Investigation of Process Parameters of Phosphogypsum for Preparing Calcium Sulfoaluminate Cement

Abstract

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 (C4A3S¯) 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 °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 C4A3S¯ produced gradually increased. Temperatures above 1300 °C resulted in the decomposition of C4A3S¯. The calcination time did not significantly affect the mineral composition of the clinker or the strength of the cement. C4A3S¯ was observed to be rounded and hexagonal platelets with crystal sizes of 1 to 2 μm, a relatively small size that is favorable to the hydration of C4A3S¯, as observed by SEM images. In addition, the high calcination temperature affected the particle morphology of C4A3S¯, 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.