JP4567169B2 - How to recover precious metals - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for recovering a noble metal from an organic solvent in which a noble metal compound used as a catalyst in an organic synthesis reaction or the like is dissolved.
[0002]
[Prior art]
In many cases, noble metals such as platinum or palladium coexist with inorganic compounds or exist as inorganic compounds of noble metals, and various methods for recovering noble metals from such inorganic states have been reported. For example, when recovering precious metals from automobile exhaust gas purification catalysts, a method has been reported in which amphoteric metals such as aluminum, zinc, tin, lead, and antimony are added to an alkali hydroxide aqueous solution, reduced, precipitated, and recovered (specialty). Kaihei 7-25878).
[0003]
On the other hand, as a method for recovering the noble metal from the noble metal compound dissolved in the organic solvent used by dissolving in the solvent in the organic synthesis reaction, the organic solvent is distilled off and the residue is incinerated to obtain an inorganic noble metal compound, It is further concentrated. However, a large amount of organic components are contained in the residue and the combustion apparatus becomes large, and depending on the organic synthesis reaction, the foreign matter contained in the residue is different. As a result, phosphoric acid having a high hygroscopic property is generated, and the treatment of the exhaust gas is complicated. When sulfur is contained, sulfurous acid gas is generated, and an exhaust gas facility for sulfurous acid gas treatment is required.
[0004]
[Problems to be solved by the invention]
The present invention is a method for recovering a noble metal from an organic solvent in which the noble metal compound is dissolved by directly precipitating the noble metal without burning the organic solvent in which the noble metal compound is dissolved.
[0005]
[Means for Solving the Problems]
The present invention is a method for recovering a noble metal, characterized in that a base metal and a mineral acid are added to an organic solvent in which the noble metal compound is dissolved, the noble metal is reduced and precipitated, and the precipitate is collected by filtration.
[0006]
The method of the present invention will be described in detail as follows.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The noble metal in the present invention is a noble metal is gold, silver, ruthenium, rhodium, palladium, osmium, iridium, or platinum. Is exemplified.
Examples of the organic solvent include organic solvents that dissolve these noble metal compounds. Examples include aliphatic hydrocarbons, aromatic hydrocarbons, ether compounds, alcohol compounds, or aprotic compounds such as tetrahydrofuran, dimethylformamide, and acetonitrile. Although there are polar solvents and the like, all organic solvents can be employed in the method of the present invention as long as they are used in organic synthesis reactions. Moreover, it is the residue of the kettle obtained by removing a solvent from the reaction mixture which used these as a reaction solvent.
Specifically, organic synthesis reactions that are usually catalyzed by precious metal compounds such as Heck reaction of halides and olefins, deallylation reactions or cross-coupling reactions of organic metals and halides are removed. It is usually the residue of a distillation still and contains 0.01 to 1% of noble metal.
[0008]
Magnesium, aluminum, zinc, iron, tin and lead, and alloys containing them can be adopted as the base metal, but lead is preferred from the standpoint of effect and economy, and usually a powder of 5 to 200μ is used. Is done. The amount used is 6 to 16 parts by weight with respect to 100 parts by weight of the organic solvent, and if it is less than this, the yield of the noble metal is low, and even if it exceeds this, the yield does not rise significantly. As the mineral acid, hydrochloric acid, sulfuric acid or nitric acid is used, and concentrated hydrochloric acid is usually used.
[0009]
A predetermined amount of base metal powder is added to the organic solvent in which the noble metal compound is dissolved. Thereafter, the mineral acid is added to the mixture of the organic solvent in which the noble metal compound is dissolved and the base metal powder while mixing. When mixing is intense, the temperature rises and the subsequent filterability deteriorates. It is possible to add a mineral acid in advance and then add and mix a base metal powder, but care must be taken because hydrogen gas to be added at once may be generated rapidly.
The amount of mineral acid used is added and mixed so that the pH of the mixture is 1 or less. Usually, it is about 300-500 weight part with respect to 1000 weight part of organic solvents. Mixing after addition continues at room temperature for 3-5 hours. When the pH exceeds 1, the yield of noble metal tends to decrease. The end point of the reduction reaction can be confirmed by the completion of the generation of hydrogen and the stabilization of the pH (pH 0.9 to 1).
[0010]
After completion of the reduction reaction, it is possible to collect the precipitated noble metal by filtration without neutralization. However, it is necessary to manufacture the equipment with an acid-resistant material, and the equipment cost becomes high.
Therefore, in some cases, it is advantageous to carry out filtration after neutralization.
Neutralization is slightly different depending on the type of base metal used, and is performed by adding a caustic soda aqueous solution to adjust the pH to 3 to 5, preferably 4 to 4.5. For example, pH is preferably 4 to 4.5 when zinc is used, pH 4 to 6 when aluminum is used, pH 4 to 6 when magnesium is used, and pH 3 to 5 when iron powder is used. Even if the pH is higher than these, the quality of the precious metal recovered by precipitation of the base metal is lowered, but the yield of the precious metal is hardly affected.
The adjusted solution with adjusted pH is filtered and separated into a precipitate and a filtrate. A normal method can be employed for filtration, and a Nutsche or a centrifuge can be employed.
[0011]
The obtained precipitate is washed with water as necessary to obtain a recovered precipitate. In the collected precipitate, the precious metal is usually concentrated to 10 to 30% in terms of dry state.
Various ordinary methods can be employed to recover the precious metal from the recovered precipitate obtained.
For example, it can be baked at about 700 ° C. to remove moisture and remaining organic substances, and further concentrated.
The function of the base metal in the present invention is not to precipitate the noble metal in the organic solvent due to the difference in ionization tendency, but is expected to be precipitated by reducing the noble metal compound by active hydrogen in the nascent stage generated by the reaction with hydrochloric acid. The
[0012]
EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the scope of the present invention is not limited to an Example.
[0013]
【Example】
Example 1
The target compound and solvent are recovered by distillation from an organic synthesis reaction mixture containing 62% phosphoric acid ethyl ester, 21% sodium butyrate, 0.3% palladium acetate (containing 0.1% as PdO) and 17% other organic substances. 100 kg of zinc powder (average particle size 12μ) is added to 1.0 ton of the remaining residue and stirred for about 4 hours. Further, 340 kg (280 liters) of 36% concentrated hydrochloric acid is added over about 3 hours, and further 2 hours. Stir.
Further, 20% aqueous sodium hydroxide solution was added to neutralize to pH 4, and the precipitate was filtered. The filtrate was 1.24 tons. The obtained precipitate was washed with 0.6 ton of water to obtain 8.9 kg of wet solid. The water content was 55% and the palladium content was 0.9 kg (the palladium content was 22.5% in the dry state).
Further, it was calcined at 600 ° C. for 30 minutes to obtain 3.6 kg of calcined product of 3.6 kg (palladium 0.9 kg, content 25%).
[0014]
Reference Example The same residue as that used in Example 1 was inserted into a combustion kiln (diameter 0.55 m × length 8 m) at a speed of 10.6 kg / hour, and the residue was burned at a temperature of 750 to 800 ° C. It was. The pot residue became a fine powder with a small bulk specific gravity. The exhaust gas piping and the bag filter were corroded due to the condensation of phosphoric acid and the bag filter was clogged, making it impossible to continue combustion.
[0015]
【The invention's effect】
According to the present invention, when recovering a noble metal from an organic solvent in which the noble metal compound is dissolved, the organic substance can be recovered without including a step of burning. Therefore, the apparatus is economical and suitable as an industrial production method.

Claims (5)

A base metal and a mineral acid selected from magnesium, aluminum, zinc, iron, tin, and lead are added to phosphoric acid ethyl ester in which palladium acetate is dissolved, palladium is reduced and precipitated, and the precipitate is collected by filtration. A method for recovering palladium . The method according to claim 1, wherein the precipitate is collected by filtration after adjusting the pH to 4 to 8 by adding an aqueous caustic soda solution. The method according to claim 1 or 2, wherein the base metal is aluminum, zinc, tin or lead. The method of Claim 3 which adds 6-16 weight part of base metals with respect to 100 weight part of organic solvents. Mineral acid hydrochloride, claims 3 sulfuric acid or nitric acid to 4 A method according.