Method for separating yttrium from ammonium carboxylate-fatty acid radical ionic liquid

Abstract

The invention discloses a method for separating yttrium from ammonium carboxylate-fatty acid radical ionic liquid, and due to challenges brought by similar ion radiuses of HREEs, a series of functionalized ionic liquids with potential extraction and separation characteristics are synthesized, and the feasibility of the functionalized ionic liquids for separating Y from HREEs is evaluated. Experimental results show that [N16MOP] [HDA] is an optimal extraction system for separating Y from other HREEs, and the separation coefficient of Ho / Y reaches 2.8. Based on an ion pair extraction mechanism, one molecule of HoCl3 is extracted from two molecules of [N16MOP] [HDA]. 0.1 mol / L hydrochloric acid can load complete reverse extraction of REs. And after 6 times of recycling, the extraction separation capability of the organic phase is still kept stable, and good recoverability is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrometallurgy, and in particular relates to a method for separating yttrium from ammonium carboxylate-fatty acid radical ion liquid. Background Art

[0002] Rare earth elements (such as scandium (Sc) in the fourth period of Group IIIB in the periodic table, yttrium (Y) in the fifth period, and all lanthanide elements in the sixth period) are key strategic resources. As one of the important materials, the unique physical and chemical properties of rare earths are of great significance for promoting and developing high-tech fields. Due to the increasing demand for rare earth resources and the instability of the supply of rare earth elements, the mining of rare earth resources will continue to increase. Among many innovative functional materials, the heavy rare earth element yttrium (Y) is widely used in fluorescence, magnetism, optics, catalysis and other fields. Fluorescent lamps are a type of lighting that consumes less energy and is more durable. The phosphor of the fluorescent powder contains a large amount of high-purity yttrium oxide, so a large amount of high-purity yttrium oxide is needed to make this phosphor.

[0003] Yttrium (Y) is stored in large quantities in ion-adsorption rare earth ores (IATREOs), which are widely distributed in seven provinces in southern China. They contain more heavy rare earths than other rare earth deposits and are therefore one of the main sources of heavy rare earths. However, extracting and separating yttrium (Y) from other rare earth elements is a challenging task because rare earth elements have similar chemical properties and are very close in the periodic table. In the ion-adsorption rare earth ore separation process, the in-situ leaching solution is cleaned and then separated from each other. The content of yttrium (Y) in the ion-adsorption rare earth ore can determine the flow of the separation process. When the mixed rare earth feed solution contains more than 65% yttrium (Y), yttrium (Y) can be separated first. However, when the yttrium (Y) content in the feed is less than 60%, the extraction order between lanthanides and yttrium (Y) is unstable. This is because the extraction order varies with environmental conditions such as temperature and feed composition, which may cause the extraction order of lanthanides to be earlier than yttrium (Y). Therefore, for rare earth feed solutions with medium yttrium (Y) content, it is necessary to first use P507 to separate the rare earths in the feed solution into two components: light and medium rare earths (La-Dy) and heavy rare earths (Ho-Lu, Y), and then separate yttrium (Y) from the mixed heavy rare earth feed solution. For rare earth feed solutions with low yttrium (Y) content, it is necessary to add a process for separating light rare earths and medium rare earths. In this extraction and separation process, saponified cyclopentane acid (NA, a compound widely present in petroleum with a simple source) is usually used as an extractant. In mixed rare earth feed solutions, NA can preferentially extract rare earth elements other than yttrium (Y), so it is often used for the separation of yttrium (Y). However, there are some problems in the process of separating yttrium (Y) by saponifying cyclopentane acid, such as complex extractant composition, unstable system, and easy emulsification when the pH value is too high (>5). In order to overcome these problems, the Shanghai Institute of Organic Chemistry has developed a carboxylic acid extractant, namely secondary carbonylphenoxyacetic acid (CA-12), for the separation of yttrium (Y). Compared with cyclopentane acid, CA-12 has higher extraction selectivity. The research results show that in the CA-12-TBP extraction system, the purity and yield of yttrium (Y) can be increased to 99.5% and 95%, respectively, through 15 stages of extraction and 10 stages of washing.

[0004] Ionic liquid (IL) is a molten salt with a melting point below 100°C at room temperature. It is composed of cations and anions and has good chemical stability and thermal stability. Due to the strong adjustability of the chemical structure of ionic liquids, ionic liquids with a series of excellent properties can be prepared by design and are widely used in catalysis, electrochemistry, biochemistry, nanotechnology, separation technology and other fields. By designing ionic liquids with specific hydrophilicity, selectivity and renewability, selective separation of the target can be achieved. This separation method can not only reduce the generation of waste and reduce environmental pollution through recycling, but also improve the extraction efficiency, reduce the reaction activation energy, and reduce energy consumption, thereby reducing the cost of the entire extraction process and improving sustainability. Studies have found that the acidic aqueous biphasic system (AcABS) based on tributyltetradecylphosphonium chloride ([P44414][Cl]) ionic liquid has better advantages than other extraction solvents. This system uses the leachate itself as a salting-out agent to achieve "one-pot" leaching and separation of key metals without the need for stripping. In addition, functionalized ionic liquids (FILs) can be obtained by functionalizing ionic liquids (ILs), which can expand the application fields of ionic liquids and give ionic liquids specific functions. FILs can optimize their separation performance by selecting different functional groups to achieve more precise and efficient separation. In addition, the introduction of groups can make ILs have lower toxicity and better biodegradability to reduce the impact on the environment and health.

[0005] The use of carboxylic acid extractants faces the problem of generally reduced extraction performance due to the presence of dimers. Although the traditional saponification method is feasible, it is difficult to solve the problem of emulsification and the generation of a large amount of saponification wastewater. Therefore, it is urgent to develop new ILs extractants to solve the above problems. Summary of the invention

[0006] In order to improve the above technical problems, the present invention provides a carboxylate ammonium-fatty acid anion ionic liquid having a structure shown in the following formula I:

[0007]

[0008] in:

[0009] R 1 , R 2 , R 3 , R 5 The same or different, independently selected from C 1-16 Alkyl, for example methyl, ethyl, propyl, tert-butyl, hexyl, octyl, hexadecyl;

[0010] n is an integer from 0 to 5, for example, n is selected from 0, 1, 2, 3, 4 or 5;

[0011] R4 Selected from C 1-5 Alkylene or aryl, for example methylene, ethylene, propylene, butylene, pentylene, phenyl.

[0012] According to an embodiment of the present invention, Formula I is selected from the following structures:

[0013]

[0014]

[0015] The present invention also provides a method for preparing the ionic liquid of the structure shown in Formula I, comprising reacting a compound of the structure shown in Formula II with 2-hexyldecanoic acid (HDA) completely saponified by NaOH to prepare the ionic liquid of the structure shown in Formula I;

[0016]

[0017] in:

[0018] R 1 , R 2 , R 3 , R 4 , R 5 , n independently have the definitions as described above.

[0019] According to an embodiment of the present invention, the molar ratio of the compound of the structure represented by Formula II to 2-hexyldecanoic acid (HDA) completely saponified by NaOH is 1:(1-5), exemplified by 1:1, 1:3, and 1:5.

[0020] According to an embodiment of the present invention, the preparation method can be carried out in the presence of a solvent such as an organic solvent. For example, the organic solvent can be selected from methanol.

[0021] According to an embodiment of the present invention, the preparation method further comprises the step of separating a solid product from the reaction mixture after the reaction is completed. For example, the reaction solution is dissolved in dichloromethane, washed with water, and the dichloromethane is removed by rotary evaporation and the product is dried to obtain a compound with the structure shown in Formula I.

[0022] The present invention also provides the ionic liquid represented by formula I as described above for separation of yttrium (Y). Preferably, it is used for separation of yttrium from ion-adsorption rare earth ores. More preferably, it is used for separation of yttrium from ion-adsorption rare earth ores with yttrium (Y) content higher than 60%.

[0023] The present invention also provides a method for separating yttrium using the ionic liquid shown in Formula I above, comprising using the ionic liquid with the structure shown in Formula I as an extractant, and separating yttrium from the ion-adsorption type rare earth ore through extraction and stripping.

[0024] The present invention also provides yttrium (Y) separated and prepared by the above method.

[0025] The present invention also provides yttrium (Y) separated and prepared by the above method, which can be applied to the fields of fluorescence, magnetism, optics and catalysis.

[0026] According to an embodiment of the present invention, the yttrium (Y) is used to prepare a fluorescent lamp.

[0027] Beneficial effects of the present invention:

[0028] The present invention successfully synthesized a series of ionic liquids and studied their feasibility of efficiently separating Y from heavy rare earths. The inventors of the present invention unexpectedly found that based on the appropriate pKa value, the extraction capacity of rare earth elements is the highest in ionic liquids based on HDA anions. The introduction of functionalized structures into ionic liquid cations can change the physicochemical properties of ionic liquids, and based on the changes in inductive effect and steric hindrance, the functionalization of cations provides the possibility of enhancing the affinity and selective extraction between ionic liquids and rare earth elements. At the same time, the addition of modifiers can eliminate the emulsification phenomenon of hexadecyl ammonium ionic liquid systems and improve the extraction efficiency. And the selectivity and phase separation of the extraction process can be improved by controlling the salt concentration of the aqueous phase.

[0029] [N 16 MOP][HDA] as an extractant is the best extraction system for separating Y from other heavy rare earths. 16 In the MOP][HDA] extraction system, kinetic and thermodynamic studies have shown that the extraction of heavy rare earth elements in this system is less dependent on temperature and the extraction rate is very fast. 16 MOP][HDA] is the best extraction system for separating Y from other heavy rare earths (HREEs), with a Ho / Y separation factor of 2.8. The extraction mechanism is based on an ion pair mechanism, in which two molecules [N 16 MOP][HDA] extracts one molecule of HoCl 3 . [N 16 MOP][HDA] can achieve a Ho extraction loading capacity of 0.73 g / L at a concentration level of 0.02 mol / L. The easy stripping and good recyclability confirm its potential for sustainable separation of Y from heavy rare earths. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Based on [N 888 C 1 EO] + Structural diagram of carboxylate ionic liquids.

[0031] Figure 2 Based on [HDA] - Structure diagram of functionalized ionic liquids.

[0032] Figure 3 The extraction and separation performance of ionic liquids for different organic carboxylic acid anions.

[0033] Figure 4 This is the extraction and separation performance of different quaternary ammonium cation ionic liquids.

[0034] Figure 5 The effect of phase modifiers on interfacial phenomena.

[0035] Figure 6 The effect of phase modifier on extraction behavior.

[0036] Figure 7 The effect of initial acidity of the aqueous phase.

[0037] Figure 8 The effect of NaCl concentration on the extraction and separation behavior.

[0038] Fig. 9 For [N 16 Kinetics and thermodynamics of the MOP][HDA] extraction system.

[0039] Fig.10 For [N 16 Extraction loading capacity of MOP][HDA].

[0040] Fig.11 This is the result of the stripping and recycling experiment of the extractant. DETAILED DESCRIPTION

[0041] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0042] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0043] Example 1

[0044] 1. Experiment

[0045] 1.1 Reagents and instruments

[0046] The simulated solution of rare earth chloride was prepared by dissolving rare earth oxides with hydrochloric acid and diluting with deionized water. Rare earth oxides with a purity higher than 99.9% were purchased from Fujian Changting GoldenDragon Rare-earth Co., Ltd. Tributyl phosphate (TBP) and kerosene (also known as No. 260 solvent oil) with a purity of 90% were provided by Luoyang AODA Chemical Co., Ltd. Common organic solvents such as ethanol, methanol, acetonitrile, and dichloromethane were all from Sinopharm Chemical Group Co., Ltd. with analytical purity. The purity and sources of other chemical reagents involved in this article are shown in Table S1.

[0047] Table S1Table 1 Main reagents involved

[0048]

[0049]

[0050] The pH of the rare earth solution was adjusted by dilute solutions of hydrochloric acid and sodium hydroxide, and the pH in all aqueous solutions was measured using a pHs-3C digital pH meter (Shanghai Rex Instrument Factory). The content of metal elements in the aqueous phase was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) Horiba Ultima 2, with a quantification limit of ppb. AV III-500BRUKER and Nicolet iS50 spectrometers were used to analyze the NMR and IR spectra of the samples, respectively. TGA-DSC analyzer (Mettler Toledo, TGA / DSC 1) was used to determine the thermal stability of ionic liquids (ILs) from 30°C to 600°C. Viscosity and density were analyzed using a rotational viscometer (NDJ-8S) and a Biolin automatic surface tension meter Sigma 701, respectively.

[0051] 1.2 Synthesis of ionic liquids

[0052] Dissolve trioctylamine with ethyl bromoacetate, methyl bromoacetate, ethyl 3-bromopropionate, methyl 6-bromohexanoate, 1-chloropinacolone, and methyl 3-(bromomethyl)benzoate in methanol (methanol is used in an amount sufficient to dissolve the raw materials) at a molar ratio of 1:1.2, and stir at 60°C for 6 hours. After rotary evaporation to remove methanol, the product is dissolved in dichloromethane (dichloromethane is used in an amount sufficient to dissolve the product) and washed several times with distilled water, and the following products are obtained after removing the solvent:

[0053] (2-ethoxy-2-oxyylideneethyl)trioctylammonium bromide ([N 888 C 1EO][Br]), yellow viscous liquid;

[0054] (2-Methoxy-2-oxyylideneethyl)trioctylammonium bromide ([N 888 C 1 MO][Br]), yellow viscous liquid;

[0055] (3-ethoxy-3-oxypropylidenepropyl)trioctylammonium bromide ([N 888 C 2 EO][Br]), yellow waxy solid;

[0056] (6-methoxy-6-oxyhexylidene) trioctylammonium bromide ([N 888 C 5 MO][Br]), yellow waxy solid;

[0057] (3,3-Dimethyl-2-oxybutylidene)trioctylammonium chloride ([N 888 C 1 DO][Cl]), yellow liquid;

[0058] [(3-(Methoxycarbonyl)phenyl)methyl]trioctylammonium bromide ([N 888 MOP][Br]), white waxy solid.

[0059] For the synthesis of the long carbon chain ammonium cation part, hexadecyldimethylamine was dissolved in methanol (methanol is used in an amount sufficient to dissolve the raw materials) with ethyl bromoacetate, ethyl 3-bromopropionate, methyl 6-bromohexanoate, methyl 3-(bromomethyl)benzoate, and 1-bromooctane at a ratio of 1:1.2, and stirred at 60°C for 6 hours. After rotary evaporation to remove methanol, the product was dissolved in dichloromethane (dichloromethane is used in an amount sufficient to dissolve the product) and washed several times with distilled water, and the following products were obtained after removing the solvent:

[0060] Hexadecyl(2-ethoxy-2-oxyylideneethyl)dimethylammonium bromide ([N 16 C 1 EO][Br]), white solid;

[0061] Hexadecyl(3-ethoxy-3-oxypropylidene)dimethylammonium bromide ([N 16 C 2 EO][Br]), white solid;

[0062] Hexadecyl(6-methoxy-6-oxyhexylidene)dimethylammonium bromide ([N 16 C 5 MO][Br]), white solid;

[0063] Hexadecyl[(3-(methoxycarbonyl)phenyl)methyl]dimethylammonium bromide ([N 16 MOP][Br]), white solid;

[0064] Hexadecyldimethyl(octyl)ammonium bromide ([N 1,1,8,16 ][Br]), white solid.

[0065] [N 888 C 1 EO][Br] was dissolved in methanol with 2-hexyldecanoic acid (HDA), 4-isobutyl-α-methylphenylacetic acid (IAMP), neodecanoic acid (NDA), N-dodecanoylsarcosine (NLS), and bis(2-ethylhexyl)glycine (DEHG) completely saponified by NaOH at a molar ratio of 1:1, stirred, and reacted at 40-60°C for 6 h. The synthesis of DEHG was prepared according to the reported literature (Sasaki Y, Uto M, Oshima T, et al. Synthesis of a carboxylic acid extractant containing an amino group and its selective extraction of In (III) and Ga (III) [J]. 2016, 23 (1): 1-8. or Zeng Z, Gao Y, Liu C, et al. A novel functionalized ionic liquid [DOC4mim] [DEHG] for impurity removal of aluminum in rare earth leaching solution [J]. Separation and Purification Technology, 2022, 296: 121388.). After removing methanol, the product was dissolved in dichloromethane and washed several times with deionized water to remove the generated inorganic salts. After rotary evaporation to remove dichloromethane, the product was placed in a vacuum drying oven and dried at 60 ° C for 12 hours to obtain the following ionic liquids:

[0066] [N 888 C 1 EO][HDA]: light yellow liquid, 79.8% yield, IR (characteristic peak, cm -1 ):1700 (cation C=O); 1632 (anion C=O), 1H NMR (500 MHz, deuterated chloroform, δ): 4.07 (q, J = 7.0 Hz, 2H), 3.86 (d, J = 13.2 Hz, 2H), 3.50–3.43 (m, 6H), 2.19 (tt, J = 8.4, 5.7 Hz, 1H), 1.68–1.58 (m, 6H), 1.53 (ddd, J = 13.1, 8.6, 4.6 Hz, 4H), 1.36–1.24 (m, 53H), 0.92–0.84 (m, 15H).

[0067] [N 888 C 1 EO][NDA]: yellow liquid, 79.5% yield, IR (characteristic peak, cm -1 ):1697 (cation C=O), 1633 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 4.21 (d, J = 7.5 Hz, 2H), 4.06 (t, J = 6.7 Hz, 2H), 3.51–3.44 (m, 6H), 2.00 (h, J = 6.8 Hz, 2H), 1.63 (ddd, J = 12.8, 8.8, 4.9 Hz, 8H), 1.35–1.26 (m, 35H), 1.20–1.13 (m, 2H), 1.15–1.06 (m, 2H), 0.93–0.80 (m, 18H).

[0068] [N 888 C 1 EO][IAMP]: orange-yellow liquid, 76.4% yield, IR (characteristic peak, cm -1 ): 1708 (cation C=O), 1633 (anion C=O), 1512 (benzene ring); 1 H NMR (500 MHz, deuterated chloroform, δ): 7.27–7.20 (m, 2H), 7.04 (d, J = 8.0 Hz, 2H), 4.67–4.57 (m, 2H), 4.06 (t, J = 6.7 Hz, 2H), 3.71 (s, 1H), 3.48–3.41 (m, 6H), 2.41 (d, J = 7.2 Hz, 2H), 1.82 (dt, J = 13.5, 6.7 Hz, 1H), 1.65–1.57 (m, 6H), 1.44 (d, J = 7.2 Hz, 3H), 1.30 (ddd, J = 19.8, 8.7, 5.1 Hz, 33H), 0.89 (dt, J = 7.1, 3.6 Hz, 15H).

[0069] [N 888 C 1 EO][NLS]: orange liquid, 67.4% yield, IR (characteristic peak, cm-1 ):1748 (cation C=O), 1637 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 4.87 (s, 2H), 4.11 (d, J = 17.5 Hz, 2H), 3.98 (s, 2H), 3.51–3.44 (m, 6H), 2.98–2.93 (m, 3H), 2.38–2.33 (m, 2H), 1.74 (tt, J = 8.0, 4.5 Hz, 2H), 1.66–1.59 (m, 6H), 1.35–1.24 (m, 49H), 0.88 (td, J = 7.0, 2.4 Hz, 12H).

[0070] [N 888 C 1 EO][DEHG]: yellow liquid, 74% yield, IR (characteristic peak, cm -1 ):1740 (cation C=O), 1622 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 4.14–4.10 (m, 2H), 4.07 (t, J = 6.7 Hz, 2H), 3.64 (t, J = 6.7 Hz, 02), 3.29–3.25 (m, 6H), 2.55 (dd, J = 10.1, 5.7 Hz, 2H), 2.51 (d, J = 6.4 Hz, 2H), 1.50 (td, J = 11.8, 10.0, 6.1 Hz, 10H), 1.41–1.23 (m, 47H), 0.94–0.83 (m, 21H).

[0071] Figure 1 Based on [N 888 C 1 EO] + Structural diagram of carboxylate ionic liquids.

[0072] Similarly, N 888 C 1 MO][Br]、[N 888 C 2 EO][Br]、[N 888 C 5 MO][Br]、[N 888 C 1 DO][Cl]、[N 888 MOP][Br], methyl trioctyl ammonium chloride ([A336][Cl]), [N 16 C 1 EO][Br]、[N 16 C 2 EO][Br]、[N 16 C5 MO][Br]、[N 16 MOP][Br]、[N 1,1,8,16 ][Br] and 2-hexyldecanoic acid (HDA) completely saponified by NaOH were dissolved in methanol (methanol is used in an amount sufficient to dissolve the raw materials) at a molar ratio of 1:1 and stirred at 60°C for 6 hours. After removing methanol, the product was dissolved in dichloromethane (dichloromethane is used in an amount sufficient to dissolve the product) and washed several times with deionized water to remove the generated inorganic salts. After rotary evaporation to remove dichloromethane, the product was placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the following ILs:

[0073] [N 888 C 1 MO][HDA]: orange liquid, 63.7% yield, IR (characteristic peak, cm -1 ):1704 (cation C=O), 1632 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 5.31 (s, 2H), 3.78 (s, 3H), 3.50-3.43 (m, 6H), 2.23 (ddd, J = 8.5, 5.5, 3.0 Hz, 1H), 1.67--1.59 (m, 6H), 1.56 (dt, J = 9.5, 4.7 Hz, 4H), 1.35-1.21 (m, 50H), 0.90-0.85 (m, 15H).

[0074] [N 888 C 2 EO][HDA]: yellow liquid, 78.5% yield, IR (characteristic peak, cm -1 ):1712 (cation C=O), 1568 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 4.06 (d, J = 6.7 Hz, 2H), 3.70-3.61 (m, 2H), 3.32 (s, 6H), 2.73-2.68 (m, 2H), 2.19 (tt, J = 9.4, 5.0 Hz, 1H), 1.61-1.48 (m, 10H), 1.29-1.25 (m, 50H), 0.90-0.86 (m, 18H).

[0075] [N 888 C 5 MO][HDA]: light yellow liquid, 65% yield, IR (characteristic peak, cm -1 ):1760(C=O); 1H NMR (500 MHz, deuterated chloroform, δ): 3.69 (s, 3H), 3.42 (t, J = 6.7 Hz, 8H), 2.49-2.45 (m, 2H), 2.34 (q, J = 7.1 Hz, 1H), 1.67 (dq, J = 14.7, 7.2 Hz, 8H), 1.62-1.55 (m, 2H), 1.51-1.45 (m, 4H), 1.45-1.36 (m, 2H), 1.32-1.26 (m, 50H), 0.92-0.86 (m, 15H).

[0076] [N 888 C 1 DO][HDA]: orange-yellow liquid, 70.2% yield, IR (characteristic peak, cm -1 ):1713 (cation C=O), 1568 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 4.07 (s, 2H), 2.70-2.63 (m, 6H), 2.19 (tt, J=9.4, 5.0 Hz, 1H), 1.65-1.49 (m, 6H), 1.42-1.33 (m, 4H), 1.33-1.24 (m, 59H), 0.92-0.84 (m, 15H).

[0077] [N 888 MOP][HDA]: yellow liquid (white waxy solid after cooling), 82.2% yield, IR (characteristic peak, cm -1 ):1722 (cation C=O), 1620,1607 (anion C=O), 1587 (benzene ring); 1 H NMR (500 MHz, deuterated chloroform, δ): 8.16-7.98 (m, 2H), 7.57 (t, J = 7.8 Hz, 2H), 5.13 (s, 2H), 3.93 (d, J = 9.8 Hz, 3H), 3.35-3.28 (m, 6H), 2.36 (tt, J = 8.7, 5.4 Hz, 1H), 1.80 (q, J = 9.7, 8.0 Hz, 6H), 1.60 (dq, J = 14.2, 6.4 Hz, 4H), 1.36-1.23 (m, 50H), 0.88 (ddt, J = 7.2, 4.9, 2.6 Hz, 15H).

[0078] [A336][HDA]: orange liquid, 96% yield, IR (characteristic peak, cm -1 ):1760(C=O); 1H NMR(500MHz,Chloroform-d,δ):3.47-3.34(m,6H),3.14(s,3H),2.42-2.31(m,1H) ),1.71-1.61(m,6H),1.61-1.52(m,4H),1.42-1.21(m,50H),0.90-0.85(m,15H).

[0079] [N 16 C 1 EO][HDA]: pale yellow liquid (white waxy solid after cooling), 71.2% yield, IR (characteristic peak, cm -1 ):1707 (cation C=O), 1635, 1604 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 3.95 (s, 2H), 3.78 (s, 2H), 3.57 -3.50 (m, 2H), 3.27 (s, 6H), 2.27 (tt, J = 8.6, 5.5 Hz, 1H), 1.74 - 1.67 (m, 2H), 1.57 (tt, J = 8.5, 4.9 Hz, 4H), 1.41 (dt, J = 13.8, 6.7 Hz, 4H), 1.36 - 1.19 (m, 45H), 0.87 (tt, J = 7.1, 2.4 Hz, 9H).

[0080] [N 16 C 2 EO][HDA]: light yellow liquid, 62.3% yield, IR (characteristic peak, cm -1 ):1710 (cation C=O), 1568 (anion C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 5.30 (s, 2H), 3.60-3.54 (m, 2H), 3.50 (s, 8H), 2.68-2.60 (m, 2H), 1.57 (qt, J = 8.5, 4.7 Hz, 6H), 1.39 (ddd, J = 12.6, 9.4, 5.5 Hz, 4H), 1.33-1.23 (m, 46H), 0.87 (td, J = 7.0, 4.4 Hz, 9H).

[0081] [N 16 C 5 MO][HDA]: yellow liquid, 86% yield, IR (characteristic peak, cm -1 ): 1735 (cation C=O), 1565 (anion C=O); 1H NMR (500 MHz, deuterated chloroform, δ): 4.07 (s, 3H), 3.66 (s, 4H), 3.33 (s, 6H), 2.36-2.24 (m, 2H), 2.23 (s, 1H), 1.77-1.60 (m, 6H), 1.57-1.48 (m, 4H), 1.45-1.38 (m, 2H), 1.37-1.33 (m, 2H), 1.25 (s, 44H), 0.89–0.84 (m, 9H).

[0082] [N 16 MOP][HDA]: pale yellow liquid (white waxy solid after cooling), 69.7% yield, IR (characteristic peak, cm -1 ): 1731 (cation C=O), 1618 (anion C=O), 1573 (benzene ring); 1 H NMR (500MHz, deuterated chloroform δ) 8.12 (s, 1H), 8.08 (d, J = 7.7 Hz, 1H), 8.03 (d, J = 7.6 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 5.07 (s, 2H), 3.90 (s, 3H), 3.48-3.40 (m, 2H), 3.29 (s, 6H), 2.33 (tt, J = 8.6, 5.4 Hz, 1H), 1.85-1.72 (m, 2H), 1.63-1.50 (m, 2H), 1.42 (dd, J = 13.2, 7.2 Hz, 2H), 1.22 (d, J = 12.0 Hz, 46H), 0.85 (t, J = 6.6 Hz, 9H). This shows that the present invention successfully prepared [N 16 MOP][HDA] ionic liquid.

[0083] [N 1,1,8,16 [HDA]: light yellow liquid, 73.6% yield, IR (characteristic peak, cm -1 ):1736(C=O); 1 H NMR (500 MHz, deuterated chloroform, δ): 3.39 (ddd, J = 13.7, 5.8, 2.9 Hz, 4H), 3.35 (s, 6H), 2.35-2.28 (m, 4H), 2.27 (s, 1H), 1.72-1.58 (m, 4H), 1.39 -1.33 (m, 6H), 1.27 (d, J = 14.5 Hz, 50H), 0.94-0.84 (m, 12H).

[0084] Figure 2 Based on [HDA] - Structure diagram of functionalized ionic liquids.

[0085] 1.3 Extraction and stripping experiments

[0086] The extraction and stripping experiments were conducted by mixing the aqueous phase and the organic phase in a closed test tube and placing them in a constant temperature air bath shaker. The shaking speed was 400 rpm / s, the volume ratio of the two phases was always 1:1, and the volume of the organic phase or the aqueous phase was 3-5 ml. As the most common solvent extraction diluent, kerosene was used to dilute the extractant to increase the mass transfer rate of extraction and stripping. Unless otherwise stated, in order to achieve extraction and stripping equilibrium, the shaking time in the extraction and stripping experiments was 30 minutes.

[0087] In the recycling experiment of the extractant, after adding NaOH solution to the organic phase for regeneration, 0.5 mol / L NaCl solution was used for washing because water washing easily leads to emulsification, and the volume ratio of washing phase to organic phase was 1:1. Under the extraction conditions with unclear phase interface, filter paper was used for filtration before determining the metal content of the aqueous phase. In the phase modifier experiment, the final organic phase volume was consistent with different phase modifier addition amounts. After extraction and stripping, centrifugation was performed at 3000 rpm for 2 minutes to quickly separate the phases. The element content in the organic phase was calculated by mass conservation.

[0088] The rare earth content in the organic phase is calculated by the conservation of rare earth content between the two phases. The extraction efficiency (E%), stripping efficiency (S%), distribution ratio (D), and separation coefficient (β) are calculated by the following formula:

[0089]

[0090]

[0091]

[0092]

[0093] Among them, M e and M i represent the concentration of metals in the initial aqueous phase and the concentration of metals in the aqueous phase after the extraction reaches equilibrium, M s represents the concentration of metal in the aqueous phase when the stripping stage reaches equilibrium, D 1 and D 2 is the distribution ratio of the two components during one extraction.

[0094] 1.4 Results and Discussion

[0095] 1.4.1 Different anion structures

[0096] In the ionic liquid extraction system, since the negative charge center is located in the anion structure after deprotonation, the structure of the anion often determines their basic extraction and selectivity. When they are used as an organic carboxylic acid extractant for extraction alone, the stronger the acidity of the extractant, the stronger its extraction ability. This is because they all need to undergo a process of ionizing protons before the extraction reaction after contacting the aqueous phase. The easier this process is, the more free carboxylate ions there are, and the stronger the stability of the extractant formed by combining with metal ions. In addition, the actual ionic liquid is not a simple sphere. They have a more complex shape and can assign "directivity" to a specific interaction area. Therefore, in solvent extraction, its shape can be adaptively changed according to the interaction with the substance to be extracted. Geometric structure and steric hindrance are also important factors affecting extraction and selectivity. Different metal ions have different ionic radii, and the larger the steric hindrance, the more difficult it is for the metal ion to interact with the extractant molecule, but their "screening" ability for metal ions will be stronger. After a lot of attempts, the inventors selected several organic carboxylic acids and combined them with carboxylate functionalized cations to form functionalized ionic liquids. In the preparation of ionic liquid extractants, some carboxylic acids with long straight chains (such as oleic acid, lauric acid, etc.) are not suitable for use as extractants because they are waxy solids after combining with carboxylate functionalized cations and do not turn into liquids when heated to 60°C. Figure 3 As shown in the figure, the selected organic carboxylic acids include two fatty acids (HDA and NDA), two carboxylic acids containing nitrogen at the β position (NLS and DEHG) and a benzene ring carboxylic acid (IAMP). It can be seen from the figure that as the concentration of the ionic liquid increases from 0.02 mol / L to 0.04 mol / L, the increase in the amount of rare earth extracted by the two fatty acid ionic liquids is the largest, which is significantly higher than the ionic liquids containing benzene ring carboxylic acid anions and nitrogen-containing carboxylic acid anions. The reason for the above results may be related to the acidity dissociation constant (Ka) and steric hindrance of the selected organic carboxylic acids. In the acidic extraction system, the acidity dissociation constant and steric hindrance of the extractant significantly affect the extraction and selectivity. These characteristics are affected by the chemical structure of the extractant. Taking di(2-ethylhexyl) phosphate (P204), 2-ethylhexyl phosphate mono-2-ethylhexyl ester (P507) and di(2,4,4-trimethylpentyl)phosphonic acid (Cyanex272) as examples, their extraction abilities are arranged in the order of P204>P507>Cyanex272, because the number of alkoxy groups connected to phosphorus in their structures decreases. The electron-donating effect brought by the alkoxy group enhances the reaction of the organic phosphoric acid molecule HA with water to generate the acid ion A- and the protonated water molecule H 3 O +The trend of increasing acidity leads to an increase in acidity. The higher the charge density of oxygen atoms on the deprotonated organophosphoric acid, the easier it is for the ion exchange-based extraction process to occur. However, for the ionic liquid saponified organophosphoric acid extractant, in the chlorinated system, the extraction ability of [A336][P204] for all rare earths is not always higher than that of [A336][P507]. The pKa values ​​of saturated fatty acids (HDA and NDA) and ibuprofen in the present invention are similar, about 4.9. However, due to the electrostatic induction provided by the β-position N atom in NLS and DEHG, [N 888 C 1 EO][NLS], [N 888 C 1 The pKa value of EO][DEHG] ionic liquid is lower.

[0097] 1.4.2 Different cation structures

[0098] The cationic structure of ionic liquids has a great influence on extraction efficiency, separation effect, etc. Therefore, in the study of ionic liquid extraction and separation, the design and optimization of the cationic structure is very important. First, the cationic structure has an important influence on the hydrophobicity and affinity of the ionic liquid extractant. Hydrophobicity and affinity are very important physical and chemical properties of ionic liquid extractants in the separation and extraction process, because they determine the interaction strength between the ionic liquid extractant and the substance to be extracted. Changes in the cationic structure can affect the interaction between the ionic liquid and the anions and other molecules, thereby affecting the hydrophobicity and affinity of the ionic liquid extractant, and ultimately affecting the separation and extraction effect. For example, with the increase in the length of the alkyl side chain in the cationic structure and the increase in the number of substitutions, the affinity of the ionic liquid (IL) to the substance to be extracted will decrease, and the hydrophobic carbon chain has a certain shielding effect on the cation. Secondly, the cationic structure will also affect the thermodynamic properties of the ionic liquid (including the solubility, melting point, heat capacity and thermal conductivity of the ionic liquid). In addition, the cationic structure will also affect the micellization process of the ionic liquid, and the micellization process is closely related to the formation of the third phase in solvent extraction. The present invention uses HDA as the anion part of the functionalized ionic liquid, selects several compounds carrying oxygen-containing functional groups and connects them to trioctylamine and an amine with a long carbon chain and two methyl groups to serve as the cation part of the ionic liquid.

[0099] like Figure 4 As shown, the present invention studies the extraction behavior of heavy rare earth aqueous solution by these ionic liquids at concentrations of 0.02 mol / L and 0.04 mol / L. As can be seen from the figure: [N 888 C 1 EO][HDA], [N 888 C 1 MO][HDA], [N 888 C5 MO][HDA] and [N 16 MOP][HDA] has a higher molecular weight than [A336][HDA] or [N 1,1,8,16 ][HDA] has better extraction performance. This means that the functionalization of cations can enhance the affinity of ionic liquids with rare earth ions, or may also have a coordination effect with rare earth ions. However, not all structures that replace methyl groups can improve the ability of ionic liquids to extract rare earth ions. For functionalized trioctylamine, when the position of the functional group is far away from the positive charge center (greater than or equal to two carbon chains), the inductive effect will be significantly weakened, which will be greatly unfavorable for the extraction of rare earths, and even worse than ionic liquids with alkyl chain structures. For example, [N 888 C 2 MO][HDA] and [N 888 C 5 MO][HDA] extraction system is difficult to achieve the extraction of rare earths, even if their concentration in the organic phase is increased. For functionalized hexadecyl dimethyl tertiary amine, only by introducing ester-substituted benzene and distance N + The extraction efficiency can be improved only when the ester functional group is farther away. 16 MOP][HDA] and [N 16 C 5 MO][HDA] relative to [N 1,1,8,16 ][HDA] has better extraction ability, indicating that the introduction of functional groups can indeed improve the affinity of ionic liquids with REs ions in the aqueous phase. We believe that even if the two short carbon chains on N greatly reduce the steric hindrance of ionic liquids and the obstacles to the affinity of ionic liquids with the aqueous phase, it still cannot well explain the differences shown by the quaternary ammonium ions of functionalized trioctylamine. In summary, based on the influence of cations on ionic liquids, the substituted structure may affect the physicochemical properties of ionic liquids in three aspects. First, the introduced functionalized structure provides the possibility of rare earth coordination with cations, increasing the interaction between ionic liquids and extractants; the substituted structure may produce an inductive effect and greater steric hindrance on the N that loses electrons in the positive charge center of the cation, affecting the interaction between anions and cations; the substituted structure will change the hydrophobicity and increase the affinity of ionic liquid molecules with rare earth ions.

[0100] Figure 5 and Figure 6 Theoretical calculations of electrostatic potential and ionic bond lengths for six TQ-ILs and HQ-ILs with extraction and separation capabilities are presented. Functionalization of cations induces an electrostatic induction effect, which shortens the ionic bond length. This effect is also reflected in the viscosity, where functionalized quaternary ammonium ionic liquids exhibit higher viscosities than pure alkylammonium ionic liquids. However, for [N 16 C 5For [MO][HDA], the grafted functional groups that are too far away from the positive charge center will increase the ionic bond length due to the increased steric hindrance of the molecule. In addition, the molecular electrostatic potential surface shows that the added functional groups in the cation have a negative potential. Therefore, these functional groups are likely to form a coordination cavity near the anionic carboxylate group, which is beneficial to metal coordination.

[0101] 1.4.3 Effect of phase modifiers

[0102] In solvent extraction, the generation of a third phase is a common problem due to the surfactant effect of the extractant. The generation of emulsification may reduce the separation efficiency and extraction rate and affect the stability of the solution. Adding phase modifiers (such as isooctyl alcohol, TBP, TOPO, etc.) can improve the above problems to a certain extent. Figure 5 The interfacial phenomena after extraction are shown when using isooctyl alcohol and TBP as phase modifiers in different volume ratios. The interfacial phenomena after extraction are better for trioctyl ammonium ionic liquids because the short carbon chain ester group connected is closer to the positive charge center and can be surrounded by other hydrophobic structures. For hexadecyl ammonium ionic liquids, since the shielding effect of cations on water molecules is smaller, the critical micelle concentration of the molecules is lower, and emulsification is easy to occur. The addition of TBP and isooctyl alcohol at a volume ratio of 10-15% of the organic phase can effectively eliminate the generation of the third phase.

[0103] Figure 6 The results in (where 0% means no isooctyl alcohol and TBP were added) show that the addition of isooctyl alcohol may affect the extraction performance due to the generation of intermolecular hydrogen bonds, while the addition of TBP has a general promoting effect on the extraction. This shows that although the addition of phase modifiers is to help the extractant molecules to be better dispersed in the organic phase, it will also produce more complex effects that affect the performance of extraction and separation. The improvement in the extraction efficiency of the system with TBP as a phase modifier may be the result of synergistic extraction.

[0104] 1.4.4 Effect of water phase acidity

[0105] As a neutral extractant, ionic liquids do not release protons during the extraction process, but their affinity for large steric cations is far less than that of protons. Therefore, ionic liquids may be more sensitive to the acidity of the aqueous phase, which is why ionic liquids are more easily stripped by acid than acidic extractants and traditional saponified acidic extractants. Figure 7 The extraction behavior of the six extractants after the initial pH of the added mixed rare earth solution, i.e., the aqueous phase, was changed. As can be seen from the figure, when the H + When the concentration of H is higher than 0.001 mol / L, the extraction reaction of rare earth is difficult to occur. +The result of participating in competitive extraction. When the solution pH increases from 2 to 3, the extraction efficiency has a "jump" and continues to increase slowly with the increase of pH. Therefore, it is necessary to control the pH of the aqueous phase to not less than 3 for the extraction of rare earths without hydrolyzing the rare earths.

[0106] 1.4.5 Effect of aqueous phase salting-out agent concentration

[0107] In a neutral extraction system, the addition of a salting-out agent is a common method for improving extraction efficiency. The addition of a salting-out agent increases the ionic strength in the aqueous solution, which increases the activity of the solute. Since rare earth cations are extracted into the organic phase together with the negative ions that achieve charge balance with them, increasing the concentration of negative ions in the aqueous solution is beneficial to the forward reaction. Emulsification is easy to occur in an aqueous phase with low salt concentration. By increasing the salt concentration in the aqueous phase, phase separation can also be improved, which is a result of increased ionic strength of the solution. By changing the amount of NaCl added to the aqueous phase, Figure 8 The effect of NaCl concentration on the four extraction systems is shown. It can be seen from the figure that the addition of NaCl can significantly enhance the extraction process, and this effect is more significant for ionic liquids with functionalized cations. And as the NaCl concentration increases, the ionic liquids with functionalized cations have a higher selective extraction ability for rare earth elements other than Y. 16 In the MOP][HDA] extraction system, unlike other heavy rare earth elements, the extraction efficiency of Y increases first and then decreases with the change of NaCl concentration, which increases the separation coefficient of Ho / Y from 1.8 to 2.8. Figure 8 As shown in Figure E, the increase in NaCl concentration gradually improved [N 16 The phase separation of the MOP][HDA] extraction system was observed. When NaCl was not added, the interface between the two phases could not be seen clearly. However, after adding 0.5 mol / L NaCl solution, the interface was clearly visible and no third phase appeared. Therefore, the addition of salting-out agent is crucial to improve the extraction performance, selectivity and phase separation. 16 The MOP][HDA] extraction system has significant advantages for the separation of Y from heavy rare earths.

[0108] 1.4.6 Thermodynamics and kinetics

[0109] Extraction kinetics and thermodynamics are two important aspects of solvent extraction and have important effects on the efficient extraction and separation of rare earths. By studying the kinetic and thermodynamic characteristics of rare earth extraction with ionic liquids, the optimal reaction time and reaction temperature can be determined, thus achieving efficient rare earth extraction and separation. Generally speaking, the extraction reaction rate depends on the speed of the interaction between the ionic liquid and rare earth ions, while the equilibrium time depends on factors such as reactant concentration, temperature, and the molecular structure of the ionic liquid. By studying the kinetic characteristics of rare earth extraction with ionic liquids, the optimal reaction time can be determined, thus achieving efficient rare earth extraction and separation. In terms of extraction thermodynamics, understanding the thermodynamic characteristics of the reaction is very important for understanding the driving force and control factors of the reaction. The thermodynamic parameters in the extraction process include reaction heat, reaction entropy, and reaction free energy, etc. These parameters determine the direction and rate of the reaction, and also determine the energy change and the magnitude of heat absorption and release during the reaction process. Therefore, the thermodynamic parameters can be used to optimize the reaction conditions and improve the extraction and separation efficiency of rare earths. In the [N 16 MOP][HDA] extraction system, its kinetic and thermodynamic characteristics in the extraction and separation of heavy rare earths were studied by changing the oscillation time and oscillation temperature. Fig. 9 The results in 16 show that the extraction reaction of [N

[0110] 1.4.7 Study on Loading Capacity

[0111] The extraction loading capacity is a key factor determining the amount of extractant used and the efficiency of extracting the target substance. In order to extract more heavy rare earth elements except Y into the organic phase. In the countercurrent extraction process, the separation performance of the two most difficult-to-separate components is mainly considered. In the [N 16 MOP][HDA] extraction system, the extraction order of heavy rare earth elements is Y < Ho < Er < Tm < Yb < Lu. Due to the difficulty in separating Ho and Y, HoCl 3 solution was used as the aqueous phase, and the same organic phase was repeatedly contacted with fresh feed solution to determine the final extraction loading capacity of [N 16 MOP][HDA] for Ho. The organic phase was extracted with multiple portions of fresh aqueous phase, Fig.10 and the results show that the extraction efficiency of the first extraction exceeds 80%, while the extraction efficiency of the second extraction is only about 10%. After that, the organic phase becomes saturated, and [N 16The Ho extraction loading capacity of MOP][HDA] at a concentration level of 0.02 mol / L can reach 0.73 g / L. These findings imply that at limited concentrations, most of the extractant molecules can fully participate in the extraction process at the first contact.

[0112] 1.4.8 Stripping and recycling of extractant

[0113] The stripping process is an important step that must be experienced in solvent extraction. Considering that other anions may be introduced, the present invention uses hydrochloric acid as a stripping agent. Fig.11 The results show that [N 16 The stripping of MOP][HDA] extraction system is relatively simple. Deionized water can strip 50% of Y and 30% of other heavy rare earths. 0.1 mol / L hydrochloric acid solution can completely strip all the loaded rare earths into water. Considering the cost issue, the recyclability is an important factor for the extractant to be used in the actual production process. In the recycling process, the extractant needs to maintain good stability and be able to achieve extraction and separation effects close to the previous one, which is an important basis for sustainable engineering. In order to investigate [N 16 In order to improve the stability of the MOP][HDA] extraction system, the present invention uses 0.2 mol / L HCl solution as a stripping agent to ensure that the rare earth loaded in the organic phase can be completely stripped. The study of the acidity of the aqueous phase shows that ionic liquids have strong extractability for acids. In order to neutralize the acid in the organic phase, a 0.15 mol / L NaOH solution with the same volume as the organic phase is added. Since water washing will cause emulsification, a 0.5 mol / L NaCl solution is used to wash the organic phase instead of water. The results of the cyclic extraction show that in the 6 extraction cycles, the regenerated [N 16 The extraction and separation capabilities of MOP][HDA](ILs) remained stable. Fig.11 The infrared characterization results of D in the extraction showed that the structure of the extractant in the organic phase before extraction and the organic phase after regeneration did not change. Therefore, the above results support [N 16 The MOP][HDA] extraction system has the advantages of easy stripping and good recyclability.

[0114] In summary, the present invention successfully synthesized a series of ionic liquids and evaluated their feasibility for efficient separation of Y from heavy rare earths. Based on the appropriate pKa value, the extraction capacity of rare earth elements is the highest in ionic liquids based on HDA anions. The introduction of functionalized structures in ionic liquid cations can change the physicochemical properties of ionic liquids, and based on the changes in inductive effect and steric hindrance, the functionalization of cations provides the possibility of enhancing the affinity and selective extraction between ionic liquids and rare earth elements. The addition of modifiers can eliminate the emulsification phenomenon of hexadecyl ammonium ionic liquid systems and improve the extraction efficiency. Controlling the salt concentration of the aqueous phase can improve the selectivity and phase separation of the extraction process. [N 16 MOP][HDA] as an extractant is the best extraction system for separating Y from other heavy rare earth elements. In this extraction system, kinetic and thermodynamic studies have shown that the extraction of heavy rare earth elements in this system is less dependent on temperature and the extraction rate is very fast. The extraction mechanism is based on the ion pair mechanism, in which two molecules [N 16 MOP][HDA] extracts one molecule of HoCl 3 . [N 16 MOP][HDA] can achieve a Ho extraction loading capacity of 0.73 g / L at a concentration level of 0.02 mol / L. The easy stripping and good recyclability confirm its potential for sustainable separation of Y from heavy rare earths.

[0115] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carboxylate ammonium-fatty acid radical ionic liquid, It is characterized in that The ionic liquid has the structure shown in the following formula I: in: R 1 , R 2 , R 3 , R 5 The same or different, independently selected from C 1-16 Alkyl, for example methyl, ethyl, propyl, tert-butyl, hexyl, octyl, hexadecyl; n is an integer from 0 to 5, for example, n is selected from 0, 1, 2, 3, 4 or 5; R 4 Selected from C 1-5 Alkylene or aryl, for example methylene, ethylene, propylene, butylene, pentylene, phenyl.

2. The ionic liquid according to claim 1, It is characterized in that Formula I is selected from the following structures:

3. The method for preparing the ionic liquid according to claim 1 or 2, It is characterized in that The preparation method comprises reacting a compound having a structure shown in formula II with 2-hexyldecanoic acid (HDA) completely saponified by NaOH to prepare an ionic liquid having a structure shown in formula I; in: R 1 , R 2 , R 3 , R 4 , R 5 , n independently have the definitions as described in claim 1.

4. The preparation method according to claim 3, It is characterized in that The molar ratio of the compound represented by the formula II to 2-hexyldecanoic acid (HDA) completely saponified by NaOH is 1:(1-5).

5. The preparation method according to claim 3, It is characterized in that The preparation method can be carried out in the presence of a solvent such as an organic solvent. For example, the organic solvent can be selected from methanol.

6. The ionic liquid represented by formula I according to claim 1 or 2 is used for separation of yttrium (Y).

7. The use according to claim 6, It is characterized in that The ionic liquid represented by formula I is used for separating yttrium from ion-adsorption rare earth ores, and more preferably for separating yttrium from ion-adsorption rare earth ores with a yttrium (Y) content higher than 60%.

8. The method for separating yttrium using the ionic liquid of formula I according to claim 1 or 2, It is characterized in that The method comprises using an ionic liquid having a structure shown in formula I as an extractant, and separating yttrium from an ion-adsorption type rare earth ore through extraction and stripping.

9. Yttrium (Y) separated and prepared by the method of claim 8.

10. The yttrium (Y) separated and prepared by the method of claim 8 is used in the fields of fluorescence, magnetism, optics and catalysis.

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