US3715291A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of recovering silver from waste silver solutions
Assignee: Photographic Silver Recovery Ltd
•
Filing: 1970-09-09
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Granted: 1973-02-06
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Expires: 1990-09-09
Abstract
Abstract The recover of silver from waste silver solutions, especially spent photographic processing liquids, is effected with a silver recovery machine, such as a rotating cathode machine, and an auxiliary tank installed immediately upstream of the silver recovery machine to receive the silver waste solution from film processing equipment or other source. A metering pump delivers the waste solution from the auxiliary tank to the silver recovery machine, the pump being started and stopped in dependence upon changes in the level of the waste solution in the auxiliary tank. The silver recovery machine is arranged to operate only while the metering pump is running, this operation being at a constant current setting.
Inventors
- 👤 J Bentley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 09:40
CPC Classifications
C; C25; C25C; C25C1/00; C25C1/20
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
229 words
A method for recovering silver from waste silver solutions, especially spent photographic processing liquids, said method utilizing: an electrically operated silver recovery machine of the type which includes an electrical supply for passing electric current between two electrodes and through waste silver solution in said machines; a feed line via which waste silver solutions having predetermined average silver concentrations are supplied for processing; an auxiliary tank arranged to receive waste silver solutions from said feed line; and a pump arranged to deliver waste silver solutions from said auxiliary tank to said silver recovery machine; said method comprising the steps of: sensing the level of waste silver solutions in said auxiliary tank; operating said pump, in dependence on the level of waste silver solutions in said auxiliary tank, to deliver waste silver solutions at a constant flow rate from said auxiliary tank to said silver recovery machine, said pump being rendered inoperative when the level of waste silver solutions in said auxiliary tank recedes below a specified level; and in time coincidence with operation of said pump, operating said electrical supply at a constant current insufficient to produce silver sulfide in waste silver solutions having said predetermined average silver concentration, said electrical supply being rendered inoperative when said pump is rendered inoperative, whereby said recovery machine is operative throughout times when said pump is operating but not at other times.
Claim 2
Independent Claim
229 words
A method for recovering silver from waste silver solutions, especially spent photographic processing liquids, said method utilizing: an electrically operated silver recovery machine of the type which includes an electrical supply for passing electric current between two electrodes and through waste silver solution in said machines; a feed line via which waste silver solutions having predetermined average silver concentrations are supplied for processing; an auxiliary tank arranged to receive waste silver solutions from said feed line; and a pump arranged to deliver waste silver solutions from said auxiliary tank to said silver recovery machine; said method comprising the steps of: sensing the level of waste silver solutions in said auxiliary tank; operating said pump, in dependence on the level of waste silver solutions in said auxiliary tank, to deliver waste silver solutions at a constant flow rate from said auxiliary tank to said silver recovery machine, said pump being rendered inoperative when the level of waste silver solutions in said auxiliary tank recedes below a specified level; and in time coincidence with operation of said pump, operating said electrical supply at a constant current insufficient to produce silver sulfide in waste silver solutions having said predetermined average silver concentration, said electrical supply being rendered inoperative when said pump is rendered inoperative, whereby said recovery machine is operative throughout times when said pump is operating but not at other times.
Claim 3
Dependent Claim
32 words
The method according to claim 1 wherein said pump and said silver recovery machine are started and stopped together under the control of liquid-level responsive electrical switches associated with the auxiliary tank.
Claim 4
Dependent Claim
18 words
The method according to claim 1, further comprising a high liquid-level warning switch associated with the auxiliary tank.
Claim 5
Dependent Claim
23 words
The method according to claim 1 further comprising an overflow pipe connection to conduct overflow from said auxiliary tank into said recovery machine.
Claim 6
Dependent Claim
38 words
The method according to claim 4 wherein the delivery of waste solution by said pump to said recovery machine is via a further pipe which extends from the auxiliary tank to the recovery machine inside said overflow pipe.
Claim 7
Dependent Claim
17 words
The method according to claim 1 wherein said pump, when operating, delivers pulses of said waste solution.
Claim 8
Dependent Claim
37 words
The method according to claim 6 wherein flow delivery from the pump to the recovery machine is arranged in a manner to ensure that there are air breaks between successive liquid pulses of the delivered pump flow.
Claim 9
Dependent Claim
54 words
The method according to claim 7, wherein the delivered pump flow is directed into the upper end of a down-pipe of a relatively large diameter in the recovery machine, the upper portion of said down-pipe, which is above the liquid level in the recovery machine, having a side wall aperture that opens to atmosphere.
References Cited (Backward Citations)
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Cited
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Cited
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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) | 1976-02-06 | 1976-08-07 | 1977-02-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-02-06 | 1980-08-07 | 1981-02-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-02-06 | 1984-08-07 | 1985-02-06 | $7700.00 | Window Closed / Lapsed |