Abstract
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.
Highlights
Phosphogypsum is mainly obtained from the phosphate fertilizer industry and is a solid waste residue produced by a wet preparation of phosphoric acid
It is projected that the total amount of phosphogypsum will double by 2025–2045 [1,2]
The water content of the phosphogypsum was less than 5%, and the particle size was less than 1 mm
Summary
Phosphogypsum is mainly obtained from the phosphate fertilizer industry and is a solid waste residue produced by a wet preparation of phosphoric acid. The global cumulative emissions of phosphogypsum total approximately 6 billion tons, which is increasing at a rate of 150 million tons/year. It is projected that the total amount of phosphogypsum will double by 2025–2045 [1,2]. Phosphogypsum is an industrial by-product of gypsum with a low utilization rate owing to its large discharge, complex impurity composition, and difficult treatment. Effective treatment and efficient utilization of phosphogypsum are urgently needed. Phosphorus impurities in phosphogypsum mainly consist of soluble phosphorus (H3 PO4 , H2 PO4− , and HPO4 2− ), insoluble phosphorus (Ca3 (PO4 )2 ), and eutectic phosphorus (CaHPO4 ·2H2 O). The fluorinecontaining impurities in phosphogypsum mainly consist of soluble fluorine (NaF and KF)
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