Utilization of Industrial Waste Phosphogypsum as Geomaterial: A Review

Phosphogypsum (PG) is a waste product of phosphate fertilizer and phosphoric acid industries. Vast quantities of the waste product are generally left stockpiled on the ground or discharged into rivers or ponds, and pose serious environmental concerns. Several countries are facing problems with the handling, storage, and utilization of PG. This article is a comprehensive review of the physicochemical, microstructural, geotechnical, radiation, and leaching characteristics of raw PG. The performance of PG with other admixtures (cement, fly ash, lime, ground granulated blast furnace slag) and soils (clays, loess, sands) has also been reviewed. In addition, the factors, such as pH, calcination, forms of PG, and curing methods, that affect the geotechnical, durability, and leaching characteristics of PG mixtures are also discussed. Based on the review, it has been observed that raw PG has high sulfate content, high water absorption capacity, and high variability in strength, leaching, and radioactivity properties; thus, using raw PG alone as a backfill or embankment material is not suitable. However, the geotechnical, durability, and leaching properties of PG may be enhanced by using it in combination with other admixtures. The excessive usage of PG should also be undertaken with caution, as the higher amount of PG may lead to a decrease in the strength and the formation of cracks. There are studies that have reported the optimum content of PG; however, the range is quite varied and can differ for soil types. Therefore, it is recommended to investigate the optimum content of PG before the start of any road or ground improvement project. The compaction characteristics of PG-admixed soils are highly contrasting and hence need more comprehensive studies. The strength characteristics and resilient modulus are also highly variable and hence need more exhaustive research for actual usage of PG in road construction. Other critical issues that require attention have been highlighted, and associated research gaps that could be explored in future research works have been identified.