Device for preparing calcium sulfate whisker from phosphogypsum

Abstract

The utility model relates to a kind of calcium sulfate whisker device prepared by phosphogypsum, belong to phosphogypsum resource utilization technical field. Mainly including raw material pretreatment system, hydrothermal reactor system, crystal growth control device, separation and purification unit and drying setting device;The utility model uses structure by raw material pretreatment system, hydrothermal reactor system and separation and purification unit and drying setting device, and the efficient conversion from raw material to finished product is ensured. Among them, the combination of multilayer grading crystallization chamber and rotating seed implantation device realizes the grading control and uniform distribution of crystal growth;pH adjusting system and ion concentration adjusting device are precisely controlled by multi-point sensor array and local adjusting nozzle, accurately control reaction environment, improve whisker quality;In addition, temperature gradient distribution and variable pitch spiral conveying structure further optimize seed feeding and growth conditions, significantly improve the yield and morphological consistency of calcium sulfate whisker, reduce production energy consumption.

Description

Technical Field

[0001] This utility model belongs to the field of phosphogypsum resource utilization technology, specifically relating to an apparatus for preparing calcium sulfate whiskers from phosphogypsum. Background Technology

[0002] Phosphogypsum, an industrial byproduct, contains a large amount of calcium sulfate and has high resource utilization value, making it an ideal raw material for preparing calcium sulfate whiskers. Calcium sulfate whiskers are inorganic fibrous materials with a high aspect ratio, typically between 10 and 200, possessing excellent properties such as high strength, high modulus, high temperature resistance, and good chemical stability. Calcium sulfate whisker preparation technology refers to the technique of controlling crystallization conditions to preferentially grow calcium sulfate into fibrous crystals along a specific direction. The hydrothermal method is one of the main methods for preparing calcium sulfate whiskers. This involves achieving directional crystallization growth of calcium sulfate in a high-temperature, high-pressure hydrothermal environment by controlling parameters such as temperature, pressure, pH, and ion concentration. During the hydrothermal reaction, differences in solubility drive the recrystallization process, forming a whisker structure with a high aspect ratio under the action of a crystal-directing agent.

[0003] However, in actual production, the technology for preparing calcium sulfate whiskers from phosphogypsum still faces some key challenges. On the one hand, the high impurity content and complex composition of phosphogypsum raw materials directly affect the purity and morphology control of the whiskers, leading to unstable product quality. On the other hand, the uniformity and precise control of reaction conditions during crystal growth are difficult, especially in large-scale production. Uneven distribution of temperature, pressure, and chemical environment within the reactor can easily cause inconsistent whisker growth, affecting their aspect ratio and performance. This not only limits the improvement of production efficiency but also increases the difficulty of subsequent separation, purification, and product finalization. Utility Model Content

[0004] To overcome the challenges of uniform and precise control of reaction conditions in the prior art, which easily leads to inconsistent whisker growth and affects their aspect ratio and performance, thus limiting production efficiency and increasing the difficulty of subsequent separation, purification, and product shaping, this invention provides a device for preparing calcium sulfate whiskers from phosphogypsum. The coordinated use of a raw material pretreatment system, a hydrothermal reactor system, a separation and purification unit, and a drying and shaping device ensures efficient conversion from raw materials to finished product. Specifically, the combination of a multi-layered, graded crystallization chamber and a rotating crystal planting device achieves graded control and uniform distribution of crystal growth; the pH adjustment system and ion concentration adjustment device, through a multi-point sensor array and local adjustment nozzles, precisely control the reaction environment and improve whisker quality; furthermore, the temperature gradient distribution and variable-pitch spiral conveying structure further optimize seed placement and growth conditions, significantly improving the yield and morphological consistency of calcium sulfate whiskers while reducing production energy consumption.

[0005] To achieve the above objectives, this utility model is implemented through the following technical solution: A device for preparing calcium sulfate whiskers from phosphogypsum mainly includes a raw material pretreatment system, a hydrothermal reactor system, and a separation and purification unit. The raw material pretreatment system includes a phosphogypsum pretreatment reactor, an acid washing device, a neutralization filter, and a dryer connected in sequence. The hydrothermal reactor system includes a high-pressure hydrothermal reactor, a heating device, a pressure control system, and a stirring device. The heating device is located at the bottom of the high-pressure hydrothermal reactor, and the stirring device is located at the top of the high-pressure hydrothermal reactor. The dryer is connected to the high-pressure hydrothermal reactor via a pipeline. The separation and purification unit includes a high-speed centrifuge, a multi-stage washing device, an ultrasonic cleaner, and a filter separator connected in sequence. The high-pressure hydrothermal reactor is connected to the high-speed centrifuge via a pipeline. The high-pressure hydrothermal reactor has multiple graded crystallization chambers inside. Each graded crystallization chamber is separated by a partition and has an independent temperature control area. A rotary crystal implantation device is installed above the uppermost graded crystallization chamber. The rotary crystal implantation device includes a seed storage chamber and a spiral conveying mechanism. The pH adjustment system and ion concentration adjustment device include a multi-point sensor array and a local adjustment nozzle.

[0006] The multi-layered crystallization chamber has a three-layer structure, with each layer being one-third the total height of the high-pressure hydrothermal reactor. The partitions are equipped with connecting holes arranged in a circular array, with the array radius being half the radius of the partition. Each partition layer has 10 holes evenly distributed. The diameter of the connecting holes gradually decreases along the height of the high-pressure hydrothermal reactor: 10mm for the upper layer, 15mm for the middle layer, and 20mm for the lower layer, with a hole spacing of 50mm to ensure a stable slurry flow rate of 0.5-1.0m / s. The bottom of the spiral conveying mechanism of the rotary crystal implantation device extends into the upper-layered crystallization chamber. The spiral conveying mechanism adopts a variable pitch structure, with the pitch gradually decreasing along the conveying direction. The heating device provides an independent heating area for each layer of the crystallization chamber, forming a temperature gradient distribution from bottom to top.

[0007] The multi-point sensor array includes a pH sensor, an ion concentration sensor, and a temperature sensor. The sensors are evenly distributed in a grid pattern on the inner wall of the high-pressure hydrothermal reactor. Each local adjustment nozzle is set in a one-to-one correspondence with a sensor. Each local adjustment nozzle is connected to an independent regulating liquid storage tank. The regulating liquid storage tank includes an acid regulating liquid storage tank, an alkaline regulating liquid storage tank, and an ion replenishment liquid storage tank. The multi-point sensor array and the local adjustment nozzles are connected to the data processing module of the control system.

[0008] The device also includes a crystal growth control device connected to a high-pressure hydrothermal reactor, which includes a pH adjustment system, an ion concentration adjustment device, a crystal shape guiding agent addition device, and a reaction time controller.

[0009] The ion concentration adjustment device includes a calcium ion addition device and a sulfate ion addition device.

[0010] The device also includes a drying and shaping device, comprising a vacuum drying chamber, a fluidized bed dryer, a microwave-assisted drying device, and an anti-agglomeration treatment system connected in sequence, and the filter separator is connected to the vacuum drying chamber via a pipeline.

[0011] The beneficial effects of this utility model are: This invention utilizes a combination of a raw material pretreatment system, a hydrothermal reactor system, a separation and purification unit, and a drying and shaping device to ensure efficient conversion from raw materials to finished products. Specifically, the combination of a multi-layered, graded crystallization chamber and a rotary crystal planting device enables graded control and uniform distribution of crystal growth. The pH adjustment system and ion concentration adjustment device, through a multi-point sensor array and localized adjustment nozzles, precisely regulate the reaction environment, improving whisker quality. Furthermore, the temperature gradient distribution and variable-pitch spiral conveying structure further optimize seed placement and growth conditions, significantly improving the yield and morphological consistency of calcium sulfate whiskers while reducing production energy consumption. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the three-dimensional structure of a rotary crystal implantation device and a high-pressure hydrothermal reactor.

[0013] Figure 2 This is a three-dimensional schematic diagram of the internal structure of a rotary crystal implantation device and a high-pressure hydrothermal reactor.

[0014] Figure 3 This is a schematic diagram of the preparation process of this utility model.

[0015] Figure label: 1. Phosphogypsum pretreatment reactor; 2. Acid washing device; 3. Neutralization filter; 4. Dryer; 5. High-pressure hydrothermal reactor; 6. Heating device; 7. Pressure control system; 8. Stirring device; 9. pH adjustment system; 10. Ion concentration adjustment device; 11. Crystallization guide agent addition device; 12. Reaction time controller; 13. High-speed centrifuge; 14. Multi-stage washing device; 15. Ultrasonic cleaner; 16. Filter separator; 17. Vacuum drying oven; 18. Fluidized bed dryer; 19. Microwave-assisted drying device; 20. Anti-agglomeration treatment system; 21. Multi-layer graded crystallization chamber; 22. Rotary crystal implantation device; 23. Storage bin; 24. Screw conveyor mechanism. Detailed Implementation

[0016] To make the objectives, technical solutions, and beneficial effects of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, so as to facilitate the understanding of those skilled in the art.

[0017] This utility model discloses an apparatus for preparing calcium sulfate whiskers from phosphogypsum. The apparatus mainly includes a raw material pretreatment system, a hydrothermal reactor system, and a separation and purification unit. The raw material pretreatment system includes a phosphogypsum pretreatment reactor 1, an acid washing device 2, a neutralization filter 3, and a dryer 4 connected in sequence. The hydrothermal reactor system includes a high-pressure hydrothermal reactor 5, a heating device 6, a pressure control system 7, and a stirring device 8. The heating device 6 is located at the bottom of the high-pressure hydrothermal reactor 5, and the stirring device 8 is located at the top of the high-pressure hydrothermal reactor 5. The dryer 4 is connected to the high-pressure hydrothermal reactor 5 through a pipeline. The separation and purification unit includes a high-speed centrifuge 13, a multi-stage washing device 14, an ultrasonic cleaner 15, and a filter separator 16 connected in sequence. The high-pressure hydrothermal reactor 5 is connected to the high-speed centrifuge 13 through a pipeline, realizing a continuous process from raw material pretreatment to product drying, effectively improving the efficiency and product quality of converting phosphogypsum into calcium sulfate whiskers.

[0018] The phosphogypsum pretreatment reactor 1 has a volume of 100-300L and is made of 316L stainless steel. It is equipped with a stirring device to remove soluble phosphates and fluorides from the phosphogypsum. The pretreatment temperature is controlled at 60-80℃, and the reaction time is 2-3 hours to ensure complete dissolution of impurities. The acid washing device 2 is located below the pretreatment reactor 1, using a 5-10% dilute hydrochloric acid solution. The acid washing temperature is 40-60℃, and the time is 1-2 hours, mainly to remove impurities such as iron and aluminum oxides.

[0019] Neutralization filter 3 adopts a plate and frame filter structure, equipped with acid-resistant filter cloth, with a filtration area of ​​10-20 m². Residual acid is neutralized by adding lime slurry, adjusting the pH to 6-7, followed by solid-liquid separation. Dryer 4 uses a rotary dryer with a diameter of 1.5 m and a length of 8 m. The drying temperature is controlled at 100-120℃ to dry the pretreated phosphogypsum to a moisture content of less than 2%, ensuring the effectiveness of subsequent hydrothermal reactions.

[0020] The high-pressure hydrothermal reactor 5 is a pressure-resistant vessel made of Hastelloy alloy, with a volume of 100L, a design pressure of 12MPa, and a working pressure of 8-10MPa. It is lined with a PTFE anti-corrosion layer. The high-pressure hydrothermal reactor 5 is equipped with an electric heating jacket with a heating power of 20kW and a temperature control accuracy of ±2℃. The stirring device 8 uses an anchor-type stirrer with an adjustable speed of 10-50rpm to prevent mechanical damage to the whiskers during growth. Furthermore, the high-pressure hydrothermal reactor 5 is equipped with multi-layered graded crystallization chambers 21. Each graded crystallization chamber 21 is separated by partitions and has an independent temperature control area. The multi-layered graded crystallization chamber 21 has a three-layer structure, with each layer being one-third the total height of the high-pressure hydrothermal reactor 5. Each partition is made of corrosion-resistant stainless steel and is fixedly welded to the inner wall of the high-pressure hydrothermal reactor 5. The partitions are provided with connecting holes, which are distributed in a circular array in the central area of ​​the partitions. The array radius is 1 / 2 of the partition radius, and 10 holes are evenly distributed in each partition layer. This ensures that the material flows slowly between layers while maintaining pressure balance. The diameter of the connecting holes gradually decreases along the height of the high-pressure hydrothermal reactor 5, with the upper layer having a diameter of 10 mm, the middle layer 15 mm, and the lower layer 20 mm. The hole spacing is 50 mm, ensuring that the slurry flow rate is stable at 0.5-1.0 m / s. This layered structure allows the reactants to experience a gradually changing crystallization environment in different height areas. During operation, the slurry flows upward from the bottom layer, and the flow rate is controlled through gradually decreasing connecting holes. The connecting holes can compensate for the flow rate changes caused by pressure reduction, so that the flow rate of the slurry as it passes through each layer of partition remains basically stable. This ensures that the crystals have sufficient and similar residence time in each layer for the specific growth of that stage (nucleation in the lower layer, extension in the middle layer, and refinement in the upper layer). This helps the whiskers to gradually extend their aspect ratio in different layers. Compared with traditional single-cavity reactors, this structure improves the uniformity of the whisker aspect ratio by more than 20%.

[0021] A rotary crystal planting device 22 is installed above the graded crystallization chamber 21. The rotary crystal planting device 22 includes a seed storage chamber 23 and a spiral conveying mechanism 24. The spiral conveying mechanism 24 adopts a variable pitch structure, with the pitch gradually decreasing along the conveying direction. For example, the pitch linearly decreases from 10 mm at the inlet end to 5 mm at the outlet end. The rotary crystal planting device 22 is fixed to the top of the high-pressure hydrothermal reactor 5 by a flange. The bottom of the spiral conveying mechanism 24 extends into the interior of the upper graded crystallization chamber 21, so that the seed crystals are evenly distributed in the reaction system, thereby promoting precise control of the nucleation process.

[0022] The heating device 6 employs electric heating and sets up independent heating zones for each layer of the hierarchical crystallization chamber 21, forming a temperature gradient distribution from bottom to top. For example, the temperature of the lower layer is controlled at 150-180℃, the middle layer at 130-150℃, and the upper layer at 120-130℃, thereby promoting the hierarchical growth of calcium sulfate whiskers and avoiding the uneven morphology caused by a single temperature zone. The temperature gradient of the multi-layer hierarchical crystallization chamber 21 ensures that whiskers nucleate rapidly in the lower layer, extend in the middle layer, and are refined in the upper layer, with an aspect ratio of over 80. The heating device 6 is divided into three stages: preheating, heating up, and holding. In the preheating stage, the reaction system is heated from room temperature to 80℃. In the heating stage, the temperature is increased to the set temperature of 120-180℃ at a rate of 2℃ / min. In the holding stage, the reaction temperature is maintained for 6-10 hours. The pressure control system 7 includes a precision pressure gauge, a safety valve, an automatic pressure relief device, and a pressure recorder to ensure that the pressure during the reaction process remains stable within the set range.

[0023] The working process of the high-pressure hydrothermal reactor 5 is as follows: During operation, the heating device 6 starts working and executes the "preheating" program. The three graded crystallization chambers 21 are heated through independent heating zones, causing the entire reaction system to rise steadily and uniformly from room temperature to approximately 80°C. This process avoids violent vaporization of raw materials containing crystalline phases, ensuring the stability of the equipment and materials. After preheating, the slurry is pumped from the bottom of the reactor 5 into the lower graded crystallization chamber 21. Simultaneously, the rotary crystal planting device 22 at the top is activated, driving the screw conveyor mechanism 24 to rotate via a motor. The rotation speed is adjustable from 5-20 rpm and is connected to the central control system to synchronize the feeding speed with the reaction process. The seed crystals enter the screw channel from the storage chamber 23. As the screw pitch decreases, the seed crystals are gradually compressed and metered during transport, achieving slow and uniform feeding, allowing the seed crystals to be dispersed within the space of the upper graded crystallization chamber 21. Simultaneously, the slurry flows upward from the lower-level graded crystallization chamber 21 at the bottom of the high-pressure hydrothermal reactor 5, passing sequentially through the circularly arrayed connecting holes on each layer's partitions. Seed crystals introduced into the upper crystallization chamber 21 begin to settle under gravity. Because the system controls the upward flow velocity of the slurry to be less than the settling velocity of the seed crystals, the seed crystals overcome fluid resistance and settle downwards layer by layer through the connecting holes on the partitions. Newly introduced fine seed crystals encounter the slurry with the lowest temperature (120-130℃) and reduced concentration, beginning to grow gently, reducing crystal defects and refining the surface. Seed crystals that have begun to grow settle to the middle layer, contacting the medium-temperature slurry at 130-150℃. At this temperature, axial growth of the crystals is significantly advantageous, the whisker length increases rapidly, and the aspect ratio is greatly improved. Finally, the seed crystals reach the high-temperature lower layer at 150-180℃, where the slurry activity is highest. This not only promotes rapid crystal nucleus formation but also provides sufficient growth momentum for the crystals that have settled here, causing them to further coarsen. By using a countercurrent operation where the slurry flows from bottom to top and the seed crystals settle from top to bottom, the fresh, highly active slurry is preferentially used for the growth of large crystals in the lower layer, while the slurry with reduced concentration is used for the gentle growth of new seed crystals in the upper layer. This significantly improves the utilization rate of raw materials and effectively inhibits harmful secondary nucleation, ensuring the uniformity of product morphology.

[0024] The pH adjustment system 9 and ion concentration adjustment device 10 include a multi-point sensor array and local adjustment nozzles. The multi-point sensor array includes a pH sensor, an ion concentration sensor, and a temperature sensor. The sensors are evenly distributed in a grid pattern on the inner wall of the high-pressure hydrothermal reactor 5. For example, 4-6 sensor points are set in each layer of the crystallization chamber 21 to achieve precise local control of the reaction environment. Each local adjustment nozzle is configured to correspond one-to-one with a sensor. Each local adjustment nozzle is connected to an independent regulating liquid storage tank via a precision metering pump. The regulating liquid storage tank includes a calcium ion storage tank and a sulfate ion storage tank, which automatically replenishes the consumed ions according to the reaction progress, maintaining the Ca²⁺ / SO₄²⁻ molar ratio between 1.0 and 1.2. The multi-point sensor array and local adjustment nozzles are connected to the data processing module of the control system. The data processing module uses a PID control algorithm to automatically calculate the regulating liquid demand of each area based on sensor data and control the nozzle actions. For example, when a sensor detects that the pH value deviates from the 9-10 range, the corresponding nozzle 27 sprays acidic or alkaline regulating liquid, with the spray rate controlled at 0.1-1 L / min. By using a multi-point sensor array to monitor the pH value of the reaction system in real time, and by automatically adding acid or alkali through local adjustment nozzles, the pH value is maintained within the optimal whisker growth range of 9-10. Compared with traditional global adjustment, this local adjustment avoids global fluctuations, making the pH value stable within ±0.2, achieving efficient conversion of phosphogypsum, providing more precise crystal growth control, thereby optimizing whisker growth conditions and ensuring product purity and morphological consistency.

[0025] The crystal-directing agent addition device 11 stores surfactants such as citric acid and EDTA, which are added quantitatively via a peristaltic pump at a dosage controlled between 0.5% and 2.0%, guiding calcium sulfate to preferentially grow along the c-axis to form whiskers with a high aspect ratio. The reaction time controller 12 adopts a PLC control system, which controls the reaction time according to a preset program and can dynamically adjust the reaction time based on the whisker growth monitored online.

[0026] The high-speed centrifuge 13 is a horizontal screw discharge centrifuge with a rotation speed of 3000-8000 rpm and a separation factor of 1500-3000, which can efficiently separate whisker products and mother liquor, with a separation efficiency of over 98%. The multi-stage washing device 14 includes three countercurrent washing tanks, each with a volume of 50L, using deionized water for washing at a temperature of 40-50℃ to remove residual impurities and mother liquor from the surface of the whiskers.

[0027] The ultrasonic cleaner 15 has a power of 1000W, a frequency of 28kHz, and a cleaning time of 10-15 minutes. It can remove fine particles tightly attached to the surface of whiskers without damaging the whisker structure. The filter separator 16 uses a combination of filter screens with different pore sizes, namely 100 mesh, 200 mesh, and 400 mesh, to grade the whiskers according to their aspect ratio and length, thus producing products of different specifications.

[0028] The vacuum drying oven 17 has a volume of 1 m³, an operating temperature of 60-80℃, and a vacuum degree of -0.08 MPa. It is equipped with shelf heating and a circulating fan to ensure uniform drying of the whiskers. The fluidized bed dryer 18 has a diameter of 0.8 m and a height of 2 m. The drying medium is hot air at a temperature of 70℃, and the fluidizing air velocity is 0.8-1.2 m / s to prevent the whiskers from agglomerating during the drying process.

[0029] The microwave-assisted drying device 19 has a power of 5kW and a frequency of 2450MHz. It adopts continuous microwave drying with a drying time of 5-10 minutes, which can quickly and uniformly dry the whiskers while maintaining their intact morphology. The anti-agglomeration treatment system 20 adds dispersants such as stearic acid through atomizing nozzles at a dosage of 0.1-0.3% to prevent whisker agglomeration during the drying process.

[0030] The specific workflow of this utility model is as follows: Step 1: Raw material pretreatment 500 kg of industrial phosphogypsum was added to pretreatment reactor 1, along with 1000 L of deionized water to form a slurry. The mixture was heated to 70°C and stirred for 2 hours to remove soluble phosphates. The slurry was then fed to acid washing device 2 and acid-washed with 8% hydrochloric acid solution for 1.5 hours to remove metallic impurities. After neutralization and filtration by neutralization filter 3, the slurry was sent to dryer 4 to dry to a moisture content of 1.5%.

[0031] Step 2: Hydrothermal reaction 200 kg of pretreated phosphogypsum was added to the high-pressure hydrothermal reactor 5, along with 500 L of deionized water. The stirring device 8 was started, with the speed set to 30 rpm. The temperature was raised to 150 °C via the heating device 6, and the pressure naturally increased to 1.2 MPa. Simultaneously, the rotary crystal planting device 22 fed pretreated crystal seeds from the seed storage chamber 23 into the multi-layer graded crystallization chamber 21 via the screw conveyor mechanism 24. The pH adjustment system 9 and the ion concentration adjustment device 10 adjusted the pH value to 9.5 in real time through a multi-point sensor array and local adjustment nozzles. 2 kg of citric acid was added as a crystal shaping agent via the crystal shaping agent addition device 11, and the reaction conditions were maintained for 8 hours. During this period, ions were replenished as needed via the ion concentration adjustment device 10.

[0032] Step 3: Separation and purification After the reaction is complete, the temperature is cooled to room temperature, and the reaction product is removed after depressurization. The whisker-containing slurry is fed into a high-speed centrifuge 13 and separated at 5000 rpm for 10 minutes to obtain wet whisker material. The wet material is then fed into a multi-stage washing device 14 for three-stage countercurrent washing, with each stage lasting 30 minutes. It is then washed in an ultrasonic cleaner 15 for 12 minutes, and finally classified through a filter separator 16.

[0033] Step 4: Drying and Shaping The graded whiskers were first dried in a vacuum drying oven 17 for 2 hours at a temperature of 75°C and a vacuum degree of -0.08 MPa. Then they were transferred to a fluidized bed dryer 18 for fluidized bed drying for 1 hour. Finally, they were microwave dried for 8 minutes using a microwave-assisted drying device 19, while a dispersant was sprayed in through an anti-agglomeration treatment system 20 to prevent agglomeration.

[0034] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although the utility model has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of this utility model.

Claims

1. An apparatus for preparing calcium sulfate whiskers from phosphogypsum, characterized in that: The apparatus for preparing calcium sulfate whiskers from phosphogypsum includes a raw material pretreatment system, a hydrothermal reactor system, and a separation and purification unit. The raw material pretreatment system includes a phosphogypsum pretreatment reactor (1), an acid washing device (2), a neutralization filter (3), and a dryer (4) connected in sequence. The hydrothermal reactor system includes a high-pressure hydrothermal reactor (5), a heating device (6), a pressure control system (7), and a stirring device (8). The heating device (6) is located at the bottom of the high-pressure hydrothermal reactor (5), and the stirring device (8) is located at the top of the high-pressure hydrothermal reactor (5). The dryer (4) is connected to the high-pressure hydrothermal reactor (5) through a pipe. The separation and purification unit includes a high-speed centrifuge (13), a multi-stage washing device (14), an ultrasonic cleaner (15), and a filter separator (16) connected in sequence. The high-pressure hydrothermal reactor (5) is connected to the high-speed centrifuge (13) through a pipe. The high-pressure hydrothermal reactor (5) is equipped with a multi-level graded crystallization chamber (21). Each graded crystallization chamber (21) is separated by a partition and has an independent temperature control area. A rotary crystal implantation device (22) is provided above the uppermost graded crystallization chamber (21). The rotary crystal implantation device (22) includes a seed storage chamber (23) and a spiral conveying mechanism (24). The device also includes a crystal growth control device connected to the high-pressure hydrothermal reactor (5). The crystal growth control device includes a pH adjustment system (9), an ion concentration adjustment device (10), a crystal shape guide agent addition device (11), and a reaction time controller (12). The pH adjustment system (9) and the ion concentration adjustment device (10) include a multi-point sensor array and a local adjustment nozzle.

2. The apparatus for preparing calcium sulfate whiskers from phosphogypsum according to claim 1, characterized in that: The multi-layer graded crystallization chamber (21) has a three-layer structure. The height of each layer is one-third of the total height of the high-pressure hydrothermal reactor (5). The partition is provided with connecting holes in a circular array. The array radius is 1 / 2 of the partition radius. Each partition has 10 holes evenly distributed. The diameter of the connecting holes gradually decreases along the height direction of the high-pressure hydrothermal reactor (5). The diameter of the connecting holes in the upper layer is 10 mm, in the middle layer it is 15 mm, and in the lower layer it is 20 mm. The hole spacing is 50 mm. The bottom of the spiral conveying mechanism (24) of the rotary crystal implantation device (22) extends into the upper graded crystallization chamber (21). The spiral conveying mechanism (24) adopts a variable pitch structure. The pitch gradually decreases along the conveying direction. The heating device (6) sets up an independent heating area for each graded crystallization chamber (21) to form a temperature gradient distribution from bottom to top.

3. The apparatus for preparing calcium sulfate whiskers from phosphogypsum according to claim 1 or 2, characterized in that: The multi-point sensor array includes a pH sensor, an ion concentration sensor, and a temperature sensor. The sensors are evenly distributed in a grid pattern on the inner wall of the high-pressure hydrothermal reactor (5). The local adjustment nozzles are set one-to-one with the sensors. Each local adjustment nozzle is connected to an independent adjustment liquid storage tank. The adjustment liquid storage tanks include an acidic adjustment liquid storage tank, an alkaline adjustment liquid storage tank, and an ion replenishment liquid storage tank. The multi-point sensor array and the local adjustment nozzles are connected to the data processing module of the control system.

4. The apparatus for preparing calcium sulfate whiskers from phosphogypsum according to claim 1, characterized in that: The ion concentration adjustment device (10) includes a calcium ion addition device and a sulfate ion addition device.

5. The apparatus for preparing calcium sulfate whiskers from phosphogypsum according to claim 1, characterized in that: The device also includes a drying and shaping device, comprising a vacuum drying chamber (17), a fluidized bed dryer (18), a microwave-assisted drying device (19), and an anti-agglomeration treatment system (20) connected in sequence. The filter separator (16) is connected to the vacuum drying chamber (17) via a pipe.

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