Method for extracting lithium hydroxide from waste lithium iron phosphate waste material by short process

Abstract

The application belongs to the technical field of waste recycling, and provides a method for extracting lithium hydroxide from waste lithium iron phosphate waste through a short process; the particle size is controlled through multi-stage mechanical crushing and air flow crushing of the waste, and the activity of the waste is improved through calcination treatment; then, a synergistic solvent system is used for leaching experiments, combined with ultrasonic intensification technology, to improve the dissolution efficiency of lithium elements, impurities in the leaching solution are effectively removed through gradient impurity removal and deep purification steps, and high-purity lithium ion leaching solution is obtained; in the subsequent purification stage, modified bipolar membrane electrodialysis technology is introduced to realize efficient separation and concentration of lithium ions, and finally high-purity lithium hydroxide is obtained through separation and crystallization; the process is short and simple to operate, the energy consumption and cost of resource recycling are reduced, and the application has good environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of waste recycling technology and relates to a short-process method for extracting lithium hydroxide from waste lithium iron phosphate. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the application of lithium iron phosphate batteries is becoming increasingly widespread. Due to their excellent cycle life, high safety, low cost, and environmental friendliness, lithium iron phosphate batteries have become one of the most widely used battery types in the new energy vehicle field. However, with the rapid increase in the number of new energy vehicles, the generation of waste lithium iron phosphate batteries is also showing an explosive growth trend.

[0003] Waste lithium iron phosphate batteries mainly consist of positive electrode plates, negative electrode plates, electrolytes, and separators. The positive electrode plates contain a large number of recyclable valuable metal elements, with lithium being the most economically valuable. The recycling of these metal resources not only helps alleviate the pressure on lithium supply but also reduces the environmental damage caused by mineral resource extraction. However, current traditional waste battery recycling methods face many problems: complex processes, high economic costs, and some treatment methods (such as high-temperature incineration or acid-base dissolution) may generate secondary pollution, such as waste gas, wastewater, and solid waste, threatening the ecological environment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a short-process method for extracting lithium hydroxide from waste lithium iron phosphate (LFP) materials. The method involves pre-treating the waste material through crushing, pulverizing, and roasting to activate the lithium components and optimize particle size to improve subsequent leaching efficiency. During the leaching stage, a synergistic solvent system supplemented with ultrasonic enhancement technology is used to ensure complete dissolution of lithium elements. Simultaneously, gradient impurity removal and deep purification steps are employed to remove impurities, preparing a high-purity lithium-ion solution. Subsequently, modified bipolar membrane electrodialysis technology is used to separate and concentrate lithium ions, combined with separation and purification techniques, ultimately yielding high-purity lithium hydroxide to meet the needs of practical production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for short-process extraction of lithium hydroxide from waste lithium iron phosphate, the method comprising:

[0007] S1, the lithium iron phosphate waste is sequentially subjected to jaw crushing, hammer crushing, air jet milling and roasting to obtain pretreated waste;

[0008] S2, the pretreated waste is subjected to leaching experiments, gradient impurity removal and deep purification in sequence to obtain lithium ion leachate;

[0009] S3, the leachate was subjected to bipolar membrane electrodialysis, separation and purification in sequence, and lithium hydroxide was obtained by centrifugation;

[0010] The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane. The preparation method of the modified bipolar membrane is as follows: the bipolar membrane is placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, and then subjected to plasma treatment with a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane is placed in a grafting solution at a reaction temperature of 65±1℃ for 4-5h. After washing and drying, it is soaked in 0.1M NaCl solution for 24h to obtain the modified bipolar membrane.

[0011] The grafting solution contains 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent is an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water.

[0012] Jaw crushers and hammer crushers initially reduce the size of the waste material, using mechanical force to break large pieces into smaller particles and expose more of the internal structure, thereby increasing the specific surface area. Subsequently, air jet milling further refines the particles, improving the uniformity of the waste and enhancing the reaction kinetics of the subsequent leaching stage by increasing the particle specific surface area. During roasting, organic matter and volatile impurities in the lithium iron phosphate waste are thermally decomposed, and the solid structure undergoes corresponding physical and chemical changes. The high temperature disrupts the crystal structure of the material, releasing lithium ions, making it easier to dissolve in subsequent leaching. Furthermore, roasting removes moisture and some impurities, providing a purer pre-treated waste for subsequent impurity removal and deep purification.

[0013] Pre-treated waste is added to the leachate, which consists of choline chloride, ethylene glycol, and ascorbic acid. Choline chloride and ethylene glycol form a eutectic solvent, which not only has excellent dissolving power for lithium but also stabilizes the reaction environment of the leachate. Ascorbic acid, as a reducing agent, can destroy any oxide layer that may form on the surface of the waste, reducing the binding energy of lithium and making it easier for lithium to be released into the solution in ionic form. To further enhance leaching efficiency, ultrasonic enhancement technology is introduced. Ultrasonic waves generate instantaneous high temperature, high pressure, and strong shear force in the liquid through cavitation, destroying the passivation layer on the surface of the waste particles and increasing the activity of the leaching reaction interface. The pulsed ultrasonic mode design avoids solvent overheating or excessive dispersion of waste that may occur with continuous ultrasonication. In addition, the phased addition of ascorbic acid ensures a concentration gradient of the reducing agent, avoiding the inhibitory effect of excessively high local concentrations on the leaching process. Gradient impurity removal is achieved by adjusting the pH of the solution in stages, allowing different impurities to precipitate and separate gradually according to their chemical properties. In the first stage of purification, an alkaline solution is added to adjust the pH to a specific range, causing iron and other metallic impurities in the solution to preferentially precipitate as hydroxides. Stirring promotes precipitation, while plate and frame filtration effectively separates the solid and liquid components, ensuring complete purification. The second stage further optimizes the pH and uses carbonate formation to react with metal ions, generating insoluble carbonate precipitates to remove remaining soluble impurities. Ceramic membrane filtration technology, with its high-precision pore size, not only efficiently separates minute particulate impurities but also ensures maximum lithium ion retention, improving solution purity. Deep purification further removes trace amounts of residual impurity ions from the solution using chelating resin adsorption technology.

[0014] Bipolar membrane electrodialysis selectively separates lithium ions from the leachate. The bipolar membrane consists of a cation exchange membrane, an anion exchange membrane, and an intermediate hydrolysis layer. Under an applied electric field, water molecules in the hydrolysis layer are electrolyzed to generate hydrogen ions and hydroxide ions. The cation exchange membrane allows only lithium ions to pass through, while the anion exchange membrane prevents the migration of anions, thus achieving the separation and enrichment of lithium ions. Modified bipolar membranes grafted with methacryloylethyl sulfobetaine possess excellent lithiumophilic properties, enhancing the interaction between lithium ions and the membrane surface, thereby increasing the migration rate of lithium ions and improving the separation purity.

[0015] As a preferred technical solution of the present invention, in S1, the feed particle size of the jaw crusher is ≤100mm and the discharge particle size is 10-20mm, for example, it can be 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm or 20mm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] In some optional instances, the hammer crusher is configured with a screen aperture of 2 mm and a rotor speed of 2800-3000 rpm, such as 2800 rpm, 2820 rpm, 2840 rpm, 2860 rpm, 2880 rpm, 2900 rpm, 2920 rpm, 2940 rpm, 2960 rpm, 2980 rpm, or 3000 rpm, and the material is crushed to D90 ≤ 2 mm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0017] In some optional examples, the pressure of the air jet mill is 0.75-0.85 MPa, for example, 0.75 MPa, 0.76 MPa, 0.77 MPa, 0.78 MPa, 0.79 MPa, 0.80 MPa, 0.81 MPa, 0.82 MPa, 0.83 MPa, 0.84 MPa, or 0.85 MPa, and the speed of the classifier wheel is 3000-3100 rpm, for example, 3000 rpm, 3010 rpm, 3020 rpm, 3030 rpm, 3040 rpm, 3050 rpm, 3060 rpm, 3070 rpm, 3080 rpm, or 3090 rpm. Alternatively, the feed rate can be 3100 rpm, with a feed rate of 9-10 kg / h, such as 9.0 kg / h, 9.1 kg / h, 9.2 kg / h, 9.3 kg / h, 9.4 kg / h, 9.5 kg / h, 9.6 kg / h, 9.7 kg / h, 9.8 kg / h, 9.9 kg / h, or 10.0 kg / h. The output particle size D50 is 20-40 μm, such as 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, or 40 μm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0018] In some optional examples, the calcination is achieved by heating at a rate of 5°C / min to 500-510°C and holding at that temperature for 3-3.5 hours. For example, the temperature could be 500°C, 501°C, 502°C, 503°C, 504°C, 505°C, 506°C, 507°C, 508°C, 509°C, or 510°C, and the duration could be 3 hours, 3.05 hours, 3.1 hours, 3.15 hours, 3.2 hours, 3.25 hours, 3.3 hours, 3.35 hours, 3.4 hours, or 3.45 hours. Alternatively, after 3.5 hours, the temperature is lowered to 200°C at a rate of 2°C / min and then allowed to cool naturally. The air flow rate is 1.8-2.0 L / min, for example, 1.80 L / min, 1.82 L / min, 1.84 L / min, 1.86 L / min, 1.88 L / min, 1.90 L / min, 1.92 L / min, 1.94 L / min, 1.96 L / min, 1.98 L / min, or 2.00 L / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In a preferred embodiment of the present invention, in step S2, the leaching solution for the leaching experiment is choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:(0.3-0.4), for example, 1:2:(0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or 0.40), at a temperature of 80±2℃, for example, 78.0℃, 78.4℃, 78.8℃, 79.2℃, 79.6℃, 80.0℃, 80.4℃, 80.8℃, 81.2℃, or 81.6℃. Alternatively, at 82.0℃, ascorbic acid is added in three equal-weight intervals, and the final leachate has a transmittance of ≥90% at a wavelength of 450nm, but this is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] In some optional instances, the leaching experiment employs ultrasonic-enhanced leaching, using an ultrasonic transducer at a frequency of 25 kHz ± 0.5%, a power density of 50 W / L ± 5%, in pulse mode, with a working time to intermittent time ratio of 2:1.

[0021] In some optional examples, the leaching experiment temperature is 105±2℃, for example, it can be 103.0℃, 103.4℃, 103.8℃, 104.2℃, 104.6℃, 105.0℃, 105.4℃, 105.8℃, 106.2℃, 106.6℃, or 107.0℃; the stirring rate is 450-500 rpm, for example, 450 rpm, 455 rpm, 460 rpm, 465 rpm, 470 rpm, 475 rpm, 480 rpm, 485 rpm, 490 rpm, 495 rpm, or 500 rpm; and the solid-liquid ratio is 1:(8-9), for example, it can be 1:(8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9). (or 9.0), the time is 2-3 hours, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] In some optional instances, the gradient cleanup is:

[0023] Primary impurity removal: Adjust the pH to 4.8-5.0 using 10wt.% NaOH, stir at 200-250rpm for 30-40min at 60-65℃, then perform plate and frame filtration at a pressure of 0.6-0.8MPa with a filter cloth precision of 5μm. For example, the filter cloth can be 4.8, 4.9, or 5.0. The temperature can be 60.0℃, 60.5℃, 61.0℃, 61.5℃, 62.0℃, 62.5℃, 63.0℃, 63.5℃, 64.0℃, 64.5℃, or 65.0℃, and the temperature can be 200rpm, 205rpm, 210rpm, 215rpm, 220rpm, 225rpm, 230rpm, 235rpm, 240rpm, or 245rpm. Or 250 rpm, for example, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but not limited to the listed values, other unlisted values ​​within this range also apply.

[0024] Secondary impurity removal: Adjust the pH to 8.2-8.4 using 15 wt.% Na2CO3, stir at 50-100 rpm for 60-70 min at room temperature, filter through a ceramic membrane with a pore size of 0.2 μm and a transmembrane pressure difference of 0.2 MPa. For example, the values ​​can be 8.2, 8.3, or 8.4, and the stirring times can be 50 rpm, 55 rpm, 60 rpm, 65 rpm, 70 rpm, 75 rpm, 80 rpm, 85 rpm, 90 rpm, 95 rpm, or 100 rpm, and the stirring times can be 60 min, 61 min, 62 min, 63 min, 64 min, 65 min, 66 min, 67 min, 68 min, 69 min, or 70 min. However, these values ​​are not limited to the listed values ​​and other unlisted values ​​within this range are also applicable.

[0025] In some optional examples, the deep purification adsorption column is a chelating resin with a height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

[0026] In a preferred embodiment of the present invention, in step S3, the bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane, the cation exchange membrane is a CMB membrane with a thickness of 0.15 mm and a sheet resistance ≤ 3 Ω·cm. 2 The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28±1.4 mA / cm². 2 When the temperature is 35±1℃, the flow rate in the concentration chamber is 65L / h, and the pH in the concentration chamber is >13-13.2, the separation and purification steps begin.

[0027] In some optional examples, the evaporation temperature for separation and purification is 85±2℃, the vacuum degree is 3-5Kpa, the stirring speed is 120-150rpm, and the crystallization time is 2-3h. For example, the evaporation temperature can be 83.0℃, 83.4℃, 83.8℃, 84.2℃, 84.6℃, 85.0℃, 85.4℃, 85.8℃, 86.2℃, 86.6℃, or 87.0℃; the vacuum degree can be 3.0KPa, 3.2KPa, 3.4KPa, 3.6KPa, 3.8KPa, 4.0KPa, 4.2KPa, 4.4KPa, 4.6KPa, 4.8KPa, or 5.0KPa; and the vacuum degree can be 120rpm, 123rpm, 126rpm, 129rpm, 132rpm, 135rpm, 138rpm, 141rpm, 144rpm, or 147rpm. Or 150 rpm, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, other unlisted values ​​within this range also apply.

[0028] In some optional examples, the modified bipolar film is prepared by:

[0029] The bipolar membrane was placed in 1M NaOH and washed with alkali at 40℃ for 2 hours, then placed in 0.5M HCl and washed with acid at 25℃ for 1 hour. It was then subjected to plasma treatment at a power of 80W, an O2 flow rate of 20 sccm, and a treatment time of 3 minutes to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane was placed in a grafting solution at a reaction temperature of 65±1℃ for a reaction time of 4-5 hours, for example, 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h, or 5.0h. After washing and drying, it was immersed in 0.1M NaCl solution for 24 hours to obtain a modified bipolar membrane. However, the results are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0030] In some optional examples, the grafting solution contains 1.5 M of methacryloyl ethyl sulfobetaine, 0.15 M of ethylene glycol dimethacrylate, 0.03 M of azobisisobutyronitrile, and is a methanol-water solution with a methanol-to-deionized water volume ratio of 3:1.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Through the synergistic effect of multiple steps such as mechanical crushing, roasting, ultrasonic enhanced leaching and bipolar membrane electrodialysis, the efficient recovery of lithium element in waste lithium iron phosphate waste is achieved, and the lithium extraction rate is improved; (2) Compared with the traditional complex multi-step process, this solution integrates key technologies such as mechanical pretreatment, chemical leaching, electrodialysis separation and crystallization purification through short process design, reducing intermediate steps and reaction links, and reducing operation difficulty and process cost. Attached Figure Description

[0032] Figure 1 This is a photograph of the recovered lithium hydroxide obtained in Example 1 of the present invention. Detailed Implementation

[0033] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0034] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0035] Example 1

[0036] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate materials, the method specifically including the following steps:

[0037] S1 involves sequentially subjecting lithium iron phosphate waste to jaw crushing, hammer crushing, air jet milling, and roasting to obtain pretreated waste.

[0038] The jaw crusher has a feed particle size ≤100mm and an output particle size of 10mm. The hammer crusher is configured with a screen aperture of 2mm, a rotor speed of 2800rpm, and the material is crushed to D90≤2mm. The airflow pulverizer has a pressure of 0.75MPa, a classifier wheel speed of 3000rpm, a feed rate of 9kg / h, and an output particle size D50 of 20μm. The calcination is carried out by heating to 500℃ at 5℃ / min and holding for 3h, followed by cooling to 200℃ at 2℃ / min and then natural cooling, with an air flow rate of 1.8L / min.

[0039] S2, the pretreated waste was subjected to leaching experiments, gradient impurity removal, and deep purification sequentially to obtain a lithium-ion leaching solution. The leaching solution consisted of choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:0.3. Ascorbic acid was added in three equal mass intervals at 78°C. The final leaching solution had a transmittance of ≥90% at a wavelength of 450nm. The leaching experiment employed ultrasonic-enhanced leaching using an ultrasonic transducer at a frequency of 25kHz, a power density of 50W / L, pulse mode, and a working time to intermittent time ratio of 2:1. The leaching experiment was conducted at a temperature of 103°C, a stirring rate of 450rpm, a solid-liquid ratio of 1:8, and a duration of 2 hours. The gradient impurity removal consisted of: First-stage impurity removal using 10wt.%... The pH was adjusted to 4.8 with NaOH, stirred at 200 rpm for 30 min at 60℃, and then filtered by plate and frame filter press at a pressure of 0.6 MPa with a filter cloth precision of 5 μm. For secondary impurity removal: the pH was adjusted to 8.2 with 15 wt.% Na2CO3, stirred at 50 rpm for 60 min at room temperature, and then filtered through a ceramic membrane with a pore size of 0.2 μm and a transmembrane pressure difference of 0.2 MPa. The adsorption column for deep purification was made of chelating resin with a column height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

[0040] S3, the leachate is subjected to bipolar membrane electrodialysis, separation, and purification sequentially, and lithium hydroxide is obtained by centrifugation. The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane, the cation exchange membrane is a CMB membrane with a thickness of 0.15 mm and a sheet resistivity ≤3 Ω·cm. 2The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28 mA / cm². 2 The temperature was 35℃, the flow rate in the concentration chamber was 65L / h, and the pH in the concentration chamber was >13 before proceeding to the separation and purification step. The evaporation temperature for separation and purification was 83℃, the vacuum degree was 3Kpa, the stirring speed was 120rpm, and the crystal growth time was 2h. The bipolar membrane was placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, followed by plasma treatment at a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane was placed in a grafting solution, the reaction temperature was 65℃, and the reaction time was 4h. After washing and drying, it was placed in 0.1M NaOH. The modified bipolar membrane was obtained by soaking in NaCl solution for 24 hours. The grafting solution contained 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent was an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water.

[0041] Figure 1 This is a photograph of the lithium hydroxide recovered in this embodiment.

[0042] Example 2

[0043] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate materials, the method specifically including the following steps:

[0044] S1 involves sequentially subjecting lithium iron phosphate waste to jaw crushing, hammer crushing, air jet milling, and roasting to obtain pretreated waste.

[0045] The jaw crusher has a feed particle size ≤100mm and an output particle size of 20mm. The hammer crusher is configured with a screen aperture of 2mm, a rotor speed of 2850rpm, and the material is crushed to D90≤2mm. The air jet mill has a pressure of 0.85MPa, a classifier wheel speed of 3100rpm, a feed rate of 10kg / h, and an output particle size D50 of 30μm. The calcination is carried out by heating to 503℃ at 5℃ / min and holding for 3.5h, followed by cooling to 200℃ at 2℃ / min and then natural cooling, with an air flow rate of 2.0L / min.

[0046] S2, the pretreated waste was subjected to leaching experiments, gradient impurity removal, and deep purification in sequence to obtain a lithium-ion leaching solution. The leaching solution in the leaching experiment consisted of choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:0.4. Ascorbic acid was added in three equal mass intervals at a temperature of 82°C. The final leaching solution had a transmittance of ≥90% at a wavelength of 450nm. The leaching experiment employed ultrasonic-enhanced leaching using an ultrasonic transducer at a frequency of 25... The leaching experiment was conducted at kHz, with a power density of 50 W / L, pulse mode, and a working time to intermittent time ratio of 2:1. The leaching temperature was 107℃, the stirring rate was 460 rpm, the solid-liquid ratio was 1:8.3, and the time was 2.2 h. The gradient purification process consisted of: first-stage purification: adjusting the pH to 4.9 with 10 wt.% NaOH, stirring at 210 rpm for 34 min at 61℃, followed by plate and frame filtration at a pressure of 0.7 MPa and a filter cloth precision of 5 μm; second-stage purification: adjusting the pH to 8.4 with 15 wt.% Na2CO3, stirring at 60 rpm for 64 min at room temperature, followed by ceramic membrane filtration with a pore size of 0.2 μm and a transmembrane pressure difference of 0.2 MPa. The deep purification adsorption column was a chelating resin with a column height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

[0047] S3, the leachate is subjected to bipolar membrane electrodialysis, separation, and purification sequentially, and lithium hydroxide is obtained by centrifugation. The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane, the cation exchange membrane is a CMB membrane with a thickness of 0.15 mm and a sheet resistivity ≤3 Ω·cm. 2 The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28 mA / cm². 2 The temperature was 34℃, the flow rate in the concentration chamber was 65L / h, and the pH in the concentration chamber was >13.2 before proceeding to the separation and purification step. The evaporation temperature for separation and purification was 85℃, the vacuum degree was 5Kpa, the stirring speed was 130rpm, and the crystal growth time was 3h. The bipolar membrane was placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, followed by plasma treatment at a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane was placed in a grafting solution, the reaction temperature was 64℃, and the reaction time was 5h. After washing and drying, it was placed in 0.1M NaOH. The modified bipolar membrane was obtained by soaking in NaCl solution for 24 hours. The grafting solution contained 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent was an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water.

[0048] Example 3

[0049] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate materials, the method specifically including the following steps:

[0050] S1 involves sequentially subjecting lithium iron phosphate waste to jaw crushing, hammer crushing, air jet milling, and roasting to obtain pretreated waste.

[0051] The jaw crusher has a feed particle size ≤100mm and an output particle size of 15mm. The hammer crusher is configured with a screen aperture of 2mm, a rotor speed of 3000rpm, and the material is crushed to D90≤2mm. The air jet mill has a pressure of 0.80MPa, a classifying wheel speed of 3020rpm, a feed rate of 9.3kg / h, and an output particle size D50 of 40μm. The calcination is carried out by heating to 510℃ at 5℃ / min and holding for 3.1h, followed by cooling to 200℃ at 2℃ / min and then natural cooling, with an air flow rate of 1.9L / min.

[0052] S2, the pretreated waste was subjected to leaching experiments, gradient impurity removal, and deep purification sequentially to obtain a lithium-ion leachate. The leachate in the leaching experiment consisted of choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:0.33. Ascorbic acid was added in three equal-mass intervals at 80°C. The final leachate had a transmittance of ≥90% at a wavelength of 450nm. The leaching experiment employed ultrasonic-enhanced leaching using an ultrasonic transducer at a frequency of [frequency missing]. The leaching experiment was conducted at 25 kHz, with a power density of 50 W / L, pulsed mode, and a working time to intermittent time ratio of 2:1. The temperature was 105 °C, the stirring rate was 500 rpm, the solid-liquid ratio was 1:9, and the time was 3 h. The gradient purification process consisted of: first-stage purification: adjusting the pH to 5.0 with 10 wt.% NaOH, stirring at 250 rpm for 40 min at 65 °C, followed by plate and frame filtration at a pressure of 0.8 MPa and a filter cloth precision of 5 μm; second-stage purification: adjusting the pH to 8.3 with 15 wt.% Na2CO3, stirring at 100 rpm for 70 min at room temperature, followed by ceramic membrane filtration with a pore size of 0.2 μm and a transmembrane pressure difference of 0.2 MPa; the deep purification adsorption column was a chelating resin with a column height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

[0053] S3, the leachate is subjected to bipolar membrane electrodialysis, separation, and purification sequentially, and lithium hydroxide is obtained by centrifugation. The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane, the cation exchange membrane is a CMB membrane with a thickness of 0.15 mm and a sheet resistivity ≤3 Ω·cm. 2 The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28 mA / cm². 2The temperature was 36℃, the flow rate in the concentration chamber was 65L / h, and the pH in the concentration chamber was >13.1 before proceeding to the separation and purification step. The evaporation temperature for separation and purification was 87℃, the vacuum degree was 4Kpa, the stirring speed was 150rpm, and the crystal growth time was 2.3h. The bipolar membrane was placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, followed by plasma treatment at a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane was placed in a grafting solution, the reaction temperature was 66℃, and the reaction time was 4.3h. After washing and drying, it was placed in 0.1M NaOH. The modified bipolar membrane was obtained by soaking in NaCl solution for 24 hours. The grafting solution contained 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent was an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water.

[0054] Example 4

[0055] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate materials, the method specifically including the following steps:

[0056] S1 involves sequentially subjecting lithium iron phosphate waste to jaw crushing, hammer crushing, air jet milling, and roasting to obtain pretreated waste.

[0057] The jaw crusher has a feed particle size ≤100mm and an output particle size of 18mm. The hammer crusher is configured with a screen aperture of 2mm, a rotor speed of 2900rpm, and the material is crushed to D90≤2mm. The airflow pulverizer has a pressure of 0.78MPa, a classifier wheel speed of 3080rpm, a feed rate of 9.7kg / h, and an output particle size D50 of 35μm. The calcination is carried out by heating to 507℃ at 5℃ / min and holding for 3.3h, followed by cooling to 200℃ at 2℃ / min and then natural cooling, with an air flow rate of 1.8L / min.

[0058] S2, the pretreated waste was subjected to leaching experiments, gradient purification, and deep purification sequentially to obtain a lithium-ion leachate. The leachate in the leaching experiment consisted of choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:0.38. Ascorbic acid was added in three equal mass intervals at a temperature of 79°C. The final leachate had a transmittance of ≥90% at a wavelength of 450nm. The leaching experiment employed ultrasonic-enhanced leaching using an ultrasonic transducer at a frequency of 25kHz, a power density of 50W / L, pulse mode, and a working time to intermittent time ratio of 2:1. The leaching temperature was 106°C, the stirring rate was 480rpm, the solid-liquid ratio was 1:8.6, and the time was 2.7h. The gradient purification consisted of: First-stage purification: adjusting the pH to 4.8 using 10wt.% NaOH. The filter was stirred at 240 rpm for 37 min at 64℃, then plate and frame filter press at a pressure of 0.65 MPa and a filter cloth precision of 5 μm. For secondary impurity removal, the pH was adjusted to 8.2 using 15 wt.% Na2CO3, stirred at 80 rpm for 68 min at room temperature, and then filtered through a ceramic membrane with a pore size of 0.2 μm and a transmembrane pressure difference of 0.2 MPa. The deep purification adsorption column was made of chelating resin with a height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

[0059] S3, the leachate is subjected to bipolar membrane electrodialysis, separation, and purification sequentially, and lithium hydroxide is obtained by centrifugation. The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane, the cation exchange membrane is a CMB membrane with a thickness of 0.15 mm and a sheet resistivity ≤3 Ω·cm. 2 The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28 mA / cm². 2 The temperature was 35℃, the flow rate in the concentration chamber was 65L / h, and the pH in the concentration chamber was >13.2 before proceeding to the separation and purification step. The evaporation temperature for separation and purification was 86℃, the vacuum degree was 5Kpa, the stirring speed was 140rpm, and the crystal growth time was 2.7h. The bipolar membrane was placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, followed by plasma treatment at a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane was placed in a grafting solution at a reaction temperature of 65℃ for 4.8h. After washing and drying, it was placed in 0.1M HCl solution. The modified bipolar membrane was obtained by soaking in NaCl solution for 24 hours. The grafting solution contained 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent was an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water.

[0060] Comparative Example 1

[0061] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate. The difference between this method and Example 1 is that the bipolar membrane used in S3 is not modified, while other process parameters and operating conditions are exactly the same as in Example 1.

[0062] Comparative Example 2

[0063] This embodiment provides a short-process method for extracting lithium hydroxide from waste lithium iron phosphate. The difference between this method and Example 1 is that the amount of ascorbic acid in S2 is 0, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0064] Determination of lithium content in lithium iron phosphate waste: Take 500±20mg of waste, add a mixture of nitric acid and hydrochloric acid (volume ratio 3:1) to completely dissolve it, take part of the supernatant and make up to 100mL to obtain the sample to be tested, use ICP-MS to detect and measure the concentration of lithium in the solution, and the lithium content in the waste is found to be 3.2wt.%.

[0065] Purity determination method: Dissolve 500±20mg of lithium hydroxide in deionized water to obtain a lithium hydroxide solution. Add excess sodium carbonate solution to the lithium hydroxide solution and stir thoroughly to form lithium carbonate precipitate. After filtration and thorough drying, weigh the precipitate. The purity calculation formula is: Purity (%) = (mass of lithium carbonate * 6.94 / 73.89) / mass of lithium hydroxide * 100%, where 6.94 represents the molar mass of lithium and 73.89 represents the molar mass of lithium carbonate.

[0066] Recovery rate determination method: final recovered lithium mass = lithium hydroxide mass * purity; recovery rate = final recovered lithium mass / initial lithium mass in waste. Test results are shown in Table 1.

[0067] Table 1. Test results of the short-process extraction method for lithium hydroxide from waste lithium iron phosphate materials in Examples 1-4 and Comparative Examples 1-2

[0068] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 purity(%) 99.5 99.5 99.6 99.5 93.7 94.2 Recovery rate (%) 93.4 92.7 93.6 92.9 87.8 88.3

[0069] As shown in Table 1, compared to Example 1, the purity and recovery rate of Comparative Example 1 decreased; the purity and recovery rate of Comparative Example 2 also decreased. Comparative Example 1 used an unmodified bipolar membrane, which has poor selectivity for other ions. These impurity ions may compete with lithium ions for migration, thereby reducing the lithium ion enrichment efficiency. In Comparative Example 2, the amount of ascorbic acid was 0. Ascorbic acid is a strong reducing agent that can reduce iron impurities in waste lithium iron phosphate to a lower oxidation state. Lower oxidation state iron has lower solubility; therefore, ascorbic acid can effectively inhibit the dissolution of iron impurities. Without the addition of ascorbic acid, iron impurities may dissolve as Fe. 3+When lithium dissolves into the leaching solution, the leaching efficiency of lithium is significantly reduced, leading to a decrease in recovery rate and purity.

[0070] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for short-process extraction of lithium hydroxide from waste lithium iron phosphate, characterized in that, The method includes: S1, the lithium iron phosphate waste is sequentially subjected to jaw crushing, hammer crushing, air jet milling and roasting to obtain pretreated waste; S2, the pretreated waste is subjected to leaching experiments, gradient impurity removal and deep purification in sequence to obtain lithium ion leachate; S3, the leachate was subjected to bipolar membrane electrodialysis, separation and purification in sequence, and lithium hydroxide was obtained by centrifugation; The bipolar membrane used in the bipolar membrane electrodialysis is a modified bipolar membrane. The preparation method of the modified bipolar membrane is as follows: the bipolar membrane is placed in 1M NaOH and washed with alkali at 40℃ for 2h, then placed in 0.5M HCl and washed with acid at 25℃ for 1h, and then subjected to plasma treatment with a power of 80W, an O2 flow rate of 20sccm, and a treatment time of 3min to obtain a pretreated bipolar membrane. Under a nitrogen atmosphere, the pretreated bipolar membrane is placed in a grafting solution at a reaction temperature of 65±1℃ for 4-5h. After washing and drying, it is soaked in 0.1M NaCl solution for 24h to obtain the modified bipolar membrane. The grafting solution contains 1.5 M methacryloyl ethyl sulfobetaine, 0.15 M ethylene glycol dimethacrylate, and 0.03 M azobisisobutyronitrile. The solvent is an aqueous methanol solution with a volume ratio of 3:1 between methanol and deionized water. The leaching solution used in the leaching experiment consisted of choline chloride, ethylene glycol, and ascorbic acid, with a molar ratio of choline chloride, ethylene glycol, and ascorbic acid of 1:2:(0.3-0.4). Ascorbic acid was added in three equal-mass intervals at a temperature of 80±2℃. The final leaching solution exhibited a transmittance of ≥90% at a wavelength of 450nm. The leaching experiment was conducted using ultrasonic-enhanced leaching with an ultrasonic transducer at a frequency of 25kHz±0.5%, a power density of 50W / L±5%, in pulse mode, and with a working time to intermittent time ratio of 2:

1. The leaching experiment was conducted at a temperature of 105±2℃, a stirring rate of 450-500 rpm, a solid-liquid ratio of 1:(8-9), and a time of 2-3 h. The gradient cleanup is as follows: Primary impurity removal: Adjust the pH to 4.8-5.0 with 10wt.% NaOH, stir at 200-250rpm for 30-40min at 60-65℃, filter by plate and frame press at a pressure of 0.6-0.8MPa and a filter cloth precision of 5μm; Secondary impurity removal: Adjust the pH to 8.2-8.4 using 15 wt.% Na2CO3, stir at 50-100 rpm for 60-70 min at room temperature, filter with ceramic membrane (pore size 0.2 μm, transmembrane pressure difference 0.2 MPa); The deep purification adsorption column is a chelating resin with a height-to-diameter ratio of 5:1 and a flow rate of 2 BV / h.

2. The method for short-process extraction of lithium hydroxide from waste lithium iron phosphate as described in claim 1, characterized in that, In S1: The jaw crusher has a feed particle size of ≤100mm and a discharge particle size of 10-20mm. The hammer crusher is configured with a screen aperture of 2mm, a rotor speed of 2800-3000rpm, and the material is crushed to D90≤2mm.

3. The method for short-process extraction of lithium hydroxide from waste lithium iron phosphate as described in claim 1, characterized in that, In S1: The pressure of the airflow pulverizer is 0.75-0.85 MPa, the speed of the classifier wheel is 3000-3100 rpm, the feed rate is 9-10 kg / h, and the output particle size D50 is 20-40 μm. The calcination process involves heating to 500-510℃ at a rate of 5℃ / min and holding for 3-3.5 hours, followed by cooling to 200℃ at a rate of 2℃ / min and then allowing it to cool naturally. The air flow rate is 1.8-2.0L / min.

4. The method for short-process extraction of lithium hydroxide from waste lithium iron phosphate as described in claim 1, characterized in that, In S3: The cation exchange membrane used in the bipolar membrane electrodialysis is a CMB membrane with a thickness of 0.15 mm and a sheet resistivity ≤ 3 Ω·cm. 2 The anode is ruthenium-iridium-titanium, the cathode is stainless steel, the electrode chamber solution is 0.5M H₂SO₄, and the current density is 28±1.4 mA / cm². 2 When the temperature is 35±1℃, the flow rate in the concentration chamber is 65L / h, and the pH in the concentration chamber is >13-13.2, the separation and purification steps begin.

5. The method for short-process extraction of lithium hydroxide from waste lithium iron phosphate as described in claim 1, characterized in that, In S3: The evaporation temperature for separation and purification is 85±2℃, the vacuum degree is 3-5Kpa, the stirring speed is 120-150rpm, and the crystal growth time is 2-3h.

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