Preparation and properties of II-anhydrite calcined from phosphogypsum

Phosphogypsum (PG) has not been used effectively as cementitious material due mainly to the adverse effects of the soluble P2O5. This paper investigated the effect of calcination on the soluble P2O5 content of PG and properties, including size distribution, rheology, setting time, and strength development of Ⅱ-anhydrite calcined from PG. Grinding was used to activate the anhydrite further. The results showed that the soluble P2O5 content decreased as long as the calcination temperature was higher than 200 ºC and decreased from 0.581% to 0.007% after calcination of 800 ºC for 1 h. The 3-day and 28-day strengths of Ⅱ-anhydrite calcined at 800 ºC were 3.10 MPa and 14.24 MPa, respectively, and 17.60 MPa and 35.72 MPa after ball milling of 10 min, respectively. Calcination of 800 ºC made the surfaces and edges of PG particles melt and blur, reducing the water requirement of the Ⅱ-anhydrite and promoting its activity.