JPH0288786A - Production of high purity metal or alloy - Google Patents

Abstract

PURPOSE:To produce a high purity metal at high efficiency by arranging a cathode so that main electrode surface facing to an electrolytic bath vessel consists of only with the cathode and executing main electrolytic reaction at between the back face of this cathode and an anode. CONSTITUTION:Fused salt 4 (for example, 50wt.% LiF-50wt.% NdF3) is arranged into the electrolytic bath vessel 3 made of austenite series stainless steel and a crucible 9 lining the inside with Ta is set at low part of the vessel 3 and on this, a dummy electrode 11 made of an electrolytic pure iron is concentrically arranged. Iron cathodes 1 are arranged at the electrolytic bath vessel 3 side in the fused salt 4 and the graphite anode 2 is arranged at between the these cathodes 1. By this constitution, the electrolysis is executed with the anode 2 and the cathode 1 and electrolytic generated Nd is allowed to react with Fe of the cathodes 1 and deposited in the crucible 9 as the drips 10 of Nd-Fe alloy to obtain the Nd-Fe alloy 5. This Nd-Fe alloy 5 is sucked up with a vacuum suction device 7 and NdF3 corresponding to consumed quantity is supplied into the fused salt 4 through a raw material supplied device 8.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing high-purity metals or alloys by electrolytic method, and particularly relates to a method for producing high-purity metals or alloys by electrolytic method.
The present invention relates to a molten salt electrolysis method suitable for producing Nd and Nd alloys as raw materials for d-Fe-B magnets, but is also applicable to aqueous solution electrolysis and molten salt electrolysis in general.

(Prior art) As a method for obtaining Nd or Nd alloy by molten salt electrolysis method,
There is a report on the use of a LiF-NdFi-NdiO3 electrolytic bath.

(Example: Morris et al., NJ, S., Bur, M' nRep
, Invest, No. 69573 ~ 5% (50 ppm), and Nd-F with Mo = O, O'2% (200 ppm) in an electrolytic cell with Mo lining.
Examples are shown in which e-alloys were produced.

The method for reducing nonmetallic impurities such as carbon and oxygen was solved by the aforementioned molten salt electrolysis method proposed by the applicant.
It has become possible to produce high-purity Nd, etc., with O = 40 ppm and O = 70 ppm. The molten salt used in this method is
N d F as a neodymium metal source in LiP 3. N
d 203, i.e. L i F N
d F 3 system or L mixed with Nd20i
i F NdFi NCl20i system, and BaF
2. A system to which CaF2 or the like is appropriately added is used. Also, N
Nd(13) may be used instead of dF.

In the case of LiF-NdF, 96-65m0ρ%, more preferably 95-75mo (1% LiF and 4-35m
oρ%, more preferably 5 to 25 moρ% N d F
It is said that a composition consisting of 3 is good.

In the case of LiF-NdF3-Nd203 system, the above 1967
〉 The applicant has filed PCT/JP-87-01011 (Japanese Patent Application No. 61-307,308, Japanese Patent Application No. 62-204879)
No. 62-220893), by collecting neodymium or neodymium alloy at the bottom of the bath and including oxygen gas in the atmosphere above the bath, the powdered carbon produced from the carbon electrode is exhausted. In addition to stabilizing the electrolytic bath, by using a plate-shaped electrode at least as an anode, the critical current density can be increased and neodymium or neodymium alloy (hereinafter also referred to as Nd, etc.) can be removed with high current density and current efficiency. ) was proposed for the molten salt electrolysis method.

In Nd-Fe-B permanent magnets, in addition to non-metallic impurities such as carbon and oxygen, metal impurities also generally degrade magnetic properties, so Nd, etc. used in permanent magnets are required to have a small amount of impurities. .

According to Japanese Patent Publication No. 63-12947, Nd2O is added to the L i F N d F 3 system with a preferable composition of W (%) < 0.00 in an electrolytic cell lined with W.

It is said that a composition in which a few wt % of is added and mixed is good.

When rare earth metals are produced electrolytically using a LiF-rare earth compound based molten salt, this component is eluted and transferred to Nd etc. due to corrosion of the electrolytic bath, which is considered to be the cause of impurity contamination with Nd etc. In order to prevent the contamination of such impurities, the properties generally required of the electrolytic bath material are: (1) Corrosion resistance against high-temperature molten salt.

2> Must have high temperature strength to hold molten salt at high temperatures.

The present applicant proposed the use of austenitic stainless steel as a material that satisfies the above requirements and is inexpensive (Japanese Patent Application No. 62-233697).

By using austenitic stainless steel as the bath material, high purity Nd and Nd can be obtained with respect to non-metallic elements.
-Fe alloy could be manufactured, but it was found that Ni and Cr, which are components of austenitic stainless steel used in electrolytic baths, were sometimes mixed into the product.

(Problem to be solved by the invention) When an electrolytic bath made of iron-based material is used, the contained element is N.
We are not aware of any prior reports regarding reducing the purity of d and Nd-Fe alloys.

Therefore, the present inventors used Cr stainless steel.

When we investigated the cause of the mixing of different metals such as Ni into Nd, we found that there was corrosion due to electrochemical causes, in addition to the simple corrosion due to the high-temperature molten salt mentioned above.

Therefore, it is not possible to produce high-purity Nd or the like only by using a material that satisfies the above requirements 1) and 2) for the electrolytic bath.

Therefore, the present invention provides an electrolytic method for rare earth metals or alloys that reduces the amount of metal components other than Fe mixed into the electrolytic metal in an electrolytic method using iron-based materials, particularly stainless steel, as the material for the electrolytic bath. The purpose is to

The second method is to place an anode and a cathode in an electrolytic bath and manufacture metals or alloys by electrolysis. This method is characterized by causing the main electrolytic reaction to occur between the surface of the anode and the cathode.The third method is a method for producing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath. , the main electrode surface facing the electrolytic bath consists of an anode and a cathode,
A method characterized in that the electrode has a shape and arrangement that allows the main electrolytic reaction to occur between the back surface of the anode and the back surface of the cathode, and that electrolysis is performed by disposing a conductive shield between the anode and the electrolytic cell. The fourth method is to produce metals or alloys by electrolysis by arranging an anode and a cathode in an electrolytic bath, in which the main electrode surface facing the electrolytic bath is composed of the anode and the cathode. , the shape of the electrode that causes the main electrolytic reaction to occur on the back surface of the anode and the back surface of the cathode, and furthermore, the present invention uses ceramic materials such as Ag2O3 and refractory metals such as Mo, Ta, and W in the electrolytic bath. An object of the present invention is to provide a melting electrolytic method for rare earth metals or alloys that can reduce the amount of impurities mixed in than conventional methods.

(Means for Solving the Problems) As a result of various studies on the causes of dissolution of the electrolytic bath material mixed into Nd, the present inventors found that the material of the electrolytic bath undergoes electrolytic corrosion due to changes in the potential of the anode, cathode, and electrolytic bath. They discovered this, studied countermeasures, and completed the present invention.

As a measure to prevent this electrolytic corrosion, the following method is proposed as a method that can produce high-purity metal and does not damage the electrolytic bath.

The first is a method for producing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, in which the main electrode surface facing the electrolytic bath consists only of the cathode. The method is characterized in that the main electrolytic reaction is carried out between the back surface and the anode, and the method is characterized in that the electrolysis is carried out by having a slotted arrangement and by arranging a conductive shield between the cathode and the electrolytic cell. , Fifth, in a method of manufacturing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath is composed of an anode and a cathode, and Electrolysis is performed in an electrolytic bath having a shape and arrangement of electrodes that allow the main electrolytic reaction to occur on the back surface of the anode and the back surface of the cathode, and in which a conductive shield is arranged between each of the anodes, each cathode, and the electrolytic bath. This method is characterized by the following.

The above methods 1 to 5 will be described in detail later, but in principle, the cations and anions leaked to areas other than the main reaction surface react with the electrolytic bath, causing troubles due to electrolytic corrosion. The first method is to prevent reactions caused by cations by changing the shape and arrangement of the electrodes, and the second method is to prevent reactions caused by anions by changing the shape and arrangement of the electrodes. In other words, the first and second methods are solutions based mainly on the shape and arrangement of the electrodes.

On the other hand, in the third to fifth methods, the solution is not the shape and arrangement of the electrodes, but the solution is to place a conductive shield between the electrolytic bath and the electrodes. The third method is to prevent reactions caused by cations, the fourth method is to prevent reactions caused by anions, and the fifth method is to prevent reactions by both cations and anions.

In other words, the fifth method is a complete solution, but in various electrolytic reactions, both cationic and anionic reactions are not necessarily the cause of troubles, and solving problems caused by one of these reactions can be economical. This is because it may be sufficient in some cases.

Specific examples of electrode arrangement in the first method include (a) a hollow cylindrical or rectangular cylindrical cathode with an anode placed in the center of the cathode, or a configuration in which these electrodes are arranged concentrically; ) The cathode is plate-shaped. When electricity is applied without grounding the anode or cathode, the potential difference between the anode and cathode is 7μ, but the potential of the anode and cathode will change depending on the insulation of the electrolytic bath, rectifier, and other circuits, and other reasons.

Therefore, the potential difference between the anode and the cathode is constant at 7V, but the potential difference between the anode and the electrolytic bath and between the cathode and the electrolytic bath will change due to reasons such as deterioration of the insulator.

Let us now assume that electrolysis is carried out to produce a Nd-Fe alloy under the following conditions, with the potentials of the anode and cathode being +5 and -2 with respect to the earth.In this case, the potential of the electrolytic bath is grounded. If it is not, it will be between +5V and -2V, so a detailed explanation will be given below assuming that it is IV.

When NdF3 is electrolyzed in LiF N d F 3-based molten salt using a graphite anode and an iron cathode, (1) the reaction at the anode is C+ nI” −+CF, +ne− (1) (2) the reaction at the cathode is The reaction is conducted using Fe+Nd''+3e-+Nd-Fe alloy (2) as the pole.
An arrangement in which the anode is sandwiched between the cathodes is possible. In the case of (a), the cathode and the anode, and in the case of (b), the anode may have any shape such as a plate-shaped cylinder, a prism, a polygonal prism, or the like. (B)
In this case, the cathode can be sandwiched between the anode from both sides, at each side of a triangle or square, or at other contours.

As for electrolytic bath materials in molten salt electrolysis such as Nd, corrosion caused by high-temperature molten salt can be solved by materials that satisfy the requirements 1) and 2) mentioned above.
It was found that electrolytic baths are subject to electrolytic corrosion due to the potentials of the anode and cathode. Next, we will discuss the potentials of the electrolytic bath, anode, and cathode related to electrolytic corrosion of the electrolytic bath. Note that since the electrolytic bath is usually not grounded, its potential is between the anode voltage and the cathode voltage.

If a DC voltage of 7V is applied between the cathode and #41i, the potential difference between the anode and the cathode will be 7■.

When the anode is grounded, the anode becomes 0■ and the cathode becomes -7V, and when the cathode is grounded, the anode becomes +7■ and the cathode becomes OV.

(By Equation 11, CF is generated at the anode, and the cathode reaction (2
), a Nd-Fe alloy is generated at the cathode. These (+1. +21) are the main reactions in electrolysis. In addition to this reaction, there are also side reactions in which F- and Nd3+ ions leaked between the anode and the electrolytic bath and between the cathode and the electrolytic bath behave as shown below. .This causes trouble.

(3) Side reactions that occur between the anode and the electrolytic cell The side reactions will be explained below with reference to the drawings (FIGS. 2 and 3).

In the figure, 1 is an anode, 2 is a cathode, 3 is an electrolytic bath, 4 is an electrolytic bath, and 5 is a Nd-Fe alloy.

Since the anode 1 has a high potential with respect to +5■ and the electrolytic bath 3 with +1■, the electrolytic bath 3 has a relatively low potential, and the leaked Nd3+ reacts with the electrolytic bath material that has a relatively low potential. . (Note that since the anode has a relatively high potential, F- ions leaking between the anode and the electrolytic cell react with the anode side and do not react with the electrolytic cell.) As a result, the shaded area (3')
The components in the stainless steel in the electrolytic bath 3 react with Nd and F
E, Cr, Ni, etc. are eluted and incorporated into the Nd-Fe-B alloy 5.

(4) Side reactions occurring between the cathode and the electrolytic bath cathode 2 (third
(Fig.) is -2V, which is 3cm lower voltage than +IV of the electrolytic bath 3, so the electrolytic bath 3 has a relatively high potential, and F- reacts with the electrolytic bath material. (In addition, since the cathode has a relatively low potential of 12cm, Nd3 leaked between the cathode and the electrolytic tank
(+ reacts with the cathode side and does not react with the electrolytic bath) A reaction between F- and the electrolytic bath occurs in the shaded area (3'').

As mentioned above, Nd”
- If the ions leak, they will react with the electrolytic bath due to the side reactions (3) and (4) above, reducing the purity of the collected Nd, etc., and it is thought that electrolytic corrosion will occur that will damage the electrolytic bath.

When the side reaction (3) occurs, Nd' → ions react with the material used in the electrolytic bath, and if the electrolytic bath is made of austenitic stainless steel, such as 5US-31, electrolytic corrosion can be completely eliminated by simply setting the potential of the electrolytic bath. It is difficult to solve the problem. This reaction can be thought of as a reaction in which cations and anions individually occur between the anode and the electrolytic bath, or a reaction that occurs between the cathode and the electrolytic bath, but the reactions related to electrolytic corrosion can be summarized as follows.

1. Set the electrolytic bath potential higher than the anode potential.

Reaction (4), in which the anion (F-) reacts with the electrolytic bath material, cannot be resolved.

2. Set the potential of the electrolytic bath between the anode and cathode.

Reactions (3) and (4), where cations (Nd3+) and anions (F-) react with the electrolytic bath material, cannot be resolved.

3. Set the potential of the electrolytic bath to be lower than the potential of the cathode.

Reaction (3) cannot be resolved.

For the above reasons, it is not possible to prevent both reactions (3) and (4) by simply maintaining the potential of the electrolytic bath at an appropriate value, so the problem of electrolytic corrosion is not solved. If phase O8 is used in the reaction amount, the components Ni and Cr will be eluted and contamination problems will occur. That is, the purity of the Nd-Fe alloy deteriorates, and the deterioration of the electrolytic bath material is accelerated. Next, when the reaction (4) occurs, the material used in the electrolytic bath reacts with F- ions,
The damage will cause trouble. For example, if iron-based materials are used in an electrolytic bath, iron and fluorine will react and problems will occur due to reaction products. However, this trouble is N
This is minor compared to the trouble caused by the reaction between d3+ ions and the electrolytic bath.

Therefore, in order to deal with the above problems, (3) and (4)
Particularly in the case of manufacturing Nd-Fe alloys, it is necessary to create conditions in which the side reaction (3) does not occur, or to consider a system in which there is no problem even if it occurs. Therefore, as a specific method for preventing electrolytic corrosion, a method of maintaining the potential of the electrolytic bath at an appropriate value can be considered.

There are three relative levels of potential in an electrolytic bath as shown below, so it is possible to select an appropriate value from these levels, but since side reactions between cations and anions occur as mentioned above, the following The reason is thought to be determined by the radiation potential difference, so it is possible to prevent either reaction (3) or (4) or reduce the amount of reaction by determining the relative potential of the electrolytic bath. However, since the potential is a relative value and changes depending on the insulation state, relatively controlling the potential of the electrolytic bath involves economic loss.

After considering these points, we developed a method based on electrode shape and electrode arrangement as a fundamental solution to electrolytic corrosion.

This method solves the problem by simply changing the shape and arrangement of the electrodes, without having to control the potential of the electrolytic bath. The first and second claims are solutions based on this electrode shape and arrangement, and the first method is a method for preventing tortuosity caused by cations among the troubles of the electrolytic corrosion mechanism described above,
The second method is to prevent torpor caused by anions.

Electrolytic corrosion caused by cations or anions accompanying electrolytic reactions can be solved by this method. However, the above method cannot simultaneously solve problems caused by both cations and anions.

In various electrolytic reactions, both cation and anion reactions are not necessarily the cause of trouble, and it may be economically sufficient to solve the problem of one of these reactions, so the above-mentioned The solution can be quite effective in this sense.

Furthermore, when Nd--Fe alloys are produced by molten salt electrolysis, troubles caused by cations (Nd ions) are significant, as will be described later, so by adopting the first method, it can be greatly improved.

(Function) When producing Nd-Fe by molten salt electrolysis, it is necessary to use the electrode facing the electrolytic bath as the cathode in order to prevent the reaction caused by cations (Nd3+), which is the biggest cause of electrolytic corrosion in the electrolytic bath. And it is sufficient. Further, in order to prevent electrolytic corrosion of the electrolytic bath due to anions (F-), the electrode facing the electrolytic bath may be an anode opposite to that in the above example. The expected effects of the arrangement of the electrodes are as described above, and although this method can prevent side reactions of either anions or cations, the arrangement of the electrodes in the method tube 1 of the present invention, in which one tube is surrounded by a cathode, is This is undesirable (see Japanese Patent Application No. 62-220893).

That is, according to the electrode arrangement in which only the cathode faces the electrolytic bath, it is possible to produce high-purity metal without damaging the electrolytic bath material, but the anode area cannot be increased, which reduces production efficiency. It turns out. Therefore, in order to increase production efficiency, it is necessary to increase the anode area.
In order to resolve the conflicting conditions of a part of the anode facing the electrolytic bath and reducing the purity of the metal, we investigated various ways to prevent damage to the electrolytic bath while increasing the anode area. The third, fourth, and fifth methods of the invention have been discovered.

As mentioned above, the leaked cations and anions react with the electrolytic bath, damaging the electrolytic bath and deteriorating the metal purity in the product. As a method, a conductive shield is placed in front of the electrolytic bath to cause the leaked cations and anions to actively react, and side reactions of both anions and cations cannot be prevented at the same time.

However, in actual operation, a considerable effect can be achieved by preventing only the reaction caused by one of the two ions (i.e., the cation).

In other words, the amount of loss due to electrolytic corrosion in various electrolysis is different depending on reaction (3) and reaction (4), and only one of them may be a problem, so the arrangement should be appropriate for that electrolysis. By doing so, the problem can be solved.

That is, in the case of Nd-Fe electrolysis, the electrolytic bath and Nd3
The reaction with + ions has a greater negative effect than the reaction between the electrolytic bath and F ions, such as deteriorating the metal purity and damaging the electrolytic bath material. This problem can be almost solved by arranging the electrodes to prevent direct contact with the electrolytic bath.

However, the production amount is mainly determined by the anode current density, and the production amount will be larger if the anode area is larger than the cathode area.
From this point on, all you have to do is rotate around the anode.

We thought that the problem could be solved by selecting a material for the conductive shield that would not deteriorate the quality of the metal in the product even if it reacted with the ions.

This concept will be applied and explained to Nd-Fe molten salt electrolysis.

To simplify the explanation, it is assumed that the potential of this conductive shield is the same as that of the electrolytic bath.

Reaction in electrolytic bath 3 due to Ndj+ ions (see Figure 2)
is much smaller than the amount of reaction between the anode 1 and the cathode 2, so a conductive shield is placed between the anode 1 and the electrolytic bath 3 facing it, as shown in FIG. attachment,
The reaction between the Nd'+ ions and the electrolytic bath is carried out using this shield (hereinafter referred to as a dummy electrode), and the material of the dummy electrode is selected so that the reaction product does not become an impurity in the target metal (for example, Nd-Fe). Make it the same as the target metal component (
For example, a method was considered to protect the electrolytic bath by making the dummy electrodes made of Fe.

In this case, since stainless steel does not have any corrosion resistance, the Fe dummy electrode melts considerably during electrolysis and is incorporated into the Nd-Fe alloy.
Since it is the same as , there is no problem of a decrease in purity due to this.

Since the purpose of the dummy electrode is to shield between the anode and the electrolytic bath, it is naturally desirable that the dummy electrode has a larger area than the anode.

In this way, by placing the dummy electrode between the anode and the electrolytic bath facing the anode, the trouble caused by the side reaction (3) occurring between the anode and the electrolytic bath, that is, the trouble caused by cations (Nd ions) is solved. This method is the third aspect of the present invention.

Similarly, troubles caused by reactions occurring between anions (F-) and the electrolytic bath, that is, side reactions occurring between the cathode and the electrolytic bath (4), can be avoided by placing a dummy electrode between the cathode and the electrolytic bath facing it.
The problem can be solved for the same reason by arranging it as shown in Figure 0, and this method is the fourth aspect of the present invention.

In this sense, the third and fourth aspects of the present invention, which deal with troubles (side reaction 3) caused by cations (Nd ions), can be very effective.

In addition, when producing Nd-Fe alloys by molten salt electrolysis, side reactions (3
) is a major problem, so it can be greatly improved by adopting the third invention.

However, since the problem of side reaction (4) caused by anions cannot be completely eliminated, adopting the fifth invention provides a more complete solution to the problem.

In other words, when the NdFe alloy that is particularly taken up in this invention is produced by molten salt electrolysis, 1) there are no restrictions on electrode shape and arrangement, 2) side reactions due to cations (3) and side reactions due to anions (4). ). 3) The problem can be solved by simply installing a conductive shield (in this case, an iron plate), which is cheap and simple. For the above reasons, the fifth invention is the most suitable.
This is to prevent troubles caused by F ions (side reaction 4), so in order to simultaneously solve both troubles caused by cations (side reaction 3) and troubles caused by anions (side reaction 4), it is necessary to If a conductive shield is placed in the facing electrolytic bath as shown in FIG. 13, both problems can be solved at the same time, and this method is the fifth aspect of the present invention.

In other words, the third, fourth, and fifth aspects of the present invention are simple methods of arranging conductive shields without restrictions on the shape and arrangement of electrodes, and the third aspect of the present invention solves side reaction 3 caused by cations. The fourth invention solves side reaction 4 due to anions, and the fifth invention solves side reaction 3 due to cations.
and side reaction 4 due to anions are solved at the same time.

In various electrolytic reactions, the main cause of trouble is not necessarily both trouble caused by cations (side reaction 3) and trouble caused by anions (side reaction 4), so if one of these troubles is solved, It is often economically sufficient and can be said to be the third or fourth category.

The operation of the dummy electrode in the case where iron is used as the dummy electrode when producing a Nd-Fe alloy using the L i F N d F 3 system will be described in detail below.

First, the main reaction between the anode and the cathode is as described above, and the main reaction in which N d F 3 undergoes electrolysis and reacts with the graphite anode is C+nl" -+ CFn+nC-...fl) The reaction with the iron cathode is Fe+Nd''+3e-+Nd-Fe alloy... (2) Second, the reaction between the anode and cathode and the iron dummy electrode to prevent galvanic corrosion is caused by the potential between the anode, cathode, and dummy electrode. The following three cases are possible.

When both the anode and the cathode are shielded by dummy electrodes, the reactions between the anode and the dummy electrode and between the cathode and the dummy electrode, which cause electrolytic corrosion in the electrolytic cell, will be explained in an easy-to-understand manner, as in the previous explanation. The potential difference between the anode and cathode is 7V, and the potential with respect to ground is +5V for the anode and 12V for the cathode.
Since the potential of the electrolytic bath is not grounded, it is between +5V and -2V, so it is assumed that it is +IV.

In this case, due to the way the potential of the dummy electrode is set, Nd ions and F leaked between the anode and the dummy electrode and between the cathode and the dummy electrode.
The behavior of ions is different, and the following three types can be considered depending on how the potential of the dummy electrode is set. Among the reactions between the anode and the dummy electrode and the dummy electrode of the cathode in this case, the reactions that cause electrolytic corrosion of the electrolytic bath are considered to be summarized as follows.

1) When the potential of the dummy electrode is higher than that of the anode, anion (F
-) reacts with the dummy electrode, the side reaction (4) occurs,
Damage to the dummy electrode occurs, but the electrolytic bath is F with the dummy electrode.
-Protected against ions so no galvanic corrosion problems occur. There is no problem because Nd3+ ions do not react with the dummy electrode.

2) There is no problem if the potential of the dummy electrode is set to be between the anode and the cathode, and the dummy electrode is consumed by the amount of reaction, but the electrolytic bath is protected from Nd'+ ions by the dummy electrode. so no problem will occur.

There is no problem since F- ions do not react with the dummy electrode.

For the above reasons, the problem of purity deterioration due to electrolytic corrosion can also be solved by installing a dummy electrode. Since the dummy electrode becomes a consumable electrode, it is necessary to replace it with a new dummy electrode when it is severely damaged, that is, before the electrolytic bath is subject to electrolytic corrosion. However, the degree of damage to the dummy electrode is not small because the damage to the dummy electrode is not caused by the main electrolytic reaction but by leaked ions. Therefore, it is generally sufficient to replace the battery once every few months.

It is also possible to create an electrolytic bath using iron material without using iron dummy electrodes, but in this case, the following problems occur.

1) Iron has no product purity problems due to reaction with Nd3+ ions, and has some degree of corrosion resistance against the molten salt mentioned above, but if the potential of the dummy electrode is not intentionally set in the gasification atmosphere above the molten salt, In this case, the potential of the dummy electrode is between the anode potential and the cathode potential. In this state, side reactions (
3) and (4), the cation (Nd3+
) and the anion (F~) react with the dummy electrode. The dummy electrode is damaged by the reaction between the anion (F-) and the dummy electrode (4), and the reaction between the cation (Nd3+) and the dummy electrode (3) produces an Nd-Fe alloy, which is obtained by electrolysis. Incorporated into the Nd-Fe alloy. However, the alloy produced by the reaction with the dummy electrode is
- Since it is the same as the Fe alloy, there is no problem of purity deterioration.

Therefore, since both anions and cations react with the dummy electrode, the electrolytic bath is protected and the problem of damage to the electrolytic bath does not occur.

3) When the potential of the dummy electrode is set lower than the cathode potential, the reaction (3) in which cations (Nd3+) react with the dummy electrode occurs, and an Nd-Fe alloy is produced.

However, the produced Nd-Fe alloy is the same as the product and corrodes severely. This corrosion is severe, making iron unsuitable as a material for electrolytic baths that must withstand long-term use.

From the above, it can be seen that the installation of the dummy electrode according to the present invention is highly effective in performing smooth electrolysis operations while preventing deterioration of the purity of Nd etc. and damage to the electrolytic bath.

The main movement of ions due to electrolysis occurs between the anode and the cathode, and the main reaction between the anode and the cathode occurs. Some other ions leak outside of the electrolytic bath between the two electrodes and react between the electrolytic bath and the anode or cathode, causing electrolytic corrosion, damaging the electrolytic bath material and deteriorating the purity of the manufactured alloy. The basic idea behind the electrolytic corrosion prevention method using dummy electrodes is to shield the electrolytic bath from leaked ions by placing a shield (dummy electrode) that undergoes a reaction by leaked ions into the ion leakage area and causing a reaction. It prevents erosion.

As mentioned above, the potential of the dummy electrode can be set in three ways, but the purpose can be achieved with either method.If the dummy electrode is set without insulation from the electrolytic bath, it will have the same potential as the electrolytic bath, so this method is generally used. This is actually the simplest and most practical method.

The dummy electrode must be installed between the electrode and the electrolytic bath, but if only cation damage is a problem, it is sufficient to install it only between the anode and the electrolytic bath as described in the third aspect of the present invention. If only damage to anions is a problem, it is sufficient to install it only between the cathode and the electrolytic bath as described in Section 4 of the present invention, and if damage to both cations is a problem, Section 5 of the present invention is sufficient. As described in , it may be installed both between the cathode and the electrolytic bath and between the anode and the electrolytic bath, or it may be installed over the entire circumference of the electrolytic bath.

The method for preventing galvanic corrosion using dummy electrodes according to Sections 3, 4, and 5 of the present invention, particularly the invention according to Section 5 of the present invention, has the following advantages: 1) There are no restrictions on electrode shape and arrangement, and the electrolytic system can be freely designed. 2) Cation The present invention is an effective method that can be generally applied to those involving electrolytic reactions, considering that it is a fast corrosion reaction that can solve both the problems of side reactions (3) and anions (4) at the same time. I can say that.

(Example) FIGS. 1(a) and 1(b) show an apparatus according to an embodiment of the present invention.

Austenitic stainless steel (SUS-310S
Molten salt 4 (composition LiF5Qwj%-N d F 350
wt%) were placed. A metal crucible 9 made of 5US-31O8 and lined with Ta on the inside was set below the electrolytic bath 3 so as to receive droplets 10 of the NdFe alloy produced at the anode 2.

This includes graphite anode 1 and iron negative f! When electrolyzed with 2, the electrolytically generated Nd reacts with Fe at the cathode to form Nd-
The droplets 10 of the Fe alloy accumulate in the metal receiver from below the crucible 9 and become the Nd-Fe alloy 5. This Nd-Fe alloy 5 is collected using a vacuum suction device 7. 3) A conductive shield (iron plate in the case of Nd-Fe production), which is an inexpensive material and has a simple shape, can be installed inside the electrolytic bath to improve product purity. It is highly practical and economical as it can prevent damage to the product.

Although the present invention has been explained using a method for producing Nd-Fe by molten salt electrolysis as an example, it is obvious from the description that it can be applied to molten salt electrolysis in general, and metals and non-metals can be produced by electrolysis including aqueous solution electrolysis. It can also be applied to general methods of manufacturing metals.

In the case of molten salt electrolysis of Nd-Fe, troubles caused by turbulent cations were the main cause of trouble, but in general, in the electrolysis of halogen compounds, the corrosion caused by generated anions, that is, halogens, is often large, so the present invention solves this problem. It is also effective in prevention. Corrosion caused by chemical reactions increases the reaction rate as the reaction temperature increases, and is often a problem at high temperatures. However, the electrolytic corrosion discussed in this invention is a reaction by ions, and this reaction occurs even at relatively low temperatures. In addition, NdF3 equivalent to 100% of the molten salt 2 is supplied from the raw material supply device 8.
supply to.

In this experiment, electrolysis was carried out for 7 hours in an oxidizing atmosphere, with the bath surface of the molten salt 4 exposed to the atmosphere, and the temperature of the molten salt reached 880°C. In some examples, a dummy electrode 11 made of electrolytic pure iron to prevent electrolytic corrosion was installed concentrically between the electrolytic bath 3 and the electrode 1.2.

Table 1 shows the conditions and results of electrolysis using each method in the examples.
They are summarized in a list.

The results were analyzed using the following method.

1. Impurities in the produced alloy φ Analysis of the produced alloy 2. Damage to the electrolytic bath / Structure observation using EPMA etc. 5US-31O8 has magnetism, but it loses its magnetism when attacked by Nd. Magnetic Investigation of Materials Using the equipment shown in Figures 1 (a) and (b), experiments related to electrode shape and electrode arrangement as well as experiments related to dummy electrodes were conducted.The purpose of this experiment was to investigate the electrode shape and arrangement. The objective is to investigate the relationship between changes in the purity of the produced Nd-Fe alloy due to the shape and arrangement of the dummy electrode and damage to the electrolytic bath.
In the following explanation, the metal receiver is crucible 9, vacuum suction device 7,
The raw material supply device 8 will be described with reference to figures whose illustrations are omitted.

(Conventional example) As shown in Fig. 2 (a, b), plate-shaped electrodes (1, 2)
were placed one by one and electrolyzed under the conditions of Example 1 in Table 1. As a result, Ni and Cr in the electrolytically generated Nd-Fe were 2000p.
It reached pm. As a result of investigating the material of the electrolytic bath, only the material on the anode side was selectively damaged, and 5NS-31O8
It was found that Nd, which was not present in the raw material, was incorporated into 5US-310S, and on the other hand, the content of Ni and Cr in 5O3-310S was reduced compared to the content in the raw material.

In the electrolytic bath 3 on the cathode (2) side, the same phenomenon as on the anode (1) side was not observed. However, in experiments using F and reaction electrodes, anodes 1 are placed on both sides as shown in Figure 6, and N
Severe damage (3') due to d ions occurs in the electrolytic bath 3 facing the anode, while in the opposite arrangement, slight damage occurs in the part 3' facing the anode, as shown in Figure 7. I only received it. The purity of Ni and Cr in the metal reaches 1500 to 4500 ppm in the electrode arrangement shown in Figure 6, while it reaches 300 to 500 ppm in the arrangement shown in Figure 7.
It stayed in.

Reference Example 3 and Example 3 As shown in FIGS. 8 and 9, experiments were conducted using an electrode arrangement in which a cylindrical electrode was surrounded by four plate electrodes.

The electrode arrangement shown in Figure 8, with the cathode in the center and surrounded by four anodes 1 (
In Reference Example 3), the material of the electrolytic bath 3 around the entire circumference was damaged by Nd ions, and the amount of NiCr in the metal was 2500 to 4000 ppm as shown in Table 1, whereas the anode 1 In the electrode arrangement shown in FIG. 9 (Example 3) in which the electrode is surrounded by four cathodes 2 around the electrode, slight damage was observed in the electrolytic bath on the cathode side, which was thought to be caused by Nd ions.

Reference Example 1 and Example 1 Figure 4 (Reference Example 1) in which the experiment was conducted with a cylindrical cathode in the center and the cylindrical anode 1 arranged around it; Figure 5 (Example 1) in which the arrangement of utility poles was reversed. Experiments were conducted by changing the shape and arrangement of the cathode and anode on the two sides. A typical example of this is shown in the fourth section.
The results are shown in Examples 2 and 3 of Table 1.

In the arrangement shown in FIG. 4, in which the anode 1 is cylindrical and the cathode 2 is placed in the center, the electrolytic bath 3 facing the anode 1 has an N
Damaged by d ions (3°). As a result, Ni and C1- in the metal were also 1500 to 40 as shown in Table 1.
It reached 00ppm. On the other hand, in the arrangement shown in Figure 5, which is the opposite electrode arrangement to that shown in Figure 4, there was no damage to the electrolytic bath due to Nd ions, and the Ni and Cr content in the metal was less than 150 ppm, as shown in Table 1. .

Reference Example 2 and Example 2 There was no damage to the three plate-shaped molds as shown in FIGS. 6 and 7, and the amounts of Ni and Cr in the metal were 150 ppm.

From the above reference examples and examples, when the electrode arrangement is such that the electrode facing the electrolytic bath is used as the anode, the damage to the electrode bath is large and the amount of Ni and Cr in the metal is large, and when the electrode arrangement is reversed, the amount of Ni and Cr in the metal is large. It can be seen that the reason why the amount of Cr is small is that the damage caused by Nd ions is much greater than the damage caused by F ions.

The average current in the arrangement in which the electrode facing the electrolytic bath is the cathode is lower than that in the reference example, and this electrode arrangement is not preferable from the point of view of improving production efficiency.

However, it will be appreciated that this method is a highly effective method of producing high purity metal.

Next, we conducted an experiment in which dummy electrodes were installed.

In Figures 10 to 13, plate-shaped (Figure 10.11), curved (Figure 12) and cylindrical (Figure 13) iron dummy electrodes are shown between the electrode 4 or 2 and the electrolytic bath 3. 11 were placed.

Reference Example 4 and Example 4 In FIG. 10 (Reference Example 4), plate-shaped electrodes were used for both the anode and the anode, and a plate-shaped dummy electrode 11 was placed on the cathode side.
FIG. 11 (Embodiment 4) shows the arrangement on the anode side. In FIG. 10, the electrolytic bath 3 on the anode side has been damaged by Nd ions, and the Ni and Cr in the metal have reached 2000 to 5000 ppm as shown in Example 8 of Table 1. but,
The slight damage to the electrolytic bath 3, which was thought to be caused by the reaction with F ions on the cathode side described in Example 1, was not observed at all because the dummy electrode 11i11 was placed on the cathode side.

On the other hand, a dummy electrode 11 is placed on the anode side shown in FIG.
In the example in which Nd ions were arranged, no damage due to Nd ions was observed, and the amount of Ni and Cr in the metal remained at 200 to 300 ppm.

Example 5 As shown in FIG. 12, an electrode arrangement in which two plate-shaped anodes 2 were arranged around one plate-shaped cathode 1 was adopted, and the electrode arrangement was the same as that in FIG. 5. Two half-white dummy electrodes 1 on the anode side
1 was placed to prevent corrosion caused by Nd ions. In the example shown in Fig. 12 in which a simple cylindrical dummy electrode is arranged, the non-electrolytic bath is not damaged by Nd ions, and the Ni
.

Although the amount of Cr was also reduced to 150 to 200 ppm, some electrolytic corrosion due to F ions was observed in the areas without the dummy electrode.

Example 6 As shown in FIG. 13, an electrode arrangement in which two plate anodes 1 are arranged around one plate cathode 2, and these electrodes 1.2 are entirely surrounded by a cylindrical dummy electrode 11. The aim was to prevent corrosion of both F ions and Nd ions.

With the electrode arrangement shown in Fig. 13, no damage to the electrolytic bath of Nd ions and F ions was observed, and the amount of Ni and Cr was 50 to 1100.
The best value is less than pp. Moreover, the average current also shows a high value.

As described above, by arranging the dummy electrodes, the production amount of metal can be increased, damage to the electrolytic bath can be prevented, and high purity metal can be manufactured.

(Effects of the Invention) As detailed above, according to the present invention, in an apparatus for manufacturing metal by molten salt electrolysis, 1) shape and arrangement of electrodes 2) by not using dummy electrodes. The following excellent effects can be obtained.

1. High purity metal can be produced.

2. Since damage to the electrolytic bath can be prevented, products with high purity can be manufactured at low cost.

3. By installing dummy electrodes, you can freely arrange the electrodes.
In addition, high-purity metal can be manufactured with high efficiency.

[Brief explanation of the drawing]

Figures 1 <a) and (b) are diagrams of the electrolysis installation used in the experiment; Figures 2 (a), (b) and Figure 3 (a> (b) are illustrations of the conventional electrolysis method; Figure 4) Figures (a), (b) to Figure 9 (a>(b) are explanatory diagrams of anode and cathode arrangement, Figures 10 (a>, (b) to Figures 13 (a) and (b) are anodes, It is an explanatory diagram of the cathode and dummy electrode arrangement. In each figure, (a) is the plane side, and (b) is the plan view (a).
FIG. 2 is a sectional view taken along the center line (horizontal line on the paper).

Claims (1)

[Claims] 1. In a method for manufacturing metals or alloys by electrolysis by arranging an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath is composed only of the cathode. A method for producing a high purity metal or alloy, characterized in that the main electrolytic reaction is carried out between the back surface of the cathode and the anode. 2. In a method of manufacturing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath consists only of the anode, and the surface of the anode and the cathode are A method for producing a high-purity metal or alloy, characterized by carrying out a main electrolytic reaction between the two. 3. In a method of manufacturing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath is composed of the anode and the cathode, and the back side of the anode A high-purity metal or alloy having an electrode shape and arrangement that allows the main electrolytic reaction to occur between the back surface of the anode and the cathode, and a conductive shield placed between the anode and the electrolytic cell to perform electrolysis. manufacturing method. 4. In a method of manufacturing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath is composed of an anode and a cathode, and the back surface of the anode and Production of a high-purity metal or alloy, which has an electrode shape and arrangement that allows the main electrolytic reaction to occur on the back surface of the cathode, and in which electrolysis is performed by disposing a conductive shield between the cathode and the electrolytic cell. Method. 5. In a method of manufacturing metals or alloys by electrolysis by placing an anode and a cathode in an electrolytic bath, the main electrode surface facing the electrolytic bath is composed of an anode and a cathode, and the back surface of the anode and Electrolysis is carried out in an electrolytic bath having a shape and arrangement of electrodes that allow the main electrolytic reaction to occur on the back surface of the cathode, and in which a conductive shield is arranged between each of the anodes, each cathode, and the electrolytic bath. A method for producing high-purity metals or alloys. 6. The method for producing a high purity metal or alloy according to any one of claims 1 to 5, wherein the electrolytic bath is a molten salt. 7. The method for producing a high purity metal or alloy according to any one of claims 1 to 5, wherein the electrolytic bath is an aqueous solution.