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

近年来，稀土元素在磁性、电子和光学材料等领域中已成为工业上不可或缺的元素。虽然它们被用作金属、氧化物和其他化合物，但金属的生产对这个项目很感兴趣。由于稀土金属在化学上非常活泼，生产稀土的主要方法是熔盐电解法。在本项目中，研究了含稀土化合物的熔盐的摩尔体积、电导率、粘度、表面张力和电极行为等物理化学性质。使用的熔融盐是氯化物。所用的稀土氯化物有LaCl3、CeCl3和SmCl3。测量了稀土氯化物-碱氯化物二元熔体的密度、电导率和粘度。从二元熔体的密度计算出的摩尔体积与加法系数呈正偏差。摩尔电导率随盐的混合而降低。随着碱阳离子半径的增大，这一趋势变得更强。另一方面，这些行为与稀土离子的种类无关，这些现象表明在混合熔体中形成了络合离子。认为价态为+3的稀土离子形成较强的库仑场，然后与氯离子结合形成LnCl4-和LnCl6^&lt；3-&Gt；配位阴离子(Ln为稀土元素)。此外，本项目还研究了Ln^&lt；3+&gt；的电极行为和熔盐中Nd2 O3的还原。

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.