GB2078782A - Agitating Photographic Fix Solutions in Electrolytic Recovery of Silver Therefrom - Google Patents

Abstract

The top edge of a cathode plate 14 is fixed to a horizontal shaft just above the solution 12 in a container of used fix solution and the plate is caused to oscillate about the shaft centre in the manner of a pendulum, causing a pressure difference to occur in the body of the solution between one side of the plate and the other. As the liquid flows around the edges of the plate to correct this difference at each oscillation, vortices are induced in the liquid which vigorously agitate the surface of the plate. <IMAGE>

Description

SPECIFICATION Silver Recovery Agitation System In the photographic process only a part of the silver present in the emulsion coating is used to form the permanent image. That part which is not thus used is dissolved out into the fix or/and bleach solutions as silver ions, depending on whether black and white or colour film or paper is being processed. The presence of these silver ions in increasing quantity reduces the efficiency of the fixing process and, if disposed of in drainage systems, is a severe pollutant and is a waste of a valuable commodity. For this reason silver recovery devices are used to remove these siver ions from solution.

Two types of recovery are common, one using ion exchange technique, the other using electrolysis.

This patent is concerned with that type of recovery using electrolysis. Commonly the electrolytic recovery system consists of a container to hold the electrically conducting fix solution, an anode of a corrosion resistant conductor such as carbon and a cathode often of stainless steel, together with an external D.C.

voltage supply. When the D.C. current is applied across the anode and cathode silver ions migrate to the cathode and are plated on to it as metallic silver.

It is advantageous to agitate the solution during this process by movement of the anode or cathode or a separate pump or agitator or a combination of these. This is often achieved by a continuously rotating cathode. This prevents the formation of silver sulphide in the fix solution which may occur if the solution adjacent to the cathode becomes denuded of silver ions, as this spoils the fix solution for re-use and contaminates the silver plate. With agitation a higher recovery current may be used without sulphiding. Once a heavy plate is collected the cathode must be removed from the container and the silver broken from it.

Many of the present cathode constructions used to agitate the liquid are complex and not easy to remove from the apparatus.

This invention is concerned with means of agitating the fix container by use of a flat cathode plate which can subsequently be removed easily for breaking off the silver.

Reference to the drawings gives a better understanding of the invention.

Fig. 1 is a side section view of the silver recovery container.

Fig. 2 is a top view of the same container.

Fig. 3 shows a section through a similar system with more than one cathode plate.

In Fig. 1: No. 11 is the solution container.

No. 12 is the fix or bleach fix solution contained in it.

No. 13 is the anode or anodes which may be fitted both sides of the cathode No. 14.

In Fig. 2: No. 7 is a gap at least at one end of the cathode between the cathode and the side wall of the tank.

In use the tank may be filled with solution to any level. The cathode is made to oscillate in directions 15, 16 pivoting at 17 in the manner of a pendulum. Movement in the direction 15 causes an increase in solution pressure on that side causing a flow of liquid through gap 7 and formation of a vortex on side 16 with subsequent vigorous agitation of the whole body of solution and most particularly adjacent to the cathode surface. On the return swing the reverse action occurs.

The pivot 17 is generally positioned above the solution level and the cathode plate can be detached at this point by releasing wing nut 18.

Insulating blocks are fitted at position 19 to prevent any possibility of the anode and cathode touching.

Fig. 3 shows a similar tank with two cathode plates.

Speeds of oscillation up to 60 per minute have been used.

When the plate moves in direction 15 vortices occur in the liquid at 19 and vice versa when moving in the opposite direction. The liquid flow causes the vortices to move towards the centre of the plate.

Claims

1. A means of agitating the liquid in a silver recovery system by which the cathode is caused to oscillate about a fixed horizontal axis in the manner of a pendulum, causing the liquid pressure to increase on one side of the plate and to decrease on the opposite side of the plate with subsequent flow of liquid from one side of the plate to the other causing vortices to agitate the cathode surface.

2. A silver recovery agitation system as in Claim 1 with anode and cathode connections reversed.

3. A silver recovery agitation system as in Claim 1 but with two or more oscillating plates.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Silver Recovery Agitation System In the photographic process only a part of the silver present in the emulsion coating is used to form the permanent image. That part which is not thus used is dissolved out into the fix or/and bleach solutions as silver ions, depending on whether black and white or colour film or paper is being processed. The presence of these silver ions in increasing quantity reduces the efficiency of the fixing process and, if disposed of in drainage systems, is a severe pollutant and is a waste of a valuable commodity. For this reason silver recovery devices are used to remove these siver ions from solution. Two types of recovery are common, one using ion exchange technique, the other using electrolysis. This patent is concerned with that type of recovery using electrolysis. Commonly the electrolytic recovery system consists of a container to hold the electrically conducting fix solution, an anode of a corrosion resistant conductor such as carbon and a cathode often of stainless steel, together with an external D.C. voltage supply. When the D.C. current is applied across the anode and cathode silver ions migrate to the cathode and are plated on to it as metallic silver. It is advantageous to agitate the solution during this process by movement of the anode or cathode or a separate pump or agitator or a combination of these. This is often achieved by a continuously rotating cathode. This prevents the formation of silver sulphide in the fix solution which may occur if the solution adjacent to the cathode becomes denuded of silver ions, as this spoils the fix solution for re-use and contaminates the silver plate. With agitation a higher recovery current may be used without sulphiding. Once a heavy plate is collected the cathode must be removed from the container and the silver broken from it. Many of the present cathode constructions used to agitate the liquid are complex and not easy to remove from the apparatus. This invention is concerned with means of agitating the fix container by use of a flat cathode plate which can subsequently be removed easily for breaking off the silver. Reference to the drawings gives a better understanding of the invention. Fig. 1 is a side section view of the silver recovery container. Fig. 2 is a top view of the same container. Fig. 3 shows a section through a similar system with more than one cathode plate. In Fig. 1: No. 11 is the solution container. No. 12 is the fix or bleach fix solution contained in it. No. 13 is the anode or anodes which may be fitted both sides of the cathode No. 14. In Fig. 2: No. 7 is a gap at least at one end of the cathode between the cathode and the side wall of the tank. In use the tank may be filled with solution to any level. The cathode is made to oscillate in directions 15, 16 pivoting at 17 in the manner of a pendulum. Movement in the direction 15 causes an increase in solution pressure on that side causing a flow of liquid through gap 7 and formation of a vortex on side 16 with subsequent vigorous agitation of the whole body of solution and most particularly adjacent to the cathode surface. On the return swing the reverse action occurs. The pivot 17 is generally positioned above the solution level and the cathode plate can be detached at this point by releasing wing nut 18. Insulating blocks are fitted at position 19 to prevent any possibility of the anode and cathode touching. Fig. 3 shows a similar tank with two cathode plates. Speeds of oscillation up to 60 per minute have been used. When the plate moves in direction 15 vortices occur in the liquid at 19 and vice versa when moving in the opposite direction. The liquid flow causes the vortices to move towards the centre of the plate. Claims

1. A means of agitating the liquid in a silver recovery system by which the cathode is caused to oscillate about a fixed horizontal axis in the manner of a pendulum, causing the liquid pressure to increase on one side of the plate and to decrease on the opposite side of the plate with subsequent flow of liquid from one side of the plate to the other causing vortices to agitate the cathode surface.

2. A silver recovery agitation system as in Claim 1 with anode and cathode connections reversed.

3. A silver recovery agitation system as in Claim 1 but with two or more oscillating plates.