Liquid-liquid mineral separation via ionic-liquid complexation of monazite and bastnäsite—An alternate route for rare-earth mineral beneficiation

Abstract

The potential of liquid-liquid mineral separation mediated by ionic liquids (ILs) to beneficiate rare earth (RE) bearing minerals was investigated for the first time. Liquid-liquid separation tests were performed on actual RE-bearing ores whereas the role of ionic liquids was exposed using model monazite, bastnäsite, calcite and dolomite single minerals. The multiphase beneficiation system consisted of aqueous pulps in which IL/kerosene and IL/n-hexane non-polar phases were emulsified using three types of phosphonium/ammonium ionic liquids to evaluate their chelation potential. The aqueous pulp pH played a crucial role in terms of mineral recoveries with the highest RE mineral recoveries achieved at pH 4–7. Also, the newly proposed beneficiation method was found to outperform micro-flotation of the same minerals in terms of selectivity. Zeta potential measurements, Fourier transform infrared spectroscopy, and density functional theory simulations were used to interpret the mechanisms governing this new mineral separation route. The ionic liquid anionic moiety was demonstrably found to directly interact through formation of covalent bonds with the metal cation active centers, contrary to the cationic moiety which at most was involved in weaker “non-surface” Coulombic/van de Waals interactions as ion-pair co-ion. Hence with regard to the potential of ionic liquids in minerals beneficiation, liquid-liquid mineral separation could be envisaged as a new alternative for RE mineral separation instead of flotation.