JP2002088419A - Method for reducing and recovering palladium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively recovering palladium when the palladium as a valuable element is reduced and recovered from hydrochloric acid acidic solution by the use of sulfurous acid gas. SOLUTION: In the method for reducing and recovering the palladium, effective palladium reduction with the sulfurous acid gas is performed by making selenium, or the like, coexist with the hydrochloric acid acidic solution containing the palladium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for wet recovery of valuable resources, and more particularly, to a method for reducing and recovering valuable palladium from a liquid. In particular, it is effectively used for treating a leachate of an automobile waste catalyst.

[0002]

2. Description of the Related Art Since palladium is chemically stable, oxidizing aqua regia or hydrochloric acid is often used as a leachate. As a reducing agent for reducing and recovering palladium dissolved in these liquids from an aqueous solution, for example, borohydride, sodium borohydride, hydrazine and the like are known. However, these reducing agents are not only expensive, but also consume acids in the solution at the same time, and are often economically undesirable.

[0003] On the other hand, as a reducing agent which does not consume acids, sulfur dioxide gas can be mentioned. This sulfurous acid gas is relatively easily available and has the advantage of being inexpensive. However, palladium is not easily reduced to metal even by passing sulfurous acid gas through a hydrochloric acid solution containing palladium. This is thought to be because the chloro complex of palladium formed in the hydrochloric acid solution is in a highly oxidized state, and is only reduced to the chloro complex in a low oxidized state, but not reduced to metallic palladium.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for reducing and recovering palladium by a wet method, which solves the above problems.

[0005]

Means for Solving the Problems The present inventors have conducted various studies on a method for recovering palladium from a palladium-containing hydrochloric acid-containing acidic solution. A method for reducing and recovering palladium by blowing sulfurous acid gas into an acidic solution, wherein selenium and / or tellurium coexist in a liquid to efficiently reduce palladium. (2) The concentrations of coexisting selenium and tellurium are each 1 g
/ L or more and 0.5 g / L or more. I will provide a. (3) The method for reducing and recovering palladium according to (1) or (2), wherein the target treatment liquid is a leachate obtained by treating an automobile waste catalyst.

[0006]

The structure of the present invention will be described below in detail. Although the configuration has been described using an example, the present invention is not limited to this example.

Since palladium is chemically stable, for example, oxidizing aqua regia or hydrochloric acid is often used as a leachate. As a reducing agent for recovering palladium dissolved in these liquids from an aqueous solution, for example, borohydride, sodium borohydride, hydrazine and the like are known. However, these reducing agents are not only expensive, but also consume acids in the solution at the same time, and are often economically undesirable.

On the other hand, as a reducing agent that does not consume acids, sulfurous acid gas can be mentioned. However, palladium is not reduced even when sulfurous acid gas is passed through a hydrochloric acid solution containing palladium.

The present inventors have conducted various studies on the reduction and recovery of palladium from an acidic hydrochloric acid solution. By doing so, it has been found that palladium can be easily reduced with sulfurous acid gas.

When sulfur dioxide is blown into a hydrochloric acid solution in which only palladium is dissolved, the oxidation-reduction potential becomes 80
0 to 1,000 mV (vs. Ag / AgCl) to 40
It drops to around 0 mV and reaches equilibrium. However, palladium is dissolved in the liquid without being reduced.

As a hydrochloric acid solution containing palladium, for example, there is a solution obtained by leaching a waste catalyst for automobiles. The composition of this leachate is, for example, Pd = 0.5 to 10 g / L, HCl = 20
２００200 g / L, and selenium and tellurium are not contained in the liquid because they are not contained in the spent catalyst. After selenium or the like is added to this solution, when a sulfurous acid gas is blown, the oxidation-reduction potential becomes 800 to 1,000 mV (vs. Ag / AgC
from 1) to around 400 mV and reach equilibrium. At this time, the palladium concentration in the liquid gradually decreased to 400 mV
And it becomes almost zero. Coexisting components such as selenium also show almost the same behavior. This reaction is thought to be due to coprecipitation and the like. Note that even if a metal other than selenium and tellurium, for example, iron and the like coexist, palladium cannot be reduced and recovered. Liquid temperature is 7
0 ° C. or higher is preferred. If the temperature is lower than this, the reduced selenium becomes rubbery, which makes subsequent handling difficult. Further, the acid concentration shows a value that does not substantially change before and after the introduction of the sulfurous acid gas. Therefore, when selenium and the like coexist,
It has been found that palladium in hydrochloric acid solution can be reduced and recovered without consuming acid.

The reduced slag contains palladium and selenium. For example, selenium sublimates by heating the reduced slag, so that palladium and selenium can be easily separated. The sublimated selenium is recovered as selenium dioxide,
It is possible to repeat into the process.

As described above, a method for recovering palladium from hydrochloric acid acidic solution has been established.

【Example】

An embodiment of the present invention will be described below. Note that the present invention is not limited to the embodiments.

Embodiment 1

[0015] A liquid obtained by leaching a waste automobile catalyst with hydrochloric acid was assumed. Since selenium and tellurium are not contained in the spent catalyst,
Neither selenium nor tellurium is present in the leaching solution. Palladium chloride was dissolved in 0.5 L of 3 M / L hydrochloric acid, and the palladium concentration was adjusted to 1 g / L to prepare a test solution.

Selenic acid was dissolved in this test solution to adjust the selenium concentration to 5 g / L. After the temperature was raised to 80 ° C., sulfuric acid gas was blown at 0.1 L / min. As a result, the redox potential reached equilibrium at 430 mV. Table 1 shows the results at this time. Nearly 100% of palladium and selenium were reduced, and no hydrochloric acid was consumed.

[0017]

[Table 1]

Embodiment 2

Selenous acid was dissolved in the test solution of Example 1 and the selenium concentration was adjusted as shown in Table 2. After the selenium concentration-adjusted solution was heated to 80 ° C., sulfurous acid gas was added at 0.1 L / m.
In was blown in, and reduction was continued until the oxidation-reduction potential became equilibrium. As a result, the oxidation-reduction potential was 400 to 4
Equilibrium was reached at 50 mV. Table 2 shows the results at this time.

[0019]

[Table 2] As can be seen from Table 2, the initial selenium concentration was 1.0
The reduction of palladium was efficiently performed at g / L or more.

Embodiment 3

Tellurium dioxide was dissolved in the test solution of Example 1 and the tellurium concentration was adjusted as shown in Table 3. After the solution was heated to 80 ° C., sulfurous acid gas was blown in in the same manner as in Example 1.

[0021]

[Table 3] As can be seen from Table 3, the initial tellurium concentration was 0.5
The reduction of palladium was efficiently performed at g / L or more.

Embodiment 4

Selenous acid and tellurium dioxide were dissolved in the test solution of Example 1, and the concentrations of selenium and tellurium were adjusted as shown in Table 4. After the solution was heated to 80 ° C., sulfurous acid gas was blown in in the same manner as in Example 1.

[0023]

[Table 4] As can be seen from Table 4, even when selenium and tellurium were present in the solution at the same time, palladium was reduced efficiently.

[0024]

Comparative Example 1 Liquid of Example 1 (palladium concentration 1 g / L)
After heating to 80 ° C., sulfurous acid gas was blown in in the same manner as in Example 1.

[0025]

[Table 5] Compared to the results in Table 1, the results in Table 5 show that palladium was not reduced even after sulfur dioxide gas was blown,
It can be understood that almost all of the liquid remains.

[0026]

As described above, the coexistence of selenium and / or tellurium of the present invention makes it possible to easily and easily recover palladium in a hydrochloric acid acidic solution by using sulfurous acid gas.

[Brief description of the drawings]

FIG. 1 shows one embodiment of a processing flow of the present invention.

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Claims (3)

[Claims] 1. A method for reducing and recovering palladium by blowing sulfurous acid gas into a hydrochloric acid solution containing palladium, wherein selenium and / or tellurium coexist in the liquid to efficiently reduce palladium. Method for reducing and recovering palladium. 2. The method according to claim 1, wherein the coexisting concentrations of selenium and tellurium are 1 g / L or more and 0.5 g / L or more, respectively. 3. The method for reducing and recovering palladium according to claim 1, wherein the target treatment liquid is a leachate obtained by treating an automobile waste catalyst.