The Use of Phosphogypsum as a Source of Raw Materials for Gypsum-Based Materials

Gypsum binders and the products based on them are widely in demand in the construction materials market, which is due to their easy production technology, lower energy consumption, and low environmental impact in relation to Portland cement. Not only natural gypsum (NG), but also phosphogypsum (PG), which is a by-product of the synthesis of orthophosphoric acid from phosphorite rock, can be used as a source of raw materials for the production of gypsum materials. PG is produced annually in large quantities throughout the world. In chemical composition, PG mainly consists of calcium sulfate dihydrate CaSO4·2H2O, so it is a good potential analogue of natural gypsum, which is used as the main component of gypsum building materials. Thus, the useful recycling of PG as a technogenic resource with valuable properties will expand the raw material base for the production of gypsum materials. This approach to handling technogenic resources fits well with the principles of a circular economy. However, like any technogenic resource, PGs from different enterprises normally differ in their deposits of the original phosphate rock and production technologies. Therefore, PG contains a large number of undesirable impurities, the proportion and composition of which vary over a wide range. This feature does not allow for predicting the properties of PG-based materials without a preliminary detailed study of PG. This research was aimed at carrying out a comprehensive study of the characteristics of PGs from three different industrial plants to evaluate their relationship with the properties of gypsum materials based on them. It was found that PGs have significant differences in their structural and morphological characteristics both in relation to each other and in relation to NG. Also, binders based on PG and NG have significant differences in their physical properties. The average density, compressive strength, and flexural strength for the PG binders with equal workability are lower than those of NG binders. At a water/solid ratio (W/S) < 0.7, all PG binders exhibit comparable compressive strength to NG binders. Thus, PG can act as an alternative to natural gypsum in gypsum binders.