LT4298B - Method for electrolytic recovery of silver and electrolyzer - Google Patents

Abstract

This invention describes an electrolytic method and device for regenerating silver, by which silver is deposited on the electrode, placed into an electrolytic solution through a process of electrolysis. In the cathode environment, where the deposition takes place, a constant turbulent-whirling flow of solution is generated, and the layer of silver, deposited on the cathode during the electrolysis, is mechanically supported; this enhances the efficiency of silver regeneration and the convenience of using the device.

Description

BACKGROUND OF THE INVENTION The present invention relates to an electrolytic method for recovering metal and to an apparatus for realizing this method, namely, a method for recovering silver from spent photographic solutions and an electrolyzer for use in this method.

There is a known method of electrolytic silver regeneration in which silver is deposited on the electrolytic solution by passing it through a volumetric cathode.

An electrolyser for this embodiment is known, having a bath with an electrolytic solution inlet and outlet, coupled to an electrolytic solution reservoir, a volumetric cathode and anode in the bath, including a semipermeable membrane, and the volumetric electrodes consisting of a packet of sandwiched stainless steel. mesh meshes (see French Patent No. 2573221, G 03 C 5/395; C 25 C 1/20).

The disadvantages of the known electrolytic silver regeneration method and the electrolyser for its realization are the following:

- volumetric cathodes can become clogged as the silver coatings of adjacent layers increase, resulting in a limited lifetime of unused silver cathode package potential;

- it is difficult to remove the silver without damaging the fine meshes of the stainless steel cathodic package (silver brushed).

The closest technical solution is the known electrolytic recovery of silver, where silver is deposited on the flat cathode by electrolysis from the electrolytic solution.

An electrolyzer of this embodiment is known, having a bath with an electrolytic solution inlet and outlet, coupled to an electrolytic solution reservoir, and having a flat anode in the bath, including a flat cathode separated from the anodes by a semipermeable membrane, respectively , which allows the electrolytic solution to move around the cathode (see German Pat. No. 2534920, G03C 11/24).

The disadvantages of the known electrolytic silver regeneration method and the electrolyser for its realization are the following:

- long-term uninterrupted operation is not possible because the silver deposited on the flat cathode is in the form of a bulk precipitate, which, as the silver layer grows, falls off the cathode and gradually stops or even completely blocks the circulation of the solution as it accumulates in the bottom. Thus, the silver in the electrolyser of this design must be frequently cleaned, which requires the disassembly and assembly of the electrolyser, i. y. a lot of hard work, which makes its operation awkward and expensive;

- due to insufficient intensity of solution mixing in the cathode working surface environment, the rate of silver recovery is low and low residual silver concentrations in the electrolytic solution cannot be achieved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a convenient and inexpensive electrolytic silver regeneration process and device that allows deposition of silver from spent photographic solutions to produce a bulky, thick, easy-to-remove flat cathodic silver layer and to increase silver deposition rates.

The essence of the invention is that in an electrolytic silver regeneration process, when silver is electrolyzed from an electrolytic solution, it flows through a flat cathode and generates a constant turbulent turbulent flux in the cathode environment where the silver is deposited, during mechanical retention.

Creating a constant turbulent-vortex flow of the solution results in vigorous mixing of the electrolyte in the cathode environment where the silver deposition takes place, while significantly increasing the efficiency of silver recovery by ensuring a low residual concentration of silver in the solution after regeneration. The mechanical retention of the growing silver layer on the cathode during electrolysis facilitates the operation of the electrolyser, since a light, thick layer of silver is formed on the cathode which does not need to be removed frequently and is simple and does not require complicated equipment.

The electrolytic silver regeneration process thus provided according to the invention can:

- to obtain a lean, compact 0.6 - 0.9 cm thick, 5 - 7 kg. (cathodic block) with a silver plating content> 99% purity

- obtain a residual silver concentration of <10 mg / l in solution (without use of bulk working volume cathodes).

To solve the above problem, the proposed electrolyser having a bath with an electrolytic solution inlet and outlet connected to the electrolytic solution reservoir has at least two anodes in the bath, including a flat cathode separated from the anodes by a semipermeable membrane located on either side of the cathode, respectively. a cathode assembly comprising a semi-permeable first and second membranes separating the cathode from the anode and an insulating material in a frame, comprising first and second cathodic cavities sealed on either side of the cathode, respectively. a turbulator is placed to create a turbulent vortex flow of solution at the cathode surface, and a clamping device that mechanically holds the silver layer growing during electrolysis on the working surface of the cathode, at one end of the cathodic block, the first and second cathodic cavities communicate with one another, and at the other end of the block, the frame has openings for delivering electrolytic solution to and from the second cathodic cavity, respectively.

To improve the silver regeneration process by creating a turbulent-vortex flow of solution, as well as providing a non-volatile, compact silver sediment growth, said turbulator, housed in each cathodic cavity, comprises a flexible corrugated plastic sheet secured at the respective ends of the frame to , contacting the tops of the waffles with the silver layer growing on this surface during the electrolysis and interacting with the clamping means that ensures the contact of the tops of the waffles with the silver layer during the operation of the electrolyzer.

The clamping means comprises a porous, reversibly compressible, plastic gasket that fills a cathodic cavity in the first cathodic cavity between the turbulator and an additional semipermeable membrane embedded in a frame parallel to the first membrane, leaving a gap between the supplied electrolyte and the cathodic cavity the space between the turbulator therein and the second membrane, leaving only a small unfilled cavity at the outlet.

To increase the efficiency of silver recovery in the electrolyzer, the electrolyser bath is connected to the solution inlet and outlet ports and the cathodic unit is connected to the different electrolytic solution reservoirs through the solution supply and outlet ports.

Detailed Description of the Invention The present invention will be explained in more detail by the drawings which schematically depict the electrolyzer and its parts.

Fig. 1 is a schematic view of an electrolyzer;

Fig. 2 is a longitudinal sectional view of the cathode assembly;

Fig. 3 is a side view of the cathode assembly of Fig. 2;

Fig. 4 is a top view of the cathode assembly of Fig. 2;

Fig. 5 is a view of a segment of a turbulator plate.

The proposed electrolytic silver regeneration process has the following sequence of operations: the electrolytic solution, in this case the spent photographic solution, is passed through an electrolytic bath in which an electrolytic silver is deposited on a flat cathode in the bath and a continuous turbulent flow of solution, while mechanically supporting the silver layer on the cathode during electrolysis.

The electrolyzer implementing the present silver recovery method is schematically illustrated in Fig. 1. The electrolyzer comprises a bath 1 containing anodes 2 spaced parallel to each other, spaced apart by cathode blocks 3. The cathode unit 3, the longitudinal section of which is shown in Fig. 2, has a flat cathode 4 fixed in an insulating material frame 5 between two semipermeable membranes 6 and 7 mounted in frame 5 to form closed first cathodic cavity 8 and second cathodic cavity 9. Each cathodic cavity 8 and 9 are respectively provided with turbulators 10 and 11. The turbulator, the segment of which is shown in Fig. 5, is flexible, corrugated plastic sheet. The turbulators 10 and 11 are housed in respective cathodic cavities 8 and 9 such that each of them covers the respective working surface of the cathode 4 in contact with the tops of its corrugations. In the first cathodic cavity 8, a porous, elastic plastic gasket is housed

12, which fills the cathodic cavity between the turbulator 10 and the additional semipermeable membrane 13 mounted in a frame 5 parallel to the first lateral membrane 6, leaving a gap 14 therebetween to move the feed electrolyte toward cathode cavities 8 and 9 through cavity 15 in cathode 4. a cavity 9 housed in cavity 9 fills the cavity between the turbulator 11 and the lateral second membrane 7, leaving only a small unfilled cavity 17 at the outlet. All anodes and cathodes are connected to their respective DC inlets (not shown). In the upper part of the cathode unit 3, the supply and outlet openings of the frame 5 are provided with respective supply nozzles 18 for supplying the electrolytic solution to the first cathodic cavity 8 and discharge nozzles 19 from the second cathodic cavity 9. The reservoir 21 of the electrolytic solution 20, in this case the used photographic solution, is sealed by a cap 22, hydraulically connected to a manifold 25 via a pump 23, a rotometer 24 which is hermetically sealed with respective flexible plastic tubes 26 fittings 18. The outlet fittings 19 of each cathode unit 3 are hermetically connected to a manifold 28 by means of flexible tubes 27, the outlet of which through the tap 29 is hermetically connected to a reservoir 21 located below the level of the bath. In addition, manifold 28 is hydraulically connected via tap 30 to reservoir 32 of anolyte 31, sealed by cap 33. Exit of reservoir 32 located above bath level 1 is connected via tap 34 to bath 1 supply port 35. Bathtub 1 outlet port 36 via cementing column 37 connected to sewerage system 38.

Operation of the electrolyser according to the invention. the electric power to the electrolyser is switched on (not shown in the drawing). Electrolytic silver deposition in the electrolyser bath 1 located in cathode units 3 is carried out using anodes 2 and anolyte (regenerated spent photographic fixative and bleaching solution mixture) 31 which, through the tap 34, flows into the bath 1. Regenerating electrolytic solution 20, in this case a spent photographic solution (such as a fixative solution or a mixture of fixative and bleaching solution) is fed from reservoir 21 by means of a pump 23 via a rotator 24 to a manifold 25, from which flexible plastic tubes 26 enter the first cathode cavities 8 of cathode units 3 the solution 20 entering the first cathodic cavity 8 of the cathode assembly 3, fills it and moves downwardly in communication with the second cathodic cavity 9 through a notch 15 in the cathode 4 through which the solution enters the second cathodic cavity 9 and rises therethrough. As the regenerated solution 20 flows through corrugated borehole turbulators 10 and 11 at the working surfaces of the cathode 4, a constant turbulent vortex flow of the solution is created, i. y. the solution is stirred vigorously. The created turbulent-vortex flow of the solution intensifies the rate of silver regeneration, which settles on the 4 working surfaces of the cathode. In the first cathodic cavity 8, the pressure created between the semipermeable membranes 6 and 13 presses the membrane 13, which continuously presses the turbulator 10 at the cathode 4 through the porous gasket 12 (e.g., the foam). a layer of silver growing on the working surface of the cathode 4, and the y holds. In the second cathodic cavity 9, the electrolytic solution 20 is pumped upwardly by the principle of contacting vessels, since the reservoir 21, where the solution 20 flows from the cathodic unit 3, is below the level of the bath. The suction force acting on the contacting vessels draws the electrolytic solution 20 from the second cathode cavity 9 through the outlet nozzles 19, the flexible plastic tubes 27, the manifold 28 with the tap 30, the tap 29 back to the reservoir 21. This semiconductive membrane 7 is operated by this pulling force. the porous gasket 16 presses the turbulator 11 with the tops of the corrugations to the working surface of the cathode, on which the layer of deposited silver grows. The silver layer on the cathode 4 pushes the turbulators 10 and 11, which come into contact with the tops of the waffles to the new position). The elastic, soft porous gaskets 12 and 16, pressed by the turbulators 10 and 11, respectively move away from the surface of the cathode 4. In this way, the gap between the surface of the cathode 4 and the turbulator remains the same throughout the process. The porous gaskets 12 and 16 prevent the solution from flowing between the membranes 7 and 13 and the turbulators 11 and 10 by chance, i. y. causes the solution to flow only between the cathode 4 and the turbulators 10 and 11, under which the solution is stirred vigorously. After regeneration of silver, screw taps 29 and 34, screw screw 30 and pump solution from tank 21 are pumped into a tank 32 in which it is already stored as anolyte 31. Then screw taps 29 and 34, screw screw 30 and tank 21 are filled with a new used photographic solution for regeneration. and the regeneration cycle is repeated again. The anolyte 31 is continuously renewed during the electrolysis by discharging it in a certain flow from the reservoir 32. The excess anolyte used is discharged through the discharge port 36 into the cementation column 37, from which the silver is finally discharged into the sewer 38.

Claims (5)

DEFINITION OF INVENTION 1.Electrolytic recovery of silver, where silver is deposited on a flat cathode by electrolysis from an electrolytic solution, characterized in that it produces a steady-state turbulent-turbulent solution flow in the cathode environment where the silver is deposited. mechanically holds the silver layer of the cathode. 2.An electrolyzer having a bath with an electrolytic solution inlet and outlet and connected to an electrolytic solution reservoir, having at least two anodes in the bath, including a flat cathode separated from the anodes by a semipermeable membrane located on either side of the cathode, moving the solution in the cathode environment, characterized in that the cathode is housed in a cathode assembly consisting of a semipermeable first and second membrane separating the cathode from the anode and an insulating material in a frame forming first and second cathodic cavities respectively on both sides of the cathode, each containing a turbulator to create a turbulent-vortex flow of solution at the cathode surface, and a clamping device that mechanically holds down the silver layer growing on the cat during electrolysis the skin working surface, at one end of the cathodic block, the first and second cathode cavities communicate with one another, and at the other end of the block, the frame has openings for supplying and discharging electrolytic solution to the first cathodic cavity, respectively. 3. Electrolyzer according to claim 2, characterized in that the turbulator is formed by a flexible corrugated plastic sheet, inserted in the cathodic cavity so as to cover the entire working surface of the cathode by contacting the tops of the waffles with the silver layer growing on this surface during electrolysis. means for ensuring said contact of the waffle tops with the silver layer during electrolyser operation. 4, The electrolyzer of claim 2 wherein the clamping means comprises a porous, elastic plastic gasket that fills a cathodic cavity in the first cathodic cavity between the turbulator and an additional semipermeable membrane mounted in a frame parallel to the first membrane, leaving a gap therebetween and said second cathodic cavity fills said cavity between the turbulator therein and the second membrane, leaving only a small unfilled cavity at the outlet. 5. An electrolyzer according to claims 2 to 4, characterized in that the electrolyzer bath is connected to different electrolytic solution reservoirs through the solution inlet and outlet nozzles and the cathodic unit through the solution supply and outlet ports.