Metal extractants

Abstract

The present invention aims to provide an extractant for extracting metal ions, particularly rare metals, which preferably allows for the selective recovery of metals by back extraction, and a method for extracting metals using the said metal extractant. [Solution] A hydrophobic deep eutectic solvent comprising a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid and / or hydrophobic catechol compound.

Description

[Technical Field]

[0001] The present invention relates to a hydrophobic deep eutectic solvent, a metal extractant containing the same, and a method for extracting and back-extracting metals. [Background technology]

[0002] In recent years, rare metals, particularly rare earth elements, have a wide range of applications, including magnets, battery materials, abrasives, phosphors, alloys, and optical glass, and their uses are expanding year by year. Rare earth elements are a collective term for 17 elements in total: scandium, yttrium, and 15 lanthanides. Scandium is extremely expensive and is used as an additive in high-strength aluminum alloys for aerospace applications and as scandia-stabilized zirconia (ScSZ), an electrolyte material for solid oxide fuel cells (SOFCs). Other rare metals, such as indium and zirconium, are also expected to see increased demand in the future.

[0003] Unlike other rare earth elements, scandium rarely concentrates in nature. Minerals with Sc as the main component include saltbaitite ((Sc,Y)Si2O7) and tortbaitite (Sc2Si2O7), but neither is found in sufficient quantities to be considered an ore. Currently, Sc is found as a byproduct of other metal ores. Nickel oxide is an example of a metal ore containing trace amounts of Sc.

[0004] Scandium contained in nickel oxide ore can be recovered from a leachate obtained by adding sulfuric acid to nickel oxide ore and pressurizing the leaching process. For example, Patent Document 1 shows that nickel and scandium can be recovered from oxide ore by performing a leaching step in which oxide ore is leached with acid under high temperature and pressure to obtain a leachate containing nickel and scandium; a first neutralization step in which a neutralizing agent is added to the leachate to adjust the pH to a range of 2 to 4 to remove iron and aluminum from the leachate as precipitates; a second neutralization step in which a neutralizing agent is added to the solution after the precipitates have been removed in the first neutralization step to adjust the pH to a range of greater than 4 to 7.5 to recover scandium from the solution as a precipitate; and a third neutralization step in which a neutralizing agent is added to further adjust the pH to greater than 7.5 to recover nickel from the solution as a precipitate.

[0005] However, attempting to operate industrially using the method described in Patent Document 1 presents various challenges. For example, because the pH adjustment range in the first neutralization step and the pH adjustment range in the second neutralization step are close together, scandium may precipitate along with iron and aluminum in the first neutralization step, potentially leading to a decrease in scandium extraction rate. Similarly, in the second neutralization step, iron and aluminum may precipitate along with scandium, potentially leading to a decrease in scandium purity, both of which are undesirable. Furthermore, adding a neutralizing agent generates a large amount of precipitate, but generally, precipitates obtained by adding alkali to acid are unstable, have poor filterability, and may result in increased costs due to the need to expand the scale of equipment. Therefore, it is preferable to minimize the number of neutralization steps, and selectively separating scandium from a scandium-containing solution by means such as solvent extraction is an effective method. However, scandium has chemical properties similar to other rare earth elements and iron. For this reason, selectively extracting scandium from a solution containing rare earth elements and / or iron using solvent extraction is extremely difficult.

[0006] One reported method for separating and recovering scandium is solvent extraction using alkyl phosphate esters such as 2-ethylhexyl 2-ethylhexylphosphonic acid (PC-88A) as the extractant (Patent Document 2). However, this method extracts not only scandium but also other rare earth elements, iron, and other elements. In particular, the leachate obtained by acid leaching and neutralizing nickel oxide ore contains many impurities such as aluminum, magnesium, calcium, manganese, iron, calcium, and nickel. This presents problems such as the time and cost involved in scrubbing, as well as the treatment of wastewater generated during scrubbing. Furthermore, to extract scandium, a practical extraction rate cannot be obtained unless the pH is maintained above a certain level. In the pH range suitable for scandium extraction, the extraction rate of the aforementioned impurities also increases, making it difficult to selectively separate only scandium. Thus, it is difficult to obtain an extractant that can selectively and effectively extract scandium from a system containing such impurities. Even in solvent extraction methods using phosphate esters having alkylcyclohexyl groups as extractants (Patent Document 3), at pH levels suitable for scandium extraction, not only scandium but also other rare earth elements, iron, and other elements are extracted.

[0007] When attempting to selectively extract scandium using conventional extractants and solvent extraction methods, raising the pH of the solution to around 4-5 increases the scandium extraction rate. However, this not only increases the amount of neutralizing agent required, but also promotes the formation of iron hydroxide, leading to co-precipitation of scandium and other valuable elements, resulting in losses. Furthermore, when attempting to separate scandium from such iron-containing solutions by ion exchange or solvent extraction, there is a problem in that inclusions called cladding tend to form during the extraction process.

[0008] Extraction and back-extraction of extractants containing chelating and / or complexing agents are proton-dominant reversible reactions. After extracting metal ions with the extractant, the metal ions are back-extracted from the extractant phase to the aqueous phase by adjusting the pH to a level where metal ion extraction does not occur by contacting the extractant phase with the aqueous phase. When using solvent extraction methods, a process is required that allows for extraction and back-extraction solely by pH setting, enabling highly efficient separation and recovery of the target component.

[0009] In solvent extraction methods (Patent Document 4) that use a composition obtained by dissolving N-lauroyl sarcosine in organic solvents such as kerosene, toluene, benzene, xylene, n-hexane, cyclohexane, 1,2-dichloroethane, chloroform, and carbon tetrachloride as an extractant, the selectivity for scandium, other rare earth elements, and iron is insufficient, and these are also extracted when scandium is extracted. Furthermore, scandium extraction occurs even at low pH levels suitable for back extraction, resulting in the problem that there is no pH range suitable for back extraction.

[0010] In a solvent extraction method (Patent Document 5) using a composition prepared by dissolving the diketone compound 2-tenoyltrifluacetone and trioctylphosphine oxide (TOPO), a compound having a phosphine oxide group, in organic solvents such as benzene, toluene, xylene, n-hexane, chloroform, dichloromethane, and 1-octanol as an extractant, the scandium extraction rate is high at approximately 30% even at a low pH of -0.1. However, since there are no pH conditions suitable for back extraction, it cannot be considered an appropriate process.

[0011] Ionic liquids have the advantage of being safer than conventional extractants that primarily consist of organic solvents, due to their non-volatile or low-volatility, non-flammable or flame-retardant properties. However, their monotonous reactivity makes it difficult to construct processes for selectively extracting target components. While it is possible to impart specific reactivity by introducing ligands to cations or anions, this is not practical from a cost perspective.

[0012] Deep eutectic solvents (DES) are known as solvents with characteristics similar to ionic liquids. Deep eutectic solvents are liquid compositions at room temperature that can be easily obtained by mixing a hydrogen-bond accepting compound (HBA (hydrogen-bond acceptor)) and a hydrogen-bond donor compound (HBD (hydrogen-bond donor)). Due to their hydrogen-bonding network, they have low volatility and unique reactivity. Because of the abundance of HBA and HBD combinations and their low cost, they have recently attracted attention as environmentally friendly solvents that can replace ionic liquids.

[0013] Patent Document 6 describes an invention using a deep eutectic solvent prepared by mixing a compound containing a hydroxyl group with a trialkylphosphine oxide compound as an extractant. In a solvent extraction method using a deep eutectic solvent obtained by mixing N-lauroyl sarcosine (NLS) and tri-n-octylphosphine oxide (TOPO) in a weight ratio of 2:1 as an extractant, the extraction rate of scandium in pH 1 to 3 was close to 100%. However, other rare earth elements and iron were also extracted. Furthermore, since there is no pH range in which back extraction is possible, scandium cannot be recovered alone by back extraction.

[0014] Zirconium is a rare metal that is expected to be recovered from sources such as electronic equipment waste and electrolytes in solid oxide fuel cells. Patent Document 7 describes an extractant used for the separation and recovery of zirconium and scandium, intended for the recycling of scandia-stabilized zirconia (ScSZ), an electrolyte material for solid oxide fuel cells (SOFCs). While selective extraction of zirconium allows for separation from scandium, the extraction rate of zirconium exceeds 90% in the pHeq range of 0.2 to 4.0, and there is no equilibrium pH (pHeq) range suitable for back-extraction of zirconium.

[0015] Indium is a rare metal expected to be recovered from electronic waste, compound semiconductor substrates, CIS solar cells, CIGS solar cells, etc. CIS-based solar cells and CIGS solar cells have a structure in which a back electrode layer, a light absorption layer, a buffer phase, and a transparent electrode layer are laminated in this order from the upper surface of the substrate glass, and the light absorption layer contains copper, indium, gallium, selenium, etc. Among them, indium is expensive, and the indium recovery technology from CIS-based solar cells and CIGS-based solar cells is very useful.

[0016] Thus, there is still a need for an extractant that selectively extracts metals, particularly rare metals, by solvent extraction and preferably separates and recovers them selectively and efficiently by back extraction.

Prior Art Documents

Patent Documents

[0017]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0018] An object of the present invention is to provide a metal extractant that extracts metal ions, particularly rare metals, and can preferably selectively recover metals by back extraction, and a method for extracting metals using the metal extractant. [Means for solving the problem]

[0019] To solve the aforementioned problems, the inventors diligently conducted research on extractants and solvent extraction methods. As a result of various studies, they focused on deep eutectic solvents that can be easily obtained by mixing HBA and HBD. Deep eutectic solvents can be complexed and / or chelated with metal ions by using compounds with complexing and / or chelating properties as constituent components. The inventors believed that the desired reactivity could be imparted by designing a composition based on the HSAB rule. Furthermore, they focused on the synergistic effect of combining multiple types of components, which brings about the imparting of specific reactivity and improvement of extraction performance.

[0020] As a result, we discovered a novel hydrophobic deep eutectic solvent containing (1) a hydrophobic sulfoxide compound as HBA and a hydrophobic carboxylic acid or hydrophobic catechol compound as HBD, a total of two basic components, and (2) a novel hydrophobic deep eutectic solvent containing a hydrophobic sulfoxide compound as HBA and a total of three basic components, a hydrophobic carboxylic acid and a hydrophobic catechol compound as HBD, thus completing the present invention.

[0021] In other words, the present invention relates to the following: [1] Hydrophobic sulfoxide compounds and, Hydrophobic carboxylic acids and / or hydrophobic catechol compounds, A hydrophobic deep eutectic solvent containing [the specified element]. [2] Hydrophobic sulfoxide compounds, Formula (1): R 2 -(R 1 ) n -S(=O)-(R 1 ) n -R 2 (1) During the ceremony, R 1 These are, independently, a linear or branched alkylene group having 1 to 4 carbon atoms, and a linear or branched alkenylene group having 2 to 4 carbon atoms. n is, independently of each other, 0 or 1, R 2 each is, independently of each other, a substituted or unsubstituted aromatic group, selected from compounds represented by the hydrophobic deep eutectic solvent according to [1] above. [3] R 2 is a substituted or unsubstituted phenyl group, the hydrophobic deep eutectic solvent according to [2] above. [4] The hydrophobic sulfoxide compound is diphenyl sulfoxide, the hydrophobic deep eutectic solvent according to [1] above. [5] The hydrophobic carboxylic acid is a hydrophobic carboxylic acid containing an aromatic group, the hydrophobic deep eutectic solvent according to any one of [1] to [4] above.

[0022] [6] The hydrophobic carboxylic acid is selected from the group consisting of phenylacetic acid, benzoic acid, 3-phenylpropionic acid, 4-phenylbutanoic acid, 5-phenylpentanoic acid, 6-phenylhexanoic acid, (±)-p-tolylpropionic acid, salicylic acid, 2-fluorobenzoic acid, 2,6-difluorobenzoic acid, 3-fluorosalicylic acid, 6-fluorosalicylic acid, 2-fluoro-6-(trifluoromethyl)benzoic acid, o-toluic acid, p-toluic acid and m-toluic acid, the hydrophobic deep eutectic solvent according to any one of [1] to [5] above. [7] The hydrophobic catechol compound is selected from catechols in which at least one of the 3-position, 4-position and 5-position is mono-, di- or tri-substituted with an alkyl group, the hydrophobic deep eutectic solvent according to any one of [1] to [6] above. [8] The hydrophobic catechol compound is 4-tert-butylcatechol, the hydrophobic deep eutectic solvent according to any one of [1] to [7] above. [9] Further comprising a hydrogen bond donating compound (HBD), the HBD not being a hydrophobic carboxylic acid and a hydrophobic catechol compound, the hydrophobic deep eutectic solvent according to any one of [1] to [8] above.

[10] The hydrogen bond donating compound (HBD) is hydrophobic phenols, the hydrophobic deep eutectic solvent according to [9] above.

[0023]

[11] A hydrophobic deep eutectic solvent according to any one of [1] to

[10] , comprising a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid.

[12] A hydrophobic deep eutectic solvent according to any one of [1] to

[10] , comprising a hydrophobic sulfoxide compound and a hydrophobic catechol compound.

[13] A hydrophobic deep eutectic solvent according to any one of [1] to

[12] , comprising a hydrophobic sulfoxide compound, a hydrophobic carboxylic acid, and a hydrophobic catechol compound.

[14] A metal extractant comprising the hydrophobic deep eutectic solvent described in any of [1] to

[13] above.

[15] The metal extractant according to

[14] , wherein the metal is selected from scandium, zirconium, and indium.

[16] A method for extracting a metal, comprising the step of extracting a metal using the metal extractant described in

[14] above.

[17] The method according to

[16] , wherein the metal is selected from scandium, zirconium and indium.

[18] A step of extracting the metal to be recovered into the organic phase to obtain an organic phase containing the metal to be recovered, which includes contacting an aqueous phase containing the metal to be recovered with an organic phase containing the metal extractant described in

[14] or

[15] above, and adjusting the equilibrium pH, and A process of back-extracting the target metal by bringing an organic phase containing the target metal into contact with an acidic solution. A method for recovering metals, including [specific metals].

[0024]

[19] The method according to

[18] , wherein the metal to be recovered is selected from scandium, zirconium, and indium.

[20] A step of contacting a solution containing scandium and iron with an organic phase containing a metal extractant containing the hydrophobic deep eutectic solvent described in

[13] above, adjusting the equilibrium pH to extract scandium into the organic phase and obtain a scandium-containing organic phase, and A scandium-containing organic phase is brought into contact with an acidic solution, and scandium is back-extracted to obtain a scandium-containing solution. including, A method for producing a scandium-containing solution.

[21] The method according to

[20] , wherein the scandium and iron-containing solution is a solution obtained by acid leaching a scandium and iron-containing nickel oxide ore.

[22] A step of contacting an acid leaching of zirconium-containing ore, which contains at least zircon or baddeleyite, with an organic phase containing the metal extractant described in

[14] , adjusting the equilibrium pH to extract zirconium into the organic phase and obtain a zirconium-containing organic phase, A process of obtaining a zirconium-containing solution by contacting a zirconium-containing organic phase with an acidic solution and back-extracting the zirconium. including, A method for producing a zirconium-containing solution.

[0025]

[23] A step of contacting a solution containing indium and at least one metal other than indium with an organic phase containing the metal extractant described in

[14] , adjusting the equilibrium pH to extract indium into the organic phase and obtain an indium-containing organic phase, A process of contacting an indium-containing organic phase with an acidic solution to back-extract indium and obtain an indium-containing solution. including, A method for producing an indium-containing solution.

[24] The method for producing an indium-containing solution according to

[23] , wherein the solution containing indium and at least one metal other than indium is an indium-containing acid leaching obtained by acid leaching of CIS solar cells and / or CIGS solar cell waste containing indium.

[25] A step of contacting a solution containing scandium and zirconium with an organic phase containing the metal extractant described in

[14] above, adjusting the equilibrium pH to selectively extract zirconium into the organic phase, thereby obtaining a zirconium-containing organic phase and a scandium-containing solution, and A step of contacting the zirconium-containing organic phase with an acidic solution to back-extract zirconium and obtain a zirconium-containing solution, including, A method for producing a scandium-containing solution or a zirconium-containing solution, comprising separating and recovering scandium and zirconium.

[26] The method according to

[25] , wherein the solution containing scandium and zirconium is a zirconium and scandium-containing acid leachate obtained by acid leaching solid oxide fuel cell electrolyte waste. [Effects of the Invention]

[0026] The metal extractant containing the hydrophobic deep eutectic solvent of the present invention enables selective extraction of metals and easy recovery of the metals by back extraction. The metal extractant of the present invention can selectively extract scandium from a solution containing at least scandium. It can selectively extract scandium from a solution containing scandium, other rare earth elements, iron, etc., without generating inclusions called cladding or extracting impurities. Furthermore, after the extraction of scandium, it can be back-extracted simply by adjusting the pH.

[0027] Conventional solvent extraction methods using extractants have the problem that when extraction curves are obtained for Fe and Sc with the vertical axis representing extraction rate and the horizontal axis representing equilibrium pH, the extraction curve for Fe is obtained at a lower pH, meaning that the extraction efficiency is in the order of Fe > Sc, and scandium cannot be selectively extracted. Furthermore, because scandium is extracted with high efficiency even at low pH, scandium cannot be back-extracted. However, with the solvent extraction method using the metal extractant of the present invention, the extraction efficiency is in the order of Sc > Fe > other rare earth elements, or Sc > other rare earth elements > Fe, and scandium can be selectively extracted. In addition, since there is a pH range in the low pH region where scandium is not extracted, scandium can be back-extracted.

[0028] Furthermore, conventional solvent extraction methods use large quantities of organic solvents as extractants, which are solutions of complexing agents and / or chelating agents such as carboxylic acids, diketone compounds, and alkyl phosphate esters dissolved in organic solvents such as kerosene, toluene, benzene, xylene, n-hexane, cyclohexane, 1,2-dichloroethane, chloroform, and carbon tetrachloride. In contrast, the solvent extraction method using the metal extractant of the present invention does not require the use of organic solvents.

[0029] Furthermore, the metal extractant of the present invention exhibits high extraction efficiency for indium and zirconium, and does not extract indium and zirconium in the low pH range, thus enabling back-extraction of indium and zirconium.

[0030] The hydrophobic deep eutectic solvent contained in the metal extractant of the present invention is low-volatility, making it safer than conventional solvent extraction methods that use large amounts of organic solvents, and it generates less cladding compared to conventional extractants composed of organic solvents and complexing agents and / or chelating agents. Furthermore, it is relatively inexpensive and exhibits unique reactivity, making it more practical than expensive ionic liquids with monotonous reactivity. [Brief explanation of the drawing]

[0031] [Figure 1] This figure shows the extraction behavior of each metal ion in Example A. [Figure 2] This figure shows the extraction behavior of each metal ion in Example 1. [Figure 3] This figure shows the extraction behavior of each metal ion in Example 2. [Figure 4] This figure shows the extraction behavior of each metal ion in Example B. [Figure 5] This figure shows the extraction behavior of each metal ion in Example C. [Figure 6] This figure shows the extraction behavior of each metal ion in Example D. [Figure 7] This figure shows the extraction behavior of each metal ion in Example E. [Figure 8] This figure shows the extraction behavior of each metal ion in Comparative Example 1. [Figure 9] This figure shows the extraction behavior of each metal ion in Example 3. [Figure 10] This figure shows the extraction behavior of each metal ion in Example 4. [Figure 11] This figure shows the extraction behavior of each metal ion in Example 5. [Figure 12] This figure shows the extraction behavior of each metal ion in Example 6. [Figure 13] This figure shows the extraction behavior of each metal ion in Example 7. [Figure 14] This figure shows the extraction behavior of each metal ion in Comparative Example 2. [Figure 15] This figure shows the extraction behavior of each metal ion in Comparative Example 3. [Figure 16] This figure shows the extraction behavior of each metal ion in Comparative Example 4. [Figure 17] This figure shows the extraction behavior of each metal ion in Example 8. [Figure 18] This figure shows the extraction behavior of each metal ion in Comparative Example 5. [Figure 19] This figure shows the extraction behavior of each metal ion in Example 9. [Figure 20] This figure shows the extraction behavior of each metal ion in Example 10. [Figure 21] This figure shows the extraction behavior of each metal ion in Example 15. [Figure 22] This figure shows the extraction behavior of each metal ion in Example 16. [Figure 23] This figure shows the extraction behavior of each metal ion in Example 17. [Figure 24] This figure shows the extraction behavior of each metal ion in Example 18. [Figure 25] This figure shows the extraction behavior of scandium ions in Example 19. [Figure 26] This figure shows the extraction behavior of scandium ions in Example 20. [Figure 27] This figure shows the extraction behavior of indium ions in Example 21. [Figure 28] This figure shows the extraction behavior of scandium ions in Example 22. [Modes for carrying out the invention]

[0032] The present invention will be described in detail below based on preferred embodiments of the present invention. The hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound as HBA and a hydrophobic carboxylic acid and / or hydrophobic catechol compound as HBD as basic constituent components. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid. In another embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid, but does not contain a hydrophobic catechol compound. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic catechol compound. In another embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic catechol compound, but does not contain a hydrophobic carboxylic acid. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound, a hydrophobic carboxylic acid as the HBD, and a hydrophobic catechol compound. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound and a hydrophobic catechol compound. In one embodiment, the hydrophobic deep eutectic solvent of the present invention comprises a hydrophobic sulfoxide compound, a hydrophobic carboxylic acid, and a hydrophobic catechol compound.

[0033] A hydrophobic deep eutectic solvent is a deep eutectic solvent (DES) that exhibits hydrophobicity. DES is a liquid composition at room temperature obtained by mixing HBA and HBD. Room temperature is defined as 20°C ± 15°C, i.e., in the range of 5°C to 35°C. In a preferred embodiment, the hydrophobic deep eutectic solvent of the present invention has a low freezing point. The freezing point may be 5°C or lower, and more preferably -5°C or lower. Due to its low freezing point, the hydrophobic deep eutectic solvent of the present invention has the advantage of being less prone to solidification and easier to handle during storage, transportation, and use as an extractant after manufacturing. HBA and HBD are solids at room temperature, or one of them is solid at room temperature. When mixed, a eutectic melting point depression occurs, and they become liquid at room temperature. DES has physical properties similar to ionic liquids. DES has a low vapor pressure, is flame-retardant, has high thermal and electrochemical stability, and readily dissolves various substances. Furthermore, it is generally more environmentally friendly and less toxic than ionic liquids. Because it can be easily prepared by simply mixing HBA and HBD, it can be provided at a low cost.

[0034] [Hydrophobic deep eutectic solvent] In hydrophobic deep eutectic solvents, the compounds used as HBA components are hydrophobic sulfoxide compounds. Sulfoxide compounds are a group of compounds in which two carbon atoms are bonded to a sulfinyl group -S(=O)-, and are sulfoxide compounds that have one or more hydrophobic groups (functional groups) that confer hydrophobicity. In one embodiment, a hydrophobic deep eutectic solvent is, Formula (1): R 2 -(R 1 ) n -S(=O)-(R 1 ) n -R 2 (1) During the ceremony, R 1 These are, independently, a linear or branched alkylene group having 1 to 4 carbon atoms, and a linear or branched alkenylene group having 2 to 4 carbon atoms. n is either 0 or 1, independently of each other. R 2 Each of these is independently a substituted or unsubstituted aromatic group. It is selected from compounds represented by the following:

[0035] In equation (1), n ​​is either 0 or 1, preferably n is 0. R 2 Examples of aromatic groups include aromatic hydrocarbon groups. Examples of aromatic hydrocarbon groups, though not limited to these, include C6-C22 aryl groups such as phenyl groups, naphthyl groups, and anthryl groups. Preferably, the aromatic hydrocarbon group is a phenyl group. Aromatic groups may be substituted with substituents. Examples of substituents include C1-4 saturated or unsaturated hydrocarbon groups and halogens. Examples of C1-4 saturated or unsaturated hydrocarbon groups include C1-4 alkyl groups and C2-4 alkenyl groups. Preferred substituents are C1-4 alkyl groups and halogens such as F, Cl, I, and Br.

[0036] R 2 Based on the relationship between melting point and molecular size, an unsubstituted phenyl group or a substituted phenyl group in which a hydrogen atom of the phenyl group is replaced by a substituent is preferred. Therefore, preferred hydrophobic sulfoxide compounds are diphenyl sulfoxide or diphenyl sulfoxide derivatives. Diphenyl sulfoxide derivatives are compounds having a structure in which diphenyl sulfoxide is substituted with substituents. Examples of substituents include C1-C4 saturated or unsaturated hydrocarbon groups and halogens. Preferred diphenyl sulfoxide derivatives are compounds in which both phenyl groups are substituted with C1-C4 alkyl groups or halogens, particularly compounds in which the substitution occurs at the p-position of the phenyl group, such as di-P-tolyl sulfoxide and bis(4-chlorophenyl) sulfoxide. From the viewpoint of ease of dissolution, hydrophobic sulfoxides with a melting point of 150°C or less and / or a molecular weight of 300 or less are preferred. Hydrophobic sulfoxide compounds may be included in the hydrophobic deep eutectic solvent one or more types.

[0037] The compounds used as HBD components in the hydrophobic deep eutectic solvent of the present invention are two components: a hydrophobic carboxylic acid and a hydrophobic catechol compound. A hydrophobic carboxylic acid is a carboxylic acid having a hydrophobic group (functional group) that confers hydrophobicity. While not particularly limited, any hydrophobic carboxylic acid is preferable, but carboxylic acids containing aromatic groups are preferred. Examples of hydrophobic carboxylic acids include phenylacetic acid, benzoic acid, 3-phenylpropionic acid, 4-phenylbutanoic acid, 5-phenylpentanoic acid, 6-phenylhexanoic acid, 2-phenylbutyric acid, p-hydroxybenzoic acid, m-hydroxybenzoic acid, salicylic acid, 3,5-tert-butylsalicylic acid, (±)-2-(p-tolyl)propionic acid, o-toluic acid, p-toluic acid, m-toluic acid, 2-ethylbenzoic acid, 4-ethylbenzoic acid, 3,5-dimethylbenzoic acid, 2,4- Dimethylbenzoic acid, 3,4-dimethylbenzoic acid, 2,5-dimethylbenzoic acid, 2,6-dimethylbenzoic acid, 2,3-dimethylbenzoic acid, 3-methylsalicylic acid, 4-methylsalicylic acid, 5-methylsalicylic acid, 2-fluorobenzoic acid, 3-fluorobenzoic acid, 4-fluorobenzoic acid, 2,3-difluorobenzoic acid, 2,4-difluorobenzoic acid, 2,5-difluorobenzoic acid, 2,6-difluorobenzoic acid, 3,4-difluorobenzoic acid, 3,5-difluorobenzoic acid,

[0038] Preferred ingredients include 2-(trifluoromethyl)benzoic acid, 3-(trifluoromethyl)benzoic acid, 4-(trifluoromethyl)benzoic acid, 4-(trifluoromethyl)salicylic acid, 2-fluoro-3-(trifluoromethyl)benzoic acid, 2-fluoro-5-(trifluoromethyl)benzoic acid, 2-fluoro-6-(trifluoromethyl)benzoic acid, 3-fluoro-4-(trifluoromethyl)benzoic acid, 3-fluoro-5-(trifluoromethyl)benzoic acid, 4-fluoro-2-(trifluoromethyl)benzoic acid, 4-fluoro-3-(trifluoromethyl)benzoic acid, 3,5-bis(trifluoromethyl)benzoic acid, 3-fluorosalicylic acid, 4-fluorosalicylic acid, 5-fluorosalicylic acid, 6-fluorosalicylic acid, caffeic acid, and 3,4-dihydroxyhydrocinnamic acid. More preferred are benzoic acid, 3-phenylpropionic acid, 4-phenylbutanoic acid, 5-phenylpentanoic acid, salicylic acid, (±)-2-(p-tolyl)propionic acid, 2-fluorobenzoic acid, 2,6-difluorobenzoic acid, 3-fluorosalicylic acid, 6-fluorosalicylic acid, 2-fluoro-6-(trifluoromethyl)benzoic acid, o-toluic acid, p-toluic acid, m-toluic acid, and the like. The hydrophobic carboxylic acid may be present in the hydrophobic deep eutectic solvent in one or more types.

[0039] In this specification, "catechol compound" refers to a general term for compounds having two hydroxyl groups at the ortho position on a benzene ring. A "hydrophobic catechol compound" is a catechol compound that has one or more hydrophobic groups (functional groups) that confer hydrophobicity. Examples of hydrophobic groups in catechol compounds include C1-6, preferably C1-4 saturated or unsaturated hydrocarbon groups. A preferred hydrophobic group is the tert-butyl group. Preferred hydrophobic catechol compounds are catechols in which the 3rd, 4th, and 5th positions are monosubstituted, disubstituted, or trisubstituted with alkyl groups. While not particularly limited, 4-tert-butylcatechol, 3,5-di-tert-butylcatechol, 3-methylcatechol, 4-methylcatechol, 4-ethylcatechol, and 4-ethylcatechol are preferred. More preferred are 4-tert-butylcatechol and 3,5-di-tert-butylcatechol. The hydrophobic catechol compounds may be present in the hydrophobic deep eutectic solvent in groups of one or more.

[0040] The hydrophobic deep eutectic solvent of the present invention is a hydrophobic deep eutectic solvent that contains a total of three basic components: a hydrophobic sulfoxide compound as HBA, and a hydrophobic carboxylic acid and a hydrophobic catechol compound as HBD. The hydrophobic deep eutectic solvent of the present invention may consist of these components, and further, HBDs other than the hydrophobic carboxylic acid and hydrophobic catechol compound may be added as needed. In this case, the hydrophobic sulfoxide compound may be added in the required amount as appropriate.

[0041] Other hydrogen bond donors (HBDs) that can be added, besides hydrophobic carboxylic acids and hydrophobic catechol compounds, include hydrophobic phenols and nitrogen-containing heterocyclic compounds. In this specification, "phenols" refers to a general term for compounds having a hydroxyl group on an aromatic substituent. "Hydrophobic phenols" are compounds among "phenols" that have one or more hydrophobic groups (functional groups) that confer hydrophobicity. Examples of hydrophobic groups in phenols include C1-7, preferably C1-4 saturated or unsaturated hydrocarbon groups.

[0042] Nitrogen-containing heterocyclic compounds are any compounds having a saturated or unsaturated nitrogen-containing heterocyclic ring containing at least one nitrogen atom in its ring structure, and include compounds in which the ring has a functional group. Examples of such compounds include 2-methyl-8-quinolinol and 8-quinolinol.

[0043] Further compounds that can be added to provide preferred hydrogen bonds include 2-tert-butylphenol, 3-tert-butylphenol, 4-tert-butylphenol, 2-tert-butyl-p-cresol, 6-tert-butyl-o-cresol, 6-tert-butyl-m-cresol, 4-sec-butyl-2,6-di-tert-butylphenol, 2-tert-butyl-4-ethylphenol, 2-tert-butyl-4,6-dimethylphenol, and 2,6- Examples include di-tert-butyl-p-cresol, 4,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-4-ethylphenol, 2,4-di-tert-butylphenol, 2,6-di-tert-butylphenol, 3,5-di-tert-butylphenol, 2,4,6-tri-tert-butylphenol, 2-methyl-8-quinolinol, 8-quinolinol, 4-benzylpyrogallol, thymol (2-isopropyl-5-methylphenol), etc. More preferably are 4-tert-butylphenol and thymol.

[0044] Hydrophobic deep eutectic solvents can be obtained by mixing hydrophobic sulfoxide compounds, hydrophobic carboxylic acids, and hydrophobic catechol compounds. Shaking and heating may be performed during mixing as needed. HBA and HBD may be solids individually or one of them may be solid at room temperature, and mixing them causes eutectic melting point depression, resulting in a liquid at room temperature. Specifically, the mixture consists of three components: a hydrophobic sulfoxide compound as HBA, and a compound selected from a total of three components: a hydrophobic carboxylic acid and a hydrophobic catechol compound as HBD, or a compound selected from a total of four components including an additional hydrogen bonding donor. The time required for liquefaction varies depending on the components mixed, but is generally around 20 to 120 minutes at room temperature. The time required for liquefaction can be shortened by heating (for example, to about 50 °C) and shaking.

[0045] The mixing ratio of HBA and HBD can be adjusted to any appropriate ratio depending on the types of HBA and HBD used. It is preferable that one compound be present in a mixture of at least 0.1% by weight of the total. The molar ratio of the hydrophobic sulfoxide compound (HBA) to the hydrophobic carboxylic acid (HBD1) is preferably in the range of 1:1 to 2:1, the molar ratio of the hydrophobic sulfoxide compound (HBA) to the hydrophobic catechol compound (HBD2) is preferably in the range of 1:1 to 2:1, and the molar ratio of the hydrophobic sulfoxide compound (HBA) to the compound that provides additional hydrogen bonds (HBD3) is preferably in the range of 1:1 to 2:1. By combining these, the hydrophobic deep eutectic solvent of the present invention is completed.

[0046] A more preferable condition is that the number of moles of the constituent components other than the hydrophobic sulfoxide compound are equal. When using one type each of hydrophobic sulfoxide compound (HBA), hydrophobic carboxylic acid (HBD1), and hydrophobic catechol compound (HBD2), it is preferable that their molar ratio is in the range of 3:1:1 to 4:1:1. When using two types of hydrophobic carboxylic acid (HBD1), it is preferable that the molar ratio of hydrophobic sulfoxide compound (HBA), hydrophobic carboxylic acid 1 (HBD1-1), hydrophobic carboxylic acid 2 (HBD1-2), and hydrophobic catechol compound (HBD2) is in the range of 4:1:1:1 to 6:1:1:1. When adding a hydrogen bond donating compound (HBD3), it is preferable that the molar ratio of the hydrophobic sulfoxide compound (HBA), hydrophobic carboxylic acid (HBD1), hydrophobic catechol compound (HBD2), and additional hydrogen bond donating compound (HBD3) be in the range of 4:1:1:1 to 6:1:1:1.

[0047] In the basic configuration of the hydrophobic deep eutectic solvent of the present invention, the concentration of the hydrophobic sulfoxide is not particularly limited, but the content is preferably 40% by weight or more, and more preferably 60% by weight or more, relative to the total weight of the hydrophobic deep eutectic solvent. In the basic configuration of the hydrophobic deep eutectic solvent of the present invention, the concentration of the hydrophobic carboxylic acid is not particularly limited, but the content is preferably 1% by weight or more, and more preferably 10% by weight or more, relative to the total weight of the hydrophobic deep eutectic solvent. In the basic configuration of the hydrophobic deep eutectic solvent of the present invention, the concentration of the hydrophobic catechol compound is not particularly limited, but the content is preferably 0.1% by weight or more, and more preferably 2.1% by weight or more, relative to the total weight of the hydrophobic deep eutectic solvent. In the basic configuration of the hydrophobic deep eutectic solvent of the present invention, the concentration of hydrogen-bonding compounds (HBDs) other than hydrophobic carboxylic acids and hydrophobic catechol compounds that can be added is not particularly limited, but the content is preferably 5% by weight or more, and more preferably 10% by weight or more, relative to the total weight of the hydrophobic deep eutectic solvent. The hydrophobic compounds used in the present invention (sulfoxides, carboxylic acids, catechols, and HBDs which can be added) are preferably compounds with a solubility in water (at 20°C) of 1.0 g / 100 mL or less.

[0048] [Metal extractants] This invention relates to a metal extractant containing the hydrophobic deep eutectic solvent of the present invention. The metal extractant of the present invention can be used for the extraction, preferably extraction and back-extraction, of metal ions. The extraction and back-extraction mechanism of metal ions is a proton-dominant reversible reaction that occurs in the hydrophobic deep eutectic solvent components acting as complexing agents or chelating agents with the metal ions. By setting and adjusting the pH to an appropriate value, the extraction and back-extraction of metal ions can be easily controlled. In this specification, descriptions relating to the extraction of various metals are used interchangeably with descriptions relating to the extraction of various metal ions unless otherwise specified.

[0049] In this specification, when a metal extraction operation is performed and an extraction curve is obtained for each metal with the vertical axis representing the extraction rate and the horizontal axis representing the equilibrium pH, metals whose extraction curve is obtained on the lower pH side are understood to have good extraction efficiency because they can be selectively extracted at a specific pH. If there is a difference in extraction efficiency between the target metal and other metals, the metal with higher extraction efficiency can be selectively extracted, so the target metal is not limited. Multiple types, for example, two types of metals, may be separated from other metals and extracted together. The metals to be extracted can be selected from, for example, scandium, indium, and zirconium. Scandium, indium, and zirconium can be extracted individually or in combination of two or more by adjusting the equilibrium pH.

[0050] The pH conditions for selectively extracting scandium from a solution containing iron and other rare earth elements are those where the extraction efficiency is in the order of Sc > Fe > other rare earth elements, or Sc > other rare earth elements > Fe. The pH conditions for back-extracting scandium are those in a pH range where scandium extraction does not occur, or in a pH range where the scandium extraction rate is extremely low. Scandium is extracted, and after phase separation of the extractant phase and the aqueous phase, the aqueous phase is removed. The extractant is brought into contact with a new aqueous phase for back-extraction, and the pH is adjusted to a low pH range where scandium extraction does not occur, thereby back-extracting scandium from the extractant phase to the aqueous phase.

[0051] In a preferred embodiment of the present invention, the hydrophobic deep eutectic solvent is characterized by having three basic components: a hydrophobic sulfoxide compound as HBA, and a hydrophobic carboxylic acid and a hydrophobic catechol compound as HBD. Surprisingly, however, if only one of the HBD components is present, scandium cannot be separated from Fe and selectively extracted. In solvent extraction methods using a hydrophobic deep eutectic solvent containing only hydrophobic sulfoxide compounds as HBA and hydrophobic carboxylic acids as HBD as the extractant, the extraction efficiency at all pH levels follows the order Fe > Sc > other rare earth elements, and conditions for selective extraction of scandium cannot be obtained (Example A).

[0052] On the other hand, in solvent extraction methods using hydrophobic deep eutectic solvents containing only hydrophobic sulfoxide compounds or hydrophobic catechol compounds as HBAs as extractants, the extraction behavior of scandium and iron is similar, and conditions suitable for selective extraction of scandium cannot be obtained (Example B).

[0053] In contrast, with a hydrophobic deep eutectic solvent containing a diphenyl sulfoxide compound as HBA and hydrophobic carboxylic acid and hydrophobic catechol compounds as HBD, the extraction efficiency was in the order of Sc > Fe > other rare earth elements, allowing for selective extraction of scandium. The change in extraction behavior is thought to be due to the synergistic effect of 4-tert-butylcatechol. Furthermore, since there is a pH range in which scandium is not extracted, scandium can be back-extracted, for example, at pH 2.0 or below.

[0054] [Methods for extracting metals] The separation and recovery of metals according to the present invention is performed by solvent extraction. A solution (aqueous phase) containing the metal extractant of the present invention and various metal ions is used. The solution is not particularly limited as long as it contains various metal ions and can form an aqueous phase, but typically the solution is an aqueous solution. The concentrations of the metals contained in the solution (aqueous phase) are, independently, 1 × 10⁻⁶. -4 It is preferably ~1M, more preferably 1×10 -3 It is approximately 0.1M.

[0055] In the case of scandium extraction, the aforementioned solution (aqueous phase) contains scandium, and may also contain iron, rare earth elements, magnesium, calcium, aluminum, chromium, manganese, nickel, cobalt, zirconium, and the like. Rare earth elements are the 17 elements: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0056] In the case of zirconium extraction, the aforementioned solution (aqueous phase) contains zirconium, and may also contain other elements such as scandium.

[0057] In the case of indium extraction, the aforementioned solution (aqueous phase) contains indium, and may also contain copper, zinc, gallium, selenium, molybdenum, tin, and the like.

[0058] The present invention relates to a solvent extraction method for metal ions, and the method includes a step of extracting the target metal into the organic phase to obtain an organic phase containing the target metal, which includes contacting an aqueous phase containing the target metal with an organic phase containing the metal extractant of the present invention, and adjusting the equilibrium pH. The equilibrium pH is adjusted by adding an acid or base to the aqueous and / or organic phase. The pH is adjusted to an equilibrium pH where the extraction of other coexisting metals is minimal and the target metal is predominantly extracted. Preferably, the pH is adjusted to a level where the extraction rate of the target metal is 50% or higher, preferably 60% or higher, and more preferably 70% or higher. Even at pH levels where the extraction rate is not 100%, it is possible to achieve 100% extraction by repeating the extraction operation.

[0059] The acid used to adjust the pH is not particularly limited, but examples include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, or organic acids such as formic acid, acetic acid, and oxalic acid. Inorganic acids are preferred, and hydrochloric acid, nitric acid, and sulfuric acid are more preferred. Only one type of acid may be used, or two or more types of acids may be mixed and used as needed. Furthermore, preferred bases for adjusting the pH include NaOH, KOH, LiOH, NH3, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and choline. More preferably, NaOH, KOH, and NH3 are used. Ammonia water is preferred for NH3. Only one type of base may be used, or two or more types of bases may be mixed and used as needed.

[0060] [Reverse extraction method] After extracting the target metal, the extractant phase and the aqueous phase are separated, and the aqueous phase is removed. The extractant is brought into contact with a new aqueous phase for back-extraction and shaken thoroughly. pH adjustment is performed using an acid during back-extraction. By adjusting the pH to a low pH range where extraction of the target metal does not occur, scandium is back-extracted from the extractant phase into the aqueous phase. The acid used for back-extraction is not particularly limited, but inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, or organic acids such as formic acid, acetic acid, and oxalic acid are preferred. Hydrochloric acid, nitric acid, and sulfuric acid are more preferred.

[0061] [Methods for recovering metal] The present invention also provides a method for recovering a metal, comprising the steps of: contacting an aqueous phase containing the metal to be recovered with an organic phase containing the metal extractant of the present invention; and adjusting the equilibrium pH, thereby extracting the metal to be recovered into the organic phase to obtain an organic phase containing the metal to be recovered; and A process of back-extracting the target metal by bringing an organic phase containing the target metal into contact with an acidic solution. The method includes the foregoing. The metals to be recovered can be selected from, for example, scandium, indium, and zirconium.

[0062] In this specification, “acidic solution” is used to lower the pH and functions as a solvent for back extraction. The acidic solution is not particularly limited as long as it can lower the pH and become an aqueous phase, but it may be a solution containing an acid and water, an aqueous organic solvent, or a mixture thereof. Typically it is an aqueous solution of an acid, and is not particularly limited, but may be water containing an inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, or phosphoric acid, or an organic acid such as formic acid, acetic acid, or oxalic acid. A preferred acidic aqueous solution is an aqueous solution of an inorganic acid, and more preferably an aqueous solution of hydrochloric acid, nitric acid, or sulfuric acid. Only one type of acid may be used, or two or more types of acids may be mixed as needed. In addition, a water-soluble organic solvent may be mixed with the acid aqueous solution in an amount ranging from 1 to 90% by weight.

[0063] The aqueous phase containing the metal to be recovered may include a solution containing the metal to be recovered and water, an aqueous solvent, or a mixture thereof that can form the aqueous phase. Typically, the aqueous phase is an aqueous solution, which may contain a water-soluble organic solvent in the range of 1 to 90% by weight. When the metal to be recovered is selected from scandium, indium, and zirconium, the aqueous phase containing the metal to be recovered may be the solution used in the method for producing the scandium, indium, or zirconium-containing solution described below. Furthermore, the equilibrium pH during extraction and the equilibrium pH during back-extraction may also be the same conditions as those used in the same production method.

[0064] [Method for producing a scandium, indium, or zirconium-containing solution] The present invention also relates to a method for producing a scandium-containing solution from a solution containing scandium and a metal other than scandium. Solutions containing scandium and metals other than scandium are not particularly limited, as long as they contain scandium and metals other than scandium and can form an aqueous phase, but include solutions containing scandium and metals other than scandium with water, aqueous organic solvents, or mixtures thereof. Typically, the solution is an aqueous solution containing scandium and metals other than scandium, and the aqueous solution may contain a water-soluble organic solvent in the range of 1 to 90% by weight. Examples include solutions containing scandium and iron and / or rare earth elements, such as process solutions for nickel oxide ore, specifically solutions obtained by acid leaching of nickel oxide ore. The process solution for nickel oxide ore may contain magnesium, aluminum, scandium, chromium, manganese, iron, nickel, and cobalt. The pH when extracting scandium into the organic phase can vary depending on the composition of the hydrophobic deep eutectic solvent of the present invention and is not limited thereto, but an equilibrium pH of 2.0 to 4.0 is preferred, and a pH of 2.5 to 3.5 is more preferred. The pH when back-extracting scandium into the aqueous phase is not particularly limited as long as it is in a low pH range where scandium extraction does not occur or occurs only in very small amounts, but for example, it is pH 0.9 or lower.

[0065] The present invention also relates to a method for producing a scandium-containing solution from a solution containing zirconium and a metal other than zirconium. Solutions containing zirconium and metals other than zirconium are not particularly limited, as long as they contain zirconium and metals other than zirconium and can form an aqueous phase, but examples include solutions containing scandium and metals other than scandium with water, an aqueous organic solvent, or a mixture thereof. Typically, the solution is an aqueous solution containing scandium and metals other than scandium, and the aqueous solution may contain a water-soluble organic solvent in the range of 1 to 90% by weight. Examples of such solutions include solutions obtained by acid leaching the electrolyte of a solid oxide fuel cell, which may contain scandium and indium in addition to zirconium.

[0066] The present invention also relates to a method for producing a scandium-containing solution from an acid leachate of an ore containing zirconium, such as at least zircon (ZrO2) or baddeleyite (ZrSiO4), wherein the steps and conditions can be referred to in the context of a method for producing a scandium-containing solution from a solution containing scandium and a metal other than scandium, by substituting "a solution containing scandium and a metal other than scandium" with "an acid leachate of an ore containing zirconium, such as at least zircon (ZrO2) or baddeleyite (ZrSiO4)."

[0067] The pH when extracting zirconium into the organic phase may vary depending on the composition of the hydrophobic deep eutectic solvent of the present invention, and is not limited thereto, but an equilibrium pH of 1.2 to 2.7 is preferred. The pH when zirconium is back-extracted into the aqueous phase is not particularly limited as long as it is in a low pH range where zirconium extraction does not occur or occurs only in very small amounts, but for example, the equilibrium pH is 0.9 or lower.

[0068] The present invention also relates to a method for producing a scandium-containing solution from a solution containing indium and a metal other than indium. Solutions containing indium and other metals are not particularly limited, as long as they contain indium and other metals and can form an aqueous phase, but examples include solutions containing indium and other metals and water, an aqueous organic solvent, or a mixture thereof. Typically, the solution is an aqueous solution containing indium and other metals, and the aqueous solution may contain a water-soluble organic solvent in the range of 1 to 90% by weight. Examples of such solutions include acid leaching solutions of indium ore such as sphalerite and indium copper steel, acid leaching solutions of CIS and CIGS solar cell waste containing indium, acid leaching solutions of flat panel display waste with transparent conductive films such as ITO and IZO films, acid leaching solutions of waste materials such as light-emitting diodes, and waste liquids from the etching process of ITO and IZO substrates. These solutions contain, in addition to indium, copper, gallium, selenium, zinc, iron, manganese, cadmium, nickel, cobalt, germanium, molybdenum, tin, etc. An indium-containing solution can be produced by extracting indium using the hydrophobic deep eutectic solvent of the present invention as an extractant, followed by back-extraction.

[0069] The pH when extracting indium into the organic phase may vary depending on the composition of the hydrophobic deep eutectic solvent of the present invention, and is not limited thereto, but an equilibrium pH of 2.5 to 3.0 is preferred. The pH when back-extracting indium into the aqueous phase is not particularly limited as long as it is in a low pH range where indium extraction does not occur or occurs only in very small amounts, but for example, the equilibrium pH is 1.9 or lower.

[0070] The present invention also relates to a method for separating and recovering scandium and zirconium from a solution containing scandium and zirconium using the extractant of the present invention. The present invention also relates to a method for producing a scandium solution or a zirconium solution from a solution containing scandium and zirconium. Solutions containing scandium and zirconium are not particularly limited, as long as they contain scandium and zirconium and can form an aqueous phase, but examples include solutions containing scandium and zirconium with water, an aqueous organic solvent, or a mixture thereof. Typically, the solution is an aqueous solution containing scandium and zirconium, which may contain a water-soluble organic solvent in an amount ranging from 1 to 90% by weight. An example of such a solution is a solution obtained by crushing waste material containing scandia-stabilized zirconia (ScSZ), which is an electrolyte material for solid oxide fuel cells (SOFCs), and then acid-leaching the resulting powder.

[0071] Methods for separating and recovering scandium and zirconium, and methods for producing scandium solution or zirconium solution, a) A step of contacting a solution containing scandium and zirconium with an organic phase containing the metal extractant of the present invention, adjusting the equilibrium pH to selectively extract zirconium into the organic phase, thereby obtaining a zirconium-containing organic phase and a scandium-containing solution, and b) A step of contacting the zirconium-containing organic phase with an acidic solution to back-extract zirconium and obtain a zirconium-containing solution, Includes.

[0072] a) The equilibrium pH range during zirconium extraction in step a) is not necessarily limited to this range, as it varies depending on the components of the hydrophobic deep eutectic solvent, but the equilibrium pH range can be set to 1.5 to 3.0. b) On the other hand, in step b), the equilibrium pH range when back-extracting zirconium is not necessarily limited, but it can be set to pH 1.0 or lower. [Examples]

[0073] The embodiments of the present invention will be described below. The present invention is not limited in any way to the embodiments described below, and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0074] [Extraction performance of the metal extractant of the present invention] The prepared hydrophobic deep eutectic solvent was used as the extractant, and metal ion extraction tests were conducted by solvent extraction. The test conditions are as shown in Table 1 below. Table 1 Test conditions for Example 1 [Table 1]

[0075] The extractants used in the test are shown in Table 2 below. In Table 2, HBA and HBD1-3 were all solids. Table 2 Components of the extractants used in Examples A-E, Comparative Example 1, and Examples 1-7 [Table 2]

[0076] Metal aqueous solutions were prepared by dissolving an appropriate amount of nitrate of each metal in ultrapure water so that the concentration of each metal was 10 ppm (10 mg / L), and then adjusting the pH to 0-14 by adding appropriate amounts of nitric acid and ammonia water. A portion of each metal aqueous solution was taken to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0077] Two mL of extractant and two mL of metal aqueous solution were added to a 7 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 1. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was taken to prepare a sample for equilibrium pH measurement (pHeq) and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0078] The extraction rate was calculated using the following formula. Extraction rate (%) = (Initial metal ion concentration - Metal ion concentration in the aqueous phase after equilibrium) / Initial ion concentration × 100

[0079] Figure 1 shows the extraction behavior of each metal ion in Example A (vertical axis: extraction rate, horizontal axis: pHeq). By mixing diphenyl sulfoxide (melting point: 71 °C) and (±)-2-(p-tolyl)propionic acid (melting point: 40 °C) in a molar ratio of 1:1, the freezing point was lowered to -10 °C, and a hydrophobic deep eutectic solvent was obtained. In the solvent extraction method using the obtained hydrophobic deep eutectic solvent as the extractant, the extraction efficiency at all pH levels was in the order of Fe > Sc > other rare earth elements, and conditions for selective extraction of scandium could not be obtained.

[0080] Figure 2 shows the extraction behavior of each metal ion in Example 1. By mixing diphenyl sulfoxide (melting point: 71 °C), (±)-2-(p-tolyl)propionic acid (melting point: 40 °C), and 4-tert-butylcatechol (melting point: 58 °C) in a molar ratio of 3:1:1, the freezing point was reduced to -10 °C, and a hydrophobic deep eutectic solvent was obtained. In the solvent extraction method using the obtained hydrophobic deep eutectic solvent as the extractant, the extraction efficiency was in the order of Sc > Fe > other rare earth elements, and scandium could be selectively extracted. Furthermore, scandium was not extracted at pH 2.0 or lower. Subsequently, scandium could be back-extracted from the scandium-containing extractant with near 100% efficiency using a new aqueous phase containing 2 mol / L sulfuric acid, 2 mol / L nitric acid, or 2 mol / L phosphoric acid.

[0081] Figure 3 shows the extraction behavior of each metal ion in Example 2. By mixing diphenyl sulfoxide, (±)-2-(p-tolyl)propionic acid, and 4-tert-butylcatechol in a molar ratio of 22:20:1, the freezing point was reduced to -10 °C, and a hydrophobic deep eutectic solvent was obtained. The extraction efficiency was in the order of Sc > Fe > other rare earth elements, and scandium could be selectively extracted. The content of 4-tert-butylcatechol in Example 2 was 2.1% by weight.

[0082] Even with 3-phenylpropionic acid (melting point: 47 °C), 4-phenylbutanoic acid (melting point: 52 °C), 5-phenylpentanoic acid (melting point: 60 °C), and benzoic acid (melting point: 122 °C), which have higher melting points than (±)-2-(p-tolyl)propionic acid (melting point: 40 °C) in Example 2, mixing them with hydrophobic sulfoxide compounds and hydrophobic catechol compounds lowered their freezing points, yielding hydrophobic deep eutectic solvents. In solvent extraction methods using these as extractants, the extraction efficiency was in the order of Sc > Fe > other rare earth elements, allowing for selective extraction of scandium. Furthermore, since scandium extraction does not occur at pH 2.0 or below, scandium can be back-extracted.

[0083] Examples B to E are compositions containing a total of two components: diphenyl sulfoxide as HBA and a hydrophobic carboxylic acid or hydrophobic catechol compound as HBD. These can extract scandium from iron-free systems with high efficiency and are extremely effective as metal extractants in the present invention. However, to selectively extract scandium from iron-containing systems, it is necessary to include a total of three components: diphenyl sulfoxide, a hydrophobic carboxylic acid, and a hydrophobic catechol compound. Figure 4 shows the extraction behavior of each metal ion in Example B. Scandium was not extracted at pHeq less than 2.8. Above pHeq 2.8, the extraction behavior of scandium and iron was similar, and there were no conditions suitable for the selective extraction of scandium. Figure 5 shows the extraction behavior of each metal ion in Example C. Scandium was not extracted at pHeq less than 2.0. The extraction rate of scandium at pHeq 2-6 was low, less than 20%, and there were no conditions that allowed for highly efficient scandium extraction. Figure 6 shows the extraction behavior of each metal ion in Example D. Scandium was not extracted at pHeq less than 1.4. The extraction efficiency at pHeq 1.1 to 6 was in the order of Fe(III) > Sc > other rare earth elements, and there were no conditions that allowed for the selective extraction of scandium. Figure 7 shows the extraction behavior of each metal ion in Example E. Scandium was not extracted at pHeq less than 2.1. The extraction efficiency at pHeq 2.1 to 5 was in the order of Sc > Fe(III) > other rare earth elements, but the selectivity was low.

[0084] Comparative Example 1 is a composition containing HBD1 and HBD2, which are the basic components of the present invention, but HBA is not diphenyl sulfoxide. Because Comparative Example 1 extracts scandium at a low pHeq, back-extraction after scandium extraction is difficult. Figure 8 shows the extraction behavior of each metal ion in Comparative Example 1. Since the extraction rate of scandium at pHeq 0.9-6 was 95-100%, back-extraction of scandium is difficult. Furthermore, significant amounts of iron and other rare earth elements were extracted.

[0085] Examples 3 to 7 are metal extractants according to a preferred embodiment of the present invention. These enable selective extraction and back-extraction of scandium. Figure 9 shows the extraction behavior of each metal ion in Example 3. Scandium was not extracted at pHeq less than 1.25. The extraction efficiency at pHeq 1.25 and above was in the order of Sc > Fe(III) > other rare earth elements, indicating that conditions were obtained that allowed for selective extraction and back-extraction of scandium. The freezing point of the composition in Example 3 is 0 °C. Figure 10 shows the extraction behavior of each metal ion in Example 4. Scandium was not extracted at pHeq less than 1.2. The extraction efficiency at pHeq 1.2 or higher was in the order of Sc > other rare earth elements > Fe(III), indicating that conditions were obtained that allowed for selective extraction and back-extraction of scandium. Figure 11 shows the extraction behavior of each metal ion in Example 5. Scandium was not extracted at pHeq less than 1.9. The extraction efficiency at pHeq 1.9 or higher was in the order of Sc > Fe(III) > other rare earth elements, indicating that conditions were obtained that allowed for selective extraction and back-extraction of scandium. The composition of Example 5 contains 4-tert-butylphenol as the third component of HBD. The freezing point of the composition of Example 5 is -5 °C, which is lower than that of the composition of Example 3. The freezing point was lowered by adding 4-tert-butylphenol.

[0086] Figure 12 shows the extraction behavior of each metal ion in Example 6. Scandium was not extracted at pHeq less than 1.1. The extraction efficiency at pHeq 1.1 or higher was in the order of Sc > other rare earth elements > Fe(III), indicating that conditions were obtained that allowed for selective extraction and back-extraction of scandium. Example 6 contains 4-tert-butylphenol as the third component of HBD. The addition of 4-tert-butylphenol improved the selective extraction performance of scandium. In addition, the freezing point was lowered. Figure 13 shows the extraction behavior of each metal ion in Example 7. Scandium was not extracted at pHeq less than 1.2. The extraction efficiency at pHeq 1.2 or higher was in the order of Sc > Fe(III) > other rare earth elements, indicating that conditions were obtained that allowed for selective extraction and back-extraction of scandium.

[0087] A comparison of Examples A-E and Examples 1-4 showed that a hydrophobic deep eutectic solvent obtained by mixing three basic components—a hydrophobic sulfoxide compound, a hydrophobic carboxylic acid, and a hydrophobic catechol compound—can be used as a means to selectively recover scandium from systems containing iron. Example 2 showed that 4-tert-butylcatechol was effective at a content of 2.1%. Examples 5-6 showed that the addition of HBDs other than hydrophobic catechol compounds and hydrophobic carboxylic acids is possible and effective in lowering the freezing point and improving the selective extraction performance of scandium. Example 7 showed that two or more hydrophobic carboxylic acids can be used as HBDs as needed.

[0088] [Comparison with prior art documents] Patent documents 2 (Japanese Patent Publication No. 9-291320), 4 (Japanese Patent Publication No. 2021-178997), and 6 (Japanese Patent Publication No. 2022-74480) mentioned above describe scandium extractants. Extraction tests for each metal ion were conducted by solvent extraction using compositions from prior art and the metal extractant of the present invention as extractants. The test conditions are shown in Table 3 below. The test content was to confirm the selective extraction performance of scandium from aqueous solutions containing scandium, iron, and other rare earth elements (Y, La, Ce, Nd, Tb, Dy), and to confirm the presence or absence of conditions suitable for back extraction. Table 3 Test conditions for Comparative Examples 2-4 and Example 8 [Table 3]

[0089] The extractants used in the test are shown in Table 4 below. Table 4 Components of the extractants used in Comparative Examples 2-4 and Example 8 [Table 4]

[0090] Metal aqueous solutions were prepared by dissolving an appropriate amount of nitrate of each metal in ultrapure water so that the concentration of each metal was 0.1 mmol / L, and then adjusting the pH to 0-14 by adding appropriate amounts of nitric acid and aqueous ammonia. A portion of each metal aqueous solution was taken to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured by ICP-MS.

[0091] 1.5 mL of extractant and 1.5 mL of metal aqueous solution were added to a 4 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 3. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was collected and sampled for pHeq measurement and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0092] Comparative Example 2 used a toluene solution containing 0.5 mol / L mono-2-ethylhexyl (2-ethylhexyl)phosphonate as the extractant. Figure 14 shows the extraction behavior of each metal ion in Comparative Example 2. The extraction rate of scandium was 90-100% at pHeq 0.3-2.4 and 75-100% at pHeq 2.4-6.1. While scandium could be extracted with high efficiency, pHeq conditions suitable for back-extraction could not be obtained. In addition, Fe(III) was also extracted at pHeq 0.3-2.4.

[0093] Comparative Example 3 used a toluene solution containing 0.5 mol / L N-lauroyl sarcosine (NLS) as the extractant. Figure 15 shows the extraction behavior of each metal ion in Comparative Example 3. The extraction efficiency at pHeq 0.1 to 1.5 was in the order of Sc > other rare earth elements > Fe(III), and the extraction efficiency at pHeq 1.5 to 3.3 was in the order of Sc > Fe(III) > other rare earth elements. The extraction rate of scandium at pHeq 0.1 to 1.0 was 12 to 24%, and suitable pHeq conditions for back-extraction of scandium could not be obtained.

[0094] Comparative Example 4 used a hydrophobic deep eutectic solvent obtained by mixing tri-n-octylphosphine oxide (TOPO) and NLS in a weight ratio of 1:2 as the extractant. Figure 16 shows the extraction behavior of each metal ion in Comparative Example 4. The extraction efficiency at pHeq 0.2 to 1.1 was in the order of Sc > other rare earth elements > Fe(III), and the extraction efficiency at pHeq 1.1 to 3.4 was in the order of Sc > Fe(III) > other rare earth elements. The extraction rate of scandium at pHeq 0.2 to 3.4 was over 99%, indicating that pHeq conditions suitable for back-extraction of scandium could not be obtained.

[0095] Example 8 is the scandium extractant of the present invention, composed of diphenyl sulfoxide, (±)-2-(p-tolyl)propionic acid, and 4-tert-butylcatechol (molar ratio 3:1:1). Figure 17 shows the extraction behavior of each metal ion in Example 8. The extraction efficiency at pHeq 0 to 5.5 was Sc > Fe(III) > other rare earth elements. Scandium was not extracted at pHeq 0 to 1.0, so scandium can be back-extracted with high efficiency.

[0096] The extraction rates for Comparative Example 3 and Example 8 are shown in Tables 5 and 6. Example 8, which is the scandium extractant of the present invention, demonstrated superior selective extraction performance of scandium compared to Comparative Example 3, which is a conventional extractant.

[0097] Table 5 Extraction rate of Comparative Example 3 [Table 5]

[0098] Table 6 Extraction rate of Example 8 [Table 6]

[0099] [Extraction of scandium from nickel oxide ore processing solution] The aforementioned Patent Document 5 (Japanese Patent Publication No. 2015-057505) is an invention relating to the extraction of scandium from a process solution of nickel oxide ore. Extraction tests for each metal ion were conducted by solvent extraction using the composition according to the embodiment of the invention described in Patent Document 5 and the scandium extractant of the present invention as extractants. The test conditions are as shown in Table 7 below. The test content was to confirm the selective extraction performance of scandium from a metal aqueous solution (Mg, Al, Sc, Cr(III), Mn, Fe(II), Ni, Co) simulating the process solution of nickel oxide ore, and to confirm the presence or absence of conditions suitable for back extraction.

[0100] Table 7 Test conditions for Comparative Example 5 and Example 9 [Table 7]

[0101] The extractants used in the test are shown in Table 8 below. Table 8 Components of the extractants used in Comparative Example 5 and Example 9 [Table 8]

[0102] Metal aqueous solutions were prepared by dissolving an appropriate amount of sulfate of each metal in ultrapure water so that the concentration of each metal was 10 ppm, and then adjusting the pH to 0-14 by adding appropriate amounts of sulfuric acid and ammonia water. A portion of each metal aqueous solution was taken to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured by ICP-MS.

[0103] 1.5 mL of extractant and 1.5 mL of metal aqueous solution were placed in a 4 mL polypropylene vial, and after sealing, the vial was shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 7. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was taken to prepare a sample for pHeq measurement and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0104] Comparative Example 5 used a toluene solution containing 0.5 mol / L tri-n-octylphosphine oxide (TOPO) and 0.5 mol / L 2-thenoyltrifluoroacetone as the extractant. Figure 18 shows the extraction behavior of each metal ion in Comparative Example 5. The extraction behavior of scandium and Fe(II) was similar at pHeq 0.1 to 6.6. No pHeq conditions were obtained that allowed for selective extraction of scandium. Furthermore, the extraction rate of scandium at pHeq 0.1 to 6.6 was 78 to 100%, and no pHeq conditions suitable for back-extraction of scandium were obtained.

[0105] Example 9 is the scandium extractant of the present invention, composed of diphenyl sulfoxide, salicylic acid, 4-tert-butylcatechol, and 4-tert-butylphenol (molar ratio 4:1:1:1). Figure 19 shows the extraction behavior of each metal ion in Example 9. The extraction efficiency at pHeq 2.5 to 5.0 was Sc > Fe(II) > other metals. Scandium was not extracted at pHeq 0.2 to 1.9, indicating that scandium can be back-extracted with high efficiency.

[0106] [Separation and recovery of zirconium and scandium from scandia-stabilized zirconia] Patent Document 7 (Japanese Patent Publication No. 2016-132804) describes an invention of an extractant used for the separation and recovery of zirconium and scandium, with the aim of recycling ScSZ. The method involves acid leaching of ScSZ followed by solvent extraction to separate and recover zirconium and scandium. While selective extraction of zirconium allows for separation from scandium, the extraction rate of zirconium in the pHeq range of 0.2 to 4.0 exceeds 90%, and there is no pHeq range suitable for back-extraction of zirconium.

[0107] Extraction tests for zirconium and scandium were conducted using a solvent extraction method with the metal extractant of the present invention. The test conditions are shown in Table 9. Table 9 Test conditions for Example 10 [Table 9]

[0108] The extractants used in the test are shown in Table 10 below. Table 10 Components of the extractant used in Example 10 [Table 10]

[0109] Metal aqueous solutions were prepared by dissolving an appropriate amount of sulfate of each metal in ultrapure water so that the concentration of each metal was 10 ppm, and then adjusting the pH to 0-14 by adding appropriate amounts of sulfuric acid and ammonia water. A portion of each metal aqueous solution was taken to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured by ICP-MS.

[0110] 1.5 mL of extractant and 1.5 mL of metal aqueous solution were added to a 4 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 9. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was collected and sampled for pHeq measurement and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0111] Example 10 is the scandium extractant of the present invention, composed of diphenyl sulfoxide, benzoic acid, and 4-tert-butylcatechol (molar ratio 3:1:1). The extraction behavior of each metal ion is shown in Figure 20. The extraction efficiency at pHeq 1.1 to 3.5 was Zr > Sc. The zirconium extraction rate at pHeq 1.2 to 2.7, where the scandium extraction rate was extremely low, was 42 to 98%. Zirconium extraction did not occur at pHeq 0.1 to 0.9. Scandium was extracted at pHeq 3.1 and above.

[0112] Back-extraction tests for zirconium were conducted. The test conditions are shown in Table 11.

[0113] Table 11 Test conditions for Examples 11-14 [Table 11]

[0114] From Figure 20, it is assumed that by setting the pHeq to around 2.5-3.0, most of the zirconium will be extracted into the extractant phase, and scandium will remain in the aqueous phase. The pH of the metal aqueous solution was adjusted so that the pHeq during zirconium extraction was 2.5. 1.5 mL of the extractant and 1.5 mL of the metal aqueous solution were placed in 4 mL polypropylene vials, sealed tightly, and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 12. After standing, the extractant phase and aqueous phase were separated, and a portion of the aqueous phase was taken to prepare samples for pHeq measurement and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical samples was measured by ICP-MS. The number of samples was N=4 (Examples 11-14).

[0115] The pHeq of the aqueous phase (N=4) was 2.5 in all cases. The extraction rate of zirconium was 98-99%. Scandium was not extracted.

[0116] After separating the aqueous phase, 1.5 mL of back-extracting agent was added to the container containing the extractant phase. The container was sealed and shaken thoroughly to reach equilibrium. H2SO4 was used as the back-extracting agent. The concentrations of H2SO4 were 1 mol / L and 2 mol / L. Shaking was performed in the order of conditions 1 and 2 in Table 12. After standing, the extractant phase and aqueous phase separated, and a portion of the aqueous phase was taken to prepare a sample for pHeq measurement and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0117] The results of the back-extraction test are shown in Table 12. When zirconium was back-extracted using 1 mol / L H2SO4 as the back-extracting agent, the pHeq of the aqueous phase (N=2) was 0.5 and 0.6. The back-extraction rates of zirconium were 90% and 96%. When zirconium was back-extracted using 2 mol / L H2SO4 as the back-extracting agent, the pHeq of the aqueous phase (N=2) was 0.2 and 0.4. The back-extraction rates of zirconium were 99% and 96%.

[0118] Table 12 Extraction and back extraction rates of zirconium [Table 12]

[0119] Using the metal extractant of the present invention, zirconium and scandium were successfully separated and recovered from a metal aqueous solution simulating an acid leaching solution of ScSZ using the solvent extraction method. The solvent extraction method using the metal extractant of the present invention can be applied to the recycling process of ScSZ.

[0120] [Indium separation and recovery process from CIS and CIGS solar cells] We conducted tests to simulate the recovery of indium from acid-leached solutions of CIS and CIGS solar cell waste materials containing indium. Extraction tests for indium were conducted using a solvent extraction method with the metal extractant of the present invention. The test conditions are as shown in Table 13 below.

[0121] Table 13 Test conditions for Example 15 [Table 13]

[0122] The extractant used in the test is Example 15 shown in Table 15 below.

[0123] Table 14 Components of the extractant used in Example 15 [Table 14]

[0124] The metal aqueous solutions used in the evaluation simulated the state of crushed CIS solar cell waste material that had undergone acid leaching. To achieve a concentration of 10 ppm (10 mg / L) for each metal, appropriate amounts of nitrate were dissolved in ultrapure water, and appropriate amounts of nitric acid and ammonia water were added to adjust the pH to 0-14. A portion of each metal aqueous solution was collected to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0125] Two mL of extractant and two mL of metal aqueous solution were added to a 7 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 1. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was taken to prepare a sample for equilibrium pH measurement (pHeq) and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0126] Example 15 is a metal extractant composed of diphenyl sulfoxide, (±)-2-(p-tolyl)propionic acid, and 4-tert-butylphenol (molar ratio 22:20:1). Figure 21 shows the extraction behavior of each metal ion in Example 15. Indium showed the highest extraction efficiency and could be extracted selectively. Since indium is not extracted at pHeq 2.0 or below, it is possible to back-extract indium with high efficiency. The solvent extraction method using the metal extractant of the present invention can be applied to the separation and recovery process of indium from CIS-type solar cells and CIGS-type solar cells, and to the production method of indium solutions.

[0127] [Indium-selective extraction properties of hydrophobic deep eutectic solvents containing hydrophobic sulfoxide compounds and hydrophobic carboxylic acids] As described above, the present invention particularly prefers a composition containing a total of three basic components: a hydrophobic sulfoxide compound as HBA, and a hydrophobic carboxylic acid and a hydrophobic catechol compound as HBD. However, a composition containing a hydrophobic sulfoxide compound as HBA and a hydrophobic carboxylic acid as HBD, but not containing a hydrophobic catechol compound, is also effective as a metal extractant.

[0128] Tests were conducted to simulate the recovery of indium from solutions obtained by acid leaching of indium-containing CIS and CIGS solar cell waste materials using a solvent extraction method with a hydrophobic deep eutectic solvent containing a hydrophobic sulfoxide compound as HBA and a hydrophobic carboxylic acid as HBD as the metal extractant. The test conditions are shown in Table 15 below.

[0129] Table 15 Test conditions for Examples 16-18 [Table 15]

[0130] The extractants used in the test are those shown in Examples 16-18 in Table 16 below.

[0131] Table 16 Components of the extractants used in Examples 16-18 [Table 16]

[0132] The metal aqueous solutions used in the evaluation simulated the state of crushed CIS solar cell waste material that had undergone acid leaching. To achieve a concentration of 10 ppm (10 mg / L) for each metal, appropriate amounts of nitrate were dissolved in ultrapure water, and appropriate amounts of nitric acid and ammonia water were added to adjust the pH to 0-14. A portion of each metal aqueous solution was collected to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0133] Two mL of extractant and two mL of metal aqueous solution were added to a 7 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 1. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was taken to prepare a sample for equilibrium pH measurement (pHeq) and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0134] Example 16 is a metal extractant composed of diphenyl sulfoxide and (±)-2-(p-tolyl)propionic acid (molar ratio 1:1). Figure 22 shows the extraction behavior of each metal ion in Example 16. Indium showed the highest extraction efficiency and could be extracted selectively. Since indium is not extracted at pHeq 1.7 or below, it is possible to back-extract indium with high efficiency. The solvent extraction method using the metal extractant of the present invention can be applied to the separation and recovery process of indium from CIS-type solar cells and CIGS-type solar cells, and to the production method of indium solutions.

[0135] Example 17 is a metal extractant composed of diphenyl sulfoxide and 4-phenylbutanoic acid (molar ratio 1:1). Figure 23 shows the extraction behavior of each metal ion in Example 17. Indium showed the highest extraction efficiency and could be extracted selectively. Since indium is not extracted at pHeq 1.8 or below, it is possible to back-extract indium with high efficiency. The solvent extraction method using the metal extractant of the present invention can be applied to the separation and recovery process of indium from CIS-type solar cells and CIGS-type solar cells, and to the production method of indium solutions.

[0136] Example 18 is a metal extractant composed of diphenyl sulfoxide and 2-phenylbutyric acid (molar ratio 1:1). Figure 24 shows the extraction behavior of each metal ion in Example 18. Indium showed the highest extraction efficiency and could be extracted selectively. Since indium is not extracted at pHeq 1.8 or below, it is possible to back-extract indium with high efficiency. The solvent extraction method using the metal extractant of the present invention can be applied to the separation and recovery process of indium from CIS-type solar cells and CIGS-type solar cells, and to the production method of indium solutions.

[0137] [Scandium extraction properties of hydrophobic deep eutectic solvents containing hydrophobic sulfoxide compounds and hydrophobic carboxylic acids] A test was conducted to simulate the recovery of scandium from a solution obtained by acid leaching of scandium using a solvent extraction method with a hydrophobic deep eutectic solvent containing a hydrophobic sulfoxide compound as HBA and a hydrophobic carboxylic acid as HBD as the metal extractant. The test conditions are as shown in Table 17 below.

[0138] Table 17 Test conditions for Examples 19-20 [Table 17]

[0139] The extractants used in the test are those shown in Examples 19-20 in Table 18 below.

[0140] Table 18 Components of the extractants used in Examples 19-20 [Table 18]

[0141] For the evaluation, the metal aqueous solutions were prepared by dissolving an appropriate amount of nitrate of each metal in ultrapure water, and then adding appropriate amounts of nitric acid and ammonia water to adjust the pH to 0-14, so that the scandium concentration was 10 ppm (10 mg / L). A portion of each metal aqueous solution was taken to prepare samples for measuring the metal ion concentration. The metal ion concentration of the analytical samples was measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0142] Two mL of extractant and two mL of metal aqueous solution were added to a 7 mL polypropylene vial, which was then sealed and shaken thoroughly to reach equilibrium. Shaking was performed in the order of conditions 1 and 2 in Table 1. After standing, the mixture separated into the extractant phase and the aqueous phase. A portion of the aqueous phase was taken to prepare a sample for equilibrium pH measurement (pHeq) and metal ion concentration measurement. pHeq was measured using a pH meter. The metal ion concentration of the analytical sample was measured by ICP-MS.

[0143] Example 19 is a metal extractant composed of diphenyl sulfoxide and (±)-2-(p-tolyl)propionic acid (molar ratio 1:1). Figure 25 shows the extraction behavior of scandium ions in Example 19. Scandium was extracted with high efficiency at pHeq 2.9 and above. Scandium was not extracted at pHeq 1.8 and below, so scandium can be back-extracted with high efficiency.

[0144] Example 20 is a metal extractant composed of diphenyl sulfoxide and 4-phenylbutanoic acid (molar ratio 1:1). Figure 26 shows the extraction behavior of scandium ions in Example 20. Scandium was extracted with high efficiency at pHeq 2.7 and above. Scandium was not extracted at pHeq 1.8 and below, so scandium can be back-extracted with high efficiency.

Claims

1. Hydrophobic sulfoxide compounds, Hydrophobic carboxylic acids and / or hydrophobic catechol compounds, A hydrophobic deep eutectic solvent containing a

2. Hydrophobic sulfoxide compounds, Formula (1): R ２ -(R １ ) ｎ -S(=O)-(R １ ) ｎ -R ２ (1) During the ceremony, R １ Each of these is independently a linear or branched alkylene group having 1 to 4 carbon atoms, or a linear or branched alkenylene group having 2 to 4 carbon atoms. n is independently either 0 or 1. R ２ These are, independently, substituted or unsubstituted aromatic groups. Selected from compounds represented by The hydrophobic deep eutectic solvent according to claim 1.

3. R ２ The hydrophobic deep eutectic solvent according to claim 2, wherein R is a substituted or unsubstituted phenyl group.

4. The hydrophobic deep eutectic solvent according to claim 1, wherein the hydrophobic sulfoxide compound is diphenyl sulfoxide.

5. The hydrophobic deep eutectic solvent according to claim 1, wherein the hydrophobic carboxylic acid is a hydrophobic carboxylic acid containing an aromatic group.

6. The hydrophobic deep eutectic solvent according to claim 1, wherein the hydrophobic carboxylic acid is selected from the group consisting of phenylacetic acid, benzoic acid, 3-phenylpropionic acid, 4-phenylbutanoic acid, 5-phenylpentanoic acid, 6-phenylhexanoic acid, (±)-p-tolylpropionic acid, salicylic acid, 2-fluorobenzoic acid, 2,6-difluorobenzoic acid, 3-fluorosalicylic acid, 6-fluorosalicylic acid, 2-fluoro-6-(trifluoromethyl)benzoic acid, o-toluic acid, p-toluic acid, and m-toluic acid.

7. The hydrophobic deep eutectic solvent according to claim 1, wherein the hydrophobic catechol compound is selected from catechols in which at least one of the 3, 4, and 5 positions is monosubstituted, disubstituted, or trisubstituted with an alkyl group.

8. The hydrophobic deep eutectic solvent according to claim 1, wherein the hydrophobic catechol compound is 4-tert-butylcatechol.

9. Furthermore, the hydrophobic deep eutectic solvent according to claim 1, comprising a hydrogen bond donating compound (HBD), wherein the HBD is not a hydrophobic carboxylic acid or a hydrophobic catechol compound.

10. The hydrophobic deep eutectic solvent according to claim 9, wherein the hydrogen bond donating compound (HBD) is a hydrophobic phenol.

11. The hydrophobic deep eutectic solvent according to claim 1, comprising a hydrophobic sulfoxide compound and a hydrophobic carboxylic acid.

12. The hydrophobic deep eutectic solvent according to claim 1, comprising a hydrophobic sulfoxide compound and a hydrophobic catechol compound.

13. Hydrophobic sulfoxide compounds, hydrophobic carboxylic acids, hydrophobic catechol compounds, A hydrophobic deep eutectic solvent according to claim 1, comprising:

14. A metal extractant comprising the hydrophobic deep eutectic solvent according to any one of claims 1 to 13.

15. The metal extractant according to claim 14, wherein the metal is selected from scandium, zirconium, and indium.

16. A method for extracting metal, comprising the step of extracting a metal using the metal extractant described in claim 11.

17. The method according to claim 16, wherein the metal is selected from scandium, zirconium, and indium.

18. A step of extracting the metal to be recovered into the organic phase to obtain an organic phase containing the metal to be recovered, which includes contacting an aqueous phase containing the metal to be recovered with an organic phase containing the metal extractant described in claim 14, and adjusting the equilibrium pH, and A process of back-extracting the target metal by bringing an organic phase containing the target metal into contact with an acidic solution. A method for recovering metals, including [specific metals].

19. The method according to claim 18, wherein the metal to be recovered is selected from scandium, zirconium, and indium.

20. A step of contacting a solution containing scandium and iron with an organic phase containing a metal extractant containing the hydrophobic deep eutectic solvent described in claim 13, adjusting the equilibrium pH, and extracting scandium into the organic phase to obtain a scandium-containing organic phase, and A scandium-containing organic phase is brought into contact with an acidic solution, and scandium is back-extracted to obtain a scandium-containing solution. including, A method for producing a scandium-containing solution.

21. The method according to claim 20, wherein the solution containing scandium and iron is a solution obtained by acid leaching a nickel oxide ore containing scandium and iron.

22. A step of contacting an acid leaching of zirconium-containing ore, which contains at least zircon or baddeleyite, with an organic phase containing the metal extractant described in claim 14, adjusting the equilibrium pH, and extracting zirconium into the organic phase to obtain a zirconium-containing organic phase, and A process of obtaining a zirconium-containing solution by contacting a zirconium-containing organic phase with an acidic solution and back-extracting the zirconium. including, A method for producing a zirconium-containing solution.

23. A step of contacting a solution containing indium and at least one metal different from indium with an organic phase containing the metal extractant described in claim 14, adjusting the equilibrium pH to extract indium into the organic phase and obtain an indium-containing organic phase, and A process of contacting an indium-containing organic phase with an acidic solution to back-extract indium and obtain an indium-containing solution. including, A method for producing an indium-containing solution.

24. A method for producing an indium-containing solution according to claim 23, wherein the solution containing indium and at least one metal other than indium is an indium-containing acid leaching solution obtained by acid leaching of waste materials of CIS solar cells and / or CIGS solar cells containing indium.

25. A step of contacting a solution containing scandium and zirconium with an organic phase containing the metal extractant described in claim 14, adjusting the equilibrium pH to selectively extract zirconium into the organic phase, and obtaining a zirconium-containing organic phase and a scandium-containing solution, and A step of contacting the zirconium-containing organic phase with an acidic solution to back-extract zirconium and obtain a zirconium-containing solution, including, A method for producing a scandium-containing solution or a zirconium-containing solution, comprising separating and recovering scandium and zirconium.

26. The method according to claim 25, wherein the solution containing scandium and zirconium is a zirconium and scandium-containing acid leaching obtained by acid leaching of solid oxide fuel cell electrolyte waste material.

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