Phosphogypsum

Phosphogypsum is a waste by-product of the wet-process manufacture of phosphoric acid from phosphate rock. It consists mainly of calcium sulfate dihydrate (CaSO4·2H2O), often with residual phosphates and a variety of impurities.

Because the phosphate rock contains naturally occurring radionuclides, phosphogypsum can contain measurable levels of radium-226 and other radionuclides. The material may also include fluorides, trace metals, and organic contaminants. Its radioactivity is the central concern in many regulatory decisions about handling and use.

Phosphogypsum is produced wherever wet-process phosphoric acid is made, resulting in large volumes that are typically stored in piles or stacks on land. The management of these stacks is a major environmental issue in some regions, with concerns about leaching, dust, and gas release.

Uses are restricted in many jurisdictions because of radiological concerns. In many places, phosphogypsum cannot be used in agricultural products or consumer building materials; disposal is often as waste in stacks, though some limited, carefully controlled applications exist, such as in cementitious materials after treatment or as fill, depending on local regulations.

Research continues into safer disposal methods and potential value-added uses, including radiation shielding materials and extraction of minor elements, but regulatory frameworks remain the dominant factor governing its handling.