Method for extracting lithium from water produced from gas field with high sodium-lithium ratio

Abstract

The invention discloses a method for extracting lithium from gas field produced water with a high sodium-lithium ratio, and belongs to the technical field of chemical engineering. The mass ratio of sodium to lithium in the gas field produced water is (100-1000): 1, and the method comprises the following steps: S1, nanofiltration: carrying out nanofiltration on the gas field produced water, and intercepting divalent ions to obtain nanofiltration produced water and nanofiltration concentrated water; s2, adsorbing and extracting lithium, namely adjusting the pH value of the sodium-filtered produced water, treating the sodium-filtered produced water through a lithium-sodium adsorption and separation device filled with an adsorbent to realize sodium-lithium separation, and collecting the adsorbed lithium-extracted produced water; s3, desorption of lithium ions: eluting the adsorbent with an acid solution to desorb the lithium ions from the adsorbent, and collecting an eluent; s4, concentration: carrying out reverse osmosis treatment on the eluent, and treating the reverse osmosis concentrated solution through an electrodialysis device to obtain a concentrated lithium-containing concentrated solution; and S5, lithium precipitation: adjusting the pH value of the lithium-containing concentrated solution, adding a lithium precipitation agent, and crystallizing and precipitating lithium to obtain industrial-grade lithium carbonate. The process is simple, the lithium recovery rate during lithium precipitation can be effectively increased, and full-automatic continuous operation can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and particularly relates to a method for extracting lithium from produced water of gas fields with a high sodium-lithium ratio. Background Art

[0002] The water quality of produced water from gas fields is related to the mine depth, well area location, mining technology and the composition of chemical additives during the mining process. The water quality is complex, the water volume increases significantly, and the salinity is generally tens of thousands to hundreds of thousands of mg / l or more. The lithium content in gas field water is 20 - 70 mg / L, belonging to the type of brine with high sodium and low lithium.

[0003] The existing research on liquid lithium extraction mainly focuses on salt lake brine, and often adopts a technical route combining "adsorption + membrane concentration". The main treatment target is to separate lithium ions from divalent magnesium ions. However, it is found in the treatment process of the high-sodium and low-lithium system of gas field water that the presence of sodium, a co-valent cation, will reduce the proportion of lithium salts in the concentrated solution of membrane concentration, thus restricting the increase in the concentration of lithium ions in the concentrated solution, resulting in an increase in the amount of mother liquor for lithium precipitation in the production of the same output of lithium carbonate and a decrease in the recovery rate of lithium carbonate.

[0004] In addition, in the existing technology, there are also teams that further evaporate and separate the mother liquor for lithium precipitation in order to improve the recovery rate. The evaporation crystallization process generally adopts triple-effect evaporation technology or mechanical vapor recompression evaporation crystallization (MVR) technology. No matter which evaporation crystallization technology is adopted, there are problems such as fouling of heat exchange tubes caused by high heat transfer temperature difference and high superheat, and problems of lithium salt crystallization and precipitation due to high crystal supersaturation during the evaporation crystallization process.

[0005] For the lithium carbonate production process, controlled by the solubility of lithium carbonate, the supernatant after precipitation contains about 2 g / L of lithium ions. In order to make the recovery rate of lithium ions during the lithium precipitation process above 90%, it is required that the lithium ion concentration in the raw liquid for lithium precipitation is above 20 g / L. Therefore, reducing the sodium-lithium ratio and increasing the lithium concentration in the raw liquid for lithium precipitation helps to improve the overall lithium recovery rate in the lithium carbonate production process and reduce the production cost. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for extracting lithium from produced water of gas fields with a high sodium-lithium ratio, aiming at the deficiencies of the existing technology, which can not only remove divalent impurity ions, but also reduce the sodium-lithium ratio in gas field water and increase the lithium ion concentration, thereby effectively improving the recovery rate of lithium precipitation.

[0007] To achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0008] A method for extracting lithium from produced water of gas fields with a high sodium-lithium ratio disclosed by the present invention, wherein the mass ratio of sodium to lithium in the produced water of the gas field is 100 - 1000:1, and the method comprises the following steps:

[0009] S1. Nanofiltration: The produced water from the gas field is subjected to nanofiltration through a nanofiltration membrane to achieve the retention of divalent ions, obtaining nanofiltration permeate and nanofiltration concentrate;

[0010] S2. Lithium extraction by adsorption: After adjusting the pH value of the nanofiltration permeate to weak acidity to weak alkalinity, it is treated by a lithium-sodium adsorption and separation device equipped with an adsorbent. The adsorbent selectively adsorbs lithium, thereby realizing the separation of sodium and lithium, and collecting the effluent as the produced water for lithium extraction by adsorption;

[0011] S3. Desorbing lithium ions: The adsorbent is eluted with an acid solution to desorb lithium ions from the adsorbent, and the eluate is collected;

[0012] S4. Concentration: The eluate is treated by a reverse osmosis device to obtain reverse osmosis concentrate, and the reverse osmosis concentrate is treated by an electrodialysis device to obtain a concentrated lithium-containing concentrate; Preferably, the lithium ion concentration in the lithium-containing concentrate is 20-25 g / L.

[0013] In some embodiments of the present invention, it further includes step S5:

[0014] S5. Lithium precipitation: After adjusting the pH value of the lithium-containing concentrate to 7-9, a lithium precipitation agent is added for crystallization precipitation of lithium to obtain industrial-grade lithium carbonate; Preferably, the lithium precipitation agent includes at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and carbon dioxide.

[0015] In some embodiments of the present invention, the nanofiltration concentrate obtained in step S1 is reinjected into the gas field as reinjection water;

[0016] Preferably, the divalent cation removal rate of the nanofiltration permeate obtained in step S1 is more than 99%.

[0017] In some embodiments of the present invention, in step S2, the pH value of the nanofiltration permeate is adjusted to 5-9.

[0018] In some embodiments of the present invention, in step S2, the type of the adsorbent is a manganese-based or titanium-based lithium extraction adsorbent.

[0019] In some embodiments of the present invention, in step S2, the nanofiltration permeate with adjusted pH value is passed through the lithium-sodium adsorption and separation device at a flow rate of 0.5-20 BV / h.

[0020] In some embodiments of the present invention, in the produced water for lithium extraction by adsorption in step S2, the sodium ion content is 70-100% of the sodium ion content in the nanofiltration permeate, and the lithium ion content is 0-30% of the lithium ion content in the nanofiltration permeate.

[0021] In some embodiments of the present invention, in step S3, the adsorbent is eluted with a hydrochloric acid solution;

[0022] Preferably, the concentration of the hydrochloric acid solution for eluting the adsorbent is 0.2-5 wt.%.

[0023] Preferably, the sodium-lithium ratio in the eluent is 1:10 to 1:1.

[0024] In one embodiment of the present invention, the Li content in the eluent is 0.81 g / L, the Na content is 0.095 g / L, and the sodium-lithium ratio is 1:8.5.

[0025] In one embodiment of the present invention, the Li content in the eluent is 1.2 g / L, the Na content is 0.15 g / L, and the sodium-lithium ratio is 1:8.

[0026] In one embodiment of the present invention, the Li content in the eluent is 0.72 g / L, the Na content is 0.10 g / L, and the sodium-lithium ratio is 1:7.2.

[0027] In some embodiments of the present invention, the water produced from lithium extraction by adsorption is mixed with the nanofiltration concentrate and reinjected into the gas field as reinjection water; another part is treated by bipolar membrane electrodialysis to obtain hydrochloric acid solution and sodium hydroxide solution respectively;

[0028] Preferably, the current density during bipolar membrane electrodialysis is controlled to be 400-800 A / m 2 ;

[0029] Preferably, the concentration of the hydrochloric acid solution produced by bipolar membrane electrodialysis is 0.5-4 mol / L;

[0030] Preferably, the concentration of the sodium hydroxide solution produced by bipolar membrane electrodialysis is 0.5-4 mol / L.

[0031] In some embodiments of the present invention, the hydrochloric acid solution obtained by bipolar membrane electrodialysis is returned as a desorbent to step S3 to elute the adsorbent.

[0032] In some embodiments of the present invention, the sodium hydroxide solution obtained by bipolar membrane electrodialysis is returned to step S2 to adjust the pH value of the nanofiltration-produced water; or / and is used to adjust the pH of the lithium-containing concentrate in step S5.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention is scientifically designed and ingeniously conceived. The present invention uses an adsorption separation method to reduce the sodium-lithium ratio in the lithium precipitation raw material liquid, and can reduce the sodium-lithium ratio from 100:1 to 1000:1 during nanofiltration-produced water to 1:10 to 1:1 in the eluent, and then uses reverse osmosis and electrodialysis methods to increase the lithium concentration to more than 20 g / L for lithium precipitation. The process is simple, can effectively improve the lithium recovery rate during lithium precipitation, and can realize fully automatic continuous operation.

[0035] By using the adsorption method to reduce the sodium-lithium ratio in the raw solution for lithium precipitation, and the reverse osmosis and electrodialysis methods to increase the lithium concentration, the section of evaporative crystallization for sodium chloride precipitation can be omitted, and the lithium ion concentration in the desired raw solution for lithium precipitation can be greater than 20 g / L, simplifying the process flow and effectively avoiding problems such as easy fouling and blockage, difficulty in long-term continuous operation, and reduction in the overall lithium ion recovery rate during the evaporative crystallization process.

[0036] The present invention adopts a bipolar membrane system to prepare hydrochloric acid and sodium hydroxide from the salt solution after lithium extraction through the bipolar membrane, which are used as the desorbing solution and the pH regulator for lithium precipitation respectively, so as to solve the problems of on-site acid-base transportation and storage and realize the resource utilization of salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Appendix Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0039] A method for extracting lithium from high-sodium-lithium ratio gas field produced water disclosed by the present invention, wherein the mass ratio of sodium to lithium in the gas field produced water is 100-1000:1, and the method includes the following steps:

[0040] S1. Nanofiltration: Nanofiltrate the gas field produced water through a nanofiltration membrane to intercept divalent ions, obtaining nanofiltration product water and nanofiltration concentrate; the removal rate of divalent cations in the nanofiltration product water is more than 99%, and the nanofiltration concentrate is reinjected into the gas field as reinjection water.

[0041] S2. Lithium extraction by adsorption: After adjusting the pH value of the nanofiltration product water to weak acidity to weak alkalinity, pass it through a lithium-sodium adsorption and separation device filled with an adsorbent at a flow rate of 0.5-20 BV / h. The adsorbent selectively adsorbs lithium, thereby realizing sodium-lithium separation, and collecting the effluent as the product water for lithium extraction by adsorption; preferably, the pH value of the nanofiltration product water is adjusted to 5-9.

[0042] The sodium ion content in the product water for lithium extraction by adsorption is 70-100% of the sodium ion amount in the nanofiltration product water, and the lithium ion content in the product water for lithium extraction by adsorption is 0-30% of the lithium ion amount in the nanofiltration product water.

[0043] Mix a part of the product water for lithium extraction by adsorption with the nanofiltration concentrate and reinject it into the gas field as reinjection water; the other part of the product water for lithium extraction by adsorption is treated by bipolar membrane electrodialysis to obtain hydrochloric acid and sodium hydroxide solutions respectively; during bipolar membrane electrodialysis, the current density is controlled at 400-800 A / m2 ; The concentration of hydrochloric acid obtained by bipolar membrane electrodialysis is 0.5 - 4 mol / L, and the concentration of sodium hydroxide solution obtained by bipolar membrane electrodialysis is 0.5 - 4 mol / L.

[0044] The hydrochloric acid obtained by bipolar membrane electrodialysis is used as a desorbent in step S3 to elute the adsorbent; the sodium hydroxide solution obtained by bipolar membrane electrodialysis is returned to step S2 to adjust the pH value of the nanofiltration product water; or / and enters step S5 to adjust the pH value of the lithium-containing concentrate.

[0045] S3. Desorb lithium ions: Use an acid solution to elute the adsorbent to desorb lithium ions from the adsorbent, and collect the eluate; the sodium-to-lithium ratio in the eluate is 1:10 to 1:1.

[0046] In some embodiments of the present invention, a hydrochloric acid solution is used to elute the adsorbent; preferably, the concentration of the hydrochloric acid solution for eluting the adsorbent is 0.2 - 5 wt.%.

[0047] S4. Concentration: Treat the eluate with a reverse osmosis device to obtain a permeate, and treat the permeate with an electrodialysis device to obtain a concentrated lithium-containing concentrate; preferably, the lithium ion concentration in the lithium-containing concentrate is 20 - 25 g / L.

[0048] S5. Lithium precipitation: After adjusting the pH value of the lithium-containing concentrate, add a lithium precipitation agent for crystallization precipitation of lithium to obtain industrial-grade lithium carbonate; preferably, the lithium precipitation agent includes at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and carbon dioxide.

[0049] Example 1

[0050] This example discloses a method for extracting lithium from high-sodium-to-lithium ratio gas field produced water using the method of the present invention. The main ion composition concentrations of the gas field produced water in this example are shown in Table 1:

[0051] Table 1 Ion composition of the gas field produced water in Example 1

[0052] Element Li Na Cl Ca Mg pH Concentration, g / L 0.075 10.9 19.2 1.27 0.12 2.4

[0053] S1. Nanofiltration: Nanofiltrate the gas field produced water through a nanofiltration membrane to intercept divalent ions, obtaining nanofiltration product water and nanofiltration concentrate; the divalent cation removal rate of the nanofiltration product water is 98%, and the nanofiltration concentrate is reinjected into the gas field as reinjection water;

[0054] The main ion composition concentrations of the nanofiltration product water are shown in Table 2:

[0055] Table 2 Ion composition of the nanofiltration product water in Example 1

[0056] Element Li Na Cl Ca Mg pH Concentration, g / L 0.075 10.9 19.2 0.015 0.0021 2.4

[0057] S2. Lithium extraction by adsorption: Add sodium filtration product water to sodium hydroxide solution to adjust the pH value to 7.5, and pass it through the lithium-sodium adsorption and separation device filled with manganese-based lithium extraction adsorbent at a flow rate of 6BV / h. The adsorbent selectively adsorbs lithium, thus realizing the separation of sodium and lithium. Collect the effluent as the product water of lithium extraction by adsorption;

[0058] The main ion composition concentrations of the product water of lithium extraction by adsorption are shown in Table 3:

[0059] Table 3 Ion composition of the product water of lithium extraction by adsorption in Example 1

[0060] Element Li Na Cl Ca Mg pH Concentration, g / L 0.002 11.2 19.8 0.008 0.001 2.4

[0061] Using the product water of lithium extraction by adsorption as the bipolar membrane feed water, the current density during bipolar membrane electrodialysis is controlled at 600 A / m 2 ; 2.4 mol / L hydrochloric acid solution and 2.2 mol / L sodium hydroxide solution are prepared. The obtained hydrochloric acid is used to desorb lithium ions in step S3, and the obtained sodium hydroxide is returned to step S2 to adjust the pH value of the nanofiltration product water, and is also used to adjust the pH value of the lithium-containing concentrated solution before lithium precipitation in step S5.

[0062] S3. Desorbing lithium ions: Elute the adsorbent with 0.5 wt% hydrochloric acid at a flow rate of 2BV / h to desorb lithium ions from the adsorbent, and collect the eluate; the proportion of lithium ions in the eluate reaches 90%. The main ion composition concentrations in the eluate are as follows:

[0063] Table 4 Ion composition of the eluate in Example 1

[0064] Element Li Na Cl pH Concentration, g / L 0.81 0.095 5.3 6.5

[0065] S4. Concentration: Treat the eluate with a reverse osmosis device to obtain a reverse osmosis concentrate, and then treat the reverse osmosis concentrate with an electrodialysis device to obtain a concentrated lithium-containing concentrated solution;

[0066] The main ion composition concentrations of the lithium-containing concentrated solution are as follows:

[0067] Table 5 Ion composition of the lithium-containing concentrated solution in Example 1

[0068] Element Li Na Cl pH Concentration, g / L 21.5 1.9 90.6 6.5

[0069] S5. Lithium precipitation: After adjusting the pH value of the lithium-containing concentrated solution to 7.5, introduce carbon dioxide to crystallize and precipitate lithium at 80 °C, then perform liquid-solid separation. The solid is washed and dried to obtain industrial-grade lithium carbonate; the lithium ion concentration in the filtrate is 1.9 g / L, and the lithium recovery rate is 91.2%.

[0070] Example 2

[0071] This embodiment discloses a method for extracting lithium from produced water in a gas field with a high sodium-lithium ratio by using the method of the present invention. The main ion composition concentrations of the produced water in the gas field in this embodiment are shown in Table 6:

[0072] Table 6 Ion composition of the produced water in the gas field of Example 2

[0073] Element Li Na Cl Ca Mg pH Concentration, g / L 0.11 10.7 18.7 1.05 0.05 5.4

[0074] S1. Nanofiltration: The produced water in the gas field is subjected to nanofiltration through a nanofiltration membrane to achieve the retention of divalent ions, obtaining nanofiltration permeate and nanofiltration concentrate; the removal rate of divalent cations in the nanofiltration permeate is 90%, and the nanofiltration concentrate is reinjected into the gas field as reinjection water;

[0075] The main ion composition concentrations of the nanofiltration permeate are shown in Table 7:

[0076] Table 7 Ion composition of the nanofiltration permeate of Example 2

[0077] Element Li Na Cl Ca Mg pH Concentration, g / L 0.10 10.7 18.7 0.11 ND 5.6

[0078] S2. Adsorptive lithium extraction: Sodium hydroxide solution is added to the nanofiltration permeate to adjust the pH value to 5, and it is passed through a lithium-sodium adsorption separation device equipped with a manganese-based adsorbent at a flow rate of 0.5 BV / h. The adsorbent selectively adsorbs lithium, thereby achieving the separation of sodium and lithium, and collecting the effluent as the water produced by adsorptive lithium extraction;

[0079] The main ion composition concentrations of the water produced by adsorptive lithium extraction are shown in Table 8:

[0080] Table 8 Ion composition of the water produced by adsorptive lithium extraction of Example 2

[0081] Element Li Na Cl Ca Mg pH Concentration, g / L 0.015 10.7 18.7 1.05 0.05 6.2

[0082] Using the water produced by adsorptive lithium extraction as the bipolar membrane feed water, the current density during bipolar membrane electrodialysis is controlled at 400 A / m 2 ; 0.5 mol / L hydrochloric acid solution and 0.5 mol / L sodium hydroxide solution are prepared. The obtained hydrochloric acid is used for desorbing lithium ions in step S3, and the obtained sodium hydroxide is returned to step S2 to adjust the pH value of the nanofiltration permeate, and is also used to adjust the pH value of the lithium-containing concentrated solution before lithium precipitation in step S5.

[0083] S3. Desorbing lithium ions: Eluting the adsorbent with 0.1 wt% hydrochloric acid at a flow rate of 0.5 BV / h to desorb lithium ions from the adsorbent, and collecting the eluate; the proportion of lithium ions in the eluate reaches 90%. The main ion composition concentrations in the eluate are as follows:

[0084] Table 9 Ion composition of the eluate of Example 2

[0085] Element Li Na Cl pH Concentration, g / L 1.2 0.15 6.2 5.2

[0086] S4. Concentration: The eluate is treated by a reverse osmosis device to obtain reverse osmosis concentrate. The reverse osmosis concentrate is treated by an electrodialysis device to obtain a concentrated lithium-containing concentrate.

[0087] The concentration of the main ions in the lithium-containing concentrate is as follows:

[0088] Table 10 Ion composition of the lithium-containing concentrate in Example 2

[0089] Element Li Na Cl pH Concentration, g / L 24.5 2.9 95.4 7.1

[0090] S5. Lithium precipitation: After adjusting the pH value of the lithium-containing concentrate to 8, carbon dioxide is introduced to crystallize and precipitate lithium at 80 °C, and then liquid-solid separation is carried out. The solid is washed and dried to obtain industrial-grade lithium carbonate; the lithium ion concentration in the filtrate is 1.5 g / L, and the lithium recovery rate is 93.8%.

[0091] Example 3

[0092] This example discloses a method for extracting lithium from high-sodium-to-lithium ratio gas field produced water by using the method of the present invention. The concentration of the main ions in the gas field produced water in this example is shown in Table 11:

[0093] Table 11 Ion composition of the gas field produced water in Example 3

[0094]

[0095]

[0096] S1. Nanofiltration: The gas field produced water is nanofiltrated through a nanofiltration membrane to intercept divalent ions, obtaining nanofiltration product water and nanofiltration concentrate; the divalent cation removal rate of the nanofiltration product water is 92%, and the nanofiltration concentrate is reinjected into the gas field as reinjection water.

[0097] The concentration of the main ions in the nanofiltration product water is shown in Table 12:

[0098] Table 12 Ion composition of the nanofiltration product water in Example 3

[0099] Element Li Na Cl Ca Mg pH Concentration, g / L 0.021 20.5 32.8 0.28 0.02 3.5

[0100] S2. Lithium extraction by adsorption: The sodium-filtered product water is adjusted to pH 9 by adding sodium hydroxide solution and passed through a lithium-sodium adsorption separation device equipped with a titanium-based adsorbent at a flow rate of 20 BV / h. The adsorbent selectively adsorbs lithium, thereby realizing the separation of sodium and lithium, and collecting the effluent as the product water of lithium extraction by adsorption.

[0101] The concentration of the main ions in the product water of lithium extraction by adsorption is shown in Table 13:

[0102] Table 13 Ion composition of the product water of lithium extraction by adsorption in Example 3

[0103] Element Li Na Cl Ca Mg pH Concentration, g / L 0.003 20.5 32.8 0.57 0.1 3.5

[0104] Using the water produced from lithium extraction by adsorption as the feed water for the bipolar membrane, the current density during bipolar membrane electrodialysis is controlled at 800 A / m 2 ; A 1 mol / L hydrochloric acid solution and a 1 mol / L sodium hydroxide solution are prepared. The obtained hydrochloric acid is used to desorb lithium ions in step S3, and the obtained sodium hydroxide is returned to step S2 to adjust the pH value of the nanofiltration-produced water, and is also used to adjust the pH value of the lithium-containing concentrated solution before lithium precipitation in step S5.

[0105] S3. Desorbing lithium ions: Eluting the adsorbent with 1 wt% hydrochloric acid at a flow rate of 5 BV / h to desorb lithium ions from the adsorbent, and collecting the eluate; the proportion of lithium ions in the eluate reaches 90%. The main ion composition concentrations in the eluate are as follows:

[0106] Table 14 Ion composition of the eluate in Example 3

[0107] Element Li Na Cl pH Concentration, g / L 0.72 0.10 5.8 4.9

[0108] S4. Concentration: Treating the eluate with a reverse osmosis device to obtain a reverse osmosis concentrate, and treating the reverse osmosis concentrate with an electrodialysis device to obtain a concentrated lithium-containing concentrated solution;

[0109] The main ion composition concentrations in the lithium-containing concentrated solution are as follows:

[0110] Table 15 Ion composition of the lithium-containing concentrated solution in Example 3

[0111] Element Li Na Cl pH Concentration, g / L 20.4 2.8 164 4.2

[0112] S5. Precipitating lithium: After adjusting the pH value of the lithium-containing concentrated solution to 8.5, introducing carbon dioxide to crystallize and precipitate lithium at 80 °C, then performing liquid-solid separation. The solid is washed and dried to obtain industrial-grade lithium carbonate; the lithium ion concentration in the filtrate is 1.4 g / L, and the lithium recovery rate is 93.1%.

[0113] The above embodiments are only one of the preferred embodiments of the present invention and should not be used to limit the protection scope of the present invention. Any modifications or polishings made without substantial significance in the main design concept and spirit of the present invention, as long as the technical problems solved are still the same as those of the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio, characterized in that, the mass ratio of sodium to lithium in the produced water of the gas field is 100:1 to 1000:1, and the method comprises the following steps: S1. Nanofiltration: subjecting the produced water of the gas field to nanofiltration through a nanofiltration membrane to intercept divalent ions, obtaining nanofiltration product water and nanofiltration concentrate; S2. Adsorptive lithium extraction: after adjusting the pH value of the nanofiltration product water to weakly acidic to weakly alkaline, treating it through a lithium-sodium adsorption and separation device filled with an adsorbent, and the adsorbent selectively adsorbs lithium, thereby realizing the separation of sodium and lithium, and collecting the effluent as the product water of adsorptive lithium extraction; S3. Desorbing lithium ions: eluting the adsorbent with an acid solution to desorb lithium ions from the adsorbent, and collecting the eluate; S4. Concentration: treating the eluate with a reverse osmosis device to obtain reverse osmosis concentrate, and treating the reverse osmosis concentrate with an electrodialysis device to obtain a concentrated lithium-containing concentrate; preferably, the lithium ion concentration in the lithium-containing concentrate is 20-25 g / L.

2. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, it further comprises step S5: S5. Lithium precipitation: after adjusting the pH value of the lithium-containing concentrate to 7-9, adding a lithium precipitation agent for crystallization precipitation of lithium to obtain industrial-grade lithium carbonate; preferably, the lithium precipitation agent comprises at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and carbon dioxide.

3. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, the nanofiltration concentrate obtained in step S1 is reinjected into the gas field as reinjection water; preferably, the divalent cation removal rate of the nanofiltration product water obtained in step S1 is more than 99%.

4. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, in step S2, the pH value of the nanofiltration product water is adjusted to 5-9.

5. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, in step S2, the type of the adsorbent is a manganese-based or titanium-based lithium extraction adsorbent.

6. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, in step S2, the nanofiltration product water with adjusted pH value is passed through the lithium-sodium adsorption and separation device at a flow rate of 0.5-20 BV / h.

7. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, the sodium ion content in the product water of adsorptive lithium extraction in step S2 is 70-100% of the sodium ions in the nanofiltration product water, and the lithium ion content in the product water of adsorptive lithium extraction is 0-30% of the lithium ions in the nanofiltration product water.

8. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1, characterized in that, in step S3, the adsorbent is eluted with a hydrochloric acid solution; preferably, the concentration of the hydrochloric acid solution for eluting the adsorbent is 0.2-5 wt.%; preferably, the sodium-lithium ratio in the eluate is 1:10 to 1:

1.

9. The method for extracting lithium from produced water of a gas field with a high sodium-lithium ratio according to claim 1 or 2, characterized in that, The water produced from lithium extraction by adsorption is mixed with the nanofiltration concentrate and reinjected into the gas field as reinjection water; another part is treated by bipolar membrane electrodialysis to obtain hydrochloric acid solution and sodium hydroxide solution respectively; Preferably, the current density during bipolar membrane electrodialysis is controlled at 400 - 800 A / m 2 ; Preferably, the concentration of the hydrochloric acid solution produced by bipolar membrane electrodialysis is 0.5 - 4 mol / L; Preferably, the concentration of the sodium hydroxide solution produced by bipolar membrane electrodialysis is 0.5 - 4 mol / L.

10. A method for extracting lithium from produced water in a gas field with a high sodium-lithium ratio according to claim 8, characterized in that, The hydrochloric acid solution obtained by bipolar membrane electrodialysis is returned as a desorbent to step S3 to elute the adsorbent; preferably, the sodium hydroxide solution obtained by bipolar membrane electrodialysis is returned to step S2 to adjust the pH value of the nanofiltration produced water; or / and is used to adjust the pH of the lithium-containing concentrate in step S5.

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