CA1061284A - Recovery of silver from used photographic solutions - Google Patents
Recovery of silver from used photographic solutionsInfo
- Publication number
- CA1061284A CA1061284A CA202,727A CA202727A CA1061284A CA 1061284 A CA1061284 A CA 1061284A CA 202727 A CA202727 A CA 202727A CA 1061284 A CA1061284 A CA 1061284A
- Authority
- CA
- Canada
- Prior art keywords
- silver
- pump
- solution
- waste
- cell
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
- C25C7/06—Operating or servicing
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Metals (AREA)
- Silver Salt Photography Or Processing Solution Therefor (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In an intermittently-operating electrolytic cell for the recovery of silver from used photographic bleach-fix solution, the cathode assembly and the solution are automatically separated when the plating current is switched off. A buffer tank upstream of the cell, from which solution is delivered to the cell by a metering pump during plating, has a bottom level switch that switches off the cell and feed and switches on an emptying pump for pumping the cell solution back to the buffer tank. The emptying pump is stopped by a cell bottom level switch; and a filling pump is started by a top level switch of the buffer tank, which also starts the plating cell and the metered feed, the filling pump being stopped by a top level switch of the cell. The cathode assembly is self-draining.
In an intermittently-operating electrolytic cell for the recovery of silver from used photographic bleach-fix solution, the cathode assembly and the solution are automatically separated when the plating current is switched off. A buffer tank upstream of the cell, from which solution is delivered to the cell by a metering pump during plating, has a bottom level switch that switches off the cell and feed and switches on an emptying pump for pumping the cell solution back to the buffer tank. The emptying pump is stopped by a cell bottom level switch; and a filling pump is started by a top level switch of the buffer tank, which also starts the plating cell and the metered feed, the filling pump being stopped by a top level switch of the cell. The cathode assembly is self-draining.
Description
, .
This invention relates to the recovery of silver from used photo-; graphic solutions and is an improvement in or modification of the invention described in our Patent Number 920086.
A combined ~leach Fix Solution now extensively used to process colour print paper can be de--silvered and prepared for re-use by the system disclosed in our Patent Number 920086.
However, the Ferric EDTA complex in the solution gives rise to the difficulty that it softens and re-dissolves the silver back from the cathode into the solution when the plating curren-t is switched off. The plating bath may be fed, by the metered flow sys-tem described in our Patent, with a constant volume of silver in solution to match a preset plating current amperage - it is then important to ~ ensure that -the silver already collected on the cathode is protected :~ from the bleach effect of the solution during shut down periods of ..
the apparatus.
In -the early design of our equipment it was considered that, when the solution flow from the photographic processor to the recovery cell ceased during shut down, a low preset holding current should be applied to maintain the silver on the cathode - in effect, counter-acting the solvent action of the bleach. But experiments in thisdirection lead to problems of overplating the solution, causing the silver on the cathode to soften, blacken and re-dissolve back into the solution. It has further been discovered that too low a plating ~ current allows the silver to re-dissolve, with a high loss of solid silver back into the solution.
It is therefore an object of the invention to eliminate the , problem of silver loss back into the solution from the cathode during shut down periods.
According to the present invention there is provided a method for recovering silver from waste silver solutions, especially .'' ~, .
' ~
~'"
` ~ , ' , ' ' ` ' ` ' , ' ' . ' ; `: ' ' ' ` ~ . ' : ' `
` ~06~8~
. ' .
.. spent photographic processing liquids, sai.d method utilizing: an '. electrically operated silver recovery machine of the type which ~ includes an electrical supply for passing electric current between . .
two electrodes, one of which is a self-draining cathode assembly, and through waste silver solution in said machine; 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 feea 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 constan-t 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; in substantial time coincidence with operation of said pump, operating said electrical supply at a constant current ~ insufficient to produce silver sulfide in waste silver solutions ~' 20 having said predetermined average silver concentration, said electrical . supply being rendered inoperative when said pump is rendered in- A, ~ operative whereby said recovery machine is operative substantially . throughout times when said pump is operating but substantially not at ` other times; and in substantial time coincidence with the rendering inoperative of said pump and said electrical supply, automatically separating the cathode assembly and the waste silver solution, whereby I the cathode assembly is substantially only immersed in the solution : when said recovery machine and said pump are operative.
According to the present invention, means are provided whereby the cathode and the plating solution are automatically ~ - 2a -::
~.
~4`
, ' ' ' . ~".
~ ' , '' ..
separated from one another when the plating current is switched orf.
One way of accomplishing this is by an automatic drain and re-fill system for -the plating cell which comes into operation as soon as -the level of solution in the buffer tank .~ .: .
",.
,, '~
.
` , :, .~ 2b ; , : .
.,,''~, ' 1061~8 .
reaches a low level switch. H~wever, even if the plating cell is emptied, silver on the cathode will sti:Ll~e softened and dissolved by residual puddles of solution left on the cathode plates. Therefore, as a further feature of the invention, a self-draining cathode asse~bly is employed. Conventionally, the cathode is of the multiple flat disc type, the discs being disposed horizontally on a vertical shaft driven by an ' electric motor above the plating tank. These flat cathode discs are now ` dished into a conical form so that the solution drains down to the centre.
A series of holes drilled at the lo~vest level of each disc allows the surplus solution from each disc to drain off to the botto~ of -the tank leaving the cathode silver surface free of solution.
; Alternatively, instead of the plating cell being drained and refilled, the self-draining assembly can be raised vertically, by electro-mechanica~L
jacks or similar means, clear of the plating bath and lowered again each time the plating current is switched off and subsequently switched on.
One arrangement operating according to the invention is shcwn by way of example in the accompanying drawings, in which:-Figure 1 is a general diagram of a silver recovery plant, and Figures 2 and 3 are a diagrammatic cross-sectional elevation and plan of the cathode assembly of the recovery cell.
~- As in our Patent Number 920 086 , the silver recovery cell or plating tank 11 is preceded by a buffer or store tank 12, which receives the used photographic solution to be processed and from which the solution is pumped to the recovery cell intermittently by a metering pump 13, the flow rate of the pump being chosen to match the plating current employed as explained in our prior patent. The buffer tank 12 is provided with top and bottom level switches A and D; the recovery cell 11, similarly has two further level switches B and E. Apart from the metering pump 13, a cell emptying pwmp and delivery line 14 is provided for pumping solution from the recovery cell 11 back to the buffer tank 12, and a ` 3 ;- filling pump and dell~ery line 15 for returning the solution from the buffer tar~ to the recovery cell.
Assume that the unit is on stand-b~, with the recovery cell initially empty, the plating current switched off and all three pumps idle. The buffer tar~ 12 fills with used photographic solution un-til the top level switch A is reached. Operation of this switch starts the metering pump 13 and the filling pump 15 and switches on the plating current. The recovery cell 11 then fills rapidly until the level of the switch B at the top of this cell is reached, whereupon the filling p~ 15 is switched off but ; 10 the metering pu~p remains on. At this time the level in the buffer tank ~ will have fallen to the store level indicated at C. With the metering pump ~ operating plating continues until the level in the buffer tank 12 has fallen . to the bottom level s~vitch D. The metering pump and the plating current ~ are then switched off and the cell er~tying pump 14 is switched on. The cell 11 rapidly empties until the bottom level switch E of the cell is reached, at which point the pump 14 is stopped and the cath~de in the cell ii is dry. The level in the buffer tank 12 will th~n have risen to the stand-by level indicated at F and the unit remains on stand-by until the level - switch A is again reached.
In order to avoid electrical continuity between the recovery cell - solution and the solution in the buffer tank, air break arrangements are provided in the cell emptying and filling lines at 16 and 17.
- Figures 2 and 3 show the self-draining cathode assembly. The~ cathode discs 18 are clamped at intervals up the cathode drive shaft 19 with intervening spacers 20. To promote draining, each cathode disc is of frusto-conical form with drain holes 21 near the centre. ~lthough as shown the cathode discs are assembled with the smaller diameters of their frusto-conical forms l~verm~st, they could be inverted, the solution then draining outward over the cathode discs instead of inward.
:
:~ .
., ~ 4 .
This invention relates to the recovery of silver from used photo-; graphic solutions and is an improvement in or modification of the invention described in our Patent Number 920086.
A combined ~leach Fix Solution now extensively used to process colour print paper can be de--silvered and prepared for re-use by the system disclosed in our Patent Number 920086.
However, the Ferric EDTA complex in the solution gives rise to the difficulty that it softens and re-dissolves the silver back from the cathode into the solution when the plating curren-t is switched off. The plating bath may be fed, by the metered flow sys-tem described in our Patent, with a constant volume of silver in solution to match a preset plating current amperage - it is then important to ~ ensure that -the silver already collected on the cathode is protected :~ from the bleach effect of the solution during shut down periods of ..
the apparatus.
In -the early design of our equipment it was considered that, when the solution flow from the photographic processor to the recovery cell ceased during shut down, a low preset holding current should be applied to maintain the silver on the cathode - in effect, counter-acting the solvent action of the bleach. But experiments in thisdirection lead to problems of overplating the solution, causing the silver on the cathode to soften, blacken and re-dissolve back into the solution. It has further been discovered that too low a plating ~ current allows the silver to re-dissolve, with a high loss of solid silver back into the solution.
It is therefore an object of the invention to eliminate the , problem of silver loss back into the solution from the cathode during shut down periods.
According to the present invention there is provided a method for recovering silver from waste silver solutions, especially .'' ~, .
' ~
~'"
` ~ , ' , ' ' ` ' ` ' , ' ' . ' ; `: ' ' ' ` ~ . ' : ' `
` ~06~8~
. ' .
.. spent photographic processing liquids, sai.d method utilizing: an '. electrically operated silver recovery machine of the type which ~ includes an electrical supply for passing electric current between . .
two electrodes, one of which is a self-draining cathode assembly, and through waste silver solution in said machine; 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 feea 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 constan-t 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; in substantial time coincidence with operation of said pump, operating said electrical supply at a constant current ~ insufficient to produce silver sulfide in waste silver solutions ~' 20 having said predetermined average silver concentration, said electrical . supply being rendered inoperative when said pump is rendered in- A, ~ operative whereby said recovery machine is operative substantially . throughout times when said pump is operating but substantially not at ` other times; and in substantial time coincidence with the rendering inoperative of said pump and said electrical supply, automatically separating the cathode assembly and the waste silver solution, whereby I the cathode assembly is substantially only immersed in the solution : when said recovery machine and said pump are operative.
According to the present invention, means are provided whereby the cathode and the plating solution are automatically ~ - 2a -::
~.
~4`
, ' ' ' . ~".
~ ' , '' ..
separated from one another when the plating current is switched orf.
One way of accomplishing this is by an automatic drain and re-fill system for -the plating cell which comes into operation as soon as -the level of solution in the buffer tank .~ .: .
",.
,, '~
.
` , :, .~ 2b ; , : .
.,,''~, ' 1061~8 .
reaches a low level switch. H~wever, even if the plating cell is emptied, silver on the cathode will sti:Ll~e softened and dissolved by residual puddles of solution left on the cathode plates. Therefore, as a further feature of the invention, a self-draining cathode asse~bly is employed. Conventionally, the cathode is of the multiple flat disc type, the discs being disposed horizontally on a vertical shaft driven by an ' electric motor above the plating tank. These flat cathode discs are now ` dished into a conical form so that the solution drains down to the centre.
A series of holes drilled at the lo~vest level of each disc allows the surplus solution from each disc to drain off to the botto~ of -the tank leaving the cathode silver surface free of solution.
; Alternatively, instead of the plating cell being drained and refilled, the self-draining assembly can be raised vertically, by electro-mechanica~L
jacks or similar means, clear of the plating bath and lowered again each time the plating current is switched off and subsequently switched on.
One arrangement operating according to the invention is shcwn by way of example in the accompanying drawings, in which:-Figure 1 is a general diagram of a silver recovery plant, and Figures 2 and 3 are a diagrammatic cross-sectional elevation and plan of the cathode assembly of the recovery cell.
~- As in our Patent Number 920 086 , the silver recovery cell or plating tank 11 is preceded by a buffer or store tank 12, which receives the used photographic solution to be processed and from which the solution is pumped to the recovery cell intermittently by a metering pump 13, the flow rate of the pump being chosen to match the plating current employed as explained in our prior patent. The buffer tank 12 is provided with top and bottom level switches A and D; the recovery cell 11, similarly has two further level switches B and E. Apart from the metering pump 13, a cell emptying pwmp and delivery line 14 is provided for pumping solution from the recovery cell 11 back to the buffer tank 12, and a ` 3 ;- filling pump and dell~ery line 15 for returning the solution from the buffer tar~ to the recovery cell.
Assume that the unit is on stand-b~, with the recovery cell initially empty, the plating current switched off and all three pumps idle. The buffer tar~ 12 fills with used photographic solution un-til the top level switch A is reached. Operation of this switch starts the metering pump 13 and the filling pump 15 and switches on the plating current. The recovery cell 11 then fills rapidly until the level of the switch B at the top of this cell is reached, whereupon the filling p~ 15 is switched off but ; 10 the metering pu~p remains on. At this time the level in the buffer tank ~ will have fallen to the store level indicated at C. With the metering pump ~ operating plating continues until the level in the buffer tank 12 has fallen . to the bottom level s~vitch D. The metering pump and the plating current ~ are then switched off and the cell er~tying pump 14 is switched on. The cell 11 rapidly empties until the bottom level switch E of the cell is reached, at which point the pump 14 is stopped and the cath~de in the cell ii is dry. The level in the buffer tank 12 will th~n have risen to the stand-by level indicated at F and the unit remains on stand-by until the level - switch A is again reached.
In order to avoid electrical continuity between the recovery cell - solution and the solution in the buffer tank, air break arrangements are provided in the cell emptying and filling lines at 16 and 17.
- Figures 2 and 3 show the self-draining cathode assembly. The~ cathode discs 18 are clamped at intervals up the cathode drive shaft 19 with intervening spacers 20. To promote draining, each cathode disc is of frusto-conical form with drain holes 21 near the centre. ~lthough as shown the cathode discs are assembled with the smaller diameters of their frusto-conical forms l~verm~st, they could be inverted, the solution then draining outward over the cathode discs instead of inward.
:
:~ .
., ~ 4 .
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for recovering silver from waste silver solutions, said method utilizing: an electrically operated silver recovery machine of the type which includes an electrical supply for passing electric current between two electrodes, one of which is a self-draining cathode assembly, and through waste silver solution in said machine;
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; in substantial 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 substantially throughout times when said pump is operating but not at other times; and in substantial time coincidence with the rendering inoperative of said pump and said electrical supply, automatically separating the cathode assembly and the waste silver solution, whereby the cathode assembly is substantially only immersed in the solution when said recovery machine and said pump are operative.
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; in substantial 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 substantially throughout times when said pump is operating but not at other times; and in substantial time coincidence with the rendering inoperative of said pump and said electrical supply, automatically separating the cathode assembly and the waste silver solution, whereby the cathode assembly is substantially only immersed in the solution when said recovery machine and said pump are operative.
2. A method according to claim 1, wherein in substantial time coincidence with the rendering inoperative of said pump and said electrical supply the solution is automatically pumped out of the silver recovery machine, said solution being pumped back into the machine when said pump and said electrical supply again become operative.
3. A method according to claim 1, wherein in substantial time coincidence with the rendering inoperative of said pump and said electrical supply the cathode assembly is automatically lifted clear of the solution in the silver recovery machine, said cathode assembly being re-immersed in said solution when said pump and said electrical supply again become operative.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB3065073A GB1462868A (en) | 1973-06-27 | 1973-06-27 | Electrolytic recovery for silver from used photographic solutions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1061284A true CA1061284A (en) | 1979-08-28 |
Family
ID=10310965
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA202,727A Expired CA1061284A (en) | 1973-06-27 | 1974-06-18 | Recovery of silver from used photographic solutions |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US3901777A (en) |
| JP (1) | JPS5741555B2 (en) |
| CA (1) | CA1061284A (en) |
| DE (1) | DE2429288A1 (en) |
| FR (1) | FR2235211B2 (en) |
| GB (1) | GB1462868A (en) |
| IT (1) | IT1054173B (en) |
| SE (1) | SE7408402L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4561957A (en) * | 1984-06-11 | 1985-12-31 | Palazzolo James C | Electrolytic silver recovery system |
| US4802961A (en) * | 1987-12-23 | 1989-02-07 | Woog Manfred J | Silver removal apparatus and method |
| DE4445637C2 (en) * | 1994-12-21 | 1998-07-16 | Kodak Ag | Silver recovery arrangement |
| DE69710174D1 (en) * | 1997-01-31 | 2002-03-14 | Agfa Gevaert Nv | Electrolysis cell and method for removing silver from silver-containing aqueous solutions |
| US6860976B2 (en) * | 2000-06-20 | 2005-03-01 | Lynntech International, Ltd. | Electrochemical apparatus with retractable electrode |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2615839A (en) * | 1948-04-12 | 1952-10-28 | Henry O Willier | Recovery of precious metals from photographic baths |
| US3330755A (en) * | 1962-08-14 | 1967-07-11 | Electro Cell Corp | Electrolytic apparatus |
| US3342718A (en) * | 1964-01-21 | 1967-09-19 | William M Adams | Apparatus for the recovery of silver from used photographic fixing solutions by electrolysis |
| US3458425A (en) * | 1967-01-09 | 1969-07-29 | Charles I Tolle | Cathode structure for electrolytic apparatus |
| CA920086A (en) * | 1969-09-11 | 1973-01-30 | S. Bentley James | Recovery of silver from waste photographic and like solutions |
| US3616332A (en) * | 1969-12-17 | 1971-10-26 | Texas Instruments Inc | Process for recovering silver from scrap materials and electrolyte composition for use therein |
| US3705716A (en) * | 1971-07-09 | 1972-12-12 | Eastman Kodak Co | Monitoring silver recovery |
-
1973
- 1973-06-27 GB GB3065073A patent/GB1462868A/en not_active Expired
-
1974
- 1974-06-18 CA CA202,727A patent/CA1061284A/en not_active Expired
- 1974-06-19 DE DE2429288A patent/DE2429288A1/en not_active Ceased
- 1974-06-19 US US480828A patent/US3901777A/en not_active Expired - Lifetime
- 1974-06-25 IT IT24404/74A patent/IT1054173B/en active
- 1974-06-26 FR FR7422255A patent/FR2235211B2/fr not_active Expired
- 1974-06-26 SE SE7408402A patent/SE7408402L/xx unknown
- 1974-06-27 JP JP49074182A patent/JPS5741555B2/ja not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2235211A2 (en) | 1975-01-24 |
| IT1054173B (en) | 1981-11-10 |
| DE2429288A1 (en) | 1975-01-16 |
| SE7408402L (en) | 1974-12-30 |
| US3901777A (en) | 1975-08-26 |
| GB1462868A (en) | 1977-01-26 |
| JPS5068910A (en) | 1975-06-09 |
| JPS5741555B2 (en) | 1982-09-03 |
| FR2235211B2 (en) | 1978-06-02 |
| AU6986874A (en) | 1975-12-11 |
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