JPS5997536A - Method for recovering ruthenium from metallic electrode - Google Patents

Abstract

PURPOSE:To recover simply and efficiently Ru as RuCl from a coating contg. Ru oxide on the base material of a metallic electrode by removing the coating by a mechanical method, reducing it under heating, adding a soln. of an oxidizing agent to the resulting metallic Ru, carrying out vacuum distillation, and introducing generated RuO4 into hydrochloric acid. CONSTITUTION:A sand blast method is applied to the surface of a used metallic electrode having a coating contg. Ru oxide to remove mechanically the coating. The resulting granular body contg. grain of the coating is heated in air or a reducing atmosphere to reduce Ru oxide to metallic Ru. A soln. of an oxidizing agent such as about 5-15% NaClO soln. is added to the granular body contg. metallic Ru, and distillation is carried out under about 1-650mm.Hg reduced pressure. Generated RuO4 vapor is introduced into about 10-35% hydrochloric acid, dissolved, and recovered as Ru chloride after reaction. The prepd. Ru chloride soln. of high purity is used again in the manufacture of a metallic electrode. Metallic Ru may be recovered from the soln. by reduction.

Description

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

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

Although such metal electrodes have a long lifespan, the electrode coating gradually wears out and becomes less active during use.
When a certain level of performance cannot be maintained, it is necessary to replace the electrode with a new one. In such used metal electrodes, a considerable amount of precious metal components such as expensive ruthenium remain in the coating, and it is industrially important to recover and effectively utilize the residue.

Conventionally, as a technology related to this type of technology,
According to No. 2.697B and Special Publication No. 15144 of 1973,
A method of removing a metal electrode coating using molten salt is known. Furthermore, JP-A No. 51-68493 describes a method for solubilizing poorly soluble substances containing ruthenium or its compounds, and JP-A No. 51-68498 describes an oxidative distillation method for soluble ruthenium or its compounds. . These are helpful as partial steps in the process of recovering ruthenium from metal electrodes, but do not relate to the entire process. Further, JP-A-51-68499 discloses a method for recovering ruthenium by treating a poorly soluble substance containing ruthenium or its compound. However, in this method, the coating is removed by anodization in an electrolytic bath, which requires a long time, and further requires a molten salt treatment step, an acidic solution dissolution step,
Since it requires a reduction treatment step, etc., it requires complicated and long-time treatment and a large amount of expense, and cannot be said to be an industrially optimal method for recovering ruthenium.

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

In a method for recovering ruthenium from a metal electrode, the present invention involves peeling off a coating layer containing ruthenium oxide on a metal electrode substrate by mechanical means such as blasting, and releasing the resulting peeled product in air or in a reducing atmosphere. After reducing ruthenium oxide to ruthenium metal by heating inside, oxidizer mud is added and distilled under reduced pressure, and the generated ruthenium tetroxide is introduced into hydrochloric acid and recovered as ruthenium chloride. It is something.

The present invention will be explained in detail below.

The method of the present invention is divided into (1) mechanical stripping step, (2) thermal reduction step, (3) oxidative distillation step, and (4) collection step.

(1) In the mechanical peeling process, the coating layer is removed by sandblasting, which sprays a grid made of alumina, silica, etc. with excellent heat and chemical resistance onto the surface of a used metal electrode that has a coating layer containing ruthenium oxide. The method of It is also possible to apply other means such as a buffing method and a wire brush method. The metal substrate from which the coating has been removed is
It can be used as it is again as an electrode base.

(2) In the thermal reduction step, the powder containing the coating layer particles obtained in the peeling step is heated and fired to reduce the ruthenium oxide contained therein to metallic ruthenium. When the heating is carried out in air, a temperature in the range of 1400°C to 2000°C is suitable; however, in an atmosphere containing a reducing gas such as HnlCO, a lower temperature of 700°C to 1200°C is sufficient for ruthenium oxide. It can be decomposed and reduced into metal ruthenium. At the same time, easily volatile heavy metals such as mercury are completely removed in this step.

(3) In the oxidative distillation step, an oxidizing agent solution is added to the granular material containing metal ruthenium obtained in the thermal reduction step, and vacuum distillation is performed. At this time, metal ruthenium is oxidized to volatile ruthenium tetroxide, and pure RuO4 is generated in gaseous form. As the oxidizing agent solution, a 5-15% sodium hypochlorite solution or a solution in which chlorine gas is blown into an alkaline solution is suitable, but other solutions such as hydrogen peroxide solution or sodium peroxide solution are also suitable. You can also. It is efficient to carry out the distillation under a reduced pressure of about 1 to 650 mmHg, and in order to stabilize the generated ruthenium tetroxide, it is preferable to carry out the distillation at a temperature of 200° C. or lower.

(4) In the collection step, the ruthenium tetroxide generated in the previous step is introduced into about 10 to 65% hydrochloric acid, dissolved and reacted, and recovered as ruthenium chloride. The obtained high-purity ruthenium chloride solution can be used again for manufacturing metal electrodes, and if necessary, it can also be recovered as a concentrated solidified product or subjected to reduction treatment and recovered as metal ruthenium. .

As described above, using the method of the present invention described in detail, ruthenium could be easily recovered with high purity using a metal electrode having a coating layer containing ruthenium oxide. Moreover, the recovery rate of ruthenium was 85% or more based on the ruthenium content of the coating layer, as shown in the following examples.

Example 1 Alumina sand 1
Q02 was sprayed at a pressure of 2s/σ1, and the coating layer was peeled off by blasting. The obtained exfoliated powder containing blasted sand was heated in air at 1500° C. for 2 hours. After cooling,
The mixture was placed in a distillation flask, 1 ton of 10% sodium hypochlorite solution was added, and vacuum distillation was performed at 90°C and 250 mmHg. The generated ruthenium tetroxide was collected in concentrated hydrochloric acid to obtain a ruthenium chloride solution. Ruthenium recovery rate is 85%
◇ Example 2. -5 In the method of Example 1, the recovery treatment was carried out in the same manner as the atmosphere and temperature in the thermal reduction step and the temperature and pressure in the oxidative distillation step.

As a reference example, heating was performed at a relatively low temperature, and the results are summarized in Table 1.

Table-1

Claims (5)

[Claims] (1) Mechanically peel off the coating layer containing ruthenium oxide on the metal electrode substrate, heat the resulting peeled product to reduce the ruthenium oxide to ruthenium metal, and then add an oxidizing agent solution and distill under reduced pressure. A method for recovering ruthenium from a metal electrode, characterized in that the generated ruthenium tetroxide is introduced into hydrochloric acid and recovered as ruthenium chloride. (2) The method according to claim (1), wherein the coating layer is peeled off by a blasting method, a buffing method, or a wire brushing method. (3) The method according to claim (1), wherein the peeled material is heated in air at 1400°C to 2000°C. (4) Claim No. 1, wherein the peeled material is heated at 700A to 1200°C in a reducing atmosphere containing Hm, CO, etc.
Section method. (5) The method according to claim (1), wherein a sodium hypochlorite solution is used as the oxidizing agent solution, and vacuum distillation is performed at 200° C. or lower and 1 to 650 mHg.