JPS63173951A - Electrolytic cell for flow coulometry - Google Patents

Abstract

PURPOSE:To achieve a higher detection sensitivity of an electrolytic cell, by providing current collecting bodies contacting an working electrode at two points separately on the upstream and downstream sides of a liquid to be inspected to upgrade the current efficiency. CONSTITUTION:A hollow cylindrical electrolytic diaphragm 1 is arranged in a housing container 7 having inlet and outlet nozzles 5 and 6 and two current collectors 12a and 12b of the same diameter are bonded at both ends thereof. A housing body is made up of the electrolytic diaphragm 1 and the current collecting bodies 12a and 12b and a working electrode 16 made of a carbon fiber bundle is housed therein with the tip parts 15a and 15b contacting the inside of the current collectors 15a and 15b. A cylindrical counter electrode 4 is arranged on the circumference of the electrolytic diaphragm 1 and piercing a part thereof, a reference electrode 3 is arranged with a liquid junction positioned on the external surface of the electrolytic diaphragm 1. A liquid to be inspected from the nozzle 5 is electrolyzed while passing through the working electrode 16 and an electrolytic current is collected to the current collectors 12a and 12b. The density of ions of the liquid being inspected is determined by detecting the current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the invention] (Industrial field of application) The present invention is an electrochemical measuring instrument, in particular a measuring instrument for measuring highly concentrated dissolved substances in a solution, such as uranium or the like in a nuclear fuel reprocessing facility. This invention relates to a detector that measures the valence and concentration of plutonium by electrochemical methods.

(Prior Art) The main process of nuclear fuel reprocessing is to separate uranium and plutonium contained in spent nuclear fuel from fission products by a solvent extraction method, and further refine the uranium and plutonium. In order to operate this process continuously and economically, it is necessary to detect the chemical state, such as the concentration of uranium and plutonium in the solution and their valences, in addition to the temperature, pressure flow rate, etc.

As a device to measure the concentration and valence in this solution,
An electrolytic cell for flow coulometry using constant potential electrolysis has been developed, and an example thereof is shown in FIG. This electrolytic cell includes a working electrode housing body consisting of a combination of an electrolytic diaphragm 1 made of a cylindrical alumina porous material and a graphite current collector 2 of the same diameter adhered to one end of the electrolytic diaphragm 1, and this working electrode housing body. a reference electrode 3 arranged so that the liquid junction is located on the outer surface of the electrolytic diaphragm 1; a cylindrical counter electrode 4 made of platinum steel arranged around the outer periphery of the electrolytic diaphragm 1; and a test liquid artificial nozzle 5. An electrically insulating storage container 7 having an outlet nozzle 6 and a counter electrode liquid 8 such as a solution of the same kind as the test liquid filled in the storage container 7 or a potassium chloride solution, and a central part inside the working electrode housing. 14
The working electrode 9 is made of a bundle of carbon fibers such as grady carbon, which is folded in two and filled so that the bent tip is located inside the current collector 2.

Here, a method for quantitative analysis using this electrolytic cell for flow coulometry will be briefly described.

In order to quantitatively analyze the ions to be measured, it is necessary to electrolyze (oxidize or reduce) all the ions to be measured while the test liquid passes through the working electrode 9 portion. Since the oxidation or reduction reaction at this time is a surface reaction of the working electrode 9, the electrolytic diaphragm 1 has a diameter of several tens of μm in order to accelerate the progress of the reaction.
A working electrode 9 is disposed using a bundle of thin carbon fibers, etc. as described below, with a filling ratio of the bundle to the cross section of the test liquid flow path of about 88% to increase the surface area. For this reason, the flow resistance of the working electrode 9 portion becomes extremely large, and a large pressure is required to introduce the test liquid. Under these conditions, the pore size, porosity, thickness, etc. of the electrolytic diaphragm 1 are such that the amount of test liquid leaking from the working electrode 9 side to the counter electrode 4 side through the electrolytic diaphragm 1 is compared to the total flow rate of the test liquid. is selected so that it is within a negligible range. In such an electrolytic cell for flow coulometry, an electrolytic potential of the ion to be measured based on the potential of the reference electrode 3 is applied to the working electrode 9 from a potentiostat,
When the test liquid containing the ions to be measured is flowed at a constant flow rate,
An electrolytic current having a magnitude shown in the following equation flows between the working electrode 9 and the counter electrode 4.

i=n*Fecef (where i is the electrolytic current (A), n is the number involved in the electrolysis of the ion to be measured, F is the Faraday constant number (clone/mo
l), c is the concentration of the analyte (a+ol/fl)
, f indicates the test liquid flow f:k (j!/sec))
Since n and F are known, the concentration of the ion to be measured can be determined by measuring the electrolytic current flowing between the working electrode 9 and the electrode 4.

As mentioned above, the quantitative analysis of nitric acid and plutonium ions (Pu", P u ") in the nuclear fuel reprocessing process is 10-3 aol/j! It can be carried out up to a certain concentration.

(Problems to be Solved by the Invention) As described above, when performing quantitative analysis using an electrolytic cell for flow coulometry, the test liquid is introduced from the inlet nozzle 5 of the storage container 7 and electrolyzed by the working electrode 9. and is discharged from the outlet nozzle 6. This electrolytic action of the test liquid occurs when the test liquid passes over the surface of the working electrode 9, but it has been found that most of the electrolytic action takes place at the upstream working electrode part. .

In a conventional flow coulometry electrolytic cell in which only one current collector 2 is provided downstream of the test liquid, the current generated by electrolysis of the test liquid is transferred to the current collector installed downstream. was collected and this current was detected. However, the current generated at the working electrode 9 at a position away from the current collector 2 is detected to be lower than the actual value due to a potential drop due to the resistance of the working electrode 9, reducing current collection efficiency.

In addition, the working electrode 9 is required to have a large surface area in order to increase electrolysis efficiency, but increasing the surface area may cause an even larger potential drop, so there are restrictions on the shape of the working electrode. .

Furthermore, since the working electrode 9 is fixed at only one end, the working electrode 9 near the inlet nozzle 5 will fluctuate due to the inflow of the test liquid, causing turbulent flow of the test liquid, and the working electrode 9 and convergence. There was a problem in that it caused poor contact with the electric body 2. In addition, after assembling the device, the working electrode 9 and the current collector 2 are
It is difficult to check the contact status with the device, and if a contact failure occurs, the device must be reassembled, which poses problems in terms of reliability and maintainability.

The present invention has been made in consideration of these points,
An object of the present invention is to provide an electrolytic cell for flow coulometry that can improve current collection efficiency and improve measurement accuracy and detection sensitivity.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a cylindrical working electrode storage body that includes an electrolytic diaphragm and a current collector, through which a test liquid flows, and a working electrode that is filled in the working electrode storage body. An electrolytic cell for flow coulometry, comprising: an electrolytic section consisting of a counter electrode, a reference electrode, and a counter electrode provided outside the working electrode housing; and a storage container in which the working electrode housing and the electrolytic section are housed. The present invention is characterized in that current collectors are provided at two positions, one on the inflow side of the test liquid and the other on the outflow side of the electrolytic diaphragm.

(Function) According to the present invention, the test liquid introduced into the working electrode housing is electrolyzed while passing through the working electrode part, and the current generated by this electrolysis is transmitted to the two tills on the inflow side and the outflow side.
The ion concentration of the test liquid is determined by detecting the current collected by a current collector provided at a certain location.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing an embodiment of an electrolytic cell for flow coulometry according to the present invention, and the same parts as those of the electrolytic cell shown in box 3 in the drawing are given the same reference numerals. In the figure, reference numeral 7 denotes an electrically insulating storage container having an inlet nozzle 5 and an outlet nozzle 6 for the test liquid, and inside this storage container 7, an electrolytic part IMlkl made of a hollow cylindrical alumina porous body is installed. It is disposed so that its axis substantially coincides with a line connecting the axes of the inlet nozzle 5 and the outlet nozzle 6.

Two graphite current collectors 12a and 12b having the same diameter are adhered to both ends of the electrolytic diaphragm 1, and these two current collectors 12a and 12b are connected to the inner wall of the storage container 7 and the electrolytic diaphragm 1, respectively. The end portion is interposed between the end portion and the end portion. Electrolytic diaphragm 1 and current collector 12a.

12b constitutes a storage body that stores the working electrode,
A working electrode 16 made of a bundle of carbon fibers is housed within the housing. This working electrode 16 is made by folding a bundle of flexible carbon fiber or grady carbon fiber into three, which has a length approximately three times the length of the working electrode housing, and has two bent tip portions 15a and 15b. Each current collector 12
a.

12b so as to be in contact with each other.

Working electrode lead wires 13a, 13b (usually gold wires) are connected to the outer surface of each current collector 12a, 12b, respectively, so that current can be supplied to the working electrode 16, and the current collector The outer surfaces of the working electrodes 12a and 12b and the working electrode lead wires 13a and 13b are coated with an electrical insulator to prevent contact with the counter electrode 8 filled in the storage container 7.

A cylindrical counter electrode 4 made of platinum steel is disposed around the outer periphery of the electrolytic diaphragm 1. A reference electrode 3 is inserted through a part of the counter electrode 4, and a liquid junction is located on the outer surface of the electrolytic diaphragm 1. It is arranged so that A counter electrode wire lead wire 11 is connected to the counter electrode 4 from outside the storage container 7 .

According to this embodiment having such a configuration, the test liquid introduced into the working electrode housing from the inlet nozzle 5 is electrolyzed while passing through the working electrode 16, and the current generated by this electrolysis is Current collectors 12a are installed on the upstream side and the downstream side.

12b, and by detecting this current, the ion concentration of the test liquid can be determined.

According to this embodiment, since the current collectors 12a and 12b are provided at two locations, one on the upstream side and one on the downstream side, the influence of the voltage drop due to the working electrode 16 is reduced to half that of the conventional one. Therefore, the current collection efficiency by the current collectors 12a and 12b is high, and it is possible to improve measurement accuracy and detection sensitivity. Second
The figure is a diagram showing the plateau characteristics of the ion electrolytic current when using this embodiment in comparison with the conventional example. As is clear from this figure, according to this example, the plateau region was expanded compared to the conventional example, and the current collection efficiency was able to be significantly improved. In addition, the rise of the electrolytic current to the plateau region became steeper, improving current detection sensitivity. Therefore, even if the set voltage fluctuates, stable ion concentration measurement is possible.

Further, since both end portions 15a and 15b of the working electrode 16 are placed in contact with the current collectors 12a and 12b, the working electrode 16 can be held securely, and the current collectors 12a and 1
Good contact between the working electrode 2b and the working electrode 16 can be maintained at all times. Therefore, even if the flow rate of the test liquid is increased to measure a low concentration, for example, contact failure of the working electrode 16 due to flow fluctuations will not occur.

Furthermore, since the working electrode lead wires 13a and 13b are connected to the current collectors 12a and 12b at both ends, respectively, this working electrode lead wire 13a.

By measuring the resistance between 13b and the like, it is possible to easily check the contact state between the current collector and the working electrode, the deterioration state of the working electrode, etc. after the device is assembled.

In addition, since the working electrode 16 is securely held, the test liquid for cleaning can be flowed back from both the artificial nozzle 5 and the outlet nozzle 6, so that the inside of the working electrode housing is always kept clean. It is possible to maintain this condition.

(Effects of the Invention) As explained above, according to the present invention, current collection efficiency is improved by providing the current collectors in contact with the working electrode at two locations, one on the upstream side and one on the downstream side of the flow of the test liquid. It is possible to improve the detection sensitivity and measurement accuracy of the electrolytic cell.

Further, it is possible to easily confirm the contact between the working electrode and the current collector during measurement, and to maintain the contact between the two reliably. This improves reliability as an M1 constant device and allows it to be used as an in-line measuring device in a plant.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of an electrolytic cell for flow coulometry according to the present invention, FIG. 2 is a diagram showing plateau characteristics of electrolytic current according to the embodiment and a conventional example, and FIG. 3 is a diagram showing a conventional electrolytic cell. FIG. 2 is a longitudinal sectional view showing an example of an electrolytic cell for flow coulometry. 1... Electrolytic diaphragm, 3... Reference electrode, 4... Counter electrode,
5... Inlet nozzle, 6... Outlet nozzle, 7... Storage container, 8... Counter electrode, 12a, 12b-... Current collector, 13a. 13b... Working electrode lead wire, 16... Working electrode. Applicant's agent Sato-Yu 81 Illustration 2

Claims (1)

[Scope of Claims] 1. A cylindrical working electrode housing including an electrolytic diaphragm and a current collector, through which a test liquid flows, a working electrode filled in the working electrode housing, and the working electrode housing. In an electrolytic cell for flow coulometry, the electrolytic cell includes an electrolytic section including a counter electrode, a reference electrode, and a counter electrode provided outside the body, and a storage container in which the working electrode storage body and the electrolytic section are housed,
An electrolytic cell for flow coulometry, characterized in that the current collector is provided at two positions on the inflow side and outflow side of the test liquid of the electrolytic diaphragm. 2. The electrolytic cell for flow coulometry according to claim 1, wherein the current collector has the same cylindrical shape as the electrolytic diaphragm and is bonded to both ends of the electrolytic diaphragm. 3. The working electrode is formed by folding into three a bundle of flexible fibrous working electrode material that is approximately three times as long as the working electrode housing;
2. The electrolytic cell for flow coulometry according to claim 1, wherein the working electrode housing is filled with each tip portion closely disposed within the respective current collector.