JPH0413884A - Regenerating method for electrolyzer for recovering silver - Google Patents

Abstract

PURPOSE:To rapidly regenerate an electrolyzer by electrodepositing metallic silver from photographic processing liquid in the electrolyzer by electrolysis and thereafter substituting the aq. soln. of substance which is allowed to react with silver sulfide and/or sulfur to produce soluble sulfur compd. for the photographic processing liquid. CONSTITUTION:The inside of an electrolyzer main body 1 is comparted into an anodic chamber 4 and a cathodic chamber 3 by a diaphragm 2. Metallic silver is electrodeposited and recovered by conducting electricity to anodes 5, a power supply cathode 10 formed of a base piece and side pieces and three- dimensional cathodes 9, and by electrolyzing photographic processing liquid. When electrolysis is completed, an aq. soln. contg. substance described hereunder e.g. alkali hydroxide having >=10pH is substituted for photographic processing liquid and voltage is impressed. The substance is allowed to react with silver sulfide and/or sulfur to produce soluble sulfur compd. Thereby, sulfur and silver sulfide deposited on the diaphragm 2 and the electrodes 5, 9, 10 are rapidly removed and the electrolyzer main body 1 is regenerated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for regenerating an electrolytic cell used for recovering silver from a solution containing silver ions by electrolysis, and more specifically, When a photographic processing solution such as a fixing solution or a bleach-fixing solution in a photographic processing process is supplied from a fixing tank or a bleach-fixing tank to a silver recovery electrolytic tank, and the silver ions are electrodeposited and recovered by an electrolytic reaction in the electrolytic tank, The sulfur and silver sulfide generated in the electrolytic cell due to thiosulfate contained in the photographic processing solution are treated with an aqueous solution containing a regenerating agent to quickly convert the sulfur and silver sulfide into soluble substances. This invention relates to a method for regenerating an electrolytic cell by dissolving it in a liquid.

(Prior Art) After image exposure, a photosensitive material is processed through the processing steps of color development, bleach-fixing, washing and/or stabilization, for example in paper photosensitive material processing.

Such photographic processing steps include steps such as a color development step, a bleaching step, a bleach-fixing step, a fixing step, a stabilizing step, and a washing step, and each step is performed in a separate processing tank. Silver ions dissolved from the processing of the photosensitive material are present in the processing solution in each processing step, and the concentration of silver ions gradually increases as processing time progresses. In particular, photographic processing is a so-called heterogeneous reaction between silver halide in a light-sensitive material and a processing solution, and various processing chemicals in the processing solution move through the gelatin film, causing a reaction, and the by-products are This is carried out under the condition that it moves through the gelatin membrane and diffuses into the processing solution. Therefore, if a large amount of reaction by-products are present in the processing solution, it will affect the photographic processing performance. By replenishing the deterioration treatment solution, or by connecting electrolysis equipment for the purpose of withdrawing or replacing the deteriorated treatment solution, or recovering silver components, to the treatment tank, silver ions in the treatment solution are removed by an electrolytic reaction in the electrolysis tank of the electrolysis equipment. The mainstream is to use various methods to collect and remove.

(Problems to be Solved by the Invention) According to the electrolytic recovery method described above, silver components can be recovered with considerable efficiency. The silver ion concentration in the processing solution decreases.

The photographic processing solution contains thiosulfate ions in addition to silver ions, and if the electrolysis of the photographic processing solution whose concentration of silver ions has decreased is continued, silver sulfide and sulfur will begin to be produced due to the reaction between the silver ions and the thiosulfate ions. . Since this sulfur and silver sulfide may have an adverse effect on the photosensitive material, it is desirable to avoid producing silver sulfide in the photographic processing solution. Silver ions produced by sulfur and silver sulfide 1 m W ? 74 degrees is approximately 0.5 to Ig/ff, and in conventional electrolytic silver recovery, when the silver ion concentration approaches this value, electrolysis is stopped, the photographic processing solution is discarded, and sulfur and silver sulfide are removed from the photographic processing solution. This prevents the generation of

However, since it is undesirable to discard photographic processing solutions containing silver from environmental and economical reasons, if electrolysis is continued for a long time, insoluble sulfur-containing substances such as sulfur and silver sulfide will be produced. These substances are usually fine powders, and depending on the structure of the electrode, for example, when a three-dimensional electrode made of felt-like carbon fiber is used, the holes in the electrode are blocked by the fine powder substances, causing clogging. This results in a significant decrease in electrolytic efficiency.

(Purpose of the Invention) The present invention aims to solve problems caused by insoluble sulfur-containing substances such as sulfur and silver sulfide produced when silver ions are electrolytically recovered from a photographic processing solution containing thiosulfate using an electrolytic bath. It is an object of the present invention to provide a method for quickly regenerating the silver recovery electrolytic cell which has suffered from a decrease in electrolytic efficiency due to clogging.

(Means for Solving the Problems) The present invention provides a method for electrolytically recovering metallic silver by supplying a photographic processing solution containing thiosulfate to an electrolytic cell, in which the electrodeposited silver is recovered after electrolysis is completed. A method for regenerating an electrolytic cell for silver recovery, characterized in that the electrolytic cell is regenerated by replacing the photographic processing solution with an aqueous solution of a substance that reacts with silver sulfide and/or sulfur to produce a soluble sulfur compound. be.

The present invention will be explained in detail below.

The present invention aims to remove soluble sulfur compounds by reacting with the sulfur-containing substances in an electrolytic cell for silver recovery whose members are clogged with finely powdered insoluble sulfur-containing substances such as sulfur and silver sulfide. This is a method of regenerating the electrolytic cell by treating it with an aqueous solution in which the substances that can be generated are dissolved.

The electrolytic cell targeted by the present invention is not particularly limited, and includes a developer solution,
Photographic processing solutions containing thiosulfate such as bleach, fixer, bleach-fix solution, stabilizing solution, and washing water are supplied to recover silver, and sulfur and silver sulfide are also removed due to the thiosulfate. can be used for any silver recovery electrolytic cell in which it precipitates as a fine powder and clogs the electrodes and reduces electrolytic efficiency, but it often contains thiosulfate and high concentrations of silver ions. Preferably, it is an electrolytic cell for recovering silver used for bleaching solution, fixing solution, bleach-fixing solution, stabilizing solution, etc.

The structure of the electrolytic cell for silver recovery is not limited to any particular structure, and an electrolytic cell of any structure can be used. It is possible to use a relatively large electrolytic cell using a large three-dimensional electrode type electrolytic cell or a plate-like or perforated plate-like electrode that can increase the processing capacity. In particular, in the three-dimensional electrode type electrolytic cell, the three-dimensional electrode is easily clogged with finely powdered sulfur or silver sulfide, so the method of the present invention can be effectively used. Furthermore, in the case of a diaphragm type electrolytic cell in which the electrolytic cell is divided into an anode chamber and a cathode chamber using a diaphragm, the diaphragm is likely to be clogged by the electrodeposited sulfur and silver sulfide. Since the cell is a diaphragm type electrolytic cell, the method of the present invention can be efficiently applied to the rotating cathode type electrolytic cell.

Whichever type of electrolytic cell is used, it is preferable to use an electrode with a large surface area as the cathode on which silver is deposited, and the electrode may be shaped, for example, in the form of granules, spheres, felts, woven fabrics, porous blocks, etc. carbon-based materials such as activated carbon, graphite, and carbon fiber, which have the same shape, and metal materials such as nickel, copper, stainless steel, iron, and titanium, which have the same shape, and materials that are coated with precious metals on these metal materials. It is desirable to use three-dimensional electrodes.

However, it is also possible to use the rod-shaped, plate-shaped, and porous electrodes used in the above-mentioned rotating cathode electrolytic cell for silver recovery.

The counter electrode, that is, the anode, is not particularly limited, but it is desirable that it has a shape and arrangement that allows smooth transfer of current between it and the cathode. In the case of an electrolytic cell containing a cylindrical three-dimensional cathode, it is preferable that the anode is cylindrical to surround the three-dimensional electrode and mesoche-shaped in order to facilitate the flow of the electrolyte. Graphite, carbon material, platinum group metal oxide coated titanium material (dimensionally stable electrode), platinum coated titanium material, nickel material, etc. can be used.

The electrolytic cell for silver recovery used in the method of the present invention is usually located close to a photographic processing tank, each of which has one or more integrated developing tank, bleaching tank, fixing tank (or bleach-fixing tank), stabilizing tank, and washing tank. It is preferable that the electrolytic cell be connected to one of the photographic processing tanks. The electrolytic cell may be connected to any of the photographic processing tanks. For example, when using a photographic processing tank having a plurality of fixing tanks, the plurality of electrolytic cells may be connected to all or part of the fixing tank. Can be connected.

The photographic processing solution in the photographic processing tank is supplied to the electrolytic tank for silver recovery having the above-mentioned structure to perform electrolysis. As for the supply method of this photographic processing solution, there is a one-time method in which the photographic processing solution is supplied to the electrolytic cell at a constant rate and the same amount as the supplied amount is taken out, and a one-time method in which a fixed amount of the photographic processing solution is supplied to the electrolytic cell at once. There is a hatch type in which the photographic processing solution is taken out of the electrolytic bath at once after electrolysis for a certain period of time, and either supply method may be used, but especially in the case of the hatch type, silver concentration tends to decrease and sulfur and Because of the significant silver sulfide formation, the present invention is more effective for hatch-type silver recovery systems. While the silver ion concentration in the supplied photographic processing solution is high, the current is used to reduce the silver ions and deposit metallic silver, and no sulfur or silver sulfide is deposited.
When the silver ion concentration becomes low, the sulfur and silver sulfide are deposited simultaneously with the electrodeposition of silver due to reduction G of the thiosulfate contained in the photographic processing solution, and the dirt usually becomes fine powder. Electrodeposition gradually clogs and clogs the members in the electrolytic cell, especially the electrodes, reducing electrolytic efficiency.

When the electrolytic efficiency has decreased to such an extent that economical operation cannot be carried out, the electricity supply is stopped and the photographic processing solution in the electrolytic cell is replaced with an aqueous solution of a substance that reacts with silver sulfide and/or sulfur to produce soluble sulfur compounds. Replace. The aqueous solution may simply flow through the electrolytic cell in which silver sulfide, etc. has been electrodeposited, but, for example, in the case of the above-mentioned rotating cathode electrolytic cell, the substituted aqueous solution may be stirred to mix the aqueous solution with the electrodeposited silver sulfide, etc. It is desirable to increase the contact efficiency.

The aqueous solution of the substance that produces this soluble sulfur compound is a highly concentrated aqueous alkali hydroxide solution, preferably p)
Examples include an aqueous solution of thorium hydroxide or potassium hydroxide with a pH of 110 or more, preferably 12 or more, or a sulfite such as sulfite, potassium sulfite, or ammonium sulfite with a pH of 0.05 mol/I1 or more.

It is believed that the alkali hydroxide, such as sodium hydroxide, reacts with the precipitated sulfur and silver sulfide to convert the sulfur and silver sulfide into soluble sulfur compounds.

S + Na0II = NazS (NaSH)
+ 1120AgS + Na0tl →
NazS 18 gzo + 1120 Also, the sulfite, such as 1-lium sulfite, reacts with the precipitated sulfur and silver sulfide according to the following formula to convert the sulfur and silver sulfide into soluble sulfur compounds.

S + Na25O: + -NazSzOs8gS+N
5O3-Na2S203+AgBy stopping the operation of the electrolytic cell in which sulfur and silver sulfide have been deposited due to long-term operation and replacing the photographic processing solution in the electrolytic cell with the alkali hydroxide aqueous solution or sulfite aqueous solution described above. Dissolves precipitated sulfur and silver sulfide. At this time, if an anode potential of about 0.5 to +2 V is applied in the same direction as the voltage application direction during silver recovery, the anodic formation of sulfur and silver sulfide is promoted, and the precipitates are almost completely dissolved in 1 to 2 hours. I can do it.

Next, a method for regenerating an electrolytic cell according to the present invention will be described in detail with reference to an electrolytic cell not shown in the drawings.

FIG. 1 is a longitudinal sectional view showing an example of a monopolar electrolytic cell to which the present invention can be applied.

A cylindrical electrolytic cell body 1 made of vinyl chloride resin or the like has a diaphragm 2 such as a cylindrical ion exchange membrane with a bottom located inside it, which separates a cathode chamber 3 in the center and a donut-shaped area around it. It is divided into an anode chamber 4. The donut-shaped anode chamber 4 accommodates a donut-shaped anode 5 located between the inner wall of the main body 1 and the outer surface of the diaphragm 2 and made of a carbonaceous material or a platinum group oxide-coated titanium material.

A three-dimensional cathode 6 made of carbon VK glue or the like is housed in the diaphragm 2 into a cylindrical Fel I shape, and the three-dimensional cathode 6
includes a base piece 7 in the center and a pair of side pieces 8 that branch laterally and are bent downward near the base end of the base piece 7.
A solid or hollow power feeding cathode 10 is formed with a pointed end 1 and a viscous tip engaging part 9 at the lower ends of the base piece 7 and the side pieces 8 via an enlarged diameter step. The current is supplied by

For example, when a photographic processing solution containing silver ions is supplied as an electrolyte to this electrolytic cell, the silver ions are reduced on the two-dimensional cathode 6 and deposited as metallic silver on the three-dimensional cathode 6 or in the electrolyte. It floats or is deposited on the bottom surface of the diaphragm 2. After a certain period of time has passed after the start of the operation, the three-dimensional cathode 6
When a sufficient amount of metallic silver is precipitated in the upper G, the electrolytic efficiency decreases, and it becomes necessary to take out the precipitated silver out of the tank and to remove the sulfur and silver sulfide deposited on the diaphragm and the power supply electrode-L. Become. To take out the deposited silver, after stopping the current supply, the power feeding cathode 10 is pulled upward and taken out from the main body 1, and the three engaging portions 9 at the tip of the power feeding cathode 10 engage with the three-dimensional cathode 6, respectively. The power supply cathode 1 is engaged with the inside of the power supply cathode 1.
0 and the three-dimensional cathode 6 are also taken out of the tank. Then, a substitute three-dimensional cathode or the three-dimensional cathode 6 is cleaned to remove the deposited silver, and the three-dimensional cathode is again engaged with the power supply cathode 10 to perform electrolysis as shown in FIG. It can be assembled into a tank. and a diaphragm 2 and a repowering electrode 5.
In order to remove the sulfur and silver sulfide deposited in step 10, you can either replace the photographic processing solution in the electrolytic cell with a highly concentrated alkali hydroxide aqueous solution or sulfite aqueous solution and leave it as is for 2 to 3 days.
Alternatively, by applying a positive voltage between the repowering electrodes 5 and 10 and leaving it for 1 to 2 hours, the precipitated sulfur and silver sulfide are dissolved in the aqueous solution and removed from the diaphragm and the electrodes. It is possible to prevent clogging, etc.

FIG. 2 is a longitudinal sectional view illustrating an electrolytic cell for silver recovery with a bag-like diaphragm to which the present invention can be applied.

A plate-shaped graphite anode 15 is installed close to the side wall of a box-shaped electrolytic cell 11 whose wall surface is made of an organic polymer material with electrically insulating strain, such as vinyl chloride resin. It is separated from a cathode chamber 14 by a side wall and a diaphragm 12 that is U-shaped in side view.

A cylindrical stainless steel rotating cathode 16 is used for medium heat in the electrolytic tank 11.
is installed, and the cathode 16 rotates by receiving the rotational force of the motor via the rotating shaft and the connecting plate.

At least one of the anode chamber 13 and the cathode chamber 14 includes:
] 3 Processing power for the fixing process, etc. containing diosulfate and silver ions is supplied as an electrolytic solution 18 through a processing liquid supply pipe (path shown). The rotating cathode 16t; L stirs the electrolyte 18 in the cathode chamber 14 to promote contact between the cathode 16 and silver ions in the electrolyte 18. ν] The silver ions are reduced on the ions 16 and deposited as metallic silver particles on the cathode 16 or in the cathode chamber 14.

Alternatively, it may be deposited on the bottom plate of the cathode chamber 14 and collected as appropriate.

(Example) A method for repopulating an electrolytic cell for silver recovery according to the present invention will be described below, but the present invention is not limited to the examples.

Example 1 Silver was recovered from a fixer using the electrolytic cell shown in FIG.

The electrolytic cell body is made of vinyl chloride and has a bottomed cylindrical shape with an inner diameter of 150+ m and a depth of 1501 m, and the inner wall of the electrolytic cell body has an outer diameter of 130 mm, an inner diameter of 125 mm, and a height of 120 nm.
F' is made of titanium material coated with iridium oxide.
- A oak-shaped anode was installed. A bottomed cylindrical diaphragm made of polypropylene having an outer diameter of 120 cm and a thickness of 3 cm was installed inside the donut-shaped anode by fixing its peripheral edge to the bottom plate of the electrolytic cell body by welding.

A three-dimensional cathode formed from felt carbon fiber into a cylindrical shape and having a diameter of 1101ffi, a height of 1201 mm, and a porosity of 50% was housed in the diaphragm. A titanium power supply cathode having three viscous tip engaging parts was connected to the upper surface of the three-dimensional cathode by inserting the tip engaging parts into the three-dimensional cathode.

Add 1 cup of fixing running liquid with the following composition into the electrolytic cell body.
When silver was recovered by circulating treatment under the electrolytic conditions of supplying at a rate of 0.01/min and constant current control of an electrolytic current of 2 A, the electrolytic voltage was maintained at 2.5 to 5.0 V. After 20 minutes from the start of electrolysis, precipitation of black particles believed to be caused by silver sulfide began to be observed on the three-dimensional electrode, both supply electrodes, and the diaphragm. The silver concentration in the fixed shield liquid is 0.5g/jl
' had decreased.

(Composition of fixer running liquid) Ammonium 1000 sulfate 100 g /
ff Anhydrous sodium bisulfite 1-lium 18g/l
Mek sulfite I/Rium 3g/(!E
DTA Fe (II[) NH-4 salt 50g
1llIE D "FA-4, H1g/A sthorium carbonate L4g/l4 silver ion
5.63 g/βpI-I
7.4 30 minutes after starting electrolysis
Over time, the amount of circulating fluid decreased from the initial 10 p/min to 0.567 min, and many yellow precipitates thought to be sulfur compounds were observed.

In place of the above fixer, 50 g/β of sulfite was added to the electrolytic bath.
Liu 1, 1-lium hydroxide aqueous solution p l (14
An aqueous solution adjusted to the above was added, and the operation was continued for 5 hours.

As a result, the circulating fluid volume recovered to 101/min, and about 95% of the yellow precipitate disappeared. Also, the silver concentration in the liquid is 0.1 p p
It can be seen that the sulfur component is efficiently dissolved without dissolving the silver.

When this aqueous solution of 1-lium sulfite was again replaced with the fixing solution and silver was recovered, silver could be recovered very well until 2 hours after the start of operation, as in the above-mentioned operation.

The fixing solution in the electrolytic cell was heated to a state immediately before clogging under the same conditions as in Example 1, and the fixing solution in the electrolytic cell was hydrated by containing 1-lium sulfite and/or sodium hydroxide as shown in Table 1. When the circulating fluid volume was measured after 1 hour and 5 hours when the tank was replaced with a regenerating fluid whose pH was adjusted to the pH shown in the table with thorium and operated with or without energization, Table 1 Q shows: The results were obtained.

From Table 1, if sulfite is not added, p
Recovery of circulating fluid volume is observed when H is 10 or more, and when thorium sulfite is added, recovery of circulating fluid volume is seen even when pH is less than 10. It can be seen that recovery is occurring.

Furthermore, it can be seen that under the same conditions, if the operation is continued while energizing after replacing with the regeneration liquid, the amount of circulating liquid is quickly recovered.

Example 3 A rotating cathode type electrolytic cell having the specifications shown below was connected to a bleach-fixing tank of a photographic processing tank via an electrolyte supply pipe and an electrolyte take-out pipe, and a bleach-fixing lamp 1 ε) having the following composition was prepared. Table E D Go A F e-NH4150g/
Adjust the pH of the running liquid of E silver ion 8.32g/to acetic acid and aqueous ammonia (28%).
I adjusted it to 7.4.

At the beginning of electrolysis, silver was deposited on the cathode and silver recovery was performed smoothly, but after about 30 hours after the start of electrolysis, yellow sludge, which is thought to be mainly composed of sulfur, accumulated in the diaphragm on the anode side and the cathode The silver on top turned black, the silver recovery rate decreased, and a hydrogen sulfide odor was observed.

The bleach-fix solution was replaced with regeneration solution No. 6 of Example 2, and electricity was applied for 2 hours. As a result, about 80% of the yellow sludge disappeared, and the black surface of the cathode changed to silver. Thereafter, when the bleach-fix solution having the above composition was substituted again and electricity was applied, silver could be recovered very well.

(Effects of the Invention) The present invention provides a photographic processing solution containing thiosulfate in an electrolytic bath Q.
In the method of electrolytically recovering metallic silver by supplying this, the above-mentioned 'wax treatment solution' after the electrolysis is completed and the electrodeposited silver is recovered,
A solution reacting with silver sulfide and/or sulfur was supplied to the electrolytic cell, silver was recovered under the electrolysis conditions shown below, and then circulated to the bleach-fixing tank.

(Electrolytic cell specifications) Electrolytic cell size: Vertical 500 ma x Width 500 im x Height 70
0 Tsuru anode: length 250 fins x width 500 mm x thickness Ion■
Cathode: A stainless steel plate (S U 3316) with a diameter of 35Qn+ x height of 500 mm was used at a rotation speed of 200 times/min. Diaphragm: Tetron ( Product name) Woven fabric (electrolytic conditions) Applied current: DC 50A (constant current) Anode current density: 1.11A/dm2 Cathode current density -
1, QIA/dm2 Electrolyte Hatch method is used to supply electrolyte to all near 0n tanks) (Composition of bleach constant running solution) Ammonium thiosulfate 70g/j! A method for regenerating an electrolytic cell for silver recovery, characterized in that the electrolytic cell is regenerated by replacing 18 g of ammonium sulfite/(1) with an aqueous solution of a substance that generates a soluble sulfur compound (Claim 1).

In the silver electrolytic recovery method, as electrolysis continues, the concentration of silver ions in the photographic processing solution decreases, and the reaction between the decreased concentration of silver ions and diosulfate ions makes it easier to generate sulfur and silver sulfide. Silver sulfide often causes clogging of electrodes and diaphragms and does not affect electrolytic conditions adversely. In conventional electrolytic silver recovery, photographic processing solutions containing a considerable concentration of silver ions are discarded as is in order to avoid deterioration of electrolytic conditions due to silver sulfide and sulfur. However, even if sulfur and silver sulfide, which easily cause clogging of electrodes and diaphragms, are generated, the sulfur and silver sulfide can be dissolved in the aqueous solution by the method of the present invention using a highly concentrated alkali hydroxide aqueous solution or sulfite aqueous solution. Since the electrolytic cell can be easily regenerated and cleaned, even if all or most of the silver ions in the photographic processing solution are precipitated and recovered, the electrolytic cell can be regenerated without causing any deterioration, and further silver can be recovered. Collection can continue.

The aqueous solution of a substance that reacts with silver sulfide and/or sulfur to produce a soluble sulfur compound used in the method of the present invention includes:
Alkaline hydroxide water i8 with po1o or higher? &(Claim 2
) or an aqueous solution of sulfite (claim 3), and the latter aqueous solution has a pH of 10 or more (claim 4), or a concentration of 0.05 mol/min.
The effect becomes remarkable when p or less (Claim 5).

No matter which aqueous solution you use, if you dissolve sulfur and silver sulfide while applying a positive voltage, the sulfur and silver sulfide will be dissolved more quickly than when no voltage is applied, and the circulating fluid will be dissolved. It is possible to recover the sharpness (claim 6).

Furthermore, if a three-dimensional electrode type electrolytic cell with a large surface area is used for silver recovery (Claim 7), although it is advantageous in terms of silver recovery efficiency, it is likely to be clogged by precipitated sulfur and silver sulfide. Since the method of the present invention effectively eliminates the blockage, it becomes possible to take full advantage of the characteristics of the three-dimensional electrode type electrolytic cell, which is optimal for silver recovery.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example of an electrolytic cell for silver recovery to which the present invention can be applied, using a fibrous cathode as a three-dimensional electrode constituent material, and FIG. FIG. 3 is a vertical cross-sectional view showing an example of a tank. - Electrolytic cell body cathode chamber 4 - Anode 6... - Mounting frame 8 - Tip engaging part... Electrolytic cell main body/Anode chamber 14... Anode 16... Electrolyte 2... Diaphragm/Anode chamber three-dimensional cathode・Side force piece 10...Power feeding cathode 12...Diaphragm・-Cathode chamber・Cathode guard\↑

Claims (1)

[Scope of Claims] (1) In a method for electrolytically recovering metallic silver by supplying a photographic processing solution containing thiosulfate to an electrolytic cell, the photographic processing is performed after electrolysis is completed and the electrodeposited silver is recovered. A method for regenerating an electrolytic cell for silver recovery, characterized in that the electrolytic cell is regenerated by replacing the liquid with an aqueous solution of a substance that reacts with silver sulfide and/or sulfur to produce a soluble sulfur compound. (2) The regeneration method according to claim 1, wherein the aqueous solution of the substance that reacts with silver sulfide and/or sulfur to produce a soluble sulfur compound is an aqueous alkali hydroxide solution having a pH of 10 or more. (3) The regeneration method according to claim 1, wherein the aqueous solution of the substance that reacts with silver sulfide and/or sulfur to produce a soluble sulfur compound is an aqueous solution containing sulfite. (4) The regeneration method according to claim 3, wherein the pH of the aqueous solution containing sulfite is 10 or more. (5) The regeneration method according to claim 3 or 4, wherein the concentration of sulfite is 0.05 mol/l or more. (6) The regeneration method according to any one of claims 1 to 5, wherein the regeneration is performed while flowing a current in a positive direction. (7) The regeneration method according to any one of claims 1 to 6, wherein the electrolytic cell is a three-dimensional electrode type electrolytic cell.