Separation of rare earth metal elements by electromigration in melts

为了弄清熔盐中的导电机理，用逆流电迁移法测定了氯化稀土熔体的内部迁移率。如果稀土元素之间的迁移率有明显的差异，则可以使用逆流电迁移来分离这些元素。因此，这种方法预计将特别适用于核燃料的后处理。我们做了以下实验。在1073 K时，用逆流电迁移法测定了熔融混合体系（Y, La）Cl_3中内部阳离子迁移率的相对差异。测量了混合体系的电导率。根据这些数据计算了Y^<3+>和La^<3+>的内部阳离子迁移率b。在所有浓度下，La^<3+>比Y^<3+>的流动性强20- 30%。这可能是因为Y-Cl对的相互作用比La-Cl对强。因此，这种方法更适用于这些离子的分离。而Y^<3+> (0.900 A)的离子半径明显小于La^<3+> (1.032 A)，纯LaCl_3的摩尔体积略小于纯熔融YCl_3。这表明这些熔体的结构有很大的不同。在混合体系中，b_Y和b_<La>均随摩尔体积的增大而减小，其变化趋势与其他体系如单价和二价阳离子体系相同。用类似的方法测定了混合体系（Y, Dy）Cl_3中的b。在这种情况下，两个阳离子的离子半径几乎相同，Y^<3+>为0.900 A, Dy^<3+>为0.912 A。b_Y明显大于b_<Dy>。因此，可以推测，当离子半径几乎相同时，质量差（Y: 88.9059和Dy: 162.50）起了作用。用逆流电迁移法研究了纯DyCl_3中Dy^<3+>在b中的同位素效应。Dy的主要稳定同位素质量数分别为160（2.34%）、161（18.9%）、162（25.5%）、163（24.9%）和164（28.2%）。定义为mu=(b/b)/(M/M)的质量效应值约为-0.030，在973 K-1043 K范围内几乎与温度无关，其绝对值较大。综上所述，推测稀土氯化物中的导电物质为单原子离子，可以采用熔融体系中的逆流电迁移法分离稀土金属。少

In order to clucidate the mechanism of electric conduction in molten salts, the internal mobilities of rare carth chloride melts have been measured by a countercurrent electromigration method. If there is an appreciable difference in the mobilities among the rare earth elements, countercurrent electromigration may be used for separation of these elements. Then, this method is expected to be useful particularly for reprocessing of the nuclear fuels. We have performed the following experiments.In the molten mixture system (Y, La)Cl_3 relative differences in internal cation mobilities have been measured at 1073 K by a countercurrent electromigration method. The electric conductivities of the mixture system have been measured. From these data the internal cation mobilities b of Y^<3+> and La^<3+> have been calculated. At all the concentrations La^<3+> is more mobile than Y^<3+> by 20-30 %. This is presumably because the interaction for Y-Cl pair is stronger than that for La-Cl pair. Thus, … More this method is applicable for separation of these ions. while the ionic radius of Y^<3+> (0.900 A) is distinctively smaller than that of La^<3+> (1.032 A), the molar volume of pure LaCl_3 is slightly smaller than that of pure molten YCl_3. This suggests that the structure of these melts is considerably different. In the mixture system, both b_Y and b_<La> decrease with increasing molar volume, the trend of which is the same as that in other systems such as monovalent and divalent cation systems.By a similar method b's in the mixture system (Y, Dy)Cl_3 have been measured. In this case the ionic radii of the two cations are nearly the same, that is 0.900 A for Y^<3+> and 0.912 A for Dy^<3+>. b_Y is appreciably greater than b_<Dy>. Thus, it can be conjectured that, when the ionic radii are nearly the same, the difference in the masses (Y : 88.9059 and Dy : 162.50) plays a role.The isotope effect in b of Dy^<3+> has veen studied in pure DyCl_3 also by countercurrent electromigration. The mass numbers of the main stable Dy isotopes are 160(2.34 %), 161(18.9 %), 162(25.5 %), 163(24.9 %) and 164(28.2 %). The value of the mass effect defined as mu=( b/b)/( M/M) is about -0.030 nearly independent of temperature in the range 973 K-1043 K, whose absolute value is relatively large.In conclusion, electrically-conducting species in rare earth chlorides are conjectured to be monoatomic ions and countercurrent electromigration method in molten systems can be used for separation of rare earth metals. Less