Effect of Al3+ and Mg2+ on the flotation of fluorapatite using fatty- and hydroxamic-acid collectors - A multiscale investigation

Fluorapatite flotation is influenced by the dissolved lattice metal ions. Al3+ and Mg2+ from the associating gangue minerals influence the adsorption of collector molecules onto the fluorapatite surface during flotation. Hence, unveiling new insights on such interactions in the context of froth flotation at an atomic level paves the way for improving flotation selectivity. An original multiscale approach has been developed involving flotation experiments, electro-kinetic and adsorption density measurements, X-ray photoelectron spectroscopy studies, and density functional theory simulations. Fatty acid establishes an enhanced interaction with the bare apatite surface compared to the hydroxamates. Na+ counter-ion contributes to the adsorption of fatty acid on bare apatite. Both Al3+ and Mg2+ ions are beneficial for the adsorption of fatty acid, thereby the fluorapatite flotation. For octanohydroxamic acid, the presence of Al3+ results in a stronger collector-apatite interaction, and therefore an enhanced flotation. For fatty acid and hydroxamates, adsorption of Mg2+ leads to an improved collector-apatite interaction. Benzohydroxamic acid is more vigorously adsorbed than octanohydroxamic acid in the presence of Mg2+. Fatty acid establishes a stronger interaction with bare and Al3+/Mg2+-treated fluorapatite, as opposed to hydroxamates. Mg2+ is more favorable than Al3+ in fluorapatite flotation using both fatty acid and hydroxamates.