CA2028847A1 - Method of recovering silver from photographic processing solutions - Google Patents
Method of recovering silver from photographic processing solutionsInfo
- Publication number
- CA2028847A1 CA2028847A1 CA002028847A CA2028847A CA2028847A1 CA 2028847 A1 CA2028847 A1 CA 2028847A1 CA 002028847 A CA002028847 A CA 002028847A CA 2028847 A CA2028847 A CA 2028847A CA 2028847 A1 CA2028847 A1 CA 2028847A1
- Authority
- CA
- Canada
- Prior art keywords
- silver
- sulphide
- metal
- sulphite
- fixer
- 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.)
- Abandoned
Links
Abstract
A method of recovering silver from used photographic fixer solutions characterised in that the solution contains an alkali metal sulphite as the sole silver halide solvent.
Description
: ` . ' ~ . ~, 1 A METHOD OF RECOVE~ING SILVER FROM PHOTOGRA~IC
PROCESSING SOL~IONS
': ~
.~
~ This invention relates to a method of recovering ~~; 5 silver from photographic processing solutions and, in particular to recovering silver from sulphite fixer solutions.
In processing both black-and-white and colour 7 photographic silver halide materials it is necessary 10 to remove unwanted silver halide from the developed material. This is customarily accomplished by using a fixer solution which contains a silver halide solvent, usually a thiosulphate.
.~ Methods are known for recovering silver from 15 spent thiosulphate fixer solutions. It is not, :~i however, possible to use any of these methods "in-line" to extend the working life of the solutions without continuous solutlon monitoring and solution adjustment, nor does removal of silver leave a 20 solution for disposal (i.e. a solution containing thiosulphate) which is fully environmentally acceptable.
In our cofiled appli^a-ion (No.90905501.4 - PCT
3 EP 90/00607) there is described and claimed a method . 1 for removing unwanted silver chloride from photographic materials using a fixer comprising an alkali metal sulphite as sole silver halide solvent.
According to the preser.t invention there is provided a method of recovering silver from used photographic fixer solutions characterised in that the 3' solution contains an alkali metal sulphite ~M-SO3 wherein M is an alkali me~al) as the sole silver halide solvent and that the silver is recovered by:
1. Electrochemical deposition of silver, `~ E St~
.
~. : - . .
. ~
:~k;
,. ,~'' : ''. ~ ' ':' ~. ~3 ~ 2-: .:
, .
PROCESSING SOL~IONS
': ~
.~
~ This invention relates to a method of recovering ~~; 5 silver from photographic processing solutions and, in particular to recovering silver from sulphite fixer solutions.
In processing both black-and-white and colour 7 photographic silver halide materials it is necessary 10 to remove unwanted silver halide from the developed material. This is customarily accomplished by using a fixer solution which contains a silver halide solvent, usually a thiosulphate.
.~ Methods are known for recovering silver from 15 spent thiosulphate fixer solutions. It is not, :~i however, possible to use any of these methods "in-line" to extend the working life of the solutions without continuous solutlon monitoring and solution adjustment, nor does removal of silver leave a 20 solution for disposal (i.e. a solution containing thiosulphate) which is fully environmentally acceptable.
In our cofiled appli^a-ion (No.90905501.4 - PCT
3 EP 90/00607) there is described and claimed a method . 1 for removing unwanted silver chloride from photographic materials using a fixer comprising an alkali metal sulphite as sole silver halide solvent.
According to the preser.t invention there is provided a method of recovering silver from used photographic fixer solutions characterised in that the 3' solution contains an alkali metal sulphite ~M-SO3 wherein M is an alkali me~al) as the sole silver halide solvent and that the silver is recovered by:
1. Electrochemical deposition of silver, `~ E St~
.
~. : - . .
. ~
:~k;
,. ,~'' : ''. ~ ' ':' ~. ~3 ~ 2-: .:
, .
2. Metal exchange with a less noble metal, ~, 3. Addition of a powerful reducing agent to ' `7` 5 reduce the silver sulphite complex to silver metal and the free ligand, ~ 4. Precipitation of silver sulphide by the .,.;~
~ , addition of a water soluble sulphide, ,.~j 10 "r~ 5. Precipitation of silver sulphide by contacting .: the silver laden fixer with an insoluble sulphide -.~ either added as the free solid or suspended ln a matrix, .;~ 15 6. Adci~ion of a càtionic or anionic ion exchange . resin, or '.~ 7. Destruction of the silver sulphite complex by :` 20 the addition of a powerful oxidant or a mineral acid.
":~ J
The advantages of the present invention are that ; treated fixers can be discharged into sewer systems in ~,~ 25 areas where limits on silver and thiosulphate ~, discharge are low; valuable silver is recovered and available for refining and reuse; and in-line silver :s recovery which increases the life of the flxer and therefore reduces chemical cost to the user becomes - 30 possible.
-~ A number of the above methods of recovering . silver from thiosulphate or thiosulphate plus sulphite fixers are known and similar methods may also be used ~ in the present case. Such methods include:
.~ 35 ' ' C~ SE s~EF
. .
~: ' ' ' ' ' .
'' ' ~ ' . ' !:, .
^~- 3 1 Electrochemical deposition of silver, ' Metal exchange with a less noble metal and :s 5 Addition of a powerful reducing agent to reduce ~i the silver sulphite complex to silver metal and the free ligand.
- There are, however, additional methods which are ^`'? 10 not efficient or practical for thiosulphate-containing fixers but are practical for sulphite-only fixers and i these are:
:, .. .
Precipitation of silver sulphide by the addition of a water soluble sulphide, ' ! Precipitation of silver sulphide by contacting the silver laden fixer with an insoluble sulphide :~ either added as the free solid or suspended in a matrix, Addition of a cationic or anionic ion exchange resin, or Destruction of the silver sulphite complex by the addition of a powerful ox1dant or a mineral acid.
i Electrochemical silver recovery is carried out by 1 passing current through seasoned fixer between two electrodes made of a suitable material which may be essentially metallic or of one of many forms of carbon. Silver is deposited on the cathode. The electrodes may or may not be rotated to improve J' plating ~uality and efficiency.
,, .
~, S~ TlT~TE SH
. . .
`
,,~ . .
~;~
i. `~
;l Metal exchange is a process by which a metal that is more electronegative than silver is added to the -~ fixer in one of many forms, e.g. wire, powder or ~j; billets. The electronegative metal displaces the '~ 5 silver from the silver complex preclpitating it on the metal surface. Suitable metals include First Row Transition Metals.
Silver can also be precipitated by addition of a ~- powerful reducing agent to the fixer. Complexed silver is reduced and precipitates. Suitable agents ~ would include alkali metal borohydrides and ?;; ' dithionites, alkali metal hydrides and mixed metal -~ hydrides, e.g. lithium aluminium hydride.
~- Silver can be recovered as silver sulphide from the fixers by addition of an aqueous solution of water ~J soluble sulphides. These include the alkali metal, ,?~;, alkaline earth metal and a~monium sulphides and polysulphides.
Silver can be recovered as silver sulphide by contacting the seasoned fixer with sulphides that are essentially water insoluble. These are all the metal ~'7 sulphides excluding those of alkali metals, alkaline ~ earth metals and silver sul?hide.
''"t Ion-exchange resins can be used to recover silver from sulphite fixers. Both cationic and anionic resins of the so called 'strong' and 'weak' types.
j For cationic resins silver ions displace the preabsorbed resin counter ion. For anionic resins the silver complex displaces the resin counter ion.
. 30 Silver can be recovered from sulphite fixers by destroying the sulphite by the addition of a powerful oxidising agent, e.g. hydrogen peroxide, alkali metal '; and ammonium persulphates, alkali metal and ammonium -1 dichromates and alkali metal and ammonium permanganates. Once the sulphite is destroyed the "2 S~JE~;T~TIJTE SHEET
;~. . ~ - .. . ,~ .
,,.~ , . ` ~ ~ . . . . . . -,-?.
~ `
free silver can react with any ions present in solution. If fixing was carried out on silver ~` chloride, the reaction will be with chloride ions, -~- precipitating out silver chloride. Addition of a ,,t',~".,~ 5 strong mineral acid would have a similar effect, removing the sulphite and allowing the silver to react with anions such as chloride remaining in the fixer.
In apparatus wherein the fixer is recirculated .,.
some silver-recovery can be achieved "in-line".
Methods suitable in this approach are electrochemical reduction, treatment with ion-exchange resins and i treatment with a supported (matrix) of an insoluble metal sulphide. Such in-line recovery of silver will extend the working life of the fixer solution thus reducing cost to the user.
The following examples are included for a better understanding of the invention:
-, EXAMPLES ~-8 In all the following examples the same model seasoned .~ sulphite fixer_was used. This was made by dissolving 1.3 g/l silver chloride in a 50 g/l anhydrous sodium sulphite solution. Silver concentration in the fixer was measured using a colorimetric technique marketed 'A~ 25 by Dr Lange. The starting silver concentration in the ;~ test fixer was 820 + 50 mg/l (as metal).
For each test 100 mls of the silver laden fixer was taken and stirred in a beaker with the test reagent ~,;
; for 5 minutes and then filtered. For the ~ 30 electrochemical method two clean stainless steel . ..,~
plates were placed in the solution. The submerged ~: 2 area of each pla~e was 10 cm . The electrodes were connected to a 100 mA constant current power supply.
The solution was electrolysed for 10 minutes. The ~ 35 table below summarises the results.
t~ , . . .
. . I .
SUBSTITUTE SHEET
.~, . , .
:,: . :, - , `
: ~ ;
o ~n O ~
, X
'', Q
w N ~ Z ~ ^ N N ~D
0 ~ 3 n o (D t,7 s ~ n J (D ~ ~ ~ ~ Q
;j r; ~ ~- 1~ (~
:~ ~ O O rr ~ o " J 3 1~ S
'.: D, ~ t~ ~ Q
; tn ~ ~ :J' (D
: ~ N 1-- ~: ~ H 1-- r;
.j (D tn ~ ~ :~ Q
,,;1 0 ro I a~
' 1 .
~ O
~ , addition of a water soluble sulphide, ,.~j 10 "r~ 5. Precipitation of silver sulphide by contacting .: the silver laden fixer with an insoluble sulphide -.~ either added as the free solid or suspended ln a matrix, .;~ 15 6. Adci~ion of a càtionic or anionic ion exchange . resin, or '.~ 7. Destruction of the silver sulphite complex by :` 20 the addition of a powerful oxidant or a mineral acid.
":~ J
The advantages of the present invention are that ; treated fixers can be discharged into sewer systems in ~,~ 25 areas where limits on silver and thiosulphate ~, discharge are low; valuable silver is recovered and available for refining and reuse; and in-line silver :s recovery which increases the life of the flxer and therefore reduces chemical cost to the user becomes - 30 possible.
-~ A number of the above methods of recovering . silver from thiosulphate or thiosulphate plus sulphite fixers are known and similar methods may also be used ~ in the present case. Such methods include:
.~ 35 ' ' C~ SE s~EF
. .
~: ' ' ' ' ' .
'' ' ~ ' . ' !:, .
^~- 3 1 Electrochemical deposition of silver, ' Metal exchange with a less noble metal and :s 5 Addition of a powerful reducing agent to reduce ~i the silver sulphite complex to silver metal and the free ligand.
- There are, however, additional methods which are ^`'? 10 not efficient or practical for thiosulphate-containing fixers but are practical for sulphite-only fixers and i these are:
:, .. .
Precipitation of silver sulphide by the addition of a water soluble sulphide, ' ! Precipitation of silver sulphide by contacting the silver laden fixer with an insoluble sulphide :~ either added as the free solid or suspended in a matrix, Addition of a cationic or anionic ion exchange resin, or Destruction of the silver sulphite complex by the addition of a powerful ox1dant or a mineral acid.
i Electrochemical silver recovery is carried out by 1 passing current through seasoned fixer between two electrodes made of a suitable material which may be essentially metallic or of one of many forms of carbon. Silver is deposited on the cathode. The electrodes may or may not be rotated to improve J' plating ~uality and efficiency.
,, .
~, S~ TlT~TE SH
. . .
`
,,~ . .
~;~
i. `~
;l Metal exchange is a process by which a metal that is more electronegative than silver is added to the -~ fixer in one of many forms, e.g. wire, powder or ~j; billets. The electronegative metal displaces the '~ 5 silver from the silver complex preclpitating it on the metal surface. Suitable metals include First Row Transition Metals.
Silver can also be precipitated by addition of a ~- powerful reducing agent to the fixer. Complexed silver is reduced and precipitates. Suitable agents ~ would include alkali metal borohydrides and ?;; ' dithionites, alkali metal hydrides and mixed metal -~ hydrides, e.g. lithium aluminium hydride.
~- Silver can be recovered as silver sulphide from the fixers by addition of an aqueous solution of water ~J soluble sulphides. These include the alkali metal, ,?~;, alkaline earth metal and a~monium sulphides and polysulphides.
Silver can be recovered as silver sulphide by contacting the seasoned fixer with sulphides that are essentially water insoluble. These are all the metal ~'7 sulphides excluding those of alkali metals, alkaline ~ earth metals and silver sul?hide.
''"t Ion-exchange resins can be used to recover silver from sulphite fixers. Both cationic and anionic resins of the so called 'strong' and 'weak' types.
j For cationic resins silver ions displace the preabsorbed resin counter ion. For anionic resins the silver complex displaces the resin counter ion.
. 30 Silver can be recovered from sulphite fixers by destroying the sulphite by the addition of a powerful oxidising agent, e.g. hydrogen peroxide, alkali metal '; and ammonium persulphates, alkali metal and ammonium -1 dichromates and alkali metal and ammonium permanganates. Once the sulphite is destroyed the "2 S~JE~;T~TIJTE SHEET
;~. . ~ - .. . ,~ .
,,.~ , . ` ~ ~ . . . . . . -,-?.
~ `
free silver can react with any ions present in solution. If fixing was carried out on silver ~` chloride, the reaction will be with chloride ions, -~- precipitating out silver chloride. Addition of a ,,t',~".,~ 5 strong mineral acid would have a similar effect, removing the sulphite and allowing the silver to react with anions such as chloride remaining in the fixer.
In apparatus wherein the fixer is recirculated .,.
some silver-recovery can be achieved "in-line".
Methods suitable in this approach are electrochemical reduction, treatment with ion-exchange resins and i treatment with a supported (matrix) of an insoluble metal sulphide. Such in-line recovery of silver will extend the working life of the fixer solution thus reducing cost to the user.
The following examples are included for a better understanding of the invention:
-, EXAMPLES ~-8 In all the following examples the same model seasoned .~ sulphite fixer_was used. This was made by dissolving 1.3 g/l silver chloride in a 50 g/l anhydrous sodium sulphite solution. Silver concentration in the fixer was measured using a colorimetric technique marketed 'A~ 25 by Dr Lange. The starting silver concentration in the ;~ test fixer was 820 + 50 mg/l (as metal).
For each test 100 mls of the silver laden fixer was taken and stirred in a beaker with the test reagent ~,;
; for 5 minutes and then filtered. For the ~ 30 electrochemical method two clean stainless steel . ..,~
plates were placed in the solution. The submerged ~: 2 area of each pla~e was 10 cm . The electrodes were connected to a 100 mA constant current power supply.
The solution was electrolysed for 10 minutes. The ~ 35 table below summarises the results.
t~ , . . .
. . I .
SUBSTITUTE SHEET
.~, . , .
:,: . :, - , `
: ~ ;
o ~n O ~
, X
'', Q
w N ~ Z ~ ^ N N ~D
0 ~ 3 n o (D t,7 s ~ n J (D ~ ~ ~ ~ Q
;j r; ~ ~- 1~ (~
:~ ~ O O rr ~ o " J 3 1~ S
'.: D, ~ t~ ~ Q
; tn ~ ~ :J' (D
: ~ N 1-- ~: ~ H 1-- r;
.j (D tn ~ ~ :~ Q
,,;1 0 ro I a~
' 1 .
~ O
3 ~ O ~ '4 ~ ~ O C
., Q ~
~ 3 O.
.', _ ~
o ~ n C 1'-~-3 `, o o o o o o ~n o I+ I+ I+ I+ I+ I+ I+ I+ ~ 1-:~ o o o o o C> o ~
~ ~t n .~ o o O o O O ~ O ~ ~D
I+ I+ I+ I+ I+ I+ I+ I+ a~
~,i O O O O O ~ O O ~ ~ C
`:
~1 .
, . . .
5U~1 IT~IT~ SHE1-.
, .
., . . .- ; . .
~- . . ; , . . .. ` .
, . .
., ... . . .
. .
., Q ~
~ 3 O.
.', _ ~
o ~ n C 1'-~-3 `, o o o o o o ~n o I+ I+ I+ I+ I+ I+ I+ I+ ~ 1-:~ o o o o o C> o ~
~ ~t n .~ o o O o O O ~ O ~ ~D
I+ I+ I+ I+ I+ I+ I+ I+ a~
~,i O O O O O ~ O O ~ ~ C
`:
~1 .
, . . .
5U~1 IT~IT~ SHE1-.
, .
., . . .- ; . .
~- . . ; , . . .. ` .
, . .
., ... . . .
. .
Claims (4)
1. A method of recovering silver from used photographic fixer solutions characterised in that the solution contains an alkali metal sulphite (M-SO3 wherein M is an alkali metal) as the sole silver halide solvent and that the silver is recovered by:
1. Electrochemical deposition of silver, 2. Metal exchange with a less noble metal, 3. Addition of a powerful reducing agent to reduce the silver sulphite complex to silver metal and the free ligand, 4. Precipitation of silver sulphide by the addition of a water soluble sulphide, 5. Precipitation of silver sulphide by contacting the silver laden fixer with an insoluble sulphide either added as the free solid or suspended in a matrix, 6. Addition of a cationic or anionic ion-exchange resin, or 7. Destruction of the silver sulphite complex by the addition of a powerful oxidant or a mineral acid.
2. A method as claimed in Claim 1 in which working fixer solution is passed through a recovery module and returned to the fixing tank after removal of silver.
3. A method as claimed in Claim 2 in which the recovery module employs electrochemical reduction, an ion exchange resin or a supported matrix of an insoluble metal sulphide.
4. A method of photographic processing which employs a fixing bath containing an alkali metal sulphite as sole silver halide solvent from which silver is recovered by the method of any of Claims 1-3.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002028847A CA2028847A1 (en) | 1989-04-26 | 1990-04-13 | Method of recovering silver from photographic processing solutions |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8909577.2 | 1989-04-26 | ||
| GB8909577A GB8909577D0 (en) | 1989-04-26 | 1989-04-26 | A method of recovering silver from photographic processing solutions |
| GB898927964A GB8927964D0 (en) | 1989-12-11 | 1989-12-11 | Method and apparatus for recovering silver from a photographic fixing solution |
| CA002028847A CA2028847A1 (en) | 1989-04-26 | 1990-04-13 | Method of recovering silver from photographic processing solutions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2028847A1 true CA2028847A1 (en) | 1990-10-27 |
Family
ID=27168826
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002028847A Abandoned CA2028847A1 (en) | 1989-04-26 | 1990-04-13 | Method of recovering silver from photographic processing solutions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2028847A1 (en) |
-
1990
- 1990-04-13 CA CA002028847A patent/CA2028847A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |