Abstract Supply of rare earth elements (REEs) critical to the development and maintenance of industrialized economies has become uncertain in recent years owing to the limited number of REE producers. In order to develop alternative REE sources, new mines are being explored and end-of-life secondary sources have been targeted for REE recovery. However, the composition of ores and secondary sources often differ significantly from one source to another and hydrometallurgical practices are not rigorously established or matured for many alternative REE sources. This presents a challenge in processing these materials while minimizing the entrainment of impurities. This work presents a comprehensive and systematic review on recent progress in impurity removal during REE processing. A large number of original research articles covering techniques including solvent extraction, ion exchange, precipitation, and other emerging technologies have been reviewed in detail and critically assessed to understand the role and behaviour of specific impurities in REE processing (including Al, Ca, Mg, Fe, Si, Th, U, Ti, Zr, Hf, Cr, Mo, Mn, Co, Ni, Cu, Zn, Sn, Pb, and Bi). Control of the most troublesome impurities for industry (Al, Fe, Th, U) depends on their concentration, redox ratio, and the degree of purity required. Most aluminum, ferric iron, thorium, and uranium(IV) selectively precipitate as hydroxides prior to REEs. Ferrous iron does not usually co-extract with REEs in their ion exchange or solvent extraction circuits. Precipitation of REE oxalates is effective to partition REEs and uranyl (UO22+) species. To remove thorium and uranium to the highest degree requires separate solvent extraction or ion exchange steps designed to specifically extract these impurities by anion exchange.

中文翻译：

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稀土元素加工过程中杂质去除的最新进展：综述

摘要 近年来，由于 REE 生产商数量有限，对工业化经济的发展和维持至关重要的稀土元素 (REE) 的供应变得不确定。为了开发可替代的 REE 来源，正在探索新的矿山，并且已将报废的二次资源作为 REE 回收的目标。然而，矿石和次要来源的组成通常因一个来源而异，并且湿法冶金实践对于许多替代 REE 来源没有严格建立或成熟。这对加工这些材料同时最大限度地减少杂质的夹带提出了挑战。这项工作对 REE 处理过程中去除杂质的最新进展进行了全面系统的回顾。大量涉及溶剂萃取、离子交换、沉淀和其他新兴技术的原创研究文章已经过详细审查和严格评估，以了解特定杂质（包括铝、钙、镁、 Fe、Si、Th、U、Ti、Zr、Hf、Cr、Mo、Mn、Co、Ni、Cu、Zn、Sn、Pb 和 Bi)。工业上最麻烦的杂质（Al、Fe、Th、U）的控制取决于它们的浓度、氧化还原比和所需的纯度。大多数铝、三价铁、钍和铀 (IV) 在 REE 之前选择性地以氢氧化物形式沉淀。二价铁通常不会在离子交换或溶剂萃取回路中与 REE 共萃取。REE 草酸盐的沉淀可有效分离 REE 和铀酰 (UO22+) 物质。