Metal ion extraction method and oil phase

Abstract

The present invention provides: a metal ion extraction method for extracting metal ions into an oil phase by mixing an aqueous phase containing metal ions with an oil phase containing an extraction agent, and then separating the phases, the oil phase containing at least one solvent selected from hydrocarbon solvents containing aliphatic hydrocarbons represented by the formula CnH(2n+2) (where n is an integer between 19 and 40) and edible oils, the metal ion extraction method satisfying condition A and / or B below; and an oil phase to be used in a metal ion extraction method, the oil phase containing an extraction agent and at least one solvent selected from the above hydrocarbon solvents and edible oils.　Condition A: The aqueous phase and the oil phase are merged in mid-circulation, and both phases are mixed. Condition B: The mixing temperature of the aqueous phase and the oil phase is between 40°C and 95°C.

Description

Method for extracting metal ions and oil phase

[0001] This invention relates to a method for extracting metal ions and an oil phase.

[0002] Valuable metals such as precious metals and rare earth metals are essential elements for precision equipment, and ensuring a stable supply and availability of high-purity metals is a major challenge. These valuable metals are typically mined as mixtures with two or more other metals, requiring isolation and purification (high-purity extraction) of the desired metal from the mining mixture. Furthermore, the amount of valuable metals that can be extracted from mines is limited, making the stable supply of precious metals, essential for precision equipment, a significant challenge. Therefore, technologies for recovering valuable metals from industrial waste without relying on mining are gaining importance. In particular, with the spread of electric vehicles, the amount of lithium-ion battery (LiB) waste is increasing year by year. LiBs use positive electrode active materials containing metallic elements such as cobalt and nickel, and the demand for cobalt, nickel, and manganese is expected to increase significantly. To meet this increased demand for valuable metals, it is desirable not only to increase mining volume but also to establish metal recycling technologies from waste LiBs.

[0003] Wet extraction (solvent extraction) is widely used as a method for isolating and purifying target valuable metals from mining mixtures and as a method for recycling metals from waste. In wet extraction, an organic phase containing a metal extractant is brought into contact with an aqueous solution (aqueous phase) containing metal element ions (simply called "metal ions"), mixed, and allowed to stand to separate the two phases. The metal ions to which the metal extractant is coordinated then move (extract) into the organic phase (oil phase). By removing this organic phase, the metal ions are back-extracted, and if necessary, purified, it becomes possible to isolate and purify the target metal and recycle it as (high-purity) metal.

[0004] In such wet extraction methods, low-viscosity, non-polar solvents are typically used, both in batch and continuous extraction methods, from the viewpoint of miscibility with the aqueous phase (extraction performance) and phase separation with the aqueous phase (phase separation performance). For example, Patent Document 1 proposes a method for separating metals, comprising an extraction step in which an organometallic solution containing valuable metals such as cobalt, nickel, manganese, and lithium, and impurity metals such as iron, is contact-mixed with a water-insoluble organic phase containing an organophosphinic acid represented by a specific formula, thereby extracting the impurity metals into the water-insoluble organic phase. As an example of this extraction step, Patent Document 1 describes a batch extraction step in which a water-insoluble organic phase containing an organophosphinic acid extractant and an aliphatic hydrocarbon solvent (D70, manufactured by Japan Chemtec Co., Ltd.) and an organometallic solution are shaken at 25°C. Furthermore, Patent Document 2 proposes a method for separating and recovering a sulfuric acid solution containing a specific metal, obtained by dissolving a spent desulfurization catalyst used to remove sulfur components from crude oil, using a phosphonic acid monoester as an extractant and a shaking method (batch method). In this separation and recovery method, as an example of the separation and extraction process for each metal, Patent Document 2 describes a separation and extraction process in which nickel and cobalt are extracted by shaking at 25°C using an extraction solvent (oil phase) containing "EXXOL D80 (manufactured by Exxon Chemicals, trade name) which has paraffin as its main component" and a specific extractant, and a sulfuric acid solution.

[0005] JP 2016-060926 JP 9-235628 JP

[0006] As mentioned above, conventional wet extraction methods generally use aliphatic hydrocarbon solvents such as D70 and EXXOL D80, and petroleum-based solvents such as kerosene. However, although these solvents are widely used in wet extraction methods, they have relatively low boiling points (flash points), and safety considerations must be taken into account during use and implementation of the extraction method. Specifically, while installing and increasing safety equipment improves safety when implementing wet extraction methods using such solvents, it leads to increased implementation costs and equipment costs. Therefore, especially with an eye towards industrialization, there has been a desire to develop a wet extraction method that can maintain or improve the extraction performance and phase separation (phase separation) of conventional wet extraction methods using petroleum-based solvents, while using highly safe solvents. However, Patent Documents 1 and 2 do not address this point of view at all.

[0007] The present invention aims to provide a method for extracting metal ions that is excellent in terms of metal ion extraction performance and phase separation, while using a solvent for the oil phase used in a wet extraction method that can lead to further improvements in safety. Furthermore, the present invention aims to provide an oil phase used in a wet extraction method that contributes to further improvements in safety, as well as to metal ion extraction performance and phase separation.

[0008] The inventors of this invention considered that using a solvent with a higher flash point than conventional solvents as the solvent for the oil phase in conventional wet extraction methods that use solvents with relatively low boiling points (flash points) could lead to further improvements in safety. However, when the inventors proceeded with their investigations based on this idea, they encountered new problems specific to high-flash-point solvents: when an oil phase containing a high-flash-point solvent is applied to a wet extraction method, the extraction performance of metal ions decreases due to reduced miscibility with the aqueous phase, and once the aqueous phase and oil phase are mixed, the phase separation with the aqueous phase is poor. Therefore, the inventors continued their investigations from various angles to solve these new problems and found that by performing the wet extraction method in a continuous flow manner instead of a batch manner, or by performing the mixing with the aqueous phase at a specific temperature regardless of whether it is a batch or continuous flow manner, it is possible to improve both the problems of poor miscibility and poor phase separation with the aqueous phase while enhancing the safety effect of the oil phase containing a high-flash-point solvent. This invention was completed after further investigation based on these findings.

[0009] In other words, the above problem was solved by the following means: <1> A method for extracting metal ions, comprising mixing an aqueous phase containing metal ions and an oil phase containing an extractant, and then separating the phases to extract the metal ions into the oil phase, wherein the oil phase contains at least one solvent selected from a hydrocarbon solvent containing aliphatic hydrocarbons represented by the following formula and edible oil, and satisfies at least one of the following conditions A and B. Formula: C ｎ H （２ｎ＋２）However, n is an integer between 19 and 40. Condition A: The aqueous phase and the oil phase are brought together in the middle of flow and mixed. Condition B: The mixing temperature of the aqueous phase and the oil phase is 40 to 95°C. <2> The method for extracting metal ions according to <1>, wherein the hydrocarbon solvent is liquid paraffin. <3> The method for extracting metal ions according to <1> or <2>, wherein the flash point of the oil phase is 250°C or higher. <4> The method for extracting metal ions according to any one of <1> to <3>, satisfying conditions A and B. <5> The method for extracting metal ions according to any one of <1> to <4>, wherein the aqueous phase contains two or more metal ions, and at least one of these metal ions is separated and extracted from the other metal ions. <6> The method for extracting metal ions according to any one of <1> to <5>, wherein the extractant is an acidic extractant. <7> The method for extracting metal ions according to <6>, wherein the acidic extractant contains a phosphoric acid compound. <8> The method for extracting metal ions according to <6> or <7>, wherein the acidic extractant is represented by the following formula (I). (Formula I), R １ and R ２ represents a substituent, at least one of which is a hydrocarbon group having 9 or more carbon atoms. X represents -OH or -SH. Y represents an oxygen atom or a sulfur atom. Z １ and Z ２ represents a single bond, -O-, -NH-, or -S-. <9> An oil phase used in a method for extracting metal ions, in which an aqueous phase containing metal ions and an oil phase are mixed and then phase-separated to extract the metal ions into the oil phase, the oil phase containing an extractant, a hydrocarbon solvent containing an aliphatic hydrocarbon represented by the following formula, and at least one solvent selected from edible oils. Formula: C ｎ H （２ｎ＋２） However, n is an integer between 19 and 40.

[0010] The present invention provides a method for extracting metal ions that offers excellent metal ion extraction performance and phase separation while using a solvent for the oil phase used in a wet extraction method, which can lead to further improvements in safety. Furthermore, the present invention provides an oil phase for use in a wet extraction method that contributes to further improvements in safety, as well as to metal ion extraction performance and phase separation. The above and other features and advantages of the present invention will become clearer from the following description with reference to the attached drawings as appropriate.

[0011] Figure 1 is a schematic front view showing an example of an extraction apparatus suitably used in the flow-type extraction method for metal ions of the present invention. Figure 2 is a schematic front view showing another example of an extraction apparatus suitably used in the flow-type extraction method for metal ions of the present invention. Figure 3 shows a modified example of a flow tube used in an extraction apparatus suitably used in the flow-type extraction method for metal ions of the present invention.

[0012] In this invention, when describing the content, physical properties, etc., of components by indicating numerical ranges, if the upper and lower limits of the numerical range are described separately, either upper or lower limit can be appropriately combined to form a specific numerical range. On the other hand, when describing multiple numerical ranges represented by "~", the upper and lower limits forming the numerical range are not limited to the specific combination of upper and lower limits described before and after "~" as a specific numerical range, but can be a numerical range formed by appropriately combining the upper and lower limits of each numerical range. In this invention, a numerical range represented by "~" means a range that includes the values ​​described before and after "~" as the lower and upper limits. In this invention, the designation of a compound (for example, when referring to it with "compound" at the end) includes not only the compound itself, but also its salts and ions. It also includes derivatives in which parts have been altered, such as by introducing substituents, to the extent that the effects of this invention are not impaired. In the present invention, substituents, linking groups, etc. (hereinafter referred to as substituents, etc.) that are not explicitly stated as substituted or unsubstituted may have appropriate substituents. Therefore, in the present invention, even when simply referred to as a YYY group, this YYY group includes not only an unsubstituted form but also a further substituted form. The same applies to compounds that are not explicitly stated as substituted or unsubstituted. Preferred substituents include, for example, groups selected from substituent G described later. In the present invention, when there are multiple substituents, etc. indicated by a specific symbol, or when multiple substituents, etc. are specified simultaneously, it means that each substituent, etc. may be the same as or different from the others. Furthermore, even if not specifically stated, when multiple substituents, etc. are adjacent to each other, they may be linked to each other or fused to form a ring.

[0013] In this specification, "metallic elements belonging to different groups in the periodic table" are referred to as "heterogroup metallic elements," and "heterogroup metallic elements of the same period in the periodic table" are sometimes referred to as "same-period heterogroup metallic elements." Furthermore, "ions of heterogroup metallic elements" and "ions of heterogroup metallic elements of the same period" are sometimes referred to as "heterogroup metallic ions" and "same-period heterogroup metallic ions," respectively. In this invention, unless otherwise specified, "ppm" indicating content, etc., is based on mass and represents "mass ppm."

[0014] [[Method for Extracting Metal Ions of the Present Invention]] The method for extracting metal ions of the present invention (hereinafter sometimes referred to as "the extraction method of the present invention") relates to a method for extracting metal ions by mixing an aqueous phase containing metal ions with an oil phase containing an extractant, and then separating the phases to extract the metal ions into the oil phase. The extraction method of the present invention, by performing an extraction and separation cycle that satisfies at least one of the following conditions A and B using the aqueous phase and oil phase described later, can move (extract) metal ions present in the aqueous phase to the oil phase with high extraction performance, while using solvents and oil phases that can lead to further improvements in safety, and moreover, can rapidly separate the aqueous phase and oil phase once they have been mixed (exhibits excellent phase separation). When there are two or more types of metal ions present in the aqueous phase, at least one specific metal ion from the two or more types of metal ions can be moved (extracted) to the oil phase with high extraction performance while maintaining excellent phase separation. Thus, the present invention can maintain, and preferably further improve, the extraction performance exhibited by the organic solvent and oil phase used in conventional wet extraction methods, while using solvents and oil phases that can lead to further improvements in safety in a wet extraction method. Condition A: The aqueous phase and the oil phase are combined and mixed during the flow process. Condition B: The mixing temperature of the aqueous phase and the oil phase is between 40 and 95°C.

[0015] The extraction method of the present invention can be carried out in either a batch or flow manner. However, when the extraction method of the present invention is carried out in a batch manner, the aqueous phase and the oil phase are mixed at a mixing temperature of at least 40 to 95°C (satisfying condition B above), and other conditions can be determined as appropriate. On the other hand, when the extraction method of the present invention is carried out in a flow manner (satisfying condition A above), the conditions are not particularly limited and can be determined as appropriate. Conditions A and B, and further details of each condition in the extraction method will be explained in the batch extraction method and flow extraction method described later.

[0016] The extraction method of the present invention is a method for extracting metal ions in which an aqueous phase containing metal ions and an oil phase containing an extractant are mixed and then phase-separated. Any method that satisfies at least one of conditions A and B is acceptable. A method that satisfies conditions A and B is preferred because it can achieve an even higher level of both extraction performance and phase separation while using solvents and oil phases that can lead to further improvements in safety. The extraction method of the present invention that satisfies condition A is a so-called flow extraction method, in which the aqueous phase and oil phase described later are merged during flow, the two phases are mixed, and then phase-separated to extract the metal ions into the oil phase. The details thereof will be described later.

[0017] In the extraction method of the present invention, extraction performance means the amount of metal ions that can be extracted into the oil phase. If the aqueous phase contains two or more types of metal ions, in addition to the extraction amount, it also means the extraction resolution (selectivity) of the metal ions extracted into the oil phase. In the present invention, the ability to extract metal ions in a high amount is not unique, as it depends on the content of metal ions present in the aqueous phase, the content of the extractant in the oil phase, etc. However, for example, for the metal ions extracted into the oil phase at the maximum extraction rate among the metal ions extracted in the extraction separation cycle (mixing and phase separation cycle, for example, steps 1 to 3 described later in the flow extraction method) (specific metal ions to be extracted), it means that the amount of said metal ions extracted into the oil phase CA is a high value, defined as the ratio of the difference between the content CI of said metal ions in the aqueous phase (before extraction) and the content (residual amount) C1 of said metal ions in the aqueous phase (after extraction) [(CI - C1) / CI] × 100 (%), and that the said metal ions can be extracted into the oil phase. In the present invention, the extraction amount (the above percentage) CA is preferably 80% or more, and under the conditions of the examples described later, it is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more. Ideally, the upper limit is 100%, but in practice, it is preferably 99.5% or less, and can also be 99% or less.

[0018] In the present invention, the ability to extract metal ions with high extraction resolution (high selectivity) is not unique, as it depends on the number and content of metal ions present in the aqueous phase and the content of the extractant in the oil phase, but it means that one specific metal ion can be selectively extracted from two or more metal ions present in the aqueous phase. Furthermore, when extracting two or more metal ions into the oil phase, including those with low extraction rates, the ability to extract metal ions with high selectivity is similarly not unique, but it means that among the two or more extracted metal ions, the amount extracted of the specific metal ion to be extracted (usually one) falls within the extraction amount range described above, and the amount of the remaining metal ions extracted is less than 30%. The amount of the remaining metal ions extracted is calculated in the same way as the amount extracted of the specific metal ion to be extracted, and under the conditions of the examples described later, it is preferably less than 20%, more preferably less than 10%, and even more preferably less than 5%. In the present invention, room temperature refers to the temperature in a room temperature environment, specifically a temperature range of 20 to 30°C.

[0019] In the present invention, "excellent phase separation" means that the mixed aqueous phase and oil phase can be rapidly separated, although this is not unique as it depends on the mixing ratio of the aqueous phase and oil phase, the type of organic solvent, etc. Specifically, it is preferable that the mixed aqueous phase and oil phase separate in less than 15 minutes after being allowed to stand, more preferably in less than 10 minutes, even more preferably in less than 5 minutes, and particularly preferably in less than 3 minutes, under the conditions of the examples described later.

[0020] The mixing state for phase separation in the extraction method of the present invention is not particularly limited, but it is usually a mixing state in which (all) metal ions contained in the aqueous phase are in extraction equilibrium. In the extraction method of the present invention, the mixing of the aqueous phase and the oil phase is carried out when the mixture of both phases has a pH suitable for the metal ions to be extracted. In the present invention, the "state with a suitable pH" is defined as the point at which the mixing of a predetermined amount of aqueous solution containing a pH adjusting agent into both phases is completed, or the point at which the mixing of the pH-adjusted aqueous phase or pH-adjusted oil phase, as described later, is completed.

[0021] In the flow extraction method of the present invention, the metal ions to be extracted are not particularly limited and can be determined as appropriate, for example, as described below. In the extraction method of the present invention, the metal ions to be extracted into the oil phase are those contained in the aqueous phase if there is only one type of metal ion. On the other hand, if there are multiple types of metal ions contained in the aqueous phase, the metal ions to be extracted into the oil phase are ideally one specific type of metal ion, but including those with low extraction rates, there may be two or more types of metal ions, or even all types. In other words, in the flow extraction method of the present invention, when the aqueous phase contains multiple types of metal ions, at least one of those metal ions can be separated and extracted from the other (residual) metal ions. However, the metal ions extracted into the oil phase with a high extraction amount (also referred to in the present invention as "metal ions for extraction purpose or target of extraction") are at least one of two or more types of metal ions (groups) (not all types, but some types). For example, as ions of valuable metal elements, two or more heterogroup metal ions, specifically two or more metal ions belonging to groups 1 to 14 of the periodic table (preferably groups 2 to 14, more preferably groups 7 to 12, and even more preferably groups 8 to 11), preferably two or more heterogroup metal ions, and particularly preferably one metal ion from among the same periodic heterogroup metal ions, namely cobalt ions and nickel ions, or one metal ion from among the same periodic heterogroup metal ions, namely manganese ions, cobalt ions, and nickel ions, can be extracted into the oil phase in high extraction amounts.

[0022] The extraction method of the present invention allows for the extraction of two or more metal ions (groups) present in the aqueous phase, including those with low extraction rates, into the oil phase. In this case, one of the metal ions can be extracted with a high extraction yield, preferably with high extraction resolution (selectivity). In particular, it can be applied to new applications such as the separation and recovery of two or more metal ions, especially heterogroup metal ions. Heterogroup metal ions of the same period usually have similar physical and chemical behaviors, making it difficult to separate and recover one of them with a high extraction yield, preferably with high selectivity. However, the extraction method of the present invention allows for the extraction of both heterogroup metal ions of the same period with similar physical and chemical behaviors, particularly metal ions belonging to Group 9 (especially cobalt ions) and metal ions belonging to Group 10 (especially nickel ions), which are required due to the rapid spread of lithium-ion batteries in recent years. In this case, one of the metal ions can be recovered with a high extraction yield, preferably with high extraction resolution. Similarly, for metal ions belonging to Group 7 (especially manganese ions) and metal ions belonging to Group 10 (especially nickel ions), metal ions belonging to Group 9 (especially cobalt ions), or metal ions belonging to Group 2 (especially magnesium ions), and further, for metal ions belonging to Group 10 (especially nickel ions) and metal ions belonging to Group 11 (especially copper ions), it is possible to extract both regardless of the extraction rate, while recovering one of the metal ions with a high extraction amount, preferably with a high extraction resolution. Therefore, the present invention can greatly contribute to the further spread of electric vehicles and, ultimately, to the construction of a sustainable society.

[0023] [Fluids used in the extraction method of the present invention] In the extraction method of the present invention, fluids consisting of an aqueous phase, an oil phase, and an aqueous solution containing a pH adjusting agent are prepared. <Aqueous phase> The water forming the aqueous phase is not particularly limited, but (ultra)pure water, ion-exchanged water, etc. can be used.

[0024] In the present invention, the aqueous phase may contain one type of metal ion, but it is preferable that it contains at least two types. The number of types of metal ions contained in the aqueous phase is not particularly limited as long as it is one or more types, for example, it can be 2 to 15 types, preferably 2 to 8 types, and more preferably 2 to 5 types. The metal ions contained in the aqueous phase may contain ions of metal elements belonging to groups 1 to 14 of the periodic table, preferably metal ions belonging to groups 2 to 14, and may also contain metal ions belonging to groups 15 to 17. In the present invention, it is preferable that it contains two or more types of metal ions belonging to groups 1 to 14, more preferably two or more types of metal ions belonging to groups 2 to 14, and even more preferably at least one transition metal element ion (a metal element belonging to groups 3 to 12). In embodiments containing at least one transition metal element, it is preferable to contain two or more metal ions belonging to groups 2 to 12, more preferably two or more metal ions belonging to groups 4 to 12, even more preferably two or more metal ions belonging to groups 7 to 12, particularly preferably two or more metal ions belonging to groups 8 to 12, even more preferably two or more metal ions belonging to groups 9 to 12, and most preferably two or more metal ions belonging to groups 9 and 10. The metal ions belonging to each group are not particularly limited, but metal ions belonging to periods 3 to 6 of the periodic table are preferred, and metal ions belonging to periods 4 or 5 are more preferred.

[0025] The combination of multiple metal ions is not particularly limited, but examples of combinations of groups include combinations of Group 2 and Group 7, combinations of Group 7 and Group 10, combinations of Group 9 and Group 10, combinations of Group 9 and Group 12, combinations of Group 9 and Group 11, combinations of Group 9, Group 10 and Group 12, combinations of Group 4 and Group 9, combinations of Group 10 and Group 11, combinations of Group 7, Group 9 and Group 10, and combinations of Group 7, Group 8, Group 9 and Group 10. In the present invention, there may be two or more metal ions belonging to each group, but it is preferable to have one type in order to show high selectivity.

[0026] Specific combinations of metal ions include, for example, combinations containing Mg and Mn, combinations containing Mn and Ni, combinations containing Co and Ni, combinations containing Co and Zn, combinations containing Co and Cu, combinations containing Rh and Ni, combinations containing Zr and Rh, combinations containing Ni and Cu, combinations containing Mn, Co and Ni, and combinations with Mn, Fe, Co and Ni. The multiple metal ions contained in the aqueous phase may include metal ions of the same group or metal ions of different groups. The number of different metal ions contained in the aqueous phase may be two or more, preferably two to four, and more preferably two.

[0027] The metal elements belonging to each group are not particularly limited, and appropriate atoms can be used. For example, as the metal elements belonging to Group 1, Li, Na, Rb, and Cs are preferably mentioned. As the metal elements belonging to Group 2, Mg, Ca, Sr, and Ba are preferably mentioned. As the metal elements belonging to Group 3, Sc and Y are preferably mentioned. As the metal elements belonging to Group 4, Ti, Zr, and Hf are preferably mentioned. As the metal elements belonging to Group 5, V, Nb, and Ta are preferably mentioned. As the metal elements belonging to Group 6, Cr, Mo, and W are preferably mentioned. As the metal elements belonging to Group 7, Mn and Tc are preferably mentioned. As the metal elements belonging to Group 8, Fe, Ru, and Os are preferably mentioned. As the metal elements belonging to Group 9, Co, Rh, and Ir are preferably mentioned. As the metal elements belonging to Group 10, Ni, Pd, and Pt are preferably mentioned. As the metal elements belonging to Group 11, Cu, Ag, and Au are preferably mentioned. As the metal elements belonging to Group 12, Zn, Cd, and Hg are preferably mentioned. As the metal elements belonging to Group 13, Al, Ga, In, and Tl are preferably mentioned. As the metal elements belonging to Group 14, Ga, Sn, and Pb are preferably mentioned. As the metal elements belonging to Group 15, Sb and Bi are preferably mentioned. The metal elements belonging to Group 16 are not particularly limited, and Te is preferably mentioned.

[0028] The metal ions can be prepared as appropriate. For example, various metal salts (salts of inorganic acids such as nitric acid and sulfuric acid of typical elements or organic acids such as acetic acid), mixtures of mined metals (ions), recovered materials from metal wastes, other wastes such as metal recoveries from waste batteries (LiB), and further mixtures thereof can be used. Examples of the metal recoveries from waste LiB include recoveries by known methods such as wet treatment and electrolysis.

[0029] The total content of metal ions in the aqueous phase is not particularly limited and is set as appropriate. For example, it can be 1.0×10 ３ to 1.0×10 ６ mass ppm, and 1.0×10 ３~1.0 x 10 ５ The mass is preferably ppm, and is 1.0 × 10 ３ ~8.0 x 10 ４ It is more preferable that the concentration be in ppm by mass. In particular, since the extraction method of the present invention can achieve a high extraction yield, the total content of metal ions in the aqueous phase can be set to a high level. The total content of metal ions belonging to groups 9 to 12 among the metal ions is not particularly limited and can be set as appropriate, for example, 1.0 × 10⁻¹⁶ ３ ~8.0 x 10 ４ The mass can be ppm, and it is 1.0 × 10 ３ ~5.0 x 10 ４ It is preferable that the mass be ppm. The total content of metal ions belonging to groups 1 to 8 and groups 13 to 17 among the metal ions is not particularly limited and can be set as appropriate, for example, 1.0 × 10 ３ ~6.0 x 10 ４ The mass can be ppm, and it is 1.0 × 10 ３ ~3.0 x 10 ４ It is preferable that the mass be ppm. The content of metal ions belonging to each group is not particularly limited and can be set as appropriate, for example, 1.0 × 10 ３ ~6.0 x 10 ４ The mass can be ppm, and it is 1.0 × 10 ３ ~5.0 x 10 ４ The mass is preferably ppm. If two or more metal ions belonging to each group are present, the total content of metal ions belonging to each group shall be used.

[0030] In the present invention, when the aqueous phase contains metal ions from different groups, the content of metal ions belonging to one group may be greater or less than the content of metal ions belonging to other groups. The extraction method of the present invention allows for highly selective separation and recovery of metal ions when the aqueous phase contains metal ions from different groups, so it is not necessary to set the content of metal ions belonging to different groups in a specific ratio. For example, the mass ratio of the content of metal ions belonging to one other group (e.g., metal ions extracted at the maximum extraction rate) to the content of metal ions belonging to a specific group (e.g., metal ions extracted at the maximum extraction rate) [content of metal ions belonging to a specific group: content of metal ions belonging to one other group] is, for example, 1.0 × 10⁻⁶. ２ : 1 to 1.0 x 10 ４ It can be done as 1.0 × 10 ２ : 10-5.0 x 10 ３ It is preferable to do so, 1.0 × 10 ２ : 50-1.0 x 10 ３ It is preferable to do so.

[0031] The pH of the aqueous phase is not particularly limited and can be set as appropriate, but considering the solubility of metal ions, the formation of complex ions, etc., it is preferably 0.1 to 10, and more preferably 2.0 to 9.0. The pH of the aqueous phase is usually set within the above range, but in the present invention, an aqueous solution containing a pH adjusting agent can also be added to the aqueous phase in any amount, or in an amount that results in a predetermined mixed pH when the aqueous phase and oil phase are mixed. In these cases, the pH of the aqueous phase may be outside the above range. The pH of the aqueous phase can be adjusted, for example, using an acid or alkali (an aqueous solution containing a pH adjusting agent including an acid or alkali). As the acid, any known acid can be used without particular limitation, and examples include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, oxalic acid, organic phosphoric acid, and organic sulfonic acid. As the alkali, any known alkali can be used without particular limitation, and examples include inorganic alkalis and organic alkalis, with inorganic alkalis being preferred. Examples of inorganic alkalis include metal alkalis such as hydroxides and carbonates of Group 1 or Group 2 metals, as well as aqueous ammonia and ammonium chloride. Examples of organic alkalis include organic ammonium salts.

[0032] The temperature of the aqueous phase (during storage and at the start of distribution) is not particularly limited and can be, for example, 10 to 60°C, or between 15°C and less than 40°C. The density of the aqueous phase (kg / m³) ３ The temperature (25°C) is not particularly limited and cannot be uniquely determined by the metal ion content, etc., but for example, 9.0 × 10 ２ ~2.0 x 10 ３ kg / m ３ This is, for example, the kinetic energy E, which will be discussed later. ＳＴ It is preferable in that it is easy to set the kinetic energy E to a suitable value. ＳＴ Setting this value to a suitable value is preferable because it allows for an increase in the amount of metal ions extracted.

[0033] The aqueous phase may, if necessary, contain ligands (compounds) that coordinate to metal ions or compounds that generate ligands. The aqueous phase can be prepared by dissolving metal ions in water. The preparation conditions for the aqueous phase are not particularly limited. For example, the preparation temperature can usually be 10 to 60°C, but it can be determined considering the solubility of metal ions, etc.

[0034] The aqueous phase may contain a masking agent in addition to the metal ions mentioned above. Known masking agents can be used without particular limitation. Examples include monodentate ligands such as ammonia and chelating agents such as dithizone. In the extraction method of the present invention, the extractant can coordinate to the metal ions on its own and extract these metal ions into the oil phase. Therefore, the aqueous and oil phases do not need to contain compounds that cooperate with the extractant to extract the metal ions, such as compounds that coordinate to the metal ions or compounds that generate ligands, such as known extractants. In the extraction method of the present invention, typically, an aqueous phase containing specific metal ions as essential components and an oil phase containing an extractant as an essential component are used.

[0035] <Oil Phase> The extraction method of the present invention uses an oil phase (corresponding to "the oil phase of the present invention") containing an extractant, a hydrocarbon solvent including an aliphatic hydrocarbon represented by the formula described later, and at least one solvent selected from edible oils. This oil phase can be used in a method for extracting metal ions in which an aqueous phase containing metal ions and the oil phase are mixed and then phase-separated to extract the metal ions into the oil phase. Preferably, it can be used in a method for extracting metal ions in which an aqueous phase containing metal ions and the oil phase are mixed under conditions that satisfy at least one of conditions A and B described later, and then phase-separated to extract the metal ions into the oil phase.

[0036] (Organic solvent) The oil phase (organic phase) contains at least one solvent selected from hydrocarbon solvents containing aliphatic hydrocarbons represented by the following formula and edible oils as an organic solvent. Formula: C ｎ H （２ｎ＋２） However, n is an integer between 19 and 40.

[0037] The aliphatic hydrocarbon represented by the above formula is not particularly limited, and examples include chain-type saturated aliphatic hydrocarbons having 19 to 40 carbon atoms. The hydrocarbon solvent may be any solvent that mainly contains the aliphatic hydrocarbon represented by the above formula, and the hydrocarbon solvent may contain one or more types of aliphatic hydrocarbons. In the present invention, "mainly contained" means contained in the highest concentration among the constituent components. Here, the content of aliphatic hydrocarbons is the total content of the aliphatic hydrocarbons when the hydrocarbon solvent contains two or more types of aliphatic hydrocarbons. The (total) content of aliphatic hydrocarbons in the hydrocarbon solvent is not particularly limited, and can be, for example, 80% by mass or more. The hydrocarbon solvent may also contain solvents other than aliphatic hydrocarbons, such as chain-type saturated aliphatic hydrocarbons, chain-type unsaturated hydrocarbons, aromatic hydrocarbons, and other organic solvents used in conventional wet extraction methods.

[0038] The number of carbon atoms in the aliphatic hydrocarbon contained in the hydrocarbon solvent (n in the above formula) may be 19 to 40, but it is preferably 20 to 39, more preferably 26 to 37, and even more preferably 30 to 36, in order to suppress a decrease in phase separation properties, maintain excellent phase separation properties, further improve safety, and enhance extraction performance. Examples of hydrocarbon solvents include liquid paraffin. The hydrocarbon solvent may be a solvent consisting of aliphatic hydrocarbons represented by the above formula, or a mixture containing aliphatic hydrocarbons represented by the above formula, etc. Commercial hydrocarbon solvents (usually mixtures) can be used.

[0039] Edible oils are not particularly limited and include, for example, linseed oil, perilla oil, olive oil, canola oil, sesame oil, rice bran oil, corn oil, salad oil, soybean oil, rapeseed oil, palm oil, safflower oil, etc.

[0040] As the organic solvent, at least one of the above-mentioned hydrocarbon solvents and edible oils can be selected and used from the viewpoint of safety improvement effect, extraction performance and phase separation, taking into account the type of metal ions and extraction conditions. From the viewpoint of extraction performance and phase separation, hydrocarbon solvents, particularly liquid paraffin, are preferred as the organic solvent, and from the viewpoint of safety improvement effect, edible oil is preferred. Two or more of the hydrocarbon solvents and edible oils can also be used as the organic solvent, and when two or more are used, hydrocarbon solvents and edible oils can be used in combination.

[0041] As the solvent selected from hydrocarbon solvents and edible oils, a high flash point solvent is preferred. For example, an organic solvent whose flash point in the oil phase is 150°C or higher is preferred in terms of improving safety. In the extraction method of the present invention, for even greater safety, an organic solvent whose flash point in the oil phase is 200°C or higher is more preferable, an organic solvent whose flash point is 220°C or higher is even more preferable, and an organic solvent whose flash point is 250°C or higher is particularly preferable. The upper limit of the flash point is not particularly limited, but a higher limit contributes to further improvement of safety. However, from the viewpoint of miscibility with the aqueous phase and phase separation, it can be, for example, 350°C or lower, and is preferably 300°C or lower. The flash point of the oil phase can be measured by the Cleveland open method (Japanese Industrial Standard (JIS) K 2265-4).

[0042] (Extractant) The extractant is not particularly limited as long as it exhibits solubility in organic solvents, is present in the oil phase, coordinates with metal ions present near the interface between the aqueous and oil phases, and has the function of moving these metal ions to the oil phase. An extractant can be appropriately selected and used from among various known metal extractants. In the present invention, solubility in organic solvents means the property that the extractant can dissolve in organic solvents at the content described later. As for the extractant, it is preferable to use an acidic extractant, which can further enhance extraction performance while maintaining excellent phase separation, more preferably an acidic extractant selected from phosphoric acid compounds, and even more preferably a compound represented by (Formula I) (acidic extractant) described later.

[0043] The extractant used in the extraction method of the present invention is not particularly limited, and examples include extractants used in wet extraction methods, with extractants used in wet extraction methods for metal ions being preferred. In terms of extraction performance, the extractant used in the extraction method of the present invention is more preferably an acidic extractant consisting of an acidic compound having at least one active hydrogen atom, and examples of acidic extractants include various known acidic extractants or phosphoric acid compounds represented by the following formula (I). Examples of active hydrogen atoms include hydroxyl groups (including phenolic hydroxyl groups and hydroxyl groups bonded to phosphorus or sulfur atoms), carboxyl groups, and active hydrogen atoms in sulfanyl groups. The acidic extractant exhibits acidity, and its pKa is not particularly limited and can take an appropriate value, but is preferably 0.1 to 12. The pKa can be measured by neutralization titration.

[0044] Known acidic extractants include phosphoric acid compounds, carboxylic acid compounds, sulfonic acid compounds, oxime compounds, β-diketone compounds, and oxin compounds. Phosphoric acid compounds include phosphoric acid compounds, phosphonic acid compounds, phosphinic acid compounds, and various compounds in which the oxygen atom of these compounds is replaced with a sulfur atom or a nitrogen atom. Carboxylic acid compounds include compound VA-10, which was used in the examples described later.

[0045] The acidic extractant used in the extraction method of the present invention is preferably a compound represented by the following formula (I), in that it can further enhance the extraction performance of the metal ions to be extracted. The compound represented by the following formula (I) includes a phosphate group, a phosphonic acid group, a phosphinic acid group, and a compound having an acid group in which at least one oxygen atom of these acid groups is replaced with a sulfur atom or a nitrogen atom. For example, a phosphate ester compound (R １ OP(=O)(OH)-OR ２ ), phosphonic acid ester compounds (R １ -P(=O)(OH)-OR ２ , R １ OP(=O)(OH)-R ２ ) or phosphinate compounds (R １ -P(=O)(OH)-R２ This includes phosphate compounds such as ), thiophosphate compounds obtained by converting at least one oxygen atom in each of the above phosphate compounds to a sulfur atom, and compounds obtained by replacing the oxygen atom (-O-) bonded to P with a nitrogen atom. The acidic extractant represented by (Formula I) is preferably a phosphate compound, more preferably a phosphate ester compound, a phosphonic acid ester compound, or a phosphinic acid ester compound, even more preferably a phosphonic acid ester compound or a phosphinic acid ester compound, and particularly preferably a phosphonic acid monoester compound or a phosphinic acid monoester compound, in terms of extraction amount and selectivity.

[0046] In (Equation I), R １ and R ２ Each of these indicates a substituent. However, R １ and R ２ At least one substituent is a hydrocarbon group having 9 or more carbon atoms. １ and R ２ The substituents that can be used are not particularly limited and include various substituents and groups formed by combinations of substituents. In the present invention, the above "various substituents" alone are R １ and R ２ A substituent is a substituent that becomes a substituent, and the above-mentioned "group with a combination of substituents" refers to a substituent formed by combining multiple substituents. In order to clearly distinguish between the above-mentioned "various substituents" and the above-mentioned "group with a combination of substituents," for convenience, the above-mentioned "various substituents" are sometimes called "single substituents," and the above-mentioned "group with a combination of substituents" are sometimes called "composite substituents." A composite substituent is formed by removing hydrogen atoms from a required number of single substituents from among the single substituents that constitute it, and then bonding multiple single substituents. In a composite substituent, the position in which a particular substituent is substituted by another substituent is not particularly limited and can be determined as appropriate. For example, when a phenyl group is substituted by another substituent, the substitution position may be any of the positions 2 to 4 with respect to the bonding position of the phenyl group. In the present invention, R １ and R ２Substituents that can be taken as such are interpreted as single substituents whenever possible. For example, the 2-ethylhexyl group can be interpreted as a composite substituent in which an ethyl group substitutes a hexyl group, but it is interpreted as a branched alkyl group. Similarly, the hexyloxy group can be interpreted as a composite substituent combining a hexyl group and an oxygen atom, but it is interpreted as an alkoxy group.

[0047] R １ and R ２ The substituents that can be used (including single substituents and complex substituents) may be hydrocarbon groups composed only of carbon and hydrogen atoms, or they may be heteroatom-containing substituents containing at least one heteroatom such as a nitrogen atom, an oxygen atom, or a sulfur atom. １ and R ２ It is preferable, in terms of extractable amount and selectivity, that all possible substituents are hydrocarbon groups. The heteroatom-containing substituent preferably contains an oxygen atom or a sulfur atom as the heteroatom, and preferably an oxygen atom. The number of heteroatoms contained in the heteroatom-containing substituent is not particularly limited and can be 1 to 4, and preferably 1. In the heteroatom-containing substituent, the heteroatom may be located anywhere in the substituent, for example, inside or at the end of the atomic chain constituting the substituent. A heteroatom-containing substituent (e.g., an alkoxy group) in which the bonding heteroatom is located at the end is, on its own, R １ and R ２ It is preferable that the substituent does not become a substituent that can be taken as such. There are no particular limitations on heteroatom-containing substituents, and examples include complex substituents such as alkoxy groups, aryloxy groups, heterocyclic oxy groups, alkylthio groups, arylthio groups, heterocyclic thio groups, etc., which are combined with an aryl group (substituents including a ring structure), as described in substituent G below.

[0048] R １ and R ２The individual substituents that can be used are not particularly limited, and any suitable substituents can be cited, for example, groups selected from substituent G described later. Among these, hydrocarbon groups such as alkyl groups, alkenyl groups, alkynyl groups, and aryl groups, heterocyclic groups, etc. are preferred, and alkyl groups are even more preferred in terms of extractable amount and selectivity.

[0049] The alkyl, alkenyl, and alkynyl groups that can be taken as individual substituents may be linear, branched, or cyclic, but branched chains are more preferred in terms of extractable amount and selectivity. The aryl and heterocyclic groups that can be taken as individual substituents are the same as the corresponding groups in substituent G described later.

[0050] R １ and R ２ The composite substituents that can be used are not particularly limited and include groups formed by combining multiple substituents selected from (single) substituents, for example, substituent G. The number of single substituents constituting the composite substituent is not particularly limited and can be 2 to 6, and preferably 2 to 4. Examples of composite substituents include groups formed by combining hydrocarbon groups (groups formed by combining an alkyl group, alkenyl group, or alkynyl group with an aryl group), groups formed by combining a hydroxyl group with an aryl group (hydroxyaryl group), groups formed by combining an alkoxy group or alkylthio group with an aryl group, and groups formed by combining an alkyl group, alkenyl group, or alkynyl group with an amino group. When the composite substituent contains an oxygen atom or sulfur atom bonded to an alkyl group, the oxygen atom and sulfur atom are interpreted as atoms derived from the alkoxy group or alkylthio group. For example, the composite substituent "alkyl group-oxygen atom-phenyl group-" is interpreted as a group formed by combining an alkoxy group and a phenyl group, and not as a group formed by combining an alkyl group and a phenoxy group, nor as a group formed by combining an alkyl group, an oxygen atom, and a phenyl group. The above interpretation also applies when the complex substituent contains an oxygen atom bonded to an alkenyl group or alkynyl group.

[0051] As for the compound substituent, those containing a ring structure are preferred in terms of extractability and selectivity. The ring structure contained in the compound substituent is not particularly limited, and examples include ring structures derived from cycloalkyl groups, aryl groups, heterocyclic groups, etc., with ring structures derived from aryl groups and aromatic heterocyclic groups being preferred, and ring structures derived from aryl groups being more preferred in terms of extractability and selectivity. Specifically, as for the compound substituent containing a ring structure, preferred are groups that combine an alkyl group and an aryl group, alkoxy groups or groups that combine an alkylthio group and an aryl group, alkoxyaryl groups are more preferred, and alkoxyphenyl groups are even more preferred.

[0052] R １ and R ２ Among the substituents that can be used, alkyl groups, or composite substituents containing a ring structure combining an alkoxy group or an alkylthio group with an aryl group are preferred in terms of extractability and selectivity. Of the preferred substituents, alkoxy groups, alkylthio groups, and composite substituents containing a ring structure are preferably those with 9 or more carbon atoms.

[0053] R １ Possible substituents and R ２ The combinations with substituents that can be taken as are not particularly limited, R １ and R ２ The substituents that can be taken as described above can be combined as appropriate. For example, the molecular structure of the substituent is not particularly limited, １ and R ２The substituents that can be used are preferably combinations that include substituents having a branched structure (combinations in which at least one substituent has a branched structure) in terms of extractability and selectivity, more preferably combinations of substituents having branched structures, and more preferably combinations of substituents having a branched structure and substituents having a ring structure (particularly complex substituents). Here, the substituents having a branched structure are not particularly limited, but among those mentioned above, examples include hydrocarbon groups such as alkyl groups, alkenyl groups, and alkynyl groups, single substituents or complex substituents containing hydrocarbon groups, and single substituents such as alkyl groups, or complex substituents such as groups combining alkoxy groups or alkylthio groups with aryl groups are preferred, and groups combining alkyl groups or alkoxy groups with aryl groups are more preferred. In the present invention, the substituent having a branched structure may be any substituent having 3 or more carbon atoms, but in terms of extractability and selectivity, it is preferable that the substituent has 9 or more carbon atoms.

[0054] Furthermore, there are no particular restrictions on the type of substituent, R １ and R ２ In terms of extractable amount and selectivity, combinations of single substituents or combinations of a single substituent and a complex substituent are preferred. In the case of combinations of single substituents, the same (type) substituents may be combined, or different (type) substituents may be combined. Examples of combinations of the same substituents include combinations of alkyl groups, alkenyl groups, and alkynyl groups. In the above combinations of the same substituents, the carbon chains of the individual substituents to be combined may be the same or different, but it is preferable that they are all branched chains. Also, the number of carbon atoms of the individual substituents to be combined may be the same or different.

[0055] On the other hand, examples of combinations of different substituents include combinations in which one substituent is a hydrocarbon group, and combinations of two of an alkyl group, an alkenyl group, and an alkynyl group are more preferable. In the combinations of the different substituents, the carbon chains of the alkyl group, alkenyl group, or alkynyl group may be the same or different, but it is preferable that all are branched chains. Also, the number of carbon atoms of the alkyl group, alkenyl group, or alkynyl group may be the same or different.

[0056] As combinations of a single substituent and a complex substituent, combinations of an alkyl group, an alkenyl group, an alkynyl group, and a complex substituent containing a ring structure are preferable, and combinations of an alkyl group and a complex substituent obtained by combining an alkoxy group and an aryl group are more preferable.

[0057] R １ Among the combinations of possible substituents for R ２ and possible substituents for R

[0058] In the compound represented by (Formula I), for R １ and R ２ the possible substituents can be appropriately selected from the above-mentioned substituents, but at least one of the substituents of R １ and R ２ is a hydrocarbon group having 9 or more carbon atoms. When at least one of the substituents of R １ and R ２ is a hydrocarbon group having 9 or more carbon atoms, a high extraction amount can be achieved, and preferably a high selectivity can also be achieved. In the present invention, in terms of the extraction amount and the selectivity amount, when at least one of R １ and R ２ is a hydrocarbon group having 9 or more carbon atoms, Z １ and Z ２Preferably, one of the bonds is a single bond and the other is -O-. The total number of carbon atoms constituting the hydrocarbon group having 9 or more carbon atoms (hereinafter simply referred to as the number of carbon atoms) is preferably 10 or more, more preferably 12 or more, even more preferably 14 or more, and particularly preferably 16 or more, in terms of extractable amount and selectivity. On the other hand, the upper limit of the number of carbon atoms is not particularly limited and can be determined as appropriate, for example, it can be 30 or less, preferably 24 or less, and more preferably 20 or less.

[0059] The hydrocarbon group having 9 or more carbon atoms is not particularly limited, but among the hydrocarbon groups mentioned above, alkyl groups, alkenyl groups, or alkynyl groups are preferred, and alkyl groups are more preferred. The hydrocarbon group having 9 or more carbon atoms may be linear or branched, but branched is preferred. When the hydrocarbon group having 9 or more carbon atoms is branched, the number of branched carbon atoms is not particularly limited as long as there is one or more, and examples include one or two branches and three or more branches. In the embodiment having three or more branched carbon atoms, the number of branched carbon atoms is the same as that of the hydrocarbon group having three or more branched carbon atoms described later. As for the hydrocarbon group having 9 or more carbon atoms, alkyl groups having 9 or more carbon atoms are preferred, and branched alkyl groups having one or more branched carbon atoms and 9 or more carbon atoms are more preferred. Examples of linear alkyl groups having 9 or more carbon atoms include n-nonyl group, n-decyl group, n-dodecyl group, n-tetradecyl group, n-hexadecyl group, etc. Examples of alkyl groups having 9 or more carbon atoms and one or two branched carbon atoms include 1-ethyl-1-methylhexane, 8-methylnonane, 2-butyloctane, 2-hexyldecane, 2-ethyldecane, 2-octyldecane, 2-hexyldodecane, 2-octyldodecane, and 2-decyltetradecane. Examples of alkyl groups having 9 or more carbon atoms and three or more branched carbon atoms include 2,5,7,7-tetramethyloctane, 2-(1,3,3-trimethyl-1-butyl)-5,7,7-trimethyloctane, 2-(1,3,3-trimethyl-1-butyl)-5,7,7-trimethyloctane, and 2-(4-methylhexyl)-8-methyldecyl.

[0060] In the compound represented by (Formula I), R １ and R ２ The substituents that can be taken can be appropriately selected from the substituents mentioned above, but when considering the molecular structure and number of carbon atoms of the substituents, in terms of extractable amount and selectivity, R １ and R ２ Preferably, at least one of them is a hydrocarbon group having three or more branched carbon atoms.

[0061] The hydrocarbon group having three or more branched carbon atoms is not particularly limited, but usually includes those having three or more branched carbon atoms (tertiary carbon atoms) among alkyl groups, alkenyl groups or alkynyl groups having a branched structure. The number of branched carbon atoms present in this hydrocarbon group is not particularly limited as long as it is three or more, and for example, it can be 3 to 8, preferably 3 to 6, and more preferably 4 to 6. The number of carbon atoms of the hydrocarbon group having three or more branched carbon atoms is not particularly limited, and it is preferably 9 or more, and preferably 12 or more. That is, it is preferable that a hydrocarbon group having 9 or more carbon atoms has three or more branched carbon atoms. Such a hydrocarbon group is as described above. <​​​​​​​​​​​​​​​​１ and R ２ The substituent that can be the other is not particularly limited and may be a hydrocarbon group having 9 or more carbon atoms, or a substituent other than a hydrocarbon group having 9 or more carbon atoms (preferably a hydrocarbon group having 8 or fewer carbon atoms).

[0064] In formula I, X represents -OH or -SH, and is preferably -OH. In formula I, Y represents an oxygen atom or a sulfur atom, and is preferably an oxygen atom. In formula I, Z １ and Z ２ Each represents a single bond, -O-, -NH-, or -S-, and is preferably a single bond or -O-. In (Formula I), Z １ and Z ２ Both are preferably single bonds or -O- bonds, Z １ and Z ２ Among these combinations, in terms of extraction amount and selectivity, Z １ and Z ２ It is more preferable that one of the bonds is a single bond and the other is -O-.

[0065] The compound represented by (Formula I) is, in (Formula I), R １ and R ２ And Y, X, Z １ and Z ２ They can be formed by combining them as appropriate, and it is preferable to form them by combining preferred ones of each symbol. In formula (I), R １ -Z １ - and R ２ -Z ２ Even if - has a substituent -O-, -S-, or -NH-, and these can be interpreted as a single substituent (e.g., an alkoxy group), if these are not interpreted as a single substituent, -O-, -S-, or -NH- are treated as Z １ or Z ２ Let the substituent be R １ or R ２ This is how it is interpreted. In the present invention, R １ and R ２ and Z １ and Z ２As for combinations, various combinations are possible, but in terms of initial extraction volume and repeated durability, R １ and R ２ In a preferred embodiment, both are hydrocarbon groups having 9 or more carbon atoms, and R １ and R ２ In another preferred embodiment, one of the atoms is a hydrocarbon group having 9 or more carbon atoms, and the other is a substituent other than a hydrocarbon group having 9 or more carbon atoms (preferably a hydrocarbon group having 8 or fewer carbon atoms). In another preferred embodiment, the hydrocarbon group having 9 or more carbon atoms forms a single bond with Z １ or Z ２ Z may be bound to -O-, -NH-, or -S- in terms of initial extraction volume and repeated durability. １ or Z ２ It is preferable that it is bonded to R. １ and R ２ and Z １ and Z ２ A preferred specific combination is the combination of extractants E-1 to E-3 in the examples described later.

[0066] The molecular weight of the compound represented by (Formula I) is not particularly limited, but can be, for example, 350 to 50,000, and if the oil phase contains an organic solvent, it is preferably 400 to 10,000 in terms of solubility in the organic solvent.

[0067] The compound represented by (Formula I) may have substituents, and examples of substituents include groups selected from substituent G described later. The compound represented by (Formula I) can be synthesized by referring to known synthesis methods, such as the synthesis method described in the examples described later.

[0068] Specific examples of compounds represented by (Formula I) include those synthesized in the examples, as shown below, but the present invention is not limited to these.

[0069]

[0070] - Substituent G - Alkyl group (preferably an alkyl group having 1 to 20 carbon atoms, e.g., methyl, ethyl, isopropyl, t-butyl, pentyl, heptyl, 1-ethylpentyl, benzyl, 2-ethoxyethyl, 1-carboxymethyl, etc.), alkenyl group (preferably an alkenyl group having 2 to 20 carbon atoms, e.g., vinyl, allyl, oleyl, etc.), alkynyl group (preferably an alkynyl group having 2 to 20 carbon atoms, e.g., ethynyl, butadiinyl, phenylethynyl, etc.), cycloalkyl group (preferably a cycloalkyl group having 3 to 20 carbon atoms, e.g., cyclopropyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, etc.) In this invention, the term alkyl group usually includes cycloalkyl groups, but this is described separately here.), aryl groups (preferably aryl groups having 6 to 26 carbon atoms, e.g., phenyl, 1-naphthyl, 4-methoxyphenyl, 2-chlorophenyl, 3-methylphenyl, etc.), aralkyl groups (preferably aralkyl groups having 7 to 23 carbon atoms, e.g., benzyl, phenethyl, etc.), heterocyclic groups (preferably heterocyclic groups having 2 to 20 carbon atoms, more preferably heterocyclic groups of 5 or 6 members having at least one oxygen atom, a sulfur atom, or a nitrogen atom. Heterocyclic groups include aromatic heterocyclic groups and aliphatic heterocyclic groups.For example, tetrahydropyran ring group, tetrahydrofuran ring group, 2-pyridyl, 4-pyridyl, 2-imidazolyl, 2-benzimidazolyl, 2-thiazolyl, 2-oxazolyl, pyrrolidone group, etc.), alkoxy group (preferably an alkoxy group having 1 to 20 carbon atoms, for example, methoxy, ethoxy, isopropyloxy, benzyloxy, etc.), aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, 4-methoxyphenoxy, etc.), heterocyclic oxy group (a group in which an -O- group is bonded to the above heterocyclic group), alkoxycarbonyl group (preferably Or, alkoxycarbonyl groups having 2 to 20 carbon atoms, for example, ethoxycarbonyl, 2-ethylhexyloxycarbonyl, dodecyloxycarbonyl, etc.), aryloxycarbonyl groups (preferably aryloxycarbonyl groups having 7 to 26 carbon atoms, for example, phenoxycarbonyl, 1-naphthyloxycarbonyl, 3-methylphenoxycarbonyl, 4-methoxyphenoxycarbonyl, etc.), heterocyclic oxycarbonyl groups (groups in which an -O-CO- group is bonded to the above heterocyclic group), amino groups (preferably amino groups having 0 to 20 carbon atoms, alkylamino groups, arylamino groups, for example, amino(-NH). ２), N,N-dimethylamino, N,N-diethylamino, N-ethylamino, anilino, etc.), sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, for example, N,N-dimethylsulfamoyl, N-phenylsulfamoyl, etc.), acyl group (including alkylcarbonyl group, alkenylcarbonyl group, alkynylcarbonyl group, arylcarbonyl group, heterocyclic carbonyl group, preferably an acyl group having 1 to 20 carbon atoms, for example, acetyl, propionyl, butyryl, octanoyl, hexadecanoyl, acryloyl, methacryloyl, crotonoyl, benzoyl, naphthoyl, nicotinoyl, etc.), acyl Oxy groups (including alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, and heterocyclic carbonyloxy groups, preferably acyloxy groups having 1 to 20 carbon atoms, for example, acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, nicotinoyloxy, etc.), allyloxy groups (preferably allyloxy groups having 7 to 23 carbon atoms, for example, benzoyloxy, naphthoyloxy, etc.), carbamoyl groups (preferably carbamoyl groups having 1 to 20 carbon atoms, for example, N,N-dimethylcarbamoyl, N-phenylcarbamoyl, etc.), acylamino group (preferably an acylamino group having 1 to 20 carbon atoms, e.g., acetylamino, benzoylamino, etc.), alkylthio group (preferably an alkylthio group having 1 to 20 carbon atoms, e.g., methylthio, ethylthio, isopropylthio, benzylthio, etc.), arylthio group (preferably an arylthio group having 6 to 26 carbon atoms, e.g., phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio, etc.), heterocyclic thio group (a group in which an -S- group is bonded to the above heterocyclic group), alkylsulfonyl group (preferably an alkylsulfonyl group having 1 to 20 carbon atoms, e.g., methylsulfonyl, ethylsulfonyl, etc.), arylsulfonyl group (preferably carbon Arylsulfonyl groups with 6 to 22 carbon atoms, for example, benzenesulfonyl), alkylsilyl groups (preferably alkylsilyl groups with 1 to 20 carbon atoms, for example, monomethylsilyl, dimethylsilyl, trimethylsilyl, triethylsilyl), arylsilyl groups (preferably arylsilyl groups with 6 to 42 carbon atoms, for example, triphenylsilyl), alkoxysilyl groups (preferably alkoxysilyl groups with 1 to 20 carbon atoms, for example, monomethoxysilyl, dimethoxysilyl, trimethoxysilyl, triethoxysilyl), aryloxysilyl groups (preferably aryloxysilyl groups with 6 to 42 carbon atoms, for example, triphenyloxysilyl), phosphoryl groups (preferably phosphate groups with 0 to 20 carbon atoms, for example, -OP(=O)(R, Ｐ ) ２ ), phosphonyl group (preferably a phosphonyl group having 0 to 20 carbon atoms, for example, -P(=O)(R Ｐ ) ２ ), phosphenyl group (preferably a phosphenyl group having 0 to 20 carbon atoms, for example, -P(R Ｐ ) ２ ), phosphonic acid group (preferably a phosphonic acid group having 0 to 20 carbon atoms, for example, -PO(OR Ｐ ) ２ Examples include sulfo groups (sulfonic acid groups), carboxyl groups, hydroxyl groups, sulfanyl groups, cyano groups, and halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc.). Ｐis a hydrogen atom or a substituent (preferably a group selected from substituent G). Furthermore, each of the groups listed as substituent G may be further substituted with substituent G. The alkyl group, alkylene group, alkenyl group, alkenylene group, alkynyl group and / or alkynylene group, etc. may be cyclic or linear, and may be linear or branched.

[0071] The content of the extractant in the oil phase is set appropriately, taking into consideration the content of metal ions, the amount of coordination to metal ions, etc. For example, the content of the extractant in the oil phase is 20 to 1.0 × 10 ４ It can be expressed as millimoles / L (mM), and is 50 to 2.0 × 10 ３ It is preferable to use a ratio of millimoles / L, and 50 to 1.0 × 10 ３ It is preferable to use millimoles / L.

[0072] The temperature of the oil phase (during storage and at the start of flow) is not particularly limited and can be, for example, 10 to 60°C, or 15°C or more and less than 40°C. In the present invention, an aqueous solution containing a pH adjusting agent can be added to the oil phase in any amount, or in an amount that results in a predetermined mixed pH when the aqueous phase and oil phase are mixed. Density of the oil phase (kg / m³) ３ The temperature (25°C) is not particularly limited and cannot be uniquely determined by the type of organic solvent, the type or content of the extractant, etc., but for example, 5.0 × 10 ２ ~1.5 x 10 ３ kg / m ３ This is, for example, the kinetic energy E, which will be discussed later. ＳＴ It is preferable in that it is easy to set the kinetic energy E to a suitable value. ＳＴ Setting this value to a suitable level is preferable because it allows for increased extraction and selectivity of metal ions, and also provides excellent phase separation.

[0073] The oil phase is used as a solution in an organic solvent. The oil phase, as a solution of the extractant, can be prepared by dissolving the extractant in an organic solvent. The preparation conditions for the oil phase are not particularly limited. For example, the preparation temperature can usually be 10 to 60°C, but it can be determined considering the solubility of metal ions, etc.

[0074] <Aqueous Solution Containing pH Adjuster> In the present invention, it is preferable to use an aqueous solution containing a pH adjuster. The water used to form the aqueous solution of the pH adjuster is not particularly limited, but (ultra)pure water, ion-exchanged water, etc., can be used. Examples of pH adjusters to be contained in the aqueous solution containing the pH adjuster include the acids and alkalis that can be used to adjust the pH of the aqueous phase. Among these, the inorganic acids and inorganic alkalis are preferred, and hydrochloric acid or an aqueous solution of hydrochloric acid, and alkali hydroxide (hydroxides of Group 1 elements) are more preferred. The content of the pH adjuster in the aqueous solution containing the pH adjuster is set appropriately and determined to achieve a predetermined pH. The temperature of the aqueous solution containing the pH adjuster (during storage and at the start of circulation) is not particularly limited, and can be, for example, 10 to 60°C, or 15°C or more and less than 40°C. The aqueous solution containing the pH adjuster can be prepared by dissolving the pH adjuster in water. The preparation conditions for the aqueous solution containing the pH adjuster are not particularly limited. For example, the preparation temperature can usually be 10 to 60°C, but can be determined considering the solubility of metal ions, etc.

[0075] The extraction method of the present invention can employ both batch extraction methods such as stirring and shaking, and flow extraction methods, depending on the extraction conditions. It is preferable to use a flow extraction method because it can further improve the extraction performance, particularly the phase separation, to a higher level.

[0076] Despite being a simple method, the extraction method of the present invention can extract metal ions from the aqueous phase into the oil phase with a high extraction yield, and preferably with high selectivity. In particular, when the aqueous phase contains two or more types of metal ions, a specific metal ion can be extracted into the oil phase with a high extraction yield, and preferably with high selectivity. Therefore, the extraction method of the present invention can also be described as a method for separating and recovering a specific metal ion from the metal ions present in the aqueous phase.

[0077] The specific metal ion to be extracted or separated and recovered is not uniquely determined by the group or period of the metal ion, its content, the type of extractant, etc. For example, when extracting metal ions belonging to Group 9 and metal ions belonging to Group 10 into the oil phase, the metal ions belonging to Group 9 can be separated and recovered with a high extraction amount, preferably with high selectivity. In particular, when extracting Co ions as Group 9 metal ions and Ni ions as Group 10 metal ions, Co ions can be separated and recovered with a high extraction amount, preferably with high selectivity. Similarly, when extracting metal ions belonging to Group 7 and metal ions belonging to Group 9 into the oil phase, the metal ions belonging to Group 7 can be separated and recovered with a high extraction amount, preferably with high selectivity. In particular, when extracting Mn ions as Group 7 metal ions and Co ions as Group 9 metal ions, Mn ions can be separated and recovered with a high extraction amount, preferably with high selectivity. Furthermore, when extracting metal ions belonging to Group 9 and metal ions belonging to Group 11 into the oil phase, the metal ions belonging to Group 11 can be separated and recovered with a high extraction amount, preferably with high selectivity. Also, when extracting metal ions belonging to Group 2 and metal ions belonging to Group 7 into the oil phase, the metal ions belonging to Group 7 can be separated and recovered with a high extraction amount, preferably with high selectivity, and in particular, when extracting Mg ions as metal ions belonging to Group 2 and Mn ions as metal ions belonging to Group 7, Mn ions can be separated and recovered with a high extraction amount, preferably with high selectivity. Also, when extracting metal ions belonging to Group 7 and metal ions belonging to Group 10 into the oil phase, the metal ions belonging to Group 7 can be separated and recovered with a high extraction amount, preferably with high selectivity, and in particular, when extracting Mn ions as metal ions belonging to Group 7 and Ni ions as metal ions belonging to Group 10, Mn ions can be separated and recovered with a high extraction amount, preferably with high selectivity. Furthermore, when extracting metal ions belonging to Group 10 and metal ions belonging to Group 11 into the oil phase, metal ions belonging to Group 11 can be separated and recovered with a high extraction amount, preferably with high selectivity. In particular, when extracting Ni ions as metal ions belonging to Group 10 and Cu ions as metal ions belonging to Group 11, Cu ions can be separated and recovered with a high extraction amount, preferably with high selectivity.Furthermore, when extracting metal ions belonging to Group 9, Group 10, and Group 12 into the oil phase, the metal ions belonging to Group 10 are usually not extracted, while the metal ions belonging to Group 12 can be separated and recovered with a high extraction amount, preferably with high selectivity.

[0078] The extraction method of the present invention, whether batch or flow, can extract and recover specific metal ions from the aqueous phase into the oil phase with high extraction yield, preferably high selectivity. In particular, the extraction method of the present invention can extract two or more metal ions present in the aqueous phase while recovering one of them with high extraction yield, preferably high selectivity. Therefore, by subjecting the aqueous phase containing two or more metal ions back-extracted from the oil phase to the extraction method of the present invention, the selectivity of one metal ion can be further increased without significantly reducing the recovery yield (recovery rate), and as a result, high-purity metal ions can be recovered in high yield (recovery rate).

[0079] [Batch Extraction Method] When the extraction method of the present invention is performed using a batch extraction method (hereinafter sometimes referred to as "the batch extraction method of the present invention"), there are no particular limitations on the batch extraction method used, and various conventionally known batch extraction methods can be applied. Examples of batch extraction methods include extraction methods using a stirrer (magnetic stirrer tip, mechanical stirrer, etc.), extraction methods using a mixer such as a mixer settler, and extraction methods using a shaker. The aqueous phase, oil phase, and pH adjusting agent (pH adjusting agent-containing aqueous solution) used in the batch extraction method of the present invention are the same as the aqueous phase, oil phase, and pH adjusting agent (pH adjusting agent-containing aqueous solution) used in the extraction method of the present invention described above.

[0080] In the batch extraction method of the present invention, condition B: the mixing temperature of the aqueous phase and the oil phase is set to 40 to 95°C. This allows for excellent extraction performance and phase separation while contributing to improved safety. The preferred mixing temperature is the same as the preferred mixing temperature (condition B) in the flow extraction method described later. In the batch extraction method of the present invention, the mixing temperature refers to the temperature of the mixture of the aqueous phase and the oil phase after pH adjustment. On the other hand, the temperature of the mixture of the aqueous phase and the oil phase before pH adjustment is not particularly limited and can be set as appropriate, but it is preferable to set it to the same as the confluence temperature in the flow extraction method of the present invention described later. In the batch extraction method of the present invention, mixing conditions other than the above mixing temperature can be set as appropriate. For example, the stirring conditions (stirring speed, stirring time, etc.) can be set as long as they allow the aqueous phase and the oil phase to be mixed (conditions under which the extractant coordinates with the metal ions), and can be set as appropriate depending on the combination of metal ions and extractant, the mixing temperature, and the mixing device. For example, the stirring speed can be 80 rpm or more, and is preferably 100 to 200 rpm. The stirring time (mixing time) is not uniquely determined by stirring conditions, etc., but it can be, for example, 10 minutes to 24 hours.

[0081] The mixing ratio of the aqueous phase and the oil phase in the mixing of the aqueous phase and the oil phase is set appropriately according to the content (concentration) of metal ions, the content (concentration) of the extractant, etc., and is not uniquely determined. For example, when mixing the aqueous phase and the oil phase, the oil phase can be mixed in a ratio of 50 to 2000 mL to 100 mL of aqueous phase, and a ratio of 80 to 1000 mL is preferable. On the other hand, focusing on the metal ions present in the aqueous phase, it is preferable to mix the oil phase in a ratio of 0.5 to 20 moles of extractant relative to the total content (moles) of metal ions, and it is more preferable to mix the oil phase in a ratio of 1.0 to 10 moles of extractant. Furthermore, the content of the extractant relative to the total content of metal ions to which the extractant can coordinate (also called the mixing amount; the ratio of moles of extractant to the total number of moles of metal ions: molar ratio) can be, for example, 1.0 to 10.0 times, and 1.5 to 7.0 times is preferable. Here, the metal ions to which the extractant can coordinate refer to the metal ions that the extractant coordinates to and are extracted into the oil phase.

[0082] In mixing the aqueous and oil phases, the pH of the mixed system (combined solution) is usually adjusted. Here, the pH set for a specific metal ion to be extracted is not unique, but is appropriately determined considering the pKa of the extractant, the complex formation constant of the extractant and metal ion, the coordination number of the metal ion, etc. It is preferable to set the pH of the mixed system to the same value as the pH of the three-liquid combined solution in the flow extraction method described later. The pH can be adjusted using a pH adjusting agent or an aqueous solution containing a pH adjusting agent, as described later. In mixing the aqueous and oil phases, the mixing of the aqueous and oil phases is performed after adjusting the pH of the mixed system.

[0083] In the batch extraction method of the present invention, the separation method for separating the phases after mixing the aqueous phase and the oil phase is not particularly limited, and examples include the separation method described in step 3 of the preferred extraction method of the present invention, which will be described later. The phase separation conditions are not particularly limited and can be set as appropriate, as long as the conditions are such that the aqueous phase and the oil phase separate into two layers. In the present invention, even if an oil phase with poor phase separation properties is used, it is preferable to perform the mixing temperature at the above temperature, and then, although the temperature may drop slightly during standing in some cases, to perform the phase separation while basically maintaining the same temperature, at least 40°C. In the batch extraction method of the present invention, high phase separation properties can be achieved regardless of the phase separation conditions, so the standing time applied to conventional wet extraction methods using an oil phase can be adopted. The standing time in the batch extraction method of the present invention can usually be 1 to 30 minutes after mixing stops. In the batch extraction method of the present invention, phase separation proceeds quickly, so the standing time can also be set to a short time, for example, preferably 1 minute or more and less than 15 minutes. Details of the standing time are as described above regarding phase separation properties.

[0084] In this way, the batch extraction method of the present invention can be carried out. In the batch extraction method of the present invention, despite being a simple method, metal ions in the aqueous phase can be extracted into the oil phase with a high extraction amount, preferably with high selectivity, and by rapid phase separation.

[0085] [Flow-type extraction method] When the extraction method of the present invention is carried out as a flow-type extraction method in which the aqueous phase and the oil phase are combined during flow and mixed (Condition A) (hereinafter sometimes referred to as "the flow-type extraction method of the present invention"), various known flow devices can be used. The flow-type extraction method of the present invention will be described with reference to devices suitably used in the flow-type extraction method of the present invention.

[0086] <Extraction apparatus suitably used in the flow-type extraction method of the present invention> The extraction apparatus suitably used in the flow-type extraction method of the present invention (hereinafter sometimes referred to as "extraction apparatus suitable for the present invention") is not particularly limited, but for example, it has an aqueous phase flow pipe connected to an aqueous phase storage tank and for flowing (transferring) the aqueous phase to a confluence located downstream of the aqueous phase storage tank in the flow direction; an oil phase flow pipe connected to an oil phase storage tank and for flowing (transferring) the oil phase to a confluence located downstream of the oil phase storage tank in the flow direction; a confluence connected to the downstream side of the aqueous phase flow pipe and the oil phase flow pipe in the flow direction; a mixing section (mixing flow pipe) extending from the confluence section; a pH adjusting agent transfer pipe connecting a pH adjusting agent-containing aqueous solution storage tank and the mixing section or confluence section for flowing (transferring) the pH adjusting agent-containing aqueous solution from the pH adjusting agent-containing aqueous solution storage tank to the mixing section or confluence section; and a separation section connected to the downstream side of the mixing section in the flow direction. Here, the aqueous phase storage tank, aqueous phase flow pipe, oil phase storage tank, oil phase flow pipe, confluence section, mixing section, pH adjusting agent-containing aqueous solution storage tank, pH adjusting agent transfer pipe, and separation section can be the same as the configuration, arrangement, etc., of the aqueous phase storage tank, aqueous phase flow pipe, oil phase storage tank, oil phase flow pipe, confluence section, mixing section, pH adjusting agent-containing aqueous solution storage tank, pH adjusting agent transfer pipe, and separation section in the extraction apparatus 1 or 2 described later. In this apparatus, each step of the flow-type extraction method of the present invention can be suitably carried out. Hereinafter, the upstream side and the downstream side with respect to the flow direction of the oil phase, aqueous phase, or combined liquid may be simply referred to as the downstream side and the upstream side, respectively.

[0087] (Extraction device 1) As shown in Figure 1, the extraction device 1 includes a water phase storage tank 5 for containing and storing the water phase, a water phase flow pipe 11 connected to the water phase storage tank 5 and for the water phase to flow to a confluence 13 located downstream of the water phase in the flow direction from the water phase storage tank 5, an oil phase storage tank 6 for containing and storing the oil phase, and an oil phase flow pipe 12 connected to the oil phase storage tank 6 and for the oil phase to flow to a confluence 13 located downstream of the oil phase in the flow direction from the oil phase storage tank 6. Extraction apparatus 1, an example of an extraction apparatus suitable for the present invention, is suitable as an extraction apparatus that preferably implements an extraction method in which, among the flow-type extraction methods of the present invention described later, the following steps are performed in order: first, the step of combining the aqueous phase and the oil phase and continuing to flow them; second, the step of combining the combined two-liquid solution with an aqueous solution containing a pH adjuster and continuing to flow them; and third, the step of separating the combined three-liquid solution after the extraction of the metal ions to be extracted has reached extraction equilibrium. The aqueous phase storage tank 5 and the oil phase storage tank 6 each only need to have a capacity that allows the extraction and separation cycle to be carried out in a flow-type manner, and their capacities can be set to appropriate capacities according to the extraction conditions, etc.

[0088] As shown in Figure 1, the extraction device 1 has a water phase flow pipe 11 and an oil phase flow pipe 12 arranged opposite each other in a straight line, and has a confluence section 13 that connects the open end of the tapered section 11a and the open end of the tapered section 12a to merge the two phases. Here, the water phase flow pipe 11 has a tapered section 11a on the downstream side (confluence section 13 side) in the flow direction of the water phase, and the oil phase flow pipe 12 has a tapered section 12a on the downstream side (confluence section 13 side) in the flow direction of the oil phase. In this way, the water phase flow pipe 11 and the oil phase flow pipe 12 have their inner diameters reduced towards the downstream side by the tapered sections 11a and 12a, respectively, and depending on the shape of each tapered section, the opening diameter of the open end of each tapered section is smaller (narrower diameter) than the inner diameter of the upstream opening end of each tapered section (the connection part with a flow pipe having a constant inner diameter). The cross-sectional shape perpendicular to the centerline of each flow pipe 11 and 12 and the tip sections 11a and 12a is not particularly limited, and various shapes, such as circular, elliptical, semicircular, polygonal, etc., can be adopted. The constant inner diameter of each flow pipe 11 and 12 (the inner diameter of the upstream opening end of the tip section) is not particularly limited and can be determined as appropriate, for example, it can be 0.1 to 100 mm, and it is preferable to set it to 0.5 to 10 mm in order to improve the mixing state. The flow diameter (inflow diameter) of the water phase and oil phase flowing from each flow pipe 11 and 12 into the confluence section 13 is reduced by the tip sections 11a and 12a compared to the flow diameter of the water phase and oil phase flowing through each flow pipe 11 and 12. At this time, the ratio of the inner diameter of the opening end of the tip section to a constant inner diameter in each flow pipe 11 and 12 (inner diameter of the opening end of the tip section / inner diameter of the connection part with the constant inner diameter of the flow pipe) is not particularly limited and is determined appropriately according to the flow speed, etc., and is preferably the same as the reduction ratio of the flow diameters of both phases described later. The inner diameters of the water phase flow pipe 11 and the oil phase flow pipe 12 may be different, but it is preferable that they be set to be the same. Furthermore, the inner diameters of the opening ends of the tip section 11a and 12a, and the reduction ratio of the inner diameter of the tip section 11a (the ratio of the above inner diameters) and the reduction ratio of the inner diameter of the tip section 12a may be different, but are usually set to be the same considering the mixing state, etc. In the present invention, inner diameter refers to equivalent diameter, which will be described in detail later.

[0089] The aqueous phase flow pipe 11 and the oil phase flow pipe 12 are usually provided with a transfer mechanism (not shown in Figure 1) for circulating (transferring) the aqueous phase or the oil phase. The transfer mechanism is not particularly limited as long as it can circulate the aqueous phase or the oil phase, and various types of pumps can be used.

[0090] Furthermore, the extraction device 1 has a tubular mixing section 14 that extends from the confluence section 13 in a direction approximately perpendicular to the aqueous phase flow pipe 11, and a pH adjusting agent transfer pipe 15 is connected to the middle of the mixing section 14 to transfer the pH adjusting agent-containing aqueous solution from the pH adjusting agent-containing aqueous solution storage tank 7 to the mixing section 14. The mixing section 14 has a tapered section (reverse taper section) whose inner diameter gradually increases downstream from the connection point with the confluence section 13. The dimensions of this tapered section are not particularly limited and can be set as appropriate, for example, they can be the same ratio as the reduction ratio of the flow diameters of both phases, which will be described later. The mixing section 14 is divided into a pre-mixing section 14a from the connection point with the confluence section 13 to the connection point with the pH adjusting agent transfer pipe 15, and a post-mixing section 14b from the connection point with the pH adjusting agent transfer pipe 15 to the connection point with the separation section 16. The pH adjusting agent-containing aqueous solution storage tank 7 is a tank that contains and stores the pH adjusting agent-containing aqueous solution, and the pH adjusting agent transfer pipe 15 connects the pH adjusting agent-containing aqueous solution storage tank 7 and the mixing unit 14, and flows the pH adjusting agent-containing aqueous solution from the pH adjusting agent-containing aqueous solution storage tank 7 to the mixing unit 14 located downstream in the flow direction of the pH adjusting agent-containing aqueous solution. The pH adjusting agent-containing aqueous solution storage tank 7 only needs to have a capacity that allows the extraction and separation cycle to be carried out in a flow manner, and is set to an appropriate capacity depending on the extraction conditions, etc. In addition, the pH adjusting agent transfer pipe 15 is usually provided with the transfer mechanism described above (not shown in Figure 1) for flowing (transferring) the pH adjusting agent-containing aqueous solution. The inner diameters of the mixing unit 14, pH adjusting agent transfer pipe, etc. can be set within the above range that can be taken as a constant inner diameter in each flow pipe 11 and 12.

[0091] The extraction apparatus 1 preferably has a heating device (not shown in Figure 1) in at least the downstream mixing section 14b that heats the three-liquid confluence. The extraction apparatus 1 may further have a heating device (not shown in Figure 1) in at least one of the following: the aqueous phase flow pipe 11 (especially the downstream portion such as the tip section 11a), the oil phase flow pipe 12 (especially the downstream portion such as the tip section 12a), the confluence section 13, the upstream mixing section 14a, and the pH adjusting agent transfer pipe 15 (especially the downstream portion such as the tip section) that heats the aqueous phase, oil phase, pH adjusting agent-containing aqueous solution, and confluence. The heating device can be any device capable of heating to a temperature higher than at least one of the temperatures of the aqueous phase stored in the aqueous phase storage tank 5, the oil phase stored in the oil phase storage tank 6, and, as appropriate, the pH adjusting agent-containing aqueous solution stored in the pH adjusting agent-containing aqueous solution storage tank 7. For example, various known heating devices such as heaters, electric heating tubes, jackets containing a heating medium, aluminum block heaters, water baths, oil baths, and microwave heating devices can be used.

[0092] Furthermore, the extraction device 1 has a separation unit 16 connected to the downstream end in the flow direction of the mixing unit 14, which allows the incoming three-liquid mixture to stand and separate into an aqueous phase and an oil phase. The separation unit 16 can be made of a general storage container, separation column, settler, separatory funnel, etc., and has an oil phase discharge pipe 16a for discharging the phase-separated oil phase and an aqueous phase discharge pipe 16b for discharging the phase-separated aqueous phase. Valves and transfer means, such as various pumps, may be interposed in the oil phase discharge pipe 16a and the aqueous phase discharge pipe 16b, respectively. The separation unit 16 may be equipped with various known heating devices.

[0093] In the extraction apparatus 1, it is preferable to install a static mixer in at least one of the flow paths of the pre-mixing section 14a and the post-mixing section 14b in the mixing section 14, and it is even more preferable to install the static mixer in the flow path of the post-mixing section 14b in order to further improve the mixing state of the three-liquid combined liquid.

[0094] A static mixer is a stationary mixer without a drive unit. It mixes a fluid that enters the mixer by sequentially dividing, rejoining, and reversing its direction using stationary mixing elements installed inside the mixer. Examples of static mixers include the Sulzer type, Kenix type, Toray type, and Noritake Company type. A static mixer preferably has four or more mixing elements, and more preferably has six to thirty. These mixing elements are preferably arranged continuously in a mixer tube with a length of 10 cm to 2 m. Alternatively, multiple static mixers of this configuration can be arranged in series. In this case, the entire series-arranged static mixers form a single unit, which constitutes the static mixer of this invention. The size of the static mixer used in this invention is appropriately set according to the scale of production, etc. For example, the equivalent diameter inside the tube of the static mixer can be 1 to 100 mm. Even if the internal cross-section of the static mixer is larger than that of the flow pipe, the flow pipe and the static mixer can be connected via a connecting tube or the like. The length of the static mixer can be approximately 5 mm to 20 m. When multiple static mixers are arranged in series, the above length refers to the total length of the multiple static mixers arranged in series (including the spacing between static mixers). When multiple static mixers are arranged in series, the spacing between adjacent static mixers can be appropriately set considering the difference between the internal cross-section of the static mixer and the internal cross-section of the reaction channel connected to it. For example, the spacing between adjacent static mixers can be 100 cm or less, 70 cm or less, 40 cm or less, 20 cm or less, or 10 cm or less.

[0095] Examples of materials for static mixers include perfluoroalkoxyalkanes (PFA), Teflon (registered trademark), aromatic polyetherketone resins, stainless steel, copper or copper alloys, nickel or nickel alloys, titanium or titanium alloys, quartz glass, lime soda glass, etc. From the viewpoint of flexibility and chemical resistance, PFA, Teflon (registered trademark), stainless steel, nickel alloys, or titanium are preferred.

[0096] In the extraction apparatus 1, a three-way pipe having (formed) terminal sections 11a and 12a, such as a T-tube or Y-tube, can be used as the aqueous phase flow pipe 11, the oil phase flow pipe 12, the confluence section 13, and the mixing section 14. In the extraction apparatus 1, the aqueous phase flow pipe 11, the oil phase flow pipe 12, the confluence section 13, and the pre-mixing section 14a may be referred to as the "oil-water mixing section," and the pH adjusting agent transfer pipe 15 and the post-mixing section 14b may be referred to as the "pH adjusting section."

[0097] (Extraction device 2) As shown in Figure 2, the extraction device 2 includes an aqueous phase storage tank 5 for containing and storing the aqueous phase, an aqueous phase flow pipe 11 connected to the aqueous phase storage tank 5 and for the aqueous phase to flow to a confluence 23 located downstream of the aqueous phase in the flow direction from the aqueous phase storage tank 5, an oil phase storage tank 6 for containing and storing the oil phase, an oil phase flow pipe 12 connected to the oil phase storage tank 6 and for the oil phase to flow to a confluence 23 located downstream of the oil phase in the flow direction from the oil phase storage tank 6, a pH adjusting agent-containing aqueous solution storage tank 7 for storing the pH adjusting agent-containing aqueous solution, and a pH adjusting agent transfer pipe 15 connected to the pH adjusting agent-containing aqueous solution storage tank 7 and for the pH adjusting agent-containing aqueous solution to flow to a confluence 23 located downstream of the pH adjusting agent-containing aqueous solution in the flow direction from the pH adjusting agent-containing aqueous solution storage tank 7. This extraction device 2 has basically the same configuration as extraction device 1, except that the pH adjusting agent transfer pipe 15 is connected to the junction 23. However, the mixing section 24 of extraction device 2 is not divided into a pre-mixing section 14a and a post-mixing section 14b, unlike the mixing section 14 of extraction device 1.

[0098] Extraction apparatus 2, another example of an extraction apparatus suitable for the present invention, is an extraction method among the flow-type extraction methods of the present invention described later, in which the process of combining the aqueous phase and the oil phase and continuing to flow the two-liquid mixture and the pH adjusting agent-containing aqueous solution are combined and further flowed in a single step, and is suitable as an extraction apparatus for suitably carrying out an extraction method in which the aqueous phase, the oil phase and the pH adjusting agent-containing aqueous solution are combined at once and further flowed.

[0099] In the extraction apparatus 2, the aqueous phase storage tank 5, the oil phase storage tank 6, and the pH adjusting agent-containing aqueous solution storage tank 7 are the same as those in the extraction apparatus 1.

[0100] As shown in Figure 2, the extraction apparatus 2 has a pH adjusting agent transfer pipe 15 positioned at approximately a right angle to the aqueous phase flow pipe 11 and oil phase flow pipe 12, which are arranged on the same line, and has a confluence section 23 that connects the open end of the tapered section 11a, the open end of the tapered section 12a, and the open end of the pH adjusting agent transfer pipe 15 to combine the aqueous phase, oil phase, and pH adjusting agent-containing aqueous solution. Here, the aqueous phase flow pipe 11 has a tapered section 11a on the downstream side (confluence section 23 side) in the flow direction of the aqueous phase, the oil phase flow pipe 12 has a tapered section 12a on the downstream side (confluence section 13 side) in the flow direction of the oil phase, and the pH adjusting agent transfer pipe 15 may also have a tapered section on the downstream side (confluence section 23 side) in the flow direction of the pH adjusting agent-containing aqueous solution. Here, the aqueous phase flow pipe 11 and oil phase flow pipe 12 are the same as the aqueous phase flow pipe 11 and oil phase flow pipe 12 of the extraction apparatus 1. For example, the water phase flow pipe 11 and the oil phase flow pipe 12 have their inner diameters reduced downstream by the terminal sections 11a and 12a, respectively. Depending on the shape of each terminal section, the opening diameter of the opening end of each terminal section is smaller than the inner diameter of the upstream opening end of each terminal section (the connection point with the flow pipe having a constant inner diameter). The flow diameter (inflow diameter) of the water phase and oil phase flowing from each flow pipe 11 and 12 into the confluence section 23 is reduced by the terminal sections 11a and 12a compared to the flow diameter of the water phase and oil phase flowing through each flow pipe 11 and 12. The ratio of the inner diameter of the opening end of the terminal section to the constant inner diameter of each flow pipe 11 and 12 (inner diameter of the opening end of the terminal section / inner diameter of the connection point with the constant inner diameter terminal section in the flow pipe) is not particularly limited and is determined appropriately according to the flow velocity, etc., and is preferably the same as the reduction ratio of the flow diameters of both phases described later. Furthermore, the pH adjusting agent transfer tube 15 is identical to the pH adjusting agent transfer tube 15 of the extraction device 1, except for the connection position.

[0101] Furthermore, the extraction device 2 has a mixing section 24 that extends from the confluence section 23 along the flow direction extension of the pH adjusting agent transfer pipe 15. The mixing section 24 has a tapered section (reverse taper section) whose inner diameter gradually increases toward the downstream side in the flow direction from the connection point with the confluence section 23. Preferably, the extraction device 2 has a heating device (not shown in Figure 2) in at least the mixing section 24 for heating the three-liquid confluence liquid. In the extraction device 2, a heating device may further be provided in at least one of the following: the aqueous phase flow pipe 11 (especially the downstream portion such as the tapered end 11a), the oil phase flow pipe 12 (especially the downstream portion such as the tapered end 12a), the confluence section 23, and the pH adjusting agent transfer pipe 15 (especially the downstream portion such as the tapered end) for heating the aqueous phase, oil phase, pH adjusting agent-containing aqueous solution, and confluence liquid. The heating device can be any device capable of heating to a temperature higher than at least one of the temperatures of the aqueous phase stored in the aqueous phase storage tank 5, the oil phase stored in the oil phase storage tank 6, and the pH adjusting agent-containing aqueous solution stored in the pH adjusting agent-containing aqueous solution storage tank 7, as described above.

[0102] Furthermore, the extraction device 2 is connected to the downstream end of the mixing unit 24 in the flow direction and has a separation unit 16 that allows the incoming three-liquid mixture to stand and separates it into an aqueous phase and an oil phase. This separation unit 16 has the same configuration as the separation unit 16 of the extraction device 1.

[0103] In the extraction apparatus 2, it is preferable to install a static mixer in the flow path of the mixing section 24 in order to greatly improve the mixing state of the three-liquid combined liquid. The static mixer is as described in the extraction apparatus 1. In the extraction apparatus 2, a four-sided pipe having (formed) tapered ends 11a and 12a, such as a cross pipe, can be used as the aqueous phase flow pipe 11, the oil phase flow pipe 12, the pH adjusting agent transfer pipe 15, the confluence section 23, and the mixing section 24. This extraction apparatus 2 is preferable in that the flow path length of the mixing section 24 can be shortened. In addition, in the extraction apparatus 2, the configuration of the aqueous phase flow pipe 11, the oil phase flow pipe 12, the pH adjusting agent transfer pipe 15, the confluence section 23, and the mixing section 24 also serves as the "oil-water mixing section" and the "pH adjustment section" of the extraction apparatus 1, and is sometimes referred to as the "oil-water mixing pH adjustment section".

[0104] In extraction devices 1 and 2, the aqueous phase flow pipe 11 and the oil phase flow pipe 12 are configured such that their inner diameter decreases (shrinks) toward the downstream side due to the tapered sections 11a and 12a. However, in an extraction device suitable for the present invention, the aqueous phase flow pipe and the oil phase flow pipe are not limited to having tapered sections. For example, as shown in Figure 3, pipes connected to a large diameter section 11b and a small diameter section 11c can be used. Similarly, the pH adjusting agent transfer pipe 15 is configured such that its inner diameter decreases (shrinks) toward the downstream side due to the tapered section. However, in an extraction device suitable for the present invention, the pH adjusting agent transfer pipe is not limited to having tapered sections. For example, it may be composed of a pipe with a constant inner diameter. In the present invention, a constant inner diameter means not only having exactly the same inner diameter, but also having an inner diameter ratio [maximum inner diameter / minimum inner diameter] greater than 1.0 and less than or equal to 1.1. Furthermore, in extraction devices 1 and 2, the flow pipes connected to the confluence section 13 or 23 are arranged at an angle that is approximately right-angle. However, in an extraction device suitable for the present invention, the angle of the pipes connected to the confluence section is not particularly limited. For example, a double pipe or a pipe with two internal flow paths can be used as the aqueous phase flow pipe and the oil phase flow pipe. In this case, the arrangement of the two pipes will be parallel, and the confluence angle between the flowing aqueous phase and oil phase will be small, approximately 0°. In the flow-type extraction method of the present invention, it is preferable to set the arrangement angle between the aqueous phase flow pipe and the oil phase flow pipe (the confluence angle between the aqueous phase and the oil phase) to a certain angle, in order to improve the mixing state due to the impact generated when the two phases merge due to collision. Specifically, this is the same as the confluence angle described later.

[0105] Although extraction apparatuses 1 and 2 are equipped with a pH adjusting agent-containing aqueous solution storage tank 7 and a pH adjusting agent transfer pipe 15, when using aqueous and / or oil phases to which a pH adjusting agent-containing aqueous solution has been pre-added in an amount that results in a predetermined pH at the time of mixing, the extraction apparatus used in the present invention does not need to be equipped with a pH adjusting agent-containing aqueous solution storage tank 7 and a pH adjusting agent transfer pipe 15. The amount added to achieve a predetermined pH at the time of mixing can be appropriately determined by the content of metal ions, the concentration of the pH adjusting agent-containing aqueous solution, the pH set for the metal ions, etc.

[0106] <Flow-type extraction method of the present invention> The flow-type extraction method of the present invention is a method in which an aqueous phase containing metal ions and an oil phase containing an extractant and the above-mentioned organic solvent are combined during the flow process, the two phases are mixed, and then phase separation is performed, thereby enabling the extraction of metal ions contained in the aqueous phase into the oil phase. When the aqueous phase contains two or more types of metal ions, the flow-type extraction method of the present invention is a method in which an aqueous phase containing two or more types of metal ions and an oil phase containing an extractant and the above-mentioned organic solvent are combined during the flow process, the two phases are mixed, and then phase separation is performed, thereby enabling the extraction of at least one of the two or more types of metal ions contained in the aqueous phase into the oil phase from the other types of metal ions.

[0107] In the flow extraction method of the present invention, it is preferable to merge the aqueous phase and the oil phase by utilizing the collision of each phase (both phases) as they are flowing, as this can further improve extraction performance and phase separation. In the present invention, "merging by utilizing the collision of each phase" means merging the flowing aqueous phase and the flowing oil phase by bringing them into contact with each other. For example, the two phases can be brought into contact and merged while maintaining an angle between the flow direction of the aqueous phase and the flow direction of the oil phase. Here, the angle between the flow directions is not particularly limited and can be greater than 0° and less than or equal to 180°. It can be set to an angle (excluding 0°) as described in the section on merging angles later, as this can improve the mixing state. Various conditions in the flow extraction method of the present invention will be described later in the section on preferred extraction methods of the present invention.

[0108] In the flow extraction method of the present invention, the temperature when the two phases are mixed or during mixing (regardless of when they merge) (hereinafter referred to as the "mixing temperature") is not particularly limited, but it is preferable to set it to any temperature in the range of 20 to 95°C, and more preferably to any temperature in the range of 40 to 95°C (i.e., it is preferable to satisfy conditions A and B) in order to improve the extraction performance and phase separation of the metal ions to be extracted. The mixing temperature can be appropriately determined considering the extraction performance of the metal ions to be extracted, and the higher the temperature, the more the extraction performance and phase separation tend to improve. In the present invention, the decomposition and deterioration of the extractant can be suitably suppressed by minimizing the thermal history applied to the extractant, and excellent repeated durability can be achieved. In order to further improve the extraction performance and phase separation, the mixing temperature is preferably 40°C or higher, more preferably 50°C or higher, even more preferably above 60°C, and particularly preferably 80°C or higher within the above temperature range. The upper limit of the mixing temperature is not particularly limited, but it is preferably 95°C or lower in that it can suppress deterioration of the mixing state of the aqueous phase and the oil phase, more preferably 93°C or lower, and particularly preferably 91°C or lower in that it has an excellent balance between selectivity and extraction amount.

[0109] In the flow extraction method of the present invention, the mixing temperature is preferably higher than the temperature of at least one of the aqueous phase and the oil phase at the start of flow, and more preferably higher than the temperature of both the aqueous phase and the oil phase at the start of flow, in order to achieve a good balance between the extraction performance and phase separation of the metal ions to be extracted at a high level. Specifically, the flow extraction method of the present invention set to a preferred mixing temperature is a method in which the aqueous phase containing metal ions and the oil phase containing the extractant and the above-mentioned organic solvent are brought together during flow, the two phases are mixed at a temperature higher than the temperature of at least one of the aqueous phase and the oil phase at the start of flow, and then the phases are separated. That is, at least the temperature when the two phases are mixed or during mixing (regardless of when they are brought together) is adjusted to the above temperature relationship. A preferred flow extraction method of the present invention, which adjusts the temperature at least at the time of mixing (after adjusting the three-liquid mixture to a predetermined pH) to a temperature higher than the temperature of at least one of the aqueous and oil phases at the start of flow, can move (extract) specific metal ions coordinated by the extractant from the aqueous phase to the oil phase with high extraction performance and phase separation, and can further enhance the phase separation between the aqueous and oil phases once they have been mixed. In the present invention, the mixing temperature refers to the final temperature reached during the mixing process.

[0110] The temperature difference between the temperatures of both phases at the start of flow and the mixing temperature is not particularly limited, but it is preferably 0 to 90°C, more preferably 10 to 90°C, more preferably 20 to 80°C, and even more preferably 30 to 70°C, in order to further increase the extraction amount while maintaining high selectivity and high phase separation.

[0111] When mixing the combined aqueous and oil phases with the pH adjusting agent-containing aqueous solution, the temperature of the pH adjusting agent-containing aqueous solution is not particularly limited and may be low, the same temperature as the mixing temperature, or high.

[0112] In the flow extraction method of the present invention, the temperature at the time of or during the joining of the two phases (hereinafter referred to as the "joining temperature") is not particularly limited and can be any temperature in the range of 15 to 95°C, preferably any temperature in the range of 20 to 95°C, and more preferably any temperature in the range of 40 to 95°C. The joining temperature may be the same temperature as or lower than the temperatures of the aqueous and oil phases at the start of flow, but it is preferable that it be higher than the temperature of at least one (more preferably both) of the aqueous and oil phases at the start of flow in order to further improve the extraction performance of the metal ions to be extracted. In the present invention, the joining temperature means the final temperature reached during the flow process. The joining temperature, which is set to a temperature higher than the temperatures of the aqueous and oil phases at the start of flow, is not particularly limited and is preferably within the same range as the mixing temperature. In the present invention, the joining temperature may be the same temperature as or different from the mixing temperature, and depending on the flow velocity, flow rate, etc. of both phases, the mixing temperature may be higher than the joining temperature. Furthermore, in the present invention, the temperature difference between the temperatures of both phases at the start of flow and the confluence temperature is not particularly limited, and it is preferable to set it within the same range as the temperature difference between the temperatures of both phases at the start of flow and the mixing temperature as described above. Note that the temperature difference between the temperatures of both phases at the start of flow and the mixing temperature, and the temperature difference between the temperatures of both phases at the start of flow and the confluence temperature, may be the same or different.

[0113] In this invention, the temperatures of the aqueous phase and the oil phase at the start of flow may be the same or different.

[0114] The various conditions in the flow extraction method of the present invention will be explained later in the section on preferred extraction methods of the present invention.

[0115] (Preferred Extraction Method of the Present Invention) The flow extraction method of the present invention is a method of combining an aqueous phase containing metal ions and an oil phase containing an extractant and the above-mentioned organic solvent during flow, mixing the two phases, and then separating the phases. The flow extraction method of the present invention is not particularly limited as long as it can mix and separate phases as described above, and is preferably a flow wet extraction method having at least the following steps 1 to 3 (sometimes referred to as "the preferred extraction method of the present invention"). In the preferred extraction method of the present invention, an aqueous phase containing metal ions, an oil phase containing an extractant, and an aqueous solution containing a pH adjuster are used as appropriate. Step 1: A step of combining the flowing aqueous phase and oil phase and continuing to flow Step 2: A step of mixing the aqueous phase and oil phase with the aqueous solution containing a pH adjuster and continuing to flow Step 3: A step of separating the three-liquid mixture after the extraction of the metal ions to be extracted has reached extraction equilibrium

[0116] The preferred extraction method of the present invention can be suitably carried out using the extraction apparatus suitable for the present invention described above. The preferred extraction method of the present invention will be specifically described below with reference to the extraction apparatus 1 shown in Figure 1 and the extraction apparatus 2 shown in Figure 2.

[0117] [Step 1] In the flow extraction method of the present invention, the following Step 1 is performed using the prepared aqueous phase and oil phase. Step 1: A step in which the flowing aqueous phase and oil phase are combined and continued to flow.

[0118] In step 1, when using the extraction device 1, the aqueous phase or oil phase is transferred and circulated in the aqueous phase circulation pipe 11 and the oil phase circulation pipe 12 from the aqueous phase storage tank 5 and the oil phase storage tank 6 using a transfer mechanism, such as various pumps. In step 1, the aqueous phase and the oil phase are merged during the flow.

[0119] In Step 1 of the Preferred Extraction Method of the Present Invention and in the Preferred Extraction Method of the Present Invention (hereinafter referred to as "Step 1, etc."), the confluence conditions are not particularly limited and can be determined as appropriate. The mixing ratio of the aqueous phase and the oil phase can be the mixing ratio described in the batch extraction method of the Present Invention, and preferably, it is a ratio that satisfies the ratio (moles) to the content [content (moles) of the extractant / total content (moles) of metal ions contained in the aqueous phase] and / or the ratio of the content of the extractant to the total content of metal ions to which the extractant can coordinate [moles of the extractant / total number of moles of metal ions to which the extractant can coordinate], as described later. Setting the following conditions as confluence conditions, for example, conditions for transferring the aqueous phase and the oil phase and conditions for mixing the two phases, is preferable in terms of extraction performance and phase separation. It is preferable that at least one of the aqueous phase and the oil phase satisfies the following preferred ranges, etc., for each of the following conditions, and it is more preferable that both satisfy the following preferred ranges, etc., in terms of extraction performance and phase separation. For each condition, if both the aqueous phase and the oil phase meet the following preferred ranges, the conditions for the aqueous phase and the conditions for the oil phase may be the same or different.

[0120] In step 1, etc., the temperature at the time of confluence of the aqueous and oil phases (before pH adjustment) is not particularly limited and is as described above. The confluence temperature can be lower than the temperatures of the aqueous and oil phases at the start of flow, but is usually the same, preferably the mixing temperature described later. Setting the confluence temperature within the same range as the mixing temperature described later can further improve extraction performance and phase separation. When using a pH-adjusted aqueous or oil phase, the confluence temperature is set within the same range as the mixing temperature described above.

[0121] In process 1, etc., the flow velocity of the water phase cannot be uniquely determined depending on the internal pressure, the inner diameter of the water phase flow pipe 11, the ratio of the above inner diameters (inner diameter of the open end of the tip section / inner diameter of the connection section with a constant inner diameter tip section in the flow pipe), etc., but for example, 1.0 × 10 －３ ~1.0 x 10 ３ It can be set to L / min, and the mixing state can be improved, hence 3.0 × 10 －３ ~5.0 x 10 ２It is preferable to set the flow rate to L / min, which allows for a high level of both extraction volume and selectivity as extraction performance, and is also excellent in phase separation. Therefore, it is more preferable to set it to 6.0 to 30 mL / min, even more preferable to set it to 4.0 to 13.0 mL / min, and particularly preferable to set it to 5.0 mL / min. Similarly, the internal pressure (flow pressure) of the aqueous phase cannot be uniquely determined, but for example, it can be set to 0.01 to 5.0 MPa, and it is preferable to set it to 0.03 to 2.5 MPa in which the mixing state can be improved. The flow rate of the oil phase cannot be uniquely determined depending on the internal pressure, the inner diameter of the oil phase flow pipe 12, the ratio of the above inner diameters, etc., but for example, 1.0 × 10 －３ ~1.0 x 10 ３ It can be set to mL / min, and the mixing state can be improved, hence 3.0 × 10 －３ ~5.0 x 10 ２ It is preferable to set the flow rate to mL / min, as this allows for a high level of both extraction volume and selectivity, as well as excellent phase separation. Therefore, it is more preferable to set it to 4.0 to 30 mL / min, even more preferable to set it to 5.0 to 13.0 mL / min, and particularly preferable to set it to 6.0 to 13.0 mL / min. Similarly, the internal pressure (flow pressure) of the oil phase cannot be uniquely determined, but for example, it can be set to 0.01 to 5.0 MPa, and it is preferable to set it to 0.03 to 2.5 MPa in that it can improve the mixing state.

[0122] The flow rates of the aqueous phase and the oil phase per unit time can be appropriately determined by the inner diameter of each flow pipe, the ratio of the metal ion content to the extractant content, and the flow rates per unit time can be set to different amounts or to the same amount. In step 1, regardless of the flow rate per unit time, the ratio (moles) of the metal ion content to the extractant content when the aqueous phase and the oil phase are mixed [extractant content (moles) / total metal ion content (moles) in the aqueous phase] is preferably 0.5 to 50.0 times, more preferably 1.0 to 20.0 times, and even more preferably 1.0 to 10.0 times. Furthermore, the ratio of the extractant content to the total amount of metal ions to which the extractant can coordinate (also called the mixing amount) [moles of extractant / total moles of metal ions to which the extractant can coordinate] can be, for example, 1.0 to 25.0 times, preferably 1.0 to 15.0 times, more preferably 1.0 to 10.0 times, and even more preferably 1.0 to 7.0 times. Here, the metal ions to which the extractant can coordinate refer to the metal ions to which the extractant coordinates and is extracted into the oil phase.

[0123] As described above, the water phase flowing through the water phase flow pipe 11 and the oil phase flowing through the oil phase flow pipe 12 are led to the confluence section 13 and merged with each other. At this time, the flow diameters of both phases may be constant, decreasing, or increasing, but it is preferable that they are constant or decreasing. Here, a constant flow diameter is synonymous with a constant inner diameter of each flow pipe. When the flow diameters of both phases are decreased and the two phases are merged, the reduction ratio of the flow diameter (the ratio of the inner diameters mentioned above) is not uniquely determined by the flow velocity, internal pressure, etc., but for example, it is preferable that it is 0.9 or less with respect to the inner diameter and flow velocity of each flow pipe. The reduction ratio of the flow diameters of both phases is more preferably 0.8 or less, even more preferably 0.6 or less, and particularly preferably 0.55 or less, in terms of improving the mixing state, specifically, maintaining rapid phase separation (also called phase separation or liquid separation) of both phases after mixing, while achieving a high level of both extraction volume and selectivity, and furthermore, also providing excellent phase separation. The lower limit of the reduction ratio is not particularly limited, and can be 0.1 or more in terms of suppressing excessive internal pressure load and providing excellent workability, and is preferably 0.2 or more, and more preferably 0.3 or more, in terms of improving the mixing state as described above. The distance between the end opening of the water phase flow pipe 11 and the end opening of the oil phase flow pipe 12 (length of the confluence section 13 (impact region)) is appropriately determined considering the mixing state (impact force) of the water phase and the oil phase, and can be, for example, 1 to 100 mm.

[0124] In the present invention, the flow conditions and confluence conditions of the aqueous phase and the oil phase can be appropriately selected from the above conditions, but the conditions for each phase converging, particularly for each phase converging due to collision between the two phases, are the kinetic energy per unit area and per unit time (in the present invention, this may simply be referred to as "kinetic energy") E ＳＴ Setting this is preferable because it allows for a high level of both extraction volume and selectivity, and also provides excellent phase separation. In the present invention, the kinetic energy E per unit area and per unit time ＳＴ (J / sec / m ２ ) is calculated from the density of the fluid (aqueous phase and oil phase), the linear velocity and volumetric flow rate at the confluence 13 (end opening of each flow pipe), and the cross-sectional area using the following formula (EＳＴ It can be calculated using the formula (E ＳＴ ) E ＳＴ = (1 / 2) × ρ × u ２ ×Q×(1 / A) Equation (E ＳＴ In this case, ρ is the density of the fluid being circulated (kg / m³). ３ ) where u is the linear velocity (m / sec) of the fluids being circulated at the time of confluence (when flowing into the confluence section 13), and Q is the volumetric flow rate (m) of the fluids being circulated at the time of confluence (when flowing into the confluence section 13). ３ / sec) where A is the cross-sectional area (m²) calculated from the inner diameter at the end opening (junction 13) of each flow pipe. ２ )

[0125] Here, the density of the fluid is ρ (kg / m³). ３ ) is calculated by measuring the mass W (g) of the fluid used when making up the fluid to be measured in a 100 mL volumetric flask, and then (W / 100) × 1000 (kg / m ３ The linear velocity u (m / sec) of the fluid is calculated by multiplying the fluid flow rate (mL / min) by 60 × 10⁻¹⁰. －６ × 1 / A(m) -２ It can be calculated by multiplying by ). In the present invention, the above linear velocities of the aqueous phase and the oil phase are not particularly limited, for example, 1.0 × 10 －４ ~1.0 x 10 －１ It is preferable to set it to m / sec, 5.0 × 10 －４ ~5.0 x 10 －２ It is more preferable to use m / sec. Fluid volume flow rate Q (m ３ The value ( / sec) can be converted from the above flow rate (mL / min).

[0126] In the present invention, the above kinetic energy E ＳＴ Increasing the kinetic energy E enhances the mixing state due to collisions between the aqueous and oil phases, further improving extraction yield and selectivity, as well as further improving phase separation. In the present invention, the kinetic energy E ＳＴ This can be appropriately set considering the flow conditions and confluence conditions of the aqueous and oil phases as described above. For example, the kinetic energy E ＳＴIn addition, it is possible to increase the interface area between the aqueous and oil phases, thereby further improving extraction yield and selectivity, and also further improving phase separation, resulting in a concentration of 50 J / sec / m². ２ It is preferable to have the above, 2.0 × 10 ２ J / sec / m ２ It is more preferable to have the above, 5.0 × 10 ２ J / sec / m ２ It is even more preferable to have the above. On the other hand, the above kinetic energy E ＳＴ One advantage is that it can improve phase separation, 1.0 × 10 ５ J / sec / m ２ The following is preferable, as it allows for further improvement of extraction volume and selectivity while maintaining high phase compatibility: 1.6 × 10 ４ J / sec / m ２ It is more preferable to use the following: 1.0 × 10 ４ J / sec / m ２ It is even more preferable to have the following: 5.0 × 10 ３ J / sec / m ２ The following is particularly preferable: Kinetic energy E ＳＴ One preferred embodiment is, regardless of the above upper and lower limits, 30 to 1.5 × 10 ２ J / sec / m ２ Preferably, 40 to 1.0 × 10 ２ J / sec / m ２ It is more preferable that the concentration be 50-80 J / sec / m ２ It is even more preferable that this be the case.

[0127] In the present invention, the conditions for carrying out step 1 etc. can be appropriately selected from the above conditions, and the conditions can be appropriately combined and set. In the present invention, the conditions for carrying out step 1 etc. can be appropriately balanced to improve extraction amount, selectivity and phase separation, and among the above conditions, the flow rate, the reduction ratio of flow diameter (ratio of inner diameter), and kinetic energy E ＳＴIt is preferable to set at least one of the following, and in order to achieve a high level of both extraction amount, selectivity and phase separation, it is more preferable to set the flow rate and the reduction ratio of the flow diameter to any of the above ranges by combining them, and in order to achieve an even higher level of balance of both extraction amount, selectivity and phase separation, the reduction ratio of the flow rate and the flow diameter and the kinetic energy E ＳＴ It is even more preferable to combine the above and set them within any of the above ranges. For example, set the flow rate within the range of 6.0 to 30 mL / min, the flow diameter reduction ratio within the range of 0.2 to 0.9, and the kinetic energy E ＳＴ 50 to 1.0 x 10 ５ J / sec / m ２ It is preferable to set each of these conditions within the range or within the range defined in one of the preferred embodiments. In this embodiment, each of the combined conditions can also be within the preferred range described above. In this embodiment, conditions other than these can be combined, for example, it is also preferable to combine the above ratio (moles) [extractant content (moles) / total content of metal ions contained in the aqueous phase (moles)] and / or content [moles of extractant / total number of moles of metal ions that the extractant can coordinate].

[0128] In this invention, the flow diameter, as well as the inner diameter of the flow pipe and the opening diameter of the tip section, are defined as "equivalent diameters." "Equivalent diameter" is also called the equivalent (straight) diameter and is a term used in the field of mechanical engineering. When an equivalent circular pipe is assumed for a pipe or flow path with an arbitrary internal cross-sectional shape, the diameter of the internal cross-section of that equivalent circular pipe is called the equivalent diameter. The equivalent diameter (deq) is defined as deq = 4A / p, where A is the internal cross-sectional area of ​​the pipe and p is the wet-edge length (internal circumference) of the pipe. When applied to a circular pipe, this equivalent diameter coincides with the diameter of the internal cross-section of the circular pipe. The equivalent diameter is used to estimate the flow or heat transfer characteristics of the pipe based on the data of the equivalent circular pipe, and represents the spatial scale (representative length) of the phenomenon. For a square pipe with an internal cross-section of side a, the equivalent diameter is deq = 4a ２ / 4a = a, in an equilateral triangular tube with side length a, deq = a / 3 １／２For flow between parallel plates with a flow path height h, deq = 2h (see, for example, "Dictionary of Mechanical Engineering" edited by the Japan Society of Mechanical Engineers, 1997, Maruzen Co., Ltd.).

[0129] In step 1, the confluence angle of the aqueous phase and the oil phase is not particularly limited. In the extraction device 1, the confluence angle is 180° (opposing), but in the present invention, the confluence angle can be 0 to 180°, and it is preferable to set it to 30 to 180°, more preferably to 90 to 180°, and even more preferably to 150 to 180°, as the mixing state can be improved by using collisions between the aqueous phase and the oil phase to confluence them. In step 1, as described above, the flowing aqueous phase and the flowing oil phase are confluenced and mixed in the confluence section 13, preferably by colliding the two phases to confluence and mix them, and then transferred to the mixing section 14, where they continue to flow through the internal passages of the mixing section 14.

[0130] [Step 2] In the flow extraction method of the present invention, the following Step 2 is performed. Step 2 may be performed after Step 1, or together with Step 1. Step 2 is a pH adjustment step, which starts the mixing of the aqueous phase and the oil phase. Step 2: A step in which the aqueous phase, the oil phase and the aqueous solution containing the pH adjuster are combined and further passed through the mixture.

[0131] - Step 2A - Step 2A is a step in which pH adjustment is performed following Step 1. For example, when using the extraction device 1, the pH adjusting agent-containing aqueous solution is circulated from the pH adjusting agent-containing aqueous solution storage tank 7 into the pH adjusting agent transfer pipe 15 using a transfer mechanism, such as various pumps, and then transferred to the mixing section 14. At this time, the amount of pH adjusting agent-containing aqueous solution circulated is set to an amount at which the pH of the three-liquid confluence mixed in the mixing section 14 reaches a predetermined value. The set pH is not unique, but is appropriately determined considering the pKa of the extractant, the complex formation constant of the extractant and metal ions, the coordination number of the metal ions, etc. The pH of the three-liquid confluence (the aqueous phase in it) can be 0.01 to 14. For example, in terms of extraction amount and selectivity, it is preferably 0.1 to 10, more preferably 0.5 to 7.0, even more preferably 1.0 to 6.5, particularly preferably 2.5 to 6.5, and most preferably 3.0 to 6.5. A specific example of pH for metal ions is the range of ±0.2 of the pH value set for each metal ion in the examples described later. Furthermore, the flow rate of the aqueous solution containing the pH adjusting agent cannot be uniquely determined, depending on the internal pressure of the pH adjusting agent transfer pipe, the inner diameter of the pH adjusting agent transfer pipe 15, the internal pressure of the mixed liquid flowing in the mixing section 14, etc., but it can be, for example, 0.05 to 10.0 mL / min. Similarly, the internal pressure (flow pressure) of the aqueous solution containing the pH adjusting agent cannot be uniquely determined, and is set to a pressure that allows it to be transferred into the mixing section 14.

[0132] As described above, in step 2, which involves further circulation, the two-liquid mixture of the aqueous phase and oil phase that were combined in step 1 (also called the oil-water mixture) is combined with the pH adjusting agent-containing aqueous solution and further circulated. Specifically, in the flow-type extraction method of the present invention, when the extraction device 1 is used, the pH adjusting agent-containing aqueous solution circulating in the pH adjusting agent transfer pipe 15 is transferred to the mixing section 14, where the oil phase and aqueous phase (two-liquid mixture) circulating in the downstream mixing section 14b are combined with the pH adjusting agent-containing aqueous solution and mixed. This results in a three-liquid mixture of both phases and the pH adjusting agent-containing aqueous solution (also called the adjusting agent mixture), and its pH can be adjusted to the predetermined value. After that, the three-liquid mixture is further circulated in the downstream mixing section 14b and transferred to the separation section 16.

[0133] In the present invention, when using the extraction device 1, it is preferable to mix the aqueous phase, oil phase, and pH adjusting agent-containing aqueous solution (three-liquid confluence) at a temperature higher than the temperature of at least one of the aqueous phase and oil phase at the start of flow. The temperature conditions at this time are as described in the flow extraction method of the present invention. When using the extraction device 1 and the extraction device 2, as described above, heating devices provided in the aqueous phase flow pipe 11 (especially the downstream portion such as the tip section 11a), the oil phase flow pipe 12 (especially the downstream portion such as the tip section 12a), the confluence section 13, the mixing section 14, the pH adjusting agent transfer pipe 15 (especially the downstream portion such as the tip section), etc., can heat both phases flowing through the pipes, as well as the pH adjusting agent-containing aqueous solution, and the combined phases (three-phase confluence) can be heated to a predetermined temperature. Furthermore, the temperature of the two-liquid confluence solution from the time of confluence of the aqueous and oil phases until immediately before mixing with the pH adjusting agent-containing aqueous solution (confluence temperature) may be lower than or the same as the temperature of at least one of the aqueous and oil phases at the start of flow, but it is preferable that the temperature be higher than the temperature of the aqueous and oil phases at the start of flow, as this improves the mixing state and further enhances the extraction amount, selectivity, and phase separation.

[0134] - Step 2B - Step 2B is a step in which pH adjustment is performed in Step 1. For example, when using the extraction device 2, in Step 1, the pH adjusting agent-containing aqueous solution is directly introduced to the confluence 23 from the pH adjusting agent transfer pipe 15 connected to the confluence 23, and the three liquids flowing into the confluence 23, namely the aqueous phase, the oil phase, and the pH adjusting agent-containing aqueous solution, are combined. The flow conditions at this time can be set to be the same as the flow conditions in the method using the extraction device 1. In this way, the aqueous phase, the oil phase, and the pH adjusting agent aqueous solution are combined all at once. Specifically, the aqueous phase flowing through the aqueous phase flow pipe 11, the oil phase flowing through the oil phase flow pipe 12, and the pH adjusting agent-containing aqueous solution flowing through the pH adjusting agent transfer pipe 15 are transferred to the confluence 23, and the three liquids are combined (by collision) in the confluence 23 to obtain a three-liquid combined liquid with the pH adjusted to the predetermined value. Subsequently, the three-liquid combined liquid is further circulated through the mixing section 24, and the aqueous phase and oil phase are mixed while being transported to the separation section 16. In this step 2B, the pH of the three-liquid combined liquid is adjusted to a predetermined value in the confluence section 23, and mixing of the aqueous phase and oil phase begins (the confluence section 23 corresponds to a part of the mixing section 24).

[0135] In step 2B, it is preferable that the aqueous phase, oil phase, and pH adjusting agent-containing aqueous solution (three-liquid confluence) are combined and mixed at a temperature higher than the temperature of at least one of the aqueous phase and oil phase at the start of flow. The temperature conditions, the location and type of heating device, etc., at this time are as described in the flow extraction method of the present invention. When combined and mixed at such a temperature, the mixing state is improved from the time the aqueous phase, oil phase, and pH adjusting agent-containing aqueous solution are combined, further increasing selectivity and extraction amount, and also improving phase separation. Moreover, the length of the mixing section 24 (mixing time) can be shortened.

[0136] In the present invention, in steps 2A and 2B, at least one of the aqueous phase and the oil phase may be a phase to which an aqueous solution containing a pH adjusting agent has been added in any amount.

[0137] - Step 2C - Step 2C is a step in which pH adjustment is performed in Step 1, and is performed using a pH-adjusted aqueous phase and / or pH-adjusted oil phase, in which an aqueous solution containing a pH adjusting agent has been added to the aqueous phase and / or oil phase in an amount that results in a predetermined mixed pH when the aqueous phase and oil phase are mixed. The pH adjusting agent added to the aqueous phase and / or oil phase in advance has been described above as an aqueous solution, but it may also be the pH adjusting agent itself. In Step 2C, for example, extraction devices 1 and 2 that do not have a pH adjusting agent transfer pipe 15 can be used. In Step 2C, for example, in Step 2 using extraction device 1 or 2, the aqueous phase and oil phase (at least one of which is pH-adjusted) are directly led from each transfer pipe 11 and 12 to the confluence section 13 or 23, and the two liquids flowing into the confluence section 13 or 23 are combined. The flow conditions, etc. at this time can be set to the same conditions as the flow conditions, etc. in the method using extraction device 1. In this way, the aqueous phase and the oil phase (at least one of which has been pH-adjusted) are combined all at once. Specifically, the aqueous phase flowing through the aqueous phase flow pipe 11 and the oil phase flowing through the oil phase flow pipe 12 are transferred to the confluence section 13 or 23, where the two liquids are mixed (by collision) in the mixing section 13 or 23. This mixing results in a pH-adjusted two-liquid confluence liquid (corresponding to the three-liquid confluence liquid described above) with a pH adjusted to a predetermined value. Subsequently, the pH-adjusted two-liquid confluence liquid is transferred to the separation section 16 by flowing it through the mixing section 14 or 24, while mixing the aqueous phase and the oil phase. In this step 2C, the pH of the three-liquid confluence liquid is adjusted to a predetermined value in the confluence section 23, and mixing of the aqueous phase and the oil phase begins (the confluence section 23 corresponds to a part of the mixing section 24).

[0138] In step 2C, it is preferable that the aqueous phase and the oil phase (pH-adjusted two-liquid confluence) are combined and mixed at a temperature higher than the temperature of at least one of the aqueous and oil phases at the start of flow. The temperature conditions, the location and type of the heating device, etc., at this time are as described in the flow extraction method of the present invention. When combined and mixed at such a temperature, the mixing state is improved from the time the aqueous phase and the oil phase (at least one of which is pH-adjusted) are combined, further increasing selectivity and extraction amount, and also improving phase separation. Moreover, the length of the mixing section 24 (mixing time) can be shortened.

[0139] In the present invention, the three-liquid confluence is separated into an aqueous phase and an oil phase in step 3, which will be described later. However, the point at which extraction equilibrium is reached may be before the phase separation, or after it has been transferred to the separation section 16 of the extraction apparatus 1 and 2. In order to achieve an even higher level of balance between selectivity, extraction volume, and phase separation, it is preferable that the extraction of the metal ions to be extracted from the three-liquid confluence reaches extraction equilibrium during the flow in step 1 or step 2 (until it is introduced into the standing section 16). Specifically, it is preferable that the extraction of the metal ions to be extracted reaches extraction equilibrium while the three-liquid confluence is flowing through the downstream mixing section 14b or mixing section 24 of the mixing section 14. In the present invention, since both phases are mixed at approximately the same temperature as the mixing temperature, preferably 40 to 95°C, even during flow (after pH adjustment), it is considered that the extraction of metal ions is promoted during flow through the mixing section 14 or 24, and extraction equilibrium is reached quickly.

[0140] In the present invention, the fact that the extraction of the target metal ions has reached extraction equilibrium can be confirmed and identified by various methods. For example, it can be confirmed and identified by measuring that the pH of the three-liquid confluence liquid is constant after pH adjustment with a pH adjusting agent (flowing through the downstream mixing section 14b or mixing section 24), or by measuring that the content (residual amount) of the target metal ions in the aqueous phase sampled from the three-liquid confluence liquid is constant. In the present invention, in order to reach extraction equilibrium for the extraction of the target metal ions while the three-liquid confluence liquid is flowing through the downstream mixing section 14b or mixing section 24, the above confirmation and identification methods should be performed on the three-liquid confluence liquid in advance, and the flow time (flow path length), as well as the flow rate, inner diameter, etc. of the downstream mixing section 14b or mixing section 24 should be determined based on the results obtained. The time required to reach extraction equilibrium for the target metal ions cannot be uniquely determined, as it depends on the content of metal ions in the aqueous phase, the type of extractant, the temperature, etc. However, it can be measured as the elapsed time from mixing the aqueous phase and the oil phase (after pH adjustment), ranging from 1 minute to 24 hours, and preferably from 1 to 60 minutes.

[0141] In at least one of steps 1 and 2, it is preferable to circulate the combined liquid (combined liquid) through a channel containing a static mixer, as this greatly improves the mixing state of the combined liquid. When using extraction device 1, a static mixer can be installed in at least one of the channels of the pre-mixing section 14a and the post-mixing section 14b in the mixing section 14, and it is more preferable to install the static mixer in the channel of the post-mixing section 14b, as this further improves the mixing state of the three-liquid combined liquid. When using extraction device 2, a static mixer is installed in the channel of the mixing section 24.

[0142] [Step 3] In the flow extraction method of the present invention, the following Step 3 is then performed. Step 3: After the extraction of the metal ions to be extracted has reached extraction equilibrium, the three-liquid mixture is separated into an aqueous phase and an oil phase (phase separation).

[0143] The separation method in step 3 is not particularly limited, and known separation methods, such as the standing method and centrifugal separation method, can be applied. The standing method is preferred because it has a simple apparatus configuration and excellent workability. The phase separation conditions are not particularly limited and can be set as appropriate, as long as the conditions under which the three-liquid mixture separates into an aqueous phase and an oil phase. In the present invention, even if an oil phase with poor phase separation properties is used, high phase separation properties can be achieved because it is a flow extraction method. Therefore, the standing time for the standing method in step 3 can be the same as the standing time applied to conventional wet extraction methods using an oil phase, and can usually be 1 to 30 minutes after being transferred to the separation unit 16. In the flow extraction method of the present invention, since phase separation after mixing proceeds rapidly, the standing time can also be set to a short time, preferably, for example, 1 minute or more and less than 15 minutes. Details of the standing time are as described above regarding phase separation properties. The temperature of the three-liquid confluence during phase separation is not particularly limited, but from the viewpoint of phase separation properties, it is preferable that it be higher than the temperature of at least one of the aqueous and oil phases at the start of flow, and preferably approximately the same temperature as the temperature of the three-liquid confluence (mixing temperature) (mixing temperature ± 5°C).

[0144] In the flow extraction method of the present invention, the temperature at which each of steps 1 to 3 is carried out (excluding the confluence temperature and mixing temperature) is not particularly limited and may be at room temperature, a temperature higher than room temperature, or a temperature lower than room temperature.

[0145] In the flow extraction method of the present invention, steps 1 to 3 described above can be performed to extract metal ions from the aqueous phase to which the extractant has coordinated, into the oil phase. If the aqueous phase contains two or more types of metal ions, at least one type of metal ion from the two or more types of metal ions present in the aqueous phase to which the extractant has coordinated, can be extracted into the oil phase. Ideally, the number of types of metal ions extracted into the oil phase is one, but it may be two or more types, including those with low extraction rates. In this case, for example, it can be 2 to 10 types, preferably 2 to 6 types, and more preferably 2 or 3 types. The two or more metal ions extracted into the oil phase from the two or more types of metal ions are not particularly limited, but for example, it is preferable that they be the same as the two or more heterogroup metal ions (combinations) contained in the aqueous phase as described above.

[0146] In the flow extraction method of the present invention, steps 2B and 2C, in which a pH adjustment step is performed when the two phases are combined in step 1, are preferred in that they can improve the mixing state of the two phases, and step 2C, in which a pH-adjusted aqueous phase and / or a pH-adjusted oil phase is used, is more preferred in that it can further improve the mixing state of the two phases.

[0147] <Multi-cycle extraction method> The extraction method of the present invention can also perform a large number of extraction and separation cycles in a batch extraction method and a flow extraction method (for example, a series of extraction and separation cycles of steps 1 to 3 in a flow extraction method). The extraction method of the present invention, which performs a series of extraction and separation cycles many times (sometimes referred to as the multi-cycle extraction method of the present invention), can perform the extraction and separation cycles as long as it can maintain high extraction yield, high selectivity, and even better phase separation, for example, 2 to 100 cycles, preferably 5 to 50 cycles. In the multi-cycle extraction method of the present invention, the phase-separated oil phase can be reused as the oil phase for the next extraction and separation cycle, thereby reducing extraction costs. At this time, if necessary, metal ions can be back-extracted from the phase-separated oil phase, and the content of the extractant can be adjusted. The phase-separated oil phase (used oil phase) is usually used after back-extracting metal ions, but it can also be used without back-extraction, taking into consideration the content of metal ions in the aqueous phase, the amount extracted, etc. As a method for back-extracting (isolating) metal ions from the oil phase, known methods can be applied without particular limitation. For example, this can be done by making the liquid phase acidic, for example, pH 4 or lower, using an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid. This back-extraction method may be batch-type or flow-type. The back-extraction apparatus used in the flow-type back-extraction method is not particularly limited, but an extraction apparatus suitable for the present invention may be used from the viewpoint of workability, cost reduction, etc. The multi-cycle extraction apparatus suitably used in the multi-cycle extraction method of the present invention is not particularly limited, and examples include extraction apparatus usable in each of the batch-type extraction methods described above, or the above-mentioned extraction apparatuses 1 and 2 in the flow-type extraction method, and further extraction apparatuses 1 and 2 with the pH adjusting agent transfer pipe 15 removed. Furthermore, there are no particular limitations on the multi-cycle extraction apparatus that is suitably used in the flow-type multi-cycle extraction method of the present invention that reuses the oil phase. For example, in the extraction apparatuses 1 and 2 described above, the oil phase discharge pipe 16a connected to the separation section 16 is connected to the oil phase storage tank 6, or to the middle of the confluence section with the oil phase storage tank 6 in the oil phase flow pipe 12, via an apparatus that back-extracts metal ions from the oil phase.

[0148] In the flow-type multi-cycle extraction method of the present invention, steps 2B and 2C, in which a pH adjustment step is performed when mixing the two phases in step 1 of each cycle, are preferred in that they can improve the mixing state of the two phases, and step 2C, in which a pH-adjusted aqueous phase and / or a pH-adjusted oil phase is used, is more preferred in that it can further improve the mixing state of the two phases.

[0149] [Other Steps] The extraction method of the present invention may include steps other than steps 1 to 3 in the above-described extraction and separation cycle, for example, in a flow extraction method. For example, steps include back-extracting (isolating) metal ions from the phase-separated oil phase (a step of recycling the oil phase by back-extracting metal ions from the oil phase), recovering the back-extracted metal ions as a compound (salt), purifying the back-extracted metal ions or their compound, purifying the extractant recovered from the oil phase, and further, removing ions of metal elements belonging to Group 1 or Group 2 of the periodic table from the aqueous phase in advance. Known methods can be applied without particular limitation as methods for recovering the back-extracted metal ions as a compound.

[0150] The present invention will be described in more detail below based on examples, but the present invention is not to be construed as being limited thereto. In the following examples, "parts" and "%" representing the composition are by mass unless otherwise specified. In the present invention, "room temperature" means 25°C.

[0151] [Synthesis and Preparation of Compounds] The compounds shown below will be synthesized or prepared. PC-88A ((2-ethylhexyl)phosphonic acid mono-2-ethylhexyl) shown below will be a commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd.). VA-10 shown below will be a commercially available product (Versatic acid 10, manufactured by Hexion Co., Ltd.). Cyanex272 shown below will be a commercially available product (di(2,4,4-trimethylpentyl)phosphinic acid, manufactured by Science Co., Ltd.).

[0152]

[0153] <Synthesis of Compound E-1> Compound E-1 can be synthesized as follows. Specifically, 89 g of diethyl phosphite (manufactured by Tokyo Chemical Industries, Ltd.) and 450 g of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) are added to a 1 L three-necked round-bottom flask and stirred well. While cooling the three-necked round-bottom flask with ice, 23.2 g of sodium hydride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) is added and stirred for 20 minutes while still ice-cooled. After that, the reaction mixture is heated and stirred in a flux state for 30 minutes. Next, while cooling the three-necked round-bottom flask with ice, 70.0 g of 1-bromo-2-ethylhexane (manufactured by Tokyo Chemical Industries, Ltd.) is added dropwise to the obtained reaction mixture over 20 minutes, and then stirred at an internal temperature of 45°C for 24 hours. After adding 300 g of water to the reaction mixture obtained in this way, extraction is performed with toluene, and the solvent is removed by vacuum distillation to obtain 105 g of a yellow liquid.

[0154] Next, add the obtained yellow liquid and 400 g of dichloromethane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a 1 L three-necked round-bottom flask and stir well. Add 113 g of bromotrimethylsilane (manufactured by Tokyo Chemical Industries, Ltd.) to the three-necked round-bottom flask and stir at room temperature for 4 hours. After removing the solvent from the obtained reaction solution under reduced pressure, add 530 g of methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and stir at an internal temperature of 40°C for 3 hours. Add 200 mL of aqueous sodium hydroxide solution (4 mol / L) to the reaction solution obtained in this way, and wash the aqueous phase twice with toluene. Add 65 mL of concentrated hydrochloric acid to the obtained aqueous solution, extract with toluene, and then remove the solvent under reduced pressure to obtain 41.2 g of compound A (yield 59%, 2 steps). Add 20.0 g of compound A to a 500 mL three-necked flask and Fineoxocol 180N (branched C １８ H ３７Add 23.6 g of OH (manufactured by Nissan Chemical Industries) and 120 g of tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), stir, and raise the temperature to a flux state. Then, add a solution of 23.4 g of dicyclohexylcarbodiimide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) dissolved in 120 g of tetrahydrofuran dropwise over 3 hours, and stir for 4 hours. Allow the resulting reaction solution to return to room temperature, remove the white solid by filtration, and remove the solvent from the obtained filtrate under reduced pressure. Dissolve the obtained crude product in toluene, wash with water, and then remove the solvent under reduced pressure to obtain 30.5 g (yield 71%) of compound E-1, a pale yellow liquid.

[0155] The synthesized compound E-1 is, １ Identification can be performed using m / z values ​​obtained from H-NMR (instrument: BRUKER 400) and HPLC-MS.

[0156] <Synthesis of Compound E-2> In the synthesis of Compound E-1, 1-bromo-2-ethylhexane and fineoxocol 180N are used as shown in the above chemical formula R １ and R ２ Compound E-2 can be synthesized in the same manner as compound E-1, except that the corresponding group is changed to a bromide and an alcohol. The synthesized compound E-2 can be identified in the same manner as compound E-1.

[0157] <Synthesis of Compound E-3> Fineoxocol 180N (branched C) in a 500 mL three-necked round-bottom flask. １８ H ３７ Add 20.0 g of OH (manufactured by Nissan Chemical Industries), 39.4 g of carbon tetrabromide (manufactured by Fujifilm Wako Pure Chemical Industries), and 130 g of dichloromethane (manufactured by Fujifilm Wako Pure Chemical Industries), and stir while cooling in an ice bath. To the resulting reaction solution, add a solution consisting of 39.0 g of triphenylphosphine (manufactured by Fujifilm Wako Pure Chemical Industries) and 110 g of dichloromethane dropwise over 10 minutes. Then, raise the temperature of the reaction solution to room temperature and stir for 2 hours. Add a 4 M sodium hydroxide solution to this solution, extract with dichloromethane, and then remove the solvent under reduced pressure to obtain the product (branched C １８ H ３７Br) can be obtained as a pale yellow liquid (yield 92%). Add 1.5 g of magnesium (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 100 g of diethyl ether to a 300 mL three-necked round-bottom flask and stir at room temperature. Add 18.0 g of the above product dropwise to generate Grignard's reagent. Subsequently, while maintaining the temperature of the reaction mixture below 15°C, add 4.2 g of dibutyl phosphite, then raise the temperature of the reaction mixture and stir under flux for 5 hours. While cooling the resulting reaction mixture in an ice bath, add 10% sulfuric acid dropwise, wash the organic layer with 15% aqueous sodium carbonate solution, and remove the solvent under reduced pressure. The obtained crude product is purified by column chromatography and branched C is obtained by substituting the two hydroxyl groups respectively. １８ H ３７ Two-group phosphorous acid can be obtained as a colorless, transparent liquid (85% yield). 78 g of hydrogen peroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 10.0 g of the above-mentioned phosphorous acid are added to a 200 mL three-necked round-bottom flask and stirred at room temperature. The reaction mixture is then heated to 65°C and stirred for 24 hours. After adding 100 g of saturated sodium thiosulfate aqueous solution, the mixture is extracted with toluene, and the solvent is removed by reduced pressure to obtain compound E-3 as a colorless, transparent liquid (95% yield). The synthesized compound E-3 can be identified in the same manner as compound E-1.

[0158] [Preparation of Metal Ion-Containing Aqueous Solutions W1 to W4] <Preparation of Co Ion and Ni Ion-Containing Aqueous Solution W1> Add 57.2 g of cobalt(II) sulfate heptahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 53.7 g of nickel(II) sulfate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a 1 L volumetric flask, make up with ultrapure water, and dissolve by stirring at 40°C. Then cool to room temperature (25°C) to prepare Co ion and Ni ion-containing aqueous solutions as metal ion-containing aqueous solution W1. The density of this aqueous solution W1 according to the above measurement method is 1.06 × 10⁻⁶ ３ kg / m ３The result was as follows: <Preparation of Mn ion and Ni ion-containing aqueous solution W2> Except for adding 52.6 g of manganese(II) sulfate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) instead of 57.2 g of cobalt(II) sulfate heptahydrate in the preparation of Co ion and Ni ion-containing aqueous solution W1, the Mn ion and Ni ion-containing aqueous solution W2 is prepared in the same manner as the preparation of Co ion and Ni ion-containing aqueous solution W1. The density of this aqueous solution W2 measured by the above method is 1.06 × 10⁻⁶ ３ kg / m ３ The result was as follows: <Preparation of Mn ion and Mg ion-containing aqueous solution W3> In the preparation of Co ion and Ni ion-containing aqueous solution W1, 52.6 g of manganese(II) sulfate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added instead of 57.2 g of cobalt(II) sulfate heptahydrate, and 121.5 g of magnesium(II) sulfate heptahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added instead of 53.7 g of nickel(II) sulfate hexahydrate, otherwise the metal ion-containing aqueous solution W3 was prepared in the same manner as the preparation of Co ion and Ni ion-containing aqueous solution W1. The density of this aqueous solution W3 according to the above measurement method was 1.08 × 10⁻⁶. ３ kg / m ３ The result was as follows: <Preparation of Cu ion and Ni ion-containing aqueous solution W4> In the preparation of Co ion and Ni ion-containing aqueous solution W1, the Cu ion and Ni ion-containing aqueous solution was prepared in the same manner as the preparation of Co ion and Ni ion-containing aqueous solution W1, except that 47.1 g of copper(II) sulfate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added instead of 57.2 g of cobalt(II) sulfate heptahydrate. The density of this aqueous solution W4 measured by the above method was 1.05 × 10⁻⁶. ３ kg / m ３ That was the case.

[0159] The content (concentration CI) of each metal ion in each ion-containing aqueous solution W1 to W4 prepared as described above is 1.2 × 10⁻⁶. ４ It is ppm.

[0160] <Preparation of Extractant Solution (Oil Phase)> Add the synthesized or prepared extractant and the required amount of pH adjusting agent-containing aqueous solution (4M sodium hydroxide aqueous solution or 4M hydrochloric acid) to the pH at the time of mixing as shown in the "pH" column of Table 1 to a 1 L volumetric flask. Dissolve each extractant solution at room temperature by stirring after making up the volume using the organic solvent shown in the "Oil Phase Solvent" column of Table 1. The extractant concentration in each extractant solution is 500 mM. The density of each extractant solution measured by the above method is 8.4 × 10⁻⁶. ２ kg / m ３ The results were as follows. The liquid paraffin, rapeseed oil, salad oil, kerosene, and pentadecan used in the examples were commercially available products. Furthermore, the EXXOL D80 (trade name) used in Comparative Example 4 is a commercially available product manufactured by Exxon Chemicals.

[0161] A mixer settler (5L) is prepared as an extraction apparatus for implementing the batch extraction method. An extraction apparatus 1 (flow reactor) shown in Figure 1 is prepared as an extraction apparatus for implementing the flow extraction method. In extraction apparatus 1, each component is as shown below. That is, the inner diameter (equivalent diameter) of the aqueous phase flow pipe 11 and the oil phase flow pipe 12 is 1 mm. The length of the tip section 11a and the tip section 12a and the inner diameter (equivalent diameter) of the opening end are 1 mm and 0.5 mm, respectively. Therefore, the ratio of the inner diameter of the opening end of the tip section to the inner diameter of each flow pipe (reduction ratio of flow diameter) is 0.5. The confluence section 13 is a cylindrical pipe body with the same diameter as the inner diameter of the opening ends of the tip sections 11a and 12a, and its length (distance between the aqueous phase flow pipe 11 and the oil phase flow pipe 12) is 2 mm. The mixing section 14 has a pre-mixing section 14a and a post-mixing section 14b, both consisting of a wide-ended section and a pipe section with a constant inner diameter. The connection diameter (equivalent diameter) of the wide-ended section to the confluence section 13 is 0.5 mm, the length of the pipe section is 100 mm, and the inner diameter (equivalent diameter) of the pipe section is 1 mm. The length of the post-mixing section 14b is 100 mm, and the inner diameter (equivalent diameter) of the pipe section is 1 mm. The total length of the pre-mixing section 14a and the post-mixing section 14b is determined by confirming and identifying the time (length) required for extraction equilibrium for the three-liquid combined solution. The separation section 16 uses a vial tube with an inner diameter of 36 mm. Note that the pH adjusting agent-containing aqueous solution storage tank 7 and the pH adjusting agent transfer pipe 15 are not provided.

[0162] [Example 1] Example 1 involves extracting metal ions using the batch extraction method described above with the mixer settler. Specifically, a metal ion-containing aqueous solution W1 (25°C) and an oil phase (25°C) containing the extractant PC-88A and the organic solvent shown in the "Type" column of the "Oil Phase Solvent" column in Table 1 are each added to the mixer settler in a quantity of 50% by volume and stirred. The internal temperature of the mixer settler (also called the mixing temperature or extraction temperature) is adjusted to 40°C and stirred for 60 minutes, after which the three-liquid mixture is allowed to stand at the same temperature. After confirming that the oil phase and aqueous phase have separated into two phases, the aqueous phase is extracted by liquid-liquid separation and selective extraction of Co ions is performed. After cooling the extracted aqueous phase to 25°C, the pH and the content (residual amount) of Co ions and Ni ions are measured. The Co ion and Ni ion content is measured using an inductively coupled plasma atomic emission spectrometer (ICP-OES) (Optima 7300D (trade name), manufactured by PerkinElmer). The pH is measured using a pH meter (SK-620pHII, manufactured by Satotec). In Example 1, it can be confirmed that the three-liquid mixture after stirring has already reached extraction equilibrium by sampling the three-liquid mixture at different time points and collecting the samples in vials, and observing that their pH levels become constant.

[0163] [Examples 2-5] In Example 1, the organic solvent used in the oil phase was replaced with the organic solvent shown in the "Type" column of the "Oil Phase Solvent" column in Table 1, except that the mixing temperature (standing temperature and phase separation temperature) was changed from 40°C to 60°C as needed. In addition, selective extraction of Co ions was performed in the same manner as in Example 1, and the pH of the aqueous phase after cooling to 25°C and the content of Co ions and Ni ions were measured in the same manner as in Example 1. In each example, it was confirmed that the three-liquid mixture after stirring had already reached extraction equilibrium by sampling the three-liquid mixture at different points in time, collecting it in vials, and observing that their pH became constant.

[0164] [Example 6] Example 1 extracts metal ions using a flow extraction method with the extraction apparatus 1 described above. Specifically, an aqueous metal ion-containing aqueous solution W1 (25°C) stored in the aqueous phase storage tank 5 is sent from the aqueous phase flow pipe 11 to the oil phase storage tank 6 from the oil phase flow pipe 12, and an oil phase (25°C) containing the extractant PC-88A and the organic solvent shown in the "Type" column of the "Oil Phase Solvent" column in Table 1 is sent from the oil phase flow pipe 12 to the confluence section 13 at a flow rate (flow rate) of 6.0 mL / min (internal pressure 0.1 MPa). The aqueous metal ion-containing aqueous solution W1 and the oil phase are combined at the confluence section 13, and the combined liquid is continued to flow through the mixing section 14 at 25°C (steps 1 and 2C). The mixing temperature in steps 1 and 2C is set to the value shown in the "Mixing Temperature" column of Table 1 (in Example 6, the temperature at the start of flow is maintained). The confluence and mixing conditions in steps 1 and 2C are shown in the "Confluence and Mixing Conditions" column of Table 1 (the same applies to Examples 7 to 16). The flow rate of the confluence liquid flowing through the confluence section 14 is 12.0 mL / min. The three-liquid confluence liquid flowing out from the downstream mixing section 14b has already reached extraction equilibrium, which can be confirmed by collecting the three-liquid confluence liquid into vials every minute and observing that their pH becomes constant. The three-liquid confluence liquid is then transferred and collected into a vial serving as the separation section 16. After that, the three-liquid confluence liquid is allowed to stand at the same temperature to confirm that the organic phase (oil phase) and aqueous phase have separated into two phases. The aqueous phase is then separated (step 3) to perform selective extraction of Co ions. The pH of the aqueous phase (25°C) thus extracted and the content of Co ions and Ni ions are measured in the same manner as in Example 1.

[0165] [Examples 7-9] In Examples 7-9, selective extraction of Co ions was performed in the same manner as in Example 6, except that the mixing temperature was changed from 25°C to the temperature shown in the "Mixing Temperature" column of Table 1. The pH of the aqueous phase after cooling to 25°C and the content of Co and Ni ions were measured in the same manner as in Example 1. The three-liquid combined solution was heated to a predetermined temperature using heaters installed on the outer circumference of the confluence section 13 and the mixing section 14. In each example, it was confirmed that the three-liquid combined solution flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid combined solution in vials for one minute at a time and observing that their pH became constant.

[0166] [Examples 10-14] In Example 9, the oil phase containing the extractant shown in the "Extractant (Oil Phase)" column of Table 1 was replaced with an oil phase containing the extractant shown in the "Extractant (Oil Phase)" column of Table 1, to which the necessary amount of pH adjusting agent-containing aqueous solution to achieve the pH at the time of mixing shown in the "pH" column of Table 1 was added. Except for this, the selective extraction of Co ions in Examples 10-14 was carried out in the same manner as in Example 9, and the pH of the aqueous phase after cooling to 25°C and the content of Co ions and Ni ions were measured in the same manner as in Example 1. In each example, it was confirmed that the three-liquid combined liquid flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid combined liquid in vials for one minute at a time and observing that their pH became constant.

[0167] [Examples 15 and 16] In Example 8, the oil phase containing an organic solvent shown in the "Type" column of the "Oil Phase Solvent" column in Table 1 was used instead of the oil phase containing liquid paraffin. In Example 15 and 16, selective extraction of Co ions was performed in the same manner as in Example 8, and the pH of the aqueous phase after cooling to 25°C and the content of Co ions and Ni ions were measured in the same manner as in Example 1. In each example, it was confirmed that the three-liquid mixture flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid mixture into vials for one minute at a time and observing that their pH became constant.

[0168] [Comparative Examples 1-4] In Comparative Examples 1-4, selective extraction of Co ions was performed in the same manner as in Example 1, except that the organic solvent used in the oil phase was replaced with the organic solvent shown in the "Type" column of the "Oil Phase Solvent" column in Table 1, and the mixing temperature (standing temperature and phase separation temperature) was changed from 40°C to the temperature shown in the "Mixing Temperature" column in Table 1 as necessary. The pH of the aqueous phase and the content of Co ions and Ni ions after cooling to 25°C as necessary were measured in the same manner as in Example 1. In each comparative example, it was confirmed that the three-liquid mixture flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid mixture into vials for 1 minute at a time and observing that their pH became constant.

[0169] <Calculation of Kinetic Energy> In each embodiment of the flow extraction method, the kinetic energy E of both the aqueous phase and the oil phase is calculated. ＳＴ The results calculated as described above are shown in Table 1.

[0170] <Evaluation 1: Measurement of the Flash Point of the Oil Phase> The flash point of each oil phase used in each example and comparative example is measured using the measurement method described above. The improvement in safety is evaluated based on the measured flash point according to evaluation criterion 1 below. The results are shown in Table 1. This test indicates that the higher the flash point of the oil phase, the higher the safety that can be ensured in carrying out the extraction method. In this test, D or higher is considered a pass. - Evaluation Criterion 1 - A: Flash point of the oil phase is 250°C or higher B: Flash point of the oil phase is 220°C or higher and less than 250°C C: Flash point of the oil phase is 200°C or higher and less than 220°C D: Flash point of the oil phase is 150°C or higher and less than 200°C E: Flash point of the oil phase is less than 150°C

[0171] <Evaluation 2: Evaluation of Extraction Amount and Selectivity> In each example and comparative example, for the same metal ion, the extraction rate (unit: %) of the metal ion is calculated based on the following formula, using the metal ion concentration CI in the prepared metal ion-containing aqueous solution W1 and the metal ion concentration C1 in the aqueous phase after the extraction operation. Extraction rate (%) = [(CI - C1) / CI] × 100 In this test, for metal ions with a high extraction amount (metal ions to be extracted), the extraction amount is evaluated based on evaluation criterion 1 below. The results are shown in Table 1. For metal ions to be extracted, a higher extraction rate indicates that a larger amount can be extracted into the oil phase. In this test, a score of D or higher is considered a pass. On the other hand, for metal ions with a low extraction amount (metal ions other than those to be extracted), the extraction amount is evaluated based on evaluation criterion 2 below. The results are shown in Table 1. For metal ions other than those to be extracted, a lower extraction rate indicates that the amount extracted into the oil phase can be reduced. In this test, a score of D or higher is considered a pass. For each example and comparative example, if the extraction rate is D or higher for the target metal ion and D or higher for other metal ions, it indicates that the extraction of other metal ions can be suppressed, and the target metal ion can be selectively (with good selectivity) extracted into the oil phase. - Evaluation Criteria 1 - A: Extraction rate of 95% or higher B: Extraction rate of 90% or higher and less than 95% C: Extraction rate of 85% or higher and less than 90% D: Extraction rate of 80% or higher and less than 85% E: Extraction rate of less than 80% - Evaluation Criteria 2 - A: Extraction rate of less than 5% B: Extraction rate of 5% or higher and less than 10% C: Extraction rate of 10% or higher and less than 20% D: Extraction rate of 20% or higher and less than 30% E: Extraction rate of 30% or higher

[0172] <Evaluation 3: Evaluation of Phase Separation> In each example and comparative example, the time required for the three-liquid mixture (aqueous and oil phases mixed at a predetermined pH) to separate into two phases, aqueous and oil, after mixing was completed (after stirring stopped in the batch extraction method, and after reaching the separation unit 16 in the flow extraction method) was measured (phase separation time). The measured phase separation time was evaluated based on the following evaluation criteria. The results are shown in Table 1. In this test, a shorter phase separation time indicates better phase separation. In this test, a D or higher is considered a pass. - Evaluation Criteria - A: Phase separation time less than 3 minutes B: Phase separation time 3 minutes or more, less than 5 minutes C: Phase separation time 5 minutes or more, less than 10 minutes D: Phase separation time 10 minutes or more, less than 15 minutes E: Phase separation time 15 minutes or more

[0173]

[0174] [Examples 18, 21 and 24] The extractions for Examples 18, 21 and 24 were carried out in the same manner as in Example 4, except that the metal ion-containing aqueous solution shown in the "Aqueous Phase" column of Table 2 was used instead of the metal ion-containing aqueous solution W1 used in Example 4, and the oil phase to which the necessary amount of pH adjusting agent-containing aqueous solution to achieve the pH at the time of mixing shown in the "pH" column of Table 2 was added was used instead of the oil phase used in Example 4. The pH of the aqueous phase (25°C) and the metal ion content were measured in the same manner as in Example 1. The confluence conditions and mixing conditions in steps 1 and 2C of each example are shown in the "Confluence Conditions and Mixing Conditions" column of Table 2 (the same applies to Examples 19, 20, 22, 23, 25 and 26). In each example, it was confirmed that the three-liquid confluence after stirring had already reached extraction equilibrium by sampling the three-liquid confluence at various points in time, collecting the samples in vials, and observing that their pH became constant.

[0175] [Examples 19, 22, and 25] The extractions for Examples 19, 22, and 25 were carried out in the same manner as in Example 6, except that the metal ion-containing aqueous solution shown in the "Aqueous Phase" column of Table 1 was used instead of the metal ion-containing aqueous solution W1 used in Example 6, and the oil phase to which the necessary amount of pH adjusting agent-containing aqueous solution to achieve the pH at the time of mixing shown in the "pH" column of Table 2 was added was used instead of the oil phase used in Example 6. The pH of the aqueous phase (25°C) and the metal ion content were measured in the same manner as in Example 1. In each example, it was confirmed that the three-liquid combined liquid flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid combined liquid in vials for one minute at a time and observing that their pH became constant.

[0176] [Examples 20, 23, and 26] The extractions for Examples 20, 23, and 26 were carried out in the same manner as in Example 7, except that the metal ion-containing aqueous solution shown in the "Aqueous Phase" column of Table 1 was used instead of the metal ion-containing aqueous solution W1 used in Example 7, and the oil phase to which the necessary amount of pH adjusting agent-containing aqueous solution to achieve the pH at the time of mixing shown in the "pH" column of Table 2 was added was used instead of the oil phase used in Example 7. The pH of the aqueous phase (25°C) and the metal ion content were measured in the same manner as in Example 1. In each example, it was confirmed that the three-liquid combined liquid flowing out from the downstream mixing section 14b had already reached extraction equilibrium by collecting the three-liquid combined liquid in vials for one minute at a time and observing that their pH became constant.

[0177] <Calculation of Kinetic Energy> In Examples 18 to 26, the kinetic energy E of both the aqueous phase and the oil phase was calculated. ＳＴ The results calculated as described above are shown in Table 2.

[0178] <Evaluation 1: Measurement of the flash point of the oil phase> For Examples 18 to 26, the flash point of each oil phase was measured using the measurement method described above, in the same manner as in Example 1, and the effect on improving safety was evaluated. The results are shown in Table 2.

[0179] <Evaluation 2: Evaluation of Extraction Amount and Selectivity> For Examples 18 to 26, the extraction rate (unit: %) of each metal ion was calculated in the same manner as in Example 1, and the extraction amount was evaluated. The results are shown in Table 2.

[0180] <Evaluation 3: Evaluation of Phase Separation> For Examples 18 to 26, the phase separation time of the three-liquid combined solution was measured in the same manner as in Example 1 to evaluate the phase separation. The results are shown in Table 2.

[0181]

[0182] The results in Tables 1 and 2 show the following: While conventional wet extraction methods using organic solvents exhibit some degree of extraction performance and phase separation, their low flash points necessitate careful consideration of safety aspects in use and implementation (Comparative Examples 1, 3, and 4). Furthermore, even when using an oil phase containing liquid paraffin as the organic solvent, a batch extraction method with a mixing temperature set to 25°C, while contributing to improved safety, is inferior in both extraction performance (extraction amount, selectivity) and phase separation (Comparative Example 4).

[0183] In contrast, in a batch extraction method using a mixer-settler, using an oil phase containing liquid paraffin mainly composed of aliphatic hydrocarbons having 21 to 35 carbon atoms, and setting the mixing temperature to 40°C or 60°C (Condition B), improves safety and satisfies extraction performance and phase separation (Examples 1 to 5).

[0184] On the other hand, in the flow extraction method using extraction device 1 (flow reactor) (Condition A), if an oil phase containing liquid paraffin or edible oil mainly composed of aliphatic hydrocarbons with 35 carbon atoms is used, it is possible to achieve further improvements in safety regardless of the mixing temperature, and the extraction performance and phase separation are also improved compared to the batch extraction method (Examples 1 to 5), and it is possible to extract the target metal ion (Co ion) from two or more metal ions into a phase-separated oil phase in a short time with high extraction yield and high selectivity (Examples 6 to 9, 15 and 16). In the flow extraction method (Condition A), if the two phases are mixed at a temperature higher than the temperature of the aqueous and oil phases at the start of flow, for example, 40 to 90°C (Condition B), it is possible to further increase the extraction yield and selectivity of the target metal ion (Co ion) (Examples 6 and 7 to 9). Furthermore, in the flow extraction method (Condition A), using a phosphate-based compound among acidic extractants as the extractant can further enhance the extraction amount and selectivity of the target metal ions (Co ions) (Examples 9-14). It can be understood that the results depending on the type of extractant are similar in the batch extraction method.

[0185] Furthermore, as shown in Table 2, in the batch extraction method, using an oil phase containing liquid paraffin mainly composed of aliphatic hydrocarbons with 35 carbon atoms and setting the mixing temperature to 40°C (Condition B) contributes to improved safety, satisfies extraction performance and phase separation, and enables the extraction of the target metal ion (Mn ion or Cu ion) from two or more metal ions into a phase-separated oil phase with high extraction yield and high selectivity in a short time (Examples 18, 21, and 24). On the other hand, in the flow extraction method (Condition A), using an oil phase containing liquid paraffin mainly composed of aliphatic hydrocarbons with 35 carbon atoms achieves further improvement in safety regardless of the mixing temperature, and also improves extraction performance and phase separation compared to the batch extraction method (Examples 18, 21, or 24), enabling the extraction of the target metal ion from two or more metal ions into a phase-separated oil phase with even higher extraction yield and even higher selectivity in a short time (Examples 19, 20, 22, 23, 25, and 26). In the flow extraction method (Condition A), mixing the two phases at a temperature higher than the temperatures of the aqueous and oil phases at the start of flow (Condition B) shows that it is possible to achieve an even higher level of balance between the extraction performance of the target metal ions and the phase separation properties of the two phases.

[0186] From the above results, it can be seen that the extraction method of the present invention achieves improved safety while also being excellent in metal ion extraction performance and phase separation, even without implementing advanced safety measures such as permanently installing advanced safety equipment. Furthermore, it can be seen that the oil phase of the present invention can realize an extraction method that is excellent in metal ion extraction performance and phase separation while also achieving the aforementioned improvement in safety. Therefore, the extraction method of the present invention, regardless of whether it is a batch extraction method or a flow extraction method, can simultaneously solve the conflicting problems of improved extraction performance and phase separation and improved safety (cost reduction), and its technical significance is great in that it can achieve improved safety without implementing advanced safety measures.

[0187] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0188] This application claims priority based on Japanese Patent Application No. 2024-228731, filed in Japan on 25 December 2024, the contents of which are incorporated herein by reference as part of this specification.

[0189] 1, 2 Extraction device 5 Water phase storage tank 6 Oil phase storage tank 7 pH adjuster-containing aqueous solution storage tank 11 Water phase flow pipe 11a Tapered part (tapered part) 11b Large diameter part 11c Small diameter part 12 Oil phase flow pipe 12a Tapered part (tapered part) 13, 23 Merging part 14, 24 Mixing part 14a Pre-mixing part 14b Post-mixing section 15 pH adjuster transfer pipe 16 Separation section 16a Oil phase discharge pipe 16b Water phase discharge pipe

Claims

1. A method for extracting metal ions, comprising mixing an aqueous phase containing metal ions with an oil phase containing an extractant, and then separating the phases to extract the metal ions into the oil phase, wherein the oil phase contains at least one solvent selected from a hydrocarbon solvent containing aliphatic hydrocarbons represented by the following formula and edible oil, and satisfies at least one of the following conditions A and B. Formula: C ｎ H （２ｎ＋２） However, n is an integer between 19 and 40. Condition A: The aqueous phase and the oil phase are combined during flow and mixed. Condition B: The mixing temperature of the aqueous phase and the oil phase is between 40 and 95°C.

2. The method for extracting metal ions according to claim 1, wherein the hydrocarbon solvent is liquid paraffin.

3. The method for extracting metal ions according to claim 1, wherein the flash point of the oil phase is 250°C or higher.

4. A method for extracting metal ions according to claim 1, satisfying conditions A and B.

5. The method for extracting metal ions according to claim 1, wherein the aqueous phase contains two or more metal ions, and at least one of these metal ions is separated and extracted from the other metal ions.

6. The method for extracting metal ions according to claim 1, wherein the extractant is an acidic extractant.

7. The method for extracting metal ions according to claim 6, wherein the acidic extractant contains a phosphate compound.

8. The method for extracting metal ions according to claim 6, wherein the acidic extractant is represented by the following formula (I). (Formula I), R １ and R ２ represents a substituent, at least one of which is a hydrocarbon group having 9 or more carbon atoms. X represents -OH or -SH. Y represents an oxygen atom or a sulfur atom. Z １ and Z ２ represents a single bond, -O-, -NH-, or -S-.

9. An oil phase used in a method for extracting metal ions, which involves mixing an aqueous phase containing metal ions with an oil phase and then separating the phases to extract the metal ions into the oil phase, the oil phase comprising an extractant, a hydrocarbon solvent containing an aliphatic hydrocarbon represented by the following formula, and at least one solvent selected from edible oils. Formula: C ｎ H （２ｎ＋２） However, n is an integer between 19 and 40.

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