Ionic-liquid collectors for rare-earth minerals flotation⿿Case of tetrabutylammonium bis(2-ethylhexyl)-phosphate for monazite and bastnäsite recovery

Abstract

Application of tetrabutylammonium bis(2-ethylhexyl)-phosphate ([N4444][DEHP]), a room temperature ionic liquid (IL), as an aqueous collector for flotation of model monazite and bastnäsite minerals was investigated through micro-flotation tests, zeta potential measurements, Fourier Transform Infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The ionic liquid was shown to have superior performance to float both model rare-earth (RE) minerals as compared with calcite, dolomite and quartz minerals as typical gangue minerals. Parallel to this, micro-flotation tests of a rare-earth ore containing bastnäsite and monazite minerals were found in line with [N4444][DEHP] stronger collecting power towards RE model minerals even outperforming hydroxamic acid-containing collectors. With regard to the mineral surface chemistry, zeta potential measurements, FTIR characterization and XPS analysis, it was established that [N4444][DEHP] uptake on bastnäsite and monazite surfaces was via chemisorption involving specifically the PO and PO groups of the IL anionic moiety. IL anionic and cationic interactions during RE mineral flotation were rationalized in terms of an inner synergistic pathway: IL anionic moiety chemisorbing on bastnäsite and monazite surfaces prompting uptake of cationic moiety via electrostatic attraction and/or via hydrophobic chain interactions of the cation alkyl chains with the chemisorbed IL anionic layer. Finally, for calcite as the most responsive among gangue minerals, the characterization techniques divulged the weaker IL-surface interactions. Hence, this investigation opens up new prospects for more selective ionic-liquid collectors to be used in the flotation of RE minerals.