Preparation of functionalized MOF-coated lithium phosphate core-shell composite material and application of functionalized MOF-coated lithium phosphate core-shell composite material in impurity removal of crude lithium phosphate
By utilizing the sieving-adsorption synergistic mechanism of functionalized MOF@lithium phosphate core-shell composite material, the problems of poor selectivity and high lithium loss rate in the removal of crude lithium phosphate in existing technologies are solved, achieving efficient and simple deep purification of impurities, and the product purity reaches battery-grade standards.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies for efficiently removing multivalent metal impurities such as calcium, magnesium, iron, and aluminum from crude lithium phosphate suffer from poor selectivity, high lithium loss rate, and complex processes, making it difficult to achieve high-purity preparation of battery-grade lithium phosphate.
By employing functionalized MOF@lithium phosphate core-shell composite material, large impurity ions are screened through physical sieving and confinement by utilizing the pore size difference of the lithium phosphate shell, and impurity ions are captured by the electrostatic effect and van der Waals force of the core, thus achieving deep purification.
It achieves highly selective and efficient removal of multivalent metal impurities under acidic conditions, with a lithium loss rate of less than 3%. The process is simple, environmentally friendly, and the product purity is close to battery-grade requirements.
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Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of battery material preparation, in particular to preparation of a functional MOF lithium phosphate core-shell composite material and application of the functional MOF lithium phosphate core-shell composite material in impurity removal of crude lithium phosphate. BACKGROUND
[0002] With the rapid development of new energy vehicles and energy storage industries, the demand for and purity requirements of battery-grade lithium phosphate, a precursor of a key lithium battery positive electrode material, are increasing. At present, battery-grade lithium phosphate is mainly prepared by a double decomposition method using battery-grade lithium carbonate as a raw material, which is high in cost. Therefore, development of a technology for preparing battery-grade products from crude lithium phosphate (commonly obtained from lithium mica lithium extraction and recycled materials) which is more widely sourced and lower in cost is of great significance for cost reduction and efficiency improvement and resource comprehensive utilization.
[0003] Crude lithium phosphate often contains various metal impurities such as calcium, magnesium, iron and aluminum, and the deep removal of the impurities is a core challenge for product upgrading. Existing technologies such as chemical precipitation are prone to introduce new impurities and have a high lithium loss rate; solvent extraction has a complex process and has the risk of organic pollution; ion exchange resin method is widely used, but has limited selectivity and poor separation effect on calcium and magnesium impurities with similar ionic radii, and the competitive adsorption under a high lithium background leads to a decrease in lithium yield. Therefore, development of a new green and efficient impurity removal technology with high selectivity, high adsorption capacity and low lithium loss has become a key breakthrough in the field. SUMMARY
[0004] The application aims to overcome the above problems in the prior art and provide preparation of a functional MOF lithium phosphate core-shell composite material and application of the functional MOF lithium phosphate core-shell composite material in impurity removal of crude lithium phosphate. The material can not only efficiently remove Ca 2+ , Mg 2+ , but also has a significant removal effect on Fe 3+ , Al 3+ and other multivalent metal cations, so that deep purification of the impurities can be achieved and the product purity can be close to the battery-grade requirement after one-time treatment.
[0005] To achieve the above purpose, the application provides a preparation method of a functional MOF lithium phosphate core-shell composite material, which comprises the following steps: (1) mixing lithium phosphate, water and phosphoric acid to obtain a lithium dihydrogen phosphate stock solution; (2) mixing MIL-101 (Al)-NH2 and water, and obtaining a MOF suspension after stirring; (3) mixing the lithium dihydrogen phosphate stock solution and the MOF suspension, filtering the obtained solid product, and then washing and drying the solid product to obtain the functional MOF lithium phosphate core-shell composite material; The functionalized MOF@lithium phosphate core-shell composite material is a core-shell structure, wherein the shell layer is lithium phosphate, and the inner core is MIL-101(Al)-NH2; and the mass ratio of the inner core and the shell layer is 1:1-3.
[0006] Preferably, in step (1), the lithium phosphate, water and phosphoric acid are mixed in a mass ratio of 1:(20-40):(1.0-1.5).
[0007] Preferably, in step (2), the concentration of MIL-101(Al)-NH2 in the MOF suspension is 2-10 g / L.
[0008] Preferably, in step (3), the operation of mixing the lithium dihydrogen phosphate stock solution with the MOF suspension comprises: adding the lithium dihydrogen phosphate stock solution into the MOF suspension at a speed of 0.5-2 mL / min, and controlling the pH value of the system to be 8.4-8.6 during the adding process.
[0009] The second aspect of the present application provides an application of the functionalized MOF@lithium phosphate core-shell composite material prepared by the above preparation method in impurity removal of crude lithium phosphate.
[0010] The third aspect of the present application provides a method for removing impurities from crude lithium phosphate, comprising: S1, mixing crude lithium phosphate, water and sulfuric acid, stirring and filtering to obtain a lithium phosphate acidizing liquid; S2, mixing the lithium phosphate acidizing liquid with the functionalized MOF@lithium phosphate core-shell composite material prepared by the above preparation method, adsorbing at 20-50℃, and then filtering to obtain an impurity-removed lithium phosphate acidizing liquid.
[0011] Preferably, the operation of mixing the crude lithium phosphate, water and sulfuric acid comprises: mixing the crude lithium phosphate and water in a mass ratio of 1:(2.5-3.0) to prepare a slurry, then adding sulfuric acid after heating to 45-90℃, and controlling the pH value of the system to be 2.5-3.5.
[0012] Preferably, the liquid-solid ratio of the lithium phosphate acidizing liquid and the functionalized MOF@lithium phosphate core-shell composite material is controlled to be 200 mL:0.4-1.2 g.
[0013] Preferably, the adsorption temperature is 25-45℃.
[0014] The fourth aspect of the present application provides an application of the impurity-removed lithium phosphate acidizing liquid obtained by the above method in preparation of battery-grade lithium phosphate.
[0015] Metal-organic framework (MOF) is a kind of crystalline porous material self-assembled by metal ions and organic ligands, which has adjustable structure and huge specific surface area. Through functional design, it can be endowed with the ability of "molecular recognition" for specific ions. Accordingly, the present application aims to realize efficient and selective capture of impurity ions through the synergistic effect of its precise pore size and functional groups, and to provide a new technical path for the preparation of low-cost and high-performance battery-grade lithium phosphate.
[0016] The impurity removal principle of the functionalized MOF@lithium phosphate core-shell composite material is based on the "sieving-adsorption" synergistic mechanism, which realizes the high selectivity and deep purification of multivalent metal impurities under acidic conditions.
[0017] The core principle is as follows: 1. Physical sieving and confinement: The amorphous lithium phosphate shell layer constitutes a primary sieving unit, which can preferentially allow impurity ions such as Ca 2+ , Mg 2+ with larger hydrated ion radii to enter the material interior, while partially blocking hydrated lithium ions (Li + ) outside, achieving preliminary separation.
[0018] 2. Surface adsorption and capture: The impurity ions entering the material interior will face a second line of defense. They will be effectively captured through electrostatic interaction, van der Waals force, etc. by contacting the large internal surface of the composite material. At the same time, the unprotonated sites in the MOF framework and the shell layer can also interact specifically with these impurity ions, thus being firmly fixed.
[0019] This process pre-enriches impurities through size sieving of the shell layer and achieves deep removal using the excellent adsorption capacity of the core, ultimately efficiently removing calcium, magnesium, iron, aluminum, and other multivalent metal ions while ensuring extremely low loss of lithium.
[0020] Compared with the prior art, the present application has the following advantages: 1. Extremely high selectivity and extremely low lithium loss: The unique "sieving-adsorption" synergistic mechanism of the composite material allows the lithium phosphate shell layer to preferentially capture multivalent impurity ions such as calcium and magnesium based on the difference in hydrated ion radii, while effectively excluding hydrated lithium ions, thereby controlling the lithium loss rate to below 3% while achieving deep impurity removal, which is much lower than traditional methods.
[0021] 2. Good purification depth and wide applicability: The material not only efficiently removes Ca 2+ , Mg 2+ , but also has significant removal effect on Fe 3+ , Al 3+ and other multivalent metal cations, achieving deep purification of impurities and making the product purity close to the battery-grade requirement after one treatment.
[0022] 3. The process is more concise and environmentally friendly: the entire process can be completed in a single acidic system, avoiding the complex operation and secondary pollution problems caused by repeated pH adjustment, large use of precipitants or organic solvents, and the process is shorter and more in line with green production requirements. DETAILED DESCRIPTION
[0023] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.
[0024] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood as including values approximately near these ranges and values within these ranges. For ranges of values, the endpoints of the ranges are combined with the individual points to form new ranges that are within the scope of the present application.
[0025] In addition, the technical solutions of each embodiment provided by the present application can be combined with each other, but it must be based on the realization of the ordinary skilled in the art, when the combination of technical solutions appears contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application.
[0026] In one aspect, the present application provides a preparation method of a functional MOF@lithium phosphate core-shell composite material, comprising: (1) mixing lithium phosphate, water and phosphoric acid to obtain a lithium dihydrogen phosphate stock solution; (2) mixing MIL-101(Al)-NH2 and water, and stirring to obtain a MOF suspension; (3) mixing the lithium dihydrogen phosphate stock solution and the MOF suspension, filtering to obtain a solid product, and then washing and drying to obtain the functional MOF@lithium phosphate core-shell composite material; The functional MOF@lithium phosphate core-shell composite material has a core-shell structure (composed of an inner core and a shell layer wrapping the outside of the inner core), wherein the shell layer is lithium phosphate and the inner core is MIL-101(Al)-NH2. In the functional MOF@lithium phosphate core-shell composite material, the mass ratio of the inner core to the shell layer is 1:1-3.
[0027] In the functionalized MOF@lithium phosphate core-shell composite material, the mass ratio of the core and the shell is 1:1-3. If the mass ratio of the core and the shell is <1:1, the shell is too thin, the lithium phosphate shell is not completely and discontinuously covered, the impurity ions can directly contact the MOF core, and the selectivity is reduced. If the mass ratio of the core and the shell is >1:3, the shell is too thick, the MOF pore entrance can be blocked, the mass transfer resistance is increased, the impurity ions are difficult to diffuse to the internal MOF high-efficiency adsorption site, the adsorption kinetics is slowed down, and the amorphous shell that is too thick can be more easily peeled off in stirring. In the optimal range (1:1-1:3), the shell is complete and uniform, and an ideal core-shell structure can be formed.
[0028] In a specific embodiment, the mass ratio of the core and the shell is 1:2.5.
[0029] The lithium phosphate in the functionalized MOF@lithium phosphate core-shell composite material belongs to a protective layer, and the main purpose is to protect the MIL-101(Al)-NH2(MOF) core. The MIL-101(Al)-NH2 is directly combined with lithium phosphate, is consistent with the main product, and can supplement lithium loss because the calcium and magnesium ions are adsorbed when ion exchange occurs, and the lithium ions in the solution can supplement the lithium loss.
[0030] In step (1), since the lithium phosphate is difficult to dissolve in water, the acid is added only to dissolve the lithium phosphate, and the lithium dihydrogen phosphate is naturally formed after the lithium phosphate is added with the acid. Preferably, the lithium phosphate, water and phosphoric acid are mixed in a mass ratio of 1:(20-40):(1.0-1.5), and the solid is completely dissolved under stirring to obtain a clear lithium dihydrogen phosphate stock solution.
[0031] In a specific embodiment, the mass fraction of the phosphoric acid used is 85wt%, and the lithium phosphate, water and phosphoric acid are mixed in a mass ratio of 1:25:1.2.
[0032] The MIL-101(Al)-NH2 used can be commercially available or self-prepared. Specifically, the MIL-101(Al)-NH2 used in the application is self-prepared, and the preparation method is as follows: The aluminum source, 2-amino terephthalic acid and an organic solvent are mixed, and a dispersion liquid is obtained after ultrasonic treatment, and then a hydrothermal reaction is performed. After the hydrothermal reaction is completed, the solid phase material is collected by centrifugal separation, and the obtained solid phase material is washed and dried to obtain MIL-101(Al)-NH2.
[0033] Furthermore, in the above-mentioned method for preparing MIL-101(Al)-NH2, the aluminum source is one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate. Among them, aluminum nitrate is the most commonly used and most effective aluminum source. Chloride ions in aluminum chloride may be corrosive to equipment and are more difficult to remove from the macropores of MOF, which may affect the material properties. Sulfate ions in aluminum sulfate may participate in coordination. 2-Aminoterephthalic acid directly determines the presence of amino functional groups in the MIL-101(Al)-NH2 framework.
[0034] Preferably, the molar ratio of the aluminum source to 2-aminoterephthalic acid is 1-2:1. A slight excess of aluminum source helps to promote nucleation and improve crystallinity.
[0035] In the above method for preparing MIL-101(Al)-NH2, the organic solvent is... N,N The amount of organic solvent used in the preparation of 2-dimethylformamide is a key parameter affecting crystal quality and reaction success. Therefore, the amount of organic solvent needs to be sufficient to ensure that the Al content in the dispersion obtained after ultrasonic mixing of the aluminum source, 2-aminoterephthalic acid, and organic solvent is within a certain range. 3+ The molar concentration is 0.03-0.12 mol / L, for the following reasons: 1. Ensure sufficient dissolution and diffusion: This concentration range ensures that the metal salt and organic ligands are fully dissolved and provides enough space for molecules to move freely and arrange in an orderly manner, thereby growing MOF crystals with high crystallinity and few defects.
[0036] 2. Optimize crystal growth kinetics: When the concentration is too low (<0.03 mol / L), the reactants are too diluted, making nucleation difficult and the reaction rate slow, which may lead to low yield or incomplete crystal growth. When the concentration is too high (>0.12 mol / L), the reaction is too fast, which easily produces a large number of tiny crystal nuclei, resulting in non-uniform crystal size and even the formation of amorphous impurities that block the pores.
[0037] In one specific implementation, Al 3+ The molar concentration is 0.067 mol / L, and the volume of organic solvent used is 750 mL.
[0038] In the above method for preparing MIL-101(Al)-NH2, the ultrasound is performed at room temperature for 15-20 minutes to ensure that the MIL-101(Al)-NH2 particles are evenly dispersed and do not clump together.
[0039] The room temperature mentioned in this invention refers to 20-25℃.
[0040] In the above method for preparing MIL-101(Al)-NH2, the hydrothermal reaction conditions are: temperature 120-140℃ and time 20-28h.
[0041] In a specific embodiment, the hydrothermal reaction is carried out at a temperature of 130°C for 24 hours.
[0042] Preferably, the hydrothermal reaction is allowed to cool naturally to room temperature (do not rush to remove, rapid cooling can cause crystal defects).
[0043] In a specific embodiment of the present application, the solid phase material is washed with DMF and anhydrous ethanol (first washed with DMF, which serves as a preliminary cleaning after synthesis and ensures the stability of the material structure, and then washed with ethanol, which is equivalent to solvent replacement, replacing the DMF in the pores, and the boiling point of ethanol is low, which is conducive to subsequent drying, and impurities have high solubility in ethanol, which is easy to remove), to remove the solvent molecules adsorbed in the pores and possible residual ligands, and then dried at 120°C and a vacuum degree of -0.1 MPa (relative pressure) for 12 hours.
[0044] In a preferred embodiment, the concentration of MIL-101 (Al)-NH2 in the MOF suspension in step (2) of the present application is 2-10 g / L.
[0045] Further preferably, in step (2), the stirring is carried out at room temperature, and the stirring speed is 200-500 r / min.
[0046] In a specific embodiment, in step (2), the stirring speed is 400 r / min.
[0047] In a preferred embodiment, the specific operation of mixing the lithium dihydrogen phosphate stock solution with the MOF suspension includes: slowly adding the lithium dihydrogen phosphate stock solution to the MOF suspension at a speed of 0.5-2 mL / min, preferably 1 mL / min, at room temperature, and the addition time is 2.5-4 hours, preferably 4 hours, and the pH value of the system is controlled to be accurately maintained in the range of 8.4-8.6 during the addition.
[0048] The reason for using dropwise addition is: 1. Control the nucleation kinetics and promote heterogeneous nucleation; 2. Ensure uniformity of coating, which helps the uniform growth of lithium phosphate on the outer surface of the MOF to form a complete and dense shell; 3. Facilitate accurate control of reaction conditions, and rapid addition can cause a sharp fluctuation in pH value.
[0049] In the above preparation method, the amount of lithium phosphate in step (1) and MIL-101 (Al)-NH2 in step (2) ensures that the mass ratio of the inner core to the shell layer in the functionalized MOF@lithium phosphate core-shell composite material is 1:1-3.
[0050] The dropwise addition time is calculated from the start of dropwise addition of the lithium dihydrogen phosphate stock solution.
[0051] Therefore, in the specific embodiment of the present application, the amount of water added in the lithium phosphate is not only to consider the sufficient dissolution of lithium phosphate with the acid, but also to ensure that the lithium dihydrogen phosphate stock solution can be added at the above-mentioned dropping speed for 2.5-4h to carry out the reaction.
[0052] Preferably, the lithium hydroxide solution with a concentration of 0.1 mol / L can be used to control the pH value of the system, because the lithium hydroxide can not only adjust the pH value, but also appropriately supplement the lithium ion content in the system.
[0053] In a specific embodiment, the solid product obtained by filtering in step (3) is washed with deionized water to remove the physically adsorbed impurity ions, and finally vacuum dried at 80℃ for 6h to obtain the functionalized MOF@lithium phosphate core-shell composite material.
[0054] The second aspect of the present application provides an application of the functionalized MOF@lithium phosphate core-shell composite material prepared by the above preparation method in impurity removal of crude lithium phosphate.
[0055] The third aspect of the present application provides a method for removing impurities from crude lithium phosphate, comprising: S1, mixing crude lithium phosphate, water and sulfuric acid, stirring and filtering to obtain a lithium phosphate acidizing liquid; S2, mixing the lithium phosphate acidizing liquid with the functionalized MOF@lithium phosphate core-shell composite material prepared by the above preparation method, adsorbing at 20-50℃, and then filtering to obtain the impurity-removed lithium phosphate acidizing liquid.
[0056] The crude lithium phosphate in the present application is mainly from salt lake brine and waste lithium battery recycling; the contents of metal calcium, magnesium, aluminum and iron impurities are relatively high, and the purity is about 80%, i.e. crude lithium phosphate.
[0057] Specifically, the specific operation of mixing crude lithium phosphate, water and sulfuric acid includes: mixing crude lithium phosphate and water according to a mass ratio of 1: (2.5-3.0) to prepare slurry, then heating to 45-90℃ and adding sulfuric acid (sulfuric acid plays a role in adjusting pH and dissolving lithium phosphate, or the temperature can be raised after adding sulfuric acid), and the pH value of the system is controlled at 2.5-3.5.
[0058] In a specific embodiment, the mass fraction of the sulfuric acid used is 98%.
[0059] Preferably, the stirring time is 1h.
[0060] In order to achieve better impurity removal effect, the liquid-solid ratio of the lithium phosphate acidizing liquid to the functionalized MOF@lithium phosphate core-shell composite material is controlled at 200mL: 0.4-1.2g.
[0061] Preferably, the temperature of the adsorption is 25-45℃; if the temperature is too high, the lithium phosphate shell layer may be sintered, causing the pore to be blocked and the specific surface area to decrease; the coordination bond of the MOF framework may become unstable at a high temperature in the water phase, with the risk of structure collapse, thereby permanently inactivating, and thus it is more appropriate within the above range.
[0062] Further, the rotation speed of the adsorption is 200 rpm, and the time is 4 h.
[0063] The removal effect of the functionalized MOF@lithium phosphate core-shell composite material on various metal ions is shown in Table 1. Table 1 Removal effect of various metal ions and analysis table The fourth aspect of the present application provides a use of the impurity-removed lithium phosphate acidizing liquid obtained by the above method in the preparation of battery-grade lithium phosphate.
[0064] The present application will be described in detail below through examples. The experimental methods in the following examples are all conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are all commercially available unless otherwise specified.
[0065] Room temperature in the following examples refers to 25℃.
[0066] Example 1 (1) 7.5 g of high-purity lithium phosphate was weighed into a beaker, 187.5 g of deionized water was added, and 85wt% phosphoric acid was slowly added dropwise while stirring until the lithium phosphate was completely dissolved, the mass ratio of lithium phosphate, water and phosphoric acid was 1:25:1.2, forming a clear and transparent lithium dihydrogen phosphate stock solution; (2) Synthesized by solvothermal method, weighed aluminum nitrate nonahydrate (18.76 g, 0.05 mol) and 2-amino terephthalic acid (9.05 g, 0.05 mol) in a polytetrafluoroethylene liner, 750 mL of N,N dimethylformamide was added, ultrasonic was performed at room temperature for about 15 min until the ligand was uniformly dispersed to form a white dispersion, the Al 3+ molar concentration was 0.067 mol / L, the reaction kettle was put into a preheated oven, and hydrothermal reaction was carried out at 130℃ for 24 h, after the hydrothermal reaction was completed, the oven was turned off and naturally cooled to room temperature (do not take out quickly, rapid cooling may cause crystal defects), the solid phase material was collected by centrifugal separation, and the solid phase material was washed by DMF and anhydrous ethanol and dried at 120℃ and a vacuum degree of-0.1 MPa for 12 h to obtain 10.6 g of MIL-101 (Al)-NH2 (MOF), and the reaction yield was 85%; The reaction yield here = (the actual dry weight of MOF obtained / the theoretical yield of MOF) x 100% (actual yield: the mass of the dried MOF powder after washing and activation after the reaction; theoretical yield: estimated based on the number of moles of aluminum salt (Al 3+ ) and the chemical formula of the ideal unit cell of the MOF. For MIL-101 (Al)-NH2, 1 mol of Al 3+ about a certain mass of MOF can be generated, and in this embodiment, according to the 0.05 mol of the input, the theoretical yield is about 12.5 g); 5 g of MIL-101 (Al)-NH2 powder was weighed and added to a three-necked flask together with 1000 ml of deionized water, the temperature was controlled at 25°C, mechanical stirring was started, the stirring speed was 400 r / min, the MOF was uniformly dispersed in the water to form a MOF suspension, the concentration of MIL-101 (Al)-NH2 in the MOF suspension was 5 g / L, and the lithium dihydrogen phosphate stock solution prepared in step (1) was slowly added to the MOF suspension at a rate of 1 mL / min at room temperature, and a dilute lithium hydroxide solution (0.1 M) was used for automatic titration at the same time, so that the pH value of the reaction system was accurately maintained at 8.5±0.1, and the time for dropping was controlled for 4 h, so that lithium phosphate nucleated and grew on the surface of the MOF in a heterogeneous phase to form a complete shell layer, after the dropping was completed, vacuum filtration device was used for filtration, the solid product obtained by filtration was washed with deionized water three times to remove physically adsorbed impurity ions, and finally, vacuum drying was performed at 80°C for 6 h, thereby obtaining 11.5 g of functionalized MOF@lithium phosphate core-shell composite material, which was a core-shell structure, the shell layer was lithium phosphate, the inner core was MIL-101 (Al)-NH2, the mass ratio of the inner core to the shell layer was 1:2.5, and the reaction yield was 92%; The reaction yield here = (the actual dry weight of MOF obtained / the theoretical yield of MOF) x 100% (actual yield: the mass of the dried MOF powder after washing and activation after the reaction; theoretical yield: estimated based on the number of moles of aluminum salt (Al 3+ ) and the chemical formula of the ideal unit cell of the MOF. For MIL-101 (Al)-NH2, 1 mol of Al 3+ about a certain mass of MOF can be generated, and in this embodiment, according to the 0.05 mol of the input, the theoretical yield is about 12.5 g); 5 g of MIL-101 (Al)-NH2 powder was weighed and added to a three-necked flask together with 1000 ml of deionized water, the temperature was controlled at 25°C, mechanical stirring was started, the stirring speed was 400 r / min, the MOF was uniformly dispersed in the water to form a MOF suspension, the concentration of MIL-101 (Al)-NH2 in the MOF suspension was 5 g / L, and the lithium dihydrogen phosphate stock solution prepared in step (1) was slowly added to the MOF suspension at a rate of 1 mL / min at room temperature, and a dilute lithium hydroxide solution (0.1 M) was used for automatic titration at the same time, so that the pH value of the reaction system was accurately maintained at 8.5±0.1, and the time for dropping was controlled for 4 h, so that lithium phosphate nucleated and grew on the surface of the MOF in a heterogeneous phase to form a complete shell layer, after the dropping was completed, vacuum filtration device was used for filtration, the solid product obtained by filtration was washed with deionized water three times to remove physically adsorbed impurity ions, and finally, vacuum drying was performed at 80°C for 6 h, thereby obtaining 11.5 g of functionalized MOF@lithium phosphate core-shell composite material, which was a core-shell structure, the shell layer was lithium phosphate, the inner core was MIL-101 (Al)-NH2, the mass ratio of the inner core to the shell layer was 1:2.5, and the reaction yield was 92%; (3) 200 g of crude lithium phosphate sample was mixed with 500 g of deionized water to prepare a slurry, the slurry was stirred and heated to 60°C, 98% sulfuric acid was added dropwise, the pH value of the system was controlled at 3.0, stirring was performed for 1 h, and then filtration was performed, the filtrate was a lithium phosphate acidification liquid, and the crude lithium phosphate and the lithium phosphate acidification liquid were subjected to ICP to detect the content of metal impurity ions, as shown in Table 2; Table 2 Test results of element contents in crude lithium phosphate and acidification liquid (4) Take 200 mL of acidified solution into a conical flask, add 0.6 g of the functionalized MOF@lithium phosphate core-shell composite material obtained in step (2) into the conical flask, seal, place the conical flask in a constant temperature oscillation shaker, set the temperature to 25°C and the rotation speed to 200 rpm, carry out adsorption for 4 h to ensure that the adsorption reaction reaches equilibrium, after the reaction is completed, use a vacuum filtration device to filter and separate the adsorbed material, and collect the filtrate, which is the impurity-removed lithium phosphate acidified solution.
[0067] Example 2 The method of Example 1 is followed, except that in step (4), the adsorption temperature is 45°C.
[0068] Example 3 The method of Example 1 is followed, except that in step (4), 200 mL of acidified solution is taken into a conical flask, and 1.2 g of the functionalized MOF@lithium phosphate core-shell composite material obtained in step (2) is added into the conical flask.
[0069] Example 4 The method of Example 1 is followed, except that in step (4), 1000 mL of acidified solution is taken into a conical flask, and 3.0 g of the functionalized MOF@lithium phosphate core-shell composite material obtained in step (2) is added into the conical flask.
[0070] Comparative Example 1 The method of Example 1 is followed, except that in step (4), the adsorption temperature is 70°C.
[0071] Comparative Example 2 The method of Example 1 is followed, except that in step (4), an equal amount of MIL-101(Al)-NH2 is used instead of the functionalized MOF@lithium phosphate core-shell composite material.
[0072] Comparative Example 3 Take 100 mL of D401 chelating resin to pack a column and pretreat according to the instructions. Take 200 mL of the impurity-removed acidified solution to remove Ca and Mg by column chromatography, and set the column chromatography rate to 4.0 BV / h. Collect the impurity-removed lithium phosphate acidified solution after column chromatography.
[0073] Comparative Example 4 The method of Example 1 is followed, except that in step (2), an equal amount of commercial NH2-MIL-53(Fe) is used instead of MIL-101(Al)-NH2 to prepare the functionalized MOF@lithium phosphate core-shell composite material, and the same method is used to carry out adsorption with the functionalized MOF@lithium phosphate core-shell composite material.
[0074] Test Example 1 The impurity-removed lithium phosphate acidification solution in Examples 1-4 and Comparative Examples 1-4 was sent for ICP to determine the content of metal impurity ions, and the yield was calculated, and the results are shown in Table 3.
[0075] The yield in the following table is calculated in terms of the absolute amount of lithium: Lithium loss = (V1*c1-V2*c2) / (V1*c1), Yield = (1-lithium loss)*100%; Wherein, V1 is the volume of the acidification solution before impurity removal, mL; V2 is the volume of the acidification solution after impurity removal, mL; c1 is the lithium concentration in the acidification solution before impurity removal, g / L; c2 is the lithium concentration in the acidification solution after impurity removal, g / L. Table 3: Substance content and yield of examples and comparative examples As shown in Table 3: Examples 1-4 can efficiently remove impurity ions while retaining lithium: a. After impurity removal, the Li concentration is maintained at 22.959-24.835 g / L, with little loss; b. The removal effect of Fe, Al, Ca, and Mg is significant (especially Ca and Mg are reduced to very low levels); c. The yield is higher than 97%, and the lithium recovery efficiency is high.
[0076] Comparative examples (especially Comparative Example 4) perform poorly: The Li concentration of Comparative Example 4 is reduced to 16.221 g / L, with a serious loss; The removal effect of Ca and Mg in Comparative Examples 1-3 is obviously not as good as that of the examples; The yield of Comparative Example 4 is only 62.34%.
[0077] As can be seen from the above, the examples (especially Example 1) ensure high lithium yield (98.49%) while achieving deep impurity removal (Ca and Mg removal rate > 93%), and have excellent industrial application potential.
[0078] As can be seen from the above results, the functionalized MOF@lithium phosphate core-shell composite material has a good impurity removal effect on divalent metal ions, especially calcium and magnesium ions, and has no significant effect on soluble monovalent ions such as potassium and sodium.
[0079] It should be understood that parts not elaborated in the specification are all prior art.
[0080] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.
Claims
1. A method for preparing a functionalized MOF@lithium phosphate core-shell composite material, characterized in that, The preparation method comprises the following steps: (1) mixing lithium phosphate, water and phosphoric acid to obtain a lithium dihydrogen phosphate stock solution; (2) mixing MIL-101 (Al)-NH2 and water, and stirring to obtain a MOF suspension; (3) mixing the lithium dihydrogen phosphate stock solution and the MOF suspension, filtering to obtain a solid product, and then washing and drying to obtain a functionalized MOF@lithium phosphate core-shell composite material; The functionalized MOF@lithium phosphate core-shell composite material has a core-shell structure, wherein the shell layer is lithium phosphate, and the inner core is MIL-101 (Al)-NH2; and the mass ratio of the inner core to the shell layer is 1:1-3.
2. The production method according to claim 1, characterized by, In step (1), the lithium phosphate, water and phosphoric acid are mixed at a mass ratio of 1:(20-40):(1.0-1.5).
3. The preparation method according to claim 1, characterized in that, In step (2), the concentration of MIL-101 (Al)-NH2 in the MOF suspension is 2-10 g / L.
4. The method of claim 1, wherein, In step (3), the operation of mixing the lithium dihydrogen phosphate stock solution and the MOF suspension comprises: dropping the lithium dihydrogen phosphate stock solution into the MOF suspension at a speed of 0.5-2 mL / min, and controlling the pH value of the system to be 8.4-8.6 during the dropping process.
5. Application of the functionalized MOF@lithium phosphate core-shell composite material prepared by the preparation method in any one of claims 1-4 in impurity removal of crude lithium phosphate.
6. A method for impurity removal of crude lithium phosphate, characterized by, The preparation method comprises the following steps: S1, mixing crude lithium phosphate, water and sulfuric acid, stirring and filtering to obtain a lithium phosphate acidification solution; S2, mixing the lithium phosphate acidification solution and the functionalized MOF@lithium phosphate core-shell composite material prepared by the preparation method in any one of claims 1-4, adsorbing at 20-50℃, and then filtering to obtain an impurity-removed lithium phosphate acidification solution.
7. The method of claim 6, wherein, The operation of mixing the crude lithium phosphate, water and sulfuric acid comprises: mixing the crude lithium phosphate and water at a mass ratio of 1:(2.5-3.0) to prepare a slurry, then adding sulfuric acid after heating to 45-90℃, and controlling the pH value of the system to be 2.5-3.
5.
8. The method of claim 6, wherein, The liquid-solid ratio of the lithium phosphate acidification solution to the functionalized MOF@lithium phosphate core-shell composite material is controlled to be 200 mL:0.4-1.2 g.
9. The method of claim 6, wherein, The adsorption temperature is 25-45℃.
10. Application of the impurity-removed lithium phosphate acidification solution obtained by the method in any one of claims 6-9 in preparation of battery-grade lithium phosphate.