Innovative Methodology to Enrich Britholite (Ca₃Ce₂[(Si,P)O₄]₃F) Phase from Rare-Earth-Rich Slag by Super Gravity

Abstract

A new approach to enriching britholite phase from the rare-earth-rich slag by super gravity was investigated. The Bayan Obo iron ore, which was used as raw material, was reduced and melting separated to produce iron nugget and rare-earth-rich slag. Subsequently, the slag was heat-treated and enriched in the super gravity filed. The volume fraction and equivalent diameter of britholite phase were measured by scanning electron microscope (SEM) and image analyzer, whereas the mineral composition and chemical component were characterized by X-ray diffraction and X-ray fluorescence. The results indicated that the samples obtained by the gravity coefficient G ≥ 500, t ≥ 15 minutes, and T ≥1423 K (1150 °C) show significant layers and britholite phase present gradient size distribution in the sample along the super gravity. The layered sample was central cut and characterized by SEM, and it is difficult to find any britholite particles in the upper area of the sample. The britholite phase gathers at the middle and bottom areas of the sample. The mechanism of moving speed of britholite particles in super gravity field was discussed, and the conclusion indicates that the moving speed of britholite particles is proportional to the square of the britholite particle size. As a result, large britholite particles move farther than the small ones and gather at the bottom of the sample, whereas small britholite particles accumulate in the middle of the sample. Under the hypothesis that rare earth (RE) exists in the slag in terms of RE₂O_3, with the gravity coefficient G = 500, t = 15 minutes, and T = 1423 K (1150 °C), the mass fraction of RE₂O₃ in the concentrate is up to 23.29 pct whereas that of the tailing is just 5.57 pct. Considering that the mass fraction of RE₂O₃ is 12.01 pct in the parallel sample, the recovery ratio of RE in the concentrate is up to 71.19 pct by centrifugal enrichment.