Depression mechanism of acid for flotation separation of fluorapatite and dolomite using ToF-SIMS and XPS

The flotation separation of apatite and dolomite poses a long-standing challenge in the mineral processing industry because of their similar physicochemical properties. In this study, phosphoric acid (H3PO4) and sulfuric acid (H2SO4) were used as inhibitors for fluorapatite. The effects of both H3PO4 and H2SO4 on reverse flotation separation were analyzed by using micro-flotation tests, Zeta potential tests, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The results of micro-flotation tests indicate that H3PO4 or H2SO4 exhibits a strong selective depression effect on fluorapatite, but is not sensitive to dolomite flotation. The TOF-SIMS and XPS results further demonstrate that the addition of H3PO4 or H2SO4 interferes with the adsorption of NaOL on the fluorapatite surface, thereby reducing the floatability of fluorapatite, while the floatability of dolomite is almost unaffected. The CaHPO4(or CaH2PO4+) generated on the surface of fluorapatite in acidic media is the major species that inhibits fluorapatite. As small amount of CaSO4 can be observed when H2SO4 is used as an inhibitor, which also has an inhibitory effect on fluorapatite.