From crystal structure to flotation selectivity: Collector adsorption mechanisms on rutile and ilmenite

Rutile and ilmenite are the main commercial titanium minerals, but they can respond differently to the same collector even though both contain Ti-related surface sites. This review compares the two minerals to examine how their surface properties and reagent conditions affect collector adsorption and flotation. Crystal structure, chemical composition, dissolution and hydroxylation are discussed together with the adsorption of fatty acid, hydroxamic acid and phosphonic acid collectors. The effects of pH, collector dosage, metal-ion activation, surface treatment and collector formulation are also compared. The available studies show that crystal structure alone cannot explain the different flotation responses of rutile and ilmenite. Mineral surface condition, solution composition and reagent treatment also play important roles. Chemical interactions between collector groups and surface metal sites are supported in many systems, but the exact adsorption structures and the importance of Fe- and Ti-related sites are not always clearly determined. Fatty-acid collectors often require gangue depression to achieve effective separation. Hydroxamic-acid flotation is strongly affected by collector formulation and metal-ion treatment, while phosphonic-acid collectors and their derivatives can perform well under very different pH conditions. Across the three collector classes, stronger adsorption or higher recovery of the target mineral does not necessarily lead to better separation from gangue. Future studies should determine which collector species and surface sites are involved during flotation, clarify how metal ions improve collector adsorption, and examine how collector adsorption affects hydrophobicity and bubble attachment. Multiscale modelling and data-driven methods may also help improve collector screening when combined with reliable experimental data. This comparison provides a clearer basis for understanding the different reagent responses of rutile and ilmenite and for selecting collectors under specific mineral and flotation conditions.