Abstract:

Silicon，aluminum，and magnesium oxides et al.were added to phosphogypsum based on batching calculations to meet the requirements of acidity coefficient，hydrogen ion index and viscosity coefficient for slag wool production.The sulfur escape from phosphogypsum ingredients and the physical phase structure of slags were investigated by thermogravimetric analysis，determination of melting characteristics，and high-temperature reduction roasting and melting experiments.The results showed that the addition of carbon could promote the decomposition of phosphogypsum，and the n（C）/n（S）of 0.5 was favorable to the desulfurization of the system.The reducing agents（graphite，anthracite，coke） and ingredients could decrease the characteristic melting temperatures of phosphogypsum.The CaO-MgO-SiO₂-Al₂O₃ quaternary phase diagram showed that the ingredient system formed the lowest eutectic point at 1 255.73 ℃.The phase evolution of phosphogypsum and its ingredients during high-temperature roasting illustrated that CaS was the intermediate product of CaSO₄ reduction process，and the SiO₂ in the ingredients combined with more CaO to promote the reaction between CaS and CaSO₄.The high-temperature reduction melting experiments showed that the amount of carbon had a significant impact on the sulfur content of slag and the desulfurization rate of the system.The phosphogypsum ingredients with M_k=1.4，pH of 4.85，and n（C）/n（S） of 0.5 with coke as a reducing agent were melted in the corundum crucible at 1 450 ℃ for 20 min，the desulfurization rate could reach 99.05%，while the slag formed was amorphous with a good glass phase structure.

Key words: phosphogypsum ingredients, thermal analysis, desulfurization rate, phase evolution