JPH07104432B2 - Method and apparatus for removing ruthenium in aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and a device for removing ruthenium in radioactive liquid waste.

[Conventional technology]

Conventionally, as a method of removing the metal in the aqueous solution as electrically insoluble, U.S. Patent Nos. 3890244, 3891741, and
There is a 3922231 issue.

These are the spent nuclear fuel Purex.
Technesium, ruthenium, palladium and rhodium are deposited as metals on the cathode of the electrode immersed in the reprocessing waste liquid and removed from the aqueous solution. In one of the examples cited in these patents, for technesium, palladium and rhodium, 99% was deposited on the cathode and removed by treatment for 48 hours, but ruthenium 60
Only% was removed.

In order to effectively remove a substance dissolved in an aqueous solution (to remove a high decontamination coefficient in a short time with a small device) in such an electrochemical method, the electrode area is increased and the substance between the electrodes is increased. It is argued that there is a need to improve mobility characteristics. (A. Tay Coon, Chemistry and Industry, July 1978, p. 447 (A.
T.Kuhn, Chem. & Ind., 1978,1, July, p447) However, the fact that ruthenium in an aqueous solution such as a reprocessing waste solution is deposited as a metal on an electrode causes ruthenium to become very chemically in a nitric acid solution. It was found to be difficult due to the formation of safe nitrosyl complexes.

Another method for electrochemically removing ruthenium, which exists as a nitrosyl complex in an aqueous solution, is described in "The 1989 Annual Meeting" of the Japan Atomic Energy Society (April 4-6, 1989, Osaka Univ.) Discussed on page 271 in the separate volume.

That is, a platinum-plated titanium electrode is immersed in a simulated waste liquid consisting of an aqueous sodium nitrate solution, and the electrode is -2.0 + 1.575V.
When an alternating potential is applied in the range of (standard sweet water potential), ruthenium in the solution does not precipitate on the electrode but precipitates and is removed as an insoluble ruthenium compound in the solution.

In this method, the nitrosyl complex of ruthenium is once oxidized on the anode to a highly chemically reactive compound (presumed to be ruthenium tetraoxide) in the higher oxidation state, and then insoluble in the lower oxidation state on the cathode. It is based on the principle that it is reduced to the compound (estimated to be ruthenium dioxide).

[Problems to be Solved by the Invention]

In the above conventional technique, a voltage is applied to an electrode immersed in an aqueous solution of an electrolyte to cause an oxidation reaction on the anode and a reduction reaction on the cathode, respectively, thereby changing the ruthenium compound in the aqueous solution into an insoluble ruthenium compound. It gives the principle of the method of removal, but does not show the specific method and device for realizing the technique.

An object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can efficiently make ruthenium insoluble.

Another object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can reduce the amount of ruthenium higher order oxides returned to the nitrosyl complex.

Another object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can further reduce the amount of ruthenium higher order oxides returned to the nitrosyl complex.

Another object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can efficiently make ruthenium insoluble by adjusting the contact period between the cathode and the anode according to the decrease in the ruthenium concentration.

Another object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can promote oxidation and reduction reactions on electrodes.

Another object of the present invention is to provide a method and an apparatus for removing ruthenium in an aqueous solution, which can significantly reduce the amount of water-soluble ruthenium.

[Means for Solving the Problems]

The features of the inventions of claims 1 and 8 for achieving the above object are that a voltage is applied between electrodes immersed in an aqueous solution containing a ruthenium compound to cause oxidation reaction on the anode and reduction reaction on the cathode, respectively. In a method of converting a ruthenium compound in an aqueous solution into an insoluble ruthenium compound and removing the ruthenium compound, at least a pair of perforated plate electrodes in which the electrodes are laminated is provided, and the aqueous solution is passed across the perforated plate electrodes. .

In order to achieve the above object, the invention of claim 7 is characterized in that a voltage is applied between electrodes immersed in an aqueous solution containing a ruthenium compound to cause an oxidation reaction on the anode and a reduction reaction on the cathode. In the device for removing the ruthenium compound of, by converting it to an insoluble ruthenium compound,
There is at least a pair of perforated plate electrodes that are the electrodes, a unit that periodically switches the electrical polarity of the perforated plate electrode, and a unit that allows the aqueous solution to pass through the gap between the perforated plate electrodes. .

The features of the inventions of claims 2 and 9 for achieving the above-mentioned other object are that adjacent electrodes of the laminated porous plate-shaped electrodes have different electrical polarities.

The features of the inventions of claims 3 and 10 for achieving the above other object are to periodically switch the electrical polarity of the perforated plate electrode.

A feature of the invention of claim 11 that achieves the other object is that the surface area of the perforated plate electrode located near the outlet of the aqueous solution is smaller than that of the perforated plate electrode located near the inlet of the aqueous solution. Is also big.

The features of the inventions of claims 4 and 12 for achieving the above-mentioned other object are any one of a plurality of cylindrical electrodes arranged concentrically in the laminated porous plate electrode and a spiral electrode. A large number of holes are provided in the radial direction to allow the aqueous solution to pass in the radial direction from the center of the porous plate electrode.

The features of the inventions of claims 5 and 13 for achieving the above-mentioned other object are to allow the aqueous solution to pass through in a pulsating manner.

The features of the inventions of claims 6 and 14 for achieving the above-mentioned other object are to repeatedly circulate the aqueous solution to pass through the laminated perforated plate electrodes.

[Action]

The principle of the method of removing a ruthenium compound in an aqueous solution by converting it to an electrochemically insoluble ruthenium compound is that the nitrosyl complex, which is usually chemically stable and has a low ruthenium oxidation state, is oxidized on the anode. It decomposes the chemical bond between ruthenium and the nitrosyl group to form a compound that is soluble but highly reactive, and ruthenium becomes a compound in a higher oxidation state (presumed to be ruthenium tetroxide), followed by ruthenium on the cathode. Is reduced to an insoluble compound in a low oxidation state (presumed to be ruthenium dioxide).

If the ruthenium tetrachloride, a highly soluble and highly reactive ruthenium oxide, is not reduced immediately on the cathode, it will volatilize as it is, or it will react with the nitric oxide formed by the oxidative decomposition of the nitrosyl complex and again react with nitrosyl. It returns to the complex.

Therefore, in order to establish the present method, a small amount of soluble higher oxides formed in the aqueous solution on the anode is immediately brought into contact with the cathode and reduced to form an insoluble lower oxide, and the aqueous solution is separated into the cathode and the cathode. Repeated contact between them is required.

Thus, the present invention operates so that the aqueous solution is repeatedly and sufficiently contacted with the electrode composed of the anode and the cathode.

That is, the invention of claim 7 makes it easier to contact the electrode and the ruthenium compound by passing the aqueous solution through the gap between at least a pair of stacked plate-shaped electrodes, than immersing the pair of plate-shaped electrodes in the solution. And can be done sufficiently. Therefore, ruthenium can be efficiently insolubilized.

According to the inventions of claims 1 and 8, ruthenium can be efficiently insolubilized similarly to the invention of claim 7. In particular, since the aqueous solution is passed while intersecting (for example, orthogonal to) the perforated plate electrodes, the aqueous solution surely passes between the perforated plate electrodes.

The inventions of claims 2 and 9 produce the same effect as that of the invention of claim 1, and since the adjacent electrodes of the laminated porous plate-shaped electrodes have different electrical polarities, they are formed on the anode. The ruthenium higher-order oxide can be reduced to an insoluble ruthenium compound on the adjacent cathode and reduce the amount of ruthenium higher-order oxide returning to the nitrosyl complex.

The inventions of claims 3 and 10 produce the same effect as the invention of claim 1, and since the electric polarity of the perforated plate electrode is periodically switched, it is easier to contact the ruthenium compound with the anode and the cathode. Therefore, the amount of ruthenium higher order oxide returning to the nitrosyl complex can be further reduced.

The invention of claim 11 produces the same effect as the invention of claim 1, and the surface area of the perforated plate electrode located near the outlet of the aqueous solution is larger than that of the perforated plate electrode located near the inlet of the aqueous solution. Therefore, the contact period of the ruthenium compound with respect to the anode and the cathode is short on the inlet side where the concentration of ruthenium is high, and the contact period of the ruthenium compound with respect to the anode and the cathode becomes longer as the ruthenium concentration decreases (as it approaches the outlet side). This makes it suitable for the electrochemical removal of ruthenium. That is, as described above, since the contact period between the cathode and the anode can be adjusted according to the decrease in the ruthenium concentration, ruthenium can be made insoluble more efficiently.

The inventions of claims 4 and 12 produce the same effects as the invention of claim 11.

Since the inventions of claims 5 and 13 produce the same effect as the invention of claim 1, and pass the aqueous solution in a pulsating manner,
The contact between the ruthenium compound in the aqueous solution and the anode and the cathode is promoted as compared with the case of a single flow, and the oxidation and reduction reactions of the ruthenium compound on the electrode can be promoted.

The features of the inventions of claims 6 and 14 produce the same effect as that of the invention of claim 1, and since the aqueous solution is repeatedly circulated to pass through the laminated porous plate electrodes, the water-soluble ruthenium contained in the aqueous solution is The amount can be significantly reduced.

〔Example〕

 An embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 denotes a container, which constitutes the main body device of the present invention and is filled with an aqueous solution of an electrolyte. 2 is the inlet connecting to the container,
An outlet 3 constitutes a flow path for the aqueous solution. The aqueous solution containing ruthenium flows in through the inlet, and the aqueous solution with reduced ruthenium concentration flows out through the outlet. Reference numeral 4 denotes a plate electrode, which is composed of a pair or a plurality of pairs of an anode and a cathode. Four
In order to make the electrode of the electrode in an aqueous solution of electrolyte, sufficient corrosion resistance is required, and in order to make it difficult to generate hydrogen on the surface of the cathode and oxygen on the surface of the anode, respectively, in this embodiment, the titanium film coated with platinum is used. Is used. The surface of the electrode made of platinum is suitable for causing a reaction of oxidizing ruthenium in the aqueous solution on the anode and reducing it on the cathode. The plate-shaped electrode of No. 4 can also enhance the effect of the device by making it a porous plate. When a porous plate electrode is used, it is usually processed into a state called expanded metal. The electrodes of No. 4 have a necessary gap between the electrodes by an electrode supporting portion (not shown), and at the same time form a stacked electrode state while maintaining electrical insulation between the electrodes. The electrode support portion is made of a material having necessary strength and electrical insulation. The function of the electrode supporting portion can be replaced by separating it with a perforated plate having an electrode insulating property (not shown), and the structure of the device can be simplified. 6 and 7 are electrical connections, which are connected to the electrodes to supply current to the electrodes and keep them at a constant voltage. 7 is 6
Is an electrical connection having a polarity different from. The electrical connection is made by 6 and 7, and the laminated plate-like electrodes are made up of electrodes having different electrical polarities for each adjacent one. Reference numeral 8 denotes a polarity switching device which periodically switches the electrical polarities of the electrical connections 6 and 7 so that the electrical polarities of all the laminated plate electrodes are periodically switched. It is preferable to switch the electrical polarity in a state usually called a rectangular wave.

Another embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 denotes a container, which constitutes the main body device of the present invention and is filled with an aqueous solution of an electrolyte. 2 is the inlet connecting to the container,
An outlet 3 constitutes a flow path for the aqueous solution. The aqueous solution containing ruthenium flows in through the inlet, and the aqueous solution with reduced ruthenium concentration flows out through the outlet. Reference numeral 4 denotes a perforated plate electrode, which is a titanium plate processed into an expanded metal and coated with a platinum film in this embodiment. In this embodiment, unlike the above-described embodiments, the aqueous solution passes through the perforated plate-shaped electrodes at right angles to the laminated perforated plate-shaped electrodes. Reference numeral 5 denotes a separator, which is a porous plate having an electrode insulating property and maintains a necessary space between the electrodes, and at the same time forms a stacked electrode state while maintaining electrical insulation between the electrodes. Since the separator 5 has a perforated plate shape, it does not hinder the flow of the aqueous solution orthogonal to the laminated perforated plate electrodes. 6 and 7 are electrical connections, which are connected to the electrodes to supply current to the electrodes and keep them at a constant voltage. It is an electrical connection with a polarity different from 7 and 6. Due to the electrical connections 6 and 7, the laminated perforated plate-like electrodes are constituted by electrodes having different electrical polarities for each adjacent one. Reference numeral 8 is a polarity switching device, which periodically switches the electrical polarities of the electrical connections 6 and 7 so that the electrical polarities of all the laminated porous plate-shaped electrodes are periodically switched. It is preferable to switch the electrical polarity in a state usually called a rectangular wave. A modification to this embodiment is characterized in that the surface area of the perforated plate electrode near the outlet of the aqueous solution is larger than the surface area of the perforated plate electrode near the inlet of the aqueous solution. There is an advantage that the reaction area of the electrode is increased and the reaction rate is kept high as the water-soluble ruthenium compound is changed to the insoluble ruthenium compound and the concentration of the water-soluble ruthenium decreases.

Another embodiment of the present invention will be described with reference to FIG.

Reference numeral 1 denotes a cylindrical container which constitutes the main body device according to the present embodiment and is filled with an aqueous solution of electrolyte. Reference numeral 2 is an inlet connected to the container, and 3 is an outlet, which constitutes a flow path of the aqueous solution. The aqueous solution containing ruthenium flows in through the inlet, and the aqueous solution with reduced ruthenium concentration flows out through the outlet. In the present embodiment, unlike the above-mentioned two embodiments, the inlet 2 is inserted in the center of the container 1 and has a discharge port for discharging an aqueous solution although the tip is closed. The outlet 3 is connected to a space that partitions a part of the container 1. Reference numeral 4 denotes a perforated plate electrode, which is formed by concentrically laminating a plurality of pairs of perforated plate cylindrical electrodes each having an anode and a cathode and having different diameters. Reference numeral 5 is a perforated plate-shaped cylindrical separator having a different diameter, which is made of an electrically insulating material. The separator keeps the space required for the cylindrical perforated plate electrode and at the same time maintains the electrical insulation between the electrodes. Further, the separator has a perforated plate shape and allows the aqueous solution to pass in the radial direction from the center of the cylindrical perforated plate electrode. 6 and 7 are electrical connections which are connected to the electrodes to supply current to the electrodes and keep them at a constant voltage. 7 is an electrical connection having a polarity different from 6.
Due to the electrical connections 6 and 7, the laminated perforated plate-like electrodes are constituted by electrodes having different electrical polarities for each adjacent one. The perforated plate electrode 4 can also be arranged in a spiral shape around the inlet 2 instead of being cylindrical. In this case, the separators 5 are also stacked and arranged in a spiral shape. 8 is a polarity switching device, which is an electrical connection 6 and 7
Periodically switching the electrical polarity at
The electrical polarities of all the stacked porous plate electrodes are periodically switched. It is preferable to switch the electrical polarity in a state usually called a rectangular wave.

In the present example, as the ruthenium concentration of the aqueous solution is decreased, the effect of increasing the electrode surface area can be achieved, and at the same time, the aqueous solution can be brought into contact with the electrode surface most uniformly. Therefore, in terms of electrode surface area and device volume, Be economical. In particular, the adoption of the spiral perforated plate electrode can reduce the number of electrodes and the number of electrode connections, and thus can simplify the apparatus.

Another embodiment of the present invention will be described with reference to FIG.

Reference numeral 9 is a ruthenium removing device, which applies a voltage to an electrode immersed in an aqueous solution of an electrolyte to cause an oxidation reaction on the anode and a reduction reaction on the cathode, thereby converting the ruthenium compound in the aqueous solution into an insoluble ruthenium compound. An apparatus for changing and removing, in which a pair of or a plurality of pairs of plate-shaped electrodes or porous plate-shaped electrodes laminated inside are arranged, and an inlet and an outlet for an aqueous solution are provided. 10 is a tank that receives an aqueous solution containing ruthenium and sends it to the ruthenium removing device 9,
Receiving the ruthenium-removed aqueous solution having a reduced concentration of ruthenium again through the ruthenium removal device, and further connecting the respective pipes for circulating the ruthenium-removed device to discharge the aqueous solution with a sufficiently reduced ruthenium concentration. ing. Reference numeral 11 denotes a pump for feeding the aqueous solution in the tank 10 to the ruthenium removing device 9. A pulsation generator 12 pulsates the aqueous solution sent to the ruthenium removing device 9 by the pump 11.

This embodiment, which is characterized in that the aqueous solution is repeatedly circulated in the apparatus, requires that the ruthenium concentration in the aqueous solution to be treated fluctuates and the ruthenium concentration in the treated aqueous solution be kept constant low. It It gives the most suitable performance under general conditions. Further, the embodiment characterized in that the flow of the aqueous solution in the device is pulsating, promotes the contact between the aqueous solution and the electrode as compared with the case of a single flow, ruthenium of the present invention is a basic principle of The oxidation / reduction reaction on the electrode can be promoted.

〔The invention's effect〕

According to the first, seventh and eighth aspects of the present invention, the electrode and the ruthenium compound can be contacted easily and sufficiently, and ruthenium can be efficiently insolubilized. In particular, in the inventions of claims 1 and 8, since the aqueous solution is passed while intersecting (for example, orthogonal to) the perforated plate electrodes, the aqueous solution is surely passed between the perforated plate electrodes.

The inventions of claims 2 and 9 produce the same effect as the invention of claim 1, and can reduce the amount of ruthenium higher-order oxides returning to the nitrosyl complex.

The inventions of claims 3 and 10 produce the same effect as the invention of claim 1, and can further reduce the amount of ruthenium higher order oxides returned to the nitrosyl complex.

According to the eleventh aspect of the invention, the same effect as that of the first aspect of the invention is produced, and since the contact period between the cathode and the anode can be adjusted according to the decrease of the ruthenium concentration, ruthenium can be made insoluble more efficiently.

The inventions of claims 4 and 12 produce the same effect as the invention of claim 11.

The inventions of claims 5 and 13 produce the same effect as the invention of claim 1, and promote the contact between the ruthenium compound in the aqueous solution and the anode and the cathode, thereby promoting the oxidation and reduction reactions of the ruthenium compound on the electrode. Can be made.

The features of the inventions of claims 6 and 14 produce the same effect as the invention of claim 1, and since the aqueous solution is repeatedly circulated, the amount of water-soluble ruthenium contained in the aqueous solution can be remarkably reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an apparatus which is an embodiment of the present invention. FIG. 2 is a sectional view showing the structure of an apparatus which is another embodiment of the present invention. FIG. 3 is a sectional view showing the structure of an apparatus according to another embodiment of the present invention. FIG. 4 is a system diagram showing the configuration of the apparatus which is an embodiment of the present invention. 1 ... Container, 2 ... Inlet, 3 ... Outlet, 4 ... Plate-shaped electrode or perforated plate-shaped electrode, 5 ... Separating member or separator, 6, 7 ...
… Electrical connection, 8 …… Polarity switching device, 9 …… Ruthenium removal device, 10 …… Tank, 11 …… Pump, 12 …… Pulsation device.

Claims (14)

[Claims] 1. A ruthenium compound in an aqueous solution is converted into an insoluble ruthenium compound by applying a voltage between electrodes immersed in an aqueous solution containing a ruthenium compound to cause an oxidation reaction on the anode and a reduction reaction on the cathode, respectively. A method of removing ruthenium in an aqueous solution, wherein in the method of changing and removing, at least a pair of perforated plate-shaped electrodes in which the electrodes are laminated, and the aqueous solution is allowed to pass through the perforated plate-shaped electrodes. 2. The method for removing ruthenium in an aqueous solution according to claim 1, wherein adjacent electrodes of the laminated porous plate electrodes have different electrical polarities. 3. The method for removing ruthenium in an aqueous solution according to claim 1, wherein the electrical polarity of the porous plate electrode is periodically switched. 4. The laminated perforated plate-shaped electrode is any of a plurality of concentric cylindrical electrodes and a spiral electrode, and a large number of holes are provided in a radial direction,
The method for removing ruthenium in an aqueous solution according to claim 1, wherein the aqueous solution is passed in a radial direction from the center of the porous plate electrode. 5. The method for removing ruthenium from an aqueous solution according to claim 1, claim 2, claim 3 or claim 4, wherein the aqueous solution is allowed to pass through in a pulsating manner. 6. The method for removing ruthenium in an aqueous solution according to claim 1, claim 2, claim 3 or claim 4, wherein the aqueous solution is repeatedly circulated to pass through the laminated porous plate electrodes. 7. A ruthenium compound in an aqueous solution is converted into an insoluble ruthenium compound by applying a voltage between electrodes immersed in an aqueous solution containing a ruthenium compound to cause an oxidation reaction on the anode and a reduction reaction on the cathode, respectively. In the apparatus for changing and removing, at least a pair of perforated plate electrodes that are the electrodes, a means for periodically switching the electrical polarity of the perforated plate electrodes, and the aqueous solution in the gap between the perforated plate electrodes. An apparatus for removing ruthenium in an aqueous solution, which comprises: 8. A ruthenium compound in an aqueous solution is converted into an insoluble ruthenium compound by applying a voltage between electrodes immersed in an aqueous solution containing a ruthenium compound to cause oxidation reaction on the anode and reduction reaction on the cathode, respectively. An apparatus for removing ruthenium in an aqueous solution, comprising: at least a pair of perforated plate electrodes, which are the electrodes, and a means for passing the aqueous solution across the perforated plate electrodes. . 9. The apparatus for removing ruthenium in an aqueous solution according to claim 8, wherein adjacent electrodes of the laminated porous plate electrodes have different electrical polarities. 10. The apparatus for removing ruthenium in an aqueous solution according to claim 8, further comprising means for periodically switching the electric polarity of the perforated plate electrode. 11. The ruthenium removal in the aqueous solution according to claim 8, wherein the surface area of the perforated plate electrode located near the outlet of the aqueous solution is larger than that of the perforated plate electrode located near the inlet of the aqueous solution. apparatus. 12. The laminated perforated plate electrode is one of a plurality of concentric circularly arranged cylindrical electrodes and a spiral electrode, wherein a large number of holes of the perforated plate electrode are arranged in a radial direction. A device for removing ruthenium in an aqueous solution according to any one of claims 7 to 11, which is provided in. 13. The apparatus for removing ruthenium in an aqueous solution according to claim 7, further comprising means for pulsatingly flowing the aqueous solution. 14. A means for circulating the aqueous solution repeatedly to pass through the laminated porous plate-shaped electrodes.
The ruthenium removal apparatus in the aqueous solution which is any one of -12.