Role of phosphogypsum impurities on strength and microstructure of selenite plaster

摘要

The effect of phosphatic, fluoride and organic impurities as present in waste phosphogypsum were studied on the setting time, strength development and microstructure of the selenite gypsum plaster. The results showed that these impurities affect the physical properties of the plaster in a similar fashion as observed in the setting and hardening of the phosphogypsum plaster. The selenite plaster sets fast with a fall in strength. The selenite plaster which normally crystallizes into long interlocking needle shaped crystals has been found to be modified to prismatic, lath, and tabular shaped crystals of variable sizes interspersed with radiating crystals and anhedral to subhedral microcrystallites having irregular boundaries and poor stacking. It is concluded that formation of prismatic and lath-like crystal of different morphology affect the normal setting and strength characteristics of selenite gypsum plaster to a great extent. The effect is more pronounced when soluble phosphatic, fluoride and organic matter were added to the selenite plaster than the sparingly and less soluble compounds intermixed.