Selective Extraction of Rare Earth Elements Over TiO2 From Bauxite Residues After Removal of Their Fe-, Si-, and Al-Bearing Constituents

Abstract

In our previous study, an intermediate material enriched with multiple rare earth elements (REEs, e.g., La2O3, Ce2O3, Sc2O3, and Y2O3) and TiO2 was obtained after removing iron, silica, and alumina from bauxite residues. For valorization of this valuable intermediate material, the selective leaching and separation of REEs and TiO2 by phosphoric acid leaching was investigated. Approximately 90% of REEs was leached from the material using 8- to 10-mol/L H3PO4 liquor at 150°C, while 98% of TiO2 was precipitated as Ti(HPO4)2·H2O in the leached residue, achieving selective extraction of REEs over TiO2. Scrubbing with dilute H3PO4 liquor during filtration could facilitate the formation of Ti(HPO4)2·H2O. The high extraction of REEs was a result of their distribution in the perovskite lattice, as demonstrated by the positive correlation between dissolutions of REEs and perovskite. A route for stepwise extraction of Fe, Si, Al, REEs, and Ti from bauxite residue was established.