The recent progress of ion exchange for the separation of rare earths from secondary resources – A review

The challenge towards modern technologies has been enquiring and culminating in the continuously expanding use of rare earth elements (REEs). The non-renewable primary resources of REEs such as bastnasite, monazite, and xenotime, are 78% dominated by China, and their exhaustive exploitation and future availability have raised global concerns. The recycling of end-of-life (EOL) products containing rare earths, waste streams in mining, and metallurgical industry, also referred to as secondary resources - has therefore become an alternative. This, however, requires advanced separation and extraction technologies to achieve high yields from the raw materials and high purities of the recovered REEs. Hydrometallurgy, starting with leaching, and having solvent extraction as the solution purification step, has been employed worldwide for capturing REEs from primary and secondary resources, with high reported recycling efficiencies. Among the frequently used processes, ion exchange (IX) has become one potential method due to its high selectivity, simple use and maintenance, and easy accessibility. This review briefly highlights the updated separation and extraction technologies used to separate REEs from sulfate-based solutions and secondary sources and mostly focuses on ion exchange separation systems. Significant benefits of IX are outlined, and the content of this review emphasizes that IX can still be used as an efficient, economical, and green method for the enhanced extraction of REEs from secondary sources.