来源：ACS Publications
Rare earth elements (REEs) have been identified as “critical” metals because of their strategic applications in high-end energy devices such as wind turbine generators for enhanced energy production, permanent magnets, and electric vehicle batteries. Coal, on the other hand, is a conventional energy source and has been used for combustion-based energy production. Ash is generated as a waste product during combustion. Both combustion and ash waste are detrimental to the clean energy goal. The study demonstrates the extraction of REEs from coal ash and aims to present coal as a potential clean energy resource. Coal ash can be used as a material that can be potentially recycled to obtain REEs. In this study, a microfluidic technology-based coiled flow inverter (CFI) device has been employed for extracting REEs from coal ash. A liquid–liquid extraction (LLE) process has been carried out employing CFI microfluidic technology (CFI-MT), using an organic extracting liquid (D2EHPA diluted with kerosene). The results obtained in this work show that CFI-MT can have significant enhancements in extraction efficiencies with respect to batch extraction. The study demonstrates the future application of CFI-MT as a promising and intensified method for the REE extraction process through waste recycling. Furthermore, the novel aspect of the present study corresponds to the first-time application of CFI-MT for REE extraction from coal ash. The study also demonstrates CFI-MT as a promising tool for exploiting waste materials as an alternate resource for metal extraction.