阅读说明：本技术 从盐湖卤水中提取氢氧化锂和氢氧化钠的方法及装置 (Method and device for extracting lithium hydroxide and sodium hydroxide from salt lake brine ) 是由 徐川 严新星 陈欣 何霞 杨艳辉 谢宇充 于 2021-08-06 设计创作，主要内容包括：本发明涉及从盐湖卤水中提取氢氧化锂和氢氧化钠的方法及装置,属于电渗析技术领域。本发明解决的技术问题是提供一种新的双极膜电渗析系统,采用该系统,可以在电渗析同时,将锂钠初步分离,减少氢氧化锂的重结晶次数,缩短工艺流程。本发明双极膜电渗析装置,采用两张对锂钠有一定分离率的阳膜,将碱室分为了两个(即第一碱室和第二碱室),该装置在处理盐湖卤水时,能同时得到氢氧化锂和氢氧化钠溶液,还能更大限度的使锂通过膜,减少盐溶液中锂的存留量,分离率达80％。本技术可减少氢氧化锂的重结晶次数,缩短工艺流程,氢氧化钠也可返盐湖的前工段,回收利用。(The invention relates to a method and a device for extracting lithium hydroxide and sodium hydroxide from salt lake brine, belonging to the technical field of electrodialysis. The invention solves the technical problem of providing a novel bipolar membrane electrodialysis system, which can initially separate lithium and sodium during electrodialysis, reduce the recrystallization times of lithium hydroxide and shorten the process flow. The bipolar membrane electrodialysis device adopts two anode membranes with a certain separation rate on lithium sodium, divides the alkali chamber into two (namely the first alkali chamber and the second alkali chamber), can simultaneously obtain lithium hydroxide and sodium hydroxide solution when treating salt lake brine, can enable lithium to pass through the membranes to a greater extent, reduces the retention amount of lithium in the salt solution, and has the separation rate of 80%. The technology can reduce the recrystallization times of the lithium hydroxide, shorten the process flow, and return the sodium hydroxide to the previous working section of the salt lake for recycling.)

1. Bipolar membrane electrodialysis device, including negative pole (1), positive pole (2) and at least a set of membrane group (3), negative pole (1) is located the cathode chamber, and positive pole (2) are located the anode chamber, and membrane group (3) are located between negative pole (1) and positive pole (2), its characterized in that: the membrane group (3) comprises a cathode membrane (302), a bipolar membrane (301), a first anode membrane (303) and a second anode membrane (304) which are sequentially arranged from a cathode end to an anode end, an acid chamber (312) is formed between the cathode membrane (302) and the bipolar membrane (301), a salt chamber (311) is arranged on the other side of the cathode membrane (302), a first alkali chamber (313) is formed between the bipolar membrane (301) and the first anode membrane (303), a second alkali chamber (314) is formed between the first anode membrane (303) and the second anode membrane (304), and the salt chamber (311) is formed between the second anode membrane (304) and the cathode membrane (302); the first positive membrane (303) and the second positive membrane (304) both adopt membranes with lithium-sodium separation rate.

2. The bipolar membrane electrodialysis device according to claim 1, wherein: the first positive membrane (303) and the second positive membrane (304) both adopt a cation exchange membrane coated with a compound A on the surface, wherein the compound A is aminobenzene grafted polyether-ether-ketone, aminobenzene grafted polyether valia, mononitrobenzene grafted polyether-ether-ketone, aminobenzene grafted polyla, mononitrobenzene grafted polyether valia or methylphthalene grafted polyvinyl alcohol.

3. A method for extracting lithium hydroxide and sodium hydroxide from salt lake brine is characterized by comprising the following steps:

a. pretreatment: pretreating salt lake brine to obtain a solution containing lithium, sodium and chloride ions;

b. bipolar membrane electrodialysis: adding a solution containing lithium, sodium and chloride ions as a salt solution into a salt chamber (311) of a bipolar membrane electrodialysis device, adding 0.1-1 mol/L LiOH solution into a first alkali chamber (313), adding 0.1-1 mol/L NaOH solution into a second alkali chamber (314), adding 0.1-1 mol/L hydrochloric acid solution into an acid chamber (312), adding 0.1-1 mol/L NaOH solution into a cathode chamber and an anode chamber, and performing bipolar membrane electrodialysis; the bipolar membrane electrodialysis device employs the bipolar membrane electrodialysis device according to claim 1 or 2;

c. taking out: the liquids in the first base chamber (313) and the second base chamber (314) are taken out, and a lithium hydroxide solution is obtained in the first base chamber (313), and a sodium hydroxide solution is obtained in the second base chamber (314).

4. The method of claim 3, wherein the extraction of lithium hydroxide and sodium hydroxide from salt lake brine comprises: in the step a, the following method is adopted for pretreatment: drying in the sun by a salt pan process, removing sodium chloride, potassium chloride, sodium sulfate and magnesium chloride in salt lake brine, then adjusting the pH value, removing sulfur, and removing boron, calcium and magnesium by ion exchange resin to obtain a solution containing lithium, sodium and chloride ions;

or adopting the following pretreatment method: subjecting the salt lake brine to an adsorption and desorption process of lithium extraction resin, concentrating, purifying and removing calcium and magnesium ions to obtain a solution containing lithium, sodium and chloride ions;

or adopting the following pretreatment method: and (2) drying in the air by a salt pan process, removing sodium chloride, potassium chloride and magnesium sulfate in salt lake brine, further separating divalent ions and primary ions by a nanofiltration membrane, removing calcium, magnesium and boron by resin, and concentrating to obtain a solution containing lithium, sodium and chloride ions.

5. The method of claim 3, wherein the extraction of lithium hydroxide and sodium hydroxide from salt lake brine comprises: in the step b, the current density of the bipolar membrane electrodialysis is 200-800A/m²。

6. The method of claim 3, wherein the extraction of lithium hydroxide and sodium hydroxide from salt lake brine comprises: and (b) preparing a lithium hydroxide product by circulating and crystallizing the lithium hydroxide solution obtained in the first alkali chamber (313), and returning the sodium hydroxide solution obtained in the second alkali chamber (314) and the acid solution obtained in the acid chamber (312) to the step (a).

Technical Field

The invention relates to a method and a device for extracting lithium hydroxide and sodium hydroxide from salt lake brine, belonging to the technical field of electrodialysis.

Background

At present, lithium salt products are mainly obtained by extracting lithium from lithium ores and lithium from salt lake brine, the lithium extraction technology by the lithium ore method has long development time and relatively mature technology, then the resource reserve of lithium ores in China is very limited, and the ever-increasing market demand cannot be met by simply depending on lithium ores. The salt lake brine contains abundant lithium resources and has great mining value, so the heat of extracting lithium from the salt lake brine is higher and higher in recent years.

The bipolar membrane is a novel ion exchange composite membrane, which is usually formed by compounding a cation exchange layer, an interface hydrophilic layer and an anion exchange layer and is a reaction membrane in the true sense. Under the action of a direct current electric field, the bipolar membrane can dissociate water to obtain hydrogen ions and hydroxyl ions on two sides of the membrane respectively. By utilizing the characteristic, the bipolar membrane electrodialysis system combining the bipolar membrane and other anion-cation exchange membranes can convert the salt in the salt lake brine into corresponding acid and alkali without introducing new components. Therefore, the bipolar membrane electrodialysis system is widely applied to lithium extraction from brine.

The invention patent with publication number CN 112209412A discloses a method for extracting lithium and battery-grade lithium hydroxide monohydrate, wherein the method is used for removing impurities and concentrating lithium-containing brine to obtain a lithium-rich concentrated solution; carrying out bipolar membrane alkali preparation treatment on the lithium-rich concentrated solution to obtain mixed alkali liquor and hydrochloric acid solution; carrying out evaporation crystallization treatment on the mixed alkali liquor to obtain an evaporation crystallization precipitate and an evaporation crystallization end point mother liquor; subjecting the evaporated and crystallized precipitate to a first dissolution recrystallization treatment to obtain a first recrystallized precipitate and a first recrystallization mother liquor; subjecting the first recrystallized precipitate to a second dissolution recrystallization treatment to obtain lithium hydroxide monohydrate and a second recrystallization mother liquor.

The invention patent with publication number CN112593094A discloses a process and a device for extracting lithium from a salt lake, wherein an adsorption method is coupled with a membrane method, and lithium hydroxide is prepared by using carbonate type salt lake brine. Specifically, an adsorbent is adopted for adsorption, a desorbent is used for desorbing the adsorbent, calcium and magnesium ions are removed from the desorbed solution through purified resin after the desorbed solution is concentrated, acid and alkali solutions are obtained through bipolar membrane electrolysis, and the alkali solution is crystallized to obtain lithium hydroxide and crystallization mother liquor.

The invention patent with publication number CN111924861A discloses a preparation method of lithium hydroxide, which comprises the steps of adsorbing by adopting an adsorbent, filtering lithium-containing analytic liquid, and then performing deacidification treatment to obtain deacidified analytic liquid; adjusting the pH value, and performing nanofiltration to remove calcium and magnesium to obtain nanofiltration product water; concentrating the nanofiltration water to obtain a lithium-rich concentrated solution; then treating by a bipolar membrane to obtain a mixed alkali solution; and (3) carrying out evaporative crystallization on the mixed alkali solution to obtain the lithium hydroxide.

Therefore, at present, a bipolar membrane electrodialysis system is adopted, and the obtained alkali liquor is a mixed solution of lithium hydroxide and sodium hydroxide, and then is separated in a recrystallization mode. Repeated recrystallization can result in low utilization rate of lithium, high energy consumption and long process flow, which is not beneficial to production.

Disclosure of Invention

In view of the above drawbacks, the present invention provides a novel bipolar membrane electrodialysis system, which can initially separate lithium and sodium during electrodialysis, reduce the number of recrystallization of lithium hydroxide, and shorten the process flow.

The bipolar membrane electrodialysis device comprises a cathode, an anode and at least one group of membrane groups, wherein the cathode is positioned in a cathode chamber, the anode is positioned in an anode chamber, the membrane groups are positioned between the cathode and the anode, the membrane groups comprise a cathode membrane, a bipolar membrane, a first anode membrane and a second anode membrane which are sequentially arranged from a cathode end to an anode end, an acid chamber is formed between the cathode membrane and the bipolar membrane, a salt chamber is arranged at the other side of the cathode membrane, a first alkali chamber is formed between the bipolar membrane and the first anode membrane, a second alkali chamber is formed between the first anode membrane and the second anode membrane, and a salt chamber is formed between the second anode membrane and the cathode membrane; and the first positive membrane and the second positive membrane are both membranes with lithium-sodium separation rate.

In a specific embodiment, the first positive membrane and the second positive membrane are both cation exchange membranes coated with a compound a on the surface, wherein the compound a is aminobenzene grafted polyether ether ketone, aminobenzene grafted polyether valia, mononitrobenzene grafted polyether ether ketone, aminobenzene grafted poly valia, mononitrobenzene grafted polyether valia, or methylphthalene grafted polyvinyl alcohol.

The second technical problem solved by the invention is to provide a method for extracting lithium hydroxide and sodium hydroxide from salt lake brine.

The invention relates to a method for extracting lithium hydroxide and sodium hydroxide from salt lake brine, which comprises the following steps:

a. pretreatment: pretreating salt lake brine to obtain a solution containing lithium, sodium and chloride ions;

b. bipolar membrane electrodialysis: adding a solution containing lithium, sodium and chloride ions as a salt solution into a salt chamber of a bipolar membrane electrodialysis device, adding 0.1-1 mol/L LiOH solution into a first alkali chamber, adding 0.1-1 mol/L NaOH solution into a second alkali chamber, adding 0.1-1 mol/L hydrochloric acid solution into an acid chamber, adding 0.1-1 mol/L NaOH solution into a cathode chamber and an anode chamber, and performing bipolar membrane electrodialysis; the bipolar membrane electrodialysis device adopts the bipolar membrane electrodialysis device;

c. taking out: and taking out the liquid in the first alkali chamber and the second alkali chamber to obtain a lithium hydroxide solution in the first alkali chamber and obtain a sodium hydroxide solution in the second alkali chamber.

In one embodiment of the present invention, in step a, the following method is adopted for pretreatment:

drying in the sun by a salt pan process, removing sodium chloride, potassium chloride, sodium sulfate and magnesium chloride in salt lake brine, then adjusting the pH value, removing sulfur, and removing boron, calcium and magnesium by ion exchange resin to obtain a solution containing lithium, sodium and chloride ions;

or adopting the following pretreatment method: subjecting the salt lake brine to an adsorption and desorption process of lithium extraction resin, concentrating, purifying and removing calcium and magnesium ions to obtain a solution containing lithium, sodium and chloride ions;

or adopting the following pretreatment method: and (2) drying in the air by a salt pan process, removing sodium chloride, potassium chloride and magnesium sulfate in salt lake brine, further separating divalent ions and primary ions by a nanofiltration membrane, removing calcium, magnesium and boron by resin, and concentrating to obtain a solution containing lithium, sodium and chloride ions.

In one embodiment of the invention, 200-800A/m is introduced according to the membrane area²The current of (2).

In one embodiment of the invention, the lithium hydroxide solution obtained in the first alkali chamber is crystallized by circulation to obtain a lithium hydroxide product, and the sodium hydroxide solution obtained in the second alkali chamber and the acid solution obtained in the acid chamber are both returned to step a.

Compared with the prior art, the invention has the following beneficial effects:

the bipolar membrane electrodialysis device adopts two anode membranes with a certain separation rate on lithium sodium, divides the alkali chamber into two (namely the first alkali chamber and the second alkali chamber), can simultaneously obtain lithium hydroxide and sodium hydroxide solution when treating salt lake brine, can enable lithium to pass through the membranes to a greater extent, reduces the retention amount of lithium in the salt solution, and has the separation rate of 80%. The technology can reduce the recrystallization times of the lithium hydroxide, shorten the process flow, and return the sodium hydroxide to the previous working section of the salt lake for recycling.

Drawings

FIG. 1 is a schematic view of a bipolar membrane electrodialysis device of the present invention, wherein 1-cathode; 2-an anode; 3-membrane group; 301-a bipolar membrane; 302-negative mask; 303-a first positive membrane; 304-a second positive membrane; 311-salt chamber; 312-acid compartment; 313-a first base chamber; 314-second base chamber.

Detailed Description

As shown in fig. 1, the bipolar membrane electrodialysis device of the present invention comprises a cathode 1, an anode 2 and at least one membrane group 3, wherein the cathode 1 is located in a cathode chamber, the anode 2 is located in an anode chamber, the membrane group 3 is located between the cathode 1 and the anode 2, the membrane group 3 comprises a cathode membrane 302, a bipolar membrane 301, a first anode membrane 303 and a second anode membrane 304 which are sequentially arranged from a cathode end to an anode end, an acid chamber 312 is formed between the cathode membrane 302 and the bipolar membrane 301, a salt chamber 311 is formed on the other side of the cathode membrane 302, a first base chamber 313 is formed between the bipolar membrane 301 and the first anode membrane 303, a second base chamber 314 is formed between the first anode membrane 303 and the second anode membrane 304, and a salt chamber 311 is also formed between the second anode membrane 304 and the cathode membrane 302; the first positive membrane 303 and the second positive membrane 304 both use membranes having a separation rate for lithium and sodium.

In the conventional bipolar membrane electrodialysis system, only one positive membrane is arranged in one membrane group, namely, a negative membrane, a partition plate, a bipolar membrane, a partition plate, a positive membrane and a partition plate are generally adopted and sequentially arranged to form 1 membrane group, while the bipolar membrane electrodialysis device adopts two positive membranes, and divides an alkali chamber into two parts, namely, the negative membrane, the partition plate, the bipolar membrane, the partition plate, a lithium-sodium separation positive membrane, the partition plate, the lithium-sodium separation positive membrane and the partition plate are sequentially arranged to form 1 membrane group, wherein the negative membrane and the positive membrane are separated by the partition plate to form an acid chamber, the negative membrane and the positive membrane are separated by the partition plate to form a first alkali chamber 313, the two positive membranes form a second alkali chamber 314, and the positive membrane and the negative membrane form a salt chamber 311. By this means, lithium and part of sodium preferentially pass through the membrane into the second alkaline chamber 314, and most of the lithium and part of the sodium in the second alkaline chamber 314 then pass into the first alkaline chamber 313, resulting in a lithium-rich alkaline solution, which is also lower relative to the lithium remaining in the salt solution.

The negative membrane 302 of the present invention is an anion exchange membrane commonly used in the art.

The membrane with the separation rate of lithium and sodium in the invention refers to that the membrane has certain selectivity on lithium ions due to different passing rates of lithium ions and sodium ions, so that the membrane can pass a large amount of lithium ions and a small amount of sodium ions. In one embodiment of the present invention, the membrane having a separation rate for lithium sodium has a separation rate for lithium ions and sodium ions of 70% or more.

According to the present invention, the first positive film 303 and the second positive film 304 both use positive films having a certain selectivity to lithium, and in one embodiment of the present invention, the separation rate of lithium by the first positive film 303 and the second positive film 304 is 70 to 80%. In a specific embodiment, the first positive film 303 and the second positive film 304 are both cation exchange membranes coated with a compound a, which is aminobenzene grafted polyether ether ketone, aminobenzene grafted polyether valia, mononitrobenzene grafted polyether ether ketone, aminobenzene grafted poly valia, mononitrobenzene grafted polyether valia, or methylphthalene grafted polyvinyl alcohol.

Wherein, the cation exchange membrane can adopt a common cation membrane in the field, such as a sulfonic acid type macromolecular compound, and the structural formula of the cation exchange membrane is as follows:

the cation exchange membrane may be commercially available, for example, Japanese ASTOM membrane or the like.

The first positive membrane 303 and the second positive membrane 304 of the present invention can be obtained by coating the compound a on a cation exchange membrane. The compound A is aminobenzene grafted polyether ether ketone, aminobenzene grafted polyether valia, mononitrobenzene grafted polyether ether ketone, aminobenzene grafted poly valia, mononitrobenzene grafted polyether valia or methylphthalene grafted polyvinyl alcohol. The crystal branch type of the cation exchange membrane coated with the compound A has more interception function to ions.

The coating can be carried out by coating the compound A on one side of the cation exchange membrane or coating the compound A on both sides of the cation exchange membrane.

The method of coating is a conventional method in the art, and in one embodiment of the present invention, the following method may be employed:

putting a certain amount of the compound A into a certain amount of deionized water, and stirring to form emulsion. Pouring the emulsion into a glass vessel, immersing the cleaned cation exchange membrane into the emulsion, and vertically irradiating for 60-150 min by using ultraviolet light. And taking the cation exchange membrane out of the emulsion, cleaning the cation exchange membrane by using deionized water, and freeze-drying the cation exchange membrane in a vacuum freeze-drying machine for 12 hours to obtain the cation exchange membrane.

Among them, aminobenzene-grafted polyether ether ketone, aminobenzene-grafted polyether valia, mononitrobenzene-grafted polyether ether ketone, aminobenzene-grafted poly valia, mononitrobenzene-grafted polyether valia, or methylphthalene-grafted polyvinyl alcohol can be prepared by a conventional method. For example, when preparing aminobenzene grafted polyether-ether-ketone, commercially available polyether-ether-ketone can be adopted, amine groups are grafted to polyether-ether-ketone, then the amine groups of the ammonia salt are punched and activated to obtain aminobenzene grafted polyether-ether-ketone, and the specific method is as follows:

weighing dry polyetheretherketone powder, placing in a flask, adding concentrated sulfuric acid with concentration more than 95%, stirring and dissolving. Placing the flask in a water bath at 60 ℃, adding N-methyl-2-pyrrolidone and aniline during stirring, uniformly stirring, and pouring the solution into a large amount of ice-water mixture for settling. Washing the precipitate with deionized water to be neutral, drying at 100 ℃, and then carrying out heat treatment at 130 ℃ for 1-2 h.

The remaining compounds A, such as aminobenzene-grafted polyether (valia), mononitrobenzene-grafted polyether (ether-ketone), aminobenzene-grafted polymer (valia), mononitrobenzene-grafted polymer (polymer-valia), mononitrobenzene-grafted polyether (polyether-ether-ketone), are grafted in the same manner as aminobenzene-grafted polyether (ether-ketone).

The methyl phthalyl benzo grafted polyvinyl alcohol is prepared by the following method: dissolving polyvinyl alcohol in deionized water, heating at 90 ℃ under continuous stirring until a transparent solution is obtained, adding methyl phthalyl benzene and concentrated hydrochloric acid, and carrying out reflux reaction for 12 hours under the protection of high-purity nitrogen to obtain the methyl phthalyl benzene grafted polyvinyl alcohol.

In the bipolar membrane electrodialysis device, the membrane groups 3 can be one group or multiple groups. In one embodiment of the present invention, the film groups 3 are arranged in 10 groups. Thus, between each set of membrane modules there are an acid compartment, a base compartment and a salt compartment, which in one embodiment of the invention are interconnected, the first base compartment being interconnected, the second base compartment being interconnected, the salt compartments being interconnected, the acid-base salt solutions therein being circulated in the respective compartments by peristaltic pumps, respectively, the Cl being^-And Li⁺/Na⁺In a direct current electric fieldUnder the action of the hydrogen peroxide, the hydrogen peroxide respectively crosses a negative membrane and a positive membrane to enter an adjacent acid chamber and an adjacent alkali chamber, and then is subjected to water dissociation with a bipolar membrane (BPM) catalyst layer to generate H⁺And OH^-Combining to produce hydrochloric acid and lithium/sodium hydroxide.

In another embodiment of the present invention, the membrane group 3 is provided in 60 groups or 120 groups.

The second technical problem solved by the invention is to provide a method for extracting lithium hydroxide and sodium hydroxide from salt lake brine.

The invention relates to a method for extracting lithium hydroxide and sodium hydroxide from salt lake brine, which comprises the following steps:

a. pretreatment: pretreating salt lake brine to obtain a solution containing lithium, sodium and chloride ions;

b. bipolar membrane electrodialysis: adding a solution containing lithium, sodium and chloride ions as a salt solution into a salt chamber 311 of a bipolar membrane electrodialysis device, adding 0.1-1 mol/L LiOH solution into a first alkali chamber 313, adding 0.1-1 mol/L LNaOH solution into a second alkali chamber 314, adding 0.1-1 mol/L hydrochloric acid solution into an acid chamber 312, adding 0.1-1 mol/L NaOH solution into a cathode chamber and an anode chamber, and performing bipolar membrane electrodialysis; the bipolar membrane electrodialysis device adopts the bipolar membrane electrodialysis device;

c. taking out: the liquids in the first base chamber 313 and the second base chamber 314 are taken out, and a lithium hydroxide solution is obtained in the first base chamber 313, and a sodium hydroxide solution is obtained in the second base chamber 314.

Pretreatment methods commonly used in the art are suitable for use in the present invention.

In one embodiment of the invention, the following pretreatment method is employed:

and (2) drying in the sun by a salt pan process, removing sodium chloride, potassium chloride, sodium sulfate and magnesium chloride in salt lake brine, then adjusting the pH value, removing sulfur, and removing boron, calcium and magnesium by ion exchange resin to obtain a solution containing lithium, sodium and chloride ions.

In another embodiment of the invention, the following pretreatment method is employed: and (3) subjecting the salt lake brine to an adsorption and desorption process of lithium extraction resin, concentrating, and removing calcium and magnesium ions by using purified resin to obtain a solution containing lithium, sodium and chloride ions.

In another embodiment of the invention, the following pretreatment method is employed: and (2) drying in the air by a salt pan process, removing sodium chloride, potassium chloride and magnesium sulfate in salt lake brine, further separating divalent ions and primary ions by a nanofiltration membrane, removing calcium, magnesium and boron by resin, and concentrating to obtain a solution containing lithium, sodium and chloride ions.

The current density of the bipolar membrane electrodialysis can be adjusted according to the membrane area, and in one embodiment of the invention, 200-800A/m is introduced according to the membrane area²The current of (2).

In order to reduce the cost and improve the material utilization rate, in an embodiment of the present invention, the lithium hydroxide solution obtained in the first alkali chamber 313 is crystallized by circulation to obtain a lithium hydroxide product, and both the sodium hydroxide solution obtained in the second alkali chamber 314 and the acid solution obtained in the acid chamber 312 are returned to step a, wherein the sodium hydroxide solution may be returned to a lithium extraction brine section, for example, for pH adjustment, resin regeneration, and the like, and the acid solution may also be returned to step a for pH adjustment, resin desorption, and the like.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

In the examples, the bipolar membrane electrodialysis apparatus shown in FIG. 1 was used.

The bipolar membrane electrodialysis device shown in fig. 1 comprises a cathode 1, an anode 2 and membrane groups 3, wherein the cathode 1 is located in a cathode chamber, the anode 2 is located in an anode chamber, the membrane groups 3 are located between the cathode 1 and the anode 2, each membrane group 3 comprises a cathode membrane 302, a bipolar membrane 301, a first anode membrane 303 and a second anode membrane 304 which are sequentially arranged from a cathode end to an anode end, an acid chamber 312 is formed between the cathode membrane 302 and the bipolar membrane 301, a first alkali chamber 313 is formed between the bipolar membrane 301 and the first anode membrane 303, a second alkali chamber 314 is formed between the first anode membrane 303 and the second anode membrane 304, and a salt chamber 311 is formed between the second anode membrane 304 and the cathode membrane 302. 10 groups of membrane groups 3 and 1 membrane stack consisting of two polar membranes are arranged between the cathode 1 and the anode 2. The acid chambers 312 between each set of membranes are in communication with each other,the salt chambers 311 are communicated with each other, the first alkali chambers 313 are communicated with each other, the second alkali chambers 314 are also communicated with each other, and the acid-alkali salt polar liquid is respectively circulated in the corresponding compartments through a peristaltic pump. Wherein the effective area of the membrane is 0.55m²And a partition board is arranged between every two adjacent films, the thickness of the partition board is 0.75mm, the films are ionic liquid impregnated organic films, the thickness of each film is about 1mm, and the electrode plates are made of titanium coated ruthenium iridium.

Example 1

1. Taking salt lake brine, and drying in the sun by a salt pan process to remove a large amount of sodium chloride, potassium chloride and the like.

2. Then drying in the sun to remove a large amount of sodium chloride, sodium sulfate, potassium chloride, magnesium chloride and the like.

3. Adjusting the pH value, removing sulfur, passing through resin, and removing boron, calcium, magnesium and other ions to obtain a solution A, wherein the main ions in the solution A are lithium, sodium, chlorine and the like;

4. the membrane coated by the aminobenzene grafted polyether-ether-ketone compound is used as a first positive membrane and a second positive membrane to form the bipolar membrane electrodialysis device.

5. Adding 1mol/L NaOH solution into the cathode chamber and the anode chamber as polar liquid, adding 0.1mol/L LiOH solution into the first alkali chamber 313 as initial alkali solution 1, adding 0.1mol/L NaOH solution into the second alkali chamber 314 as initial alkali solution 2, adding 0.05 mol/L hydrochloric acid solution into the acid chamber 312 as initial acid solution, adding solution A diluted by about one time into the salt chamber 311 as salt solution, controlling the flow rate of the acid-base salt polar liquid at 10L/min, and controlling the flow rate at 600A/m²The bipolar membrane electrodialysis is carried out under the current density of (2) to (20.5V), the concentration of acid and alkali liquor is gradually increased along with the bipolar membrane electrodialysis, and when the concentration of acid and alkali in the alkali liquor reaches 10 percent, the alkali liquor is taken out (one of the alkali liquor exceeds the proper water supplement), so as to obtain the lithium hydroxide and sodium hydroxide solution.

The ion concentrations in the initial salt solution, the first base compartment 313, the second base compartment 314, the acid compartment 312 and the salt compartment 311 after electrodialysis were measured and the results are shown in table 1.

TABLE 1 (unit: g/L)

Group of	Li+	Na+	Cl-	OH-
					Initial salt solution	28.82	31.45	194.72	——
First alkali chamber	19.76	5.50	0.15	52.07
					Second alkali chamber	4.12	49.54	0.28	46.62
Acid chamber	0.14	0.16	84.31	——
					Salt chamber	3.29	11.79	34.91	——

Example 2

1. Salt lake brine is taken and is subjected to adsorption and desorption process of lithium extraction resin

2. Concentrating, and removing calcium and magnesium ions by using a purification resin to obtain a solution A, wherein the main ions in the solution A are lithium, sodium, chlorine and the like;

3. the membrane coated by the aminobenzene grafted polyether-ether-ketone compound is used as a first positive membrane and a second positive membrane to form the bipolar membrane electrodialysis device.

4. Adding 1mol/L NaOH solution into the cathode chamber and the anode chamber as polar liquid, adding 0.1mol/L LiOH solution into the first alkali chamber 313 as initial alkali solution 1, adding 0.1mol/L NaOH solution into the second alkali chamber 314 as initial alkali solution 2, adding 0.05 mol/L hydrochloric acid solution into the acid chamber 312 as initial acid solution, adding solution A diluted by about one time into the salt chamber 311 as salt solution, controlling the flow rate of the acid-base salt polar liquid at 10L/min, and controlling the flow rate at 800A/m²The concentration of acid and alkali liquor is gradually increased along with the bipolar membrane electrodialysis, and when the concentration of acid and alkali in the alkali liquor reaches 10 percent, the alkali liquor is taken out (one of the alkali liquor exceeds the concentration of the acid and alkali and can be supplemented with water properly), so that lithium hydroxide and sodium hydroxide solution are obtained.

The ion concentrations in the initial salt solution, the first base compartment 313, the second base compartment 314, the acid compartment 312 and the salt compartment 311 after electrodialysis were measured and the results are shown in table 2.

TABLE 2 (unit: g/L)

Example 3

1. Taking salt lake brine, and drying in the sun by a salt pan process to remove a large amount of sodium chloride, potassium chloride, magnesium sulfate and the like;

2. further separating divalent ions by a nanofiltration membrane, removing calcium, magnesium, boron and the like by resin, and increasing the concentration of the solution to about 20 by Electrodialysis (ED) to obtain a solution A, wherein the main ions in the solution A are lithium, sodium, chlorine and the like;

3. the membrane coated by the aminobenzene grafted polyether-ether-ketone compound is used as a first positive membrane and a second positive membrane to form the bipolar membrane electrodialysis device.

4. Adding 1mol/L NaOH solution into the cathode chamber and the anode chamber as polar liquid, adding 0.1mol/L LiOH solution into the first alkali chamber 313 as initial alkali solution 1, adding 0.1mol/L NaOH solution into the second alkali chamber 314 as initial alkali solution 2, adding 0.05 mol/L hydrochloric acid solution into the acid chamber 312 as initial acid solution, adding solution A into the salt chamber 311 as salt solution, controlling the flow of the acid-base polar liquid at 10L/min, and controlling the flow at 400A/m²The concentration of acid and alkali liquor is gradually increased along with the bipolar membrane electrodialysis, and when the concentration of acid and alkali in the alkali liquor reaches 10 percent, the alkali liquor is taken out (one of the alkali liquor exceeds the concentration of the acid and alkali and can be supplemented with water properly), so that lithium hydroxide and sodium hydroxide solution are obtained.

The ion concentrations in the initial salt solution, the first base compartment 313, the second base compartment 314, the acid compartment 312 and the salt compartment 311 after electrodialysis were measured and the results are shown in table 3.

TABLE 3 (unit: g/L)

Group of	Li+	Na+	Cl-	OH-
					Initial salt solution	28.00	33.42	193.58	——
First alkali chamber	24.71	8.26	0.14	66.10
					Second alkali chamber	4.12	46.39	0.32	44.29
Acid chamber	0.23	0.21	79.63	——
					Salt chamber	4.61	9.83	38.56	——

Example 4

1. Taking salt lake brine, and drying in the sun by a salt pan process to remove a large amount of sodium chloride, potassium chloride, magnesium sulfate and the like;

2. further separating divalent ions by a nanofiltration membrane, removing calcium, magnesium, boron and the like by resin, and increasing the concentration of the solution to about 20 by Electrodialysis (ED) to obtain a solution A, wherein the main ions in the solution A are lithium, sodium, chlorine and the like;

3. the membranes coated with the mononitrobenzene grafted polyether brav compound are the first positive membrane and the second positive membrane to form the bipolar membrane electrodialysis device.

4. Adding 1mol/L NaOH solution into the cathode chamber and the anode chamber as polar liquid, adding 0.1mol/L LiOH solution into the first alkali chamber 313 as initial alkali solution 1, adding 0.1mol/L NaOH solution into the second alkali chamber 314 as initial alkali solution 2, adding 0.05 mol/L hydrochloric acid solution into the acid chamber 312 as initial acid solution, adding solution A into the salt chamber 311 as salt solution, controlling the flow of the acid-base polar liquid at 10L/min, and controlling the flow at 600A/m²The concentration of acid and alkali liquor is gradually increased along with the bipolar membrane electrodialysis, and when the concentration of acid and alkali in the alkali liquor reaches 10 percent, the alkali liquor is taken out (one of the alkali liquor exceeds the concentration of the acid and alkali and can be supplemented with water properly), so that lithium hydroxide and sodium hydroxide solution are obtained.

The ion concentrations in the initial salt solution, the first base compartment 313, the second base compartment 314, the acid compartment 312 and the salt compartment 311 after electrodialysis were measured and the results are shown in table 4.

TABLE 4 (unit: g/L)

Group of	Li+	Na+	Cl-	OH-
					Initial salt solution	23.88	20.44	152.67	——
First alkali chamber	19.76	5.11	0.10	51.78
					Second alkali chamber	3.29	41.28	0.19	38.51
Acid chamber	0.12	0.18	63.52	——
					Salt chamber	3.79	9.44	33.78	——

Comparative example 1

Using the procedure of example 4, only a commercially available common cation membrane (i.e., a membrane without a lithium-sodium separation function) was used as the first cation membrane, and the second cation membrane was omitted, and the ion concentrations of the resulting solutions were as shown in Table 5.

TABLE 5 (unit: g/L)

Group of	Li+	Na+	Cl-	OH-
					Initial salt solution	23.88	20.44	152.67	——
Alkali chamber	18.12	23.59	0.23	61.44
					Acid chamber	0.17	0.21	82.14	——
Salt chamber	4.12	9.04	34.84	——

Comparative example 2

Using the procedure of example 4, only a commercially available common cation membrane (i.e., a membrane without a lithium-sodium separation function) was used as the first cation membrane and the second cation membrane, and the ion concentrations of the respective solutions obtained were as shown in Table 6.

TABLE 6

Therefore, the bipolar membrane electrodialysis device with two special cation exchange membranes can simultaneously obtain lithium hydroxide and sodium hydroxide solution, so that lithium can pass through the membranes to a greater extent, the lithium storage amount in the salt solution is reduced, and the lithium-sodium separation rate is improved. The method for treating the salt lake brine can reduce the recrystallization times of the lithium hydroxide and shorten the process flow, and the sodium hydroxide can also be returned to the previous working section of the salt lake for recycling.