A Novel Process to Recover Gypsum from Phosphogypsum

In this study, we investigated a coarse phosphogypsum containing 49.63% SO₃, 41.41% CaO, 10.68%, 4.47% SiO₂, 1.28% P₂O₅, 0.11% F, CaSO₄·2H₂O purity of 80.65%, and whiteness of 27.68. Phosphogypsum contains calcium sulfate dehydrate as the main mineral, with small amounts of brushite, quartz, muscovite, and zoisite. Harmful elements, such as silicon, phosphorus, and fluorine, are mainly concentrated in the +0.15 mm and -0.025 mm fraction, which can be pre-selected and removed by the grading method to further increase the CaSO₄·2H₂O content. Gypsum was recovered using a direct flotation method, which included one roughing, one scavenging, and two cleaning operations, from -0.15 mm to +0.025 mm. The test results show that a gypsum concentrate with a CaSO₄·2H₂O purity of 98.94%, CaSO₄·2H₂O recovery of 80.02%, and whiteness of 37.05 was achieved. The main mineral in the gypsum concentrate was gypsum, and limited amounts of muscovite and zoisite entered the gypsum concentrate because of the mechanical entrainment of the flotation process.