Extracting agent for selectively recovering lithium from aqueous solution as well as preparation method and application of extracting agent

Abstract

The invention belongs to the field of metal ion recovery, and particularly relates to an extraction agent for selectively recovering lithium from an aqueous solution and a preparation method and application of the extraction agent, the extraction agent comprises a hydrogen bond donor and a hydrogen bond acceptor, the hydrogen bond donor is at least one beta-diketone compound, and the hydrogen bond acceptor is trioctylphosphine oxide and N, N-diethyl lauramide. The extraction agent provided by the invention can be used for recovering lithium from an aqueous solution with high selectivity in a wide pH range.

Description

Technical Field

[0001] This invention belongs to the field of metal ion recovery, and particularly relates to an extractant for selectively recovering lithium from aqueous solutions, its preparation method and application, specifically an eco-friendly and highly efficient ternary hydrophobic deep eutectic solvent extractant for selectively recovering lithium from aqueous solutions, its preparation method and application. Background Technology

[0002] Lithium is crucial for green technologies and has wide applications in various fields, including nuclear energy, aerospace, lithium batteries, alloy manufacturing, glass, and ceramics. Lithium-ion batteries are widely used in mobile phones, laptops, and electric vehicles due to their high charging and energy transfer efficiency. Furthermore, lithium plays a clearly defined role as an active metal in nuclear fusion research and development.

[0003] Globally, approximately 59% of lithium reserves are concentrated in continental salt lakes. Extracting lithium from aqueous solutions in these lakes is a more environmentally sustainable alternative to traditional mineral mining, while also reducing production costs. With advancements in extraction technology, existing industrial techniques for lithium extraction from salt lakes include precipitation, membrane separation, adsorption, electrochemical methods, and solvent extraction. Current research indicates that solvent extraction offers advantages such as high selectivity, good stability, and cost-effectiveness, making it the preferred method for industrial lithium extraction.

[0004] Extractants for lithium extraction from aqueous solutions using solvent methods have been extensively studied and can be categorized into β-diketones, crown ethers, and organophosphorus compounds. For brines with high sodium-to-lithium ratios, β-diketone-based extraction systems exhibit high selectivity. Pranolo et al. achieved a lithium-sodium separation coefficient of 1560 at a synergistic system of α-acetyl-m-dodecyl acetophenone (LIX 54) and 4-trialkylphosphine oxide (C923) at a 2:1 molar ratio. Wang et al. developed a synergistic extraction system using 1-phenyl-3-heptyl-13-propanedione and C923 to effectively separate lithium from complex solutions. Zhang et al. investigated β-diketone and organophosphorus systems to recover lithium from various waste liquids, reporting high extraction efficiencies. Li et al. synthesized a novel β-diketone ionic liquid for the efficient and selective extraction of lithium from salt lake brines.

[0005] The extraction methods described above are all liquid-liquid extractions, which typically require large amounts of organic solvents, posing a significant environmental hazard. Therefore, reducing or eliminating the use of these organic solvents has become crucial. Furthermore, lithium-ion extraction usually requires adjusting the feed solution to a pH greater than 7. Current extractants, such as aldehydes, ketones, and crown ethers, form stable complexes under alkaline conditions, necessitating the use of large quantities of alkaline solutions. The discharge of these alkaline solutions after use negatively impacts natural resources, limiting the industrial applicability of these extractants. Moreover, considering the diverse pH values ​​in salt lakes and brines worldwide, developing extractants capable of effectively extracting lithium ions over a wide pH range is essential.

[0006] Ionic liquids (ILs) are a class of molten salts with melting points below 100°C, typically composed of asymmetric anions and cations. Their unique physicochemical properties make them widely applicable in electrochemistry, biotechnology processes, analytical chemistry, solvents, catalysis, and engineering. Due to their low flammability, non-volatility, and high thermal stability, ionic liquids have attracted considerable interest in solvent extraction. Furthermore, the tunability of ionic liquids' anions and cations makes them "designable solvents," allowing the introduction of specific functional groups onto their anions and cations to form mission-specific ionic liquids (TSILs). Compared to traditional molecular extractants (MEs), the tunable properties of ionic liquids offer significant advantages in solvent extraction processes; for example, some ionic liquids exhibit higher partition coefficients and enhanced selectivity, thereby improving separation efficiency by reducing the volume of diluent required and shortening the duration of the separation process.

[0007] Although ionic liquids are promising alternatives to traditional organic solvents and have shown significant potential in separation and purification, they suffer from significant drawbacks such as high viscosity and potential toxicity. In 2003, Abbott et al. introduced a novel class of designed solvents called deep eutectic solvents (DESs). DESs are formed by combining hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) in a specific ratio to create a room-temperature liquid phase. DESs are typically synthesized from natural or readily available compounds and possess similar thermal stability, chemical stability, and low volatility to ionic liquids, while also being non-flammable. Furthermore, DESs offer advantages such as simple preparation, no need for purification, high raw material utilization, low cost, wide availability of raw materials, and easy biodegradability.

[0008] In recent years, hydrophobic deep eutectic solvents (HDESs) have attracted widespread attention in the field of liquid-liquid extraction. HDESs are a class of DESs composed of hydrophobic HBA and HBD components. When mixed with water, they can form a stable hydrophobic phase. HDESs have shown significant advantages in solvent extraction due to their low miscibility with water, wide liquid phase range, and thermal stability. HDESs have been widely used to extract and separate various elements from aqueous phases, including heavy metals, rare and precious metals, and organic pollutants.

[0009] However, there is still no hydrophobic deep eutectic solvent that can effectively extract lithium from aqueous solutions over a wide pH range. Summary of the Invention

[0010] To overcome the shortcomings of existing technologies, this invention provides an extractant for selectively recovering lithium from aqueous solutions, its preparation method, and its application. This extractant can selectively recover lithium from aqueous solutions over a wide pH range.

[0011] In a first aspect, the present invention provides an extractant comprising a hydrogen bond donor and a hydrogen bond acceptor, wherein the hydrogen bond donor is selected from at least one β-diketone compound and the hydrogen bond acceptor is trioctylphosphine oxide or N,N-diethyldodecanoamide.

[0012] According to an embodiment of the present invention, the β-diketone organic compound is selected from at least one of 2-thiophenecarboxyltrifluoroacetone, LIX-54, and LIX-54-100, for example, 2-thiophenecarboxyltrifluoroacetone.

[0013] According to an embodiment of the present invention, the extractant is composed of N,N-diethyldodecanoamide, 2-thiopheneyl trifluoroethyl ketone and trioctylphosphine oxide.

[0014] According to an embodiment of the present invention, in the extractant, the molar ratio of N,N-diethyldodecanoamide, 2-thiophenecarboxyltrifluoroacetone and trioctylphosphine oxide is (0.1-5):(0.2-3):1, preferably the molar ratio of N,N-diethyldodecanoamide, 2-thiophenecarboxyltrifluoroacetone and trioctylphosphine oxide is (0.25-3):(0.5-2):1, for example 1:4:2, 1:2:1, 2:2:1, 3:2:1, 4:2:1.

[0015] According to an embodiment of the present invention, the water content in the extractant is less than or equal to 3%, preferably less than or equal to 2%, for example 2.01%, 0.95%, 1.62%, 1.47%, or 1.26%.

[0016] According to an embodiment of the present invention, the density of the extractant is less than 1.1 g / cm³. -3 For example, 1.046 g / cm³ -3 1.035g / cm -3 1.016 g / cm -3 0.982 g / cm -3 0.969 g / cm -3According to an embodiment of the invention, the viscosity of the extractant is less than 50 mPa s, for example, 48.68 mPa s, 44.74 mPa s, 31.24 mPa s, 20.26 mPa s, or 12.24 mPa s.

[0017] According to an embodiment of the present invention, the extractant is a ternary hydrophobic deep eutectic solvent.

[0018] According to an embodiment of the present invention, the extractant is a transparent liquid.

[0019] According to an embodiment of the invention, the extractant does not contain other organic solvents, such as sulfonated kerosene.

[0020] Secondly, the present invention provides a method for preparing the above-mentioned extractant, comprising the following steps:

[0021] N,N-diethyldodecylamide, 2-thiophenecarboxyltrifluoroacetone and trioctylphosphine oxide were added to a reaction vessel and mixed in a molar ratio of (0.1-5):(0.2-3):1. The mixture was heated to 330-350 K and mixed for 10-60 min. Then it was cooled to room temperature to obtain the extractant.

[0022] According to an embodiment of the present invention, the temperature at which the mixture is heated is 335–345 K, for example, 343.15 K.

[0023] According to an embodiment of the present invention, the mixing time of the mixture is 20 to 40 minutes, for example, 30 minutes.

[0024] Thirdly, the present invention provides an application of the above-mentioned extractant in the extraction of lithium ions.

[0025] According to an embodiment of the present invention, the lithium ions are present in an aqueous solution, and preferably, the aqueous solution also includes Na, K or other metal ions.

[0026] According to an embodiment of the present invention, the pH of the aqueous solution is 1 to 13, preferably 2 to 13, for example 3 to 13.

[0027] Fourthly, the present invention provides a method for extracting lithium ions from an aqueous solution using the above-mentioned extractant, comprising the following steps:

[0028] Extraction is performed by contacting the above-mentioned extractant with an aqueous solution containing lithium ions.

[0029] According to an embodiment of the present invention, the extraction by contacting the extractant with an aqueous solution containing lithium ions includes the following steps: stirring and mixing the extractant with the aqueous solution containing lithium ions, and then centrifuging to separate the phases.

[0030] According to an embodiment of the present invention, the stirring speed is 200 to 500 rpm, for example, 300 rpm.

[0031] According to an embodiment of the present invention, the stirring time is 10 to 60 minutes, for example, 30 minutes.

[0032] According to an embodiment of the present invention, the centrifugation speed is 300 to 10000 rpm, for example, 6000 rpm.

[0033] According to an embodiment of the present invention, the centrifugation time is 3 to 20 minutes, for example, 5 minutes.

[0034] According to an embodiment of the present invention, the volume ratio of the extractant to the lithium-ion-containing aqueous solution is 1:3 to 3:1, for example, 1:1.

[0035] According to an embodiment of the present invention, the concentration of lithium ions in the lithium-ion-containing aqueous solution is greater than or equal to 0.1 g / L, for example, 0.2 g / L.

[0036] According to an embodiment of the present invention, the leaching temperature is less than or equal to 320K, preferably less than or equal to 300K, and more preferably less than or equal to 298K.

[0037] According to an embodiment of the present invention, the leaching time is less than or equal to 20 minutes, preferably less than or equal to 15 minutes, for example, 10 minutes.

[0038] According to an embodiment of the present invention, the leaching process further includes the following step: adding a back-extraction agent to the centrifuged organic phase for back-extraction.

[0039] According to an embodiment of the present invention, the stripping agent is selected from one or more of hydrochloric acid, sulfuric acid, and nitric acid solutions, for example, hydrochloric acid solution.

[0040] According to an embodiment of the present invention, the concentration of the hydrochloric acid solution is 0.01 to 0.06 mol / L.

[0041] According to an embodiment of the present invention, the back-extraction includes the following steps: mixing the centrifuged organic phase with a back-extraction agent, and then centrifuging to separate the phases to obtain the back-extracted organic phase.

[0042] According to an embodiment of the present invention, the stirring speed is 200 to 500 rpm, for example, 300 rpm.

[0043] According to an embodiment of the present invention, the stirring time is 10 to 60 minutes, for example, 30 minutes.

[0044] According to an embodiment of the present invention, the centrifugation speed is 300 to 10000 rpm, for example, 6000 rpm.

[0045] According to an embodiment of the present invention, the centrifugation time is 3 to 20 minutes, for example, 5 minutes.

[0046] According to an embodiment of the present invention, after adding a back-extraction agent to the centrifuged organic phase for back-extraction, the method further includes the following steps: adding a regenerating extractant to the back-extracted organic phase to remove the back-extraction agent from the back-extracted organic phase, thereby obtaining an extractant.

[0047] According to an embodiment of the present invention, the regeneration extractant is selected from at least one of weakly alkaline solutions, such as an aqueous solution of sodium bicarbonate or an aqueous solution of sodium carbonate.

[0048] According to an embodiment of the present invention, the concentration of the sodium carbonate aqueous solution is 0.01 to 0.06 mol / L, for example, 0.05 mol / L.

[0049] Beneficial effects

[0050] 1) The HDES synthesized in this invention exhibits high extraction efficiency and selectivity for Li(I) over a wide pH range (2-13), representing a significant improvement over systems requiring extraction in highly alkaline environments. At pH values ​​greater than 3, HDES maintains stable extraction efficiency, with negligible extraction of K(I), while extraction of Na(I) is only significant under highly alkaline conditions (≥13). This is a significant improvement compared to existing methods requiring pH ≥12. HDES preferentially interacts with H(I) in acidic environments, indicating a competitive relationship between H(I) and Li(I) at lower pH levels, which expands the potential industrial applications of HDES.

[0051] 2) HDES exhibits excellent separation performance for alkali metals other than Li(I), maintaining a clear and transparent phase throughout the extraction process, indicating the formation of an emulsion or third phase. HDES demonstrates rapid kinetics during extraction, reaching equilibrium within 10 minutes, demonstrating good practicality. Furthermore, three-stage countercurrent extraction experiments verified the high efficiency of this HDES, achieving a Li(I) extraction rate of 99%.

[0052] 3) The HDES of this invention provides a more environmentally friendly Li(I) extractant and extraction method, reducing the need for excess alkaline solution and offering a feasible solution for the efficient recovery of lithium from low-pH solutions. This advancement provides a new perspective and solution for future industrial applications, addressing the growing demand for lithium recovery technology in an efficient and sustainable manner. The superior performance of the HDES of this invention at pH values ​​corresponding to actual lithium mother liquor makes it a promising extraction solution.

[0053] 4) The HDES in this invention is composed of β-diketone compounds, trioctylphosphine oxide and N,N-diethyldodecylamide. The resulting extractant is an organic phase with low viscosity, which does not require the addition of organic solvents such as sulfonated kerosene for dilution. The preparation method is simple and avoids the use of excessive organic solvents. Attached Figure Description

[0054] Figure 1 (a) is the structural formula for TOPO, HTTA, and DEDOA; Figure 1 (b) is a physical image of the HDESs prepared in Example 1;

[0055] Figure 2 (a) FT-IR spectra of TOPO, HTTA, DEDOA and HDESs prepared in Example 1 (molar ratio of TOPO, HTTA and DEDOA is 1:2:2); Figure 2 (b) is a mixture of TOPO, HTTA, DEDOA, and HDESs prepared in Example 1 (with a molar ratio of TOPO, HTTA, and DEDOA of 1:2:2). 1 H NMR spectrum;

[0056] Figure 3 A schematic diagram showing the electrostatic potentials of HTTA, TOPO, and DEDOA mapped onto a van der Waals surface.

[0057] Figure 4 The left side is a bar graph of Li(I) extracted by HDES and its precursors (HTTA, TOPO, DEDOA) in Example 2; Figure 4 The right side shows a line graph of Li(I) extracted from samples 1-5 in Example 1;

[0058] Figure 5 (a) Effect of DEDOA molar content on the alkali metal E% extracted by HDES; Figure 5 (b) Effect of HDES prepared for HTTA and TOPO on the extraction of alkali metal E%;

[0059] Figure 6 Comparison of FT-IR spectra before and after HDES extraction of Li(I);

[0060] Figure 7 The chemical structural formulas for HTTA and the enols formed by HTTA reacting with H(I) in water;

[0061] Figure 8 This is a schematic diagram of the mechanism of selective separation of Li(I) by HDES;

[0062] Figure 9 This is a graph showing the effect of aqueous phase pH on extraction efficiency.

[0063] Figure 10 Photos of the extraction at different pH values;

[0064] Figure 11 This is a graph showing the effect of aqueous phase pH on extraction efficiency.

[0065] Figure 12 For logarithm D Li Relationship with 1000 / T Li(I) extraction;

[0066] Figure 13 The effect of the volume ratio of organic phase to aqueous phase on Li(I) extraction;

[0067] Figure 14 The effect of different concentrations of HCl on the back-extraction of Li(I) supported on HTTS:TOPO:DEDOA (2:1:2);

[0068] Figure 15 (a) shows the effect of 5 HDES cycles on E%. Figure 15 (b) is a comparison of the FT-IR spectra before and after cycling;

[0069] Figure 16 McCabe-Thiele plots of Li(I) extraction at different O / A ratios at room temperature;

[0070] Figure 17 This is a flowchart of an intermittent countercurrent extraction experiment.

[0071] Figure 18 This is a flowchart of a three-stage countercurrent extraction experiment. Detailed Implementation

[0072] The following detailed description, in conjunction with specific embodiments, provides a more comprehensive understanding of the extractant, its preparation method, and its application. It should be understood that the following embodiments are merely illustrative and explanatory of the invention and should not be construed as limiting the scope of protection of the invention. All technologies implemented based on the above description of the invention are covered within the scope of protection intended by the invention.

[0073] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0074] The chemicals and reagents used in the following examples are shown in Table 1.

[0075] Table 1 shows the chemicals and materials used in the following examples.

[0076]

[0077]

[0078] The instruments used in the tests in the following examples

[0079] The concentration of metal ions in the aqueous phase was quantitatively determined using an inductively coupled plasma optical emission spectrometer (ICP ULTIMA 2), while the concentration of metal ions encapsulated in HDES was determined using the principle of mass conservation.

[0080] Instruments used to characterize the physical properties of HDES: a biotinylate surface tension meter (Sigma 701) for surface tension measurement, a rotational viscometer (NDJ-5, Shanghai, China) for viscosity analysis, a Metrohm 831KF Coulometer for accurate determination of moisture content, and a HACH DR3900 visible spectrophotometer for optical performance evaluation. The acidity level of the aqueous phase was measured using a pH-3c digital pH meter (Shanghai, China); an AVIII-500 Bruker spectrometer using dimethyl sulfoxide (DMSO) as solvent was used to obtain the properties of HDES. 1 1H NMR spectra; Fourier transform infrared (FT-IR) spectra of HDES were carefully recorded using a Thermo Nicolet IS50 instrument, with wavenumbers ranging from 400 to 4000 cm⁻¹. -1 .

[0081] Calculation method of HDES structure

[0082] The configurations of the HBD and HBA structures were established using GaussView 5.0 software, followed by quantum chemical calculations using Gaussian 09. Density functional theory (DFT) calculations were performed at the B3LYP / 6-311G(d,p) level, enhanced using Grime's DFT-d3(BJ) method to incorporate van der Waals interactions and ensure optimization of the stable configuration. Electrostatic potential analysis and visualization were then performed using Multiwfn 3.8 software and VMD 1.9.3 program.

[0083] Extraction Experimental Methods

[0084] Unless otherwise stated, all extraction experiments in the following examples are liquid-liquid extraction experiments, performed at room temperature. The initial pH standard of the experimental solutions was 7.0, and the sodium ion concentration was [missing value].+ ), potassium ions (K) + The concentrations of both were 1.4 g / L, and the lithium ion concentration (Li) was... + The concentration of the extractant is 0.2 g / L. To ensure the balance during the extraction process, the extractant is first mixed with the experimental solution to obtain the extract. The ratio of organic phase (extract) to aqueous phase (experimental solution) (O / A) in the extract is set as needed. Unless otherwise specified, the O / A ratio is 1:1. The extract is stirred at 300 rpm for 30 minutes and then centrifuged at 6000 rpm for 5 minutes to achieve complete phase separation.

[0085] Subsequently, experimental parameters were optimized, including adjusting the initial pH, equilibration time, and O / A ratio, to maximize lithium extraction efficiency. The thermodynamics of lithium extraction by HDES was investigated. The mechanism of lithium extraction by HDES was elucidated by FT-IR analysis. Back-extraction experiments were conducted using the same method, with HCl solution as the back-extraction agent. The stability of HDES was evaluated over five cycles. The countercurrent experiment used Li₂CO₃ precipitation mother liquor as the feed liquid.

[0086] To ensure the accuracy of the experimental results, all extraction experiments were conducted three times under the same conditions, and the average value was taken. Parameters such as extraction rate (E%), distribution ratio (D), separation factor (β), dissolution rate (S%), and organic-to-water ratio (O / A) were defined and calculated according to Formulas 1-5.

[0087]

[0088] In formulas 1-5, C i C e and C o M represents the elemental concentrations in the feed solution, extract, and HDES, respectively. o and M s D1 and D2 represent the number of moles of elements loaded into the HDES phase before and after stripping, respectively, and D1 and D2 represent the distribution ratios of element 1 and element 2, respectively. o and V a These represent the volumes of HDES and the aqueous solution, respectively.

[0089] Characterization of HDESs

[0090] Preparation Example 1

[0091] In this embodiment, 10 HDESs were prepared by combining TOPO (trioctylphosphine oxide), DEDOA (N,N-diethyldodecanoamide), and HTTA (2-thiophenecarboxylic acid trifluoroacetone). The chemical structures of TOPO, DEDOA, and HTTA are as follows: Figure 1 As shown in a.

[0092] The specific preparation method is as follows: As shown in Table 2, according to the molar ratio of HTTA:TOPO:DEDOA of 1:0:2, 1:0:1, 2:0:3, 1:0:2, 1:0:3, 4:2:1, 2:1:1, 2:1:2, 2:1:3, and 2:1:4, HTTA, TOPO, and DEDOA were weighed and added to a glass container. The mixture was mixed at room temperature, heated to 343.15 K and reacted for 30 min. After cooling to ambient temperature (298.15 K), the solution was allowed to stand for 48 hours to obtain the corresponding HDESs (hereinafter referred to as Sample 1, Sample 2, Sample 3, Sample 4, Sample 5, Sample 6, Sample 7, Sample 8, Sample 9, and Sample 10).

[0093] See Figure 1 As shown in (b), all HDES prepared in this embodiment exhibited good clarity and transparency, even after being cooled to room temperature and stored for 48 hours, and the prepared HDES had consistent flowability.

[0094] See Table 2 for the physical and chemical properties of the HDES prepared in this embodiment. These findings highlight the strong hydrophobicity of the extractant and its density difference with water, thus illustrating the key role of these advantageous physical and chemical properties in defining the excellence of these extractants.

[0095] Table 2 shows the physicochemical properties of HDES at 25±2℃.

[0096]

[0097] use 1 HDES variants were characterized by 1H NMR and FT-IR spectroscopy. The HDES variant corresponding to sample 8 (HTTA:TOPO:DEDOA = 2:1:2) was used as a representative sample. (See [link to relevant documentation]). Figure 2 As shown in (b), HDES's 1 The absence of identifiable new peaks in the 1H NMR spectrum indicates a lack of chemical reactivity between its components; see also Figure 2 As shown in (a), a significant change was observed in the FT-IR spectrum: the stretching vibration peak of the P=O group in TOPO decreased from 1145 cm⁻¹. -1 It has clearly moved to 1153cm -1 The stretching vibration peak of the CN group in DEDOA is from 1427 cm⁻¹ -1 It has clearly moved to 1460cm -1 The stretching vibration peak of the C=O group in HTTA is from 1576 cm⁻¹. -1 It has clearly moved to 1633cm -1 2854cm -1 The peak represents enol-type HDES.1 1H NMR and FT-IR spectroscopy confirmed the presence of hydrogen bond interactions among the HDES components, providing supplementary evidence to support the dissolution of intramolecular hydrogen bonds in enol-type HTTA molecules.

[0098] Electrostatic potential (ESP) analysis is a key method for predicting and elucidating hydrogen bond interaction sites, intermolecular bonding orientations, and thermodynamic characteristics in various chemical systems. For example... Figure 3 As shown, regions with negative electrostatic potentials (ESPs) are represented in blue, while regions with positive ESPs are represented in red. Of particular note are the largest negative ESP values ​​(-55.83 kcal / mol, -46.61 kcal / mol, -31.94 kcal / mol) located near oxygen atoms, and the largest positive ESP values ​​(55.46 kcal / mol, 40.59 kcal / mol) located near highly activated hydrogen atoms in the HTTA and DEDOA groups. These observations are consistent with the characterization results from 1H NMR and FT-IR spectroscopy, indicating that the regions near oxygen atoms and highly activated hydrogen atoms are areas of enhanced reactivity. Therefore, we infer that TOPO may form intermolecular hydrogen bonds with DEDOA and HTTA at these active sites, providing further empirical support for hydrogen bonding interactions among HDES components.

[0099] Example 1

[0100] Screening of HDESs: The extraction and separation performance of HDESs in liquid-liquid extraction is intrinsically related to their specific composition. This example investigates the effect of HDES composition on Li(I) extraction efficiency and separation from other alkali metals. Figure 4 As shown on the left, when HTTA, TOPO, or DEODA are used independently as extractants and dissolved in sulfonated kerosene according to the above extraction method to extract Li(I) from the experimental solution, the extraction efficiency of Li(I) is negligible. This indicates that the extraction ability of a single precursor HTTA, TOPO, or DEODA for Li(I) is not strong.

[0101] Conversely, when HTTA, TOPO, and DEDOA were synthesized into HDES (sample 8), HDES exhibited excellent extraction efficiency (greater than 95%). This synergistic effect highlights the collaborative role of different components in HDES in optimizing Li(I) extraction efficiency. However, see... Figure 4 As shown on the right, HDES synthesized solely from HTTA and DEDOA (samples 2, 3, 4, and 5) did not exhibit effective extraction and separation capabilities.

[0102] Emulsification and three-phase formation during extraction are highly undesirable because they disrupt the extraction environment, lead to extractant loss, reduce product yield, and significantly decrease production efficiency. Using an HDES formulation composed of HTTA, TOPO, and DEDOA as the extractant is highly recommended due to its excellent phase separation properties, which yields a clear and transparent organic and aqueous phase, thus maintaining an optimal extraction environment.

[0103] Example 2

[0104] HDES extraction performance test with different ratios

[0105] For HDES (control 1, sample 6, sample 7, sample 8, sample 9, and sample 10) prepared using different ratios of HTTA, TOPO, and DEDOA as extractants in Example 1, the extraction performance was tested according to the extraction method described above.

[0106] Comparison 1 is HDES prepared by HTTA and TOPO at a molar ratio of 2:1, as described in the currently published literature Synergistic Deep Eutectic Solvents for Lithium Extraction.

[0107] like Figure 5 As shown in (a), HDES prepared using HTTA and TOPO alone did not show significant extraction efficiency for alkali metals. Incorporating DEDOA into HTTA and TOPO significantly improved the extraction efficiency of Li(I). The extraction efficiency of Li(I) gradually increased with increasing DEDOA molar ratio while maintaining good separation specificity, as evidenced by the minimal extraction of Na(I) and K(I). The results indicate that the extraction efficiency of HDES for alkali metals is directly proportional to the molar ratio of DEDOA in the HDES. Without affecting the separation performance of Na(I) and K(I), HDES with a high DEDOA molar ratio exhibits high selectivity and high extraction rate for Li(I).

[0108] To rigorously demonstrate that the addition of DEDOA provides a synergistic effect rather than a dilution effect, the inventors conducted a series of extraction experiments. HDES was synthesized using the method described in Example 1, with HTTA and TOPO in a 2:1 molar ratio, and dissolved in sulfonated kerosene to obtain a 0.3 mol / L organic phase. Extraction performance was then tested according to the aforementioned extraction method. Figure 5 As shown in (b), the results indicate that HDES prepared using only HTTA and TOPO lacks the ability to extract alkali metals. These findings highlight the important role of DEDOA in the selective extraction of Li(I), emphasizing its significant contribution to improving the extraction efficiency and selectivity of HDES for Li(I).

[0109] like Figure 6 As shown, the tensile vibration peaks of key functional groups in sample 8 changed significantly before and after HDES extraction of Li(I). The C=O tensile vibration peak in HTTA changed from 1633 cm⁻¹ to 1633 cm⁻¹. -1 It has clearly moved to 1640cm -1 The presence of this indicates a strong complexation with Li(I), thus confirming the interaction between them; the P=O tensile vibration peak of TOPO increased from 1153 cm⁻¹. -1 Redshifted to 1168cm -1 This indicates a coordination interaction between the P=O group and Li; the CN vibration peak of DEDOA changes from 1461 cm⁻¹. -1 Redshifted to 1463cm -1 This indicates that DEDOA participated in the extraction process. The above FT-IR analysis confirms that HTTA plays the role of the main active ingredient in the extraction process, while TOPO and DEDOA play an important synergistic role, thereby improving selectivity and extraction efficiency.

[0110] In aqueous solution, metal ions such as Li(I) are usually coordinated with multiple H2O molecules. During extraction, HDES competes with the H2O molecules bound to Li(I). The coordination environment of metal ions is dynamically regulated according to the valence state and stability of the ions. Specifically, Li(I) is usually surrounded by 4 H2O molecules. During extraction, HDES effectively replaces these H2O molecules and forms new coordination complexes with Li(I). The redshift of the vibrational peak in FT-IR analysis highlights and proves the strong affinity of HDES for Li(I), which is beneficial for efficient extraction.

[0111] See Figure 7 As shown, molecular dynamics simulations reveal that in the protonated form of HTTA, due to the strong coordination between Li(I) and the oxygen atom in water, Li(I) primarily exhibits a strong electrostatic interaction with H₂O molecules, while the interaction energy between Li(I) and other substances in this system is negligible. Conversely, in the deprotonated HTTA system, the electrostatic interaction between Li(I) and H₂O is significantly weakened, while the electrostatic interaction between Li(I) and TTA⁻ dominates. This indicates that the electrostatic interaction between Li(I) and TTA⁻ is the main driving force for selective lithium extraction. Furthermore, moderate interactions between Li(I) and TOPO and DEDOA were observed by FT-IR spectroscopy, highlighting their crucial roles in the extraction process. These results demonstrate that all components of HDES (HTTA, TOPO, and DEDOA) participate in the extraction of Li(I).

[0112] See Figure 8The figure shows the mechanism of selective extraction of Li(I) by the ternary HDES system. It fully demonstrates that HTTA alone cannot effectively extract Li(I) and is prone to emulsification. Therefore, the special extraction performance of HDES for Li(I) comes from the synergistic effect, which not only improves the extraction efficiency, but also prevents emulsification by replacing the water molecules around Li(I).

[0113] Example 3

[0114] Effect of aqueous phase pH on extraction performance

[0115] The extraction efficiency of existing extractants is highly dependent on pH value, and some extractants are prone to decomposition under acidic conditions, especially extreme acidic conditions. Therefore, pH is a key factor in the extraction process. It is well known that OH- in the form of β-diketenol... - The radical can complex with metal ions, and the pH of the aqueous phase significantly affects the enol tautomerism of β-diketones, thus affecting the extraction efficiency of metal ions. Traditionally, HDES requires a strongly alkaline environment to achieve high lithium extraction efficiency, consistent with conventional co-extraction systems. This typically requires the use of large amounts of alkaline solutions, causing serious health and environmental problems.

[0116] The novel HDES synthesized in this invention can effectively extract Li(I) over a wide pH range (including acidic and alkaline conditions), which is a substantial improvement over existing technologies and expands the potential range of applications.

[0117] In this embodiment, HDES prepared from sample 8 was used. The extraction method described above was followed, except that the pH values ​​of the experimental solutions were set sequentially to 1, 3, 5, 7, 9, 11, and 13 for extraction performance testing.

[0118] like Figure 9 As shown, the extraction efficiency of Li(I) remains stable at pH values ​​greater than 3, while the extraction efficiency of K is negligible, and Na(I) only shows significant extraction efficiency under highly alkaline conditions (pH = 13). These findings indicate that HDES preferentially interacts with H(I) in more acidic environments, suggesting a competitive relationship between H(I) and Li(I) at lower pH levels.

[0119] like Figure 9 As shown in Tables 3-4, the HDES prepared by this invention not only has excellent extraction efficiency for Li(I), but also has excellent separation effect for other alkali metals (Na, K) in a wide pH range (1-13).

[0120] See Figure 10The figure shows the physical images of the extraction system after extraction performance tests at different pH values. In the pH range of 1 to 13, no emulsification or the formation of a third phase was observed at the end of the extraction process. The organic phase and the aqueous phase were separated with a clear interface. Both the organic phase and the aqueous phase were transparent, indicating that the β-diketone system in this embodiment has excellent extraction effect.

[0121] Table 3β Li / Na Effects on different pH values

[0122]

[0123] Table 4β Li / K Effects on different pH values

[0124]

[0125] Example 4

[0126] Dynamics and effects of HDES

[0127] Dynamics study

[0128] Using sample 10 prepared in Example 1 as the HDES extractant, the extraction method described above was followed, except that the equilibrium time between the organic phase and the experimental solution was varied (10 min, 15 min, 20 min, 25 min, 30 min) to investigate the extraction kinetics of Li(I), Na(I), and K(I) by HDES in chlorine medium. Figure 11 As shown, the extraction kinetics of the ternary HDES system are very fast. The extraction efficiencies of Li(I), Na(I) and K(I) reach 97.33%, 8.73% and 2.09% respectively within 10 min, and the extraction process reaches equilibrium and saturation within 10 min.

[0129] Thermodynamic studies

[0130] The thermodynamic properties of the HDES extractant are crucial for elucidating the extraction behavior of the HDES system. Sample 8 prepared in Example 1 was used as the HDES extractant, and the extraction method described above was followed, except that the extraction temperature was changed (298.15K, 303.15K, 308.15K, 313.15K, 318.15K).

[0131] like Figure 12 As shown, in the range of 298.15–318.15 K, the distribution efficiency of Li(I) decreases with increasing temperature. This trend indicates that the increased temperature enhances molecular motion, making the complex formed between lithium ions and the extractant unstable. The relationship between enthalpy change (ΔH°) and lithium ion distribution ratio as a function of temperature can be determined by the van Hoff equation shown in Formula 6.

[0132] See Figure 12 As shown, there is a clear linear relationship between logD and the reciprocal of the extraction temperature. Plotting logD at 1000 / T yields a slope corresponding to -ΔH° / 2.303R. Figure 12 A strong linear correlation was observed with a slope of 0.6, yielding a ΔH° of -11.5 kJ·mol⁻¹. The negative enthalpy indicates that the extraction of Li(I) is exothermic; therefore, increasing the temperature under constant pressure will decrease the extraction efficiency of Li(I).

[0133]

[0134] Example 5

[0135] Compared to the impact on extraction performance

[0136] The amount of HDES used plays a crucial role in the extraction efficiency of lithium ions. This example studies the effect of the organic-water (O / A) ratio on the extraction of Li(I) from inorganic solutions. Sample 8 prepared in Example 1 was used as the HDES extractant, and the extraction method was followed as described above, except that the O / A ratio was changed to (1:3, 1:2, 1:3, 1:1, 2:3, 3:1). The extraction performance of HDES is as follows: Figure 13 As shown, the extraction efficiency significantly increases with increasing HDES volume fraction. Specifically, the extraction efficiency of Li(I) is 59.04% when the O / A ratio is 1:3, and increases to 98.81% when the O / A ratio is 3:1. This trend is because with increasing HDES volume fraction, more active sites in the organic phase are available for Li(I) coordination, thereby increasing the binding probability and extraction efficiency of Li(I).

[0137] At an O / A ratio of 3:1, increasing the Na(I) extraction rate reduces the separation factor. Furthermore, a larger O / A ratio also increases the cost of HDES reagents. El Achkar et al. pointed out that water can form hydrogen bonds with DES components and integrate into the DES supramolecular complex. Exceeding a certain water content threshold, these complexes may degrade, leading to the formation of an aqueous solution of the HDES components. Therefore, the optimal O / A ratio was determined to be 1:1, which ensures the stability of the organic phase after extraction, maximizes the separation coefficient, and, considering economic feasibility, minimizes cross-contamination with Na(I).

[0138] Example 6

[0139] Back-extraction experiment

[0140] After quantitative extraction (using the extractant from Preparation Example 8, with an initial pH of 7.0, sodium and potassium ion concentrations of 1.4 g / L, lithium ion concentration of 0.2 g / L, and an organic phase to aqueous phase ratio of 1:1, the extract was first stirred at 300 rpm for 30 minutes, then centrifuged at 6000 rpm for 5 minutes to achieve complete phase separation; the separated organic phase was used as the back-extraction organic phase), the back-extraction process was investigated using hydrochloric acid. In this example, HCl with a concentration of 0.01–0.06 mol / L was used as the dissolution solution in 15 ml of... In centrifuge tubes, 2 mL of HCl aqueous solutions with concentrations of 0, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, and 0.06 mol / L were added sequentially. The HCl aqueous solutions of different concentrations were mixed with 2 mL of back-extraction organic phase at a volume ratio of 1:1 and mechanically shaken at 300 rpm for 30 minutes at room temperature. Then, the mixture was centrifuged at 6000 rpm for 5 minutes to ensure complete phase separation, resulting in an aqueous phase and a separated organic phase. The aqueous phase was carefully extracted with a syringe, and the concentration of Li(I) in the aqueous phase was determined using ICP-Ultimaa 2.

[0141] from Figure 14 The results show that deionized water is ineffective in stripping Li(I). However, when the HCl concentration is 0.02 mol / L, about 24% of Li(I) in the back-extracted organic phase is stripped. In the range of HCl concentration of 0.03 to 0.05 mol / L, the dissolution rate of Li(I) is significantly improved, and the dissolution rate can reach 93% at a concentration of 0.05 mol / L. The above experiments show that HCl aqueous solution has excellent stripping performance on HDES after back-extraction of alkali metals.

[0142] Example 7

[0143] Regeneration and recycling experiments

[0144] To evaluate the regeneration and recycling performance of the HDES extractant, after the extraction test in Example 6, 2 mL of 0.05 mol / L Na2CO3 solution was added to 2 mL of the separated organic phase to regenerate the extractant and mix. The mixture was stirred for 30 minutes to remove HCl from the organic phase. After oil-water separation, 2 mL of regenerative extractant was added to the organic phase again for extraction, and the process was repeated 5 times.

[0145] like Figure 15 As shown in Figure a, after 5 cycles, the change in extraction efficiency of organics relative to Li(I) is negligible, as... Figure 15As shown in b, FT-IR analysis showed that the main C=O and P=O bonds in HDES did not change significantly. This observation confirms the excellent stability of HDES throughout the extraction cycle. After 5 cycles, HDES maintained a hydrophobic, homogeneous and transparent liquid state.

[0146] Overall, ternary HDES exhibits significant renewability and reusability, characterized by low viscosity, hydrophobicity, low toxicity, efficient phase separation from water, high selectivity for Li(I), anti-saponification, and absence of volatile and toxic organic solvents.

[0147] Example 8

[0148] Countercurrent extraction experiment

[0149] To evaluate the number of extraction stages required for complete extraction of Li(I), the effect of the ratio was investigated, and a McCabe-Thiele extraction stage was constructed. Figure 16 A 1:1 ratio was chosen because a higher ratio would co-extract more other alkali metals, while a lower ratio would require too many extraction stages. The results showed that the three-stage intermittent countercurrent extraction method could extract most of Li(I). Li(I) was recovered from the actual lithium precipitation mother liquor using HDES with a HTTA:TOPO:DEDOA ratio of 2:1:2. The changes in ion concentration after extraction are shown in Table 5.

[0150] Table 5. Changes in metal ion concentration after three-stage countercurrent extraction.

[0151]

[0152] Efficient lithium recovery from Li₂CO₃ mother liquor is crucial for addressing the surge in lithium demand, but it also presents significant challenges. Previous studies have explored various high-density ether extractants (HDES), including β-diketones and neutral extractants, as novel extraction media for recovering Li(I) from aqueous solutions. While these HDES exhibit good extraction efficiency and selectivity for Li(I), they typically require a pH ≥ 12 to achieve optimal extraction rates. In contrast, the ternary HDES presented in this invention demonstrates superior extraction and separation performance at a pH of 9, corresponding to the actual lithium precipitation mother liquor. This technological advancement provides a new perspective and solution for future industrial applications.

[0153] Figure 17 A flowchart of three-stage countercurrent extraction is depicted, in which "H0" and "A0" represent the fresh organic phase and the fresh lithium mother liquor, respectively. The organic phase and the aqueous phase flow countercurrently, and each phase is contacted with the other phase three times before separation. These stages are labeled as "H0 and A2", "H1 and A1" and "H2 and A0" respectively, indicating that they contact, mix and separate in sequence.

[0154] Figure 18 This study presents a three-stage countercurrent extraction series experiment. The process begins in the first stage, where fresh organic phase (H0) and fresh aqueous phase (A0) are mixed and subsequently separated. The extract (A1) from the first stage is introduced into the second stage to interact with the fresh organic phase. This process continues in subsequent stages, with mixing and separation occurring sequentially. When the number of extraction stages reaches seven or more, the process effectively simulates countercurrent extraction. By measuring the concentration of Li(I) in the effluent aqueous phases of stages 7, 9, and 11 and taking the average value, the partition ratio and separation coefficient were calculated. After three stages of countercurrent extraction, the extraction rate of Li(I) was determined to be 99%.

[0155] The HDES synthesized in this invention exhibits high extraction efficiency and selectivity for Li(I) over a wide pH range (including acidic conditions), representing a significant improvement over traditional systems requiring highly alkaline environments. At pH values ​​greater than 3, HDES maintains stable extraction efficiency, while K(I) extraction is negligible, and Na(I) extraction is only significant under highly alkaline conditions. This indicates that HDES preferentially interacts with H(I) in acidic environments. This characteristic suggests a competitive relationship between H(I) and Li(I) at lower pH levels, expanding the potential range of industrial applications.

[0156] Furthermore, HDES exhibited excellent separation performance for other alkali metals, maintaining a clear and transparent phase throughout the extraction process, indicating the absence of emulsions or third-phase formation. The rapid kinetics of HDES, reaching equilibrium within 10 minutes, further underscores its practicality. Moreover, three-stage countercurrent extraction experiments validated the high efficiency of this HDES, achieving a Li(I) extraction rate of 99%, a significant improvement compared to existing methods at pH ≥ 12.

[0157] Therefore, the HDES in this invention provides a more environmentally friendly method, reducing the need for excess alkaline solutions, and offers a feasible solution for the efficient recovery of lithium from low-pH solutions. This advancement provides a new perspective and solution for future industrial applications, helping to address the growing demand for lithium recovery technologies in an efficient and sustainable manner. The superior performance of the HDES at pH values ​​corresponding to actual lithium mother liquor demonstrates its application potential.

[0158] The specific embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An extractant, characterized in that, The extractant comprises a hydrogen bond donor and a hydrogen bond acceptor, the hydrogen bond donor is at least one β-diketone compound, and the hydrogen bond acceptor is trioctylphosphine oxide and N,N-diethyldodecanamide. Preferably, the β-diketone organic compound is selected from at least one of 2-thiophenecarbonyl trifluoroacetone, LIX-54, and LIX-54-100.

2. The extractant according to claim 1, characterized in that, The extractant is composed of N,N-diethyldodecanamide, 2-thiophenecarbonyl trifluoroacetone, and trioctylphosphine oxide. Preferably, in the extractant, the molar ratio of N,N-diethyldodecanamide, 2-thiophenecarbonyl trifluoroacetone, and trioctylphosphine oxide is (0.1-5):(0.2-3):

1.

3. The extractant according to claim 1 or 2, characterized in that, The water content in the extractant is less than or equal to 3%. Preferably, the viscosity of the extractant is less than 50 mPa s. Preferably, the extractant is a ternary hydrophobic deep eutectic solvent.

4. A process for the preparation of the extractant according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: N,N-diethyldodecanamide, 2-thiophenecarbonyl trifluoroacetone, and trioctylphosphine oxide are added into a reaction container in a molar ratio of (0.1-5):(0.2-3):1, mixed, heated to 330-350 K, mixed for 10-60 min, and then cooled to room temperature to obtain the extractant.

5. Use of the extractant of any one of claims 1-3 or the extractant prepared by the method of claim 4 in extracting lithium ions.

6. Use according to claim 5, characterized in that, The pH of the lithium ion solution is 1-13, and preferably the pH of the aqueous solution is 2-13.

7. A method for extracting lithium ions from an aqueous solution using an extractant prepared according to the method of any one of claims 1 to 3 or claim 4, characterised in that, The method comprises the following steps: The extractant is contacted with the aqueous solution containing lithium ions for leaching. Preferably, contacting the extractant with the aqueous solution containing lithium ions for leaching comprises the following steps: stirring and mixing the extractant with the aqueous solution containing lithium ions, and then centrifuging to separate the phases.

8. The method of claim 7, wherein the aqueous solution is an aqueous solution of lithium ions. The stirring speed is 200-500 rpm, and the stirring time is 10-60 min. Preferably, the volume ratio of the extractant to the aqueous solution containing lithium ions is 1:3-3:

1. Preferably, in the aqueous solution containing lithium ions, the concentration of lithium ions is greater than or equal to 0.1 g / L. Preferably, the leaching temperature is less than or equal to 320 K, and the leaching time is less than or equal to 20 min.

9. The method of extracting lithium ions from an aqueous solution according to claim 7 or 8, characterized in that, After the leaching, the following step is further included: adding a stripping agent to the organic phase after centrifugation for stripping. Preferably, the stripping agent is selected from one or more of hydrochloric acid, sulfuric acid, and nitric acid solution. Preferably, the concentration of the stripping agent is 0.01-0.06 mol / L. Preferably, the stripping comprises the following steps: stirring and mixing the organic phase after centrifugation with the stripping agent, and then centrifuging to separate the phases to obtain a stripped organic phase.

10. The method of claim 9, wherein the aqueous solution is an aqueous solution of lithium ions. After adding the stripping agent to the organic phase after centrifugation for stripping, the following step is further included: adding a regenerated extractant to the stripped organic phase to remove the stripping agent in the stripped organic phase to obtain the extractant. Preferably, the regenerated extractant is selected from at least one weak alkaline solution, such as sodium bicarbonate aqueous solution and sodium carbonate aqueous solution.

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