US3660079A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Precious metals recovery method
Assignee: Midland Processing Inc
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Filing: 1971-01-28
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Granted: 1972-05-02
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Expires: 1991-01-28
Abstract
Abstract Photographic emulsion scrap is broken down into a liquid dispersion in a hot solution of an acid such as hydrochloric acid. A finely divided metal powder, such as zinc powder, is added to the liquid dispersion causing a chemical displacement of the silver and other precious metal combined in halide salts within the photographic emulsion scrap to cause the metals to precipitate for mechanical separation from the remaining liquid.
Inventors
- 👤 Hargovind L Govani
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 18:10
CPC Classifications
C; C22; C22B; C22B11/00; C22B11/04; C22B11/042; C22B11/046; C22B11/06; Y; Y02; Y02P; Y02P10/00; Y02P10/20
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
20 words
A method as claimed in claim 1 wherein said acid is hydrochloric acid and said metal powder is zinc powder.
Claim 2
Dependent Claim
22 words
A method as claimed in claim 2 wherein the precious metals contained within the photographic emulsion consist essentially of silver and palladium.
Claim 3
Dependent Claim
26 words
A method as claimed in claim 2 wherein the precious metals contained in the photographic emulsion scrap consist primarily of silver in combination in silver halides.
Claim 4
Dependent Claim
59 words
A method as claimed in claim 4 wherein additions of said zinc powder are made while maintaining the acidity of the liquid dispersion by additions of hydrochloric acid when needed until no silver halides remain within the dispersion to thereby obtain a substantially complete conversion of the silver halides to zinc halides and a maximum yield of metallic silver.
Claim 5
Dependent Claim
80 words
A method as claimed in claim 4 wherein an amount of zinc powder is added which is in excess of the amount needed to provide one zinc atom for every two silver atoms present to assure a complete displacement of all of the silver in the silver halides by zinc, and sufficient hydrochloric acid is employed to provide a final dispersion which is acidic to assure a substantially complete combination of all remaining zinc present into soluble zinc halide salts.
Claim 6
Dependent Claim
90 words
A method as claimed in claim 4 wherein said emulsion scrap includes film material coated with the emulsion and wherein the initial heating step is carried out to at least 170* F. while applying mechanical agitation to thereby strip the emulsion from the film as a combination step with the forming of a liquid dispersion of the emulsion in the acid, and wherein there is provided the additional step of straining the dispersion to remove the stripped film therefrom prior to the step of adding the finely divided metal powder.
Claim 7
Dependent Claim
16 words
A method as claimed in claim 7 wherein the emulsion-bearing film is chopped prior to processing.
Claim 8
Dependent Claim
13 words
A method as claimed in claim 7 wherein the film includes unexposed film.
Claim 9
Dependent Claim
13 words
A method as claimed in claim 7 wherein the film includes exposed film.
Claim 10
Dependent Claim
44 words
A method as claimed in claim 7 wherein a number of successive batches of film material coated with emulsion are added to the acid solution for stripping of the emulsion and then strained from the dispersion before the step of adding the metal powder.
Claim 11
Dependent Claim
53 words
A method as claimed in claim 7 wherein the stripped film removed from the liquid dispersion in rinsed at least once and the resultant rinse liquid is used as make-up water to maintain the volume of the solution, any excess being saved for use as part of the acid solution for subsequent batches.
Claim 12
Dependent Claim
37 words
A method as claimed in claim 12 wherein the stripped film material is rinsed a second time, and the liquid resulting from the second rinse is filtered to remove residual silver halides therefrom for subsequent silver recovery.
Claim 13
Dependent Claim
42 words
A method as claimed in claim 4 wherein the solid silver precipitate is washed and drained at least once after the initial separation of the liquid from the solid precipitate to thereby remove residual amounts of impurities remaining in the wet precipitate.
Claim 14
Dependent Claim
36 words
A method as claimed in claim 4 including the additional step of melting the solid silver precipitate while protecting the molten metal from atmospheric oxygen, and then casting the liquid metal in usable solid metal castings.
Claim 15
Dependent Claim
18 words
A method as claimed in claim 15 wherein the solid silver precipitate is dried before the melting step.
Claim 16
Dependent Claim
71 words
A method as claimed in claim 4 including the additional step of adding sodium hydroxide to the liquid which has been separated from the solid silver precipitate to thereby convert the zinc salts present in the liquid to sodium salts and to cause the formation of zinc hydroxide as a precipitate, and then separating the liquid from the zinc hydroxide precipitate and smelting the zinc hydroxide to recover the zinc therefrom.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-05-02 | 1975-11-01 | 1976-05-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-05-02 | 1979-11-01 | 1980-05-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-05-02 | 1983-11-01 | 1984-05-02 | $7700.00 | Window Closed / Lapsed |