Preparation of belite-sulphoaluminate cement using phosphate rock acid-insoluble residue

In the phosphorous-sulfur two-step process involved in the clean production of phosphoric acid, the acidolysis of phosphate rock yields a solid filter phosphate rock acid-insoluble residue (PAIR). Herein, belite-sulfoaluminate cement is prepared using the PAIR as the main silica source to promote the residue resource utilization. The PAIR has practical feasibility for belite-sulfoaluminate cement preparation. Preparation conditions comprising the basicity coefficient of the raw meal of 1.187, clinker calcination temperature of 1200 degrees C, and the holding time for clinker calcination of 1.0 h are employed. Under these conditions, calcium sulfoaluminate and dicalcium silicate, the main mineral phases of the clinker, are fully formed, exhibiting contents close to the theoretical design value. The high amounts of fluorine and phosphorus in the PAIR reduce the clinker sintering temperature by 50 degrees C-150 degrees C and activate the clinker mineral phase. The maximum alpha' dicalcium silicate content in the clinker is 20.233%. The hydration and mechanical properties of the prepared belite-sulfoaluminate cement are better than those of commercial 42.5 grade cement. Moreover, its 28-day compressive strength can reach 64 MPa.