melts show positive deviation from an additivity. Molar electrical conductivity decreases by mixing the salts. These tendency becomes strong as the radius of alkali cation becomes large. On the other hand, the behaviors are independent of the kind of rare earth ion.These phenomena indicate that complex ions are formed in the mixture melt. It is considered that the rare earth ions with +3 of valent make strong coulombic field, then combine with Cl^- ion and form LnCl_4^- and LnCl_6^<3-> complex anion(Ln is lanthanide).Other than mentioned above, electrode behaviors of Ln^<3+> and the reduction of Nd_2O_3 in molten salt have investigated in this project.