JPH02159399A - Method and device for electrolytic treatment - Google Patents

Abstract

PURPOSE:To deposit and elute a desired component with excellent electric power efficiency by incorporating a specific mediator into a counter electrode liquid at the time of electrolytically depositing or eluting the desired component in an electrolyte on working electrodes and recovering or thickening the same in a diaphragm type electrolytic cell. CONSTITUTION:The soln. contg. the desired component is passed to the working electrodes 2a, 2b and while the counter electrode liquid is passed to the counter electrodes 3a, 3b, both the electrodes are energized to deposit and recover the desired component on the working electrodes 2a, 2b or the elute is passed to the working electrodes deposited with the desired component to elute and thicken the desired component in the diaphragm type electrolytic cell 1 constituted by repeatedly laminating electron conductive partition plates 5, the working electrodes 2a, 2b, diaphragms 4, the counter electrodes 3a, 3b, and the electron conductive partition plates 5. The carbon electrodes which contain 1 to 30%C of carbon atoms C of at least one kind of O, N and halogen and are deposited with 1 to 1000mg/cm<2> Ag are used as the working electrodes of this case. The mediator having the oxidation reduction potential of <=1V difference from the oxidation reduction potential of the desired component is incorporated into the counter electrode liquid. The deposition and recovery of the desired component and the thickening by the elution thereof are executed with the excellent voltage efficiency and current efficiency.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method and apparatus for electrochemically recovering and concentrating useful components contained in a solution or removing impure components. be.

(Prior art) A method of recovering, concentrating, or removing a target component in a solution by making it insolubilized by cathodic electrodeposition, precipitating it, and eluting it again, that is, an electrolytic treatment method A component with a relatively noble reduction potential,
This is particularly effective for metals that are responsible.

However, when the oxidation-reduction potential of the target component is base, it is difficult to electrodeposit it efficiently because side reactions such as hydrogen generation reactions are likely to occur, unlike when the responsible component is electrolyzed. An example of successful cathodic electrodeposition for components with a base redox potential is the amalgam method using a mercury electrode, which can suppress hydrogen generation due to its high hydrogen overvoltage. This method is used to concentrate and purify sodium hydroxide, but
Since mercury is used, it is not a desirable method from an environmental hygiene perspective. Therefore, the base ingredients have no environmental health problems, and the cost is low, just like the culprit ingredients.
The realization of efficient electrolytic treatment methods and electrolytic treatment equipment is awaited.

(Problems to be Solved by the Invention) The purpose of the present invention is to improve the reactivity of target components on the electrode surface, increase the hydrogen overvoltage, and suppress hydrogen generation, especially against base components including halogens. Another object of the present invention is to provide an electrolytic treatment method with high voltage efficiency and high current efficiency, and an electrolytic treatment apparatus that is suitable for implementing the method and that causes fewer health and safety problems.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides (1) a diaphragm-type electrolytic cell in which a diaphragm is arranged between a working electrode and a counter electrode to partition the two electrodes. The target component contained in the solution is electrodeposited on the working electrode while flowing a solution containing the target component to the working electrode and a counter electrode solution to the counter electrode, and then the eluate is passed to the working electrode. In an electrolytic treatment method in which a target component electrodeposited on the working electrode is eluted, a counter electrode solution containing a mediator having an oxidation-reduction potential with a difference of 1 V or less from the oxidation-reduction potential of the target component during electrodeposition and elution. An electrolytic treatment method characterized by using (2) electrodeposition;
A working electrode is flowed with a solution containing the target component to be eluted, and a counter electrode containing a mediator having a redox potential with a difference of 1 V or less between the redox potential of the target component to be electrodeposited and eluted is flowed. It has a diaphragm type electrolytic cell in which a diaphragm is placed between the two electrodes and a diaphragm is placed between them, and when the working electrode is analyzed by X-ray photoelectron spectroscopy (ESCA), oxygen, nitrogen or halogen (3) an electrolytic treatment device comprising a carbon material in which the number of at least one of the atoms is within the range of 1 to 30% of the number of carbon atoms; Between the working electrode through which a solution containing the target component is flowed and the counter electrode through which a counter electrode containing a mediator having a redox potential difference of 1 V or less from the redox potential of the target component to be electrodeposited and eluted is flown. It has a diaphragm type electrolytic cell in which a diaphragm is arranged to partition the two electrodes, and the working electrode is 1 to 1000 m
An electrolytic treatment apparatus is provided, characterized in that it is made of a carbon material supporting silver in an amount of g/cm2.

The details of the present inventions 1.2 and 3 will be explained below with reference to the flow sheets of the embodiments shown in the drawings.

In the figure, a diaphragm electrolytic cell 1 includes an electronically conductive partition plate 5, flow-through electrodes (working electrodes) 2a and 2b, a diaphragm 4, and a flow-through electrode (
It is constructed by repeatedly laminating counter electrodes 3a and 3b and an electronically conductive partition plate 5. The flow-through electrode is
For example, working electrodes 2a and 2 for electrodeposition and elution
b, and counter electrodes 3a and 3b. When the purpose is cathodic electrodeposition, the working electrode is used as a cathode during electrodeposition and as an anode during elution. The counter electrode is the opposite of the working electrode. Also, when anodic electrodeposition is intended, the electrodes are reversed from those for cathodic electrodeposition.

As the diaphragm 4, an ion exchange membrane or a microporous membrane is used. Ion exchange membranes are effective in improving current efficiency in electrolysis. For example, when using a cation exchange membrane in an acidic solution, the substances that permeate through the membrane are mainly protons (hydronium ions), which have low permeation resistance;
Electrolysis with excellent voltage efficiency and current efficiency becomes possible.

Microporous membranes are inferior to ion exchange membranes in terms of ion permselectivity, so the current efficiency is not higher than that of ion exchange membranes, but their permeation resistance is sufficiently low, so overall, they are It is preferably used as a diaphragm in a diaphragm-type electrolytic cell of a processing device.

For the electronically conductive partition plate 5, a metal plate, a carbon plate, or the like is used.

In the first invention, a mediator having an oxidation-reduction potential close to the electrodeposition and elution reaction potential of the target component, that is, a potential difference from the above potential of 1 V or less, is used for the counter electrode reaction. Listing such mediators in descending order of magnitude, they are: Zn0/Zn', Fe'/Fe", Cr"/C
r", Ti"/Ti', Pb0/Pb"N i'/
N i", F e' edta/F e" ed
ta.

Fe"nta/Fe"nta, Cu'/Cu" ferrocyan ion/ferricyan ion.

Naphthoquinone sulfonic acid reduced/oxidized state, hydroquinone/quinone, I-/I'-, Br/Br3 (however,
F66d11:! Iron tylenediaminetetracarborate. Fenta: iron nitrilotriacetic acid complex. ) etc.

In the diaphragm electrolytic cell 1, the processing liquid is sent from the processing liquid piping 6 to the working electrode 2a. On the other hand, the counter electrode containing the mediator is sent from the counter electrode tank 8 to the counter electrode 3a by the pump 12, further led to the counter electrode 3b by the counter electrode circulation pipe 10, and circulated to the counter electrode tank 8. At the working electrode 2a,
The target component in the treatment solution is reduced, precipitated, and electrodeposited on the electrode. After the treatment, the treatment liquid passes through the treatment liquid discharge pipe 11 and is further circulated to the working electrode 2a in order to proceed with electrodeposition of the target components remaining in the treatment liquid, or after the desired electrodeposition is completed. Sometimes it is discharged outside the system. During this time, elution, which will be described later, is performed at the working electrode 2b.

When a predetermined electrodeposition is completed on the working electrode 2a, the feeding of the processing liquid is switched to feeding the eluate from the eluate tank 7a, and elution of the electrodeposited components is started. The eluate elutes the target component from the working electrode 2a and becomes a recovered or concentrated liquid.
The working electrode 2a passes through the concentrate pipe 9 and advances the elution.
further circulated or led out of the system. At this time, a treatment liquid is fed to the working electrode 2b, and the electrodeposition of the target component is switched to. By repeating the above operations, electrodeposition and elution are performed alternately between the working electrodes 2a and 2b.

The treatment liquid and the counter electrode are not limited to aqueous solutions.

For example, when electrolysis is performed in an organic solvent for the purpose of electrodeposition or elution of alkali metals or alkaline earth metals, a non-aqueous solution type is naturally used as the counter electrode.

The above operation can be carried out by using a mediator with a redox potential that is small in difference from the redox potential of the component as a counter electrode, even if the target is a component with a base redox potential. Voltage efficiency is significantly improved, and target components can be smoothly electrodeposited and eluted. In particular, in the region where the difference between the two potentials is within 1V,
Hydrogen generation is suppressed and stable electrolysis takes place. For example, when recovering nickel in an acidic solution, if a Cr'/Cr'' ion system is used as a mediator,
This makes it possible to recover nickel very efficiently.

Present invention 2 will be explained. In the figure, working electrodes (flow-through type electrodes) 2a and 2b of a diaphragm type electrolytic cell 1 are made of a woven fabric, a nonwoven fabric, a knitted fabric, a porous molded body, or the like made of a carbon material. These carbon materials have a ratio of at least one of oxygen, halogen, and nitrogen atoms on the surface to 1% of the number of carbon atoms.
It is processed so that it exists in the amount of 30% to 30%. A solution containing a target component to be electrodeposited and eluted is flowed onto such a working electrode. When the number of the above-mentioned atoms introduced onto the surface of the working electrode is less than 1% of the number of carbon atoms, the reactivity at the working electrode decreases significantly and the overvoltage increases.
The hydrogen overvoltage decreases and hydrogen begins to be generated from the cathode. For example, the ratio of the number of oxygen atoms to the number of carbon atoms is 1
% generates several times more hydrogen at -0.5 V (based on saturated Amagi electrode) in 4N-HCl than an electrode with 1.5-2.5%, which is the object of the present invention. Unable to carry out electrolysis.

On the other hand, if the ratio of the number of atoms of the above elements exceeds 30%,
The electrical resistance of the electrode surface increases dramatically.

When this ratio is 37 to 38%, the electrical resistance is about twice as high as when it is 25 to 27%, making it impossible to carry out efficient electrolysis and thus failing to achieve the object of the present invention.

Measured values by ESCA are used to quantify the number of atoms on the surface. This uses an AIK, or MgK, X-ray source, and the sample is bundled into a plate and measured at right angles to the detector. O, for the number of carbon atoms,
, N or halogen atoms are detected as a percentage.

In addition, methods for making these elements exist on the surface of the carbon material serving as the electrode include (a) heat treatment in an atmospheric gas containing oxygen, nitrogen, nitrogen compounds, halogens, etc. (b) plasma treatment in the above atmosphere ( c) Heat treatment in an acidic aqueous solution (d) Electrolytic treatment, etc. can be used.

Due to the presence of these elements on the surface of carbon,
Electron exchange reactions with metal ions occur quickly, increasing the hydrogen overvoltage and lowering the electrode resistance. As a result, both voltage efficiency and current efficiency improve.
- Comparing the cell resistances of a nitrogen-introduced carbon electrode, a halogen-introduced carbon electrode, an oxygen-introduced carbon electrode, and an untreated carbon electrode in a Cr-based redox flow battery, it is found that the oxygen-introduced electrode is compared to the untreated carbon electrode. Approximately 70% when using a nitrogen introduction electrode and a halogen introduction electrode, and approximately 50% when using a nitrogen introduction electrode and a halogen introduction electrode.
decreases to Accordingly, the life of the electrode is greatly extended.

The electrolytic treatment apparatus according to the second aspect of the present invention using the above electrode as a working electrode is suitable for carrying out cathodic electrodeposition.

Although the counter electrodes (flow-through type electrodes) 3a and 3b do not necessarily need to be subjected to the same treatment as the working electrode, voltage and current efficiency tend to improve when the same surface treatment is applied.

When the target component is electrodeposited or eluted at the working electrode, the counter electrode contains a mediator that is electrodeposited at the working electrode and has a redox potential that is 1 V or less different from the redox potential of the target component to be eluted. Drain the liquid.

In the electrolytic treatment apparatus according to the third invention, the counter electrode of the diaphragm electrolytic cell is electrodeposited at the working electrode as in the second invention,
The difference between the redox potential of the target component to be eluted is 1V.
A counter-electrolyte containing a mediator having a redox potential of: For the working electrode, 1 to 1000 mg/c
m2 of silver is supported and a solution containing the target component is flowed. When the supported amount of silver is less than 1 mg/cm2, it loses its function as a silver electrode, and when it exceeds 1000 mg/cm, the permeation of the electrolyte is hindered by the deposited silver, and eventually the electrode becomes a flow-through type electrode. begins to lose its function.

Methods for supporting silver include electrodeposition and electroless plating.

A diaphragm electrolytic cell having this electrode is suitable for anodic electrodeposition and is capable of separating ions containing halogens and sulfur.

Embodiments of the present invention are not limited to those using an integrated diaphragm cell as shown in the drawings. independent 2
It is also possible to use two diaphragm-type electrolytic cells, perform the electrodeposition operation in one electrolytic cell, and perform the elution operation in the other electrolytic cell, and repeat this operation alternately. In this case, the opposite electrodes of both electrolytic cells have a difference of 1 from the redox potential of the target component.
A counter-electrolyte containing a mediator with a redox potential of V or less is flowed. Among the electrodes of both electrolytic cells, it is preferable to use an electrode made of the above-mentioned surface-treated carbon material as at least the working electrode, depending on the target component to be treated.

Even when one diaphragm type electrolytic cell is used, electrodeposition and elution can be alternately repeated over time by using the same mediator as the counter electrode.

(Function) In the present invention, the mediator used in the counter electrode is a substance that has a catalytic action to cause a good electrode reaction of the substance to be electrolyzed. That is, it reacts with both the electrolyte and the electrode to catalytically assist the electrode reaction of the electrolyte.

In the method of the present invention 1, irrespective of the electrodeposition operation or the elution operation, the counter electrode is a mediator with a redox potential close to that of the target component, that is, a mediator with a redox potential close to the redox potential of the target component. By using a mediator having an oxidation-reduction potential of 1 V or less for the reaction at the counter electrode, voltage efficiency is significantly improved and electrolysis can be performed stably.

The electrolytic treatment apparatus according to the second aspect of the present invention includes a counter electrode through which a counter electrode containing the above-mentioned mediator is flowed, and a working electrode made of a surface-treated carbon material, that is, the surface of the carbon electrode is chemically treated, and the surface of the carbon electrode is chemically treated. It has a diaphragm type electrolytic cell using an electrode in which oxygen, nitrogen or halogen is present on the surface of the electrode. By using such a diaphragm electrolytic cell,
The reactivity between the electrode and the ions of the target substance, especially metal ions, is improved, the hydrogen overvoltage is increased, and an electrolytic treatment device with high voltage efficiency and current efficiency can be constructed despite not using mercury. It becomes like this.

The electrolytic treatment apparatus according to the third aspect of the present invention has a diaphragm electrolytic cell having a counter electrode through which a solution containing the above-mentioned mediator is flowed, and a working electrode made of a silver electrode that forms a stable salt with halogen etc. Anodic electrodeposition of sulfur compounds, etc. is possible.

(Example) Example 1 10cm long to use as an electrode for a diaphragm electrolytic cell.

Width 1 cm, thickness 0. 3cm, basis weight 400g/
m' carbon felt was immersed in nitric acid and boiled for about 15 minutes to undergo oxidation treatment. This was thoroughly washed with water, air-dried, and used as an electrode.

The surface and cut surfaces of this carbon felt were examined using ESCA (
The analysis was performed using ESCA750 (manufactured by Shimadzu Corporation). At this time, MgK was used as the excitation X-ray. Carbon was quantified using C□ and peak (bond energy value 286.6 eV) with a step width of 0.1 el/.

Scanning width 20eV, sampling time 100Q
The measurement was performed at m5ec/channel, 8 repetitions, and a measurement temperature of 20°C. 01 for oxygen determination. Using the peak (binding energy value 533.1 eV), step width 0°l eV,
Scanning width 20e■, sampling time 1000m
The measurement was carried out at 5 ec/channel, 8 repetitions, and a measurement temperature of 20°C. In addition, as a sensitivity coefficient of each peak, C1s is 1.
00, 08. 2.85 was used. The ratio of the number of carbon and oxygen atoms was determined as the ratio of each measured peak area divided by the sensitivity coefficient.

The measurement results showed that the number of oxygen atoms was 3% of the number of carbon atoms on both the felt surface and the cut surface.

A small single electrolytic cell was fabricated using this carbon felt as a working electrode and a counter electrode, a cation exchange membrane as a diaphragm, and a carbon plate as an electronically conductive partition plate. The structure of the electrolytic cell was an electronic conductive partition plate/working electrode/net/diaphragm/counter electrode/electron conductive partition plate, and an attempt was made to recover zinc from a weakly acidic aqueous solution. The purpose of the net is to prevent dendrites generated as a result of zinc electrodeposition from breaking the diaphragm.

The concentration of zinc in the treatment solution was approximately 6501+I1m. For the counter electrode, an acidic aqueous solution of hydrochloric acid using chromium chloride as a mediator was used in circulation as a counter electrode.

On the other hand, about 5 Qppm of zinc in the treatment solution was electrodeposited on the working electrode, which is the cathode, when it passed through the electrolytic cell once. Therefore, we adopted a circulation method for the treatment solution to completely electrodeposit zinc on the working electrode. Zinc was determined by polarography.

After the electrodeposition was completed, zinc was eluted and recovered using the above working electrode as an anode. 3ml of 2N-HCI
was used as a recovery liquid and circulated through the electrolytic cell to elute zinc.

As a result, the concentration of zinc in the recovered liquid was approximately 2%.

Table 1 shows other conditions and results along with the following comparative examples.

Comparative Example 1 Table 1 shows the electrodeposition voltage, etc. when attempting to recover zinc using the same treatment solution as in Example 1 but using simple 2N-HCI without using a mediator as the counter electrode. .

Comparative Example 2 An attempt was made to recover zinc using the same treatment solution as in Example 1, using a ferrocyan/ferricyan mediator with a potential difference of 1.1 V between the redox potential and zinc as the counter electrode solution. Table 1 shows the electrodeposition voltage, etc. in each case.

Since the power required for electrodeposition is approximately proportional to the electrodeposition voltage, Example 1 shown in Table 1 and Comparative Example 1 corresponding thereto
When compared with the results of Comparative Example 2, it can be seen that Example 1 required about 25% of the power of Comparative Example 1 and about 40% of Comparative Example 2.

Moreover, in the example, no external power is required during elution.

Example 2 An electrolytic solution used in a redox flow type secondary battery was continuously purified. That is, HCI was added to a solution of low-grade ferrochrome to obtain 3N-HCI, which was used as it was as the above electrolyte. However, this electrolytic solution contains several tens of ppm of nickel, and during charging and discharging, a large amount of hydrogen is generated at the Cr electrode, which is the cathode of the redox flow type secondary battery.

Therefore, using the two small car electrolyzers used in Example 1,
Using the above electrolyte as a treatment solution, the treatment solution is passed through one electrolytic cell, and after electrodeposition is performed for a certain period of time to remove nickel, the flow path is switched, and the other electrolytic cell is subjected to electrodeposition for a certain period of time. processed. While electrodeposition was being performed in one electrolytic cell, elution treatment was performed in the other electrolytic cell with a 3N-HCI aqueous solution to clean the electrodes. Cr"7Cr" was used as the mediator of the counter electrode.

Table 2 shows the results of a charge/discharge experiment of a redox flow type secondary battery using the electrolyte purified in this manner.

Comparative Example 3 Table 2 shows the results of a charge/discharge experiment of a redox flow type secondary battery using the unpurified electrolyte of Example 2.

Example 3 Halogen ions in an aqueous solution were removed and recovered using a carbon felt electrode on which silver was supported by an electroless method. The working electrode was the same as that used in Example 1, but silver was supported on non-oxidized carbon felt by electroless plating. First, carbon felt was impregnated little by little with a 0.3N silver nitrate aqueous solution using a pipette, and formaldehyde was then sprinkled on a heater to reduce and precipitate silver. Finally silver 200-3
00 mg/cm2 was loaded and used as a working electrode.

Using this working electrode and untreated carbon felt as the counter electrode, two small cell cells having the same configuration as in Example 1 were manufactured and used as an electrolytic cell. For the mediator, 0゜2M F e ""
An aqueous edta solution was used.

A voltage of +0.05 V was applied to the counter electrode of a small cell, and an aqueous solution containing iodine of 0.OOIM was poured into a copper-supported carbon electrode serving as an anode, so that more than 99% of the iodine ions were iodized. It was captured as silver. To recover the iodine ion concentrate, set the copper-supported electrode side to the opposite electrode at -0.3V.
and 0. It was concentrated by flowing IN H and SO2. The recovery rate was 90%.

The theoretical electrolytic voltage is 0°27V for both electrodeposition and elution.
It is.

An attempt was made to recover iodine without using the above mediator, but if the counter electrode was used for a gas generation reaction, the voltage applied to the single cell would not only require about five times the voltage applied in the above case, but also require control of the electrode potential. However, this could not be carried out with high accuracy, and a problem occurred in which silver was eluted.

(Effects of the Invention) According to the present invention, since the difference between the redox potential of the target component to be electrodeposited and eluted on the working electrode side and the redox potential of the mediator on the counter electrode side is 1 V or less, electrolytic It does not require a large voltage to be applied to the tank, which reduces the amount of power required, and has the effect of making it easier to control the electrolytic voltage over the entire surface of the electrode.

The present invention 2 is suitable for cathodic electrolytic treatment as an electrolytic treatment apparatus that enhances the effect of the present invention 1, and the reactivity of the target component is greatly enhanced on the electrode surface of the diaphragm electrolytic cell of the apparatus. That is, by implementing the present invention 1 with the electrolytic treatment apparatus according to the present invention 2, it is possible to reduce the required power, stabilize the electrolytic voltage, and facilitate control.

Moreover, it is safe and does not use harmful substances such as mercury.
This is an electrolytic treatment device that poses no problems from a sanitary standpoint.

The third aspect of the present invention, contrary to the second aspect of the present invention, is an electrolytic treatment apparatus that utilizes anodic electrodeposition to efficiently recover or remove halogens and sulfur compounds.

[Brief explanation of the drawing]

The drawing is a flow sheet illustrating one embodiment of the invention. 1: Electrolytic cells 2a, 2b: Working electrodes 3a, 3b: Counter electrode 4: Diaphragm 5: Electronically conductive partition plate 6: Processing liquid piping 7a, 7b: Eluate liquid tank 8: Counter electrode liquid tank 9: Recovery/concentrate liquid piping 10 : Counter-electrode circulation pipe 11: Processing liquid discharge pipe

Claims (3)

[Claims] (1) Using a diaphragm electrolytic cell in which a diaphragm is placed between the working electrode and the counter electrode to partition the two electrodes, a solution containing the target component is passed through the working electrode, and a counter electrode solution is passed through the counter electrode. However, in an electrolytic treatment method in which a target component contained in a solution is electrodeposited on a working electrode, an eluent is passed through the working electrode to elute the target component electrodeposited on the working electrode.
An electrolytic treatment method characterized in that during electrodeposition and elution, a counter electrode solution containing a mediator having an oxidation-reduction potential that differs from the oxidation-reduction potential of a target component by 1 V or less is used. (2) A mediator having a redox potential where the difference between the working electrode, through which a solution containing the target component to be electrodeposited and eluted is flowed, and the redox potential of the target component to be electrodeposited and eluted is 1V or less. The cell has a diaphragm type electrolytic cell in which a diaphragm is placed between the two electrodes and a counter electrode through which a counter electrode containing .
When analyzed by A), the number of atoms of at least one of oxygen, nitrogen, or halogen is 1 to 30% of the number of carbon atoms.
An electrolytic treatment device characterized in that it is made of a carbon material within the range of . (3) A mediator having a redox potential in which the difference between the working electrode through which a solution containing the target component to be electrodeposited and eluted is flowed and the redox potential of the target component to be electrodeposited and eluted is 1V or less. It has a diaphragm type electrolytic cell in which a diaphragm is placed between the two electrodes and a counter electrode through which a counter electrode solution containing is flowed, and the working electrode supports 1 to 1000 mg/cm^2 of silver. An electrolytic treatment device characterized in that it is made of carbon material.