Reinforced recovery of REEs/Nb/Ti from low-grade concentrate mixture: Selective recovery of Nb/Ti

In previous work, we developed an H 2 SO 4 -Fe 2 (SO 4 ) 3 roasting and water leaching method to leach rare earth elements (REEs), niobium (Nb), and titanium (Ti) from a low-grade concentrate mixture of the Baerzhe ore deposit in China ( Ge et al., 2024 ). However, conventional chemical precipitation and fluorine-ligand extraction methods for separating REEs/Nb/Ti in the leach solution face challenges, including co-precipitation of REEs and Nb/Ti, low recovery efficiency, and significant environmental concerns. To address these issues, a novel two-step solvent extraction process for efficient separation and recovery of Nb and Ti from leach solution was proposed in this work. The quaternary ammonium salt extractant (N263-CO 3 2- ) was employed to selectively co-extract Nb and Ti from the leach solution for achieving effective separation them from REEs. The resultant Nb(OH) 5 /Ti(OH) 4 precipitates were dissolved in H 2 C 2 O 4 -H 2 SO 4 mixture for selective extraction of [NbO(C 2 O 4 ) 2 - ] using tri-n-octylamine (TOA). The extraction mechanism confirmed that N263 preferentially extracts Nb/Ti via anion exchange, with the primary contribution from N263-CO 3 2- to Nb/Ti extraction, followed by N263-SO 4 2- , while protonated TOA selectively extracts [NbO(C 2 O 4 ) 2 - ] through anion–cation association. Ultimately, the recovery efficiencies of Nb and Ti reached 96.0 % and 69.0 %, respectively, producing Nb 2 O 5 (99.6 %) and TiO 2 (99.2 %), with REEs losses < 0.5 %. This study offers a novel approach for the efficient selective separation and recovery of Nb/Ti from leach solution.