The past decade has seen a surging increase in demand for rare earth elements (REEs) around the globe due to their extensive applications in the manufacturing of electronics, medical devices, sustainable energy devices, and catalysts. To mitigate the potential supply scarcity and economic setback caused by major exporting countries’ strict policy, cost effective and environmentally friendly technologies for REE production are urgently needed. Since municipal solid waste incineration (MSWI) ash is a large-volume by-product of waste treatment that contains REEs, an effective recovery process could make it a promising source for REE recovery and address the waste management issue at the same time. However, significant knowledge gaps need to be filled in order to develop a feasible and green technology for REE recovery.  In this study, we systematically characterized the speciation of REEs in representative MSWI ash samples, and designed a close-loop treatment system for REE extraction with high recovery efficiency, minimal waste generation, and low operating cost. The elemental composition, morphology, and mineralogy of size-fractionated ash samples were characterized using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD). Based on the distribution and speciation of REEs, appropriate ligands were selected to extract REEs and separate them from other metals. The impacts of influencing solution chemistry on the extraction and separation efficiency were examined to optimize reaction conditions. Waste residuals during each step were upcycled to generate useful products. Overall, this treatment system demonstrated high extraction efficiency of REEs from MSWI ash, effective separation of REEs from other metals, generation of multiple marketable products, and minimal production of secondary wastes.

Close-loop treatment system for the recovery of rare earth elements from municipal solid waste incineration ash

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