JPS6126796A - Recovering apparatus of silver in spent bleaching fixer solution - Google Patents

Abstract

PURPOSE:To precipitate Ag at cathode surface with superior electrolytic power efficiency, by isolating a cathode vessel and an anode vessel with a diaphragm having specified small holes, in electrolytic recovering of Ag from spent bleaching fixer soln. CONSTITUTION:Electrolytic cell is divided to the cathodic vessel 4 and the anodic vessel 6 with the diaphragm 2, in recovering electrolytically Ag dissolved from fixing solution for color photograph contg. bleaching agent besides dissolving Ag. A resin film 28 such as polypropylene having many small holes of 0.003-2.0mu diameter whose both surfaces are held in-between resin sheets 30, 30 such as polyvinyl chloride having many holes 31 is used for the diaphragm 2. Aqueous soln. contg. electrolyte such as aqueous NaOH soln. is poured in the vessel 6, spent bleaching fixer soln. is poured in the vessel 4, and electrolysis is performed while revolving the cathode 3 by a motor 11. Ag in bleaching fixer solution is precipitated on the cathode 3, and entry of bleaching agent into the vessel 6 is prevented by the diaphragm 2. Consequently, useless power consumption due to repeated reaction in which Ag is oxidized in the vessel 6, entered again into the vessel 4 and reduced, is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Technical Field The present invention relates to an apparatus for recovering silver from a bleach-fix solution for color photography.

[Background Art] A photographic fixer is used to stop the development of a developed film or photosensitive paper and to remove unexposed portions. Therefore, the fixer contains an unexposed fraction, and silver is recovered from the used fixer. In order to recover silver from the fixing solution, an upstream electrolysis method has been generally used. That is, by supplying a used bleach-fix solution to an electrolytic cell equipped with a cathode and an anode and energizing it, the silver ions in the bleach-fix solution are converted into metallic silver by the reduction action of the cathode, and the silver is converted into metallic silver. It is made to precipitate on the surface. This method makes silver pure 1
This is a very effective method for collecting information. However, this method (i.e., the direct electrolytic method in which the cathode and anode directly interact with the processing solution) does not pose any particular problems when recovering silver from the fixer for black and white photography, but it This method cannot be said to be suitable in the case of a fixer solution. In other words, fixing solutions for color photography contain bleaching agents to dissolve and remove silver images and dye images that are ultimately unnecessary, and this bleaching agent reduces silver recovery efficiency. That's what happens. That is, a reduction reaction occurs at the cathode, and silver is deposited as shown in equation (1).

Ag++e-→Ai+ (metallic silver)...(1)
At this time, the bleaching agent in the fixing solution, for example, the iron complex of ethylenediami7tetraacetic acid [EDTA-Fe([1 )] undergoes a reduction reaction at the cathode, and the trivalent iron becomes divalent as shown in equation (2).

EDTA-Fe(I[l) 10e--+EDTA-F
e(II)-(2) Thus EDTA-Fe(D
I) undergoes a reduction action to EDTA-Fe(It) at the cathode, and the electric power for electrolysis is consumed in this reduction action, which is unavoidable in recovering silver by electrolytic method. However, in the above-mentioned direct electrolysis method, EDTA-Fe(■) produced by the reduction action at the cathode
is transferred to the anode, and is then subjected to oxidation by the anode, changing to EDTA-Fe(n[) as shown in equation (3).

EDTA-Fe(n) - EDTA-Fe(II) 10e--(3) Then, EDTA-Fe(I [[), in which iron has become trivalent, returns to the cathode, and the above ( 2) It will undergo a reduction action in the same reaction as in equation.

In this way, the direct electrolysis method uses EDTA mixed in the fixing solution.
-Fe(III) is subjected to the reduction action twice, and EDTA-Fe(III) is subsequently subjected to the reduction action many times at the cathode in the same manner. In other words, E, DTA-Fe(
Since I[[) and EDTA-Fe(If) are mixed in the electrolytic bath, such reactions of reduction and oxidation are repeated many times. Therefore, EDTA-Fe(II
If the amount of I) is small and it undergoes the reduction action only once at the cathode, the power consumed for this reduction action is small, but since it is subjected to the reduction action at the cathode many times. The power consumed for this reduction action is enormous, and the direct electrolysis method ultimately requires a large amount of power to recover a given amount of silver, resulting in a very low recovery rate of silver per unit charge. This is expected to decrease. In addition, in the above, EDTA-
Although Fe(III) has been explained above, the same can be said about bleaches in general.

[Object of the Invention] The present invention has been made in view of the above points, and it is possible to minimize the power consumed by reducing the bleaching agent at the cathode, and to improve the bleach-fixing process. It is an object of the present invention to provide a silver recovery device for a used bleach-fix solution that has excellent recovery efficiency of silver from the solution.

[Disclosure of the Invention] According to the silver recovery device for used bleach-fix solution according to the present invention, a silver recovery container 1 is connected to a cathode 3 by a diaphragm 2 that does not allow the processing solution to pass through but allows electricity to pass therethrough. It is characterized by being divided into a cathode tank 4 to which a bleach-fix solution is supplied and an anode tank 6 in which an anode 5 is disposed. By separating and performing electrolysis using a diaphragm method, the above purpose is achieved by preventing the treated bleach-fix solution that has undergone a reduction reaction in the cathode tank 4 from undergoing an oxidation reaction in the anode tank 6. The present invention will now be described in detail by way of examples.

1 and 2 show an example of the apparatus of the present invention, in which a diaphragm 2 formed in the shape of a square cylinder is arranged inside a silver recovery container 1 formed in the shape of a square cylinder with a bottom. This diaphragm 2 partitions the interior of the silver recovery container 1 into an inner cathode tank 4 and an outer anode [6].

Here, the Fi@ membrane 2 is made by extruding and stretching a resin film 28 made of polypropylene, other polyethylene, polyethylene terephthalate, polytetrafluoroethylene, polycarbonate, etc., so that the pore diameter is 0.003 to 2.
．． It is formed with a countless number of small holes 7, 7, . This interval 1
11J2 has small holes 7, 7... whose size is 0.003 to 2.
．． Since it is 0 μ, the bleach-fix solution cannot pass through, but electricity cannot be passed between the cathode tank 4 and the anode tank 6 through the bleach-fix solution filled in the small holes 7, 7... It is possible. Here, if the diameter of the small hole 7 is less than 0.003μ, the bleach-fix solution cannot enter into the small hole 7 at all, and electricity cannot flow through the diaphragm 2 between the cathode tank 4 and the anode tank 6. However, the diameter of the small hole 7 is 2.0.
If μ is exceeded, even if the water levels of the liquid in the cathode tank 4 and the anode tank 6 are equal, the liquid will pass through the small hole 7 and the liquid will flow between the cathode tank 4 and the anode tank 6. More preferably small holes 7,7
The diameter of ... is preferably set to O, Oa to 0.5μ, and the best results can be obtained within this range. Incidentally, the diameter of the small hole 7 was measured by measuring an enlarged photograph taken with an electron microscope. When using this diaphragm 2, a non-woven fabric 29 made of chemical fibers such as polyester is attached to one side of the diaphragm 2 as shown in FIG. 3(b) to improve mechanical strength, and further, as shown in FIG. 3(a), In this way, it is sandwiched between resin plates 30 and 30 made of polyvinyl chloride or the like with holes 31 and reinforced with the resin plates 30 and 30 to be finished into a plate shape. This material is used by assembling four pieces into a square tube shape. And silver collection container 1
A cylindrical body 10 is raised from the center of the bottom surface of the cylindrical body 10, and the lower end is passed through the cylindrical body 10 through a rotary shaft 12 connected to an electric motor 11. The rotary shaft 12 is rotatably supported on the cylindrical body 10 by a bearing 13. A disc-shaped support plate 14 is attached to the upper end of the rotating shaft 12 that is led upward from the upper end of the cylinder 1.0, and a cathode 3 formed in the shape of a cylindrical drum made of stainless steel or the like is attached to this support plate 14. The cathode 3 is placed in the cathode tank 4 with the upper end thereof fixed with a bolt/nut 15 or the like. Further, an anode 5 formed of an artificial graphite plate or the like is attached to the inner surface of each side of the silver recovery container 1 so as to face the inside of the anode tank 6.

The apparatus according to the present invention formed as described above is used to recover silver from a used bleach-fix solution. First, the anode tank 6 is filled with a solution containing a suitable electrolyte such as a caustic soda solution. In addition, the cathode bath 4 is filled with a used bleach-fix solution from which silver is to be recovered. Here, it is preferable to set the liquid levels in the cathode tank 4 and the anode tank 6 to be approximately equal, so that a large pressure difference due to the water level difference does not occur between the cathode tank 4 and the anode tank 6. It is better to keep it that way. Thereafter, the cathode 3 formed as a drum is driven to rotate by an electric motor 11, and the cathode 3 and anode 5 are energized. The conditions for electrolysis by energization can be set using a current regulator and a timer. When electricity is applied in this way, electricity flows through the diaphragm 2 and electrolysis occurs, a reduction reaction occurs near the cathode 3 of the cathode cell 4, an oxidation reaction occurs near the anode 5 of the anode 1/fI6, and the cathode cell 4 Now, the above (1)
) Silver ions in the bleach-fix solution are reduced to metallic silver, which is deposited on the surface of the cathode 3. In the cathode tank 4, in addition to the reaction of formula (1), the reaction of the above (2)
) The bleach contained in the bleach-fix solution also undergoes a reduction reaction. Here, the distance between the cathode tank 4 and the anode tank 6 is 1!
Since the liquid in the cathode tank 4 and the liquid in the anode tank 6 are separated by 2, the liquid in the cathode tank 4 and the liquid in the anode tank 6 do not flow, and the bleach reduced in the cathode tank 4 has an oxidizing effect in the anode tank 6. This prevents the bleaching agent from being oxidized or, conversely, from being subjected to the reduction action again in the cathode tank 4. Therefore, it is possible to prevent the bleach contained in the bleach-fix solution from undergoing repeated reduction and oxidation reactions between the cathode 3 and the anode 5, as in the case of the conventional direct electrolysis method. This means that the amount of electricity consumed to reduce and oxidize can be kept low.

In addition, when depositing silver on the surface of the cathode 3, only the Ag+ contained in the bleach-fix solution that comes into contact with the cathode 3 undergoes a reduction reaction and is deposited as metallic silver. If the solution inside is in a stationary state, the Ag+ concentration in the bleach-fix solution near the surface of the cathode 3 will drop to almost zero in a very short time, and the reducing action at the cathode 3 will be (
It mainly works to decompose thiosulfate ions and water, which are contained as main components in the fixing solution as shown in equations 4) and 5).

52032+ 2e-→S2-+ SO32-...(
4) H" + e--1/ 2 H2↑ ・(5)
Then, the 52- (sulfur ion) generated in this way diffuses into the liquid and reacts with unreacted Ag+ to form fine particles of A.
g2S (silver sulfide) is generated, and normal metallic silver is continuously deposited on the cathode 3, thereby running out. Therefore, in the above device, the cathode 3 is formed as a rotating drum, and as the cathode 3 is rotated, the liquid in the cathode tank 4 is agitated, and this problem does not occur. This is to prevent this.

As described above, electrolysis is carried out to deposit silver on the cathode 3. When the set electrolysis time has elapsed, the rotation of the cathode 3 of the rotary drum is stopped, and the current supply is also stopped. After the treated solution from which silver has been removed is discharged, a used bleach-fix solution for recovering silver is supplied into the cathode tank 4. Thereafter, by repeating the same operations as above, it is possible to recover a predetermined amount of silver from the used bleach-fix solution.

In addition to the resin film described above, the diaphragm 2 may also be made of ceramics, asbestos, etc., but ceramics and asbestos cannot be formed as thinly as resin films, and the small holes 7 may be blocked. This is undesirable because it easily peels off. In other words, if electrolysis is not performed for a long time, the water in the bleach-fix solution that has entered the small holes 7 will evaporate and crystals and insoluble sulfur will precipitate. The length of the small hole 7 becomes longer and the small hole 7 is easily blocked by these holes. If the small hole 7 is blocked in this way, the electrical flow between the cathode M4 and the anode tank 6 is reduced. This will seriously hinder their efforts.

Next, further explanation will be provided using specific experimental examples.

Experimental Example 1 Using the apparatus shown in FIG. 1, silver was recovered from a used bleach-fix solution. Here, the capacity of the cathode tank 4 of the apparatus is set to 40 liters, and the capacity of the anode tank 6 is set to 27 liters. As the diaphragm 2, a 25μ thick polypropylene film in which many small holes 7 with a diameter of 0.1μ are provided is used, and one side of this polypropylene film has a thickness of 75μ.
Polypropylene non-woven fabric is layered, and this is further layered to a thickness of 5.
First, 4.60 g/LFe (II
I) as EDTA-Fe(III) 5500mg/
The used bleach-fix solution containing 40 liters is supplied to the cathode tank 4, and a 20% caustic soda solution is supplied to the anode tank 6, and then the cathode 3 and the anode 5. The cathode 3 was driven to rotate at the same time as the current was applied. The current of energization is 3O
A was maintained, and the time of this electrolytic treatment was 5 hours.

Immediately after the electrolytic treatment was completed, the treated liquid was discharged from the cathode tank 4, and the Ag+ concentration of this liquid was measured and found to be 0.
．． It was 065g/I. Therefore, the yield of silver per unit current/unit time is 1.2 g-Ag/A-H.

For comparison, silver was recovered by direct electrolysis without using diaphragm 2 and using other conditions as in Experimental Example 1. In this case, the silver yield was 0.5-0.6 g-Ag/A-H.

A polycarbonate film with a thickness of 40μ and provided with many small holes 7 with a diameter of 0.25μ was used as the diaphragm 2 for the diaphragm 2.
+ is 3.82g/l, Fe(III) is EDTA-F
e(I[[) as 450011? Electrolytic treatment was carried out in the same manner as in Experimental Example 1, except that a used bleach-fix solution containing /I was used.

The electrolysis time at this time was 4 hours. Further, when the treated liquid in the cathode tank 4 was sampled and the Ag+ concentration was measured, it was 0.082 g/l. Therefore, the yield of silver per unit current/unit time is 1.25 g-g/A·4.

Comparative Experimental Example 2 For comparison, silver was recovered by direct electrolysis without using the diaphragm 2 and using other conditions as in Experimental Example 2. In this case, the silver yield was 0.62 g-Ag/A.H.

As seen in Experimental Example 1.2 and Comparative Experimental Example 1.2 above, it is confirmed that by using the apparatus of the present invention, silver can be recovered in good yield with the same electricity consumption.

[Effect of the Invention J As described above, in the present invention, a silver recovery container is provided with a cathode tank and a used bleach-fix solution is supplied with a cathode through a diaphragm that does not allow processing solution to pass through but allows electricity to pass through. Since the silver recovery device is configured by partitioning the anode tank into an anode tank where the anode is installed, the cathode tank and the anode tank are separated by a diaphragm, and the liquid in the anode tank is prevented from flowing into the cathode tank during electrolysis operation. It is possible to prevent the bleach from flowing into the anode tank, and the bleach that has been oxidized in the anode tank is reduced again in the cathode tank.
It is possible to prevent the bleach contained in the bleach-fix solution from undergoing repeated reduction and oxidation reactions at the cathode and anode, as in the case of conventional direct electrolysis methods. By keeping down the amount of electricity consumed to reduce and oxidize the bleaching agent, silver can be efficiently recovered with minimal electricity consumption.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the device of the present invention, Fig. 2 is a schematic perspective view of the same, and Fig. 3 (a), (b,) are exploded perspective views of a diaphragm used in the same. FIG. 1 is a silver recovery container, 2 is a diaphragm, 3 is a cathode, 4 is a cathode bath, 5
is an anode, 6 is an anode tank, and 7 is a small hole.

Claims (4)

[Claims] (1) The silver recovery container is divided into a cathode tank in which a cathode is installed and used bleach-fix solution is supplied, and an anode tank in which an anode is installed, by a diaphragm that does not allow the processing solution to pass through but allows electricity to pass through. A silver recovery device for used bleach-fix solution, characterized in that: (2) The used diaphragm according to claim 1, characterized in that the diaphragm is formed with a large number of fine holes penetrating the front and back sides, and the inside diameter of the holes is 0.003 to 2.0μ. Silver recovery equipment for bleach-fix solution. (3) Claim 1 or 2, characterized in that the cathode is formed in the shape of a cylindrical drum that is rotationally driven.
A device for recovering silver from used bleach-fix solution as described in Section 1. (4) The use according to any one of claims 1 to 3, wherein the diaphragm is sandwiched between a pair of reinforcing perforated resin plates and provided in the silver recovery container. Silver recovery equipment for bleach-fix solution.