Process and system for the preparation of battery-grade lithium fluoride from industrial lithium carbonate

Abstract

A process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate, comprising introducing CO2 gas into an industrial lithium carbonate slurry to convert it into a soluble lithium bicarbonate solution; removing metal ion impurities from the lithium bicarbonate solution using ion exchange resin; mixing the purified lithium bicarbonate solution with HF raw material to obtain lithium fluoride slurry; using the clear liquid produced by the next stage of membrane washing as washing water for the previous stage of membrane washing to continuously wash the lithium fluoride slurry between two adjacent stages of membrane washing; sequentially performing pyrolysis reaction and membrane filtration on the lithium-containing waste liquid produced during the process to obtain lithium carbonate slurry which is recycled to the carbonization reaction process, and membrane filtration mother liquor which is added with a precipitating agent to recover lithium; and drying the washed lithium fluoride slurry to obtain battery-grade lithium fluoride product. The present application realizes continuous reaction and continuous membrane washing of lithium fluoride, improves the uniformity of lithium fluoride product, reduces the impurity content of the product, and improves the quality of the product.

Description

Technical Field

[0001] This invention belongs to the field of lithium fluoride preparation technology, specifically relating to a process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate. Background Technology

[0002] With the rapid development of battery technology, green energy technologies, represented by lithium batteries, are constantly changing people's daily lives. Lithium hexafluorophosphate is the most important electrolyte lithium salt used in lithium-ion batteries, and battery-grade lithium fluoride is a key raw material for producing the electrolyte lithium hexafluorophosphate. During the lithium fluoride production process, metal ions and impurities severely affect the product quality of battery-grade lithium fluoride, thus impacting the performance of lithium batteries.

[0003] Currently, the main methods for producing battery-grade lithium fluoride include the direct method, the extraction method, and the metathesis method. The direct method prepares lithium fluoride by reacting high-purity lithium carbonate with hydrofluoric acid solution. This method has excessively high requirements for the quality of the raw material lithium carbonate, which must reach electronic grade, and the production cost is also high. Other methods cannot directly obtain high-purity lithium fluoride. Chinese patent CN114538481A discloses a process for preparing lithium fluoride from industrial-grade lithium carbonate. This method involves sequentially performing slurry carbonization, two precision filtrations, resin impurity removal, decarbonization pyrolysis, three stirring washes, and high-purity carbonization on industrial-grade lithium carbonate to obtain a refined lithium bicarbonate solution, which is then reacted with hydrofluoric acid. The product is filtered and washed three times to obtain battery-grade lithium fluoride. This method is complex, has a long process, involves two carbonizations and multiple washings, has a high estimated cost, high water consumption, and a low lithium yield. The obtained lithium fluoride product only meets the national standard for second-grade lithium fluoride. Summary of the Invention

[0004] To address the above-mentioned technical problems, the present invention aims to provide a process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate. This process enables continuous reaction and continuous membrane washing of lithium fluoride, improves the uniformity of lithium fluoride products, reduces the impurity content of the products, improves the quality of the products, and ensures that the purity of lithium fluoride products produced on a large scale is 99.99% or higher.

[0005] To achieve the above objectives, the present invention provides a process for preparing battery-grade lithium fluoride from industrial lithium carbonate, comprising:

[0006] Carbonization reaction process: CO2 gas is introduced into a lithium carbonate slurry made by mixing industrial lithium carbonate with pure water to carry out the carbonization reaction. After a certain reaction time, the mixture is filtered through a membrane. The clear liquid obtained by membrane filtration is a lithium bicarbonate solution. If the concentrated liquid obtained by filtration contains unreacted lithium carbonate, it is returned to continue the carbonization reaction.

[0007] Resin impurity removal process: The membrane filtration solution obtained during the carbonization reaction is passed through an ion exchange resin to remove metal ion impurities from the lithium bicarbonate solution, resulting in a purified lithium bicarbonate solution.

[0008] Synthesis reaction process: The lithium bicarbonate purification solution is mixed with HF solution or HF gas to carry out the synthesis reaction. The resulting reaction mixture is filtered through a membrane, and the clear liquid is returned to continue to participate in the synthesis reaction. The concentrated liquid obtained by membrane filtration is lithium fluoride slurry.

[0009] Multi-stage membrane washing process: Between two adjacent membrane washing stages, the supernatant produced by the next stage membrane washing is used as the washing water for the previous stage membrane washing to continuously wash the lithium fluoride slurry.

[0010] Lithium recovery process: The lithium-containing waste liquid generated during the process is subjected to pyrolysis and membrane filtration in sequence. The resulting lithium carbonate slurry is recycled for the carbonation reaction process. The membrane filtration mother liquor is added with a precipitant for lithium recovery.

[0011] Post-processing: The washed and qualified lithium fluoride slurry is dried to obtain battery-grade lithium fluoride products.

[0012] In some technical solutions, the multi-stage membrane washing process further includes:

[0013] Segmented processing steps: The clarified solution generated from the primary membrane washing is processed in segments, with the initial clarified solution being returned to the synthesis reaction process and the later clarified solution being transported to the lithium recovery process; and / or,

[0014] Wash water treatment steps: The post-washing clarified liquid generated from the primary membrane washing is subjected to membrane separation treatment through nanofiltration membrane and / or reverse osmosis membrane. The clarified liquid obtained from membrane separation is reused as wash water makeup water, and the concentrated liquid obtained from membrane separation is used for subsequent lithium recovery.

[0015] Some technical solutions also include a reagent removal process before the carbonization reaction process. The reagent removal process specifically involves: mixing industrial-grade lithium carbonate with pure water to prepare a lithium carbonate slurry, adding a metal complexing agent to cause heavy metal ions in the lithium carbonate slurry to form complexes and transfer to the solution, removing them by membrane filtration, and then allowing the membrane-filtered slurry to enter the carbonization reaction process and the clear liquid from the membrane filtration to enter the lithium recovery process.

[0016] In some technical solutions, the carbonization reaction temperature is 20–40°C, and the reaction time is 0.5–4 hours; and / or,

[0017] The synthesis reaction is carried out at a temperature of 20–85°C for a reaction time of 1–6 h; and / or,

[0018] The temperature of the washing water is 60–90°C; and / or,

[0019] The temperature of the pyrolysis reaction is 50–100°C.

[0020] According to another aspect of the present invention, the present invention further provides a system for preparing battery-grade lithium fluoride from industrial lithium carbonate, comprising:

[0021] A raw material purification unit for the purification of industrial lithium carbonate includes a carbonation reactor, a second membrane filtration device, and an ion exchange resin tank. The carbonation reactor is used to convert lithium carbonate slurry into a soluble lithium bicarbonate solution. The outlet of the carbonation reactor is connected to the second membrane filtration device. The concentrated liquid outlet of the second membrane filtration device is connected back to the carbonation reactor, and the clear liquid outlet is connected to the ion exchange resin tank to remove metal ion impurities from the lithium bicarbonate solution.

[0022] The synthesis reaction unit is equipped with a synthesis reactor and a third membrane filtration device connected in sequence. The synthesis reactor is connected to the purified liquid outlet of the ion exchange resin tank and is used to mix lithium bicarbonate purified liquid with HF solution or HF gas to prepare lithium fluoride. The clear liquid outlet of the third membrane filtration device is connected back to the synthesis reactor.

[0023] A multi-stage membrane washing unit is connected to the concentrate outlet of the third membrane filtration device and includes at least two sets of membrane washing devices arranged in series. Between two adjacent sets of membrane washing devices, the clear liquid outlet of the next stage membrane washing device is connected back to the washing water inlet of the previous stage membrane washing device.

[0024] The lithium recovery unit includes a pyrolysis device and a fourth membrane filtration device connected in sequence. The pyrolysis device is equipped with a lithium-containing waste liquid inlet for heating and precipitating lithium carbonate. The concentrated liquid outlet of the fourth membrane filtration device is connected back to the carbonization reactor, and the clear liquid outlet is connected to the lithium recovery unit.

[0025] The post-processing unit is connected to the concentrate outlet of the final membrane washing unit and is used to dry the washed qualified lithium fluoride slurry to obtain battery-grade lithium fluoride products.

[0026] In some technical solutions, the clarified liquid outlet of the primary membrane scrubbing unit is connected to two parallel streams, one of which is connected back to the synthesis reactor and the other is connected to the lithium recovery unit.

[0027] In some technical solutions, the multi-stage membrane washing unit further includes a membrane separation device connected in series to the pipeline between the first-stage membrane washing device and the lithium recovery unit. The clear liquid outlet of the membrane separation device is connected back to the water replenishment point on the pipeline between adjacent membrane washing devices, and the concentrated liquid outlet is connected to the pyrolysis device.

[0028] In some technical solutions, the multi-stage membrane washing unit is further provided with a buffer tank, which is located on the pipeline between the first-stage membrane washing device and the concentrated liquid outlet of the third membrane filtration device and / or on the pipeline between two adjacent membrane washing devices, for buffering lithium fluoride slurry and mixing lithium fluoride slurry with washing water.

[0029] In some technical solutions, the raw material purification unit further includes a reagent removal tank and a first membrane filtration device connected in sequence. The reagent removal tank is used for industrial-grade lithium carbonate slurry preparation and is equipped with a reagent inlet to allow heavy metal ions in the lithium carbonate slurry to form complexes and transfer to the solution. The concentrated liquid outlet of the first membrane filtration device is connected to the lithium carbonate slurry inlet of the carbonation reactor, and the clear liquid outlet is connected to the lithium recovery unit.

[0030] In some technical solutions, the synthesis reactor is connected to a purified liquid inlet pipe and an HF pipe. A nozzle or atomizer is installed at one end of the purified liquid inlet pipe that extends into the HF pipe. The gas-liquid input direction of the HF pipe is opposite to the input direction of the purified liquid; and / or,

[0031] A first demister is installed at the top of the carbonization reactor, and a second demister is installed at the top of the synthesis reactor. Both the first and second demisters are connected to a CO2 recovery device.

[0032] The present invention, by employing the above technical solution, has at least the following beneficial effects:

[0033] 1. This invention proposes a process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate. Through multi-stage membrane series connection and inter-stage water replenishment, continuous membrane washing is achieved. The wash water from the first-stage membrane washing is treated in stages. The initial wash water contains a relatively large amount of unreacted lithium bicarbonate, and this portion is directly returned to the lithium fluoride reactor to participate in the reaction. The later wash water contains relatively less unreacted lithium bicarbonate, and this portion is treated by membrane separation. The clarified liquid is reused as makeup water for membrane washing, and the concentrated liquid is used for lithium recovery through pyrolysis and the addition of phosphoric acid. The entire process achieves a high lithium yield with virtually no loss, a comprehensive yield of over 96%, and minimal wastewater discharge.

[0034] 2. The present invention proposes a process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate. Before the carbonization reaction, a reagent is used to remove impurities, which reduces the content of metal ion impurities in the lithium bicarbonate solution entering the ion exchange resin, improves the service life of the ion exchange resin, and reduces the production cost of lithium fluoride.

[0035] 3. The present invention proposes a system for preparing battery-grade lithium fluoride from industrial lithium carbonate. In the synthesis reactor, lithium bicarbonate purification solution is added to the HF pipeline by spraying or atomizing through a nozzle, and comes into countercurrent contact with HF. This can ensure uniform feeding, avoid excessively high local concentrations, and improve reaction efficiency.

[0036] 4. The present invention proposes a process and system for preparing battery-grade lithium fluoride from industrial lithium carbonate, which can realize continuous reaction and continuous membrane washing of lithium fluoride, improve the uniformity of lithium fluoride products, reduce the impurity content of products, improve product quality, and ensure that the purity of lithium fluoride products produced on a large scale is 99.99% or higher. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings and their markings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the process flow and system for preparing battery-grade lithium fluoride from industrial lithium carbonate according to an embodiment of the present invention.

[0039] The meanings of the symbols marked in the figure are as follows:

[0040] 100—Drug removal tank; 101—First membrane filtration device;

[0041] 200—Carbonization reactor; 201—First demister; 202—Second membrane filtration device;

[0042] 300—Ion exchange resin tank;

[0043] 400—Synthesis reactor, 401—HF pipeline, 402—Nozzle, 403—Second demister, 404—Third membrane filtration device;

[0044] 500—Multi-stage membrane washing unit; 501—First-stage membrane washing device; 502—Second-stage membrane washing device; 503—Buffer tank; 600—Membrane separation device.

[0045] 700—Pyrolysis unit; 701—Fourth membrane filtration unit; 800—Lithium recovery unit;

[0046] 900—CO2 recovery unit. Detailed Implementation

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0048] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0049] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0050] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0051] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0052] According to one aspect of the present invention, a process for preparing battery-grade lithium fluoride from industrial lithium carbonate is provided; please refer to [reference needed]. Figure 1 The specific process is shown below:

[0053] Chemical impurity removal process: Industrial-grade lithium carbonate is mixed with pure water to form a lithium carbonate slurry. Chemicals are added to remove metal cation impurities. The chemicals are metal complexing agents, including NTA and EDTA, which can form complexes with heavy metal ions in the lithium carbonate slurry and transfer them to the solution for membrane filtration. The membrane-filtered slurry enters the carbonation reactor 200. The clear liquid from the membrane filtration contains a small amount of dissolved lithium carbonate and enters the lithium recovery process. The reaction temperature for chemical impurity removal is 60-90℃.

[0054] Carbonization reaction process: The slurry produced by membrane filtration during the reagent removal process is added to carbonization reactor 200, water is added for pulping, and CO2 gas is introduced to carry out the carbonization reaction. After a certain reaction time, membrane filtration is performed. The clear liquid obtained from membrane filtration is a lithium bicarbonate solution. The concentrated liquid obtained from filtration contains unreacted lithium carbonate, so it is returned to carbonization reactor 200 to continue the reaction. CO2 gas can be introduced through the membrane or coil at the bottom of carbonization reactor 200. The temperature of the carbonization reaction is 20-40℃, and the reaction time is 0.5-4h.

[0055] Resin impurity removal process: The membrane filtration solution obtained during the carbonization reaction is passed into the ion exchange resin tank 300 to further remove metal ion impurities in the lithium bicarbonate solution, resulting in a purified lithium bicarbonate solution. The rinsing water from the ion exchange resin tank 300 is directly reused in the reagent impurity removal tank 100.

[0056] Synthesis reaction process: Lithium bicarbonate purification solution is sprayed or atomized into synthesis reactor 400 through nozzle 402, and then HF solution or HF gas is added to carry out the synthesis reaction. The two raw materials are in countercurrent contact to increase the contact area and improve the reaction efficiency. The resulting reaction mixture is filtered through a membrane, and the clear liquid is returned to synthesis reactor 400 to continue to participate in the reaction. The slurry obtained from membrane filtration is washed by the membrane. The temperature of the synthesis reaction is 20-85℃, and the reaction time is 1-6h.

[0057] Multi-stage membrane washing process: The lithium fluoride slurry produced by membrane filtration during the synthesis reaction is continuously washed with washing water at a temperature of 60–90°C. Continuous membrane washing is achieved through multi-stage membrane washing in series and inter-stage makeup water. The clarified liquid produced by the first-stage membrane washing is processed in stages. The initial clarified liquid, containing a relatively large amount of unreacted lithium bicarbonate, is returned to the synthesis reactor 400 to continue the reaction. The later clarified liquid is treated by membrane separation through nanofiltration and / or reverse osmosis membranes. The clarified liquid obtained from membrane separation is reused as makeup water, and the concentrated liquid obtained from membrane separation is used for subsequent lithium recovery. The clarified liquid produced by the subsequent membrane washing in the multi-stage membrane washing process is used as the washing water for the previous membrane washing, thus achieving continuous washing of lithium fluoride.

[0058] Lithium recovery process: The clear liquid from membrane filtration during the reagent removal process and the concentrated liquid obtained from membrane separation during multi-stage membrane washing are combined and subjected to pyrolysis reaction at a temperature of 50-100℃. The solubility of lithium carbonate dissolved in the mixture decreases with increasing temperature, resulting in the precipitation of some lithium carbonate precipitate. In addition, lithium bicarbonate in the mixture is converted into lithium carbonate precipitate. The lithium carbonate slurry obtained by membrane filtration is returned to carbonation reactor 200 for reuse. Phosphoric acid is added to the obtained membrane filtration mother liquor for reaction, and lithium phosphate precipitate is obtained by filtration for lithium recovery.

[0059] Post-processing: The qualified lithium fluoride slurry from the multi-stage membrane washing process is dried to obtain battery-grade lithium fluoride products.

[0060] According to another aspect of the present invention, a system for preparing battery-grade lithium fluoride from industrial lithium carbonate is further provided, see reference. Figure 1 The system specifically includes a raw material purification unit, a synthesis reaction unit, a multi-stage membrane washing unit 500, a lithium recovery unit, and a post-processing unit.

[0061] The aforementioned raw material purification unit is used for the purification of industrial lithium carbonate. It includes a carbonation reactor 200, a second membrane filter device 202, and an ion exchange resin tank 300. The carbonation reactor 200 is equipped with a lithium carbonate slurry inlet and a CO2 gas inlet. An agitator is installed inside the carbonation reactor 200 for adding water to the lithium carbonate slurry to carry out the carbonation reaction. The outlet of the carbonation reactor 200 is connected to the second membrane filter device 202 through a carbonation pump. The concentrated liquid outlet of the second membrane filter device 202 is connected back to the carbonation reactor 200, and the clear liquid outlet is connected to the ion exchange resin tank 300 to remove metal ion impurities from the lithium bicarbonate solution.

[0062] In some preferred embodiments, the above-mentioned raw material purification unit further includes a reagent removal tank 100 and a first membrane filtration device 101 connected in sequence. The reagent removal tank 100 is used for industrial-grade lithium carbonate slurry preparation, and the reagent removal tank 100 is provided with a reagent inlet to allow heavy metal ions in the lithium carbonate slurry to form complexes and transfer to the solution. The concentrated liquid outlet of the first membrane filtration device 101 is connected to the lithium carbonate slurry inlet of the carbonation reactor 200, and the clear liquid outlet is connected to the lithium recovery unit.

[0063] This invention performs reagent purification before the carbonization reaction, which reduces the content of metal ion impurities in the lithium bicarbonate solution entering the ion exchange resin, improves the service life of the ion exchange resin, and reduces the production cost of lithium fluoride.

[0064] The above-mentioned synthesis reaction unit is equipped with a synthesis reactor 400 and a third membrane filter 404 connected in sequence. The synthesis reactor 400 is connected to the lithium bicarbonate purification liquid outlet of the ion exchange resin tank 300, and is used to mix the lithium bicarbonate purification liquid with HF solution or HF gas to prepare lithium fluoride. The clear liquid outlet of the third membrane filter 404 is back connected to the synthesis reactor 400 through a synthesis pump.

[0065] In some preferred embodiments, the synthesis reactor 400 is connected to a lithium bicarbonate purification liquid inlet pipe and an HF pipe 401. A nozzle 402 or an atomizer is provided at one end of the lithium bicarbonate purification liquid inlet pipe that extends into the HF pipe 401. The gas-liquid input direction of the HF pipe 401 is opposite to the input direction of the lithium bicarbonate purification liquid.

[0066] In this invention, the lithium bicarbonate purification solution used in the lithium fluoride synthesis reaction is brought into countercurrent contact with HF gas or HF liquid, which can effectively increase the contact area between the two and improve the reaction efficiency.

[0067] The multi-stage membrane washing unit 500 is connected to the concentrated liquid outlet of the third membrane filtration device 404, and includes at least two sets of membrane washing devices arranged in series. Between two adjacent sets of membrane washing devices, the clear liquid outlet of the next stage membrane washing device is connected back to the washing water inlet of the previous stage membrane washing device.

[0068] In one specific embodiment, the multi-stage membrane washing unit 500 includes a buffer tank 503, a primary membrane washing device 501, and a secondary membrane washing device 502 connected in series. The buffer tank 503 is connected to the concentrate outlet of the third membrane filtration device 404. The slurry outlet of the primary membrane washing device 501 is connected to the secondary membrane washing device 502. The secondary membrane washing device 502 outputs qualified LiF material, and the separated clear liquid is returned to the buffer tank 503. After being stirred and mixed in the buffer tank 503, it enters the primary membrane washing device 501.

[0069] Specifically, the clarified liquid outlet of the primary membrane scrubbing device 501 is connected to two parallel streams, one of which is connected back to the synthesis reactor 400, and the other is connected to the lithium recovery unit. In this embodiment, the clarified liquid produced by the primary membrane scrubbing device 501 is processed in stages. Since the clarified liquid in the early stage contains a relatively large amount of unreacted lithium bicarbonate, it can be returned to the synthesis reactor 400 to continue the reaction. The clarified liquid in the later stage can be used for lithium recovery.

[0070] Preferably, a membrane separation device 600 is installed on the pipeline between the primary membrane washing device 501 and the lithium recovery unit, and the clear liquid outlet of the membrane separation device 600 is connected back to the water replenishment point on the pipeline between the two membrane washing devices.

[0071] The lithium recovery unit includes a pyrolysis device 700 and a fourth membrane filtration device 701 connected in sequence. The pyrolysis device 700 is equipped with a lithium-containing waste liquid inlet for heating to precipitate lithium carbonate. The concentrated liquid outlet of the fourth membrane filtration device 701 is connected back to the carbonization reactor 200, and the clear liquid outlet is connected to the lithium recovery device 800. By adding phosphoric acid to react, lithium phosphate precipitate is obtained through filtration for lithium recovery.

[0072] The above-mentioned post-processing unit is connected to the concentrated liquid outlet of the secondary membrane washing device 502, and is used to dry the washed qualified lithium fluoride slurry to obtain battery-grade lithium fluoride products.

[0073] In some preferred embodiments, the system further includes a gas recovery unit having a first demister 201 disposed on top of the carbonization reactor 200, a second demister 403 disposed on top of the synthesis reactor 400, and a CO2 recovery device 900 connected to the first demister 201 and the second demister 403 respectively.

[0074] This invention achieves continuous membrane washing through multi-stage membrane series connection and inter-stage water replenishment. The wash water from the first-stage membrane washing is treated in stages. The wash water in the early stage contains a relatively large amount of unreacted lithium bicarbonate, and this part of the wash water is directly returned to the lithium fluoride reactor to participate in the reaction. The wash water in the later stage contains a relatively small amount of unreacted lithium bicarbonate, and this part of the wash water is treated by membrane separation. The clear liquid is reused as wash water for membrane washing replenishment, and the concentrated liquid is used for lithium recovery through pyrolysis and the addition of phosphoric acid. The entire process has a high lithium recovery rate with virtually no loss, and the overall recovery rate reaches over 96%, with minimal wastewater discharge.

[0075] This invention enables continuous reaction and continuous membrane washing of lithium fluoride, which can improve the uniformity of lithium fluoride products, reduce the impurity content of products, improve product quality, and ensure that the purity of lithium fluoride products produced on a large scale is 99.99% or higher.

[0076] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A process for preparing battery-grade lithium fluoride from industrial lithium carbonate, characterized in that, include: Carbonization reaction process: CO2 gas is introduced into a lithium carbonate slurry made by mixing industrial lithium carbonate with pure water to carry out the carbonization reaction. After a certain reaction time, the mixture is filtered through a membrane. The clear liquid obtained by membrane filtration is a lithium bicarbonate solution. If the concentrated liquid obtained by filtration contains unreacted lithium carbonate, it is returned to continue the carbonization reaction. Resin impurity removal process: The membrane filtration solution obtained during the carbonization reaction is passed through an ion exchange resin to remove metal ion impurities from the lithium bicarbonate solution, resulting in a purified lithium bicarbonate solution. Synthesis reaction process: The lithium bicarbonate purified liquid is sprayed into the HF pipeline through a nozzle or atomizer and mixed countercurrently with HF solution or HF gas to carry out the synthesis reaction. The resulting reaction mixture is filtered through a membrane, and the clear liquid is returned to continue to participate in the synthesis reaction. The concentrated liquid obtained by membrane filtration is lithium fluoride slurry. Multi-stage membrane washing process: The lithium fluoride slurry is continuously washed with membranes. Between two adjacent membrane washing stages, the clear liquid produced by the next membrane washing stage is used as the washing water for the previous membrane washing stage. The clarified liquid generated from the first-stage membrane washing is processed in stages. The first-stage clarified liquid, which contains a relatively large amount of unreacted lithium bicarbonate, is fed back to the synthesis reaction process. The second-stage clarified liquid is sent to the membrane separation unit for nanofiltration and / or reverse osmosis. The clarified liquid obtained from membrane separation is reused as washing water makeup water, and the concentrated liquid obtained from membrane separation enters the lithium recovery process. Lithium recovery process: The lithium-containing waste liquid generated during the process is subjected to pyrolysis and membrane filtration in sequence. The resulting lithium carbonate slurry is recycled for the carbonation reaction process. The membrane filtration mother liquor is added with a precipitant for lithium recovery. Post-processing: The washed and qualified lithium fluoride slurry is dried to obtain battery-grade lithium fluoride products.

2. The process according to claim 1, characterized in that, It also includes a reagent removal process before the carbonization reaction process. The reagent removal process specifically involves: mixing industrial-grade lithium carbonate with pure water to prepare a lithium carbonate slurry, adding a metal complexing agent to cause heavy metal ions in the lithium carbonate slurry to form complexes and transfer to the solution, and then removing them by membrane filtration. The membrane-filtered slurry enters the carbonization reaction process, and the clear liquid from the membrane filtration enters the lithium recovery process.

3. The process according to claim 1, characterized in that, The carbonization reaction is carried out at a temperature of 20–40°C for a reaction time of 0.5–4 hours; and / or, The synthesis reaction is carried out at a temperature of 20–85°C for a reaction time of 1–6 h; and / or, The temperature of the washing water is 60–90°C; and / or, The temperature of the pyrolysis reaction is 50–100°C.

4. A system for preparing battery-grade lithium fluoride from industrial lithium carbonate, characterized in that, include: A raw material purification unit for the purification of industrial lithium carbonate includes a carbonation reactor, a second membrane filtration device, and an ion exchange resin tank. The carbonation reactor is used to convert lithium carbonate slurry into a soluble lithium bicarbonate solution. The outlet of the carbonation reactor is connected to the second membrane filtration device. The concentrated liquid outlet of the second membrane filtration device is connected back to the carbonation reactor, and the clear liquid outlet is connected to the ion exchange resin tank to remove metal ion impurities from the lithium bicarbonate solution. The synthesis reaction unit includes a synthesis reactor and a third membrane filtration device connected in sequence. The synthesis reactor is connected to the purified liquid outlet of the ion exchange resin tank and is used to mix lithium bicarbonate purified liquid with HF solution or HF gas to prepare lithium fluoride. The clear liquid outlet of the third membrane filtration device is connected back to the synthesis reactor. The synthesis reactor is connected to a purified liquid inlet pipe and an HF pipe. A nozzle or atomizer is installed at one end of the purified liquid inlet pipe that extends into the HF pipe. The gas-liquid input direction of the HF pipe is opposite to the input direction of the purified liquid. A multi-stage membrane washing unit is connected to the concentrate outlet of the third membrane filtration device and includes at least two sets of membrane washing devices arranged in series. Between two adjacent sets of membrane washing devices, the clear liquid outlet of the next stage membrane washing device is connected back to the washing water inlet of the previous stage membrane washing device. The supernatant outlet of the first-stage membrane washing unit is connected to two parallel streams, one of which is connected back to the synthesis reactor and the other is connected to the lithium recovery unit. The multi-stage membrane washing unit also includes a membrane separation device connected in series to the pipeline between the first-stage membrane washing unit and the lithium recovery unit. The supernatant outlet of the membrane separation device is connected back to the water replenishment point on the pipeline between adjacent membrane washing units, and the concentrated liquid outlet is connected to the pyrolysis unit. The lithium recovery unit includes a pyrolysis device and a fourth membrane filtration device connected in sequence. The pyrolysis device is equipped with a lithium-containing waste liquid inlet for heating and precipitating lithium carbonate. The concentrated liquid outlet of the fourth membrane filtration device is connected back to the carbonization reactor, and the clear liquid outlet is connected to the lithium recovery unit. The post-processing unit is connected to the concentrate outlet of the final membrane washing unit and is used to dry the washed qualified lithium fluoride slurry to obtain battery-grade lithium fluoride products.

5. The system according to claim 4, characterized in that, The multi-stage membrane washing unit is also equipped with a buffer tank, which is located on the pipeline between the first-stage membrane washing device and the concentrated liquid outlet of the third membrane filtration device and / or on the pipeline between two adjacent membrane washing devices, for buffering lithium fluoride slurry and mixing lithium fluoride slurry with washing water.

6. The system according to claim 4, characterized in that, The raw material purification unit also includes a reagent removal tank and a first membrane filtration device connected in sequence. The reagent removal tank is used for industrial-grade lithium carbonate slurry preparation and is equipped with a reagent inlet to allow heavy metal ions in the lithium carbonate slurry to form complexes and transfer to the solution. The concentrated liquid outlet of the first membrane filtration device is connected to the lithium carbonate slurry inlet of the carbonation reactor, and the clear liquid outlet is connected to the lithium recovery unit.

7. The system according to claim 4, characterized in that, A first demister is installed at the top of the carbonization reactor, and a second demister is installed at the top of the synthesis reactor. Both the first and second demisters are connected to a CO2 recovery device.

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