JPS593938B2 - Method for recovering platinum group elements from platinum-based catalysts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering platinum group elements from a platinum-based catalyst using alumina, carbon, or the like as a carrier.

Platinum-based catalysts are widely used in the petrochemical industry, automobile exhaust gas purification, etc. However, since platinum group elements are expensive and limited, it is desirable to recover platinum group elements from waste catalysts in order to conserve resources.

Conventional methods for recovering platinum group elements from platinum-based catalysts include an alkali dissolution method and an aqua regia dissolution method, but each method requires complicated post-treatment after dissolution.

There has also been reported a method of treating with a mixture of hydrogen peroxide and 1N to 12N hydrochloric acid at a mixing ratio (115-5):1, but this method is not suitable for extracting platinum group elements. It has the disadvantage of requiring a long time or high temperature.

Furthermore, the high concentration of expensive hydrogen peroxide increases processing costs, and the high concentration of hydrogen peroxide increases the amount of alumina extracted, complicating post-treatment.

The purpose of the present invention is to solve the drawbacks of the above-mentioned conventional methods and recover platinum group elements with simple operation and in a short time. Hydrochloric acid with a concentration of 20% by weight or more is added to a platinum-based catalyst, or a catalyst is added to hydrochloric acid, and then a hydrogen peroxide solution is added at a ratio of 1.5 to 15% by volume based on the amount of hydrochloric acid used in the catalyst-hydrochloric acid system. The present invention provides a method for recovering platinum group elements from a platinum-based catalyst, characterized by dissolving the platinum group elements by sequentially adding .

In this case, it is best to use hydrochloric acid and hydrogen peroxide in the above proportions, and although extraction is possible at room temperature, better results can be obtained by heating.

If hydrochloric acid is less than 20% by weight, the solubility decreases, so 20% by weight or less
% or more by weight is used.

Although the hydrogen peroxide solution used had a concentration of 30% by weight, it is not limited thereto.

However, if the hydrogen peroxide solution is too low, the platinum group elements will not dissolve, so it is preferably 30% by weight or more.

The hydrogen peroxide solution may be added immediately after adding the hydrochloric acid, but it is preferable to wait some time.

The present invention will be explained in more detail below with reference to Examples.

Example 1 Catalyst 6 with 9.9cm of platinum supported on the alumina surface, OI
17.8 mg of 30% hydrochloric acid and 2.2 mg of hydrogen peroxide were added to the solution in this order and allowed to react at room temperature for 80 minutes, thereby dissolving the platinum on the catalyst surface.The aqueous solution was analyzed by atomic absorption spectrometry, and the result was 7.0. of platinum was detected.

Reference Example: The same amount of catalyst with the same composition as that used in Example 1 was immersed in a mixed solution of 17.8 mg of 30% hydrochloric acid and 2.2 mg of hydrogen peroxide solution, and reacted at room temperature for 80 minutes. When analyzed by atomic absorption spectrophotometry, platinum was immediately detected at 1.4.

For each of the above Example 1 and Reference Example, the change in platinum extraction rate depending on the extraction time is shown graphically in FIG.

The figure shows that the platinum extraction rate is much higher when the platinum is added sequentially than when the mixture is added.

Example 2 35% to 6.0 g of catalyst of the same composition as that used in Example 1
Add 20-1 of hydrochloric acid and 0.5-1 of hydrogen peroxide in this order.
The reaction was carried out at room temperature for 0 minutes, and by repeating this process again, most of the platinum on the catalyst surface was dissolved, and when analyzed by atomic absorption spectrophotometry, 9.5111 g of platinum was detected.

Example 3 Catalyst 6 with 9.5cm of palladium supported on the alumina surface
．． After adding 10-1 of 35% hydrochloric acid and 1-1 of hydrogen peroxide to 0 g in this order, the mixture was reacted at room temperature for 20 minutes.

When the solution was analyzed by atomic absorption spectrophotometry, 8.6% palladium was detected.

Example 4 Catalyst with 1.0μ of rhodium supported on alumina surface 6.
OII was soaked with sodium chloride, baked in chlorine gas to obtain sodium rhodate, extracted in the same manner as in Example 1, and analyzed by atomic absorption spectrophotometry.
mp of rhodium was detected.

Example 5 Zirconia was used as a carrier in the reactions of Examples 1 to 4.

Although carbon, spinel, silica, etc. were used, the same results as in Examples 1 to 4 were obtained.

Example 6 The scale of Examples 1 to 5 was increased by about 105 times, and various methods of adding the hydrogen peroxide solution were used accordingly.

First, 680 kg of a catalyst in which 1 mm of platinum is uniformly dispersed on the alumina support surface is immersed in 2 parts of hydrochloric acid, and aqueous hydrogen peroxide is added to this catalyst bed from above the extractor 1 using the method shown in Figure 2. ], insert a pipe 4 vertically into the center of the extractor 1 and install nozzles 5 in the pipe 4 at appropriate intervals to add water (as shown in Fig. 3), from the external pipe 4 into the extractor 1. Two series of method (C) in FIG. 4 were conducted in which several pipes 4 were passed horizontally at intervals and a nozzle 5 was provided in the same way as method B.

However, in method C, when hydrochloric acid is immersed, hydrochloric acid will enter the hydrogen peroxide solution introduction system, so pressurized air is introduced and removed through the bypass 6, and then the flow of pressurized air is switched off with the switching valve 7. Switch to measuring tube 8.

A predetermined amount of hydrogen peroxide solution is measured in advance into the measuring tube 8, and is supplied by pressurized air into the catalyst immersed in hydrochloric acid.

For each of the above cases A, B, and C, the platinum recovery rate after 1 hour was investigated and compared, and the results are shown in Table 1.

According to Table 1 above, it can be seen that method C for supplying hydrogen peroxide solution is the most excellent.

In general, when concentrated hydrochloric acid and hydrogen peroxide are mixed, it is thought that when the hydrogen peroxide is added to the hydrochloric acid, chlorine gas and oxygen gas are violently generated, and the concentrated hydrochloric acid turns into diluted hydrochloric acid.

From this, it is considered that if hydrochloric acid and hydrogen peroxide solution are left to stand after mixing, the decomposition reaction described above will proceed, the effect of hydrogen peroxide will disappear, and the concentration of hydrochloric acid will decrease, thereby worsening the extraction effect.

However, if platinum group elements are already present at the time of mixing, the generated chlorine gas and oxygen gas will attack the surface of the metal, oxidize it, and cause the metal to react with the chlorine ions in the hydrochloric acid to form complex ions and become water-soluble. It is thought that

On the other hand, when hydrochloric acid is added to hydrogen peroxide, only chlorine gas is generated, and the decomposition is not as severe as when hydrogen peroxide is added to hydrochloric acid.

However, when hydrogen peroxide is added to the metal, the decomposition of the hydrogen peroxide is accelerated and its effect disappears at this stage.

For these reasons, it is considered that the best way to prepare the extraction solution is to add hydrogen peroxide solution to hydrochloric acid in the presence of the catalyst to be treated.

Regarding the order of preparation of the extraction solution and the treatment method, there is no change in the extraction rate whether hydrochloric acid is added to the catalyst to be treated or the catalyst is added to the hydrochloric acid.

Figure 5 shows the relationship between the extraction rate of platinum extracted within a certain period of time and the concentration of hydrochloric acid. Then the extraction effect becomes a dog.

Table 2 below shows the change in extraction rate when the amount of 30% hydrogen peroxide solution added to 20% hydrochloric acid was changed.

In this case, as can be seen from the table, platinum and alumina in the platinum catalyst are extracted, and as the amount of hydrogen peroxide increases, the extraction rate of each tends to increase.
! Above, only the amount of alumina extracted increased.

If carrier components such as alumina are mixed in the platinum extract from the catalyst, a process to separate platinum and alumina will be required when reusing the solution, so the smaller the amount of alumina eluted, the better. Needless to say, it can be seen that adding too much hydrogen peroxide does not improve the effect.

The present invention is an extraction method in which the extraction effect is improved by the reaction of hydrochloric acid and hydrogen peroxide solution by sequential addition of both, and by repeating this method two or three times, it is possible to obtain an extraction amount close to 100%.

Furthermore, in the present invention, the elution of carrier components such as alumina can be extremely reduced by adjusting the volume ratio of hydrochloric acid and hydrogen peroxide solution added.

In addition, since stirring is not required during extraction, the catalyst does not disintegrate during processing and less powder is generated.

As described above, with the recovery method of the present invention, platinum group elements can be extracted in high yield with a simple ζ-type operation at a relatively low temperature (room temperature is sufficient) and in a short extraction time. It has many advantages, such as being inexpensive because only a small amount is required.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between extraction time and platinum extraction rate.
Figure 2 is a flow sheet for the apparatus for method (5) used in Example 6 of the present invention', Figure 3 is a flow sheet for the apparatus for method (5) used in Example 6 of the present invention', and Figure 4 is a flow sheet for the apparatus for method (5) used in Example 6 of the present invention'. FIG. 5 is a flow sheet of the device EC) used in Example 6 of the present invention, and is a graph showing changes in platinum extraction rate depending on extraction time and hydrochloric acid concentration of the extraction solution. In the figure, 1...Extractor, 2...Liquid level of hydrochloric acid, 3...Top surface of catalyst, 4...Pipe, 5... ... Nozzle, 6 ... Air bypass, 7 ... Switching valve, 8 ... Metering tube.

Claims (1)

[Claims] 1. Add chlorine at a concentration of 20% by weight or more to a platinum-based catalyst in which a platinum group element is supported on a carrier made of alumina, etc., or add a catalyst to hydrochloric acid, and then add the catalyst to hydrochloric acid based on the amount of hydrochloric acid used in the catalyst-hydrochloric acid system. A method for recovering platinum group elements from a platinum-based catalyst, characterized by dissolving the platinum group elements by sequentially adding hydrogen peroxide solution at a ratio of 1.5 to 15% by volume.