Pulse electro-catalytic magnesium-lithium separation and extraction method

Abstract

The application belongs to the technical field of salt lake brine resource utilization and electro-catalysis, and particularly relates to a pulse electro-catalysis magnesium-lithium separation and extraction method. ‑ Preferentially with Mg 2+ Form Mg(OH)2 precipitate; and in the intermittent stage, OH ‑ Plasma is redistributed through diffusion, and pH gradually tends to be balanced, which not only effectively alleviates the HER efficiency decay problem caused by ion consumption, inhibits the formation of a high-alkaline microenvironment on the cathode surface, but also promotes the generated Mg(OH)2 precipitate to accumulate at the bottom of the cathode chamber under the action of gravity, thereby overcoming the magnesium-lithium co-precipitation problem caused by the over-alkaline local microenvironment in the traditional constant potential / constant current electrolysis process and the electrode passivation inactivation problem caused by the precipitate product wrapping the catalytically active sites.

Description

Technical Field

[0001] This invention belongs to the field of salt lake brine resource utilization and electrocatalysis technology, specifically relating to a pulse electrocatalytic method for magnesium-lithium separation and extraction. Background Technology

[0002] Mineral resources are the lifeblood and foundation of industry, and a strategic material guarantee supporting economic and social development. During this strategic period of accelerated global energy structure transformation towards green and low-carbon development and profound adjustments in the industrial chain, the security of the supply chain for key mineral resources such as lithium and magnesium has become a decisive factor in the strategic position and industrial competitiveness of enterprises in the global green industrial revolution. Lithium, as the driving force of the new energy revolution, directly determines the technological breakthroughs and market competitiveness of enterprises in the power battery and energy storage industries due to its stable supply. Magnesium, with its unique lightweight properties, plays an indispensable supporting role in high-end manufacturing fields such as aerospace equipment and new energy vehicles. Although over 80% of lithium resources and 5 billion tons of magnesium resources are found in salt lake brines, their actual development and utilization rate remains insufficient.

[0003] A high magnesium-to-lithium ratio (≥8) is a core technological bottleneck in the development of salt lake brine resources. The fundamental reason is that Mg and Li are arranged diagonally in the periodic table, resulting in similar ionic radii (Mg...). 2+ 0.72Å vs Li + 0.76 Å) and similar hydrated ionic radii ([Mg(H2O)6] 2+ 4.28 Å vs [Li(H2O)4] + The magnesium-to-lithium ratio (Mg / L) is 3.82 Å, which poses significant separation challenges. Precipitation is the mainstream process for lithium extraction from low Mg / L ratio (Mg / L < 8) brine in salt lakes, but it suffers from problems such as high consumption of alkali metal reagents and poor selectivity in magnesium-to-lithium separation when treating brine with a high Mg / L ratio. Although electrodialysis can treat brine with a high Mg / L ratio, its industrial application is limited by economic constraints such as high equipment investment and high energy consumption due to the alternating configuration of anion and cation exchange membranes. Therefore, developing a new magnesium-to-lithium separation technology that is highly efficient, energy-saving, economical, environmentally friendly, and suitable for brine with a high Mg / L ratio has become a key breakthrough for realizing the industrial utilization of magnesium-to-lithium resources in salt lakes.

[0004] Renewable energy-driven water electrolysis technology is currently the mainstream process route for large-scale green hydrogen production. Its electrochemical process involves two closely coupled half-reactions: the cathode hydrogen evolution reaction (HER, 2H₂O + 2e⁻). - → 2OH - + H2) and the anodic oxygen evolution reaction (OER, 4OH) - → O2 + 2H2O + 4e -The classic constant potential / constant current electrolysis of salt lake brine has many drawbacks: (1) continuous electrolysis will cause OH on the cathode surface. - Accumulation forms a localized highly alkaline microenvironment, causing magnesium and lithium co-precipitation, which cannot be effectively separated; (2) Mg 2+ With OH - (2) Mg(OH)2 precipitate is formed in situ on the electrode surface and blocks the electrode, causing the catalyst to passivate and deactivate; (3) The concentration of reactants near the cathode decreases, resulting in lag in HER reaction kinetics. Summary of the Invention

[0005] To address the problems of the prior art, this invention provides a pulsed electrocatalytic method for separating and extracting magnesium and lithium, which overcomes the problems of magnesium and lithium co-precipitation caused by excessive alkalinity in the local microenvironment of the electrode in the traditional constant potential / constant current electrolysis process, as well as the electrode passivation and deactivation caused by the precipitated products encapsulating the catalytic active sites.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for the separation and extraction of magnesium and lithium via pulsed electrocatalysis, comprising:

[0008] An electrode system is formed by a working electrode and a counter electrode. The working electrode is placed in the cathode chamber and the counter electrode is placed in the anode chamber. The cathode chamber and the anode chamber are separated by a proton exchange membrane. Both the cathode chamber and the anode chamber are filled with water containing magnesium ions and lithium ions as electrolyte.

[0009] A constant current is applied to the working electrode for a preset electrolysis time to carry out the electrolysis reaction. The application of the constant current to the working electrode is stopped for a preset interval time. This process is repeated several times. The electrolyte in the cathode chamber is subjected to solid-liquid separation to obtain magnesium hydroxide precipitate.

[0010] Preferably, the preset electrolysis time is 600-1800 s and the preset interval time is 300-900 s.

[0011] Furthermore, the ratio of the preset electrolysis time to the preset interval time is 1.0-3.0.

[0012] Preferably, the cathode chamber is connected to a first electrolyte storage tank, the inlet of the cathode chamber is connected to the outlet of the first electrolyte storage tank via a pump, and the outlet of the cathode chamber is connected to the inlet of the first electrolyte storage tank via a pump; the anode chamber is connected to a second electrolyte storage tank, the inlet of the anode chamber is connected to the outlet of the second electrolyte storage tank via a pump, and the outlet of the anode chamber is connected to the inlet of the second electrolyte storage tank via a pump; the flow rate of the electrolyte is controlled by the pump.

[0013] Preferably, the liquid obtained from solid-liquid separation is evaporated to extract lithium.

[0014] Preferably, the constant current is 50-200 mA.

[0015] Preferably, the water containing magnesium and lithium ions is salt lake brine or geothermal brine.

[0016] Preferably, the working electrode is a nickel-based electrode.

[0017] Furthermore, the nickel-based electrode is a nickel mesh, a nickel-chromium alloy mesh, or a nickel-copper alloy mesh.

[0018] Preferably, the electrode system further includes a reference electrode.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The pulsed electrocatalytic magnesium-lithium separation and extraction method of this invention is carried out by alternating between applying a constant current to the working electrode and stopping the application of the constant current, thereby achieving pulsed electrolysis through a periodic "on / off" potential mode, dividing the entire process into an electrolysis stage and an intermittent stage. During the electrolysis stage, a suitable amount of OH- is generated at the cathode. - Prefers Mg 2+ The combination forms Mg(OH)2 precipitate, which is attributed to Mg 2+ Its high charge density makes it effective against OH - The electrostatic attraction is much stronger than that of Li. + Meanwhile, Mg(OH)₂ has a low solubility product constant (Ksp≈1.8×10⁻⁶). -11 This promotes the preferential formation of Mg(OH)2 precipitate, while Li + Due to strong hydration and a high solubility product constant (Ksp≈6.9×10⁻⁶), -2 OH remains in the solution; however, during the intermittent phase, OH... - Plasma is redistributed through diffusion, and the pH gradually becomes more balanced. This not only effectively alleviates the HER efficiency decay caused by ion consumption and inhibits the formation of a highly alkaline microenvironment on the cathode surface, but also promotes the enrichment of the generated Mg(OH)2 precipitate at the bottom of the cathode chamber under gravity. This overcomes the problems of magnesium-lithium co-precipitation caused by excessive alkalinity in the local microenvironment of the electrode and electrode passivation and deactivation caused by the precipitate products encapsulating the catalytic active sites in the traditional constant potential / constant current electrolysis process. High-purity Mg(OH)2 precipitate and high-purity lithium solution are obtained, which can be used for subsequent simple lithium extraction processes.

[0021] Furthermore, the preset electrolysis time and preset interval time selected in this invention can ensure electrolysis efficiency while effectively avoiding the problems of magnesium-lithium co-precipitation and precipitate products encapsulating catalytic active sites.

[0022] Furthermore, the present invention can obtain battery-grade lithium salt products by evaporating the liquid obtained from solid-liquid separation. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The X-ray diffraction pattern of the clean nickel mesh in Example 1;

[0025] Figure 2 The time-potential curves of the clean nickel mesh in Example 2 are obtained by continuous static electrolysis for 5000 s in simulated high magnesium-to-lithium ratio salt lake brine at different constant currents (50 mA, 100 mA and 150 mA).

[0026] Figure 3 The time-potential curve of the clean nickel mesh in Example 2 is obtained by continuous flow electrolysis at a constant current of 100 mA for 5000 s in simulated high magnesium-to-lithium ratio salt lake brine.

[0027] Figure 4 The time-potential curve of the clean nickel mesh in Example 2 is obtained by static electrolysis at a constant current of 100 mA for 1200 s in simulated high magnesium-to-lithium ratio salt lake brine.

[0028] Figure 5 The Raman curves of the clean nickel mesh in Example 2 are obtained by static electrolysis at a constant current of 100 mA for different times (0 s, 200 s, 400 s, 600 s, 800 s, 1000 s, 1200 s, 1400 s, 1600 s and 1800 s) in simulated high magnesium-to-lithium ratio salt lake brine.

[0029] Figure 6 The time-potential curves of the clean nickel mesh in Example 2 are obtained from five sets (30 cycles per set) of pulse electrolysis in simulated high magnesium-to-lithium ratio salt lake brine.

[0030] Figure 7 The linear sweep voltammetric curves of the clean nickel mesh after each pulse electrolysis in simulated high magnesium-to-lithium ratio salt lake brine in Example 2 are shown.

[0031] Figure 8 The X-ray diffraction pattern of the precipitated product in Example 2;

[0032] Figure 9The time potential curves are for simulating high magnesium-to-lithium ratio salt lake brine by periodic pulse electrolysis of a clean nickel mesh in a flowing electrolytic cell for 230 h, as described in Example 3.

[0033] Figure 10 This is a digital photograph of Mg(OH)2, a product of a high magnesium-to-lithium ratio salt lake brine, produced by 230-hour periodic pulse electrolysis in Example 3. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0036] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0037] Furthermore, it should be noted that the terms "first," "second," etc., used in this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be used interchangeably where appropriate.

[0038] During water electrolysis, OH- ions are generated in situ on the cathode surface. - The core mechanism of magnesium-lithium precipitation separation, which leads to a localized alkaline microenvironment, lies in the difference in the pH required for precipitation of the two substances: Mg 2+ Mg(OH)₂ precipitate forms at pH ≈ 9.3, but Li₂ significantly adsorbs on the surface of Mg(OH)₂ when pH > 11. + This leads to co-precipitation. To address this, the present invention avoids the problem of magnesium-lithium co-precipitation by using a pulsed electrolysis mode with periodic "on / off" potentials.

[0039] Specifically, the pulsed electrocatalytic magnesium-lithium separation and extraction method of the present invention includes:

[0040] An electrode system is formed by a working electrode and a counter electrode. The working electrode is placed in the cathode chamber and the counter electrode is placed in the anode chamber. The cathode chamber and the anode chamber are separated by a proton exchange membrane. Both the cathode chamber and the anode chamber are filled with water containing magnesium ions and lithium ions as electrolyte.

[0041] A constant current is applied to the working electrode for a preset electrolysis time to carry out the electrolysis reaction. The application of the constant current to the working electrode is stopped for a preset interval time. This process is repeated several times. The electrolyte in the cathode chamber is subjected to solid-liquid separation to obtain magnesium hydroxide precipitate.

[0042] The pulsed electrocatalytic magnesium-lithium separation and extraction method of this invention is carried out by alternating between applying a constant current to the working electrode and stopping the application of the constant current, thereby achieving pulsed electrolysis through a periodic "on / off" potential, dividing the entire process into an electrolysis stage and an intermittent stage. During the electrolysis stage, a suitable amount of OH- is generated at the cathode. - Prefers Mg 2+ The combination forms Mg(OH)2 precipitate, which is attributed to Mg 2+ Its high charge density makes it effective against OH - The electrostatic attraction is much stronger than that of Li. + Meanwhile, Mg(OH)₂ has a low solubility product constant (Ksp≈1.8×10⁻⁶). -11 This promotes the preferential formation of precipitate, while Li + Due to strong hydration and a high solubility product constant (Ksp≈6.9×10⁻⁶), -2 OH remains in the solution; however, during the intermittent phase, OH... - Plasma is redistributed through diffusion, and the pH gradually becomes more balanced. This not only effectively alleviates the problem of HER efficiency decay caused by ion consumption and inhibits the formation of a highly alkaline microenvironment on the cathode surface, but also promotes the enrichment of the generated Mg(OH)2 precipitate at the bottom of the cathode chamber under gravity. This overcomes the problem of magnesium-lithium co-precipitation caused by excessive alkalinity in the local microenvironment of the electrode and the problem of electrode passivation and deactivation caused by the precipitate products encapsulating the catalytic active sites in the traditional constant potential / constant current electrolysis process. High-purity Mg(OH)2 precipitate and high-purity lithium solution are obtained, and the high-purity lithium solution is used for subsequent simple lithium extraction processes.

[0043] During the electrolysis process involving multiple cyclic "on / off" potential cycles, the quality of water containing magnesium and lithium ions is gradually improved, and magnesium and lithium are deeply separated, ultimately yielding a high-purity lithium solution for subsequent simple lithium extraction processes. Based on the pulsed electrocatalytic magnesium-lithium separation and extraction method provided by this invention, clean hydrogen energy, high-purity magnesium hydroxide, and battery-grade lithium salt products can be produced simultaneously.

[0044] In some preferred embodiments of the present invention, the preset electrolysis time is 600-1800 s, for example, it can be 600 s, 700 s, 800 s, 900 s, 1000 s, 1100 s, 1200 s, 1300 s, 1400 s, 1500 s, 1600 s, 1700 s, 1800 s, etc. More preferably, the preset electrolysis time is 800-1600 s. Too short a preset electrolysis time will reduce production efficiency, but too long a time can easily lead to magnesium-lithium co-precipitation and electrode passivation and deactivation caused by precipitate products encapsulating catalytic active sites. Therefore, the preset electrolysis time should be set reasonably. The preset electrolysis time selected in the present invention can both ensure electrolysis efficiency and effectively avoid the problems of magnesium-lithium co-precipitation and precipitate products encapsulating catalytic active sites.

[0045] In some preferred embodiments of the present invention, the preset interval time is 300-900 s, for example, it can be 300 s, 400 s, 500 s, 600 s, 700 s, 800 s, 900 s, etc. More preferably, the preset interval time is 400-800 s. The length of the preset interval time also has a certain impact on the electrolysis efficiency and the magnesium-lithium separation effect. When the preset interval time is too short, the ion diffusion is incomplete, and when the preset interval time is too long, the electrolysis efficiency will be reduced. Therefore, the preset interval time should be set reasonably.

[0046] In some preferred embodiments of the present invention, the ratio of the preset electrolysis time to the preset interval time is 1.0-3.0, for example, it can be 1.0, 1.5, 2, 2.5, 3.0, etc., and more preferably, the ratio of the preset electrolysis time to the preset interval time is 2. A reasonable match between the preset electrolysis time and the preset interval time can better avoid the problems of magnesium-lithium co-precipitation and precipitate products encapsulating catalytic active sites.

[0047] In one specific embodiment of the present invention, the preset electrolysis time is 1200 s and the preset interval time is 600 s.

[0048] In some preferred embodiments of the present invention, the cathode chamber is connected to a first electrolyte storage tank, the inlet of the cathode chamber is connected to the outlet of the first electrolyte storage tank via a pump, and the outlet of the cathode chamber is connected to the inlet of the first electrolyte storage tank via a pump; the anode chamber is connected to a second electrolyte storage tank, the inlet of the anode chamber is connected to the outlet of the second electrolyte storage tank via a pump, and the outlet of the anode chamber is connected to the inlet of the second electrolyte storage tank via a pump; the flow rate of the electrolyte is controlled by the pump, thereby achieving circulation of the electrolyte in the cathode chamber and the anode chamber respectively. The yield of precipitated products can be increased by increasing the volume of electrolyte in the first electrolyte storage tank and the volume of electrolyte in the second electrolyte storage tank.

[0049] In this invention, the flow rate of the electrolyte can be controlled at 5-20 mL / min.

[0050] In some preferred embodiments of the present invention, the high-purity lithium solution obtained from solid-liquid separation can be evaporated to extract lithium, thereby realizing the recycling of lithium.

[0051] In some preferred embodiments of the present invention, the constant current applied to the working electrode is 50-200 mA, for example, it can be 50 mA, 70 mA, 80 mA, 100 mA, 120 mA, 150 mA, 180 s, 200 mA, etc. More preferably, the constant current applied to the working electrode is 80-120 mA. Applying too small a constant current will reduce production efficiency, but applying too large a constant current will easily lead to excessive power consumption, so the magnitude of the constant current should be reasonable.

[0052] In some preferred embodiments of the present invention, the water containing magnesium ions and lithium ions can be salt lake brine or geothermal brine, wherein the molar ratio of magnesium ions to lithium ions is 5-30, more preferably 5-20.

[0053] In some preferred embodiments of the present invention, the working electrode is a nickel-based electrode, such as a nickel mesh, a nickel-chromium alloy mesh, and a nickel-copper alloy mesh.

[0054] In some preferred embodiments of the present invention, the counter electrode may be a platinum electrode or a graphite electrode.

[0055] The electrode system used in this invention can be a two-electrode system or a three-electrode system. When a three-electrode system is used, the electrode system also includes a reference electrode. The three-electrode system is composed of a working electrode, a reference electrode, and a counter electrode. The reference electrode can be an Ag / AgCl electrode.

[0056] In some preferred embodiments of the present invention, the proton exchange membrane used may be Nafion NR212.

[0057] The present invention also constructs a flow electrolytic cell reaction system to achieve deep separation and continuous production of magnesium and lithium.

[0058] Specifically, the flowing electrolyzer reaction system includes: an electrode system consisting of a working electrode and a counter electrode; a cathode chamber, an anode chamber, and a proton exchange membrane for isolating the cathode chamber and the anode chamber; a first electrolyte storage tank and a second electrolyte storage tank; a first pump, a second pump, a third pump, and a fourth pump; the working electrode is placed in the cathode chamber, and the counter electrode is placed in the anode chamber; the inlet of the cathode chamber is connected to the outlet of the first electrolyte storage tank via the first pump, and the outlet of the cathode chamber is connected to the inlet of the first electrolyte storage tank via the second pump; the inlet of the anode chamber is connected to the outlet of the second electrolyte storage tank via the third pump, and the outlet of the anode chamber is connected to the inlet of the second electrolyte storage tank via the fourth pump;

[0059] When the system is working, both the cathode chamber and the anode chamber are filled with water containing magnesium ions and lithium ions as electrolytes. The flow rate of the electrolyte entering the cathode chamber is controlled by a first pump, and the flow rate of the electrolyte entering the anode chamber is controlled by a third pump. The system operates in a pulse electrolysis mode with multiple periodic "on / off" potentials, gradually realizing the deep separation and continuous production of magnesium and lithium.

[0060] The cathode chamber and anode chamber described in this invention can be provided using an H-type electrochemical reaction cell.

[0061] Example 1: Pretreatment and Characterization of Nickel Mesh

[0062] High-purity nickel mesh (99.95%, 60 mesh, 0.5 mm thickness) was cut into 1 cm × 2 cm rectangular sheets and ultrasonically cleaned sequentially in acetone, ethanol, and deionized water (100 W, 30 min). It was then ultrasonically treated with a 2 mol / L H₂SO₄ solution (100 W, 30 min) to thoroughly remove surface impurities. After repeated washing with deionized water until neutral, the high-purity nickel mesh was dried in a 60℃ oven for 3 h to obtain clean nickel mesh.

[0063] Figure 1 X-ray diffraction pattern of a clean nickel mesh. Figure 1 The clean nickel mesh has three significant characteristic diffraction peaks. The peaks at ~44.51°, ~51.85° and ~76.73° correspond to the (111), (200) and (220) crystal planes of metallic nickel, respectively, which are consistent with Ni (PDF#04-0850). This proves that the clean nickel mesh has high purity and a single phase composition.

[0064] Example 2: Assembly and performance testing of the three-electrode system

[0065] In an H-type electrochemical reaction cell, a standard three-electrode system was constructed, consisting of a clean nickel mesh working electrode fixed by a platinum sheet electrode clamp, an Ag / AgCl reference electrode, and a high-purity platinum sheet counter electrode. The reaction medium in both electrode chambers was 30 mL of simulated high magnesium-to-lithium ratio brine from a salt lake (a mixed aqueous solution of 0.5 mol / L MgCl2 and 0.03 mol / L LiCl, with a magnesium-to-lithium mass ratio of ≈58 and a pH of ≈8.5), and the chambers were separated by a Nafion NR212 proton exchange membrane. The test platform was an electrochemical workstation (Shanghai Chenhua CHI760E).

[0066] (1) Constant current continuous static electrolysis

[0067] As a control, a constant current continuous static electrolysis test was conducted using the above standard three-electrode system. That is, a constant current of 50mA, 100mA and 150mA was applied to conduct a continuous static electrolysis reaction, and the chronopotential curves of electrolysis for 5000 s were obtained, and the change of potential over time was observed.

[0068] Figure 2 Chronopotential curves of clean nickel mesh were obtained by continuous static electrolysis for 5000 s in simulated high magnesium-to-lithium ratio brine using different constant currents (50 mA, 100 mA, and 150 mA). The results show that the clean nickel mesh exhibits basic HER performance in the electrolysis of simulated high magnesium-to-lithium ratio brine. However, the chronopotential curves during continuous electrolysis at different constant currents (50 mA, 100 mA, and 150 mA) show significant differences. The stability of the working electrode decreases with increasing constant current, mainly due to the in-situ generation of OH groups on the cathode surface of the clean nickel mesh under different constant currents. - Different concentrations (with the same electrolysis time, applying a higher current produces more OH-) - Applying a low current produces less OH - ), and OH - With Mg in the electrolyte 2+ The Mg(OH)2 precipitate is formed and encapsulates the nickel mesh electrode, leading to passivation and deactivation of the nickel active sites. Figure 2 The illustration clearly shows that after continuous static electrolysis at a constant current of 100 mA for 5000 s, the surface of the nickel mesh was coated with a thick layer of precipitate. This result indicates that when OH- ions are present on the cathode surface... - When a localized highly alkaline microenvironment is formed, the resulting Mg(OH)2 precipitate can clog the electrode, causing catalyst passivation and deactivation.

[0069] (2) Constant current continuous flow electrolysis

[0070] Based on the above standard three-electrode system, two bottles of simulated high magnesium-to-lithium ratio salt lake brine (a mixed aqueous solution of 0.5 mol / L MgCl2 and 0.03 mol / L LiCl, with a magnesium-to-lithium mass ratio of ≈58 and pH ≈8.5) were prepared and connected to the cathode and anode chambers of the H-type electrochemical reaction cell through pipelines. A four-channel peristaltic pump controlled the liquid flow rate at 10 mL / min to build a flow electrolysis cell reaction device.

[0071] As a control, a constant current continuous flow electrolysis test was conducted using a flow electrolyzer reactor. That is, a constant current of 100 mA was applied for continuous electrolysis reaction, while the electrolyte in the cathode and anode chambers was circulated. The chronopotential curves of electrolysis for 5000s were obtained, and the change of potential over time was observed.

[0072] Figure 3 Chronopotential curves of clean nickel mesh obtained by continuous flow electrolysis at a constant current of 100 mA for 5000 s in simulated high magnesium-to-lithium ratio salt lake brine. Figure 3 The inset clearly shows that after continuous electrolysis at a constant current of 100 mA for 5000 s, the nickel mesh surface was still covered with a thick layer of precipitated products. This result indicates that the electrolyte flow has little effect on the overall reaction system, and the problem of precipitated products covering catalytic active sites cannot be overcome by simply using electrolyte flow.

[0073] (3) Constant current pulse static electrolysis

[0074] Under static conditions, using a periodic "on / off" potential pulse electrolysis mode, a single cycle consisted of a constant current (100 mA) electrolysis time of 1200 s and an intermittent (0 mA) time of 600 s. Five sets of experiments were repeated using the same nickel mesh cathode for 30 cycles per set (each set using fresh simulated high magnesium-to-lithium ratio brine). Precipitated products were collected after every 30 cycles. Timo-potential curves for different pulse periods and Raman curves for different electrolysis times were obtained, and the degree of scaling on the nickel mesh surface was observed. Linear sweep voltammetry curves were recorded at a scan rate of 10 mV / s.

[0075] Figure 4 The chronopotential curves of the clean nickel mesh were obtained by static electrolysis at a constant current of 100 mA for 1200 s in simulated high magnesium-to-lithium ratio brine. The results show that Mg(OH)₂ precipitate stably formed on the upper layer of the electrolyte during 1200 s electrolysis at a constant current (100 mA), while the catalytic activity of the clean nickel mesh cathode remained stable, indicating that the electrode surface was not significantly coated with precipitate products at this time.

[0076] Figure 5Raman curves of clean nickel mesh obtained by static electrolysis at a constant current of 100 mA for different times (0 s, 200 s, 400 s, 600 s, 800 s, 1000 s, 1200 s, 1400 s, 1600 s, and 1800 s) in simulated high magnesium-to-lithium ratio brine of a salt lake are shown in the figure. The results in the figure show that after static electrolysis at a constant current of 100 mA for 600 s, the cleaning effect is achieved at 275 cm⁻¹. -1 and 443 cm -1 The presence of a characteristic peak belonging to magnesium hydroxide at this point indicates that the preset electrolysis time starting point can be selected at 600 s. As the electrolysis time continues to increase to 1200 s, the peak at 275 cm⁻¹ appears. -1 and 443 cm -1 The characteristic peak at 275 cm⁻¹ gradually increases, indicating a gradual increase in the enrichment of magnesium hydroxide precipitate. Based on this, the electrolysis time was further extended to 1800 s, and the peak at 275 cm⁻¹ was observed. -1 and 443 cm -1 The characteristic peak intensity remained essentially unchanged, indicating that a thin layer of magnesium hydroxide had begun to form on the electrode surface. Therefore, the present invention sets the preset electrolysis time to 600-1800 s.

[0077] Figure 6 Chronopotential curves of five pulse electrolysis cycles (30 cycles per cycle) in simulated high magnesium-to-lithium ratio brine for cleaning nickel mesh. Figure 6 It can be seen that compared to constant current continuous electrolysis ( Figure 2 The scaling phenomenon on the nickel mesh surface was significantly improved after periodic pulse electrolysis, and approximately 1 g of precipitated product was obtained in each group of experiments. This result demonstrates that the pulse electrolysis mode of this invention can effectively overcome the problem of precipitated products encapsulating catalytic active sites.

[0078] Figure 7 Linear sweep voltammetry curves of the nickel mesh after each set of periodic pulse electrolysis in simulated high magnesium-to-lithium ratio brine were obtained. With the increase of the number of periodic pulse electrolysis sets, scaling on the nickel mesh surface increased slightly, and the corresponding HER activity decreased slightly.

[0079] Figure 8 The X-ray diffraction pattern of the collected precipitate is shown in the figure. The results show that the precipitate has 9 characteristic diffraction peaks. The characteristic diffraction peaks at ~18.53°, ~32.88°, ~37.98°, ~50.78°, ~58.67°, ~62.11°, ~68.21°, ~68.89° and ~72.07° correspond to the (001), (100), (101), (102), (110), (111), (103), (200) and (201) crystal planes of Mg(OH)2, which are consistent with Mg(OH)2 (PDF#44-1482), proving that the product is Mg(OH)2 and has high purity.

[0080] Example 3: Construction and performance testing of a flowing electrolyzer reactor

[0081] Based on the above standard three-electrode system, two bottles of simulated high magnesium-to-lithium ratio salt lake brine (a mixed aqueous solution of 0.5 mol / L MgCl2 and 0.03 mol / L LiCl, with a magnesium-to-lithium mass ratio of ≈58 and pH ≈8.5) were prepared and connected to the cathode and anode chambers of the H-type electrochemical reaction cell through pipelines. A four-channel peristaltic pump controlled the liquid flow rate at 10 mL / min to build a flow electrolysis cell reaction device.

[0082] Figure 9 The timing potential curve of clean nickel mesh was simulated in a high magnesium-to-lithium ratio brine lake using a 230-hour periodic pulse electrolysis process in a flowing electrolyzer. By constructing a flowing electrolyzer reactor, the clean nickel mesh could be continuously and stably operated for at least 230 hours in a periodic "on / off" potential pulse electrolysis mode.

[0083] Figure 10 Digital photographs of Mg(OH)₂ produced from high-Mg-to-Li ratio brine in a 230-h periodic pulse electrolysis simulation. The results show a total production of ~22 g of Mg(OH)₂, with a production rate of ~95 mg / (h / cm²). 2 ).

[0084] In summary, this invention ingeniously utilizes the locally alkaline microenvironment generated in situ during the cathode hydrogen evolution reaction. By dynamically controlling the local microenvironment at the electrode interface through a periodic "on / off" potential pulse electrolysis mode, it overcomes the electrode passivation and deactivation problems caused by excessive alkalinity in the local electrode microenvironment during traditional constant potential / constant current electrolysis processes, which result in magnesium-lithium co-precipitation and the encapsulation of catalytic active sites by precipitate products. This technology significantly simplifies the traditional lithium extraction process from salt lakes, achieves efficient synergy between hydrogen production and mineral resource development, and provides a new approach for the development of high magnesium-to-lithium ratio salt lake resources.

[0085] Obviously, the above embodiments of the present invention are merely examples to illustrate the present invention more clearly, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all implementation methods here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for separating and extracting magnesium and lithium via pulsed electrocatalysis, characterized in that, include: An electrode system is formed by a working electrode and a counter electrode. The working electrode is placed in the cathode chamber and the counter electrode is placed in the anode chamber. The cathode chamber and the anode chamber are separated by a proton exchange membrane. Both the cathode chamber and the anode chamber are filled with water containing magnesium ions and lithium ions as electrolyte. The molar ratio of magnesium ions to lithium ions in the electrolyte is 5-30. A constant current is applied to the working electrode for a preset electrolysis time to carry out the electrolysis reaction. The application of the constant current to the working electrode is stopped for a preset interval time. This cycle is repeated several times. The electrolyte in the cathode chamber is subjected to solid-liquid separation to obtain magnesium hydroxide precipitate. The constant current is 80-120 mA. The preset electrolysis time is 600-1800 s, and the preset interval time is 300-900 s; the ratio of the preset electrolysis time to the preset interval time is 1.0-3.

0.

2. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 1, characterized in that, The cathode chamber is connected to a first electrolyte storage tank. The inlet of the cathode chamber is connected to the outlet of the first electrolyte storage tank via a pump, and the outlet of the cathode chamber is connected to the inlet of the first electrolyte storage tank via a pump. The anode chamber is connected to a second electrolyte storage tank. The inlet of the anode chamber is connected to the outlet of the second electrolyte storage tank via a pump, and the outlet of the anode chamber is connected to the inlet of the second electrolyte storage tank via a pump. The flow rate of the electrolyte is controlled by the pump.

3. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 1, characterized in that, Lithium is extracted by evaporation of the liquid obtained from solid-liquid separation.

4. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 1, characterized in that, The water containing magnesium and lithium ions is salt lake brine and geothermal brine.

5. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 1, characterized in that, The working electrode is a nickel-based electrode.

6. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 5, characterized in that, The nickel-based electrode is a nickel mesh, a nickel-chromium alloy mesh, or a nickel-copper alloy mesh.

7. The pulsed electrocatalytic magnesium-lithium separation and extraction method according to claim 1, characterized in that, The electrode system also includes a reference electrode.

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