JPS59123730A - Method for recovering iridium from metallic electrode - Google Patents

Abstract

PURPOSE:To recover efficiently iridium as a hydrochloric acid soln. of a chloride by dissolving and stripping the coating layer of an electrode base body, adding hydrochloric acid thereto, and separating the hydroxide of a heavy metal then making the soln. acidic and passing the soln. through an ion exchange resin. CONSTITUTION:The surface of a used metallic electrode is treated with a molten salt of an alkali metal hydroxide contg. an oxidizing agent, and the coating layer contg. iridium oxide is dissolved and stripped. Water is added thereto after cooling to prepare an aq. soln., and the metal hydroxide of heavy metal formed by neutralization with a hydrochloric acid is separated away. A hydrochloric acid is further added to such aq. soln. to make the soln. acidic and the soln. is brought into contact with a cation exchange resin whereby the alkali metal and residual ion of heavy metal, etc. coexisting therein are removed. Iridium is obtd. as a pure hydrochloric acid soln. by the above-mentioned treatment. The iridium hydrochloric acid soln. of iridium is reusable for producing the metallic electrode, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering iridium from metal electrodes.

In recent years, insoluble metal electrodes in which an electrode coating containing ruthenium or iridium oxides is provided on a valve metal substrate such as titanium have been widely used as insoluble electrodes in various fields of electrochemistry, especially in the salt electrolysis industry. .

These metal-containing electrodes have a long lifespan, but if the electrode coating gradually wears out or becomes less active during use, and it becomes impossible to maintain a certain level of performance, it is necessary to replace the electrode with a new one. It needs to be replaced. In such used metal electrodes, an equivalent amount of precious metal components such as expensive iridium remains in the coating, and it is industrially important to recover and effectively utilize this.

Previously, there were 17 related technologies related to this type of technology.
No. 6-26978 and Japanese Patent Publication No. 48-15144 disclose a method of removing a metal electrode coating using a molten salt.

In addition, JP-A No. 51-68493 describes a method for solubilizing poorly soluble substances containing ruthenium or its compounds.
No. 68498 describes an oxidative distillation process for soluble ruthenium or its compounds. Furthermore, JP-A-51-6
No. 8499 discloses a method for recovering ruthenium by treating a poorly soluble substance containing ruthenium or a compound thereof.

However, all of these methods involve a partial process of recovering precious metals from metal electrodes or recovery of ruthenium, and no method was known for recovering iridium in the coating from metal electrodes.

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a method for easily and efficiently recovering iridium from a metal electrode.

The present invention provides a method for recovering iridium from a metal electrode, in which a coating layer containing iridium oxide on a metal electrode substrate is dissolved in a molten alkali metal hydroxide salt containing an oxidizing agent, and after cooling, water is added. After making an aqueous solution and neutralizing it by adding hydrochloric acid to separate the produced valve metal hydroxide, further adding hydrochloric acid to make the solution acidic, then removing the alkali metal using a cation exchange resin, iridium This method is characterized by obtaining a hydrochloric acid solution of chloride.

In the present invention, the valve metal means titanium, tantalum, zirconium, and niobium that are commonly used as electrode substrates or electrode coating components.

Hereinafter, the present invention will be explained in detail.

First, the surface of a used metal electrode having a coating layer containing iridium oxide is brought into contact with a molten alkali metal hydroxide salt containing an oxidizing agent by immersion or the like to dissolve and peel off the coating layer. As the oxidizing agent, alkali metal nitrates such as NaN0m and KNOs, alkali metal peroxides such as Na1O1 and KIO1, alkaline earth metal peroxides, potassium permanganate, etc. can be used, and the amount thereof is determined based on the total amount of the melt. It is preferable to set it to about 20X or less on a standard basis. As the alkali metal hydroxide, KOH and NaOH are preferably used. The molten salt temperature in the molten salt dissolution step is approximately 550 to 60
A temperature of 0° C. is suitable, and the treatment time is usually about 5 to 30 minutes, and the coating layer can be easily dissolved without damaging the electrode substrate.

Next, the iridium-containing melt obtained in the molten salt dissolving step is cooled, water is added to form an aqueous solution, and hydrochloric acid is added to neutralize the solution. The amount of water added is approximately 2-10% of the melt
It is preferable to double the amount. The aqueous melt solution is alkaline and is neutralized to around neutrality by adding hydrochloric acid to precipitate the dissolved valve metal in the coating layer or from the electrode base as a hydroxide. After the generated valve metal hydroxide is separated and removed by r separation, etc., hydrochloric acid is added to make it acidic, and then the solution is brought into contact with a cation exchange resin to remove coexisting alkali metals and residual Completely removes valve metal ions, etc.

Iridium can thus be obtained as a pure hydrochloric acid solution. It is believed that iridium exists in the form of chloroiridate ions in the hydrochloric acid solution. The iridium hydrochloric acid solution can be adjusted to a concentration of t″!! or temperature and used again for manufacturing metal electrodes, etc.
Furthermore, it can be distilled under reduced pressure under conditions of 1 to 650 vaHg + 110°C or less, concentrated and solidified, and recovered as iridium chloride. Of course, it is also possible to reduce iridium chloride and recover it as metallic iridium. On the other hand, the metal base from which the coating layer has been removed can be reused as it is as an electrode base.

As detailed above, by the method of the present invention, iridium can be easily recovered in high purity from a metal electrode having a coating layer containing iridium oxide. As shown in the following examples, the recovery rate of iridium can be 85% or more based on the iridium content of the coating layer.

Example 1 Sodium hydroxide 50% as a melting agent for molten salt A molten salt was formed by using 5 tons of potassium permanganate as an oxidizing agent and maintaining the temperature at 500° C. in a nickel crucible. 6 for this
When three electrodes having coating layers containing iridium oxide on titanium substrates were immersed for 20 minutes, the coating layers were completely dissolved in the molten salt. The molten salt from which the titanium base material had been removed was cooled to room temperature, 150 cr of water was added thereto to form an aqueous solution, and then hydrochloric acid was added to neutralize it. The solution was allowed to stand until a sufficient amount of precipitate such as titanium hydroxide was formed, and then the precipitate was separated by separation, and an equal amount of hydrochloric acid was added to the solution. A cation exchange resin layer in which the obtained liquid was made into H type (DIAIO manufactured by Mitsubishi Chemical Corporation)
N-8KIB) to separate and remove alkali metal ions such as sodium and potassium to obtain a hydrochloric acid solution of iridium chloride as an effluent.

In addition, solid iridium chloride could be obtained by distilling this solution under reduced pressure at 15 mmHg and 40°C. The recovery rate of iridium was 87%.

For comparison, the amount of oxidizing agent K M n O4 was set to 0.5
When the same procedure was carried out using F, the recovery rate was 72%.

Example Z Iridium was recovered in the same manner as in Example 1 except that KNOs 5 was used as the oxidizing agent.

The recovery rate was 86%.

Example 6 Iridium was recovered in the same manner as in Example 1 except that KOH50y was used as the melting agent for the molten salt.

The recovery rate was 89%.

patent applicant

Claims (4)

[Claims] (1) A coating layer containing iridium oxide on a metal electrode substrate is dissolved in a molten alkali metal hydroxide salt containing an oxidizing agent, and after cooling, water is added to make an aqueous solution, and hydrochloric acid is added to neutralize it, After separating the produced valve metal hydroxide, hydrochloric acid is further added to make the solution acidic, and then the alkali metal is removed using a cation exchange resin to obtain a hydrochloric acid solution of iridium chloride. , a method for recovering iridium from metal electrodes. (2) The method according to claim (1), wherein the dissolution with the molten salt is carried out at 350 to 600°C. (3) The method according to item (1), wherein 2 to 10 times the amount of water is added to the molten salt after dissolving the coating layer. (4) The method according to claim (1), wherein a hydrochloric acid solution of iridium chloride is distilled under reduced pressure at 1 to 650 Hg and below 110°C to concentrate and solidify.