A stimuli-responsive graphene oxide composite film, and a preparation method and application thereof

Abstract

The application discloses a kind of stimulus-responsive graphene oxide composite membranes and preparation method and application thereof, belong to membrane separation and resource recovery technical field.The preparation method of the stimulus-responsive graphene oxide composite membrane includes the following steps: graphene oxide dispersion liquid and sodium alginate dispersion liquid are mixed while adjusting pH value to 3~5, vacuum filtration is carried out, and membrane material is obtained;The membrane material is mixed with calcium chloride solution, dried, and the stimulus-responsive graphene oxide composite membrane is obtained.The graphene oxide composite membrane has the advantages of membrane separation and intelligent response system, is suitable for lithium battery recovery waste liquid, mining wastewater and other various complex environments, and has important scientific significance and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation and resource recycling technology, and more specifically relates to a stimulus-responsive graphene oxide composite membrane, its preparation method and application. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles and energy storage, the demand for lithium resources continues to grow rapidly. Lithium iron phosphate (LFP) dominates the cathode material for power batteries due to its low cost, high safety, and good cycle stability. However, the production and recycling processes of LFP batteries generate large amounts of low-concentration lithium-containing wastewater. In this wastewater, lithium ions typically coexist with multivalent metals such as iron ions. The complex chemical composition and low concentration of LFP lead to problems such as high reagent consumption, complex processes, low selectivity, and secondary pollution in traditional lithium recovery processes (e.g., chemical precipitation, solvent extraction, ion exchange, and electrochemical methods).

[0003] Traditional chemical precipitation and solvent extraction methods, while achieving high lithium purity, have narrow operating windows and require strict pH control, often involving the use of large amounts of chemical reagents and wastewater discharge, which is inconsistent with the trend of green chemical engineering. Adsorption / ion exchange methods perform well in high-concentration brines, but have limited adsorption capacity in dilute solutions; electrochemical methods require high energy consumption and complex equipment, limiting their application in continuous industrial production. Therefore, achieving selective enrichment of low-concentration lithium ions under mild aqueous conditions has become a significant technical bottleneck in the current lithium recovery field.

[0004] In recent years, membrane separation technology has attracted widespread attention due to its low energy consumption, continuous operation, and strong structural designability. Among them, nanofiltration membranes and ion exchange membranes can achieve selective ion transport through size sieving and charge repulsion, but their performance is often limited by the "permeability-selectivity trade-off," and they are prone to problems such as chemical degradation and membrane structure collapse in complex systems containing polyvalent metal ions.

[0005] Graphene oxide is considered an ideal matrix material for constructing two-dimensional layered ion channels due to its tunable interlayer spacing, abundant oxygen-containing functional groups (carboxyl, hydroxyl, and epoxy groups), and excellent mechanical stability. The nanochannels between graphene oxide layers can achieve selective ion separation by regulating ion transport through a combination of electrostatic repulsion and size sieving. However, pristine graphene oxide films are prone to expansion or compaction in aqueous environments, leading to changes in interlayer spacing and channel instability. Furthermore, the limited difference in hydration radii between lithium and iron ions results in poor selectivity when relying solely on physical sieving. In addition, lithium ions require partial dehydration to enter the nanochannels of graphene oxide, a process with a high energy barrier, further weakening the selective enrichment effect of lithium.

[0006] Therefore, developing a structurally stable, environmentally friendly, and stimulus-responsive composite membrane based on graphene oxide can not only achieve efficient and selective separation of lithium ions and iron ions under mild aqueous conditions, but also provide a new approach for the enrichment and resource utilization of lithium in dilute solutions. Summary of the Invention

[0007] The purpose of this invention is to provide a stimulus-responsive graphene oxide composite membrane, its preparation method, and its applications, thereby addressing the problems existing in the prior art. This graphene oxide composite membrane combines the advantages of membrane separation and intelligent response systems, making it suitable for various complex environments such as lithium battery recycling wastewater, mining and metallurgical wastewater, and salt lake brine, and possessing significant scientific value and application prospects.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] One of the technical solutions of this invention is: a method for preparing a stimulus-responsive graphene oxide composite film, comprising the following steps:

[0010] The graphene oxide dispersion and sodium alginate dispersion were mixed and the pH value was adjusted to 3-5. The mixture was then vacuum filtered to obtain the membrane material.

[0011] The membrane material is mixed with a calcium chloride solution and dried to obtain the stimulus-responsive graphene oxide composite membrane.

[0012] Preferably, the concentration of the graphene oxide dispersion is 1 mg / mL; and the concentration of the sodium alginate dispersion is 2 mg / mL.

[0013] Preferably, the O / C ratio of graphene oxide in the graphene oxide dispersion is 0.3~0.5, and the surface functional groups include carboxyl groups, hydroxyl groups and epoxy groups.

[0014] Preferably, the mixing time of the graphene oxide dispersion and the sodium alginate dispersion is 5 to 15 minutes.

[0015] Preferably, the vacuum filtration includes: placing the mixed liquid obtained by mixing in a vacuum filter for vacuum filtration for 3-6 hours, wherein the membrane used for vacuum filtration includes a polyethersulfone filter membrane with a thickness of 47 mm and a pore size of 0.03 μm.

[0016] Preferably, the concentration of the calcium chloride solution is 0.1~0.5 mol / L.

[0017] Preferably, the specific steps for mixing the membrane material and the calcium chloride solution are as follows: mixing the membrane material with an excess of calcium chloride solution.

[0018] Preferably, the drying temperature is 25~30℃, the humidity is 30~40%, and the time is 12~24h.

[0019] The second technical solution of the present invention is to provide a stimulus-responsive graphene oxide composite film prepared by the above preparation method.

[0020] The third technical solution of the present invention is to provide the application of the above-mentioned stimulus-responsive graphene oxide composite membrane in the field of lithium enrichment, wherein the lithium enrichment field is the enrichment and separation of lithium in low-concentration waste liquid containing polymetallic ions in battery recycling or hydrometallurgy.

[0021] The stimulus-responsive graphene oxide composite membrane prepared in this invention consists of graphene oxide sheets and sodium alginate self-assembled to form hydrophilic interlayer nanochannels. Subsequently, calcium ion crosslinking is used to regulate the channel geometry and interfacial charge, thereby achieving lithium enrichment. Specifically, introducing natural polymer sodium alginate into the interlayer effectively enhances the membrane's structural stability and hydration environment regulation capability. Sodium alginate is a widely available and inexpensive natural anionic polysaccharide containing abundant carboxyl groups, which can form complex crosslinked structures with metal ions. In particular, the "egg-box model" complexation characteristic of calcium ions with sodium alginate enables the formation of a controllable ionic crosslinking network within the graphene oxide interlayer. When sodium alginate is inserted into the graphene oxide interlayer, it stabilizes the nanochannel structure through hydrogen bonding and electrostatic interactions, while simultaneously providing specific coordination sites for metal ions. The introduction of calcium ions for post-treatment crosslinking not only improves the mechanical properties and structural stability of the composite membrane but also endows the system with stimulus-responsive characteristics: Ca... 2+ The complexation can dynamically adjust the charge distribution and channel size between the composite membrane layers, thereby controlling the permeation behavior of ions with different valence states. While maintaining a constant permeation amount of iron ions, it can further weaken the migration of lithium ions, thus achieving lithium enrichment. Based on this characteristic, a two-stage linkage enrichment system achieves high selectivity and a high enrichment factor for simulated lithium iron phosphate waste liquid, with low energy and reagent consumption and continuous operation. The membrane is suitable for lithium enrichment and separation in battery recycling and hydrometallurgical waste liquids containing multiple metal ions.

[0022] The present invention discloses the following technical effects:

[0023] This invention utilizes a layered composite structure co-assembled with graphene oxide and sodium alginate, which is stabilized through hydrogen bonding and ion interactions, significantly suppressing expansion and compaction under aqueous conditions. Compared to pure graphene oxide membranes, the introduction of sodium alginate improves the membrane's water stability, interlayer spacing, and mechanical properties, ensuring the membrane maintains flux and selectivity stability during long-term operation. The hydrophilic microenvironment provided by sodium alginate lowers the ion dehydration barrier, and combined with the nanochannels and interfacial charge effects of graphene oxide, achieves high water flux while improving the separation selectivity for lithium and iron ions. By introducing calcium ions to form an "egg-box" crosslinking, the membrane's channel geometry and interfacial charge can be dynamically controlled, endowing graphene oxide with a dynamically tunable functional structure, achieving a transition from selective lithium ion permeation to selective iron ion permeation, thus achieving lithium enrichment. Attached Figure Description

[0024] Figure 1 The images are scanning electron microscope (SEM) images of the graphene oxide and sodium alginate composite film, where a is the surface of the pure graphene oxide film, b is the surface of the GO / SA1 composite film, c is the surface of the GO / SA2 composite film, and d is the cross-section of the GO / SA1 composite film.

[0025] Figure 2 X-ray diffraction patterns of graphene oxide and sodium alginate composite films with different sodium alginate contents;

[0026] Figure 3 The graph shows the thickness test results of composite films of graphene oxide and sodium alginate with different sodium alginate contents.

[0027] Figure 4 Fourier transform infrared spectra of graphene oxide, sodium alginate, and composite membrane of graphene oxide and sodium alginate.

[0028] Figure 5 Photographs of the osmosis apparatus used in water flux and ion permeation capacity experiments;

[0029] Figure 6 The graph shows the changes in water flux and interlayer spacing of graphene oxide and sodium alginate composite membranes with different sodium alginate contents.

[0030] Figure 7 The graphs show the changes in water flux and interlayer spacing of the graphene oxide and sodium alginate composite membranes prepared at different pH values.

[0031] Figure 8 A comparison of the ion permeation capacity of different metal cations in graphene oxide membranes and graphene oxide and sodium alginate composite membranes.

[0032] Figure 9The graph shows the concentration changes of lithium ions and iron ions during 8 hours of permeation in a composite membrane of graphene oxide and sodium alginate and a composite membrane of calcium ions doped with graphene oxide and sodium alginate. In the graph, a represents lithium ions and b represents iron ions.

[0033] Figure 10 To simulate the changes in the molar ratio of lithium ions to iron ions in lithium iron phosphate waste liquid with different lithium ion to iron ion molar ratios during the lithium enrichment process in a two-stage linkage enrichment system composed of a graphene oxide and sodium alginate composite membrane and a calcium ion-doped graphene oxide and sodium alginate composite membrane. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0040] The graphene oxide used in the following examples was purchased from Graphenea, Inc., USA, with an initial concentration of 4 mg / mL, a monolayer graphene oxide content greater than 95%, and an O / C ratio of 0.3-0.5. Unless otherwise specified, all other raw materials used are commercially available products, and the source of these commercially available products does not affect the technical effects of this invention.

[0041] Example 1

[0042] This embodiment provides the construction of composite membranes of graphene oxide and sodium alginate with different sodium alginate contents. The specific steps are as follows:

[0043] Preparation of graphene oxide and sodium alginate composite membranes with different sodium alginate contents:

[0044] Take 6 1 mL portions of graphene oxide dispersion (concentration 1 mg / mL) and another 1 mL portion of sodium alginate dispersion (concentration 2 mg / mL). The amounts of sodium alginate dispersion used are 0 mL, 0.25 mL, 0.5 mL, 1 mL, 1.5 mL, and 2 mL, respectively.

[0045] The above 1 mL graphene oxide dispersion was added to sodium alginate dispersions with different concentrations, and deionized water was added to bring the mixed solutions with different sodium alginate contents to a uniform total volume of 10 mL. The mixture was stirred for 10 min. The graphene oxide and sodium alginate mixed solutions with different sodium alginate contents were labeled as pure graphene oxide membrane GO, GO / SA, etc. 0.5 , GO / SA1, GO / SA2, GO / SA3, GO / SA4 (GO, GO / SA 0.5 The volumes of sodium alginate dispersions corresponding to GO / SA1, GO / SA2, GO / SA3, and GO / SA4 are 0 mL, 0.25 mL, 0.5 mL, 1 mL, 1.5 mL, and 2 mL, respectively.

[0046] The above-obtained mixed solutions of graphene oxide and sodium alginate with different sodium alginate contents were poured into a vacuum filtration device. The substrate was a polyethersulfone filter membrane with a thickness of 47 mm and a pore size of 0.03 μm. The membrane was filtered until it was dry, and the filtration time was 3 to 6 hours.

[0047] The dried composite membrane obtained after vacuum filtration was transferred to a drying cabinet. The drying cabinet was kept at a temperature of 25°C and a humidity of 30%. After drying for 24 hours, composite membranes of graphene oxide and sodium alginate with different sodium alginate contents were obtained.

[0048] Example 2

[0049] This embodiment provides the construction of composite membranes of graphene oxide and sodium alginate at different pH values. The specific steps are as follows:

[0050] Preparation of composite membranes of graphene oxide and sodium alginate with different pH values:

[0051] Take 1 mL of graphene oxide dispersion (concentration 1 mg / mL); and take 0.5 mL of sodium alginate dispersion (concentration 2 mg / mL).

[0052] The graphene oxide dispersion was added to the sodium alginate dispersion and stirred for 10 minutes. Then, 8.5 mL of deionized water was added to bring the total volume of the graphene oxide and sodium alginate mixture to a uniform 10 mL. A certain amount of dilute hydrochloric acid or sodium hydroxide solution was then added to the mixture to adjust the pH to 2, 4, 6, 8, and 10, respectively. The graphene oxide and sodium alginate mixtures with different pH values ​​were denoted as GO / SA. 1-2 GO / SA 1-4 GO / SA 1-6 GO / SA 1-8 GO / SA 1-10 ;

[0053] The above-obtained mixed solutions of graphene oxide and sodium alginate with different pH values ​​were poured into a vacuum filtration device. The substrate was a polyethersulfone filter membrane with a thickness of 47 mm and a pore size of 0.03 μm. The filtration was carried out until the membrane surface was dry, and the filtration time was 3 to 6 hours.

[0054] The dried composite membrane obtained by vacuum filtration was transferred to a drying cabinet at a temperature of 25°C and a humidity of 30% for 24 hours to obtain composite membranes of graphene oxide and sodium alginate with different pH values.

[0055] Example 3

[0056] This embodiment provides a method for preparing a calcium ion-crosslinked graphene oxide and sodium alginate composite membrane, the specific steps of which are as follows:

[0057] Preparation of calcium ion crosslinked graphene oxide and sodium alginate composite membrane:

[0058] Take 1 mL of graphene oxide dispersion (concentration 1 mg / mL); and take 0.5 mL of sodium alginate dispersion (concentration 2 mg / mL).

[0059] Add the above graphene oxide dispersion to the sodium alginate dispersion and stir for 10 min; then add 8.5 mL of deionized water to make the mixed solution of graphene oxide and sodium alginate reach a uniform total volume of 10 mL. Then add a certain amount of dilute hydrochloric acid or sodium hydroxide solution to the mixed solution to adjust the pH value to 4.

[0060] The above-obtained mixed solution of graphene oxide and sodium alginate was poured into a vacuum filtration device. The substrate was a polyethersulfone filter membrane with a thickness of 47 mm and a pore size of 0.03 μm. The membrane was filtered until it was dry, and the filtration time was 3 to 6 hours.

[0061] After the above filtration process is completed, add 10 mL of calcium chloride solution with a concentration of 0.1 mol / L to the vacuum filtration device and continue vacuum filtration until the surface of the membrane is dry.

[0062] The dried composite membrane obtained after vacuum filtration was transferred to a drying cabinet at a temperature of 25°C and a humidity of 30% for 24 hours to obtain a calcium ion crosslinked graphene oxide and sodium alginate composite membrane.

[0063] The composite membranes obtained in the above embodiments were characterized as follows:

[0064] 1. Characterization of surface and cross-sectional morphology:

[0065] Field emission scanning electron microscopy (FEM) was used to characterize the surface morphology and cross-section of pure graphene oxide and a series of composite films with different sodium alginate contents, and the differences in morphology were compared.

[0066] Figure 1 The images show scanning electron microscope (SEM) images of the graphene oxide and sodium alginate composite film, where a is the surface of the pure graphene oxide film, b is the surface of the GO / SA1 composite film, c is the surface of the GO / SA2 composite film, and d is the cross-section of the GO / SA1 composite film.

[0067] according to Figure 1 It can be seen that pure graphene oxide film ( Figure 1 a) Composite membranes GO / SA1 and GO / SA2 with a smooth surface and containing different sodium alginate contents. Figure 1 b, Figure 1 c) The surface exhibits obvious wrinkles and undulations, and the cross-section of the composite membrane ( Figure 1 d) It has a clear layered stacked structure with distinct interlayer interfaces, proving that the composite membrane is a typical two-dimensional layered channel.

[0068] 2. Characterization of the interlayer structure of graphene oxide:

[0069] X-ray diffraction was used to characterize the interlayer structure of pure graphene oxide and a series of composite films with different sodium alginate contents. The interlayer spacing of graphene oxide was calculated by substituting the 2θ peaks in the X-ray diffraction images into the Bragg formula.

[0070] Figure 2 X-ray diffraction patterns of graphene oxide and sodium alginate composite films with different sodium alginate contents.

[0071] according to Figure 2 It is known that the interlayer spacing of pure graphene oxide (GO) is 9.22 Å. The introduction of sodium alginate will increase the overall interlayer spacing of graphene oxide. The interlayer spacing of graphene oxide in composite films with different sodium alginate contents has increased to varying degrees. Among them, the interlayer spacing of GO / SA1 is the largest, reaching 9.95 Å, indicating that the introduction of sodium alginate effectively opens up the interlayer channels.

[0072] 3. Thickness characterization:

[0073] The thickness of pure graphene oxide and a series of composite films with different sodium alginate contents was characterized by a micrometer, and the thickness differences of composite films with different sodium alginate contents were compared.

[0074] Figure 3 The figure shows the thickness test results of composite films of graphene oxide and sodium alginate with different sodium alginate contents.

[0075] according to Figure 3 It is known that the thickness of the pure graphene oxide film is approximately 13 μm. With the increase of sodium alginate content, the film thickness increases accordingly. When the sodium alginate content is 300% (i.e., the amount of sodium alginate dispersion used in Example 1 is 1.5 mL), the composite film thickness can reach 45 μm, indicating that the intercalated sodium alginate has a significant impact on the overall film thickness and stacking density. This demonstrates the difference between the microscopic changes in interlayer spacing and the macroscopic changes in film thickness resulting from the introduction of sodium alginate. It also shows that a larger composite film thickness and stacking density will reduce the lithium enrichment efficiency, and a smaller composite film thickness and stacking density will reduce the film stability.

[0076] 4. Representation of functional groups:

[0077] Fourier transform infrared spectroscopy was used to characterize the functional groups of pure graphene oxide, sodium alginate powder, and a series of composite films with different sodium alginate contents, and the differences in functional groups in different materials were compared.

[0078] Figure 4 Fourier transform infrared spectrum of graphene oxide, sodium alginate, and composite film of graphene oxide and sodium alginate.

[0079] according to Figure 4 It is known that both graphene oxide and sodium alginate contain abundant oxygen-containing functional groups (such as hydroxyl and carboxyl groups). The composite film exhibits a methylene characteristic peak unique to sodium alginate, proving that sodium alginate has successfully self-assembled with graphene oxide, achieving a peak at 3300 cm⁻¹. -1 The shift in the left and right hydroxyl peaks indicates that graphene oxide and sodium alginate are stably bonded mainly through hydrogen bonds.

[0080] 5. Characterization of water permeability:

[0081] A custom-designed permeation apparatus was used to test the water permeation performance of pure graphene oxide, a series of composite membranes with different sodium alginate contents, and composite membranes with different pH values. The permeation apparatus used for the tests included... Figure 5 As shown in the diagram. The membrane to be tested was sandwiched in the middle of the osmosis apparatus. 20 mL of deionized water was placed on the left side, and 20 mL of sucrose solution (2.5 mol / L) was placed on the right side to provide osmotic pressure. The sucrose on the right side was weighed before the experiment. The total osmosis time lasted 12 hours. After the osmosis experiment was completed, the mass of the sucrose on the right side was weighed again. The difference between this mass and the mass before the osmosis experiment was used to calculate the difference in water permeability performance between the different membranes.

[0082] The formula for calculating water flux is: (mass of sucrose on the right side after 12 hours - initial mass of sucrose) / (osmotic pressure provided by sucrose × membrane area providing osmosis × osmosis time).

[0083] A 2.5 mol / L sucrose solution provides an osmotic pressure of 61 bar, and the membrane area is 7.85 × 10⁻⁶. -4 m -2 The infiltration time is 12 hours.

[0084] Figure 6 The graphs show the changes in water flux and interlayer spacing of graphene oxide and sodium alginate composite membranes with different sodium alginate contents.

[0085] according to Figure 6 It can be seen that the introduction of sodium alginate increases the water flux of the composite membrane, which is consistent with the increasing interlayer spacing trend calculated by X-ray diffraction. The moderate expansion of the channels facilitates the transport of water molecules. Among them, the GO / SA2 composite membrane has the highest water flux, reaching 40 mL / h. -1 m -2 bar -1 This demonstrates a positive correlation between interlayer spacing and water flux. Appropriately increasing the water flux improves ion separation efficiency, which in turn facilitates lithium collection.

[0086] Figure 7 The graphs show the changes in water flux and interlayer spacing of the graphene oxide and sodium alginate composite membranes prepared at different pH values.

[0087] according to Figure 7 It was found that the composite membrane of graphene oxide and sodium alginate exhibited relatively high water flux in the pH range of 4-6. Comparing the interlayer spacing at different pH values, both excessively high and low pH values ​​caused interlayer shrinkage, leading to a decrease in water flux. This indicates that the pH value during preparation can be used as an important parameter for controlling channel geometry and the hydrophilic environment. A suitable pH value can ensure an appropriate increase in water flux, which will improve ion separation efficiency and thus facilitate lithium collection.

[0088] 6. Characterization of ion permeability (short-term):

[0089] Using a custom-designed permeation device ( Figure 5 To test the ion permeation (short-term) performance of pure graphene oxide and the GO / SA1 described in Example 1, the membrane to be tested was sandwiched in the middle of the permeation device, with 20 mL of the same ion salt solution (containing lithium chloride, nickel chloride, cobalt chloride, manganese chloride, and ferric chloride, with a concentration of 0.1 mol / L on both sides) on both sides. Silver / silver chloride electrodes were connected to both sides, and a Keithley digital source meter was used to scan the voltage within a small bias range of -0.3 to 0.3 V. The changes in the permeation capacity of different ions were compared by fitting and normalizing the slope of the measured IV curve.

[0090] Figure 8 A comparison of the ion permeation capacity of different metal cations in graphene oxide membranes and composite membranes of graphene oxide and sodium alginate.

[0091] according to Figure 8 It can be seen that in pure graphene oxide membranes, lithium ions and manganese ions have relatively high ion diffusion coefficients. In composite membranes with added sodium alginate, the diffusion coefficients of most ions have decreased to varying degrees, and the difference between the diffusion coefficients of lithium ions and iron ions is the most significant, indicating that the composite membrane has a stronger ability to suppress and distinguish high-valence iron ions.

[0092] 7. Characterization of ion permeability (long-term):

[0093] Using a custom-designed permeation device ( Figure 5 To test the long-term ion permeation performance of the sodium alginate composite membrane GO / SA1 and the calcium ion crosslinked composite membrane of Example 3, the membranes to be tested were sandwiched in the middle of the permeation device. 20 mL of ion salt solution (containing lithium chloride, nickel chloride, cobalt chloride, manganese chloride, and ferric chloride, all at a concentration of 0.1 mol / L) was placed on the left side, and 20 mL of sucrose solution (2.5 mol / L) was placed on the right side to provide osmotic pressure. Samples were taken from the sucrose solution on the right side every 2 hours. At the 6th hour, calcium chloride solution (2 mol / L, 1 mL) was added to the left side to determine the effect of calcium ions on ion permeation performance. Each sample was taken in 1 mL volume and diluted with 2 wt% dilute nitric acid solution. The ion concentration of all samples was determined using inductively coupled plasma mass spectrometry (ICP-MS) to measure the long-term ion permeation capacity.

[0094] Figure 9 The graph shows the concentration changes of lithium ions and iron ions during 8 hours of permeation in a composite membrane of graphene oxide and sodium alginate and a composite membrane of calcium ions doped with graphene oxide and sodium alginate. In the graph, a represents lithium ions and b represents iron ions.

[0095] according to Figure 9 It is evident that introducing calcium ion crosslinking into the composite membrane of graphene oxide and sodium alginate significantly reduces lithium ion permeation, while iron ion permeation remains largely unaffected. This result indicates that calcium ion crosslinking can further weaken lithium ion migration while maintaining iron ion permeation, demonstrating the potential for programmable control of channel geometry and interfacial charge. This suggests that the calcium ion crosslinked graphene oxide and sodium alginate composite membrane of this invention is more conducive to achieving efficient and selective separation of lithium ions and iron ions, and is suitable for various complex environments such as lithium battery recycling wastewater and mining wastewater containing a large amount of interfering iron ions.

[0096] 8. Testing of lithium iron phosphate waste liquid simulating different lithium-ion to iron-ion molar ratios:

[0097] Using a custom-designed permeation device ( Figure 5 To test the lithium enrichment performance of a two-stage linkage enrichment system consisting of a sodium alginate composite membrane GO / SA1 and a calcium ion crosslinked composite membrane from Example 3, the sodium alginate composite membrane GO / SA1 was sandwiched in the middle of the permeation device. The left side contained 20 mL of an ionic salt solution (containing lithium chloride and ferric chloride; the lithium chloride concentration was 0.1 mol / L, and the ferric chloride concentration was set to 0.1 mol / L, 0.4 mol / L, and 0.8 mol / L respectively, depending on the initial lithium-iron molar ratio; the total volume of the mixed solution was 20 mL). The right side contained 20 mL of sucrose solution (2.5 mol / L) to provide osmotic pressure. Samples were taken from the sucrose solution on the right side after 2 hours; the solution on the right side was called permeate 1. In the second stage, a calcium ion cross-linked composite membrane was sandwiched in the middle of the permeation device. The left side contained 20 mL of ion salt solution (permeate 1 with different initial lithium-iron molar ratios from the first stage), and the right side contained 20 mL of sucrose solution (2.5 mol / L) to provide osmotic pressure. Samples were taken from the left side solution after 2 hours. The left side solution is the retentate 2. The sample volume was 1 mL, and 2 wt% dilute nitric acid solution was added to dilute it. The lithium enrichment efficiency of the two-stage linkage enrichment system was determined by inductively coupled plasma mass spectrometry to determine the ion concentration of all samples.

[0098] Calculation of selective separation factor: Separation factor = (Lithium ion concentration) 渗透 / Iron ion concentration 渗透 ) / (Lithium ion concentration) 初始 / Iron ion concentration 初始 ).

[0099] Figure 10To simulate the changes in the lithium-to-iron ion molar ratio during the lithium enrichment process of lithium iron phosphate waste liquid with different lithium-ion to iron-ion molar ratios in a two-stage linkage enrichment system composed of a graphene oxide and sodium alginate composite membrane and a calcium-doped graphene oxide and sodium alginate composite membrane, this study investigated the lithium-ion to iron-ion molar ratio variations. Figure 10 In the simulation, the lithium iron phosphate waste liquid first passes through a sodium alginate-containing composite membrane GO / SA1, where Li ions will selectively permeate. The permeate is called permeate 1. Then, permeate 1 passes through a calcium ion cross-linked composite membrane, where Fe ions will selectively permeate while Li ions are retained. The retained liquid obtained in this part is called retained liquid 2. Figure 10 The 1:1, 1:4, and 1:8 ratios represent the molar ratios of Li ions and Fe ions in the simulated lithium iron phosphate waste liquid.

[0100] according to Figure 10 It is evident that the composite membrane of graphene oxide and sodium alginate exhibits lithium enrichment effects for different initial lithium-ion to iron-ion molar ratios, with the best effect observed at the initial molar ratio, achieving a selective separation factor of 649. Furthermore, using a two-stage linkage enrichment system, the lithium-ion to iron-ion molar ratio in the retentate can be further increased by 4.2% after passing through the composite membrane cross-linked with calcium ions. This demonstrates that this two-stage linkage enrichment system can achieve gradient lithium enrichment from battery waste liquid.

[0101] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0102] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The application of a graphene oxide composite film that selectively allows Fe ions to pass through while retaining Li ions in the field of lithium enrichment, characterized in that, The method for preparing the graphene oxide composite film that selectively allows Fe ions to pass through while retaining Li ions includes the following steps: Take 1 mL of graphene oxide dispersion with a concentration of 1 mg / mL; and take 0.5 mL of sodium alginate dispersion with a concentration of 2 mg / mL. Add the above graphene oxide dispersion to the sodium alginate dispersion and stir for 10 min; then add 8.5 mL of deionized water to make the mixed solution of graphene oxide and sodium alginate reach a uniform total volume of 10 mL. Then add a certain amount of dilute hydrochloric acid or sodium hydroxide solution to the mixed solution to adjust the pH value to 4. The above-obtained mixed solution of graphene oxide and sodium alginate was poured into a vacuum filtration device. The substrate was a polyethersulfone filter membrane with a thickness of 47 μm and a pore size of 0.03 μm. The membrane was filtered until it was dry, and the filtration time was 3 to 6 hours. After the above filtration process is completed, add 10 mL of calcium chloride solution with a concentration of 0.1 mol / L to the vacuum filtration device and continue vacuum filtration until the surface of the membrane is dry. The dried composite membrane obtained by vacuum filtration was transferred to a drying cabinet. The drying cabinet was kept at a temperature of 25°C and a humidity of 30%. After drying for 24 hours, a calcium ion crosslinked graphene oxide and sodium alginate composite membrane was obtained. The lithium enrichment field refers to the enrichment and separation of lithium from low-concentration waste liquid containing polymetallic ions in battery recycling or hydrometallurgical processes. The O / C ratio of the graphene oxide is 0.3~0.5.

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