Phoshogypsum is a waste generated during the processing of phosphate ore, such as apatite (mostly fluorapatite), to produce phosphoric acid. In the wet process of phosphoric acid production, the ore is treated with sulphuric acid and it forms phosphoric acid, gypsum and hydrofluoric acid. The gypsum, called phosphogypsum, can have highly variable characteristics that are very much dependent on the processed ore feed. It can contain different residues of calcium phosphates and -hydrogen phosphates, fluorides and trace metals such as REE, naturally occurring radionuclides and organic matter. Due to the environmentally harmful properties the material is mostly dumped on large stockpiles and only little amounts are reutilized for other processes (Tayibi et al. 2009).
Tayibi, H., M. Choura, F. A. Lopez, F. J. Alguacil, and A. López-Delgado, 2009: Environmental impact and management of phosphogypsum. Journal of Environmental Management, 90, 2377-2386.