JP4524593B2 - Noble metal solution and method for dissolving and recovering noble metal using this solution - Google Patents

Description

  The present invention relates to a precious metal solution and a precious metal dissolution / recovery method using the precious metal, and in particular, electronic components, electronic devices, medical devices, jewelry, and the like having members made of precious metals. The present invention relates to a precious metal solution for dissolving and recovering precious metals from industrial equipment and the like, and a method for dissolving and recovering precious metals using this solution.

  In various industrial fields such as electronic parts, electronic equipment, medical parts, medical equipment, jewelry, automobiles and chemical plants, members made of various precious metals such as gold, silver, platinum and palladium are used in various places. ing. Since these noble metal members are expensive, it is desirable to collect and reuse these parts and equipment when they become scrap. However, for example, precious metal members used as electronic components and large-scale integrated circuits and wiring materials in electronic devices are difficult to collect and reuse individually because of the high-density mounting. . For this reason, in such a case, generally, the parts including these noble metal members are pulverized, and when molded with resin or the like, after incinerating the mold part, the noble metals are dissolved from the incineration residue, A method of extracting and collecting is employed.

  In dissolving this noble metal, industrially, a mineral acid such as hydrochloric acid, nitric acid, sulfuric acid, or an alkaline cyanide solution is used in combination with an oxidizing agent as necessary. .

  Among these precious metal solutions, aqua regia with a combination of hydrochloric acid and nitric acid can dissolve precious metals such as gold, platinum and palladium, but at the same time dissolves many other metal components together. It is unsuitable to selectively dissolve and recover species. On the other hand, a combination of an alkaline cyanide solution and an oxidizing agent can selectively dissolve gold and silver, but extremely toxic cyanide is used, and in some cases, cyanide gas is generated. Therefore, there is a serious problem in terms of handling of the dissolved solution and maintenance of the working environment. For these reasons, there is a need for a highly selective and safe dissolution method for dissolving noble metals.

  In addition to the aqua regia dissolution method, the chemical engineering papers (Vol. 27 No. 3 (2001)) include bleaching powder-hydrochloric acid / sodium chloride method, iron (III) -sulfuric acid / thiourea method, iodine / iodide method. Each leaching dissolution method by is described.

  Of these, the bleaching powder-hydrochloric acid / sodium chloride method can dissolve gold and palladium, but the dissolution rate per unit time is only about 1/3 compared with other methods. Further, in the iron (III) -sulfuric acid / thiourea method, gold and silver can be dissolved, but the dissolution rate of gold is lower than that in the bleaching powder-hydrochloric acid / sodium chloride method.

In contrast, in the iodine / iodide method, gold and palladium can be dissolved. In particular, for gold, a dissolution rate comparable to that of an aqua regia system can be obtained. Since the complex stability constant of iodine with iodine is high, it is suitable for selective dissolution of gold from a material containing a large amount of gold. However, the iodine / iodide method contains iodine, so depending on the temperature and usage conditions, iodine sublimates in small amounts, causing problems and work on corrosion of metal materials such as the inside of equipment and piping. Had a problem of diffusion to the environment.
Chemical Engineering Papers (Vol.27 No.3 (2001))

  The present invention can selectively and efficiently dissolve and extract a noble metal from a noble metal member, particularly a large-scale integrated circuit or wiring material in an electronic component or electronic device, and does not contain a toxic substance such as cyan, Also, there is no problem of equipment corrosion or environmental pollution due to sublimation, and a safe and highly stable solution, and this solution can be used to efficiently and selectively dissolve precious metals in a high yield. The object is to provide a method of recovery.

Solution of the noble metal of the present invention, iodine and / or iodide ions, ethylene glycol, diethylene glycol, propylene glycol, and the one or more organic solvents selected from the group consisting of glycerol, relative to the organic solvent 1 to 90% by weight of water .

  The method for dissolving a noble metal of the present invention is characterized in that the noble metal is brought into contact with such a solution to dissolve the noble metal in the solution.

  The noble metal recovery method of the present invention is thus characterized in that after the noble metal is dissolved in the solution, a reducing agent is added to precipitate the noble metal.

That is, as a result of intensive studies to solve the above problems, the present inventors have found that noble metals, particularly gold, can be used as long as it is a solution obtained by adding iodine and / or iodide ions to a specific organic solvent containing water. the can be dissolved in high speed and high density, yet it is possible to suppress the sublimation of iodine, and after dissolving the noble metal in the solution, by adding a reducing agent, and reducing the noble metal ions dissolved The inventors have found that noble metals can be recovered easily and with a high yield, thereby completing the present invention.

  The precious metal solution of the present invention is a safe and highly stable solution that does not contain toxicity such as cyanide, and there are few problems of sublimation of iodine. The problem of diffusion to the environment can be suppressed. For example, by simply immersing a noble metal member in such a solution of the present invention, noble metals, particularly gold, can be selectively dissolved at a high speed and a high concentration, and a reducing agent can be added to the solution in which the noble metal is dissolved. By adding, the dissolved noble metal ions can be reduced and the noble metal can be easily recovered in a high yield.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, the noble metal solution containing iodine and / or iodide ions and a specific organic solvent will be described.

  It is preferable to adjust the iodide ion in the solution of the present invention using an iodide salt or the like. The cation of the iodide salt is not particularly limited as long as it stably dissolves a noble metal, particularly gold, and does not adversely affect the dissolution of the noble metal. Specifically, alkali metal ions, ammonium ions, 1 2, 3, or quaternary alkyl ammonium ions, phosphonium ions, sulfonium ions, and the like. Alkali metal ions such as sodium ions and potassium ions are preferable, and potassium ions are particularly preferable. These cations may be used alone or in combination of two or more cations.

As the oxidizing agent, iodine (I ₂ ) may be used directly, or an oxidizing agent that oxidizes iodide ions (I ⁻ ) in the liquid to form iodine (I ₂ ) may be added. As such an oxidizing agent, any oxidizing agent can be used as long as it can oxidize iodide ions (I ⁻ ) in the solution to form iodine (I ₂ ). Specific examples include iodic acid (HIO ₃ ), periodic acid (HIO ₄ ), and salts thereof. Among these, iodine (I ₂ ) is preferably used when preparing a solution in consideration of solubility in the solution and stability in the solution.

What is necessary is just to select suitably the content of the iodine element in the solution of this invention according to the quantity of the noble metal ion to dissolve. That is, when adjusting the solution, the amount of oxidizing agent such as iodine (I ₂ ) required for the desired amount of precious metal dissolved may be selected as necessary.

The elemental iodine content in the solution of the present invention is the amount of iodide ions or noble metal complex ions of noble metal in the solution, and the remaining amount when iodine (I ₂ ) is used to dissolve the noble metal. Regardless of the form of iodine present, the total amount of iodine contained in the solution is a value converted to iodine element. This value may be obtained by calculating from the amount of the raw material used when preparing the solution. The content of elemental iodine in the solution of the present invention is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, and particularly preferably 5% by weight with respect to the whole solution. % Or more. The upper limit of this content is usually 75% by weight or less, preferably 50% by weight or less, more preferably 30% by weight or less, and particularly preferably 20% by weight or less. If the content of elemental iodine is less than this lower limit, the solubility of noble metals will be inferior. If the content is too high, the solubility of noble metals will improve, but the amount of iodine sublimation will increase and corrosion and work of metal materials such as equipment will occur. It is not preferable due to environmental discharge.

Further, when containing both iodine (I ₂₎ and iodide ions in solution, iodine (I ₂₎ the weight ratio of iodide ions (iodine (I _2): Iodide ions), a noble metal There is no particular limitation as long as it can be dissolved stably and the desired effect of the present invention is not impaired.

However, if the content of iodine (I ₂ ) in the solution is too high, for example, when dissolving a noble metal, the sublimation of iodine (I ₂ ) in the solution becomes significant, and the change in the dissolution rate increases due to the composition change. In addition, problems such as device corrosion and iodine diffusion due to iodine sublimation may be undesirable. Therefore, the iodine (I ₂ ) content in the solution of the present invention is preferably low as long as the performance as a solution is not impaired. When iodine and iodide ions are used as the iodine source, the weight at the time of charging is usually used. as a ratio, iodine _(I 2): the iodide ion, 1: 2 to 1: 1000, preferably 1: 3 to 1: 100, more preferably 1: 5 to 1: 30.

  The solution of the present invention contains at least one of polyhydric alcohol, polyether, and cyclic lactone as an organic solvent. The solution of the present invention only needs to contain these organic solvents, and may further contain water.

  Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, pinacol and the like as the polyhydric alcohol having two alcoholic hydroxyl groups. Examples of the polyhydric alcohol having 3 alcoholic hydroxyl groups include glycerin, and examples of the compound having 4 or more alcoholic hydroxyl groups include sorbitol. As the polyhydric alcohol, low molecular weight polyvinyl alcohol or the like can also be used.

  As the polyether, a water-soluble solvent having 2 to 5 alcoholic hydroxyl groups is preferable, and examples thereof include polyethylene oxide, polypropylene oxide, and polyphenylene oxide. Examples of the polyethylene oxide include diethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol. Examples of the polypropylene oxide include propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, and polypropylene glycol. Also, glycols of ethylene / propylene copolymer obtained by block copolymerization of ethylene oxide and propylene oxide can be used.

  The cyclic lactone is preferably a 5- or 6-membered cyclic lactone, and includes β-lactone, γ-lactone, δ-lactone, and the like.

  These organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The type of the organic solvent used in the present invention is not particularly limited as long as it is a liquid at room temperature and can be satisfactorily dissolved in noble metal and has sufficient solubility in the solute, but 2 to 5 alcoholic substances in the molecule. A water-soluble solvent having a hydroxyl group or a cyclic lactone having a 5- to 6-membered ring is preferable.

  Of these organic solvents, the water-soluble solvent having an alcoholic hydroxyl group is more preferably a dihydric alcohol or a trihydric alcohol. Among them, ethylene glycol, diethylene glycol, propylene glycol, and glycerin are preferable, and the cyclic lactone is preferably γ-butyrolactone. . Among these, ethylene glycol and diethylene glycol are particularly preferable. Most preferred is diethylene glycol, which is advantageous in that the dissolution rate of the noble metal is high.

  The content of the organic solvent in the solution of the present invention is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 55% by weight or more with respect to the whole solution. In general, it is 95% by weight or less, preferably 90% by weight or less, more preferably 85% by weight or less, and particularly preferably 80% by weight or less. If the amount of the organic solvent is larger than this range, the proportion of other components such as iodine is relatively reduced, so that the solubility of the noble metal is poor. If the amount of the organic solvent is small, the stability of the solution is poor.

  When the solution of the present invention contains water, the content thereof is usually 1% by weight or more, preferably 5% by weight or more, more preferably 7% by weight or more, particularly preferably 10% by weight based on the entire solution. The above is usually 85% by weight or less, preferably 50% by weight or less, more preferably 40% by weight or less, and particularly preferably 30% by weight or less. The ratio of water to the organic solvent is preferably 1% by weight or more, preferably 5% by weight or more, more preferably 7% by weight or more, particularly preferably 10% by weight or more, and usually 90% by weight or less, preferably It is 60% by weight or less, more preferably 50% by weight or less, and particularly preferably 40% by weight or less.

  When the solution contains water, the solubility of iodide ions and the solubility of iodine thereby are also improved, and the effect of increasing the amount of dissolved noble metal is obtained, but the water content is from the above range. If the amount is too large, the dissolution amount of the noble metal is decreased, and the sublimation amount of iodine is increased, which is not preferable.

The solution of the present invention may further contain a water-soluble polymer (including oligomers). By containing the water-soluble polymer, the wettability of the substance to be dissolved is improved, the complexation stabilization of the dissolved noble metal ions and The effect of suppressing sublimation of iodine is exhibited. In this case, the type of the water-soluble polymer to be used is not particularly limited as long as it dissolves well in the solution and has sufficient solubility in the solvent, but the solubility of the noble metal in the solution and iodine In consideration of the effect of suppressing sublimation, the water-soluble polymer has at least one substituent selected from the following substituent groups (D1) to (D3) in the main chain or side chain of the repeating unit structure. Is preferred.
(D1) Acidic substituent group: —CO ₂ H, —SO ₃ H, —PO ₃ H ₂
(D2) Basic substituent group: —CONR—, —CH ₂ —NR—CH ₂ —, —NR ₂
-NR ₄ ⁺
(D3) Non-electrolyte substituent: —OH
(However, R represents either a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, —CH ₂ —, or a halogen atom. When two or more R exist in one substituent, R is the same. Or it may be different)

  Examples of water-soluble polymers having substituent groups (D1) to (D3) include polyvinyl alcohol, polyacrylamide, polyacrylic acid, polyvinyl pyrrolidone, water-soluble alkyd, polyvinyl ether, polymaleic acid copolymer, polyethyleneimine and the like as synthetic organic substances. Is mentioned. Semi-synthetic products include soluble starch, carboxyl starch, British gum, dialdehyde starch, dextrin, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, cationic starch, viscose, methylcellulose, ethylcellulose, carboxymethylcellulose, Examples thereof include hydroxyethyl cellulose. Examples of organic natural products include starch, starch, funari, agar, alginate, gum arabic, tragacanth gum, troro-aloe, konjac, glue, gazein, gelatin, egg white, plasma protein, pullulan, dextran and the like. These water-soluble polymers may be used alone or in combination of two or more.

  Among these water-soluble polymers, those having alcoholic hydroxyl groups and / or amide groups as water-soluble functional groups are more preferable. Specifically, polyvinyl alcohol, starch, soluble starch, carboxyl starch, dextrin, α-cyclohexane. Dextrin, β-cyclodextrin, γ-cyclodextrin, polyacrylamide, and polyvinylpyrrolidone, particularly preferably polyvinylpyrrolidone alone or a mixture with any of the water-soluble polymers described above.

  The molecular weight of the water-soluble polymer is not particularly limited as long as it suppresses sublimation of iodine and has sufficient solubility in the medium, but the weight average molecular weight is preferably 500 to 3000000, more preferably 700 to 2000000, particularly preferably 1000 to 1500,000.

  The amount of these water-soluble polymers added to the dissolving solution is not particularly limited as long as it is a concentration that can be dissolved in the dissolving solution, but the content in the dissolving solution is preferably 0.0001 to 5% by weight. More preferably, it is 0.0005 to 1 weight%, Most preferably, it is 0.001 to 0.5 weight%. When the addition amount of the water-soluble polymer is less than the above range, the above-mentioned effect due to the addition of the water-soluble polymer cannot be sufficiently obtained, and when it is too much, the viscosity of the solution is increased, which is not preferable.

  In addition, a surfactant may be added to the solution of the present invention for the purpose of improving the wettability of the processing object for dissolving the noble metal and the permeability of the processing object at a narrow interval. Examples of the surfactant to be added include anionic, cationic, amphoteric, and nonionic surfactants. Among them, anionic, amphoteric, and nonionic surfactants are preferable, and anionic and nonionic surfactants are particularly preferable. . Examples of anionic surfactants include carboxylic acid type, sulfonic acid type, sulfate ester type, and phosphate ester type, amphoteric surfactants include amino acid type and betaine type, and nonionic surfactants include polyethylene glycol type. , Polyhydric alcohol type, acetylene alcohol type, alkanolamide type and the like. These surfactants may be used alone or in combination of two or more different kinds as appropriate.

Among anionic surfactants, sulfonic acid type (having —SO ₃ — group), sulfate ester type (having —OSO ₃ — group), and carboxylic acid type (having —CO ₂ — group), Those having at least one —SO ₃ — group, —OSO ₃ — group or —CO ₂ — group are preferable. Specifically, alkylsulfonic acid, alkylbenzenesulfonic acid, alkylsulfuric acid ester, alkylether sulfate ester, alkyl Carboxylic acids and their salts are preferably used.

  Among the nonionic surfactants, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, etc. are used as polyethylene glycol type, and polyoxyethylene polyoxyethylene polytype is used as polyalkylene glycol type. Oxypropylene ether, polyoxyethylene polyoxypropylene alkyl ether, etc., glycerin fatty acid ester, sorbitan fatty acid ester, etc. as polyhydric alcohol type, alkyne-ols, alkyne-diols, alkanolamide type, alkyl carboxylic acid as acetylene alcohol type Examples include monoethanolamide and ethanolamide when alkylcarboxylic acid. Of these surfactants, alkyne- (di) ol, alkylcarboxylic acid diethanolamide and the like are preferably used from the viewpoint of excellent solubility and chemical stability.

  The amount of these surfactants added to the solution is preferably 30% by weight or less, more preferably 0.0001 to 10% by weight, and particularly preferably 0.005 to 5% by weight as the content in the solution. It is. When the addition amount of the surfactant is less than the above range, a sufficient addition effect cannot be obtained, and when the addition amount is too large, the solubility of the noble metal is lowered and the solution is foamed.

  The solution of the present invention may contain a buffer for stabilizing the solubility of the noble metal. The buffer is not particularly limited as long as it exhibits ionic dissociation, but boric acid, carboxylic acid, carbonic acid, sulfurous acid, sulfuric acid, hypophosphorous acid, phosphoric acid, diphosphoric acid, halogen acids, alkali metal or alkaline earth metal Hydroxides, ammonia, various amines, diamines, quaternary ammoniums, alkali metal salts, alkaline earth metal salts, ammonium salts thereof, and the like can be used. These buffering agents may be used alone, or two or more different kinds may be used in appropriate combination. Of these buffers, carboxylate, sulfate, phosphate, and diphosphate are more preferable. Of these, tartaric acid, citric acid, malic acid, lactic acid, fumaric acid, succinic acid, potassium salt of sodium acid, sulfuric acid, phosphoric acid and diphosphoric acid, sodium salt, ammonium salt and the like are preferably used from the viewpoint of stability and solubility. It is done.

  The amount of these buffers added to the solution is preferably 30% by weight or less, more preferably 0.1 to 20% by weight, and particularly preferably 1 to 10% by weight as the content in the solution. When the addition amount of the buffering agent is less than the above range, a sufficient addition effect cannot be obtained, and when it is too large, the viscosity of the solution is increased and the liquid stability is lowered.

  In addition, since the noble metal solution of the present invention does not substantially contain cyan, it is excellent in safety, can be easily treated with waste liquid, and has a low environmental burden. Here, “substantially free of cyan” means that cyan is not actively contained, preferably it does not contain at all. When preparing a solution, cyan is inevitably mixed as an impurity. Of course, it is preferable that the cyan content is low. Specifically, it is preferably 1% by weight or less, more preferably 0.1% by weight or less, and particularly preferably 0.01% by weight or less.

  The method for producing the solution of the present invention is not particularly limited. For example, the solution of the present invention can be obtained by mixing an iodine source, an organic solvent, and other components blended as necessary in a predetermined blend. it can. Preferably, a method is used in which iodine and iodide ions, that is, an iodine compound, are added to a solution containing an organic solvent.

  Next, the method for dissolving and recovering the noble metal of the present invention using such a noble metal solution of the present invention will be described.

  In the method for dissolving a noble metal of the present invention, the noble metal, a waste material having a noble metal member practically (hereinafter sometimes referred to as “object to be treated”) is contacted with the noble metal solution of the present invention as described above. Let Although there is no restriction | limiting in particular as this contact method, The method of immersing a process target object in the solution of this invention is the most effective. In this case, the object to be treated may be simply immersed in the solution and allowed to stand, but it is preferable to generate a liquid flow of the solution by power such as stirring and ultrasonic vibration.

  As the temperature when the solution is brought into contact with the object to be treated, if it is excessively high, precipitation of the solute due to evaporation of the solvent component of the solution is caused, and if it is excessively low, the solubility of the noble metal is reduced. The range of 80 ° C. is preferable, and it is generally preferable to treat at room temperature (20 to 30 ° C.).

  Although the contact (immersion time) varies depending on the shape of the object to be treated (the degree of exposure of the noble metal), the dimensions, the composition of the solution used, and the type of the noble metal, about 1 to 100 hours is usually sufficient.

  Further, the amount of the solution to be used is not particularly limited as long as it can sufficiently dissolve the noble metal in the object to be treated according to its composition, but in the solution of the present invention, the noble metal is usually added. Since about 0.01 to 10% by weight can be dissolved, the amount of the solution to be used may be appropriately determined according to the dissolution concentration.

  In the recovery method of the present invention, a reducing agent is added to the solution (hereinafter sometimes referred to as “noble metal eluate”) in which the noble metal is dissolved in this way to reduce the noble metal ions and precipitate the metal. Let

The reducing agent used here is not particularly limited as long as it has sufficient solubility in the noble metal eluate, is stable at room temperature, and has a reducing ability for the noble metal ions in the noble metal eluate. In order to reduce the noble metal complex in the noble metal eluate and iodine or triiodine ions as the oxidizing agent, the standard electrode potential E ⁰ [V vs NHE] of the reducing agent may be E ⁰ ≦ 0.6. Preferably, E ⁰ ≦ 0.3, especially E ⁰ ≦ 0.1, in order to further improve the reduction precipitation rate of noble metal ions and increase the recovery yield of noble metal.

  Examples of such a reducing agent include borohydride, phosphonate, hypophosphite, thiosulfate, sulfite, dithionite and the like for inorganic compounds, and hydrazine, ethylenediamine, urea, and the like for organic compounds. Examples include various amines such as thiourea and dimethylaminoborane, diamines, and imines, various aldehydes such as formaldehyde, acetaldehyde, and propionaldehyde, and various thiols such as methanethiol, ethanethiol, and propanethiol. In addition, ascorbic acid or the like can be used as the reducing compound. These reducing agents may be used individually by 1 type, and may use 2 or more types together.

  Among these reducing agents, thiosulfate, sulfite, dithionite, ascorbic acid and the like are preferable in consideration of the precious metal reducing ability and workability in the recovery method of the present invention, and sulfite and ascorbic acid are more preferable. . As these salts, alkali metal salts are preferable, and sodium salts and potassium salts are particularly preferable.

  The amount of the reducing agent added is not particularly limited as long as it is a concentration that can reduce all the precious metal ions dissolved in the precious metal eluate, but is preferably 0.001 to 50% by weight with respect to the precious metal eluate. Preferably it is 0.01-30 weight%, Most preferably, it is 0.1-10 weight%. If the amount of the reducing agent used is too small, the dissolved noble metal ions cannot be sufficiently reduced and precipitated, and even if the amount is higher, no further improvement in the recovery rate can be expected, which is not preferable in terms of drug cost.

  By adding a reducing agent, the noble metal ions in the noble metal eluate are deposited as noble metals. Therefore, the precious metal deposited can be collected by filtration, washed with water and dried as necessary.

  In addition, although the liquid after collect | recovering a noble metal cannot melt | dissolve a noble metal by the reduction | decrease of an iodine density | concentration, it can be reused for melt | dissolution of a noble metal again by adding iodine.

  According to such a precious metal solution and precious metal dissolving and recovery method of the present invention, after precious metals such as gold, silver, platinum, and palladium, or precious metals in alloys containing these precious metals are efficiently dissolved. , It can be deposited again and recovered. The present invention is particularly effective for the selective recovery of gold from gold, gold alloys such as gold and copper alloys, gold and nickel alloys, and the like.

  Next, specific embodiments of the present invention will be described using examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, gold is 99.99% pure gold manufactured by Ishifuku Metal Industry Co., Ltd., iodine is 99.7% pure product manufactured by Joint Resource Industries Co., Ltd., and other reagents. Was evaluated using a special reagent grade manufactured by Wako Pure Chemical Industries.

<Gold dissolution test>
Example 1
After mixing 33.99 g of ethylene glycol and 10.76 g of ion-exchanged water, 4.25 g of potassium iodide was added and dissolved. To this solution, 0.50 g of iodine was added and dissolved by stirring at room temperature to obtain a dark brown solution.

  After 0.50 g of a pure gold plate having a thickness of 0.1 mm was immersed in this solution, the solution was stirred at room temperature using a magnetic stirrer. After immersion of the pure metal plate, the pure metal plate was pulled up and weighed at each elapsed time of 8 to 64 hours. The weight ratio of decrease in each elapsed time with respect to the initial weight of the pure gold plate was calculated as a dissolution rate in wt%. The results are shown in Table 1.

(Examples 2, 3, and 4)
In the same manner as in Example 1 except that propylene glycol was used in Example 2 instead of ethylene glycol, glycerin was used in Example 3, and diethylene glycol was used in Example 4, the dissolution rate at each elapsed time after pure metal plate soaking was used. And the results are shown in Table 1.

(Example 5)
After mixing 32.20 g of ethylene glycol and 10.15 g of ion-exchanged water, 6.40 g of potassium iodide was added and dissolved. 0.75 g of iodine was added to this solution and dissolved by stirring at room temperature to obtain a dark brown solution.

  A pure gold plate was immersed in this solution in the same manner as in Example 1, the dissolution rate at each elapsed time was calculated, and the results are shown in Table 1.

(Example 6)
After mixing 30.38 g of ethylene glycol and 9.62 g of ion-exchanged water, 8.50 g of potassium iodide was added and dissolved. To this solution, 1.00 g of iodine was added and dissolved by stirring at room temperature to obtain a dark brown solution.

  A pure gold plate was immersed in this solution in the same manner as in Example 1, the dissolution rate at each elapsed time was calculated, and the results are shown in Table 1.

(Comparative Example 1)
4.25 g of potassium iodide was added to 44.75 g of ion-exchanged water and dissolved. To this solution, 0.50 g of iodine was added and dissolved by stirring at room temperature to obtain a dark brown solution.

  A pure gold plate was immersed in this solution in the same manner as in Example 1, the dissolution rate at each elapsed time was calculated, and the results are shown in Table 1.

  Table 1 shows that the solution of the present invention is excellent in gold solubility. It can also be seen that the dissolution rate of gold is particularly fast when diethylene glycol is used.

<Iodine sublimation test>
(Example 7)
After mixing 33.99 g of ethylene glycol and 10.76 g of ion-exchanged water, 4.25 g of potassium iodide was added and dissolved. To this solution, 0.50 g of iodine was added and dissolved by stirring at room temperature to obtain a dark brown solution.

  The total amount of the solution was put in a 250 ml polyethylene container, capped, and allowed to stand at 25 ° C. for 3 hours. The iodine concentration in the gas phase in the container was measured using a Kitagawa type gas detector tube (117SB type), and the results are shown in Table 2.

(Examples 8 to 11)
A solution was prepared in the same manner as in Example 7 except that each organic solvent described in Table 2 was used instead of ethylene glycol, and the iodine concentration in the gas phase was measured in the same manner. Indicated.

(Example 12)
After mixing 26.78 g of ethylene glycol and 8.47 g of ion-exchanged water, 12.75 g of potassium iodide was added and dissolved. To this solution, 1.50 g of iodine was added and dissolved by stirring at room temperature to prepare a dark brown solution. For this solution, the iodine concentration in the gas phase was measured in the same manner as in Example 7, and the results are shown in Table 2.

(Comparative Example 2)
4.25 g of potassium iodide was added to 44.75 g of ion-exchanged water and dissolved. To this solution, 0.50 g of iodine was added and dissolved by stirring at room temperature to prepare a dark brown solution. For this solution, the iodine concentration in the gas phase was measured in the same manner as in Example 7, and the results are shown in Table 2.

(Comparative Example 3)
To 35.25 g of ion-exchanged water, 12.75 g of potassium iodide was added and dissolved. To this solution, 1.50 g of iodine was added and dissolved by stirring at room temperature to prepare a dark brown solution. For this solution, the iodine concentration in the gas phase was measured in the same manner as in Example 7, and the results are shown in Table 2.

  From Table 2, it can be seen that the solution of the present invention is excellent in the effect of suppressing sublimation of iodine.

<Gold recovery test>
(Example 13)
After mixing 33.99 g of ethylene glycol and 10.76 g of ion-exchanged water, 4.25 g of potassium iodide was added and dissolved. To this solution, 0.50 g of iodine was added and dissolved by stirring at room temperature to obtain a dark brown solution.

  After 0.50 g of a pure gold plate having a thickness of 0.1 mm was immersed in this solution, the solution was stirred and dissolved at room temperature using a magnetic stirrer.

As a reducing agent, 0.50 g of ascorbic acid (E ⁰ [V vs NHE] (25 ° C.) = 0.1) was added to this gold solution and stirred and dissolved at room temperature. As a result, the dark brown solution became transparent. Gold particles were deposited. When this was separated by filtration, washed with water and dried, 0.49 g of granular material was obtained. When this granular material was observed with SEM-EDX (“SuperScan330” manufactured by Shimadzu Corporation), the main component of the granular material was gold. The recovery rate for dissolved gold was calculated and the results are shown in Table 3.

(Examples 14 and 15)
Instead of ascorbic acid, thiourea (E ⁰ [V vs NHE] (25 ° C.) = − 0.5) was used as a reducing agent in Example 14, and sodium sulfite (E ⁰ [V vs NHE] (25 ° C.) was used in Example 15. ) = 0.2), except that each was used in the same manner as in Example 13, and the recovery rate relative to the dissolved gold was calculated. The results are shown in Table 3.

  Table 3 shows that gold can be efficiently recovered when ethylene glycol is used as a solvent. Even if another organic solvent according to the present invention such as diethylene glycol is used, it can be efficiently recovered in the same manner.

  As is clear from the above results, the solution of the present invention has a very low volatile content of iodine, can dissolve a high concentration of noble metal in a short time, and can be reduced to a solution containing noble metal dissolved therein. By adding the agent, the precious metal can be recovered at a high recovery rate.

  According to the present invention, in particular, it is possible to efficiently recover and effectively reuse expensive noble metals used as large-scale integrated circuits and wiring materials from waste materials such as electronic components and electronic devices. The technology of the present invention is useful for reducing the amount of waste and effectively using resources.

Claims (9)

Iodine and / or iodide ions, one or more organic solvents selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, and glycerin, and 1 to 90% by weight of water with respect to the organic solvent. A precious metal solution characterized by containing. 2. The noble metal solution according to claim 1, wherein the content of the organic solvent is 10 to 95 wt% with respect to the entire solution. 3. The precious metal solution according to claim 1 , wherein the content of water is 1 to 85 wt% with respect to the entire solution. The noble metal solution according to any one of claims 1 to 3 , further comprising an oxidizing agent. A method for dissolving a noble metal, wherein the noble metal is brought into contact with the solution according to any one of claims 1 to 4 to dissolve the noble metal in the solution. The method for dissolving a noble metal according to claim 5 , wherein the temperature of the solution for dissolving the noble metal is 20 to 80 ° C. A method for recovering a noble metal, comprising dissolving the noble metal in a solution by the method for dissolving a noble metal according to claim 5 or 6 , and then depositing the noble metal by adding a reducing agent. The method for recovering a noble metal according to claim 7 , wherein the standard electrode potential E ⁰ [V vs NHE] (25 ° C.) of the reducing agent is 0.6 or less. The method for recovering a noble metal according to claim 8 , wherein the reducing agent is one or more selected from the group consisting of thiosulfate, sulfite, nitrite, and ascorbic acid.