Physical and chemical properties and hydration characteristics of building phosphogypsum.

Thermal analyzer, SEM, XRD and BET were used to characterize the physical and chemical properties of building phosphogypsum and its hydration process. The results indicate that the particles of building phosphogypsum are distributed in multiple gradations and are laminate structure containing many pores and slits which can be responsible for its high water requirement. The insoluble impurities in building phosphogypsum are mainly quartz, anhydrite, calcium hydrogen phosphate and iron sulfide. Moreover, calcium hydrogen phosphate is uniformly distributed among hemihydrate gypsum particles presenting as solid solution, which is gradually released during hydration, resulting in the decrease of pH in solution. Building phosphogypsum prepared by phosphogypsum without the pretreatment of water wash sets fast and the final gypsum crystal are coarse leading to loose microstructure with lower strength. [ABSTRACT FROM AUTHOR]