JP2504810B2 - Method for reducing sulfoxide in organic solvent and method for extracting noble metal using the reduction - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for reducing sulfoxide present in an organic solvent to a corresponding sulfide, and particularly utilizing the reduction, containing gold and / or platinum. It relates to a method for solvent extraction of a noble metal without causing precipitation of other base metals.

(Prior art and its problems) An acidic aqueous hydrochloric acid solution containing gold, such as gold, palladium, platinum, rhodium, and a platinum group metal, is used in, for example, a copper electrolytic slime treatment step of copper refining, or a silver electrolytic slime treatment step of silver refining. Generate at.

When the silver electrolytic slime is decomposed with nitric acid, a silver extract and a residue are obtained, and the silver extract is neutralized to once obtain a precipitate, which is dissolved in hydrochloric acid, and gold, platinum, rhodium, palladium, An acidic aqueous hydrochloric acid solution containing a base metal is obtained. On the other hand, even if the residue is subjected to an acid treatment using hydrochloric acid and hydrogen peroxide, the acidic aqueous hydrochloric acid solution can be similarly obtained.

As a method for separating gold, platinum, rhodium and palladium from such a hydrochloric acid acidic aqueous solution, a chemical precipitation separation method has been conventionally adopted. However, in this method, there are problems in that the separation efficiency of the metal is low and the process is complicated and requires skill, and the actual yield is low and the loss of time and money is large.

For this reason, recently, attention has been focused on a solvent extraction method, which has the advantages that the processing steps can be simplified and shortened, the selective separation of metals is sensitive, and the separated metals can be easily purified and recovered. Various concrete methods have been proposed.

For example, in U.S. Pat. No. 3,985,552, when gold, platinum, rhodium and palladium are separated from the acidic hydrochloric acid solution by a solvent extraction method, ferrous sulfate is added to precipitate gold, and the precipitate is separated. A method is disclosed in which the obtained filtrate is brought into contact with an organic solvent using sulfide as an extraction solvent to separate an organic phase containing palladium and an aqueous phase.

However, in the method, when the acidic hydrochloric acid aqueous solution contains tin, zinc or the like in addition to gold, platinum, rhodium and palladium, the sulfide and, if necessary, an organic solvent added with 2-ethylhexanol or octanol is added. When the gold or palladium is extracted by using, the sulfide is oxidized to the corresponding sulfoxide by the gold or platinum, and the palladium is back-extracted from this organic solvent, and then the palladium is again extracted from the acidic aqueous hydrochloric acid solution. A precipitate of the sulfoxide containing tin, zinc, and platinum is generated, which makes the extraction operation difficult.

Also in applications other than these metal extractions, it may be desirable to reduce the sulfoxide present in the organic solvent and convert it to the corresponding sulfide.

(Object of the Invention) It is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art and to make it possible to reuse the organic solvent containing sulfide, particularly after extraction of palladium and / or gold. It is intended to achieve the above object by adding hydrogen sulfide gas and acetic anhydride to an organic solvent to reduce the corresponding sulfoxide, which is an oxide of sulfide, to return to the sulfide.

Another object of the present invention is to provide a method capable of easily reducing sulfoxide in an organic solvent to the corresponding sulfide during extraction with a solvent other than gold or palladium or in applications other than these solvent extractions.

(Means for Solving the Problems) First, the present invention relates to sulfoxide RS (═O) R ′ (R and R ′ are alkyl groups or aryl groups) contained in an organic solvent, hydrogen sulfide gas and A sulfoxide reduction method (hereinafter sometimes referred to as the first invention) characterized by reducing to a corresponding sulfide R-S-R 'with acetic anhydride, and secondly from a medium containing gold and / or palladium. In the method of extracting the gold and / or palladium using an organic solvent, a sulfide R—S—R ′ (R and R ′ are alkyl groups or aryl groups) is added to the organic solvent, and hydrogen sulfide gas and Sulfoxide RS (= generated by oxidation of the sulfide by adding acetic anhydride)
O) R'is reduced to the sulfide to extract the noble metal.

 The present invention will be described in more detail below.

In the present invention, the sulfoxide present in the organic solvent is reduced to the corresponding sulfide according to the following formula (Ac
It is a CH ₃ CO-).

As used _{+ H 2 S → R-S} -R '+ 2AcOH + 1 / 8S 8 the second invention ^{- R-S (= O)} R' + Ac 2 O → ^{[R-S + (-OAc) -R} '+ AcO ] The organic solvent is an aliphatic solvent or an aromatic solvent such as Shelsol D70 or Shelsol 71I (trade name of Shell Chemistry) which is immiscible with water, and the sulfide is diluted with the solvent. The organic solvent used in the first invention is not particularly limited, and usual organic solvents such as chloroform, acetone and various alcohols can be used.

Substituents of sulfide and sulfoxide used in the present invention are not particularly limited, and may be an alkyl group having about 1 to 10 carbon atoms or an aryl group having about 6 to 10 carbon atoms,
Particularly preferred sulfides and sulfides are di-n-hexyl sulfide and di-n-hexyl sulfoxide, respectively.

In the first invention, acetic anhydride is added to the sulfoxide-containing organic solvent so that the ratio of organic phase / aqueous phase is 0.5: 1 to 10: 1, preferably 1: 1 to 5: 1. , Contact both phases by stirring. While stirring, hydrogen sulfide gas is bubbled at a temperature of 20 to 90 ° C. for preferably 1 hour or more. The bubbling reduces the sulfoxide to the corresponding sulfide according to the above reaction formula.

After the bubbling, the stirring is stopped and allowed to stand still to separate the organic solvent and the acetic anhydride, and acetic anhydride is removed. Then, when the hydrogen sulfide remaining in the organic solvent remains to such an extent that it interferes with the subsequent operation, it is removed by washing with, for example, about 0.5 N sodium carbonate.

Also in the case of the second invention, acetic anhydride is added to the organic solvent containing the sulfide and gold and / or palladium and optionally rhodium or platinum, and the both phases are stirred in the same manner. Contact. While stirring, hydrogen sulfide gas is bubbled at a temperature of 20 to 90 ° C. for preferably 1 hour or more. By the bubbling, the sulfoxide contained in the organic solvent is reduced to the corresponding sulfide, and the sulfoxide does not adversely affect the extraction of palladium and the like.

According to the present invention, the sulfoxide concentration can be reduced to about 0.01% by weight. In the second invention, when the amount of sulfoxide is reduced to 0.01% by weight, even if the organic solvent extracted with the metal to be extracted and other metals removed by filtration or the like is used again for the metal extraction, Precipitation of the base metal such as tin or zinc does not occur, the organic solvent can be repeatedly used for extraction operations, and complicated operations such as precipitation removal are unnecessary.

(Example) The present invention will be described in more detail based on the following examples, but the present invention is not limited to the examples.

Example 1 Di-n-hexyl sulfide was dissolved in shell zone D70 containing 0.1% by weight of di-n-hexyl sulfoxide to prepare a 20% by volume solution to prepare an organic solvent.

Acetic anhydride was added to the organic solvent so that the ratio of organic phase / aqueous phase was 2: 1 and the mixture was stirred, and hydrogen sulfide gas was bubbled for 1 hour. Di-n-hexyl in the organic solvent was then added. Sulfoxide was reduced to a concentration of 0.005% by weight.

Example 2 Example 1 except that the amount of di-n-hexyl sulfoxide was 1.42% by weight, the ratio of organic phase / aqueous phase was 1: 1 and bubbling of hydrogen sulfide gas was continued for 3 hours. When a similar operation was performed, di-n-hexyl sulfoxide in the organic solvent was reduced until its concentration became 0.01% by weight.

Example 3 A mixture of 100 g of platinum, 10 g of rhodium and 20 g of palladium, 5 g of zinc and 5 g of tin was dissolved in 12% hydrochloric acid to prepare a hydrochloric acid acidic aqueous solution. To shell sol D70 containing 20% by volume of di-n-hexyl sulfide and 1.0% by weight of di-n-hexyl sulfoxide, acetic anhydride was added to this organic solvent in a ratio of 2: 1 and stirred. Further, hydrogen sulfide gas was bubbled for 1 hour.

 Then the organic and aqueous phases were vigorously stirred for 30 minutes.

The organic phase is separated from the aqueous phase, the organic phase is mixed with an equal amount of water and stirred vigorously, palladium is transferred to the aqueous phase and separated,
It was concentrated and dried to obtain 20 g of palladium (yield 100%). At this time, no precipitation was observed and palladium could be recovered efficiently.

Comparative Example A An attempt was made to recover palladium by the same operation as in Example 3 except that hydrochloric acid was used instead of acetic anhydride and hydrogen sulfide gas was not bubbled. During the extraction of palladium from the organic phase into the aqueous phase, platinum precipitation occurred and pure palladium could not be obtained.

(Effect of the Invention) In the present invention, firstly, the sulfoxide contained in the organic solvent is reduced to the corresponding sulfoxide by using acetic anhydride and hydrogen sulfide gas.

Therefore, it becomes possible to reduce the sulfoxide present in the organic solvent to the corresponding sulfide, preferably at room temperature, and particularly to easily remove the sulfoxide which is preferably not present in the reaction system from the reaction system.

In the present invention, secondly, when extracting the gold and / or palladium from the medium containing gold and / or palladium with an organic solvent, sulfide is added to the organic solvent, and acetic anhydride and The noble metal is extracted while reducing the sulfoxide generated by the oxidation of the sulfide to the sulfide using hydrogen sulfide gas.

Therefore, the presence of zinc, tin, etc., will precipitate the noble metal, especially the metal that precipitates during palladium extraction and inhibits smooth extraction, and the corresponding sulfoxide generated by oxidation of the sulfide by gold, platinum, etc. will be extracted. It can be reduced to the harmless sulfide, and the isolation by extraction of palladium or the like can be carried out more smoothly.

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Claims (4)

(57) [Claims] 1. A sulfoxide RS contained in an organic solvent.
A method for reducing sulfoxide, which comprises reducing (= O) R '(R and R'are alkyl groups or aryl groups) to the corresponding sulfide R-S-R' with hydrogen sulfide gas and acetic anhydride. 2. The method according to claim 1, wherein hydrogen sulfide remaining after being dissolved in an organic solvent is washed with a sodium carbonate solution to be removed. 3. A method for extracting gold and / or palladium from a medium containing gold and / or palladium by using an organic solvent, wherein the sulfide RS is contained in the organic solvent.
-R '(R and R'are alkyl or aryl groups), hydrogen sulfide gas and acetic anhydride are added to form sulfoxide RS (= O) R'.
The noble metal is extracted while reducing the sulfide to the sulfide. 4. The method according to claim 3, wherein hydrogen sulfide dissolved in an organic solvent and remaining is washed with a sodium carbonate solution to be removed.