Lithium adsorbent and preparation method thereof

Abstract

The invention discloses a lithium adsorbent with a net-shaped communicating pore channel and a preparation method thereof, and the adsorption performance and desorption efficiency of the lithium adsorbent with the cross-linked net-shaped pore channel prepared by the method are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium extraction by adsorption, and relates to a preparation method of a lithium adsorbent. Background Art

[0002] With the rapid development of the new energy vehicle industry, the market demand for lithium carbonate, a key raw material for power batteries, has been driven. Global lithium resources mainly exist in salt lake brines and ores; among the currently proven lithium resources, salt lake brines account for 58%. There are various ways to extract lithium resources from salt lakes, and the adsorption method is an efficient, environmentally friendly and low-cost method. The lithium adsorbent material is the most critical part of the lithium extraction by adsorption method. The adsorption capacity, adsorption and desorption efficiency and service life of the lithium adsorbent directly determine the cost efficiency of lithium extraction from salt lakes. The internal structure of the lithium adsorbent, including porosity, pore distribution, pore size, etc., directly affects its performance such as adsorption capacity and adsorption and desorption efficiency, and is a key index that needs to be regulated during the preparation process.

[0003] CN 106622103 B discloses a preparation method of aluminum-based lithium adsorbent particles. This method is to mix aluminum-based adsorbent powder with a hydrophobic polymer solution, and then dry and crush it. The obtained adsorbent particles have the problems of being embedded with active sites and low adsorption capacity.

[0004] Adding a pore-forming agent is a common method for making pores in adsorbents. Commonly used pore-forming agents include inorganic salt powders such as calcium carbonate, and organic polymer particles of polyvinylpyrrolidone. Pores formed by post-treatment such as etching are mostly discontinuous pores; and it is difficult for the pore-forming agent to contact with the aqueous solution, resulting in no pores being formed inside the adsorbent, and lithium ions in the brine cannot contact with the effective adsorption components, which will greatly affect the adsorption effect. Compared with discontinuous pores, through-holes or pore channels with a network structure are more conducive to the contact between lithium ions and the adsorbent. By replacing the pore-forming agent with long fibrous cellulose, a fiber network structure of connected pore channels can be prepared, which greatly improves the adsorption capacity and adsorption and desorption efficiency. However, cellulose is not easily soluble in water and organic solvents, and the etching and dissolution in the adsorbent are still difficult problems to be solved. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a lithium adsorbent with a network-connected pore channel and a preparation method thereof.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] A preparation method of a lithium adsorbent, comprising the following steps:

[0008] (1) Dissolve the polymer matrix material in its good solvent to obtain a polymer solution;

[0009] (2) Swell the cellulose porogen in an alkaline solution, filter to remove water, and dry it;

[0010] (3) Add the lithium adsorbent precursor and the swollen porogen obtained in step (2) to the polymer solution in step (1), and mix to obtain a uniform dispersion;

[0011] (4) Dropwise add the dispersion into a poor solvent of the polymer, and the polymer wraps the lithium adsorbent precursor and the porogen and precipitates to obtain uniform particles;

[0012] (5) Separate the particles from the solvent to obtain adsorbent particles;

[0013] (6) Remove the porogen from the formed adsorbent particles by intermittent ultrasonic etching in water to obtain a porous lithium adsorbent material.

[0014] Furthermore, the polymer matrix material described in step (1) is selected from one or more of high molecular polymers such as polyvinyl chloride and polyvinylidene fluoride, and preferably polyvinylidene fluoride with a molecular weight of 300,000 - 800,000.

[0015] Furthermore, the polymer good solvent described in step (1) is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and N-methylpyrrolidone (NMP), and preferably N,N-dimethylacetamide.

[0016] Furthermore, the concentration of the polymer solution described in step (1) is 5wt% - 30wt%, and preferably 10wt% - 20wt% solution concentration.

[0017] Furthermore, the porogen described in step (2) is carboxylated nanocellulose with a size of 1 - 50 nm in diameter and 1000 - 5000 nm in length, and preferably 5 - 30 nm in diameter and 2000 - 3000 nm in length.

[0018] Furthermore, the alkaline solution described in step (2) is selected from aqueous solutions of LiOH, NaOH, and KOH, with a concentration of 0.5wt% - 20wt%, and preferably 5wt% - 15wt% aqueous LiOH solution.

[0019] Furthermore, the swelling temperature described in step (2) is 5 - 25 °C, and preferably 10 - 15 °C.

[0020] Furthermore, the swelling time described in step (2) is 1 min - 10 min, and preferably 2 - 5 min.

[0021] Furthermore, the lithium adsorbent precursor described in step (3) is an aluminum-based adsorbent, and the precursor is an aluminum salt such as LiCl·2Al(OH)3·nH2O (n = 0.5 - 3).

[0022] Furthermore, the mass ratio of the lithium adsorbent precursor to the polymer described in step (3) is 56:1 to 1:1, preferably 4:1 to 2:1.

[0023] Furthermore, the mass ratio of the adsorbent precursor to the pore-forming agent described in step (3) is 0.5:1 to 5:1, preferably 1:1 to 3:1;

[0024] Furthermore, the poor solvent of the polymer described in step (4) is one or more of water ethanol and toluene, preferably ethanol.

[0025] Furthermore, the ultrasonic treatment described in step (6) is pulsed, the ultrasonic intensity is 100 - 2000 w, preferably 500 - 1000 w. The ultrasonic treatment time is 1 - 5 min, stop the ultrasonic wave, soak in the solution for 1 - 5 min, and then continue the ultrasonic wave for 1 - 5 min, and repeat until the cellulose pore-forming agent is completely dissolved.

[0026] Furthermore, the water temperature described in step (6) is 40 - 80 °C, preferably 50 - 60 °C.

[0027] On the other hand, the present invention also provides a lithium adsorbent prepared by the above method.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) Compared with granular pore-forming agents, nanofibers can prepare interconnected pores with an interconnected network structure;

[0030] (2) Uniform and continuous nanopores can be obtained after the nanofiber pore-forming agent is etched by the method of swelling first and then ultrasonic treatment;

[0031] (3) The interconnected network pores effectively improve the adsorption capacity and adsorption / desorption efficiency of the adsorbent. Specific Embodiments

[0032] The following further illustrates the present invention through specific examples. The examples described in the present invention are only for the purpose of illustrating the present invention and do not limit the scope of the present invention.

[0033] Table 1: Raw materials and sources

[0034]

[0035]

[0036] Preparation method of LiCl·2Al(OH)3·nH2O: Aluminum chloride and lithium chloride with a molar ratio of 2:1 are mixed and dissolved. The mixed solution is placed in an open crystallizer, and the reaction temperature is controlled at 75 °C. Sodium hydroxide is added dropwise under stirring for coprecipitation. The addition is stopped when the pH reaches 6 - 7. The precipitate is separated by centrifugation, dried at 60 °C, and ground to obtain the LiCl·2Al(OH)3·nH2O precursor.

[0037] Testing method:

[0038] Adsorption capacity: Take 100 g of the delithiated adsorbent and add it to the adsorption column. Pump in the brine with a lithium concentration of C0 (ppm) at a flow rate of 2 BV. Stop feeding when the concentration of the effluent is higher than 150 ppm. The feeding volume is L. Then the adsorption capacity (mg / g) = C0 * L / 100 g.

[0039] Desorption amount: Elute the lithium-adsorbed adsorbent with 0.1 M hydrochloric acid and detect the Li concentration C1 (g / L) in the desorption solution.

[0040] The adsorption brine is Zabuye raw brine, and its main components are shown in Table 2 below:

[0041] Table 2: Main composition of Zabuye raw brine

[0042]

[0043] Example 1

[0044] Dissolve 1 Kg of polyvinylidene fluoride (PVDF) in N,N-dimethylacetamide (DMAC) at 80 °C to obtain a 15 wt% polymer solution; soak the carboxymethyl nanocellulose pore former with a diameter of 5 - 30 nm and a length of 2000 - 3000 nm in a 10 wt% LiOH aqueous solution at 15 °C for 3 min, filter to remove water, and dry; add 3 Kg of LiCl·2Al(OH)3·nH2O and 1.5 Kg of the pore former to the polymer solution, and mix them by mechanical stirring to obtain a uniform dispersion; drop the dispersion into 1 L of ethanol drop by drop, and the polymer wraps the lithium adsorbent precursor and the pore former to precipitate, obtaining uniform particles; after the particles are completely precipitated and formed, separate them from the solution by filtration, place the formed adsorbent particles in water for ultrasonic treatment, set the ultrasonic intensity to 1000 w, and the ultrasonic treatment time to 2 min. Stop ultrasonic treatment, soak in the solution for 3 min, and then continue ultrasonic treatment for 2 min. Repeat this process until the cellulose pore former is completely dissolved to obtain a lithium adsorbent with an interconnected network of pores.

[0045] Example 2

[0046] Dissolve 1 Kg of polyvinylidene fluoride (PVDF) in N,N-dimethylformamide (DMF) at 80 °C to obtain a 10 wt% polymer solution; soak the carboxymethyl nanocellulose pore-forming agent with a diameter of 1 - 20 nm and a length of 1000 - 2000 nm in a 5 wt% NaOH aqueous solution at 15 °C for 2 min, filter to remove water, and dry; add 4 Kg of LiCl·2Al(OH)3·nH2O and 1.3 Kg of the pore-forming agent to the polymer solution, and mix by mechanical stirring to obtain a uniform dispersion; dropwise add the dispersion to 1 L of ethanol, and the polymer wraps the lithium adsorbent precursor and the pore-forming agent to precipitate, obtaining uniform particles; after the particles are completely precipitated and formed, separate them from the solution by filtration, place the formed adsorbent particles in water for ultrasonic treatment, set the ultrasonic intensity to 500 w, and the ultrasonic treatment time to 3 min, stop ultrasonic treatment, soak in the solution for 3 min, and then continue ultrasonic treatment for 3 min, and repeat this process until the cellulose pore-forming agent is completely dissolved to obtain a lithium adsorbent with an interconnected network of pores.

[0047] Example 3

[0048] Dissolve 1 Kg of polyvinyl chloride (PVC) in N-methylpyrrolidone (NMP) at 80 °C to obtain a 20 wt% polymer solution; soak the carboxymethyl nanocellulose pore-forming agent with a diameter of 1 - 20 nm and a length of 3000 - 5000 nm in a 15 wt% KOH aqueous solution at 10 °C for 5 min, filter to remove water, and dry; add 2 Kg of LiCl·2Al(OH)3·nH2O and 2 Kg of the pore-forming agent to the polymer solution, and mix by mechanical stirring to obtain a uniform dispersion; dropwise add the dispersion to 1 L of water, and the polymer wraps the lithium adsorbent precursor and the pore-forming agent to precipitate, obtaining uniform particles; after the particles are completely precipitated and formed, separate them from the solution by filtration, place the formed adsorbent particles in water for ultrasonic treatment, set the ultrasonic intensity to 1000 w, and the ultrasonic treatment time to 2 min, stop ultrasonic treatment, soak in the solution for 3 min, and then continue ultrasonic treatment for 2 min, and repeat this process until the cellulose pore-forming agent is completely dissolved to obtain a lithium adsorbent with an interconnected network of pores.

[0049] Example 4

[0050] 1 kg of polyvinyl chloride (PVC) was dissolved in N,N-dimethylformamide (DMF) at 80 °C to obtain a 5 wt% polymer solution; a carboxymethyl nanocellulose pore former with a diameter of 30 - 50 nm and a length of 1000 - 2000 nm was soaked and swollen in a 0.5 wt% LiOH aqueous solution at 5 °C for 1 min, filtered to remove water, and dried; 5 kg of LiCl·2Al(OH)3·nH2O and 1 kg of the pore former were added to the polymer solution and mixed by mechanical stirring to obtain a uniform dispersion; the dispersion was added dropwise to 1 L of toluene, and the polymer wrapped the lithium adsorbent precursor and the pore former to precipitate, obtaining uniform particles; after the particles were completely precipitated and formed, they were separated from the solution by filtration, and the formed adsorbent particles were placed in water and sonicated, with the sonication intensity set at 100 w and the sonication treatment time of 5 min, then the sonication was stopped, soaked in the solution for 3 min, and then sonicated for another 5 min, and this was repeated until the cellulose pore former was completely dissolved, obtaining a lithium adsorbent with an interconnected network of pores.

[0051] Example 5

[0052] 1 kg of polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP) at 80 °C to obtain a 30 wt% polymer solution; a carboxymethyl nanocellulose pore former with a diameter of 30 - 50 nm and a length of 3000 - 5000 nm was soaked and swollen in a 20 wt% LiOH aqueous solution at 25 °C for 10 min, filtered to remove water, and dried; 1 kg of LiCl·2Al(OH)3·nH2O and 2 kg of the pore former were added to the polymer solution and mixed by mechanical stirring to obtain a uniform dispersion; the dispersion was added dropwise to 1 L of water, and the polymer wrapped the lithium adsorbent precursor and the pore former to precipitate, obtaining uniform particles; after the particles were completely precipitated and formed, they were separated from the solution by filtration, and the formed adsorbent particles were placed in water and sonicated, with the sonication intensity set at 2000 w and the sonication treatment time of 1 min, then the sonication was stopped, soaked in the solution for 3 min, and then sonicated for another 1 min, and this was repeated until the cellulose pore former was completely dissolved, obtaining a lithium adsorbent with an interconnected network of pores.

[0053] Comparative Example 1

[0054] 1 kg of polyvinylidene fluoride (PVDF) was dissolved in N,N-dimethylacetamide (DMAC) at 80 °C to obtain a 15 wt% polymer solution; 3 kg of LiCl·2Al(OH)3·nH2O and 1.5 kg of calcium carbonate with a particle size range of 5 - 30 nm were added to the polymer solution and mixed by mechanical stirring to obtain a homogeneous dispersion; the dispersion was added dropwise to 1 L of ethanol, and the polymer precipitated, encapsulating the lithium adsorbent precursor and the pore-forming agent, to obtain uniform particles; after the particles were completely precipitated and formed, they were separated from the solution by filtration, and the formed adsorbent particles were sonicated in 0.1 M hydrochloric acid with a sonication intensity set at 1000 w and a sonication treatment time of 2 min, then the sonication was stopped, and the particles were soaked in the solution for 3 min, and then sonicated for another 2 min, and this was repeated until the calcium carbonate pore-forming agent was completely dissolved, to obtain the lithium adsorbent.

[0055] Comparative Example 2

[0056] 1 kg of polyvinylidene fluoride (PVDF) was dissolved in N,N-dimethylacetamide (DMAC) at 80 °C to obtain a 15 wt% polymer solution; short cellulose with a diameter of 5 - 30 nm and a length of 50 - 100 nm was soaked and swollen in a 10 wt% aqueous LiOH solution at 15 °C for 3 min, filtered to remove water, and dried; 3 kg of LiCl·2Al(OH)3·nH2O and 1.5 kg of a pore-forming agent were added to the polymer solution and mixed by mechanical stirring to obtain a homogeneous dispersion; the dispersion was added dropwise to 1 L of ethanol, and the polymer precipitated, encapsulating the lithium adsorbent precursor and the pore-forming agent, to obtain uniform particles; after the particles were completely precipitated and formed, they were separated from the solution by filtration, and the formed adsorbent particles were sonicated in water with a sonication intensity set at 1000 w and a sonication treatment time of 2 min, then the sonication was stopped, and the particles were soaked in the solution for 3 min, and then sonicated for another 2 min, and this was repeated until the cellulose pore-forming agent was completely dissolved, to obtain the lithium adsorbent.

[0057] Comparative Example 3

[0058] 1 kg of polyvinylidene fluoride (PVDF) was dissolved in N,N-dimethylacetamide (DMAC) at 80 °C to obtain a 15 wt% polymer solution; 3 kg of LiCl·2Al(OH)3·nH2O and 1.5 kg of carboxymethyl nanocellulose pore-forming agent with a diameter of 5 - 30 nm and a length of 2000 - 3000 nm were added to the polymer solution and mixed by mechanical stirring to obtain a homogeneous dispersion; the dispersion was added dropwise to 1 L of ethanol, and the polymer precipitated, encapsulating the lithium adsorbent precursor and the pore-forming agent, to obtain uniform particles; after the particles were completely precipitated and formed, they were separated from the solution by filtration, and the formed adsorbent particles were soaked in water for 24 h to obtain the lithium adsorbent.

[0059] Table 3: Evaluation Results

[0060] Specification Adsorption capacity mg / g Desorption efficiency g / L Example 1 20.4 2.1 Example 2 18.9 1.9 Example 3 19.2 1.9 Example 4 17.5 1.8 Example 5 17.8 1.6 Comparative Example 1 12.4 1.0 Comparative Example 2 15.2 1.2 Comparative Example 3 4.5 0.3

[0061] As can be seen from Table 3, the samples prepared by the present invention have a high adsorption capacity and desorption efficiency in real brine. In Comparative Example 1, the fiber was replaced with a granular calcium carbonate pore former with the same particle size range, reducing the internal connectivity and pore length of the adsorbent, and the adsorption capacity decreased significantly; in Comparative Example 2, the cellulose length was reduced, thus reducing the pore length, resulting in a decrease in the adsorption capacity. In Comparative Example 3, the carboxymethyl nanocellulose was not pre-swollen at low temperature and ultrasonically treated later, and it was difficult to dissolve and etch away the cellulose wrapped by the adsorbent, resulting in too few internal pores in the adsorbent and a significant reduction in the adsorption capacity.

Claims

1. A preparation method of a lithium adsorbent, comprising the following steps: (1) Dissolve the polymer matrix material in its good solvent to obtain a polymer solution; (2) Swell the cellulose pore-forming agent in an alkaline solution, filter to remove water, and dry; (3) Add the lithium adsorbent precursor and the swollen pore-forming agent obtained in step (2) to the polymer solution in step (1), and mix to obtain a uniform dispersion; (4) Dropwise add the dispersion into the poor solvent of the polymer, and the polymer wraps the lithium adsorbent precursor and the pore-forming agent and precipitates to obtain uniform particles; (5) Separate the particles from the solvent to obtain adsorbent particles; (6) Remove the pore-forming agent from the formed adsorbent particles by intermittent ultrasonic etching in water to obtain a porous lithium adsorbent material.

2. The preparation method according to claim 1, wherein, The polymer matrix material described in step (1) is selected from one or more of high molecular polymers such as polyvinyl chloride and polyvinylidene fluoride, and preferably polyvinylidene fluoride with a molecular weight of 300,000 - 800,000.

3. The preparation method according to claim 1 or 2, characterized in that, The good solvent for the polymer in step (1) is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and N-methylpyrrolidone (NMP), and preferably N,N-dimethylacetamide; and / or, the concentration of the polymer solution in step (1) is 5wt% - 30wt%, preferably 10wt% - 20wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, The pore-forming agent described in step (2) is carboxylated nanocellulose, with a size of 1 - 50 nm in diameter and 1000 - 5000 nm in length, preferably 5 - 30 nm in diameter and 2000 - 3000 nm in length; and / or, the alkaline solution described in step (2) is selected from aqueous solutions of LiOH, NaOH, and KOH, with a concentration of 0.5wt% - 20wt%, preferably 5wt% - 15wt% aqueous LiOH solution.

5. The preparation method according to any one of claims 1-4, characterized in that, The swelling temperature in step (2) is 5 - 25 °C, preferably 10 - 15 °C; the swelling time is 1 min - 10 min, preferably 2 - 5 min.

6. The preparation method according to any one of claims 1-5, characterized in that, The lithium adsorbent precursor in step (3) is an aluminum-based adsorbent, and the precursor is an aluminum salt such as LiCl·2Al(OH)3·nH2O.

7. The preparation method according to any one of claims 1-6, characterized in that, The mass ratio of the lithium adsorbent precursor to the polymer in step (3) is 56:1 - 1:1, preferably 4:1 - 2:1; and / or, the mass ratio of the adsorbent precursor to the pore-forming agent in step (3) is 0.5:1 - 5:1, preferably 1:1 - 3:

1.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The poor solvent for the polymer in step (4) is one or more of water ethanol and toluene, and preferably ethanol.

9. The preparation method according to any one of claims 1-8, characterized in that, The ultrasonic treatment in step (6) is pulsed, with an ultrasonic intensity of 100 - 2000 w, preferably 500 - 1000 w; preferably, the ultrasonic treatment time is 1 - 5 min, stop ultrasonic, soak in the solution for 1 - 5 min, and then continue ultrasonic for 1 - 5 min, and repeat until the cellulose pore-forming agent is completely dissolved.

10. A lithium adsorbent prepared by the preparation method according to any one of claims 1 - 9.

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