JPH021896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering noble 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 is not suitable when precious metals or precious metal alloys are coated on materials such as copper alloys, nickel alloys, printed circuit boards, ceramics, etc. by plating, cladding, baking, etc., or when they contain base metals. Not.
For example, if you try to dissolve this material with a strong acid such as nitric acid or aqua regia, it is highly corrosive and will dissolve base metals and base metals, generating NOx and chlorine gas, causing equipment and equipment to decay 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 base metal may also be dissolved, making reduction difficult, and wastewater treatment of the used alkaline cyanide solution is expensive and uneconomical.

The present invention was made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a highly efficient noble metal solvent extraction method that selectively dissolves noble metals or noble metal alloys, is easy to handle, and is recyclable. .

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 precious metals, which is characterized by extracting precious metals into an organic solvent and then back-extracting the precious metal ions into an aqueous alkaline solution to precipitate the noble metals or noble metal compounds.

In the present invention, a mixed solution containing iodine and iodide is used because an iodide aqueous solution alone will form an iodide film or oxide film on the surface of the precious metal during the reaction, significantly reducing recovery efficiency. This is to prevent the formation of a film or an oxide film. Therefore, even if the coating layer of noble metal or noble metal alloy has a thickness of 0.1 mm or more, it can be melted. Here, iodide refers to an aqueous solution consisting of a compound that liberates iodine ions in an aqueous solution, including potassium iodide,
There are iodides such as sodium iodide. Also,
Iodine, together with the aqueous iodide solution, plays a role in preventing the formation of an iodide film or an oxide film on noble metals such as palladium.

When noble metals such as gold, silver, and palladium and noble metal alloys such as silver-palladium alloy, gold-palladium alloy, gold-silver alloy, and silver-palladium-copper alloy are immersed in this mixed solution,
Selectively noble metals or noble metal alloys are 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 used. Next, add this noble metal solution to
Add an organic solvent such as MIBK or ethyl ether, and shake the whole mixture 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 expensive 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, gold contains MIBK (meta-isobutyl ketone), a mixture of MIBK and isoamyl acetate, ethers (R'-O-R), thioethers (R'-S-R), amberite-
Palladium such as LA1 has thioethers (R'-S-R), X1-8A (oxime solvent)
MIBK, n-octylaniline, etc. for platinum, MIBK, amberite for osmium, etc.
LA1, TOPO (trioctylsulfine oxide), etc. Iridium includes MIBK, tributiphosphate, n-octylaniline, etc. Use the above solvents by diluting them with a diluent. As the diluent, a single or mixed solvent such as non-aqueous xylene, toluene, octane, methylcyclohexane, kerosene, kerosene, carbon tetrachloride, trichlene, etc. is used.

In addition, a masking agent such as EDTA, acetic acid, tartaric acid, citric acid, etc. can be used in combination, if necessary. This masking agent increases the hydrophilicity of base metal elements and noble metal elements other than the noble metal elements to be extracted, and prevents them from migrating into the organic solvent. Since the extraction is not complete in one go, it is usually repeated 3 to 6 times to extract and concentrate only the necessary precious metal elements in the organic solvent.

After the extraction is completed in this manner, the organic solvent is separated and back-extracted into an 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 used to precipitate a desired noble metal element or noble metal compound using a conventional reduction method.

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

Examples of oxidizing agents include hydrogen peroxide, ozone, manganese peroxide, dichromic acid, sodium peroxide, chlorine, and bromine. When salts are formed, they can be separately crystallized and recovered. In addition, examples of reducing agents for precipitating noble metals or noble metal compounds include hydrazine, hydrazine dichloride, hydroxylamine, sulfur dioxide, sodium bisulfite, sodium thiosulfate,
Hydrosulfite, sodium hypophosphite,
Examples include sodium borohydride.

Examples and comparative examples will be described below.

Example 1 1 kg of iron-nickel alloy clad with 2 microns of gold (containing 4.4% gold) was immersed in mixed solution 5 of 2 parts of iodine, 9 parts of potassium iodide, and 22 parts of water. The gold was dissolved in 20 minutes, and the iron-nickel base material was hardly dissolved. This dissolved solution was subjected to solvent extraction with 5% MIBK2 x 5 times and back-extracted with 40% KOH aqueous solution 0.1.

When this solution was reduced with hydrazine, the purity
43.6g of 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
The process was repeated 10 times to recover gold from a total of 10 kg of scrap material, and even in the final process, the gold recovery rate was 99.9%.
It was hot.

Example 2 When a ceramic material with baked silver/palladium paste was immersed in a mixed solution 7 similar to that of Example 1 with 20% ethyl alcohol added, both silver and palladium were dissolved in 60 minutes (silver 3
g/, palladium 0.8 g/).

After neutralizing the iodine in this dissolved solution with 5% KOH solution, palladium was extracted with octyl sulfite solvent 2 x 7 times, and 15% NH ₄ OH aqueous solution 500
Back extracted in mm.

When this solution was reduced with hydrazine dihydrochloride, 5.4 g of palladium with a purity of 99.80 was reduced. The silver remains in the raffinate and is separated from the palladium. This is reduced with hydrazine hydrate to produce silver with a purity of 99.0%.
20.1g was obtained. Note that there are no iodine ions in the organic solvent, and the raffinate (potassium iodide) is reused.

Example 3 2.5 g of iron-nickel alloy tape material (containing 12.5% palladium) containing 20 microns of silver-palladium alloy in a mixed solution of 1 part iodine, 4 parts sodium iodide, 10 parts water, and 3 parts ethyl alcohol.
When immersed in the liquid, palladium was selectively dissolved in 120 minutes. Combine this solution with 1 part MIBK and 9 parts diluent.
When the mixture was extracted with 2x5 portions, back-extracted with a 20% KOH aqueous solution, and reduced with sodium borohydride, 303 g of palladium with a purity of 99.80 was precipitated and recovered.

Conventional example: Dissolve the same material as in Example 1 together with the base in aqua regia, extract chloroauric acid solution 4.3 (HCl concentration 7%) with 1 part MIBK and 9 parts diluent 2 x 5 times, and invert with 40% NaOH aqueous solution. Extracted. When this solution was reduced with hydrazine, 43.4g of gold with a purity of 99.97% was precipitated and recovered with a recovery rate of 98.7%. However, the recovered aqueous potassium chloride solution could not be reused as the initial aqua regia 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. . 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.

Claims (1)

[Claims] 1 After selectively dissolving the precious metal or noble metal alloy by immersing it in a mixed aqueous solution containing iodine and iodide, add an organic solvent (extractant and diluent) to this dissolved solution.
1. A method for recovering precious metals, which comprises adding precious metal ions to an organic solvent to extract the precious metal ions, and then back-extracting the precious metal ions into an aqueous alkaline solution to precipitate a single noble metal or a noble metal compound.