熔析直拉法提纯稀土金属钆过程金属杂质的迁移与分离机制

This project is based on the technical bottleneck and key problems of the existing purification methods of rare earth metals, introduce the liquation refining and czochralski separation technology, aims to study the separation behavior and transferring law of metallic impurities in rare earth metal gadolinium (Gd) during the purification process. First, the occurrence state, micro area distribution and diffusion coefficient, distribution coefficient of typical metallic impurities in Gd will be deeply studied by various analytical methods and thermodynamic calculation softwares s uchas SEM, XAFS, BL15U1, FACTSAGE and CALPHAD et al. Next, the efficient Gd-M liquation refining system will be build by synthetical optimization selection of liquation medium, stretching methods and influence factors. Finally, theseparation behavior and transferring law of metallic impurities in Gd during the purification process will be explored by combine the difference of their existence form and thermodynamic parameters before and after the liquation refining with the crystal growth behavior of Gd. The success of this project will be helpful toexpand the research methods and results of metallic impurities to other impurities (C, N and O et al.), realize the efficient synchronization separation of kinds of impurities, which will lay the groundwork for the new energy, efficient and economy purification technology route of rare earth metal and make a significant theoretical and practical contribution to innovation the existing purification technologies and ptomoting sustainable development of the rare earth industry in the near future.

本项目基于现有稀土金属提纯的技术瓶颈与关键问题，引入熔析直拉净化分离技术，以稀土金属钆中金属杂质为对象，研究其净化过程的分离行为与迁移规律。首先，协同SEM、XAFS、上海光源BL15U1等多种分析手段与FACTSAGE、CALPHAD等热力学计算软件研究钆中典型金属杂质的嵌布方式、微区分布等赋存特征与分配系数、扩散系数等热力学特性；其次，综合熔析介质、拉伸方式与影响因素的优化选择构建高效的Gd-M熔析净化分离体系；最终，结合熔析前后钆中金属杂质的存在形式、热力学参数的差异性与析出钆的晶面生长行为，探讨金属杂质在熔析过程的分离行为与迁移规律。本项目的实施可起到以点带面的作用，即通过研究典型金属杂质这个点带动其他杂质（C/N/O等）的整个面，实现多类型杂质的同步高效分离，对创新节能高效的稀土金属提纯技术路线，完善超高纯稀土金属制备技术，推动稀土产业可持续发展都具有重要意义。

本课题基于熔析净化法，针对稀土金属钆提纯过程中存在的关键共性问题，深入研究稀土金属钆中典型金属杂质的赋存特征，计算其分配系数、扩散系数等热力学数据，综合熔析介质、直拉分离手段与影响因素的优化选择构建高效的熔析净化体系，结合熔析前后钆中金属杂质的存在形式、热力学参数的差异性，分析Fe、Ti等典型金属杂质在熔析过程的分离行为，提出稀土金属钆杂质净化的新思路。本项目的实施将有助于稀土金属中典型杂质的物理化学赋存与高效富集分离研究，对创新完善高纯稀土金属制备技术及推动稀土应用产业发展具有重要意义。.通过理论计算和测试分析，钆中Ti、Al、Fe、Cu的平衡分配系数分别为0.018、0.273、0.117、0.123，均小于1，主要偏析于基体钆晶界处，以两种或多种元素聚集，以合金杂质相等沉淀化合物的形式分布，形成不同的杂质相区域，各个分区杂质相的组成有所不同。综合考量选择Al-Gd熔析体系，其中典型金属杂质Ti、Al、Fe、Cu的平衡分配系数分别为0.4、0.03、0.04、1.1，杂质依然主要以富Al杂质相形式偏析或固浓。在97.5wt%Gd-2.5wt%Al质量比、加热温度1450℃、下拉速率3μm/s条件下，降温至冷却沿两相界面切开合金得到提纯Gd，对比纯钆体系和Al-Gd溶析体系下，Ti由1333ppm降至65ppm、18ppm，Fe含量分别由132ppm降至68ppm、10ppm，溶析体系下两种杂质去除效果明显好于纯Gd体系，Fe、Ti去除率分别达到98.6%、92.4%。