Patent US4857211A successfully refreshed from Google Patents.
US4857211A
Expired / Lapsed
US
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Cleaning of filter surfaces
Assignee: Rhodia Chimie SAS
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Filing: 1987-05-07
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Granted: 1989-08-15
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Expires: 2007-05-07
Abstract
Abstract Encrusted filter surfaces that have been used for filtering wet process phosphoric acid slurries are effectively cleaned, e.g., of crystalline deposits, by washing same with a solution of fluosilic acid.
Inventors
- 👤 Guy Nineuil
- 👤 Louis Rivoirard
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 17:25
CPC Classifications
C; C01; C01B; C01B25/00; C01B25/16; C01B25/18; C01B25/22; C01B25/222; C01B25/223; C01B25/225; C01B25/2208
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
69 words
A process for the cleaning of a filter surface that has been used for the filtration of a wet process phosphoric acid slurry, comprising washing said filter surface with a solution consisting essentially of fluosilicic acid, wherein said filter surface has been preliminarily mechanically stripped of the solid filter cake formed thereon the preliminarily stripped filter surface bearing encrusted deposits of crystalline solids which are removed by said solution.
Claim 2
Dependent Claim
69 words
A process for the cleaning of a filter surface that has been used for the filtration of a wet process phosphoric acid slurry, comprising washing said filter surface with a solution consisting essentially of fluosilicic acid, wherein said filter surface has been preliminarily mechanically stripped of the solid filter cake formed thereon the preliminarily stripped filter surface bearing encrusted deposits of crystalline solids which are removed by said solution.
Claim 3
Dependent Claim
22 words
The process as defined by claim 1, the washing comprising spraying the solution of fluosilicic acid onto said filter surface under pressure.
Claim 4
Dependent Claim
22 words
The process as defined by claim 1, said solution of fluosilicic acid having a concentration of from 0.5 to 5% by weight.
Claim 5
Dependent Claim
22 words
The process as defined by claim 1, said solution of fluosilicic acid having a concentration of from 1 to 2% by weight.
Claim 6
Dependent Claim
22 words
The process as defined by claim 1, said solution of fluosilicic acid having a concentration of from 1 to 1.5% by weight.
Claim 7
Dependent Claim
21 words
The process as defined by claim 3, the temperature of said solution of fluosilicic acid ranging from 70° to 90° C.
Claim 8
Dependent Claim
19 words
The process as defined by claim 3, the temperature of said solution of fluosilicic acid being about 80° C.
Claim 9
Dependent Claim
13 words
The process as defined by claim 1, said phosphoric acid slurry comprising gypsum.
Claim 10
Dependent Claim
13 words
The process as defined by claim 1, said phosphoric acid slurry comprising plaster.
Claim 11
Dependent Claim
18 words
The process as defined by claim 1, said phosphoric acid slurry produced by sulfuric acidulation of phosphate rock.
Claim 12
Dependent Claim
30 words
The process as defined by claim 1, comprising preheating said solution of fluosilicic acid by contacting same with gases evolved during the wet process production of said phosphoric acid slurry.
Claim 13
Dependent Claim
27 words
The process as defined by claim 1, said solution of fluosilicic acid having been produced by absorbing, in water, gases evolved upon concentration of filtered phosphoric acid.
Claim 14
Dependent Claim
14 words
The process as defined by claim 1, said filter surface comprising a metal screen.
Claim 15
Dependent Claim
16 words
The process as defined by claim 15, said metal screen having a filter cloth disposed thereon.
Claim 16
Dependent Claim
14 words
The process as defined by claim 1, said phosphoric acid slurry comprising calcium sulfate.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-08-14 | 1993-02-13 | 1993-08-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-08-14 | 1997-02-13 | 1997-08-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-08-14 | 2001-02-13 | 2001-08-15 | $7700.00 | Window Closed / Lapsed |