Radioactivity and Elemental Composition of Phosphogypsum Produced From Three Phosphate Rock Sources

Abstract

Phosphogypsum, a by-product of phosphate fertilizer production, is produced in large quantities worldwide. Most phosphogypsum is stockpiled while lesser quantities are recycled or dumped into water. Phosphogypsum is primarily CaSO4·2H2O, but also contains impurities of environmental concern such as residual acids, fluoride, heavy metals and naturally-occurring radionuclides. Impurity composition within phosphogypsum can vary greatly depending on the source of phosphate rock used in phosphoric acid production. This study was undertaken to obtain detailed information on the composition of phosphogypsum produced from the processing of rock from Florida, Togo and Idaho, to define more clearly the chemical issues of importance to management and use of the by-product. All freshly produced phosphogypsum had sufficiently high fluoride levels that leaching and decomposition of silicate minerals beneath repositories might occur. Phosphogypsum from Idaho rock had elevated Ag, Cd and Se concentrations, and the greatest Ra-226 activity concentrations (up to 1780 Bq kg— 1). Radon-222 emanation coefficients ranged between 12-51%.