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US3607016A Expired / Lapsed US ⏱️ 0.0 years remaining

Process for recovering sodium fluosilicate in the production of phosphoric acid

Assignee: Societa Italiana Resine SpA SIR
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Filing: 1968-11-25
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Granted: 1971-09-21
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Expires: 1988-11-25
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Abstract

Abstract A process for preparing sodium fluosilicate comprising treating mineral phosphates with an excess amount of aqueous sulfuric acid, removing excess sulfate from the resulting solution by precipitating the excess sulfate in the form of calcium sulfate by adding to the solution a stoichiometric quantity to said sulfate of phosphorites at a temperature of from 50* to 80* C., and then curing the precipitate at a temperature of from 20* to 40* C. for a period of time of from 1 to 5 hours, and then precipitating fluorine and silica from the solution in the form of sodium fluosilicate, after separating calcium sulfate therefrom, by adding monosodium phosphate, bisodium phosphate or a mixture thereof to the solution in a quantity such that the atomic ratio of the sodium contained in the mono- or bisodium phosphate to the fluorine contained in the solution is within the range of from 1:1 to 2.5:1, the precipitation being carried out at a temperature of from 40* to 100* C.

Inventors

  • 👤 Filippo Barilli
  • 👤 Giorgio Cozza
  • 👤 Giancarlo Aglietti
  • 👤 Ferdinando Ligorati

Bibliographic Details

Application Number —
Jurisdiction US
Data Source google_patents
Last Synchronized 2026-11-06 05:16
CPC Classifications
C; C01; C01B; C01B33/00; C01B33/08; C01B33/10; C01B33/103

Claims Analysis

Total Claims: 12
Claim 1
Independent Claim 58 words
The method of claim 1 where the precipitated calcium sulfate which is removed from the solution is recycled to the solution prior to the calcium sulfate precipitation step in an amount of from 2 to 8 percent by weight of the solution, said calcium sulfate precipitation being carried out at a temperature of from 60* to 70* C.
Claim 2
Dependent Claim 28 words
The method of claim 2 wherein the calcium sulfate is recycled to the solution in a quantity of from 3 to 5 percent by weight of the solution.
Claim 3
Dependent Claim 44 words
The method of claim 1 wherein the solution to which the mono-or bisodium phosphates are added contains from 200 to 450 g./l. of phosphate as P2O5, up to 35 g./l. of fluoride as F , and up to 18 g./1. of silicate as SiO2.
Claim 4
Dependent Claim 20 words
The method of claim 1 wherein the temperature of precipitation of said sodium fluosilicate varies from 60* to 80* C.
Claim 5
Dependent Claim 21 words
The method of claim 1 wherein said mono- or bisodium phosphates are added in the form of an aqueous solution thereof.
Claim 6
Dependent Claim 51 words
The method of claim 1 wherein said sodium fluosilicate is precipitated in the form of crystals and wherein said crystals are separated from the solution by filtering at a temperature of from 40* to 100* C., subsequently washed with water at a temperature of from 20* to 40* C. and dried.
Claim 7
Dependent Claim 19 words
The method of claim 7 wherein said crystals are filtered at a temperature of from 60* to 80* C.
Claim 8
Dependent Claim 39 words
The method of claim 1 wherein the phosphate solution which results after the precipitation of said sodium fluosilicate is recycled to the solution which results from the calcium sulfate precipitation as the phosphate used to precipitate said sodium fluosilicate.
Claim 9
Dependent Claim 51 words
The method of claim 1 wherein said sodium fluosilicate is precipitated in at least 98 percent purity and wherein the phosphate solution which results after the precipitation of said sodium fluosilicate contains not more than 1 g./l. of fluoride as F and not more than 0.5 g./l. of silicate as SiO2.
Claim 10
Dependent Claim 38 words
The method of claim 1 wherein said phosphorite has a composition comprising from about 51.1 to about 51.6 percent CaO, from about 32.1 to about 33.4 percent P2O5, and from about 2.255 to about 2.45 percent F .
Claim 11
Dependent Claim 31 words
The method of claim 1 wherein the stoichiometric quantity of phosphorites corresponds to the excess amount of sulfuric acid present after treatment of said mineral phosphates with the aqueous sulfuric acid.
Claim 12
Dependent Claim 11 words
The method of claim 1 wherein said phosphorites are finely divided.

References Cited (Backward Citations)

US2271712A Cited
US3493336A Cited
US3506394A Cited
US3462242A Cited

USPTO Annuity & Maintenance Windows

Annuity Stage Window Opens Payment Deadline Surcharge Period Until Estimated Fee Status
3.5 Years (Year 4) 1974-09-20 1975-03-22 1975-09-21 $2000.00 Window Closed / Lapsed
7.5 Years (Year 8) 1978-09-20 1979-03-22 1979-09-21 $3760.00 Window Closed / Lapsed
11.5 Years (Year 12) 1982-09-20 1983-03-22 1983-09-21 $7700.00 Window Closed / Lapsed

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