A carbon dioxide reinforced carbonation reaction system and method for lithium carbonate purification

Abstract

The application discloses a carbon dioxide reinforced carbonization reaction system and method for lithium carbonate purification. The device comprises a carbonization kettle, a circulating pump, a cooling device, and a micro-bubble generating device externally arranged on the carbonization kettle. The micro-bubble generating device is provided with a tubular porous medium membrane assembly and a flow guide disc. The circulating pump divides the slurry at the bottom of the kettle into two branches. The first branch returns to the kettle body after heat exchange by the cooling device, and the second branch is mixed with fresh lithium carbonate slurry and then sent to the micro-bubble generating device. The method controls the pressure difference between the shell and the pipe to be 50-400 kPa, so that the carbon dioxide is cut by the slurry to generate micro-bubbles through the nano-pores of the porous medium membrane, the three-phase mixed slurry is formed and sent to the carbonization kettle, the reaction is carried out at 15-30 DEG C and 0-100 kPa positive pressure, and the reaction endpoint is determined by the fact that the pH value of the system is stabilized at 7.6-8.3 and the decrease amplitude is less than 0.02 in a continuous time. The application greatly improves the gas-liquid-solid three-phase contact area through the external micro-bubble generating device, significantly improves the carbon dioxide absorption rate and reaction efficiency, eliminates the plugging of the gas distribution hole in the kettle from the source, and ensures the long-period continuous and stable operation.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate purification technology, and in particular to a carbon dioxide-enhanced carbonation reaction system and method for lithium carbonate purification. Background Technology

[0002] Lithium carbonate (Li₂CO₃) is the most fundamental lithium salt product in the production of cathode materials for lithium-ion batteries. It is widely used in the preparation of mainstream lithium battery cathode materials such as lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, and ternary materials, as well as in the production of electrolyte additives such as lithium hexafluorophosphate. In recent years, the rapid development of the new energy vehicle and energy storage industries has greatly stimulated the demand for battery-grade lithium carbonate materials for lithium-ion batteries. The requirements for purity, impurity content, and particle size distribution of battery-grade lithium carbonate materials have become increasingly stringent. Faced with increasingly stringent product quality requirements and growing market demand, the economical and efficient purification of industrial-grade lithium carbonate to battery-grade is not only a key technological link connecting upstream lithium resource development with downstream new energy industries, but also an important technological support for the sustainable development of lithium battery resources.

[0003] The carbonation-pyrolysis method is currently the most widely used and industrially valuable technology for purifying industrial-grade lithium carbonate. Its core principle is based on the fact that lithium bicarbonate has a much higher solubility in water than lithium carbonate. In the carbonation process, industrial-grade lithium carbonate is mixed with water to form a slurry, and carbon dioxide gas is introduced for aeration. This causes the lithium carbonate to react with carbon dioxide and water to form highly soluble lithium bicarbonate (Li2CO3+CO2+H2O→2LiHCO3). Most insoluble impurities (such as calcium, magnesium, silicon, etc.) are filtered out as solid residues in this process. Subsequently, the purified lithium bicarbonate solution is pyrolyzed to reprecipitate high-purity lithium carbonate (2LiHCO3→Li2CO3↓+CO2↑+H2O).

[0004] Currently, the industrial production of industrial-grade lithium carbonate commonly employs a process where carbon dioxide is bubbled through gas distribution pipes (gas distribution plates) at the bottom of the carbonization reactor. Numerous Φ5-10mm vent holes are opened on the surface of the gas distribution component, allowing carbon dioxide to disperse and be introduced into the lithium carbonate slurry system. However, this process still faces the following problems in actual production: First, the bubbles generated by the perforated gas distribution pipe (gas distribution plate) are usually relatively large in size and have a small specific surface area. The gas-liquid-solid three-phase contact area between carbon dioxide and lithium carbonate slurry is limited, resulting in low system mass transfer efficiency. This not only prolongs the carbonization reaction cycle and restricts the production capacity of the device, but also often requires increasing the volume of the carbonization reactor and adopting a multi-device series arrangement to make up for the production capacity shortfall, which significantly increases the project's infrastructure investment cost.

[0005] Secondly, the large bubbles generated by the gas distribution pipe (gas distribution plate) rise quickly, causing a large amount of carbon dioxide to escape directly from the liquid surface with the bubbles before participating in the carbonization reaction. This results in a low carbon dioxide utilization rate, which increases the cost of raw material consumption and also increases carbon dioxide emissions.

[0006] Third, the gas distribution openings on the gas distribution pipe (gas distribution plate) are prone to airflow deviation and uneven gas distribution. Lithium carbonate crystal salts are very easy to adhere and block the vent holes. As the number of blockage points gradually increases, the gas flow rate of the gas distribution component continues to decrease. During production, it is often necessary to stop production regularly to empty the carbonization reactor and manually enter the reactor for cleaning. The maintenance workload is large and affects the continuity of production and the operating efficiency of the equipment.

[0007] Therefore, developing a lithium carbonate carbonization purification equipment and method that can improve carbon dioxide utilization, enhance reaction mass transfer efficiency, solve the problem of clogging of gas distribution holes, and ensure long-term continuous and stable operation has important application value. Summary of the Invention

[0008] To address these issues, this invention provides a carbon dioxide-enhanced carbonation reaction system and method for lithium carbonate purification, which solves the problems of low carbon dioxide absorption and utilization rate, poor reaction mass transfer efficiency, long carbonation cycle and large equipment investment, easy scaling and clogging of gas distribution components, and the need for frequent shutdowns for manual cleaning in existing lithium carbonate carbonation purification processes.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, comprising a carbonation kettle, a circulating pump, a cooling device, and a microbubble generator externally placed in the carbonation kettle; The microbubble generator includes a tubular porous media membrane assembly. The microbubble generator has a shell side, a tube side, a carbon dioxide inlet, a feed inlet, and a discharge outlet. The carbon dioxide inlet is connected to the shell side, the feed inlet is connected to the tube side, and the discharge outlet is connected to the feed inlet of the carbonization reactor. The inlet of the circulating pump is connected to the bottom outlet of the carbonization reactor, and the outlet of the circulating pump is divided into a first branch and a second branch. The first branch is connected to the inlet of the cooling device, and the outlet of the cooling device is connected to the upper return port of the carbonization reactor; The second branch line merges with the lithium carbonate slurry feed line and is then connected to the feed inlet of the microbubble generator.

[0010] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, the microbubble generator further includes a guide plate, which is located at the bottom feed section of the microbubble generator. The guide plate adopts a composite structure of circumferentially expanding inclined guide plates and grid-like guide plates.

[0011] As a preferred embodiment of the carbon dioxide-enhanced carbonization reaction system for lithium carbonate purification, the tubular porous dielectric membrane module has a membrane pore size of 50nm~500nm, and the membrane material of the tubular porous dielectric membrane module is selected from one or more composites of Al2O3, ZrO2, TiO2, and SiC.

[0012] As a preferred embodiment of the carbon dioxide-enhanced carbonization reaction system for lithium carbonate purification, the cooling device is a water cooler, which is externally placed in the carbonization reactor. After the slurry in the first branch flows through the water cooler for heat exchange and cooling, it returns to the reactor body from the top of the carbonization reactor.

[0013] As a preferred embodiment of the carbon dioxide-enhanced carbonization reaction system for lithium carbonate purification, the cooling device is a cooling jacket installed on the outer wall of the carbonization reactor. The cooling jacket is provided with a cooling medium inlet and outlet for introducing the cooling medium to regulate the temperature of the reaction system.

[0014] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, the outlet of the microbubble generator is connected to the inlet of the lower section of the side wall of the carbonation reactor via a pipeline, and all inlet points are evenly arranged circumferentially in the lower section of the reactor body.

[0015] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, the microbubble generator is arranged at the bottom of the carbonation vessel, the bottom of the carbonation vessel is provided with a conical head, and the outlet of the microbubble generator is fixedly connected to the conical head as a whole through a flange.

[0016] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, the tubular porous media membrane assembly is supported and fixed within the microbubble generator by upper and lower tube sheets, and a fluororubber O-ring is provided between the upper and lower tube sheets and the membrane tube of the tubular porous media membrane assembly.

[0017] This invention also provides a carbon dioxide-enhanced carbonation reaction method for lithium carbonate purification, employing the aforementioned carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, comprising the following steps: S1. Prepare lithium carbonate slurry by mixing industrial-grade lithium carbonate with water, mix it with the circulating slurry of the second branch through the feed pipeline, and send it into the microbubble generator. S2. Carbon dioxide is introduced into the microbubble generator, and the tube side pressure is controlled to be P1 and the shell side pressure is P2. The pressure P2-P1 is maintained at 50~400 kPa. Under the pressure difference, carbon dioxide passes through the membrane pores of the tubular porous medium membrane module and is sheared and broken by the slurry flowing in the tube side to form a solid-liquid-gas three-phase mixed slurry rich in carbon dioxide microbubbles. S3. The three-phase mixed slurry is fed into the carbonization reactor for carbonization reaction; at the same time, a portion of the slurry in the reactor is sent to the cooling device for heat exchange via the first branch through the circulation pump and then returned to the carbonization reactor, controlling the temperature of the reaction system to be 15~30℃; the unabsorbed carbon dioxide tail gas at the top of the carbonization reactor is discharged and sent to the carbon dioxide recovery device for reuse. S4. When the slurry in the carbonization reactor transforms into a clear liquid phase, and the pH value of the system is stably maintained at 7.6~8.3, and the pH decrease is less than 0.02 within a continuously set time, the reaction is determined to be complete, and the lithium bicarbonate solution is discharged.

[0018] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction method for lithium carbonate purification, in step S1, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is controlled to be 1.5:1 to 2.0:1, and is adjusted in real time according to the solid content of lithium carbonate slurry and the carbon dioxide emission in the tail gas at the top of the carbonation reactor.

[0019] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction method for lithium carbonate purification, in step S3, the carbonation reactor is controlled to operate under a positive pressure condition of 0~100kPa gauge pressure.

[0020] As a preferred embodiment of the carbon dioxide-enhanced carbonation reaction method for lithium carbonate purification, in step S3, the temperature of the reaction system is controlled within the range of 20~25℃.

[0021] The present invention has the following advantages: This invention employs an external microbubble generator, using a tubular porous membrane module as the dispersion element. Pressure difference drives carbon dioxide through nanoscale membrane pores, where it is sheared and broken up by the rapidly flowing slurry, generating micron-sized microbubbles. Compared to existing technologies that use perforated gas distribution pipes or discs for bubble generation, the microbubble surface area of ​​this invention is increased several times, significantly increasing the gas-liquid-solid three-phase contact area between carbon dioxide and the lithium carbonate slurry. This greatly improves the system's reaction mass transfer efficiency and significantly shortens the carbonization reaction cycle. Enterprises no longer need to compensate for production capacity shortages by scaling up reactor volume or connecting multiple devices in series, thus effectively reducing equipment infrastructure investment.

[0022] Because the microbubbles of this invention rise slowly within the carbonization reactor, their residence time in the liquid phase is significantly extended, ensuring that most of the micro-dispersed carbon dioxide is fully absorbed and participates in the reaction before escaping the liquid surface. This effectively improves the utilization efficiency of carbon dioxide and directly reduces the raw material consumption cost of carbon dioxide. At the same time, the content of unreacted carbon dioxide in the exhaust gas is greatly reduced, alleviating the load on subsequent exhaust gas recovery devices and meeting the requirements of green and low-carbon production.

[0023] This invention abandons the traditional structure of a gas distribution pipe (gas distribution plate) built into the bottom of the carbonization reactor, transferring the carbon dioxide gas distribution process to an external microbubble generator. A specially designed guide plate is installed within this device to eliminate liquid phase flow deviation. This structural design eliminates the gas distribution components inside the carbonization reactor that are easily blocked by lithium carbonate crystallization salts, preventing scale buildup and clogging. The production process no longer requires frequent shutdowns to empty the reactor or manual cleaning, significantly reducing maintenance workload and ensuring long-term, continuous, and stable operation of the lithium carbonate carbonization purification unit.

[0024] This invention controls the temperature of the carbonization reaction system within the optimal range of 15°C to 30°C by using an external water cooler or a cooling jacket on the reactor wall; at the same time, it combines the operation under positive pressure conditions of 0 to 100 kPa gauge pressure inside the reactor with precise pH determination of the endpoint to ensure that the carbonization reaction is complete and sufficient, and to guarantee the high stability and consistency of the final lithium bicarbonate solution quality. Attached Figure Description

[0025] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0026] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0027] Figure 1 This is a schematic diagram of a carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the carbon dioxide-enhanced carbonation reaction method for lithium carbonate purification provided in an embodiment of the present invention; Figure 3 A schematic diagram of a first alternative scheme for the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification provided by the present invention; Figure 4 A schematic diagram of a second alternative scheme for the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification provided by the present invention; Figure 5 A schematic diagram of a third alternative scheme for the carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification provided by the present invention.

[0028] In the diagram: 1. Carbonization vessel; 2. Water cooler; 3. Microbubble generator; 3-1. Tubular porous media membrane module; 3-2. Guide plate; 4. Circulation pump. Detailed Implementation

[0029] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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. Example 1

[0030] See Figure 1 This invention provides a carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, including a carbonation reactor 1, a circulating pump 4, a cooling device, and a microbubble generator 3 externally mounted on the carbonation reactor 1. The microbubble generator 3 includes a tubular porous dielectric membrane assembly 3-1, and has a shell side, a tube side, a carbon dioxide inlet, a feed inlet, and a discharge outlet. The carbon dioxide inlet is connected to the shell side, the feed inlet is connected to the tube side, and the discharge outlet is connected to the feed inlet of the carbonation reactor 1. The inlet of the circulating pump 4 is connected to the bottom outlet of the carbonation reactor 1, and the outlet of the circulating pump 4 is divided into a first branch and a second branch. The first branch is connected to the inlet of the cooling device, and the outlet of the cooling device is connected to the upper return port of the carbonation reactor 1. The second branch merges with the lithium carbonate slurry feed pipeline and then connects to the feed inlet of the microbubble generator 3.

[0031] In this process, the nanoscale pores of the tubular porous dielectric membrane module 3-1, under the pressure difference between the shell side and the tube side, enable carbon dioxide to be generated in the form of micron-sized bubbles. This changes the traditional structure of the carbonization reactor 1 with its built-in gas distribution plate, fundamentally avoiding the risk of crystallization blockage of lithium carbonate crystallized salt in the gas distribution holes inside the reactor. Furthermore, the flow distribution loop of the circulating pump 4 achieves thermal balance and material circulation in the reaction system, thereby significantly improving the gas-liquid-solid three-phase contact mass transfer efficiency between carbon dioxide and lithium carbonate slurry.

[0032] In this embodiment, the microbubble generator 3 further includes a guide plate 3-2, which is disposed at the bottom feeding section of the microbubble generator 3. The guide plate 3-2 adopts a composite structure of a circumferentially expanding inclined guide plate and a grid-like guide plate.

[0033] Specifically, through the combined effect of the circumferentially expanding inclined guide plate and the grid-like guide plate, the radial feed can be uniformly converted into axial laminar flow, effectively eliminating the liquid phase deviation phenomenon inside the microbubble generator 3, ensuring that the slurry flow rate entering each branch porous media membrane module 3-1 is uniformly distributed, thereby ensuring the generation quality and dispersion uniformity of carbon dioxide microbubbles.

[0034] In this embodiment, the pore size of the tubular porous dielectric membrane module 3-1 is 50nm~500nm, and the membrane material of the tubular porous dielectric membrane module 3-1 is selected from one or more composites of Al2O3, ZrO2, TiO2, and SiC.

[0035] Specifically, controlling the pore size of the tubular porous dielectric membrane module 3-1 within the nanometer range is the physical basis for generating a large number of micron-sized highly dispersed carbon dioxide bubbles, greatly expanding the gas-liquid contact interface and improving the carbon dioxide utilization rate per unit volume. The selection of high-performance multi-component composite ceramic materials with specific compositions ensures that the device maintains structural stability and operational reliability even under long-term exposure to alkaline lithium carbonate slurry scouring, solid particle friction, and reaction temperature fluctuations.

[0036] In this embodiment, the cooling device is a water cooler 2, which is externally placed in the carbonization kettle 1. After the slurry in the first branch flows through the water cooler 2 for heat exchange and cooling, it returns to the kettle body from the top of the carbonization kettle 1.

[0037] Specifically, considering the exothermic nature of the carbonization reaction, an external water cooler 2 is used in conjunction with the circulation structure of the first branch. Its temperature control principle involves drawing the high-temperature slurry from the carbonization reactor 1 outside for efficient heat exchange. This design not only flexibly meets the heat exchange area requirements under different production capacities and significantly improves heat exchange efficiency, but also greatly facilitates daily inspection and maintenance of the equipment. Simultaneously, it avoids the potential risk of leakage due to corrosion or wear of traditional built-in cooling coils, which could lead to contamination of the lithium carbonate reaction slurry by the cooling medium, ensuring that the reaction system remains stable within the target low-temperature range.

[0038] In this embodiment, the outlet of the microbubble generator 3 is connected to the inlet of the lower section of the side wall of the carbonization reactor 1 through a pipe, and all inlet points are evenly arranged in the lower section of the reactor body along the circumference.

[0039] Specifically, the three-phase mixed slurry, rich in carbon dioxide microbubbles after being processed by the microbubble generator 3, is introduced circumferentially from the feed inlet in the lower part of the side wall of the carbonization reactor 1 at multiple points, maximizing the upward floating path of carbon dioxide microbubbles in the liquid phase within the carbonization reactor 1. Through uniform circumferential distribution, a stable upward microbubble flow field is constructed inside the carbonization reactor 1, effectively suppressing localized aggregation between bubbles. This significantly prolongs the residence time of carbon dioxide microbubbles in the lithium carbonate slurry, providing sufficient contact time for the carbonization reaction of lithium carbonate and carbon dioxide.

[0040] In this embodiment, the tubular porous media membrane assembly 3-1 is supported and fixed inside the microbubble generator 3 by upper and lower tube sheets, and a fluororubber O-ring is provided between the upper and lower tube sheets and the membrane tube of the tubular porous media membrane assembly 3-1.

[0041] Specifically, the stable sealing of the tubular porous media membrane module 3-1 is a prerequisite for maintaining the pressure difference between the shell side and the tube side of the microbubble generator 3. The installation method, employing rigid support from upper and lower tube sheets and combined with fluororubber O-ring seals, ensures absolute reliability of the equipment's airtightness under high pressure differential conditions ranging from 50 to 400 kPa. The fluororubber material, with its excellent resistance to acid and alkali media and aging resistance, ensures that the seals can withstand long-term service in alkaline lithium carbonate slurry without easily failing, preventing short-circuit leakage of high-pressure carbon dioxide from the tube sheet gaps to the tube side, and ensuring that all carbon dioxide gas strictly follows the designed path through the nanoscale pores of the tubular porous media membrane module 3-1.

[0042] See Figure 2 This invention also provides a method for enhancing the carbonation reaction with carbon dioxide for lithium carbonate purification, using the aforementioned carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, comprising the following steps: S1. Prepare lithium carbonate slurry by mixing industrial-grade lithium carbonate with water, mix it with the circulating slurry of the second branch through the feed pipeline, and send it into the microbubble generator 3.

[0043] The step of pre-mixing fresh lithium carbonate slurry with the circulating slurry extracted from the second branch of circulating pump 4 ensures the continuous and stable operation of the microbubble generator 3. Sufficient circulating material not only provides the necessary tube-side flow rate to enhance the shearing and stripping effect of the lithium carbonate slurry on carbon dioxide gas permeating the membrane pores, but also dilutes and regulates the solid content, smoothing out operational disturbances caused by fluctuations in the fresh industrial-grade lithium carbonate feed, and ensuring that the inlet of the microbubble generator 3 always maintains a stable and uniform fluid state.

[0044] S2. Carbon dioxide is introduced into the microbubble generator 3, and the tube side pressure is controlled to be P1 and the shell side pressure is controlled to be P2. The pressure P2-P1 is maintained at 50~400kPa. Under the pressure difference, carbon dioxide passes through the membrane pores of the tubular porous medium membrane module 3-1 and is sheared and broken by the slurry flowing in the tube side to form a solid-liquid-gas three-phase mixed slurry rich in carbon dioxide microbubbles.

[0045] By controlling the shell-side pressure P2 to be higher than the tube-side pressure P1 and maintaining a stable shell-side and tube-side pressure difference of 50~400 kPa, a stable driving force is provided for carbon dioxide to penetrate the nanoscale membrane pores. When high-pressure carbon dioxide permeates through the pores of the inner wall of the tubular porous dielectric membrane module 3-1 in an extremely fine stream, it is stripped and broken by the strong shear force generated by the high-speed flowing lithium carbonate slurry in the tube side, thereby forming a large number of uniformly sized carbon dioxide microbubbles, constructing a highly dispersed solid-liquid-gas three-phase mixed system.

[0046] S3. The three-phase mixed slurry is fed into the carbonization reactor 1 for carbonization reaction; at the same time, a portion of the slurry in the reactor is sent to the cooling device via the first branch through the circulating pump 4 and then returned to the carbonization reactor 1 for heat exchange, and the temperature of the reaction system is controlled at 15~30℃; the unabsorbed carbon dioxide tail gas at the top of the carbonization reactor 1 is discharged and sent to the carbon dioxide recovery device for reuse.

[0047] Entering the S3 carbonization reaction stage, the three-phase mixed slurry rich in carbon dioxide microbubbles slowly rises within the carbonization reactor 1, greatly extending the gas-liquid-solid multiphase contact time and making the carbonization reaction of lithium carbonate and carbon dioxide more complete and thorough. Simultaneously, closed-loop temperature control via an external cooling device driven by the first branch of the circulating pump 4 strictly limits the reaction system temperature to the range of 15~30℃. This temperature window matches the high solubility characteristics of lithium bicarbonate, effectively preventing the reverse decomposition reaction of lithium bicarbonate caused by excessively high temperatures. Unabsorbed carbon dioxide tail gas exiting from the top of the carbonization reactor 1 is recovered.

[0048] S4. When the slurry in the carbonization reactor 1 is transformed into a clear liquid phase, and the pH value of the system is stably maintained at 7.6~8.3, and the pH decrease is less than 0.02 within a continuously set time, the reaction is determined to be complete, and the lithium bicarbonate solution is discharged.

[0049] Specifically, when the milky white, turbid lithium carbonate suspension transforms into a clear, transparent lithium bicarbonate liquid phase, and the system's pH value remains stable between 7.6 and 8.3 without significant fluctuations over a set period, it indicates that the chemical reaction in the system has reached dynamic equilibrium. This combined physical appearance and chemical parameter determination mechanism effectively avoids problems such as insufficient reaction leading to substandard product purity or excessive reaction consuming extra energy, ensuring the stability of lithium bicarbonate product yield and purity during continuous carbonization production.

[0050] In this embodiment, in step S1, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is controlled to be 1.5:1 to 2.0:1, and is adjusted in real time according to the solid content of lithium carbonate slurry and the carbon dioxide emission in the tail gas at the top of the carbonization reactor 1.

[0051] Specifically, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is set and dynamically linked with the monitoring of carbon dioxide emissions in the tail gas at the top of carbonation reactor 1. Based on the dynamic supply and demand balance law of the carbonation reaction, the gas intake is adjusted in real time according to the actual solid content of lithium carbonate slurry and the carbon dioxide emission concentration in the tail gas. This ensures that the gas supply system is always in the optimal gas-liquid-solid supply and consumption matching state, avoids reaction stagnation due to insufficient gas supply, and prevents resource waste caused by excessive gas supply and carbon dioxide overflow.

[0052] In this embodiment, in step S3, the carbonization reactor 1 is controlled to operate under a positive pressure condition of 0~100kPa gauge pressure.

[0053] Specifically, the carbonization reactor 1 is controlled to operate under a specific positive pressure condition, utilizing the promoting effect of pressure on chemical equilibrium. Positive pressure significantly increases the physical solubility of carbon dioxide in the liquid phase of the lithium carbonate slurry, increases the driving force for interphase mass transfer, and promotes the forward carbonization reaction of lithium carbonate. Simultaneously, this positive pressure environment effectively isolates the system from external air, preventing oxygen or impurities from contaminating the reaction medium, thereby further improving the chemical safety of the lithium carbonate purification reaction system.

[0054] In this embodiment, in step S3, the temperature control range of the reaction system is 20~25℃.

[0055] Specifically, the temperature range of the carbonization reaction system is further optimized to a narrower range of 20~25℃. This optimized temperature range is at the highest window of the lithium bicarbonate solubility curve. At this temperature, the carbonization reaction rate is moderate and the conversion efficiency is high. At the same time, it can prevent premature pyrolysis and precipitation of lithium bicarbonate caused by excessively high local temperature to the greatest extent, thereby ensuring a high yield and high quality of the final lithium carbonate purification process. Example 2

[0056] See Figure 3 This invention provides a carbon dioxide-enhanced carbonization reaction system for lithium carbonate purification. In this alternative solution, the outer wall of the carbonization reactor 1 is equipped with a wrap-around cooling jacket. The cooling jacket has independent inlet and outlet for the cooling medium. The temperature of the carbonization reaction system is controlled by circulating the cooling medium into the cooling jacket. By adjusting the feed temperature and circulation flow rate of the cooling medium, the temperature of the carbonization reaction system is stably controlled between 15 and 30°C, preferably within the range of 20 to 25°C.

[0057] In terms of system circulation structure and material conveying, a circulation pump 4 is configured. The inlet of the circulation pump 4 is led out from the bottom of the carbonization reactor 1, and it extracts the lithium carbonate-lithium bicarbonate mixed slurry from the bottom of the reactor. The extracted slurry is mixed with the fresh industrial lithium carbonate feed slurry introduced by the external feed pipeline, and then sent to the microbubble generator 3 through the pipeline. In terms of gas supply control, the gas-liquid volume ratio of the introduced carbon dioxide to the lithium carbonate slurry is controlled at 1.5:1~2.0:1. The specific gas intake needs to be dynamically adjusted according to the real-time solid content of the lithium carbonate slurry and the carbon dioxide emission concentration in the tail gas at the top of the carbonization reactor 1, while maintaining the carbonization reactor 1 in a positive pressure condition of 0~100kPa.

[0058] Regarding the internal structure of the microbubble generator 3, the device has a feed inlet at the bottom. Industrial lithium carbonate mixed slurry, as the continuous phase, is transported to this inlet via a bottom pipeline. The slurry pressure at the inlet is controlled at P1. After entering the microbubble generator 3, the slurry first undergoes uniform distribution through the guide plate 3-2 built into the bottom feed section, and then flows upward into the tube-side channel of the tubular porous dielectric membrane module 3-1. Carbon dioxide, as the dispersed phase, is introduced into the shell-side of the device from the air inlet on the side wall of the microbubble generator 3. The shell-side pressure is controlled at P2, and the pressure difference between the shell-side and tube-side, P2-P1, is maintained within the range of 50~400 kPa through differential pressure control. Driven by this pressure difference, carbon dioxide gas permeates through the nanoscale pores of the tubular porous dielectric membrane module 3-1. At the membrane pore outlet, it is stripped and broken by the shear force generated by the rapidly flowing lithium carbonate slurry in the tube, thereby generating a large number of highly dispersed micron-sized microbubbles. These microbubbles are then fully mixed with the continuous lithium carbonate slurry to form a solid-liquid-gas three-phase mixed slurry rich in carbon dioxide microbubbles.

[0059] In the discharge and conveying path, the aforementioned microbubble-rich three-phase mixed slurry is discharged from the top discharge port of the microbubble generator 3 and connected to the side wall feed port of the carbonization reactor 1 through an external pipeline. The side wall feed port is configured with a multi-point feeding structure, with all feed points evenly distributed circumferentially at the height of the lower section of the carbonization reactor 1. The large amount of carbon dioxide microbubbles fed into the carbonization reactor 1 floats gently to the surface in the liquid phase inside the reactor, greatly increasing the specific surface area of ​​the gas-liquid-solid three-phase contact and promoting the full reaction of lithium carbonate and carbon dioxide into soluble lithium bicarbonate. The carbon dioxide that is not completely absorbed by the slurry during the reaction is collected at the top of the reactor and discharged as tail gas to an external carbon dioxide recovery device for recycling. Example 3

[0060] See Figure 4This invention provides a carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification. In terms of equipment space layout and structural connection, the microbubble generator 3 is directly arranged at the bottom of the carbonation vessel 1, omitting the external connecting pipes. Its top outlet is fixedly connected to the conical end cap at the bottom of the carbonation vessel 1 through a flange, forming a bottom-connected integrated structure, which reduces pressure drop and energy consumption during material transportation.

[0061] In the cooling and circulation loop, the carbonization reactor is equipped with an external cooling circulation pipeline. The lithium carbonate-lithium bicarbonate mixed slurry is drawn out from the upper part (slightly above the vessel body) of the carbonization vessel 1 by the circulation pump 4 and flows through the external water cooler 2 for heat exchange and cooling. By adjusting the slurry circulation flow rate through the water cooler 2, the temperature of the carbonization reaction system is stably controlled at 15~30℃, preferably within the range of 20~25℃. After cooling, the slurry is pumped out by the circulation pump 4 and divided into two streams: the first stream of slurry returns directly to the vessel body from the feed port on the side of the conical part of the carbonization vessel 1; the second stream of slurry is mixed with fresh industrial lithium carbonate feed slurry introduced from the external feed pipeline and then sent to the microbubble generator 3 located at the bottom of the vessel body to complete the pre-dispersion and mixing of carbon dioxide microbubbles.

[0062] Regarding the structural setup of the gas control and microbubble generator 3, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is controlled at 1.5:1 to 2.0:1. The specific gas intake is adjusted based on the real-time solid content of the lithium carbonate slurry and the carbon dioxide emission from the tail gas at the top of the carbonization reactor 1, while maintaining a positive pressure condition of 0~100kPa inside the carbonization reactor 1. The industrial lithium carbonate mixed slurry, as the continuous phase, is fed into the microbubble generator 3 via a pipeline from the inlet at the bottom. The inlet pressure is controlled at P1. After entering the device, the slurry first passes through the bottom guide plate 3-2 for rectification and uniform distribution, ensuring a uniform flow rate before entering the tube-side channel of the tubular porous dielectric membrane module 3-1. Carbon dioxide, as the dispersed phase, is introduced into the shell side from the gas inlet on the side wall of the microbubble generator 3. The shell-side pressure is controlled at P2, and the pressure difference between the shell side and the tube side, P2-P1, is maintained at 50~400kPa. Driven by this pressure difference, carbon dioxide gas passes through the nanoscale membrane pores of the tubular porous dielectric membrane module 3-1 and is torn apart by the shear force generated by the rapidly flowing lithium carbonate slurry inside the tube, generating a large number of micron-sized carbon dioxide microbubbles, which are fully mixed with the continuous phase of lithium carbonate slurry to form a solid-liquid-gas three-phase mixed slurry containing a large number of microbubbles.

[0063] Since the top outlet of the microbubble generator 3 is directly connected to the conical end cap flange at the bottom of the carbonization vessel 1, the three-phase mixed slurry discharged from the top of the microbubble generator 3 directly enters the interior of the carbonization vessel 1. A large number of carbon dioxide microbubbles rise slowly from bottom to top in the liquid phase inside the vessel, significantly increasing the specific surface area of ​​the gas-liquid-solid three-phase contact, promoting the full reaction of lithium carbonate and carbon dioxide into soluble lithium bicarbonate; the carbon dioxide that is not completely absorbed by the slurry collects at the top of the vessel, is discharged as tail gas, and sent to the carbon dioxide recovery device for reuse. Example 4

[0064] See Figure 5 This invention provides a carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification. This alternative solution integrates a bottom-integrated connection and jacketed cooling design in its overall equipment structure. First, a microbubble generator 3 is placed at the bottom of the carbonation reactor 1. Its top outlet is connected to the conical end cap at the bottom of the reactor 1 via a flange, achieving seamless connection between the reactor body and the microbubble generator. Second, the carbonation reactor 1 employs an external jacketed cooling method. A wrap-around cooling jacket is installed on the outer wall of the reactor body. The temperature of the carbonation reaction system is directly controlled by introducing a cooling medium with a set temperature into the cooling jacket. By precisely adjusting the feed temperature and circulation flow rate of the cooling medium, the temperature of the carbonation reaction system is stably controlled between 15 and 30°C, preferably within the range of 20 to 25°C.

[0065] In the circulating material conveying structure, the system is equipped with a circulating pump 4. The inlet of the circulating pump 4 draws out a portion of the circulating slurry from the extraction port at the upper part of the carbonization reactor 1. The drawn-out circulating slurry is directly mixed with the fresh industrial lithium carbonate feed slurry introduced by the external feed pipeline. The mixed slurry is then sent through the pipeline to the microbubble generator 3 located at the bottom of the reactor body to complete the pre-dispersion mixing of carbon dioxide microbubbles. In terms of gas supply, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is controlled at 1.5:1~2.0:1, and is dynamically adjusted according to the real-time solid content of lithium carbonate slurry and the carbon dioxide emission in the tail gas at the top of the carbonization reactor 1, while maintaining the positive pressure condition of 0~100kPa inside the carbonization reactor 1.

[0066] Regarding the internal structure and operation of the microbubble generator 3, industrial lithium carbonate mixed slurry, as the continuous phase, is pumped into the microbubble generator 3 from the inlet at the bottom via a pipeline, with the inlet pressure controlled at P1. The slurry first passes through the guide plate 3-2 built into the bottom feed section of the device. The guide plate, with its composite structure of circumferentially expanding inclined guide plates and grid-like guide plates, rectifyes the slurry, eliminating flow deviation, and then enters the tube-side channel of the tubular porous dielectric membrane module 3-1. Carbon dioxide, as the dispersed phase, is introduced into the shell side from the air inlet on the side wall of the microbubble generator 3, with the shell-side pressure controlled at P2, and the pressure difference P2-P1 between the shell side and the tube side maintained at 50~400 kPa. Under this pressure difference, carbon dioxide permeates through the nanoscale membrane pores of the tubular porous dielectric membrane module 3-1 and is broken into a large number of micron-sized microbubbles by the shearing action of the rapidly flowing lithium carbonate slurry in the tube-side channel. It is then fully mixed with the continuous phase of lithium carbonate slurry to form a solid-liquid-gas three-phase mixed slurry rich in carbon dioxide microbubbles.

[0067] Because the top outlet of the microbubble generator 3 is connected to the bottom of the carbonization reactor 1 by an integrated flange, the microbubble-rich three-phase mixed slurry, after being generated, is directly discharged from the top of the microbubble generator 3 and directly enters the interior of the carbonization reactor 1. A large number of carbon dioxide microbubbles entering the carbonization reactor 1 rise slowly from bottom to top in the liquid phase inside the reactor, significantly increasing the specific surface area of ​​the gas-liquid-solid three-phase contact, promoting the full reaction of lithium carbonate and carbon dioxide, and converting it into soluble lithium bicarbonate. During the reaction, carbon dioxide that is not completely absorbed by the slurry collects at the top of the reactor, is discharged as tail gas, and sent to the carbon dioxide recovery device for recycling.

[0068] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification, characterized in that, It includes a carbonization kettle (1), a circulation pump (4), a cooling device, and a microbubble generator (3) externally placed in the carbonization kettle (1). The microbubble generator (3) includes a tubular porous medium membrane assembly (3-1). The microbubble generator (3) is provided with a shell side, a tube side, a carbon dioxide inlet, a feed inlet and a discharge outlet. The carbon dioxide inlet is connected to the shell side, the feed inlet is connected to the tube side, and the discharge outlet is connected to the feed inlet of the carbonization reactor (1). The inlet of the circulating pump (4) is connected to the bottom outlet of the carbonization kettle (1), and the outlet of the circulating pump (4) is divided into a first branch and a second branch. The first branch is connected to the inlet of the cooling device, and the outlet of the cooling device is connected to the upper return port of the carbonization kettle (1); The second branch line merges with the lithium carbonate slurry feed line and is then connected to the feed inlet of the microbubble generator (3).

2. The carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The microbubble generator (3) also includes a guide plate (3-2), which is located at the bottom feed section of the microbubble generator (3). The guide plate (3-2) adopts a composite structure of a circumferentially expanding inclined guide plate and a grid-like guide plate.

3. The carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The pore size of the tubular porous dielectric membrane module (3-1) is 50nm~500nm, and the membrane material of the tubular porous dielectric membrane module (3-1) is selected from one or more composites of Al2O3, ZrO2, TiO2, and SiC.

4. The carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The cooling device is a water cooler (2), which is placed outside the carbonization kettle (1). After the slurry in the first branch flows through the water cooler (2) for heat exchange and cooling, it returns to the kettle body from the top of the carbonization kettle (1).

5. A carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The cooling device is a cooling jacket installed on the outer wall of the carbonization kettle (1). The cooling jacket is provided with a cooling medium inlet and outlet for introducing the cooling medium to regulate the temperature of the reaction system.

6. A carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The outlet of the microbubble generator (3) is connected to the inlet of the lower section of the side wall of the carbonization reactor (1) through a pipe, and all inlet points are evenly arranged in the lower section of the reactor body along the circumference.

7. A carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The microbubble generator (3) is arranged at the bottom of the carbonization kettle (1). The bottom of the carbonization kettle (1) is provided with a conical head. The outlet of the microbubble generator (3) is fixedly connected to the conical head through a flange.

8. A carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to claim 1, characterized in that, The tubular porous media membrane assembly (3-1) is supported and fixed inside the microbubble generator (3) by upper and lower tube sheets, and a fluororubber O-ring is provided between the upper and lower tube sheets and the membrane tube of the tubular porous media membrane assembly (3-1).

9. A method for enhancing carbonation reaction with carbon dioxide for the purification of lithium carbonate, characterized in that, The carbon dioxide-enhanced carbonation reaction system for lithium carbonate purification according to any one of claims 1 to 8 includes the following steps: S1. Prepare lithium carbonate slurry by mixing industrial-grade lithium carbonate with water, mix it with the circulating slurry of the second branch through the feed pipeline, and send it into the microbubble generator (3). S2. Carbon dioxide is introduced into the microbubble generator (3), and the tube side pressure is controlled to be P1 and the shell side pressure is controlled to be P2. The pressure P2-P1 is maintained at 50~400kPa. Under the pressure difference, carbon dioxide passes through the membrane pores of the tubular porous medium membrane module (3-1) and is sheared and broken by the slurry flowing in the tube side to form a solid-liquid-gas three-phase mixed slurry rich in carbon dioxide microbubbles. S3. The three-phase mixed slurry is fed into the carbonization reactor (1) for carbonization reaction; at the same time, a portion of the slurry in the reactor is sent to the cooling device through the first branch via the circulating pump (4) and then returned to the carbonization reactor (1) for heat exchange, and the temperature of the reaction system is controlled at 15~30℃; the unabsorbed carbon dioxide tail gas at the top of the carbonization reactor (1) is discharged and sent to the carbon dioxide recovery device for reuse; S4. When the slurry in the carbonization kettle (1) is transformed into a clear liquid phase, and the pH value of the system is stably maintained at 7.6~8.3, and the pH decrease is less than 0.02 within a continuously set time, the reaction is determined to be complete, and the lithium bicarbonate solution is discharged.

10. A method for enhancing carbon dioxide carbonation reaction for lithium carbonate purification according to claim 9, characterized in that, In step S1, the gas-liquid volume ratio of carbon dioxide to lithium carbonate slurry is controlled to be 1.5:1 to 2.0:1, and is adjusted in real time according to the solid content of lithium carbonate slurry and the carbon dioxide emission in the tail gas at the top of the carbonization reactor (1). In step S3, the carbonization reactor (1) is controlled to operate under a positive pressure condition of 0~100kPa gauge pressure; In step S3, the temperature of the reaction system is controlled within the range of 20~25℃.

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