JPH0387400A - Single-electrode electrolytic cell and electrolyzing method - Google Patents

Abstract

PURPOSE:To efficiently recover an electrolyzed product by placing an electrode of fibrous carbon in the electrode chamber of a singleelectrode electrolytic cell separated by a diaphragm having a filtration function and transferring the electrolyte to a counter electrode chamber through the diaphragm after electrolysis. CONSTITUTION:The single-electrode electrolytic cell 1 is separated by the diaphragm 3 into two electrode chambers. A filtration function is imparted to the diaphragm 3 in the cell 1 by using a. cartridge filter, etc. The fibrous carbon 8 connected to a current collector 7 is placed at least in the separated cathode chamber 5 as a cathode, and an anode 6 is arranged in an anode chamber 4. A current is applied to the cell 1, an electrolyte to be treated such as the waste soln. contg. noble metals is supplied to the cathode chamber 5, and electrolysis is carried out. The solid component in the electrolyte produced by electrolysis is deposited on the cathode 8 and in the cathode chamber 5. After electrolysis, the inside of the cathode chamber 5 is pressurized to transfer the electrolyte to the anode chamber 4 through the membrane 3. The solid component such as noble metals is collected by the diaphragm 3, and efficiently recovered.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a monopolar electrolytic cell used for recovering useful components produced by electrolysis in solutions such as waste liquid treatment and metal recovery, and its electrolyzer. Regarding the method.

(Prior art and its problems) Electrolysis has conventionally been used to treat plating waste liquid and recover precious metals and the like from the waste liquid. For example, when waste liquid treatment is performed by a method other than electrolysis, the waste liquid generally contains waste organic matter that is highly viscous and difficult to handle, making it difficult to perform normal treatment operations and often resulting in the waste organic matter being unable to be decomposed and being disposed of as is. ing. However, when the waste liquid is treated using electrolysis, the organic matter is decomposed on the electrode surface simply by introducing the waste liquid into an electrolytic cell, and can be decomposed into harmless gases, water, and the like.

Organic electrolysis, which is used to generate organic reactions and convert organic compounds into other compounds, almost completely suppresses the side reactions that occur almost inevitably in normal organic reactions, and produces the desired compounds in high yields. and selectivity.

As described above, electrolytic reactions have many advantages compared to general organic and inorganic reactions, and are therefore widely used industrially. Various techniques have been proposed.

For example, there is a method of using a porous electrode as an electrode, and it is known that this method increases the surface area of the electrode and contacts the electrolyte over a wide area, increasing the rate of electrolytic reaction. However, when electrolysis is carried out using, for example, a porous carbon plate as an electrode, the electrode reaction actually occurs only on the flat surface facing the counter electrode, and the area contributing to electrolysis does not increase.

In order to overcome these drawbacks, the present applicant proposed an electrolytic cell and an electrolytic method using fibrous carbon as an electrode, particularly a cathode (Japanese Patent Application No. 1-128553).

In this electrolysis method, the electrolytic reaction can be efficiently caused by using an electrode with an increased surface area of the electrode surface that contributes to the electrolytic reaction.In particular, when used to recover metals from waste liquid, the metal ions in the solution are When a single metal is electrodeposited on the fibrous carbon cathode and then the polarity of both electrodes is reversed and electricity is continued, the electrodeposited metal is redissolved and the metal ions in the waste liquid can be purified and recovered. .

However, in such metal recovery, the metal ions in the solution are not always deposited as simple metals on the fibrous carbon cathode, and when the metal ions react with other components in the solution due to electrolysis. A metal compound is produced, and the metal compound is not deposited on the fibrous carbon cathode but floats or precipitates in the cathode chamber. In such a state, even if the polarity is reversed and electricity is continued, the floating or precipitated metal compounds will not be redissolved and cannot be recovered.

(Objective of the Invention) The present invention is an apparatus for efficiently recovering not only simple metals but also metal compounds when recovering metals through electrolytic reactions, or for efficiently recovering products generated in organic electrolysis or anodic oxidation electrolysis. and a method.

(A half-dead solution to the problem) The present invention firstly provides a monopolar electrolytic cell that is divided into two electrode chambers by a diaphragm, in which the diaphragm has a filtering function and the current collector has a filtration function. It is a monopolar electrolytic cell characterized in that connected fibrous carbon is used as an electrode in at least one electrode chamber to perform electrolysis, and secondly, two
While energizing the monopolar electrolytic cell, which contains fibrous carbon connected to a current collector in at least one electrode chamber of the monopolar electrolytic cell divided into electrode chambers, the fibrous carbon is used as an electrode. An electrolytic solution to be treated is supplied to an electrode chamber containing carbon, and solid content in the electrolytic solution generated by electrolysis is transferred onto the fibrous carbon electrode and/or into the electrode chamber containing the fibrous carbon electrode. The electrolytic method is characterized in that the electrolytic solution is caused to precipitate, the electrolytic solution is transferred into a counter electrode chamber through the diaphragm, and the solid content is collected and recovered by the diaphragm.

The present invention will be explained in detail below.

The monopolar electrolytic cell and electrolysis method according to the present invention are applicable to waste liquid treatment, metal recovery from catalyst waste liquid such as petroleum refining catalysts and automobile catalysts, recovery of solid components in organic electrolysis and anodic oxidation electrolysis, waste liquid for photographic development, etc. It can be used in electrolysis, particularly for recovering metal ions in solution, such as recovering silver from photographic fixers.

The present invention uses a fibrous carbon electrode connected to a current collector as at least one electrode. As mentioned above, when electrolysis is performed using a normal porous material such as a porous carbon plate as an electrode,
Even if the electrode itself has a high surface area, the only part that effectively functions as an electrode is the surface facing the counter electrode, and it actually has little effect on increasing the electrolytic area.

On the other hand, in the electrolytic cell according to the present invention using a fibrous carbon electrode, although the reason is not clear, almost the entire surface of each fiber of the fibrous carbon electrode undergoes an electrode reaction, resulting in an increase in the effective electrode area. becomes enormous. This effect is due to the fact that the length of the fibrous carbon is long enough so that there is no potential gradient within the electrode and the potential is the same in every part of the electrode, so electrolytic reactions occur in any part of the electrode and almost the entire surface of the electrode acts as an electrode. It can be assumed that this is because it functions.

Therefore, the current density becomes extremely small, thereby dramatically improving current efficiency. For example, when recovering precious metals in waste liquid by electrolytically depositing them on a cathode, the concentration of the precious metals is 1.
0 to 1000 mg/ (about 1 mg/l)
If a conventional plate-shaped carbon cathode is used to reduce the current efficiency to less than It increases to about 30%.

As the fibrous carbon used in the present invention, commercially available fibrous carbon may be used, and fibrous carbon having a bottom shape such as felt or cotton-like may be used as is.

Since the fibrous carbon itself does not have an electrolysis voltage reduction function, in order to reduce power consumption by reducing the voltage, it is necessary to support a noble metal catalyst such as palladium, ruthenium, or platinum on the fibrous carbon. There is. This makes it possible to reduce the electrolytic voltage and promote the electrolytic reaction, as well as to extend the life of the fibrous carbon electrode.

The fibrous carbon electrode is used as a cathode in ordinary metal recovery to construct a monopolar electrolytic cell, but depending on the polarity of the electrolyte, it can also be used as an anode in, for example, organic electrolysis or anodic oxidation electrolysis. In the present invention, the diaphragm that divides the electrolytic cell into an anode chamber and a cathode chamber has a filtration function, so that it can be transferred from one electrode chamber to the other electrode chamber, that is, from the cathode chamber to the anode chamber, or vice versa. While the electrolyte is permeating through the electrolyte, the electrodeposited metal, the electrodeposited metal compound, the anodic oxidation product, etc. floating or precipitated in the electrolyte are filtered and recovered by the diaphragm. Therefore, in the present invention, in the case of recovering metals from waste liquid, etc., an electrolytic solution containing metal ions to be collected by filtration is supplied to the cathode chamber, and the electrolytic solution is guided through the diaphragm to the other anode chamber, where the metal ions are collected. The recovered electrolyte is taken out from the anode chamber. On the other hand, in the case of recovering products of organic electrolysis or anodic oxidation, the electrolytic solution to be treated is supplied to the anode chamber and the electrolytic treatment is performed, and then the electrolytic solution is introduced to the cathode chamber through the diaphragm and the products are recovered. The electrolyte solution is removed from the cathode chamber.

As a diaphragm having such a filtration function, various materials such as cartridge filters and filter cloths can be used.As electrolysis continues, deposited metals accumulate on the diaphragm and the permeation efficiency of the electrolyte solution decreases. To prevent this, it is preferable to use an easily replaceable diaphragm, for example, a cartridge filter, and to periodically replace it.

The present invention is particularly useful for recovering silver from waste solutions for photographic development and for recycling fixing solutions for photographic development. In particular, in the silver recovery, it may be preferable to recover silver as solid silver or a silver compound. A high concentration of silver ions is dissolved in the waste solution for photographic development, and as mentioned above, attempts have been made to recover silver by electrolytic methods, but in addition to silver ions, the waste solution also contains sulfur-containing compounds such as sodium thiosulfate. is dissolved, and under normal electrolysis conditions, the metal ions react with the sulfur in the sulfur-containing compound on the cathode to form a precipitate containing sulfur such as silver sulfide, and most of the precipitate is not deposited on the cathode. It either floats in the electrolyte or precipitates and deposits on the bottom plate of the cathode chamber.

On the other hand, when recovering some of the silver that accumulates in the fixer and maintaining the silver concentration in the fixer within a certain range to extend the life of the fixer, it is necessary to not only recover silver but also to maintain the silver concentration in the fixer within a certain range. For example, if silver in the fixer is electrodeposited as silver sulfide, the sulfur concentration in the fixer will decrease and it will no longer be possible to use the fixer as a fixer with a certain level of performance. It disappears. Therefore, in the case of silver recovery from the fixer, it is necessary to electrodeposit and recover silver in the form of metallic silver.

Not only in the case of such photographic waste liquids and fixing liquids, but also in the case of recovering other metals, depending on the liquid properties of the liquid to be treated, it is preferable to electrodeposit the metal as a single substance or as a metal compound. In some cases, it is preferable. In order to cause one of these two to occur almost selectively, it is best to control the current density value, and in general, in ordinary low current density electrolysis, the reaction between silver ions and other anions is inhibited, and the reaction between silver ions and other anions is inhibited and At high current densities, the formation of metal compounds takes precedence and the compounds precipitate, and the precipitates are usually not deposited on the cathode but are deposited or suspended in the cathode chamber. . Even if priority is given to the electrodeposition of an elemental metal onto the cathode, a small amount of a metal compound may be generated and the compound may precipitate or float, and all of the elemental metal that is generated may also be deposited onto the cathode. However, some of it may settle or float.

In order to take these precipitates out of the electrolytic cell and collect them,
As described above, even if the polarity of the electrode is reversed and electricity is applied, the precipitate does not come into contact with the electrode, so the precipitate does not dissolve and cannot be recovered.

Therefore, in the present invention, as described above, the electrolytic solution containing precipitated or floating metallic silver/or silver compounds is trapped in the diaphragm by passing through the diaphragm and moving from one electrode chamber to the other electrode chamber. Please collect and collect them.

This type of monopolar electrolytic cell can have not only a vertical structure in which the electrodes are arranged vertically, but also a horizontal structure in which the electrodes are arranged horizontally, and other electrolytic cell structures are not particularly limited.

In this diaphragm-type electrolytic cell, it is possible to fill the entire electrode chamber with the fibrous carbon electrode, which allows the electrode to come into contact with the diaphragm, enabling so-called zero-gap type electrolysis, and reducing the electrolysis voltage. In addition, it is possible to further increase the electrolytic area.

If metal ions and the like are recovered using an electrolytic cell or an electrolytic method that does not have such a configuration, the target component can be recovered with a recovery rate of over 99% in many cases, although it depends on the conditions.

Next, a preferred example of a monopolar electrolytic cell according to the present invention will be explained based on the accompanying drawings, but the present invention is not limited to this electrolytic cell.

FIG. 1 is a 4-1 cross-sectional view showing an embodiment of a monopolar electrolytic cell of the present invention useful for waste liquid treatment, metal recovery, etc.

Reference numeral 1 denotes a cylindrical electrolytic cell whose upper opening is sealed by a lid 2, and a cylindrical cartridge filter 3 that functions as a diaphragm and has both upper and lower ends closed is installed in the center of the electrolytic cell 1. The electrolytic cell 1 is divided by the cartridge filter 3 into an anode chamber 4 inside the cartridge filter 3 and a cathode chamber 5 between the cartridge filter 3 and the outer wall of the electrolytic cell 1. An anode 6 made of, for example, a cylindrical titanium substrate coated with iridium oxide is installed in the anode chamber 4, while an anode 6 is installed in the cathode chamber 5.
For example, a cylindrical titanium current collector 7 is installed near the outer wall of the cartridge filter 3, and a felt-like fibrous carbon cathode 8 is filled between the current collector 7 and the cartridge filter 3 so as to close the space. has been done.

Reference numerals 9 and 10 denote a liquid supply tank and a waste liquid tank installed outside the electrolytic cell 1, respectively, and the photographic waste liquid stored in the liquid supply tank 9 is passed through the liquid supply line 12 by a liquid supply pump 11 to the cathode chamber. 5, the silver ions in the waste liquid are reduced to metallic silver on the fibrous carbon cathode 8 and electrodeposited on the cathode 8, or the sulfur-containing compounds or ions in the waste liquid, such as thiosulfate ions, are The silver reacts with hydrogen sulfide generated by decomposition on the cathode and is converted into a sulfur-containing silver compound, which floats in the electrolytic solution or precipitates on the bottom plate of the electrolytic cell 1, reducing the silver concentration in the electrolytic solution.

When the internal pressure in the cathode chamber 5 is increased by continuing to supply the liquid, the electrolyte in the cathode chamber passes through the cartridge filter 3 and transfers to the anode chamber 4, and at the time of the transfer, the silver compound floating in the electrolyte or existing as a precipitate is removed. is filtered and collected by the cartridge filter 3. In the anode chamber, an oxygen generation reaction normally occurs due to water electrolysis.

The same amount of electrolyte as the electrolyte transferred to the anode chamber 4 through the cartridge filter 3 is transferred to the anode chamber 4 at one end.
The waste liquid tank 10 is passed through the waste liquid line 13 located at the upper part.
Take it out. Further, the gas generated in the bipolar chamber by the electrolytic reaction is guided by the gas discharge pump 14 through the gas discharge line 15 to the liquid supply tank 9, where it is used for bubbling the stored liquid, and the hydrogen sulfide contained in the exhaust gas is absorbed.

Through such operations, metal ions such as silver in the electrolyte solution, which is photographic waste liquid, are collected in the cartridge filter 3, especially in the form of metal compounds, but in order to actually recover the silver compounds, etc. This is done by stopping the electrolysis and taking out the cartridge filter when a large amount of the silver compound etc. has accumulated in the cartridge filter 3. The electrolytic solution in which the concentration of metal ions such as silver has decreased is taken out to the aforementioned waste liquid tank 10, and is reused or disposed of as necessary.

The remaining metal to be recovered, which is partially electrodeposited on the fibrous carbon cathode 8, can be recovered by inverting the polarity of the two electrodes and applying electricity using the fibrous carbon cathode 8 as an anode. They are dissolved and recovered as ions; in this case, a metal electrode, a graphite electrode, or the like is used as a counter electrode, a cathode. Note that 16 is a circulation line, and the electrolyte in the cathode chamber is circulated through the line 1 without passing through the cartridge filter 3.
The liquid is taken out of the tank through 6 and circulated to the liquid supply tank 9 for reuse.

In this example, it has been explained that silver ions from photographic waste liquid are mainly recovered in the form of a sulfur-containing silver compound, but the present invention is not limited to this. It can be used to recover other components that are susceptible to. Furthermore, even in the case of metal recovery in which most of the metal is electrodeposited on the cathode in the form of an elemental metal, a small amount may float in the electrolyte, and the present invention is effective in reliably recovering such small amounts of components. be.

In the illustrated electrolytic cell, only the method of filling the cathode chamber with fibrous carbon is shown, but for example, a thin felt-like fibrous carbon can be bonded to the cathode current collector and used for electrolysis.

Furthermore, in the illustrated electrolytic cell, the outside of the cylindrical electrolytic cell main body is the cathode chamber and the inside is the anode chamber, but it is also possible to conversely have the outside as the anode chamber and the inside as the cathode chamber. Since the fibrous carbon cathode is housed in the cartridge filter, both the substance filtered by the cartridge filter and the substance electrodeposited on the fibrous carbon cathode can be collected at once by simply removing the cartridge filter. This is more convenient because it allows you to

(Example) Next, an example of metal recovery using the monopolar electrolytic cell of the present invention will be described, but this example is not intended to limit the present invention.

Silver ions in a photographic bleach-fix solution were recovered as silver sulfide using a monopolar electrolytic cell shown in FIG.

The electrolytic cell body has a diameter (inner diameter) of 12 cm and a length of 26.5 cm.
The inside of the main body was partitioned with a cartridge filter manufactured by Toyo Roshi Co., Ltd. with a diameter of 64 mm and a length of 250 ntm, so that the volumes of the anode chamber and cathode chamber were 900 cc and 2100 cc, respectively.

As an anode, a titanium base material coated with idium oxide with a diameter of 22 mm, a length of 250 mm, and an effective electrode area of 1.57 dm2 was used as a cathode current collector, and an effective electrode area of 6.0 dm2 was used as a cathode current collector.
A titanium material having a diameter of 9 dm" was used, and 580 cc of a felt-like fibrous carbon cathode ("Carboron-P Felt" manufactured by Nippon Carbon Co., Ltd.) was filled between the current collector and the diaphragm.

The total amount of 3. Silver content is 13 in Ol.
While circulating the photographic developer waste solution having a concentration of 60 mg/l through the circulation line at a rate of 1.01/min, the amount of current was set to a constant current of 10 AH, the voltage was set to 4.3 to 4.5 ■, and the temperature of the solution was set to 30 to 30. Electrolysis was performed at 50° C. for 60 minutes. Hydrogen sulfide was not detected in the gas generated during electrolysis, but 20 to 30 ppm was detected in the liquid supply tank.

After the electricity was stopped, the cartridge filter was removed and the amount of silver recovered was measured, and it was found to be 4079 mg, and the silver recovery rate was 99.
．． 97%, and the silver content in the electrolytic tailings was 0.4 mg/l. Further, no silver precipitation was detected in the electrolytic cell, and the cathode current density was 10.1%.

FIG. 2 shows the changes in voltage and silver concentration over time in this example.

Otoyo Group 1 An electrolytic cell similar to that in Example 1 was used, and the total amount of 6.5% was placed in the cathode chamber of the electrolytic cell. A photographic developing waste solution containing 1360 mg/l of silver in O4 was supplied at a rate of 90 cc/min without circulation, with a constant current of 10 AH and a voltage of 5.2-6.
Electrolysis was performed for 60 minutes at OV and liquid temperature of 25 to 30°C. Hydrogen sulfide was not detected in the gas generated during electrolysis, but 40 to 50 ppm was detected in the liquid supply tank.

After stopping the electricity supply, the cartridge filter was taken out and the amount of silver recovered was measured, and it was 8094 mg, and the silver recovery rate was 99.
．． 19%, the silver content in the electrolytic tailings was 11.0 mg/l, and the cathode current density was 20.1%.

Voltage and SR in this example? Figure 3 shows the change in a degree over time.

Using the same electrolytic cell as in Example 1, a photographic developing waste solution having a total amount of 3.6β and a silver content of 4850 mg/It was added to the cathode chamber of the electrolytic cell. On! While supplying and circulating at a speed of /min, the current amount is a constant current of 20AH, and the voltage is 5.1 ~
Electrolysis was performed for 180 minutes at 6.3 V and a liquid temperature of 33 to 52°C. Hydrogen sulfide was not detected in the gas generated during electrolysis, but 3 to 5 ppm was detected in the liquid supply tank.

After the electricity was stopped, the cartridge filter was taken out and the amount of silver recovered was measured, and it was 17,455 mg, and the silver recovery rate was 9.
9.97%, and the silver content in the electrolytic tailings was 0.8 mg/l. Further, no silver precipitation was detected in the electrolytic cell, and the current efficiency of the cathode was 7.2%.

FIG. 4 shows the changes in voltage and silver concentration over time in this example.

(Effects of the Invention) The present invention uses a monopolar electrolytic cell in which carbon maintained in a fibrous form after molding is used as an electrode, and the diaphragm that partitions the bipolar chambers has a filtering function, and the electrolytic cell. This is an electrolytic method.

The fibrous carbon electrode differs from porous electrodes such as conventional carbon electrodes in which only the part facing the counter electrode exhibits an electrode effect, and the fibrous carbon is sufficiently long so that there is no potential gradient within the electrode. Since the potential is the same in all parts of the electrode, it is assumed that electrolytic reactions occur in any part of the electrode, and almost the entire surface of the electrode functions as an electrode, making the electrolytic conditions more favorable, including reducing the current density. be able to.

The monopolar electrolytic cell of the present invention uses a fibrous carbon electrode having such characteristics and a diaphragm having a filtering function. When the electrolytic solution containing the suspended matter is passed through the diaphragm and transferred to the opposite electrode, the floating or precipitated precipitate is removed by the diaphragm. By filtering, solids that are not deposited on the electrodes can be efficiently recovered.

For example, in a photographic waste solution or a fixer for photographic development that contains silver ions and sulfur-containing compounds or ions, the silver ions and sulfur-containing compounds react with each other in a normal electrolytic reaction to remove solids such as floating particles or precipitates of silver sulfide. However, when the electrolytic cell according to the present invention is used, the solid content is captured by the diaphragm when the electrolyte moves through the diaphragm. By removing the diaphragm from the electrolytic cell, the target component adhering to the diaphragm can be recovered. The present invention is also useful for recovering other metal ions and products of organic electrolysis or anodic oxidation.

Moreover, the recovery rate usually shows a good value exceeding 99%, and the target component can be obtained in either solid or solution form.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of a monopolar electrolytic cell of the present invention, FIG. 2 is a graph showing the relationship between electrolysis time, voltage, and silver concentration in Example 1, and FIG. 3 is a graph showing the relationship between electrolysis time, voltage, and silver concentration in Example 1. , a graph showing the relationship between electrolysis time, voltage and silver concentration in Example 2,
FIG. 4 is a graph showing the relationship between electrolysis time, voltage, and silver concentration in Example 3. 1 ・ 3 ・ 4 ・ 6 ・ 8 ・ 10 ・ 12 ・ 14 ・ 16 Electrolytic cell 2... Lid body cartridge filter anode chamber 5... Cathode chamber anode 7... Cathode current collector fibrous carbon cathode 9...Liquid supply tank waste liquid tank 11...Liquid supply pump liquid supply line 13...Waste liquid line discharge pump 15...Discharge line to circulation line In the figure. Kasaki M/Gendaizu Xl to de0/, JOBD trb i
t. Official world θ hand, ff (suna

Claims (2)

[Claims] (1) In a monopolar electrolytic cell divided into two electrode chambers by a diaphragm, the diaphragm has a filtration function, and fibrous carbon connected to a current collector is used as an electrode in at least one electrode chamber. A monopolar electrolytic cell that is used to perform electrolysis. (2) Fibrous carbon connected to a current collector is housed in at least one electrode chamber of a monopolar electrolytic cell divided into two electrode chambers through a diaphragm having a filtration function, and a single electrode is used as an electrode. While supplying electricity to the polar electrolytic cell, an electrolytic solution to be treated is supplied to the electrode chamber containing the fibrous carbon, and the solid content in the electrolytic solution generated by electrolysis is transferred onto the fibrous carbon electrode and/or An electrolysis method characterized in that the fibrous carbon electrode is deposited in an electrode chamber containing the electrode, the electrolyte is transferred through the diaphragm into the counter electrode chamber, and the solid content is collected and recovered by the diaphragm.