Carbothermal reduction followed by sulfuric acid leaching of Bayan Obo tailings for selective concentration of iron and rare earth metals

Abstract

• Carbothermal reduction–H 2 SO 4 leaching of high-fluorine Bayan Obo tailings is studied. • More than 99% of Fe is reduced to the metallic state as the basicity increases to 1.87. • Approximately 97% of Fe and 83% of the REEs were separated and extracted. • Leaching temperature (>25 °C) and H 2 SO 4 concentration (>2 mol/L) hinder the leaching of rare earth elements. In this work, carbothermal reduction followed by sulfuric acid (H 2 SO 4 ) leaching of Bayan Obo tailings has been studied for the selective concentration of Fe and rare earth (RE) minerals. The effect of basicity on the metallization rate of Fe, transfer behaviors of metallic Fe and RE elements, phase composition, and element migration was investigated using XRD, SEM-EDS, EDS mapping, and FT-IR spectroscopy. At a roasting temperature of 1100–1200 °C and a basicity of 1.87, more than 99% of Fe was metallized and 97.91% of Fe and 94.94% of RE were separated magnetically. After roasting, the RE elements mainly existed in Ca 2 RE 8 (SiO 4 ) 6 O 2 and Ca 8 RE 2 (PO 4 ) 6 O 2 , 88% of which were leached out by H 2 SO 4 at 25 °C with an initial concentration of 2 mol/L and a stirring speed of 900 r/min. The precipitation of RE 2 (SO 4 ) 3 was responsible for the incomplete recovery of RE elements during leaching.