Bayan Obo ore has abundant rare earth (RE) reserves, and RE elements (REEs) are mainly transferred into the RE‐bearing slag. However, the utilization of RE‐bearing slag is greatly limited due to the serious lack and ambiguity of RE crystals. In this study, in situ separation of RE crystals from RE‐bearing slag via supergravity was developed, and the high‐purity crystals of britholite with various REEs contents were selectively separated from the CaO–SiO 2 –CaF 2 –P 2 O 5 –Ce 2 O 3 system with a high REEs recovery ratio of 95.58%–98.65%. On this basis, the chemical formula, the crystal structure, and the formation mechanism of britholite were characterized from the high‐purity crystals through a combination of the Rietveld refinement and DFT calculation. It was found that the britholite was verified to be evolved from Ca 5 (PO 4 ) 3 F, there would be an SiO 4 4− instead of a PO 4 3− when a Ce 3+ replaced a Ca 2+ , the chemical formula changed from Ca 5 (PO 4 ) 3 F to Ca 4.377 Ce 0.623 Si 0.6 P 2.4 O 12 F, Ca 3.956 Ce 1.044 Si 1.01 P 1.99 O 12 F, and Ca 3.176 Ce 1.824 Si 1.93 P 1.07 O 12 F with the increase of REEs content, and the substitution range of REEs was between 0 and 2. This study supplements some necessary basic data of RE crystals, which provides the theoretical reference for efficient recovery of RE resources and sustainable utilization of RE‐bearing slag.
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