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US4139431A
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Process and apparatus for the removal of silver from fixer solutions
Assignee: Ilford Imaging Switzerland GmbH
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Filing: 1978-02-22
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Granted: 1979-02-13
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Expires: 1998-02-22
Abstract
Abstract An electrolytic process is used to reduce the silver content of fixer solution to a level such that it can be discharged as effluent. In the process silver is removed from aqueous fixer solutions by circulating the solution in a closed cycle through an electrolytic cell such that the residence time in the cell is not greater than one minute for each passage. The electrode loading is within the range between 5 and 15 mA/cm 2 initially but is reduced in at least one further chronologically consecutive stage. Exhausted developer solution may be added to the fixer solution to act as a pH controlling redox system.
Inventors
- 👤 Rudolf Scheidegger
- 👤 August Zurrer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 21:45
CPC Classifications
C; C25; C25C; C25C1/00; C25C1/20; G; G03; G03C; G03C5/00; G03C5/26; G03C5/395; G03C5/3954
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
54 words
An electrolytic process for removing silver from photographic fixer solution wherein the solution is circulated in a closed cycle including a reservoir and an electrolytic cell, the residence time of the fixer solution in said cell being not greater than 1 minute, the electrode loading (mA/cm 2 ) being reduced in chronologically consecutive stages.
Claim 2
Dependent Claim
54 words
An electrolytic process for removing silver from photographic fixer solution wherein the solution is circulated in a closed cycle including a reservoir and an electrolytic cell, the residence time of the fixer solution in said cell being not greater than 1 minute, the electrode loading (mA/cm 2 ) being reduced in chronologically consecutive stages.
Claim 3
Dependent Claim
16 words
The process according to claim 1, wherein said residence time is not greater than 30 seconds.
Claim 4
Dependent Claim
19 words
The process according to claim 1, wherein said residence time is in the range from 5 to 20 seconds.
Claim 5
Dependent Claim
47 words
The process according to claim 1, wherein the electrode loading is carried out in two stages, the current density in the first stage being between 5 and 15 mA/cm 2 , and in the second stage between 2 and 50% of the value in the first stage.
Claim 6
Dependent Claim
19 words
The process according to claim 1, wherein a pH-controlling redox system is added to the solution to be treated.
Claim 7
Dependent Claim
16 words
The process according to claim 5, wherein the pH controlling redox system is exhausted developer solution.
Claim 8
Dependent Claim
26 words
The process according to claim 6, wherein 0.1 to 0.5 parts of exhaust developer solution are added to 1 part of the solution to be treated.
References Cited (Backward Citations)
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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) | 1982-02-12 | 1982-08-14 | 1983-02-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1986-02-12 | 1986-08-14 | 1987-02-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1990-02-12 | 1990-08-14 | 1991-02-13 | $7700.00 | Window Closed / Lapsed |