Phosphogypsum

The industry of the phosphate-enriched fertilizers (superphosphate triples primarily) and of Acid phosphoric produces enormous tonnages of gypsum (1,7 T produced per ton of phosphate).

The phosphogypsum is resulting from the manufacture of the phosphoric acid following the reaction: Ca10 (PO4) 6F2 + 10:2 SO4 + 20:2 O - - - > 6:3 PO4 + 10 CaSO4,2H2O + 2 HF.

This phosphogypsum , very slightly with significantly radioactive because of the uranium traces present in the phosphatic ore. It is still often poured in Mer, which is source of Pollution and Eutrophisation.

Phosphogypsum contaminated by other metals or dyes can be recovered after treatment fading of waste water of textile industries.

Environment and Health

Manure " normal superphosphate " is replaced little by little by triple superphosphate. It contains also the gypsum resulting from the monocalcic manufacture of phosphate of manure.

In term of tonnage, the phosphogypsum resulting from the production of superphosphate is the first source of waste very slightly radioactive. In France, the second after the nuclear power. One produces approximately 60 t/an million of them in the world, that is to say more than 50% of the production of natural gypsum|Data French company of Chemistry]

In France, country among most consuming manure, 6 million T of phosphogypsum was produced annually in the Eighties, including 900.000 T by each unit of Grand-Quevilly, Grand Crowns and of Le Havre, that is to say as much as all the production of natural gypsum. The management of the phosphogypsum dumps is added in France to that of the 200.000 ton of waste TFA awaited resulting from the beginning of dismantling of the nuclear plants (evaluation made in the year 2000).

For only the producing Tunisia large of phosphates, 10 million tons of phosphogypsum would annually be produced (source: CNRS

The phosphogypsum as a toxic waste should not be any more thrown at sea. It starts to be recycled or is more often stored in the form of Terril, Crassier (also named “stackings” in Canada. Radon (carcinogenic radioactive gas and potentially person in charge of changes) can degas phosphogypsum or plasterboards manufactured with phosphogypsum.

Many studies aimed at substituting it for the natural Gypse, in particular to produce squares of Plâtre or to add some in cement. The drying of this plaster of synthesis proved not very profitable, but the manufacture of the " variety; alpha" Hémihydrate of the Sulfate of calcium, by Autoclavage in the presence of additives Minéraux gives crystals of more important size, allowing a less expensive drying.

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