Electrodialysis-nanofiltration integrated membrane, preparation method and lithium extraction process
By developing an eNF membrane with integrated nanofiltration and electrodialysis functions, the problem of the need for additional enrichment steps in the lithium separation process of conventional nanofiltration membranes is solved, efficient separation of lithium magnesium and lithium enrichment are achieved, and the process flow is simplified.
Patent Information
- Application Number
- CN202510085691.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-20
- Publication Date
- 2025-05-06
AI Technical Summary
Conventional nanofiltration membranes require additional enrichment steps during lithium separation, resulting in complex processes.
Through a one-step co-scraping and interface polymerization process, an integrated film integrating nanofiltration and electrodialysis functions is developed, called eNF membrane. The membrane achieves mono/divalent ion separation and monovalent ion concentration during electrodialysis.
The eNF membrane passes through the pore size screening of the nanofiltration layer and the south effect, combined with the electrochemical process of the ion exchange layer, realizes efficient separation of lithium magnesium and enrichment of lithium, simplifying the lithium extraction process.
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Figure CN119926176A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an electrodialysis-nanofiltration integrated membrane, a preparation method and a lithium extraction process, and belongs to the technical field of nanofiltration membranes. Background Art
[0002] Extracting lithium from salt lakes, especially those with high magnesium-to-lithium ratios, has the potential to alleviate the shortage of lithium resources. Extracting lithium from salt lakes using efficient ion-selective membranes can significantly reduce chemical and energy consumption. However, the similar hydration radius of lithium and magnesium ions limits the applicability of membranes in this extraction process. Electrodialysis (ED) is a promising separation technology that is widely used in the field of seawater desalination. In the electrodialysis process, ion exchange membranes play a key role in facilitating selective ion separation. However, conventional ion exchange membranes often lack the selectivity required for effective separation of monovalent and multivalent ions. In order to expand the application range of ED in complex industrial processes, it is necessary to improve the selectivity of ion exchange membranes, especially for monovalent ions. Recently, significant progress has been made in the development of monovalent selective ion exchange membranes by layer-by-layer self-assembled polyelectrolytes. These membranes have excellent separation capabilities for magnesium and lithium ions during electrodialysis. However, the preparation process of monovalent selective ion exchange membranes remains intricate, resulting in high membrane preparation costs. Nanofiltration membranes can combine size sieving and Donan effect simultaneously to achieve monovalent / multivalent ion separation. Typically, nanofiltration membranes have a negative charge on their surface, so they need to be modified with positively charged polyelectrolytes (such as polyethyleneimine) before being used in magnesium and lithium ion separation processes. However, lithium ions separated by nanofiltration require additional enrichment by reverse osmosis or electrodialysis, which increases process flow and operating costs. Summary of the invention
[0003] The technical problem to be solved by the present invention is that in the process of separating lithium by conventional nanofiltration membranes, it is necessary to further enrich the lithium-containing solution, which makes the process steps complicated. The present invention has developed for the first time an integrated membrane that integrates nanofiltration and electrodialysis functions through a one-step co-scraping and interfacial polymerization (IP) process. This integrated eNF membrane can achieve monovalent / divalent ion separation and monovalent ion concentration during the electrodialysis process. First, the nanofiltration layer can achieve precise separation of monovalent / divalent ions through the Donan effect and pore size screening; then, during the electrodialysis process, the ion exchange layer will repel ions of the same charge and attract ions of the opposite charge, thereby achieving the concentration of ions from the fresh water side to the concentrated water side; finally, under the synergistic effect of the nanofiltration layer and the ion exchange layer, the eNF membrane can achieve the separation of monovalent / divalent ions and the enrichment of monovalent ions in one step ( Figure 1 ). This eNF membrane that integrates electrodialysis and nanofiltration provides an efficient and scalable new membrane material and process for mixed ion separation and ion concentration.
[0004] An electrodialysis-nanofiltration integrated membrane comprises a first integrated membrane and a second integrated membrane;
[0005] The first integrated film comprises: a base layer;
[0006] A cation exchange resin support layer, a polymer support layer and a positively charged nanofiltration membrane layer are sequentially loaded on the surface of the base layer;
[0007] The second integrated film comprises: a base layer;
[0008] An anion exchange resin support layer, a polymer support layer and a negatively charged nanofiltration membrane layer are sequentially loaded on the surface of the base layer.
[0009] The cation exchange resin support layer is formed by mixing cation exchange resin and polymer; the anion exchange resin is formed by mixing anion exchange resin and polymer; the main substrate used in the polymer support layer is polymer.
[0010] The polymer includes polyethylene glycol and polymer; the polymer is one or a mixture of regenerated cellulose, diacetyl cellulose, triacetyl cellulose, mixed cellulose, polysulfone, sulfonated polysulfone, polyethersulfone, polypropylene, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polysulfoneamide, polyether ketone, polyfatty amide, polyimide, and polyetherimide.
[0011] The functional groups in the cation exchange resin are one or more of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups or phenolic hydroxyl groups; the functional groups in the anion exchange resin are one or more of quaternary amine groups, primary amine groups, secondary amine groups or tertiary amine groups.
[0012] The base layer is non-woven fabric.
[0013] The negatively charged nanofiltration membrane has a negative zeta potential value in the range of pH 5-10; the positively charged nanofiltration membrane has a positive zeta potential value in the range of pH 3-6.
[0014] The negatively charged nanofiltration membrane is obtained by interfacial polymerization of piperazine monomers and acyl chloride monomers, and the positively charged nanofiltration membrane is obtained by interfacial polymerization of amine monomers and acyl chloride monomers.
[0015] The method for preparing the electrodialysis-nanofiltration integrated membrane comprises the following steps:
[0016] Dissolving a cation exchange resin in a polymer solution to obtain a first resin solution; coating the first resin solution on a base layer, and then coating the polymer solution, and then performing a coagulation bath to obtain a first resin-based membrane; forming a positively charged nanofiltration membrane layer on the surface of the first resin-based membrane by an interfacial polymerization method to obtain a first integrated membrane;
[0017] The anion exchange resin is dissolved in the polymer solution to obtain a second resin solution; the second resin solution is coated on the base layer, and then the polymer solution is further coated, followed by a coagulation bath to obtain a second resin base membrane; a negatively charged nanofiltration membrane layer is formed on the surface of the second resin base membrane by interfacial polymerization to obtain a second integrated membrane.
[0018] The polymer solution contains 10-30% of polymer, 30-55% of solvent and 30-55% of polyethylene glycol in weight percentage; the concentration range of the first resin solution is 5-20%, and the concentration range of the second resin solution is 5-20%.
[0019] The coating method is knife coating.
[0020] In the process of forming a positively charged nanofiltration membrane layer by interfacial polymerization, the aqueous solution contains 0.5-5wt% piperazine monomers, the contact time is 1-10min, and the oil phase solution contains 0.05-0.5wt% acyl chloride monomers, the contact time is 0.5-5min;
[0021] In the process of forming the negatively charged nanofiltration membrane layer by interfacial polymerization, the aqueous solution contains 0.5-5wt% amine monomers, the contact time is 1-10 minutes, and the oil phase solution contains 0.05-0.5wt% acyl chloride monomers, the contact time is 0.5-5 minutes.
[0022] An electrodialysis device comprises a cation exchange membrane and an anion exchange membrane, wherein the cation exchange membrane is a first integrated membrane and the anion exchange membrane is a second integrated membrane; and wherein the dilute liquid chamber is formed by a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane facing each other, and the concentrated liquid chamber is formed by a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane facing each other.
[0023] A lithium extraction process for separating magnesium from lithium is carried out using an electrodialysis device. After an electric field is formed, monovalent ions pass through a first integrated membrane to reach a concentrated chamber, while divalent ions are retained in a dilute chamber by the first integrated membrane.
[0024] The beneficial effects of the present invention are:
[0025] Through the differentiated construction of the ion exchange layer and nanofiltration layer of the iNF membrane, an electrodialysis-nanofiltration integrated membrane was successfully prepared, realizing the integrated integration of the electrodialysis-nanofiltration process. Compared with the traditional segmented integration process, this integrated integration process can simultaneously realize the separation of mixed ions and ion enrichment processes. The nanofiltration layer can achieve efficient separation of lithium and magnesium through pore size screening and Donnan effect. The ion exchange layer realizes the enrichment of lithium resources based on electrochemical processes and dialysis diffusion processes. Through the synergistic effect of the nanofiltration layer and the ion exchange layer, lithium-magnesium separation and lithium concentration are achieved in one step, simplifying the lithium extraction process from salt lakes.
[0026] Since the integrated membrane has good separation performance for monovalent and divalent salts, it can also be applied to other wastewater resource utilization to deeply separate monovalent and divalent ions therein. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 :Schematic diagram of electrodialysis-nanofiltration integrated membrane separation.
[0028] Figure 2 : Schematic diagram of the electrodialysis process.
[0029] Figure 3 :SEM photos of the membrane. (a) Surface morphology without transition layer, no nodular structure on the surface; (b) Surface morphology with transition layer, nodular structure on the surface.
[0030] Figure 4 :eNF + and eNF - Zeta potential of the membrane surface, 1 mM KCl solution was used as the background electrolyte.
[0031] Figure 5 : NF + and eNF + The process of ion transfer through a membrane in an electric field.
[0032] Figure 6 : Electrodialysis performance of eNF membrane at different magnesium-lithium mass ratios. DETAILED DESCRIPTION
[0033] Preparation of eNF membrane
[0034] Preparation of two double-layer basement membranes
[0035] Anion exchange resin (AER) and cation exchange resin (CER) were placed in a freeze dryer to remove moisture. Then, the resins were placed in a planetary nano ball mill for crushing. Finally, the crushed resin powder was filtered with a 400 mesh sieve to obtain the desired anion exchange resin powder and cation exchange resin powder. A specified amount of polyethersulfone (PES) was dissolved in a mixed solution of N,N-dimethylacetamide (DMAc) and polyethylene glycol 400 (PEG 400) and vigorously stirred at 56°C for 8h to prepare a PES solution. Subsequently, the PES solution and the anion exchange resin powder were mixed and vigorously stirred at 30°C until a uniform PES-AER solution was formed (so that the resin concentration was about 10%). The PES solution and the cation exchange resin powder were mixed and vigorously stirred at 30°C until a uniform PES-CER solution was formed (so that the resin concentration was about 10%).
[0036] Two double-layer base membranes with different properties were prepared using a one-step co-scraping technique. (1) A PES-AER solution as a support layer was scraped onto a glass plate with non-woven fabric using a scraper with a thickness of 100 μm; (2) A second 200 μm scraper was used to scrape the PES solution onto the support layer; (3) Both scrapers were scraped at a constant speed; (4) The prepared double-layer base membrane was immersed in a coagulation bath and then stored in deionized water. The obtained base membrane was named PES-AER base membrane. PES-CER base membrane was prepared using the same steps. In addition, a single-layer PES base membrane was prepared as a control group.
[0037] Table 1 Properties of anion and cation exchange resins
[0038]
[0039]
[0040] Table 2 Preparation conditions of double-layer base film
[0041]
[0042] Preparation of integrated eNF membrane
[0043] Detailed preparation steps of the integrated eNF membrane: PIP / water solution (2 wt / v%) was poured on the dried PES-AER base membrane and soaked for 5 min, and then the excess solution was removed using a roller. Next, the membrane was soaked in TMC / n-hexane solution (0.1 wt / v%) for 2 min, and the excess solution was poured off. Finally, the membrane was stored in deionized water, and the resulting membrane was named eNF -The polyethyleneimine (PEI) / water solution (2 wt / v%) was poured onto the dried PES-CER-based membrane and soaked for 5 min, and then the excess solution was removed using a roller. Next, the membrane was soaked in TMC / n-hexane solution (0.1 wt / v%) for 2 min, and the excess solution was poured off. Finally, the membrane was stored in deionized water, and the resulting membrane was named eNF + In addition, a control NF membrane without adding ion exchange resin was prepared on the PES-based membrane using the same interfacial polymerization process.
[0044] The surface chemical properties and membrane structure of the prepared eNF membrane were analyzed by FESEM, FTIR, XPS, Zeta streaming potential analyzer, etc. The membrane pore size and the cation concentration in the mixed solution were tested by TOC and ICP, respectively.
[0045] Electrodialysis separation performance test
[0046] The eNF was characterized using a six-chamber electrodialysis device. - Membranes and eNF + The ion transport performance of the membrane, the effective membrane area of the system is 6.25cm 2 , the current is provided by a DC power supply ( Figure 2 ). A negatively charged nanofiltration membrane is loaded on the surface of the anion exchange membrane, and a positively charged nanofiltration membrane is loaded on the surface of the cation exchange membrane. The two are arranged alternately, and one side of the negatively charged nanofiltration membrane is opposite to the other side of the positively charged nanofiltration membrane, forming a dilute liquid chamber, while the cation exchange membrane is opposite to the anion exchange membrane, forming a concentrated liquid chamber; a positive electrode is set on the other side of the dilute chamber, and a negative electrode is set on the other side of the concentrated chamber. When an electric field is applied between the positive and negative electrodes, lithium ions pass through the positively charged nanofiltration membrane loaded on the surface of the cation exchange membrane and enter the concentrated chamber, while magnesium ions remain in the dilute chamber.
[0047] To reduce the resistance in the system, the initial solution in the concentration chamber is 200 mL of 0.01 M LiCl solution. Therefore, when testing the lithium content in the concentration chamber, the initial lithium content needs to be excluded. The initial solution in the dilution chamber is 1000 mL of 0.07 M LiCl and 0.42 M MgCl 2 The initial solution in the polar chamber was 500 mL of 0.2 M Na 2 SO 4 The flow rate of the solution in the dilution chamber, concentration chamber and pole chamber is 1 L h -1 For eNF - Membrane, nanofiltration layer faces the dilution chamber; for eNF + Membrane, nanofiltration layer faces the concentrating chamber.
[0048] In order to evaluate the ion transport properties of the membrane, the ion flux was calculated based on the change in ion concentration in the concentrating compartment:
[0049]
[0050] Among them, J M n+ It is M n+ Ion flux through the membrane (mol m -2 h -1 );c t and c 0 (mol L -1 ) are time t(h) and initial time M n+ The concentration of ions in the concentration chamber; V is the volume of the solution in the concentration chamber (L); A m is the effective membrane area (m 2 ).
[0051] Mg of membrane 2+ and Li + The permeation selectivity between is calculated as follows:
[0052]
[0053] in, is the lithium-magnesium selectivity. A value greater than 1 indicates that the membrane is selective for Li + Selective; J Li + and J Mg 2+ Respectively represent Li + and Mg 2+ By eNF + Ion flux through the membrane (mol m -2 h -1 );c Li + and c Mg 2+ They are Li in the concentration chamber. + and Mg 2+ concentration.
[0054] The recovery rate of ions (Y,%) was calculated by the following formula:
[0055]
[0056] Among them, m M n+ and m M n+’ They represent the mass of ions in the concentrating compartment and the initial mass of ions in the diluting compartment, respectively.
[0057] In the electrodialysis process, the current efficiency (η,%) and specific energy consumption (W, kWh mol -1 Li + )for:
[0058]
[0059] Among them, c Li + and V Li + Li + Concentration in the concentrating compartment (mg L -1 ) and volume (L); z is Li + valence state; F is the Faraday constant (96485C mol -1 ); I and t are the current (A) and the test time (h); U is the applied voltage (V); n Li + Li in the concentration chamber + The increase in the number of moles.
[0060] The water absorption rate was determined as follows: the membrane was soaked in deionized water at 25°C for 24 hours, then the membrane was taken out, the excess solution was rolled off with a roller, and the weight of the wet membrane was quickly weighed on an analytical balance. The membrane was vacuum dried at 60°C until the weight no longer changed, and the weight of the dry membrane was obtained. The water absorption rate (WU, %) of the membrane was calculated using the following formula:
[0061]
[0062] Among them, W wet and W dry Represent the wet film weight (g) and dry film weight (g), respectively.
[0063] The ion exchange capacity (IEC) of the membrane was determined by acid-base back titration. Before the determination, the membrane was rinsed with deionized water and then immersed in 4 wt% HCl, 4 wt% NaOH and 4 wt% HCl for 24 h, followed by thorough rinsing with deionized water. Then, each sample was immersed in 2 M NaCl solution for 24 h, 2 drops of phenolphthalein were added and titrated with 0.1 M NaOH. The IEC of the membrane (mmol g) was calculated using the following formula: -1 ):
[0064]
[0065] Among them, c NaOH is the concentration of NaOH, ΔV is the volume of NaOH consumed (mL), W dry is the mass of the dry film (g).
[0066] The membrane pore size and pore size distribution were measured using PEG solutions of different molecular weights at a concentration of 100 ppm as feed solution. TOC was used to analyze the solute concentration on the feed side and the permeate side. The pore size distribution of the membrane can be expressed as follows:
[0067]
[0068] Among them, r p is the effective pore radius of the membrane, μ p is the molecular radius when R = 50%, σ p It is the ratio of the molecular radius when R = 84.13% to the molecular radius when R = 50%. The MWCO of the membrane is equal to the molecular radius when R = 90%.
[0069] The integrated eNF membrane matrix was prepared by a one-step co-blade coating method. The membrane matrix has a unique double-layer structure, with the top layer consisting of pure PES and the bottom layer consisting of a mixture containing PES and ion exchange resin. A typical IP process was performed on the base membrane to form a dense polyamide layer. According to the above method, four NF membranes were prepared, namely NF + NF - 、eNF + and eNF - In addition, a double-layer base film without interfacial polymerization was prepared as a control group.
[0070] First, the formation of the nanofiltration layer was studied to confirm the successful preparation of the eNF membrane. For the double-layer base membrane without a transition layer, it was difficult to form a complete nanofiltration layer because the membrane surface was too rough. The base membrane with a transition layer and an ion exchange layer was prepared by a one-step co-scraping technique. The membrane surface changed from a wavy structure to a smooth structure. After interfacial polymerization, a typical nodular structure appeared on the membrane surface, indicating that the nanofiltration layer was successfully formed ( Figure 3 ). Cation exchange resin and anion exchange resin were successfully introduced into the double-layer base membrane. The ion exchange layer composed of ion exchange resin and PES can show specific ion rejection behavior under electric field. The surface potential of eNF membrane was characterized by Zeta streaming potential analyzer. Figure 4 As shown in the figure, the eNF- membrane prepared with PIP as the aqueous monomer exhibits a significant negative potential, which is due to the hydrolysis of the exposed acyl chloride groups of TMC into carboxyl groups. When the hydrogen ions of the carboxyl groups are ionized, the membrane exhibits a negative potential. The eNF+ membrane prepared with PEI as the aqueous monomer exhibits a significant positive potential. Although the eNF+ membrane also has exposed acyl chloride groups, the membrane exhibits a positive potential due to the greater number of exposed amino groups of PEI. Due to the charge on the surface of the eNF membrane, the membrane has excellent monovalent / divalent ion selectivity.
[0071] Electrodialysis performance test
[0072] The ion transport properties of the eNF membrane were tested using a homemade electrodialysis device. 0.2 M Na 2 SO 4 Solution (500 mL). The dilution chamber was added with 0.07 M LiCl and 0.42 M MgCl 2 The mixed solution (1000mL) was added to the concentration chamber to reduce the resistance of the test system. 0.01M lithium chloride (200mL) was added to the concentration chamber to reduce the resistance of the test system. Therefore, when detecting the lithium content in the concentration chamber, the interference of the initial lithium content needs to be eliminated. For comparison, a NF membrane without an ion exchange layer and a double-layer base membrane without a nanofiltration layer were selected (Table 3 lists the physicochemical properties and electrodialysis performance of the three membranes).
[0073] Table 3 Physicochemical properties and electrodialysis performance of the three membranes
[0074]
[0075] Due to the Donan effect, NF membranes have good lithium-magnesium separation selectivity, but Li + The flux is very low. This is because the NF membrane is composed of pure PES polymer, and the surface resistance of the membrane is relatively large, which hinders the transfer of ions. The double-layer base membrane shows the opposite trend, with a higher ion flux and poor lithium-magnesium selectivity. This is because the double-layer base membrane has a larger pore size and weaker surface charge, which makes Mg 2+ and Li + The difference in the rate of passing through the membrane is small, resulting in poor lithium-magnesium selectivity. In contrast, the eNF membrane exhibits excellent lithium-magnesium selectivity and ion flux. This is because the nanofiltration layer of the eNF membrane can achieve precise separation of monovalent / divalent ions through the Donnan effect. At the same time, under the action of the electric field, the ion exchange layer of the eNF membrane can repel ions of the same charge and promote the transport of ions of the opposite charge. The synergistic effect of the nanofiltration layer and the ion exchange layer makes Li + Mg is continuously enriched from the dilution chamber to the concentration chamber, and Mg 2+ The above results show that the eNF membrane with nanofiltration and ion exchange functions can simultaneously separate lithium and magnesium and achieve lithium enrichment under potential drive.
[0076] In order to verify the ion transfer mechanism of eNF membrane in electric field, the physical and chemical properties of NF membrane and eNF membrane were characterized. The pore size distribution of the two membranes was tested using four neutral organic compounds: PEG 200, PEG 400, PEG 600 and PEG 1000, and the surface charge change of the membrane was studied using Zeta potential analyzer. + Membranes and eNF + The surface pore sizes of the membranes are 0.46 and 0.45 nm, respectively, which are close to those of Mg 2+The hydration radius of Li (0.428nm) is larger than that of Li + The hydration radius of the membrane is 0.382nm, and the electrostatic repulsion of the membrane to Li+ is weak, so most of the Li + Can permeate the membrane. In addition, NF + and eNF + The surface of the membrane exhibits a typical positive charge. Due to the reasonable construction of surface pore size and surface charge, NF + Membranes and eNF + The membrane exhibits excellent lithium-magnesium selectivity. However, since the NF membrane is not doped with conductive materials, the membrane surface resistance is large, which hinders the transfer of ions in the electric field and leads to low ion flux. The above results show that the key to the simultaneous separation of lithium and magnesium and lithium enrichment of eNF membranes lies in: (1) the pore size of the membrane surface is close to that of Mg 2+ The hydration radius is larger than Li + hydration radius; (2) the membrane surface carries positive charge; (3) an ion exchange layer that promotes ion transport. Based on the above three points, the eNF membrane can achieve lithium-magnesium separation through pore size screening and Donan effect. At the same time, under the drive of the external electric field, the selective permeability of the ion exchange layer is utilized to cause directional migration of anions and cations, thereby achieving lithium resource enrichment. The specific ion transfer process is as follows Figure 5 shown.
[0077] The effect of the feed solution magnesium-lithium ratio on the separation performance of eNF membrane was studied by using a homemade electrodialysis device. Solutions with magnesium-lithium mass ratios of 1, 20, and 50 were prepared respectively. + The concentration of Li was 0.07 M. The prepared solution was placed in the dilution chamber and operated continuously for 24 hours. The Li + and Mg 2+ content, and calculate the magnesium-lithium mass ratio. Figure 6 As shown in the figure, the mass ratios of magnesium to lithium in the concentrating chamber under the three conditions are 0.041, 0.84 and 3.36 respectively. The above results show that with the increase of the mass ratio of magnesium to lithium, the lithium-magnesium selectivity of the eNF membrane decreases, but it is still at a high level. Under the condition of a magnesium-to-lithium mass ratio of 20, the performance parameters of the eNF in the electrodialysis process were studied in detail. As shown in the figure, during the entire test process, Li + The flux continued to decline, while Mg 2+ The flux remains basically unchanged. This is because the Li + The decrease in concentration leads to an increase in resistance, which limits the Li + However, during the entire test, Li + The flux is about Mg 2+ The flux is 4 times higher. This is due to the Donnan exclusion effect of the nanofiltration layer, which hinders the Mg 2+The transmembrane transport of Li+Mg+ makes the eNF membrane show excellent lithium-magnesium selectivity. + The recovery rate can reach 45%, while Mg 2+ As low as 2.75%. Further extending the test time, Li + The recovery rate of Mg increased to 65%, while 2+ The recovery rate is always low. This shows that the eNF membrane can achieve accurate separation of lithium and magnesium and recovery of lithium resources through the electrodialysis process. In addition, after 24 hours of testing, the Li + The concentration rises to 600 mg / L, which is the initial Li + The above results show that the eNF membrane can achieve the separation of lithium and magnesium and lithium enrichment through the synergistic effect of the nanofiltration layer and the ion exchange layer.
[0078] The specific energy consumption and performance of the single electrodialysis process, single nanofiltration process, electrodialysis-nanofiltration segmented integrated process and electrodialysis-nanofiltration integrated process are listed in Table 4. It can be found that the electrodialysis-nanofiltration integrated process achieves the best performance with lower energy consumption. The above results show that the electrodialysis-nanofiltration integrated membrane provides a new, efficient, green and scalable option for lithium extraction from salt lakes.
[0079] Table 4 Comparison of specific energy consumption and performance of single electrodialysis process, single nanofiltration process, electrodialysis-nanofiltration segmented integrated process and electrodialysis-nanofiltration integrated process
[0080]
[0081]
[0082] It can be seen that the preparation process of this integrated eNF membrane is simple and efficient, and it achieves efficient extraction of salt lake lithium resources with high cost-effectiveness. This multi-separation function integrated process provides a simple, economical and environmentally friendly new way to separate complex materials in the future. In addition, it can also be applied to the resource reuse of other water sources in the salt lake industry, such as the tailings water discharged from the salt lake industry during the development of salt lake resources, after the initial extraction of potassium, magnesium and other resources, which still contains a certain amount of lithium, as well as the wastewater from the evaporation crystallization, precipitation and other process steps in the salt lake industry, the lithium in which can be recovered through further treatment.
Claims
1. An electrodialysis-nanofiltration integrated membrane, characterized in that: including a first integrated membrane and a second integrated membrane; The first integrated film comprises: a base layer; A cation exchange resin support layer, a polymer support layer and a positively charged nanofiltration membrane layer are sequentially loaded on the surface of the base layer; The second integrated film comprises: a base layer; An anion exchange resin support layer, a polymer support layer and a negatively charged nanofiltration membrane layer are sequentially loaded on the surface of the base layer.
2. The electrodialysis-nanofiltration integrated membrane according to claim 1, characterized in that: The cation exchange resin support layer is formed by mixing cation exchange resin and polymer; the anion exchange resin is formed by mixing anion exchange resin and polymer; the main substrate used in the polymer support layer is polymer.
3. The electrodialysis-nanofiltration integrated membrane according to claim 1, characterized in that: The polymer includes polyethylene glycol and polymer; the polymer is one or a mixture of regenerated cellulose, diacetyl cellulose, triacetyl cellulose, mixed cellulose, polysulfone, sulfonated polysulfone, polyethersulfone, polypropylene, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl chloride, polysulfoneamide, polyether ketone, polyfatty amide, polyimide, and polyetherimide.
4. The electrodialysis-nanofiltration integrated membrane according to claim 1, characterized in that: The negatively charged nanofiltration membrane has a negative zeta potential value in the range of pH 5-10; the positively charged nanofiltration membrane has a positive zeta potential value in the range of pH 3-6.
5. The electrodialysis-nanofiltration integrated membrane according to claim 1, characterized in that: The negatively charged nanofiltration membrane is obtained by interfacial polymerization of piperazine monomers and acyl chloride monomers, and the positively charged nanofiltration membrane is obtained by interfacial polymerization of amine monomers and acyl chloride monomers.
6. The method for preparing the electrodialysis-nanofiltration integrated membrane according to claim 1, characterized in that: The steps include: Dissolving a cation exchange resin in a polymer solution to obtain a first resin solution; coating the first resin solution on a base layer, and then coating the polymer solution, followed by a coagulation bath to obtain a first resin base film; forming a positively charged nanofiltration membrane layer on the surface of the first resin-based membrane by interfacial polymerization to obtain a first integrated membrane; dissolving an anion exchange resin in the polymer solution to obtain a second resin solution; The second resin solution is applied on the base layer, and then the polymer solution is applied, followed by a coagulation bath to obtain a second resin base film; A negatively charged nanofiltration membrane layer is formed on the surface of the second resin-based membrane by interfacial polymerization to obtain a second integrated membrane.
7. The preparation method according to claim 6, characterized in that: The polymer solution contains 10-30% of polymer, 30-55% of solvent and 30-55% of polyethylene glycol in weight percentage; the concentration range of the first resin solution is 5-20%, and the concentration range of the second resin solution is 5-20%.
8. The preparation method according to claim 6, characterized in that: In the process of forming a positively charged nanofiltration membrane layer by the interfacial polymerization method, the aqueous phase solution contains 0.5-5wt% piperazine monomers, the contact time is 1-10 minutes, and the oil phase solution contains 0.05-0.5wt% acyl chloride monomers, the contact time is 0.5-5 minutes; in the process of forming a negatively charged nanofiltration membrane layer by the interfacial polymerization method, the aqueous phase solution contains 0.5-5wt% amine monomers, the contact time is 1-10 minutes, and the oil phase solution contains 0.05-0.5wt% acyl chloride monomers, the contact time is 0.5-5 minutes.
9. An electrodialysis device, comprising a cation exchange membrane and an anion exchange membrane, wherein the cation exchange membrane is the first integrated membrane described in claim 1, and the anion exchange membrane is the second integrated membrane described in claim 1; and wherein the dilute liquid chamber is formed by a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane facing each other, and the concentrated liquid chamber is formed by a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane facing each other.
10. A lithium extraction process for separating monovalent and divalent ions, characterized in that: The electrodialysis device according to claim 9 is used to form an electric field so that monovalent ions pass through the first integrated membrane to reach the concentrated chamber, while divalent ions are retained in the dilute chamber by the first integrated membrane.