A method for extracting lithium from salt lake brine based on a selective adsorbent

Abstract

The present invention relates to a method for extracting lithium from salt lake brine based on a selective adsorbent, belonging to the technical field of lithium extraction from salt lakes. In the present invention, montmorillonite is modified with alkylammonium bromide to increase the interlayer spacing of montmorillonite and improve its specific surface area. Then, polyethylene glycol diglycidyl ether is used to modify the montmorillonite again, and polyethylene glycol diglycidyl ether can be inserted into the montmorillonite layer by using the oxygen atoms in its molecular chain through hydrogen bonding and molecular chain entanglement. Finally, an epoxy curing agent containing crown ether is reacted with the modified montmorillonite to bond the crown ether groups to the inside and outside of the montmorillonite layer through chemical bonds, improving the uniformity of the distribution of the crown ether groups, and further increasing the adsorption amount and adsorption selectivity of the adsorbent for lithium ions.

Description

Technical Field

[0001] The present invention relates to a method for extracting lithium from salt lake brine based on a selective adsorbent, and belongs to the technical field of lithium extraction from salt lakes. Background Art

[0002] Lithium is widely used in modern industrial production, and the large market demand makes the development of lithium resources particularly important. Lithium resources in nature mainly exist in two forms. One exists in solid ores (such as spodumene, petalite, lepidolite, etc.), and the other exists in liquid ores (such as salt lake brine and underground brine). Among them, the salt lake brine in liquid ores contains a large amount of lithium resources. However, most of the lithium resources in salt lake brine are brines with a high magnesium-lithium ratio, and the content of lithium elements is relatively low. Therefore, how to efficiently extract lithium from salt lake brine has always been a research hotspot.

[0003] At present, the technologies for extracting lithium from salt lake brine mainly include precipitation method, solvent extraction method, evaporation crystallization method, adsorption method, etc. Among them, the adsorption method is considered to be a more promising method for lithium extraction. The adsorption method refers to the physical and chemical reactions between the solute and the adsorbent, forming strong chemical bonds, hydrogen bonds, surface coordination, imprinting, sieving, and electrostatic interactions. The adsorption method is suitable for recovering lithium from low-grade lithium-containing salt lake brines. Currently, common inorganic lithium adsorbents include manganese-based ion sieves and aluminum salt adsorbents. For example, Chinese patent document CN112777614B uses a dilute acid solution to pre-desorb the manganese-based ion sieve adsorbent, and utilizes the characteristic of different sodium-lithium desorption sequences to desorb most of the sodium and a small part of the lithium first, and then uses a dilute acid solution to desorb the adsorbent to achieve the purpose of reducing the sodium-lithium ratio in the qualified liquid. However, the minimum sodium-lithium ratio in the desorbed liquid obtained is 0.5, and the adsorption selectivity between lithium and sodium is poor. In addition, the manganese-based lithium adsorbent requires an alkaline environment for adsorption and an acidic environment for desorption, which consumes a large amount of acid and alkali solutions, and the dissolution loss is very serious. The aluminum salt adsorbent has good selectivity, but the adsorption capacity of lithium ions is low, only 0.6 - 0.9 mg / g. Therefore, it is urgent to develop a method for extracting lithium from salt lake brine that simultaneously has high adsorption capacity, high selectivity, and good use stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for extracting lithium from salt lake brine based on a selective adsorbent to solve the problems of low adsorption capacity, poor selectivity, and poor use stability when extracting lithium ions from salt lakes by the adsorption method at present.

[0005] The present invention provides a method for extracting lithium from salt lake brine based on a selective adsorbent, including the following steps:

[0006] (1) Mix alkylammonium bromide and montmorillonite in water at 60 - 80 °C for 2 - 6 h, separate the solid from the liquid, and wash the separated solid with water until there are no bromide ions in the washing liquid to obtain organophilic montmorillonite; the alkylammonium bromide is dodecyltrimethylammonium bromide, tridecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, pentadecyltrimethylammonium bromide, or hexadecyltrimethylammonium bromide; the mass ratio of alkylammonium bromide to montmorillonite is 25 - 30:100;

[0007] (2) Mix polyethylene glycol diglycidyl ether and the organophilic montmorillonite dispersion under reflux at 60 - 75 °C for 2 - 6 h, then remove the solvent, dry, and grind to obtain intercalated montmorillonite; the mass of polyethylene glycol diglycidyl ether is 5 - 10% of the mass of the organophilic montmorillonite; the number-average molecular weight of the polyethylene glycol diglycidyl ether is 600 - 1000;

[0008] (3) Heat the intercalated montmorillonite and an epoxy curing agent in a solvent under the action of a catalyst to 95 - 105 °C, mix and react for 6 - 8 h, then remove the solvent and grind to obtain a lithium ion adsorbent; the epoxy curing agent is a benzo-12-crown-4 dicarboxylic acid compound or composed of a benzo-12-crown-4 dicarboxylic acid compound and a cycloboroxane tricarboxylic acid compound with a mass ratio of 5:0.1 - 0.4; the structural formula of the benzo-12-crown-4 dicarboxylic acid compound is as follows:

[0009] ;

[0010] The structural formula of the cycloboroxane tricarboxylic acid compound is as follows:

[0011] ;

[0012] (4) Use the lithium ion adsorbent to adsorb lithium ions in the salt lake brine, then perform acid washing to desorb the lithium ions from the lithium ion adsorbent and enter the acid solution, and finally recover and extract the lithium ions in the acid solution.

[0013] Preferably, the montmorillonite in step (1) is used in the form of a montmorillonite dispersion, and the mass fraction of the montmorillonite dispersion is 5 - 10%.

[0014] Preferably, the average particle size of the montmorillonite in step (1) is 15 - 30 μm.

[0015] Preferably, the mixing method in step (1) is as follows: Add the alkylammonium bromide to the montmorillonite dispersion, and then perform the mixing.

[0016] Preferably, the mixing and refluxing method in step (2) is as follows: dissolve polyethylene glycol diglycidyl ether in acetone to obtain a polyethylene glycol diglycidyl ether solution with a mass fraction of 40 - 50%; then conduct the said mixing and refluxing on the polyethylene glycol diglycidyl ether solution and an organophilic montmorillonite dispersion with a mass fraction of 5 - 10%.

[0017] Preferably, the average particle size of the intercalated montmorillonite is 20 - 40 μm.

[0018] Preferably, in step (3), under nitrogen protection, disperse the intercalated montmorillonite into N,N - dimethylformamide to obtain an intercalated montmorillonite dispersion with a mass fraction of 10 - 15%, then add an epoxy curing agent, and then conduct the said heating.

[0019] Preferably, in step (3), the average particle size of the lithium ion adsorbent is 20 - 30 μm.

[0020] Preferably, in step (3), the boroxolane tricarboxylic acid compound is prepared by reacting 4,4′,4″-(boroxolane - 2,4,6)-tribenzoyl chloride with mercaptoacetic acid; the molar ratio of 4,4′,4″-(boroxolane - 2,4,6)-tribenzoyl chloride to mercaptoacetic acid is 1:3.1 - 3.5.

[0021] Preferably, in step (3), the preparation method of the boroxolane tricarboxylic acid compound is as follows: mix 4 - carboxyphenylboronic acid and thionyl chloride with a molar ratio of 1:20 for 50 min, then heat up to 80 °C and conduct a mixed reaction for 20 h, remove the excess thionyl chloride, and obtain 4,4′,4″-(boroxolane - 2,4,6)-tribenzoyl chloride after drying; then fully dissolve 4,4′,4″-(boroxolane - 2,4,6)-tribenzoyl chloride in dichloromethane to obtain a solution with a mass fraction of 5 - 10%, then at 0 - 5 °C, dropwise add a dichloromethane solution of mercaptoacetic acid with a mass fraction of 5 - 10% to the 4,4′,4″-(boroxolane - 2,4,6)-tribenzoyl chloride solution, then add triethylamine, stir and react at 0 - 5 °C for 5 - 8 h, filter, rotary evaporate the filtrate, wash with water to remove the unreacted mercaptoacetic acid, and obtain the boroxolane tricarboxylic acid compound after drying.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) By using alkylammonium bromide to modify montmorillonite, the present invention can increase the interlayer spacing of montmorillonite and improve its specific surface area. Then, polyethylene glycol diglycidyl ether is used to modify montmorillonite again, and polyethylene glycol diglycidyl ether can be inserted into the montmorillonite layers through hydrogen bonding and molecular chain entanglement using the oxygen atoms in its molecular chain. Finally, an epoxy curing agent containing crown ether is reacted with the modified montmorillonite, so that the crown ether groups are bonded to the inside and outside of the montmorillonite layers through chemical bonds, improving the distribution uniformity of the crown ether groups, and further increasing the adsorption amount and adsorption selectivity of the adsorbent for lithium ions.

[0024] (2) By using carboxy-crown ether and boroxolane tricarboxylic acid compound as a compound curing agent, the present invention can significantly increase the adsorption capacity and desorption rate of the adsorbent for lithium ions. This may be because on the one hand, the boroxolane tricarboxylic acid compound can increase the crosslinking degree of the epoxy resin, and on the other hand, it can introduce a large number of boroxolane structures to increase the adsorption sites for lithium ions. And due to the cyclic structure of boroxolane, it can cooperate with the cyclic crown ether to jointly adsorb lithium ions and increase the adsorption capacity of lithium ions. In addition, boroxolane has hydrophobicity, and it can form a good amphoteric structure with the polyhydroxyl groups formed after the epoxy resin is ring-opened, improving the surface activity, and further increasing the migration rate of lithium ions and reducing its movement barrier, thereby further increasing the adsorption capacity and desorption rate of lithium ions.

[0025] (3) The present invention uses an adsorbent with good adsorption capacity, reusability and good adsorption selectivity for lithium ions to adsorb lithium ions in salt lake brine, and through acid desorption, the lithium ions enter the acid solution, realizing the extraction and utilization of lithium ions in salt lake brine, and having good application prospects. Description of the Drawings

[0026] Figure 1 is the 1H NMR spectrum of the benzo-12-crown-4 dicarboxylic acid compound in the present invention;

[0027] Figure 2 is the 1H NMR spectrum of the boroxolane tricarboxylic acid compound in Example 3 of the present invention. Detailed Embodiments

[0028] The following examples are intended to further illustrate the content of the present invention rather than limit the protection scope of the present invention.

[0029] The preparation method of the benzo-12-crown-4 dicarboxylic acid compound used in the present invention is as follows:

[0030] (1) Dissolve 0.01 mol of benzo-12-crown-4 in 25 mL of chloroform, cool it to -5 °C under nitrogen protection, then dropwise add 0.1 mol of chlorosulfonic acid. After the addition is complete, continue stirring at room temperature for 6 h. Pour the reaction mixture into ice water, let it stand for layering, concentrate the organic phase by rotary evaporation, and crystallize it with n-heptane to obtain benzo-12-crown-4 sulfonyl chloride.

[0031] (2) Stir 5-hydroxymethyl-1,3-benzoic acid (as shown in Formula 1) and dichloromethane evenly to obtain a solution with a mass fraction of 5%. Then, at 0 °C, dropwise add a chloroform solution of benzo-12-crown-4 sulfonyl chloride with a mass fraction of 5%. After the addition is complete, add triethylamine (the molar ratio of 5-hydroxymethyl-1,3-benzoic acid, benzo-12-crown-4 sulfonyl chloride, and triethylamine is 1:1:1.2). Then, stir and react at 5 °C for 10 h, filter, rotary evaporate the filtrate, and after drying, obtain a benzo-12-crown-4 dicarboxylic acid compound (as shown in Formula 2), and its 1H NMR spectrum is as Figure 1 shown.

[0032]

[0033] Formula 1

[0034]

[0035] Formula 2 Example 1

[0036] The method for extracting lithium from salt lake brine based on a selective adsorbent in this example includes the following steps:

[0037] (1) Disperse montmorillonite with an average particle size of 15 μm in deionized water to obtain a montmorillonite dispersion with a mass fraction of 10%.

[0038] (2) Add tetradecyltrimethylammonium bromide to the montmorillonite dispersion. The mass ratio of tetradecyltrimethylammonium bromide to montmorillonite is 30:100. Then, stir at 60 °C for 6 h, filter, and wash the filter cake with water until there are no bromide ions in the washing liquid to obtain organic montmorillonite.

[0039] (3) Disperse the organic montmorillonite in deionized water to obtain an organic montmorillonite dispersion with a mass fraction of 5%; dissolve polyethylene glycol diglycidyl ether (number average molecular weight of 800) in acetone to obtain a polyethylene glycol diglycidyl ether solution with a mass fraction of 40%; stir and reflux the polyethylene glycol diglycidyl ether solution and the organic montmorillonite dispersion at 60 °C for 6 h, then rotary evaporate to remove the solvent, dry, and grind to obtain intercalated montmorillonite with an average particle size of 20 μm; the mass of polyethylene glycol diglycidyl ether in the polyethylene glycol diglycidyl ether solution is 5% of the mass of the organic montmorillonite in the organic montmorillonite dispersion.

[0040] (4) Under nitrogen protection, the intercalated montmorillonite was dispersed in N,N-dimethylformamide to obtain an intercalated montmorillonite dispersion with a mass fraction of 10%. Then, an epoxy curing agent (the epoxy curing agent is a benzo-12-crown-4 dicarboxylic acid compound, and the molar amount of carboxyl groups in the epoxy curing agent is equal to the molar amount of epoxy groups in the intercalated montmorillonite) and a catalyst (the catalyst is triethylbenzylammonium bromide, and the mass of the catalyst is 1% of the mass of the epoxy curing agent) were added. The mixture was heated to 95 °C and stirred for 8 h. After the reaction ended, it was cooled to room temperature, vacuum dried at 80 °C to remove the solvent, and then ground to obtain a lithium ion adsorbent with an average particle size of 30 μm.

[0041] (5) The lithium ion adsorbent was used to adsorb lithium ions in the salt lake brine, and then the lithium ion adsorbent adsorbed with lithium ions was pickled to desorb the lithium ions from the lithium ion adsorbent and enter the acid solution, and then the lithium ions in the acid solution were recovered and extracted. Example 2

[0042] The difference between the method for extracting lithium from salt lake brine based on a selective adsorbent in this example and the method for extracting lithium from salt lake brine based on a selective adsorbent in Example 1 is only that the epoxy curing agent in step (4) of the method for extracting lithium from salt lake brine based on a selective adsorbent in this example is composed of a benzo-12-crown-4 dicarboxylic acid compound and 4-carboxyphenylboric acid with a mass ratio of 5:0.3. Example 3

[0043] The difference between the method for extracting lithium from salt lake brine based on a selective adsorbent in this example and the method for extracting lithium from salt lake brine based on a selective adsorbent in Example 1 is only that the epoxy curing agent in step (4) of the method for extracting lithium from salt lake brine based on a selective adsorbent in this example is composed of a benzo-12-crown-4 dicarboxylic acid compound and a boroxolane tricarboxylic acid compound with a mass ratio of 5:0.2. The preparation method of the boroxolane tricarboxylic acid compound is as follows: Add 4-carboxyphenylboronic acid and thionyl chloride with a molar ratio of 1:20 to a reaction kettle, then introduce nitrogen into the reaction kettle, stir at room temperature for 50 min, then heat up to 80 °C and stir and react for 20 h. Remove the excess thionyl chloride by distillation under reduced pressure, and obtain a white powdery solid after vacuum drying, which is 4,4′,4″-(boroxolane-2,4,6)-tribenzoyl chloride; then dissolve 4,4′,4″-(boroxolane-2,4,6)-tribenzoyl chloride fully in dichloromethane to obtain a solution with a mass fraction of 5%. Then, at 0 °C, dropwise add a dichloromethane solution of mercaptoacetic acid with a mass fraction of 5% to the 4,4′,4″-(boroxolane-2,4,6)-tribenzoyl chloride solution. The molar ratio of mercaptoacetic acid to 4,4′,4″-(boroxolane-2,4,6)-tribenzoyl chloride is 3.5:1. Then add triethylamine (the molar amount of triethylamine is equal to the molar amount of mercaptoacetic acid), stir and react at 0 °C for 8 h, filter, rotary evaporate the filtrate, wash with water to remove the unreacted mercaptoacetic acid, and obtain the boroxolane tricarboxylic acid compound after drying (the nuclear magnetic hydrogen spectrum of the boroxolane tricarboxylic acid compound is as shown in Figure 2 shown), and the structural formula is as follows:

[0044] . Example 4

[0045] The difference between the method for extracting lithium from salt lake brine based on a selective adsorbent in this example and the method for extracting lithium from salt lake brine based on a selective adsorbent in Example 3 is only that the epoxy curing agent in step (4) of the method for extracting lithium from salt lake brine based on a selective adsorbent in this example is composed of a benzo-12-crown-4 dicarboxylic acid compound and a boroxolane tricarboxylic acid compound with a mass ratio of 5:0.1. Example 5

[0046] The difference between the method for extracting lithium from salt lake brine based on a selective adsorbent in this example and the method for extracting lithium from salt lake brine based on a selective adsorbent in Example 3 is only that the epoxy curing agent in step (4) of the method for extracting lithium from salt lake brine based on a selective adsorbent in this example is composed of a benzo-12-crown-4 dicarboxylic acid compound and a boroxolane tricarboxylic acid compound with a mass ratio of 5:0.4. Example 6

[0047] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the tetradecyltrimethylammonium bromide in step (2) of the lithium extraction method from salt lake brine based on a selective adsorbent in this example is replaced by cetyltrimethylammonium bromide. Example 7

[0048] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the tetradecyltrimethylammonium bromide in step (2) of the lithium extraction method from salt lake brine based on a selective adsorbent in this example is replaced by dodecyltrimethylammonium bromide. Example 8

[0049] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the number-average molecular weight of polyethylene glycol diglycidyl ether in step (3) of the lithium extraction method from salt lake brine based on a selective adsorbent in this example is 600. Example 9

[0050] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the number-average molecular weight of polyethylene glycol diglycidyl ether in step (3) of the lithium extraction method from salt lake brine based on a selective adsorbent in this example is 1000.

[0051] Comparative Example 1

[0052] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that steps (1) to (2) are omitted in the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example, and instead, montmorillonite with an average particle size of 15 μm is directly dispersed in deionized water to obtain a 10% (by mass) montmorillonite dispersion; then, the polyethylene glycol diglycidyl ether solution and the montmorillonite dispersion are stirred and refluxed.

[0053] Comparative Example 2

[0054] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that step (3) is omitted in the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example, and at the same time, the intercalated montmorillonite in step (4) is replaced by the organophilic montmorillonite obtained in step (2).

[0055] Comparative Example 3

[0056] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the number-average molecular weight of polyethylene glycol diglycidyl ether in step (3) of the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example is 200.

[0057] Comparative Example 4

[0058] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the number-average molecular weight of polyethylene glycol diglycidyl ether in step (3) of the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example is 2000.

[0059] Comparative Example 5

[0060] The difference between the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example and the lithium extraction method from salt lake brine based on a selective adsorbent in Example 3 is only that the epoxy curing agent in step (4) of the lithium extraction method from salt lake brine based on a selective adsorbent in this comparative example is a boroxine tricarboxylic acid compound.

[0061] Effect Example 1

[0062] To evaluate the adsorption effect of the lithium-ion adsorbents in the examples and comparative examples, 0.1 g of the lithium-ion adsorbent was weighed and placed in a 250 mL flask. Then, 100 mL of a lithium salt solution (the lithium salt solution was a lithium chloride solution with a lithium ion concentration of 100 mg / L) was added. Subsequently, it was placed in a constant temperature water bath shaker at a temperature of 30 °C and a rotation speed of 120 r / min. The supernatant was continuously taken to measure the lithium ion concentration therein until the adsorption reached equilibrium. According to the change in the lithium ion concentration in the solution before and after adsorption, the saturated adsorption capacity X1 of the lithium-ion adsorbent for lithium ions was calculated. In addition, the lithium-ion adsorbent saturated with lithium ions was placed in a 250 mL flask, and then 150 mL of hydrochloric acid with a concentration of 0.3 mol / L was added. The flask was sealed with plastic wrap and then placed in a constant temperature water bath shaker at a temperature of 25 °C and a rotation speed of 120 r / min for oscillating desorption. After 8 h, the desorption ended. The supernatant was taken to measure the lithium ion concentration therein. According to the change in the lithium ion concentration in the hydrochloric acid before and after desorption, the desorption rate of lithium ions was calculated. The desorption rate was equal to the ratio of the mass of lithium ions desorbed into the hydrochloric acid from the lithium-ion adsorbent saturated with lithium ions to the mass of lithium ions in the lithium-ion adsorbent saturated with lithium ions. Finally, the lithium-ion adsorbent was cycled repeatedly for saturated lithium adsorption and desorption of lithium ions according to the above method, and the saturated adsorption capacity X10 of the adsorbent for lithium ions after the 10th desorption of lithium ions was recorded. The saturated adsorption capacity X1 of the lithium-ion adsorbents for lithium ions, the lithium ion desorption rate, and the saturated adsorption capacity X10 of the adsorbent for lithium ions after the 10th desorption of lithium ions in each example and comparative example are shown in Table 1.

[0063] Table 1 Saturated adsorption capacity of lithium-ion adsorbents for lithium ions in each example and comparative example,

[0064] Lithium ion desorption rate and saturated adsorption capacity of the adsorbent for lithium ions after the 10th desorption of lithium ions

[0065] Lithium ion adsorbent Saturated adsorption capacity X1 (mg / g) Desorption rate (%) Saturated adsorption capacity X10 (mg / g) Example 1 16 92.1 12 Example 2 18 91.8 15 Example 3 35 99.2 34 Example 4 28 98.5 26 Example 5 27 98.7 26 Example 6 25 97.2 20 Example 7 24 97.6 18 Example 8 32 98.9 31 Example 9 36 99.4 35 Comparative Example 1 5 85.2 3 Comparative Example 2 3 86.7 2 Comparative Example 3 13 84.3 8 Comparative Example 4 11 85.8 7 Comparative Example 5 0.5 81.2 0.4

[0066] As can be seen from Table 1, when the adsorbent material prepared by using only the benzo-12-crown-4 dicarboxylic acid compound as the epoxy curing agent in Example 1 has a relatively high adsorption capacity and desorption rate for lithium ions. When the benzo-12-crown-4 dicarboxylic acid compound and 4-carboxyphenylboronic acid are used together as the epoxy curing agent in Example 2, the adsorption capacity of the prepared adsorbent material for lithium ions is increased, which may be due to the introduction of boron element increasing the adsorption sites of lithium ions. When the cyclohexaboroxane tricarboxylic acid compound curing agent is introduced in Examples 3-5, the adsorption capacity and desorption rate of the prepared adsorbent material for lithium ions are significantly increased. This may be because the cyclohexaboroxane tricarboxylic acid compound can, on the one hand, increase the crosslinking degree of the epoxy resin, and on the other hand, introduce a large number of cyclohexaboroxane structures, increasing the adsorption sites of lithium ions. And due to the cyclic structure of cyclohexaboroxane, it can cooperate with the cyclic crown ether to jointly adsorb lithium ions, increasing the adsorption capacity of lithium ions. In addition, cyclohexaboroxane has hydrophobicity, and it can form a good amphoteric structure with the polyhydroxyl groups formed after the epoxy resin is ring-opened, increasing the surface activity, and then increasing the migration rate of lithium ions and reducing its movement barrier, thereby further increasing the adsorption capacity and desorption rate of lithium ions. In addition, according to Examples 3-5, as the amount of the cyclohexaboroxane tricarboxylic acid compound increases, the adsorption capacity and desorption rate of the prepared adsorbent material for lithium ions show a trend of first increasing and then decreasing. This may be because when the amount of the cyclohexaboroxane tricarboxylic acid compound is small, it is not sufficient to play its role. When the amount of the cyclohexaboroxane tricarboxylic acid compound is too large, the crosslinked structure is too dense, which is not conducive to the unfolding of the active structure during the montmorillonite adsorption process and affects the adsorption and desorption process. As can be seen from Comparative Examples 1-2, modifying montmorillonite with ammonium bromide can increase the adsorption capacity and desorption rate of the adsorbent material for lithium ions, because ammonium bromide can open the montmorillonite structure and increase its specific surface area; and modifying montmorillonite with polyethylene glycol diglycidyl ether can also increase the adsorption capacity and desorption rate of the adsorbent material for lithium ions, because polyethylene glycol diglycidyl ether can be inserted into montmorillonite to provide chemical bonding stable sites for the subsequent crown ether and cyclohexaboroxane, thereby increasing the adsorption capacity and desorption rate of lithium ions. According to Comparative Examples 3-4, the molecular weight of polyethylene glycol diglycidyl ether affects the adsorption capacity and desorption rate of lithium ions, which may be because too large or too small molecular weight of polyethylene glycol diglycidyl ether is not conducive to its insertion into montmorillonite and the subsequent introduction of crown ethers and cyclohexaboroxane structures with suitable chain lengths. In addition, according to Example 3 and Examples 6-7, the carbon chain length of ammonium bromide affects the adsorption capacity and desorption rate of lithium ions, which may be because the carbon chain length affects the modification of montmorillonite and the subsequent introduction of crown ethers and cyclohexaboroxane structures with suitable chain lengths.

[0067] Effect Example 2

[0068] To evaluate the adsorption selectivity of the lithium-ion adsorbents in the examples and comparative examples for lithium ions, 0.1 g of the lithium-ion adsorbent was weighed and placed in a 250 mL flask. Then, 100 mL of simulated salt lake brine (the simulated salt lake brine was prepared by mixing sodium chloride, magnesium chloride, potassium chloride, lithium chloride, calcium chloride and water, with the concentration of sodium element being 1200 mg / L, the concentration of magnesium element being 2000 mg / L, the concentration of potassium element being 600 mg / L, the concentration of lithium element being 50 mg / L, and the concentration of calcium element being 80 mg / L) was added. Then, it was placed in a constant temperature water bath shaker at a temperature of 30 °C and a rotation speed of 120 r / min. After 24 h, the concentrations of various metal ions were measured, and based on the changes in the concentrations of metal ions in the solution before and after adsorption, the adsorption amounts of the lithium-ion adsorbent for various metal ions were calculated. The adsorption amounts of the lithium-ion adsorbents in each example and comparative example for various metal ions are shown in Table 2.

[0069] Table 2 Adsorption amounts of lithium-ion adsorbents in each example and comparative example for various metal ions

[0070]

[0071] As can be seen from Table 2, the adsorbents used in the examples of the present invention all have good selective adsorption properties for lithium ions, which are significantly better than the selective adsorption properties of the adsorbents in the comparative examples, and can be used for the extraction of lithium ions from salt lake brine.

Claims

1. A method for extracting lithium from salt lake brine based on a selective adsorbent, characterized in that: The following steps are involved: (1) mixing alkylammonium bromide and montmorillonite in water at 60-80° C. for 2-6 hours, separating the solid from the liquid, and washing the separated solid with water until no bromide ions are present in the washing liquid, thereby obtaining an organic montmorillonite; the alkylammonium bromide is dodecyltrimethylammonium bromide, tridecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, pentadecyltrimethylammonium bromide or hexadecyltrimethylammonium bromide; and the mass ratio of the alkylammonium bromide to the montmorillonite is 25-30:100; (2) Mixing polyethylene glycol diglycidyl ether and an organic montmorillonite dispersion at 60-75° C. and refluxing for 2-6 hours, then removing the solvent, drying, and grinding to obtain intercalated montmorillonite; the mass of the polyethylene glycol diglycidyl ether is 5-10% of the mass of the organic montmorillonite; and the number average molecular weight of the polyethylene glycol diglycidyl ether is 600-1000; (3) heating the intercalated montmorillonite and the epoxy curing agent to 95-105° C. in a solvent under the action of a catalyst, mixing and reacting for 6-8 hours, then removing the solvent and grinding to obtain a lithium ion adsorbent; the epoxy curing agent is a benzo-12-crown-4 dicarboxylic acid compound or is composed of a benzo-12-crown-4 dicarboxylic acid compound and a boroxine tricarboxylic acid compound in a mass ratio of 5:0.1-0.4; the structural formula of the benzo-12-crown-4 dicarboxylic acid compound is as follows: ； The structural formula of the boroxine tricarboxylic acid compound is as follows: ； (4) A lithium ion adsorbent is used to adsorb lithium ions in salt lake brine, and then acid washing is performed to desorb lithium ions from the lithium ion adsorbent into acid solution, and finally the lithium ions in the acid solution are recovered and extracted.

2. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: The montmorillonite in step (1) is used in the form of a montmorillonite dispersion, and the mass fraction of the montmorillonite dispersion is 5-10%.

3. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: The average particle size of the montmorillonite in step (1) is 15-30 μm.

4. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 2, characterized in that: The mixing method in step (1) is as follows: adding alkylammonium bromide to the montmorillonite dispersion and then performing the mixing.

5. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: The mixing and refluxing method in step (2) is as follows: dissolving polyethylene glycol diglycidyl ether in acetone to obtain a polyethylene glycol diglycidyl ether solution with a mass fraction of 40-50%; then mixing and refluxing the polyethylene glycol diglycidyl ether solution and an organic montmorillonite dispersion with a mass fraction of 5-10%.

6. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: The average particle size of intercalated montmorillonite is 20~40μm.

7. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: In step (3), under nitrogen protection, the intercalated montmorillonite is dispersed in N,N-dimethylformamide to obtain an intercalated montmorillonite dispersion with a mass fraction of 10-15%, and then an epoxy curing agent is added, and then the heating is performed.

8. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: In step (3), the average particle size of the lithium ion adsorbent is 20-30 μm.

9. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 1, characterized in that: In step (3), the boroxine tricarboxylic acid compound is prepared by reacting 4,4′,4″-(boroxine-2,4,6)-tribenzoyl chloride and thioglycolic acid; the molar ratio of 4,4′,4″-(boroxine-2,4,6)-tribenzoyl chloride to thioglycolic acid is 1:3.1-3.

5.

10. The method for extracting lithium from salt lake brine based on a selective adsorbent as claimed in claim 9, characterized in that: In step (3), the preparation method of the boroxine tricarboxylic acid compound is as follows: 4-carboxyphenylboronic acid and thionyl chloride in a molar ratio of 1:20 are mixed for 50 minutes, then the temperature is raised to 80° C., mixed and reacted for 20 hours, excess thionyl chloride is removed, and 4,4′,4″-(boroxine-2,4,6)-tribenzoyl chloride is obtained after drying; then 4,4′,4″-(boroxine-2,4,6)-tribenzoyl chloride is fully dissolved in dichloride. The reaction mixture is prepared by adding 5-10% thioglycolic acid in dichloromethane to a 4,4′,4″-(boroxine-2,4,6)-tribenzoyl chloride solution at 0-5°C, and then adding triethylamine. The mixture is stirred at 0-5°C for 5-8h and filtered. The filtrate is evaporated and washed with water to remove unreacted thioglycolic acid. The boroxine tricarboxylic acid compound is obtained after drying.

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