An extractant, a method for preparing the same and a method for selectively separating gadolinium (III) and aluminum (III)

Abstract

The application discloses an extractant, a preparation method thereof and a method for selectively separating gadolinium (III) and aluminum (III), and develops a synergistic extraction system by using a mixture of four kinds of trialkyl phosphine oxides and 2-thiophene carbonyl trifluoroacetone. Compared with P113 and HTTA used alone, the extraction system of the application significantly improves the extraction and separation efficiency of gadolinium (III). When the molar fraction of HTTA is 0.6, almost 100% of Gd (III) is extracted. At this time, the synergistic coefficient of the extraction system reaches 1495. The synergistic extraction system of the application has an excellent separation coefficient (β>5000) for gadolinium (III) / aluminum (III) and has no emulsification phenomenon. Even after five regeneration cycles, the P113- HTTA synergistic system of the application still maintains high extraction and separation efficiency, and provides a new strategy for the separation of RE and Al.

Description

Technical Field

[0001] This invention belongs to the field of extraction and separation technology, and relates to an extractant and its preparation method, as well as a method for selectively separating gadolinium(III) and aluminum(III). Background Technology

[0002] Rare earth elements (REs), including scandium, yttrium, and 15 lanthanides, are widely used in many advanced manufacturing fields, including hybrid vehicles, display devices, nuclear energy applications, and superconductors. As a recognized strategic element, renewable energy plays a vital role in economic development and technological progress due to its diverse and unique applications. With the increasing demand for renewable elements, efforts are being intensified to develop efficient separation and purification methods. However, the similar electronic structures and physicochemical properties among REs present challenges to achieving high-purity separation. Currently, solvent extraction, chromatographic separation, electrochemical separation, precipitation, and crystallization are commonly used methods for separating and purifying REs.

[0003] Among various methods, solvent extraction is the most widely used and effective method for separating renewable energy sources in industrial applications. This method also performs well in separating impurity elements from rare earth elements (RE), and has become an important process for producing high-purity RE. Co-extraction has been widely studied and used in rare earth separation processes, and it can significantly improve the extraction and separation capabilities of the extraction system. For example, a mixture of HEHAMP ((2-ethylhexylamino)methylphosphonic acid mono-2-ethylhexyl ester) and CA12 (sec-octylphenoxy-substituted acetic acid) was used for the co-extraction of rare earth elements from chloride media. A significant positive synergistic effect was observed when the molar ratio of HEHAMP to CA12 was 2:3, and the separation factor of adjacent heavy rare earth elements was much higher than that of the single system. LIX984 (a mixture of LIX860N (5-nonylsalicylic acid oxime) and LIX84 (2-hydroxy-5-nonylacetaldehyde oxime) in a 1:1 (volume ratio)) and N263 (methyltrioctylammonium chloride) were used as synergistic extractants to extract and recover vanadium and tungsten from the acid leaching solution of denitrification waste catalysts, yielding V2O5 and WO3 products. Using Cyanex923 (a neutral extractant, trialkylphosphine oxide) and TBP (tributyl phosphate) as extractants, Fe(III) could be selectively separated from pickling waste liquid through a reverse synergistic extraction effect. A combination of Cyanex572 (a commercial extractant manufactured by Cytec Industries Inc.) and Cyanex923 was used to extract Th(IV) from the leachate of rare earth radioactive waste.

[0004] Similar to most rare earth element cations (REs), aluminum ions carry a trivalent charge (Al(III)), making them a major impurity element in ion-based rare earth separation. The presence of aluminum ions not only reduces the purity of rare earth products but also affects the solvent extraction process. Using 3-((bis(2-ethylhexyloxy))phosphoryl)-3-phenylpropionic acid (PPPA) as the extractant, aluminum competes with rare earth elements during rare earth chloride solution extraction. The aqueous two-phase system (ATPSs) formed by p-tert-octylphenyl polyethylene glycol ether (TX-100) and electrolyte has the potential to separate transition metal Al from REs, but significant co-extraction of REs occurs during separation, resulting in low selectivity for RE extraction. Furthermore, emulsification caused by aluminum hydroxide colloids formed from Al(III) ions complicates the separation process. In the rare earth separation industry, naphthenic acids (NAs) are commonly used to remove aluminum impurities. However, naphthenic acids emulsify during aluminum extraction, thus adversely affecting the extraction process. Summary of the Invention

[0005] To improve the above-mentioned technical problems, the present invention provides an extractant comprising 2-thiophene carbonyl trifluoroacetone (HTTA) and trialkylphosphine oxide.

[0006] According to an embodiment of the present invention, the molar ratio of HTTA to trialkylphosphine oxide in the extractant is 5:1 to 1:5, and exemplary ratios are 5:1, 4:1, 3:1, 2:1, 1.5:1 (i.e., 3:2), 1:1, 1:1.5 (i.e., 2:3), 1:2, 1:3, 1:4 or 1:5.

[0007] According to an embodiment of the present invention, the HTTA has the structure shown in formula (a):

[0008]

[0009]

[0010] According to an embodiment of the present invention, the alkyl group in the trialkylphosphine oxide is selected from C10. 6-8 At least one of the alkyl groups, for example, the same or different alkyl groups, is independently selected from one of alkyl and octyl. Specifically, the trialkylphosphine oxide has at least one of the structures shown in formulas (b), (c), (d), and (e) as follows:

[0011]

[0012] In some embodiments, the trialkylphosphine oxide is a mixture of compounds having the structures shown in formulas (b), (c), (d), and (e), denoted as P113.

[0013] In some embodiments, the content of the compound with the structure shown in formula (b) in the trialkylphosphine oxide is 25 to 30 wt%, for example 29 wt%.

[0014] In some embodiments, the content of the compound with the structure shown in formula (c) in the trialkylphosphine oxide is 1 to 5 wt%, for example 3 wt%.

[0015] In some embodiments, the content of the compound with the structure shown in formula (d) in the trialkylphosphine oxide is 20 to 30 wt%, for example 25 wt%.

[0016] In some embodiments, the content of the compound with the structure shown in formula (e) in the trialkylphosphine oxide is 35 to 45 wt%, for example 41 wt%.

[0017] According to an exemplary embodiment of the present invention, the contents of the compounds having the structures shown in formulas (b), (c), (d), and (e) in the trialkylphosphine oxide are 29 wt%, 3 wt%, 25 wt%, and 41 wt%, respectively.

[0018] The present invention also provides a method for preparing the above-mentioned extractant, comprising mixing HTTA and trialkylphosphine oxide to prepare the extractant.

[0019] According to an embodiment of the present invention, the molar ratio of HTTA and trialkylphosphine oxide is 5:1 to 1:5, and exemplary ratios are 5:1, 4:1, 3:1, 2:1, 1.5:1 (i.e., 3:2), 1:1, 1:1.5 (i.e., 2:3), 1:2, 1:3, 1:4 or 1:5.

[0020] According to an embodiment of the present invention, the trialkylphosphine oxide has the definition described above.

[0021] According to an embodiment of the present invention, the preparation method is carried out in the presence of a solvent. For example, the solvent may be selected from kerosene.

[0022] This invention also provides the application of the above-described extractant in the extraction and separation of rare earth elements. For example, its application in separating rare earth elements from mine leachate containing aluminum impurities. Preferably, it is used in separating gadolinium (Gd) from mine leachate containing aluminum impurities.

[0023] The present invention also provides a method for extracting and separating gadolinium (Gd), comprising mixing the above-mentioned extractant with a gadolinium (Gd)-containing liquid and performing extraction and separation.

[0024] According to an embodiment of the present invention, the gadolinium (Gd)-containing liquid also contains aluminum.

[0025] When aluminum is present, after extraction, aluminum and gadolinium (Gd) can be separated. Gadolinium (Gd) is extracted into the organic phase, while aluminum remains in the aqueous phase.

[0026] According to an embodiment of the present invention, after extraction, the process further includes back-extracting gadolinium (Gd) using a back-extraction agent. For example, the back-extraction agent is selected from one or more of water, inorganic acids, oxalates, and oxalic acid. Preferably, the inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and sulfuric acid, and the oxalate includes, but is not limited to, sodium oxalate and ammonium oxalate, more preferably sodium oxalate.

[0027] According to an embodiment of the present invention, the molar concentration of the back-extraction agent, inorganic acid, oxalate and oxalic acid, is between 0.5-3.5 mol / L, preferably between 1.5-3.5 mol / L, and exemplary concentrations are 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2 mol / L, 3 mol / L or 3.5 mol / L.

[0028] According to an embodiment of the present invention, the pH value during extraction is 1.5 to 3.5, exemplarily 1.5, 2.0, 2.5, 3.0 or 3.5.

[0029] According to an embodiment of the present invention, the ratio of organic phase to aqueous phase (O / A) during extraction is 1:5 to 2:1, with examples being 1:5, 1:4, 1:3, 1:2, 1:1 or 2:1.

[0030] According to an embodiment of the present invention, the extraction temperature is 20-45°C.

[0031] The present invention also provides a method for separating gadolinium (Gd) from mine leachate, comprising contacting the above-mentioned extractant with the mine leachate to extract, separate and recover gadolinium (Gd) therein.

[0032] The present invention also provides a complex comprising HTTA, trialkylphosphine oxide and gadolinium (Gd), wherein each HTTA molecule forms a coordinate bond with a Gd(III) metal ion through C=O to form six 1:1 Gd / HTTA units; and each trialkylphosphine oxide molecule forms a coordinate bond with a Gd(III) metal ion through P=O to form two 1:1 Gd / trialkylphosphine oxide units.

[0033] According to an embodiment of the present invention, in the complex, the trialkylphosphine oxide unit is coordinated with Gd(III) in a monocoordinate mode, and the HTTA unit is combined with Gd(III) in a dicoordinate mode to form an 8-coordinate gadolinium complex.

[0034] According to an embodiment of the present invention, the trialkylphosphine oxide has the definition described above.

[0035] According to an embodiment of the invention, the complex has substantially the following properties: Figure 6 The atomic structure shown in (e) is shown in the middle.

[0036] The present invention also provides a method for preparing the complex, comprising mixing the above-mentioned extractant with a gadolinium (Gd)-containing liquid to prepare the complex.

[0037] Beneficial effects of the present invention

[0038] As an important rare earth element, gadolinium (Gd) is widely used in environmental protection, nuclear reaction masking agents, magnetic resonance imaging, electronic information, high-strength alloys, and biomedicine. The inventors of this invention unexpectedly discovered through extensive experiments that HTTA exhibits excellent selectivity for rare earth elements (especially Gd) and Al, making it suitable for separating Al and rare earth elements from mine leachate. Compared to previous separation methods, this invention uses a mixture of HTTA and trialkylphosphine oxides to recover Gd(III) from Al(III), demonstrating a highly significant positive synergistic effect. The HTTA and trialkylphosphine oxide synergistic system of this invention exhibits high selectivity for rare earth elements (especially Gd) and Al.

[0039] The HTTA and trialkylphosphine oxide synergistic system of this invention can achieve highly selective separation of gadolinium(III) and aluminum(III). When the concentration ratio of trialkylphosphine oxide to HTTA is 2:3, the synergistic extraction coefficient reaches 1495. This invention systematically studies the effects of Al(III) concentration, pH, temperature, and equilibration time on Gd(III) extraction. In the HTTA and trialkylphosphine oxide synergistic system of this invention, the separation coefficient of Gd(III) / Al(III) is greater than 5000, showing good separation performance. Slope analysis and infrared spectroscopy analysis indicate that the extraction mechanism of Gd(III) in the HTTA and trialkylphosphine oxide synergistic system is ion exchange. According to DFT calculations, the binding energy is negative, indicating that the formation of gadolinium complexes is energy-favorable. Under optimized extraction conditions, using HCl as a stripping agent can completely strip Gd(III) from the organic phase. Countercurrent extraction shows that after two-stage extraction, Gd(III) can be almost completely recovered from aluminum-containing industrial feedstocks, and the purity of the extracted Gd is greater than 99%. The P113-HTTA extraction system of the present invention has the potential to be used in the separation of gadolinium(III) and aluminum(III). Attached Figure Description

[0040] Figure 1 (a) shows the structure of HTTA; Figure 1 (b), (c), (d), and (e) show the structures of the P113 mixture.

[0041] Figure 2In the middle (a) and (b), the distribution ratio and synergistic enhancement coefficient of Gd(III) extracted by HTTA, P113, and mixed HTTA and P113 are respectively.

[0042] Figure 3 (a) represents Al 3+ Effect of concentration on the extraction of Gd(III), [Gd(III)] = 0.03 mol / L, [HTTA] = [P113] = 0.15 mol / L, O / A = 1, t = 30 min, T = 30 ℃; Figure 3 (b) shows the extraction effect.

[0043] Figure 4 The effect of initial pH of the aqueous phase on the extraction of Gd(III) was investigated. [Gd(III)] = [Al(III)] = 0.03 mol / L, [HTTA] = [P113] = 0.15 mol / L, O / A = 1, t = 30 min, and T = 30 ℃.

[0044] Figure 5 In the figures (a) and (b), the effects of temperature and time on the extraction of Gd(III) are shown respectively. [Gd(III)] = [Al(III)] = 0.03 mol / L, [HTTA] = [P113] = 0.15 mol / L, and O / A = 1.

[0045] Figure 6 In the middle (a), the slope analysis of log[HTTA] and logD is presented; Figure 6 (b) shows the slope analysis of log[P113] and logD; Figure 6 (c) shows the slope analysis of equilibrium pH and log D; Figure 6 The middle (d) image shows the infrared contrast of the synergistic extraction system (the aqueous phase is a feed solution containing only one element, Gd (0.03 mol / L), O / A = 1, t = 10 min, T = 30 °C). Figure 6 (e) shows the optimized geometry of the HTTA / Gd / P113 complex.

[0046] Figure 7 The effect of O / A on the extraction of Gd(III) was determined by the following parameters: [Gd(III)] = 0.0347 mol / L, [Al(III)] = 0.0316 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, t = 10 min, and T = 30 °C.

[0047] Figure 8In Figure (a), the effect of HCl concentration on the extraction of Gd(III) is shown. [Gd(III)] = 0.0347 mol / L, [Al(III)] = 0.0316 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, t = 10 min, T = 30 °C. Figure 8 (b) shows the effect of loading on the extraction of Gd(III), where [Gd(III)] = 0.03 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, and T = 30℃; Figure 8 (c) shows the effect of recycling on the extraction of Gd(III); Figure 8 The image (d) shows a comparison of the infrared spectra before and after Gd(III) extraction ([Gd(III)] = 0.0347 mol / L, [Al(III)] = 0.0316 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, t = 10 min, T = 30 ℃).

[0048] Figure 9 (a) shows McCabe-Thiele plots of Gd(III) extraction at different O / A ratios; Figure 9 (b) represents the purity of Gd and Al during intermittent countercurrent extraction; Figure 9 (c) shows the concentration distribution of Gd and Al in the aqueous phase; Figure 9 In the middle (d), the concentration distribution of Gd and Al in the organic phase is shown.

[0049] Figure 10 For HTTA, P113 and HTTA-P113 1 H NMR spectrum.

[0050] Figure 11 The pH values ​​of the aqueous phase before (initial pH) and after (equilibrium pH) P113-HTTA extraction were compared. [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, [Gd(III)] = 0.03 mol / L, O / A = 1, t = 10 min, T = 30 ℃. Detailed Implementation

[0051] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory 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 covered within the scope of protection intended by the present invention.

[0052] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0053] Example

[0054] 1.1 Reagents and Materials

[0055] HTTA was purchased from Adamas with a purity of 98%. P113 was purchased from Shanghai Laya Chemical Co., Ltd. with a purity of 98%, wherein the contents of the compounds with structures shown in formulas (b), (c), (d), and (e) were 29 wt%, 3 wt%, 25 wt%, and 41 wt%, respectively. All experiments were conducted using deionized water.

[0056] 1.2 Main Instruments and Analytical Methods

[0057] The pH of the aqueous phase was assessed using a pHS-3C digital pH meter (Shanghai, China). The concentration of metal ions in the aqueous phase was quantitatively analyzed using an inductively coupled plasma optical emission spectrometer (ICP ULTIMA 2, 131 Horiba Jobin Riviera Ltd.). A Thermo Nicolet IS50 instrument was used to capture wavelengths in the range of 400–4000 cm⁻¹. -1 Fourier transform infrared (FT-IR) spectrum. 1 The 1H NMR spectra were obtained using an AV III-500-140 Bruker spectrometer.

[0058] 1.3 Extraction Experiment

[0059] 0.3333 g HTTA and 0.348 g P113 were dissolved in 10 mL kerosene and mixed evenly to obtain the HTTA-P113 synergistic extraction system (0.15 mol / L HTTA and 0.1 mol / L P113).

[0060] All extraction reactions were carried out at room temperature, with the mixture of aqueous and organic phases mechanically vibrated at 300 rpm for 30 minutes in 15 mL centrifuge tubes. The aqueous and organic phases were then centrifuged at 6000 rpm for 5 minutes to ensure complete separation. Extraction conditions, including initial pH, Al(III) concentration, time, and temperature, were optimized to maximize Gd(III) extraction efficiency. The synergistic extraction mechanism of Gd(III) was determined by slope analysis, Fourier transform infrared analysis, nuclear magnetic resonance analysis, and theoretical calculations. HCl was used to evaluate the stripping performance of Gd(III) loaded in the organic phase. The stability of the extraction system formed by HTTA and P113 of this invention was evaluated over five cycles. Intermittent countercurrent extraction experiments simulated a countercurrent multistage solvent extraction process. Finally, three consecutive batches of extract and their corresponding organic phases were used to measure the gadolinium(III) and aluminum(III) content.

[0061] 1.4 Theoretical Calculation

[0062] In the study of rare earth elements, the characteristics of the 4f orbital electrons make relativistic effects and strong electronic correlation effects important factors that cannot be ignored. To effectively address this issue, the ab initio pseudopotential (PP) method based on small core groups is employed for lanthanides. This method, known as the quasi-relativistic Wood-Boring (WB) method, is widely used in calculations of lanthanides and is typically identified as ECP28MWB. Density functional theory (DFT) was used to calculate the complexation products of HTTA, P113, and Gd(III) metal ions, and the structures were optimized using PBE0 mixed functional theory. Since the molecular weight increases and the side chain length increases after HTTA combines with P113, some representative simplified structures (R: hexyl group in P113) were selected for subsequent calculations and analyses.

[0063] 2. Results and Discussion

[0064] 2.1 Synergistic extraction of P113 and HTTA

[0065] Synergistic extraction with mixed extractants is an effective extraction method that can enhance or weaken the extraction ability of certain metals, thereby improving metal separation. The HTTA-P113 extraction system exhibits a significant synergistic effect on Gd. The distribution ratio of Gd(III) extracted by the P113 and HTTA mixed system is significantly higher than the sum of the distribution ratios when P113 and HTTA are used alone. Figure 2 Under the same conditions in (a), the extraction capabilities of P113 and HTTA alone and in combination were compared. When HTTA was used alone, the distribution ratio of Gd(III) was 0.0281. When P113 was used alone, the distribution ratio of Gd(III) was 0.0151. Due to the low extraction capabilities of P113 and HTTA, their separation ability for Gd(III) is negligible. However, when P113 and HTTA are mixed, the synergistic extraction system exhibits higher extraction and separation capabilities. Figure 2 It can be seen that the extraction efficiency of Gd(III) generally shows a trend of first increasing and then decreasing with the increase of HTTA concentration. With a fixed total extractant concentration of 0.25 mol / L, when the concentration ratio of P113 to HTTA is 2:3, the [Gd(III)] concentration is 0.03 mol / L, pH = 3, O / A = 1, T = 30℃, and t = 30 min, the partition ratio reaches its maximum value, and the extraction synergy coefficient of Gd(III) in the system is 1495. Under the same conditions, Al(III) is difficult to extract, therefore this system can achieve a very good separation effect.

[0066] 2.2 Exploring Al 3+ Effect of concentration on the extraction of Gd(III)

[0067] The effect of aluminum ion concentration on the HTTA-P113 synergistic extraction system was studied. Figure 3 As shown in Figure (a), the extraction efficiency of Gd gradually decreased with increasing Al ion concentration, but remained above 90%. At an Al ion concentration of 0.21 mol / L, the extraction rate of Gd(III) was 95.05%, while the extraction efficiency of Al(III) remained low without significant change and no emulsification was observed. These findings indicate that, to a certain extent, increasing the Al ion concentration had no significant effect on the extraction of Gd(III) by the HTTA-P113 synergistic extraction system. The extraction phenomena are shown in the figure below. Figure 3 In (b), there was no emulsification, and the solution was clear and transparent. The high selectivity and stability of the HTTA-P113 synergistic extraction system are important factors in ensuring the extraction of Gd(III), providing a new approach for improving the selectivity and reducing emulsification in the extraction and separation of rare earth elements.

[0068] 2.3 Effect of initial pH on Gd(III) extraction

[0069] Due to their similar chemical behavior in the aqueous phase, hydrogen ions and rare earth ions engage in competitive extraction reactions, affecting the effective extraction of rare earth (RE) ions. Therefore, measures need to be taken to adjust the aqueous phase conditions, such as adjusting the pH value, to reduce the competition between hydrogen ions and RE ions. The selection of the initial pH value of the aqueous solution plays a crucial role in the extraction and separation of rare earth elements. The effect of aqueous solution pH on extraction behavior was investigated. The pH value of the aqueous phase was adjusted between 1.03 and 3.54, and the extraction behavior of Gd(III) and Al(III) under different pH conditions was measured. Figure 4 As shown, when pH is greater than 1.5, the extraction efficiency of Gd(III) tends to stabilize, while the extraction efficiency of Al(III) always tends to 0. The figure shows that under low pH conditions, the extraction system's ability to extract Gd(III) from the aqueous phase is affected, mainly due to the competitive extraction between Gd(III) and hydrogen ions. Overall, this extraction system exhibits the best extraction effect for Gd(III) at pH values ​​between 1.5 and 3.5. Within this pH range, the separation factor of gadolinium aluminum is shown in Table 1. At pH = 3, the separation factor reaches a maximum of 5875, maximizing the effective separation of Gd(III) and Al(III).

[0070]

[0071] 2.4 Effects of temperature and contact time on the extraction of Gd(III)

[0072] To further investigate the extraction behavior of P113 and HTTA, the effect of temperature on the Gd extraction equilibrium was studied. Figure 5 As shown in Figure (a), within the temperature range of 20–45 °C, temperature variation has no significant impact on the extraction efficiency of the HTTA-P113 system for Gd(III). Considering the extraction and separation of Gd(III), the HTTA-P113 system can be used directly at room temperature without incurring additional costs associated with temperature control during extraction. This invention further investigated the effect of contact time on extraction efficiency, and the results are as follows: Figure 5 As shown in Figure (b), the results indicate that the extraction efficiency of Gd(III) remained essentially unchanged after 10 min, while the extraction efficiency of Al(III) changed negligibly. This means that the HTTA-P113 extraction system requires a short time to reach equilibrium, has a high extraction efficiency for Gd(III), and the separation effect does not weaken with the increase of the two-phase equilibrium time, indicating a stable extraction system.

[0073] 2.5 Mechanism

[0074] Numerous studies have focused on exploring the mechanism of rare earth extraction using synergistic extraction systems. Based on existing mechanisms, it is speculated that protons in HTTA exchange with metal ions and enter the aqueous phase. This is of particular significance for optimizing the design and extraction conditions of the HTTA-P113 synergistic extraction system. The main extraction equilibrium can be represented by equation (1).

[0075] Below, D and the extraction equilibrium constant (K) are defined by equations (2) and (3). The symbols x, y, and z are the stoichiometry of P113, HTTA, and hydrogen ions, respectively.

[0076]

[0077] To investigate the extraction mechanism of Gd(III) in the HTTA-P113 system, slope analysis, infrared spectroscopy analysis, and theoretical calculations were performed. Fourier transform infrared spectroscopy is an important tool for elucidating the extraction mechanism. The structures of single P113, HTTA, mixtures, and HTTA-P113 before and after Gd(III) extraction were characterized using infrared spectroscopy. Figure 6 As shown in (d), 1152cm -1 The absorption peak at 1639 cm⁻¹ can be attributed to the stretching vibration of the P=O group in P113. -1 and 1574cm -1 The absorption peak at 1153 cm⁻¹ can be attributed to the stretching vibrations of the two C=O groups in HTTA. When HTTA and P113 are mixed in a certain proportion, the peak at 1153 cm⁻¹ is observed. -1 The absorption peak at 1643 cm⁻¹ is still due to the stretching vibration of the P=O group in P113. -1 and 1596cm -1The absorption peak at that point is still due to the stretching vibration of the C=O group in HTTA due to intramolecular hydrogen bonding, and in HTTA-P113... 1 No identifiable new peaks were observed in the H NMR spectrum (e.g. Figure 10 This demonstrates that there is no significant chemical reaction between HTTA and P113. After Gd(III) was extracted, the stretching vibration peaks of key functional groups in the mixed system composed of HTTA and P113 changed significantly. The stretching vibration of the C=O group in HTTA changed from 1643 cm⁻¹ to 1643 cm⁻¹. -1 Moved to 1614cm -1 The characteristic peak of the stretching vibration of the C=O group weakens, indicating a strong complexation between HTTA and Gd(III), thus confirming their strong interaction; and the P=O stretching vibration peak of P113 decreases from 1153 cm⁻¹. -1 Redshifted to 1142cm -1 This indicates that there is a coordination interaction between the P=O group of P113 and Gd(III). FT-IR spectroscopy analysis confirmed that HTTA is the main active ingredient in the mixed system, while P113 has a synergistic effect, further improving the extraction selectivity for Gd(III) through the HTTA-P113 synergistic effect.

[0078] Slope analysis is a commonly used method to determine the number of extractant molecules during extraction. To further confirm the extraction reaction of Gd(III) by HTTA-P113, this invention uses HTTA, P113, and equilibrium pH for slope analysis. According to equation (4), the linear relationship between log D(Gd) and log[P113], log[HTTA], and pH is obtained. Figure 6 As shown in (a), (b), and (c), the slope values ​​corresponding to z, x, and y are fitted to 2.3088, 3.1076, and -3.3298, respectively. Simultaneously, the pH decreased significantly before and after extraction (e.g., ...). Figure 11 (As shown), this is consistent with Figure 6 The slope analysis results in (c) are relevant. Therefore, reaction equation (1) can be written as equation (5):

[0079]

[0080] By performing slope analysis, we have determined the interactions between Gd(III) and the HTTA and P113 groups. Experimental results showed that in hydrochloric acid medium, the HTTA ligand forms a complex with Gd(III) in a 3:1 ratio. Therefore, we believe that Gd... 3+The coordination of Gd(III) with HTTA was described using a 1:3 ligand ratio. The complexation products of HTTA, P113, and Gd(III) metal ions were further calculated using density functional theory (DFT), with the structure optimized using a PBE0 mixed functional. Subsequently, considering weak interactions, the dispersion correction for D3-BJ was calculated in all calculations, and the singlet energies at the PBE0 / def2-TZVP level are shown in Table 2 below.

[0081] Table 2. Calculated single-point energies and binding energy parameters (kJ / mol) for Gd complexes with HTTA and P113. -1 )

[0082]

[0083] The results in Table 2 show that the formation of complexes between Gd(III) and HTTA, P113 is stable under the optimized reaction conditions.

[0084] The geometry-optimized structure of the HTTA-Gd(III)-P113 complex is as follows: Figure 6 As shown in (e). In this complex, each HTTA molecule forms a coordinate bond with a Gd(III) metal ion through the C=O moiety, resulting in six 1:1 Gd / HTTA units; each P113 molecule forms a coordinate bond with a Gd(III) metal ion through the P=O moiety, resulting in two 1:1 Gd / P113 units. The P113 units coordinate with Gd(III) in a monocoordinate mode, while the HTTA units bind with Gd(III) in a bicoordinate mode, thereby forming an 8-coordinate gadolinium complex.

[0085] 2.6 O / A Phase Ratio Influence

[0086] The extraction efficiency of Gd(III) is closely related to the amount of HTTA-P113 synergistic extraction system. In this invention, the effect of the organic-to-aqueous (O / A) ratio on Gd(III) extraction was rigorously investigated. The specific method is as follows: In the organic phase: [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L; in the aqueous phase: [Gd(III)] = 0.0347 mol / L, [Al(III)] = 0.0316 mol / L; extraction time t = 10 min; extraction temperature T = 30℃. By changing the volume ratio of the organic phase to the aqueous phase, the optimal O / A ratio was obtained. Within the O / A ratio range of 1:5 to 2:1, the extraction performance of the synergistic extraction system is as follows: Figure 7As shown in the figure, the extraction efficiency decreases significantly with the reduction of the organic phase. When the O / A ratio is 1:5, the extraction rate of Gd(III) by HTTA-P113 is 34.37%. However, when the O / A ratio increases to 2:1, the extraction rate of Gd(III) reaches 99.03%. This trend can be attributed to the extraction of synergistic active sites of the extractant in the organic phase. With the increase of the organic phase, more active sites are available for Gd(III) coordination, thereby improving the binding probability and extraction efficiency of Gd(III). Reducing reagent costs and improving separation efficiency are also crucial. When the O / A ratio is 2:1 or 1:1, the extraction rate of Gd(III) increases, while the effect on the extraction rate of Al(III) is relatively small, and the separation effect is obvious. Therefore, considering the high extraction efficiency (97.90%) for Gd(III) and the stability of the HTTA-P113 synergistic extraction system after extraction, while minimizing the organic phase for economical use and reducing Al(III) cross-contamination, the separation effect is best when the O / A ratio is 1:1.

[0087] 2.7 Back-extraction

[0088] From a practical application perspective, an excellent extractant not only needs to possess good extraction and separation performance, but also requires careful consideration of back-extraction. Back-extraction allows for the recovery and acquisition of high-purity metal ions from the supported organic phase, thereby achieving efficient resource utilization and recycling. After quantitative extraction of Gd(III) (during the extraction process, [Gd(III)] = 0.0347 mol / L, [Al(III)] = 0.0316 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, t = 10 min, T = 30℃), this invention used hydrochloric acid to study the back-extraction of Gd(III). The back-extraction effect of HCl on Gd(III) under different pH conditions was investigated. In this invention, the concentration of HCl used for back-extraction was 0.5–3.5 mol / L. Figure 8 As shown in Figure (a), the back-extraction efficiency of 0.5 mol / L HCl for Gd(III) in the organic phase (P113:HTTA = 2:3) is approximately 69.25%. Within the concentration range of 1.5–3.5 mol / L HCl, the back-extraction rate of Gd(III) is significantly improved, reaching 98.62% under 1.5 mol / L HCl conditions. This demonstrates that the HTTA-P113 synergistic extraction system of this invention exhibits excellent back-extraction performance.

[0089] 2.8 Regeneration and Recycling

[0090] This invention uses deionized water to regenerate the organic phase. The organic phase and deionized water are mixed at a volume ratio of 1:1 and stirred for 30 minutes to remove HCl from the organic phase. Its cyclic extraction performance was also evaluated. Figure 8 As shown in (c), after 5 cycles, the extraction rate of Gd(III) by the HTTA-P113 of the present invention did not change significantly and maintained a high extraction efficiency (approximately 95%), while the extraction efficiency of Al(III) (approximately 0.85%) remained very low. Figure 8 As shown in Figure (d), FT-IR analysis revealed that the C=O and P=O bonds of the HTTA-P113 synergistic extractant of this invention did not show significant changes in extraction and separation capabilities before and after five cycles, indicating no significant interaction between the carbon chains. This also confirms the excellent stability of the HTTA-P113 synergistic extractant over five extraction cycles. After five cycles, the organic phase remained hydrophobic, homogeneous, and transparent. These results demonstrate that the HTTA-P113 system of this invention is effective and recyclable for the separation of Gd / Al in chlorine media.

[0091] 2.9 Load Capacity Testing

[0092] In the extraction process, loading capacity refers to the maximum amount of extractant that the extractant can hold. Loading capacity determines the extraction efficiency of the system and the amount of extractant used. In rare earth separation, a high loading capacity allows for the extraction of more rare earth elements in a single extraction cycle, thus reducing the number of extraction steps and increasing extraction efficiency. It also reduces the amount of extractant used, lowering costs. Appropriate loading capacity helps ensure that the rare earth extraction and separation process proceeds under optimal conditions, resulting in higher purity rare earths. In this invention, the organic phase is repeatedly equilibrated with a fresh gadolinium-rich aqueous phase (specific experimental method: [Gd(III)] = 0.03 mol / L, [HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, T = 30℃). Extraction is performed first according to the above extraction method. After extraction, the organic and aqueous phases are separated, and the concentration of gadolinium in the aqueous phase is measured after each extraction operation. The organic phase is then reacted with a new aqueous phase of the same concentration and volume. This process is repeated until the organic phase can no longer be extracted), until the extraction rate significantly decreases, thus determining the maximum gadolinium loading capacity of the extractable organic phase. The results are as follows: Figure 8 As shown in (b), after the organic phase and the fresh gadolinium-rich aqueous phase reached the 9th equilibrium, the loading of Gd(III) on HTTA-P113 reached 10.14 g / L.

[0093] 2.10 Study on intermittent countercurrent extraction

[0094] This invention establishes the McCabe-Thiele plot and predicts the number of extraction stages required for complete Gd(III) extraction by studying the effect of ambient temperature on the extraction process. The results are as follows: Figure 9 As shown in (a). In this invention, an O / A ratio of 1:1 was used to extract Gd(III), and gadolinium was recovered from the actual industrial aluminum gadolinium feed using HTTA-P113 ([HTTA] = 0.15 mol / L, [P113] = 0.1 mol / L, T = 30 °C). The concentration of Gd in the actual industrial feed was 5456.6 mg / L (0.0347 mol / L), the concentration of Al was 852.6 mg / L (0.0316 mol / L), and the purity of Gd was 86.5 wt% (52.3 mol%). The organic phase loaded with Gd(III) was back-extracted with 1.5 mol / L HCl and regenerated with deionized water to achieve the separation of Gd(III) and Al(III). During the first equilibration of the organic phase and feed solution, 97.02% of Gd and 0.46% of Al were extracted into the organic phase, resulting in 5294.0 mg / L Gd and 12.5 mg / L Al in the raffinate (results are shown in Figure 1). Figure 9 (As shown in Figures 9(b) and 9(c)). The results showed that after two-stage extraction, Gd(III) was almost completely extracted from the feed solution, yielding an organic phase loaded with 5451.3 mg / L of Gd, with a Gd purity >99% in the back-extraction solution. The P113-HTTA synergistic extraction system of this invention has high selectivity, and the entire separation process is simple to operate and can achieve continuous production.

[0095] In summary, this invention develops a novel synergistic extraction system, P113-HTTA, capable of highly selective separation of gadolinium(III) and aluminum(III). When the concentration ratio of P113 to HTTA is 2:3, the synergistic extraction coefficient reaches 1495. In the P113-HTTA synergistic extraction system of this invention, the separation coefficient of Gd(III) / Al(III) is greater than 5000, demonstrating excellent separation performance. Slope analysis and infrared spectroscopy analysis indicate that the extraction mechanism of Gd(III) in the P113-HTTA system is ion exchange. According to DFT calculations, the binding energy is negative, indicating that the formation of gadolinium complexes is energy-favorable. Under optimized extraction conditions, using HCl as a stripping agent can completely strip Gd(III) from the organic phase. Countercurrent extraction shows that after two-stage extraction, Gd(III) can be almost completely recovered from aluminum-containing industrial raw materials, and the purity of the extracted Gd is greater than 99%. The P113-HTTA extraction system of the present invention has the potential to be used in the separation of gadolinium(III) and aluminum(III).

[0096] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An extractant, characterized in that, It includes 2-thiophene carbonyl trifluoroacetone (HTTA) and trialkylphosphine oxides.

2. The extractant as described in claim 1, characterized in that, In the extractant, the molar ratio of HTTA to trialkylphosphine oxide is 5:1 to 1:5; And / or, the alkyl group in the trialkylphosphine oxide is selected from C 6-8 At least one of the alkyl groups; And / or, the alkyl groups are the same or different, and are independently selected from one of alkyl and octyl.

3. The method for preparing the extractant according to claim 1 or 2, characterized in that, The preparation method includes mixing HTTA and trialkylphosphine oxide to prepare the extractant.

4. The use of the extractant according to claim 1 or 2 in the extraction and separation of rare earth elements. For example, its use in separating rare earth elements from mine leachate containing aluminum impurities. Preferably, its use in separating gadolinium (Gd) from mine leachate containing aluminum impurities.

5. A method for extracting and separating gadolinium (Gd), characterized in that, This includes mixing the extractant described in claim 1 or 2 with a gadolinium (Gd)-containing liquid for extraction and separation.

6. The method as described in claim 3, characterized in that, After extraction, the process also includes back-extraction of gadolinium (Gd) using a back-extraction agent; And / or, the stripping agent is selected from one or more of water, inorganic acids, oxalates and oxalic acid; And / or, the inorganic acid is selected from one or more of hydrochloric acid, nitric acid and sulfuric acid, and the oxalate includes, but is not limited to, sodium oxalate and ammonium oxalate; And / or, the molar concentration of the back-extraction agent, inorganic acid, oxalate, and oxalic acid is between 0.5 and 3.5 mol / L; And / or, the pH value during extraction is 1.5 to 3.5; And / or, the ratio of organic phase to aqueous phase (O / A) during extraction is 1:5 to 2:1; And / or, the extraction temperature is 20-45°C.

7. A method for separating gadolinium (Gd) from mine leachate, characterized in that, This includes contacting the extractant described in claim 1 or 2 with mine leachate to extract, separate, and recover gadolinium (Gd) therein.

8. A complex, characterized in that, It includes HTTA, trialkylphosphine oxide and gadolinium (Gd). Each HTTA molecule forms a coordinate bond with Gd(III) metal ions through C=O, forming 6 1:1 Gd / HTTA units; each trialkylphosphine oxide molecule forms a coordinate bond with Gd(III) metal ions through P=O, forming 2 1:1 Gd / trialkylphosphine oxide units.

9. The complex as described in claim 8, characterized in that, In the complex, the trialkylphosphine oxide unit coordinates with Gd(III) in a monocoordinate mode, and the HTTA unit binds with Gd(III) in a dicoordinate mode, forming an 8-coordinate gadolinium complex.

10. The method for preparing the complex according to claim 8 or 9, characterized in that, The preparation method includes mixing the extractant according to claim 1 or 2 with a gadolinium (Gd)-containing liquid to prepare the complex.

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