Effect of soluble phosphate on strength development of anhydrite calcined from phosphogypsum

Abstract

The soluble phosphates in phosphogypsum (PG) are generally considered to hinder its utilization without pretreatments. This paper investigated the positive effect of soluble phosphates on the strength development of anhydrite calcined from PG at 800 ºC for 1 hour. PG, washed PG with different soluble phosphate contents, washed PG added with washed water, and flue gas desulfurization gypsum (FGD) were used to prepare anhydrite. The hydration degree and strength development of anhydrite were measured. The effect mechanism was explored by XRD, FTIR, and SEM. Results showed the 28-day strength decreased from 35.9 MPa to almost no strength when the soluble P₂O₅ content decreased from 0.7480% to 0.0471%. Soluble phosphates in PG would affect the microstructure of anhydrite particles, promoting the strength development, however, they did not affect the strength of anhydrite calcined from FGD. It is concluded that the soluble phosphates in PG are beneficial for manufacturing anhydrite, which is a promising utilization.