Reverse flotation separation of quartz from fluorapatite using 1-octyl-3-methylimidazolium bromide as a selective collector

[C 8 mim]Br selectively floats quartz (88.13%) over fluorapatite (4.43%) at pH 7.01. • Binary mixture flotation with [C 8 mim]Br achieves a P 2 O 5 grade of 31.49% with 91.59% recovery, confirming superior selectivity over conventional DDA. • [C 8 mim] + selectively adsorbs on quartz via electrostatic attraction with Si-O − sites and C–H···O hydrogen bonding with silanol groups, while fluorapatite lacks these active sites. • Short-chain imidazolium ionic liquids serve as promising collectors for reverse flotation desilication of phosphate ores, offering a new reagent strategy for phosphate mineral processing. The reverse flotation separation of quartz from fluorapatite using 1-octyl-3-methylimidazolium bromide ([C 8 mim]Br) ionic liquid as a novel collector was investigated, with dodecylamine (DDA) employed as a benchmark. Micro-flotation tests showed that [C 8 mim]Br selectively collected quartz (88.13%) with negligible flotation of fluorapatite (4.43%) at pH 7.01 and 50 mg/L, demonstrating superior selectivity over DDA. Binary mixture flotation (fluorapatite: quartz = 1:1) achieved a P 2 O 5 grade of 31.49% with a recovery of 91.59%. Zeta potential and contact angle measurements revealed that [C 8 mim]Br increased the zeta potential of quartz by 14.05 mV and enhanced its contact angle from 19.41° to 79.75°, while exerting minimal influence on fluorapatite. Microcalorimetry demonstrated that the adsorption heat of [C 8 mim]Br on quartz (0.237 J/g) was significantly higher than that on fluorapatite (1.6 × 10 −3 J/g). FTIR and XPS analyses indicate that [C 8 mim]Br is adsorbed on the quartz surface mainly through electrostatic attraction between the imidazolium cation and deprotonated Si-O − sites. The optimized configuration obtained from DFT calculations shows that C-H···O hydrogen bonds exist between the protons at the C4/C5 positions of the imidazole ring and surface oxygen atoms (H···O = 1.971 Å, C-H···O = 141°), whereas no stable adsorption configuration is obtained on the fluorapatite surface. These findings demonstrate that [C 8 mim]Br is a promising selective collector for the reverse flotation desilication of siliceous-calcareous phosphate ores. [C8mim] + adsorbed on the quartz surface through electrostatic attraction with deprotonated Si-O − sites, supplemented by hydrogen bonding between the C–H proton and surface silanol groups. In contrast, the fluorapatite surface lacks such active sites for anchoring of [C8mim]+, which accounts for the selective separation. Download: Download high-res image (120KB) Download: Download full-size image