LI Zhan, CHEN Jiang, ZHANG Qin^*, SHEN Zhi-hui^*

(1. Mining College, Guizhou University, Guiyang 550025, China;
2. National ＆ Local Joint Laboratory of Engineering for Effective Utilization of Regional Mineral Resources from Karst Areas, Guizhou University, Guiyang 550025, China;
3. Guizhou Key Lab of Comprehensive Utilization of Non-metallic Mineral Resources, Guizhou University, Guiyang 550025, China)

Abstract: Phosphogypsum is a kind of large-scale industrial solid waste produced during the production of wet-process phosphoric acid. Removal of harmful impurities such as phosphorus and fluorine from the phosphogypsum is a prerequisite for its resource utilization. The removal rule of phosphorus and fluorine in phosphogypsum has been studied using the lime neutralization method and acid leaching method, and the changes of micro-morphology, surface groups, and phase compositions of phosphogypsums in the removal process of phosphorus and fluorine have been studied using SEM, FTIR, and XRD in this paper. The results show that the soluble phosphorus and partially soluble fluorine can be effectively removed from phosphogypsum, but eutectic phosphorus cannot be removed, by using the lime neutralization method. With the lime dosage of 0.4% and aging time of 12 h, the removal rates of soluble phosphorus and soluble fluorine from phosphogypsum were 93.27% and 29.07%, respectively. The total phosphorus and fluorine in phosphogypsum can be effectively removed by the heating acid leaching (55 ℃, sulfuric acid dosage of 30%) with removal rates of 98.95% and 91.07%, respectively. The crystal morphology of phosphogypsum was changed from rhomboidal to flaky shapes after the acid leaching. The removal rates of phosphorus and fluorine in phosphogypsum are increased with the increase of sulfuric acid dosage at room temperature. The total phosphorus and total fluorine were effectively removed from phosphogypsum by the acid leaching at room temperature (25 ℃, sulfuric acid dosage of 50%), with the removal rates of 95.88% and 93.13%, respectively. In addition, the morphology of the product was changed into long column, as the dihydrate gypsum was dehydrated to hemihydrate gypsum, and the characteristic absorption peak of eutectic phosphorus was disappeared after the acid leaching.

Keywords: Phosphogypsum; the lime neutralization method; the acid leaching; phosphorus; fluorine; removal

ACTA MINERALOGICA SINICA Vol. 40, No.5, 2020, page 639