Roentgenographic drying control method of extractive semi-hydrate phosphogypsum (E-CaSO4•0,5H2O)

Abstract

In the Joint Stock Company „Lifosa“ during extraction of phosphoric acid from apatites with sulphuric acid synthetic semi-hydrate gypsum (E-CaSO4•0.5H2O) which moisture content achieves about 30% is received. This technogenic product is not used in industry of building material because it has low activity and is contaminated with acidous mineral admixtures. Recently modern method of E-CaSO4•0.5H2O processing into binding materials by its mechanical activation began to investigate. However the investigation requires phosphogypsum not cooled and taken from the conveyor until beginning of hydration. Received binding material modified with addiitives after mechanical activation and neutralisation of acidous admixtures, achieves compressive strength about ~40MPa. During transportation on longer distances (100-150 km) of raw material, it becomes cooler and begins to harden. The result of such process is formation of ductile pieces which prevent usage of mechanical activation. Partially hydrated gypsum has significantly lower strength. The most massive waste product (about 1 million tons annually) is disposed in dumps, so its utilization problem is very important from the point of view of industry and protection of the environment. One of objective of the research work was to investigate usage possibilities of this waste for various sorts of dry building mixtures. In the study described control of waste dehydration and drying process was carried out by roentgenographic examination of mineralogical composition of feeding phosphogypsum and of the product discharged from drying drum. Physical and mechanical properties of hardened samples were determined as well. The received date show that optimization of drying process allows to receive useful and strong enough binding material made of dehydrated and dried phosphogypsum after its mechanical activation in the disintegrator.