Removal Impurity and Whitening of Phosphogypsum via Calcination and Acid Leaching

This is an article in the field of metallurgical engineering. Large production and storage capacity of phosphogypsum has become an important factor restricting the green and healthy development of phosphorus chemical industry. Removing impurity and whitening of phosphogypsum is a necessary way for its high consumption. Analysis results showed that there was still a small amount of black organic matter in the phosphogypsum after removing impurity and desilication by flotation, which affected its whiteness. In the paper, calcination and acid leaching were adopted to treat the phosphogysum. The whiteness of whitened phosphogysum significantly increased from 51.5% to 92.7% at the conditions of calcination temperature 600 ℃, calcination time 70 min, acid leaching time 2 h, sulfuric acid concentration 1.5 mol/L, acid leaching liquid to solid ratio 5∶1 and acid leaching temperature 90 ℃. The whitened phosphogypsum was mainly CaSO₄, and contained a small amount of CaSO₄·2H₂O and CaSO₄·0.5H₂O. The particles of the whitened phosphogypsum were irregular in shape of 15～20 μm, and the surface was smooth. The study provided a guidance for the comprehensive utilization of phosphogypsum with high consumption.