A Novel Process to Recover Gypsum from Phosphogypsum

We investigated a coarse phosphogypsum containing 49.63% SO3, 41.41% CaO, 10.68%, 4.47% SiO2, 1.28% P2O5, 0.11% F, 80.65% CaSO4·2H2O, and whiteness of 27.68. Phosphogypsum contains calcium sulfate dehydrate (CaSO4·2H2O) as the main mineral, with small amounts of brushite (CaPO3(OH)·2H2O), quartz (SiO2), muscovite (KAl2SiO10(OH)), and zoisite (Ca2Al3[SiO12]OH). Harmful elements such as silicon, phosphorus, and fluorine are mainly concentrated in the +0.15 mm and −0.025 mm faction, which can be pre-selected and removed by the grading method to further increase the CaSO4·2H2O content. 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 using a direct flotation method, which included one roughing, one scavenging, and two cleaning operations, from −0.15 mm to +0.025 mm. The main mineral in the gypsum concentrate was gypsum (CaSO4·2H2O), and limited amounts of muscovite (KAl2SiO10(OH)) and zoisite (Ca2Al3[SiO12]OH) entered the gypsum concentrate.