Membrane capacitive deionization module for treating high-mg / lithium ratio brine, method of making and use thereof

Abstract

The application provides a membrane capacitive deionization module for treating high magnesium-lithium ratio brine, a preparation method and application thereof. The magnesium-lithium ratio of the brine is 300-700. The preparation method comprises the following steps: firstly, mixing pickling lithium titanate molecular sieves, a binder, a conductive agent and a solvent, ball milling, coating the obtained slurry on the surface of a whisker carbon nanotube membrane to form a coating layer, and then taking the whisker carbon nanotube membrane including the coating layer as an electrode to assemble the membrane capacitive deionization module. The weight ratio of the pickling lithium titanate molecular sieves to the whisker carbon nanotube membrane is 1:(2-4). The membrane capacitive deionization module of the application realizes efficient adsorption of lithium ions by using the high selectivity of the pickling lithium titanate molecular sieves, uses the whisker carbon nanotube membrane as a current collector, simplifies the module structure by using the high conductivity and large specific surface area of the whisker carbon nanotube membrane, promotes the rapid transmission of electric charges and the uniform adsorption of lithium ions, and is suitable for brine treatment, especially for high magnesium-lithium ratio brine.

Description

Technical Field

[0001] This invention relates to the field of lithium extraction technology from brine, and more specifically, to a membrane capacitor deionization module for treating brine with a high magnesium-to-lithium ratio, its preparation method, and its application. Background Technology

[0002] Since its inception, capacitive deionization (CDI) technology has attracted widespread attention due to its potential advantages in water treatment and ion recovery. Traditional CDI technology is mainly based on the principle of double-layer adsorption, utilizing porous electrode materials to adsorb and release ions in water under the action of an electric field, thereby achieving water desalination or selective extraction of specific ions.

[0003] However, traditional CDI technology faces numerous challenges in processing brine resources with high magnesium-to-lithium ratios, limiting its widespread application in lithium extraction. 1. Limited Adsorption Capacity: The specific surface area and pore structure of traditional CDI electrode materials determine their adsorption capacity. These materials typically lack sufficient lithium-ion storage sites, resulting in limited lithium-ion adsorption and restricting the efficiency of lithium extraction from brine. 2. Poor Selectivity: Electrode materials generally lack high selective adsorption capacity for specific ions, especially in brine with multiple ion coexistence. Selective adsorption of lithium ions becomes difficult, often accompanied by non-selective adsorption of other ions, reducing the purity of recovered lithium. 3. Poor Electrode Cyclic Stability: During repeated charging and discharging, the structural stability of traditional CDI electrode materials is easily compromised, leading to decreased electrode performance, short cycle life, and increased cost and complexity of the lithium extraction process. 4. Low Efficiency: The ion adsorption and desorption processes of traditional CDI technology are typically slow, requiring long processing times, and energy consumption is high during the desorption stage, resulting in low overall energy efficiency, which is unfavorable for large-scale industrial applications.

[0004] In view of the above problems, it is urgent to develop new electrode materials and optimize process parameters to improve the selective adsorption capacity and efficiency of CDI technology in treating high magnesium-to-lithium ratio brines, while ensuring the cycle stability and long life of the electrodes. Summary of the Invention

[0005] The main objective of this invention is to provide a membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine, its preparation method, and its application, so as to solve the problems of limited adsorption capacity, poor adsorption selectivity for lithium ions, poor electrode cycle stability, and low efficiency of existing capacitor deionization technology when treating high magnesium-to-lithium ratio brine.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a membrane capacitor deionization module for treating brine with a high magnesium-to-lithium ratio is provided, wherein the magnesium-to-lithium ratio of the brine is 300-700. The preparation method includes the following steps: Step S1, acid-washed lithium titanate molecular sieve, binder, conductive agent and solvent are mixed sequentially and ball-milled to obtain a slurry; the slurry is coated on the surface of a whisker carbon nanotube membrane and dried to form a coating on the surface of the whisker carbon nanotube membrane; Step S2, using the whisker carbon nanotube membrane including the coating as an electrode, the electrode, ion exchange membrane, diaphragm, module frame, power supply and fluid delivery system are assembled to obtain a membrane capacitor deionization module; wherein the weight ratio of acid-washed lithium titanate molecular sieve to whisker carbon nanotube membrane is 1:(2-4).

[0007] Further, the preparation method of acid-washed lithium titanate molecular sieve includes the following steps: treating lithium titanate molecular sieve with an acid solution to obtain acid-washed lithium titanate molecular sieve; wherein, the acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid, the concentration of the acid is 0.1-0.6 mol / L, and the solid-liquid ratio of lithium titanate molecular sieve to acid solution is 1 g:(200-300) mL; the treatment is carried out under stirring at a temperature of 10-60℃, a rotation speed of 10-50 rpm, and a time of 6-48 h; and / or, lithium titanate... The preparation method of the molecular sieve includes the following steps: a lithium source and a titanium source are sequentially subjected to a second ball milling, calcination, and cooling to obtain a lithium titanate molecular sieve; wherein the lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium chloride, the titanium source includes titanium oxide and / or titanium chloride, and the molar ratio of the lithium source to the titanium source is (1.5~2.5):1; and / or, the rotation speed of the second ball milling is 300~600 rpm, and the time is 0.5~12 h; and / or, the calcination temperature is 700~1000℃, and the holding time is 2~24 h.

[0008] Further, in the slurry, the weight ratio of pickled lithium titanate molecular sieve to binder is (70-85):(5-15); and / or, the binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, and polytetrafluoroethylene; and / or, the weight ratio of pickled lithium titanate molecular sieve to conductive agent is (70-85):(5-15); and / or, the conductive agent includes one or more of conductive carbon black, Ketjen black, and carbon nanotubes; and / or, the weight ratio of pickled lithium titanate molecular sieve to solvent is (70-85):(100-300); and / or, the solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and propylene glycol.

[0009] Furthermore, the thickness of the whisker carbon nanotube film is 60–70 μm, and the density is 70–90 g / m³. 3The porosity is 20–60%; and / or the electrical conductivity of the whisker carbon nanotube film is 0.015–0.018 kS / cm, and the specific surface area is 12–18 m². 2 / g.

[0010] Further, in step S1, the slurry is coated on one or both sides of the whisker carbon nanotube film; and / or, the coating accounts for 50-100% of the area of ​​the whisker carbon nanotube film; and / or, the coating thickness is 10-250 μm and the coating density is 70-90 g / m². 3 Specific surface area is 4-16 m² 2 / g.

[0011] Furthermore, the electrode is applied to Li + Adsorption capacity q e The concentration is 5–17 mg / g, the adsorption rate is 15–60 mg / (g·h), and the electrode capacity decay is ≤5% after 250 cycles; and / or, the ion exchange membrane includes Fumasep FAA-3-50 anion exchange membrane and FuMA-Tech cation exchange membrane; and / or, the diaphragm includes polyvinylidene fluoride and / or polypropylene.

[0012] According to another aspect of the present invention, a membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine is provided, which is obtained by the above-described preparation method.

[0013] Furthermore, the membrane capacitor deionization module used to treat brine with a high magnesium-to-lithium ratio has a lithium adsorption rate of 20-70%, a magnesium removal rate of 95-99.9%, and a lithium enrichment factor of 1-10.

[0014] According to another aspect of the present invention, a method for treating high magnesium-to-lithium ratio brine is provided, comprising the following steps: forming a closed loop between the membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine and a DC voltage circuit; feeding the high magnesium-to-lithium ratio brine into the membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine; first adsorbing under conditions of pressure 0.8–1.6V and temperature 5–30°C for 10–35 min; then desorbing under conditions of pressure -0.8–-1.6V and temperature 5–30°C in acidic conditions for 10–35 min; and repeating the cycle 1–300 times.

[0015] Furthermore, in the composition of high magnesium-to-lithium ratio brines, Li + The content is 200-700 mg / L, Mg 2+ The content is 20,000–200,000 mg / L, K + The content is 100-3000 mg / L, Na + The content is 300-6000 mg / L, Ca 2+The content of magnesium-to-lithium ratio brine is 500–7000 mg / L, and the salinity is 20–40%; and / or, the pH of high magnesium-to-lithium ratio brine is 3–6; and / or, the flow rate of high magnesium-to-lithium ratio brine through the membrane capacitor deionization module used for treating high magnesium-to-lithium ratio brine is 5–300 mL / min.

[0016] This invention relates to a membrane capacitor deionization (MCDI) module comprising electrodes with a specific composition. Utilizing the high selectivity of acid-washed lithium titanate molecular sieves in the electrodes, efficient adsorption of lithium ions is achieved. The electrodes employ whisker-shaped carbon nanotube membranes as current collectors; their high conductivity and large specific surface area not only simplify the module structure but also promote rapid charge transport and uniform lithium ion adsorption. This electrode design, combined with the MCDI module, not only improves electrochemical performance, such as charge / discharge rates and adsorption capacity, but also offers environmental friendliness and economic advantages. It is suitable for brine treatment with varying salinity, particularly for brine with a high magnesium-to-lithium ratio. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A SEM image of the cross-section of the whisker carbon nanotube film of Embodiment 1 of the present invention is shown.

[0019] Figure 2 A SEM image of the surface of the whisker carbon nanotube film of Embodiment 1 of the present invention is shown;

[0020] Figure 3 A SEM image of the cross-section of the electrode of Embodiment 1 of the present invention is shown;

[0021] Figure 4 A SEM image of the surface of the electrode according to Embodiment 1 of the present invention is shown;

[0022] Figure 5 An EDS diagram of the electrode of Embodiment 1 of the present invention is shown;

[0023] Figure 6 The cyclic voltammetry curve of the electrode in Embodiment 1 of the present invention at a scan rate of 1 mV / s is shown.

[0024] Figure 7 A photograph of the uncut electrode of Embodiment 1 of the present invention is shown. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] As described in the background section of this invention, existing technologies for capacitive deionization suffer from limitations in adsorption capacity, poor selectivity for lithium ions, poor electrode cycle stability, and low efficiency when treating brine with a high magnesium-to-lithium ratio. To address these issues, in a typical embodiment of this invention, a method for preparing a membrane capacitive deionization module for treating brine with a high magnesium-to-lithium ratio of 300–700 is provided. The preparation method includes the following steps: Step S1, acid-washed lithium titanate molecular sieve, binder, conductive agent, and solvent are sequentially mixed and ball-milled to obtain a slurry; the slurry is coated onto the surface of a whisker carbon nanotube membrane and dried to form a coating on the surface of the whisker carbon nanotube membrane; Step S2, using the coated whisker carbon nanotube membrane as an electrode, the electrode is assembled with a cathode, an ion exchange membrane, a diaphragm, a module frame, a power supply, and a fluid delivery system to obtain the membrane capacitive deionization module; wherein the weight ratio of the acid-washed lithium titanate molecular sieve to the whisker carbon nanotube membrane is 1:(2–4). It should be noted that the magnesium-lithium ratio in this application refers to the weight ratio of magnesium to lithium.

[0027] The coating materials of this application include acid-washed lithium titanate molecular sieves (HTO), binders, conductive agents, and solvents. The acid-washed lithium titanate molecular sieves serve as the active centers of the electrode, participating in electrochemical reactions, storing charge, and promoting ion insertion and extraction, thereby achieving high-capacity lithium-ion adsorption. It should be noted that this application specifically uses acid-washed lithium titanate molecular sieves as the active material for the following reasons: First, acid washing effectively removes metal oxides and impurity ions from the surface of lithium titanate, expanding micropores and providing new pores, thus offering more adsorption sites; second, during acid washing, hydrogen ions displace lithium ions, increasing specific lithium-ion adsorption sites, enabling lithium ions to be directionally adsorbed on the surface or in the pores, significantly improving the adsorption capacity and rate of lithium ions; moreover, the active sites introduced by acid washing optimize the electrical conductivity and electrochemical stability of the material, ensuring high charge efficiency during charge-discharge cycles; third, acid washing enhances the hydrophilicity of lithium titanate and provides a higher surface charge density, which is beneficial for lithium-ion adsorption.

[0028] In summary, in high magnesium-to-lithium ratio brine, the electrode material in the membrane capacitor deionization module of this application, by using acid-washed lithium titanate molecular sieve as the active center, can adsorb ions based on the double-layer principle, and can also specifically adsorb lithium ions through ion intercalation reaction and ion exchange reaction. In comparison, the adsorption effect on magnesium ions is generally average. Therefore, when treating high magnesium-to-lithium ratio brine, lithium ion enrichment can be selectively achieved.

[0029] In addition, the slurry also includes a binder, which acts as a bridge between the active material, the conductive agent and the whisker carbon nanotube film matrix. This ensures the integrity and mechanical strength of the composite electrode structure, prevents the active material from falling off during charging and discharging, and guarantees the long-term stability and cycle performance of the electrode.

[0030] The addition of a conductive agent effectively improves the conductivity of the electrode, optimizing the overall electron transport path and ensuring uniform current distribution within the electrode. This, in turn, significantly increases the electrode's power density and charge / discharge rate. Furthermore, the conductive agent promotes ion exchange between the electrode and the electrolyte, enhancing the adsorption and desorption efficiency of lithium titanate for lithium ions. This improves the processing capacity and selectivity of the membrane capacitor deionization (MCDI) module, particularly when processing brines with a high magnesium-to-lithium ratio, effectively reducing the magnesium-to-lithium ratio and achieving lithium ion enrichment. The stable chemical properties of the conductive agent also provide additional structural support to the electrode, helping to maintain its morphological integrity during cycling. This effectively extends the module's lifespan and improves cycle stability (e.g., capacity decay ≤5% after 250 cycles).

[0031] In addition, the addition of solvents to the slurry not only enables the active materials, conductive agents and binders to be mixed evenly to form a stable slurry, but also promotes the uniform coating of the slurry on the current collector.

[0032] In summary, the combined effect of the components in the slurry can effectively improve the lithium adsorption capacity, cycle stability, and electrochemical performance of the electrode.

[0033] The slurry is coated onto the surface of a whisker carbon nanotube membrane and dried to form a coating on the surface of the whisker carbon nanotube membrane. It should be noted that this application specifically uses a whisker carbon nanotube membrane as the current collector. Compared with carbon nanofiber cloth and graphene membrane, the whisker carbon nanotube membrane, as a multi-micro-nano porous thin film composite material, has a large number of micropores on its surface. It is used as a current collector in lithium-ion batteries to replace metal copper foil / aluminum foil. During the coating process, the coating can penetrate into the interior of the substrate, greatly increasing the contact interface. It is a gradient interface, so there is no clearly distinguishable interface between the active material in the coating and the whisker carbon nanotube membrane. On the one hand, it can reduce the impedance of the electrode by a factor of two. On the other hand, the porous channels in the whisker carbon nanotube membrane can adsorb a large amount of electrolyte, thereby greatly improving the battery's charge and discharge capacity. While maintaining high conductivity and large specific surface area, it exhibits excellent mechanical strength, toughness, and electrochemical stability.

[0034] Furthermore, using whisker-shaped carbon nanotubes as a coating carrier not only expands the effective contact area between the electrode and the electrolyte, promoting rapid lithium-ion diffusion, but also ensures uniform slurry distribution and avoids agglomeration. Moreover, as a multi-micro-nano porous film composite material, the whisker-shaped carbon nanotube film has numerous micropores on its surface and exhibits good hydrophilicity. This allows slurries containing acid-washed lithium titanate molecular sieves to penetrate into the pores of the substrate material, providing channels for lithium-ion transport and thus enhancing lithium adsorption capacity.

[0035] Furthermore, this application specifically specifies that the weight ratio of acid-washed lithium titanate molecular sieve to whisker carbon nanotube film is 1:(2-4). Typical, but not limiting, weight ratios of acid-washed lithium titanate molecular sieve to whisker carbon nanotube film are 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or any combination of two such ratios. This ratio allows the acid-washed lithium titanate molecular sieve to be fully adsorbed onto the whisker carbon nanotube film, which has high conductivity and a large specific surface area, forming a dense and uniform coating. The high conductivity of whisker carbon nanotubes can significantly enhance the overall electron transport efficiency of the electrode, while their nanoscale pore structure helps to increase the ion diffusion rate, thereby improving the electrochemical reaction rate and efficiency of the electrode. In addition, the mechanical strength and flexibility of whisker carbon nanotubes provide a stable support structure for the lithium titanate molecular sieve, preventing the shedding of active material during charge-discharge cycles and ensuring the cycle stability and service life of the electrode. This weight ratio of composite material can also balance the adsorption capacity and mechanical properties of the electrode, enabling the electrode to exhibit excellent selective adsorption and efficient desorption of lithium ions during membrane capacitor deionization, thereby improving the efficiency and purity of lithium ion separation and enrichment from brine.

[0036] The synergistic effect of whisker carbon nanotubes and acid-washed lithium titanate molecular sieves not only improves the lithium-ion adsorption capacity and efficiency of the MCDI module, but also enhances its electrochemical stability and charge transfer capability. Even after long-term charge-discharge cycles, the decline in electrode performance is extremely limited, thus ensuring the module's sustained and efficient performance in the electrochemical lithium extraction process.

[0037] In summary, the membrane capacitor deionization module of this application utilizes the high selectivity of acid-washed lithium titanate molecular sieves to achieve efficient adsorption of lithium ions. Using a whisker-type carbon nanotube membrane as the current collector, its high conductivity and large specific surface area not only simplify the module structure but also promote rapid charge transport and uniform lithium ion adsorption. This electrode design, combined with the MCDI module, not only improves electrochemical performance, such as charge / discharge rates and adsorption capacity, but also demonstrates environmental friendliness and economic efficiency, making it suitable for brine treatment with varying salinity levels.

[0038] In a preferred embodiment, the preparation method of acid-washed lithium titanate molecular sieve includes the following steps: treating the lithium titanate molecular sieve with an acid solution to obtain acid-washed lithium titanate molecular sieve; the acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid and nitric acid, which can more effectively dissolve alkaline impurities on the surface of lithium titanate, create more vacancies for lithium ion adsorption, and enhance adsorption performance.

[0039] In a preferred embodiment, the acid concentration is 0.1–0.6 mol / L. Typically, but not limitingly, the acid concentration is within the range of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, or any two of these values. Within this range, the surface modification effect of lithium titanate can be improved more effectively, while avoiding excessive corrosion, which is more conducive to maintaining the structural integrity and stability of the material. It should be noted that if the acid concentration is too low, it may affect the degree of surface modification of lithium titanate, thereby affecting the generation of lithium ion adsorption sites and reducing adsorption efficiency; if the concentration is too high, it may excessively corrode the material, affecting the crystal structure and thus affecting adsorption performance and service life.

[0040] In a preferred embodiment, the solid-liquid ratio of lithium titanate molecular sieve to acid solution is 1 g:(200-300) mL. Typical, but not limiting, ratios of lithium titanate molecular sieve to acid solution include 1 g:200 mL, 1 g:250 mL, 1 g:300 mL, or any combination of two such ratios. Within this range, the acid washing reaction can proceed more fully, ensuring uniform surface modification and thus improving the selectivity and efficiency of lithium ion adsorption. If the solid-liquid ratio is too low, it may affect the uniformity of the acid washing reaction, thereby affecting the surface modification effect of lithium titanate and the distribution of lithium ion adsorption sites; if it is too high, it will increase processing costs and may reduce the effective contact area and acid washing efficiency.

[0041] In a preferred embodiment, the treatment is carried out under stirring at a temperature of 10–60°C, a rotation speed of 10–50 rpm, and a time of 6–48 h. Under these conditions, ion exchange can be promoted more effectively, further improving the purity and activity of lithium titanate and enhancing the ion adsorption performance of the electrode material.

[0042] In summary, controlling the acid washing parameters within the aforementioned range can not only significantly improve the lithium-ion adsorption capacity and rate of the acid-washed lithium titanate molecular sieve, but also further optimize its electrochemical performance and extend its service life. More importantly, this treatment method can significantly enhance the lithium-magnesium separation capability of lithium titanate in high magnesium-to-lithium ratio brines, providing strong support for the application of MCDI technology in lithium resource recovery.

[0043] In a preferred embodiment, the lithium titanate molecular sieve comprises Li₂TiO₃ and / or Li₄Ti₅O₃. 12 All of the above-mentioned lithium titanate molecular sieve types are suitable for fabricating the lithium titanate coated electrode of this application.

[0044] In a preferred embodiment, the preparation method of lithium titanate molecular sieve includes the following steps: sequentially subjecting a lithium source and a titanium source to a second ball milling, calcination, and cooling to obtain a lithium titanate molecular sieve; wherein the lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium chloride, and the titanium source includes titanium oxide and / or titanium chloride; the molar ratio of the lithium source to the titanium source is (1.5–2.5):1, typically but not limitingly, the molar ratio of the lithium source to the titanium source is 1.5:1, 2:1, 2.5:1, or any two of these values. Under these conditions, it is more conducive to ensuring the integrity of the molecular sieve structure and the formation of lithium ion vacancies, thereby further optimizing the electrochemical performance of the electrode.

[0045] In a preferred embodiment, the second ball milling is performed at a speed of 300–600 rpm for 0.5–12 h, which promotes deep mixing and refinement of the lithium source and titanium source, thereby facilitating the formation of uniform precursor particles. Alternatively, the calcination temperature is 700–1000 °C, typically but not limitingly, within the range of 700 °C, 800 °C, 900 °C, 1000 °C, or any two of these values, with a holding time of 2–24 h, preferably 12–24 h. These conditions allow for more precise control of the crystal structure, forming lithium titanate with a higher specific surface area and more lithium-ion exchange sites, thereby further enhancing the lithium adsorption capacity and rate. It should be noted that if the calcination time is too long or the temperature is too high, although it is beneficial to increase the site density, it may lead to excessive crystal growth and changes in the pore structure, which in turn affects the effectiveness of ion exchange sites. If the temperature is insufficient, it may affect the chemical conversion rate of the reaction, which may ultimately lead to uneven distribution of the material composition and the presence of unreacted precursors, resulting in low purity and activity of the material. If the time is too short, it may not be enough for the material to reach the required structure and crystal maturity, resulting in excessively small grain size or incomplete crystal form, which affects the conductivity, ion exchange capacity and stability of the material.

[0046] The inventors further optimized the composition of the slurry. In a preferred embodiment, the weight ratio of acid-washed lithium titanate molecular sieve to binder in the slurry is (70-85):(5-15); and / or, the binder includes one or more of polyvinylidene fluoride, carboxymethyl cellulose, and polytetrafluoroethylene; and / or, the weight ratio of acid-washed lithium titanate molecular sieve to conductive agent is (70-85):(5-15); and / or, the conductive agent includes one or more of conductive carbon black, Ketjen black, and carbon nanotubes; and / or, the weight ratio of acid-washed lithium titanate molecular sieve to solvent is (70-85):(100-300); and / or, the solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and propylene glycol. The above formulation ensures sufficient ion adsorption sites on the electrode while further optimizing its structural integrity and conductivity, promoting ion transport, and improving electrochemical reaction efficiency. Furthermore, the slurry is easy to coat, thus guaranteeing selective adsorption of lithium ions by the electrode in the membrane capacitive deionization (MCDI) module, enhancing electrode cycle stability and lifespan, reducing internal electrode impedance, and achieving rapid charge / discharge and high energy density. In a preferred embodiment, the weight ratio of acid-washed lithium titanate molecular sieve, polyvinylidene fluoride, conductive carbon black, and N-methylpyrrolidone in the slurry is 80:10:10:200.

[0047] In a preferred embodiment, the thickness of the whisker carbon nanotube film is 60–70 μm, and the density is 70–90 g / m³. 3 This condition is more conducive to ensuring the structural stability and lightweight of the membrane, with a porosity of 20-60%, typically but not limited to 20%, 30%, 40%, 50%, 60%, or any two of these values. This condition is more conducive to the rapid migration of ions in the electrolyte. The conductivity of the whisker carbon nanotube membrane is 0.015-0.018 kS / cm. This condition can further reduce the internal impedance of the electrode and increase the electrochemical reaction rate, with a specific surface area of ​​12-18 m². 2 / g, under these conditions, lithium ions have more adsorption sites and the adsorption efficiency is faster.

[0048] In a preferred embodiment, in step S1, the slurry is coated on one or both sides of the whisker carbon nanotube film; and / or, the coating covers 50-100% of the area of ​​the whisker carbon nanotube film; and / or, the coating thickness is 10-250 μm and the coating density is 70-90 g / m³. 3 Specific surface area is 4-16 m² 2 / g, under these conditions, the adsorption efficiency and transport speed of lithium ions can be further improved.

[0049] In a preferred embodiment, the drying temperature is 40–60°C, and the drying time is 4–8 hours. These conditions ensure the coating is properly set and the solvent is completely removed, which is beneficial for improving the electrochemical stability and mechanical strength of the electrode.

[0050] In a preferred embodiment, the electrode is paired with Li + Adsorption capacity q e The concentration is 5–17 mg / g, the adsorption rate is 15–60 mg / (g·h), and the electrode capacity decay is ≤5% after 250 cycles.

[0051] To improve the compatibility of the components in the membrane capacitor deionization module, in a preferred embodiment, the ion exchange membrane includes a Fumasep FAA-3-50 anion exchange membrane and a FuMA-Tech cation exchange membrane; and / or, the separator includes polyvinylidene fluoride and / or polypropylene.

[0052] In another typical embodiment of the present invention, a membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine is also provided, obtained by the above-described preparation method. The membrane capacitor deionization module of this application can efficiently adsorb lithium ions in high magnesium-to-lithium ratio brine, while effectively blocking magnesium ions, significantly improving the recovery rate and purity of lithium resources. Furthermore, the module's high conductivity and large specific surface area enhance ion transport efficiency, and its low energy consumption and long cycle life ensure operational stability.

[0053] In a preferred embodiment, the membrane capacitor deionization module used to treat brine with a high magnesium-to-lithium ratio has a lithium adsorption rate of 20-70%, a magnesium removal rate of 95-99.9%, and a lithium enrichment factor of 1-10.

[0054] In another typical embodiment of the present invention, a method for treating high magnesium-to-lithium ratio brine is also provided, comprising the following steps: forming a closed loop between the membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine and a DC voltage circuit; feeding the high magnesium-to-lithium ratio brine into the membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine; first adsorbing under conditions of 0.8–1.6V and 5–30°C for 10–35 min; then desorbing under conditions of -0.8–-1.6V and 5–30°C in acidic conditions for 10–35 min; repeating the cycle 1–300 times. As mentioned above, the electrode material of this application has high selectivity, effectively adsorbing lithium ions while repelling magnesium ions, thereby significantly improving the lithium recovery efficiency and purity. The high conductivity and large specific surface area of ​​the module can optimize the ion transport path, reduce energy consumption, and extend service life, making it particularly suitable for treating complex brines with high magnesium-to-lithium ratios.

[0055] More preferably, hydrochloric acid is used as the desorption solution. More preferably, the pH is controlled at 3 to 5 during desorption.

[0056] There are many types of brine suitable for the membrane capacitor deionization module of this application. In a preferred embodiment, the brine with a high magnesium-to-lithium ratio contains Li... + The content is 200–700 mg / L, typical but not limiting, Li + The content is 200 mg / L, 300 mg / L, 400 mg / L, 500 mg / L, 600 mg / L, 700 mg / L, or any two of these values, within a range of Mg. 2+ The content is 20,000–200,000 mg / L, typical but not limiting, Mg 2+ The content is a range of 20000 mg / L, 50000 mg / L, 100000 mg / L, 150000 mg / L, 200000 mg / L, or any two of these values, K. + The content ranges from 100 to 3000 mg / L, typically but not exclusively, K + The content is 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, or any two of these values, and Na + The content ranges from 300 to 6000 mg / L, typically but not exclusively, Na. + The content is 300 mg / L, 1000 mg / L, 2000 mg / L, 3000 mg / L, 4000 mg / L, 5000 mg / L, 6000 mg / L, or any two of these values ​​within a range. Ca 2+ The content is 500–7000 mg / L, typical but not limiting, Ca 2+ The content of the brine is 500 mg / L, 1000 mg / L, 2000 mg / L, 3000 mg / L, 4000 mg / L, 5000 mg / L, 6000 mg / L, 7000 mg / L, or any two of these values; the salinity is 20-40%, typically but not limited to 20%, 30%, 40%, or any two of these values; and / or the pH of the high magnesium-to-lithium ratio brine is 3-6, typically but not limited to 3, 4, 5, 6, or any two of these values; and / or the flow rate of the high magnesium-to-lithium ratio brine through the membrane capacitor deionization module used for treating the high magnesium-to-lithium ratio brine is 5-300 mL / min, typically but not limited to 5 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, or any two of these values.

[0057] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0058] Example 1

[0059] Preparation of acid-washed lithium titanate molecular sieves: Lithium source (Li₂CO₃) and titanium source (TiO₂) were weighed according to the stoichiometric molar ratio (Li:Ti = 2:1), and then ball-milled at 600 rpm for 1 h. The mixture was then removed and placed in a ceramic crucible, and the precursor was prepared in a muffle furnace with a heating rate controlled at 3 °C·min⁻¹. -1 It was calcined at 800℃ for 4 hours, and then the cooling rate was controlled at 3℃·min. -1 The solution was then cooled to 25°C in air to obtain Li₂TiO₃, denoted as LTO. Subsequently, it was treated with a solution of 0.2 mol·L⁻¹. -1 The lithium titanate molecular sieve was acid-washed in hydrochloric acid solution at 25°C and 25 rpm for 24 hours. The solid-liquid ratio of lithium titanate molecular sieve to acid solution was 1 g: 250 mL. + Replace with H + Then, it is washed, filtered, and dried in a vacuum drying oven for 12 hours to obtain acid-washed lithium titanate molecular sieve (i.e., H2TiO3, denoted as HTO).

[0060] Electrode preparation: Acid-washed lithium titanate molecular sieve, binder (PVDF), conductive agent (conductive carbon black), and solvent (N-methylpyrrolidone) were mixed at 25 rpm for 6 hours in a weight ratio of 80:10:10:200. The mixture was then ball-milled at 600 rpm for 2 hours, controlling the solid particle size in the slurry to ≤100 μm. The slurry was then sieved and degassed to obtain the final slurry. Using an MSK-AFA-DE400-M5 multi-functional coating machine, the slurry was coated onto a whisker carbon nanotube film (60 μm thick, 80 g / m³ density). 3 It has a porosity of 50%, an electrical conductivity of 0.017 kS / cm, and a specific surface area of ​​16.98 m². 2 A single-sided coating (containing an acid-washed lithium titanate molecular sieve and a whisker carbon nanotube membrane in a weight ratio of 1:3), with the coating covering 50% of the area of ​​the whisker carbon nanotube membrane, a coating thickness of 25 μm (substrate thickness of 70 μm), and a coating density of 80 g / m³. 3 Specific surface area is 12m² 2 / g, coating width of 220mm, ambient dew point of -30℃, after coating, dried at 25℃ to obtain electrode.

[0061] Preparation of CDI module: Assemble the above electrodes, anion exchange membrane (Fumasep FAA-3-50 anion exchange membrane), cation exchange membrane (FuMA-Tech cation exchange membrane), diaphragm (polyvinyl fluoride), module frame, power supply and fluid delivery system to obtain CDI module, and form a closed loop with DC voltage circuit, and control the voltage range applied to the anode and cathode by DC voltage circuit to be 1V.

[0062] Electrochemical desalination application of the CDI module: A peristaltic pump delivers the salt solution to be treated from the storage tank into the CDI module, and then returns it to the storage tank. The concentration of the salt solution is 20 g / L, and the flow rate is 15 mL / min. A DC voltage circuit is used to apply a 1 V voltage to the module, controlling the adsorption time for 20 min and the temperature at 25 °C for ion adsorption. Then, a reverse voltage of -1 V is applied, controlling the desorption time for 20 min and the temperature at 25 °C for desorption in an acidic environment (pH approximately 3–5) (hydrochloric acid is used as the desorption solution). A conductivity meter is used to monitor the conductivity of the salt solution at the CDI module outlet in real time, and ICP testing is performed on the desorption solution to determine the adsorption capacity.

[0063] The pH of the brine before treatment was 5.4. Specifically, the composition of the brine before and after treatment is shown in Table 1. The change in the magnesium-to-lithium ratio shows that the electrode of this application has a significant effect on reducing the magnesium-to-lithium ratio and enriching lithium ions. The adsorption capacity of lithium ions can reach over 6.39 mg / g, and the electrode capacity decreases by less than 5% after 250 cycles.

[0064] The SEM image of the cross-section of the whisker carbon nanotube film is shown below. Figure 1 SEM images of the surface are shown below. Figure 2 The figure shows the fibrous characteristics of the matrix (whisker carbon nanotube film).

[0065] SEM image of the electrode cross-section is shown below. Figure 3 As can be seen, an acid-washed lithium titanate ion sieve coating was formed on the substrate surface; the SEM image of the surface is shown below. Figure 4 It can be seen that the acid-washed lithium titanate ion sieve is uniformly coated, indicating that the lithium titanate ion sieve has been uniformly coated on the substrate and no severe agglomeration has occurred; EDS image see Figure 5 , Figure 5Figure A shows an electron microscope image at 10,000x magnification; Figure B shows the elemental distribution of Ti; Figure C shows the elemental distribution of F; Figure D shows the elemental distribution of O; and Figure E shows the elemental distribution of C. It can be seen that the various elements are uniformly distributed, and the active slurry is successfully coated on the substrate. Thanks to the coating with high pseudocapacitive properties (especially the acid-washed lithium titanate molecular sieve and conductive carbon black), this morphology can greatly promote the rapid charge transport in the electrolyte solution, thus enabling better ion adsorption during the subsequent brine adsorption process. The cyclic voltammetry curve of the electrode at a scan rate of 1 mV / s is shown in the figure. Figure 6 Thanks to the ability of acid-etched lithium titanate to store high-density charge and generate Faraday pseudocapacitance, the electrode exhibits extremely high capacitance. A photograph of the uncut electrode after coating is shown below. Figure 7 .

[0066] Example 2

[0067] The only difference from Example 1 is:

[0068] After coating, the electrode thickness is 100 μm (excluding the substrate).

[0069] Example 3

[0070] The only difference from Example 1 is:

[0071] After coating, the electrode thickness is 150 μm (excluding the substrate).

[0072] Example 4

[0073] The only difference from Example 1 is:

[0074] After coating, the electrode thickness is 200 μm (excluding the substrate).

[0075] Example 5

[0076] The only difference from Example 1 is:

[0077] The process for acid-washing lithium titanate molecular sieves differs. Specifically, lithium source (lithium hydroxide) and titanium source (TiO2) are weighed according to a stoichiometric molar ratio (Li:Ti = 1.5:1), and then mixed at 300 rpm for 12 h. Subsequently, the mixture is removed and placed in a ceramic crucible, and the precursor is prepared in a muffle furnace with a controlled heating rate of 3 °C·min. -1 It was calcined at 700℃ for 24 hours, and then the cooling rate was controlled at 3℃·min. -1 The solution was then cooled to 25°C in air to obtain lithium titanate. Subsequently, it was treated with a 0.1 mol·L⁻¹ solution. -1 The lithium titanate molecular sieve was acid-washed in hydrochloric acid solution at 60℃ and 10 rpm for 48 hours. The solid-liquid ratio of lithium titanate molecular sieve to acid solution was 1 g: 200 mL.+ Replace with H + Then, the mixture is washed, filtered, and dried in a vacuum drying oven for 12 hours to obtain acid-washed lithium titanate molecular sieves.

[0078] Example 6

[0079] The only difference from Example 1 is:

[0080] The process for acid-washing lithium titanate molecular sieves differs. Specifically, lithium source (lithium chloride) and titanium source (TiCl4) are weighed according to a stoichiometric molar ratio (Li:Ti = 2.5:1), and then mixed at 600 rpm for 0.5 h. The mixture is then removed and placed in a ceramic crucible, and the precursor is prepared in a muffle furnace with a heating rate controlled at 3 °C·min. -1 The mixture was calcined at 1000℃ for 2 hours, and then the cooling rate was controlled at 3℃·min. -1 The solution was then cooled to 25°C in air to obtain lithium titanate. Subsequently, it was treated with a 0.6 mol·L⁻¹ solution. -1 The lithium titanate molecular sieve was acid-washed in nitric acid solution at 10℃ and 50 rpm for 6 hours. The solid-liquid ratio of lithium titanate molecular sieve to acid solution was 1 g: 300 mL. + Replace with H + Then, the mixture is washed, filtered, and dried in a vacuum drying oven for 12 hours to obtain acid-washed lithium titanate molecular sieves.

[0081] Example 7

[0082] The only difference from Example 1 is:

[0083] The composition and preparation method of the slurry are different. Specifically, HTO, binder (carboxymethyl cellulose), conductive agent (Ketjen black), and solvent (N,N-dimethylformamide) are mixed at 25 rpm for 6 hours in a weight ratio of 70:5:15:100, and then ball-milled at 600 rpm for 2 hours. The solid particle size in the slurry is controlled to be ≤100 μm. Then, the slurry is sieved and degassed to obtain the slurry.

[0084] Example 8

[0085] The only difference from Example 1 is:

[0086] The composition and preparation method of the slurry are different. Specifically, HTO, binder (polytetrafluoroethylene), conductive agent (carbon nanotubes), and solvent (dimethyl sulfoxide) are mixed at 25 rpm for 6 hours in a weight ratio of 85:15:5:300, and then ball-milled at 600 rpm for 2 hours to control the solid particle size in the slurry to ≤100 μm. Then, the slurry is sieved and degassed to obtain the slurry.

[0087] Example 9

[0088] The only difference from Example 1 is:

[0089] The parameters and coating process parameters of the whisker carbon nanotube film differ. Specifically, the slurry is coated onto a whisker carbon nanotube film (20 μm thick, 90 g / m³ density). 3 It has a porosity of 20%, an electrical conductivity of 0.015 kS / cm, and a specific surface area of ​​12 m². 2 A single-sided coating (with a weight ratio of 1:2 of acid-washed lithium titanate molecular sieve to whisker carbon nanotube membrane) covering 100% of the area of ​​the whisker carbon nanotube membrane, with a coating thickness of 10 μm and a coating density of 70 g / m³. 3 Specific surface area is 4m² 2 / g, coating width of 220mm, ambient dew point of -30℃, after coating, dried at 25℃ to obtain electrode.

[0090] Example 10

[0091] The only difference from Example 1 is:

[0092] The parameters and coating process parameters of the whisker carbon nanotube film differ. Specifically, the slurry is coated onto a whisker carbon nanotube film (thickness 60 μm, density 70 g / m³). 3 It has a porosity of 60%, an electrical conductivity of 0.018 kS / cm, and a specific surface area of ​​18 m². 2 A single-sided coating (with a weight ratio of 1:4 of acid-washed lithium titanate molecular sieve to whisker carbon nanotube membrane), the coating covering 50% of the area of ​​the whisker carbon nanotube membrane, a coating thickness of 250 μm, and a coating density of 90 g / m². 3 Specific surface area is 16m² 2 / g, coating width of 220mm, ambient dew point of -30℃, after coating, dried at 25℃ to obtain electrode.

[0093] Example 11

[0094] The only difference from Example 1 is:

[0095] The flow rate of the brine and the parameters for adsorption and desorption differ. Specifically, a peristaltic pump is used to deliver the salt solution to be treated from the storage tank into the CDI module, and then back to the storage tank. The concentration of the salt solution is 20 g / L, and the flow rate is 5 mL / min. A DC voltage circuit is used to apply a voltage of 0.8 V to the module, and the adsorption time is controlled at 35 min and the temperature at 5 °C for ion adsorption. Then, the opposite voltage is applied, and the desorption time is controlled at 35 min and the temperature at 5 °C for desorption. A conductivity meter is used to monitor the conductivity of the salt solution to be adsorbed in real time at the outlet of the CDI module to determine the amount of adsorption. This step is repeated once.

[0096] Example 12

[0097] The only difference from Example 1 is:

[0098] The flow rate of the brine and the parameters for adsorption and desorption differ. Specifically, a peristaltic pump is used to deliver the salt solution to be treated from the storage tank into the CDI module, and then back to the storage tank. The concentration of the salt solution is 20 g / L, and the flow rate is 300 mL / min. A DC voltage circuit is used to apply a 1.6 V voltage to the module, controlling the adsorption time to 10 min and the temperature to 30 °C for ion adsorption. Then, the opposite voltage is applied, controlling the desorption time to 10 min and the temperature to 30 °C for desorption. A conductivity meter is used to monitor the conductivity of the salt solution to be adsorbed in real time at the outlet of the CDI module to determine the adsorption amount. This step is repeated 300 times.

[0099] Comparative Example 1

[0100] The only difference from Example 1 is that the lithium titanate molecular sieve is not acid-washed.

[0101] Analysis shows that in lithium-ion sieves that are not acid-washed, the specific active lithium adsorption sites are reduced, and the adsorption of ions is non-selective only by the dual-capacitance adsorption mechanism of the electrode material. No ion exchange reaction occurs between the lithium titanate sieve and the brine solution, resulting in poor adsorption capacity for lithium ions.

[0102] Comparative Example 2

[0103] The only difference from Example 1 is the pickling concentration; specifically, a concentration of 0.01 mol·L⁻¹ is used. -1 The lithium titanate molecular sieve was acid-washed in hydrochloric acid solution at 25°C and 25 rpm for 24 hours. The solid-liquid ratio of lithium titanate molecular sieve to acid solution was 1 g: 250 mL. + Replace with H + Then, the mixture is washed, filtered, and dried in a vacuum drying oven for 12 hours to obtain acid-washed lithium titanate molecular sieves.

[0104] Analysis shows that as the acid washing concentration decreases, the number of lithium ion adsorption vacancies in the lithium ion sieve decreases compared to Example 1, resulting in a poorer adsorption effect.

[0105] Comparative Example 3

[0106] The only difference from Example 1 is that carbon cloth is used as the current collector, and the carbon cloth is activated carbon fiber cloth (model HCP331P, which is hydrophilic).

[0107] Analysis shows that the adsorption effect decreased because the conductivity and hydrophilicity of carbon cloth are weaker than those of whisker carbon nanotube films, making it difficult for the slurry to penetrate into the matrix material, thus reducing the conductive pathway of the ion channels.

[0108] Comparative Example 4

[0109] The only difference from Example 1 is that a titanium sheet (0.1 mm thick) is used as the current collector.

[0110] Analysis shows that, compared with whisker carbon nanotube films, titanium sheets have poorer conductivity, flexibility, and bendability. Moreover, they have a smaller surface area, providing fewer adsorption active sites and thus exhibiting poorer adsorption of lithium ions.

[0111] The performance test results of the membrane capacitor deionization modules prepared in the above embodiments and comparative examples are shown in Table 2.

[0112] Test method:

[0113] Lithium-ion intercalation capacity: Electrochemical tests were performed using a three-electrode electrochemical workstation. Lithium titanate@carbon nanotube film was used as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode. CV tests were conducted within an electrochemical window of 0.01V–1V at a scan rate of 1mV / s. The specific capacitance C (F / g) was calculated using the following formula:

[0114] In the formula, V1 and V2 are the starting potential and the ending potential, respectively, in volts (V).

[0115] i represents the response current, measured in amperes (A).

[0116] m represents the effective electrode mass, in grams (g).

[0117] v represents the scanning speed, measured in V / s.

[0118] ΔV represents the voltage change, measured in volts (V).

[0119] The formula for calculating the lithium-ion intercalation capacity (Γ, mg / g) is as follows:

[0120] In the formula, C0 is the initial concentration of lithium ions, in mg / L, C t t is the lithium ion concentration at time t (in seconds), in mg / L; V is the volume of the brine before treatment, in L; and m is the total mass of the electrode (including the substrate), in g (m is 17 mg in this application).

[0121] Adsorption rate: The saturated adsorption capacity of the salt solution was tested using a custom-designed MCDI module, with the charging and discharging processes operated in constant potential mode (1V to -1V) using a CHI-760e electrochemical workstation. After assembling the electrode into the MCDI module, the solution to be adsorbed (a brine solution) was pumped into the MCDI module using a BT100-3J peristaltic pump, and the conductivity of the solution was recorded online using a DDBJ-350F handheld conductivity meter. The external dimensions of the membrane electrode were approximately 2cm × 2cm. The electrode thickness was approximately 100μm. Adsorption was performed for 20 minutes, and the changes in ion content before and after adsorption of the brine solution were measured.

[0122] Electrode capacity decay after 250 cycles: GCD tests were performed on a CHI-760E electrochemical workstation using a three-electrode system, including the test sample as the working electrode, a Pt sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. 1M LiCl was used as the electrolyte solution in the GCD tests. All GCD tests were conducted with Ag / AgCl as the reference electrode at different current densities (0.25, 0.5, 1, and 2 A / g) within an electrochemical window from -1 to +1 V, and the cycling stability of the electrode sample was tested at a current density of 1 A / g.

[0123] Lithium adsorption rate: The saturated adsorption capacity of the salt solution was tested using a custom-designed MCDI module. The charging and discharging processes were operated in constant potential mode (1V to -1V) using a CHI-760e electrochemical workstation. After assembling the electrode into the MCDI module, the solution to be adsorbed (halogen solution) was pumped into the MCDI module at an injection rate of 20 mL / min using a BT100-3J peristaltic pump, and the conductivity of the solution was recorded online using a DDBJ-350F handheld conductivity meter. The external dimensions of the membrane electrode were approximately 2 cm × 2 cm. Saturated adsorption was performed, and the change in ion content before and after adsorption of the brine solution was measured.

[0124] Magnesium removal rate: The saturated adsorption capacity of the salt solution was tested using a custom-designed MCDI module. The charging and discharging processes were operated in constant potential mode (1V to -1V) using a CHI-760e electrochemical workstation. After assembling the electrode into the MCDI module, the solution to be adsorbed (halogen solution) was pumped into the MCDI module at an injection rate of 20 mL / min using a BT100-3J peristaltic pump, and the conductivity of the solution was recorded online using a DDBJ-350F handheld conductivity meter. The external dimensions of the membrane electrode were approximately 2 cm × 2 cm. Saturated adsorption was performed, and the changes in ion content before and after adsorption of the brine solution were measured.

[0125] Lithium enrichment factor: The saturated adsorption capacity of the salt solution was tested using a custom-designed MCDI module. The charging and discharging processes were operated in constant potential mode (1V to -1V) using a CHI-760e electrochemical workstation. After assembling the electrode into the MCDI module, the solution to be adsorbed (halogen solution) was pumped into the MCDI module at an injection rate of 20 mL / min using a BT100-3J peristaltic pump, and the conductivity of the solution was recorded online using a DDBJ-350F handheld conductivity meter. The external dimensions of the membrane electrode were approximately 2 cm × 2 cm. Adsorption and desorption were performed for 20 minutes each, with ten cycles of adsorption and desorption. The changes in ion content before and after adsorption and desorption in the brine solution and desorption solution were measured.

[0126] Table 1

[0127]

[0128]

[0129] Table 2

[0130]

[0131] As can be seen from the above, the membrane capacitor deionization module of this invention utilizes the high selectivity of acid-washed lithium titanate molecular sieves to achieve efficient adsorption of lithium ions. Using a whisker carbon nanotube membrane as the current collector, its high conductivity and large specific surface area not only simplify the module structure but also promote rapid charge transport and uniform lithium ion adsorption. This electrode design, combined with the MCDI module, not only improves electrochemical performance, such as charge / discharge rate and adsorption capacity, but also possesses environmentally friendly and economical characteristics, making it suitable for brine treatment with varying salinity, especially for brine with a high magnesium-to-lithium ratio.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine, characterized in that, The magnesium-to-lithium ratio of the brine is 300-700, and the preparation method includes the following steps: Step S1: The acid-washed lithium titanate molecular sieve, binder, conductive agent and solvent are mixed in sequence and ball-milled to obtain a slurry; the slurry is coated on the surface of the whisker carbon nanotube membrane and dried to form a coating on the surface of the whisker carbon nanotube membrane. Step S2: Using the whisker carbon nanotube membrane including the coating as an electrode, the electrode, ion exchange membrane, diaphragm, module frame, power supply and fluid delivery system are assembled to obtain the membrane capacitor deionization module. The weight ratio of the acid-washed lithium titanate molecular sieve to the whisker carbon nanotube membrane is 1:(2~4). The preparation method of the acid-washed lithium titanate molecular sieve includes the following steps: sequentially subjecting a lithium source and a titanium source to a second ball milling, calcination, and cooling to obtain a lithium titanate molecular sieve; treating the lithium titanate molecular sieve with an acid solution to obtain the acid-washed lithium titanate molecular sieve; the rotation speed of the second ball milling is 300~600 rpm, and the time is 0.5~12 h; the calcination temperature is 700~1000℃, and the holding time is 2~24 h.

2. The preparation method according to claim 1, characterized in that, The acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 0.1~0.6 mol / L. The solid-liquid ratio of the lithium titanate molecular sieve to the acid solution is 1 g:(200~300) mL. The treatment is carried out under stirring at a temperature of 10~60℃, a rotation speed of 10~50 rpm, and a time of 6~48 h; and / or, The lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium chloride, and the titanium source includes titanium oxide and / or titanium chloride. The molar ratio of the lithium source to the titanium source is (1.5~2.5):

1.

3. The production method according to claim 1 or 2, characterized by, In the slurry, The weight ratio of the acid-washed lithium titanate molecular sieve to the binder is (70~85):(5~15); and / or, the binder comprises one or more of polyvinylidene fluoride, carboxymethyl cellulose, and polytetrafluoroethylene; and / or, The weight ratio of the acid-washed lithium titanate molecular sieve to the conductive agent is (70~85):(5~15); and / or, the conductive agent includes one or more of conductive carbon black, Ketjen black, and carbon nanotubes; and / or, The weight ratio of the acid-washed lithium titanate molecular sieve to the solvent is (70~85):(100~300); and / or, the solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and propylene glycol.

4. The preparation method according to claim 1 or 2, characterized in that, The thickness of the whisker carbon nanotube film is 60-70 μm, the density is 70-90 g / m 3 , the porosity is 20-60%; and / or, The whisker carbon nanotube film has an electrical conductivity of 0.015-0.018 kS / cm and a specific surface area of 12-18 m 2 / g.

5. The production method according to claim 1 or 2, characterized by, In step S1 The slurry is coated onto one or both sides of the whisker carbon nanotube film; and / or, The coating accounts for 50-100% of the area of ​​the whisker carbon nanotube film; and / or, The coating has a thickness of 10-250 μm and a coating density of 70-90 g / m 3 and a specific surface area of 4-16 m 2 / g.

6. The preparation method according to claim 1 or 2, characterized in that, The electrode pair Li + has an adsorption capacity q e of 5-17 mg / g, an adsorption rate of 15-60 mg / (g·h), and an electrode capacity attenuation amount of ≤5% after 250 cycles; and / or, The ion exchange membrane includes a Fumasep FAA-3-50 anion exchange membrane and a FuMA-Tech cation exchange membrane; and / or, The diaphragm comprises polyvinyl fluoride and / or polypropylene.

7. A membrane capacitive deionization module for treating high magnesium to lithium ratio brines, characterized in that, It is obtained by the preparation method according to any one of claims 1 to 6.

8. The membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine according to claim 7, characterized in that, The membrane capacitor deionization module used for treating brine with a high magnesium-to-lithium ratio has a lithium adsorption rate of 20-70%, a magnesium removal rate of 95-99.9%, and a lithium enrichment factor of 1-10.

9. A method for treating a high magnesium to lithium ratio brine, characterized in that, Includes the following steps: The membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine as described in claim 7 or 8 is connected to a DC voltage circuit to form a closed loop. The high magnesium-to-lithium ratio brine is fed into the membrane capacitor deionization module for treating high magnesium-to-lithium ratio brine. First, it is adsorbed for 10 to 35 minutes under conditions of pressure of 0.8 to 1.6V and temperature of 5 to 30°C. Then, it is desorbed for 10 to 35 minutes under conditions of pressure of -0.8 to -1.6V and temperature of 5 to 30°C in acidic conditions. The cycle is repeated 1 to 300 times.

10. The processing method according to claim 9, characterized in that, The content of Li in the high magnesium-lithium ratio brine is 200-700 mg / L + The content of Mg is 20000-200000 mg / L 2+ The content of K is 100-3000 mg / L + The content of Na is 300-6000 mg / L + The content of Ca is 500-7000 mg / L 2+ The salinity is 20-40%; and / or, The pH of the high magnesium-to-lithium ratio brine is 3-6; and / or, The flow rate of the high magnesium-to-lithium ratio brine through the membrane capacitor deionization module used for treating the high magnesium-to-lithium ratio brine is 5~300 mL / min.

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