JPS6312151B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering silver by electrolysis from a solution containing an iron compound having an organic acid as a ligand (hereinafter referred to as an organic acid iron compound) and a soluble silver salt. Processing of silver halide color photographic materials includes two steps: color development and desilvering. When a color photographic light-sensitive material is color-developed, the exposed silver halide is reduced to silver, and at the same time,
The oxidized aromatic primary amino developing agent reacts with the coupler to form a dye image. In the desilvering step, silver produced by development is oxidized by an oxidizing agent to silver halide, which is dissolved and removed by a silver halide solvent. As described above, the desilvering process includes the two steps of bleaching and fixing, but in actual photographic processing methods, there is a method in which the bleaching step and the fixing step are performed separately. Among these methods, there is a method in which a washing step is provided between the bleaching and fixing steps, or a method in which the fixing step is directly started from the bleaching step. There is also a bleach-fixing process in which both processes are performed simultaneously. Further, following the bath containing these soluble silver salts, a water washing step is usually provided. In recent years, the issue of environmental conservation and the saving of silver resources have become important, and there is a strong desire for a method to reduce pollution and a method to efficiently recover silver. Therefore, as a method to recover the silver flowing into the washing water and simultaneously reduce polluting substances from the washing water, a preliminary washing step (intermediate bath) is provided between the bath containing soluble silver salts and the subsequent washing step. It is also proposed that Methods for recovering silver from liquids containing soluble silver salts as described above can be broadly classified into the following four methods. [1] A method of adding a chemical that forms a poorly soluble silver salt to form a miscible silver salt and removing the precipitate. [2] A method of replacing molten silver by contacting a base metal, which is a metal with a greater tendency to ionize than silver. [3] An ion exchange method in which silver ions are adsorbed using a basic ion exchange resin. [4] An electrolytic method in which silver is deposited on the cathode by electrolysis. The first hardly soluble silver salt precipitation method has problems such as contamination of the processing solution by additive chemicals such as sulfurizing agents, impurity of recovered silver, and recovery of precipitates. The second base metal substitution method requires a base metal in an amount equivalent to silver ions, and in the case of a bleach-fix solution or fixer containing an organic acid iron compound, a base metal in an amount equivalent to silver ions and an oxidized organic acid iron compound. The agent dissolves in the processing solution, making it difficult to correct the components in case of reuse. The third method of using a basic ion exchange resin has the problem that the rate of adsorption of silver is slow and the amount of adsorption and exchange is also low. The present invention is an electrolytic method that does not have the above-mentioned problems, that is, there is no contamination due to the addition of other chemicals, there is little accumulation of chemical substances, there is no reduction in components due to reaction, there is no complicated operation, and there is a high recovery efficiency. The aim is to recover silver advantageously.
However, although the conventional silver recovery method using electrolysis has the above-mentioned advantages, it also has the following disadvantages. (1) In the case of a bleach-fix solution or fixer solution containing an organic acid iron compound, a part of the silver electrolytically deposited on the cathode is redissolved in the bleach-fix solution or fixer solution containing the organic acid iron compound. Therefore, an equilibrium between silver precipitation and redissolution occurs, and the electrolytic efficiency, ie, the amount of silver deposited per unit charge, decreases. (2) Also, since precipitated silver is redissolved in the bleach-fix solution or fixer solution containing organic acid iron compounds, simply turning off the power will cause the silver to be redissolved, so the cathode containing the precipitated silver must be removed from the electrolyte. Since silver is recovered, it is difficult to conduct electrolysis continuously. (3) In the case of a bleach-fix solution, part of the bleaching agent is also reduced by electrolysis, resulting in a lower amount of silver deposited per unit charge. The present invention aims to solve these problems. Up to now, many proposals have been made for improving the electrolytic recovery of silver from fixing solutions and bleach-fixing solutions. For example, JP-A No. 50-98837, No. 52-26315, No. 52-
115723, 53-32869, 53-60391, West German Patent No. 2333018, West German Patent No. 2429288, Belgian Patent No. 780623, US Patent No. 400056, West German Patent No. 3840455
No., No. 3964990, and No. 4069127. The methods described in these documents include electrolysis by adding a reducing agent while changing the potential, using a diaphragm, electrodialysis, automatic current control, liquid feeding, stirring, electrodes and plates, etc. Most of the technologies are related to the improvement of equipment. However, all of these methods have drawbacks such as insufficient current efficiency and large and complicated devices. The present invention differs from these methods in that it is a technique for electrolytically recovering silver from a fixing solution, a bleach-fixing solution, etc. containing an organic acid iron compound by a chemical treatment method. As a result of intensive research and numerous experiments, the present inventors have obtained the findings described above and below. That is, when a solution containing a soluble silver salt and an organic acid iron compound is electrolyzed in a conventional manner using an electrolytic device for a fixing solution or a bleach-fixing solution, the electrolytic efficiency, that is, the amount of silver deposited per unit charge decreases. In particular, electrolytic devices for fixer fluids have the disadvantage of a large drop. The cause of this decline is “The Journal of
CJ in “Photographic Science Vol 20, 1972”
This is thought to be due to the phenomenon described by Sharpl, in which silver deposited on the cathode is redissolved by the organic acid iron compound. Therefore, a first object of the present invention is to provide a silver recovery method for efficiently recovering silver from a solution containing an organic acid iron compound by an electrolytic method. A second object of the present invention is to provide a silver recovery method that efficiently recovers silver from a bleach-fix solution using an organic acid iron compound as an oxidizing agent or a fix solution in which organic acid iron compounds are mixed during the processing process. It is to provide. A third object of the present invention is to provide a silver recovery method that recovers silver with as little sulfite oxidation as possible during electrolysis of the bleach-fix solution, fix solution, etc. A fourth object of the present invention is to provide a silver recovery method for recovering silver for reusing a liquid containing an organic acid iron compound. Other objects of the invention will become apparent from the following description of the specification. The above object of the present invention is to provide a liquid containing an organic acid iron compound and a soluble silver salt having a lower stability constant for ferric ions than a compound represented by the following general formula []. This is accomplished by recovering silver by electrolysis in the presence of an amount of a compound capable of chelating substantially all of the ferric ions of the iron compound. General formula [] [In the formula, R represents an alkyl group or substituted alkyl group having 1 to 5 carbon atoms, and X represents a hydroxyl group or an amino group. According to the present invention, silver is deposited on the cathode from a solution containing a soluble silver salt and an organic acid iron compound using a commonly used electrolytic device for fixing solution or bleach-fixing solution, and then left in the electrolytic solution for a long time. Even in this case, redissolution does not occur, and the current efficiency, that is, the amount of silver deposited per unit charge, can be recovered in a larger amount than in the past. Further, normally, when electrolytic silver is recovered, sulfite is decomposed and silver sulfide is finally produced, but in the method of the present invention, sulfite is not decomposed. Further, according to the present invention, a regenerated fixer containing a soluble silver salt and an organic acid iron compound can be reused without adversely affecting fixing properties when a silver halide photographic light-sensitive material is processed. In addition, in order to improve the drawbacks of the above-mentioned silver recovery method due to the substitution method with base metals, a method of adding a compound represented by the above general formula [] used in the present invention was reported in Research Disclosure 18140 ('79.5). There is. However, this technique is clearly different from the purpose of the present invention; when silver is recovered using steel wool from the overflow liquid discharged from the fixing bath, iron is eluted and precipitation occurs, but the purpose of this technique is to prevent this precipitation. Moreover, the amount of the compound represented by the general formula [ ] is also small compared to the amount used for the purpose of the present invention. And, if such a small amount is used, the above object of the present invention cannot be achieved. In the present invention, a solution containing a soluble silver salt and an organic acid iron compound refers to silver produced by development being oxidized by an oxidizing agent (bleaching) in a desilvering step to silver halide, which is then converted into a silver halide. Indicates a solution intended to dissolve and remove silver using a silver solvent (fixing), and although it does not have desilvering properties, when these baths are continuously processed, these are inevitably brought in and accumulated by the processed light-sensitive materials. Indicates liquid. These baths include bleach-fix baths, fixing baths, one-bath development bleach-fix baths, intermediate baths, water washing baths, and the like. Next, representative examples of compounds represented by the general formula [] used in the present invention will be listed, but the compounds of the present invention are not limited to these. These compounds used in the present invention are described, for example, in West German Patent No. 2252684, US Patent No. 3400148, and Journal of Organic Chemistry No. 38.
vol., pp. 1867-1869 (1973), etc., by a general synthesis method. Further, in these compounds, all or part of the acid groups may be a salt of an alkali metal, ammonia, or an amine. Examples of the alkali metal include lithium, sodium, and potassium, and examples of the water-soluble amine include methylamine, diethylamine, triethylamine, butylamine, ethanolamine, diethanolamine, triethanolamine, and morpholine. The organic acid iron compound as a bleaching agent used in the bleach solution or bleach-fix solution containing an organic acid iron compound used in the bleaching process of the present invention oxidizes metallic silver produced by development and converts it into silver halide. At the same time, it has the effect of coloring the uncolored parts of the coloring agent, and its structure is one in which iron or metal ions are coordinated with aminopolycarboxylic acid or an organic acid of polycarboxylic acid such as oxalic acid or citric acid.
The most preferred organic acid used to form such an organic acid iron compound is, for example, a polycarboxylic acid or an aminopolycarboxylic acid represented by the following general formula [] or []. General formula [] HOCO―A ₁ ―Z―A ₂ ―COOH General formula [〕 [In each general formula, A ₁ , A ₂ , A ₃ , A ₄ , A ₅ and
A ₆ is a substituted or unsubstituted hydrocarbon group, respectively;
Z represents a hydrocarbon group or N-A ₇ (A ₇ is a hydrocarbon group or a lower aliphatic carboxylic acid). ] These polycarboxylic acids or aminopolycarboxylic acids may be alkali metal salts, ammonium salts, or water-soluble amine salts. Representative examples of the aminopolycarboxylic acid or polycarboxylic acid represented by the general formula [] or [] include the following. (1) Ethylenediaminetetraacetic acid (2) Diethylenetriaminepentaacetic acid (3) Ethylenediamine-N-(β-oxyethyl)-N,N',N'-triacetic acid Propylenediaminetetraacetic acid (4) Nitrilotriacetic acid (5) Cyclohexanediaminetetraacetic acid Acetic acid (6) Iminodiacetic acid (7) Dihydroxyethylglycine (8) Ethyl ether diamine tetraacetic acid (9) Glycol ether diamine tetraacetic acid (10) Ethylene diamine tetrapropionic acid (11) Phenyl diamine tetra acetic acid (12) Ethylene diamine tetra acetic acid di Sodium salt (13) Ethylenediaminetetraacetic acid tetra(trimethylammonium) salt (14) Ethylenediaminetetraacetic acid tetrasodium salt (15) Diethylenetriaminepentaacetic acid pentasodium salt (16) Ethylenediamine-N-(β-oxyethyl)-N,N', N'-Triacetic acid sodium salt (17) Propylenediaminetetraacetic acid sodium salt (18) Nitrilotriacetic acid sodium salt (19) Cyclohexanediaminetetraacetic acid sodium salt (20) Citric acid (21) Oxalic acid (22) Maleic acid (23) Tartaric acid (24) Succinic acid (25) Sulfamic acid (26) Phthalic acid (27) Gluconic acid The bleaching solution contains the above-mentioned organic acid iron compound as a bleaching agent, and can also contain various additives. As additives, in particular alkali halides or ammonium halides, such as potassium bromide, sodium bromide, sodium chloride,
Examples include rehalogenating agents such as ammonium bromide, and PH buffering agents such as borates, oxalates, acetates, carbonates, and phosphates, polyaminocarboxylic acids or their salts, alkylamines, and polyethylene oxides. Those known to be added to ordinary bleaching solutions may be added as appropriate. In the present invention, soluble silver salts are those produced as a result of continuous treatment in a bath for desilvering during processing of silver halide photographic materials, and examples of these soluble silver salts include silver thiosulfate complex salts, silver halide complex salts, Thioether silver complex salt, thiocyanate silver complex salt,
Examples include ammonia silver complex salt and silver acetate. The compound represented by the general formula [] used in the present invention is required to chelate substantially all of the organic acid iron compounds described above, and the amount is at least 0.5 mol per iron atom, that is, depending on the molecular structure of the compound. However, it can be added in a range of 1.3 to 500 g per 1 g of iron. Preferably, by adding 1.8 to 50 g per 1 g of iron, silver can be efficiently recovered by electrolysis. Further, the pH of the liquid to which the compound represented by the general formula [] of the present invention is added may be in the range of 2.0 to 11.0, but preferably 5.0 to 8.0. Furthermore, the method and conditions for electrolyzing a solution containing the compound represented by the general formula [] of the present invention vary depending on the composition of the solution and the electrolyzer used, so they may be determined in advance according to these factors. . Next, in order to show the liquid to which the present invention is applied, preferred processing steps used for processing photographic materials will be described, but the present invention is not limited thereto. Color development - bleaching - washing with water - fixing - washing with water - stable Color development - bleaching - pre-washing - fixing - washing with water - stable Color development - bleaching - pre-washing - fixing - pre-washing - washing - stable Color development - bleaching - fixing - pre-washing - Washing - Stable Color development - Bleach-fixing - Washing - Stable Color development - Bleach-fixing - Pre-washing - Washing - Stable First development - Washing - Reversal - Color development - Bleach adjustment - Bleach - Fixing - Washing - Stable First development - Washing - Reversal - Color development - Bleach adjustment - Bleach - Fixing - Pre-washing - Washing - Stable First development - Washing - Reversal - Color development - Bleach adjustment - Bleach-fixing - Pre-washing - Washing - Stable First development - Stopping - Washing - Reversal color development - Stop - Water washing - Bleaching - Bleach neutralization - Fixing - Water washing - Stability Silver halide photographic materials such as color negative film, color paper, and color reversal film are developed through these processing steps, but the present invention The method can be applied to any processing solution containing an organic acid iron compound and a soluble silver salt during each of the steps described above. Furthermore, the following method may be mentioned as a preferred embodiment of the present invention, but is not limited thereto. For example, the overflow liquid discharged from a bleach-fixing bath, a fixing bath, a subsequent washing bath or an intermediate bath containing a soluble silver salt and an organic acid iron compound is collected in a storage container, and the compound represented by the above-mentioned general formula [] is stored therein. silver can be recovered by electrolysis. Furthermore, two or more overflow liquids from each of the above-mentioned baths can be mixed and stored in a storage container, and the compound represented by the above-mentioned general formula [] can be added thereto to recover silver by electrolysis. Furthermore, in the fixing bath, it is also possible to add a compound represented by the above general formula [] to the overflow liquid, recover silver by electrolysis, correct components exhausted by processing, and reuse the silver. Alternatively, the compound represented by the above general formula [] may be added to the replenisher of the fixer and intermediate solution, and one or more of the overflow solutions may be mixed as described above, and the mixture may be stored in a storage container and silver may be recovered by electrolysis. can. Furthermore, in the method of adding the compound represented by the general formula [] to the replenisher, it is also possible to connect the fixing bath and an electrolytic device and recover silver by electrolysis during continuous processing. Furthermore, it can also be applied to a method for recovering silver from a bleach-fix solution using an electrodialysis method disclosed in Japanese Patent Publication No. 53-60371. That is, a concentrated solution containing an electrolyte such as thiosulfate and a silver salt obtained by electrodialysis contains a microdialyzed ferric salt of an organic acid such as ethylenediaminetetraacetic acid, which is the main component of the bleach-fix solution. Sometimes,
When recovering silver from such a solution by electrolysis, the efficiency can be increased by adding a compound represented by the general formula (). The silver recovery method according to the present invention can be applied to any liquid, not only a photographic liquid, as long as it contains the above-mentioned soluble silver salt and organic acid iron compound. According to the present invention, all of the above objects of the present invention can be achieved, and the remarkable effects of the present invention are listed as follows. (1) A solution containing a soluble silver salt and an organic acid iron compound,
When using a commonly used electrolytic device for fixing solutions or bleach-fixing solutions, silver can be recovered without reducing current efficiency. (2) It can prevent the decomposition of sulfite that occurs during electrolytic silver recovery. (3) The fixer containing the organic acid iron compound can be reused. Hereinafter, the details of the present invention will be explained with reference to Examples, but the embodiments of the present invention are not limited thereto. [Example 1] Sakura color negative film [Konishi Roku Photo Industry Co., Ltd.]
ACOM-1 camera [manufactured by Konishiroku Photo Industry Co., Ltd.]
After photographing using an automatic developing machine [Noritsu Koki Co., Ltd.]
Continuous replenishment processing (hereinafter referred to as running processing) was carried out using the following process using a hanging type H4-72S made by the company.

[Bleach bath solution]

[Ethylenediaminetetraacetic acid iron ammonium salt 100g Ethylenediaminetetraacetic acid diammonium salt 10g Ammonium bromide 150g Add water to make 1, and adjust the pH to 6.00 using aqueous ammonia or glacial acetic acid. ] [Bleach replenisher] [Ethylenediaminetetraacetic acid iron ammonium salt 118g Ethylenediaminetetraacetic acid iron diammonium salt 11.8g Ammonium bromide 177g Add water to make 1, and adjust to PH5.90 using aqueous ammonia or glacial acetic acid. ] [Fixer bath solution] [Ammonium thiosulfate 175g Anhydrous sodium sulfite 8.6g Sodium metabisulfite 2.3g Add water to make 1, and adjust the pH using 20% sulfuric acid.
Adjust to 6.00. ] [Fixer replenisher] [Ammonium thiosulfate 205g Anhydrous sodium sulfite 10.1g Sodium metabisulfite 2.7g Add water to make 1, and adjust to PH6.20 using 30% sodium hydroxide. ] The processing method was running processing according to the CNK-4 processing manual [Konishi Roku Photo Industry Co., Ltd.]. At this time, the silver concentration of the overflow liquid discharged from the fixing bath was 6 g/g/. Also, the amount of iron that was carried into the fixing bath from the bleaching bath and accumulated was 1.8 g/min.
When the overflow liquid discharged from the fixing bath is accumulated in the storage container, the pH is adjusted to 6.70 and the fixing liquid electrolytic device SP-30 [Sun Seiki Seisakusho Co., Ltd.
Co., Ltd., and electrolyzed. This was used as a comparative example for this experiment. On the other hand, as the present invention, an exemplary compound [A-2] of the compound represented by the general formula [],
After adding 3.2 g of [A-4], [1-10], and [A-12] per overflow liquid and adjusting the pH to 6.70, they were transferred to the fixing electrolytic bath as in the above comparative example and electrolyzed. did. Electrolysis conditions are cathode rotation speed 100rpm and current
0.5A/hr was applied. After electrolyzing the solution for 5 hours under these conditions, the amount of remaining silver and the amount of remaining sodium sulfite was analyzed. PH was also measured and the results are shown in Table 1. Note that the amount of residual silver and the amount of residual sodium sulfite were expressed as a percentage, with the analytical value before electrolysis being 100.

[Example 2]

Sakura color paper (roll form, manufactured by Konishiroku Photo Industry Co., Ltd.) was baked and printed, and then subjected to running processing using an automatic developer (RP-1180 processor, manufactured by Noritsu Koki Co., Ltd.). [Processing process Processing temperature (℃) Processing time Color development 33 3 minutes 30 seconds Bleach fixing 33 1 minute 30 seconds Pre-washing 25-33 1 minute seconds Water washing 25-33 3 minutes seconds] Processing solution is CPK-12 [Roku Konishi photo [manufactured by Kogyo Co., Ltd.] was used, and running treatment was performed according to the manual.
Preliminary water washing was installed to recover silver and reduce pollution, and 200 ml of replenisher was added to each square meter of color paper every ³ minutes. When the overflow liquid discharged from the bleach-fix bath and pre-washing bath containing organic acid iron compounds in the above-mentioned treatment was accumulated in a storage container, silver and ethylenediaminetetraacetic acid iron ammonium salt were analyzed, and silver was found to be 3 g/ It was hot. Also, the amount of iron was 7g/. At this time, the pH was adjusted to 7.10. Such a solution is used in an electrolytic device for bleach-fixing solution, SilV Pac-BF,S.
- Type BF [Computerized Polyurethane Abatement Co., Ltd.
Pollution abatement CO.) was transferred to an electrolytic tank for electrolysis. This was used as a comparative example for this experiment. On the other hand, as an experiment of the present invention, exemplified compounds [A-2], [A-5], [A-6], and [A-12] of the compound represented by the general formula [] were added to the above-mentioned 30 liquids by overflowing. 12.7g per liquid was added and the pH was adjusted to 7.10. Thereafter, it was transferred to an electrolytic cell and electrolyzed in the same manner as in the comparative example described above. The electrolytic conditions were a cathode rotation speed of 500 r.pm and a current of 30 A/min.
hr flowed. After electrolyzing the solution for 2 hours under these conditions, the amount of residual silver and the amount of sodium sulfite remaining were analyzed. PH was also measured and the results are shown in Table 2. In addition, the amount of residual silver and the amount of residual sodium sulfite are based on the analytical values before electrolysis.
Expressed as a percentage relative to 100.

[Example 3]

After photographing Super 8 Sakura Chrome 160 Type A [manufactured by Konishi Roku Photo Industries Co., Ltd.] using a Konica Super 8-3TL camera [manufactured by Konishi Roku Photo Industries Co., Ltd.], an automatic processor [Noritz Koki Co., Ltd.] Co., Ltd., NC8-50] was used for running treatment. Processing process Processing temperature (℃) Processing time [1st development 33.5 3 minutes 30 seconds 1st stop 38 1 minute 1st water wash 38 1 minute 30 seconds color development 43 3 minutes 40 seconds 2nd stop 38 1 minute 2nd water wash 38 1 Bleach for 1 minute and 30 seconds 38 Bleach neutralization for 1 minute and 30 seconds 38 Fix for 1 minute and 30 seconds 38 Final washing for 1 minute and 30 seconds 38 Stabilize for 1 minute and 30 seconds 38 1 minute] Bleach, bleach neutralization and fixing solutions are used as processing solutions. Except for the rest, CEK-2 (manufactured by Konishiroku Photo Industry Co., Ltd.) was used, and the amount of replenisher and processing method were carried out in accordance with the manual. Next, the compositions of bleaching, bleach neutralization, and fixing solutions are shown. [Bleach bath and replenisher] Bath solution Replenisher [ferric chloride (38w/w%)
350g/ 350g/ PH 0.75 0.75]

【table】

[Table] When running processing was carried out using the solution according to the above processing method and composition, the silver concentration of the overflow solution discharged from the fixing bath was 5.9 g/. Also, the amount of iron that was brought into the fixing bath from the bleach neutralization bath and accumulated was 0.27g/
It was hot. When the overflow liquid discharged from the fixing bath is accumulated in a storage container, the pH is adjusted to 7.80, and the electrolytic device SP-30 for fixing liquid is used.
It was transferred to an electrolytic cell manufactured by Sun Seiki Seisakusho Co., Ltd. and electrolyzed. This was used as a comparative example for this experiment. On the other hand, when the treatment liquid described above as the present invention reaches 40%, exemplified compounds [A-1], [A-3], [A-7], [A-
12] was added at 0.49g per overflow liquid,
The comparative example described above was similarly transferred to an electrolytic cell for a fixer and electrolyzed. The electrolysis conditions were the same as in Example 1. After electrolyzing for 5 hours under these conditions, the solution was analyzed for residual silver content and residual ammonium sulfite content. PH was also measured and the results are shown in Table 3.
Note that the amount of residual silver and the amount of residual ammonium sulfite were expressed as a percentage, with the analytical value before electrolysis being 100.

[Example 4]

Exemplary compound [A-12] of the compound represented by the general formula [] using the overflow liquid of Example 1
The amount of addition was varied. Addition amount is 0.05g, 1.2g, 1.6g, 2.4g, 3.2g per overflow liquid.
and adjusted the pH to 6.70. Further, the electrolytic conditions at this time were the same as in Example 1. After electrolyzing the solution for 5 hours under these conditions, the amount of remaining silver and the amount of remaining sodium sulfite was analyzed. PH was also measured and the results are shown in Table 4.
Incidentally, the amount of remaining silver and the amount of remaining sodium sulfite at this time were expressed as a percentage, with the analytical value before electrolysis being taken as 100.

[Example 5]

Sakura Color Negative Film [Konishiroku Photo Industry Co., Ltd.]
ACOM-1 camera [manufactured by Konishiroku Photo Industry Co., Ltd.]
After photographing using an automatic developing machine [Noritsu Koki
The running process was carried out using a hanging type H4-72S manufactured by Co., Ltd. according to the following steps.

[Table] The same treatment liquid as in Example 1 was used as the above treatment liquid. The silver concentrations in the bleaching, prewashing, and fixing overflow solutions from these running treatments were 1 g/in the bleaching process, 0.3g/in the prewashing process, and 6g/in the fixing process. When 40% of these overflow liquids were accumulated in the storage container, the silver and iron were analyzed again, and the result was 4.2g of silver and 2.97g of iron per unit.
It was hot at g. PH the overflow liquid like this
6.70, and electrolysis was carried out under the same conditions as in Example 1.
This was used as a comparative example for this experiment. On the other hand, in the present invention, an exemplary compound [A-2] of the compound represented by the general formula [],
[A-3] and [A-12] were added in an amount of 5.4 g per overflow liquid, and the pH was adjusted to 6.70, followed by electrolysis using the electrolyzer described above. After 5 hours of electrolysis, the amount of silver remaining in the electrolyte and the amount of sodium sulfite remaining were analyzed, and the pH was measured. The results are shown in Table 5. Incidentally, the amount of remaining silver and the remaining sodium sulfite at this time were expressed as a percentage, with the analytical value before electrolysis being taken as 100.

[Table] As is clear from Table 5, by adding the compound of the present invention represented by the general formula [], there is almost no decomposition of sodium sulfite and no fluctuation in pH, and silver is removed at the cathode by electrolysis. It can be seen that the amount of precipitation can be improved.

Claims (1)

[Claims] 1. A solution containing an iron compound having an organic acid as a ligand and a soluble silver salt having a lower stability constant for ferric ion than a compound represented by the following general formula []. A method for recovering silver, comprising recovering silver by electrolysis in the presence of a compound represented by the general formula [] in an amount capable of chelating substantially all of the ferric ions of the iron compound. General formula [] [In the formula, R represents an alkyl group or substituted alkyl group having 1 to 5 carbon atoms, and X represents a hydroxyl group or an amino group. ]