GB2132635A

GB2132635A - Regeneration of photographic fixing agents

Info

Publication number: GB2132635A
Application number: GB08329201A
Authority: GB
Inventors: Gonzalez Manuel Gomez
Original assignee: RECUPERACION DE METALES PRECIO
Current assignee: RECUPERACION DE METALES PRECIO
Priority date: 1982-11-02
Filing date: 1983-11-02
Publication date: 1984-07-11
Also published as: IT8368114A0; FR2535476A1; GB8329201D0; BR8306127A; MA19945A1; DE3339263A1

Abstract

Fixing agents are regenerated, for re-use in the processing of photographic film, by electrolysis 12 to disassociate argento-thiosulphate, recover silver and restore thiosulphate to solution and passing the resulting solution through ion exchange resin cartridges 15, 16 to remove bromide ions. The regenerated fixing agent is recycled directly to the fixing trough 4 of the film processing apparatus or, under the control of a valve responsive to the level of liquid in the electrolytic tank, to a storage tank 9. The high yield obtainable in the recovery of silver increases the useful life of the recycled fixing agent by about 15 times. Pollution is also reduced. <IMAGE>

Description

SPECIFICATION Regeneration of photographic fixing agents This invention relates to the regeneration and recycling of fixing agents for re-use in the processing of photographic films.

The processing of photographic films and paper, using an emulsion based on silver halide comprises two completely distinct steps: 1. Developing: wherein the halide of the photographic emulsion is reduced to silver in zones which have been exposed to light.

2. Fixing: wherein all the non-developed silver halide is chemically dissolved in this solution.

Photographic fixing agents generally comprise, for the main part, sodium or ammonium thiosulphate, the kinetics of the chemical reaction being as follows: BrAg+2S2O3Na2# [ Ag(S2O3)2j Na3+ BrNa While the films are being processed, the amount of thiosulphate available in the solution diminishes, with the result that the fixing capacity thereof is diminished.

At present this decrease in fixing capacity is avoided, particularly in automatic processes, by adding a certain amount of new fixing agent for each processed plate and draining comparable amounts of agent solution. This system establishes a predictable consumption of fixing agent per unit of processed film surface, the consumption varying from one piece of equipment to another.

Conventional equipment is capable only of recovering the silver which the discarded fixing agent contains and this is achieved by electrolysis -of the fixing agent which, in the absence of automatic control of the current intensity gives rise to two main defects: namely sulphurisation of the silver deposited on the cathode and low recovery yield.

Furtheremore conventional equipment, whether automatic or manual utilizes fixing agent, which is not recovered but simply discharged to waste.

An object of the present invention is to recover photographic fixing agents for re-use under optimum conditions.

In accordance with the present invention we propose a method of regenerating fixing agent for re-use in the processing of photographic films and comprising the steps of electrolysing the used fixing agent to dissociate argento-thiosulphate contained therein, recover the silver and restore the thiosulphate to solution, and passing the resulting solution through an ion-exchange resin cartridge to remove bromine or bromide ions.

We also propose apparatus for regenerating fixing agent for re-use in the processing of photographic films, comprising an electrolytic tank for receiving used fixing agent and recovering silver therefrom as a deposit on the cathode, and one or more ion exchange resin devices connected to the electrolytic tank for receiving the solution resulting from electrolysis and adapted to remove bromine and/or bromide ions from solution thereby to produce fixing agent ready for re-use.

The invention also includes apparatus for processing photographic films and comprising a fixing tank or trough connected to a storage tank containing a supply of fixing agent, in combination with such regenerating apparatus.

The solution resulting from electrolysis may be passed directly to the fixing tank or trough and/or to the storage tank as required. In the preferred embodiment, regenerated fixing agent flows constantly to the fixing tank or trough, any excess thereof being diverted to the storage tank by a control valve responsive to the level of liquid in the electrolytic tank.

It is preferred to agitate the liquid in the electrolytic tank violently and to this end an agitating pump is provided to draw liquid, preferably through a filter, from and discharge liquid into the electrolytic tank, a portion of the agitating pump outlet being delivered to the recycling conduit means.

Following electrolysis, the only remaining contaminants (molecular bromide and sodium bromide) are removed by ion exchange using any suitable ion exchange resins known to those skilled in the art.

Sulphurisation of the deposited silver can be prevented by incorporating in the electrolytic tank a colour detecting gauge (since the layer of deposited silver turns black when sulphurised) which by an electronic system modulates the current intensity in the tank.

Since the electrolytic tank operates in a closed and not an open circuit, a complete yield is obtained in the recovery of silver. Such operation is possible by tapping-off a part of the flow from the agitation pump to recycle the liquid from the fixing tank, and since a certain amount of fresh fixing agent is delivered from the storage tank to the fixing tank or trough in an automatic processing machine, each time a photographic plate is developed, the leveling valve which is preferably located on the end of an agitation tube passing into the tank, acts to ensure that excess liquid passes to the storage tank, duly regenerated and filtered.

Since it is primarily the silver concentration which destroys the effectiveness of the fixing agent, complete recovering of the silver in accordance with the invention enables the useful life of the fixing agent to be increased by at least ten times.

One disadvantage of conventional apparatus is that it is bulky and expensive to manufacture being parallelepiped in shape and formed of welded PVC plates.

In the preferred embodiment of this invention, the electrolytic tank comprises a tubular body of PVC so that the apparatus can be made more compact, the cylindrical shape enabling a greater tank capacity for a given cathode surface area. As the necessary electronic control equipment and agitating pumps may be separated from and preferably located beneath the electrolytic tank, corrosion and oxidation problems are avoided.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic illustration of an automatic photographic developing machine; and Figure 2 is a perspective view of an electrolytic tank.

The film on entering the developing machine of Figure 1 passes through an inlet 1 to a developing bath 2 and from there through a stopping bath 3 to a fixing bath 4, a rinsing bath 5 and hot air drying station 6. Developer is supplied by a pump 8 from a storage tank 7 to the developing bath 2 and a measured amount of fixing agent is supplied periodically (i.e. each time a plate is developed) by a proportioning pump 10 from a storage tank 9 to the fixing bath 4.

The level of fixing agent in tank 12 is limited by an overflow 11 from which excess liquid drains to an electrolytic tank 12 for removing silver from the fixing agent, and connected by conduits 13 and 14 each incorporating ion exchange resin cartridges 15 and 1 6, respectively to the storage tank 9 and directly to the fixing bath 4 for recycling thereto recovered fixing agent.

The electrolytic tank 12, shown in more detail in Figure 2, has a tubular body 17 of PVC material supporting a cylindrical cathode 19 arranged concentrically with a central anode 18 and within which used fixing agent is received from the fixing tank or trough along the overflow pipe 11. At the lower end of the cylindrical cathode is a filter 20 through which the fixing agent is drawn by an agitating pump 21 into a pipe 22, enabling constant circulation and creating agitation of the liquid in the tank.

A portion of the flow passing through the pipe 22 is tapped-off via an outlet 14 from the head of the pipe 22 which is connected (not shown) to the conduit 14 (Figure 1) leading via ion exchange resin cartridge 16 to the fixing tank or trough 4, to recycle reconditioned fixing agent for combination with fixing agent supplied by the pump 10 from the reserve or storage tank 9.

It will be appreciated that each time the proportioning pump delivers a measured quantity of fixing agent from the storage tank 9, the same amount of liquid flows along the overflow pipe 11 to raise the level of fixing agent in the electrolytic tank 12. Should this level rise to the top of the tube 22, a float valve 23 operates to open outlet 13 connected (not shown) to the conduit 13 incorporating the ion exchange resin cartridge 15, so that reconditioned fixing agent is also delivered to the storage tank 9.

The current density is controlled during electrolysis by an electronic controller 24 responsive to a photometric gauge 25 within the tank. By this means sulphurisation of the silver is avoided.

For flushing and cleaning the tank 12 a drainage pipe 26 is provided.

With the arrangement described above, the fixing agent is regenerated since the contaminating products incorporated therein in suspension are eliminated, whereby it is restored to its original condition and is suitable for re-use.

Substantial savings result since the useful life of the fixing agent is increased about 15 times, without altering its effectiveness. Also, there is a substantial reduction in pollution by the discharge of chemical into municipal drains.

Claims

1. A method of regenerating fixing agent for reuse in the processing of photographic films and comprising the steps of electrolysing the used fixing agent to dissociate argentothiosulphate contained therein, recover this silver and restore the thiosulphate to solution, and passing the resulting solution through an ion-exchange resin means to remove bromine or bromide ions.

2. A method according to claim 1 wherein the used fixing agent is supplied from a fixing tank or trough forming part of the film processing apparatus and connected to a storage tank containing supply of fixing agent, and wherein the solution resulting from electrolysis is passed through the ion exchange resin means either to the storage tank or directly to the fixing tank or trough.

3. Apparatus for regenerating fixing agent for re-use in the processing of photographic films, comprising an electrolytic tank for receiving used fixing agent and recovering silver therefrom as a deposit on the cathode, and one or more ion exchange resin devices connected to the electrolytic tank for receiving the solution resulting from electrolysis and adapted to remove bromine and/or bromide ions from solution thereby to produce fixing agent ready for re-use.

4. Apparatus for processing photographic film and comprising a fixing tank or trough connnected to a storage tank containing supply of fixing agent, an electrolytic tank for receiving used fixing agent from the fixing tank or trough and in which silver is recovered from the used fixing agent, and conduit means for conveying the solution resulting from electrolysis in the electrolytic tank either directly to the fixing tank or trough or to the storage tank, the conduit means incorporating one or more ion exchange resin devices for removing bromine and/or bromide ions from the said solution thereby to produce fixing agent ready for re-use.

5. Apparatus according to claim 4 wherein flow through the conduit means leading to the storage tank is controlled by a valve responsive to the level of liquid in the electrolytic tank.

6. Apparatus according to claim 4 or claim 5 wherein the electrolytic tank comprises an agitating pump draining liquid from and discharging liquid into the tank, and is connected to deliver a portion of its outlet flow to the conduit means.

7. Apparatus according to claim 6 and comprising a filter through which liquid is drawn to the agitating pump.

8. Apparatus according to any one of claims 3 to 7 and comprising control means responsive to a Sensor in the electrolytic tank, for modulating the current intensity to prevent sulphurisation of silver on the cathode.

9. Apparatus for regenerating fixing agent for re-use in the processing of photographic films constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of regenerating fixing agent for re-use in the processing of photographic films, substantially as hereinbefore described with reference to the accompanying drawings.