An eco-friendly depressant to achieve efficient and clean reverse flotation enrichment of phosphate ores

Apatite and calcite coexist in phosphate ore, resulting in a relatively low grade of phosphate ore and increasing the difficulty of phosphorus chemical production. Malic acid is considered to have potential as a flotation depressant due to its structural characteristics. The effects of malic acid on the flotation separation between apatite and calcite, as well as the differences in surface regulation, were systematically investigated through flotation experiments, zeta potential measurements, contact angle analysis, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. With a malic acid concentration of 1 × 10 −3  mol/L, the recovery of apatite decreased to 10.16 %, while the recovery of calcite remained stable at 87.59 %. The influence of interfering ions was eliminated by adding Na 2 SO 4 , and the separation performance of malic acid was verified using artificial mixed ores. Surface property characterization and morphology analysis indicated that malic acid adsorbed in a densely punctate manner on the apatite surface. The high adsorption density and strength hindered collector attachment to the apatite surface. However, the adsorption on the calcite surface was sparse and had minimal impact on its floatability. XPS results showed that malic acid adsorbed at the Ca 2+ ion sites of the minerals and interacted more strongly with apatite. DFT calculations demonstrated that the adsorption of malic acid on the apatite surface was more pronounced, and the presence of H atoms within malic acid molecules, together with solvent water molecules, further enhanced the adsorption reaction. This study provides a theoretical basis for the application of malic acid as a flotation depressant and offers new ideas for the efficient flotation separation of phosphate ore.