Effect of pretreatment on harmful impurities of phosphogypsum and on properties of II-anhydrite

Abstract

In view of the problems caused by impurities to the comprehensive utilization of phosphogypsum, this study employed a combination of calcination and lime neutralization processes to harmless treatment of impurities in phosphogypsum. The phosphogypsum was pretreated by wet neutralization and dry neutralization respectively, followed by calcination at medium temperature to obtain II-anhydrite. XRD, XRF, SEM, FTIR, and other techniques were applied for analysis of the impact of these two pretreatments on impurity removal as well as their effects on the properties of calcined II-anhydrite. Then, the calcination process was optimized to reduce calcination energy consumption. The results show that the reaction between phosphorus and lime is superior to fluorine in the process of neutralizing. When the lime content reaches 1.4%, wet pretreatment can effectively remove soluble phosphorus and fluorine, promote the release and reaction of eutectic phosphorus during calcination, and then significantly improve the performance of II-anhydrite. However, dry pretreatment has no such effect. By combining lime neutralization and calcination at 500℃, the harmful impurities in phosphogypsum are removed. Compared with no pretreatment and dry treatment, wet pretreatment shortened the setting time of II-anhydrite by 45% and 29% and increased the three-day compressive strength by 252% and 161%, respectively.