Wetting of francolite and quartz and its significance in the flotation of phosphate rock

Water contact angles in the air/water/francolite, fuel oil/water/francolite and fuel oil/water/quartz systems were measured to describe the wetting characteristics of these minerals. It was found that white francolite is more hydrophilic than black and tan francolite both in the absence and presence of fatty acid addition. Further, experimental data showed that francolite has a natural affinity for fuel oil in an aqueous environment, as indicated by advancing and receding oil contact angles of 130–140° and 0–10°, respectively. In contrast, the clean quartz surface did not show such affinity. Fatty acids dissolved in the aqueous phase further improved the hydrophobicity of francolite and enhanced the spreading of fuel oil over the francolite surface. On the other hand, fatty acids had a negligible effect on the wetting properties of the quartz surface. Based on these experimental results, the significance of high solids conditioning for effective phosphate flotation in the presence of fatty acid and fuel oil is discussed including the mechanisms of oil transfer from quartz particles to francolite particles. A new concept on the oil transfer from quartz particles to francolite particles is supported with high-speed video images of film phenomenon captured under stagnant conditions for a model system.