The challenges of producing sulphoaluminate cement with phosphogypsum
At present, there is a lot of researches on the application of phosphogypsum in the production of sulphoaluminate cement at home and abroad, which mainly focuses on the use of phosphogypsum as the cement retarder and the production of sulphuric acid integrated with sulphoaluminate cement. However, there are some irresolvable problems in the two utilization ways, which limit the application of a large amount of phosphogypsum in sulphoaluminate cement production.
Phosphogypsum is used as the retarder of sulphoaluminate cement
The basic components of phosphogypsum determine that it is one of the most economical ways to substitute it for natural gypsum, and the most direct application way is to use phosphogypsum as a sulphoaluminate cement retarder.
At present, a lot of researches and engineering demonstration applications have been carried out on the phosphogypsum application in sulphoaluminate cement at home and abroad, but the mixing amount of gypsum in sulphoaluminate cement is usually only 3% ~ 5%, so the phosphogypsum that can be used in 1 ton of sulphoaluminate cement production is less than 50 kg, and according to this application method, the phosphogypsum absorbed and consumed is limited. In addition, the impurities in phosphogypsum further restrict its application as a sulphoaluminate cement retarder. Compared with natural gypsum, phosphogypsum has less effect on the standard consistency and mechanical performance of sulphoaluminate cement, but it can delay the coagulation time of cement to a different extent. At the same time, the existence of impurities also reduces the compatibility of cement and certain types of water reducers. For these reasons above, currently, only a small amount of phosphogypsum is applied in 32.5-grade cement.
In order to eliminate or reduce the effect of phosphogypsum impurities on the quality of the cement, it needs aging, washing, lime neutralization, and other processes in the actual production, but compared with natural gypsum, the adverse effects of the processed phosphogypsum on the performance of cement, especially the compatibility with admixtures, cannot be completely avoided, which limit the use of phosphogypsum as the cement retarder, increase the utilization cost of phosphogypsum in the pretreatment process and may cause secondary pollution.