JPH03294492A - Recovering method for silver from photographic processing liquid - Google Patents

Abstract

PURPOSE:To recover silver as a silver ion-contg. soln. having comparatively high concn. by electrolyzing photographic processing liquid to deposit metallic silver on a cathode and impressing reverse current in an alkaline soln. and dissolving this metallic silver. CONSTITUTION:While supplying photographic processing liquid contg. silver ion and thiosulfate ion to an electrolyzer main body 2 via a base plate 8, electricity is conducted. Silver ion is reduced in the cathodically polarized part of a fixed bed 5 and deposited as metallic silver. The processing liquid is discharged from a cover body 7 and resupplied to the electrolyzer main body 2 from the bottom plate 8 via a circulation pipe 9. When recovery of metallic silver on the cathode is finished, processing liquid is substituted for an alkaline soln. having >=10pH. Polarities between the electrode terminals 3, 4 are reversed and electrolysis is performed. Metallic silver deposited to the upper part side of the fixed bed 5 is anodically polarized and dissolved in an electrolyte as silver ion. At this time, since silver sulfide deposited on the fixed bed 5 is converted into sodium sulfide or sodium hydrosulfide, a high-concn. silver ion soln. is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for recovering silver from a photographic processing solution containing silver ions and thiosulfate ions by electrolytic reaction. Silver ions are first deposited as metallic silver on the cathode of an electrolytic cell for silver recovery by an electrolytic reaction from a fixer, a bleach-fixer, etc. containing ions and thiosulfates, and then an electromotive force is applied in the opposite direction to the electrolytic cell. The present invention relates to a method in which the metallic silver is dissolved in a silver dissolving solution substituted with the photographic processing solution by applying an electric current, and recovered as a solution containing relatively high concentration of silver ions.

(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 the silver halide in the light-sensitive material and the processing solution, and the reaction occurs only when the various processing chemicals in the processing solution move through the gelatin film, and the by-products are mixed with the gelatin film. This is carried out under the condition that it moves through the 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 liquid, or by extracting or replacing the deterioration treatment liquid, or by connecting an electrolytic equipment for the purpose of silver component recovery to the treatment tank, and circulating the treatment liquid between the electrolytic tank and the treatment tank of the electrolytic equipment, the above-mentioned The mainstream is to use various methods such as in-line regeneration in which silver ions in the treatment solution are recovered and removed by electrolytic reaction in the electrolytic cell.

(Problems to be Solved by the Invention) When silver is recovered using this electrolytic method, silver ions in the photographic processing solution are reduced on the cathode and recovered as metallic silver.
As the recovery operation continues, the silver ion concentration in the photographic processing solution decreases and the current efficiency also decreases, and the sodium thiosulfate present in the processing solution is decomposed by electrolysis and converted to sulfide ions. Sulfide ions react with silver ions to form insoluble silver sulfide, which is deposited as fine particles around relatively large metallic silver that has already been deposited on the cathode, or deposited alone on the anode, or as fine particles. may precipitate or float in the electrolytic cell.

When this photographic processing solution containing silver sulfide is circulated through the photographic processing process, the silver sulfide in the processing solution adheres to the surface of the photosensitive material and appears as spots on the photographic paper. Circulation of photographic processing solutions into the photographic processing process must be avoided at all costs. Further, even when the photographic processing solution is not circulated, if silver sulfide generated in the electrolytic cell is recovered together with metallic silver, silver sulfide is often mixed in as an impurity, causing problems.

The photographic processing solution used in the photographic processing process normally contains silver ions at a concentration of about 8 g/l. Since almost no silver is generated, conventionally the electrolysis is stopped when the silver ion concentration in the photographic processing solution decreases to about 18/1 in order to avoid the above-mentioned problems caused by silver sulfide. Approximately 1 remaining in the photographic processing solution
In order to recover more g/l of silver, conventional methods have been to treat the photographic processing solution with an ion exchange resin, recover it as a chelate compound, or add iron ions, etc. to the photographic processing solution to remove remaining sulfide ions. Measures have been adopted to remove the iron sulfide from the photographic processing solution by precipitating it with iron sulfide and filtering it, or by blowing hydrogen gas to convert it into hydrogen sulfide. However, both methods are time-consuming and complicated methods that require equipment separate from the electrolytic system, and are also disadvantageous in terms of cost because they use other reagents and materials.

As described above, in the conventional electrolytic method, the electrolysis is stopped before reaching the silver ion concentration at which silver sulfide starts to precipitate, and the remaining silver ions are recovered from the photographic processing solution by means other than electrolysis. Silver ions were not recovered.

In addition, the metallic silver deposited on the cathode is usually redissolved and reused as a solution of relatively high concentration of silver ions, so conventional electrolytic methods are difficult to recover almost completely of the silver ions in the photographic processing solution. requires three steps: precipitation of silver ions by electrolysis, recovery of residual silver ions by means other than electrolysis, and dissolution of the deposited silver.

(Objective of the Invention) The present inventors have solved the complication of the above-mentioned conventional techniques for almost completely recovering silver ions from a photographic processing solution, and relatively easily and relatively easily recovering silver ions almost completely from a photographic processing solution. The method of the present invention was arrived at by studying various methods that can recover a solution containing silver ions at a high concentration.Therefore, the method of the present invention allows almost completely the silver ions accumulated in a photographic processing solution to be recovered as a solution containing silver ions at a relatively high concentration. The purpose is to provide a method for recovering ion-containing solutions.

(Means for Solving the Problems) The present invention provides a method for recovering silver from a photographic processing solution containing silver ions and periosulfate ions by an electrolytic reaction. After electrolyzing by applying a DC voltage in an electrolytic cell and depositing silver ions in the photographic processing solution as metallic silver on the cathode of the electrolytic cell, the photographic processing solution in the electrolytic cell is converted into a silver dissolving solution. Photographic processing characterized in that the metallic silver deposited on the cathode is dissolved in the silver solution by displacing the metal, and further applying a DC voltage in the opposite direction to recover the silver ion-containing solution with a relatively high concentration. This is a method for recovering silver from liquid.

The present invention will be explained in detail below.

The present invention enables silver sulfide, whose precipitation was suppressed in conventional methods, to be deposited on the electrodes of an electrolytic cell for silver recovery together with metallic silver when silver is recovered from a photographic processing solution containing silver ions and thiosulfate ions by an electrolytic method. The metal is precipitated or suspended as fine particles in the photographic processing solution during electrolysis, and then the photographic processing solution is replaced with a silver solution, and then a direct current electromotive force is applied in the opposite direction to the electrolytic cell. It is characterized in that silver is more efficiently dissolved in the silver solution and the silver sulfide is also dissolved in the silver solution. Therefore, by dissolving precipitated metallic silver by applying an electromotive force in the opposite direction, it is possible to obtain a highly pure silver ion-containing solution, and furthermore, by adjusting the amount of silver solution to be replaced, any relatively high-purity silver ion-containing solution can be obtained. It becomes possible to produce concentrated solutions.

As mentioned above, in conventional silver recovery using electrolytic methods, in order to suppress the precipitation of silver sulfide, it has not been attempted to continue electrolysis until metallic silver is almost completely precipitated. Contrary to the common sense of the prior art, the present invention aims at almost complete recovery of silver ions in photographic processing solutions.

The precipitation of silver sulfide, which was a disadvantage of the prior art, is not a disadvantage in the present invention, and the precipitated silver sulfide is effectively converted into other harmless compounds. The present invention not only removes silver sulfide generated due to thiosulfate, especially ammonium thiosulfate, when almost completely recovering silver ions in a photographic processing solution, but also removes silver sulfide from a photographic processing solution with a relatively low silver ion concentration. An advantage lies in the fact that solutions containing relatively high concentrations of silver ions can be obtained.

The photographic processing solution used in the present invention is a solution used in a photographic processing process containing silver ions and thiosulfate ions, such as a developing solution, a bleaching solution, a fixing solution, and a bleach-fixing solution. This is a large amount of fixer and bleach-fixer.

The structure of the electrolytic cell for silver recovery of the present invention is a three-dimensional electrode type electrolytic cell, such as a monopolar fixed bed electrolytic cell, a bipolar fixed bed electrolytic cell, a monopolar fixed bed electrolytic cell, etc. I can do it. In flat plate electrode type electrolytic cells such as rotating cylindrical electrolytic cells which are currently widely used, the current density cannot be reduced because the surface area of the electrode is small, so the precipitation of metallic silver progresses and the silver ion concentration decreases. This method is not adopted in the present invention because it is impossible to achieve almost complete silver recovery by further precipitating the silver ions in the photographic processing solution, which has become low.

At least one of the cathode and anode electrodes of the silver recovery electrolytic cell of the present invention, that is, at least the electrode that functions as a cathode during silver recovery electrolysis, is a three-dimensional electrode. Examples of three-dimensional electrodes for fixed bed electrolyzers include carbon materials, iron, stainless steel, nickel,
Porous electrodes made of conductive materials such as titanium and platinum-coated titanium molded into fibers or sponges, bead electrodes filled with glass beads in electrolytic cells or electrode chambers, and three-dimensional electrodes in fluidized bed electrolytic cells. For example, a fluidized electrode can be used in which a conductive material in the form of fine particles, chips, or short fibers is housed in an electrolytic bath or an electrode chamber and made to flow with a supplied photographic processing solution.

The counter electrode, that is, the electrode that functions as an anode during silver recovery, does not need to be a three-dimensional electrode; silver sulfide is deposited on the electrode during silver recovery electrolysis, and when an electromotive force in the opposite direction is applied, the electrode is in the form of a fiber. Since dissolution of silver sulfide is inhibited, it is preferable to use a regular flat plate electrode.The materials include graphite material, carbon material, dimensionally stable electrode (platinum group oxide coated titanium material), platinum coated titanium material. , nickel materials, etc. can be used.

When using a bipolar electrolytic cell, use a fixed bed electrolytic cell,
Porous materials through which photographic processing liquids can pass, such as carbon-based materials such as activated carbon, graphite, and carbon fibers having shapes such as granules, spheres, felts, woven fabrics, and porous blocks (sponges); One or more dielectrics made of shaped metal materials such as nickel, copper, stainless steel, iron, titanium, etc., as well as materials coated with precious metals, are placed in a DC electric field, and a DC voltage is applied to the dielectric body. It is possible to use a fixed-bed bipolar electrolytic cell containing a three-dimensional electrode that is polarized to form an anode and a cathode at one end and the other end of the dielectric. When using a three-dimensional electrode made by polarizing this dielectric material, the electrodes at both ends do not need to have an electrode function, but they do have the function of applying a voltage to the three-dimensional electrode to polarize it, that is, a power supply function. Must. No matter which type of three-dimensional electrode is used, if there is a gap in the processing tank through which the photographic processing liquid to be processed flows without coming into contact with the dielectric that functions as the three-dimensional electrode. Since precipitation of silver ions in the photographic processing solution is inhibited, it is desirable that the dielectric material is arranged so that the flow of the photographic processing solution in the processing tank does not take a short path.

When using a monopolar electrolyzer, fixed bed and fluidized bed re-electrolyzers can be used. When a fixed bed electrolytic cell is used, the three-dimensional electrode may be constructed using substantially the same material as the bipolar fixed bed electrolytic cell, such as carbonaceous particles. In addition, when a fluidized bed type electrolytic cell is used, the particles to be fluidized may be a substance that can be negatively charged by contacting the power supply cathode, and the particles may be fluidized under the same conditions as in the conventional method.

In such an electrolytic cell that can be used in the present invention, a diaphragm may or may not be used to divide the electrolytic cell into an anode chamber and a cathode chamber, but if a diaphragm is used, the diaphragm may contain thiosulfate. For example, ion exchange membranes, unglazed plates, sintered plates or pressure-bonded plates of organic polymer fibers such as polypropylene, various woven fabrics, and sintered organic polymer particles. A plate or a crimp plate can be used. Furthermore, if the resistance value of the diaphragm against ion permeation increases, not only will the electrolytic voltage increase, making it uneconomical, but also the current value will increase by the voltage increase due to the limit on the allowable power value of the DC power supply used for ordinary electrolytic cells. This may cause the required amount of electrolytic reaction to not occur. Therefore, the membrane resistance of the diaphragm is preferably 200 (V/A/ca13 or less) per unit current density.

Electrolytic treatment, which reduces silver ions in a photographic processing solution and recovers them as metallic silver, is performed by an electrolytic reaction on the cathode surface of an electrolytic cell. Therefore, when arranging a diaphragm in an electrolytic cell, moving the diaphragm closer to the anode side to enlarge the cathode chamber increases the operational efficiency of the electrolytic cell and reduces the amount of anolyte that does not participate in silver recovery, increasing silver recovery efficiency. It turns out. However, if the diaphragm is placed close to the anode, silver sulfide is generated in the narrow anode chamber due to the anodic oxidation of thiosulfate as described above, which may block the diaphragm or increase the electrolytic voltage by increasing the solution resistance in the anode chamber. Therefore, it is preferable not to make the distance between the anode surface and the diaphragm surface too narrow.

Further, the method of supplying the photographic processing solution to the electrolytic cell may be either a so-called batch method or a flow method, but in order to reduce the silver ion concentration to almost zero, the contact time of the photographic processing solution with the electrodes in the electrolytic cell is determined. If a flow type is used, it is preferable to circulate a certain amount of photographic processing solution.

Using an electrolytic cell constructed as described above, silver ions in a photographic processing solution are deposited on the cathode and the deposited silver is dissolved in a silver solution as follows.

A photographic processing solution such as a fixing solution having a silver ion concentration of about 6 to 10 g// and containing thiosulfate is supplied to the electrolytic cell for silver recovery, and an electrolytic voltage of about 2 to 4 cm and an electrolytic voltage of about 0.5 ~5A
When the photographic processing solution is electrolyzed at a current density of about /dm2, silver ions are deposited as metallic silver on the cathode with a current efficiency of about 30% at first, and as the electrolysis continues, the current efficiency decreases as the silver ion concentration decreases. Although the amount decreases, metallic silver continues to precipitate until the silver ion concentration of the photographic processing solution becomes almost zero. As the silver ion concentration decreases, precipitation of silver sulfide due to the decomposition of the thiosulfate begins to occur, and the silver sulfide particles are mainly deposited on the anode, but some of them adhere to the precipitated particles of metallic silver. Alternatively, it may be incorporated into particles, suspended in a photographic processing solution, or precipitated in an electrolytic bath.

Next, the photographic processing solution in the electrolytic cell from which silver ions have been almost completely removed by electrolysis is replaced with an arbitrary line dissolving solution. By this substitution, silver sulfide floating or precipitated in the photographic processing solution is removed. Next, when electromotive force is applied in the opposite direction to perform electrolysis, the metallic silver deposited on the electrode that functioned as a cathode in the silver deposition electrolysis is electrolytically oxidized on the electrode that functions as an anode in the silver dissolution electrolysis, and becomes silver. The silver sulfide is dissolved as ions in the silver solution which is the electrolytic solution, and at the same time, the silver sulfide deposited on the electrode that functioned as an anode in the silver recovery electrolysis is dissolved to generate silver ions and sulfide ions. The sulfide ions react with hydrogen gas generated from the electrode functioning as a cathode in root dissolution electrolysis, are converted into hydrogen sulfide, and are released outside the system. However, the reaction rate of this sulfide ion and hydrogen is slow, and in order to accelerate the reaction,
For example, it is preferable that the linear solution is alkaline or that the linear solution contains sulfite ions. Sulfide ions react with sodium hydroxide and are converted to sodium sulfide and sodium hydrosulfide, or react with sulfite ions and are converted to SOx compounds, suppressing the production of silver sulfide in the silver solution. .

By adjusting the amount of the linear solution, the silver ion concentration of the linear solution produced by this silver dissolving electrolysis can be set to an arbitrary value. In other words, a solution containing a high concentration of silver ions can be obtained by using a small amount of linear solution, and a solution containing a high concentration of silver ions can be obtained from a photographic processing solution that has a relatively low silver ion concentration before electrolysis and contains impurities. It will be done. Metallic silver of even higher purity can be produced from the highly concentrated silver ion solution thus obtained by electroless plating or by conventional techniques such as adding a reducing agent such as sodium boron hydride or hydrazine to the solution. It is possible.

As described above, according to the method of the present invention, silver sulfide can be almost completely absorbed into the photographic processing solution by a simple operation of applying electromotive force in the forward and reverse directions and replacing the electrolyte, without considering the presence of precipitated silver sulfide. of silver can be recovered.

Next, a preferred example of an electrolytic cell for silver recovery that can be used in the present invention will be described based on the accompanying drawings, but the electrolytic cell used in the method of the present invention is not limited to this electrolytic cell.

Figures 1a and 1b are longitudinal cross-sectional views showing an example of a bipolar fixed bed electrolytic cell that can be used as the electrolytic cell of the present invention, and Figure 1a is a vertical cross-sectional view showing an example of a bipolar fixed bed electrolytic cell that can be used as the electrolytic cell of the present invention. FIG. 1b shows the electrolytic cell with an electromotive force applied in the opposite direction.

A mesoche-shaped anode terminal 3 and a cathode terminal 4 are provided near the upper and lower ends of a cylindrical electrolytic cell body 2 having flanges 1 on the upper and lower sides, respectively. The electrolytic cell body 2 is preferably made of an electrically insulating material that can withstand long-term use or reuse, and is particularly made of synthetic resins such as polyepichlorohydrin, polyvinyl methacrylate, polyethylene, polypropylene, polyvinyl chloride, and polychloride. Ethylene, phenol-formaldehyde resin, etc. can be preferably used. The anode terminal 3 that provides a positive DC voltage is made of, for example, a carbon material (such as activated carbon, charcoal, coke, coal, etc.), a graphite material (such as carbon fiber, carbon cloth, graphite, etc.), or a carbon composite material (such as carbon fiber, carbon cloth, graphite, etc.).
(e.g. carbon mixed with metal in powder form and sintered), activated carbon fiber nonwoven fabric (e.g. KE-1000 felt, Toyobo Co., Ltd.), or material in which platinum, platinum, palladium or nickel is supported on it, and dimensions Stability electrode (platinum group oxide coated titanium material), platinum coated titanium material, nickel material, stainless steel material, iron material, etc. are formed. The cathode terminal 4, which faces the anode terminal 3 and applies a negative DC voltage, is made of, for example, platinum, stainless steel, titanium, nickel, Hastelloy, graphite, carbon material, mild steel, or a metal material coated with a platinum group metal. .

In the illustrated example, three fixed beds 5 are stacked between the picture electrode terminals 3.4, and four fixed beds 5 are stacked between the fixed beds 5 and between the fixed beds 5 and the picture electrode terminals 3.4. A porous diaphragm or spacer 6 is sandwiched therebetween. Each fixed bed 5 is in close contact with the inner wall of the electrolytic cell main body 2 and does not pass through the inside of the fixed bed 5, and the leakage flow of the photographic processing solution flowing between the fixed bed 5 and the side wall of the electrolytic cell main body 2 is preferably 30% or less. is arranged so that it is 10% or less. When a diaphragm is used, a woven fabric, an unglazed plate, a particle sintered plastic, a perforated plate, an ion exchange membrane, etc. are used as the diaphragm, and a woven fabric, a perforated plate, a mesh, etc. made of an electrically insulating material are used as the spacer. A rod-shaped material is used.

A lid body 7 and a bottom plate 8 are provided on both the upper and lower flanges 1, respectively.
The lid 7 and the bottom plate 8 are connected by a circulation vibrator 9, and a photographic processing solution, which is an electrolytic solution stored in a tank (not shown), is circulated using a pump (not shown). This allows you to do this.

When the electrolytic cell constructed as described above is energized while supplying a fixing solution from the fixing step of a photographic processing process through the bottom plate 8 as shown by the arrow in FIG. 1a, each of the fixed beds 5 becomes As shown in FIG. The fixer solution is reduced and precipitated as metallic silver, and the silver ion concentration is reduced. The fixer solution is discharged from the lid 7, passes through the circulation pipe 9, and is again supplied from the bottom plate 9 into the electrolytic cell 2, where the silver ions in the fixer solution are reduced. Silver recovery continues until the concentration reaches near zero.

The fixing solution whose silver ion concentration has become almost zero is replaced with an alkaline solution such as sodium hydroxide, and the polarity between the electrode terminals 3 and 4 in FIG. 1a is reversed as shown in FIG. 1b. When electrolysis is carried out while applying an electromotive force in a certain direction, the metallic silver deposited on the upper side of each fixed bed 5 is oxidized by positive polarization of the deposited portion, and dissolved in the electrolytic solution as silver ions. At the same time as the precipitated silver, the fixed bed 5
The silver sulfide precipitated on top is similarly dissolved as silver ions and sulfide ions by electrolysis, and the sulfide ions react with the sodium hydroxide present and are converted into sodium sulfide or sodium bisulfide.

Therefore, by dissolving the silver, a highly concentrated silver ion solution containing almost no sulfide ions can be obtained.

Figure 2 shows another example of an electrolytic cell that can be used in the present invention, and is a schematic vertical cross-sectional view of a fluidized bed type monopolar electrolytic cell that uses a liquid flow to fluidize conductive particles in the electrolytic cell. be.

It has a substantially cylindrical shape with an enlarged diameter stepped portion 11 and also functions as a cathode for school meals, and is made of nickel, carbon material, graphite material,
The electrolytic cell body 12 made of a conductive material such as steel, mild steel, or titanium is placed in a silver recovery circulation system 14 having an electrolyte tank 13, and a pump 15 installed in the circulation line of the circulation system 14. This allows photographic processing liquids such as fixer to circulate.

A dispersion plate 1 for photographic processing liquid is provided in the inner lower part of the electrolytic cell body 12.
6 is installed, and a rod-shaped anode 18 surrounded by a cylindrical diaphragm 17 is installed above the dispersion plate 16.

Conductive fine particles 19 are filled between the dispersion plate 16, the diaphragm 17, and the inner wall of the electrolytic cell body 12, and the fine particles 19 are supplied into the electrolytic cell body 12 by the pump 15 and through the dispersion plate 16. A photographic processing solution causes fluidization to form a fluidized bed. The enlarged diameter stepped portion 1 of the electrolytic cell body 12
Above 1 is a separation section 2 between the photographic processing solution and conductive fine particles 19.
0, and as the inner diameter increases, the fluidity decreases, and the gas and liquid components generated in small amounts by electrolysis are separated.The gas generated in small amounts is discharged from the opening 21 of the electrolytic cell body 12, and the liquid components are separated from the liquid components as described above. It is circulated to the electrolyte tank 13.

Electrolyte tank 13 of circulation system 14 having such a configuration
When a predetermined amount of a fixer or the like is contained in the fixer and the fixer is supplied to the electrolytic cell through the dispersion plate 16, the flowing fine particles 19 come into contact with the electrolytic cell main body 12 and become negatively charged, and the silver ions in the fixer are is reduced by contacting with the negatively charged flowing fine particles 19 having a very large surface area, and the fine particles 1 are reduced as metallic silver.
9.

Inside the electrolytic cell 12, inside the circulation line and the electrolyte tank 13
When the fixing solution in the solution is replaced with the W & dissolving solution and an electromotive force in the opposite direction is applied to the electrolytic cell shown in FIG. A highly concentrated silver ion aqueous solution can be obtained by dissolving in a solution. In particular, the concentration of the silver ion solution obtained can be calculated by appropriately adjusting the amount of the silver solution to be replaced and stored in the electrolyte tank 13.

FIG. 3 is a schematic vertical sectional view showing a monopolar fixed bed type electrolytic cell which is another silver recovery electrolytic cell that can be used in the present invention.

The box-shaped electrolytic cell 31 is divided into an anode chamber 33 and a cathode chamber 34 by a porous partition wall 32, and each electrode chamber has an anode 35.
and a power feeding cathode 36 are installed. A fibrous carbonaceous material 37 is filled between the power feeding cathode 36 of the cathode chamber 34 and the partition wall 32 so as not to come into contact with the anode 35, thereby forming a multi-surface area three-dimensional electrode for silver recovery. There is.

Note that 38 is an electrolytic solution outlet formed on the bottom surface of the electrolytic cell 31.

When a photographic processing solution containing silver ions and thiosulfate is supplied to this electrolytic cell 31 as in the case of FIGS. 1 and 2 and electrolysis is performed, the silver ions are reduced on the carbonaceous material 37. Precipitates as metallic silver. After taking out the photographic processing solution in which silver ions have been almost completely recovered from the electrolytic solution outlet 38, add a silver dissolving solution such as an aqueous alkali hydroxide solution in an amount calculated to obtain a silver ion solution with a predetermined concentration. When electromotive force is applied in the opposite direction and electrolysis is performed, the precipitated metallic silver is dissolved as described above, and an aqueous silver ion solution having a predetermined concentration can be obtained.

FIG. 4 is a longitudinal sectional view showing another example of a bipolar fixed bed type electrolytic cell which is an electrolytic cell for silver recovery that can be used in the present invention. This electrolytic cell is an improvement on the electrolytic cell shown in FIGS. 1a and 1b, and the same members as those in the electrolytic cell shown in FIGS. 1a and 1b are given the same reference numerals and their explanations will be omitted.

The electrolytic cell of FIG. 4 has two electrode terminals 3. instead of three fixed beds 5 and four porous membranes or spacers in the electrolytic cell body 2 of the electrolytic cells of FIGS. 1a and 1b. A large number of conductive particles 31 are present almost uniformly mixed between the conductive particles 31.
and said both electrode terminals 3 with a smaller number than said conductive particles 41.
．． It is filled with insulating particles 42 to prevent short ore formation between the holes.

When a positive electromotive force is applied to this electrolytic cell as shown in the figure, the conductive particles 31 are polarized in positive and negative directions, and the negatively charged side of the particles 31 causes a drop in the photographic processing liquid such as a fixer to be supplied. Precipitation of metallic silver occurs due to reduction of silver ions. The metallic silver is recovered as a highly concentrated silver ion aqueous solution in the same manner as in the electrolytic cells shown in FIGS. 1a and 1b.

(Example) Examples of silver recovery from photographic processing solutions containing silver ions and thiosulfate by the method of the present invention will be described below, but the examples are not intended to limit the present invention.

Using an electrolytic cell for silver recovery shown in Figure 1a and having the specifications shown below, an electrolytic silver recovery test was conducted under the electrolytic conditions shown below from a running solution of a bleach-fix solution with the following composition. .

(Composition of bleach-fix running liquid) Ammonium thiosulfate 70g/l Ammonium sulfite 18g/j! EDTA
Fe-NH4150g/j! silver ion
8.32 g/l (electrolytic cell specifications for silver recovery) Tank size: Cylindrical shape with inner diameter of 50 m5 and height of 100 fins (made of vinyl chloride) Anode terminal: Mesoche board cathode made of platinum mesochikun with a diameter of 48 mm and a thickness of 1.51 mm Terminal: Diameter 4B+sm, 1.5 fin thickness, platinum plated titanium mesoche board fixed bed, 2 carbon fibers with 45% porosity, diameter 50am
, 3 fixed beds with thickness l Q am and polyethylene spacer 4 with diameter 4811 and thickness 1.5 mm with an aperture ratio of 85%.
It was sandwiched between sheets.

(Electrolysis conditions) Applied current: DC 2OA Electrolyte amount near 0j! Metallic silver was deposited on a fixed bed while supplying the entire amount to the electrolytic cell at a flow rate of 1.5 #/min and circulating it through a circulation pipe.

When the bleach-fix solution was supplied to the electrolytic cell under these conditions and electrolysis was performed, a silver precipitate was gradually formed on the side of the fixed bed near the power supply anode terminal. When the change in silver ion concentration in the fixing solution, which is an electrolytic solution, over time during silver deposition electrolysis was measured, the results shown in Table 1 were obtained, and the silver electrodeposition voltage was about 14. Further, after about 120 minutes, the formation of black particles, which was thought to be caused by silver sulfide precipitation, was observed.

Next, the bleach-fix solution was extracted from the electrolytic bath, and the same amount of 10
Weight% sodium hydroxide aqueous solution (pH approximately 14) 50f
fi and apply an electromotive force of 8.5 V in the opposite direction to perform electrolysis, and the sodium hydroxide aqueous solution Middle East 1
When the change in silver ion concentration over time during silver dissolution electrolysis shown in the table was measured, the results shown in Table 1 were obtained.

From Table 1, the silver ion concentration in the bleach-fix solution becomes zero approximately 90 minutes after the start of silver precipitation electrolysis, and the amount of precipitated metallic silver is approximately 50 minutes.
It can be seen that it was completely dissolved in the sodium hydroxide aqueous solution within minutes.

When the aqueous sodium hydroxide solution was analyzed after stopping the electrolysis, it was found that sodium sulfide was 0.12 g/I! and sodium hydrosulfide 0.06g/j! of sulfur compounds were detected.

Using the electrolytic cell of Example 1 and under the electrolysis conditions of Example 1,
Time electrolysis was performed to deposit silver from the bleach-fix solution. Next, the pH of the sodium hydroxide aqueous solution of Example 1 was changed to 8.9.10.11.12.13 and 14 as shown in Table 2, and the sodium hydroxide solution was changed after 1 hour and 2 hours. The silver concentration and electrolytic current value in the aqueous solution were measured.

The results are shown in Table 2.

From Table 2, if the silver solution is alkaline, the silver
2 Table FiDTA-Fe-NH4140g/1 (main component of fixer) Ammonium thiosulfate 200g/1
It shows the effect of dissolving 15 g/l of ammonium sulfite, and it can be seen that almost all of the precipitated silver can be re-dissolved after 2 hours especially at pH 10 or higher.

When an attempt was made to redissolve the silver by using a bleach-fix solution or a fixing solution with the following composition instead of the sodium hydroxide aqueous solution as the silver dissolving solution, the results were almost the same as in the case of the sodium hydroxide aqueous solution. Re-dissolution of the precipitated silver occurred.

(Main component of bleach-fix solution) Ammonium thiosulfate 75 g/l Ammonium sulfite 22 g/l (Effects of the invention) The present invention electrolyzes a photographic processing solution containing silver ions and thiosulfate ions to almost completely remove the photographic processing solution. The silver ions contained therein are deposited on the cathode of a three-dimensional electrode type silver recovery electrolytic cell, and after the photographic processing solution is replaced with a silver dissolving solution, a direct current electromotive force in the opposite direction is applied to deposit on the cathode. In this method, the metallic silver is dissolved in an electrolytic solution and recovered as a solution containing relatively high concentration of silver ions (Claim 1).

When the silver ion in the photographic processing solution is almost completely reduced by electrolytic method and deposited on the cathode, the precipitation of silver sulfide particles is inevitable, and the precipitation of silver sulfide particles that adversely affect the photographic processing solution is suppressed. In the conventional electrolytic silver recovery method, which stops the precipitation of metallic silver while leaving a considerable amount of silver ions behind, complicated operations such as ion exchange resin treatment must be continued to recover further silver. are forced to do so.

When the silver ions in the photographic processing solution are almost completely deposited on the cathode by the method of the present invention, the silver sulfide particles are also deposited on the anode, the cathode, etc., but the photographic processing solution contains thiosulfate. When an electromotive force is applied in the opposite direction after replacing the solution with a silver solution that does not contain silver, the metallic silver precipitated in the silver solution is almost completely dissolved, the precipitated silver sulfide is converted to sulfide ions, and the sulfide ions are normally The silver ion aqueous solution containing almost no sulfide ions can be obtained because it reacts with hydrogen gas generated by water electrolysis to become hydrogen sulfide gas and is dissipated out of the system.

Further, by adjusting the amount of the silver dissolving solution in which the precipitated metallic silver is dissolved, an aqueous silver ion solution having an arbitrary concentration can be obtained. Therefore, if the same amount of precipitated metallic silver is dissolved by reducing the amount of the silver dissolving solution, an aqueous silver ion solution with a higher concentration can be obtained.

Therefore, according to the present invention, it is possible to obtain a silver ion aqueous solution with a high concentration and from which sulfide ions have been removed from a photographic processing solution containing silver ions at a relatively low concentration, and furthermore, the method of the present invention includes an operation of exchanging the electrolyte. However, since it is only an electrolytic operation of applying direct current electromotive force in the forward and reverse directions, silver ions in the photographic processing solution can be removed much more easily than silver recovery using conventional electrolytic methods. Enables almost complete recovery.

Although the method of the present invention is directed to photographic processing solutions, it is particularly effective when used to treat fixers and bleach-fix solutions that accumulate more silver ions than other photographic processing solutions and contain thiosulfates.

Further, a fixing solution or a bleach-fixing solution can be used as the silver dissolving solution (claim 2), and according to the present invention, the silver concentration of the fixing solution or bleach-fixing solution can be adjusted to a predetermined value.

When precipitated silver sulfide is dissolved in a silver solution, decomposition of sulfide ions occurs due to reaction with generated hydrogen gas even if the silver solution is neutral or acidic. When the liquid is an alkaline solution such as an aqueous sodium hydroxide solution, particularly an alkaline solution with a pH of 10 or more (Claim 3)
), the reaction of the sulfide ions with the sodium hydroxide promotes conversion to sodium sulfide or sodium hydrosulfide, making it possible to perform the treatment quickly.

[Brief explanation of the drawing]

Figures 1a and 1b are cross-sectional views of a bipolar fixed bed electrolytic cell that can be used in the method of the present invention. Figure 1a shows the electromotive force in the forward direction, and Figure 1b shows the electromotive force in the reverse direction. FIG. 2 is a cross-sectional view of a monopolar fluidized bed electrolytic cell that can be used in the method of the present invention, and FIG.
The figure is a sectional view of a monopolar fixed bed electrolytic cell that can be used in the method of the present invention, and FIG. 4 is a sectional view showing another example of a bipolar fixed bed electrolytic cell that can be used in the method of the present invention. It is. 11・ 13・ 14・ 16・ 18・ 20・ 31・ 33・ 35・ 37・ 41・ Expanding diameter step portion 12... Electrolytic cell body electrolyte tank Silver recovery circulation system 15... Pump distribution plate 17. ...Diaphragm anode 19...Particle separation section 21...Opening electrolytic cell body 32...Partition wall anode chamber 34...Cathode chamber anode 36...Cathode carbonaceous material 38 Conductive particles 42 -Electrolyte solution Outlet/insulating particles/flange 2... Electrolytic cell body/anode terminal/cathode terminal 5... Fixed bed/spacer 7... Lid/bottom plate 9... Circulation pipe Figure 1a Figure 1b Figure 2 Figure 3 S2

Claims (3)

[Claims] (1) In a method for recovering silver from a photographic processing solution containing silver ions and thiosulfate ions by electrolytic reaction, the photographic processing solution is electrolyzed by applying a DC voltage in a three-dimensional electrode type silver recovery electrolytic cell, After the silver ions in the photographic processing solution are deposited as metallic silver on the cathode of the electrolytic cell, the photographic processing solution in the electrolytic cell is replaced with a silver solution, and a DC voltage in the opposite direction is applied. A method for recovering silver from a photographic processing solution, characterized in that the metallic silver deposited on the cathode is dissolved in the silver dissolving solution and recovered as a relatively highly concentrated silver ion-containing solution. (2) The silver recovery method according to claim 1, wherein the silver dissolving solution is a bleach-fixing solution or a fixing solution in a photographic processing step. (3) The silver recovery method according to claim 1 or 2, wherein the silver solution is alkaline with a pH of 10 or more.