GB2316952A

GB2316952A - Portable electrolytic apparatus for recovery of silver

Info

Publication number: GB2316952A
Application number: GB9718960A
Authority: GB
Inventors: Trevor Anthony Roberts
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-09-05
Filing date: 1997-09-08
Publication date: 1998-03-11
Also published as: GB9718960D0

Abstract

An electrolytic apparatus for recovering metal from metal containing solutions, for example silver from photographic fixing solutions, comprises an apparatus arranged so as to be portable or semi portable and capable of being positioned within a container 12 containing the metal containing solution. The apparatus comprises chambers separated from one another, the first including a pump 24 and an outlet 26 for the solution to be treated and an outlet 28 for the treated solution, and the second discharge means 52 for the solution to be treated together with an anode 44 and a cathode 46.

Description

Recoverv of metals from metal containing solutions.

The present invention relates to the recovery of metal and in particular silver from metal containing solutions.

It is well known that the fixing solutions used in photochemistry contain significant quantities of silver halides, for example chloride and iodide. The metallic silver can be recovered from such solutions and recovery is usually either by metal substitution or electrolysis.

The present invention is particularly concerned with the electrolytic method of recovery.

Apparatus is known for the recovery of silver and used photochemicals using the electrolytic process in which the apparatus includes a container for the used photochemical and the normal components or carrying out an electrolytic process eg. an anode and a cathode arrangement and a supply of electrical energy. However such an apparatus tends to be relatively bulky and also expensive particularly for the small to medium sized photo laboratories.

The present invention seeks to provide a metal recovery apparatus and in particular an apparatus for recovering silver which the apparatus is portable or semi-portable and does not include a container for the used photochemicals.

Accordingly the present invention provides an electrolytic apparatus for recovering metal from metal containing solutions, for example silver from photographic fixing solutions, the apparatus arranged so as to be portable or semi-portable and capable of being positioned within a container containing the metal containing solution.

The apparatus can comprise two chambers separated from one another.

One of the chambers can include a pump and inlet for the solution to be treated and an outlet or outlets for the treated solution.

The other chamber can contain discharge means for the solution to be treated together with an anode and a cathode.

The discharge means can comprise one or more spray bars.

The anode can be in the form of an array of carbon rods.

Each of the carbon rods can be gripped by stainless steel springs.

The other chamber can also include a discharge duct which extends between the two chambers, the inlet to the discharge duct being located below the upper ends of the anodes.

The cathode means can be in the form of a stainless steel cylinder.

The cathode means can be located on a number of studs.

The apparatus can include a sealed unit which comprises the discharge means for the solution to be treated, the discharge duct for the treated solution, the array of anodes, the contact studs for the cathode and an electrical junction box.

The electrical energy supply can comprise a source of AC electrical power, a current density control, a transformer and a bridge rectifier.

The present invention will now be more particularly described with reference to the accompanying drawings, in which; Fig. 1 shows a diagrammatic representation of one form of electrolytic apparatus according to the present invention Fig.2 shows schematically the electrical power control, the sealed unit and the cathode of the apparatus shown in figure 1.

Referring to the drawing there is shown an electrolytic apparatus (10) which is positioned in a container (12) holding a used photochemical fixer (14).

The apparatus (10) comprises a housing (16) in which is located a sealed unit (18) the details for which are described below.

The sealed unit (18) divides the housing into lower and upper chambers (20 & 22), the lower chamber containing a submersible pump (24) having an inlet(26) and an outlet (28) for the solution to be treated and outlets (30 & 32) for the treated solution to exhaust back into the tank (12).

The lower chamber (20) also contains an epoxy resin filled junction box (34) to which is connected an electrical power input cable (36), a power cable (38) for the pump (24) and a cable (40) containing positive and negative supplies to the anode and cathode which forms part of the sealed unit (14).

The sealed unit (18) comprises a base (42) made from a non conducting material, an array of carbon rods (44) which form the anodes of the apparatus, a cathode (46) in the form of a stainless steel drum, an inlet tube (48) which terminates in a spray bar (50) and a discharge duct (52) for the treated solution which extends through the base (42).

The anodes (44) are each mounted in a self gripping stainless steel spring (not shown) within the base (42). The anodes are connected through the springs (not shown) to the positive supply in the cable (40).

The cathode (46) rests on stainless steel studs (54) which are connected to the negative supply of the cable (40).

Referring particularly to figure 2 the electrical power supply to the apparatus (10) comprises an AC input (56), a residual current detector (RCD) (58), a dimmer (60) to control current density and a transformer and rectifier (62). In one arrangement of the power supply, the dimmer is a 400W thyristor, the transformer has a 100VA value and the rectifier gives an output of 1.2V at approximately 3 amps DC. It has been found that with such a power supply and a flow rate of approximately 14 litres/minute through the pump (24), a silver recovery rate of 12.5gm/litre/hour can be achieved.

In use the sealed unit (18) is located within the housing (16) so that the tube (48) engages with the outlet (28) of the pump (24) and the junction box (34) is located in a recess provided in the sealed unit.

The apparatus (10) is then positioned within a tank of used photochemicals eg. a fixing solution which has been used for developing or printing with the level of the photochemical solution below the level of the studs (54). The electrical power is switched on to cause a current flow between the anode (44) and the cathode (46) and to cause the pump to operate and draw in solution to be treated through the inlet (26) and to exhaust the solution to be treated through the outlet (28). The solution flows through the tube (48) and the spray bar (50) to fill the upper chamber (22) to the level of the inlet of the discharge duct (52). The electrical current flow between the anodes (44) and the cathode (46) causes separation of the halides from the silver, and the silver is deposited on the cathode (46). The treated solution is discharged through he duct (52) from the upper chamber (22) into the lower chamber (20) and then through the outlets (30 & 32) back into the tank (12) so that there is a continuous recycling of the solution in the tank (12) through the apparatus (10). The process is continued until little or no silver containing halides remain in the solution (14).

When the silver recovery unit is switched on the power supply produces a voltage of 1.5 volts at 8 amps approximately. This electro motive force combined with the electrolyte flow which passes the cathode at a rate of approximately 25 litres per minute causes silver to plate the cathode at a very efficient rate.

As the plating progresses the conductivity of the electrolyte reduces until a point where all of the silver or virtually all of the silver has been removed from the electrolyte.

The EMF produced by the cathode and anode which is approximately 1.7 to 1.0 volts cancels out the current produced by the power supply causing the silver recovery unit to effectively cease collecting silver from the electrolyte.

Any suitable apparatus can be used for detecting the level of silver remaining in the solution (14).

A very simple method of determining how much silver is left in the electrolyte can be achieved by using a strip of polished copper approximately half an inch wide by six inches long. The polished copper strip is dipped into the electrolyte containing the silver salts. These salts immediately turn the copper a blue colour if the silver content of the electrolyte is high.

However if the silver content is zero the copper is uneffected.

It has been found that this method of measurement can detect the presence of silver resulting from one 24 exposure film in ten litres of photographic fixer.

It will be appreciated that the apparatus according to the present invention has been constructed so as to be portable or at least semi-portable so that it can be assemble and located within any suitable tank for containing used photochemicals.

An apparatus according to the present invention a voids the need for electrolytic separation apparatus in which the tank is combined with that part of the apparatus which performs the electrolytic function.

The use of a spray bar or more than one spray bar as required causes considerable turbulence in the electrolyte. It is believed that this action helps to prevent the build up of iodide or chloride ions, and sulphides.

Also the provision of an anode in the form of a number of carbon rods has been found to be beneficial for the following reasons:a). Greater turbulence is created in the electrolyte, b). The rods are self cleaning thereby reducing anode wear, c). The arrangement of the rods in a circular pattern, allows for the provision of a central outlet duct. Such an arrangement means that there is only a small obstruction, in the form of the spray bar, in the electrolyte. This allows for the almost unobstructed flow of current between the anodes and the cathode, and d). the rods are cheap.

It has been found in practice by omitting a smoothing capacitor from the power supply, the combination of the DC output and the unsmoothed AC ripple allows the silver to be readily removed from the cathode. Such an arrangement also appears to self regulate the current flow between the anodes and the cathode.

A further feature of an apparatus according to the present invention is that the power supply appears to be self-regulating in that the power supply does not have to be pre-set depending on the type of photochemical which makes up the electrolyte.

Claims

1. An electrolytic apparatus for recovering metal from metal containing solutions, for example silver from photographic fixing solutions, the apparatus arranged so as to be portable or semi portable and capable of being positioned within a container containing the metal containing solution.

2. An apparatus as claimed in claim 1 comprising two chambers separated from one another.

3. An apparatus as claimed in claim 2 in which a first one of the chambers can include a pump and an inlet for the solution to be treated and an outlet or outlets for the treated solution.

4. An apparatus as claimed in claim 2 or claim 3 in which the second one of said chambers contains discharge means for the solution to be treated together with an anode and a cathode.

5. An apparatus as claimed in claim 4 in which the discharge means comprises one or more spray bars.

6. An apparatus as claimed in claim 4 in which the anode can be in the form of an array of carbon rods.

7. An apparatus as claimed in claim 6 in which each one of the rods is gripped by a stainless steel spring.

8. An apparatus as claimed in claim 4 in which the second one of said chambers can include a discharge duct which extends between the two chambers, the inlet to the discharge duct being located below the upper ends of the anodes.

9. An apparatus as claimed in claim 4 in which the cathode can be in the form of a stainless steel cylinder.

10. An apparatus as claimed in claim 9 in which the cathode is located on a number of studs.

11. An apparatus as claimed in any one of the preceding claims including a sealed unit which includes the discharge means for the solution to be treated, the discharge duct for the treated solution, the array of anodes, the contact studs for the cathode and an electric junction box.

12. An apparatus as claimed in any one of the preceding claims including an electrical energy supply comrising a source of AC electrical power, a current density control, a transformer and a bridge rectifier.

13. An electrolytic apparatus for recovering metal from metal containing solutions constructed and arranged for use and operation, substantially as herein described, and with reference to the accompanying drawing.