Hydrothermal Processing Of Phosphogypsum Process Research

Phosphogypsum is an by-product of wet-procedure for phosphoric acid production .producing 1 ton phosphoric acid(100% PA) will produce 4. 5⁵. 0 tons phosphogypsum. In the later five years, the market demand of phosphate fertilizer in the world will increase 2. 7% every year. Chinese phosphoric acid production ability will enlarge more than half of the global. Accompanying with the phosphoric acid production enlargement;the phosphogypsum increase will become burden of the phosphoric fertilizer manufacturing enterprises who expected to keep up a steady increase. Phosphogypsum contains not only more than 80% CaSO₄·2H₂O and but also a small amount impurities, such as phosphate and fluoride, etc. These impurities will largyly impair the properties of phosphogypsum and restrict the use of phosphogypsum.In the process of hydrothermal treating phosphogypsum, every parameter of crystal growth could artificially adjusted , crystal growth characteristics could be brought into full play also. The reports that used hydrothermal treating phosphogypsum did not appeared so for. The article explored modification of phosphogypsum with the help of hydrothermal method. By combination of chemical analysis and X-ray diffraction spectra(XRD), the key chemical composition was analysed, using optical microscope and scanning electron microscope(SEM) observed crystal forms, and composition change dehydration temperature of phosphogypsum was determined by the differential thermal analysis(DTA).In the process of hydrothermal treating phosphogypsum, changing the hydrothermal technological conditions and additives could transform the hydrothermal system properties and make further improve the dissolution and crystallize characteristics of the phosphogypsum. The primary experiment goals were separating rate of PA, recovery rate of CaO and S0;i, crystal water and crystal forms of phosphogypsum. In the experiment, using single factor test method studied systematically that the hydrothermal temperature, timeand proportions of solid and liquid had an effects on the process of hydrothermal treating phosphogypsum. The additives that distinctly affected the chemical composition and crystal form of phosphogypsum were chosen. The experiment showed that the phosphogypsum hydrothermal products could acquire relatively higher separating rate of P205, recovery of CaO and S0:) at 140°C hydrothermal temperature, 4 hour hydrothermal time, 0.60 proportions of solid and liquid and acid solvent. Simultaneously, crystal forms of the phosphogypsum hydrothermal products were relatively regular. When the additives were added to the hydrothermal system, higher separating rate of P205 and recovery of CaO and S03 were obtained, and the crystal forms of the phosphogypsum hydrothermal products were more regular long column form.For investigating the compound additives to influence the phosphogypsum hydrothermal products, using orthogonal optimize experiment in the article sifted combination additives and determined that when the experiment was carried out at the optimum combination additives, the phosphogypsum hydrothermal products acquired 99.18% separating rate P205, 99.96% and 99. 40 recovery of CaO and S0:(, at the same time, crystal water content of phosphogypsum hydrothermal products approached the hemihydrates gypsum theory crystal water 6. 20%, crystal forms were slender and longer.The experimental results showed that washing the phosphogypsum was harmful to recovering the CaO and S0;i, and the phosphogypsum growth were influenced.Analyzing the mechanism of the process of hydrothermal treating phosphogypsum knew that changing the hydrothermal system technological conditions and adding suitable additives could alter system supersaturation, improve phosphogypsum growth characteristic and promote the phosphogypsum crystal good growth.