Evaluated Utilization of Middle–Heavy REE Resources in Bayan Obo Deposit: Insight from Geochemical Composition and Process Mineralogy

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The Bayan Obo is the largest carbonatite-type rare earth deposit in the world. It not only has a large amount of light rare earth element (LREE) resources but also hosts approximately 9 million tons of medium and heavy rare earth element (M+HREE) resources. However, the M+HREE resources have not received enough attention, which hinders their further utilization. In this study, we conduct a systematic investigation of the distribution and process mineralogy properties of M+HREE in different types of ores in the Bayan Obo deposit. The high-value area (>0.1%) of M+HREE elements is found concentrated in the central and deeper parts of the Main and East orebodies. The content of M+HREE varies among different types of ores, with the Aegirine type (1005 ppm) and Fluorite type (1204 ppm) showing a higher average M+HREE concentration. The minerals rich in M+HREE include bastnäsite, monazite, Ca-fluorocarbonate, Ba-fluorocarbonate, allanite, aeschynite, and fergusonite, each with concentrations exceeding 4000 ppm. Aeschynite and fergusonite, in particular, exhibit high M+HREE concentrations and are enriched in fluorite-type and aegirine-type ores. Analysis of the mixed raw ores from the production line at the concentrating plant reveals an M+HREE concentration of approximately 0.2% and a concentration of the seven target minerals at around 12%. However, the particle size distribution and monomer dissociation degree are limited to below 22.3 µm and 40%, respectively. Based on these integrated analyses, we propose that the fluorite-type and aegirine-type ores within the Main and East open-pits are potential M+HREE targets. Furthermore, the recycling and utilization of M+HREE resources in the Bayan Obo deposit require a well-structured process flow and the selection of advanced processing equipment in the future.