GB2090865A - Electrolytic Anode Protection - Google Patents
Electrolytic Anode Protection Download PDFInfo
- Publication number
- GB2090865A GB2090865A GB8100680A GB8100680A GB2090865A GB 2090865 A GB2090865 A GB 2090865A GB 8100680 A GB8100680 A GB 8100680A GB 8100680 A GB8100680 A GB 8100680A GB 2090865 A GB2090865 A GB 2090865A
- Authority
- GB
- United Kingdom
- Prior art keywords
- anode
- shield
- cell
- current
- electrolyte
- 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.)
- Granted
Links
- 229910001220 stainless steel Inorganic materials 0.000 claims abstract description 13
- 239000010935 stainless steel Substances 0.000 claims abstract description 11
- 230000007797 corrosion Effects 0.000 claims abstract description 10
- 238000005260 corrosion Methods 0.000 claims abstract description 10
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000011084 recovery Methods 0.000 claims abstract description 7
- 229910052709 silver Inorganic materials 0.000 claims abstract description 7
- 239000004332 silver Substances 0.000 claims abstract description 7
- 239000003792 electrolyte Substances 0.000 claims description 14
- VVQNEPGJFQJSBK-UHFFFAOYSA-N Methyl methacrylate Chemical compound COC(=O)C(C)=C VVQNEPGJFQJSBK-UHFFFAOYSA-N 0.000 claims description 5
- 238000005253 cladding Methods 0.000 claims description 4
- 239000004033 plastic Substances 0.000 claims description 3
- 229920003023 plastic Polymers 0.000 claims description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical class [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 2
- 239000011248 coating agent Substances 0.000 claims description 2
- 238000000576 coating method Methods 0.000 claims description 2
- 239000004020 conductor Substances 0.000 claims description 2
- 230000003247 decreasing effect Effects 0.000 claims description 2
- 230000000694 effects Effects 0.000 claims description 2
- 238000005530 etching Methods 0.000 claims description 2
- 229910002804 graphite Inorganic materials 0.000 claims description 2
- 239000010439 graphite Substances 0.000 claims description 2
- 230000002209 hydrophobic effect Effects 0.000 claims description 2
- 238000009434 installation Methods 0.000 claims description 2
- 239000011810 insulating material Substances 0.000 claims description 2
- 238000000465 moulding Methods 0.000 claims description 2
- 238000007789 sealing Methods 0.000 claims description 2
- 125000006850 spacer group Chemical group 0.000 claims description 2
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
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)
Abstract
In many forms of electrolytic cells, especially those for silver recovery using stainless steel anodes, the cell is operating on the edge of corrosion of the anode and any improvement in the operating conditions is advantageous. The placing of a non-conducting shield (34) between the anode (20) and the cathode of an electrolytic cell adjacent the point of entry (22) of the current to the anode (20) prevents a higher flow of current at the point of entry (22) than at more remote parts of the anode (20). This reduces potential differences across the anode (20) and hence the risk of corrosion. <IMAGE>
Description
SPECIFICATION
Electrolytic Anode Protection
The present invention relates to electrolytic cells, particularly but not exclusively, cells for the recovery of silver from photographic fixer solutions having a stainless steel anode.
In many forms of electrolytic cells especially those for silver recovery using stainless steel anodes the cell is operating on the edge of corrosion of the anode and any inprovement in the operating conditions is advantageous.
The resistance of stainless steels is fairly high, about 70 microhm per cm. Hence, a typical anode formed from sheet of 0.75 mm thickness would have a resistance approaching 1 milliohm per square. A current of 10 amp would thus cause a potential drop of 10 millivolts per square. The potential difference between the anode and the bulk of an electrolyte is of the order of 1 volt.
The conductivity of an electrolyte such as a photographic fixing solution at 300C. is nearly one per cent that of stainless steel, and as the anode is much thinner than the corresponding section of the electrolyte, the flow of current through the electrolyte to the cathode is higher close to the point of entry of current to the anode than at more remote parts of the anode.
Every millivolt of extra potential difference is important where a system is operating on the edge of corrosion and it is important to find a means of minimizing the effect referred to above.
If the anode were clad with an insulating coating at the point of entry of current, then current could not flow from the anode to the electrolyte at that point. However, no known hydrophobic cladding can resist becoming undermined by a warm fixing solution at the surface of the hydrophilic stainless steel. Further as the fixing solution penetrates under the cladding it becomes oxidised to strong sulphur acids and corrosion is increased rather than decreased.
According to the present invention there is provided an electrolytic cell comprising an anode and a cathode and a non-conducting shield supported therebetween, adjacent and spaced from the anode at the point of entry of current thereto.
The shield may be supported by having projections engageable with holes in the anode, to allow slight relative movement of the shield relative to the anode.
Preferably the anode-shield spacing is from 1 to 2 mm.
The shield may be made from plastics, for example methyl methacrylate.
The present invention will now be described by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a plan view of an electrolytic cell according to the present invention, in partial section;
Fig. 2 shows a side view of the cell of Fig. 1, also in partial section; and
Fig. 3 shows an isometric view of a part of the cell viewed in the direction of arrow 'A' in Fig. 1.
An electrolytic cell 10, such as for recovery of silver from a fixing solution, has a casing 12 of an insulating material, with inlet and outlet pipes, 14 and 1 6 respectively for the flow of the electrolyte through the cell 10. The cell 10 has an axial cathode 18, usually of graphite.
The anode 20 is a sheet of stainless steel roiled into a hollow cylinder. A tongue 22 is formed on the anode 20 by making a circumferential cut 24 in the cylinder from the edge 26 of the sheet.
The tongue 22 is then bent to extend radially from the anode 20.
If the anode 20 is compressed radialiy, the diameter may be reduced so that the anode 20 and the tongue 22 can be slid inside the casing 12, and when released the tongue 22 extends through a sealing grommet 28 in an aperture 30 in the casing 12. The anode 20 is located within the casing 12 by spacers 32.
A shield 34 of a non-conducting material is mounted in a position spaced from the anode 20 in the region of the tongue 22 which forms the point of entry of the current to the anode 20.
The shield 34 may be supported on the anode 20 by hooks 36, 38 and a spacing projection 40.
Typically the gap between the anode 20 and the shield 34 is 1 to 2 millimetres.
Preferably the contact between the support points of the shield 34 and the anode 20 should allow limited relative movement to prevent the occurrence of stagnant points in the electrolyte, which will accelerate corrosion. A means of achieving this is to have holes formed in the anode 20, and to have projecting legs formed on the shield 34, which may be produced as a moulding. These projecting legs are such as to require minor deformation of the shield 34 to insert then into the holes in the anode 20, but to allow the shield 34 to move slightly relative to the anode 20 in use, and also space the shield 34 from the anode 20.
In a trial installation, a shield of thin methyl methacrylate sheet about 800 mm square was spaced 2 mm from the anode. Previously, noticeable dulling of the sheet forming the anode at the point of current entry had occurred during one months operation of the cell. Subsequent to fitting of the shield, no noticeable further etching of the anode surface had occurred during a period of six months operation of the cell.
Claims
1. An electrolytic cell comprising an anode and a cathode and a non-conducting shield supported therebetween adjacent and spaced from the anode at the point of entry of current thereto.
2. An electrolytic cell as claimed in Claim 1, wherein the shield is supported by having projections engageable with holes in the anode, to allow slight relative movement of the shield relative to the anode.
3. An electrolytic cell as claimed in Claim 1 or
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (5)
1. An electrolytic cell comprising an anode and a cathode and a non-conducting shield supported therebetween adjacent and spaced from the anode at the point of entry of current thereto.
2. An electrolytic cell as claimed in Claim 1, wherein the shield is supported by having projections engageable with holes in the anode, to allow slight relative movement of the shield relative to the anode.
3. An electrolytic cell as claimed in Claim 1 or 2, wherein the anode-shield spacing is from 1 to 2mm.
4. A electrolytic cell as claimed in Claim 1,2 ot 3, wherein the shield is made from plastics, for example methyl methacrylate.
5. An electrolytic cell substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8100680A GB2090865B (en) | 1981-01-09 | 1981-01-09 | Electrolytic anode protection |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8100680A GB2090865B (en) | 1981-01-09 | 1981-01-09 | Electrolytic anode protection |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2090865A true GB2090865A (en) | 1982-07-21 |
| GB2090865B GB2090865B (en) | 1983-11-30 |
Family
ID=10518901
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8100680A Expired GB2090865B (en) | 1981-01-09 | 1981-01-09 | Electrolytic anode protection |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2090865B (en) |
-
1981
- 1981-01-09 GB GB8100680A patent/GB2090865B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2090865B (en) | 1983-11-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |