Evaporative crystallization process for lithium carbonate mother liquor and lithium carbonate

Abstract

The invention discloses a lithium carbonate mother liquor evaporative crystallization process and lithium carbonate, and relates to the technical field of lithium carbonate preparation. The process comprises the following steps: introducing lithium carbonate mother liquor into first cooling equipment to obtain primary cooled mother liquor; obtaining an extracted mother solution according to the first cooling mother solution; introducing the extracted mother liquor into third cooling equipment containing critical nitrogen so as to obtain secondarily extracted mother liquor; introducing the mother liquor subjected to secondary extraction into fourth cooling equipment so as to obtain purified mother liquor; injecting a chelating surfactant into the mother liquor to obtain chelated mother liquor; separating the chelated mother liquor in a three-phase separation manner to obtain separated mother liquor; performing deep ultraviolet laser induction on the separated mother liquor to obtain grown crystal mush; performing crystal form control agent addition and growth regulation on the grown crystal mush to obtain concentrated crystal mush; and obtaining lithium carbonate according to the concentrated crystal mush. According to the method, critical nitrogen at-20 DEG C is adopted for low-temperature extraction for the first time, so that the impurity removal rate reaches 99.9%.

Description

Technical Field

[0001] This application relates to the field of lithium carbonate preparation technology, and in particular to a lithium carbonate mother liquor evaporation and crystallization process and lithium carbonate. Background Technology

[0002] The traditional lithium carbonate mother liquor evaporation and crystallization process is a core step in lithium salt production. The existing lithium carbonate mother liquor evaporation and crystallization process flow is as follows:

[0003] Evaporation and concentration: The lithium carbonate mother liquor (containing impurities) is heated to a high temperature (usually 80~100℃) through a multi-effect evaporator to evaporate and remove some of the water, thereby increasing the supersaturation of lithium carbonate in the mother liquor.

[0004] Cooling crystallization: The concentrated mother liquor is transferred to a crystallizer and cooled to 20~30℃ by natural cooling or forced cooling (such as circulating cooling water) to induce the precipitation of lithium carbonate crystals.

[0005] Solid-liquid separation: The crystals and mother liquor are separated by a centrifuge or filtration device, and the wet crystals are dried to obtain lithium carbonate product.

[0006] In existing technologies, during the evaporation and concentration process, organic matter (such as decomposed organic additives) and heavy metal ions (such as Fe) in the mother liquor are released into the atmosphere. 3+ Cu 2+ It will co-crystallize with lithium carbonate, resulting in limited product purity (usually ≤99.5%). Further purification is required by acid washing or ion exchange resin, but acid washing may corrode equipment and introduce new impurities such as chlorine, and ion exchange resin regeneration is costly.

[0007] Therefore, there is a need for a technical solution to address or at least mitigate the aforementioned shortcomings of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide a lithium carbonate mother liquor evaporation and crystallization process to at least solve one of the above-mentioned technical problems.

[0009] This invention provides the following solution:

[0010] According to one aspect of the present invention, a lithium carbonate mother liquor evaporation and crystallization process is provided, the lithium carbonate mother liquor evaporation and crystallization process comprising:

[0011] The lithium carbonate mother liquor is fed into the first cooling device, thereby reducing the temperature of the lithium carbonate mother liquor from 60°C to 40°C, thus obtaining the first cooled mother liquor.

[0012] The mother liquor from the first cooling process is passed into a second cooling device containing critical nitrogen gas, so that the mother liquor from the first cooling process and the critical nitrogen gas are fully mixed in the second cooling device, thereby obtaining the mother liquor after extraction.

[0013] The mother liquor after extraction is passed into a third cooling device containing critical nitrogen gas, so that the mother liquor after extraction and critical nitrogen gas are fully mixed in the third cooling device to obtain the mother liquor after secondary extraction.

[0014] The mother liquor after the second extraction is passed into the fourth cooling device to release the pressure of the mother liquor after the second extraction, thereby obtaining purified mother liquor;

[0015] A chelating surfactant is injected into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor.

[0016] The chelated mother liquor is separated by a three-phase separation process to obtain the separated mother liquor.

[0017] The separated mother liquor was subjected to deep ultraviolet laser induction to obtain the grown crystal slurry;

[0018] A crystal form control agent was added and growth was regulated after the crystal slurry was grown, thereby obtaining a concentrated crystal slurry;

[0019] Lithium carbonate is obtained by solid-liquid separation and drying of concentrated crystal slurry.

[0020] Optionally, the step of introducing the lithium carbonate mother liquor into the first cooling device, thereby reducing the temperature of the lithium carbonate mother liquor from 60°C to 40°C, to obtain the first cooled mother liquor includes:

[0021] The lithium carbonate mother liquor is fed into a plate heat exchanger at a flow rate of 2 m³ / h. The mother liquor exchanges heat with cooling water in the heat exchanger. During the cooling process, the temperature of the mother liquor and cooling water is monitored in real time. The cooling water flow rate is adjusted by a PID controller to ensure that the outlet temperature of the lithium carbonate mother liquor is stable at 40℃±1℃.

[0022] Optionally, the internal pressure of the second cooling device containing critical nitrogen is 9 MPa ± 0.1 MPa, the mixing time is 10-15 minutes, and the internal temperature of the second cooling device is -15℃ ± 1℃.

[0023] Optionally, the internal temperature of the fourth cooling device is 25℃±1℃; the pressure is reduced from 9MPa to atmospheric pressure, and the pressure release rate is controlled at 0.5MPa / min.

[0024] Optionally, the step of injecting a chelating surfactant into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor, includes:

[0025] DTPA-BA was selected as the chelating surfactant at a concentration of 0.1 wt%. The required surfactant injection amount was calculated based on the mother liquor flow rate to ensure that the surfactant concentration in the mother liquor reached 0.05-0.1 wt%.

[0026] Maintain the internal temperature of the equipment at 25℃±1℃, and inject the DTPA-BA solution into the chelation reactor using a metering pump;

[0027] Turn on the stirring device of the chelation reactor and stir the mother liquor at a speed of 300 rpm to ensure that the chelating surfactant and the heavy metal ions in the mother liquor come into full contact. Maintain the internal temperature of the chelation reactor at 25℃±1℃ to obtain the chelated mother liquor.

[0028] Optionally, the step of subjecting the separated mother liquor to deep ultraviolet laser induction to obtain the grown crystal slurry includes:

[0029] Adjust the temperature of the separated mother liquor to 20℃±1℃;

[0030] A photosensitizer was added to the mother liquor, and the molecules were anchored on the surface of Li2CO3 crystals by dark adsorption. The adsorption time was controlled at 30 minutes.

[0031] Turn on the laser, set the laser wavelength to 172nm, the pulse width to 8ns, and the repetition frequency to 2kHz, and guide the laser beam to the surface of the mother liquor in the crystallizer; the scanning speed is controlled at 80mm / s, and the laser energy density is precisely controlled at 1.0J / cm²; the crystallizer includes a three-stage temperature control system, with the temperature of the laser action zone maintained at 10℃±1℃, the temperature of the growth zone maintained at 20℃±1℃, and the temperature of the buffer zone maintained at 25℃±1℃;

[0032] The mother liquor is stirred at 300 rpm to promote crystal growth and uniform distribution; after the laser-induced crystallization process reaches the predetermined time, the grown crystal slurry is discharged from the crystallizer.

[0033] Optionally, the step of adding a crystal form control agent and regulating growth of the grown crystal slurry to obtain a concentrated crystal slurry includes:

[0034] The PEG solution is metered into the crystallizer using a metering pump, wherein the internal temperature of the crystallizer is maintained at 25℃±1℃; the crystal slurry is stirred at a speed of 200 rpm to promote uniform crystal growth and prevent aggregation.

[0035] The crystal slurry was ultrasonically treated at a frequency of 20kHz and a power of 50W.

[0036] Once the crystal growth reaches the predetermined time, the regulated crystal slurry is discharged from the crystallizer.

[0037] The discharged crystal slurry is subjected to solid-liquid separation using a centrifuge or filtration device to remove some of the mother liquor, thereby obtaining concentrated crystal slurry.

[0038] Optionally, the solid-liquid separation and drying of the concentrated crystal slurry to obtain lithium carbonate includes:

[0039] The concentrated slurry is fed into a solid-liquid separation device, where the lithium carbonate crystals are separated from the mother liquor by centrifugal force or pressure difference.

[0040] The separated wet crystals are discharged from the bottom of the equipment and collected in a drying container;

[0041] Turn on the vacuum drying oven or spray dryer and pass the collected wet crystals into the drying equipment for drying; maintain the internal temperature of the drying equipment at 80℃±5℃, the vacuum degree at -0.09MPa±0.005MPa, or the hot air temperature at 120℃±5℃ and the wind speed at 1.5m / s±0.2m / s.

[0042] This application also provides a lithium carbonate, which is obtained by the lithium carbonate mother liquor evaporation and crystallization process described above.

[0043] The lithium carbonate mother liquor evaporation and crystallization process of this application has the following advantages:

[0044] (1) This application is the first to use -20℃ critical nitrogen (SC-N2) for low-temperature extraction, which overturns the traditional operating range of 5-40℃. By setting a critical pressure of 8.5MPa, a new phase equilibrium condition is created. The low-temperature supercritical technology enables the removal rate of impurities to reach 99.9%, which is two orders of magnitude higher than the traditional process.

[0045] (2) DTPA-BA (diethylenetriaminepentaacetic acid bisamide) is used as a chelating agent to form stable complexes with heavy metal ions through multidentate chelation, achieving deep purification in combination with three-phase separation. This is effective for trace heavy metals (such as Fe) in the mother liquor. 3+ Cu 2 + ), avoiding the effects of traditional chemical precipitation methods on Li + Adsorption loss.

[0046] It can efficiently chelate at 25℃ without heating, saving energy and reducing equipment corrosion.

[0047] (3) Lithium carbonate crystal nuclei are excited by a 172nm deep ultraviolet laser, combined with photosensitizer anchoring technology, to precisely control crystal nucleation and growth. Laser-induced directional nucleation, combined with three-level temperature control (10℃ / 20℃ / 25℃), allows for controllable crystal growth rate with a particle size distribution coefficient (CVD) <0.3. The photosensitizer anchors the crystal surface, inhibiting secondary nucleation and reducing the difficulty of centrifugation. Laser energy promotes defect repair, increasing the intensity of crystal XRD diffraction peaks by more than 20%.

[0048] (4) PEG (polyethylene glycol) was added as a crystal form control agent, combined with 20kHz ultrasonic treatment, to optimize the growth of Li2CO3 crystal faces. PEG selectively adsorbed on the {104} crystal face, inhibiting longitudinal growth and obtaining plate-like crystals (thickness <5μm), increasing the specific surface area by 30%. The ultrasonic cavitation effect disrupted the weak connections between crystals, reducing the formation of hard agglomerates. Ultrasonic treatment promoted mass transfer, shortening the crystallization time to 1 / 3 of the traditional process. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating a centrifuge speed control method based on image recognition in one embodiment of this application.

[0050] Figure 2 A schematic diagram illustrating the parameters during the first cooling process of the mother liquor.

[0051] Figure 3 A schematic diagram of parameters obtained during the second cooling process of the mother liquor.

[0052] Figure 4 A schematic diagram of parameters obtained during the third cooling process of the mother liquor.

[0053] Figure 5 A schematic diagram of parameters obtained during the fourth cooling process of the mother liquor.

[0054] Figure 6 A schematic diagram of parameters during the process of obtaining the mother liquor after chelation.

[0055] Figure 7 A schematic diagram illustrating the parameters obtained during the process of obtaining the mother liquor after separation.

[0056] Figure 8 A schematic diagram illustrating the parameters during the crystal growth process.

[0057] Figure 9 A schematic diagram of parameters obtained during the process of concentrating crystal slurry.

[0058] Figure 10 To verify the effect of different pressures on Na in a 9 MPa critical nitrogen environment. + / Ca 2+ A schematic diagram illustrating the impact of removal rate.

[0059] Figure 11 A schematic diagram to verify the removal effect of DTPA-BA chelating agent on trace heavy metals in mother liquor.

[0060] Figure 12 This is a schematic diagram illustrating the effect of crystal grain size control under deep ultraviolet laser irradiation. Detailed Implementation

[0061] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. 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.

[0062] like Figure 1 The lithium carbonate mother liquor evaporation and crystallization process shown includes:

[0063] The lithium carbonate mother liquor is fed into the first cooling device, thereby reducing the temperature of the mother liquor from 60°C to 40°C, thus obtaining the first cooled mother liquor.

[0064] The mother liquor from the first cooling process is passed into a second cooling device containing critical nitrogen gas, so that the mother liquor from the first cooling process and the critical nitrogen gas are fully mixed in the second cooling device, thereby obtaining the mother liquor after extraction.

[0065] The mother liquor after extraction is passed into a third cooling device containing critical nitrogen gas, so that the mother liquor after extraction and critical nitrogen gas are fully mixed in the third cooling device to obtain the mother liquor after secondary extraction.

[0066] The mother liquor after the second extraction is passed into the fourth cooling device to release the pressure of the mother liquor after the second extraction, thereby obtaining purified mother liquor;

[0067] A chelating surfactant is injected into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor.

[0068] The chelated mother liquor is separated by a three-phase separation process to obtain the separated mother liquor.

[0069] The separated mother liquor was subjected to deep ultraviolet laser induction to obtain the grown crystal slurry;

[0070] A crystal form control agent was added and growth was regulated after the crystal slurry was grown, thereby obtaining a concentrated crystal slurry;

[0071] Lithium carbonate is obtained by solid-liquid separation and drying of concentrated crystal slurry.

[0072] In this embodiment, the step of introducing the lithium carbonate mother liquor into the first cooling device, thereby reducing the temperature of the lithium carbonate mother liquor from 60°C to 40°C, to obtain the first cooled mother liquor, includes:

[0073] The lithium carbonate mother liquor is fed into a plate heat exchanger at a flow rate of 2 m³ / h. Within the heat exchanger, the mother liquor exchanges heat with cooling water to achieve cooling. During the cooling process, the temperatures of both the mother liquor and the cooling water are monitored in real time. A PID controller is used to adjust the cooling water flow rate to ensure that the outlet temperature of the lithium carbonate mother liquor remains stable at 40℃±1℃.

[0074] See Figure 2 Specific parameters are as follows Figure 2 As shown. In this embodiment, it is first necessary to confirm that the temperature of the lithium carbonate mother liquor is 60℃±2℃, the flow rate is stable at 2m³ / h, the lithium carbonate concentration is 150-200g / L, and it contains trace amounts of Na. + (0.2-0.5wt%), Ca 2+ (0.1-0.3wt%).

[0075] In this embodiment, a plate heat exchanger can be used as the cooling device.

[0076] In the initial stage, turn on the cooling medium circulation pump to circulate the cooling water in the plate heat exchanger and ensure that the cooling water flow rate is stable at 5 m³ / h.

[0077] The confirmed lithium carbonate mother liquor is fed into a plate heat exchanger at a flow rate of 2 m³ / h. The mother liquor exchanges heat with cooling water within the heat exchanger, achieving cooling.

[0078] During the cooling process, the temperatures of the mother liquor and cooling water are monitored in real time, and the cooling water flow rate is adjusted by a PID controller to ensure that the mother liquor outlet temperature is stable at 40℃±1℃.

[0079] Adjust the flow rates of mother liquor and cooling water in a timely manner according to changes in the outlet temperature of the mother liquor to maintain a stable cooling rate. The cooling rate should be controlled at 5℃ / min.

[0080] When the outlet temperature of the mother liquor stabilizes at 40℃±1℃, the cooled mother liquor is discharged into the intermediate storage tank.

[0081] See Figure 3 In this embodiment, the internal pressure of the second cooling device containing critical nitrogen is 9 MPa ± 0.1 MPa, the mixing time is 10-15 minutes, and the internal temperature of the second cooling device is -15℃ ± 1℃.

[0082] Specifically, the temperature of the mother liquor during the first cooling was confirmed to be 40℃±1℃, the flow rate was stabilized at 2m³ / h, the Li₂CO₃ concentration was 150-200g / L, and it contained trace amounts of Na. +(0.2-0.5wt%), Ca 2+ (0.1-0.3wt%).

[0083] The critical nitrogen gas (SC-N2) was confirmed to have a temperature of -15℃ ± 1℃, a pressure of 9MPa ± 0.1MPa, and a flow rate of 2m³ / h. SC-N2 needs to be prepared and stored in a critical nitrogen generator beforehand.

[0084] The temperature and pressure control system of the second cooling device is activated to lower the internal temperature of the device to -15℃±1℃ and raise the pressure to 9MPa±0.1MPa.

[0085] The mother liquor from the first cooling process and critical nitrogen gas are simultaneously introduced into the second cooling device. The mother liquor and SC-N2 are initially mixed inside the device using a specific mixer (such as a static mixer).

[0086] The temperature control system of the second cooling device maintains the internal temperature of the equipment at -15℃±1℃, ensuring that SC-N2 remains in a supercritical state.

[0087] The pressure control system maintains the internal pressure of the equipment at 9MPa±0.1MPa to prevent SC-N2 from leaving the supercritical state due to pressure reduction.

[0088] The mother liquor and SC-N2 need to be mixed inside the equipment for a sufficiently long time to ensure adequate contact and extraction. The mixing time can be adjusted according to the actual extraction effect, and is generally set to 10-15 minutes.

[0089] To promote thorough mixing of the mother liquor and SC-N2, the internal stirring device or circulating pump can be turned on to allow the mixture to circulate within the equipment.

[0090] After the mixing and extraction process has reached the predetermined time, the extracted mother liquor is discharged from the second cooling device. During the discharge process, the internal temperature and pressure of the device must be kept stable to prevent changes in the state of SC-N2 from affecting the extraction effect.

[0091] See Figure 4 The temperature of the mother liquor after extraction was confirmed to be -15℃±1℃, the flow rate was stable at 2 m³ / h, the Li₂CO₃ concentration was 150-200 g / L, and the Na₂CO₃ concentration was [not specified]. + and Ca 2+ The content has been significantly reduced.

[0092] The critical nitrogen gas (SC-N2) was confirmed to have a temperature of -15℃ ± 1℃, a pressure of 9MPa ± 0.1MPa, and a flow rate of 2m³ / h. SC-N2 needs to be prepared and stored in a critical nitrogen generator beforehand.

[0093] Check that the third cooling device (such as a supercritical fluid extractor) is intact and ensure that the inside of the device is clean and free of impurities. At the same time, confirm that the temperature and pressure control systems of the device are working properly.

[0094] The temperature and pressure control system of the third cooling device is activated, reducing the internal temperature of the device to -15℃±1℃ and increasing the pressure to 9MPa±0.1MPa.

[0095] The extracted mother liquor and critical nitrogen gas are simultaneously introduced into a third cooling device. Inside the device, the mother liquor and SC-N2 are initially mixed using a specific mixer (such as a static mixer).

[0096] The temperature control system of the third cooling device maintains the internal temperature of the equipment at -15℃±1℃, ensuring that SC-N2 remains in a supercritical state.

[0097] The pressure control system maintains the internal pressure of the equipment at 9MPa±0.1MPa to prevent SC-N2 from leaving the supercritical state due to pressure reduction.

[0098] The mixing time between the mother liquor and SC-N2 inside the equipment needs to be long enough to ensure sufficient contact and secondary extraction. The mixing time can be adjusted according to the actual extraction effect, and is generally set to 10-15 minutes.

[0099] To promote thorough mixing of the mother liquor and SC-N2, the internal stirring device or circulating pump can be turned on to allow the mixture to circulate within the equipment.

[0100] After the mixing and secondary extraction processes have reached the predetermined time, the mother liquor from the secondary extraction is discharged from the third cooling device. During the discharge process, the internal temperature and pressure of the device must be kept stable to prevent changes in the state of SC-N2 from affecting the extraction effect.

[0101] See Figure 5 In this embodiment, the internal temperature of the fourth cooling device is 25℃±1℃; the pressure is reduced from 9MPa to atmospheric pressure, and the pressure release rate is controlled at 0.5MPa / min.

[0102] Specifically, the temperature of the mother liquor after the second extraction was confirmed to be -15℃±1℃, the pressure to be 9MPa±0.1MPa, the flow rate to be stable at 2m³ / h, the Li₂CO₃ concentration to be 150-200g / L, and the Na₂CO₃ concentration to be... + and Ca 2+ The content has been significantly reduced.

[0103] Check the fourth cooling device (such as a pressure relief tank) for damage, ensuring the inside of the equipment is clean and free of impurities. Also, confirm that the equipment's temperature and pressure control systems are functioning properly, and that safety valves, rupture discs, and other safety accessories are intact and effective.

[0104] Turn on the temperature control system of the fourth cooling device to lower the internal temperature of the device to 25℃±1℃ in preparation for receiving the mother liquor after the second extraction.

[0105] The mother liquor after the second extraction is passed into the fourth cooling device. During the process, the pressure of the mother liquor will be gradually released, from 9 MPa to atmospheric pressure.

[0106] The pressure control system of the fourth cooling device slowly releases the pressure of the mother liquor, preventing sudden pressure drops from adversely affecting the properties of the mother liquor and the equipment. The pressure release rate is controlled within 0.5 MPa / min.

[0107] During the pressure release process, the temperature control system of the fourth cooling device maintains the internal temperature of the equipment at 25℃±1℃ to ensure that the mother liquor does not undergo unnecessary physical or chemical changes due to temperature changes during the pressure release process.

[0108] After the pressure of the mother liquor from the second extraction is completely released to atmospheric pressure (0.1013 MPa), the purified mother liquor is discharged from the fourth cooling device. During the discharge process, the internal temperature of the device must be kept stable to prevent the properties of the mother liquor from being affected by temperature changes.

[0109] See Figure 6 In this embodiment, the step of injecting a chelating surfactant into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor, includes:

[0110] DTPA-BA (diethylenetriaminepentaacetic acid bisamide) was selected as the chelating surfactant at a concentration of 0.1 wt%. The required surfactant injection amount was calculated based on the mother liquor flow rate to ensure that the surfactant concentration in the mother liquor reached 0.05-0.1 wt%.

[0111] Turn on the temperature control system of the chelation reactor and maintain the internal temperature of the equipment at 25℃±1℃. Quantitatively inject DTPA-BA solution into the chelation reactor using a metering pump.

[0112] Turn on the stirring device of the chelation reactor and stir the mother liquor at a speed of 300 rpm to ensure that the chelating surfactant and the heavy metal ions in the mother liquor come into full contact. Maintain the internal temperature of the chelation reactor at 25℃±1℃ to obtain the chelated mother liquor.

[0113] Specifically, the temperature of the purified mother liquor (from the fourth cooling device) was confirmed to be 25℃±1℃, the flow rate was stable at 2m³ / h, the Li₂CO₃ concentration was 150-200g / L, and it contained trace amounts of heavy metal ions (such as Na₂CO₃). + <1ppm, Ca2+ <0.5ppm, total amount of other heavy metal ions <0.1ppm).

[0114] DTPA-BA (diethylenetriaminepentaacetic acid bisamide) was selected as the chelating surfactant at a concentration of 0.1 wt%. The required amount of surfactant to be injected was calculated based on the mother liquor flow rate to ensure that the surfactant concentration in the mother liquor reached 0.05-0.1 wt%.

[0115] Check the chelation reactor or pipeline mixer for damage, ensuring the interior is clean and free of impurities. Also, confirm that the temperature control system and stirring device are functioning properly.

[0116] Turn on the temperature control system of the chelation reactor to maintain the internal temperature of the equipment at 25℃±1℃ to provide a suitable chelation reaction environment.

[0117] The DTPA-BA solution is metered into the chelation reactor or pipeline mixer using a metering pump. The injection rate must match the mother liquor flow rate to ensure that the surfactant concentration in the mother liquor is uniform and within the predetermined range.

[0118] Turn on the agitator of the chelation reactor and stir the mother liquor at 300 rpm to ensure sufficient contact between the chelating surfactant and the heavy metal ions in the mother liquor. If a pipeline mixer is used, ensure that the internal structure of the mixer can provide sufficient turbulence intensity (Re>10000) to promote mixing.

[0119] The chelation reaction time needs to be long enough to ensure that the chelating surfactant reacts fully with the heavy metal ions to form a stable complex. The reaction time can be adjusted according to the actual chelation effect, but is generally set to 30 minutes.

[0120] Maintain the internal temperature of the chelation reactor or pipeline mixer at 25℃±1℃ to optimize the chelation reaction rate and selectivity.

[0121] Once the chelation reaction has reached the predetermined time, the chelated mother liquor is discharged from the chelation reactor or pipeline mixer. During the discharge process, the internal temperature of the equipment must be kept stable to prevent temperature changes from affecting the properties of the mother liquor.

[0122] See Figure 7 In this embodiment, the chelated mother liquor is separated by a three-phase separation method to obtain the separated mother liquor, which includes:

[0123] The temperature of the mother liquor after chelation was confirmed to be 25℃±1℃, the flow rate was stable at 2m³ / h, the Li₂CO₃ concentration was 150-200g / L, and it contained trace amounts of heavy metal ions (which had formed a stable complex with the chelated surfactant) and a small amount of possible gas (such as dissolved nitrogen).

[0124] Check that the three-phase separator (such as a centrifuge or settling tank) is intact and ensure that the inside of the equipment is clean and free of impurities. Also, confirm that the equipment's temperature and pressure control systems (if applicable), as well as the drainage, venting, and slag removal systems, are functioning properly.

[0125] Turn on the temperature and pressure control system of the three-phase separator to adjust the internal working conditions of the equipment.

[0126] The chelated mother liquor is fed into a three-phase separator. Inside the separator, the mother liquor undergoes three-phase separation based on density differences: the solid phase (heavy metal-chelating agent complex), the liquid phase (purified mother liquor), and the gas phase (dissolved gas).

[0127] Maintain the internal temperature of the three-phase separator at 25℃±1℃ to optimize the separation effect.

[0128] Set an appropriate separation time based on the mother liquor flow rate and separator performance to ensure thorough separation of the solid, liquid, and gas phases. The separation time can be adjusted according to the actual separation effect.

[0129] Liquid, gas, and slag discharge control: Periodically or continuously discharge the separated liquid phase (purified mother liquor), gas phase (dissolved gas), and solid phase (heavy metal-chelating agent complex). The speed and frequency of liquid, gas, and slag discharge need to be adjusted according to the material accumulation inside the separator.

[0130] The purified mother liquor after separation is discharged from the three-phase separator. During the discharge process, the internal temperature and pressure of the equipment must be kept stable to prevent changes in the properties of the mother liquor.

[0131] See Figure 8 In this embodiment, the step of subjecting the separated mother liquor to deep ultraviolet laser induction to obtain the grown crystal slurry includes:

[0132] The temperature of the separated mother liquor was adjusted to 20℃±1℃ in preparation for laser-induced crystallization.

[0133] A photosensitizer was added to the mother liquor, and the molecules were anchored to the surface of Li₂CO₃ crystals through dark adsorption. The adsorption time was controlled at 30 minutes to ensure that the photosensitizer was fully adsorbed.

[0134] Turn on the laser, set the laser wavelength to 172nm, the pulse width to 8ns, and the repetition frequency to 2kHz. Guide the laser beam to the surface of the mother liquor in the crystallizer through the optical path system. Control the scanning speed to 80mm / s to ensure that the laser beam uniformly covers the surface of the mother liquor. Precisely control the laser energy density to 1.0J / cm². The crystallizer is equipped with a three-level temperature control system, maintaining the temperature of the laser action zone at 10℃±1℃, the temperature of the growth zone at 20℃±1℃, and the temperature of the buffer zone at 25℃±1℃.

[0135] Turn on the agitator of the crystallizer and stir the mother liquor at a speed of 300 rpm to promote crystal growth and uniform distribution; after the laser-induced crystallization process has reached the predetermined time, discharge the grown crystal slurry from the crystallizer.

[0136] In this embodiment, the step of adding a crystal form control agent and regulating the growth of the grown crystal slurry to obtain a concentrated crystal slurry includes:

[0137] The PEG solution is metered into the crystallizer using a metering pump, wherein the internal temperature of the crystallizer is maintained at 25℃±1℃; the crystal slurry is stirred at a speed of 200 rpm to promote uniform crystal growth and prevent aggregation.

[0138] The crystal slurry was ultrasonically treated at a frequency of 20kHz and a power of 50W.

[0139] Once the crystal growth reaches the predetermined time, the regulated crystal slurry is discharged from the crystallizer.

[0140] The discharged crystal slurry is subjected to solid-liquid separation using a centrifuge or filtration device to remove some of the mother liquor, thereby obtaining concentrated crystal slurry.

[0141] Specifically, the temperature of the mother liquor after separation (from the three-phase separator) was confirmed to be 25℃±1℃, the flow rate was stable at 2m³ / h, the Li₂CO₃ concentration was 150-200g / L, and it contained trace amounts of heavy metal ions (which had been stabilized through chelation) as well as photosensitizers (such as iridium complexes, at a concentration of 0.05wt%).

[0142] Check that the deep ultraviolet laser (such as the Xe2 excimer laser) is intact, ensuring stable laser output and adjustable parameters such as wavelength, pulse width, and repetition rate. Simultaneously, check that the optical path system (such as mirrors, lenses, and digital micromirror devices, DMDs) is clean and free of obstructions.

[0143] Check the crystallizer (such as a reactor with a temperature control system) for damage and ensure the inside of the equipment is clean and free of impurities. Also, confirm that the equipment's temperature control system and stirring device are functioning properly.

[0144] The temperature of the separated mother liquor was adjusted to 20℃±1℃ in preparation for laser-induced crystallization.

[0145] A photosensitizer (iridium complex) was added to the mother liquor, and the molecules were anchored to the surface of Li₂CO₃ crystals through dark adsorption. The adsorption time was controlled at 30 minutes to ensure that the photosensitizer was fully adsorbed.

[0146] Turn on the laser, set the laser wavelength to 172nm, the pulse width to 8ns, and the repetition frequency to 2kHz. Guide the laser beam to the surface of the mother liquor inside the crystallizer through the optical path system.

[0147] The laser beam forms a dynamic beam array using a digital micromirror device (DMD) to scan the mother liquor. The scanning speed is controlled at 80 mm / s to ensure uniform laser beam coverage of the mother liquor surface. The laser energy density is precisely controlled at 1.0 J / cm² to trigger explosive nucleation.

[0148] The crystallizer is equipped with a three-level temperature control system: the temperature of the laser action zone is maintained at 10℃±1℃ (precisely controlled by a liquid nitrogen micro-spray system), the temperature of the growth zone is maintained at 20℃±1℃ (controlled by a water bath circulation system), and the temperature of the buffer zone is maintained at 25℃±1℃ (controlled by air convection).

[0149] Turn on the agitator in the crystallizer and stir the mother liquor at 300 rpm to promote crystal growth and uniform distribution.

[0150] Once the laser-induced crystallization process has reached the predetermined time (determined based on crystal growth, generally 2-4 hours), the grown crystal slurry is discharged from the crystallizer. During the discharge process, the internal temperature and stirring conditions of the equipment must be kept stable to prevent crystal aggregation or breakage.

[0151] See Figure 9 In this embodiment, the solid-liquid separation and drying of the concentrated crystal slurry to obtain lithium carbonate includes:

[0152] The concentrated slurry is fed into a solid-liquid separation device, where the lithium carbonate crystals are separated from the mother liquor by centrifugal force or pressure difference.

[0153] The separated wet crystals (containing approximately 20-30 wt% water) are discharged from the bottom of the equipment and collected in a drying container;

[0154] Turn on the vacuum drying oven or spray dryer, and set the appropriate temperature, vacuum level, or hot air temperature and wind speed. Pass the collected wet crystals into the drying equipment for drying. Maintain the internal temperature of the drying equipment at 80℃±5℃, the vacuum level at -0.09MPa±0.005MPa (if using a vacuum drying oven), or the hot air temperature at 120℃±5℃ and the wind speed at 1.5m / s±0.2m / s (if using a spray dryer). The drying time is set according to the moisture content of the wet crystals and the equipment performance, generally 2-4 hours.

[0155] Specifically,

[0156] The temperature of the concentrated crystal slurry was confirmed to be 25℃±1℃, the Li2CO3 concentration was 250-300g / L, the crystal particle size distribution met expectations (e.g., D50 was between 100-200μm), and it contained trace amounts of heavy metal ions (which had been stabilized by chelation) as well as residual photosensitizers and crystal form control agents.

[0157] Check that the centrifuge or filter is in good working order and ensure that the inside of the equipment is clean and free of impurities. Also, confirm that parameters such as the equipment's speed, pressure, or vacuum level are adjustable to meet the separation requirements.

[0158] Check that the vacuum drying oven or spray dryer is in good working order and ensure that the inside of the equipment is clean and free of impurities. Also, confirm that parameters such as temperature, vacuum level, hot air temperature, and airflow rate are adjustable to meet drying requirements.

[0159] Depending on the type of equipment, turn on the centrifuge or filter and set the appropriate speed, pressure or vacuum level to prepare for solid-liquid separation.

[0160] The concentrated slurry is then fed into a solid-liquid separation device. Inside the device, the lithium carbonate crystals are separated from the mother liquor by centrifugal force or pressure difference.

[0161] The separated wet crystals (containing approximately 20-30 wt% water) are discharged from the bottom of the equipment and collected in a drying container. The mother liquor is discharged through the equipment outlet for recycling.

[0162] Turn on the vacuum drying oven or spray dryer and set the appropriate temperature, vacuum level or hot air temperature and wind speed to prepare for drying.

[0163] The collected wet crystals are passed into a drying device. Inside the device, the moisture on the surface of the wet crystals is removed through heat conduction, heat convection, or heat radiation.

[0164] Maintain the internal temperature of the drying equipment at 80℃±5℃ and the vacuum degree at -0.09MPa±0.005MPa (if using a vacuum drying oven), or the hot air temperature at 120℃±5℃ and the air velocity at 1.5m / s±0.2m / s (if using a spray dryer). The drying time is set according to the moisture content of the wet crystals and the performance of the equipment, generally set to 2-4 hours.

[0165] Once the drying process has reached the predetermined time, the dried lithium carbonate product is discharged from the drying equipment. During discharge, the internal temperature and vacuum level or hot air condition of the equipment must be kept stable to prevent the product from absorbing moisture or clumping.

[0166] This application also provides a lithium carbonate, which is obtained by the lithium carbonate mother liquor evaporation and crystallization process described above.

[0167] This application has the following advantages:

[0168] A gradient cooling system using heat exchange and critical nitrogen (SC-N2) is employed to achieve precise temperature control from 60℃ to 40℃ to -15℃ (error ±1℃). Critical nitrogen at 9MPa pressure forms a highly efficient extraction medium, and through two thorough mixing cycles of 10-15 minutes each, sodium is effectively removed. +(0.2-0.5wt%→<1ppm) and Ca 2+ (0.1-0.3wt% → <0.5ppm). Low-temperature environment inhibits impurity dissolution; combined with the high transfer performance of supercritical fluids, extraction efficiency is increased by more than 30% compared to traditional methods.

[0169] The innovative DTPA-BA diamide chelating agent forms a stable complex through multidentate coordination, achieving a chelation capacity of 150 mg / g for heavy metal ions (total <0.1 ppm). Under normal pressure reaction conditions at 25℃, it achieves a heavy metal removal rate of 99.5%, avoiding the energy consumption and secondary pollution caused by high-temperature precipitation methods.

[0170] A 172nm deep ultraviolet laser combined with a photosensitizer (iridium complex) triggers explosive nucleation via an 8ns pulsed laser, achieving a crystal growth rate of 20μm / min. A temperature control system (10℃ / 20℃ / 25℃ gradient) combined with 300rpm stirring ensures precise control of the crystal particle size D50 within 100-200μm. Ultrasonic assistance (20kHz / 50W) and a PEG crystal form control agent work synergistically to improve crystal morphology uniformity by 40%.

[0171] See Figure 10 , Figure 10 To verify the effect of different pressures on Na in a 9 MPa critical nitrogen environment. + / Ca 2+ The impact of removal rate.

[0172] The experimental procedure is as follows:

[0173] Preparation of Na + 0.3wt%, Ca 2+ A simulated mother liquor of 0.2 wt% was used. The supercritical equipment was set to pressure of 7 / 8 / 9 / 10 MPa and temperature of -15℃. After mixing for 15 minutes, samples were taken and the metal ion concentration was detected by ICP-MS. The experiment was repeated 3 times at each pressure point.

[0174] from Figure 10 It can be seen that under a pressure of 9 MPa, Na + The removal rate reached 95%, Ca 2+ With a removal rate of 92%, experiments have demonstrated that critical nitrogen gas has selective extraction capabilities for impurities in lithium mother liquor at -15℃.

[0175] See Figure 11 , Figure 11 The following is a detailed experimental procedure used to verify the removal effect of DTPA-BA chelating agent on trace heavy metals in mother liquor:

[0176] Configuration including Pb 2+ 1ppm, Cu 2+Add 0.1wt% DTPA-BA solution to a simulated mother liquor of 0.8ppm, stir at 30℃, take samples every 5 minutes, and detect the heavy metal concentration using AAS, and continue monitoring until the concentration stabilizes.

[0177] See Figure 12 , Figure 12 To verify the effect of crystal size control under 172nm deep ultraviolet laser irradiation.

[0178] The experimental procedure is as follows:

[0179] A Li₂CO₃ solution with a supersaturation of 1.2 was prepared, and a photosensitizer (iridium complex) was added. The solution was allowed to adsorb in the dark for 30 minutes. The laser parameters were set as follows: wavelength 172 nm, pulse width 8 ns, energy density 1.0 J / cm², temperature gradient (10℃ / 20℃ / 25℃) was maintained by a three-stage temperature control system, scanning speed 80 mm / s, and continuous irradiation was carried out for 2 hours.

[0180] Experimental data such as Figure 12 As shown, the crystal grain size D50 increased from the initial 50 μm to 150 μm; the standard deviation of the grain size distribution decreased from 45 μm to 28 μm; and the morphology uniformity index increased from 0.65 to 0.82.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium carbonate mother liquor evaporation and crystallization process, characterized in that, The lithium carbonate mother liquor evaporation and crystallization process includes: The lithium carbonate mother liquor is fed into the first cooling device, thereby reducing the temperature of the lithium carbonate mother liquor from 60°C to 40°C, thus obtaining the first cooled mother liquor. The mother liquor from the first cooling process is passed into a second cooling device containing critical nitrogen gas, so that the mother liquor from the first cooling process and the critical nitrogen gas are fully mixed in the second cooling device, thereby obtaining the mother liquor after extraction. The mother liquor after extraction is passed into a third cooling device containing critical nitrogen gas, so that the mother liquor after extraction and critical nitrogen gas are fully mixed in the third cooling device to obtain the mother liquor after secondary extraction. The mother liquor after the second extraction is passed into the fourth cooling device to release the pressure of the mother liquor after the second extraction, thereby obtaining purified mother liquor; A chelating surfactant is injected into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor. The chelated mother liquor is separated by a three-phase separation process to obtain the separated mother liquor. The separated mother liquor was subjected to deep ultraviolet laser induction to obtain the grown crystal slurry; A crystal form control agent was added and growth was regulated after the crystal slurry was grown, thereby obtaining a concentrated crystal slurry; Lithium carbonate is obtained by solid-liquid separation and drying of concentrated crystal slurry.

2. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 1, characterized in that, The step of introducing the lithium carbonate mother liquor into the first cooling device, thereby reducing the temperature of the lithium carbonate mother liquor from 60°C to 40°C, to obtain the first cooled mother liquor includes: The lithium carbonate mother liquor is fed into a plate heat exchanger at a flow rate of 2 m³ / h. The mother liquor exchanges heat with cooling water in the heat exchanger. During the cooling process, the temperature of the mother liquor and cooling water is monitored in real time. The cooling water flow rate is adjusted by a PID controller to ensure that the outlet temperature of the lithium carbonate mother liquor is stable at 40℃±1℃.

3. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 2, characterized in that, The internal pressure of the second cooling device containing critical nitrogen is 9 MPa ± 0.1 MPa, and the mixing time is 10-15 minutes; the internal temperature of the second cooling device is -15℃ ± 1℃.

4. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 3, characterized in that, The internal temperature of the fourth cooling device is 25℃±1℃; the pressure is reduced from 9MPa to atmospheric pressure, and the pressure release rate is controlled at 0.5MPa / min.

5. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 4, characterized in that, The step of injecting a chelating surfactant into the mother liquor, allowing the surfactant molecules to form a stable complex with trace heavy metal ions in the mother liquor through multidentate chelation, thereby obtaining the chelated mother liquor includes: DTPA-BA was selected as the chelating surfactant at a concentration of 0.1 wt%. The required surfactant injection amount was calculated based on the mother liquor flow rate to ensure that the surfactant concentration in the mother liquor reached 0.05-0.1 wt%. Maintain the internal temperature of the equipment at 25℃±1℃, and inject the DTPA-BA solution into the chelation reactor using a metering pump; Turn on the stirring device of the chelation reactor and stir the mother liquor at a speed of 300 rpm to ensure that the chelating surfactant and the heavy metal ions in the mother liquor come into full contact. Maintain the internal temperature of the chelation reactor at 25℃±1℃ to obtain the chelated mother liquor.

6. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 5, characterized in that, The step of subjecting the separated mother liquor to deep ultraviolet laser induction to obtain the grown crystal slurry includes: Adjust the temperature of the separated mother liquor to 20℃±1℃; A photosensitizer was added to the mother liquor, and the molecules were anchored on the surface of Li2CO3 crystals by dark adsorption. The adsorption time was controlled at 30 minutes. Turn on the laser, set the laser wavelength to 172nm, the pulse width to 8ns, and the repetition frequency to 2kHz, and guide the laser beam to the surface of the mother liquor in the crystallizer; the scanning speed is controlled at 80mm / s, and the laser energy density is precisely controlled at 1.0J / cm²; the crystallizer includes a three-stage temperature control system, with the temperature of the laser action zone maintained at 10℃±1℃, the temperature of the growth zone maintained at 20℃±1℃, and the temperature of the buffer zone maintained at 25℃±1℃; The mother liquor is stirred at 300 rpm to promote crystal growth and uniform distribution; after the laser-induced crystallization process reaches the predetermined time, the grown crystal slurry is discharged from the crystallizer.

7. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 6, characterized in that, The process of adding a crystal form control agent and regulating growth of the grown crystal slurry to obtain a concentrated crystal slurry includes: The PEG solution is metered into the crystallizer using a metering pump, wherein the internal temperature of the crystallizer is maintained at 25℃±1℃; the crystal slurry is stirred at a speed of 200 rpm to promote uniform crystal growth and prevent aggregation. The crystal slurry was ultrasonically treated at a frequency of 20kHz and a power of 50W. Once the crystal growth reaches the predetermined time, the regulated crystal slurry is discharged from the crystallizer. The discharged crystal slurry is subjected to solid-liquid separation using a centrifuge or filtration device to remove some of the mother liquor, thereby obtaining concentrated crystal slurry.

8. The lithium carbonate mother liquor evaporation and crystallization process as described in claim 7, characterized in that, The process of solid-liquid separation and drying of the concentrated crystal slurry to obtain lithium carbonate includes: The concentrated slurry is fed into a solid-liquid separation device, where the lithium carbonate crystals are separated from the mother liquor by centrifugal force or pressure difference. The separated wet crystals are discharged from the bottom of the equipment and collected in a drying container; Turn on the vacuum drying oven or spray dryer and pass the collected wet crystals into the drying equipment for drying; maintain the internal temperature of the drying equipment at 80℃±5℃, the vacuum degree at -0.09MPa±0.005MPa, or the hot air temperature at 120℃±5℃ and the wind speed at 1.5m / s±0.2m / s.

9. A lithium carbonate, characterized in that, The lithium carbonate is obtained by the lithium carbonate mother liquor evaporation and crystallization process as described in any one of claims 1 to 8.

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