JP7440865B2 - How to recover silver in copper electrolyte - Google Patents

Description

The present invention relates to a method for recovering silver contained as an impurity in a copper electrolyte by copper electrolytic refining.

Electrolytic refining of copper is performed using a sulfuric acid acidic copper sulfate aqueous solution as an electrolyte and blister copper produced from copper concentrate through a dry processing process as an anode. Copper). Note that, for the cathode, a thin copper plate called a seed plate separately produced from electrolytic copper, a reusable stainless steel plate, or the like is used.

The main anode reaction in copper electrolytic refining is the copper dissolution reaction. The blister copper used as an anode contains impurities such as gold, silver, lead, nickel, iron, antimony, bismuth, selenium, tellurium, and arsenic. Among them, most of the silver accumulates at the bottom of the electrolytic cell as a muddy solid substance called anode slime, but the solubility of silver chloride can be eluted into the electrolyte, and the silver eluted into the electrolyte is begins to precipitate on the cathode together with copper.

Silver is a noble metal, and by suppressing the precipitation of silver on the cathode and increasing the recovery rate, it is possible to improve the added value of the entire copper electrolytic refining process. As a method for improving the recovery rate of silver, there is a method of optimizing electrolytic conditions as disclosed in Patent Document 1, for example, but it has been difficult to recover silver eluted into the electrolytic solution.

Japanese Patent Application Publication No. 8-176878 JP2017-043556A

The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a method that can efficiently recover silver eluted into a copper electrolyte by electrolytic refining of copper.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have discovered that by bringing a copper electrolyte containing chloride ions in a specific concentration range into contact with an ammonium salt type ionic liquid, an efficient solution can be obtained. They discovered that silver can be extracted and recovered, leading to the completion of the present invention.

(1) The first aspect of the present invention is a method for recovering silver contained in a copper electrolyte, which comprises bringing the copper electrolyte into contact with an ionic liquid phase containing an ammonium salt type ionic liquid. It includes an extraction step of extracting silver contained in the liquid, and in the extraction step, the ionic liquid phase is brought into contact with a copper electrolyte having a chloride ion concentration of 0.1 mmol/L or more and 10 mmol/L or less, This is a silver recovery method in which chlorocomplex ions of silver are extracted into the ionic liquid phase.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、炭素数１～１２の置換又は非置換の炭化水素基を表し、Ｒ^１とＲ^２とＲ^３とは、同じであってもよく、互いに異なっていてもよく、それらが結合する窒素原子と共に互いに結合して環状アミンを形成してもよい。Ｒ^４は、炭素数１～４の置換又は非置換の炭化水素基を表す。Ａ^－及びＢ^－は、対アニオンを表す。ｎは、２～８の整数を表す。）で表される化合物である、銀の回収方法である。 (2) A second invention of the present invention is that in the first invention, the ammonium salt type ionic liquid has the following formula (I).

(In the formula, R ¹ , R ² and R ³ represent a substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, and R ¹ , R ² and R ³ may be the same or each other. They may be different, and may be bonded to each other together with the nitrogen atom to which they are bonded to form a cyclic amine. R ⁴ represents a substituted or unsubstituted hydrocarbon group having 1 to 4 carbon atoms. ^{A -} and B ⁻ represents a counter anion. n represents an integer from 2 to 8.) This is a method for recovering silver, which is a compound represented by

(3) The third invention of the present invention is the second invention, in which in the formula (I), A ^- is a halide ion, B ^- is N ^- (CF ₃ SO ₂ ) ₂ , and further , n is 3, which is a silver recovery method.

According to the present invention, silver eluted into a copper electrolyte can be efficiently recovered by electrolytic refining of copper.

FIG. 2 is a graph showing the relationship between the molar fraction of silver in each form and the chloride ion concentration in the solution.

Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the gist of the present invention. In this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "more than or equal to X and less than or equal to Y."

The method for recovering silver according to the present embodiment is a method for recovering silver eluted into an electrolytic solution by electrolytic refining of copper. Specifically, it includes an extraction step of bringing a copper electrolyte into contact with an ionic liquid phase containing an ammonium salt type ionic liquid to extract silver contained in the copper electrolyte.

In this silver recovery method, in the extraction step, a copper electrolyte with a chloride ion concentration of 0.1 mmol/L or more and 10 mmol/L or less is brought into contact with an ionic liquid phase containing an ammonium salt type ionic liquid. , is characterized by extracting silver chlorocomplex ions into its ionic liquid phase.

According to such a method, silver contained in the copper electrolyte can be efficiently recovered. More specifically, silver can be selectively extracted and recovered into an ionic liquid phase containing an ammonia salt type ionic liquid while suppressing the extraction of copper, iron, etc. in the copper electrolyte.

[About ammonia salt type ionic liquid]
As described above, the silver recovery method according to the present embodiment is characterized in that a copper electrolyte containing silver is brought into contact with an ionic liquid phase containing an ammonium salt type ionic liquid. Specifically, examples of the ammonia salt type ionic liquid include a compound represented by the following formula (I).

Here, in the above formula (I), R ¹ , R ² and R ³ each represent a substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, and R ¹ , R ² and R ³ are , may be the same or may be different from each other. Moreover, R ¹ , R ² and R ³ may be bonded to each other together with the nitrogen atom to which they are bonded to form a cyclic amine.

The number of carbon atoms in R ¹ , R ² and R ³ is preferably 2 to 12, more preferably 3 to 8, particularly preferably 4 to 8, from the viewpoint of improving the property of separating into two phases from the aqueous phase. In addition, the hydrocarbon groups of R ¹ , R ² and R ³ may be saturated or unsaturated, and may include an aromatic group, a cyclic hydrocarbon group, a straight chain hydrocarbon group, a branched carbonized Examples include hydrogen groups.

Substituents in the substituted hydrocarbon groups of R ¹ , R ² and R ³ include hydrocarbon groups (which may be saturated or unsaturated, aromatic groups, cyclic hydrocarbon groups, linear hydrocarbon groups). , branched hydrocarbon group, etc.), hydroxyl group, ether group, morpholino group, ester group, amide group, perfluoroalkyl group, nitrile group (cyano group), amino group, imino group, urea group, carboxyl group, carbonyl group (aldehyde group, ketone group), sulfonic acid group (sulfo group), nitro group, halogen, etc. Among these, straight-chain hydrocarbon groups and branched-chain hydrocarbon groups are preferred from the viewpoint of enhancing the property of separating into two phases from the aqueous phase. These may be used alone or in combination of two or more.

Further, R ⁴ represents a substituted or unsubstituted hydrocarbon group having 1 to 4 carbon atoms. Examples of the hydrocarbon group for R ⁴ include a straight chain hydrocarbon group and a branched chain hydrocarbon group. Specific examples include methyl group, ethyl group, propyl group, and butyl group.

Furthermore, A ⁻ and B ⁻ represent counteranions. Specifically, A ^- is preferably a halide ion from the viewpoint of ease of synthesis. Examples of B ⁻ include N ⁻ (CF ₃ SO ₂ ) ₂ (hereinafter also referred to as “NTf ₂ ⁻ ”), P ⁻ F ₆ , B ⁻ F ₄ , Cl ⁻ , CF ₃ SO ₃ ^−, and the like. Among these, B ^- is preferably N ^- (CF ₃ SO ₂ ) ₂ from the viewpoint of increasing the hydrophobicity of the compound, and Cl ^- is also preferred from the viewpoint of reducing the production cost of the ionic liquid. These may be used alone or in combination of two or more.

Further, n is an integer from 2 to 8. From the viewpoint of making the viscosity and hydrophobicity of the compound suitable as an extractant, n is preferably 2 to 6, and more preferably 3.

[Ionic liquid phase]
In the silver recovery method according to the present embodiment, an ionic liquid phase containing the above-mentioned ammonia salt type ionic liquid is used, and a copper electrolyte containing silver is brought into contact with this ionic liquid phase. As the ionic liquid phase, it is preferable to use a mixture of the above-described ammonia salt type ionic liquid compound as an extractant and a compound composed of other ionic liquids that are not involved in extraction.

Specifically, other ionic liquid compounds include, for example, a cation composed of 1-butyl-3-methylimidazolium (hereinafter also referred to as "BMIM ⁺ ") and an anion composed of N ^- (CF ₃ SO ₂ ) ₂ ionic liquids can be used. By using an ionic liquid phase formed by mixing such an ionic liquid and an ammonia salt type ionic liquid, it becomes stable as a liquid at room temperature.

In the ionic liquid phase, the content of the ammonia salt type ionic liquid is preferably 1% by mass to 50% by mass, more preferably 1% by mass to 10% by mass, based on 100% by mass of the ionic liquid. preferable.

[About the extraction process]
In the extraction step, silver contained in the copper electrolyte is extracted into an ionic liquid phase containing an ammonium salt type ionic liquid. The copper electrolyte to be treated is an electrolytic solution in which some of the impurities contained in the blister copper have been eluted through electrolytic refining of copper using blister copper as an anode, and in particular, it is an electrolyte in which silver as an impurity has been eluted. In addition, this copper electrolytic solution contains chloride ions added as an additive from the viewpoint of smoothing and uniform electrodeposition of electrolytic copper formed on the cathode.

In the silver recovery method according to the present embodiment, silver is extracted into the ionic liquid phase by bringing a copper electrolyte containing silver into contact with an ionic liquid phase containing an ammonium salt type ionic liquid. At that time, the chloride ion concentration in the copper electrolyte that is brought into contact with the ionic liquid phase is important, and specifically, the copper electrolyte that has a chloride ion concentration of 0.1 mmol/L or more and 10 mmol/L or less is brought into contact with the ionic liquid phase. .

FIG. 1 is a graph showing the relationship between the mole fraction of each form of silver and the chloride ion concentration in a solution. As shown in FIG. 1, when the chloride ion concentration in the copper electrolyte is less than 0.1 mmol (0.0001 mol)/L, the molar fraction of [AgCl ₂ ⁻ ], which is a silver chloro complex ion, is approximately It becomes zero, making extraction into the ionic liquid phase difficult. Furthermore, if the chloride ion concentration in the copper electrolyte exceeds 10 mmol (0.01 mol)/L, there is a problem that copper electrodeposited on the cathode during copper electrolysis will precipitate in the form of dendrites.

In contrast, by bringing a copper electrolyte with a chloride ion concentration in the range of 0.1 mmol/L to 10 mmol/L into contact with an ionic liquid phase containing an ammonium salt type ionic liquid, the ionic liquid phase Silver chloro complex ions can be extracted effectively.

Adjustment of the chloride ion concentration in the copper electrolyte is not particularly limited, but may be carried out, for example, by sampling a portion of the copper electrolyte, checking the chloride ion concentration by analysis, and adding hydrochloric acid as appropriate. can. For example, if it is recognized that the chloride ion concentration has decreased due to extraction into an ionic liquid phase containing an ammonium salt type ionic liquid, add hydrochloric acid to adjust the chloride ion concentration to within the above range. can do.

Here, the extraction rate of metal elements by an extraction operation in which a copper electrolyte containing silver is brought into contact with an ionic liquid phase containing an ammonium salt type ionic liquid can be calculated as follows.
(extraction rate)
When the concentration of the metal element in the copper electrolyte before the extraction operation is _C0 , and the concentration of the metal element in the copper electrolyte after the extraction operation is _C1 , the extraction rate E (%) of the metal element is calculated by the following formula: It can be calculated.
E=(C ₀ - C ₁ )/C ₀ ×100

EXAMPLES Hereinafter, the present invention will be described in more detail by showing examples, but the present invention is not limited to the following examples.

In addition, the analysis of metal elements in the copper electrolyte in the examples was performed by ICP emission spectrometry and atomic absorption spectrometry. In addition, analysis of chloride ion concentration was performed by fluorescent X-ray method using silver chloride separation.

[Synthesis of ammonium salt type ionic liquid, preparation of ionic liquid phase]
(Raw material for ammonium salt type ionic liquid)
An ammonia salt type ionic liquid was synthesized using the following raw materials. Note that these were used without further purification unless otherwise specified.
・1,3-dibromopropane (manufactured by Fujifilm Wako Pure Chemical Industries)
・1-Methylimidazole (manufactured by Tokyo Kasei Co., Ltd.)
・Lithium bis(trifluoromethanesulfonyl)imide (manufactured by Aldrich)
・Dimethylamine (manufactured by Tokyo Kasei Co., Ltd.)
・Iodomethane (manufactured by Tokyo Kasei Co., Ltd.)

Specifically, a compound (ammonium salt type ionic liquid) was synthesized according to the synthesis scheme shown in the following formula (II). Note that ¹ H-NMR of the compounds obtained in each process was analyzed using the following analytical equipment.
・^1H -NMR: Bruker Daltonics, (product name) AV400M digital NMR
・ICP-AES: Manufactured by Hitachi High-Tech Science Co., Ltd. (product name) SPECTRO ARCOS

(Synthesis of [1-(3-bromopropyl)-3-methylimidazolium bromide] (“Compound [1]))”
250 mL of an acetone solution of 200 g (1.08 mol) of 1,3-dibromopropane was added to a four-necked round-bottomed flask (1000 mL), and the inside of the flask was purged with argon. 8.21 g (100 mmol) of 1-methylimidazole was dissolved in 50 mL of acetone, and this solution was added dropwise over 30 minutes. Thereafter, the reaction solution was heated and refluxed in an oil bath set at 45° C. for 20 hours to carry out the reaction. The white solid produced during the reaction and the reaction solution were separated by decantation. Further, after dissolving the white solid in a small amount of ethanol, the white solid was reprecipitated by adding a large amount of acetone, and the product in the white solid was dissolved in acetone. The remaining solid and solution were again separated by decantation. The reaction solution and this solution were combined and concentrated under reduced pressure using a rotary evaporator and a vacuum dryer. Thereafter, a liquid separation operation was performed using the reaction solution/water, and the upper aqueous phase was taken out. Next, a liquid separation operation was performed using water (H ₂ O)/hexane, and the lower aqueous phase was taken out. The resulting aqueous solution was concentrated under reduced pressure using a rotary evaporator and a vacuum dryer. In this way, Compound 1 (C ₇ H ₁₂ Br ₂ N ₂ ) as a colorless liquid was obtained in a yield of 81% (23.3 g, 81.7 mmol).

The results of ¹ H-NMR of the obtained compound were as follows.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 2.58 (quin, J = 6.6 Hz, 2H), 3.50 (t, J = 6.2 Hz, 2H), 4.13 (s, 3H) , 4.61 (t, J = 6.8 Hz, 2H), 7.58 (t, J = 1.8 Hz, 1H), 7.64 (t, J = 1.8 Hz, 1H), 10.35 ( s, 1H)

(Synthesis of [1-(3-bromopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide)] (“Compound [2]”))
Add 150 mL of water (H ₂ O) to an eggplant flask (300 mL), and add 23.20 g (81.7 mmol) of compound [1] and 25.8 g (89.9 mmol) of lithium bis(trifluoromethanesulfonyl)imide to the water. Dissolved. Thereafter, the reaction was carried out with stirring at room temperature for 1 hour, and the reaction solution was extracted with chloroform (CHCl ₃ ). The extracted solution was dehydrated using anhydrous magnesium sulfate (MgSO ₄ ), filtered through Celite, and concentrated under reduced pressure using a rotary evaporator and a vacuum dryer. In this way, a colorless liquid compound [2] (C ₉ H ₁₂ BrF ₆ N ₃ O ₄ S ₂ ) was obtained in a yield of 91% (35.91 g, 74.2 mmol).

The results of ¹ H-NMR of the obtained compound were as follows.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 2.44 (quin, J = 6.5 Hz, 2H), 3.50 (t, J = 6.0 Hz, 2H), 3.97 (s, 3H) , 4.42 (t, J = 7.0 Hz, 2H), 7.29 (t, J = 1.8 Hz, 1H), 7.35 (t, J = 1.8 Hz, 1H), 8.85 ( s, 1H)

(Synthesis of [1-3-(dimethylaminopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide] (“Compound [3]”))
Compound [2] and dimethylamine were added to a three-neck round bottom flask (500 mL), and the inside of the flask was replaced with argon. Thereafter, the reaction solution was refluxed at room temperature for 24 hours to react. The reaction solution was concentrated under reduced pressure using a rotary evaporator. The concentrated reaction solution was mixed with CHCl ₃ /5% by mass NH ₃ aq. The upper phase was separated by 5% by mass NH ₃ aq. was removed. In addition, a liquid separation operation was performed using CHCl ₃ /H ₂ O to wash the lower CHCl ₃ phase. After dehydration with anhydrous MgSO ₄ , the organic phase was filtered through Celite and concentrated under reduced pressure using a rotary evaporator. Further, a liquid separation operation was performed using the obtained liquid/hexane to wash the ionic liquid phase. By concentrating under reduced pressure using a rotary evaporator and a vacuum dryer, compound [3] was obtained as a pale yellow liquid in a yield of 62% (11.5 g, 25.6 mmol).

The results of ¹ H-NMR of the obtained compound were as follows.
¹ H-NMR (400 MHz, CDCl ₃ ) δ=2.00 (tt, J=6.8 Hz, 6.6 Hz, 2H), 2.19 (s, 6H), 2.25 (t, J=6. 4Hz, 2H), 3.96 (s, 3H), 4.28 (t, J=6.8Hz, 2H), 7.27 (t, 1H), 7.33 (t, 1H), 8.80 (s, 1H)

(Synthesis of 1-(3-trimethylammoniumpropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (“Compound [4]”))
After adding compound [3], iodomethane, and methanol to a three-neck round bottom flask (300 mL), the reaction solution was stirred at room temperature for 24 hours. The reaction solution was concentrated under reduced pressure using a rotary evaporator and a vacuum dryer to obtain compound [4] as a pale yellow solid with a yield of 100% (1.41 g, 2.38 mmol).

The results of ¹ H-NMR of the obtained compound were as follows.
¹ H-NMR (400MHz, MeOD) δ = 2.46 (m, 2H), 3.19 (s, 9H), 3.50 (tt, 2H), 3.95 (s, 3H), 4.36 (t, J=7.2Hz, 2H), 7.62 (t, 1H), 7.70 (t, 1H), 8.99 (s, 1H)

(Preparation of ionic liquid phase)
An ionic liquid phase was prepared by mixing 1.0 g (1.7 mmol) of compound [4] with "BMIM ⁺ " and "NTf ₂ ^- " to a concentration of 5% by mass.

[Extraction of silver from copper electrolyte]
(Extraction process)
2 mL of the copper electrolyte having the liquid composition shown in Table 1 below was mixed with 0.4 g of the ionic liquid phase prepared as described above, and the mixture was horizontally reciprocated at 25°C and 100 rpm to form the copper electrolyte and ammonium salt type. An ionic liquid phase containing an ionic liquid was brought into contact with the ionic liquid phase. Here, the chloride ion concentration in the copper electrolyte was 1.1 mmol/L.

Table 2 below shows the analysis results of the ionic liquid phase obtained by the extraction operation. As can be seen from the extraction rates of each metal element shown in Table 2, 100% of silver could be extracted and recovered while hardly any copper was extracted.

Claims (1)

A method for recovering silver contained in a copper electrolyte, the method comprising:
an extraction step of extracting silver contained in the copper electrolyte by bringing the copper electrolyte into contact with an ionic liquid phase containing an ammonium salt type ionic liquid;
The ammonium salt type ionic liquid is (1-(3-trimethylammoniumpropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide),
In the extraction step, silver chlorocomplex ions are extracted into the ionic liquid phase by contacting the ionic liquid phase with a copper electrolyte having a chloride ion concentration of 0.1 mmol/L or more and 10 mmol/L or less. ,
How to recover silver.

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