JPS6139384B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for recovering palladium by solvent extraction. In particular, it concerns a method for recovering palladium contained in industrial waste and the copper smelting process. (Prior art) Palladium is currently widely used as catalysts, electrical and electronic materials, dental materials, etc., and is one of the rare metals indispensable for industrial use. It is in a position that competes for number one or number two in the world. On the other hand, considering that the only palladium resources in Japan are those produced by-products such as copper smelting, and most of the raw material copper concentrate is imported from abroad,
This means that Japan is dependent on foreign countries for almost all of its palladium resources. However, recently, in addition to relying on foreign countries, there has been an urgent need to establish technology to efficiently recover palladium from waste such as used catalysts and recycle it as a resource. . Currently, palladium is recovered from waste by dissolving the waste in aqua regia and then reducing it using powdered zinc or copper, formic acid, or formalin. However, this method has the drawback that it is very difficult to separate other metals, especially other platinum group elements with similar properties, and because it uses aqua regia, it generates harmful nitrogen oxides. . On the other hand, in recent years, from the perspective of energy saving, a selective and efficient separation technology for trace metal ions has been developed.
Solvent extraction methods and ion exchange methods are attracting attention.
Recently, metal refining plants using such solvent extraction methods and ion exchange methods have been constructed in South Africa and the United Kingdom and are in successful operation. Among these methods, the most important aspect of the solvent extraction method is to selectively separate the metal to be recovered from other metals, that is, to select an extractant with high selectivity for the target metal. be. According to Pearson's concept of “hard acids, soft acids and hard bases, soft bases” (see,
RGPearson; J.Amer.Chem.Soc., 3533
(1963)), palladium is classified as a typical soft acid. Therefore, when selectively extracting palladium, it is preferable to use a sulfur compound that acts as a soft base as an extractant. Extractants using sulfur compounds include dialkyl sulfides, petroleum sulfides contained in crude oil, and sulfoxides obtained by oxidizing these. Among these, dioctyl sulfide, which is a type of dialkyl sulfide, is used for palladium recovery at Inco's Acton refinery in the UK. The use of petroleum sulfides is also being actively developed in the Soviet Union. (Problems to be Solved by the Invention) The aforementioned dialkyl sulfides and petroleum sulfides are excellent extractants with high selectivity for palladium, but their extraction ability is still not always satisfactory. Rather, several extractions are required to almost completely recover the palladium contained in the sample aqueous phase. The object of the present invention is to develop a powerful extractant capable of almost completely recovering palladium contained in a sample aqueous phase and to find advantageous operating conditions for this purpose. On the other hand, the excellent extraction performance of the extractant means that back extraction is sometimes very difficult. It is also an object of the present invention to find an effective back extraction solution to overcome this point. (Means for solving the problems) In order to solve these problems, the present invention has the following features:
A method for recovering palladium using 1,2-bis(alkylthio)ethanes as an extractant is provided.
It has been found that this extractant has an extraction performance comparable to, or even better than, the above-mentioned sulfides, depending on the conditions. The 1,2-bis(alkylthio)ethanes used in the present invention have the general formula R ₁ --S-CH ₂ CH ₂ --S-R ₂ (where R ₁ and R ₂ are linear chains with the same or different number of carbon atoms). or branched alkyl group)
It is expressed as This 1,2-bis(alkylthio)
Ethanes can be a single type of ethane or a mixture of two or more types. A mixture may be used from the viewpoint of availability and price in the market. The number of carbon atoms in R ₁ and R ₂ in the formula is preferably 6 to 8. When the number of carbon atoms is too low, problems arise such that the complex formed by the reaction between the extractant and palladium is not soluble in organic solvents and forms a precipitate, or the extractant becomes easily soluble in water, resulting in loss of the extractant. .
Also, if the number of carbon atoms is too large, the extractant will become viscous,
A problem arises in that phase separation of aqueous phase/organic phase becomes difficult. Therefore, a compound having a carbon number within the above range is preferred because it does not have such problems, can be obtained at the lowest cost as an industrial reagent, and has excellent extraction performance. The 1,2-bis(alkylthio)ethanes used in the present invention can be prepared, for example, by the following reaction with one or two corresponding alkanethiols, 1,2-dibromoethane, and potassium hydroxide, which can be obtained at low cost as industrial chemicals. Formula R ₁ SH＋R ₂ SH＋CH ₂ BrCH ₂ Br＋2KOH →R ₁ ―S―CH ₂ CH ₂ ―S―R ₂ ＋2KBr＋
According to 2H ₂ O, it can be easily synthesized in methanol in high yield. As the alkanethiol, a linear or branched chain compound may be used, and a mixture of isomers as well as a single compound may be used as is. Possible aqueous media for dissolving palladium include chloride aqueous solutions, nitrate aqueous solutions, and sulfate aqueous solutions, but from a practical standpoint, chloride aqueous solutions, especially hydrochloric acid, are optimal in terms of price and ability to dissolve palladium. Therefore, in the present invention, it is preferable to use hydrochloric acid as the aqueous phase medium. Using hydrochloric acid as the aqueous phase medium, FIG. 1 shows the results of a comparison between the extraction performance of palladium by the conventional method and the extraction performance of palladium according to the present invention from hydrochloric acid containing palladium at a concentration of about 100 ppm. In both extractions, toluene was used as a diluent, and its concentration was 0.01 mo/ ^dm3 ;
The mixture was shaken and mixed in an incubator kept at ℃ for about 4 days. The vertical axis is the extraction percentage (%)
, and the horizontal axis indicates the aqueous phase hydrochloric acid concentration (mo/dm ³ ). The 〇 mark indicates the case where di-n-hexyl sulfide, which is a type of sulfide, is used by the conventional method, and the △ mark indicates the case where 1, which is a type of 1,2-bis(alkylthio)ethane, is used according to the present invention. , 2-bis(tertiaryhexylthio)ethane is used. From the figure, excluding the high concentration hydrochloric acid region with a concentration of 6 mo/dm ³ or more, the extraction ability when using 1,2-bis(tertiaryhexylthio)ethane used in the present invention is higher than the conventional method. It is clear that it is superior. The 1,2-bis(tertiaryhexylthio)ethane used here was prepared by the above method using tertiaryhexanethiol (manufactured by Tokyo Kaisha Ltd., isomer mixture) as a raw material. The extractant used in the present invention can be used alone or in combination with a diluent, a modifier, etc. Diluents include aliphatic hydrocarbons such as kerosene and heptane, aromatic hydrocarbons such as toluene and xylene, or polar organic compounds such as halogen-containing organic compounds such as 1,2-dichloroethane and chloroform. . Branched extractants can generally be used with any of the diluents described above. However, when 1,2-bis(n-alkylthio)ethanes, which have a straight chain, are used with aliphatic hydrocarbons or aromatic hydrocarbons with low polarity, if the palladium concentration in the organic phase increases to a certain extent, Precipitates easily.
For this reason, when using a diluent for a linear extractant, it is preferable to use a polar compound, and when using a diluent with low polarity, higher alcohols such as octyl alcohol, decyl alcohol, etc. Add as a quality agent. The palladium thus extracted from the aqueous solution with the extractant used in the present invention can be back-extracted using a back-extraction solution. In this case, it is preferable to use an aqueous solution of a thio compound selected from the group consisting of thiourea, thiosulfates such as ammonium thiosulfate and sodium thiosulfate, and thiocyanates such as ammonium thiocyanate and sodium thiocyanate as the back extraction solution. Can be reverse extracted. Thereby, even more pure palladium can be recovered. Hereinafter, the present invention will be specifically explained with reference to Examples. (Example) [Example 1] Take 0.01 dm ³ of hydrochloric acid with a concentration of 1 to 12 mo/dm ³ containing palladium at a concentration of about 100 ppm as shown below as the aqueous phase, and add 1 dm 3 of hydrochloric acid with a concentration of 0.01 mo/dm ³ as shown below. , 2-bis(tertiaryhexylthio)ethane in a toluene solution of 0.01 dm ³ in an incubator kept at 30°C for about 4 days, palladium in the aqueous phase was extracted as follows.

[Example 2]

Take 0.01 dm ³ of hydrochloric acid with a concentration of 1 to 8 mo/dm ³ containing palladium at a concentration of about 100 ppm as shown below as the aqueous phase, and dilute 1,2-bis(tertiaryhexylthio)ethane as shown below. Organic solution diluted in a concentration of 0.01 mo/dm ³
When the mixture was shaken and mixed with 0.01 dm ³ in an incubator maintained at 30°C for about 4 days, palladium in the aqueous phase was efficiently extracted as shown below.

【table】

[Example 3]

1 to 8 mo/dm ³ of hydrochloric acid containing palladium at a concentration of approximately 100 ppm as shown below as the aqueous phase.
Take ^0.01dm3 and dilute 1,2-bis(n-hexylthio)ethane with each diluent shown below.
An organic solution with a concentration ^{of 0.01 mo/dm 3 and}
When the mixture was shaken for about 4 days in an incubator kept at 30°C, palladium in the aqueous phase was completely extracted in each case as shown below.

[Example 4]

1,2-bis(n) at a concentration of 0.01 mo/ ^dm3 containing approximately 120 ppm palladium as shown below.
- Take 0.01 ^dm of 1,2-dichloroethane or chloroform solution of 1,2-hexylthio)ethane or 1,2-bis(tertiaryhexylthio)ethane,
2mo/dm ³ ammonium thiosulfate aqueous solution
When the mixture was shaken and mixed with 0.01 dm ³ , palladium in the organic phase was back extracted into the aqueous phase as follows.

[Example 5]

0.01mo/ containing 111ppm palladium
Take 0.01 dm ³ of a toluene solution of 1,2-bis(tertiaryhexylthio)ethane with a concentration of dm ³ ,
When mixed with 0.01 dm ³ of various back extraction solutions shown below at a concentration of 2 mo/dm ³ , palladium in the organic phase was back extracted into the aqueous phase in the following proportions. Back extraction solution Back extraction percentage Thiourea 85% Ammonium thiosulfate 80% Ammonium thiocyanate 74% [Example 6] Hydrochloric acid at a concentration of 2 to 10 mo/dm ³ containing palladium at a concentration of about 100 ppm as shown below as the aqueous phase A toluene solution of 1,2-bis(tertiary octylthio)ethane ^with a concentration of 0.01 mo/dm ³ was added to a toluene solution of 0.01 dm ³ of After vigorous shaking using a V-DN shaker for about 24 hours, palladium in the aqueous phase was extracted as shown below.

[Example 7]

Equimolar amounts of tertiary octanethiol, tertiaryhexanethiol and 1,2
- Take 0.01 ^dm of 0.29 g of 1,2-bis(alkylthio)ethane, which was synthesized from dibromoethane and has alkyl chains with different numbers of carbon atoms, in 100 c.c. of toluene, and prepare as follows. Approximately as shown
2 to 10 mo/containing palladium at a concentration of 100 ppm
Hydrochloric acid with a concentration of 0.01 dm ^{3 and} vigorous shaking for about 24 hours in a V-DN shaker manufactured by Iwaki Co., Ltd. installed in a 30°C air temperature chamber, the palladium in the aqueous phase was as follows. extracted as.

[Table] Palladium extracted into the organic phase is 2mo/ ^dm3
When an aqueous solution of thiourea with a concentration of 100% was mixed with equal amounts of the aqueous phase and the organic phase, 100% complete back extraction was achieved. (Effects of the Invention) According to the present invention, palladium contained in the aqueous phase can be almost completely recovered as shown in the Examples. Furthermore, back extraction can be easily performed. Further, according to the present invention, as shown in FIG. 1, it is possible to provide a recovery method that has a higher extraction ability than dialkyl sulfides, which have conventionally been excellent as extractants for palladium.

[Brief explanation of the drawing]

FIG. 1 is a graph comparing the palladium extraction performance according to the conventional method and the palladium extraction performance according to the present invention. ◯ indicates the conventional method using di-n-hexyl sulfide, and △ indicates the present method using 1,2-bis(tert-hexylthio)ethane.

Claims (1)

[Claims] 1. The extractant has the following formula R ₁ --S-CH ₂ CH ₂ --S-R ₂ (R ₁ and R ₂ in the formula are linear or branched chains having the same or different number of carbon atoms. (indicates an alkyl group)
A method for recovering palladium by solvent extraction, characterized by using one or more types of 1,2-bis(alkylthio)ethanes represented by: 2. The recovery method according to claim 1, wherein R ₁ and R ₂ have 6 to 8 carbon atoms. 3 As an extractant, the following formula R ₁ -S-CH ₂ CH ₂ -S-R ₂ (R ₁ and R ₂ in the formula represent a straight chain or branched alkyl group having the same or different number of carbon atoms) is used. Palladium is extracted with a solvent using one or more of the 1,2-bis(alkylthio)ethanes shown below, and the extracted palladium is further extracted with a thio compound selected from the group consisting of thiourea, thiosulfate, and thiocyanate. A method for recovering palladium by solvent extraction, which is characterized by back extraction into an aqueous solution of palladium.