Efficient resource utilization of gypsum in the flotation separation of apatite from calcite

A large amount of the industrial byproduct gypsum can harm the environment, so developing an innovative approach for the utilization of gypsum is highly important. In this study, gypsum was employed to increase the flotation separation efficiency of apatite from calcite. The micro-flotation test revealed that sodium oleate could not separate the two minerals without a depressant. At pH 9, following the incorporation of gypsum, apatite achieved a recovery of 83.22 %, which was 51.49 % greater than that of calcite. The artificial mixed mineral test yielded a mixed concentrate with a P₂O₅ recovery of 72.71 % and a grade of 25.88 %. Mineral surface properties were analyzed, revealing that gypsum enhanced the hydrophilicity of the calcite surface and inhibited NaOL adsorption on calcite but had a minimal impact on apatite. Ca²⁺ in the slurry facilitated SO₄^2– adsorption on the calcite surface. X-ray photoelectron spectroscopy results indicated that phosphate species on the apatite surface could adsorb Ca²⁺ from the solution, creating active sites for sodium oleate. Additionally, a higher concentration of S was observed on the calcite surface, suggesting that the adsorption capacity of gypsum dissolved in the slurry is greater on the surface of calcite. Surface morphology analysis revealed selective gypsum dissolved components adsorption on calcite rather than apatite, primarily within the 8–30 nm range, exhibiting uniform spot adsorption. These findings demonstrate the potential of gypsum as an inorganic depressant for calcite from various sources, enabling the flotation separation of apatite from calcite and thus providing a theoretical basis for the resource utilization of gypsum solid waste.