Recovery of P.sub.2 O.sub.5 values from phosphoric acid hemihydrate crystals
AssigneeOccidental Chemical Corporation
InventorsFernando Ore, Thomas E. Richards
Life of this patent
Estimating the term…
Abstract
P.sub.2 O.sub.5 values occluded in the crystals which are precipitated during the hemihydrate process for manufacturing phosphoric acid are recovered by dissolving and recrystallizing the hemihydrate crystals as dihydrate crystals in an acidic environment having a P.sub.2 O.sub.5 concentration of from about 0.1% to about 10% and a free sulfate concentration in the range of about 0.1% to about 10%. Water is used to wash the dihydrate filter cake, and the filtrate from this wash is used to redissolve the hemihydrate crystals. The free sulfate values are preferably supplied to the dihydrate crystallizer as sulfuric acid.
Claims20
In a process for recovering P.sub.2 O.sub.5 values from a first aqueous slurry of calcium sulfate hemihydrate crystals where
- (1) said first slurry is filtered in a hemihydrate filter to form a product filtrate containing said P.sub.2 O.sub.5 values and a calcium sulfate hemihydrate filter cake;
- (2) said hemihydrate filter cake is transported to a hemihydrate filter cake dissolver where said hemihydrate filter cake is dissolved;
- (3) said dissolved hemihydrate filter cake is transported to a separate dihydrate crystallizer where a second aqueous slurry, of calcium sulfate dihydrate crystals, is formed;
- and
- (4) said second slurry is transported to a dihydrate filter, separate from said hemihydrate filter, where said second slurry is filtered to form a dihydrate filter cake and a first filtrate, the improvement which comprises
- (a) maintaining the free sulfate ion concentration in said dihydrate crystallizer between about 0.1 and about 10%;
- and
- (b) maintaining the phosphoric acid concentration in said dihydrate crystallizer between about 0.1 and about 10% on a P.sub.2 O.sub.5 basis.
A process for recovering P.sub.2 O.sub.5 values from calcium sulfate hemihydrate crystals generated during the hemihydrate process for manufacturing phosphoric acid comprising:
- (1) washing said hemihydrate crystals on a hemihydrate filter with a portion of a first filtrate from a dihydrate filter, forming a hemihydrate filter cake and a product filtrate;
- (2) dissolving said hemihydrate filter cake with a second filtrate from said dihydrate filter;
- (3) recrystallizing said dissolved hemihydrate filter cake in a separate dihydrate crystallizer as calcium sulfate dihydrate crystals, at a free sulfate ion concentration of 0.1 to 10%, and a phosphoric acid concentration of 0.1 to 10% on a P.sub.2 O.sub.5 basis;
- (4) filtering said dihydrate crystals on said dihydrate filter, separate from said hemihydrate filter, to form a dihydrate filter cake and said first filtrate;
- and
- (5) washing said dihydrate filter cake countercurrently on said second filter with water to form said second filtrate.
Dependencies are inferred from the claim text.