A method for extracting lithium from sodium sulfate subtype salt lake brine by adsorption-extraction

Abstract

The present invention discloses a method for extracting lithium from sodium sulfate subtype salt lake by adsorption-extraction, which can effectively separate lithium from impurity ions such as sodium, calcium, and magnesium, and efficiently enrich and prepare lithium carbonate products. The mother liquor of lithium precipitation is effectively used and returned to the extraction section for alkalinity adjustment, so as to realize the utilization of alkali and the recovery of residual lithium. At the same time, the raffinate is used to prepare salt products or acid and alkali for the front-end process through membrane technology or solar pond / MVR and other processes, forming a separate system, thus avoiding the pollution of the environment by organic matter.

Description

Technical Field

[0001] The invention relates to the technical field of lithium extraction, and in particular to a method for extracting lithium from sodium sulfate subtype salt lake brine by adsorption-extraction. Background Art

[0002] Lithium is the lightest metal in nature and has extremely strong electrochemical activity. Its metal and compounds are widely used in aerospace, new energy, organic chemical and other industries. In recent years, with the rapid development of electrochemical energy storage and electric vehicles, lithium has been increasingly used in the field of new energy materials, and its development and utilization have also received high attention. Lithium mainly exists in spodumene, lepidolite ore and salt lake brine. In China, lithium resources in salt lake brine account for 71.9% of the total lithium resources, mainly distributed in salt lakes in Qinghai Province and Tibet Autonomous Region. The process of lithium extraction from salt lake brine is simple, with low energy consumption, eliminating the complex process of ore processing and decomposition, avoiding the generation of a large amount of acidic or alkaline solid waste, and is environmentally friendly. Therefore, compared with the process of lithium extraction from ore, the process of lithium extraction from salt lake brine has obvious technical and economic advantages and is the main way to produce lithium products in the world.

[0003] The main technologies for extracting lithium from salt lake brine include adsorption, solvent extraction, salt drying, calcination leaching and membrane separation. The calcination lithium extraction process is a high energy consumption process. During the process, a large amount of hydrogen chloride gas will be produced, which will cause serious corrosion to the equipment. The large amount of waste salt and waste residue will violate the development concept of green economy. This process is gradually eliminated by the market due to the high environmental pressure and low lithium yield. Therefore, the methods widely used in the existing technology are adsorption, solvent extraction, membrane separation and salt drying.

[0004] CN112593094A discloses a process for extracting lithium from salt lakes by adsorption-coupled membrane method. The invention directly obtains lithium hydroxide products by adsorption-membrane concentration-purification resin-bipolar membrane-evaporation crystallization for brine with high sodium-to-lithium ratio. The process is simple and the lithium extraction cycle is short. However, due to the limitations of selective separation of lithium and sodium in the adsorption stage, the sodium content in the lithium-rich solution obtained after desorption is still relatively high. Especially for salt lakes with high sodium-to-lithium ratio, some sodium will be entrained in the lithium product obtained by evaporation and crystallization, which requires further washing to improve the purity of the product, and some lithium will remain in the sodium hydroxide mother liquor after crystallization. The patent does not specify how to treat the crystallization mother liquor to achieve the utilization of alkali and the recovery of residual lithium. CN114836621A discloses a lithium extraction process by adsorption in salt lakes. The invention divides the adsorption process into two stages. First, an adsorbent is used to adsorb brine. In the second stage, an adsorbent is used to perform secondary adsorption on the bipolar membrane mixed alkali obtained in the subsequent process and the concentrated alkali mother liquor produced after concentrated crystallization. The sodium ions on the adsorbent are replaced by lithium ions in the mother liquor, so that the desorption liquid finally obtained has a lower sodium-lithium ratio. This patent uses this method to reduce the sodium-lithium molar ratio in the bipolar membrane alkali solution from 0.28 to 0.21, but does not solve the problem of complete separation of lithium and sodium. There is no further description of the adsorption effect of lithium in the solution after the crystallization mother liquor passes through the adsorption device during the secondary adsorption process and the recovery of alkali and residual lithium in the solution after adsorption.

[0005] CN108358222A discloses a membrane process for preparing lithium carbonate. The invention mainly uses nanofiltration membrane to separate divalent ions from soluble monovalent ions in brine to obtain lithium-rich permeate and lithium-poor interception liquid. The lithium-rich concentrated water and alkali-rich concentrated water obtained after evaporation and crystallization are mixed with brine to obtain lithium products. Patent CN114620750A discloses a process for extracting lithium from sodium sulfate subtype salt lake brine. The invention separates lithium-containing brine through nanofiltration membrane after pretreatment to obtain lithium-containing permeate and divalent interception liquid. The lithium-containing permeate is concentrated to obtain a high-lithium mother liquor, and the divalent interception liquid is denitrated by freezing to obtain a denitration liquid. The high-lithium mother liquor is then blended with the denitration liquid to obtain crude lithium carbonate and crystallization mother liquor. This method adopts nanofiltration permeation liquid membrane concentration process, which solves the problem of large amount of evaporated crystallization water in patent CN108358222A. However, for the treatment of carbonate or sulfate saturated brine in high-altitude cold areas, the above two patents have problems such as low membrane permeability under low temperature conditions, and membrane scaling caused by precipitation of calcium sulfate and calcium magnesium carbonate. If industrial operation is to be achieved, the brine must be heated or a multi-stage dewashing process must be carried out to reduce the brine saturation, which results in high investment and operating costs and difficulty in membrane maintenance.

[0006] CN113981243A discloses a method for extracting and separating lithium and alkaline earth metals from salt lake brine with a high sodium-lithium ratio, wherein an organic phase is prepared using diketone compounds, organophosphorus compounds and kerosene, and the brine is subjected to countercurrent extraction under the condition of adding alkali to control the pH, and the loaded organic phase is sequentially stripped of sodium, lithium, calcium and magnesium using an acidic solution, thereby achieving efficient separation of sodium, lithium and alkaline earth metals such as calcium and magnesium. For lithium extraction from salt lake brine, the extraction method has the problem of the accumulation of organic residues and the impact on the environment. In addition, how to properly handle the acidic calcium-magnesium stripping solution is not clearly stated. For brine with high calcium and magnesium content, if calcium and magnesium are not removed by pretreatment, the overall extraction process is complicated and the acid and alkali consumption is large.

[0007] In view of the high sodium-to-lithium ratio characteristics of sodium sulfate subtype salt lakes, the traditional salt-drying-evaporation concentration process can pre-concentrate most of the sodium salt by evaporation, crystallization, and precipitation to reduce the sodium-to-lithium ratio, and then extract lithium by precipitation. However, for salt lakes with low lithium concentrations, large-scale salt fields need to be built, which is not possible in some areas due to environmental and site factors. Although a single adsorption method can effectively separate lithium from sodium and other impurities, it is necessary to combine membrane technology to concentrate and enrich the desorption liquid to prepare lithium products. In addition, there is the problem of sodium entrainment in lithium products and the problem of effective recovery of residual lithium in lithium precipitation mother liquor or crystallization mother liquor. Using a single membrane method, only divalent ions such as calcium and magnesium are intercepted and lithium-sodium separation cannot be achieved, so it is not suitable for the extraction of lithium from salt lakes with high sodium-to-lithium ratios. For low-temperature brines saturated with carbonate or sulfate in high-altitude areas, there are problems such as low membrane permeability and scaling caused by precipitation of calcium sulfate and calcium magnesium carbonate salts, high requirements for membrane quality and performance, and high investment and maintenance costs. Although the single extraction method has good selectivity for lithium and can efficiently enrich lithium through relative regulation, for brines with high calcium and magnesium content, if calcium and magnesium are not removed by pretreatment, the overall extraction process is complicated, the acid and alkali consumption is large, and if the residual liquid is not properly handled and returned to the salt lake, it will cause the accumulation of organic matter. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention aims to provide a method for extracting lithium from sodium sulfate subtype salt lake brine by adsorption-extraction.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A method for extracting lithium from a sodium sulfate subtype salt lake by adsorption-extraction comprises the following steps:

[0011] Step 1: After the salt lake brine is ultrafiltered to remove suspended matter, a lithium-extracting adsorbent is used to perform cascade adsorption on the salt lake brine, and the adsorbed liquid is returned to the salt lake;

[0012] Step 2, washing the lithium-carrying adsorbent after the cascade adsorption in step 1 with a washing liquid, and returning the washing liquid obtained to the adsorption process in step 1 or to the salt lake;

[0013] Step 3, using an eluent to perform cascade desorption of lithium ions on the lithium-carrying adsorbent obtained in step 2 to obtain a lithium-rich desorption solution, and the lithium-rich desorption solution is transferred to step 5 for treatment;

[0014] Step 4, washing the adsorbent after desorption in step 3 with a washing liquid; the washing liquid obtained is returned to prepare the eluent of step 3, and the washed adsorbent is returned to step 1 for adsorption;

[0015] Step 5: After adjusting the pH of the lithium-rich desorption solution obtained in step 3, mix it with the extractant, perform 1 to 10 levels of countercurrent extraction, separate the phases after extraction equilibrium, obtain a lithium extraction residual solution and a first loaded organic phase, transfer the first loaded organic phase to step 6 for treatment, and transfer the lithium extraction residual solution to step 9 for treatment;

[0016] Step 6: The first loaded organic phase obtained in step 5 is subjected to 1 to 10 levels of countercurrent stripping or cross-current stripping, and phase separation is performed after the stripping equilibrium is reached to obtain a lithium sodium salt stripping solution and a second loaded organic phase containing calcium and magnesium. The second loaded organic phase is transferred to step 7 for treatment, and the lithium sodium salt stripping solution is transferred to step 8 for treatment;

[0017] Step 7, the second loaded organic phase obtained in step 6 is subjected to 1 to 10 levels of countercurrent stripping or cross-current stripping, and phase separation is performed after the stripping equilibrium is reached to obtain a magnesium calcium salt stripping solution and an unloaded organic phase; the obtained magnesium calcium salt stripping solution is evaporated and concentrated to obtain a crystalline salt for storage;

[0018] Step 8: Sodium carbonate is added to the lithium sodium salt stripping solution obtained in step 6 to precipitate lithium to obtain a lithium precipitation mother liquor and a lithium carbonate product, and the lithium precipitation mother liquor is returned to the extraction section of step 5;

[0019] Step 9: Separating the lithium extraction residual solution obtained in step 5 into oil and water;

[0020] Step 10, the de-oiled lithium extraction residual liquid obtained in step 9 enters the reverse osmosis system for reverse osmosis, the obtained reverse osmosis fresh water is transferred to step 11, and the obtained reverse osmosis concentrated water is transferred to step 12;

[0021] Step 11: The reverse osmosis fresh water obtained in step 10 is returned to step 2 and step 4 for use as a washing liquid and returned to step 3 for the preparation of an eluent for the lithium-carrying adsorbent;

[0022] The reverse osmosis concentrated water obtained in step 12 and step 10 enters a solar pond or an evaporation crystallization system to prepare salt products, or enters a nanofiltration system for deep impurity removal. The concentrated water after nanofiltration enters an electrodialysis-bipolar membrane system to produce acid and alkali solutions.

[0023] Furthermore, the lithium extraction adsorbent in step 1 is a titanium-based or manganese-based adsorbent.

[0024] Furthermore, in step 1, the amount of brine input is 10 to 50 BV, and the adsorption flow rate is 1 to 40 BV / h.

[0025] Furthermore, the eluent in step 3 is one of 0.05 mol / L to 2 mol / L purchased hydrochloric acid, sulfuric acid or nitric acid solutions, or the acid solution produced by the electrodialysis-bipolar membrane equipment in step 12; the water used to prepare the eluent is a mixture of one or more of pure water, tap water and reverse osmosis fresh water; the amount of eluent is 0.1 to 10 BV, and the desorption flow rate is 1 to 40 BV / h.

[0026] Furthermore, the eluent in step 2 and step 4 is a mixture of one or more of pure water, tap water and reverse osmosis fresh water.

[0027] Furthermore, the extractant used in step 5 is a combination of diketone compounds, organic phosphine compounds and kerosene; in step 5, the pH of the lithium-rich desorption solution is adjusted to 6-14 using alkali before extraction; the extraction method is to mix the extractant and the lithium-rich desorption solution adjusted with alkali in a volume ratio of 1:10-10:1 and perform 1-10 stages of countercurrent extraction, and the single-stage extraction time is 1-30min.

[0028] Further, in step 6, the first loaded organic phase obtained in step 5 and the stripping liquid are mixed in a volume ratio of 1:1 to 50:1 for 1 to 10 stages of countercurrent or cross-current stripping, and the single-stage stripping time is 1 to 30min; in step 7, the second loaded organic phase obtained in step 6 and the stripping liquid are mixed in a volume ratio of 1:1 to 50:1 for 1 to 10 stages of countercurrent or cross-current stripping, and the single-stage stripping time is 1 to 30min; the stripping liquid in step 6 and step 7 is one of 0.1 mol / L to 14 mol / L purchased hydrochloric acid, sulfuric acid or nitric acid solutions or one of the hydrochloric acid or sulfuric acid produced by the electrodialysis bipolar membrane equipment in step 12.

[0029] Furthermore, in step 8, the amount of sodium carbonate added is 1 to 8 times the molar amount of lithium, and a lithium carbonate product and a lithium precipitation mother liquor are obtained. The lithium precipitation mother liquor is returned to the extraction section of step 5 for pH adjustment and lithium recovery.

[0030] Furthermore, in step 12, the evaporation crystallization system adopts the MVR or multi-effect evaporation process; when the reverse osmosis concentrated water enters the nanofiltration system for deep impurity removal, the calcium and magnesium removal rates after nanofiltration are 85% to 95%; the hydrogen ion concentration in the acid solution produced by the electrodialysis-bipolar membrane system is 0.5 to 3 mol / L, and is reused for elution and desorption of the lithium adsorbent, and the hydroxide ion concentration in the produced alkali solution is 0.5 to 3 mol / L, and is reused for pH adjustment of the desorption solution before solvent extraction.

[0031] The beneficial effects of the present invention are as follows: the present invention realizes effective separation and efficient enrichment of lithium from impurity ions such as sodium, calcium, and magnesium to prepare lithium carbonate products, and the lithium precipitation mother liquor is effectively utilized and returned to the extraction section for alkalinity adjustment, thereby realizing the utilization of alkali and the recovery of residual lithium. At the same time, the raffinate is used to prepare salt products or acid and alkali for the front-end process through membrane technology or solar pond / MVR and other processes, forming a separate system and avoiding the pollution of the environment by organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the method of Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0034] Example 1

[0035] This embodiment uses a high sodium-lithium ratio salt lake brine as raw material, such as Figure 1 As shown, at 5°C, the brine is pumped into an adsorption device containing a titanium-based adsorbent for adsorption at a brine input volume of 36 BV and a flow rate of 18 BV / h; the lithium-loaded adsorption column after lithium adsorption is rinsed with deionized water, and then the lithium-loaded adsorbent is eluted and desorbed with a 2 BV, 0.25 mol / L HCl solution at a flow rate of 18 BV / h, the lithium-rich desorption liquid is collected for extraction, and the adsorption column after desorption is rinsed with deionized water.

[0036] The pH of the lithium-rich desorption solution is adjusted to about 9 with sodium hydroxide (if the water sample is turbid, it needs to be filtered), and a diketone combined with an organic phosphine and kerosene extraction system is used to mix the organic phase with the lithium-rich desorption solution in a volume ratio of 1:5 for three-stage countercurrent extraction. After phase separation and clarification, the lithium extraction residual solution and the first loaded organic phase are obtained respectively.

[0037] Sodium and lithium stripping: Use 5 mol / L hydrochloric acid solution to perform 3-stage countercurrent stripping on the first loaded organic phase, mix the first loaded organic phase with the hydrochloric acid solution in a volume ratio of 5:1, and after phase separation and clarification, obtain a sodium-lithium solution and a second loaded organic phase containing magnesium and calcium, respectively.

[0038] Magnesium and calcium stripping: Use 0.7 mol / L hydrochloric acid solution to perform 2-stage countercurrent stripping on the second loaded organic phase, mix the second loaded organic phase with the hydrochloric acid solution in a volume ratio of 10:1, and obtain magnesium-calcium solution and unloaded organic phase after phase separation and clarification. The obtained calcium-magnesium stripping solution can be evaporated and concentrated to obtain crystalline salt for storage.

[0039] The sodium-lithium solution obtained after stripping is added with sodium carbonate with a molar amount of 1.5 times that of lithium to precipitate lithium to produce sodium carbonate, and the lithium precipitation mother liquor is returned to the extraction section.

[0040] After deoiling, the residual solution of lithium extraction enters the reverse osmosis equipment to obtain fresh water, which is returned for elution and desorption, and the concentrated water enters the nanofiltration system for deep impurity removal. The purified concentrated water enters the electrodialysis-bipolar membrane system to produce acid and alkali. The obtained acid has a hydrogen ion concentration of 2 mol / L and is returned for desorption and stripping, and the alkali has a hydroxide ion concentration of 2 mol / L and is returned for pH adjustment of lithium-rich desorption solution before extraction.

[0041] The results of elemental analysis of the solution during the above adsorption-extraction separation process are shown in Table 1.

[0042] Table 1

[0043]

[0044] Example 2

[0045] This embodiment uses a high sodium-lithium ratio salt lake brine as raw material, such as Figure 1 As shown, at 10°C, the brine is pumped into an adsorption device containing a manganese adsorbent with an input brine volume of 50BV and a flow rate of 12BV / h for adsorption, and the adsorption liquid is collected and returned to the salt lake at regular intervals; the lithium-loaded adsorption column after lithium adsorption is rinsed with tap water, and then the lithium-loaded adsorbent is eluted and desorbed with a 4BV, 0.1mol / L sulfuric acid solution at a flow rate of 24BV / h, the lithium-rich desorption liquid is collected for extraction, and the adsorption column after desorption is rinsed with tap water.

[0046] The pH of the lithium-rich desorption solution is first adjusted to about 10 with sodium carbonate (if the water sample is turbid, it needs to be filtered), and a diketone combined with an organic phosphine and kerosene extraction system is used to mix the organic phase with the lithium-rich desorption solution in a volume ratio of 1:1 for 4-stage countercurrent extraction. The single-stage extraction time is 5 min. After phase separation and clarification, the lithium extraction residual solution and the first loaded organic phase are obtained respectively.

[0047] Sodium and lithium stripping: Use 1.7 mol / L sulfuric acid solution to perform 4-stage countercurrent stripping on the first loaded organic phase, mix the first loaded organic phase with the sulfuric acid solution in a volume ratio of 24:1, and after phase separation and clarification, obtain a sodium-lithium solution and a second loaded organic phase containing magnesium and calcium, respectively.

[0048] Magnesium and calcium stripping: Use 0.075 mol / L sulfuric acid solution to perform 3-stage countercurrent stripping on the second loaded organic phase, mix the second loaded organic phase and sulfuric acid solution in a volume ratio of 15:1, and obtain magnesium-calcium solution and unloaded organic phase after phase separation and clarification. The obtained calcium-magnesium stripping solution can be evaporated and concentrated to obtain crystalline salt for storage.

[0049] The sodium-lithium solution obtained after stripping is added with sodium carbonate twice the molar amount of lithium to precipitate lithium to produce sodium carbonate, and the lithium precipitation mother liquor is returned to the extraction section.

[0050] After deoiling, the residual solution of lithium extraction enters the reverse osmosis equipment to obtain fresh water, which is returned for elution and desorption, and the concentrated water enters the nanofiltration system for deep impurity removal. The purified concentrated water enters the electrodialysis-bipolar membrane system to produce acid and alkali. The hydrogen ion concentration in the acid is 1.8 mol / L and is returned for desorption and stripping, and the hydroxide ion concentration in the alkali is 1.8 mol / L and is returned for pH adjustment of lithium-rich desorption solution before extraction.

[0051] The results of elemental analysis of the solution during the above adsorption-extraction separation process are shown in Table 2.

[0052] Table 2 Element analysis results of solution during adsorption-extraction process

[0053]

[0054]

[0055] Example 3

[0056] This embodiment uses a high sodium-lithium ratio salt lake brine as raw material, such as Figure 1 As shown, at 20°C, the brine is pumped into an adsorption device equipped with a titanium-based adsorbent for adsorption at a brine input volume of 12BV and a flow rate of 20BV / h. The adsorption liquid is collected and returned to the salt lake at regular intervals. The adsorption column after lithium adsorption is rinsed with reverse osmosis fresh water, and then the lithium-loaded adsorbent is eluted and desorbed with a solution of 1BV and 0.3mol / LHC1 at a flow rate of 12BV / h. The lithium-rich desorption liquid is collected for extraction, and the deionized water is used to rinse the adsorption column after desorption.

[0057] The pH of the lithium-rich desorption solution is adjusted to about 8.5 with sodium hydroxide (if the water sample is turbid, it needs to be filtered), and a diketone combined with an organic phosphine and kerosene extraction system is used to mix the organic phase with the lithium-rich desorption solution in a volume ratio of 1:3 for three-stage countercurrent extraction. After phase separation and clarification, the raffinate and the first loaded organic phase are obtained respectively.

[0058] Sodium and lithium stripping: Use 5.2 mol / L hydrochloric acid solution to perform 5-stage countercurrent stripping on the first loaded organic phase, mix the first loaded organic phase with the hydrochloric acid solution in a volume ratio of 8:1, and after phase separation and clarification, obtain a sodium-lithium solution and a second loaded organic phase containing magnesium and calcium, respectively.

[0059] Magnesium and calcium stripping: Use 1.3 mol / L hydrochloric acid solution to perform 3-stage countercurrent stripping on the second loaded organic phase, mix the second loaded organic phase with the hydrochloric acid solution at a volume ratio of 20:1, and obtain magnesium-calcium solution and unloaded organic phase after phase separation and clarification. The obtained calcium-magnesium stripping solution can be evaporated and crystallized to obtain crystalline salt for storage.

[0060] The sodium-lithium solution obtained after stripping is added with sodium carbonate with a molar amount of 1.3 times that of lithium to precipitate lithium to produce sodium carbonate, and the lithium precipitation mother liquor is returned to the extraction section.

[0061] After deoiling, the raffinate enters the reverse osmosis equipment to obtain the produced water, which is returned for elution and desorption, and the concentrated water enters the nanofiltration system for deep impurity removal. The purified concentrated water enters the electrodialysis-bipolar membrane system to produce acid and alkali. The obtained acid has a hydrogen ion concentration of 1.5 mol / L and is returned for desorption and stripping, and the alkali has a hydroxide ion concentration of 1.5 mol / L and is returned for pH adjustment of lithium-rich desorption solution before extraction.

[0062] The results of elemental analysis of the solution during the above adsorption-extraction separation process are shown in Table 3.

[0063] Table 3 Elemental analysis results of solution during adsorption-extraction process

[0064]

[0065] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A method for extracting lithium from a sodium sulfate subtype salt lake by adsorption-extraction, characterized in that: The steps include: Step 1: After the salt lake brine is ultrafiltered to remove suspended matter, a lithium-extracting adsorbent is used to perform cascade adsorption on the salt lake brine, and the adsorbed liquid is returned to the salt lake; Step 2, washing the lithium-carrying adsorbent after the cascade adsorption in step 1 with a washing liquid, and returning the washing liquid obtained to the adsorption process in step 1 or to the salt lake; Step 3, using an eluent to perform cascade desorption of lithium ions on the lithium-carrying adsorbent obtained in step 2 to obtain a lithium-rich desorption solution, and the lithium-rich desorption solution is transferred to step 5 for treatment; Step 4, washing the adsorbent after desorption in step 3 with an eluent; the obtained washing liquid is returned to prepare the eluent in step 3, and the washed adsorbent is returned to step 1 for adsorption; Step 5: After adjusting the pH of the lithium-rich desorption solution obtained in step 3, mix it with the extractant, perform 1 to 10 levels of countercurrent extraction, separate the phases after extraction equilibrium, obtain a lithium extraction residual solution and a first loaded organic phase, transfer the first loaded organic phase to step 6 for treatment, and transfer the lithium extraction residual solution to step 9 for treatment; Step 6: The first loaded organic phase obtained in step 5 is subjected to 1 to 10 levels of countercurrent stripping or cross-current stripping, and phase separation is performed after the stripping equilibrium is reached to obtain a lithium sodium salt stripping solution and a second loaded organic phase containing calcium and magnesium. The second loaded organic phase is transferred to step 7 for treatment, and the lithium sodium salt stripping solution is transferred to step 8 for treatment; Step 7, the second loaded organic phase obtained in step 6 is subjected to 1 to 10 levels of countercurrent stripping or cross-current stripping, and phase separation is performed after the stripping equilibrium is reached to obtain a magnesium calcium salt stripping solution and an unloaded organic phase; the obtained magnesium calcium salt stripping solution is evaporated and concentrated to obtain a crystalline salt for storage; Step 8: Sodium carbonate is added to the lithium sodium salt stripping solution obtained in step 6 to precipitate lithium to obtain a lithium precipitation mother liquor and a lithium carbonate product, and the lithium precipitation mother liquor is returned to the extraction section of step 5; Step 9: Separating the lithium extraction residual solution obtained in step 5 into oil and water; Step 10, the de-oiled lithium extraction residual liquid obtained in step 9 enters a reverse osmosis system for reverse osmosis, the obtained reverse osmosis fresh water is transferred to step 11, and the obtained reverse osmosis concentrated water is transferred to step 12; Step 11: The reverse osmosis fresh water obtained in step 10 is returned to step 2 and step 4 for use as a washing liquid and returned to step 3 for the preparation of an eluent for the lithium-carrying adsorbent; The reverse osmosis concentrated water obtained in step 12 and step 10 enters a solar pond or an evaporation crystallization system to prepare salt products, or enters a nanofiltration system for deep impurity removal. The concentrated water after nanofiltration enters an electrodialysis-bipolar membrane system to produce acid and alkali solutions.

2. The method according to claim 1, characterized in that The lithium extraction adsorbent in step 1 is a titanium-based or manganese-based adsorbent.

3. The method according to claim 1, characterized in that In the step 1, the halogen input amount is 10 to 50 BV, and the adsorption flow rate is 1 to 40 BV / h.

4. The method according to claim 1, characterized in that The eluent in step 3 is one of 0.05 mol / L to 2 mol / L purchased hydrochloric acid, sulfuric acid or nitric acid solutions, or the acid solution produced by the electrodialysis-bipolar membrane equipment in step 12; the water used to prepare the eluent is a mixture of one or more of pure water, tap water and reverse osmosis fresh water; the amount of eluent is 0.1 to 10 BV, and the desorption flow rate is 1 to 40 BV / h.

5. The method according to claim 1, characterized in that The eluent in step 2 and step 4 is a mixture of one or more of pure water, tap water and reverse osmosis fresh water.

6. The method according to claim 1, characterized in that The extractant used in step 5 is a combination of diketone compounds, organic phosphine compounds and kerosene; in step 5, the pH of the lithium-rich desorption solution is adjusted to 6-14 using alkali before extraction; the extraction method is to mix the extractant and the lithium-rich desorption solution adjusted with alkali in a volume ratio of 1:10-10:1 and perform 1-10 stages of countercurrent extraction, and the single-stage extraction time is 1-30 minutes.

7. The method according to claim 1, characterized in that In step 6, the first loaded organic phase obtained in step 5 and the stripping liquid are mixed in a volume ratio of 1:1 to 50:1 to perform 1 to 10 stages of countercurrent or cross-current stripping, and the single-stage stripping time is 1 to 30 min; in step 7, the second loaded organic phase obtained in step 6 and the stripping liquid are mixed in a volume ratio of 1:1 to 50:1 to perform 1 to 10 stages of countercurrent or cross-current stripping, and the single-stage stripping time is 1 to 30 min; the stripping liquid in step 6 and step 7 is one of 0.1 mol / L to 14 mol / L purchased hydrochloric acid, sulfuric acid or nitric acid solutions or one of the hydrochloric acid or sulfuric acid produced by the electrodialysis bipolar membrane equipment in step 12.

8. The method according to claim 1, characterized in that In step 8, the amount of sodium carbonate added is 1 to 8 times the molar amount of lithium, and a lithium carbonate product and a lithium precipitation mother liquor are obtained. The lithium precipitation mother liquor is returned to the extraction section of step 5 for pH adjustment and lithium recovery.

9. The method according to claim 1, characterized in that: In step 12, the evaporation crystallization system adopts the MVR or multi-effect evaporation process; when the reverse osmosis concentrated water enters the nanofiltration system for deep impurity removal, the calcium and magnesium removal rates after nanofiltration are 85% to 95%; the hydrogen ion concentration in the acid solution produced by the electrodialysis-bipolar membrane system is 0.5 to 3 mol / L, and is returned to the elution and desorption of the lithium adsorbent, and the hydroxide ion concentration in the produced alkali solution is 0.5 to 3 mol / L, and is returned to the desorption liquid pH adjustment before solvent extraction.

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