Flotation Behavior and Interface Characteristics of Apatite with Co-Depression by Sulfuric Acid and Phosphoric Acid

Phosphate ore is an important strategic mineral resource. The efficient utilization of phosphate resources faces challenges such as low grade of raw ore and difficulty in discharging gangue minerals. One of the key problems to be solved urgently in the reverse flotation of phosphate ore is the effective depression of apatite. However, research on the influence mechanism of acid depressants on the surface properties and adsorption characteristics of apatite is still insufficient. In this study, the influence of different depressants (such as sulfuric acid, phosphoric acid or mixed acid of sulfur acid and phosphorus acid) on the flotation separation performance of an artificial mixture of apatite and dolomite (gangue mineral) was investigated through laboratory flotation tests. On this basis, with the addition of different depressants, the contact angle, zeta potential, XPS and TOC were used to investigate the surface wettability, surface charge, surface species and the adsorption characteristics of the collector (sodium oleate) on the apatite surface, and, accordingly, the inhibiting mechanism was discussed. The results show that, when mixed acid of sulfur acid and phosphorus acid is used as a depressant, a concentrate with a P₂O₅ grade of 33.53% and a recovery of 88.92% can be obtained, and the parameters are better than when using phosphoric acid with a P₂O₅ grade of 30.15% and a recovery of 80.12% or sulfuric acid with a P₂O₅ grade of 30.12% and a recovery of 80.58%. Our analysis shows that the mixed acid has the best inhibiting effect on apatite, which is mainly due to the following: (a) after adding the mixed acid, chemicals such as CaSO₄, CaHPO₄/Ca(H₂PO₄)₂ are generated on the surface of apatite, resulting in a significant reduction in the contact angle and stronger surface hydrophilicity; (b) the mixed acid reduces the zeta potential of apatite, produces new species and weakens the non-selective adsorption of negatively charged oleate on the surface of apatite, thus preventing the apatite from floating.