JP2008081837A - Recovering method of insoluble electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovering method for separating electrode materials and titanium or a titanium compound mainly from a used or using insoluble metal electrode to recover the base metal to be recycled as it is and the electrode material as precipitate easily recovered with sufficient concentration. <P>SOLUTION: The recovering method of the insoluble electrode is a method of separating and recovering the electrode material and a titanium base material from the insoluble metal electrode formed by covering the surface of the titanium base material with the electrode material containing iridium oxide and/or ruthenium oxide and includes a step [1] for cleaning the surface, a step [2] for applying caustic alkali solution at least on the coating surface of the electrode and spreading, a step [3] for heating and holding at about melting point of caustic alkali to cause reaction and a step [4] for dipping the insoluble metal electrode in an acid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention mainly recovers and reuses a coating layer and / or a titanium or titanium alloy substrate for an insoluble metal electrode having a coating layer containing a platinum group metal oxide on the surface of a used titanium or titanium alloy substrate. It is related with the collection | recovery method of the electrode for this.

It is well known that an insoluble metal electrode based on titanium and having a ruthenium oxide or iridium oxide coating on its surface is mainly widely used in chloralkali electrolysis, which is representative of industrial electrolysis. The life of this electrode is usually very long, and it is often used as it is for more than 10 years. However, in some cases, only the electrode material is deteriorated due to a device failure, or a non-conductive coating is formed between the electrode material and the base titanium even if the electrode material is not deteriorated like the electrode for oxygen generation. It was observed that the electrode function disappeared in a relatively short period of time.

Various electrode regeneration methods for these have been proposed. If the substrate is a sufficiently thick plate, it is cut by machining, or after removing surface deposits by blasting, etc., the residue is removed by machining, Methods such as defaceting the surface by pickling to remove surface residues have been used alone or in combination. In addition, it is said that the substrate is processed again for reuse. When such processing is performed, the base titanium or titanium alloy can be reused, but the amount of expensive electrode materials is small, and the processing materials and by-products produced by processing such as machining and blasting are used. However, since there were much more, it was practically impossible to recover. In other words, attempts have been made to collect these, and the possibility has been found, but in most cases, the collection cost is higher and it is not practically performed from the viewpoint of economy. In addition, although the chemical immersion in the alkali molten salt has been carried out, the substrate titanium or titanium alloy can be recovered, but the electrode material is dissolved in an excessive molten salt, and technically recoverable. However, the current situation is that it is not carried out from the viewpoint of economy.

If only the electrode material is recovered, the electrode can be easily peeled off by rolling, etc., and the heat can be removed by chemically peeling it or by heating it to a high temperature and rapidly cooling it. A method based on color has been proposed. In any case, the electrode material can be recovered, but titanium cannot be used as it is as a substrate, and can only be used as a raw material such as remelting.

In recent years, titanium and titanium alloy bases have become difficult to obtain due to soaring price of titanium and supply shortage. At the same time, there is a desire to collect rare metals that are very expensive, but it is impossible to collect them using the conventional method except in special cases. For example, if the substrate thickness is sufficient, the surface can be ground and recovered as described above. However, if the thickness is 1 mm or less, this is substantially impossible. There is a problem that it becomes too thin to conduct electricity well, or it is distorted, and reuse as a base material is extremely limited.
Many of these recovery techniques have been proposed, but typical patent techniques are shown below.

That is, Patent Document 1 discloses that the electrode substrate surface is dissolved by a corrosive acid to separate the coating, and the coating and the substrate are collected as a method for peeling the electrode coating. However, in reality, there is a problem that peeling of the coating is often difficult due to a stable and strong oxide between the electrode substrate and the coating and often a chemical bond between the electrode coating and the substrate metal. Patent Document 2 discloses a method in which a high concentration aqueous alkali solution is applied to the electrode surface, heated to dissolve the electrode coating in alkali, and the substrate and coating are recovered. However, depending on this, there is a problem that the titanium substrate is dissolved in the alkali at the same time, so that the substrate is greatly depleted, and the coating is dissolved in the alkali matrix, which makes it difficult to recover.

Patent Document 3 and Patent Document 4 show a method for recovering the electrode material after physically and chemically peeling the electrode material. As the peeling method, corrosion of the substrate due to acid, peeling due to polishing, etc. are shown. Although shown, in all cases, the substrate was consumed to recover the coating, and there was a possibility that the consumption of the substrate would be too large to reuse the substrate as it was.

Patent Document 5 discloses a method in which a waste electrode is rolled in advance to physically deteriorate the adhesion between the electrode material and titanium, and the surface of the titanium is corroded by acid treatment to peel off the electrode material. It is stated. Although this method is also effective, the titanium substrate and the electrode material can be recovered at the same time, but titanium cannot be reused as the substrate as it is, and it has been necessary to redissolve the recovery.

Patent Document 6 discloses that the electrode is cut and the coating is separated and recovered by barrel polishing or the like, and the base titanium is recovered. Although it is relatively simple and effective, there is a problem that the substrate cannot be reused as it is.
As shown in these figures, many studies have been made, but no suitable method for simultaneously recovering the electrode material and the base metal has been found. The substrate titanium or the titanium alloy is substantially recovered as it is as the substrate, and the electrode material is combined. The current situation is that no collection is performed.

JP 59-123730 A JP 2002-88494 A JP 2002-212650 A JP 2002-194581 A JP 2001-294948 A JP 2001-303141 A

The present invention mainly separates the electrode material and the titanium or titanium alloy substrate from the used or in-use insoluble metal electrode and recovers the substrate metal as it can be reused, and the electrode material can be easily recovered at a sufficient concentration. It was an object to provide a recovery method for recovering as a precipitate.

The present invention relates to a method for separating and recovering an electrode material and titanium substrate from an insoluble metal electrode obtained by coating the surface of a titanium substrate with an electrode material containing iridium oxide and / or ruthenium oxide, and (1) a step of cleaning the surface And (2) a step of applying a caustic alkali solution to at least the electrode coating surface and allowing it to blend, (3) a step of heating and maintaining the caustic in the vicinity of the melting point, and (4) immersion in an acid. A method for recovering an insoluble electrode having a step of performing the above steps on an electrode from which surface deposits and impurities have been removed, thereby minimizing the corrosion of the base metal and the electrode material between the base metal and the electrode material. In addition, the substrate can be separated and recovered by selectively corroding the interface, and the electrode material can be stably separated and recovered as a solid powder.

That is, the surface is first cleaned here. This method is not particularly specified and can be changed depending on the adhered matter. For example, an electrode used for caustic electrolysis of the ion exchange membrane method usually has almost no deposit, but as a surface cleaning, washing with water or acid washing dipped in dilute hydrochloric acid or the like is performed. Electrodes used for copper foil production, etc. often have heavy metal compounds such as lead sulfate and antimony oxide on the surface, so acid cleaning is performed, but if necessary, use an alkali at about 100 to 200 ° C. It can also be removed by washing to form an alkali salt and immersing it in an inorganic acid. Alternatively, by combining these, a cleaner surface can be obtained.

This is then coated with caustic. The caustic alkali is not particularly specified, but caustic soda which is highly reactive and easily available is optimal, but a mixture of caustic soda and caustic potash can also be used effectively. Although this caustic is applied, it is desirable that it is a high-concentration product, and since the actual reaction is close to the molten salt reaction, it is necessary that water jumps relatively easily and stably adheres to the electrode surface. For example, in the case of caustic soda, an aqueous solution of about 50% is applied to the electrode material. Also, for the same purpose, it is possible to immerse in a caustic alkali solution of about 20 to 50% to allow the surface to become familiar with alkali. This application is performed so that the electrode surface is completely covered and sufficiently soaked. Normally, the electrode surface is water repellent with respect to caustic and often repels liquid, but it is desirable to treat with a brush or the like until it gets wet properly, or to immerse in the liquid for a certain period of time.

Usually, it is kept at room temperature for about 10 to 30 minutes after coating and then dried at a temperature of 60 to 200 ° C. As a result, most of the water content of the caustic alkali flies away, and caustic anhydride is deposited on the surface. The drying time is not particularly specified, but is preferably about 10 to 30 minutes. However, this drying step is not essential, and when the alkali liquid is uniformly held on the electrode surface, it can be combined with the next heat treatment step.

Further, this is heat-treated at a temperature slightly higher than the melting point of the caustic. That is, since the melting point of caustic soda is about 330 ° C., it is preferably about 350 to 450 ° C., and the reaction is carried out at this temperature for about 10 minutes to 1 hour, usually about 30 minutes. Although the mechanism of this reaction is not clear, since it reacts with the acid to separate the electrode material later, alkali ions in caustic alkali react with the electrode material, the oxide between the electrode material and the substrate, and the surface of the substrate titanium. This is thought to be due to alkali complex salts. Furthermore, since the elution of the electrode material and the titanium substrate is extremely small, it is considered that the electrode material and the oxide existing between the substrate selectively react. The electrode subjected to such treatment is allowed to cool. Although this cooling may be performed in the furnace, it is desirable to cool in the atmosphere outside the furnace from the viewpoint of efficiency. Of course, it is also possible to perform the immersion treatment in the next inorganic acid without cooling, and in that case, it is necessary to pay attention to the jumping of the acid.

Then, the alkali-treated electrode is immersed in an inorganic acid such as nitric acid, hydrochloric acid or sulfuric acid. The concentration of the inorganic acid is not particularly specified, but a dilute acid of about 10 to 20% is usually desirable. The temperature of the inorganic acid is not particularly specified, but it is desirable to warm it slightly in order to speed up the reaction, and about 40 ° C. is appropriate. By this immersion, the alkali titanate is dissolved in the acid, and at the same time, the electrode material is peeled off and separated from the base metal made of titanium or a titanium alloy. At this time, peeling can be accelerated by improving the flow of the liquid by stirring the acid liquid or brushing the electrode surface. Usually, it can be sufficiently separated by a single treatment, but it can be more completely separated by repeating the steps from alkali coating to heating and firing 2 to 3 times as necessary. Here, since the electrode substance itself is stabilized by heating, it can be recovered as a precipitate with almost no dissolution in the acid. As a result, the base metal titanium or titanium alloy is hardly consumed, and the electrode material can be recovered as an oxide solid.

The acid to be used may be an inorganic acid, that is, hydrochloric acid, nitric acid or sulfuric acid as described above, or a mixed acid thereof. However, nitric acid or hydrochloric acid is desirable from the viewpoint of the solubility of the peeled dissolved product. In the case of sulfuric acid, care should be taken because the electrode substrate and the titanium in the electrode material which are slightly dissolved may precipitate as titanium sulfate or the like by repeated use. However, it does not cause any particular problem. However, since the separation from the electrode material becomes troublesome if precipitation occurs, it is clear that it is better to proceed while removing such precipitation as appropriate.

The separated oxide solid that is the electrode material can be recovered under normal conditions. For example, after reducing the platinum group metal in the electrode material by hydrogen reduction and metallizing it, ruthenium can be recovered in hypochlorous acid. It can be recovered as ruthenic acid chloride by volatilization as RuO ₄ by heat oxidation and trapping in hydrochloric acid. Moreover, if it is iridium, it can be made into an chlorinated iridate through chlorine gas together with an alkali chloride, and then the alkali can be separated and recovered as chloroiridate or iridium chloride. Otherwise, it can be recovered by dissolving in aqua regia. Of course, it can also be recovered electrolytically. At this time, titanium oxide and tantalum oxide, which are the same electrode materials, are not reduced by hydrogen, and therefore are not chlorinated and dissolved, so that they can be completely separated from the platinum group metal. Part of the electrode material may be dissolved in acid, but this is neutralized by adding ammonia to the used acid to neutralize it, and precipitating it as an ammonium salt of a platinum group metal and filtering it off. Can be recovered. This may be recovered separately from the initial oxide precipitation, but after ammonia treatment, it may be recovered by precipitation filtration simultaneously with the oxide precipitate.

In this way, the electrode substrate and the electrode material can be separated and recovered with good yield. At this time, since the oxide on the surface of the electrode base metal protects the metal itself, the consumption of the base metal does not proceed more than necessary, and the stabilized electrode material is almost eluted by the molten salt treatment under relatively low temperature conditions. Without being separated and recovered as electrode material fragments or powder. Further, since there is almost no elution of the base metal or electrode material mainly composed of titanium into the acid at this time, the consumption of the acid is only used for elution of the alkali titanate, and can be made extremely low.

Since the electrode in the present invention takes a plate-like or three-dimensional form, an expanded mesh, and other various forms, the work is performed accordingly. This will be described in the following examples, but is not limited thereto.

"Example 1"
The titanium substrate and the electrode material were collected from an electrode having a 1 mm-thick titanium expanded mesh as a substrate, which was used for salt electrolysis in an ion exchange membrane method for 5 years. Since it was an electrode used for ion exchange membrane electrolysis, there was almost no deposit on the surface, but it was washed with a neutral detergent for cleaning, and then washed with water. In order to make the surface more hydrophilic, heat treatment was performed at 300 ° C. for 15 minutes. About the electrode which performed the pre-treatment in this way, 50% caustic soda (NaOH) aqueous solution was applied to the surface so as to be sufficiently blended with a brush, and then placed in a drier kept at 40 ° C. and dried for 30 minutes. . This was put into a muffle furnace maintained at 400 ° C. and reacted by heating for 30 minutes. After heating, it was taken out from the furnace, cooled at room temperature, and immersed in a 15% aqueous hydrochloric acid solution. The immersion time was 30 minutes. When the electrode material was taken out after immersion, the electrode material was almost completely peeled off from the titanium expanded mesh of the substrate, which was the electrode substrate, and the substrate was exposed, and a black precipitate was observed in the acid solution. The acid solution was black translucent, and it was found that the electrode material was slightly dissolved.

"Example 2"
The electrode material was peeled off from the 1 mm-thick plate electrode used for copper foil production electrolysis and recovered for reuse of the substrate titanium. The electrode material of this electrode was a composite oxide of iridium oxide and tantalum oxide. Since lead sulfate and antimony oxide adhered to the surface of the electrode with an apparent thickness of about 0.5 mm, the surface deposits were first removed. It was immersed in a 25% caustic soda solution, and after the liquid had sufficiently infiltrated into the deposit, it was taken out and allowed to stand for 10 minutes, and then placed in a heating furnace maintained at 150 ° C. for 30 minutes. This produced a white film on the surface. When this was cooled and immersed in 20% nitric acid for 15 minutes, the deposits were dissolved in the nitric acid, and a black surface appeared. This was brushed in running water to completely remove surface deposits and dried. Next, a 60 wt% mixed aqueous solution in which caustic soda and caustic potash were mixed at a weight ratio of 1: 1 was applied to the surface on which the black electrode material appeared, and the mixture was allowed to stand for 10 minutes and held at 360 ° C. for 30 minutes. This was taken out of the furnace, cooled in the room, and immersed in a 25% aqueous solution of bisulfuric acid. When the electrode material was partially removed after 30 minutes, the electrode material was completely peeled from the base material when alkaline coating, heating, and acid dipping were repeated. Further, when the surface of the substrate was observed with a microscope, characteristic corrosion due to alkali melting of the base titanium was hardly observed. The electrode material was almost completely precipitated although slight dissolution was observed in the sulfuric acid solution.

"Example 3"
The same sample piece as in Example 2 was used, and the same treatment was performed, but a sample subjected to alkali coating, heating, and acid treatment only once was pickled using oxalic acid. That is, in the sample treated according to Example 2, about 30% of the electrode material apparently remains on the surface. For the purpose of removing and recovering this, a solution in which oxalic acid is dissolved in 50 ° C. pure water is used. When the electrode in which the electrode material remains is immersed in and kept at 90 ° C. for 1 hour, the electrode material precipitates in the liquid, the surface of the titanium base becomes uniform grayish white, the electrode material is removed, and the surface is slightly etched. It was seen that In the oxalic acid solution, slight elution of titanium was observed, but the color tone change due to the white metal was slight.

Example 4
The unused electrode coating with the titanium surface coated with an electrode material composed of a composite oxide of iridium oxide and tantalum oxide was peeled off. The surface of the electrode was cleaned with a neutral detergent, dried, dried, and a 40% strength aqueous solution of caustic soda was applied to the electrode material portion with a brush, followed by fusing for 15 minutes and further drying at 60 ° C. for 15 minutes. Three of these were prepared and put in furnaces maintained at temperatures of 375 ° C., 400 ° C., and 425 ° C., respectively, and heat-treated for 40 minutes. These were taken out, allowed to cool and then immersed in a 20% aqueous nitric acid solution. This process was repeated twice. The results were as follows. As a result, it was found that there was a slight difference in peeling depending on the heating temperature. That is, it was found that the higher the temperature, the better the degree of peeling, but at the same time, the dissolution of the electrode substance in the acid also increased. The electrodes subjected to these treatments were immersed and pickled in 80%, 25% hydrochloric acid for 15 minutes. As a result, gas generation was slightly observed from the electrode surface. This also caused the electrode material to peel off from all the samples and move as precipitates in the acid. Further, the titanium substrate was almost in the same state as before coating, and the surface roughness was hardly changed, so that it could be used as an electrode substrate as it was. The acid used for this was neutralized by adding ammonia. When filtered through two filter papers, the furnace liquid became a slightly yellowish transparent liquid. The iridium oxide considered to have dissolved in the acid together with the electrode stripping substance could be recovered as a precipitate.

Industrial applicability

The present invention, which can recover and reuse platinum group metals belonging to expensive and rare metals, which are surface coating layers, and titanium without deformation, is used for insoluble metal electrodes using a metal substrate mainly composed of titanium. Since it is extremely advantageous compared to the recovery of either the substrate or the platinum group metal, it will expand rapidly.

Claims (10)

A method for separating and recovering an electrode material and a titanium substrate from an insoluble metal electrode obtained by coating the surface of a titanium substrate with an electrode material containing iridium oxide and / or ruthenium oxide, and (1) cleans the surface as necessary. A step, (2) a step of applying a caustic alkali solution to at least the electrode coating surface and allowing it to blend, (3) a step of heating and maintaining at or above the melting point of the caustic alkali, and (4) an acid A method for recovering an insoluble electrode. 2. The method for recovering an insoluble electrode according to claim 1, wherein the titanium substrate is a titanium alloy substrate. 2. The method for recovering an insoluble electrode according to claim 1, wherein the caustic alkali is caustic soda, and after reacting with an aqueous caustic soda solution, the reaction is carried out at 350 to 450 ° C. for 10 to 60 minutes. The method for recovering an insoluble electrode according to claim 1, wherein the acid is an inorganic acid. The method for recovering an insoluble electrode according to claim 4, wherein the inorganic acid is nitric acid. The method for recovering an insoluble electrode according to claim 4, wherein the inorganic acid is sulfuric acid. 7. The method for recovering an insoluble electrode according to claim 1, wherein the caustic coating, heating reaction, and acid dipping treatment are repeated a plurality of times. 8. The method for recovering an insoluble electrode according to claim 1, wherein the pickling treatment is performed with a corrosive acid after the application of caustic alkali, the heating reaction, and the acid immersion treatment. The method for recovering an insoluble electrode according to claim 8, wherein the corrosive acid is hydrochloric acid and / or sulfuric acid, and pickling is performed at 80 to 110 ° C. The method for recovering an insoluble electrode according to claim 8, wherein the corrosive acid is succinic acid and the treatment is performed at a temperature of 90 ° C or higher.