Claims
- 1. A method for removing impurities from wet-process produced phosphoric acid and recovering values retained by the impurities comprising the steps of:
- forming a filter cake comprising diatomite on a surface of a porous medium;
- maintaining wet-process produced phosphoric acid containing particulate impurities at a temperature of from about 57.degree. C. to about 77.degree. C;
- filtering such phosphoric acid through the formed filter cake for removing particulate impurities from such phosphoric acid whereby such removed particulate impurities and phosphate values are retained by the filter cake;
- simultaneously with filtering such phosphoric acid, continuously removing an impurity-containing upper portion of the filter cake to expose to the wet-process phosphoric acid a fresh surface of the filter cake;
- forming an aqueous slurry of said removed portion of said filter cake; and
- filtering said slurry to recover a filtrate containing a major portion of the phosphate values retained by the filter cake for reprocessing.
- 2. The method of claim 1 wherein said filter cake is formed over the outer surface of a porous cylinder and said cylinder is rotated during filtration so that a portion of said outer surface is intermittently contacted by said acid for the filtration thereof followed by contact with blade means for removing said impurity-containing outer portion of said filter cake.
- 3. The method of claim 2 wherein said cylinder is rotated at the rate of 1 revolution per minute.
- 4. The method of claim 2 wherein said blade means is advanced about 0.005 inches per revolution.
- 5. The method as defined in claim 1 wherein said acid is maintained at a temperature between about 70.degree. C. and about 71.degree. C.
- 6. The method of claim 1 wherein the wet-process phosphoric acid contains about 50% by weight P.sub.2 O.sub.5.
- 7. In the wet process for producing phosphoric acid by the acidulation of phosphorus-bearing rock with sulfuric acid thereby to precipitate calcium sulfate and to release crude phosphoric acid containing sludge forming impurities and thereafter concentrating said crude impurity-containing phosphoric acid to a phosphate content of about 50% F.sub.2 O.sub.5 by weight, the improvement comprising the steps of:
- heating said concentrated acid to a temperature of between 57.degree. C. and about 77.degree. C.;
- forming a filter element consisting of a diatomite filter cake coat overlying the surface of a porous support member;
- intermittently contacting at least a portion of said filter element with said acid while maintaining reduced pressure on a side of said filter element opposite said filter cake thereby filtering said acid to remove at least a portion of the sludge forming impurities from said acid, cake, said filter cake impurities being retained in an outer portion of said filter cake retaining phosphate values;
- collecting said acid after filtration;
- removing said impurity-containing portion of said filter cake after contact thereof by said acid, thereby to present fresh filter surface for subsequent acid contact;
- collecting said removed outer portion of said diatomite coat;
- forming a water slurry of said collected removed outer portion;
- filtering said slurry, thereby yielding a filtrate containing a major portion of the phosphate values retained by the filter cake; and
- returning the filtrate to a phosphoric acid plant for reprocessing.
- 8. The process as defined in claim 7 wherein said acid is heated to a temperature between about 70.degree. C. and about 71.degree. C.
- 9. The process as defined in claim 7 wherein said diatomite coat is formed over the outer surface of a porous cylinder and said cylinder is rotated so that a portion of said coated outer surface is contacted by said acid for the filtration thereof followed by contact with blade means for removing said impurity-containing outer portion of said diatomite coat.
- 10. The process as defined in claim 7 wherein said cylinder is rotated at the rate of one revolution per minute.
- 11. The process as defined in claim 7 wherein said blade means is advanced about 0.005 inches per revolution.
- 12. A method for removing impurities from wet-process produced phosphoric acid and recovering values retained by the impurities comprising the steps of:
- maintaining wet-process produced phosphoric acid containing particulate impurities at a temperature of from about 57.degree. C. to about 77.degree. C.;
- filtering such phosphoric acid for removing particulate impurities from such phosphoric acid, said removed particulate impurities retaining phosphate values;
- forming an aqueous slurry of removed particulate impurities; and
- filtering said slurry to recover a filtrate containing a major portion of the phosphate values retained by the particulate impurities for reprocessing.
- 13. The method as defined in claim 12 wherein said acid is maintained at temperature between about 70.degree. C. and about 71.degree. C.
Parent Case Info
This application is a continuation of application Ser. No. 744,229, filed Nov. 23, 1976, now abandoned, which is a continuation of application Ser. No. 571,855, filed Apr. 25, 1975, now abandoned.
US Referenced Citations (11)
Foreign Referenced Citations (1)
Number |
Date |
Country |
915389 |
Nov 1972 |
CAX |
Non-Patent Literature Citations (3)
Entry |
Perry's Chem. Engr. Handbock-Perry-1960, pp. 19-60, 19-78, 19-79. |
Filtration-Filter Aids-Wheeler-Jan./Feb. 1964, pp. 41-43. |
Phosphoric Acid-PtII.varies.Slack-p. 691. |
Continuations (2)
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Number |
Date |
Country |
Parent |
744229 |
Nov 1976 |
|
Parent |
571855 |
Apr 1975 |
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