JPS5976834A - Recovering method of noble metal - Google Patents

Abstract

PURPOSE:To enable recovery of a noble metal in high purity and a high yield by treating metallic parts having the noble metal with an aq. mixed soln. of iodine and an iodine compd. to dissolve selectively the noble metal, and extracting the same into an org. solvent then extracting reversely the noble metal in an aq. alkali soln. CONSTITUTION:The sepn. and recovery of a noble metal from the state that the noble metal coexists with other metals as a result of plating, cladding, backing, etc. or being coated on ceramics, is accomplished by dipping the parts contg. the noble metal into an aq. soln. contg. iodine and an iodide such as sodium iodide or potassium iodide as a dissolving liquid to dissolve and extract selectively the noble metal alone. An org. solvent such as methyl isobutyl ketone, ethyl ether or the like is added to the solution of such noble metal under stirring to extract the noble metal into the org. solvent. The noble metal is extracted reversely by separating the org. solvent and adding an aq. soln. of KOH, then the noble metal ions in the KOH soln. are reduced by hydrazine or the like, whereby the noble metal having extremely high purity is separated and recovered in a high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for recovering precious metals by solvent extraction.

Conventionally, it has been known that noble metals are dissolved using strong acids such as aqua regia or hydrochloric acid, or alkaline cyanide solutions. However, the conventional method does not work when precious metals or precious metal alloys are coated with metals such as copper alloys, nickel alloys, printed circuit boards, ceramics, etc. by plating, cladding, baking, etc., or when they contain base metals. It's not appropriate.

For example, if you try to dissolve this material with a strong acid such as nitric acid or aqua regia, it is highly erodible and will dissolve base metals and base metals, generating NOx and chlorine gas, causing equipment and equipment to deteriorate quickly. When extracting noble metal ions with a solvent, chlorine ions and base metal chloride ions act as interfering factors, significantly reducing recovery efficiency. Furthermore, when dissolved in an alkaline cyanide solution, the composite metal may also be dissolved, making reduction difficult and the cost of wastewater treatment of the used alkaline cyanide solution being expensive and uneconomical.

The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide an efficient solvent extraction method for noble metals that selectively dissolves noble metals or noble metal alloys, is easy to handle, and can be recycled. .

The present invention involves selectively dissolving noble metals or noble metal alloys by immersing them in a mixed aqueous solution containing iodine and iodide, and then adding an organic solvent (extractant and diluent) to this dissolved solution to obtain noble metal ions. This is a method for recovering noble metals, which is characterized in that the noble metal ions are extracted into an organic solvent and then the noble metal ions are back-extracted into an alkaline aqueous solution to precipitate the noble metal alone or the noble metal compound.

In the present invention, a mixed solution containing more oxides and iodine is used because if an iodide aqueous solution is used alone, an iodide film or oxide film will be formed on the surface of the precious metal during the reaction, which will significantly reduce the recovery efficiency. This is to prevent the formation of a chemical film or an oxide film.

Therefore, the thickness of the noble metal or noble metal alloy coating layer is 0.
．． Even 1 dragon or more can be dissolved. Here, the compound refers to an aqueous solution consisting of a compound that liberates iodine ions in an aqueous solution, and includes iodides such as potassium iodide and sodium iodine. Further, iodine, together with the iodide aqueous solution, plays a role in preventing the formation of an iodide film or an oxide film of noble metals such as palladium.

In this mixed solution, gold &1. Noble metals such as palladium, silver-palladium alloys, and gold-palladium alloys.

When a single noble metal alloy such as a gold-silver alloy or a silver-palladium-copper alloy or a coated material is immersed, the noble metal or noble metal alloy is selectively melted. Therefore, it is possible to prevent elements other than the noble metal elements from dissolving in the mixed solution. The concentration of iodide and iodine in the mixed solution is determined by the amount of noble metals etc. to be dissolved, and they react even at room temperature. To accelerate the reaction, stirring or heating at a temperature of 40°C to 80°C may be performed. Next, MIB is added to this noble metal solution.
An organic solvent such as K, ethyl ether, etc. is added, and the whole is shaken using a shaker to perform solvent extraction.

At this time, other elements than the noble metal elements are difficult to dissolve unlike in the aqua regia solution, so the noble metals can be extracted with high efficiency. In addition, iodine ions have lower chemical reactivity than chloride ions and can prevent aging of valent organic solvents. Since it is thought that in the iodine complex of a noble metal, some of the iodine groups are substituted and extracted into a solvent, the type of organic solvent used differs depending on the type of noble metal. For example, M113K for gold
(meta-isobutyl ketone), a mixture of MIBK and isoamyl acetate, ethers (R'-0-R).

Thioethers (R'-3-R), amparite-
In LAl, palladium contains thioethers (R'-5
-10,
For osmium, use M113, amparite-LA 1
．． 'I'OPO (trioctylsulfine oxide), etc.
Iridium has M113, tributyphosphate l-,
n-octylaniline and the like. Use the above solvents by diluting them with a diluent. Non-aqueous xylene as a diluent;
Single or mixed solvents such as toluene, octane, methylschiff Ij'\xane, kerosene, kerosene, carbon tetrachloride, trichlene, etc. are used.

Incidentally, a masking agent such as EDT A, acetic acid, tartaric acid, citric acid, etc. can be used in combination, if necessary.

This masking agent prevents the hydrophilicity of base metal elements other than the noble metal elements to be extracted and the precious metal C# from transferring into the solvent. Since the extraction is not complete in 3 to 6 times, the process is usually repeated 3 to 6 times to extract and concentrate only the precious metal elements necessary in the organic solvent.

After the extraction is completed, the organic solvent is separated as shown below.
Back-extracted into aqueous alkaline solution. At this time, the iodide ions of the noble metal are directly extracted as an alkali compound, so that the iodine ions do not accumulate in the organic solvent and can be reused.

The back-extracted noble metal element ions are subjected to a conventional reduction method to precipitate the desired noble metal element or noble metal compound.

When regenerating the initially used mixed solution containing iodine and iodide, by adding an oxidizing agent to make the pH acidic, it can be used as the original mixed solution and chemicals can be saved.

Examples of oxidizing agents include hydrogen peroxide and ozone.

Manganese peroxide, dichromic acid, sodium peroxide.

These include chlorine and bromine. If salt occurs, remove the salt separately.
What is necessary is to crystallize it into M and collect it. In addition, examples of reducing agents for precipitating noble metals or noble metal compounds include hydrazine and hydrazine dichloride.

Hydroxylamine, sulfur dioxide, sodium bisulfite, sodium thiosulfate, hydrosulfite, next!
lI! Sodium monoxide, Sodium borohydride
, Y etc.

Hereinafter, a conventional example will be described.

[Example 1] A lkir material (containing 4.4% gold) prepared by adding 2 parts of gold to an iron-nisogal alloy and adding 2 parts of gold to it was immersed in 5β of a mixed solution of 2 parts of iodine, 9 parts of potassium iodide, and 22 parts of water. However,
Gold was melted in 20 minutes at 25°C, and the iron-Ninogal base material was hardly melted. Add this solution to 5% MIBK.
Solvent extraction with 2β x 5 times and 40% KOH aqueous solution 0.1
/ was back-extracted.

When this solution was reduced with hydrazine, the purity was 99.98.
% gold was precipitated and recovered with a recovery rate of 99.9%. In addition, the recovered aqueous potassium iodide solution was returned to the initial mixed solution for use. The above process was repeated 10 times and gold was recovered from a total of 10 kg of scrap material.
Even in the final step, the gold recovery rate was 99.9%.

[Example 2] A ceramic material made by baking a silver/palladium paste into a mixed solution 71 similar to that of Example 1 with 20% ethyl alcohol added was made into a '&? As a result of A, both silver and palladium were dissolved (3 g/L of silver, 0.8 g/β of palladium) in 60 minutes.

After neutralizing iodine in this dissolved solution with 5% KOH, palladium was extracted with octyl sulfide solvent 21×7 times, and back-extracted with 15% NH40) (aqueous solution 500we).

When this solution was reduced with hydrazine dihydrochloride, the purity was 9.
9.80% palladium was reduced by 5.4g. The silver remains in the raffinate and is separated from the palladium. This was reduced with hydrazine Hitlerde to obtain 20.1 g of silver with a purity of 99.0%. Note that there are no iodine ions in the organic solvent, and the raffinate (potassium iodide) is reused.

[Example 3] 2.5 kg of iron-Nisokel alloy tape material made by cladding 20 microns of silver-palladium alloy in a mixed fa solution lOβ of 1 part of iodine, 4 parts of sodium iodide, 10 parts of water, and 3 parts of ethyl alcohol. 12.5% content), palladium was selectively dissolved in 120 minutes. This solution was extracted with 1 part of MIBK and 9 parts of diluent 21 times 5 times, back-extracted with 20% KOH aqueous solution, and reduced with sodium borohydride. As a result, 303 g of palladium with a purity of 99.80 was precipitated and recovered. .

[Conventional example]

Same material as Example 1! 4 along with the base material in soil water and mixed with gold chloride rlIi solution 4.3A (HCI concentration 7%).
Extracted with 1 part HK and 9 parts diluent 21 times 5 times, 4 parts% Na
Back extraction was performed with an OH aqueous solution. When this solution was reduced with hydrazine, 43.4 g of gold with a purity of 99.97% was precipitated and recovered with a recovery rate of 98.7%. However, the recovered potassium chloride solution could not be reused as the original soil water or chloroauric acid solution.

As detailed above, the method for recovering precious metals according to the present invention has the effect of being able to melt the necessary precious metal or precious metal alloy without melting the base material, and also has the effect of being able to be used repeatedly if recycled. be. It goes without saying that a buffer or the like may be added, if necessary, within a range that does not inhibit the reaction of the present invention.

Applicant: Tanaka Kikinzoku Kogyo Co., Ltd.

Claims (1)

[Claims] After selectively dissolving noble metals or noble metal alloys by immersing them in a mixed aqueous solution containing iodine and iodide, an R solvent (extractant and diluent) is added to this dissolved solution to remove noble metal ions in an organic solvent. 1. A method for recovering precious metals, which comprises extracting the precious metals into an alkaline aqueous solution, and then back-extracting the precious metal ions into an alkaline aqueous solution to precipitate the noble metals or νI metal compounds.