JPH04210490A - Method for recovering silver - Google Patents

Abstract

PURPOSE:To make the amt. of silver electrodeposited per unit time almost constant and to prevent a side reaction by keeping the cathode current density in an electrolytic cell almost constant. CONSTITUTION:The main body 1 of an electrolytic cell is divided by a diaphragm 2 into a central cathode chamber 3 and a doughnut anode chamber 4 around the cathode chamber, and a doughnut anode 5 is placed in the chamber 4. A constant-current control rectifier 11 is connected between a feeder cathode 10 and the anode 5, and a silver recovery reaction is conducted in the main body 1 with an almost constant electrolytic current. A fixer contg. silver ion is supplied to the main body 1 as an electrolyte. The silver ion is reduced on a three-dimensional cathode 6 and deposited on the cathode 6 as metallic silver, or the silver ion is suspended in the electrolyte or deposited on the bottom face of the diaphragm 2. Since an almost constant current flows in the electrolyte, the amt. of silver deposited per unit time is almost constant.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for recovering silver from a solution containing silver ions by electrolysis using a constant voltage WB method, more specifically, a method for recovering silver from a solution containing silver ions. The fixing solution, bleach-fixing solution, etc. in the photographic processing process containing 2. A method for recovering silver while maintaining a cathode current density of the reaction substantially constant; 2, more specifically, supplying the fixing solution etc. from a fixing tank etc. to the silver recovery electrolytic cell; 7. In the electrolytic cell. After the silver ions are electrodeposited and recovered by an electrolytic reaction, substantially all of the photographic processing solution in the electrolytic cell is circulated to the fixing tank, etc. Through so-called in-line processing, photographs can be taken without producing silver sulfide, etc. The present invention also relates to a method of recovering silver from a treatment solution while maintaining the cathode current density of the electrolytic reaction substantially constant.

(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 emulsion of the light-sensitive material are present in the processing solution in each processing step, and the silver ion concentration 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 solution, or by withdrawing or replacing the deteriorated treatment solution, or by connecting an electrolytic equipment for the purpose of silver component recovery to the treatment tank, the silver in the treatment solution is removed by an electrolytic reaction in the electrolytic tank of the electrolysis equipment. The mainstream is to use various methods to collect and remove ions.

(Problems to be Solved by the Invention) In the conventional silver recovery method using electrolysis, constant voltage control is performed in which electrolysis is performed while maintaining the voltage at a constant value. Silver recovery using constant voltage control has the drawback that since the voltage is constant, the current value increases or decreases in accordance with the increase or decrease in silver ion concentration, and the amount of silver recovered is not constant. Furthermore, if the current value increases or decreases significantly, a large change will occur in the current-voltage curve, and undesirable side reactions may occur.

Furthermore, according to the electrolytic recovery method described above, silver components can be recovered with considerable efficiency; however, in silver recovery using the electrolytic method, the amount of silver precipitated increases as the electrolysis time continues, and therefore the silver ion concentration in the photographic processing solution decreases. do. The photographic processing solution contains thiosulfate ions in addition to silver ions, and when electrolysis of the photographic processing solution whose silver ion concentration has been reduced is continued, silver sulfide begins to be produced due to the reaction between the silver ions and the thiosulfate ions. Since silver sulfide has an adverse effect on light-sensitive materials, the formation of silver sulfide in photographic processing solutions must be avoided.

The critical concentration of silver ions for silver sulfide production is approximately 0.5 to Ig/β, and in conventional electrolytic silver recovery, when the silver ion concentration approaches this value, electrolysis is stopped, the photographic processing solution is discarded, and the silver sulfide is removed. This prevents it from contaminating the photographic processing solution. However, it is undesirable to discard photographic processing solutions containing silver from environmental and economical reasons, and a method of recovering silver while avoiding disposal of silver is desired.

(Purpose of the Invention) The present invention provides that when silver ions are recovered from a photographic processing solution by electrolysis, the amount of silver deposited per unit time is almost constant and side reactions occur by performing electrolysis using constant current control. The purpose is to provide a silver recovery method that does not require

(Means for Solving the Problems) The present invention connects a photographic processing tank and an electrolytic tank for silver recovery, and supplies a photographic processing solution containing silver ions in the photographic processing tank to the electrolytic tank for silver recovery. in the electrolytic bath, and before all the silver ions are electrodeposited, substantially all of the photographic processing solution processed in the electrolytic bath is circulated to the photographic processing bath, This is a silver recovery method characterized by electrodepositing silver while maintaining a substantially constant cathode current density.

The present invention will be explained in detail below.

The present invention connects a photographic processing tank such as a fixing tank and an electrolytic tank for silver recovery, supplies a photographic processing solution with an increased concentration of silver ions in the photographic processing tank to the electrolytic tank, and carries out a normal silver recovery electrolytic reaction. When recovering silver, by maintaining the value of the cathode current density of the current flowing in the electrolytic cell almost constant, the amount of silver recovered per unit time is made almost constant, and side reactions are suppressed. The type of photographic processing solution targeted by the present invention is not particularly limited, and developer solutions, bleaching solutions, fixing solutions, bleach-fixing solutions, stabilizing solutions, etc. can be used, but bleaching solutions with high silver ion concentration, bleaching solutions with high silver ion concentration, It is preferable to use a fixing solution, a bleach-fixing solution, a stabilizing solution, etc.

The silver recovery device used in the method of the present invention usually includes one or more developing tanks, bleaching tanks, and fixing tanks (or bleach-fixing tanks).
It is preferable to install an electrolytic cell for silver recovery in close proximity to a photographic processing tank in which a stabilizing tank and a washing tank are integrated, and to connect the electrolytic tank to any one of the photographic processing tanks.

The electrolytic cell may be connected to any photographic processing tank,
For example, when a photographic processing tank having a plurality of fixing tanks is used, a plurality of electrolytic tanks can be connected to all or part of the fixing tank.

The electrolytic cell that can be used in the present invention is not particularly limited, and any silver recovery electrolytic cell can be used, and the conventionally widely used rotating cathode type (box type) electrolytic cell can also be used, but it has a large electrode area. It is also possible to use a three-dimensional electrode type electrolytic cell or a relatively large electrolytic cell using plate-shaped or perforated plate-shaped electrodes that can increase the processing capacity. It is preferable to use a tank.

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 desirable that the anode be cylindrical to surround the three-dimensional electrode and mesh-shaped to ensure smooth flow of the electrolyte. As the material, graphite material, carbon material, platinum group metal oxide coated titanium material (dimensionally stable electrode), platinum coated titanium material, nickel material, etc. can be used.

In order to perform constant current control, a commonly used constant current control rectifier may be connected between the anode and the cathode.

In addition, hydrogen gas and oxygen gas are often generated in the silver recovery electrolytic reaction, but if these gases circulate together with the photographic processing solution from the electrolytic bath to the photographic processing bath, there is a risk that the composition of the photographic processing solution in the photographic processing bath may change. Therefore, it is desirable to install a gas separation means in the circulation line from the electrolytic tank to the photographic processing tank.

Furthermore, it is desirable to install a filtration means in the circulation line from the electrolytic cell to the photographic processing tank in order to remove impurities due to circulation of the photographic processing solution or impurities mixed in the photographic processing tank during photographic processing.

Further, in the method of the present invention, the photographic processing tank and the electrolytic tank are connected, and the connection is usually made by piping made of an electrically conductive material. Therefore, there is a risk that leakage current generated in the electrolytic bath may flow into the photographic processing bath through the piping, causing unnecessary reactions in the photographic processing solution, or that the current may damage components such as the heater. Therefore, in the present invention, it is desirable to install means for extracting the leakage current outside the system. As an example of such means, a member having higher conductivity than the photographic processing solution may be placed in a pipe connecting the electrolytic bath and the photographic processing bath or in the electrolytic bath such that one end of the member is in contact with the photographic processing solution, so that the anode and cathode are facing each other. Either connect the other end to a capacitor and use the leakage current to charge the capacitor, and then use the appropriate method. Although there are indirect means to dissipate the heat, it is preferable to adopt the former method of direct grounding for ease of installation and operation.

As a method for supplying a photographic processing solution from a photographic processing tank to an electrolytic tank in a conventional silver recovery method by electrolysis, there is a one-time method in which the photographic processing solution is supplied to the electrolytic tank at a constant rate and the same amount as the supplied amount is taken out; There is a batch type method in which a certain amount of photographic processing solution is supplied to an electrolytic cell at one time, electrolyzed for a certain period of time, and then the photographic processing liquid is taken out from the electrolytic cell all at once. Although the present invention can be applied to any supply method, a so-called in-line method is adopted in which substantially the entire amount of photographic processing liquid taken out from the electrolytic bath is circulated to the photographic processing bath.

The silver ion concentration in the fixing solution in normal photographic processing is 3 to 6.
g/! The concentration gradually decreases as electrolysis continues in the electrolytic cell. According to Ohm's law (voltage) −
(Current) x (Resistance) In the case of constant voltage control, if the silver ion concentration decreases due to continued electrolysis, that is, if the resistance increases, the current decreases and the amount of silver deposited also decreases. However, according to constant current control, when the resistance increases due to continued electrolysis, the voltage increases and the current value is maintained at a substantially constant value, so that the amount of silver deposited per unit time is also maintained at a substantially constant value. Therefore, side reactions do not occur, and the desired silver recovery reaction can be carried out with high current efficiency.

However, when the silver ion concentration decreases significantly, the current-voltage curve changes as described above, and unnecessary side reactions may occur. Therefore, it is preferable to maintain the increase/decrease in silver ion concentration within a range as small as possible, and for this purpose, it is preferable to adopt the transient type of the above-mentioned two supply methods, and furthermore, by adopting the above-mentioned in-line method. Side reactions can be suppressed more effectively and almost the entire amount of silver ions can be recovered. In other words, the silver ion concentration in the photographic processing solution is 0.
．． When the concentration is below 5 g/f, silver sulfide is produced by the reaction between silver ions and periosulfate ions present in the photographic processing solution, and this silver sulfide precipitates on the photosensitive material 1, especially on the emulsion, and deteriorates the image quality. The formation of silver sulfide in photographic processing solutions must be avoided because it causes negative effects such as blurring. Therefore, in the present invention, by performing the in-line treatment, it is possible to suppress a significant decrease in the silver ion concentration, to keep the amount of silver deposited almost constant, and to suppress the generation of silver sulfide.

For example, when an electrolytic tank is connected to a fixing tank, a part of the fixing solution in the fixing tank is supplied to the electrolytic tank so that the silver ion concentration of the fixing solution (electrolyte) in the electrolytic tank is 0.5 g / Preferably 1g/! Electrolysis is carried out using constant current control within a range that does not lead to the following: silver ions are converted into metallic silver on the cathode of the electrolytic cell, and are deposited as fine particles, suspended in the cathode chamber as fine particles, or precipitated on the bottom plate of the cathode chamber. to recover. Particularly in the case of batch-type processing, it is necessary to circulate the fixing solution into the fixing tank when the silver ion concentration approaches the above value, that is, 0.5 g/l, preferably 1 g/l, to prevent changes in the silver ion concentration over time. Must be understood. The decrease in silver ion concentration is approximately proportional to the residence time of the photographic processing solution in the electrolytic cell; The time will be equal to the electrolysis time.

Therefore, in the case of one-time processing, the relationship between the supply rate of the photographic processing solution and the silver ion concentration of the photographic processing solution taken out from the electrolytic bath is measured in advance, and the silver ions in the photographic processing solution taken out from the electrolytic bath are measured. Either the photographic processing solution is supplied to the electrolytic cell so that the concentration becomes a desired value, or the silver ion concentration taken out from the electrolytic cell is measured over time, and if it is higher than the desired value, the supply rate is reduced and if it is low, It is preferable to increase the supply rate so that it approaches the desired value.

In the case of hatch type processing, the relationship between electrolysis time and silver ion concentration is measured in advance with other electrolytic conditions kept constant, and after a predetermined period of time, the photographic processing solution in the electrolytic bath is taken out and circulated into the photographic processing bath. Alternatively, the silver ion concentration of the photographic processing solution in the electrolytic bath is measured over time, and when the concentration reaches a predetermined value, the photographic processing solution in the electrolytic bath is taken out and circulated to the photographic processing bath. It is preferable.

The electrolytic cell that can be used in the present invention and the silver recovery method using the electrolytic cell will be illustrated below with reference to the accompanying drawings, but these are not intended to limit the present invention.

Figure 1 is a vertical cross-sectional view showing an example of a monopolar electrolytic cell that can be used in the present invention, which uses a fibrous cathode as a three-dimensional electrode constituent material and is applied to silver recovery. FIG. 2 is a schematic diagram showing a connected state of a tank and a photographic processing tank.

A cylindrical electrolytic cell body made of vinyl chloride resin, etc. has a diaphragm 2 such as a cylindrical ion exchange membrane with a bottom located inside it, which separates the cathode chamber 3 in the center and the 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 titanium material coated with a platinum group metal oxide. .

A three-dimensional cathode 6 formed of felt-like carbon fiber or the like into a cylindrical shape is accommodated in the diaphragm 2, and the three-dimensional cathode 6 includes a base piece 7 at the center and a base end of the base piece 7. It consists of a pair of side pieces 8 that branch laterally and are bent downward near the base piece 7 and the side piece 8, and the lower ends of the base piece 7 and the side piece 8 are formed into a pointed shape via an enlarged diameter step. A current is supplied by a power feeding cathode 10 on which a hook-shaped tip retaining portion 9 is formed. A constant current control rectifier 11 is connected between the power feeding cathode 10 and the donut-shaped anode 5, so that the silver recovery reaction within the electrolytic cell body 1 is carried out with a substantially constant electrolytic current.

An electrolyte supply pipe 12 is installed at the upper left of the cathode chamber 3 of the electrolytic cell body 1, and an electrolyte outlet pipe 13 is installed near the diaphragm 2 on the right side of the cathode chamber in contact with the electrolyte. ing.

As shown in Fig. 2, this electrolytic cell body 1 consists of two color developing tanks (CD), one bleaching tank (BL), two fixing tanks (FIX), and three washing tanks. one each connected to each of the two fixing tanks of the photographic processing tank consisting of;
The fixing solution in the fixing tank can be configured to be supplied to the electrolytic cell main body to perform a one-time process.

When the fixing solution in the fixing tank containing silver ions is supplied as an electrolyte to the electrolytic cell main body 1 through the electrolyte supply pipe 12 by the pump 14, the silver ions are reduced on the three-dimensional cathode 6 and converted into metallic silver. It is deposited on the three-dimensional cathode 6, floating in the electrolyte, or deposited on the bottom surface of the diaphragm 2.

The fixing solution, which is an electrolytic solution, is supplied from the electrolytic solution supply pipe 12 and electrolyzed until it is taken out from the electrolytic solution take-out pipe 13. During this time, a nearly constant electrolytic current flows through the electrolytic solution, so that the electrolytic current flows at a constant rate per unit time. Since the amount of silver deposited is also approximately constant, and the current is approximately constant, only the silver recovery reaction is performed almost selectively. Furthermore, by measuring the correlation between the residence time of the electrolytic solution and the decrease in silver ion concentration, and supplying the fixing solution to the electrolytic cell main body 1 at a predetermined supply rate, the silver ion concentration of the fixing solution taken out from the electrolytic solution extraction pipe 13 will increase. does not reach a concentration below which silver sulfide formation does not occur, and the photosensitive material is not adversely affected during the fixing process in which the fixing solution is circulated and supplied.

In addition, in an electrolytic cell for silver recovery, it is necessary to take out the metallic silver that is deposited on the cathode and floating or depositing in the cathode chamber, but in the electrolytic cell shown in Figure 1, after the electricity is turned off, When the power feeding cathode 10 is pulled upward and taken out from the main body 1, the three retaining portions 9 at the tip of the power feeding cathode 10 engage with the inside of the three-dimensional cathode 6, and the power feeding cathode 1 is removed.
0 and the acid 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. Therefore, when the electrolytic cell shown in FIG. 1 is used, there is no need to disassemble the entire electrolytic cell to recover silver as in the conventional case.

FIG. 3 is a cross-sectional view of a fir showing another example of a monopolar electrolytic cell that can be used in the present invention using a heath-like material as a three-dimensional electrode constituent material, and this electrolytic cell is similar to the electrolytic cell shown in FIG. 1. Similarly, it can be connected to any photographic processing tank.

A bottomed cylindrical electrolytic cell body 21 houses along its inner wall a donut-shaped anode 22 made of carbonaceous material, nickel metal, or the like. On the inner circumferential side of the donut-shaped anode 22, there is installed a dragon-shaped body 23 formed of synthetic resin or the like, which has a cylindrical shape with a bottom, has a relatively fine mesh, and is impermeable to the metal silver to be deposited. A semicircular old capital 24 is placed between two predetermined locations on the upper edge of the basket-like body 23.

The electrolytic cell main body 21 is connected to the cage-shaped body 234 from the cage-shaped body 234.
3 into an inner cathode chamber 25 and an outer anode chamber 26. Inside the cage-like body 23, there is a three-dimensional cathode 27, which is a large number of small-diameter fine particles made of a conductive material such as a carbonaceous material.
A current is supplied to the three-dimensional cathode 27 through the anode 22 and a dragon-shaped body 23 that also serves as a diaphragm, and the current is supplied to a power feeding device suspended from slightly below the center of the detail 24 of the cage-shaped body 23. is supplied to the cathode 28. A constant current control rectifier 29 is provided between the power feeding cathode 28 and the donut-shaped anode 22.
is connected so that the silver recovery reaction within the electrolytic cell body 21 is carried out with a substantially constant electrolytic current.

Similarly, when a photographic processing solution containing silver ions is supplied to this electrolytic cell, the silver ions in the photographic processing solution are reduced on the three-dimensional cathode 27 and deposited as metallic silver on the three-dimensional cathode 27. Alternatively, silver floats in the electrolytic solution or is deposited on the bottom surface of the cage-like body 23, and since a substantially constant electrolytic current flows in the electrolytic solution, the amount of silver deposited per unit time is also substantially constant; Since it is almost constant, only the silver recovery reaction is performed almost selectively. In this electrolytic cell, the electricity is turned off, the detail 24 is pulled upward, the cage-like body 23 is taken out, and the inside of the cage-like body 23 is cleaned together with the three-dimensional cathode 27, and as necessary. Then, the three-dimensional cathode 27 can be replaced and reinstalled at a predetermined position in the electrolytic cell main body 21, and silver recovery can be restarted.

(Example) Next, an example regarding silver recovery treatment from a fixer by the method of the present invention will be described, but the present invention is not limited to this example.

Example 1 - The electrolytic cell shown in FIG. 1 was arranged as shown in FIG. 2 to recover silver from a fixer solution.

The electrolytic cell body is made of vinyl chloride resin and has a bottomed cylindrical shape with an inner diameter of 120 mm and a depth of 180 mm.
A donut-shaped anode made of a titanium material coated with n mesodic iridium oxide was installed. Inside the donut-shaped anode, a bottomed cylindrical diaphragm made of a sintered polypropylene fiber having an outer diameter of 80 mm and a thickness of 2 rIm was installed by fixing its peripheral edge to the lower part of the electrolytic cell body by welding. .

Inside the diaphragm, a three-dimensional cathode made of Noelt-like carbon fiber formed into a cylindrical shape and having a diameter of 76 m, a height of 130 m, and a porosity of 55% was housed. A power feeding cathode made of 5US316 having three conical tip retaining parts was connected to the upper surface of the three-dimensional cathode by inserting the tip retaining parts into the three-dimensional cathode.

Into this electrolytic cell body, four times the fixing running liquid with the following composition was added.
1/min and the electrolytic current s, .

When silver was recovered by a one-time process under the constant current control electrolytic conditions of A, the electrolytic voltage was maintained at 2.7 to 2.9 ■, and the silver ion concentration in the electrolyte extraction tube was 0.85 g/l.
The amount of silver deposited per unit time calculated back from the concentration was almost constant at 19.2 g/min, and no silver sulfide was detected in the electrolyte in the electrolyte outlet tube. .

(Composition of fixer running liquid) Ammonium thiosulfate 200 g/l Anhydrous sodium bisulfite 18 g/f Sodium metasulfite 3 g/2 EDTA-2
Na 0.8g/l Sodium carbonate 14g/f Silver ion
5.63 g/fpH7.4 Stop comparison■ Connect the electrolytic cell body of Example 1 to the fixed tank of the photographic processing tank,
When the electrolysis voltage was set to 2.8■ and a silver recovery reaction was carried out by constant voltage control, the cathode current density was 0.8 to 2.5A.
/d+++'', and the amount of silver deposited per unit time was not constant, producing a large amount of silver sulfide.

Silver was recovered from the fixer using the electrolytic cell shown in Figure 3.

The electrolytic cell main body is made of vinyl chloride resin and has a bottomed cylindrical shape with an inner diameter of 120 m and a depth of 180 mm. Along the inner wall of the electrolytic cell main body, a mesh-shaped iridium oxide-coated titanium plate with an outer diameter of 110 mm, an inner diameter of 108-5 and a height of 150 mm is placed. A donut-shaped anode made of wood was also installed. Inside the donut-shaped anode,
A cylindrical cage-like body made of polypropylene with an outer diameter of 80 mm and a thickness of 2III1 mm is installed, and 5
10 g of graphite particles with a particle size of 5 to 10 mm were accommodated, and a rod-shaped power supply cathode made of nickel material was installed at the center of the pot-shaped body.

520 ml of a fixing running liquid having the same composition as in Example 1 was supplied into the electrolytic cell body, and silver was recovered using a haunch method under electrolytic conditions of constant current control to an electrolytic current of 3.5.

Continuing to measure the silver ion concentration in the fixing running liquid in the electrolytic cell body, the concentration was 13 g/l after 3 hours! ,
At that point, all of the fixing running liquid was circulated through the fixing tank. The electrolysis voltage varied in the range of 2.6 to 3.2■, and the amount of silver deposited increased from 16.4 g/min at the initial stage of electrolysis to 15.7 g/min.
/min decreased slightly.

Implementation side-1 A rotating cathode electrolytic cell having the specifications shown below is 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 running liquid having the following composition is added to the electrolysis tank. The electrolytic solution was supplied to the tank through the electrolytic solution supply pipe, silver was recovered under the electrolytic conditions shown below, and then circulated to the bleach-fix tank.

(Electrolytic cell specifications) Electrolytic cell size: 500mm long x 500mm wide x 700mm high
Body anode: 4 weighted graphite plates measuring 250 mm in diameter x 500 mm in width x 10 mm in thickness are surrounded by a sack-like TEL fabric as a diaphragm. Cathode used: 350 mm in diameter x 500 plates in height. stainless steel plate (S U 3316) at a rotation speed of 200 times/min (
Electrolysis conditions) Applied current: DC 50A (constant current) Anode current density: 1.11A/di2 Cathode current density:
1.01 A/dm” Electrolyte amount near 0ff (A batch method is adopted in which the entire amount is supplied into the electrolytic cell) (Composition of bleach-fix running liquid) Ammonium thiosulfate 70 g / 1
Ammonium disulfite 18 g /
fEDTA Fe NH4 150 g/1 Silver ion 8.32 g/f Adjust the pH of this running solution to 7.4 with acetic acid and aqueous ammonia (28%).

The silver ion concentration in the bleach-fix solution in the electrolytic bath was continued to be measured, and when the concentration slightly decreased to 7.88 b/1 after 3 hours, the silver ion concentration was circulated through the electrolytic solution outlet pipe to the bleach-fix bath. .

(Effects of the Invention) The present invention connects a photographic processing tank and an electrolytic tank for silver recovery, and supplies a photographic processing solution containing silver ions in the photographic processing tank to the electrolytic tank for silver recovery. A method in which silver is electrodeposited and recovered in a photographic processing tank, and substantially all of the photographic processing solution is circulated to the photographic processing tank, characterized in that silver is deposited while maintaining a cathode current density value substantially constant. This is a silver recovery method (Claim 1).

In the method of the present invention, the cathode current density in the silver recovery reaction is always kept almost constant, so the amount of silver deposited per unit time is almost constant, and there is also the risk of side reactions occurring due to large fluctuations in the current value. Therefore, stable silver recovery can be performed.

Moreover, in the present invention, when the photographic processing solution is supplied to the electrolytic bath to recover silver, substantially all of the photographic processing solution processed in the electrolytic bath is removed from the photo-processing solution before all the silver ions are electrodeposited. Since the treatment solution is circulated, the production of silver sulfide can be effectively suppressed.

The photographic processing solution contains mucothiosulfate ions in addition to silver ions, and when a photographic processing solution containing a low concentration of silver ions is electrolyzed, the electrolysis of thiosulfate ions takes precedence due to the electrolysis of silver ions, and silver sulfide is produced. Since the silver sulfide has an adverse effect on photosensitive materials,
It is necessary to avoid this formation as much as possible, and this formation can be avoided by circulating the photographic processing solution after electrolysis into the photographic processing bath before silver sulfide formation. Although there are silver ions that are not recovered in the electrolytic bath, these silver ions are circulated to the photographic processing bath, so there is no problem of environmental pollution or economic loss, and silver recovery is extremely effective. It becomes possible to do this.

Since silver sulfide formation occurs when the silver ion concentration is 0.5 g/j2 or less, it is set to circulate to the photographic processing tank before the silver ion concentration of the photographic processing solution, which is the electrolytic solution in the electrolytic tank, reaches -J2 concentration. By doing so, it is possible to prevent the formation of silver sulfide in the photographic processing solution (Claim 2).

Silver recovery electrolytic reaction often generates hydrogen gas and oxygen gas, but these gases are transferred from the electrolytic tank to the photographic processing tank 2.
If it circulates together with the photographic processing solution, there is a risk that the composition of the photographic processing solution in the photographic processing tank will change. To prevent kneading, for example, a gas separation means is installed in the circulation line from the electrolytic cell to the photographic processing tank to separate the gas from the photographic processing solution from which the silver has been recovered, and then the photographic processing solution is transferred to the photographic processing tank. (Claim 3)

Furthermore, in order to remove impurities due to circulation of the photographic processing solution or impurities mixed in the photographic processing tank during photographic processing, a filtration means is installed in the circulation line from the electrolytic tank to the photographic processing tank, and after filtration, the photographic processing is carried out. It can be circulated to the tank (Claim 4).

iFA In normal electrolysis, leakage current inevitably occurs in the electrolytic bath.The leakage current flows into the photographic processing bath through piping, etc., and the photographic processing solution causes unnecessary reactions, or the current leaks into the heater, etc. There is a risk of damaging the components. Therefore, in the present invention, it is desirable to install a means for extracting the leakage current outside the system (Claim 5),
This makes it possible to prevent unnecessary waste of current, suppression of unnecessary side reactions, and damage to components.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of a monopolar electrolytic cell that can be used in the present invention, FIG. 2 is a schematic diagram showing a state in which the electrolytic cell shown in FIG. 1 is connected to a photographic processing tank, and FIG. , is a vertical cross-sectional view showing another example of a monopolar electrolytic cell that can be used in the present invention. l... Electrolytic cell body 2... Diaphragm 3... Cathode chamber 4... Anode chamber 5... Anode 6-... Three-dimensional cathode 7... Base piece 8... Side piece 9 ... Engagement part 10 ... Cathode for power supply 11 ... Rectifier for constant current control 12 ... Electrolyte supply pipe 13 ... - Electrolyte solution extraction pipe 14
...Pump 21...Electrolytic cell body 22...Anode 23...Case-shaped body 24...Details 25...Cathode chamber 26...Anode chamber 27...Three-dimensional cathode 28... Power feeding cathode 29 -
Rectifier for constant current control

Claims (5)

[Claims] (1) A photographic processing tank and a silver recovery electrolytic tank are connected, and a photographic processing solution containing silver ions in the photographic processing tank is supplied to the silver recovery electrolytic tank to deposit silver in the electrolytic tank. A method in which substantially all of the photographic processing solution processed in the electrolytic cell is circulated to the photographic processing tank before all silver ions are electrodeposited, while maintaining a substantially constant cathode current density. A silver recovery method characterized by electrodepositing silver. (2) Claim 1 in which the photographic processing solution in the electrolytic cell is circulated to the photographic processing tank before the silver ion concentration decreases to 0.5 g/l.
Silver recovery method described in. (3) After gas separation of the photographic processing solution from which silver was recovered,
Claim 1 or 2, wherein the photographic processing solution is circulated to a photographic processing tank.
Silver recovery method described in. (4) The silver recovery method according to any one of claims 1 to 3, wherein after filtering the photographic processing liquid from which the silver has been recovered, the photographic processing liquid is circulated to a photographic processing tank. (5) A member with higher conductivity than the photographic processing solution can be grounded at one end on the back side of the power supply electrode where the power supply anode and cathode in the silver recovery electrolytic cell do not face each other and/or in the entrance/exit piping of the electrolytic cell. The silver recovery method according to any one of claims 1 to 4, wherein the silver recovery method is installed and processed.