A method for continuous crystallization of fluorine-containing complex salts

Abstract

This invention discloses a continuous crystallization method for fluorine-containing complex salts, belonging to the field of chemical crystallization technology. It solves the problems of low efficiency in manual cleaning, interference between stirring and wall scraping, and low automation in existing technologies. The method includes: initiating a crystallization stirring process to stir the fluorine-containing complex salt solution in the crystallization tank while keeping the scraper assembly stationary; real-time monitoring of the duration of crystallization stirring and the solution temperature; when the duration reaches t and the solution temperature reaches T, the crystallization process is determined to be complete, and the process automatically switches to the wall scraping process: driving the scraper assembly to rotate and scrape off the crystal scale layer against the inner wall of the tank, while simultaneously discharging the crystal product; after the wall scraping process is completed, the scraping is automatically stopped, and the next batch of fluorine-containing complex salt solution is automatically injected, repeating steps S1 to S3. This invention simplifies the equipment structure, avoids interference of the scraper with crystal growth, improves cleaning efficiency, product yield and quality, and has a high degree of automation.

Description

Technical Field

[0001] This invention relates to the field of chemical crystallization technology, and in particular to a continuous crystallization method for fluorine-containing complex salts. Background Technology

[0002] During the cooling, concentration, and crystallization process of fluorine-containing complex salts, crystals such as potassium fluorotantalate possess inherent characteristics of strong adhesion and high crystallization tendency. They easily deposit and adhere to the inner walls of the crystallization tank, the surface of heat exchange coils, the agitator blades, and the conical bottom of the tank, forming a hard and difficult-to-clean crystalline scale layer. As the production cycle extends, the thickness of this scale layer continuously increases, significantly reducing the effective volume of the crystallization tank, decreasing the single crystallization throughput, and causing a decline in production efficiency. It also hinders heat transfer from heat exchange components, disrupts the uniformity of the temperature and concentration fields in the crystallization system, and severely affects the quality stability of the fluorine-containing complex salt products. Furthermore, the hard crystalline scale layer exacerbates mechanical wear on the agitator blades and the tank, increasing equipment operating energy consumption. The accumulation of scale also wastes valuable tantalum and niobium resources, reduces the final product yield, and may even contaminate the next batch of crystallized material, leading to production problems such as substandard product purity.

[0003] To address the problem of scale buildup in crystallization tanks, existing technologies primarily employ three methods: manual cleaning, chemical cleaning, and crystallization equipment with wall-scraping capabilities. However, all three methods suffer from significant technical drawbacks: Manual cleaning relies mainly on manual tapping and mechanical scraping, which is labor-intensive, inefficient, and prone to scratching the anti-corrosion layer on the inner wall of the crystallization tank, compromising the structural integrity of the equipment and drastically shortening its lifespan. Furthermore, manual cleaning requires machine shutdown, severely disrupting production continuity and increasing equipment maintenance and production time costs. Chemical cleaning dissolves the scale layer using chemical reagents, but it easily introduces impurity ions, leading to the loss of valuable metals such as tantalum. It also significantly increases the difficulty and cost of subsequent wastewater treatment processes, and the residue of chemical reagents can easily cause secondary pollution, affecting the purity of subsequent crystallized products.

[0004] In the existing crystallization process of fluorine-containing complex salts, manually determining the timing of cleaning and the switching between stirring and scraping can easily lead to premature cleaning interfering with crystal growth, or excessive cleaning causing excessive crystal accumulation, which seriously affects the particle size uniformity and yield of the crystal product. Furthermore, improper intervention of the scraper during the crystallization process can disrupt the microenvironment for crystal nucleation and growth, resulting in crystal breakage, smaller crystal grains, and ultimately a decline in product quality.

[0005] In summary, existing technologies for the crystallization process of fluorine-containing complex salts cannot simultaneously solve the problems of low cleaning efficiency, poor production continuity, interference with crystal growth, and unstable product quality. They also cannot meet the high-quality requirements of the chemical crystallization field for fluorine-containing complex salt crystallized products and the industrialization needs for green, efficient, and continuous production. Summary of the Invention

[0006] In view of the above, the present invention aims to provide a continuous crystallization method for fluorine complex salts to at least solve one of the problems existing in the prior art: (1) manual or chemical cleaning of scale in crystallization tanks is inefficient, easily scratches equipment or introduces impurities, and requires shutdown operation, affecting production continuity; (2) manually determining the cleaning time and the switching time between stirring and scraping the wall can easily lead to premature cleaning interfering with crystal growth and excessive crystal accumulation due to delayed cleaning, which seriously affects the uniformity of crystal particle size and yield.

[0007] The objective of this invention is mainly achieved through the following technical solutions: The first aspect of this invention provides a method for continuous crystallization of a fluorine-containing complex salt, comprising the following steps: S1: Start the crystallization stirring process to crystallize and stir the fluorine-containing complex salt solution in the crystallization tank, while keeping the scraper assembly stationary. S2: Real-time monitoring of the duration of crystallization stirring and solution temperature. When the duration reaches the preset time threshold t and the solution temperature reaches the preset temperature threshold T, the crystallization process is automatically determined to be over, and the process is automatically switched to the wall scraping process: drive the scraper assembly to rotate and scrape off the crystal scale layer attached to the inner wall of the tank, and discharge the crystal product at the same time. S3: After the wall scraping process is completed, the wall scraping will automatically stop and the next batch of fluorine-containing complex salt solution will be automatically injected, repeating steps S1 to S3.

[0008] Furthermore, the range of t is 20-50h, and the range of T is 10-20℃.

[0009] Furthermore, in the crystallization stirring process, the stirring component rotates in the forward direction, and in the wall scraping process, the scraper component rotates in the reverse direction.

[0010] Furthermore, the ratio of the servo motor's reverse rotation speed to its forward rotation speed is 1:0.5-10.

[0011] Furthermore, the forward rotation speed is 0.5-5 rpm, and the reverse rotation speed is 1-10 rpm.

[0012] Furthermore, the wall scraping process of the scraper assembly is controlled by a servo motor. When the drive current of the servo motor drops to 20-30% of the initial wall scraping current, the wall scraping is considered complete.

[0013] Furthermore, in step S2, the time for the scraper assembly to rotate and scrape the wall is 1-10 minutes.

[0014] Furthermore, the scraper assembly includes: an L-shaped scraper support and a scraper body.

[0015] Furthermore, the gap between the scraper body and the inner wall of the groove is controlled at 0.5-1mm.

[0016] Furthermore, the fluorine-containing complex salt includes at least one of potassium fluorotantalate, potassium fluoroniobate, potassium fluorotitanate, potassium fluoroaluminate, and potassium fluorozirconate.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) This invention monitors the dual signals of crystallization time and solution temperature in real time, and determines the crystallization endpoint based on the crystallization time and solution temperature. Then, it determines the timing of wall scraping based on the crystallization endpoint, replacing the traditional manual judgment and manual switching operation method. It realizes the precise automatic triggering and seamless connection from crystallization stirring to wall scraping and cleaning, greatly improving the automation level and response time of the process. There is no need to stop the machine. After the material is discharged, it can be directly injected into the next batch of materials to realize continuous production.

[0018] (2) This invention effectively avoids problems such as excessive crystal accumulation and thickened scale that are difficult to clean due to untimely switching. In addition, the entire process is operated in a closed system, and the wall scraping process does not require manual intervention by opening the cover or the introduction of any chemical cleaning reagents, thus eliminating contamination by impurity ions and loss of valuable metal resources. At the same time, it meets the green, efficient and continuous production needs of the metallurgical and chemical industry, and significantly improves product yield and utilization rate of valuable resources.

[0019] (3) In the crystallization process of the fluorine complex salt of the present invention, the timing of cleaning, stirring and wall scraping is determined according to the crystallization time and solution temperature. The wall scraping is automatically stopped after the wall scraping process is completed. This can avoid the continuous presence or improper intervention of the scraper in the crystallization process, which may damage the microenvironment for crystal nucleation and growth, resulting in crystal breakage, smaller crystal grains, and ultimately a decline in product quality.

[0020] (4) This invention can use the forward and reverse rotation control of a single servo motor to realize the working timing of stirring and scraping. During the crystallization stage, only the stirring component is driven to work, while the scraping component remains stationary. During the wall scraping stage, it automatically switches to the scraping component rotating against the wall. This method can avoid the friction of the scraper on the inner wall of the tank during the crystallization process and the interference with the crystal nucleation and growth environment, effectively ensuring the uniformity of the crystal particle size and distribution of the crystallized product. At the same time, the forward and reverse rotation control of a single servo motor can realize the automatic time-sharing of crystallization and cleaning, avoiding the repeated crystallization of retained materials as crystal seeds due to the introduction of impurities or incomplete cleaning during manual cleaning. This reduces problems such as crystal particles that are too large or too small, and also eliminates the risk of large block crystals scratching the inner wall of the tank, significantly improving product consistency and equipment operation safety.

[0021] (5) This invention achieves highly efficient and automated operation of the continuous crystallization process by employing time-sharing crystallization stirring and wall scraping, with the stirring component and scraper component rotating in opposite directions and a reasonable speed ratio (forward speed of 0.5-5 rpm, reverse speed of 1-10 rpm, preferably 1:5), and automatically determining the wall scraping endpoint when the drive current of the servo motor drops to 20-30% of the initial wall scraping current. The crystal yield can reach over 99%, and the average particle size of the obtained crystals can be maintained above 20 μm with complete crystal form; a single cleaning takes only about 10 minutes, significantly improving cleaning efficiency; at the same time, the equipment operates stably, and the failure rate can be reduced to zero. The method of this invention significantly shortens the cleaning time while ensuring high product quality and high yield. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] Figure 1 This is a schematic diagram of a crystallization device provided in an embodiment of the present invention.

[0024] Figure Labels 100: Tank body; 200: Servo motor; 300: One-way transmission assembly; 410: Stirring shaft; 420: Stirring paddle; 510: Scraper bracket; 520: Scraper body. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0026] The existing crystallization process for fluorine-containing complex salts suffers from several drawbacks. Manual or chemical cleaning of the crystallization tank is inefficient, can easily scratch equipment or introduce impurities, and requires shutdown, affecting production continuity. Determining the timing of cleaning and the switching between stirring and scraping can lead to premature cleaning interfering with crystal growth or excessive cleaning causing excessive crystal accumulation, severely impacting the uniformity of crystal size and yield.

[0027] The first aspect of this invention provides a method for continuous crystallization of a fluorine-containing complex salt, comprising the following steps: S1: Start the crystallization stirring process to crystallize and stir the fluorine-containing complex salt solution in the crystallization tank, while keeping the scraper assembly stationary. S2: Real-time monitoring of the duration of crystallization stirring and solution temperature. When the duration reaches the preset time threshold t and the solution temperature reaches the preset temperature threshold T, the crystallization process is automatically determined to be over, and the process is automatically switched to the wall scraping process: drive the scraper assembly to rotate and scrape off the crystal scale layer attached to the inner wall of the tank, and discharge the crystal product at the same time. S3: After the wall scraping process is completed, the wall scraping will automatically stop and the next batch of fluorine-containing complex salt solution will be automatically injected, repeating steps S1 to S3.

[0028] In this invention, by real-time monitoring of both crystallization time and solution temperature signals, the crystallization endpoint is determined in real time based on these signals. Then, the timing for starting the wall scraping is determined based on the crystallization endpoint. This replaces the traditional manual judgment and manual switching operation method, achieving precise automatic triggering and seamless connection from crystallization stirring to wall scraping cleaning. This significantly improves the automation level and responsiveness of the process, eliminating the need for machine shutdown. After discharge, the next batch of material can be directly injected, achieving continuous production.

[0029] According to some specific embodiments of the present invention, a temperature sensor is provided in the tank. The temperature sensor is installed on the side wall or bottom of the tank through a protective sleeve, and the probe extends into the solution to collect the solution temperature signal in real time. The temperature sensor is electrically connected to the control unit. The timing function is realized by a timer or system clock integrated inside the control unit, without the need to set a physical timer in the tank.

[0030] Specifically, the control unit determines the crystallization endpoint based on the received temperature and timing signals: when the solution temperature reaches a preset temperature threshold T, and the cumulative duration since the start of the stirring process reaches a preset time threshold t, the crystallization process is considered complete, and the wall scraping process is initiated simultaneously. This achieves automated control of the process, effectively avoiding problems such as excessive crystal accumulation and thickened scale that are difficult to clean due to untimely switching.

[0031] According to some embodiments of the present invention, the range of t is 20-50h, and the range of T is 10-20℃.

[0032] This invention limits the crystallization time t to 20. 50h, crystallization endpoint temperature T is limited to 10 20℃, unlike existing technologies that rely on human experience or fixed durations and lack a clearly defined temperature. A coarse-grained control method for time-coordination criteria. In this invention, potassium fluorotantalate is used as an example, at 20... Within 50 hours, the crystals can grow to a state of uniform particle size and complete crystal form, avoiding excessive fine crystals and filtration difficulties caused by too short a time; at the same time, the final temperature is controlled at 10°C. A temperature of 20℃ ensures sufficient crystal precipitation while preventing impurities from co-precipitating or excessive mother liquor viscosity from affecting the scraping effect at excessively low temperatures. If t < 20h or T > 20℃, crystal precipitation is insufficient, resulting in a significant decrease in yield, and residual solutes can easily induce uncontrollable secondary nucleation in subsequent batches, disrupting particle size consistency or hindering crystal growth. If t > 50h or T < 10℃, excessive crystal growth leads to coarse or caked scale layers, increasing scraping resistance, causing equipment wear, and potentially causing crystal breakage due to prolonged stirring, thus reducing product quality. For example, t can be 20h, 25h, 30h, 40h, 50h, or any two of these values. T can be 10℃, 12℃, 15℃, 18℃, 20℃, or any two of these values.

[0033] It should be noted that the timing of cleaning, stirring, and wall scraping is determined based on the crystallization time and solution temperature. The wall scraping process is automatically stopped after completion, and the scraper assembly is kept stationary during the crystallization stirring process. This avoids the continuous presence or improper intervention of the scraper during the crystallization process, which could damage the microenvironment for crystal nucleation and growth, leading to crystal breakage, smaller crystal grains, and ultimately a decline in product quality. It also replaces the traditional manual judgment and manual switching operation method, thereby improving production efficiency, product yield, and product quality stability.

[0034] According to some embodiments of the present invention, the function of keeping the scraper assembly stationary during crystallization stirring can be achieved by a one-way transmission assembly. Specifically, the one-way transmission assembly includes an inner ring, an outer ring, and a one-way overrunning clutch disposed between the inner ring and the outer ring. The stirring assembly is fixedly connected to the inner ring of the one-way transmission assembly, and the scraper assembly is fixedly connected to the outer ring of the one-way transmission assembly. The inner ring and the outer ring are engaged / disengaged by a wedge block.

[0035] According to a specific embodiment of the present invention, the one-way overrunning clutch includes a wedge, a retainer, and a spring.

[0036] According to some embodiments of the present invention, the stirring assembly rotates in the forward direction during the crystallization stirring process, and the scraper assembly rotates in the reverse direction during the wall scraping process.

[0037] In this invention, during forward rotation, a crystallization stirring process is performed. At this time, the scraper remains stationary to prevent the scraper from rubbing against the tank wall, disturbing the flow field, and damaging the crystal nucleation and growth environment during the crystallization process, thereby ensuring uniform crystal size and complete particle size.

[0038] Furthermore, compared to the forward stirring crystallization process, the reverse rotation of the wall scraping process can efficiently remove the scale layer. The crystallization stirring process and the wall scraping process rotate in opposite directions, which allows crystallization and wall scraping to be carried out in separate time without affecting the quality of the generated crystals. This eliminates the need for manual intervention, thereby improving product yield and achieving continuous automated production.

[0039] According to some embodiments of the present invention, the one-way overrunning clutch can realize forward rotation of the crystallization stirring process and reverse rotation of the wall scraping process, while ensuring that the scraper remains stationary during the crystallization stirring process. Specifically, when the servo motor rotates forward (simultaneously driving the inner ring to rotate forward), the wedge in the one-way overrunning clutch disengages from the outer ring under centrifugal force, and only the inner ring rotates alone; when the servo motor rotates in the reverse direction, the wedge is wedged between the inner ring and the outer ring under the action of spring force, driving the outer ring to rotate synchronously. At this time, the reverse rotation does not affect the quality of the generated crystal, and the entire process requires no electrical or manual intervention.

[0040] In this invention, a single servo motor can be used as the power source, providing power for stirring or scraping functions by switching between forward and reverse rotation. This achieves automatic switching of rotation direction and speed, eliminating the need for complex electrical coordination control, machine shutdown, and manual scraping. It avoids the problem of impurities being introduced or incomplete cleaning leading to repeated crystallization of retained material as seed crystals, significantly improving production efficiency and product quality stability. Furthermore, the absence of complex electrical coordination control also avoids scratches on the inner wall of the tank, preventing damage to the equipment's anti-corrosion layer and eliminating multiple potential failure points, thus extending the equipment's service life.

[0041] According to some specific embodiments of the present invention, the ratio of the rotational speed of the reverse rotation to the rotational speed of the forward rotation is 1:0.5-10.

[0042] In this invention, the ratio of the reverse rotation speed to the forward rotation speed satisfies the aforementioned range, enabling: the high forward speed to meet the requirements of solution homogenization and regular crystal growth, and the low reverse speed to avoid equipment wear and crystal breakage, ensuring the wall scraping effect, while simultaneously matching power transmission and improving equipment operational stability. For example, the ratio of the reverse rotation speed to the forward rotation speed of the servo motor can be 1:0.5, 1:1, 1:2, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any combination of the above two values.

[0043] According to some specific embodiments of the present invention, in order to achieve synergistic optimization of high-quality crystal growth and efficient cleaning, the rotation speed of the forward rotation is 0.5-5 rpm, and the rotation speed of the reverse rotation is 1-10 rpm.

[0044] In this invention, the crystallization stage requires a stirring speed of 0.5-5 rpm to provide a gentle flow field, promote uniform crystal nucleation and growth, and avoid crystal breakage caused by high shear forces. If the forward rotation speed is <0.5 rpm, the solution will be unevenly mixed, and the temperature and concentration gradients will increase, resulting in a wide crystal particle size distribution and the inclusion of impurities. If the forward rotation speed is >5 rpm, the shear force will be too high, causing severe crystal breakage, a decrease in average particle size, and a reduction in yield. If the reverse rotation speed is <1 rpm, the scraper linear velocity will be insufficient, making it difficult to completely remove the scale layer and accelerating the accumulation of residual crystals. If the reverse rotation speed is >10 rpm, the friction between the scraper and the tank wall will be intense, which will not only accelerate equipment wear but may also scratch the anti-corrosion layer and easily break the scraped crystals into fine powder, affecting the product particle size. For example, the rotation speed in the forward direction can be 0.5 rpm, 1 rpm, 1.5 rpm, 2 rpm, 3 rpm, 5 rpm, or any two of the above values, and the rotation speed in the reverse direction can be 1 rpm, 1.5 rpm, 2 rpm, 3 rpm, 5 rpm, 8 rpm, 10 rpm, or any two of the above values.

[0045] According to some embodiments of the present invention, in the initial stage of wall scraping, the crystalline scale layer has a large load, requiring the servo motor to output a high current. As the scale layer is gradually scraped away, the resistance between the scraper and the tank wall decreases significantly, and the current decreases accordingly. When the drive current of the servo motor drops to 20-30% of the initial wall scraping current, it indicates that the scale layer has been basically removed, leaving only slight frictional resistance. This range balances thoroughness and efficiency. If the threshold is set >30%, the wall scraping is insufficient, and residual scale layer will accumulate rapidly and affect the purity of the next batch of crystals. If the threshold is set <20%, the scraper will continuously idle, causing unnecessary equipment wear and increased energy consumption, and is prone to damaging the tank's anti-corrosion layer due to excessive adhesion to the wall. By adopting a dynamic current threshold of 20-30%, adaptive intelligent determination of the wall scraping endpoint is achieved without manual intervention, ensuring cleaning effect, extending equipment life, and providing a reliable batch endpoint signal for continuous production. For example, the drive current of the servo motor can drop to 20%, 22%, 25%, 28%, 30% of the initial wall scraping current, or any two of the above values.

[0046] Understandably, when the drive current of the servo motor drops to 20-30% of the initial scraping current, the scraper assembly will rotate and scrape the wall for 1-10 minutes. This duration balances the thoroughness of scraping with the cleaning efficiency, ensuring production continuity.

[0047] In this invention, taking the treatment of potassium fluorotantalate solution in a 1000L crystallization tank as an example, at the initial stage of the wall scraping process, the measured drive current of the servo motor is 8-10A; as the scale layer is gradually scraped away, the current drops to 1.6-3A within 1-10 minutes, which is 20-30% of the initial current. At this point, the wall scraping automatically stops, and visual inspection of the tank wall reveals no obvious residual scale layer, indicating a good wall scraping effect.

[0048] In some embodiments of the present invention, the stirring assembly includes a stirring shaft and a stirring paddle. The upper end of the stirring shaft is fixedly connected to the inner ring of the one-way transmission assembly; the stirring paddle is fixedly connected to the lower end of the stirring shaft and extends into the tank. When the drive motor rotates clockwise, the stirring assembly rotates synchronously with the inner ring of the one-way transmission assembly, stirring the fluorine-containing complex salt (e.g., potassium fluorotantalate) solution to ensure uniform distribution of solution concentration and temperature, thereby guaranteeing uniform crystal precipitation.

[0049] In this invention, in order to form an axial circulating flow, the stirring paddle has a three-blade structure and can be made of polytetrafluoroethylene (PTFE) or fluororubber.

[0050] In some embodiments of the present invention, the scraper assembly includes an L-shaped scraper bracket and a scraper body. The upper end of the scraper bracket is fixedly connected to the outer ring of the one-way transmission assembly, and the lower end extends to the bottom of the trough. The scraper assembly, conforming to the shape of the trough structure, enables full coverage scraping of the inner wall of both the cylindrical and conical sections of the trough, ensuring thorough cleaning.

[0051] In this invention, considering the need for enhanced corrosion resistance, moderate hardness, and to avoid scratching the tank wall, the scraper body is made of polytetrafluoroethylene.

[0052] In this invention, the scraper body is installed at the end of the scraper bracket, and the contact gap between the scraper body and the inner wall of the tank is controlled at 0.5-1mm to ensure thorough scraping. When the drive motor rotates in the reverse direction, the scraper assembly rotates synchronously with the outer ring of the one-way transmission assembly, scraping off residual potassium fluorotantalate crystals adhering to the inner wall of the tank and preventing accumulation.

[0053] According to a preferred embodiment of the present invention, the scraper body may further include: a main blade body and a movable scraper blade, wherein the movable scraper blade is hinged to the end of the main blade body via a pivot; an elastic reset member is provided between the movable scraper blade and the main blade body, wherein the elastic reset member enables the movable scraper blade to maintain a scraping posture that is in contact with the inner wall of the groove in its natural state.

[0054] When the scraper assembly encounters an obstacle on the inner wall of the tank during rotation, the movable scraper overcomes the force of the elastic reset member and rotates around the pivot to open. After passing the obstacle, it automatically returns to its scraping posture, adhering to the inner wall of the tank, under the action of the elastic reset member. For example, the obstacle may be a temperature sensor installed inside the tank.

[0055] In this invention, the continuous crystallization method for fluorine-containing complex salts operates in a completely closed system. The wall scraping process does not require manual intervention by opening the lid, nor does it require the introduction of any chemical cleaning reagents. This eliminates contamination by impurity ions and loss of valuable metal resources. At the same time, it meets the green, efficient, and continuous production needs of the metallurgical and chemical industries, and significantly improves product yield and utilization of valuable resources.

[0056] According to some specific embodiments of the present invention, in order to provide a sealed space for the crystallization of fluorine complex salt solution, to contain the solution and adapt to the scraping action of the scraper assembly, and to realize the material discharge function at the bottom outlet, a steel rotational molding tank with a cooling jacket is adopted. The tank is a sealed container with a cylindrical section at the top and a conical section at the bottom. An outlet is opened at the center of the bottom, and the top is sealed by a flange. A mounting hole for a servo motor is opened at the center of the flange, and the diameter of the hole is adapted to the output shaft of the servo motor. The servo motor is fixed to the flange at the top of the tank by a flange bracket. The output shaft of the servo motor extends vertically downward into the interior of the tank, providing a power source for the entire system.

[0057] According to some embodiments of the present invention, the fluorine-containing complex salt may be at least one of potassium fluorotantalate, potassium fluoroniobate, potassium fluorotitanate, potassium fluoroaluminate, and potassium fluorozirconate, preferably potassium fluorotantalate.

[0058] The advantages of the method of the present invention will be illustrated below through examples.

[0059] To intuitively demonstrate the advantages of the method of this invention, the following core evaluation indicators are set, and the testing methods are as follows: Crystal yield is calculated using the following formula: Crystal yield = (Actual precipitated crystal mass / Theoretical precipitated crystal mass) × 100%; Average particle size of potassium fluorotantalate crystals: The average particle size of the crystals was measured using a Fisher average particle size analyzer. The smaller the average particle size, the more severe the damage to the crystal form caused by the subsequent cleaning.

[0060] Total cleaning time per batch: refers to the total time from the start of scraping the wall with the scraper to the completion of crystallization and discharge.

[0061] The failure rate refers to the percentage of 10 batches in the production process that have failed, calculated as follows: Failure rate = (Number of failures in production / 10) × 100%.

[0062] Example 1 S1. Pour 1000L of the prepared potassium fluorotantalate solution (100g / L based on tantalum pentoxide) into the tank 100 to the preset level, close the outlet, and start the servo motor 200 to rotate clockwise in the forward direction through the control unit, with the speed set to 5rpm; the output shaft of the servo motor 200 drives the inner ring of the one-way transmission component 300 to rotate synchronously in the forward direction. At this time, the wedge block separates from the outer ring under the action of centrifugal force, and the outer ring and the scraper assembly connected to it remain stationary. The power is transmitted only through the inner ring to the stirring shaft 410 in the stirring component. The stirring shaft 410 drives the three-blade propeller stirring paddle 420 to rotate synchronously, stirring the potassium fluorotantalate solution so that the temperature and concentration of the solution are evenly distributed in the tank 100; S2. During the stirring process, the temperature sensor in the tank 100 transmits the solution temperature signal to the control unit of the servo motor 200 in real time. The control unit also times the crystallization stirring time. When the duration of the crystallization stirring process reaches the preset threshold t=30h, and the solution temperature transmitted by the temperature sensor drops from 95℃ to the preset end temperature T=15℃, the control unit automatically determines that the crystallization process is complete and triggers the servo motor direction switching command. S3. After the control unit issues the command, the servo motor 200 immediately switches to counterclockwise rotation, and the speed is automatically adjusted to 1 rpm (the speed ratio of counterclockwise to clockwise rotation is 1:5). At the same time, the discharge port at the bottom of the tank 100 is automatically opened. The output shaft of the servo motor 200 drives the inner ring of the one-way transmission component 300 to rotate synchronously in the opposite direction. At this time, the wedge is wedged between the inner and outer rings under the elastic force of the spring, so that the two form a locked state, thereby driving the scraper assembly to rotate synchronously. The movable scraper of the scraper body 520 is in contact with the inner wall of the tank 100 with a gap of 0.8mm under the action of the elastic reset component. It rotates at a low speed along the inner wall of the cylindrical section to the conical section of the tank 100 with the scraper bracket 510, scraping off the potassium fluorotantalate crystals adhering to the inner wall of the tank during the crystallization process. Scale layer; At the beginning of the wall scraping process, the servo motor's drive current is 9A. During rotation, when the movable scraper encounters the temperature sensor on the inner wall of the tank, it overcomes the force of the elastic reset component and rotates around the shaft to open. After passing the obstacle, it automatically returns to the contact state with the inner wall of the tank under the action of the elastic reset component, and continues to complete the wall scraping action. After wall scraping continues for 8 minutes, the drive current of the servo motor drops to 2A, that is, the drive current of the servo motor drops to 22% of the initial current. It is determined that the crystalline scale layer has been completely scraped off, and the reverse rotation stops, completing a single potassium fluorotantalate crystallization and automatic cleaning process. After discharge, the discharge port is closed, and a new potassium fluorotantalate solution can be injected into the tank 100 for the next production batch. The entire process does not require stopping the machine or disassembling the equipment, achieving continuous production.

[0063] Example 2 The method is the same as in Example 1, except that the servo motor is controlled to rotate at a forward speed of 5 rpm, only the stirring component works, and the crystallization stirring is carried out for 30 hours, and the solution temperature drops to 15°C. The servo motor automatically rotates in the reverse direction at a speed of 10 rpm (the ratio of the reverse speed to the forward speed is 1:0.5), and the scraper assembly rotates for 5 minutes to scrape the wall.

[0064] Everything else is the same as in Example 1.

[0065] Example 3 The method is the same as in Example 1, except that the servo motor rotates at a speed of 10 rpm in both the forward and reverse directions.

[0066] Comparative Example 1 The same stirring parameters as in Example 1 were used to complete 30 hours of crystallization stirring, and the solution temperature was reduced to 15°C. After the machine is shut down, the crystalline scale layer on the tank wall is cleaned by manual tapping and mechanical scraping. After cleaning, the discharge port is opened manually. There is no special scraper, and the cleaning tool is an ordinary metal scraper.

[0067] Comparative Example 2 After completing the same crystallization stirring process as in Example 1, stop the machine. Add dilute hydrofluoric acid solution to the tank to dissolve the scale layer, soak for 30 minutes, then drain the cleaning solution and rinse the tank three times with pure water; open the outlet to discharge the crystal mixture.

[0068] Table 1

[0069] The results above show that in Examples 1 and 2, the ratios of the reverse and forward rotation speeds were 1:5 and 1:0.5, respectively, resulting in crystal yields of 99.1% and 98.6%, and average particle sizes of 21.50 μm and 19.63 μm, respectively. Example 2, with its higher reverse rotation speed, enhanced mass transfer but increased shear force, leading to slightly finer crystals and a slight decrease in cleaning efficiency and yield. Example 3 achieved a yield of 98.8%, but the failure rate was higher than in Example 1, indicating that a consistent ratio of reverse and forward rotation speeds can, to some extent, disrupt crystal growth and cause equipment wear.

[0070] Comparative Example 1 (manual cleaning) had a yield of only 94.6%, took 25 minutes to clean, and had a failure rate of 20%; Comparative Example 2 (chemical cleaning) had a yield of 95.3%, but took the longest time to clean (40 minutes) and had a failure rate of 20%.

[0071] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for continuous crystallization of a fluorine-containing complex salt, characterized in that, Includes the following steps: S1: Start the crystallization stirring process to crystallize and stir the fluorine-containing complex salt solution in the crystallization tank, while keeping the scraper assembly stationary. S2: Real-time monitoring of the duration of crystallization stirring and solution temperature. When the duration reaches the preset time threshold t and the solution temperature reaches the preset temperature threshold T, the crystallization process is automatically determined to be over, and the process is automatically switched to the wall scraping process: drive the scraper assembly to rotate and scrape off the crystal scale layer attached to the inner wall of the tank, and discharge the crystal product at the same time. S3: After the wall scraping process is completed, the wall scraping will automatically stop and the next batch of fluorine-containing complex salt solution will be automatically injected, repeating steps S1 to S3.

2. The method according to claim 1, characterized in that, The range of t is 20-50h, and the range of T is 10-20℃.

3. The method according to claim 1, characterized in that, In the crystallization stirring process, the stirring component rotates in the forward direction, and in the wall scraping process, the scraper component rotates in the reverse direction.

4. The method according to claim 3, characterized in that, The ratio of the rotational speed in the reverse direction to the rotational speed in the forward direction is 1:0.5-10.

5. The method according to claim 3, characterized in that, The forward rotation speed is 0.5-5 rpm, and the reverse rotation speed is 1-10 rpm.

6. The method according to any one of claims 1-5, characterized in that, The wall scraping process of the scraper assembly is controlled by a servo motor. When the drive current of the servo motor drops to 20-30% of the initial wall scraping current, the wall scraping is considered complete.

7. The method according to claim 1, characterized in that, In step S2, the scraper assembly rotates and scrapes the wall for 1-10 minutes.

8. The method according to claim 1, characterized in that, The scraper assembly includes an L-shaped scraper support and a scraper body.

9. The method according to claim 8, characterized in that, The gap between the scraper body and the inner wall of the groove is controlled at 0.5-1mm.

10. The method according to claim 1, characterized in that, The fluorine-containing complex salt includes at least one of potassium fluorotantalate, potassium fluoroniobate, potassium fluorotitanate, and potassium fluoroaluminate.

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