Interaction Behavior between Coarse and Fine Particles in the Reverse Flotation of Fluorapatite and Dolomite

The precondition for efficient flotation of middle- to low-grade phosphate ore is the dissociation of apatite from gangue minerals through fine grinding. However, fine gangue minerals, such as dolomite, have a lower hardness and are thus easily overground and converted into slime during the grinding stage. The effect of -10 μm dolomite fines (Dol-10μm) on the flotation of -75 + 25 μm dolomite (Dol-75+25μm) and -75 + 25 μm fluorapatite (FAp-75+25μm) from a detailed mechanism was investigated by microflotation tests, cryo-electron microscopy analysis, contact angle measurements, bubble-particle attachment test, and EDLVO theory. It was found that Dol-10μm significantly reduced the recovery of Dol-75+25μm and FAp-75+25μm. The Dol-10μm particles could decrease the flotation recovery of Dol-75+25μm particles by masking on their surfaces, thus reducing the hydrophobicity of mineral surfaces and preventing them from floating. Furthermore, Dol-10μm particles were easily adsorbed on the FAp-75+25μm surface and could not be effectively floated, which results in fine dolomite being mixed into the concentrate at the bottom of the tank, thereby reducing the selectivity of reverse flotation for phosphate ore. The interaction energy calculation showed that the presence of NaOL led to an attractive interaction force between Dol-10μm and Dol-75+25μm, as well as between Dol-10μm and FAp-75+25μm. As a result, Dol-10μm particles presented a nonselective aggregation with Dol-75+25μm and FAp-75+25μm particles, explaining the phenomenon of "slime coating" and the depressing effect of dolomite fines on phosphate reverse flotation.