Characterístics of phosphogypsum for utilisation in roadwork fills

Phosphorus oxide for use as fertilizer is produced by using sulphuric acid to attack natural phosphates and this generates a byproduct essentially composed of hydrated calcium sulphate and known as phosphogypsum. The solubility of calcium sulphate, even in the natural rocks and soils containing gypsum, limits the utilisation of this material in slopes for linear works to a maximum calcium sulphate content of 20%. Other elements also appear in phosphogypsum that, in the event of solubilising, could contaminate the water in the surrounding area. In spite of all this, experience does exist with the use of phosphogypsum in experimental slopes designed to ascertain the possibility of storing this product in more areas capable of guaranteeing that the surroundings are not contaminated. This article reports on the characteristics of the Huelva phosphogypsum in terms of both composition and mechanical properties and the measures to be taken for its possible utilisation in roadwork fills.