阅读说明：本技术 一种氯化物型含锂盐水电化学提锂制备碳酸锂的方法 (Method for preparing lithium carbonate by electrochemically extracting lithium from chloride type lithium-containing brine ) 是由 杨文胜 周帅 王晓丽 刘长霞 于 2020-12-23 设计创作，主要内容包括：本发明涉及一种从氯化物型含锂盐水中电化学提锂直接制备碳酸锂的方法。以氯化物型含锂盐水为电解液,锂离子筛电极和氯离子捕获电极分别作为正负极构成原电池,原电池放电将盐水中锂离子嵌入锂离子筛中；以锂盐回收溶液为电解液,嵌入锂离子的锂离子筛电极和惰性电极分别作为阳极和阴极构建电解池,电解池充电将锂离子脱出到锂盐回收溶液中；重复上述嵌锂-脱锂步骤,待锂盐回收溶液中锂盐浓度接近饱和时升高温度,利用碳酸锂溶解度随温度升高而减小的特性析出碳酸锂。利用该方法可以直接获得高纯度碳酸锂,并且可以联产氢气和氯气等重要化工原料,生产成本低,易于工业化实施。(The invention relates to a method for directly preparing lithium carbonate by electrochemically extracting lithium from chloride type lithium-containing brine. Chloride type lithium-containing brine is used as electrolyte, a lithium ion sieve electrode and a chloride ion capturing electrode are respectively used as a positive electrode and a negative electrode to form a primary battery, and the primary battery discharges to embed lithium ions in the brine into a lithium ion sieve; the lithium salt recovery solution is used as electrolyte, a lithium ion sieve electrode and an inert electrode which are embedded with lithium ions are respectively used as an anode and a cathode to construct an electrolytic cell, and the electrolytic cell is charged to remove the lithium ions into the lithium salt recovery solution; and repeating the lithium intercalation-lithium removal steps, raising the temperature when the concentration of the lithium salt in the lithium salt recovery solution is close to saturation, and precipitating the lithium carbonate by utilizing the characteristic that the solubility of the lithium carbonate is reduced along with the temperature rise. The method can be used for directly obtaining high-purity lithium carbonate, can be used for coproducing important chemical raw materials such as hydrogen, chlorine and the like, has low production cost and is easy for industrial implementation.)

1. A method for directly preparing lithium carbonate by electrochemically extracting lithium from chloride type lithium-containing brine is characterized by comprising the following steps:

(1) chloride type lithium-containing brine is used as an electrolyte solution, a lithium ion sieve electrode and a chloride ion capturing electrode are respectively used as a positive electrode and a negative electrode to form a primary battery, the primary battery discharges by using the theoretical current of embedding lithium ions in a lithium ion sieve for 2-10 hours, the lithium ions in the brine are embedded in the lithium ion sieve, and meanwhile, the chloride ions in the brine are captured by the chloride ion capturing electrode;

(2) taking a lithium salt recovery solution as an electrolyte solution, taking a lithium ion sieve electrode and an inert electrode which are inserted with lithium ions in the step (1) as an anode and a cathode respectively to form an electrolytic cell, charging the electrolytic cell by using theoretical current of the lithium ion sieve for 1-5 hours to remove all lithium ions, removing the lithium ions into the lithium salt recovery solution, regenerating the lithium ion sieve electrode, and simultaneously separating hydrogen on the inert electrode cathode;

(3) taking a metal chloride solution as an electrolyte solution, and taking the capture electrode and the inert electrode for capturing chloride ions in the step (1) as a cathode and an anode respectively to form an electrolytic cell, charging the electrolytic cell by the same current in the step (2), removing the chloride ions captured by the capture electrode, regenerating the chloride ion capture electrode, and simultaneously separating out chlorine on the inert electrode anode;

(4) respectively taking the lithium ion sieve electrode regenerated in the step (2) and the chloride ion capture electrode regenerated in the step (3) as a positive electrode and a negative electrode to reconstruct the primary battery, repeating the steps (1) to (3), repeatedly using the lithium salt recovery solution in the step (2), continuously increasing the concentration of lithium ions, increasing the temperature to 60-90 ℃ when the concentration of lithium salts in the lithium salt recovery solution is close to saturation, keeping the temperature for 30-120 minutes, separating out lithium carbonate precipitate by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the increase of the temperature, leaching the precipitate by deionized water, and drying at the temperature of 200-;

(5) introducing carbon dioxide CO into the solution of the lithium carbonate precipitate separated in the step (4)₂The obtained bicarbonate solution can be used as a lithium salt recovery solution for recycling.

2. The method according to claim 1, wherein the chloride-type lithium-containing brine in step (1) is one of salt lake brine or an evaporative concentrate thereof, seawater or an evaporative concentrate thereof, and brine containing LiCl.

3. The preparation method according to claim 1, wherein the lithium ion sieve electrode in step (1) is spinel-type LiMn₂O₄Or olivine type LiFePO₄lambda-MnO obtained by electrochemical delithiation of an initial electrode consisting of electrode active material₂Or FePO₄Electrode for electrochemical cell(ii) a The initial electrode is made of spinel-type LiMn₂O₄Or olivine type LiFePO₄One of electrode active materials, one of acetylene black or conductive graphite conductive additives and one of polytetrafluoroethylene PTFE or polyvinylidene fluoride PVDF binding agents are mixed according to a certain proportion and coated on a current collector to obtain the electrode; the current collector is one of a titanium net or a nickel net, the mass percentages of the electrode active material, the conductive additive and the binder are respectively 80-90%, 5-10% and 5-10% except the current collector, and the sum of the mass percentages of the electrode active material, the conductive additive and the binder is 100%.

4. The method according to claim 1, wherein the chloride ion capturing electrode in step (1) is one of a silver Ag electrode, an activated carbon AC electrode, a polypyrrole Ppy electrode, or a polyaniline PANI electrode; the chloride ion capturing electrode is obtained by mixing and coating one of active substances such as Ag powder, active carbon AC, polypyrrole Ppy or polyaniline PANI, one of acetylene black or conductive graphite conductive additives and one of polytetrafluoroethylene PTFE or polyvinylidene fluoride PVDF binding agents on a current collector according to a certain proportion; the current collector is one of a titanium net or a nickel net, the mass percentages of the electrode active material, the conductive additive and the binder are respectively 80-90%, 5-10% and 5-10% except the current collector, and the sum of the mass percentages of the electrode active material, the conductive additive and the binder is 100%.

5. The method according to claim 1, wherein the lithium salt recovery solution in step (2) is NaHCO sodium bicarbonate₃Or potassium bicarbonate KHCO₃One of the water solutions has a concentration of 0.1 to 0.7 mol/L.

6. The method of claim 1, wherein the inert electrode in step (2) is one of a titanium mesh, a titanium-coated metal mesh, a carbon rod, a platinum mesh, or a platinum sheet.

7. The method according to claim 1, wherein the metal chloride solution in step (3) is one of sodium chloride (NaCl) solution and potassium chloride (KCl) solution, and the concentration is 0.5-1.0 mol/L.

8. The method of claim 1, wherein the inert electrode in step (3) is one of a titanium mesh, a titanium-coated metal mesh, a carbon rod, a platinum mesh, or a platinum sheet.

9. The method according to claim 1, wherein the bicarbonate in step (5) is NaHCO₃Or potassium bicarbonate KHCO₃One kind of (1).

Technical Field

The invention relates to a method for directly preparing lithium carbonate by electrochemically extracting lithium from chloride type lithium-containing brine, belonging to the technical field of extraction and utilization of lithium resources.

Background

With the popularization of intelligent electronic devices, lithium ion batteries are widely used in various electronic devices such as mobile phones, computers, cameras and the like; the development of new energy electric vehicles widens the application field of lithium ion batteries and increases the market demand of the lithium ion batteries. Therefore, development of lithium resources is urgently needed to provide high-quality low-cost battery grade lithium carbonate raw material for lithium ion batteries.

Lithium resources are divided into two main categories, namely ore lithium resources and brine lithium resources. Compared with the production of lithium salt by taking ore as a raw material, the energy consumption and the cost for producing the lithium salt by taking brine as the raw material are low, so that the main approach for obtaining the lithium salt in recent years is changed from the ore lithium resource to the brine lithium resource. However, lithium-containing brine such as salt lake brine, seawater and the like has complex composition, contains various anions and cations, and is extremely difficult to selectively extract lithium. Therefore, various lithium extraction methods including precipitation, solvent extraction, ion exchange adsorption, membrane separation, carbonization, calcination leaching, and electrochemical methods have been developed.

The electrochemical lithium extraction method has the advantages of energy conservation, environmental protection, simple operation and the like, can obviously improve the extraction efficiency of lithium ions, and has attracted extensive attention of people in recent years. In document (1), chinese patent publication No. CN105600807A, yanwensheng et al discloses a method for electrochemically extracting lithium salt from brine with high magnesium-lithium ratio. However, the electrochemical extraction of lithium from chloride-type lithium-containing brine usually results in lithium chloride LiCl, which needs to be further converted into lithium carbonate Li₂CO₃Or lithium hydroxide LiOH can be used as a raw material of the battery. Battery grade Li₂CO₃The requirement on the content of the chloride ions is severe, for example, according to the industry standard YS/T582-₂CO₃The process is complex and the cost is high. If it were possible to produce battery grade Li directly from brine by electrochemical methods₂CO₃Has important scientific significance and commercial value.

Disclosure of Invention

The invention aims to provide a method for directly preparing lithium carbonate by electrochemically extracting lithium from chloride type lithium-containing brineThe working principle is as follows: chloride type lithium-containing brine is used as an electrolyte solution, a lithium ion sieve electrode and a chloride ion capturing electrode are respectively used as a positive electrode and a negative electrode to form a primary battery, and the primary battery discharges to embed lithium ions in the brine into a lithium ion sieve; the lithium salt recovery solution is used as an electrolyte solution, a lithium ion sieve electrode and an inert electrode which are embedded with lithium ions are respectively used as an anode and a cathode to construct an electrolytic cell, the electrolytic cell is charged to remove the lithium ions into the lithium salt recovery solution, the lithium ion sieve electrode is regenerated, and hydrogen is separated out from the inert electrode; the method comprises the following steps of (1) taking a metal chloride solution as an electrolyte solution, taking a capture electrode for capturing chloride ions and an inert electrode as a cathode and an anode respectively to form an electrolytic cell, removing the chloride ions captured by the capture electrode by charging the electrolytic cell, regenerating the chloride ion capture electrode, and separating out chlorine on the inert electrode; the regenerated lithium ion sieve electrode and the chlorine ion capturing electrode can be recombined into a primary battery, the steps of lithium intercalation and lithium deintercalation are repeated, the temperature is raised when the concentration of lithium salt in the lithium salt recovery solution is close to saturation, lithium carbonate precipitate is separated out by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the temperature rise, and the precipitate is leached and dried to obtain a lithium carbonate product; introducing carbon dioxide CO into the solution from which the lithium carbonate precipitate is separated₂The obtained bicarbonate solution can be used as a lithium salt recovery solution for recycling. With lambda-MnO₂The working principle of extracting lithium from the primary battery and regenerating the two electrodes by using the lithium ion sieve electrode as the positive electrode and the activated carbon AC chloride ion capture electrode as the negative electrode is shown in figure 1. The method comprises the following specific process steps:

(1) chloride type lithium-containing brine is used as an electrolyte solution, a lithium ion sieve electrode and a chloride ion capturing electrode are respectively used as a positive electrode and a negative electrode to form a primary battery, the primary battery discharges by using theoretical current (0.1-0.5C multiplying power) of lithium ion sieve full of lithium ions for 2-10 h, the lithium ions in the brine are embedded into the lithium ion sieve, and meanwhile, the chloride ions in the brine are captured by the chloride ion capturing electrode; wherein, the chloride type lithium-containing brine is one of salt lake brine or an evaporation concentrated solution thereof, seawater or an evaporation concentrated solution thereof and brine containing LiCl; the lithium ion sieve electrode is spinel-type LiMn₂O₄Or olivine type LiFePO₄The initial electrode composed of electrode active material is electrochemically removedlambda-MnO obtained after lithium₂Or FePO₄Electrodes, starting with spinel LiMn₂O₄Or olivine type LiFePO₄The electrode comprises one of electrode active materials, one of acetylene black or conductive graphite conductive additives, one of polytetrafluoroethylene PTFE or polyvinylidene fluoride PVDF binders, and a current collector, wherein the current collector is one of a titanium net or a nickel net, the electrode active materials, the conductive additives and the binders are 80-90%, 5-10% and 5-10% in percentage by mass respectively except the current collector, and the sum of the three is 100%; the chloride ion capturing electrode is one of a silver Ag electrode, an active carbon AC electrode, a polypyrrole Ppy electrode or a polyaniline PANI electrode; the chloride ion capturing electrode is obtained by mixing and coating one of active substances such as Ag powder, active carbon AC, polypyrrole Ppy or polyaniline PANI, one of acetylene black or conductive graphite conductive additives and one of polytetrafluoroethylene PTFE or polyvinylidene fluoride PVDF binding agents on a current collector according to a certain proportion; the current collector is one of a titanium net or a nickel net, the mass percentages of the electrode active material, the conductive additive and the binder are respectively 80-90%, 5-10% and 5-10% except the current collector, and the sum of the mass percentages of the electrode active material, the conductive additive and the binder is 100%.

(2) Taking a lithium salt recovery solution as an electrolyte solution, and taking a lithium ion sieve electrode and an inert electrode which are inserted with lithium ions in the step (1) as an anode and a cathode respectively to form an electrolytic cell, wherein the electrolytic cell is charged by theoretical current (0.2-1.0C multiplying power) of the lithium ion sieve which is used for separating all lithium ions for 1-5 h, the lithium ions are separated into the lithium salt recovery solution, the lithium ion sieve electrode is regenerated, and hydrogen is separated out from the inert electrode cathode; wherein the lithium salt recovery solution is sodium bicarbonate NaHCO₃Or potassium bicarbonate KHCO₃One of the water solutions has the concentration of 0.1-0.7 mol/L; the inert electrode is one of a titanium mesh, a titanium-coated metal mesh, a carbon rod, a platinum mesh or a platinum sheet.

(3) Taking a metal chloride solution as an electrolyte solution, and taking a capture electrode and an inert electrode for capturing chloride ions in the step (1) as a cathode and an anode respectively to form an electrolytic cell, charging the electrolytic cell by the same current in the step (2), removing the chloride ions captured by the capture electrode, regenerating the chloride ion capture electrode, and simultaneously separating out chlorine on the inert electrode anode; wherein the metal chloride solution is one of a sodium chloride (NaCl) solution and a potassium chloride (KCl) solution, and the concentration of the metal chloride solution is 0.5-1.0 mol/L; the inert electrode is one of a titanium mesh, a titanium-coated metal mesh, a carbon rod, a platinum mesh or a platinum sheet.

(4) And (3) respectively using the lithium ion sieve electrode regenerated in the step (2) and the chloride ion capture electrode regenerated in the step (3) as a positive electrode and a negative electrode to reconstruct the primary battery, repeating the steps (1) to (3), repeatedly using the lithium salt recovery solution in the step (2), continuously increasing the concentration of lithium ions, increasing the temperature to 60-90 ℃ when the concentration of lithium salts in the lithium salt recovery solution is close to saturation, keeping the temperature for 30-120 minutes, separating out lithium carbonate precipitate by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the temperature increase, rinsing the precipitate by deionized water, and drying at the temperature of 200-300 ℃ to obtain a lithium carbonate product.

(5) Introducing carbon dioxide CO into the solution of the lithium carbonate precipitate separated in the step (4)₂The obtained bicarbonate solution can be used as a lithium salt recovery solution for recycling; wherein the bicarbonate is sodium bicarbonate NaHCO₃Or potassium bicarbonate KHCO₃One kind of (1).

Preparing lithium carbonate Li by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and ion chromatography₂CO₃Elemental content, Li, in the sample₂CO₃Content (wt.)>99% and chloride ion content<20ppm, no SO detected₄ ^2-Anion and Mg²⁺,Ca²⁺,K⁺,Na⁺And (5) waiting for positive ions, wherein the obtained lithium carbonate meets the index requirement of battery-grade lithium carbonate.

The method of the invention has the characteristics and advantages that: (1) the method of the invention can directly obtain Li₂CO₃With conversion to Li using LiCl₂CO₃Compared with the method, the interference of chloride ions in LiCl can be avoided, and the method is favorable for obtaining high-purity battery grade Li with low chloride ion content₂CO₃The process is simple and the cost is low; (2) the lithium ion sieve electrode and the chloride ion capture electrode can be bothRaw utilization, sodium bicarbonate NaHCO₃Or potassium bicarbonate KHCO₃The lithium salt recovery solution can be recycled; (3) the method releases electric energy in the process of extracting lithium, and the electric energy is consumed in the process of regenerating the lithium ion sieve electrode and the chloride ion capture electrode, and the released electric energy can be used for electric energy consumption of electrode regeneration; (4) the method of the invention produces hydrogen, chlorine and other important chemical raw materials in the electrode regeneration process; in conclusion, the method disclosed by the invention is low in production cost and environment-friendly.

Drawings

FIG. 1 shows a formula of lambda-MnO₂The lithium ion sieve electrode is used as the positive electrode, and the active carbon AC chloride ion capture electrode is used as the negative electrode to form a working principle schematic diagram of lithium extraction of the primary battery and regeneration of the two electrodes.

Detailed Description

Example 1

(1) Weighing 16g of spinel lithium manganate LiMn₂O₄Uniformly mixing 2g of acetylene black conductive agent and 2g of polyvinylidene fluoride (PVDF) binder (PVDF is dissolved in N-methyl pyrrolidone to form suspension with the mass fraction of 4 wt%), forming slurry, coating the slurry on a titanium mesh current collector, and drying in a vacuum oven at 75 ℃ for 12 hours to obtain LiMn₂O₄An electrode, taking the electrode as an anode and a titanium mesh as a cathode, and NaHCO with the concentration of 0.6mol/L₃The solution is used as electrolyte solution to construct an electrolytic cell, and the cell is charged to 1.1V (vs. Ag/AgCl) at a rate of 0.5C to obtain lambda-MnO₂A lithium ion sieve electrode; weighing 16g of activated carbon AC, 2g of acetylene black conductive agent and 2g of polyvinylidene fluoride PVDF binder (PVDF is dissolved in N-methyl pyrrolidone to form a suspension with the mass fraction of 4 wt%), uniformly mixing to form slurry, coating the slurry on a titanium mesh current collector, and drying in a vacuum oven at 75 ℃ for 12 hours to obtain an activated carbon AC chloride ion capture electrode; with the above-mentioned lambda-MnO₂The lithium ion sieve electrode and the active carbon AC chloride ion capture electrode are respectively used as a positive electrode and a negative electrode, the Qinghai Sitai Gineller salt lake brine is used as an electrolyte solution to construct a primary battery, the primary battery is discharged to 0.3V (vs. Ag/AgCl) at a rate of 0.5C, and lithium ions in the salt lake brine are inserted into lambda-MnO₂In the lithium ion sieve, chloride ions in the salt lake brine are captured by an activated carbon AC capture electrode.

(2) lambda-MnO with lithium ions intercalated in step (1)₂The lithium ion sieve electrode is taken as an anode, the titanium mesh is taken as a cathode, and NaHCO with the concentration of 0.6mol/L is taken₃The solution is used as electrolyte solution to construct an electrolytic cell, the electrolytic cell is charged at 0.5C multiplying power, the charge cut-off voltage is 1.1V (vs. Ag/AgCl), and lithium ions are extracted to NaHCO₃Formation of LiHCO in solution₃And further form Li₂CO₃，λ-MnO₂The lithium ion sieve electrode is regenerated, and hydrogen is separated out from the titanium mesh cathode.

(3) And (2) taking the activated carbon AC electrode for capturing the chloride ions in the step (1) as a cathode, taking a titanium mesh as an anode, and taking a NaCl solution with the concentration of 0.5mol/L as an electrolyte solution to construct an electrolytic cell, charging for 2h at the multiplying power of 0.5C, removing the chloride ions from the activated carbon electrode, regenerating the activated carbon AC chloride ion capturing electrode, and simultaneously precipitating chlorine on the titanium mesh anode.

(4) With lambda-MnO regenerated in step (2)₂And (3) the lithium ion sieve electrode and the activated carbon AC chloride ion capture electrode regenerated in the step (3) are respectively used as a positive electrode and a negative electrode to reconstruct the primary battery, the steps (1) to (3) are repeated, and NaHCO is used in the step (2)₃The lithium salt recovery solution is repeatedly used for many times, wherein the concentration of lithium ions is continuously increased until NaHCO is reached₃And when the concentration of lithium salt in the solution is close to saturation, raising the temperature to 90 ℃, keeping the temperature for 30 minutes, separating out lithium carbonate precipitate by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the temperature rise, rinsing the precipitate by deionized water, and drying at 300 ℃ to obtain a lithium carbonate product. ICP-AES and ion chromatography testing Li₂CO₃The purity was 99.3% and the chloride ion content was 18 ppm.

(5) Introducing carbon dioxide CO into the solution of the lithium carbonate precipitate separated in the step (4)₂Obtaining NaHCO₃The solution can be recycled as a lithium salt recovery solution.

Example 2

(1) 18g of olivine-type LiFePO were weighed₄1gKS-6 conductive graphite and 1g of polytetrafluoroethylene PTFE binder (PTFE is prepared into suspension with the mass fraction of 5 wt%) are uniformly mixed to form slurry, the slurry is coated on a nickel mesh current collector, and the nickel mesh current collector is dried for 8 hours in a vacuum oven at the temperature of 90 ℃ to obtain LiFePO₄An electrode as an anode and a platinum mesh as a cathodeCathode, KHCO with concentration of 0.2mol/L₃The solution is used as electrolyte solution to construct an electrolytic cell, and the electrolytic cell is charged to 1.1V (vs. Ag/AgCl) at a rate of 0.2C to obtain FePO₄A lithium ion sieve electrode; weighing 18g of silver Ag powder, 1g of KS-6 conductive graphite and 1g of polytetrafluoroethylene PTFE binder (PTFE is prepared into 5 wt% suspension), uniformly mixing to form slurry, coating the slurry on a nickel mesh current collector, and drying in a vacuum oven at 90 ℃ for 8 hours to obtain a silver Ag chloride ion capture electrode; with the above FePO₄The lithium ion sieve electrode and the silver Ag chloride ion capture electrode are respectively used as a positive electrode and a negative electrode, the Bohai Bay concentrated seawater is used as an electrolyte solution to construct a primary battery, the primary battery is discharged to 0.3V (vs. Ag/AgCl) at a rate of 0.1C, and lithium ions in the concentrated seawater are embedded into FePO₄In the lithium ion sieve, chloride ions in seawater are captured by the silver Ag capture electrode.

(2) FePO for lithium ion intercalation in step (1)₄The lithium ion sieve electrode is used as an anode, the platinum net is used as a cathode, and KHCO with the concentration of 0.2mol/L is used₃The solution is used as electrolyte solution to construct an electrolytic cell, the electrolytic cell is charged at 0.2C multiplying power, the charge cut-off voltage is 1.1V (vs. Ag/AgCl), and lithium ions are extracted to KHCO₃Formation of LiHCO in solution₃And further form Li₂CO₃，FePO₄The lithium ion sieve electrode is regenerated, and hydrogen is separated out from the platinum mesh cathode.

(3) And (2) establishing an electrolytic cell by taking the silver Ag electrode for capturing the chloride ions in the step (1) as a cathode, a platinum net as an anode and a KCl solution with the concentration of 0.7mol/L as an electrolyte solution, charging for 5 hours at the rate of 0.2C, removing the chloride ions from the silver Ag electrode, regenerating the silver Ag chloride ion capturing electrode, and simultaneously precipitating chlorine on the platinum net anode.

(4) With FePO regenerated in step (2)₄And (3) respectively using the lithium ion sieve electrode and the silver Ag chloride ion capture electrode regenerated in the step (3) as a positive electrode and a negative electrode to reconstruct the primary battery, repeating the steps (1) to (3), and performing KHCO treatment in the step (2)₃The lithium salt recovery solution is reused for many times, wherein the concentration of lithium ions is continuously increased until KHCO is reached₃Raising the temperature to 60 ℃ when the concentration of lithium salt in the solution is close to saturation, keeping the temperature for 120 minutes, separating out lithium carbonate precipitate by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the temperature rise, and removing the precipitateRinsing with the sub-water and drying at 200 ℃ to obtain the lithium carbonate product. ICP-AES and ion chromatography testing Li₂CO₃The purity was 99.5% and the chloride ion content was 12 ppm.

(5) Introducing carbon dioxide CO into the solution of the lithium carbonate precipitate separated in the step (4)₂KHCO is obtained₃The solution can be recycled as a lithium salt recovery solution.

Example 3

(1) Weighing 17g of spinel lithium manganate LiMn₂O₄Uniformly mixing 2g of acetylene black conductive agent and 1g of polyvinylidene fluoride (PVDF) binder (PVDF is dissolved in N-methyl pyrrolidone to form suspension with the mass fraction of 4 wt%) to form slurry, coating the slurry on a titanium mesh current collector, and drying in a vacuum oven at 100 ℃ for 6 hours to obtain LiMn₂O₄An electrode, which is taken as an anode, a stainless steel mesh coated with titanium is taken as a cathode, and NaHCO with the concentration of 0.4mol/L₃The solution is used as electrolyte solution to construct an electrolytic cell, and the cell is charged to 1.1V (vs. Ag/AgCl) at a rate of 1.0C to obtain lambda-MnO₂A lithium ion sieve electrode; weighing 17g of polypyrrole Ppy, 2g of acetylene black conductive agent and 1g of polyvinylidene fluoride PVDF binder (PVDF is dissolved in N-methyl pyrrolidone to form suspension with the mass fraction of 4 wt%), uniformly mixing to form slurry, coating the slurry on a titanium mesh current collector, and drying in a vacuum oven at 100 ℃ for 6 hours to obtain a polypyrrole Ppy chloride ion capture electrode; with the above-mentioned lambda-MnO₂The lithium ion sieve electrode and the polypyrrole Ppy chloride ion capture electrode are respectively used as a positive electrode and a negative electrode, a primary battery is constructed by taking chloride type factory waste saline water with LiCl concentration of about 0.05mol/L and containing various alkali metal ions and alkaline earth metal ions as an electrolyte solution, the primary battery is discharged to 0.3V (vs. Ag/AgCl) at a rate of 0.3C, and lithium ions in the saline water are inserted into lambda-MnO₂In the lithium ion sieve, chloride ions in the saline water are captured by the polypyrrole Ppy capture electrode.

(2) lambda-MnO with lithium ions intercalated in step (1)₂The lithium ion sieve electrode is taken as an anode, the stainless steel mesh coated with titanium is taken as a cathode, and NaHCO with the concentration of 0.4mol/L is taken₃The solution is used as electrolyte solution to construct an electrolytic cell, the electrolytic cell is charged at the rate of 1.0C, the charge cut-off voltage is 1.1V (vs. Ag/AgCl), and lithium ions are extracted to NaHCO₃In solutionFormation of LiHCO₃And further form Li₂CO₃，λ-MnO₂The lithium ion sieve electrode is regenerated, and hydrogen is separated out from the titanium-coated stainless steel mesh cathode.

(3) And (2) constructing an electrolytic cell by using the polypyrrole Ppy electrode for capturing chloride ions in the step (1) as a cathode, a stainless steel mesh coated with titanium as an anode and a NaCl solution with the concentration of 0.2mol/L as an electrolyte solution, charging for 1.2h at the multiplying power of 1.0 ℃, removing the chloride ions from the polypyrrole Ppy electrode, regenerating the polypyrrole Ppy chloride ion capturing electrode, and simultaneously precipitating chlorine on the anode of the stainless steel mesh coated with titanium.

(4) With lambda-MnO regenerated in step (2)₂And (3) respectively using the lithium ion sieve electrode and the regenerated polypyrrole Ppy chloride ion capture electrode in the step (3) as positive and negative electrodes to reconstruct the primary battery, repeating the steps (1) to (3), and using NaHCO in the step (2)₃The lithium salt recovery solution is repeatedly used for many times, wherein the concentration of lithium ions is continuously increased until NaHCO is reached₃And when the concentration of lithium salt in the solution is close to saturation, raising the temperature to 80 ℃, keeping the temperature for 60 minutes, separating out lithium carbonate precipitate by utilizing the characteristic that the solubility of lithium carbonate is reduced along with the temperature rise, rinsing the precipitate by deionized water, and drying at 250 ℃ to obtain a lithium carbonate product. ICP-AES and ion chromatography testing Li₂CO₃The purity was 99.7% and the chloride ion content was 15 ppm.

(5) Introducing carbon dioxide CO into the solution of the lithium carbonate precipitate separated in the step (4)₂Obtaining NaHCO₃The solution can be recycled as a lithium salt recovery solution.