Electric membrane lithium extraction method for salt lake brine with high magnesium-lithium ratio

Abstract

The invention belongs to the technical field of electric membrane lithium extraction, and particularly relates to an electric membrane lithium extraction method for salt lake brine with a high magnesium-lithium ratio. The invention discloses an electric membrane lithium extraction method for salt lake brine with a high magnesium-lithium ratio. The method comprises the following steps: preparing a lithium extraction membrane material; loading the prepared lithium extraction membrane material between two liquid pool devices, respectively installing platinum electrodes connected with an external direct-current stabilized power supply in the two liquid pools, injecting a desorption solution into the liquid pool at one side of a power supply cathode, injecting equal amount of high-magnesium lithium brine into the liquid pool at one side of a power supply anode, and extracting lithium under a set voltage; a high-magnesium-lithium brine storage tank is externally connected, a peristaltic pump is utilized to circulate a solution in the high-magnesium-lithium brine storage tank and a solution in a liquid pool on one side of a power supply anode, and lithium enrichment is carried out under set voltage by utilizing the volume difference of the solutions in the two-phase liquid pool. By preparing the high-selectivity extraction membrane material with high lithium selectivity and good stability under the external electric field, efficient and selective extraction of lithium in the brine with the high magnesium-lithium ratio is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of electro-membrane lithium extraction, and in particular relates to an electro-membrane lithium extraction method for salt lake brine with a high magnesium-to-lithium ratio. Background Art

[0002] Due to the rapid development of the new energy industry, the use of lithium-ion batteries has increased dramatically, and the green and efficient extraction technology of brine-type lithium ore has attracted widespread attention. Lithium ore resources are abundant in brine, but the low lithium concentration and high magnesium-lithium ratio have become the key factors restricting the mining of lithium ore resources.

[0003] Based on tributyl phosphate (TBP) / 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide) salt (C 4 mim[NTf 2 ]) showed a high selectivity for lithium and magnesium in lithium extraction from brine. For example, Xu et al. [Separation and Purification Technology, 2022] prepared TBP / C 4 mim[NTf 2 ]-based extraction membrane material. When the prepared material treats simulated brine with a magnesium-lithium ratio of 20, the separation factor of Li relative to Mg (SLi / Mg) can reach 23.87, but the lithium mass transfer rate of the system is slow, and the lithium permeability coefficient is only 0.0124μm / s. The external electric field can promote the directional movement of ions and improve the ion migration rate of the system. However, for brine, such as Mg 2+ 、Na + Ions with higher electric field response will react with Li + Competition occurs, thereby reducing the lithium selectivity of the membrane material. Summary of the invention

[0004] In view of the problems in the existing membrane extraction field of lithium, such as poor lithium-magnesium selectivity, low rate, poor stability, and low practicality, the purpose of the present invention is to provide a membrane lithium extraction method for salt lake brine with a high magnesium-to-lithium ratio, by preparing a high-lithium selective extraction membrane material with high selectivity and good stability under an external electric field, so as to achieve efficient and selective extraction of lithium from brine with a high magnesium-to-lithium ratio.

[0005] The technical solution of the present invention is: a method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio by electromembrane, comprising the following steps: S1: Preparation of lithium extraction membrane material, the specific process is: Adding 35%-40% of a base polymer, 30%-45% of a neutral extractant, and 15%-35% of an ionic liquid in a mass ratio into a solvent and stirring until the phase becomes homogeneous, and then volatilizing the solvent to obtain a lithium extraction membrane material; S2: Electro-membrane lithium extraction process, the specific process is: The prepared lithium extraction membrane material is loaded in the middle of two liquid pools, and platinum electrodes connected to an external DC voltage-stabilized power supply are installed in the two liquid pools respectively. The analytical solution is injected into the liquid pool on the cathode side of the power supply, and the same amount of high-magnesium lithium brine is injected into the liquid pool on the anode side of the power supply. Lithium is extracted under the set voltage; S3: Lithium-rich brine electromembrane extraction with high magnesium-lithium ratio, the specific process is: On the basis of step S2, an external high-magnesium lithium brine storage tank is connected, and a peristaltic pump is used to circulate the solution in the high-magnesium lithium brine storage tank and the liquid pool solution on the anode side of the power supply, and the volume difference of the solution in the two-phase liquid pool is used to enrich lithium at a set voltage.

[0006] The solvent in step S1 is one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and dichloromethane.

[0007] The neutral extractant in step S1 is one or two alkyl phosphates such as tributyl phosphate, triisobutyl phosphate, and trioctyl phosphate.

[0008] The ionic liquid in step S1 is one of alkyl imidazole type ionic liquids such as 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0009] The temperature range of the stirring process in step S1 is 25-50°C; the temperature range of the volatilization process is 25-70°C.

[0010] The thickness of the lithium extraction membrane material in step S1 is in the range of 70-80 nm.

[0011] In the step S1, the base polymer is one of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride, and cellulose triacetate.

[0012] The high magnesium-to-lithium ratio brine in steps S2 and S3 is Li + Mg 2+ A mixed solution or real brine with a pH between 2-6.5.

[0013] The pH range of the analytical solution used for lithium recovery in steps S2 and S3 is an acidic solution of 0.5-1.

[0014] In the steps S2 and S3, the volume ratio between the treated high magnesium-lithium ratio brine solution and the analytical solution is between 1-10, the applied external DC voltage is 0-10V, and the separation time is 24-240h.

[0015] In step S3, the rotation speed of the peristaltic pump is 30 rpm.

[0016] In the present invention, tributyl phosphate is abbreviated as TBP, triisobutyl phosphate is abbreviated as TIBP, trioctyl phosphate is abbreviated as TOP, 1-butyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt is abbreviated as C 4 mim[NTf 2 ], 1-butyl-3-methylimidazolium hexafluorophosphate is referred to as C 4 mim[PF 6 ], polyvinylidene fluoride-co-hexafluoropropylene is abbreviated as PVDF-HFP, polyvinylidene fluoride is abbreviated as PVDF, and cellulose triacetate is abbreviated as CTA.

[0017] The technical effect of the present invention is that: the present invention provides high lithium / magnesium selectivity for lithium extraction membrane materials through neutral extractants, and ionic liquids significantly reduce the membrane surface resistance of lithium extraction membrane materials, providing good electrochemical properties and lithium migration channels for lithium extraction membranes. The extraction membrane material has high lithium / magnesium selectivity and mass transfer rate, and the lower membrane resistance enables the membrane to complete the extraction of lithium at a lower voltage, thereby reducing the competitiveness of other ions in the electric field and the erosion of the electric field on the membrane. It has high stability and practicality, and realizes the efficient and selective extraction of lithium from brine with a high magnesium-to-lithium ratio.

[0018] The following is a further description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an infrared spectrum of the lithium extraction membrane material prepared in an embodiment of the present invention.

[0020] Figure 2 The membrane surface resistance comparison of the lithium extraction membrane material prepared in Example 3 of the present invention.

[0021] Figure 3 The membrane surface resistance comparison of the lithium extraction membrane material prepared in Example 4 of the present invention. DETAILED DESCRIPTION Example 1

[0022] A method for extracting lithium from a high magnesium-to-lithium ratio salt lake brine using an electro-membrane, comprising the following steps: S1: Preparation of lithium extraction membrane material, the specific process is: Adding 35%-40% of a base polymer, 30%-45% of a neutral extractant, and 15%-35% of an ionic liquid in a mass ratio into a solvent and stirring until the phase becomes homogeneous, and then volatilizing the solvent to obtain a lithium extraction membrane material; S2: Electro-membrane lithium extraction process, the specific process is as follows: The prepared lithium extraction membrane material is loaded in the middle of two liquid pools, and platinum electrodes connected to an external DC voltage-stabilized power supply are installed in the two liquid pools respectively. The analytical solution is injected into the liquid pool on the cathode side of the power supply, and the same amount of high-magnesium lithium brine is injected into the liquid pool on the anode side of the power supply. Lithium is extracted under the set voltage; S3: Lithium-rich brine electromembrane extraction with high magnesium-lithium ratio, the specific process is: On the basis of step S2, an external high-magnesium lithium brine storage tank is connected, and a peristaltic pump is used to circulate the solution in the high-magnesium lithium brine storage tank and the liquid pool solution on the anode side of the power supply, and the volume difference of the solution in the two-phase liquid pool is used to enrich lithium at a set voltage.

[0023] The solvent in step S1 is one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and dichloromethane.

[0024] The neutral extractant in step S1 is one or two alkyl phosphates such as tributyl phosphate, triisobutyl phosphate, and trioctyl phosphate.

[0025] The ionic liquid in step S1 is one of alkyl imidazole type ionic liquids such as 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0026] The temperature range of the stirring process in step S1 is 25-50°C; the temperature range of the volatilization process is 25-70°C.

[0027] The thickness of the lithium extraction membrane material in step S1 is in the range of 70-80 nm.

[0028] In the step S1, the base polymer is one of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride, and cellulose triacetate.

[0029] The high magnesium-to-lithium ratio brine in steps S2 and S3 is Li + Mg 2+ A mixed solution or real brine with a pH between 2-6.5.

[0030] The pH range of the analytical solution used for lithium recovery in steps S2 and S3 is an acidic solution of 0.5-1.

[0031] In the steps S2 and S3, the volume ratio between the treated high magnesium-lithium ratio brine solution and the analytical solution is between 1-10, the applied external DC voltage is 0-10V, and the separation time is 24-240h.

[0032] In step S3, the rotation speed of the peristaltic pump is 30 rpm.

[0033] Figure 1 The infrared spectrum of the lithium extraction membrane material prepared by the embodiment of the present invention. The present invention provides high lithium / magnesium selectivity for the lithium extraction membrane material through a neutral extractant, and the ionic liquid significantly reduces the membrane surface resistance of the lithium extraction membrane material, providing good electrochemical properties and lithium migration channels for the lithium extraction membrane. The extraction membrane material has high lithium / magnesium selectivity and mass transfer rate, and the lower membrane resistance enables the membrane to complete the extraction of lithium at a lower voltage, thereby reducing the competitiveness of other ions in the electric field and the erosion of the electric field on the membrane. It has high stability and practicality, and realizes the efficient and selective extraction of lithium from brine with a high magnesium-to-lithium ratio. Example 2

[0034] The electro-membrane lithium extraction method for high magnesium-lithium ratio salt lake brine is used as in Example 1, using TBP / C 4 mim[NTf 2 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF-HFP, 36% TBP, and 24% C in a mass ratio to N,N-dimethylacetamide. 4 mim[NTf 2 ], the solvent accounts for 75% of the total mixed solution by mass, and the mixture is stirred at 50°C until it is homogeneous, and the obtained casting solution is transferred to a flat-bottomed container, and the solvent is evaporated at 70°C to obtain a lithium extraction membrane; Step 2, loading the prepared lithium extraction membrane between two liquid pools, installing platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH value of 0.5 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium-lithium brine with a magnesium-to-lithium ratio of 1 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 5V; Among them, Li + / Mg 2+ The concentrations were 100 mg·L -1 , the effective membrane area is 26.44cm 2 The membrane thickness was 70 μm. Samples were taken every 6 h during the total 48 h of mass transfer, and deionized water and an acidic solution with a pH of 0.5 were used to adjust the pH of the two phases.

[0035] When the applied voltage is 5V, after 48h, based on TBP / C 4 mim[NTf 2 The lithium extraction rate of the lithium extraction membrane was 56.00%, the lithium recovery rate was 55.22%, and the lithium permeability coefficient was 0.382 μm·s -1 , S Li / Mg is 2.26. Example 3

[0036] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[NTf 2 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF, 33% TOP, and 27% C in a mass ratio to tetrahydrofuran. 4 mim[NTf 2 ], the solvent accounts for 83% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the resulting casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 2, loading the prepared lithium extraction membrane between two liquid pools, installing platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH value of 0.7 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium lithium brine with a magnesium-to-lithium ratio of 1-100 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 5V.

[0037] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ The concentration was 0.1 g·L -1 , 1g·L -1 , 3g·L -1 , 6g·L -1 , 10g·L -1 When the magnesium-lithium ratio is 1, 10, 30, 60, and 100, respectively. The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 6 h during the total mass transfer process of 24-48 h, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0038] After applying a voltage of 5V for 24h, based on TOP / C 4 mim[NTf 2 The lithium extraction rates of the extraction membranes were 25.10%, 26.01%, 29.70%, 52.55% and 71.91% when the magnesium-to-lithium ratios were 1, 10, 30, 60 and 100, respectively. The lithium recovery rates were 22.62%, 19.05%, 22.98%, 39.11% and 70.11%, respectively. The lithium permeability coefficients were 0.165 μm·s -1 , 0.204μm·s -1 , 0.204μm·s -1 , 0.807μm·s -1 , 1.403μm·s -1 , S Li / MgThey are 6.58, 17.39, 27.73, 62.93 and 171.12 respectively.

[0039] At 5V voltage, when the magnesium-lithium ratio was 1, only the two-phase solution was replaced and lithium extraction was performed in a cycle of 48h. After five cycles, the lithium permeability coefficient was 0.241μm·s -1 , S Li / Mg The surface resistance of the prepared lithium extraction membrane material is 8.97. Figure 2 shown. Example 4

[0040] The electro-membrane lithium extraction method for high magnesium-lithium ratio salt lake brine is used as in Example 1, using TBP / C 4 mim[PF 6 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF, 40% TBP, and 20% C in a mass ratio to tetrahydrofuran. 4 mim[PF 6 ], the solvent accounts for 80% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the obtained casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 2, the prepared lithium extraction membrane is loaded between two liquid pool devices, and platinum electrodes connected to an external DC regulated power supply are installed in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH of 1 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium lithium brine with a magnesium-to-lithium ratio of 10-100 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 5V.

[0041] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ The concentration was 1 g·L -1 , 3g·L -1 , 5g·L -1 , 7g·L -1 , 10g·L -1 , the magnesium-lithium ratios are 10, 30, 50, 70, and 100, respectively, and the effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 6 h during the total 24 h mass transfer process, and deionized water and an acidic solution with a pH of 1 were used to adjust the pH of the two phases.

[0042] After applying a voltage of 7V for 24h, based on TBP / C 4 mim[PF 6The lithium extraction rates of the extraction membranes were 55.24%, 62.81%, 67.11%, 80.19% and 82.47% when the magnesium-to-lithium ratios were 10, 30, 50, 70 and 100, respectively. The lithium recovery rates were 54.5%, 62.38%, 66.32%, 79.32% and 81.63%, respectively. The lithium permeability coefficients were 0.329 μm·s -1 , 0.458μm·s -1 , 0.498μm·s -1 , 0.797μm·s -1 , 0.883μm·s -1 , S Li / Mg They are 26, 46, 71, 128, and 213 respectively. Figure 3 shown. Example 5

[0043] The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio using an electro-membrane was used as in Example 1. 4 mim[PF 6 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% CTA, 45% TIBP, and 15% C 4 mim[PF 6 ], the solvent accounts for 90% of the total mixed solution mass. Stirring at 25°C until homogeneous, the obtained casting solution is transferred to a flat-bottomed container, and the solvent is evaporated at 25°C to obtain a lithium extraction membrane; Step 2, the prepared lithium extraction membrane is loaded between two liquid pool devices, and platinum electrodes connected to an external DC regulated power supply are installed in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH of 1 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium lithium brine with a magnesium-to-lithium ratio of 10-100 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 5V.

[0044] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ The concentration was 1 g·L -1 , 3g·L -1 , 5g·L -1 , 7g·L -1 , 10g·L -1 , the magnesium-lithium ratios are 10, 30, 50, 70, and 100, respectively, and the effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 6 h during the total 24 h mass transfer process, and deionized water and an acidic solution with a pH of 1 were used to adjust the pH of the two phases.

[0045] After applying a voltage of 7 V for 24 h, the TIBP / C 4 mim[PF 6 The lithium extraction rates of the extraction membranes were 66.07%, 68.99%, 71.01%, 73.97% and 81.07% when the magnesium-to-lithium ratios were 10, 30, 50, 70 and 100, respectively. The lithium recovery rates were 65.5%, 68.15%, 70.23%, 73.1% and 80.07%, respectively. The lithium permeability coefficients were 0.511 μm·s -1 , 0.516μm·s -1 , 0.592μm·s -1 , 0.624μm·s -1 , 0.790μm·s -1 , S Li / Mg They are 46, 67, 83, 99 and 121 respectively. Example 6

[0046] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[PF 6 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF-HFP, 36% TOP, and 24% C in a mass ratio to tetrahydrofuran. 4 mim[PF 6 ], the solvent accounts for 80% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the obtained casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 2, loading the prepared lithium extraction membrane between two liquid pools, installing platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH value of 0.5 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium lithium brine with a magnesium-to-lithium ratio of 10-100 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 5V.

[0047] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ The concentration was 1 g·L -1 , 3g·L -1 , 5g·L -1 , 7g·L -1 , 10g·L -1 , the magnesium-lithium ratios are 10, 30, 50, 70, and 100, respectively, and the effective membrane area is 26.44 cm 2The membrane thickness was 70 μm. Samples were taken every 6 h during the total 24 h mass transfer process, and deionized water and an acidic solution with a pH of 1 were used to adjust the pH of the two phases.

[0048] After applying a voltage of 7V for 24h, based on TOP / C 4 mim[PF 6 The lithium extraction rates of the extraction membranes were 41.18%, 52.54%, 83.54%, 85.11% and 87.11% when the magnesium-to-lithium ratios were 10, 30, 50, 70 and 100, respectively. The lithium recovery rates were 40.37%, 51.82%, 82.1%, 84.3% and 86.2%, respectively. The lithium permeability coefficients were 0.524 μm·s -1 , 0.852μm·s -1 , 2.03μm·s -1 , 2.22μm·s -1 , 2.14μm·s -1 , S Li / Mg They are 99, 157, 283, 297 and 173 respectively. Example 7

[0049] The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio using an electro-membrane system as in Example 1 is adopted, using TBP / TOP / C 4 mim[NTf 2 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF-HFP, 36% TBP, and 24% C in a mass ratio to N,N-dimethylformamide. 4 mim[NTf 2 ], the solvent accounts for 85% of the total mixed solution mass. Stir at 50°C until homogeneous, transfer the obtained casting solution to a flat-bottomed container, and evaporate the solvent at 70°C to obtain a lithium extraction membrane; Step 2, loading the prepared lithium extraction membrane between two liquid pool devices, installing platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of an acidic solution with a pH value of 0.5 is injected into the liquid pool on the cathode side of the power supply, and an equal amount of high-magnesium lithium brine with a magnesium-to-lithium ratio of 1-100 and a pH value of 6 is injected into the liquid pool on the anode side of the power supply, and lithium extraction is performed at a voltage of 0-10V.

[0050] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ The concentration was 0.1 g·L -1 , 1g·L -1 , 3g·L -1 , 6g·L -1 , 10g·L-1 When the magnesium-lithium ratio is 1, 10, 30, 60, and 100, respectively. The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 6 h during the total mass transfer process of 24-48 h, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0051] When the applied voltage is 0, 5, 10V, after 48h, based on TBP / TOP / C 4 mim[NTf 2 The lithium extraction rates of the extraction membranes reached 8.55%, 66.82%, and 89.27% ​​when the magnesium-to-lithium ratio was 1, and the lithium recovery rates were 7.65%, 62.23%, and 84.93%, respectively. The lithium permeability coefficients were 0.022 μm·s -1 , 0.624μm·s -1 , 1.143μm·s -1 , S Li / Mg It is divided into 2.50, 8.51 and 11.81.

[0052] After applying a voltage of 10V for 48h, based on TBP / TOP / C 4 mim[NTf 2 The lithium extraction rates of the extraction membranes were 89.27%, 94.23%, 99.15%, 96.52% and 93.13% when the magnesium-to-lithium ratios were 1, 25, 50, 75 and 100, respectively. The lithium recovery rates were 84.93%, 91.25%, 95.19%, 94.51% and 91.31%, respectively. The lithium permeability coefficients were 1.143 μm·s -1 , 1.660μm·s -1 , 2.485μm·s -1 , 1.998μm·s -1 , 1.842μm·s -1 , S Li / Mg They are 10.77, 24.62, 37.86, 43.94 and 29.42 respectively.

[0053] At a voltage of 10 V, when the magnesium-lithium ratio was 1, only the two-phase solution was replaced and lithium extraction was performed in a cycle of 48 h. After five cycles, the lithium permeability coefficient was 0.173 μm·s -1 , S Li / Mg It is 7.03. Example 8

[0054] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[NTf 2 ] The electro-membrane lithium extraction method, the specific process is: Step 1: Add 40% PVDF-HFP, 33% TOP, and 27% C in a mass ratio to tetrahydrofuran. 4 mim[NTf 2 ], the solvent accounts for 83% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the resulting casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 3, load the prepared lithium extraction membrane between two liquid pool devices, and install platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein an acidic solution with pH = 0.7 0.25L is injected into the liquid pool on the cathode side of the power supply, and a peristaltic pump is connected to the liquid pool on the anode side of the power supply to circulate simulated brine with a magnesium-to-lithium ratio of 100, which is 4 times that of the analytical solution, at 5V to enrich lithium.

[0055] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ Concentration 10g·L -1 The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 12 h during the total 240 h of mass transfer, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0056] Based on TOP / C after applying voltage of 5V for 240h 4 mim[NTf 2 The lithium concentration in the solution after the extraction membrane treatment was 369.709 mg·L -1 , the enrichment factor is 3.72, S Li / Mg It is 194, and the MLR in the recovered liquid is 0.55. Example 9

[0057] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[NTf 2 ] The specific process of the electro-membrane lithium extraction method for the actual brine sample 1 is as follows: Step 1: Add 40% PVDF-HFP, 33% TOP, and 27% C in a mass ratio to tetrahydrofuran. 4 mim[NTf 2 ], the solvent accounts for 83% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the resulting casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 3, load the prepared lithium extraction membrane between two liquid pool devices, and install platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.1L of acidic solution with pH=0.7 is injected into the liquid pool on the cathode side of the power supply, and a peristaltic pump is connected to the liquid pool on the anode side of the power supply to circulate a sample 1 brine with a magnesium-to-lithium ratio of 130, which is 10 times that of the analyzed phase, at 5V to enrich lithium.

[0058] Among them, Li + The concentration is 295 mg·L -1 ,Mg 2+ The concentration is 38.4 g·L -1 The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 12 h during the total 240 h of mass transfer, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0059] Based on TOP / C after applying voltage of 5V for 240h 4 mim[NTf 2 The lithium concentration in the solution after the extraction membrane treatment was 343.178 mg·L -1 , S Li / Mg is 197, and the MLR in the recovered liquid is 0.66. Example 10

[0060] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[NTf 2 ] The specific process of the electro-membrane lithium extraction method for the actual brine sample 2 is as follows: Step 1: Add 40% PVDF, 33% TOP, and 27% C in a mass ratio to N,N-dimethylformamide. 4 mim[NTf 2 ], the solvent accounts for 85% of the total mixed solution mass. Stirring at 50°C until homogeneous, the obtained casting solution is transferred to a flat-bottomed container, and the solvent is evaporated at 70°C to obtain a lithium-magnesium selective extraction membrane; Step 3, load the prepared lithium-magnesium selective extraction membrane between two liquid pool devices, and install platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of acidic solution with pH=0.7 is injected into the liquid pool on the cathode side of the power supply, and a peristaltic pump is connected to the liquid pool on the anode side of the power supply to circulate sample 2 brine with a magnesium-to-lithium ratio of 758, which is 4 times that of the analytical solution, at 5V to enrich lithium.

[0061] Among them, Li + The concentration is 143 mg·L -1 ,Mg 2+ The concentration is 108.1 g·L-1 The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 12 h during the total 240 h of mass transfer, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0062] Based on TOP / C after applying voltage of 5V for 240h 4 mim[NTf 2 The lithium concentration in the solution after the extraction membrane treatment was 291.745 mg·L -1 , the enrichment factor is 2.05, S Li / Mg The MLR in the recovered liquid was 8.72. Embodiment 11

[0063] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[NTf 2 ] The specific process of the electro-membrane lithium extraction method for the actual brine sample 3 is as follows: Step 1: Add 40% PVDF-HFP, 33% TOP, and 27% C in a mass ratio to tetrahydrofuran. 4 mim[NTf 2 ], the solvent accounts for 83% of the total mixed solution mass. Stirring at 40°C until homogeneous, the obtained casting solution is transferred to a flat-bottomed container, and the solvent is evaporated at 30°C to obtain a lithium-magnesium selective extraction membrane; Step 3, load the prepared lithium-magnesium selective extraction membrane between two liquid pool devices, and install platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of acidic solution with pH=0.7 is injected into the liquid pool on the cathode side of the power supply, and a peristaltic pump is connected to the liquid pool on the anode side of the power supply to circulate sample 3 brine with a magnesium-to-lithium ratio of 805, which is 4 times that of the analytical solution, at 5V to enrich lithium.

[0064] Among them, Li + The concentration is 116 mg·L -1 ,Mg 2+ The concentration is 93g·L -1 The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 12 h during the total 240 h of mass transfer, and deionized water and an acidic solution with a pH of 0.7 were used to adjust the pH of the two phases.

[0065] Based on TOP / C after applying voltage of 5V for 240h 4 mim[NTf 2 The lithium concentration in the solution after the extraction membrane treatment was 261.267 mg·L -1, the enrichment factor is 2.26, S Li / Mg It is 90.2, and the MLR in the recovered liquid is 8.92. Example 12

[0066] The method for extracting lithium from salt lake brine with a high magnesium-lithium ratio using a TOP / C 4 mim[PF 6 ] The specific process of the electro-membrane lithium extraction method for the actual brine sample 1 is as follows: Step 1: Add 40% PVDF-HFP, 36% TOP, and 24% C in a mass ratio to tetrahydrofuran. 4 mim[PF 6 ], the solvent accounts for 83% of the total mixed solution mass. Stir at 40°C until homogeneous, transfer the resulting casting solution to a flat-bottomed vessel, and evaporate the solvent at 30°C to obtain a lithium extraction membrane; Step 3, load the prepared lithium extraction membrane between two liquid pool devices, and install platinum electrodes connected to an external DC regulated power supply in the two liquid pools respectively, wherein 0.25L of acidic solution with pH=0.5 is injected into the liquid pool on the cathode side of the power supply, and a peristaltic pump is connected to the liquid pool on the anode side of the power supply to circulate a sample of brine with a magnesium-to-lithium ratio of 100, which is 4 times that of the analytical solution, at 5V to enrich lithium.

[0067] Among them, Li + Concentration: 100 mg·L -1 ,Mg 2+ Concentration 10g·L -1 The effective membrane area is 26.44 cm 2 The membrane thickness was 70 μm. Samples were taken every 12 h during the total 240 h of mass transfer, and deionized water and an acidic solution with a pH of 0.5 were used to adjust the pH of the two phases.

[0068] Based on TOP / C after applying voltage of 5V for 60h 4 mim[PF 6 The lithium concentration in the solution after the extraction membrane treatment was 325.841 mg·L -1 , enrichment factor is 3.3, S Li / Mg is 77, and the MLR in the recovered liquid is 1.36.

[0069] The electro-membrane lithium extraction system provided by the present invention not only has excellent lithium-magnesium selectivity, but also has good electrochemical properties, which enables it to achieve efficient selective extraction and enrichment of lithium at low voltage. In addition, when faced with actual brine with a high ion concentration background, the lithium-magnesium selective electro-membrane lithium extraction system can still achieve effective enrichment of lithium. This provides a reference method for the selective extraction of lithium from brine with a high magnesium-to-lithium ratio.

[0070] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio by electro-membrane extraction, characterized in that: The following steps are involved: S1: Preparation of lithium extraction membrane material, the specific process is: Adding 35%-40% of a base polymer, 30%-45% of a neutral extractant, and 15%-35% of an ionic liquid in a mass ratio into a solvent and stirring until the phase becomes homogeneous, and then volatilizing the solvent to obtain a lithium extraction membrane material; S2: Electro-membrane lithium extraction process, the specific process is as follows: The prepared lithium extraction membrane material is loaded in the middle of two liquid pools, and platinum electrodes connected to an external DC voltage-stabilized power supply are installed in the two liquid pools respectively. The analytical solution is injected into the liquid pool on the cathode side of the power supply, and the same amount of high-magnesium lithium brine is injected into the liquid pool on the anode side of the power supply. Lithium is extracted under the set voltage; S3: Lithium-rich brine electromembrane extraction with high magnesium-lithium ratio, the specific process is: On the basis of step S2, an external high-magnesium lithium brine storage tank is connected, and a peristaltic pump is used to circulate the solution in the high-magnesium lithium brine storage tank and the liquid pool solution on the anode side of the power supply, and the volume difference of the solution in the two-phase liquid pool is used to enrich lithium at a set voltage.

2. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The solvent in step S1 is one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and dichloromethane.

3. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The neutral extractant in step S1 is one or two alkyl phosphates such as tributyl phosphate, triisobutyl phosphate, and trioctyl phosphate.

4. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The ionic liquid in step S1 is one of alkyl imidazole type ionic liquids such as 1-butyl-3-methylimidazolium bistrifluoromethanesulfonyl imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.

5. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The temperature range of the stirring process in step S1 is 25-50°C; the temperature range of the volatilization process is 25-70°C.

6. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The thickness of the lithium extraction membrane material in step S1 is in the range of 70-80 nm.

7. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: In the step S1, the base polymer is one of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride, and cellulose triacetate.

8. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The high magnesium-to-lithium ratio brine in steps S2 and S3 is Li + Mg 2+ A mixed solution or real brine with a pH between 2-6.

5.

9. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: The pH range of the analytical solution used for lithium recovery in steps S2 and S3 is an acidic solution of 0.5-1.

10. The method for extracting lithium from salt lake brine with a high magnesium-to-lithium ratio according to claim 1, characterized in that: In the steps S2 and S3, the volume ratio between the treated high magnesium-lithium ratio brine solution and the analytical solution is between 1-10, the applied external DC voltage is 0-10V, and the separation time is 24-240h.

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