JPS59145739A - Method for recovering ruthenium and iridium from metallic electrode - Google Patents

Abstract

PURPOSE:To recover efficiently Ru and Ir from a metallic electrode by melting the coating layer on the base body of the electrode into a specific molten salt contg. an oxidizing agent and subjecting the same to vacuum distillation to recover an Ru-component and further removing valve metal from the soln. and removing an Ir component. CONSTITUTION:The Ru oxide and Ir oxide layer on the base body of a metallic electrode is melted in a molten salt of an alkali metal hydroxide such as KOH or the like contg. the 1st oxidizing agent such as KMnO4 or the like. Water is added to the melt after cooling and further the 2nd oxidizing agent such as gaseous chlorine is added thereto and the soln. is subjected to vacuum distillation. The RuO4 generated by the distillation is introduced into hydrochloric acid and Ru is recovered as a chloride. Hydrochloric acid is added to the remaining liquid to adjust the pH thereof and to form the hydroxide of valve metal such as Ti used in the electrode. Said hydroxide is separated. Hydrochloric acid is further added to the soln. to make the soln. acidic and the soln. is passed through a cation exchange resin to remove alkali metal. Ir is recovered as a hydrochloric acid soln. of Ir chloride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering ruthenium and 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 used in large quantities as insoluble electrodes in various fields of electrochemistry and in the brine electrolysis industry. ing.

Such metal electrodes have a long lifespan, but if the electrode coating gradually wears out or becomes less active during use and can no longer maintain its short-term performance, it is necessary to replace it with a new electrode. It needs to be replaced. A considerable amount of expensive precious metal components such as ruthenium and iridium still remain in the coating of these used metal electrodes, and it is industrially important to recover and effectively utilize these components.

Conventionally, as related to this type of technology,
-2697B and Special Publication No. 48-15144,
A method of removing a metal electrode coating using molten salt is known. Furthermore, JP-A-51-68493 describes a method for solubilizing poorly soluble substances containing ruthenium or its compounds, and JP-A-51-6B49B describes an oxidative distillation method for soluble ruthenium or its compounds. There is. Furthermore, JP-A-51
No. 68499 discloses a method for recovering ruthenium by treating a refractory substance containing ruthenium or a compound thereof.

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

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for easily and efficiently recovering both ruthenium and iridium from a metal electrode.

The present invention provides a method for recovering ruthenium and iridium from a metal electrode, in which a ruthenium oxide and iridium oxide layer on a metal electrode substrate is dissolved in an alkali metal hydroxide molten salt containing a first oxidizing agent, and then cooled. After that, water is added to make an aqueous solution, a second oxidizing agent is added and distilled under reduced pressure, the generated ruthenium tetroxide is introduced into hydrochloric acid to recover ruthenium as chloride, and hydrochloric acid is added to the distillation residue. After adjusting the pH and separating the valve metal hydroxide, further hydrochloric acid is added to make the solution acidic, and then the alkali metal is removed using a cation exchange resin, and the iridium is converted into iridium chloride with hydrochloric acid. It is characterized by being recovered as a solution.

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

The present invention will be explained in detail below.

First, a surface coating layer of a used metal electrode having a coating layer containing ruthenium oxide and iridium bioxide is dissolved in an alkali metal hydroxide molten salt containing a first oxidizing agent. The dissolution can be carried out by directly immersing the metal electrode in the molten salt or by bringing it into contact with the molten salt. You can also do this. KOH is an alkali metal hydroxide.

NaOH is preferable, and the first oxidizing agent to be contained therein includes alkali metal nitrates such as NaNOs + KNOs, alkali metal peroxides such as NaOt, K*'O*, and alkali. Earth metal peroxides, potassium permanganate, etc. can be used. The amount of the first oxidizing agent is preferably about 2% or more and about 20% or less based on the total amount of the melt. The temperature for dissolving molten salt is approximately 350-600℃
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 obtained melt containing ruthenium and iridium is cooled, water is added to make an aqueous solution, a second oxidizing agent is added, and the mixture is distilled under reduced pressure. The amount of water added is about 2-1 parts of the melt
It is preferable to use 0 times the amount. Chlorine gas is suitable as the second oxidizing agent, and distillation can be carried out while blowing it into the aqueous solution, but other oxidizing agents such as a sodium hypochlorite solution may also be used.

At this time, ruthenium, which is considered to be dissolved as a complex in the aqueous solution, is oxidized by the oxidizing agent to generate volatile ruthenium tetroxide and highly pure Rub in gaseous form. It is efficient to carry out the distillation under a reduced pressure of about 1 to 650 mHH, and the temperature is 20 mH to stabilize RuO4.
The temperature is preferably 0°C or lower. Approximately 10~
Ruthenium is recovered as chloride by introducing it into about 35% hydrochloric acid and causing a dissolution reaction. On the other hand, iridium and valve metal remain in the distillation residue. The obtained high-purity ruthenium chloride solution can be used again for manufacturing metal electrodes, and can also be recovered as a concentrated solidified product or subjected to reduction treatment and recovered as metal ruthenium, if necessary.

Next, hydrochloric acid is added to the distillation residue obtained above to adjust the pH. The purpose of this is to neutralize the alkaline distillation residue to near neutrality and to precipitate the dissolved valve metal in the coating layer or from the electrode base as a hydroxide. A suitable pH for this is in the range of about 3-11. Then, the generated valve metal hydroxide is separated and removed by another method or the like.

In this way, a mother liquor in which iridium is dissolved is obtained, but since the alkali metals used as hydroxides during dissolution with the molten salt still remain in this solution, these are removed by contacting with a cation exchange resin. do. At this time, the alkali metal and remaining valve metal ions are completely removed by making the liquid acidic by adding hydrochloric acid.

Through the above treatment, iridium is recovered as a hydrochloric acid solution of a pure iridium chloride compound. The iridium hydrochloric acid solution can be reused as it is or after being prepared to an appropriate concentration for the production of metal electrodes. Furthermore,
It can also be recovered as iridium chloride by distilling it under reduced pressure under conditions of 1 to 650 wx Hg and about 110°C or less, concentrating and solidifying it. Furthermore, it is of course possible to recover iridium chloride as metallic iridium by subjecting it to reduction treatment.

On the other hand, since the metal base from which the coating layer has been removed is hardly damaged, it can be reused as an electrode base as it is.

By the method of the present invention, as shown in the following examples, high-purity ruthenium and iridium can be efficiently and easily recovered from a metal electrode having a coating layer containing ruthenium oxide and iridium oxide, The industrial value of the present invention is extremely large.

Example 1 A molten salt was formed by using 50 g of sodium hydroxide as a melting agent and 5 g of potassium permanganate as a first oxidizing agent and maintaining the temperature at 500° C. in a nickel crucible. 3 to this
When an electrode having a coating layer containing ruthenium oxide and iridium oxide on a titanium substrate having a size of ex X 3 cnx was immersed for 20 minutes, the coating layer was completely dissolved in the molten salt. Next, add 1 to the molten salt from which 1 titanium base material was removed.
After cooling, 200 cc of water was added to dissolve it to form an aqueous solution, and then chlorine gas was blown in as a second oxidizing agent at a rate of 100 cc/min, at a pressure of 150 mHg and a temperature of 80 to 85%.
Vacuum distillation was performed at °C. The generated ruthenium tetroxide was introduced into hydrochloric acid and absorbed as ruthenium chloride. As a result, the recovery rate of ruthenium was 78%.

Next, hydrochloric acid was added to the distillation residue, the pH was adjusted to 8, and the solution was allowed to stand, and the produced precipitates such as valve metal hydroxide were separated. Furthermore, after adding an equal amount of hydrochloric acid to the R liquid, a cation exchange resin prepared into H type (DIAI manufactured by Mitsubishi Chemical Corporation) was added.
ON-8KIB) to separate and remove contained cations such as sodium and potassium, and recover iridium as a hydrochloric acid solution of pure iridium chloride. This solution was further distilled under reduced pressure at 40° C. to obtain solid iridium chloride. The recovery rate of iridium at that time was 72%.

Example Z Ruthenium and iridium were removed from the metal electrode in the same manner as in Example 7 except that the coating layer containing ruthenium oxide and iridium oxide was peeled off by puff polishing, and 10 g of the powdered coating layer was dissolved in molten salt. were collected. The recovery rate was 72% for ruthenium and 65% for iridium.

Example 3-5 Ruthenium and iridium were recovered from the metal electrode in the same manner as in Example 1, except that the melting agent, oxidizing agent, melting conditions, and distillation conditions were changed.

The results are shown in Table-IK-j.

As Reference Example 1.2, cases in which a small amount of the first oxidizing agent was used for melting and a case in which the melting time was short are shown in Table 1.

Table-1

Claims (1)

[Claims] A coating layer containing ruthenium oxide and iridium oxide on a metal electrode substrate is dissolved in a molten alkali metal hydroxide salt containing a first oxidizing agent, and after cooling, water is added to form an aqueous solution. After that, a second oxidizing agent is added and distilled under reduced pressure, and the generated ruthenium tetroxide is introduced into hydrochloric acid to recover ruthenium as chloride. Hydrochloric acid is added to the distillation residue to adjust the pH. After the metal hydroxide is generated and separated, hydrochloric acid is further added to make the solution acidic, and then the alkali metal is removed using a cation exchange resin, and iridium is recovered as a hydrochloric acid solution of iridium chloride. A method for recovering ruthenium and iridium from metal electrodes. (2) The method according to item (1), wherein the dissolution with the molten salt is carried out at 550 to 600°C. (3) The method of item (1), in which 2 to 10 times the amount of water is added to the molten salt after the coating layer has been dissolved. (4) The method according to item (1), in which vacuum distillation is carried out at 200° C. or lower and 1 to 650 wHg while blowing chlorine gas as the second oxidizing agent. (5) The method of item (1), in which hydrochloric acid is added to the distillation residue to adjust the pH from 3 to 11 Vc. (6) Step (1) in which the hydrochloric acid solution of iridium chloride is distilled under reduced pressure at 110°C or lower and 1 to 650 mHg to concentrate and solidify it.
Section method.