Investigation of Process Parameters of Phosphogypsum for Preparing Calcium Sulfoaluminate Cement

Preparing calcium sulfoaluminate cement (CAS) from solid waste phosphogypsum (PG) instead of natural gypsum is an effective way to utilize solid waste. In this paper, CAS clinker was successfully prepared from PG and the mineral content of calcium sulfoaluminate (C(4)A(3)(S) over bar) in the sample was above 65%. The effects of raw material ratio, calcination temperature, and time on clinker composition were investigated. The mechanical properties of different samples were tested. The optimum ratio for preparing CAS using PG was 42.23% limestone, 17.43% PG, and 40.34% bauxite. The optimal calcination conditions are a high temperature of 1250 degrees C for 45 min. The 3-day compressive strengths of the laboratory-prepared CAS were all above 50 MPa. It was found that as the calcination temperature increased, the amount of C(4)A(3)(S) over bar produced gradually increased. Temperatures above 1300 degrees C resulted in the decomposition of C(4)A(3)(S) over bar. The calcination time did not significantly affect the mineral composition of the clinker or the strength of the cement. C(4)A(3)(S) over bar was observed to be rounded and hexagonal platelets with crystal sizes of 1 to 2 mu m, a relatively small size that is favorable to the hydration of C(4)A(3)(S) over bar, as observed by SEM images. In addition, the high calcination temperature affected the particle morphology of C(4)A(3)(S) over bar, changing it from a well-defined polygonal structure to a molten state. The test results provide helpful information for improving PG utilization and applying PG in CAS production.