Effect of phosphatic and fluoride impurities of phosphogypsum on the properties of selenite plaster

The effect of phosphatic and fluoride impurities present in waste phosphogypsum on the setting time, strength development and morphology of selenite gypsum plaster have been studied. The results showed that soluble phosphates retard the setting and strength development of plaster while soluble fluorides decrease the setting time and reduce the density and strength. The gypsum crystals in the set plaster are modified from to euhedral to subhedral prismatic, rhombic, tabular and lath-shaped crystals of variable sizes interspersed with subhedral to anhedral needles. It is concluded that the formation of prismatic, rhombic and lathelike crystals retards the normal setting and strength development of selenite gypsum plaster. (C) 2003 Elsevier Science Ltd. All rights reserved.