Preparation method of core-shell structured granular lithium adsorbent

Abstract

The application discloses a preparation method of a core-shell structure particle lithium adsorbent, and comprises the following steps: 1) uniformly mixing thermoplastic strong acid cation exchange resin powder, lithium ion sieve powder and a lubricant, and then performing extrusion granulation to obtain a core structure particle lithium adsorbent; 2) adding the core structure particle lithium adsorbent into a modified PVC solution, stirring and then removing the modified PVC solution; and 3) placing the core structure particle lithium adsorbent into an aqueous phase, so that the modified PVC is solidified on the surface of the core structure particle lithium adsorbent, and finally a core-shell structure particle lithium adsorbent is formed. The application realizes a simple preparation process, solves the water absorption problem of the lithium ion sieve after granulation, and the core-shell structure is more conducive to fast and efficient adsorption of Li + , and the adsorption selectivity is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium extraction from salt lakes, and particularly relates to a preparation method of a granular lithium adsorbent with a core-shell structure. BACKGROUND

[0002] With the popularization and application of new energy electric vehicles, the demand for lithium ion batteries is increasing, which drives the price of lithium, a core material of lithium ion batteries, to rise. Currently, lithium ion batteries are mainly used as driving batteries in mainstream new energy electric vehicles. Lithium is an essential raw material for producing secondary lithium ion batteries, including positive electrode materials and electrolytes. Therefore, in order to meet the sustainable development of lithium resources for the new energy electric vehicle industry, it is crucial to actively seek new technologies for extracting lithium from salt lake brine and concentrated seawater.

[0003] The lithium ion sieve powder used in the existing ion exchange method has the problems of difficulty in solid-liquid separation and high dissolution loss rate when directly applied, and needs to be prepared into granules of a certain size for use. However, the adsorbent granules prepared by traditional methods all contain a certain amount of binder, and these binders are basically hydrophobic polymers, which leads to the inability of the lithium ion sieve powder to fully contact with the brine, i.e., the poor hydrophilicity of the adsorbent granules, and a significant decrease in lithium extraction efficiency.

[0004] Chinese Patent CN114011386A discloses a preparation method of lithium adsorption granules, in which LiCl·2Al(OH)3·nH2O powder, dihydric alcohol, diisocyanate, pore-forming agent and solvent are uniformly mixed, granulated to obtain primary granules; the dihydric alcohol and diisocyanate are initiated to polymerize, and the secondary granules are obtained by drying; then the secondary granules are mixed with a polyethylene-based adhesive solution, and secondary granulation is performed to remove the solvent and pore-forming agent, thereby obtaining lithium adsorption granules. The polyurethane polymerized in the early stage of the method has a certain hydrophilicity, but the hydrophilicity is very weak, and the polyethylene-based binder used in the later stage has no hydrophilicity.

[0005] Chinese Patent CN106622103A discloses a method for preparing granular adsorbents used for extracting lithium from lithium-containing brine, in which LiCl·3Al(OH)3·nH2O active ingredient powder is prepared, and then mixed with an organic compound and extruded to granulate. The granulating organic compound can be a chlorine-containing organic polymer, such as polyvinyl chloride or chlorinated polyethylene, which can be dissolved in methyl chloride, or a mixture of multiple chlorine-containing organic polymers. The binder using a chlorine-containing organic polymer has no hydrophilicity.

[0006] Chinese patent CN115487777A discloses a method for preparing a high-adsorption porous particle lithium adsorbent. A polymer is dissolved in a solvent, and a polymerizable functional monomer, styrene, divinylbenzene, 1,4-p-dichlorobenzene, and an initiator are added and stirred to dissolve. After high-temperature polymerization, a polyionic liquid is obtained. Lithium ion sieve powder and a pore-forming agent are mixed, and the polyionic liquid is added and stirred strongly. The mixture is extruded through a spinneret into an aqueous phase for solidification. The solvent and the pore-forming agent are removed by washing, and the high-adsorption porous particle lithium adsorbent is obtained after granulation. Although the particle lithium adsorbent is treated for hydrophilicity, the particle lithium adsorbent has weak selectivity for divalent and monovalent ions, and cannot quickly and efficiently adsorb lithium ions.

[0007] Therefore, how to prepare an adsorbent with strong water absorption, large saturated adsorption capacity of the particle adsorbent, fast adsorption and desorption rate of lithium ions is an urgent problem to be solved. SUMMARY

[0008] The purpose of the present application is to solve the above technical problems, and to provide a method for preparing a particle lithium adsorbent with a core-shell structure, so as to realize a simple preparation process, solve the problem of water absorption after lithium molecular sieve granulation, and the core-shell structure is more conducive to fast and efficient adsorption of Li + with high adsorption selectivity. In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0009] A method for preparing a particle lithium adsorbent with a core-shell structure, comprising the following steps:

[0010] 1) uniformly mixing thermoplastic strong acid cation exchange resin powder, lithium ion sieve powder, and a lubricant, and then extruding and granulating to obtain a particle lithium adsorbent with a core structure;

[0011] 2) adding the particle lithium adsorbent with a core structure into a modified PVC solution, stirring, and then removing the modified PVC solution;

[0012] 3) placing the particle lithium adsorbent with a core structure into an aqueous phase, so that the modified PVC is solidified on the surface of the particle lithium adsorbent with a core structure, and finally forming a particle lithium adsorbent with a core-shell structure.

[0013] Compared with the prior art, the method for preparing a particle lithium adsorbent with a core-shell structure has the following beneficial effects:

[0014] The core layer structure and the shell layer structure both have strong water absorption, which ensures that salt lake brine can freely enter the inside of the particles; the -SO3 - group with negative charge is introduced into the core layer structure, which is more conducive to forming a through positive ion channel according to the principle of attracting opposite charges; the -N + (CH3)3 group with positive charge is introduced into the shell layer structure, which has strong selectivity for divalent positive charges such as Ca 2+ and Mg2+ The electrostatic repulsion is stronger than that of the monovalent positively charged Li + 、Na + The ion is large, and Na + The ionic radius is larger than Li + The ionic radius is large, so the monovalent Li + Ions preferentially enter the shell layer and then enter the core layer structure of the lithium adsorbent. The shell structure enhances the selectivity of the lithium adsorbent, which is particularly suitable for lithium extraction from brine with a high magnesium-lithium ratio in salt lakes, thereby achieving rapid and efficient adsorption of Li + ; All the lithium molecular sieve powders are in the core layer structure, and the shell structure protects the core layer structure, further reducing the problem of dissolution rate of granular lithium molecular sieve. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0016] Example 1:

[0017] This embodiment is a method for preparing a core-shell structured lithium adsorbent particle, comprising the following steps:

[0018] Prepare thermoplastic strong acid cation exchange resin powder,

[0019] First, 5kg of styrene, 1.32kg of divinylbenzene and 0.05kg of benzoyl peroxide are mixed and dissolved, with divinylbenzene as a cross-linking agent and benzoyl peroxide as an initiator, to form a monomer mixed solution. Then, 12kg of polyolefin elastomer (POP) material is added to the monomer mixed solution for absorption immersion. The POP material is a thermoplastic elastomer material. After the absorption and polymerization of the monomers, the cross-linked polystyrene and the POP polymer alloy material form an interpenetrating network structure, while the polymer alloy material still has thermoplasticity. The absorption and immersion temperature is controlled at 60°C, and all the monomers can be absorbed and immersed in about 2 hours. Then, 40kg of deionized water is added, and the temperature is raised to 85°C for suspension polymerization reaction. The reaction is carried out for 12 hours to obtain about 17.77kg of POP white balls. The POP white balls are dried and crushed to 10-20 mesh. Sulfonation is carried out according to the sulfonation process for gel-type strong acid cations, with the sulfonation temperature controlled at 50°C for 12 hours. After the reaction, the sulfonated resin is converted to a sodium form with alkali solution and washed with pure water until neutral. The resulting product is then dried and pulverized to a fineness of 120-150 mesh to obtain a thermoplastic strong acid cation exchange resin powder. Testing according to national standard GB / T8155-2008, "Determination of Exchange Capacity of Cation Exchange Resins," shows that the prepared thermoplastic strong acid cation exchange resin powder has an exchange capacity of ≥2.3 mmol / g and a moisture content of 40-45%.

[0020] Prepare modified PVC solution,

[0021] 5g PVC was dissolved in 100-200g dimethylformamide, which was used as solvent. Then 0.35g divinylbenzene, 5-benzylvintrimethylammonium chloride and 0.05g benzoyl peroxide were added. Divinylbenzene was used as crosslinking agent. 5-benzylvintrimethylammonium chloride had -N + (CH3)3 functional group, benzoyl peroxide as initiator, after stirring evenly, raise the temperature to 85-90°C for high-temperature polymerization for 12 hours, then lower the temperature to room temperature to obtain a modified PVC solution. The viscosity of the modified PVC solution is adjusted according to the mass ratio of PVC to dimethylformamide. The larger the ratio, the greater the viscosity, while the smaller the ratio, the lower the viscosity. The control range is 100-300mPa.s.

[0022] 20kg of thermoplastic strong acid cation exchange resin powder, 75kg of manganese lithium ion sieve powder, and 1kg of erucamide were mixed evenly, and then granulated by a twin-screw extruder to obtain a core structure granular lithium adsorbent. Negatively charged -SO3 was introduced into the core layer structure. - According to the principle of opposite charges attract, the group is more conducive to the formation of a continuous positively charged cation channel.

[0023] Then the core structure particle lithium adsorbent is added to the modified PVC solution with a viscosity of 100mPa.s. The viscosity directly determines the shell thickness. The greater the viscosity, the thicker the shell, and the smaller the viscosity, the thinner the shell. After stirring, the modified PVC solution is removed, and the core structure particle lithium adsorbent is placed in the aqueous phase to solidify the modified PVC on the surface of the core structure particle lithium adsorbent, and finally a core-shell structure particle lithium adsorbent is formed. The shell thickness is about 5-9um. The shell thickness is controlled according to the viscosity of the modified PVC solution. The shell thickness should be controlled at 5-20um for the best effect. If the viscosity is too high, the shell structure layer thickness is too thick, which affects the Li+ desorption rate; if the viscosity is too low, the shell structure layer thickness is too thin, and the effect of the monovalent cation preferentially entering the internal core structure layer is not ideal, and rapid and efficient adsorption of Li cannot be achieved. + Effect. The positively charged -N is introduced into the shell structure. + (CH3)3 group, for Ca 2+ Mg 2+ The electrostatic repulsion is stronger than that of Li + 、Na + The ions are large, so that the monovalent cations preferentially enter the interior of the lithium molecular sieve particles, thereby achieving rapid and efficient adsorption of Li + .

[0024] Example 2:

[0025] The preparation of thermoplastic strong acid cation exchange resin powder and modified PVC solution is consistent with that in Example 1,

[0026] After 10 kg of thermoplastic strong acid cation exchange resin powder, 85 kg of manganese lithium ion sieve powder, and 3 kg of erucic acid amide are uniformly mixed, the mixture is granulated through a double screw extruder to obtain a core structure granular lithium adsorbent. Then, the core structure granular lithium adsorbent is added to a modified PVC solution with a viscosity of 100 mpa.s, stirred, and then the modified PVC solution is removed. The core structure granular lithium adsorbent is then placed in an aqueous phase, and the modified PVC is solidified on the surface of the core structure granular lithium adsorbent, finally forming a core-shell structure granular lithium adsorbent with a shell thickness of about 5-9 um.

[0027] Example 3:

[0028] The preparation of thermoplastic strong acid cation exchange resin powder and modified PVC solution is consistent with that in Example 1,

[0029] After 15 kg of thermoplastic strong acid cation exchange resin powder, 85 kg of titanium lithium ion sieve powder, and 2.5 kg of erucic acid amide are uniformly mixed, the mixture is granulated through a double screw extruder to obtain a core structure granular lithium adsorbent. Then, the core structure granular lithium adsorbent is added to a modified PVC solution with a viscosity of 300 mpa.s, stirred, and then the modified PVC solution is removed. The core structure granular lithium adsorbent is then placed in an aqueous phase, and the modified PVC is solidified on the surface of the core structure granular lithium adsorbent, finally forming a core-shell structure granular lithium adsorbent with a shell thickness of about 16-20 um.

[0030] Example 4:

[0031] The preparation of thermoplastic strong acid cation exchange resin powder and modified PVC solution is consistent with that in Example 1,

[0032] After 10 kg of thermoplastic strong acid cation exchange resin powder, 75 kg of aluminum lithium ion sieve powder, and 3 kg of erucic acid amide are uniformly mixed, the mixture is granulated through a double screw extruder to obtain a core structure granular lithium adsorbent. Then, the core structure granular lithium adsorbent is added to a modified PVC solution with a viscosity of 200 mpa.s, stirred, and then the modified PVC solution is removed. The core structure granular lithium adsorbent is then placed in an aqueous phase, and the modified PVC is solidified on the surface of the core structure granular lithium adsorbent, finally forming a core-shell structure granular lithium adsorbent with a shell thickness of about 10-15 um.

[0033] Comparative Example 1:

[0034] After 20 kg of thermoplastic strong acid cation exchange resin powder, 75 kg of manganese lithium ion sieve powder, and 1 kg of lubricant are uniformly mixed, the mixture is granulated through a double screw extruder to obtain a granular lithium adsorbent.

[0035] Comparative Example 2:

[0036] After 20 kg of polyolefin elastomer material (POP), 75 kg of manganese lithium ion sieve powder, and 1 kg of lubricant are uniformly mixed, the mixture is granulated through a twin-screw extruder to obtain a core structure granular lithium adsorbent. Then, the core structure granular lithium adsorbent is added to a pure PVC solution with a viscosity of 100 mpa.s, stirred, and then the pure PVC solution is removed. The core structure granular lithium adsorbent is then placed in an aqueous phase, and the pure PVC is solidified on the surface of the core structure granular lithium adsorbent to form a core-shell structure granular lithium adsorbent with a shell thickness of about 5-9 um.

[0037] The relevant tests of Examples 1-4 and Comparative Examples 1-2 are evaluated, and the test results are shown in Table 1 below. The specific test methods are as follows:

[0038] Lithium adsorption capacity and desorption rate test method: first configure a lithium salt solution, the main components and contents of the solution are as follows: lithium 1 g / L, sodium 86 g / L, magnesium 31 g / L, and anion is chloride. 10 ml of lithium adsorbent is packed in a chromatographic column, washed with 200 ml of pure water at a flow rate of 5 BV / h, then switched to 100 ml of the prepared lithium salt solution, the flow rate is 5 BV / h, and the liquid passing time is 2 h. The lithium content of the inlet and outlet liquid is tested respectively, recorded as C1 and C2 (unit: mg / mL), and the 2h lithium adsorption capacity Q = (C1-C2) x 100 / 10 is obtained.

[0039] Drain the lithium salt solution, flush the lithium adsorbent with 1 BV of saturated brine, drain, and then pass 50 ml of 40℃ pure water through the column as a desorption liquid for 0.5 h at a flow rate of 10 BV / h. The lithium content C3 (unit: mg / mL) of the desorption liquid is tested, and the 0.5h lithium desorption rate D = 50xC3 / Qx100% is obtained.

[0040] Moisture content test method: weigh the dried granular lithium adsorbent m1 (accurate to 0.1 mg), immerse it in deionized water for 24 h, take out the granular lithium adsorbent, remove the water on the surface of the granules with a centrifuge, and then weigh it to record the mass as m2. The calculation formula is as follows, and the average value of three tests is taken:

[0041] Moisture content X = (m2-m1) / m2x100%.

[0042] Annual solution loss rate (360 cycles) test method: weigh 10 ml of lithium adsorbent, dry it to a constant weight w1 (accurate to 0.1 mg), and perform one cycle of adsorption and desorption. After 30 cycles, the lithium adsorbent is taken out and dried to a constant weight w2 (accurate to 0.1 mg). The annual solution loss rate (360 cycles) La = (w1-w2) / w1 / 30x360x100%.

[0043]

[0044]

[0045] Table 1

[0046] According to the data in Table 1, examples 1-4 have increased shell structure layer compared to comparative example 1, which is beneficial to improve 2h lithium adsorption capacity and reduce annual solution loss rate (360 cycles); compared to comparative example 2, examples 1-4 have greatly improved water content, 2h lithium adsorption capacity and 0.5h desorption rate (desorption capacity / adsorption capacity), because the polyolefin elastomer material (POP) in the core structure layer of comparative example 2 has no water absorption.

[0047] When the above examples are applied, the core layer structure and the shell layer structure both have strong water absorption, which ensures that salt lake brine can freely enter the inside of the particles; the introduction of negatively charged —SO3 - groups in the core layer structure is more conducive to the formation of a through positive ion channel according to the principle of opposite charges attract; the introduction of positively charged —N + (CH3)3 groups in the shell layer structure has a larger electrostatic repulsion force on divalent positive ions Ca 2+ , Mg 2+ than monovalent positive ions Li + , Na + , and the radius of Na + ions is larger than that of Li + ions, so that monovalent Li + ions preferentially enter the shell layer and then enter the lithium adsorbent core layer structure, and the shell layer structure enhances the selectivity of the lithium adsorbent, which is particularly suitable for lithium extraction from salt lake brine with high magnesium-lithium ratio, thereby realizing rapid and efficient adsorption of Li + ; the lithium molecular sieve powder is all in the core layer structure, and the shell layer structure protects the core layer structure, further reducing the problem of solution loss rate of the particle lithium molecular sieve.

[0048] In the description of the present specification, the description of the term "specific embodiment" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above-mentioned terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0049] Although the present application has been described with reference to the above embodiments, the contents described are merely employed embodiments for facilitating the understanding of the present application, and are not intended to limit the present application. Any modification and change in the form and details can be made by any person skilled in the art without departing from the spirit and scope of the present application, and the patent protection scope of the present application shall be subject to the scope defined by the appended claims.

Claims

1. A method for preparing a core-shell structured lithium adsorbent particle, characterized in that: The following steps are involved: 1) Thermoplastic strong acid cation exchange resin powder, lithium ion sieve powder and lubricant are uniformly mixed and then extruded and granulated to obtain a core structure particle lithium adsorbent; 2) adding the core structure particle lithium adsorbent to the modified PVC solution, stirring and then removing the modified PVC solution; 3) The core-structured lithium adsorbent particles are then placed in the aqueous phase to allow the modified PVC to solidify on the surface of the core-structured lithium adsorbent particles, ultimately forming a core-shell structured lithium adsorbent particle; The manufacturing method of the thermoplastic strong acid cation exchange resin powder, The method comprises the following steps: mixing and dissolving styrene, a cross-linking agent and an initiator to prepare a monomer mixed solution; adding a polyolefin elastomer material to the monomer mixed solution for absorption and immersion, then adding deionized water and raising the temperature to carry out a suspension polymerization reaction to obtain POP white balls, drying the POP white balls and then crushing them; sulfonating the POP white balls according to the sulfonation process of gel-type strong acid cations, converting the sulfonated resin into a sodium type with alkali solution after the reaction is completed, and washing with pure water until neutral; drying and crushing the discharged material to a fineness of 120-150 meshes to obtain thermoplastic strong acid cation exchange resin powder; The manufacturing method of the modified PVC solution, The method comprises the following steps: dissolving PVC in a solvent, then adding a crosslinking agent, 5-benzylvinyltrimethylammonium chloride and an initiator, stirring evenly, performing a high-temperature polymerization reaction, and then lowering the temperature to room temperature to obtain a modified PVC solution.

2. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, wherein: The weight ratio of the thermoplastic strong acid cation exchange resin powder, the lithium ion sieve powder and the lubricant is 10-20:75-85:1-3.

3. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, characterized in that: The viscosity of the modified PVC is controlled at 100-300 mPa.s.

4. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, wherein: The thickness of the shell structure layer of the core-shell structure is controlled to be 5-20 μm.

5. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, characterized in that: The absorption and immersion temperature is controlled at 60°C.

6. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, characterized in that: The POP white balls are dried and then crushed to 10-20 mesh.

7. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, characterized in that: The sulfonation temperature was controlled at 50° C., and the sulfonation time was 12 h.

8. The method for preparing a core-shell structured lithium adsorbent particle according to claim 1, characterized in that: The high temperature polymerization reaction is carried out by raising the temperature to 85-90° C. and then lowering the temperature after 12 hours of high temperature polymerization.

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