JP2002194581A - Method for recovering platinum group metal from metal electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering platinum group metals from a waste electrode, which peels a coating layer including platinum-group metal oxide from a spent insoluble metal electrode by a simple technique, and can separately recover the platinum group metals of high purity, which is obtained by eliminating most of impurities from the peeled coating layer, effectively and in satisfactory yield. SOLUTION: This method for recovering the platinum group metals from the spent insoluble metal electrode with the coating layer including the platinum- group metal oxide, comprises peeling the coating layer from an electrode base material physically and/or chemically, reducing platinum-group metal components into metal by heating the peeled coating substance in a reducing atmosphere, then mixing it with an alkali halide powder, making it react with chlorine gas, eliminating the impurities by filtration after dissolving it in the water, and eliminating existing cations by electrodialysis to recover the platinum group metals of high purity in a satisfactory yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a platinum group metal from a metal electrode, and more particularly to a method for recovering a platinum group metal oxide which has been used in industrial electrolysis and mainly used as an electrode material. The present invention relates to a method for recovering a platinum group metal from an insoluble waste electrode provided on an electrode substrate.

[0002]

2. Description of the Related Art A so-called dimensionally stable anode (DSA) and a dimensionally stable electrode (DSE) in which a coating layer of an electrode material containing a platinum group metal oxide such as iridium or ruthenium is provided on a titanium electrode substrate. The so-called insoluble metal electrodes are used in large quantities in various electrochemical fields, such as diaphragm electrolysis. Such a metal electrode is a ceramic whose surface coating layer is stable, but has a certain chemical bond with the titanium electrode base material, and is extremely stable physically and chemically. It is known that in this way,
Even if it is extremely stable as a metal electrode, it will gradually wear out due to corrosion etc. over a long period of use, and it will not be possible to maintain a certain level of performance with a certain amount of surface coating layer left, making it unusable, and eventually being disposed of Will be done.

[0003]

As described above, it is quite difficult to peel and recover a metal or a coating layer from a metal electrode made of, for example, titanium, which is extremely physically and chemically stable. At present, there is no such method. That is, since the platinum group metal oxide is much more stable than the platinum group metal from a chemical point of view, only some special treatment methods such as alkali melting can be used. Since the platinum group metal oxide electrochemically protects the surface of the electrode substrate, it is extremely difficult to separate the coating layer from the electrode substrate.

[0004] The inventors of the present invention have developed a coating layer containing a platinum group metal oxide on the surface while protecting a titanium electrode substrate by utilizing the fact that the platinum group metal oxide is dissolved in an alkali molten salt. A high-concentration aqueous alkali solution is applied to the surface of the electrode substrate so as to dissolve it, and is heated in a furnace to evaporate the water and to make the alkali substantially in a molten state, thereby forming the coating layer in the alkali. Has been developed for practical use, which is to dissolve in water. However, this method has problems in that it is practically difficult to recover expensive platinum group metals and that large processing equipment is required. Although no problem arises when the electrode substrate is used as it is, it is practically almost impossible to recover both the electrode substrate and the coating layer containing the platinum group metal oxide.

In order to peel off the coating layer, a method has been proposed in which the surface of the electrode substrate is dissolved with a corrosive acid to peel off the coating layer from the electrode substrate (for example, JP-A-59-12).
No. 3730). However, although this method is theoretically possible, the actual problem is that the oxide layer interposed between the titanium electrode substrate and the coating layer is so strong that the coating layer does not peel off as desired. At the same time, there remains a problem that the amount of acid used is extremely large and uneconomical. Also, the recovery rate of the titanium electrode substrate is poor. Also, in the acid containing the dissolved titanium electrode base material, the coating sludge of the platinum group metal oxide is contained, but the concentration of the noble metal oxide becomes relatively small. Therefore, there was a problem that this collection would be difficult. Also, since the platinum group metal or its oxide is extremely noble electrochemically, even if it is immersed in hydrochloric acid or sulfuric acid which is corrosive to the titanium electrode base material, the platinum group metal is electrochemically protected from corrosion. There is also the problem that the action prevents the dissolution of titanium and makes the coating layer difficult to peel off.

Usually, during electrolysis, the impurity metal is chemically or anodically attached to the electrode surface in the form of oxide or lead sulfate, so that it is difficult to remove and separate the electrode. There is a problem that the mixing is inevitable. In addition, although separation and removal are possible chemically, they also have the problem that the process is complicated and that the recovery yield of platinum group metals becomes extremely poor due to repetition. It has been desired to improve the recovery method with a good yield.

The present invention has been made in view of such circumstances, and a purpose thereof is to recover a platinum group metal from a used insoluble metal electrode having a coating layer containing a platinum group metal oxide. In doing so, after removing the coating layer from the insoluble metal electrode by a simple method, the platinum from the waste electrode which can efficiently and efficiently recover and separate the high-purity platinum group metal from which the impurities have been almost removed from the peeled coating is obtained. An object of the present invention is to provide a method for recovering a group metal.

[0008]

To achieve the object, the present invention provides a method for recovering a platinum group metal from a spent insoluble metal electrode having a coating layer containing a platinum group metal oxide. The coating layer is peeled off from the titanium or titanium alloy or other noble metal electrode base material, and the peeled coating is heated in a reducing atmosphere to reduce the platinum group metal component to metal, and then mixed with an alkali halide. Then, after reacting with chlorine gas and dissolving in water, the insolubles are removed by filtration, and then the existing cations are separated and removed electrolytically to recover the platinum group metal as chloride. It is. Further, after the coating is peeled off from the electrode substrate, it is preferable to perform pickling in order to remove easily soluble substances from the coating. The acid treatment conditions in this case are not particularly limited, but for example, 20% boiling hydrochloric acid or 40% or more to remove electrode base materials such as titanium and surface deposits mixed in the coating sludge. It is desirable to treat with sulfuric acid at a temperature of 85 ° C or higher.

In the present invention, the platinum group metal is iridium and / or ruthenium, and coexists as a composite oxide with another metal oxide in the coating layer.

In the present invention, the coating layer is peeled off from the electrode substrate physically and / or chemically. There are various methods as the physical peeling, for example, a method of breaking the bonding state between the electrode base material and the coating layer by rolling the metal electrode itself by previously scratching or rolling the coating layer, or the like. Can be Examples of the chemical peeling include a method of corroding a coating interface of an electrode substrate with an acid.

In the present invention, the cations are separated and removed by removing heavy metals by electrodialysis after removing alkali metals by salting out.

In the present invention, the reducing atmosphere is a hydrogen gas atmosphere, and the heating temperature at this time is not particularly limited, but is preferably in the range of 500 to 1000 ° C. at which the platinum group metal is reduced. Desirably, it is in the range of 600 to 900 ° C. Also, the processing time at this time is not particularly limited, but is preferably about 1 to 10 hours, particularly 2 to 5 hours.
It is good to be about time. Thereby, the platinum group metal that is easily reduced is reduced to a metal, and valve metals such as titanium and tantalum are present as oxides without being reduced.

Further, in the present invention, the alkali halide is salt, and a hydrogen reduced product reduced to a metal is mixed with the salt, and the chlorine gas is reacted at a heating temperature of 500 to 800 ° C. . A particularly desirable heating temperature at this time is in the range of 550 to 750 ° C., depending on the platinum group metal to be recovered.

In the present invention, the water is diluted hydrochloric acid,
This is to dissolve in this diluted hydrochloric acid aqueous solution. Examples of the water include warm water in addition to dilute hydrochloric acid.

In the present invention, the cation exchange membrane is used as a separation membrane to perform electrolysis while supplying a solution to the anode chamber.
That is, the impurity metal is moved to the cathode compartment and separated by electrodialysis.

According to the above technical means of the present invention, when recovering a platinum group metal from a used insoluble metal electrode having a coating layer containing a platinum group metal oxide, Is physically and / or physically separated from the electrode substrate.
Alternatively, after the chemical release, the release coating is heat-treated in a reducing atmosphere. For example, 500-1 in a hydrogen gas atmosphere
Heat treatment at 000 ° C. Thereby, valve metals and other metals, such as titanium and tantalum, which are difficult to reduce remain as oxides, and the platinum group metals, some impurities, and some additives are reduced to metals. Next, this reduced product is mixed with an alkali halide powder such as salt, and is converted into a water-soluble chloride acid or a chloride salt through chlorine gas at 500 to 800 ° C. and dissolved in water such as dilute hydrochloric acid water. Insolubles such as titanium oxide and tantalum oxide are removed by filtration. Next, high purity platinum group metals are recovered as chlorides by electrically separating and removing cations such as other impurity metals present by electrodialysis. At this time, the separation and removal of cations may be performed directly by electrodialysis.However, a large amount of alkali metal salt is separated and removed by separate salting out, and then heavy metals and other metals are electrodialyzed. It can also be separated and removed.

[0017]

Embodiments of the present invention will be described. As the metal electrode, for example, on the surface of a commonly used titanium or titanium alloy electrode substrate, a coating layer of an electrode material containing a platinum group metal oxide or a complex oxide composed of a platinum group metal and another metal. For example, it is an insoluble metal electrode for industrial electrolysis that is incorporated and used in, for example, a provided electrolytic copper foil manufacturing apparatus, a diaphragm electrolysis apparatus using a diaphragm method, or a chloralkali electrolysis apparatus using an ion exchange membrane method. In special cases, the electrode substrate may be nickel or stainless steel, and the electrode in this case is used as a cathode.

In recovering the platinum group metal from the used insoluble metal electrode used in the present invention, first, a platinum group metal oxide or a composite oxide composed of a platinum group metal and another metal is used as the electrode. It is collected by peeling from the substrate, but this peeling is not particularly limited. For example, after applying a physical pretreatment such as pre-scratching the coating layer or rolling the metal electrode itself by rolling or the like to break the bonding state between the electrode substrate and the coating layer, coating the electrode substrate The coating layer is separated from the electrode substrate by performing a chemical post-treatment such as corrosion of the interface with an acid. At this time, of course, the coating layer may be mechanically peeled off, but it is expected that the platinum group metal oxide remaining on the surface of the electrode substrate will be considerably large by mechanical peeling. It is desirable to completely remove and collect by combining with acid pickling.

Next, the coated sludge (solid sludge) thus peeled is subjected to an acid treatment as it is or to remove a substance which is easily dissolved by an acid. The conditions of this acid treatment are not particularly limited, but for example, 20% boiling hydrochloric acid or 40% or more for removing electrode base materials such as titanium and surface deposits mixed in the coating sludge. Temperature 85
Desirably, the treatment is performed with sulfuric acid at a temperature of not less than ° C. By such treatment, metal components other than the oxides except for the platinum group metal can be dissolved and removed almost completely.

In this way, sludge of the electrode material mainly composed of oxide is obtained. Analysis of this sludge component revealed that it mainly consisted of valve metal oxides such as titanium and tantalum, and platinum group metals and their oxides. It was also found that some metal components or impurity components remained in addition to this.

Next, a treatment for reducing the metal by heating the sludge in a reducing atmosphere such as a hydrogen gas atmosphere is performed.
The reducing atmosphere is not particularly limited. For example, there is a reducing gas atmosphere such as an ammonia gas or a methane gas, but a hydrogen gas atmosphere having the strongest reducibility and having little possibility of contamination is most preferable. or,
The hydrogen gas atmosphere may be a hydrogen gas atmosphere at approximately atmospheric pressure, and the metal oxide is reduced to metal by heating while flowing hydrogen gas. The heating temperature in this hydrogen gas atmosphere is 500 to 1 in which only the platinum group metal is selectively and preferentially reduced.
It is desirable to set the temperature in the range of 000 ° C. The reason is 5
If the temperature is lower than 00 ° C., the reduction of the platinum group metal oxide tends to be insufficient. If the temperature exceeds 1000 ° C., the equipment such as a furnace used for heating becomes large-scale, and the processing cost increases. Another reason is that when a metal other than the platinum group metal is reduced, it becomes a chloride in a later chlorination process, becomes water-soluble and may cause impurities, so that only the platinum group metal is selectively and preferentially used. The heating temperature is 500 ~ 100
This is because the range is 0 ° C.

Therefore, according to the present invention, in a hydrogen gas atmosphere,
~ 1000 ° C is desirable, particularly preferably 600-900 ° C
In particular, at 800 ° C. or higher, an effect of evaporating and removing at least a part of arsenic and antimony which may be contained as impurities can be obtained. The processing time in the range of 500 to 1000 ° C. in the hydrogen gas atmosphere is not particularly limited, but about 1 to 10 hours is sufficient, and about 2 to 5 hours is sufficient. By performing the treatment under such reducing conditions, the platinum group metal component that is easily reduced is selectively and preferentially reduced to a metal, and valve metal oxides such as titanium and tantalum that are difficult to be reduced are not reduced. In the form of an oxide. In addition, some of the impurities volatilize and partly remain as they are, and partly reduce to metal. The reduced product in this case dissolves in hydrochloric acid.

In the present invention, the reduced product is pulverized,
After being mixed with an alkali halide powder such as salt, the mixture is heated and made into chloride by passing chlorine gas. The amount of the alkali halide at this time is not particularly limited, but is preferably, for example, about 1.2 to 1.5 times the theoretical amount of all the platinum group metals being chloride alkali salts.

The conditions for chlorination with chlorine gas are not particularly limited, but ordinary chlorination conditions may be used, and the reduced product crushed by passing chlorine gas while heating is reacted with chlorine gas. Chlorinates. In this case, the heating temperature is desirably set in the range of 500 to 800 ° C. The reason for this is that the chlorination reaction takes a long time at 500 ° C or lower, and the chlorination reaction does not proceed sufficiently, and the yield as chloride is deteriorated. This is because a substance has a high vapor pressure, and a part of the substance is volatilized, which may lower the recovery rate. By treating under such chlorination conditions, most of the platinum group metals are chlorinated to form chlorides or chloride salts. At this time, valve metal components such as titanium oxide and tantalum oxide remaining as oxides remain as they are.
In addition, some platinum group metals remain as insoluble components, which can be recovered separately or added to the next batch to recover all of the platinum group metals as chlorides.
Depending on the platinum group metal to be recovered, it is better to select a heating temperature (reaction temperature). For example, in the case of ruthenium or the like which is easily oxidized and has a high vapor pressure, a relatively low temperature of 500 to 600 ° C. is preferable. Thereby, it can be recovered at a high recovery rate.

Next, in the present invention, after the chlorination of the reduced product under such chlorination conditions, this is dissolved in water, and then the insoluble material is removed by filtration. Although the conditions at this time are not particularly limited, warm water or dilute hydrochloric acid is desirable, and the dissolution is performed by dissolving in the warm water or dilute hydrochloric acid and filtering off.

Next, the platinum group metal salt thus obtained is mainly used to separate and remove cations from a solution containing unreacted alkali halides and some impurity metal salts by electrodialysis. . The conditions of the electrodialysis at this time are not particularly limited, but the catholyte is preferably hydrochloric acid, and the solution to be treated is put on the anode side. In addition, although a cation exchange membrane is used as the ion exchange membrane, chlorine may be generated in the reaction on the anode side, and therefore it is preferable to use a perfluorosulfonic acid-based cation exchange membrane having a strong resistance to the oxidizing power. . As the anode, a normal metal electrode for generating oxygen or chlorine can be used, but it is most preferable to use a hydrogen gas diffusion electrode using hydrogen generated on the cathode side. By performing electrodialysis under such conditions, not only the generation of chlorine can be prevented, but also the cell voltage is lowered by 1 V or more. By this electrodialysis, cations such as alkali metal ions and impurities such as lead and arsenic which are present in the anode chamber move to the cathode chamber through the cation exchange membrane of the electrolytic cell. As a result, the platinum group metal, which is present as a complex ion and is an anion, remains in the anode chamber as it is and is completely separated. Also, an aqueous hydrochloric acid solution of a platinum group metal chloride remains in the anode chamber. In addition, alkali halides such as salt added in large amounts in the middle can also be separated by electrodialysis, but the alkali metal is removed in advance by salting out,
Thereafter, heavy metals can be removed by electrodialysis.
That is, the platinum group metal component is precipitated as an ammonium salt by reaction with ammonium chloride, and after separating a liquid containing an alkali metal, the platinum group metal ammonium salt, which is a precipitated oxide, is aqua regia (concentrated hydrochloric acid and concentrated nitric acid). ), And after nitric acid content is removed by volatilization, impurities are removed by electrodialysis to achieve high purity. Further, if necessary, by adjusting the hydrochloric acid concentration or the platinum group metal concentration by performing distillation under reduced pressure or the like, it can be recovered as a platinum group metal chloride aqueous solution or chloride solid. Further, if necessary, a treatment with an ion exchange resin may be added to the removal of impurities.

When two or more kinds of platinum group metal chlorides coexist, they may be separated or, depending on the use, may be recovered as they are without being separated. Of course, you can.

Next, specific embodiments 1 and 2 will be described in more detail, but it is first described that the present invention is not limited to the embodiments. Example 1 Iridium is recovered as chloride from an insoluble metal electrode having a coating layer containing a composite oxide composed of iridium and tantalum on the surface of a used titanium electrode base material used in an electrolytic copper foil manufacturing apparatus. I did it. First, in order to remove surface deposits from a metal electrode (electrode for an electrolytic copper foil), the metal electrode is immersed in a 1: 1 nitric acid solution containing hydrogen peroxide. Thus, after removing the surface deposits mainly composed of lead oxide, the coating layer was peeled off by buffing.
Then, the electrode material after the buff treatment was further subjected to an acid treatment in 20% boiling hydrochloric acid to completely remove the remaining coating material. It was confirmed that the coating treatment completely removed the coating layer from the electrode substrate by this acid treatment. This mechanical,
The oxide sludge (recovery sludge) that has been chemically stripped is 40% at 85 ° C to remove titanium metal as the electrode base material and stainless steel as the buffing substance included in the buffing process. When the treatment was performed in a sulfuric acid solution for 3 hours, it was found that the impurity metal was almost completely removed.

Next, the mixture was filtered using No. 1 filter paper manufactured by Toyo Roshi Kaisha, Ltd., and a large amount of solid sludge collected on the filter paper was washed and dried at 600 ° C. Further, the solid sludge is put in a hydrogen furnace and is heated at 800 ° C. in a hydrogen gas stream.
To perform a reduction treatment. At this time, the hydrogen pressure in the hydrogen furnace was almost atmospheric pressure. After the treatment in this manner, the state of the solid sludge was observed by X-ray diffraction. As a result, it was confirmed that iridium was reduced to metal and that tantalum oxide and titanium oxide were additionally present. Although it is a small amount,
The presence of lead and antimony was also confirmed.

Next, a hydrogen gas diffusion electrode (ELAT manufactured by E-TEK) was used as an anode for this solution, and a cation exchange membrane (Dup) was used.
ont's Nafion110), using a titanium mesh as the cathode, and a diaphragm (separation membrane)
Circulating in the anode compartment of the electrode dialysis tank using a cation exchange membrane (Nafion 315 manufactured by Dupont) as the
Electrodialysis was carried out while passing an aqueous solution of 2% hydrochloric acid. At this time,
About 50% of hydrogen in addition to the cathode-generated hydrogen was supplied from the hydrogen cylinder to the anode gas diffusion electrode. In this way the current density 10
When the treatment was performed at A / dm2 for 3 hours, the anolyte became an aqueous solution of hydrochloric acid of iridium chloride, and the content of other metals became 10 ppm or less. At this time, the current efficiency of the electrodialysis calculated from the removed metal was 34%.

Example 2 An insoluble metal electrode having a coating layer containing a composite oxide composed of iridium, ruthenium and titanium was used on an expanded titanium mesh used in ion exchange membrane type salt electrolysis. To recover ruthenium. First, peel off the coating layer from the electrode substrate.
Upon separation, the metal electrode was welded, and the metal electrode was flattened by a strong leveler treatment because the metal electrode was subjected to a large strain generated when the metal electrode was removed from the electrolytic device, and was substantially flattened. To slightly form a gap between the coating layer and the titanium metal substrate. Then, the resultant was etched by pickling with a mixed acid of hydrochloric acid and sulfuric acid to thereby peel off. At this time, a mixed acid containing 25% sulfuric acid and 20% hydrochloric acid was used as an etching solution at a temperature of 85 to 90 ° C., and the flattened metal electrode was immersed for 30 minutes. Then, the coating layer precipitated in the liquid as black sludge. At this time, it was confirmed that the coating layer was almost completely removed from the electrode substrate by etching for 30 minutes.

After the black sludge was separated by filtration and sufficiently washed with water and dried, the black sludge was placed in a hydrogen furnace and reduced as in Example 1. However, the heating temperature at this time was 600 ° C. Analysis of the black sludge by X-ray diffraction after the reduction treatment for 3 hours showed that the black sludge was composed of titanium oxide, iridium and ruthenium.

Next, the black sludge of Example 1 was used.
The mixture was mixed with sodium chloride in the same manner as described above, and chlorination was performed at 550 ° C. by passing chlorine gas. After performing this treatment for 3 hours, extraction was performed with warm water. At this time, some of the ruthenium was volatilized as ruthenium tetroxide (RuO4), so it was recovered with concentrated hydrochloric acid and added to the solution subjected to hot water extraction. The extract thus obtained was analyzed by ICP-AES. As a result, Na, CI, Ru, and Ir were detected, and no titanium coexisting substance was recognized. The amount of salt added during the chlorination was twice as large as the amount of sodium to be sodium iridate and sodium ruthenate.

An aqueous solution of ammonium chloride was added dropwise to the liquid thus obtained while stirring to cause precipitation. The dropping was stopped when the liquid became almost colorless, and the liquid was filtered using No. 5 filter paper manufactured by Toyo Roshi Kaisha, Ltd. This allows
The sodium content was completely separated. Next, this was dissolved in aqua regia, and heated while adding concentrated hydrochloric acid to completely remove nitric acid. Then, electrodialysis was performed in the same manner as in Example 1. The dialysis time at this time was 1/5 of that in Example 1. As a result, a mixed solution of pure iridic acid chloride (H2IrCl6) and ruthenic acid chloride (H2RuCl6) was obtained. At this time, since the salt was removed in advance, the time for the electrodialysis could be significantly reduced. The composition ratio of iridic acid chloride to ruthenic acid chloride was almost the same as that of the release coating peeled from the electrode substrate.

[0035]

The method for recovering a platinum group metal from a used metal electrode according to the present invention is constructed as described above, and has the following effects. . In the present invention, the coating layer containing the platinum group metal oxide is peeled from the electrode substrate, and the coating layer is heated in a reducing atmosphere to reduce the platinum group metal component to the metal, and then mixed with the alkali halide. And then react with chlorine gas, dissolve in water such as dilute hydrochloric acid, filter and remove insolubles, and then electrically separate and remove cations present by electrodialysis to recover platinum group metal chlorides. I decided to do
The platinum group metal can be easily recovered from the insoluble metal electrode as chloride or chloride acid.

[0036] In the present invention, the reduced product reduced to the metal is subjected to a treatment for chlorination with chlorine gas, and then dissolved in water such as diluted hydrochloric acid, and the post-treatment is performed in a substantially solution state. That is, after reducing the platinum group metal component to metal as described above,
Since the platinum group metal can be recovered in a form dissolved in water such as dilute hydrochloric acid water, the platinum group metal is recovered by liquid layer treatment after dissolution, and the loss of the recovery yield can be minimized. Therefore, the recovery treatment of the platinum group metal with improved yield becomes possible. In addition, since the coating layer containing the platinum group metal oxide is peeled off from the metal electrode by subjecting the insoluble metal electrode to physical and / or chemical treatment, the coating layer can be efficiently formed by a simple method. Can be peeled off.

[0037] Also, in the present invention, in a hydrogen gas atmosphere 500
By heating the exfoliated coating layer containing the platinum group metal oxide in the range of 1000 ° C., only the platinum group metal component is selectively and preferentially reduced to metal. That is, the platinum group metal component that is easy to reduce is reduced to a metal, and the electrode base material that is difficult to reduce, for example, a valve metal oxide such as titanium remains as an oxide without being reduced. This is mixed with an alkali halide as described above, further reacted with chlorine gas, dissolved in water such as dilute hydrochloric acid, and the insolubles are removed by filtration. Then, the existing cations are electrically separated by electrodialysis. By the removal, the electrode substrate which is hardly reduced can be easily separated and removed from the platinum group metal component without being eluted, and does not mix with the platinum group metal component. Therefore, it can be recovered as a high quality platinum group metal with little contamination of impurities.

[0038] In the present invention, mainly a platinum group metal salt,
Since the removal of impurities from the solution containing unreacted alkali halides and some impurity metal salts is performed by electrodialysis, pH adjustment and the like become unnecessary, and
As described above, the post-treatment can be performed in a liquid state, so that the recovery yield of the platinum group metal can be improved and secondary contamination can be prevented.

[0039] Further, in the present invention, metal oxides other than the platinum group metal present in the coating remain as oxides and do not elute, so that they can be separated and removed easily and easily. Therefore, there is no mixing with the platinum group metal recovered as chloride.

[0040] Further, in the present invention, it is mixed with an alkali halide powder such as salt and chlorinated by passing chlorine gas at 500 to 800 ° C. to make it into an aqueous solution, which is dissolved in an aqueous hydrochloric acid solution. That is, since the platinum group metal can be dissolved, it can be recovered, for example, as a mixed chloride containing iridium and ruthenium. Thereby, for example, since titanium, tantalum oxide and all other impurities can be completely separated and removed, it is possible to recover a high-purity platinum group metal with few impurities.

[0041] In addition, in the present invention, the removal of alkali metals by salting out in advance as necessary makes it possible to greatly reduce and simplify the time required for the removal of heavy metals by electrodialysis. Can be expected. Also, after the platinum group metal component is precipitated and separated as an ammonium salt by interaction with ammonium chloride,
By dissolving the platinum group metal ammonium salt in aqua regia and removing nitric acid, the electrodialysis is performed to reduce the load of the electrodialysis, remove the impurity metals, and purify the platinum group metal to be highly purified. it can.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C25B 11/08 C22B 3/00 MF Term (Reference) 4K001 AA41 BA22 CA01 CA05 DA10 DB04 DB21 DB36 4K011 AA08 AA33 AA34 BA05 BA07 CA02 DA03 DA06 4K058 AA21 BA19 BB03 BB04 CA04 CA05 CA28 CB01 CB02 CB15 DD01 DD13 DD17 DD22 DD25 EA10 EB07 EB16 ED10 FA24 FC04 FC07 FC14 FC17

Claims (8)

[Claims] In a method of recovering a platinum group metal from an insoluble metal electrode having a coating layer containing a platinum group metal oxide, the coating layer is peeled from an electrode substrate, and the peeled coating is placed in a reducing atmosphere. After heating to reduce the platinum group metal component to a metal, it is mixed with an alkali halide, reacted with chlorine gas and dissolved in water, and then filtered to remove insolubles. A method for recovering a platinum group metal from a metal electrode, wherein the platinum group metal is recovered as chloride by performing electrolytically. 2. The platinum from the metal electrode, wherein the platinum group metal according to claim 1 is iridium and / or ruthenium, and coexists in a coating layer with another metal oxide as a composite oxide. Group metal recovery method. 3. The peeling of the coating layer according to claim 1 or 2,
A method for recovering a platinum group metal from a metal electrode, which is performed physically and / or chemically. 4. The method according to claim 1, wherein the cation is separated and removed.
A method for recovering a platinum group metal from a metal electrode, which is performed by electrodialysis after removing an alkali metal by salting out. 5. The method for recovering a platinum group metal from a metal electrode according to claim 1, wherein the reducing atmosphere is a hydrogen gas atmosphere, and the heating temperature is 500 to 1000 ° C. 6. The metal electrode according to claim 1, wherein the alkali halide is salt, and the salt is mixed with a hydrogen reduced product reduced to a metal, and the mixture is reacted at 500 to 800 ° C. by passing chlorine gas. For recovering platinum group metals from coal. 7. A method for recovering a platinum group metal from a metal electrode, wherein the water according to claim 1 is a diluted hydrochloric acid solution, and the water is dissolved in the diluted hydrochloric acid solution. 8. A method according to claim 1, wherein the cation exchange membrane according to claim 1 is used as a separation membrane, electrolysis is carried out while supplying a solution to the anode chamber, and impurity metals present in the anode chamber are sent to the cathode chamber for separation. A method for recovering a platinum group metal from a metal electrode.