Produce sulphoaluminate cement with post adding phosphogypsum
In the production of sulphoaluminate cement, according to the different types of cement, some need dihydrate gypsum as post adding gypsum while some need anhydrite. Diao Jiangjing et al. explored the production of sulphoaluminate cement clinker by using phosphogypsum as the post adding gypsum, and the results showed that qualified sulphoaluminate cement clinker could be produced with phosphogypsum. However, the impurities in phosphogypsum are principal factors that affect its substitution for natural gypsum as post adding gypsum.
Due to the existence of impurities in phosphogypsum, there will be adverse effects on the hydration process of sulphoaluminate cement if phosphogypsum is directly used as post adding gypsum, which is similar to the problem of using phosphogypsum as a retarder component of ordinary Portland cement, in addition, the content of CaSO4·2H2O in phosphogypsum also affects the performance of phosphogypsum sulphoaluminate cement. The common practice is to pretreat phosphogypsum to obtain dihydrate gypsum with stable properties and satisfactory impurity content, and then use it as post adding gypsum to produce sulfoaluminate cement. Obviously, the effect of impurities in phosphogypsum from different sources will be different. Kuryatnyk et al. adopt two kinds of phosphogypsum and mix them respectively with sulphoaluminate cement clinker according to the proportion of 3:7, and the results showed that cement made from Gabes phosphogypsum has hydraulicity, while cement made from Skhira phosphogypsum has no strength due to excessive expansion resulted from the formation of ettringite in the initial matrix. Obviously, the properties of phosphogypsum need to be fully analyzed and tested if we want to use it as post adding gypsum.