JP2013133537A - Method for recovering gold from gold-containing acidic aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recovering gold from an acidic gold solution containing a chloride or bromide of an alkali metal or alkali earth metal.SOLUTION: The method for recovering gold from the gold-containing acidic aqueous solution comprises: a step of concentrating gold through solvent extraction using an extractant containing a mixture of quaternary amines and phenols from the acidic aqueous solution containing a chloride or bromide or an alkali metal or alkali earth metal and having a gold ion concentration of ≤10 mg/L; and a step of reducing gold in the extractant.

Description

  The present invention relates to a method for recovering gold from a gold-containing acidic aqueous solution. In particular, the present invention relates to a method for recovering gold from a gold-containing acidic aqueous solution after leaching a gold-containing ore such as gold ore or copper ore.

  Copper sulfide ore usually contains a small amount of gold. This gold is recovered as a by-product during copper smelting, but is recovered through the following steps in general dry smelting (Non-patent Document 1).

  In a self-fluxing furnace or a reflection furnace, the copper sulfide ore containing gold is decomposed together with iron sulfide or silicate ore at a high temperature of 1000 ° C or higher, and the purpose is mainly a high copper content solution called mat and iron oxide or silicic acid. Separated into slag containing foreign elements.

  The mat is reduced at a high temperature to obtain low-purity metallic copper called crude copper, which is electrolytically purified to obtain metallic copper having a purity of 99.99% or higher.

  Since the gold contained in the raw material is a parent copper element, it exhibits the same behavior as copper in the refining process of metallic copper, and in the last electrolytic refining process, along with other noble metals, a copper electrolytic deposit (copper electrolytic slime) It is recovered as a precipitate called.

  The method for treating this copper electrolytic deposit is shown below. It melts at high temperature with lead, condenses noble metal in lead, removes lead by oxidation, concentrates only the noble metal, and casts it into a silver plate containing a noble metal called an original silver plate. When the original silver plate is electrolyzed and the silver is purified, a precipitate containing a noble metal is produced as a silver electrolytic product. From this precipitate, noble metals other than gold are eluted with nitric acid or the like, and then melted at a high temperature to produce gold having a low purity called an original metal plate, which is electrolyzed to recover high purity gold.

  This method requires a high temperature exceeding 1000 ° C., and is originally intended for the production of metallic copper. Since gold is refined as a by-product, the processing steps become complicated and it takes a very long time to recover. There is.

  As a method for overcoming this drawback, a wet smelting method has been devised (for example, Patent Document 1). In this Patent Document 1, solid-liquid separation is performed after the copper leaching step, and the separated residue is an acidic aqueous solution containing an alkali metal or alkaline earth metal chloride and bromide, and copper and iron chloride or copper and iron bromide. And leaching gold from the residue by blowing air under atmospheric pressure, below boiling point and in the presence of iron. A method is shown in which activated carbon is introduced into this acidic aqueous solution, and gold is adsorbed on the activated carbon and recovered.

  As a gold recovery method that does not rely on activated carbon, a method is known in which copper electrolytic slime is dissolved and leached, and gold is recovered therefrom by solvent extraction using dibutyl carbitol (DBC) (Patent Document 2). .

  Regardless of the wet smelting of copper, a method of extracting a gold anion complex using a quaternary amine is shown as a method for selectively extracting gold in a wider technical range (Patent Documents 3 and 4). ).

JP 2009-235519 A JP-A-9-316561 U.S. Pat. No. 4,774,003 US Pat. No. 5,158,603

The Japan Institute of Metals Nonferrous metal smelting

  In the method of recovering the by-product gold in the above-mentioned wet copper smelting by the wet method, only about 1% of the weight of the activated carbon (usually said to adsorb 5 to 6%) is adsorbed in the activated carbon. If you recover the gold by incineration, the cost increases.

Gold dissolved in the chloride and bromide baths is monovalent or trivalent and forms complex ions with chloride or bromide ions to form Au (I) X ₂ ^- or Au (III) X _4. ^- is present in the form of, its form depends largely on the redox potential. However, in the leaching of a chloride-bromide mixed bath, gold tends to exist as Au (III).

  As seen in Patent Document 2, dibutyl carbitol (DBC) is known as a gold extractant, but this extractant has a low extraction effect on trivalent gold complexes. In addition, the solution containing bromide has a drawback that the effect of extracting gold is lowered. In addition, quaternary amines are known as the extractant (for example, manufactured by LIX 7820 BASF), which is usually used under alkaline conditions.

  This invention is made | formed in view of the said situation, and it is a subject to provide the method of collect | recovering gold | metal efficiently from the acidic gold solution containing the chloride and bromide of an alkali metal or alkaline-earth metal.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the gold extraction ability is surprisingly high when a quaternary amine and a phenol are used in an acidic aqueous solution.

  The present invention has been completed on the basis of the above findings. In one aspect, the present invention includes an alkali aqueous solution containing an alkali metal or alkaline earth metal chloride and bromide and containing gold ions at a concentration of 10 mg / L or less. Concentrating gold by solvent extraction using an extractant containing a mixture of secondary amines and phenols, and then reducing the gold in the extractant; It is a collection method.

  In one embodiment of the gold recovery method according to the present invention, the acidic aqueous solution has a pH of 1-2.

  In another embodiment of the gold recovery method according to the present invention, the acidic aqueous solution is a leached solution obtained by leaching gold from copper ore or gold ore.

  In still another embodiment of the gold recovery method according to the present invention, the acidic aqueous solution has a chloride ion concentration of 80 to 200 g / L, a bromide ion concentration of 20 to 80 g / L, and a copper ion concentration of 0.5. -30 g / L, and iron ion concentration is 0.1-5 g / L.

  In still another embodiment of the gold recovery method according to the present invention, the acidic aqueous solution has a gold ion concentration of 2 to 7 mg / L.

  In still another embodiment of the gold recovery method according to the present invention, the solvent extraction step is repeatedly performed until the gold concentration in the extractant is concentrated to 0.25 to 3.5 g / L.

  In yet another embodiment of the gold recovery method according to the present invention, the mixture of quaternary amines and phenols used in the solvent extraction step is a mixture of methyltri-n-octylammonium chloride and nonylphenol. .

  In still another embodiment of the gold recovery method according to the present invention, the extractant has a quaternary amine / phenol molar ratio of quaternary amines / phenols of 0.3 to 0.8. Used by diluting with an organic solvent.

  In still another embodiment of the gold recovery method according to the present invention, the organic solvent is an organic solvent other than n-paraffin.

  In still another embodiment of the gold recovery method according to the present invention, the method includes a step of washing the extractant with pure water after the solvent extraction step and before the reduction step.

  In still another embodiment of the gold recovery method according to the present invention, an aqueous sodium oxalate solution and / or an oxalic acid aqueous solution is used as a reducing agent in the reduction step.

  In still another embodiment of the gold recovery method according to the present invention, the amount of the reducing agent used is 1.5 to 5 molar equivalents relative to the gold contained in the extractant.

  In still another embodiment of the gold recovery method according to the present invention, the contact between the extractant and the reducing agent is performed at a liquid temperature of 60 ° C. to 95 ° C. with stirring for 3 to 5 hours.

  In still another embodiment of the gold recovery method according to the present invention, the liquid temperature is 75 ° C to 85 ° C.

  According to the present invention, gold can be efficiently recovered from an acidic gold aqueous solution containing an alkali metal or alkaline earth metal chloride and bromide. In particular, when using a solution after leaching obtained by leaching gold from copper ore or gold ore as the acidic aqueous solution, the solvent extraction can be performed without adjusting the pH, thus simplifying the treatment process. A practically beneficial effect can be obtained, such as speeding up and speeding up.

The schematic diagram of the gold | metal | money extraction apparatus by the mixer settler used in the Example is shown. The relationship between the gold concentration of the oil phase and the gold concentration of the water phase after extraction in Example 2 is shown. In a comparative example, the change of the gold | metal density | concentration in the aqueous phase before and behind extraction when DBC is repeatedly used as an extracting agent is shown.

  The present invention will be described in detail below.

<Acid aqueous solution>
An object of the present invention is to recover gold from an acidic aqueous solution containing an alkali metal or alkaline earth metal chloride and bromide and containing gold ions at a concentration of 10 mg / L or less. The acidic aqueous solution is typically, but not limited to, a liquid after leaching after a valuable metal such as copper, gold, silver, or the like is leached from a gold ore or copper ore and subjected to solid-liquid separation. Even if gold is not the main leaching target, gold may be leached incidentally, and the present invention is also applicable to the liquid after leaching when the gold is leached incidentally in addition to the case where gold is the main leaching target. It is said.

  A suitable condition for gold leaching will be described. Gold leaching proceeds by the elution of gold reacting with chlorine ions or bromine ions to form gold chloride complexes or gold bromide complexes. By using bromine ions in combination, the complex is formed at a lower potential, so that the gold leaching efficiency can be improved. Therefore, it is considered preferable to use an alkali metal or alkaline earth metal chloride and an alkali metal or alkaline earth metal bromide in combination as the leachate. A technique for recovering gold with high efficiency from the solution after leaching after leaching gold in such a mixed bath of chloride and bromide is desired. The leaching effect is not sufficient. The present invention is advantageous in that a high gold extraction effect can be obtained with respect to a mixed bath of chloride and bromide, and therefore the above acidic aqueous solution is particularly targeted.

  Further, the iron ions function to oxidize gold by trivalent iron ions oxidized under the supply of an oxidizing agent or trivalent iron ions from the beginning. Copper ions are not directly involved in the reaction, but the presence of copper ions increases the oxidation rate of iron ions. Therefore, a preferable leachate contains copper ions and iron ions. In that case, copper ions and iron ions are also contained in the acidic aqueous solution targeted by the present invention. Copper ions and iron ions can be supplied to the leachate in the form of, but not limited to, halide salts, for example copper ions are copper chloride and / or bromide, iron ions are iron chloride and / or bromide. Can be supplied as iron.

  Alkali metal chlorides include lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride and francium chloride, and alkaline earth metal chlorides include beryllium chloride, magnesium chloride, calcium chloride, strontium chloride, Although barium and radium chloride are contained, sodium chloride is preferred from the viewpoints of economy and availability. Alkali metal bromides include sodium chloride, potassium chloride, rubidium chloride, cesium chloride and francium chloride, and alkaline earth metal bromides include beryllium bromide, magnesium bromide, calcium bromide, strontium bromide, bromide bromide. Although barium and radium bromide are contained, sodium bromide is preferred from the viewpoint of economy and availability.

  It is preferable to manage the oxidation-reduction potential by carrying out the leaching step while supplying the oxidizing agent. This is because if the oxidant is not added, the oxidation-reduction potential decreases in the middle and the leaching reaction does not proceed. Although there is no restriction | limiting in particular as an oxidizing agent, For example, oxygen, air, chlorine, a bromine, hydrogen peroxide, etc. are mentioned. An oxidant with an extremely high redox potential is not necessary and air is sufficient. Air is also preferably used from the viewpoint of economy and safety.

  The leached solution thus obtained by the leaching treatment is typically an acidic aqueous solution that the present invention is intended to recover gold. In one embodiment, the chloride ion concentration is 80 to 200 g / L, and bromide ions. The concentration is 20-80 g / L, the copper ion concentration is 0.5-30 g / L, and the iron ion concentration is 0.1-5 g / L. In an exemplary embodiment, the chloride ion concentration is 170 g / L- 190 g / L, bromide ion concentration is 20 g / L to 25 g / L, copper ion concentration is 20 g / L to 25 g / L, and iron ion concentration is 3 to 20 g / L.

  In addition, the present invention targets an acidic aqueous solution containing gold ions at a concentration of 10 mg / L or less. This is based on the finding that although the gold extractant used in the present invention is generally used in an alkaline manner, high extraction efficiency can be achieved even in an acidic state. In a typical embodiment, the acidic aqueous solution contains 2-7 mg / L of gold ions.

  The acidic aqueous solution typically has a pH of 0-2, more typically 1-2. The extractant used in the present invention should generally be used on the alkali side, and it has been thought that pH adjustment is required. However, in practice, a high gold extraction rate can be achieved even under strong acid conditions without adjusting the pH after the leaching treatment. Further, there is no need to particularly adjust the redox potential.

<Extractant>
In this invention, the process of concentrating gold | metal | money by solvent extraction is performed from the acidic aqueous solution mentioned above using the extracting agent containing the mixture of quaternary amines and phenols. The reason for using an extractant containing a mixture of quaternary amines and phenols is that, by using the extractant, high extraction efficiency can be achieved on the acidic side against a diluted gold solution. is there. Moreover, since the extractant can be reused, it is more advantageous in terms of cost than using activated carbon.

で表される四級アミンを使用することができる。式中、Ｒ₁〜Ｒ₄は各々独立に炭素数２５以下の炭化水素基から選択される。Ｒ₁〜Ｒ₄の合計炭素数は１６以上であるのが好ましいが、一般には４０以下とすればよい。また、Ｒ₁〜Ｒ₄の少なくとも一つは炭素数６以上の炭化水素であるのが好ましく、一つ又は二つはメチル基であるのが好ましい。炭化水素基は飽和又は不飽和の脂肪族又は芳香族炭化水素基とすることができるが、脂肪族炭化水素基が好ましく、脂肪族飽和炭化水素基がより好ましい。例示的にはメチル、エチル、プロピル、ブチル、ペンチル、ヘキシル、へプチル、オクチル、ノニル、デシル等のアルキル基が挙げられる。四級アミンは一般には塩化物や臭化物などのハロゲン塩として供給することができる。 The quaternary amines are not limited, but those described in US Pat. No. 5,158,603 (Patent Document 4) can be used. Preferably, the following formula:

The quaternary amine represented by these can be used. In the formula, R _{1 to} R ₄ are each independently selected from hydrocarbon groups having 25 or less carbon atoms. The total number of carbon atoms of R _{1 to} R ₄ is preferably 16 or more, but generally may be 40 or less. In addition, at least one of R _{1 to} R ₄ is preferably a hydrocarbon having 6 or more carbon atoms, and one or two are preferably methyl groups. The hydrocarbon group can be a saturated or unsaturated aliphatic or aromatic hydrocarbon group, preferably an aliphatic hydrocarbon group, more preferably an aliphatic saturated hydrocarbon group. Illustrative examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like. Quaternary amines can generally be supplied as halogen salts such as chlorides and bromides.

  Preferable specific examples of the quaternary amines include methyltri n-octylammonium, methyltrin-dodecylammonium, and methyltrin-nonylammonium, and methyltrin-octylammonium is more preferable. These are preferably provided as chlorides.

で表されるフェノールを使用することができる。式中、Ｒ₅は炭素数２５以下の炭化水素基であり、ｎは０〜４である。炭化水素基は飽和又は不飽和の脂肪族又は芳香族炭化水素基とすることができるが、脂肪族炭化水素基が好ましく、脂肪族飽和炭化水素基がより好ましい。例示的にはメチル、エチル、プロピル、ブチル、ペンチル、ヘキシル、へプチル、オクチル、ノニル、デシル等のアルキル基が挙げられる。ｎは好ましくは１〜２である。 Phenols are not limited, but those described in US Pat. No. 5,158,603 (Patent Document 4) can be used. Preferably, the following formula:

Phenol represented by can be used. In the formula, R ₅ is a hydrocarbon group having 25 or less carbon atoms, and n is 0-4. The hydrocarbon group can be a saturated or unsaturated aliphatic or aromatic hydrocarbon group, preferably an aliphatic hydrocarbon group, more preferably an aliphatic saturated hydrocarbon group. Illustrative examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like. n is preferably 1-2.

  Preferable specific examples of phenols include alkylphenols such as nonylphenol and dodecylphenol, and nonylphenol is more preferable.

  The mixing ratio of quaternary amines and phenols can be, for example, quaternary amines / phenols = 0.2 to 0.9, preferably quaternary amines / phenols = 0.3 to 0. 8.

  The extractant is generally used after diluted with a suitable organic solvent. The concentration of the extractant can typically be 10-30 vol%, more typically 15-25 vol%. Although it does not limit as an organic solvent, For example, an aromatic hydrocarbon and an alicyclic saturated hydrocarbon can be used. From the viewpoint of preventing foaming and improving operability, the organic solvent is preferably an organic solvent other than n-paraffin.

<Solvent extraction>
Solvent extraction operation itself may follow a conventional method. For example, a gold-containing acidic aqueous solution (aqueous phase) and an extractant (oil phase) are contacted, and these are typically stirred and mixed with a mixer to react gold with the extractant. The reaction can be carried out at room temperature (10 to 30 ° C.) to 60 ° C. under atmospheric pressure.

  The O / A ratio, which is the volume ratio of the extractant (Or) and the aqueous solution (A), is not particularly limited, but is preferably 1/5 or less in consideration of gold concentration, and is 1/10 or less. More preferably. By repeatedly using the extractant, gold can be highly concentrated in the extractant. In a preferred embodiment of the present invention, the solvent extraction step is carried out continuously or repeatedly batchwise until the gold concentration in the extractant is concentrated to 0.25 to 3.5 g / L. The reason for concentrating the gold concentration in the extractant to the above range is that the reducing agent works efficiently in the subsequent step when the gold concentration in the extractant is 0.25 g / L or more, Moreover, it is because gold extraction efficiency can be maintained high when the gold concentration in the extractant is 3.5 g / L or less. The gold concentration in the extractant is more preferably concentrated in the range of 1 to 2 g / L.

<Washing>
During gold extraction, impurities such as iron and copper may be extracted in the solvent. Also, the leachate may be suspended in the solvent. In such a case, the extractant is washed (scrubbed) before gold reduction to remove impurities from the extractant. Washing may be performed with water (preferably pure water) or a hydrochloric acid aqueous solution of about 0.5 to 2.0 mol / L. Since water separation is poor with water alone, it is preferable to use an aqueous hydrochloric acid solution.

<Gold reduction>
After optional washing, the extracted agent after extraction and an aqueous solution containing a reducing agent may be brought into contact with each other, and stirring is preferable from the viewpoint of reaction efficiency. Examples of the reducing agent include oxalic acid and sodium oxalate, dextrose and ascorbic acid. For example, in the reduction with sodium oxalate, the reaction shown in the following formula proceeds.
2HAuCl ₄ +3 (COONa) ₂ → 2Au + 6CO ₂ + 6NaCl + 2HCl
Depending on the efficiency of the reducing agent, the amount of the reducing agent used is preferably 1.5 to 5 molar equivalents, more preferably 2 to 4 molar equivalents relative to the gold contained in the extractant.

  It is desirable to carry out at a liquid temperature of 60 ° C. to 95 ° C. for about 3 to 5 hours using sodium oxalate because of the shape of the reduced gold to be deposited. From the viewpoint of reaction rate and heating cost, the liquid temperature is preferably 75 to 85 ° C. The reduction step is preferably performed until the gold concentration in the extractant is 0.5 g / L or less, more preferably 0.1 g / L or less, from the viewpoint of gold recovery. The reduced gold settles on the bottom of the container, and can be made into a product by solid-liquid separation, recovery and washing.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these. In addition, the analysis method of the metal used in the Example was performed by ICP-AES. However, in the analysis of gold, gold in the sample was deposited by the ash blowing method, and then quantitative analysis was performed by ICP-AES.

<Example 1>
The chalcopyrite concentrate was subjected to a leaching treatment at 80 to 85 ° C. for 5 hours with a hydrochloric acid acidic leachate having the composition shown in Table 1 at a pulp concentration of 200 g / L. Air blowing and stirring were continued during the leaching process. After the leaching treatment, a liquid after leaching having the composition shown in Table 2 was obtained by solid-liquid separation.

＊全塩化物イオン及び全臭化物イオンは、浸出液の成分が完全に電離していると仮定し、臭化物イオンは臭化ナトリウムで添加し、全塩素イオン濃度が１８０ｇ／Ｌとなるよう塩化ナトリウムで調整した。

* Total chloride ion and total bromide ion are assumed to be completely ionized, and bromide ion is added with sodium bromide and adjusted with sodium chloride so that the total chloride ion concentration is 180 g / L. did.

  A schematic diagram of the apparatus used for gold extraction is shown in FIG. LIX7820 (extractant in which methyltri-n-octylammonium chloride and nonylphenol were mixed at a molar ratio of 1: 2) was mixed at a ratio of 20 vol% and Exol D80 (dearomatic hydrocarbons) was mixed at a ratio of 80 vol% (oil) Phase) and the liquid after leaching (water phase) were continuously supplied to the mixer settler at a predetermined flow rate (50 mL / min) to continuously extract gold. The oil phase was repeatedly used, and the post-extraction liquid (aqueous phase) was stored in the post-liquid tank. The O / A ratio is 1/10. The metal ion concentration in the aqueous phase was appropriately diluted with hydrochloric acid, and the metal concentration in the organic phase was appropriately diluted with xylene and then measured by ICP-AES. The results of gold extraction are shown in Table 3.

The oil phase containing gold was scrubbed with pure water (volume ratio 1: 1). The results are shown in Table 4. It can be seen that copper and iron in the oil phase are removed by scrubbing.

  The gold in the oil phase was reduced with an aqueous solution containing sodium oxalate. Sodium oxalate was added 1.2 times by weight (4 molar equivalents) with respect to the amount of gold, and stirred and reduced at 80 ° C. for 3 hours. The results are shown in Tables 5 and 6. About 75% of the gold in the oil phase was recovered as reduced gold, and its quality was 99.55%. Reduction recovery was calculated based on oil phase gold. The Au quality, Cu quality and Fe quality in the reduced gold were measured by ICP-AES after diluting with diluted hydrochloric acid.

<Example 2>
Under the same conditions as in Example 1, the oil phase was repeatedly used for gold extraction to verify the ability of the extractant. The aqueous phase Au concentration before extraction was about 4 mg / L. FIG. 2 shows the relationship between the change in gold concentration in the oil phase and the gold concentration in the aqueous phase after extraction. Extraction ability is recognized even when the gold concentration in the oil phase reaches about 3 g / L, and it is estimated that it can be up to about 3.5 g / L, so the extractant can be used repeatedly to concentrate gold. It is.

<Comparative Example 1>
The extractant mixed with 20 vol% DBC and 80 vol% Exol D80 (alicyclic saturated hydrocarbon solvent) was used, and the gold concentration of the liquid after extraction (aqueous phase) was about 1 mg / L. Except for the difference, gold was extracted from the solution after leaching in the same manner as in Example 1. The extractant was used repeatedly, and the transition of the extraction effect was examined. The extraction result is shown in FIG. From FIG. 3, it is understood that gold is hardly extracted from the beginning in DBC.

<Example 3>
With respect to the aqueous phase having the same composition as that of Example 1, the diluent for the extractant is the following aromatic hydrocarbon solvent (trade name: Solvesso 150), alicyclic saturated hydrocarbon solvent (trade name: Exol D80). ) And three kinds of normal paraffinic solvents (trade name: isoper).

  There was no difference in the extraction ratio in the aqueous phase with any diluent, but only the normal paraffin (isoper) was confirmed to form a third layer between the organic phase and the aqueous phase. The aqueous phase could not be separated. As a result, it was found that normal paraffin was not suitable for this extraction system.

Claims (14)

  Solvent using an extractant containing a mixture of quaternary amines and phenols from an acidic aqueous solution containing chlorides and bromides of alkali metals or alkaline earth metals and containing gold ions at a concentration of 10 mg / L or less A method for recovering gold from a gold-containing acidic aqueous solution, comprising a step of concentrating gold by extraction and then a step of reducing gold in the extractant.   The method for recovering gold according to claim 1, wherein the acidic aqueous solution has a pH of 1-2.   The method for recovering gold according to claim 1 or 2, wherein the acidic aqueous solution is a solution after leaching obtained by leaching gold from copper ore or gold ore.   The acidic aqueous solution has a chloride ion concentration of 80 to 200 g / L, a bromide ion concentration of 20 to 80 g / L, a copper ion concentration of 0.5 to 30 g / L, and an iron ion concentration of 0.1 to 5 g / L. The method for recovering gold according to any one of claims 1 to 3.   The gold recovery method according to any one of claims 1 to 4, wherein the acidic aqueous solution has a gold ion concentration of 2 to 7 mg / L.   The said solvent extraction process is a gold | metal collection | recovery method as described in any one of Claims 1-5 implemented repeatedly until the gold | metal density | concentration in an extractant is concentrated to 0.25-3.5 g / L.   The method for recovering gold according to any one of claims 1 to 6, wherein the mixture of quaternary amines and phenols used in the solvent extraction step is a mixture of methyltri-n-octylammonium chloride and nonylphenol.   The extractant has a molar ratio of quaternary amines and phenols of quaternary amines / phenols = 0.3 to 0.8, and is used after being diluted with an organic solvent. The method for recovering gold according to one item.   The method for recovering gold according to claim 8, wherein the organic solvent is an organic solvent other than n-paraffin.   The method for recovering gold according to any one of claims 1 to 9, further comprising a step of washing the extractant with pure water after the solvent extraction step and before the reduction step.   The method for recovering gold according to any one of claims 1 to 10, wherein in the reduction step, an aqueous solution of sodium oxalate and / or an aqueous solution of oxalic acid is used as a reducing agent.   The method for recovering gold according to claim 11, wherein the amount of the reducing agent used is 1.5 to 5 molar equivalents relative to the gold contained in the extractant.   The method for recovering gold according to claim 11 or 12, wherein the contact between the extractant and the reducing agent is performed while stirring at a liquid temperature of 60C to 95C for 3 to 5 hours.   The method for recovering gold according to claim 13, wherein the liquid temperature is 75C to 85C.

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