Method for the treatment of phosphogypsum
AssigneeCentre d'Etudes et de Recherches des Phosphates Mineraux Cerphos
InventorRobert Krempff
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Abstract
The purification of the raw phosphogypsum issued from the fabrication of phosphoric acid by reaction between phosphate rock and sulphuric acid consists of removing the extreme grain size fractions therefrom. This method has been developed after it has been found that a large part of the undesirable impurities are concentrated in the extreme grain fractions which constitute only a small percentage of the phosphogypsum. The impurities thus removed are P.sub.2 O.sub.5, F, SiO.sub.2, C, F.sub.2 O.sub.3 and Al.sub.2 O.sub.3. Purification efficiencies can be obtained of the order of 70 % for the total P.sub.2 O.sub.5 and fluorine, 60 % for silica, and 80 % for organic carbon, while water-soluble P.sub.2 O.sub.5 is substantially completely removed.
Claims9
A method for the treatment of phosphogypsum, which consists essentially of subjecting a pulp, obtained from mixing phosphogypsum and water, to a wet screening step by passing the pulp through a sieve to remove the coarse grain fractions, subjecting the pulp passing through the sieve to a flotation process to remove the fine grain fractions thereof, the granulometric limits of the treated phosphogypsum being so selected that the proportions of water-soluble P.sub.2 O.sub.5, fluorine and carbon compounds which exist as impurities in the phosphogypsum do not exceed 0.01, 0.9 and 0.1% respectively, the percentage of the carbon containing compounds being calculated on the basis of the carbon content, filtering the thus-purified phosphogypsum to obtain the solid purified phosphogypsum residue;
- washing the residue with water;
- drying the residue and baking the thus-obtained phosphogypsum residue to convert it into plaster;
- said phosphogypsum being treated by adding thereto, prior to the baking step, calcium carbonate to adjust the acidity thereof.
Dependencies are inferred from the claim text.