A multi-stage continuous reaction crystallizer and method for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride

Abstract

The application relates to a multistage continuous reaction crystallizer and method for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride, and relates to the field of inorganic chemical material preparation equipment. The crystallizer comprises a plurality of reaction units connected in series. Inner and outer guide cylinders are coaxially arranged in each unit to form a main reaction zone, a secondary reaction zone and an annular overflow clarification zone. Lithium bicarbonate and hydrogen fluoride feeding pipes are arranged in the inner guide cylinder in a staggered manner to realize cross-flow feeding. Clear liquid is transferred through overflow ports stage by stage, and crystal slurry is transferred through discharge ports stage by stage to realize multistage countercurrent contact and crystal concentration. The application realizes the continuous and large-scale production of lithium fluoride through the cooperation of double guide cylinders to strengthen mixing and grading, cross-flow feeding to inhibit explosive nucleation and multistage overflow to prolong the residence time, and the product has high purity and regular and uniform crystals.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical material preparation equipment technology, and in particular to a multi-stage continuous reaction crystallizer and method for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride. Background Technology

[0002] Lithium fluoride is the core raw material for lithium hexafluorophosphate, the electrolyte in lithium-ion batteries. Battery-grade products have stringent requirements for purity, crystal morphology, and particle size uniformity. Current mainstream processes use the reaction of lithium bicarbonate and hydrogen fluoride to produce lithium fluoride. Traditional production often uses batch reactors, which suffers from uneven material mixing and excessively high local concentrations. This leads to a burst of lithium fluoride nucleation, resulting in small and dispersed crystals that are difficult to separate into solid and liquid phases, resulting in unstable product quality.

[0003] Existing continuous reaction devices are mostly single-channel structures, which can only achieve a single circulating flow field. The mixing intensity is insufficient and there is a reaction dead zone, resulting in low mass transfer efficiency. Some multi-stage reaction devices lack scientific flow guidance and overflow design and do not adopt cross-flow feeding method. The materials are prone to back-mixing, resulting in insufficient reaction residence time, low conversion rate of unreacted raw materials, and crystals cannot be effectively graded and settled, making it difficult for the product purity to meet battery-grade standards. Summary of the Invention

[0004] The problem solved by this invention is to provide a multi-stage continuous reaction crystallizer and method for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride. Existing equipment for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride suffers from uneven mixing, severe backmixing, inability to produce continuously, and poor product quality. This invention provides a multi-stage continuous reaction crystallizer with an inner guide tube, an outer guide tube, an overflow zone, and cross-flow feeding, which realizes efficient material mixing, continuous reaction, and graded discharge, thereby improving product purity and production efficiency.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride includes multiple reaction units connected in series. Each reaction unit includes a reactor body. An inner guide tube and an outer guide tube are coaxially arranged inside the reactor body, dividing the interior of the reactor body into a main reaction zone, a secondary reaction zone, and an annular overflow clarification zone nested from the inside out. The bottom of the inner guide tube and the outer guide tube are connected to the bottom wall of the reactor body through several support arms. Both the lithium bicarbonate feed pipe and the hydrogen fluoride feed pipe extend into the inner guide cylinder and are staggered in the axial direction to form a cross-flow feed. An overflow port is located on the upper side wall of the reactor body and is connected to the annular overflow clarification zone. It is used to overflow the clarified liquid of this stage to the secondary reaction zone of the next stage reaction unit. A discharge port is located at the bottom of the reactor body and is used to discharge the crystal slurry at the bottom of this stage to the main reaction zone of the next stage reaction unit. A speed reducer is installed on the top of the reactor body. The input end of the speed reducer is connected to the output end of the motor. A stirring shaft is installed on the output end of the motor. Stirring blades are installed on the stirring shaft below the main reaction zone.

[0006] Preferably, the top of the inner guide tube is higher than the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for material flow. The top of the outer guide tube is flush with the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for crystal sedimentation and return.

[0007] Preferably, an annular weir plate is provided on the inner side of the top of the outer guide tube, and pneumatic cylinders are symmetrically installed on the top of the reactor body. The telescopic end of the pneumatic cylinder is connected to the annular weir plate, and a sealing ring is provided on the outer side of the annular weir plate, and the sealing ring is in contact with the inner wall of the outer guide tube.

[0008] Preferably, a gas distributor is provided at the bottom of the secondary reaction zone. The gas distributor is connected to an annular gas pipe via a connecting pipe, and the annular gas pipe is connected to an external gas source via an inlet pipe.

[0009] Preferably, the gas distributor is an annular tubular structure, located in the lower part of the secondary reaction zone and arranged close to the inner wall of the outer guide tube; the gas distributor has multiple downward-facing and inwardly inclined gas outlet holes.

[0010] Preferably, it also includes a clear liquid circulation feed pipe, one end of which is connected to the overflow port of the previous stage reaction unit, and the other end passes through the side wall and the outer guide tube of the reaction vessel body of this stage and extends into the secondary reaction zone of this stage reaction unit, for introducing the clear liquid from the previous stage into the secondary reaction zone of this stage.

[0011] Preferably, it also includes a crystal slurry circulation feed pipe, one end of which is connected to the outlet of the previous stage reaction unit, and the other end passes through the side wall, outer guide tube and inner guide tube of the main body of this stage reaction vessel, and extends into the main reaction zone of this stage reaction unit, for introducing the crystal slurry of the previous stage into the main reaction zone of this stage as a seed crystal.

[0012] Preferably, between adjacent reaction units, the overflow port of the previous stage is connected to the clear liquid circulation feed pipe of the next stage through a pipeline, and the discharge port of the previous stage is connected to the crystal slurry circulation feed pipe of the next stage through a pipeline, forming a multi-stage continuous reaction crystallization system.

[0013] A method for operating a multi-stage continuous reaction crystallizer for the preparation of lithium fluoride from lithium bicarbonate and hydrogen fluoride, the specific operation steps of which are as follows: The concentration of the lithium bicarbonate solution, calculated as lithium element, is 7~8.5 g / L, and the mass fraction of the hydrogen fluoride solution is 10%~30%, with a molar ratio of 1:(1~1.2). Lithium bicarbonate solution and hydrogen fluoride solution are cross-flowed into the main reaction unit. The reaction temperature is controlled at 30-50℃ and the pH is 1.0-3.0. Under stirring, the materials are circulated and mixed in the guide tube. Each stage of material stays for 30-60 minutes, with a total residence time of 90-150 minutes. The clear liquid overflows to the next stage of the secondary reaction zone, where the crystals are concentrated at the bottom. The slurry is pumped into the main reaction zone of the next stage reactor body to continue the reaction. The crystal slurry discharged from the last stage is subjected to solid-liquid separation, washed with deionized water, and dried at 120-150℃ to obtain a high-purity lithium fluoride product.

[0014] The beneficial effects of this invention are: The dual-guide tube synergistic enhancement improves mixing efficiency by 30% and eliminates dead zones through internal circulation; external circulation achieves solid-liquid separation, narrowing the crystal particle size distribution by 50% and resulting in regular morphology; cross-flow feeding controls crystal nuclei, avoiding instantaneous contact of raw materials and completely solving the problem of explosive nucleation, resulting in an average crystal particle size of 28 μm; multi-stage overflow enrichment extends material residence time, achieving a reaction conversion rate of over 99.5% and significantly improving the concentration of crystals in the final stage; continuous and large-scale production enables uninterrupted production, improving efficiency by 3 times compared to intermittent production, and ensuring a stable product purity of 99.96%, meeting battery-grade standards; The annular weir plate is adjustable. The height of the annular weir plate can be adjusted by a pneumatic cylinder to precisely control the clarity of the overflow liquid and adapt to different working conditions. The gas distribution is enhanced. A gas distributor is set at the bottom of the secondary reaction zone. The introduction of inert gas can further enhance mass transfer and promote fine crystal dissolution and crystal growth. Seed crystal introduction: The previous stage crystal slurry is introduced into the next stage main reaction zone as a seed crystal to promote crystal growth and improve crystal particle size uniformity. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the internal structure of the present invention; Figure 3 This is a cross-sectional view of the present invention.

[0016] Legend: 1. Reactor body; 2. Support arm; 3. Inner guide tube; 4. Outer guide tube; 5. Main reaction zone; 6. Secondary reaction zone; 7. Annular overflow clarification zone; 8. Lithium bicarbonate feed pipe; 9. Hydrogen fluoride feed pipe; 10. Overflow port; 11. Discharge port; 12. Reducer; 13. Motor; 14. Stirring shaft; 15. Stirring blades; 16. Annular weir plate; 17. Pneumatic cylinder; 18. Annular gas pipe; 19. Connecting pipe; 20. Gas distributor; 21. Gas inlet pipe; 22. Clear liquid circulation feed pipe; 23. Crystal slurry circulation feed pipe. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Specific implementation examples are given below.

[0019] See Figures 1-3A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride includes multiple reaction units connected in series. Each reaction unit includes a reactor body 1. An inner guide tube 3 and an outer guide tube 4 are coaxially arranged inside the reactor body 1, dividing the interior of the reactor body 1 into a main reaction zone 5, a secondary reaction zone 6, and an annular overflow clarification zone 7, nested sequentially from the inside out. The bottoms of the inner guide tube 3 and the outer guide tube 4 are connected to the bottom wall of the reactor body 1 via several support arms 2. A reducer 12 is installed on the top of the reactor body 1, with its input end connected to the output end of a motor 13. A stirring shaft 14 is installed on the output end of the motor 13, and stirring blades 15 are installed on the stirring shaft 14 below the main reaction zone 5. An annular weir plate 16 is provided on the inner side of the top of the outer guide tube 4. Pneumatic cylinders 17 are symmetrically installed on the top of the reactor body 1, with their extension and retraction ends connected to the annular weir plate 16. A sealing ring is provided on the outer side of the annular weir plate 16, and the sealing ring is... The inner wall of the outer guide tube 4 is fitted together. The height of the annular weir plate 16 can be adjusted by the pneumatic cylinder 17, which can change the cross-sectional area of ​​the channel through which the overflow clear liquid enters the annular overflow clarification zone 7, thereby precisely controlling the clarity of the overflow clear liquid. When the crystal growth is good and the sedimentation rate is fast, the height of the annular weir plate 16 can be appropriately reduced to improve the overflow efficiency. When there are more fine crystals, the height of the annular weir plate 16 can be increased to prolong the clarification time and ensure the clarity of the overflow clear liquid. A gas distributor 20 is set at the bottom of the secondary reaction zone 6. The gas distributor 20 is connected to the annular gas pipe 18 through the connecting pipe 19. The annular gas pipe 18 is connected to the external gas source through the air inlet pipe 21. The gas distributor 20 is an annular tubular structure, set at the lower part of the secondary reaction zone 6, and arranged close to the inner wall of the outer guide tube 4. The gas distributor 20 has multiple downward and inwardly inclined air outlets. The downward inclined design causes the bubbles to move downward and then turn back upward, prolonging the bubble residence time and increasing the gas-liquid contact area. The introduced inert gas can carry away the heat of reaction, and the disturbance generated by the rising bubbles enhances mass transfer, promotes the dissolution of fine crystals, and is beneficial to crystal growth. The stirring blades 15 are located at the bottom of the main reaction zone 5. The motor 13 drives the stirring shaft 14 through the reducer 12 to rotate the stirring blades 15 at high speed, driving the material to form a strong turbulent circulation from bottom to top in the inner guide tube 3. This forced internal circulation allows the fresh material to mix rapidly with the reaction liquid, eliminating local concentration unevenness, and providing a uniform supersaturation field for crystal growth. Large crystal particles settle in this area and fall to the bottom of the vessel. The material from the main reaction zone 5 overflows from the top of the inner guide tube 3 into the secondary reaction zone 6, forming a mild external circulation flow field in this area. Small crystal particles continue to grow in this area, and unreacted raw materials continue to react. At the same time, the gas distributor 20 introduces inert gas, and the generated bubbles enhance mass transfer during their ascent, promoting the dissolution of fine crystals. The area between the outer guide tube 4 and the vessel wall of the reaction vessel body 1 is the clarification zone for solid-liquid separation. Material from the secondary reaction zone 6 enters this area from the bottom of the outer guide tube 4. During the ascent, crystals settle back into the secondary reaction zone 6, and the clear liquid continues to rise to the top and is discharged to the next stage through the overflow port 10. The height of the annular weir plate 16 is adjustable and is driven by the pneumatic cylinder 17 to precisely control the clarity of the overflow clear liquid.

[0020] The top of the inner guide tube 3 is higher than the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for material flow. The top of the outer guide tube 4 is flush with the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for crystal sedimentation and return. The top of the inner guide tube 3 is higher than the reaction liquid surface to ensure that the material in the main reaction zone 5 must overflow from the top to enter the secondary reaction zone 6, forming a complete circulation path. The bottom gap between the bottom of the inner guide tube 3 and the bottom of the vessel allows the sedimented crystals to return to the stirring area for re-suspension. The top of the outer guide tube 4 is flush with the reaction liquid surface, and a bottom gap is provided between the bottom of the outer guide tube 4 and the bottom of the vessel for material in the secondary reaction zone 6 to flow into the annular overflow clarification zone 7, while allowing the sedimented crystals to return to the secondary reaction zone 6 to continue growing. Both the lithium bicarbonate feed pipe 8 and the hydrogen fluoride feed pipe 9 extend into the inner guide tube 3 and are staggered in the axial direction to form a cross-flow feed. The cross-flow layout avoids the two raw materials from instantaneous direct contact, suppressing explosive nucleation from the source. Lithium bicarbonate enters from the top and hydrogen fluoride enters from the bottom. When the two are mixed in the main reaction zone 5, they are fully dispersed to form a uniform supersaturation field, which is conducive to crystal growth. Overflow port 10 is located on the upper side wall of reactor body 1 and is connected to the annular overflow clarification zone 7. It is used to overflow the clarified liquid of this stage to the secondary reaction zone 6 of the next stage reaction unit. Discharge port 11 is located at the bottom of reactor body 1 and is used to discharge the crystal slurry at the bottom of this stage to the main reaction zone 5 of the next stage reaction unit.

[0021] It also includes a clear liquid circulation feed pipe 22, one end of which is connected to the overflow port 10 of the previous stage reaction unit, and the other end passes through the side wall of the reactor body 1 and the outer guide cylinder 4, and extends into the secondary reaction zone 6 of the reactor body 1, for introducing the clear liquid from the previous stage into the secondary reaction zone 6 of the reactor body 1. It also includes a crystal slurry circulation feed pipe 23, one end of which is connected to the outlet 11 of the previous stage reaction unit, and the other end passes through the side wall of the reactor body 1, the outer guide cylinder 4 and the inner guide cylinder 3, and extends into the main reaction zone 5 of the reactor body 1, for introducing the crystal slurry from the previous stage into the main reaction zone 5 of the reactor body 5 as seed crystals.

[0022] Between adjacent reaction units, the overflow port 10 of the previous stage is connected to the clear liquid circulation feed pipe 22 of the next stage through a pipeline, and the discharge port 11 of the previous stage is connected to the crystal slurry circulation feed pipe 23 of the next stage through a pipeline, forming a multi-stage continuous reaction crystallization system. Material flow design Lithium bicarbonate flow direction: The lithium bicarbonate solution enters from the main reaction zone 5 of the first-stage reaction unit. The overflow of the clear liquid from each stage of the reaction unit is passed down step by step. The unreacted lithium bicarbonate enters the secondary reaction zone 6 of the next stage with the clear liquid to continue the reaction, realizing multi-stage countercurrent contact. Hydrogen fluoride flow direction: The hydrogen fluoride solution is fed in a co-current manner, with each reaction unit fed independently, and reacts with lithium bicarbonate in a cross-flow manner within each unit; Crystal slurry flow: The crystal slurry that settles at the bottom of each reaction unit is discharged through the outlet 11 and enters the main reaction zone 5 of the next reaction unit through the crystal slurry circulation feed pipe 23. This crystal slurry serves as seed crystals, promoting the growth of crystals in the next stage, while simultaneously achieving gradual concentration of crystals at the bottom of the reactor.

[0023] Functional coordination of each reaction unit The first-stage reaction unit is mainly responsible for nucleation and initial growth. Fresh lithium bicarbonate and hydrogen fluoride undergo the main reaction in this stage to generate a large number of crystal nuclei. The nucleation rate is controlled by the forced circulation and cross-flow feeding of the inner guide tube 3 to avoid explosive nucleation. Intermediate stage reaction unit: mainly responsible for crystal growth. The clear liquid from the previous stage, containing unreacted raw materials, enters the secondary reaction zone 6 and meets the crystal slurry from the previous stage in the main reaction zone 5. The crystal continues to grow in a mild external circulation flow field. The gas distributor 20 introduces inert gas to enhance mass transfer and promote the dissolution of fine crystals. Final stage reaction unit: mainly responsible for crystal concentration. After multi-stage growth, the crystals have reached the target particle size and settle fully in the secondary reaction zone 6 and the annular overflow clarification zone 7. The concentration of the bottom crystal slurry is significantly increased, and it is finally discharged from the outlet 11.

[0024] Advantages of multi-stage overflow Extended residence time: The clear liquid overflows in stages, allowing unreacted lithium bicarbonate to fully contact with hydrogen fluoride in multiple reaction units. The total residence time can reach 90-150 minutes, and the reaction conversion rate is as high as 99.5% or more. Improve raw material utilization: Multi-stage contact maximizes raw material utilization and reduces waste; Crystal concentration is increased step by step: the crystal slurry is transferred step by step, and the crystals accumulate at the bottom of the vessel. The concentration of the final crystal slurry can reach 20-30%, which is beneficial for subsequent solid-liquid separation.

[0025] The concentration of the lithium bicarbonate solution, calculated as lithium element, is 7–8.5 g / L, and the mass fraction of the hydrogen fluoride solution is 10%–30%, with a molar ratio of 1:(1–1.2). The lithium bicarbonate solution and the hydrogen fluoride solution are cross-flowed into the main reaction unit. The reaction temperature is controlled at 30–50℃, and the pH is 1.0–3.0. Under stirring, the materials are circulated and mixed through a guide tube. Each stage of material residence time is 30–60 min, with a total residence time of 90–150 min. The clear liquid overflows to the next stage secondary reaction zone 6, where the crystals are concentrated at the bottom. The slurry is pumped into the main reaction zone 5 of the next stage reactor body 1 to continue the reaction. The crystal slurry discharged from the last stage is subjected to solid-liquid separation, washed with deionized water, and dried at 120–150℃ to obtain a high-purity lithium fluoride product.

[0026] Example 1 This embodiment uses a three-stage series reaction unit. The single-stage reactor body 1 has an inner diameter of 80cm and a volume of 500L. The inner guide tube 3 has an inner diameter of 40cm, a bottom gap of 10cm, and a top that is 5cm above the liquid level. The outer guide tube 4 has an inner diameter of 60cm, a bottom gap of 10cm, and a top that is flush with the liquid level. The hydrogen fluoride inlet is 20cm from the bottom of the reactor, the lithium bicarbonate inlet is 15cm from the liquid level, and the axial spacing is 30cm. The stirring blades 15 have a blade diameter of 32cm and a rotation speed of 250rpm. The gas distributor 20 is an annular tube with an outer diameter of 55cm and a tube diameter of 2cm. It has 48 evenly spaced air outlets with a diameter of 1mm. The air outlets face downward and are inclined inward at 45 degrees. The height of the annular weir plate 16 can be adjusted from 0 to 10cm. During production, lithium bicarbonate solution and 20% hydrogen fluoride solution are fed in a cross-flow manner at a molar ratio of 1:1.1. The temperature of each reaction unit is controlled by an external heat exchanger in the circulation pipeline, increasing progressively: 40℃ for the first stage, 42℃ for the second stage, and 45℃ for the third stage. The reaction pH is controlled at 2.0. The residence time for each stage is 40 minutes, with a total residence time of 120 minutes.

[0027] The work process is as follows: In the first-stage reaction unit, lithium bicarbonate enters the main reaction zone 5 through the upper feed pipe 8, and hydrogen fluoride enters the main reaction zone 5 through the lower feed pipe 9. The stirring blades 15 rotate at 250 rpm driven by the motor 13, driving the materials to form a forced circulation from bottom to top within the inner guide tube 3. The two raw materials are fully mixed and reacted during the circulation process, generating lithium fluoride crystal nuclei. Some crystals settle to the bottom of the reactor, while the clear liquid and fine crystals overflow from the top of the inner guide tube 3 into the secondary reaction zone 6. In the secondary reaction zone 6, the material forms a mild external circulation flow field, and small crystal particles continue to grow. Nitrogen gas is sprayed out from the bottom of the secondary reaction zone 6 through the gas distributor 20. During the rise of the bubbles, mass transfer is enhanced, which promotes the dissolution of fine crystals. The settled crystals return to the bottom of the vessel, and the clear liquid and suspended fine crystals enter the annular overflow clarification zone 7 from the bottom of the outer guide tube 4. In the annular overflow clarification zone 7, crystals settle back to the secondary reaction zone 6, and the clarified liquid rises to the top and is discharged through the overflow port 10. The height of the annular weir plate 16 is adjusted to 5cm to ensure the clarity of the overflow liquid. The first-stage clarified liquid enters the second-stage secondary reaction zone 6 through the clarified liquid circulation feed pipe 22, while the first-stage crystal slurry enters the second-stage main reaction zone 5 as seed crystals through the crystal slurry circulation feed pipe 23. The second and third stages repeat the above process. The crystal slurry discharged from the third stage was filtered by plate and frame filter press, washed three times with deionized water, and dried at 130℃ for 4 hours to obtain lithium fluoride product. Testing showed that the product purity was 99.97%, the average particle size was 30 μm, and the reaction conversion rate was 99.5%.

[0028] Example 2 The apparatus structure is the same as in Example 1, employing a four-stage series reaction unit. The molar ratio of lithium bicarbonate to hydrogen fluoride is 1:1.12. The hydrogen fluoride solution is fed from the bottom of the main reaction zone, while the lithium bicarbonate is fed from the top. The temperature of each reaction unit increases progressively: 40℃, 42℃, 45℃, and 48℃. The residence time for each stage is 35 minutes, with a total residence time of 140 minutes. The drying temperature is 135℃.

[0029] The product has a purity of 99.97%, an average particle size of 32 μm, and a conversion rate of 99.6%.

[0030] Example 3 The apparatus structure is the same as in Example 1, employing a two-stage series reaction unit. The molar ratio of lithium bicarbonate to hydrogen fluoride is 1:1.05, the reaction temperature is controlled at 42°C, the residence time for each stage is 50 min, and the total residence time is 100 min.

[0031] The product has a purity of 99.95%, an average particle size of 28 μm, and a conversion rate of 99.4%.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride, characterized in that, The reaction unit includes multiple reaction units connected in series. Each reaction unit includes a reaction vessel body (1). An inner guide tube (3) and an outer guide tube (4) are coaxially arranged inside the reaction vessel body (1), dividing the interior of the reaction vessel body (1) into a main reaction zone (5), a secondary reaction zone (6), and an annular overflow clarification zone (7) nested from the inside out. The bottom of the inner guide tube (3) and the outer guide tube (4) are connected to the bottom wall of the reaction vessel body (1) through several support arms (2). Both the lithium bicarbonate feed pipe (8) and the hydrogen fluoride feed pipe (9) extend into the inner guide tube (3) and are staggered in the axial direction to form a cross-flow feed. An overflow port (10) is located on the upper side wall of the reactor body (1) and is connected to the annular overflow clarification zone (7). It is used to overflow the clarified liquid of this stage to the secondary reaction zone (6) of the next stage reaction unit. A discharge port (11) is located at the bottom of the reactor body (1) and is used to discharge the crystal slurry at the bottom of this stage to the main reaction zone (5) of the next stage reaction unit. A speed reducer (12) is installed on the top of the reactor body (1). The input end of the speed reducer (12) is connected to the output end of the motor (13). A stirring shaft (14) is installed on the output end of the motor (13). The stirring shaft (14) is located below the main reaction zone (5) and has stirring blades (15).

2. The multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 1, characterized in that, The top of the inner guide tube (3) is higher than the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for material flow. The top of the outer guide tube (4) is flush with the reaction liquid surface, and a bottom gap is provided between its bottom and the bottom of the vessel for crystal sedimentation and return.

3. The multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 2, characterized in that, An annular weir plate (16) is provided on the inner side of the top of the outer guide tube (4). A pneumatic cylinder (17) is symmetrically installed on the top of the reactor body (1). The telescopic end of the pneumatic cylinder (17) is connected to the annular weir plate (16). A sealing ring is provided on the outer side of the annular weir plate (16), and the sealing ring is in contact with the inner wall of the outer guide tube (4).

4. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 3, characterized in that, A gas distributor (20) is provided at the bottom of the sub-reaction zone (6). The gas distributor (20) is connected to an annular gas pipe (18) through a connecting pipe (19). The annular gas pipe (18) is connected to an external gas source through an air inlet pipe (21).

5. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 4, characterized in that, The gas distributor (20) is an annular tubular structure, located at the lower part of the secondary reaction zone (6) and close to the inner wall of the outer guide tube (4); the gas distributor (20) has multiple downward and inwardly inclined gas outlet holes.

6. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 5, characterized in that, It also includes a clear liquid circulation feed pipe (22), one end of which is connected to the overflow port (10) of the previous stage reaction unit, and the other end passes through the side wall of the main body (1) of this stage reaction vessel and the outer guide tube (4), and extends into the sub-reaction zone (6) of this stage reaction unit, for introducing the clear liquid of the previous stage into the sub-reaction zone (6) of this stage.

7. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 6, characterized in that, It also includes a crystal slurry circulation feed pipe (23), one end of which is connected to the outlet (11) of the previous stage reaction unit, and the other end passes through the side wall, outer guide tube (4) and inner guide tube (3) of the main body (1) of this stage reaction vessel, and extends into the main reaction zone (5) of this stage reaction unit, for introducing the crystal slurry of the previous stage into the main reaction zone (5) of this stage as a seed crystal.

8. A multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 7, characterized in that, Between adjacent reaction units, the overflow port (10) of the previous stage is connected to the clear liquid circulation feed pipe (22) of the next stage through a pipeline, and the discharge port (11) of the previous stage is connected to the crystal slurry circulation feed pipe (23) of the next stage through a pipeline, forming a multi-stage continuous reaction crystallization system.

9. The operating method of a multi-stage continuous reaction crystallizer for preparing lithium fluoride from lithium bicarbonate and hydrogen fluoride according to claim 8, characterized in that, The specific steps of this method are as follows: The concentration of the lithium bicarbonate solution, calculated as lithium element, is 7~8.5 g / L, and the mass fraction of the hydrogen fluoride solution is 10%~30%, with a molar ratio of 1:(1~1.2). Lithium bicarbonate solution and hydrogen fluoride solution are cross-flowed into the main reaction unit. The reaction temperature is controlled at 30-50℃ and the pH is 1.0-3.

0. Under stirring, the materials are circulated and mixed in the guide tube. Each stage of material stays for 30-60 minutes, and the total residence time is 90-150 minutes. The clear liquid overflows to the next stage secondary reaction zone (6). The crystals are concentrated at the bottom of the secondary reaction zone (6). The slurry is pumped into the main reaction zone (5) of the next stage reactor body (1) to continue the reaction. The crystal slurry discharged from the last stage is separated into solid and liquid, washed with deionized water, and dried at 120-150℃ to obtain high-purity lithium fluoride product.

Images