GB2160546A - Electrolytic recovery of silver from photographic processing solution - Google Patents

Abstract

In the process the electrodes remain stationary while the solution is continuously agitated in their neighbourhood, the DC source and a power source for the agitation means are mounted together as a first unit, and placed out of contact with the solution in a vessel, and the electrodes and agitation means are mounted together as a second unit, operatively connected to the first unit, and placed in the solution in the vessel. The power source for agitating the solution is for preference air under pressure, creating a current of bubbles. <IMAGE>

Description

SPECIFICATION Process and apparatus for rejuvenating photographic processing solutions and recovering silver therefrom This invention relates to a process and apparatus for rejuvenating photographic processing solutions and recovering silver therefrom. It relates in particular to a simple process and a compact, convenient apparatus for carrying out these operations in small-scale photographic processing laboratories.

When a photographic processing solution, in particular a fixing solution, has been used for a certain length of time it loses its effectiveness and retards the speed of processing, partly due to the accumulation of silver in solution therein. Eventually the solution must be removed from the processing apparatus and replaced with a fresh batch.

Processes for recovering metallic sliver from spent photographic solutions are known, in particular processes employing electrolysis for this purpose. The necessary equipment, however, is complicated and expensive and usually includes at least one moving electrode such as a rotary cathode, and at least one purpose-built vessel for holding the solution being subjected to electrolysis.

Such recovery processes and apparatus are only economical when used in large-scale photographic processing laboratories. In smaller installations, which are becoming very common, the spent solutions tend to be discarded or sold very cheaply to scavenging contractors.

In conventional electrolytic recovery apparatus, moreover, the necessary agitation of the solution is commonly effected by means of rotating cathodes.

Since the cathodes tend to be heavy, the necessary mechanisms are often complicated and subject to frequent breakdown.

It is an object of the invention to alleviate some or all of the difficulties assosicated with conventional processes and apparatus for recovering silver from photographic solutions. Another object of the invention is to place at the disposal of smallscale photographic processing laboratories a simple process and compact, convenient apparatus for recovering silver from photographic processing solutions. A further object of the invention is to provide a process and apparatus for rejuvenating photographic processing solutions in the course of their use, whereby a single batch of such a solution can continue to be used efficiently for a period greatly in excess of its working lifetime under conventional conditions.

According to a first aspect of the invention, therefore, there is provided an electrolytic process for recovering metallic silver from a photographic processing solution wherein a vessel of the solution is associated with a pair of electrodes and a DC source, the process being characterized in that (a) the electrodes remain stationary with respect to the vessel for as long as the current flows, (b) the solution is continuously agitated in the neighbourhood of the electrodes by means other than said electrodes, (c) the DC source and a power source for the agitation means are mounted together as a first unit, and placed out of contact with the solution in the vessel, and (d) the electrodes and agitation means are mounted together as a second unit, operatively connected to the first unit and placed in the solution in the vessel.

Preferably the power source for agitation is a supply of air under pressure, and the agitation means converts the supply of air into a stream of air bubbles ascending through the solution. Preferably the agitation means is a tube located between anode and cathode, having a closed end and perforations in its cylindrical wall.

In a second aspect, the invention provides a process as recited above, wherein the photographic processing solution recycled between the vessel and a photographic processing machine, whereby the solution in the processing machine is continuously rejuvenated by removal of silver ions therefrom.

The invention also provides apparatus for recovering metallic silver from a photographic processing solution in a vessel, which apparatus comprises a DC source and a power source for agitation means mounted together as a first unit, a pair of stationary electrodes and agitation means mounted together as a second unit, and power transmission means for operatively connecting the units together, the first unit being adapted for convenient placement outside the vessel, and the second unit adapted for immersion in the solution in the vessel.

Lastly the invention provides apparatus as recited above, for the rejuvenation of a photographic processing solution in use, which additionally comprises means for recycling the photographic processing solution between a photographic processing machine and the vessel in which the second unit is placed.

Preferably the first unit is housed in a conventional cabinet, and can be powered by connection to an electrical AC mains supply. Preferably the second unit is enclosed in a cage through which the solution can easily penetrate and which is adapted to collect the silver and protect the electrodes against accidental mechanical damage.

The invention will be appreciated in greater detail from the following description of a particular and preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which Figure 1 is a schematic layout illustrating the process and apparatus of the invention in operation in conjunction with a conventional photographic processing machine, Figure 2 is a median sectional elevation of the second unit of the apparatus of the invention, taken along the line ll-ll and viewed in the direction of the associated arrows in Figure 3a, Figure 3a is a sectional plan view of the unit of Figure 2, taken along the line Ill-Ill in that figure and viewed in the direction of the associated arrows, Figure 3b is a cross-section of the tubular agitation means employed in the unit of Figure 2, on an enlarged scale, Figure 4a is an isometric view of the first unit of the apparatus of the invention, Figure 4b is a perspective view of the unit of Figure 4a with the control panel facing downwards and the cover removed, Figure 5a is an isometric view of the second unit of the apparatus of the invention, Figure 5b is an isometric view of the unit of Figure 5a with one of the protective shields removed to expose the interior, and Figure 6 is a circuit diagram of the apparatus of the invention.

Referring now to the drawings, the apparatus of the invention consists of a first unit 1 and a second unit 2. It is adapted to operate in conjunction with a tank 5.

The first unit 1 can be connected to an electrical AC power source by means of a conventional lead and plug 10. The first unit 1 is housed in a cabinet having a removable cover 1 a. The front of the unit 1 is a control panel presenting an on/off switch 14, an air supply pipe 16 and a pair of clamp terminals 15. Inside the unit 1 are housed a transformer 11, rectifying equipment 13, voltage and current regulating devices and programming circuitry, and an air pump 12.

The second unit 2 comprises a moulded plastics cage 21 having slidably removable shields 22 housed on opposed faces. These shields 22 are perforated by extended slots 23. Other parts of the cage 21 may also be perforated. A carbon anode 6 and a chrome steel cathode 7 are housed in the cage 21, the anode 6 being mounted on the top of the cage, and the cathode 7 mounted on the side thereof by means of a screw 7a. Said electrodes are connectable by leads 17 to respective clamp terminals 15 in the first unit 1. An agitator comprises a flexible plastics tube 8 bearing a plurality of radial perforations 8a and closed at the end by a screw 8b which additionally serves to anchor the tube 8 to the base of the cage 21.The tube 8 is disposed approximately midway between the anode 6 and the cathode 7 in the cage 21, and extends outside the cage for connection in use to the air pipe 16 of the air pump 12 in the first unit 1.

In use of the apparatus, the second unit 2 is placed standing in a tank 5 filled with photographic processing solution from which silver is to be extracted. The leads 17 and tube 8 are connected respectively to the clamp terminals 15 and air pipe 16 of the first unit 1. The plug 10 is then connected to a mains source, and voltage and current regulator means 31, 32 (Figure 6) are adjusted to effect electrolysis at a desired rate.

At invervals which may range from a few days to a few weeks the apparatus is de-energized, the second unit 2 removed from the tank and opened by removal of the shields 22, and the accumulated powdered metallic silver removed from the cage bottom 28 and the cathode for subsequent purification. The recovery cycle may then be set in operation once more.

In a preferred embodiment (Figure 1), a pump 4 is used to recycle processing solution from a photographic processing machine 3 to the tank 5 and back, and in this case the operating parameters are adjusted for optimum rejuvenation of the solution which continues to be used for photographic processing while the electrolysis is in operation.

Agitation is provided by a constant stream of bubbles which, as shown in Figure 1, rise from the perforations 8a in the tube 8 between the electrodes 6, 7 and effect continuous displacement of the solution between the electrodes. Thus the solution between said electrodes, although being depleted in silver ion content, is continuously replenished by solution from elsewhere in the tank 5.

It will be appreciated that any suitable vessel may be used in place of the tank 5, and that the first unit 1 can be placed away from said vessel on any convenient supporting surface such as a bench top. The second unit 2 is light, and its interior is easy of access, thus facilitating manual recovery of the deposited silver.

Claims (12)

1. An electrolytic process for recovering metallic silver from a photographic processing solution wherein a vessel of the solution is associated with a pair of electrodes and a DC source, the process being characterized in that (a) the electrodes remain stationary with respect to the vessel for as long as the current flows, (b) the solution is continuously agitated in the neighbourhood of the electrodes by means other than said electrodes, (c) the DC source and a power source for the agitation means are mounted together as a first unit, and placed out of contact with the solution in the vessel, and (d) the electrodes and agitation means are mounted together as a second unit, operatively connected to the first unit, and placed in the solution in the vessel.

2. A process as claimed in claim 1, characterized in that the power source for the agitation means is a supply of air under pressure, and in that the agitation means converts the supply of air into a stream of air bubbles ascending through the solution.

3. A process as claimed in claim 2, characterized in that the agitation means is a tube located between the anode and the cathode, having a closed end and perforations in its cylindrical wall.

4. A process as claimed in any of claims 1-3, characterized in that the photographic processing solution is recycled between the vessel and a photographic processing machine, whereby the solution in the processing machine is continuously rejuvenated by removal of silver ions therefrom.

5. Apparatus for recovering metallic silver from a photographic processing solution in a vessel, which apparatus comprises a DC source and a power source for agitation means mounted together as a first unit, a pair of stationary electrodes and agitation means mounted together as a second unit, and power transmission means for operatively connecting the units together, the first unit being adapted for convenient placement outside the vessel, and the second unit adapted for immersion in the solution in the vessel.

6. Apparatus as claimed in claim 5, characterized in that the power source for the agitation means is a supply of air under pressure, and in that the agitation means converts the supply of air into a stream of air bubbles ascending through the solution.

7. Apparatus as claimed in claim 5 or 6, characterized in that the agitation means is a tube located between the anode and the cathode, having a closed end and perforations in its cylindrical wall.

8. Apparatus as claimed in any of claims 5-7, additionally characterized by means for recycling the photographic processing solution between a photographic processing machine and the vessel in which the second unit is placed.

9. Apparatus as claimed in any of claims 5-8, characterized in that the first unit is housed in a cabinet and is adapted to be powered by connection to an electrical AC mains supply.

10. Apparatus as claimed in any of claims 5-9, characterized in that the second unit is enclosed in a cage through which the solution can easily penetrate, and which is adapted to protect the electrodes against accidental mechanical damage, and to collect the silver.

11. An electrolytic process as claimed in claim 1, substantially as herein described with reference to or as illustrated in the accompanying drawings.

12. Apparatus as claimed in claim 5, substantially as herein described with reference to or as illustrated in the accompanying drawings.