Process for preventing the formation of calcium sulphate scale
AssigneeFisons Limited
InventorsDouglas C. Harper, Norman Robinson, Stanislaw M. Janikowski
Life of this patent
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Abstract
The anti-scaling effect of additives added to control the formation of scale during the washing of calcium sulphate anhydrite or hemihydrate crystals is increased when the additives are added as soon as possible after the wash liquors leave the crystals. The invention is of especial use in the washing of calcium sulphate hemihydrate produced during the production of phosphoric acid and is carried out by adding the additives via the central valve of the rotating pan filter on which the hemihydrate crystals are washed.
Claims10
In a process for producing a phosphoric acid by the wet process in which a slurry of calcium sulphate hemihydrate crystals in phosphoric acid is produced, which slurry is filtered on a filter and then washed with a liquor in a number of stages, said liquor being circulated from one wash stage to the preceding wash stage, the improvement which comprises incorporating 0.0005 to 0.2% by weight of an anti-scaling additive based on the weight of the liquor into the liquor between the point at which it is separated from the crystals and the point at which it is collected for circulating back to the crystals, the additive being selected from the group consisting of a C.sub.8 to C.sub.16 alkylbenzene sulphonic acid and on alkali-metal or ammonium salt thereof;
- a mono- or di- C.sub.8 to C.sub.18 alkyl sulphate ester and an alkali - metal or ammonium salt thereof, a condensate of ethylene or propylene oxide with octyl or nonyl phenol or with a C.sub.8 to C.sub.14 alcohol, a sulphate ester of such a condensate and an alkali-metal or ammonium salt of such a sulphate ester;
- a polyacrylamide flocculating agent;
- and mixtures thereof and wherein the wash liquor is such that it contains less than 30% by weight of P.sub.2 O.sub.5 therein.
Dependencies are inferred from the claim text.