Reverse flotation purification of phosphogypsum and preparation of high whiteness CaSO4

Abstract

Waste phosphogypsum has garnered significant attention due to its severe environmental pollution. However, its low whiteness restricts its potential applications. In this study, impurities such as organic matter, metal ions, and silica were eliminated through reverse flotation, followed by the preparation of anhydrous CaSO₄. Characterization of phosphogypsum after reverse flotation and anhydrous CaSO₄ was conducted using XRF, SEM-EDS, XRD, and FT-IR. The findings indicate that organic matter and Fe₂O₃ content are the primary factors affecting phosphogypsum whiteness. Reverse flotation purification of raw phosphogypsum, initially possessing a whiteness of 50 % and a CaSO₄•2 H₂O content of 87.5 %, resulted in purified gypsum with a whiteness of 71 % and a CaSO₄•2 H₂O content of 94.5 %. The removal rates of organic matter and Fe₂O₃ reached 78.2 % and 61.3 %, respectively. Anhydrous CaSO₄ achieved a whiteness of up to 92 % with a purity of 96 %. The removal rates of P₂O₅, F, Al₂O₃, MgO, Fe₂O₃, Na₂O, K₂O and organic matter were 98.9 %, 100 %, 89.5 %, 88.1 %, 82.6 %, 86.4 %, 100 % and 80.4 %, respectively. In this study, an appropriate collector was employed to remove organic matter and SiO₂ from phosphogypsum in a single step, offering a novel approach for its purification. Compared to conventional calcination methods for anhydrous gypsum preparation, our approach demonstrates distinct advantages in terms of energy efficiency, cost-effectiveness, and substantially improved product quality. Furthermore, high-whiteness anhydrous CaSO₄ exhibits potential for use in coatings, presenting an innovative application route for phosphogypsum.