JPS6259057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering precious metals from spent catalysts.

In recent years, with stricter exhaust gas regulations, various methods have been adopted to prevent harmful substances such as sulfur dioxide gas and nitrogen oxides from being released into the atmosphere.

Among these, detoxification using catalysts is effective, has a simple structure, and is often used because it can be easily installed in automobiles. This catalyst generally uses a porous inorganic material such as alumina as a carrier, and noble metals such as platinum group elements are dispersed and supported on this carrier, and purifies harmful substances by bringing them into contact with the catalyst. There is.

In this case, since the precious metals used are very expensive, from the standpoint of economy and resource conservation, an operation is usually performed to recover only the precious metals from the used catalyst. A commonly used method for recovering this catalyst is to sinter the spent catalyst in an oxygen atmosphere to remove attached organic substances, and then extract the precious metal with an inorganic acid such as aqua regia.

However, when the catalyst is fired, not only harmful substances but also precious metals are oxidized, making it difficult to dissolve in the inorganic acid in the next step, resulting in a lower recovery rate, and activated alumina (γ-alumina) is used as a carrier. If the catalyst used is calcined at a relatively low temperature, a large amount of alumina will be eluted during extraction with an inorganic acid and the recovered liquid will become a slurry, so it is necessary to separate the aluminum to recover only the precious metals. This not only complicates the process, but also removes some precious metals during the process, resulting in a lower recovery rate.

The present inventors believe that the reason for the low recovery rate of spent catalysts calcined in an oxygen atmosphere is that the supported noble metals are oxidized, and if this is reduced in a hydrogen atmosphere, the recovery rate of the precious metals will be higher. We believe that this can be improved, and as a result of repeated research, we have completed the present invention.

In view of these circumstances, the present invention provides a method for recovering precious metals from spent catalysts, which prevents the elution of the carrier and efficiently extracts only the precious metals by controlling the oxidation and reduction temperatures.

The present invention involves the use of a catalyst in which a porous inorganic material, particularly activated alumina, supports a precious metal. It is characterized by the recovery method of precious metals extracted with acid.

Hereinafter, the present invention will be explained in detail with reference to Examples, where % represents weight %.

Example 1 34 g of spent catalysts each containing 0.14% palladium dispersed on an activated alumina carrier were calcined at a temperature of 1000°C in an oxygen atmosphere, and heated to 100°C in a hydrogen stream.
Reduction was carried out at temperatures of 200, 300, 400 and 500°C. Then, add 100 c.c. of aqua regia to each of the treated catalysts and
The precious metal was recovered by heating for a minute, and the results are shown in FIG.

Comparative Example 1 The same amount of catalyst used in Example 1 was recovered in the same manner as in Example 1, except that the reduction treatment was not performed, and the results are also shown in FIG.

Example 2 0.14% palladium and platinum on activated alumina support
34g of spent catalyst with 0.063% dispersed support was heated to 900, 1000, 1100, 1200 and
Fired at various temperatures of 1300℃ and heated in a hydrogen stream.
Reduction was performed at 500℃. Thereafter, 100 c.c. of aqua regia was added to each of the treated catalysts and heated for 30 minutes to recover the precious metals. The results are shown in Figure 2 (in the figure, the results for palladium are indicated by the symbol Pd, The results for platinum are indicated by the symbol Pt.) Comparative Example 2 The same amount of catalyst used in Example 2 was recovered in the same manner as in Example 1, except that no reduction treatment was performed, and the results are also shown in Figure 2. (In the figure, the results for palladium are represented by the symbol Pd', and the results for platinum are represented by the symbol Pt'.) Example 3 0.14% palladium was dispersed and supported on an activated alumina carrier containing 20% magnesium oxide. 35 g of the spent catalyst was calcined at 1200°C in an oxygen atmosphere and reduced at a temperature of 500°C in a hydrogen atmosphere. Thereafter, the treated catalyst was further treated in the same manner as described above to recover precious metals, and the recovery rate was 95%.

Comparative Example 3 The same amount of catalyst used in Example 3 was recovered in the same manner as in Example 1, except that no reduction treatment was performed, and the recovery rate was 28%.

Example 4 34g of spent catalyst was dispersed and supported with 0.14% of platinum on an activated alumina carrier containing 5% of cerium oxide.
It was fired at a temperature of 1200°C in an oxygen atmosphere and reduced at a temperature of 500°C in a hydrogen atmosphere. Thereafter, the treated catalyst was further treated in the same manner as described above to recover precious metals, and the recovery rate was 97%.

Comparative Example 4 The same amount of catalyst used in Example 4 was recovered in the same manner as in Example 1, except that the reduction treatment was not performed, and the recovery rate was 72%.

As can be seen from these examples and comparative examples,
By performing reduction treatment at 200℃ or higher after firing in an oxygen atmosphere, the solubility of precious metals increases,
The recovery rate will be significantly improved. Further, according to Example 2, by firing at 1000° C. or higher, γ-alumina becomes stable as α-alumina, and the alumina elution rate is reduced. Furthermore, commonly used Example 3
The reduction treatment is also effective for activated alumina carriers having compositions such as 4.

As described above, according to the present invention, the recovery rate of precious metals can be improved, and in the case of a catalyst using activated alumina as a carrier, it is possible to suppress the alumina elution rate to the extent that an aluminum separation process is unnecessary. Furthermore, unlike catalysts used in general chemical plants, automotive catalysts are recovered in either an oxidized state or a reduced state; however, by applying the method of the present invention, the catalyst can be recovered. The present invention has many excellent effects and advantages, such as being able to obtain a high and almost constant recovery rate regardless of the state of the material.

[Brief explanation of the drawing]

Figure 1 is a graph showing the palladium recovery rate versus reduction temperature in Example 1 and Comparative Example 1, Figure 2 is a graph showing the precious metal recovery rate versus firing temperature in Example 2 and Comparative Example 2, and Figure 3 is a graph showing the recovery rate of precious metal versus firing temperature in Example 2 and Comparative Example 2. , Example 2
(Comparative Example 2) A graph showing the alumina elution rate versus firing temperature.

Claims (1)

[Claims] 1 A use characterized in that a catalyst in which a noble metal is supported on a porous inorganic substance is calcined in an oxygen atmosphere at a temperature of 1000°C or higher, reduced in a hydrogen atmosphere at a temperature of 200°C or higher, and extracted with an inorganic acid. Method for recovering precious metals from used catalysts.