A method for extracting magnesium-lithium alloy using salt lake brine

Abstract

The present invention discloses a method for extracting magnesium-lithium alloy using salt lake brine, which belongs to the technical field of light metal alloy material preparation. The method comprises the following steps: using ion adsorption, analysis, concentration and liquid adjustment on salt lake brine; using metal alkaline solution to adjust the pH of the solution, while performing a first precipitation, calcining the first precipitate to obtain MgO entrained with Li2O; using sodium carbonate solution to perform a second precipitation, dehydrating and drying the second precipitate to obtain a co-precipitated solid phase of MgCO3 and Li2CO3; adding CaO for vacuum thermal decomposition; adding a reducing agent and a catalyst for vacuum thermal reduction to obtain gas phase Mg and gas phase Li, using gas co-condensation technology to obtain crude Mg-Li alloy, and then refining and purifying to make Mg-Li alloys of different proportions. The present invention can effectively reduce process complexity and magnesium-lithium alloy manufacturing costs, reduce fixed asset investment, and ensure clean and environmental protection during the preparation process.

Description

Technical Field

[0001] The present application belongs to the technical field of light metal alloy material preparation, and specifically relates to a method for extracting magnesium-lithium alloy using salt lake brine. Background Art

[0002] Salt lakes generally refer to lakes with water salinity greater than the average salinity of seawater. They also include dry salt lakes where surface brine has dried up and is composed of salt deposits and intercrystalline brine. These brine contains significant amounts of sodium, potassium, magnesium, lithium, chlorine, and sulfur, making it a key raw material for extracting magnesium and lithium. The Qinghai Salt Lake region is the richest in salt lake resources in my country. Due to excellent drying conditions, its magnesium-to-lithium ratio is very high. China's largest salt lake is the Qarhan Salt Lake in Qinghai, the crowning jewel of the Qaidam Basin. Its resources are incredibly rich, including billions of tons of magnesium salts and tens of millions of tons of lithium salts. Huge investments were made to produce magnesium metal from salt lake magnesium salts using electrolysis, but the high production costs made it impossible to compete with the existing Pidgeon process, leading to the discontinuation of production. To date, the magnesium resources in salt lakes have remained largely untapped. Although lithium salts have been developed from lithium resources in recent years, their utilization is quite limited. As we all know, magnesium-lithium alloy is the lightest structural material. It is an irreplaceable raw material in aerospace, military industry, walking machinery and many high-tech fields, and has huge potential markets at home and abroad.

[0003] At present, the methods for producing magnesium-lithium alloys at home and abroad mainly use dolomite as raw material and adopt electrolysis to produce metallic magnesium, or use dolomite as raw material and adopt Pidgeon process to produce metallic magnesium; the production process of metallic lithium uses lithium-containing ore as raw material, and obtains high-purity lithium chloride through a complex metallurgical process, and then obtains crude lithium by electrolysis, which is purified into metallic lithium; and then uses the doping method to produce magnesium-lithium alloy in a vacuum furnace. The process is particularly complex, with high requirements for equipment corrosion protection, low lithium yield, and chlorine gas generation, which increases fixed asset investment, makes environmental protection difficult, and has high manufacturing costs, which greatly limits the application field. Summary of the Invention

[0004] The present application provides a method for extracting magnesium-lithium alloy using salt lake brine, which can effectively reduce process complexity and magnesium-lithium alloy manufacturing costs, reduce fixed asset investment, and ensure clean and environmentally friendly preparation process.

[0005] An embodiment of the present invention provides a method for extracting magnesium-lithium alloy using salt lake brine, comprising the following steps:

[0006] S100: After evaporation and concentration of salt lake brine, ion adsorption and analysis are performed to remove solid impurities;

[0007] S200: Filtering through a sodium membrane or adding old brine to concentrate and adjust the solution to obtain a coprecipitation solution, wherein the adjustment is used to select the ratio of magnesium ions and lithium ions;

[0008] S300: adjusting the pH of the co-precipitation solution with a metal base solution while performing a first precipitation to obtain a first precipitate and a first solution, and calcining the first precipitate to obtain MgO entrained with Li2O, wherein the metal base is sodium hydroxide or calcium hydroxide;

[0009] S400: performing a second precipitation on the first solution using a sodium carbonate solution to obtain a second precipitate, dehydrating and drying the second precipitate to obtain a co-precipitated solid phase of MgCO3 and Li2CO3, wherein the MgCO3, Li2CO3, Li2O, and MgO are used as raw materials for thermal decomposition;

[0010] S500: adding a certain amount of CaO, performing vacuum thermal decomposition on the raw materials, and obtaining a composite oxide;

[0011] S600: adding a certain amount of reducing agent and catalyst, vacuum thermally reducing the composite oxide to obtain gaseous Mg and gaseous Li, co-condensing the gaseous Mg and gaseous Li into a solid phase or liquid phase using a rapid cooling technology to obtain a crude Mg-Li alloy, and then refining and purifying the crude Mg-Li alloy to prepare Mg-Li alloys with different proportions.

[0012] Furthermore, in step S300 and step S400, when the metal base is sodium hydroxide, only MgO entrained with Li2O is obtained after calcining the first precipitate, and the raw materials for thermal decomposition include MgCO3, Li2CO3, Li2O and MgO.

[0013] Furthermore, in step S300 and step S400, when the metal base is calcium hydroxide, CaO and MgO entrained with Li2O are obtained simultaneously after calcining the first precipitate, and the raw materials for the thermal decomposition include MgCO3Li2CO3, CaO, Li2O and MgO.

[0014] Furthermore, in step S300 and step S400, the Li2O and the MgO coexist.

[0015] Furthermore, in the step S500, the Li2O and (MgO and + CaO) in the thermally decomposed raw material are: (30-35): (78-63) Wt%, wherein the amount of Li2CO3 in the second precipitate × 30 / 74 plus the amount of Li2O in the first precipitate is Li2O and, and the amount of MgCO3 in the second precipitate × 40 / 84 plus the amount of MgO in the first precipitate is MgO and.

[0016] Furthermore, in step S300, 70-80% of the Mg in the coprecipitation solution 2+ A magnesium hydroxide precipitate is generated, and the magnesium hydroxide precipitate is calcined to obtain MgO; in the step S400, the second solution generated after the second precipitation is returned to the solution after the analysis in the step S200.

[0017] Furthermore, the step S500 specifically includes: preparing the raw materials and ball-milling them to 50-104 μm, fully mixing them, and then performing vacuum thermal decomposition for 6-8 hours in a 35-50 MPa ball press at a temperature of 850-950° C. and a vacuum degree of 5-20 Pa.

[0018] Furthermore, the step S600 specifically includes: crushing the composite oxide to 50-80 μm by ball milling, crushing the reducing agent and catalyst according to a certain ratio to 50-104 μm, fully mixing in a mixer for 40-60 minutes, pressing into 25-35 g / almond-shaped pellets in a pellet press at 45-55 MPa, adding the pellets into a reduction furnace, and reducing at 950-1150° C., vacuum 5-10 Pa, and time of 10-14 hours.

[0019] Furthermore, the reducing agent is ferrosilicon, silicon powder, aluminum powder or carbon powder, and the catalyst is CaF2, wherein the composite oxide: reducing agent: catalyst = (83-85): (13-15): 2Wt%.

[0020] Furthermore, the step S100 specifically includes: the salt lake brine is adsorbed by an ion exchange column, analyzed with pure fresh water, and solid impurities are removed by reverse osmosis, wherein the Li:Mg ratio of the salt lake brine after evaporation and concentration is 1:350-400, and the Li:Mg ratio after the ion adsorption and analysis is 1:5-7; in the step S200, the coprecipitation solution after filtering through the sodium membrane contains Mg 2+ The concentration is 0.04~0.05g / L, Li + The concentration reaches 15-21 g / L, and the coprecipitation solution after adding the old brine solution contains Li + The content accounts for 1% to 99% of the total amount of magnesium and lithium.

[0021] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0022] In the embodiment of the present invention, salt lake brine is first evaporated, concentrated, ion-adsorbed, and analyzed; then, the ratio of magnesium ions to lithium ions is adjusted and selected by filtering through a sodium membrane or adding old brine stock solution; a first precipitation is performed using a metal alkali solution, and the first precipitate is calcined to obtain MgO entrained with Li2O; the solution after the first precipitation is then precipitated for a second time using a sodium carbonate solution, and the second precipitate is dehydrated and dried to obtain a co-precipitated solid phase of MgCO3 and Li2CO3; CaO is added to the above raw materials for vacuum thermal decomposition, and a reducing agent and a catalyst are added for vacuum thermal reduction; and a crude Mg-Li alloy is obtained by gas co-condensation technology, which is finally refined and purified to prepare Mg-Li alloys with different ratios.

[0023] The embodiments of the present invention utilize salt lake brine resources with a high yield, and metallic lithium and magnesium are extracted simultaneously, effectively shortening the process, reducing process complexity, and reducing fixed asset investment. No chlorine is generated during the entire extraction process, which is clean and environmentally friendly. Different lithium-containing products can be produced using a set of equipment, greatly reducing manufacturing costs. The binary alloy composed of magnesium and lithium can meet various application scenarios.

[0024] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0026] Figure 1 The present invention provides a process flow diagram of a method for extracting magnesium-lithium alloy using salt lake brine. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 1 As shown, the method for extracting magnesium-lithium alloy using salt lake brine provided by the embodiment of the present invention may include the following steps:

[0030] Step S100: After evaporation and concentration of salt lake brine, ion adsorption and analysis are performed to remove solid impurities.

[0031] Specifically, the salt lake brine is naturally evaporated and initially concentrated, then adsorbed through an ion exchange column. Pure fresh water is then used for desorption, and then reverse osmosis is used to remove solid impurities. The Li:Mg ratio of the salt lake brine after evaporation and concentration is 1:350-400; the Li:Mg ratio of the pure fresh water desorption is 1:5-7. The liquid adsorbed by the ion exchange column is returned to the circulating brine solution. Fresh water is then added for desorption, and the exchange resin is regenerated and ion exchanged to enrich the metallic lithium ions.

[0032] To obtain magnesium-lithium alloys with varying lithium content, solutions with varying lithium contents must be prepared. Salt lake brine primarily contains magnesium ions, lithium ions, and chloride ions. Adsorbents with excellent adsorption for monovalent lithium ions are selected for adsorption and desorption, initially separating the magnesium and lithium in the brine, increasing the lithium ion concentration and reducing the ratio of magnesium to lithium ions in the solution.

[0033] Step S200: Filter through a sodium membrane or add old brine to concentrate and adjust the solution to obtain a coprecipitation solution, wherein the adjustment is used to select the ratio of magnesium ions and lithium ions.

[0034] Specifically, the ratio of magnesium to lithium ions is selected by filtering through a sodium membrane or by adding old brine to concentrate and adjust the solution. Since natural evaporation in the salt lake exceeds rainfall, natural evaporation can be used to concentrate the solution to a lithium content of 10-21g / L, which is then used as the co-precipitation solution.

[0035] During implementation, the coprecipitation solution after filtering through the sodium membrane contains Mg 2+ The concentration is 0.04~0.05g / L, Li + The concentration reaches 15-21 g / L, and lithium-rich solution is obtained. + The content accounts for 1% to 99% of the total amount of magnesium and lithium, and can be made into solutions with different lithium-magnesium ratios, and can also be configured into low-lithium solutions.

[0036] Step S300: Adjusting the pH of the coprecipitation solution with a metal base solution while performing a first precipitation to obtain a first precipitate and a first solution, and calcining the first precipitate to obtain MgO entrained with Li2O. The metal base is sodium hydroxide or calcium hydroxide.

[0037] Step S400: The first solution is precipitated for the second time using a sodium carbonate solution to obtain a second precipitate, and the second precipitate is dehydrated and dried to obtain a co-precipitated solid phase of MgCO3 and Li2CO3. The MgCO3, Li2CO3, Li2O and MgO are used as raw materials for thermal decomposition.

[0038] The steps S300 and S400 together constitute a co-deposition technique, which can be performed at room temperature and pressure.

[0039] When the metal base is sodium hydroxide, only MgO entrained with Li2O is obtained after calcining the first precipitate, and the raw materials for the thermal decomposition include MgCO3, Li2CO3, Li2O and MgO.

[0040] During implementation, the sodium hydroxide is used as the precipitant for the first precipitation. The reaction of the solution is Mg 2+ +2OH - =Mg(OH)2↓; where KSP=6×10 -10 , pksp=9.2.

[0041] Control the amount of NaOH added to allow 70-80% of Mg 2+ It precipitates in the form of Mg(OH)2, and the second precipitation is carried out with Na2CO3 as the precipitant. The reaction that occurs is

[0042] Mg 2+ +CO3 2- =MgCO3↓ KSP=3.5×10 -8 , PKSP=7.46.

[0043] 2Li + +CO3 2- =Li2CO3↓ KSP=2.5×10 -2 , PKSP=1.6.

[0044] It should be noted that KSP is the solubility product constant, and PKSP is the negative logarithm of the solubility product constant.

[0045] The Mg(OH)2 precipitated for the first time is calcined to generate MgO, and the mixture of MgCO3 and Li2CO3 precipitated for the second time is dehydrated and dried and then mixed with the MgO precipitated for the first time to form a mixture of MgO, Li2CO3 and MgCO3.

[0046] When the metal base is calcium hydroxide, CaO and MgO entrained with Li2O are obtained simultaneously after calcining the first precipitate, and the raw materials for the thermal decomposition include MgCO3, Li2CO3, CaO, Li2O and MgO.

[0047] During implementation, when Ca(OH)2 is used to adjust the pH, part of the Ca(OH)2 will co-precipitate with Mg(OH)2 during the first precipitation, and form a mixture of CaO and MgO after calcination. After mixing, there are four compounds: CaO, MgO, Li2CO3, and MgCO3, which serve as raw materials for thermal decomposition.

[0048] Furthermore, in the step S300 and the step S400, the Li2O and the MgO coexist.

[0049] Preferably, the first precipitation uses 2.5-3.5 mol sodium hydroxide solution, which is slowly added to the precipitation tank under mechanical stirring. The amount of sodium hydroxide added is calculated based on the Mg content of 70-80 wt% being precipitated, and 70-75% of the Mg in the solution is precipitated. 2+ Magnesium hydroxide precipitation is generated, 5-8% Li + It will be carried down and the magnesium hydroxide obtained will be dehydrated and decomposed into magnesium oxide. + The second precipitation uses sodium carbonate as a precipitant, or carbon dioxide as a precipitant. Lithium carbonate and magnesium carbonate are co-precipitated, with a sodium carbonate content of 3-5% by weight. The mother liquor is returned to the analytical solution, and the co-precipitated lithium carbonate and magnesium carbonate are mixed with the lithium oxide and magnesium oxide precipitated in the first precipitation to form the raw materials for thermal decomposition.

[0050] Step S500: adding a certain amount of CaO, performing vacuum thermal decomposition on the raw materials, and obtaining a composite oxide.

[0051] Specifically, the step S500 may include: preparing the raw materials and ball-milling them to 50-104 μm, fully mixing them, and then performing vacuum thermal decomposition for 6-8 hours in a 35-50 MPa ball press at a temperature of 850-950° C. and a vacuum degree of 5-20 Pa.

[0052] During implementation, CaO and MgO are used as flux inhibitors, and the thermal decomposition reaction of MgCO3 is

[0053] MgCO3(s)=MgO(s)+CO2(g)↑

[0054] Among them, MgCO3 and MgO both belong to solid phase decomposition and also belong to core shrinkage reaction. The decomposed MgO is a flux inhibitor for the thermal decomposition of Li2CO3, and the following reaction occurs:

[0055] Li2CO3=Li2O+CO2↑

[0056] Li2O+2MgO=Li2O·2MgO

[0057] Li2O+2CaO=Li2O·2CaO

[0058] The function of the flux inhibitor is to prevent the formation of liquid droplets when Li2CO3 melts and becomes liquid, and to prevent the liquid from flowing onto the lining of the thermal decomposition furnace. The adsorbed liquid is kept on the surface of the flux inhibitor for thermal decomposition, preventing the liquid from splashing and corroding the furnace lining.

[0059] The test results show that the C content in the raw material is ≤40ppm, the thermal decomposition rate of Li2CO3 is ≥99%, and the yield of Li is ≥98.5%.

[0060] The ratio of Li2O and (MgO and CaO) in the thermally decomposed raw material is (30-35): (78-63) wt%. The amount of Li2CO3 in the second precipitate × 30 / 74 plus the amount of Li2O in the first precipitate is Li2O and, while the amount of MgCO3 in the second precipitate × 40 / 84 plus the amount of MgO in the first precipitate is MgO and.

[0061] Step S600: adding a certain amount of reducing agent and catalyst, vacuum thermally reducing the composite oxide to obtain gaseous Mg and gaseous Li, co-condensing the gaseous Mg and gaseous Li into a solid phase or liquid phase using a rapid cooling technique to obtain a crude Mg-Li alloy, and then refining and purifying the crude Mg-Li alloy to prepare Mg-Li alloys with different proportions.

[0062] Specifically, the step S600 may include: crushing the composite oxide to 50-80 μm by a ball mill, crushing the reducing agent and catalyst according to a certain ratio to 50-104 μm, fully mixing in a mixer for 40-60 minutes, pressing into 25-35 g / almond-shaped pellets in a pellet press at 45-55 MPa, adding the pellets into a reduction furnace, and reducing at 950-1150° C., a vacuum degree of 5-10 Pa, and a reduction time of 10-14 hours.

[0063] When implemented, Li2O and MgO react with silicon as follows:

[0064] 2Li2O+2[Si]+CaO=4Li+CaO·2SiO2

[0065] MgO+2[Si]+CaO=Mg+CaO·2SiO2

[0066] It can be seen that Li2O and MgO are reduced to generate Li and Mg vapors.

[0067] The reducing agent may be ferrosilicon, silicon powder, aluminum powder or carbon powder, and the catalyst is CaF2, wherein the composite oxide: reducing agent: catalyst = (83-85): (13-15): 2 wt%.

[0068] The experimental data show that the reduction rate of Li is ≥99%, and the reduction rate of Mg is ≥93%.

[0069] In summary, the embodiment of the present invention first evaporates, concentrates, adsorbs ions and analyzes the salt lake brine; then filters through a sodium membrane or adds old brine stock solution to adjust and select the ratio of magnesium ions and lithium ions; uses a metal alkali solution for a first precipitation, and calcines the first precipitate to obtain MgO entrained with Li2O; then uses a sodium carbonate solution to precipitate the solution after the first precipitation for a second time, dehydrates and dries the second precipitate to obtain a co-precipitated solid phase of MgCO3 and Li2CO3, adds CaO to the above raw materials for vacuum thermal decomposition, and then adds a reducing agent and a catalyst for vacuum thermal reduction; and obtains a crude Mg-Li alloy through gas co-condensation technology, and finally refines and purifies it to make Mg-Li alloys with different proportions.

[0070] The embodiments of the present invention utilize salt lake brine resources with a high yield, and metallic lithium and magnesium are extracted simultaneously, effectively shortening the process, reducing process complexity, and reducing fixed asset investment. No chlorine is generated during the entire extraction process, which is clean and environmentally friendly. Different lithium-containing products can be produced using a set of equipment, greatly reducing manufacturing costs. The binary alloy composed of magnesium and lithium can meet various application scenarios.

[0071] The above description is only a preferred embodiment of the present invention and does not limit the technical solution of the present invention in any form. Any simple modification, form change and modification of the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for extracting magnesium-lithium alloy using salt lake brine, characterized in that: The method comprises the following steps: S100: After evaporation and concentration of salt lake brine, ion adsorption and analysis are performed to remove solid impurities; S200: Filtering through a sodium membrane or adding old brine to concentrate and adjust the solution to obtain a coprecipitation solution, wherein the adjustment is used to select the ratio of magnesium ions and lithium ions; S300: adjusting the pH of the co-precipitation solution with a metal base solution while performing a first precipitation to obtain a first precipitate and a first solution, and calcining the first precipitate to obtain MgO entrained with Li2O, wherein the metal base is sodium hydroxide or calcium hydroxide; S400: performing a second precipitation on the first solution using a sodium carbonate solution to obtain a second precipitate, dehydrating and drying the second precipitate to obtain a co-precipitated solid phase of MgCO3 and Li2CO3, wherein the MgCO3, Li2CO3, Li2O, and MgO are used as raw materials for thermal decomposition; S500: adding a certain amount of CaO, performing vacuum thermal decomposition on the raw materials, and obtaining a composite oxide; S600: adding a certain amount of reducing agent and catalyst, vacuum thermally reducing the composite oxide to obtain gaseous Mg and gaseous Li, co-condensing the gaseous Mg and gaseous Li into a solid phase or liquid phase using a rapid cooling technique to obtain a crude Mg-Li alloy, and then refining and purifying the crude Mg-Li alloy to prepare Mg-Li alloys with different ratios; In the step S500, the Li2O and (MgO and + CaO) in the thermally decomposed raw material are: (30-35): (78-63) Wt%, wherein the amount of Li2CO3 in the second precipitate × 30 / 74 plus the amount of Li2O in the first precipitate is Li2O and, and the amount of MgCO3 in the second precipitate × 40 / 84 plus the amount of MgO in the first precipitate is MgO and.

2. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: In step S300 and step S400, when the metal base is sodium hydroxide, only MgO entrained with Li2O is obtained after calcining the first precipitate, and the raw materials for the thermal decomposition include MgCO3, Li2CO3, Li2O and MgO.

3. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: In step S300 and step S400, when the metal base is calcium hydroxide, the first precipitate is calcined to simultaneously obtain CaO and MgO entrained with Li2O, and the raw materials for the thermal decomposition include MgCO3, Li2CO3, CaO, Li2O and MgO.

4. The method for extracting magnesium-lithium alloy using salt lake brine according to any one of claims 1 to 3, characterized in that: In the step S300 and the step S400, the Li2O and the MgO coexist.

5. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: In step S300, 70-80% of the Mg in the coprecipitation solution 2+ A magnesium hydroxide precipitate is generated, and the magnesium hydroxide precipitate is calcined to obtain MgO; in the step S400, the second solution generated after the second precipitation is returned to the solution after the analysis in the step S200.

6. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: The step S500 specifically includes: preparing the raw materials and ball-milling them to 50-104 μm, fully mixing them, and then performing vacuum thermal decomposition for 6-8 hours in a ball press at 35-50 MPa at a temperature of 850-950° C. and a vacuum degree of 5-20 Pa.

7. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: The step S600 specifically includes: crushing the composite oxide into 50-80 μm by ball milling, crushing the reducing agent and catalyst according to a certain ratio into 50-104 μm, fully mixing in a mixer for 40-60 minutes, pressing into 25-35 g / almond-shaped pellets in a pellet press at 45-55 MPa, adding the pellets into a reduction furnace, and reducing at 950-1150° C., a vacuum degree of 5-10 Pa, and a time of 10-14 hours.

8. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 7, characterized in that: The reducing agent is ferrosilicon, silicon powder, aluminum powder or carbon powder, and the catalyst is CaF2, wherein the ratio of the composite oxide: reducing agent: catalyst is (83-85): (13-15): 2 wt%.

9. The method for extracting magnesium-lithium alloy using salt lake brine according to claim 1, characterized in that: The step S100 specifically includes: the salt lake brine is adsorbed by an ion exchange column, desorbed using pure fresh water, and solid impurities are removed by reverse osmosis, wherein the Li:Mg ratio of the salt lake brine after evaporation and concentration is 1:350-400, and the Li:Mg ratio of the ion adsorption and desorption is 1:5-7; In the step S200, the coprecipitation solution after filtering through the sodium membrane contains Mg 2+ The concentration is 0.04~0.05g / L, Li + The concentration reaches 15-21 g / L, and the coprecipitation solution after adding the old brine solution contains Li + The content accounts for 1% to 99% of the total amount of magnesium and lithium.

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