JP4296706B2 - Method for producing palladium powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing palladium powder by reducing palladium by a wet method from a chloride solution containing a palladium chloride complex.
[0002]
[Prior art]
Palladium is mainly used as a raw material for catalysts and noble metal alloys. This palladium is refined from raw material ores containing palladium such as platinum ore, iridosmine ore, recovered from spent waste catalyst using palladium, and electrolytic slime generated by electrolytic refining of copper and nickel. .
[0003]
In this palladium recovery from electrolytic slime, it is known that palladium behaves in the same manner as silver contained in a large amount in the slime and concentrates in the crude silver. In the method of separating and recovering palladium from this crude silver, first, the crude silver is purified and recovered by electrolytic purification. The silver electrolytic slime generated during the electrolytic purification of the crude silver is dissolved with nitric acid, the silver dissolved in the nitric acid solution is removed as silver chloride, then denitrated, and ammonia water is further added to remove impurities other than palladium. Precipitate as oxide. After removing the precipitated hydroxide, hydrochloric acid is added to precipitate palladium as a crude dichlorodiammine palladium complex.
[0004]
The crude dichlorodiammine palladium complex thus obtained is dissolved in aqueous ammonia as necessary, and purified by adding hydrochloric acid to repeat the formation of a precipitate, thereby increasing the purity. Furthermore, suspending the highly purified Jikuroroji ammine palladium complex in the manner described above in water, and reduced by adding a reducing agent such as hydrazine, it was prepared palladium powder.
[0005]
The pH of the solution in which the dichlorodiammine palladium complex is suspended in water is usually about 5. Even if a reducing agent such as hydrazine is added to this solution to produce palladium powder, the pH during the production reaction is Almost no change at 5-6. However, when excess reducing agent remains in the solution at the end of the reaction, the pH gradually rises to 8-9 or more.
[0006]
However, the palladium powder obtained by the above method has a problem that the particles are very small, so that the scattering property is high and the handling property is poor. For example, when encapsulating in a nylon bag or the like, palladium powder scatters when opening and closing the sealing port, which is not preferable for environmental hygiene, and because the palladium powder adheres to the nylon bag, in order to collect this adhered palladium powder, A treatment such as incineration of the nylon bag is necessary, and there is a problem that the operation is complicated.
[0007]
On the other hand, a production method in which a highly purified dichlorodiammine palladium complex is roasted in a hydrogen atmosphere has also been implemented. According to this method, coarse palladium powder can be obtained, but a large amount of white smoke of ammonium chloride salt is generated at the time of roasting, which causes a problem in environmental hygiene.
[0008]
As a method for solving these problems, for example, a method for producing a palladium powder having large particles by a wet reduction method described in JP-A-10-130703 has been proposed. In this method, ammonia is added to a chloride solution containing a palladium chloride complex to adjust the pH to 8 to 10, and then a reducing agent such as hydrazine is added to obtain palladium powder.
[0009]
According to this method, it is possible to obtain a palladium powder having a larger particle size and less scattering than a palladium powder obtained by a conventional wet reduction method. However, since about 30% of the palladium powder obtained by reduction adheres to the stirrer and the tank wall in a dumpling form, it is necessary to manually scrape off the palladium powder adhering to each reduction treatment, which is a factor in productivity. Was not a very efficient production method.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing palladium powder that solves the above problems, that is, a method for efficiently producing palladium powder having a large particle size by a wet reduction method.
[0011]
[Means for Solving the Problems]
In the method for producing palladium powder according to the present invention, silver electrolytic slime is dissolved, silver in the solution is removed as silver chloride, and ammonia water is further added to precipitate impurities other than palladium as hydroxides. After removing the hydroxide, hydrochloric acid is added to precipitate palladium as a crude dichlorodiammine palladium complex. The obtained crude dichlorodiammine palladium complex is dissolved in aqueous ammonia, and hydrochloric acid is added to repeat precipitation formation. In a method of producing a palladium powder by purifying and suspending this highly purified dichlorodiammine palladium complex in water, adding a reducing agent and reducing it wet, the highly purified dichloroammine palladium complex is included. the chloride solution, the pH of the solution was adjusted to 7.5 <pH <8.0 by the addition of aqueous ammonia And then, the solution of the state of left-dichloro-diammine palladium complex some undissolved, hydrazine, hydrazine hydrate, hydrazine hydrochloride, reducing the palladium added reducing agent is at least one selected from hydrazine sulfate Is a method for producing palladium powder.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In order to solve the above-mentioned problems, various conditions for obtaining large-particle palladium powder were studied by a wet reduction method with low equipment costs. As a result, the conditions for reducing the dichlorodiammine palladium complex in a wet condition are reduced by adding ammonia water to the dichlorodiammine palladium complex and adding a reducing agent to the solution adjusted to pH <7.5 <pH <8.0. As a result, a palladium powder that solves the above problems could be obtained. That is, it has been found that the particle size becomes larger than before, and as a result, an easily handled palladium powder with less scattering and less adhesion is obtained.
[0013]
Usually, a method for obtaining palladium powder from a dichlorodiammine palladium complex is suspended in water as described above, and reduced by adding a reducing agent such as hydrazine. When the particle size of the reduced palladium powder is observed, it is an aggregate of 30 to 50 microns in which primary particles of about 0.1 to 1 microns are aggregated. Moreover, even if it reduces by raising pH with caustic soda, only the palladium powder of the same particle size is obtained, and a palladium powder with a big particle | grain is obtained only when melt | dissolving in ammonia water.
[0014]
The reason for this is not clear, but the size of particles that are usually generated is determined by the amount of nuclei generated during the reduction reaction and the rate of growth of the generated particles. Therefore, the complex obtained by dissolving the dichlorodiammine palladium complex obtained in the method according to the present invention in ammonia water is very stable, and therefore the amount of nuclei generated during reduction is suppressed while the degree of growth is increased. Presumed.
[0015]
When the dichlorodiammine palladium complex is suspended in water, the pH is usually about 5 as described above. When ammonia water is added thereto, the palladium complex dissolves with an increase in pH, and completely dissolves at pH 8 or higher.
[0016]
However, in the present invention, the pH of the solution adjusted with aqueous ammonia is set to 7.5 to 8.0. The reason for this is that when the pH is 8.0 or higher, the dichlorodiammine palladium complex is completely dissolved in ammonia water and then reduced using a reducing agent such as hydrazine, and a palladium powder having a large particle size is obtained. However, the palladium powder adheres on the dumpling to the used stirring blade and the tank wall, and there is a disadvantage that it is necessary to remove the adhered palladium powder.
[0017]
This phenomenon is caused by the fact that the dichlorodiammine palladium complex is very stable in a solution containing ammonia. It is presumed that the nucleus is generated above and grows.
[0018]
In the present invention, in order to suppress this phenomenon, the dichlorodiammine palladium complex is not completely dissolved in a solution to which ammonia is added, but reduction is performed in a state where a partially undissolved palladium complex remains. By using such means, the undissolved dichlorodiammine palladium complex is first reduced to produce nuclei. Since reduced palladium grows on the nucleus, palladium powder having a large particle size can be obtained without adhering to the tank wall or the stirring blade.
[0019]
On the other hand, when the pH is 7.5 or less, the palladium powder does not adhere to the tank wall or the stirring blade, but the particle size is reduced, and only palladium powder with high scatterability during handling can be obtained. is there.
[0020]
On the other hand, if the temperature for reduction is low, the reaction does not proceed sufficiently, whereas if it is high, the reaction is severe and dangerous when a reducing agent such as hydrazine is added. Therefore, the temperature range is preferably about 20 to 80 ° C, more preferably about 40 to 70 ° C. As the reducing agent to be used, any of hydrazine, hydrazine hydrate, hydrazine hydrochloride, hydrazine sulfate and the like can be used.
[0021]
【Example】
Example 1
50 kg (wet) of dichlorodiammine palladium complex is charged into an FRP tank having a capacity of 500 liters, 150 liters of pure water at 50 ° C. is added, and 16 kg of 24% ammonia water is further added. Was dissolved to such an extent that a part of it became undissolved. The pH of this solution was measured and found to be 7.5. Next, the palladium complex was reduced by adding 60% hydrazine hydrate until the palladium concentration of the solution became 0.01 g / liter or less, and the solution was filtered through a Denver filter having an inner diameter of 60 cm and recovered as palladium powder.
[0022]
The reduced palladium powder could be easily recovered without adhering to the tank wall or stirring blade. Further, the collected palladium powder had a good handleability with little scattering and no adhesion to a nylon bag or the like.
[0023]
The particle size of the obtained palladium powder was 97.7 μm at a 50% particle size, and the bulk density was 4.65 g / cc.
[0024]
(Comparative Example 1)
Except that ammonia water was not added, the dichlorodiammine palladium complex was charged into an FRP tank having a capacity of 500 liters and 150 liters of pure water at a temperature of 50 ° C. was added in the same manner as in the examples, and the palladium complex cake. It was used as a slurry. The pH of this slurry was measured and found to be about 5. Next, 60% hydrazine hydrate was added until the palladium concentration of the solution was 0.01 g / liter or less, and palladium was recovered as palladium powder.
[0025]
The recovered palladium powder was scattered during handling, such as being dried and sealed in a nylon bag, and was poor in handleability. The obtained palladium powder had a 50% particle size of 17 μm, a bulk density of 0.83 g / cc, a small particle size and a small bulk density.
[0026]
(Comparative Example 2)
50 kg (wet) of dichlorodiammine palladium complex is charged into an FRP tank having a capacity of 500 liters, 150 liters of pure water at 50 ° C. is added, and 21 kg of 24% ammonia water is further added. Was completely dissolved. The pH of this solution was measured and found to be 9.5. Next, the palladium complex was reduced by adding 60% hydrazine hydrate until the palladium concentration of the solution became 0.01 g / liter or less, and the solution was filtered through a Denver filter having an inner diameter of 60 cm and recovered as palladium powder.
[0027]
About 30% of the reduced palladium powder adheres to the tank walls and stirring blades in a dumpling form, and it is necessary to scrape the palladium powder with a stainless steel spatula, which is very poor in workability. It was.
[0028]
【The invention's effect】
According to the method for producing palladium powder according to the present invention, palladium powder which is large in particle size and easy to handle as compared with the conventional method can be obtained economically.

Claims (2)

Ammonia water is added to the chloride solution containing the dichlorodiammine palladium complex to adjust the pH of the solution to 7.5 <pH <8.0 , and then the partially dissolved dichlorodiammine palladium complex remains. the solution to the reducing agent was added, the production method of palladium powder and obtaining a reduction to palladium powder dichloro-diammine palladium complex in wet. The method for producing palladium powder according to claim 1, wherein the reducing agent is at least one selected from hydrazine, hydrazine hydrate, hydrazine hydrochloride, and hydrazine sulfate.