Selective flotation of ilmenite from diopside using 8-hydroxyquinoline: An FeN-dominated adsorption mechanism

Selective flotation separation of ilmenite from calcium–magnesium silicate gangue remains challenging because of the weak natural hydrophobicity of ilmenite and the insufficient selectivity of conventional collectors. In this study, 8-hydroxyquinoline (8-HQ), a heterocyclic N,O-donor reagent, was evaluated as a selective collector for ilmenite–diopside separation. At pH 7.0 ± 0.2 and an 8-HQ concentration of 1.0 × 1 0 − 4 mol L −1 , the single-mineral recoveries of ilmenite and diopside were 90.1% and 25.0%, respectively. Artificially mixed-mineral flotation under the selected conditions yielded a concentrate containing 43.8% TiO 2 at a recovery of 86.7%, demonstrating effective separation of ilmenite from diopside. After 8-HQ treatment, the contact angle of ilmenite increased from 42.1° to 78.2°, whereas that of diopside increased only from 27.2° to 35.8°. UV–vis analysis showed that the adsorption amount of 8-HQ on ilmenite reached 0.138 mg g −1 , approximately 3.6 times that on diopside. The appearance of an N 1s signal and slight but consistent changes in the Fe 2p and O 1s spectra further supported preferential adsorption on ilmenite. Spin-polarized PBE+ U +TS calculations yielded an adsorption energy of approximately −1.66 eV and optimized Fe N and Fe O distances of 2.14 and 2.48 Å, respectively. Partial overlap between the surface Fe 3d and 8-HQ N 2p states further supported an Fe N-dominated adsorption interaction, with the hydroxyl O group providing an auxiliary contribution. These results show that selective adsorption of 8-HQ on exposed Fe sites enhances ilmenite hydrophobicity and enables its effective flotation separation from diopside. • 8-HQ selectively separates ilmenite from diopside at neutral pH. • Mixed-mineral flotation yields 43.8% TiO 2 at 86.7% recovery. • 8-HQ adsorption on ilmenite is 3.6 times that on diopside. • XPS and DFT reveal Fe N-dominated adsorption on ilmenite. • Auxiliary Fe O interaction further stabilizes 8-HQ adsorption.