A nuclear crystal prilling fluorite calcium prilling body washing system and method

Abstract

This invention provides a washing system and method for calcium fluoride granules produced through nucleation granulation, comprising a plasma surface activation module, a supercritical fluid extraction washing module, and an intelligent control and circulation module connected in sequence. The plasma surface activation module is used to perform surface modification and impurity weakening treatment on pre-dried calcium fluoride granules. The supercritical fluid extraction purification module is used to deeply remove impurities from the surface and pores of the granules under anhydrous conditions. The intelligent control and circulation module is signal-connected to the aforementioned modules and is used to dynamically regulate the entire purification process based on online monitoring data. The plasma surface activation module includes a vibrating fluidized bed with a reaction chamber, solving the problem of incomplete removal of stubborn surface impurities by traditional water washing. Ultimately, the surface impurity removal rate of the calcium fluoride granules is stabilized at over 95%, and the product purity reaches a high standard for resource utilization.

Description

Technical Field

[0001] This invention relates to industrial wastewater treatment and resource recovery technology, specifically to a washing system and method for washing calcium fluoride granules produced by nucleation granulation. Background Technology

[0002] With the rapid development of high-tech industries such as photovoltaics, semiconductors, fluorochemicals, and lithium batteries, the production of fluoride-containing industrial wastewater is increasing daily. Fluoride ions (F⁻) are a pollutant with cumulative environmental toxicity, and their emissions are strictly limited. Traditional chemical precipitation methods, which remove fluoride by adding calcium salts (such as calcium chloride and calcium hydroxide) to produce calcium fluoride (CaF₂) sludge, have high water content, complex composition, and unstable properties, classifying them as hazardous waste. Their safe disposal is costly and poses a risk of secondary pollution.

[0003] Against this backdrop, "nuclear crystal granulation" technology has emerged and become the mainstream approach for the resource-based treatment of fluoride-containing wastewater. This technology involves adding specific forms of calcium fluoride microcrystals as seed crystals to the reaction system, inducing fluoride and calcium ions in the wastewater to crystallize and grow in layers on the seed crystal surface, ultimately forming calcium fluoride granules with uniform particle size, dense structure, and low water content. This process not only significantly reduces sludge volume but also recovers fluoride in the form of high-purity CaF2, possessing potential value as a metallurgical auxiliary material, building material raw material, and even a raw material for the preparation of high-purity hydrofluoric acid, realizing a shift in concept from "waste treatment" to "resource recovery."

[0004] Although nucleus crystal granulation technology solves the morphology problem of primary products, the resulting calcium fluoride granules must undergo crucial deep washing and refining processes to remove various impurities encapsulated or adsorbed on their surface during granulation, in order to become high-value-added commodities. Currently, the industry commonly employs a multi-stage wet washing process based on an aqueous medium. A typical process involves sequentially feeding the granulated slurry into a series of washing tanks or towers, where it is washed counter-currently or cross-currently with clean water or the washing liquid from the previous stage. Subsequently, solid-liquid separation is achieved using hydrocyclones, vibrating screens, etc., ultimately yielding clean granules.

[0005] However, this water-based wet washing technology has a series of inherent and insurmountable drawbacks: 1. Huge water consumption and secondary pollution: The washing process requires a large amount of fresh process water. More seriously, the wastewater generated after washing contains pollutants such as fluoride, suspended solids, washed-off organic matter, and heavy metals. Its water quality is complex, difficult to treat, and costly, creating a dilemma of "treating wastewater and generating new wastewater", resulting in a heavy environmental burden.

[0006] 2. Low removal efficiency for specific impurities, limiting product purity: Impurities adhering to the surface of the granules include not only soluble salts, but more commonly hydrophobic organic oils (such as cutting fluids and lubricants), silica gel, and metal hydroxides co-precipitated with calcium. Simply relying on the physical flushing and dilution effects of water flow has limited ability to remove these impurities that are firmly bound by physical adsorption or chemical forces, making deep cleaning difficult and restricting the purity level and market value of the final product.

[0007] 3. Lengthy process, complex equipment, and high energy consumption: A complete wet scrubbing line typically includes multiple units such as slurry preparation, multi-stage countercurrent washing, solid-liquid separation (centrifugation, sieving), wash water treatment, and sludge dewatering. The long process, numerous pieces of equipment, and large footprint result in high infrastructure investment and operating energy consumption. Furthermore, the complex solid-liquid separation steps can easily lead to the loss of fine particles, reducing product yield.

[0008] In summary, existing wet washing technologies for calcium fluoride granules have significant shortcomings in terms of resource consumption, environmental friendliness, potential for improving product purity, and economic efficiency. There is an urgent need for an innovative refining technology and equipment that can fundamentally eliminate dependence on water, achieve deep cleaning, simplify processes, and enhance product value. Summary of the Invention

[0009] In order to overcome the problems existing in the background art, the present invention provides a washing system and method for washing calcium fluoride granules produced by nucleation crystal granulation, so as to solve the technical problems mentioned in the background art, such as huge water consumption, secondary pollution, low efficiency in removing specific impurities, limited product purity, lengthy process, complex equipment, and high energy consumption.

[0010] To achieve the above objectives, the invention is implemented through the following technical solution: A washing system for calcium fluoride granules produced by nucleation crystal formation is characterized by comprising a plasma surface activation module 100, a supercritical fluid extraction washing module 200, and an intelligent control and circulation module connected in sequence. The plasma surface activation module 100 is used to perform surface modification and impurity weakening treatment on the pre-dried calcium fluoride granules. The supercritical fluid extraction and purification module 200 is used to deeply remove impurities from the surface and pores of the granules under anhydrous conditions. The intelligent control and circulation module is connected to the aforementioned module via signals and is used to dynamically adjust the entire refining process based on online monitoring data.

[0011] Preferably, the plasma surface activation module 100 includes: A vibrating fluidized bed 101 is provided with a reaction chamber 102. The inclination angle and amplitude of the vibrating fluidized bed 101 are adjustable, so that the material vibrates and moves forward in the reaction chamber 102. At least one pair of high-voltage pulse electrodes 103 are disposed in the reaction chamber 102, and the electrodes are connected to an external nanosecond-level high-voltage pulse power supply; A controllable atmosphere supply unit 104 is used to inject a mixture of inert gas or reactive gas into the reaction chamber 102; A dual-gate airlock valve feeding system 105 has its inlet connected to the end outlet of the vibrating fluidized bed 101 and its outlet connected to the supercritical fluid extraction and purification module 200, and is used to send the processed material into the downstream module under air-isolated conditions.

[0012] Preferably, the supercritical fluid extraction and purification module 200 includes the following units connected sequentially through pipelines to form a closed loop: A supercritical CO2 extraction unit includes a high-pressure extraction vessel 201; The impurity separation unit includes a primary separator 202 and a secondary separator 203 connected in series; A CO2 recycling unit includes a compressor 204 and a condenser 205; An extraction fluid feed system 206 is connected to the discharge pipe at the lower end of the high-pressure extraction vessel 201 for discharging impurities.

[0013] Preferably, the high-pressure extraction vessel 201 is a vertical pressure vessel with a jacket, and a heating system for adjustable and stable heating of the interior of the high-pressure extraction vessel 201 is provided inside the jacket. A rotatable material basket 2011 made of a perforated plate is provided inside the high-pressure extraction vessel 201. The middle part of the rotatable material basket 2011 is connected to a drive motor 2012 mounted on the top cover of the high-pressure extraction vessel 201 via a rotating shaft. The top cover of the high-pressure extraction vessel 201 is detachable, and the rotatable material basket 2011 can be lifted out of the high-pressure extraction vessel 201 along with the top cover. A stirring rod 2013 extending into the rotatable material basket 2011 is connected to the bottom surface of the top cover of the high-pressure extraction vessel 201. The top of the high-pressure extraction vessel 201 is connected to a double-gate airlock valve feeding system 105 via a detachable pipe, and the granules treated in the plasma surface activation module 100 are discharged into the rotatable material basket 2011. The high-pressure extraction vessel 201 is connected to an outlet pipe on its top cover, and a first back pressure regulating valve 207 is provided between the outlet pipe on the top of the primary separator 202 and the inlet pipe on the top of the secondary separator 203. A second back pressure regulating valve 208 is provided between the outlet pipe on the top of the primary separator 202 and the inlet pipe on the top of the secondary separator 203. The top of the secondary separator 203 is also provided with an outlet pipe connected to a compressor 204, which is connected to a condenser 205. The condenser 205 transports the liquefied CO2 back to the CO2 storage tank 210. Both the primary separator 202 and the secondary separator 203 are vertical containers with conical bottoms, and a metal wire mesh demister is provided inside the secondary separator 203 at the outlet pipe. The bottoms of the high-pressure extraction vessel 201, the primary separator 202, and the secondary separator 203 are connected to an impurity collection tank 209 via valves.

[0014] Preferably, the extraction fluid feeding system includes a supercritical CO2 feeding system and an entrainer precision injection unit connected in parallel. The supercritical CO2 feeding system includes a CO2 storage tank 210, a high-pressure plunger pump 211, and a tubular preheater 212 connected in sequence. The entrainer precision injection unit includes multiple high-pressure micro-injection pumps 213 connected in parallel. The multiple high-pressure micro-injection pumps 213 are respectively connected to entrainer storage tanks 214 containing different entrainers.

[0015] Preferably, the first back pressure regulating valve 207 is configured to maintain the operating pressure of the high-pressure extraction vessel 201 at a preset first high pressure value; the second back pressure regulating valve 208 is configured to maintain the operating pressure of the primary separator 202 at a second medium pressure value lower than the first high pressure value; the first high pressure value is 15-35 MPa, the second medium pressure value is 8-15 MPa, and the operating pressure of the secondary separator 203 is 2-5 MPa; the system establishes and maintains a stable stepped pressure gradient between the extraction vessel 201, the primary separator 202, and the secondary separator 203 through the regulation of the first back pressure regulating valve 207 and the second back pressure regulating valve 208.

[0016] Preferably, the intelligent control and loop module includes: A laser-induced breakdown spectroscopy online component analyzer 301, the probe of which is set at the feed inlet of the plasma surface activation module 100, is used to detect the elemental composition spectrum of the granulation surface in real time. A central controller that stores a pre-set database of "impurity spectrum-process formula"; The central controller is configured to receive spectral data from the laser-induced breakdown spectroscopy online component analyzer 301, match it with the database through an algorithm, and automatically generate and issue a set of collaborative process parameters to the plasma surface activation module 100 and the supercritical fluid extraction and purification module 200. The "collaborative process parameters" include at least the plasma working gas formulation and discharge power for the plasma surface activation module 100, and the extraction temperature and pressure, entrainer type and injection procedure for the supercritical fluid extraction and purification module 200.

[0017] A method for washing calcium fluoride granules using the washing system described above, characterized by comprising the following steps: S1: Input calcium fluoride granules with a water content of less than 10% into the plasma surface activation module 100; S2: The laser-induced breakdown spectroscopy online component analyzer 301 is started to scan the granules. The central controller matches and calls the optimal synergistic process formula from the database according to the identified impurity characteristic spectrum. S3: According to the formula, the granules are subjected to pulsed discharge plasma treatment in the plasma surface activation module 100; the pulsed discharge plasma treatment is carried out under vibration fluidization conditions, and the treatment atmosphere is selected according to the type of impurities: when organic matter is the main impurity, a mixture of argon and oxygen is used; when metal compounds are the main impurities, pure argon is used. S4: The plasma-treated granules are transferred to the high-pressure extraction vessel 201 through the double gate airlock valve feeding system 105. S5: Based on the parameters set in the formula, start the supercritical fluid extraction and purification module 200 to make the supercritical CO2 fluid continuously circulate in the closed-loop system to dynamically extract the granules. S6: After extraction, the dried high-purity calcium fluoride granules are taken out from the high-pressure extraction vessel 201, and the separated impurities are collected from the bottom of the primary separator 202 and the secondary separator 203 respectively.

[0018] Preferably, in step S5, the supercritical CO2 fluid circulation extraction process is continuous, powered by a high-pressure plunger pump 211. The path is as follows: liquid CO2 is pressurized and heated by the pump to become a supercritical fluid, which enters from the bottom of the high-pressure extraction vessel 201, penetrating the solid material layer. Simultaneously, the drive motor 2012 drives the rotatable material basket 2011 to rotate, and the stirring rod 2013 stirs the granulated material. The dissolved impurities flow out from the top, sequentially passing through the first back pressure regulating valve 207, the primary separator 202, the second back pressure regulating valve 208, and the secondary separator 203, and finally, after compression and condensation, it becomes liquid CO2 again, completing the cycle. During the continuous circulation process, the first back pressure regulating valve 207 adjusts its opening to control the pressure of the high-pressure extraction vessel 201. The pressure is constantly controlled at a first high pressure value. When the supercritical fluid carrying impurities flows through the first back pressure regulating valve 207, it undergoes adiabatic throttling expansion, and the pressure drops sharply to the second medium pressure value and enters the first-stage separator 202. At this time, most of the heavy component impurities precipitate and settle due to a sharp decrease in solubility. The fluid flowing out of the first-stage separator 202 continues to flow through the second back pressure regulating valve 208, and the pressure drops further to a low pressure and enters the second-stage separator 203. The remaining entrainer and light component impurities completely condense into liquid here, achieving separation from gaseous CO2. The clean CO2 gas is drawn and recovered by the compressor 204. The entrainer precision injection unit injects a specific type and flow rate of entrainer into the main CO2 flow path according to the formula program. The entrainer includes ethanol, acetic acid, or dilute nitric acid solution.

[0019] A calcium fluoride granule prepared by the above washing method is characterized in that the surface impurity removal rate of the calcium fluoride granule is ≥95%, the water content is ≤0.5%, and its surface has a micro-nano composite structure formed by plasma etching, with a water contact angle ≥130°, exhibiting superhydrophobicity; its BET specific surface area is increased by 20%-60% compared with that before treatment.

[0020] The beneficial effects of this invention are: Achieving deep cleaning and high product purity: Through the synergistic effect of dual energy fields—plasma activation and supercritical fluid extraction—the problem of incomplete removal of stubborn surface impurities by traditional water washing is solved. Plasma treatment effectively breaks down organic compounds, etches inorganic layers, and activates the surface, enabling subsequent selective deep extraction by supercritical CO2. Ultimately, the surface impurity removal rate of calcium fluoride granules is stabilized at over 95%, and the product purity reaches a high standard suitable for resource utilization.

[0021] Obtaining functionalized products significantly increases added value: Plasma treatment, while cleaning, constructs micro-nano composite structures on the particle surface, giving the product superhydrophobic properties (contact angle ≥130°). This characteristic makes this calcium fluoride product not only a high-purity raw material, but also a high-performance functional filler for the preparation of hydrophobic coatings, composite materials, etc., greatly enhancing its market value and application areas.

[0022] The process is highly integrated, ensuring efficient and stable operation: The traditional, lengthy multi-unit wet process of "washing-screening-dehydration-drying" is integrated into two core dry modules: "plasma activation" and "supercritical extraction." The system adopts continuous circulation and stepped pressure control, achieving fully anhydrous operation, simplifying the process, and improving equipment utilization and production continuity.

[0023] Adaptive intelligent control ensures stable quality: Based on LIBS online component analysis, the system can sense changes in incoming materials in real time and automatically match and call up the optimal process formula ("prescription"). This gives the system strong anti-interference capabilities and adaptability, ensuring that different batches of raw materials can produce stable, high-quality products, reducing reliance on the experience of operators. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a washing system for calcium fluoride granulation in nucleation crystal formation according to the present invention. Figure 1 .

[0025] Figure 2 This is a schematic diagram of the structure of a washing system for calcium fluoride granulation in nucleation crystal formation according to the present invention. Figure 2 .

[0026] Figure 3 This is a cross-sectional schematic diagram of the high-pressure extraction vessel. Detailed Implementation

[0027] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to facilitate the understanding of those skilled in the art.

[0028] like Figure 1-3As shown, this invention provides a washing system and method for granulated calcium fluoride particles produced through nucleation crystal formation. The device modifies the surface of the granules using a plasma surface activation module 100, and then dissolves and separates impurities under anhydrous conditions using a supercritical fluid extraction washing module 200. The entire process is dynamically and precisely controlled by an intelligent control and circulation module based on real-time detection data. This method ultimately produces a dry, high-purity calcium fluoride product with a superhydrophobic surface, exhibiting high added value.

[0029] The technical solution of the present invention will be described in detail and completely below with reference to the accompanying drawings and embodiments.

[0030] I. Detailed Structure and Connection Relationships of Each Module of the Device 1. Plasma surface activation module (100) This module aims to weaken and remove impurities from the surface of the granules through physicochemical synergy, creating favorable conditions for deep extraction.

[0031] Core structure: The main body of the module is a horizontally arranged vibrating fluidized bed 101, whose bed surface inclination angle (0-10°), vibration frequency (20-80 Hz), and amplitude (2-5 mm) are adjustable to ensure that the material is uniformly dispersed and conveyed forward in a single layer. A reaction chamber 102 is sealed above the bed.

[0032] Energy field system: One or more pairs of high-voltage pulse electrodes 103 are arranged in parallel at intervals on the top of the reaction chamber 102. The electrodes are made of corrosion-resistant tungsten alloy and are led out through high-voltage insulating flanges on the chamber wall to be connected to an external nanosecond-level high-voltage pulse power supply (peak voltage 10-30 kV, pulse frequency 50-300 Hz) to generate low-temperature plasma in the chamber.

[0033] Atmosphere control system: The controllable atmosphere supply unit 104 mixes inert gas (such as Ar) and reactive gas (such as O2) from the high-pressure gas cylinder in a set ratio through a mass flow controller, and then injects the mixture from the front end of the reaction chamber 102. The exhaust gas is discharged through the rear end filter.

[0034] Material transfer interface: The end of the vibrating fluidized bed 101 is connected to the inlet of the double gate airlock valve feeding system 105 via a sealed chute. The double gate airlock is existing equipment. The system consists of an intermediate transfer chamber with upper and lower gate valves, an inert gas purging interface, a pressure sensor, and an automatic control system. It is used to transport the processed material to the downstream high-pressure extraction vessel without damage and in an air-isolated manner under pressure balance conditions.

[0035] 2. Supercritical fluid extraction and washing module 200 This module constitutes a supercritical CO2 closed-loop circulation system, which is the core of achieving waterless deep cleaning.

[0036] Extraction Unit - High-Pressure Extraction Vessel 201: A vertical, jacketed pressure vessel designed for a pressure ≥35 MPa. Its detachable top cover houses a drive motor 2012, which connects to an internal porous, rotatable material basket 2011 via a mechanically sealed stirring shaft. The mesh size of the rotatable material basket 2011 is smaller than the diameter of the granules, ensuring the granules remain within the basket. The material basket can be hoisted along with the top cover for easy loading and unloading. A fixed stirring rod 2013 is also installed inside the vessel, working in conjunction with the rotating basket to prevent particle caking. The jacket is circulated with heat transfer oil, and the temperature is precisely controlled by an external temperature controller (31-80°C, accuracy ±0.5°C).

[0037] Stepped pressure separation system: Connections: The top outlet pipeline of extraction vessel 201 is sequentially connected to the first back pressure regulating valve 207, the top inlet of primary separator 202, the second back pressure regulating valve 208, and the side inlet of secondary separator 203. The top outlet of secondary separator 203 is connected to the inlet of compressor 204.

[0038] Functional Structure: The primary separator 202 is a hollow cylindrical structure with a heated cone bottom; the secondary separator 203 has a wire mesh demister installed before the gas outlet for efficient droplet collection, separating the droplets from the CO2 gas. Both separators have their cone bottoms connected to an independent impurity collection tank 209 via a dual-valve assembly.

[0039] Fluid circulation and injection system: Main circulation loop: The outlet of CO2 storage tank 210 (5-6 MPa, 5°C) is sequentially connected to high-pressure plunger pump 211 and tubular preheater 212, and finally enters from the bottom of extraction vessel 201. Low-pressure CO2 gas from secondary separator 203 is pressurized by compressor 204, cooled and liquefied by condenser 205, and then returns to CO2 storage tank 210, forming a closed loop.

[0040] The entrainer injection unit consists of 2-3 high-pressure micro-injection pumps 213 connected in parallel, with each pump independently connected to an entrainer storage tank 214 (containing ethanol, acetic acid, dilute nitric acid, etc.). After the pump outlets converge, the entrainer is injected into the main CO2 pipeline, enabling online and precise addition of the entrainer.

[0041] 3. Intelligent Control and Loop Module This module is the "brain" that enables the system to operate adaptively and intelligently.

[0042] Sensing layer: A probe of a laser-induced breakdown spectroscopy (LIBS) online component analyzer 301 is installed at the feed chute of the plasma module 100. This probe scans the falling raw granules several times per second in a non-contact manner, acquiring the elemental characteristic spectral lines (such as C 247.8 nm, Si 288.1 nm, Fe 259.9 nm, Al 396.1 nm, etc.) on its surface in real time.

[0043] Decision and Execution Layer: The central controller uses a CPU 1515-2 PN (6ES7515-2AM00-0AB0) model. The central controller (industrial PLC + industrial computer) receives LIBS spectral data and matches it with a built-in "impurity spectrum-process formulation" expert database using feature extraction algorithms (such as principal component analysis, PCA). The database pre-stores dozens of sets of optimized process parameters (i.e., "formulations") for different impurity combinations (such as "high C / low Si", "high Si / high Fe", etc.). After matching, the controller synchronously distributes the formulation parameters to all execution units via an industrial bus (such as PROFINET).

[0044] II. Detailed working process, extraction principle and parameter settings 1. Intelligent diagnosis and formula matching (steps S1-S2) When calcium fluoride granules with a moisture content of <10% are fed into the system, the LIBS analyzer 301 immediately begins operation. The central controller compares the real-time spectrum with the database. For example, if a high intensity of the C spectral line, a medium intensity of the Si spectral line, and a weak Fe spectral line are detected, it is determined to be "organosilicon complex contamination, containing trace metals," and formulation #OS-05 may be matched. Example of formulation parameters: Plasma section: atmosphere is 70% Ar + 30% O2; discharge power is 1.8 kW; processing time is 90 s (controlled by fluidized bed conveying speed).

[0045] Supercritical extraction section: extraction pressure 22 MPa; extraction temperature 55 °C; entrainer program: 4% (v / v) ethanol injected for the first 60 minutes, followed by 1% (v / v) 0.05M dilute nitric acid injected for the next 30 minutes.

[0046] 2. Plasma surface activation (step S3) After the formula is issued, the plasma module operates according to the settings.

[0047] Principle: Under the action of high-energy electrons, ion bombardment and active particles (such as O and OH free radicals), two effects occur: (1) Physical etching: micron-nano roughness is created on the particle surface, increasing the specific surface area and removing some surface impurities; (2) Chemical modification: under O2 atmosphere, long-chain organic matter is broken and oxidized into small molecules or oxygen-containing groups, which significantly improves its solubility in subsequent supercritical CO2; pure Ar atmosphere is mainly used for physical sputtering to remove metal oxides.

[0048] Process: Under vibration fluidization, the material passes uniformly through the plasma glow zone at a set speed to complete surface activation.

[0049] 3. Intelligent material transfer (step S4) After activation, the material enters the dual-gate airlock valve system 105. The controller operates automatically according to a strict sequential logic of "feeding (open V1) - closing V1 - inert gas purging and pressure balancing (charge N2 to the same pressure as the extraction vessel) - unloading (open V2) - closing V2 - depressurization and reset" to ensure safe and oxygen-free transfer.

[0050] 4. Supercritical fluid circulation extraction (step S5) – core principles and parameter control After the material enters the extraction vessel, the system starts supercritical circulation according to the formula, which is the core of the separation process.

[0051] Extraction Principle: Supercritical CO2 (temperature > 31°C, pressure > 7.38 MPa) has a density similar to liquids (0.4-0.9 g / mL) and a viscosity and diffusion coefficient similar to gases. Its solubility is extremely sensitive to pressure and temperature and can be "programmed" to adjust by adding a small amount of polar entrainer (such as ethanol). Under the high-pressure environment of the extraction vessel, supercritical CO2 can penetrate into the micropores of the particles, selectively dissolving plasma-activated impurities (small molecule organic matter, certain metal complexes).

[0052] Stepped pressure separation principle: Extraction vessel (22 MPa, 55°C): CO2 is in a supercritical state and has strong dissolving power. The fluid loaded with impurities flows out continuously under the drive of the high-pressure plunger pump 211.

[0053] As the fluid passes through the narrow orifice of the first back pressure regulating valve 207 (adiabatic throttling), pressure energy is converted into kinetic energy and dissipated, resulting in the Joule-Thomson effect, causing a sudden drop in pressure and a slight drop in temperature. When the pressure drops to the 10 MPa set by the first-stage separator, the CO2 density and solubility decrease sharply, causing heavy component impurities (large organic molecules, polymers) to become supersaturated and precipitate or settle.

[0054] After passing through the second back pressure regulating valve 208, the pressure is further reduced to 3 MPa in the secondary separator (below the critical pressure). CO2 becomes a normal gas, its dissolving ability is almost lost, and the entrainer and light impurities are completely condensed into droplets, which are captured and separated by the demister.

[0055] Pressure gradient maintenance: The first back pressure regulating valve 207 is PID regulated to maintain the extraction vessel pressure at 22 MPa; the second back pressure regulating valve 208 is regulated to maintain the primary separator pressure at 10 MPa. The two valves work together to actively construct and stably maintain a stepped pressure field of 22→10→3 MPa in the system, which is the physical basis for achieving the stepwise precipitation of impurities.

[0056] Dynamic extraction process: In a continuous cycle, fresh supercritical CO2 continuously penetrates the rotating and stirred particle bed, achieving dynamic mass transfer. Programmed injection of the entrainer enables staged targeted extraction of impurities of different polarities.

[0057] 5. Product collection (step S6) After extraction (usually 1-2 hours), the system is depressurized. The connecting pipes on the top cover of the extraction vessel are disconnected, the top cover is opened upwards, and the material basket is lifted out to obtain dry, clean calcium fluoride granules. The primary separator collects viscous, dark-colored heavy organic components, and the secondary separator collects a liquid containing entrainer and light oil. CO2 gas is compressed and condensed, with a recovery rate >99%.

[0058] III. Example: Granulation of Fluorine-Containing Wastewater from Photovoltaic Cutting Raw material: Calcium fluoride granules from photovoltaic silicon wafer cutting wastewater treatment, with a moisture content of 8%, containing polyethylene glycol cutting fluid, nano-silicon powder, silicon carbide and trace amounts of iron.

[0059] Intelligent diagnostics: LIBS spectrum shows extremely strong C and Si peaks, and a weak Fe peak. System-matched formula #PV-SiC-12.

[0060] Plasma treatment: Perform according to the formula: atmosphere 65% Ar / 35% O2, power 2.2 kW, treatment time 110 seconds.

[0061] Supercritical fluid extraction: Perform according to the formulation: pressure 25 MPa, temperature 60 °C, total time 120 minutes. Entrainer program: 0-80 minutes, 5% ethanol; 80-120 minutes, 2% acetic acid.

[0062] result: Product: Calcium fluoride granules, white and dry. Testing shows: total carbon removal rate 99.2%, total silicon removal rate 97.5%, iron not detected. SEM reveals a uniform micro-nano composite structure on the surface. BET specific surface area increased by 45%, water contact angle 158°, exhibiting superhydrophobicity.

[0063] Resource consumption: Zero process water consumption and zero process wastewater generation throughout the entire process. CO2 recycling loss rate <1%, ethanol recovery rate >90%.

[0064] Efficiency: The processing time for a single batch is approximately 2.5 hours (including loading and unloading), which is much faster than the traditional washing-drying process that takes several days.

[0065] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention 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 the present invention.

Claims

1. A washing system for washing calcium fluoride granules produced by nucleation crystal granulation, characterized in that, It includes a plasma surface activation module (100), a supercritical fluid extraction and washing module (200), and an intelligent control and circulation module connected in sequence; The plasma surface activation module (100) is used to perform surface modification and impurity weakening treatment on the pre-dried calcium fluoride granules. The supercritical fluid extraction and purification module (200) is used to deeply remove impurities from the surface and pores of the granules under anhydrous conditions; The intelligent control and circulation module is connected to the aforementioned module via signals and is used to dynamically adjust the entire refining process based on online monitoring data.

2. The washing system for washing calcium fluoride granules produced by nucleation granulation according to claim 1, characterized in that, The plasma surface activation module (100) includes: A vibrating fluidized bed (101) is provided with a reaction chamber (102). The inclination angle and amplitude of the vibrating fluidized bed (101) are adjustable, so that the material vibrates and moves forward in the reaction chamber (102). At least one pair of high-voltage pulse electrodes (103) are disposed in the reaction chamber (102), and the electrodes are connected to an external nanosecond-level high-voltage pulse power supply; A controllable atmosphere supply unit (104) is used to inject a mixture of inert gas or reactive gas into the reaction chamber (102); A dual-gate airlock valve feeding system (105) has its inlet connected to the end outlet of the vibrating fluidized bed (101) and its outlet connected to the supercritical fluid extraction and purification module (200) for feeding the processed material into the downstream module under air-isolated conditions.

3. The washing system for washing calcium fluoride granules produced by nucleation granulation according to claim 1, characterized in that, The supercritical fluid extraction and purification module (200) includes the following units connected sequentially by pipelines to form a closed loop: A supercritical CO2 extraction unit includes a high-pressure extraction vessel (201). The impurity separation unit includes a primary separator (202) and a secondary separator (203) connected in series. A CO2 recycling unit includes a compressor (204) and a condenser (205); An extraction fluid feed system (206) is connected to the discharge pipe at the lower end of the high-pressure extraction vessel (201) for discharging impurities.

4. The washing system for washing calcium fluoride granules produced by nucleation granulation according to claim 3, characterized in that, The high-pressure extraction vessel (201) is a vertical jacketed pressure vessel, and a heating system for adjustable and stable heating of the interior of the high-pressure extraction vessel (201) is installed inside the high-pressure extraction vessel (201). A rotatable material basket (2011) made of a perforated plate is installed inside the high-pressure extraction vessel (201). The center of the rotatable material basket (2011) is connected to a drive motor (2012) installed on the top cover of the high-pressure extraction vessel (201) via a rotating shaft. The top cover of the high-pressure extraction vessel (201) is detachable. The rotating material basket (2011) is designed to be lifted out of the high-pressure extraction vessel (201) along with the top cover. A stirring rod (2013) extending into the rotating material basket (2011) is connected to the bottom surface of the top cover of the high-pressure extraction vessel (201). The top of the high-pressure extraction vessel (201) is connected to a double-gate airlock valve feeding system (105) via a detachable pipe. Granulated material processed in the plasma surface activation module (100) is discharged into the rotating material basket (2011). An outlet pipe is connected to the top cover of the pressure extraction vessel (201), and a first back pressure regulating valve (207) is provided between it and the inlet pipe at the top of the primary separator (202); an outlet pipe is provided at the top of the primary separator (202), and a second back pressure regulating valve (208) is provided between it and the inlet pipe at the top of the secondary separator (203); an outlet pipe is also provided at the top of the secondary separator (203) and connected to the compressor (204), and the compressor (204) and The condenser (205) is connected and the condenser (205) transports the liquefied CO2 back to the CO2 storage tank (210); the primary separator (202) and the secondary separator (203) are both vertical containers with conical bottoms, and the secondary separator (203) is equipped with a metal wire mesh demister at the gas outlet; the bottom of the high-pressure extraction vessel (201), the primary separator (202) and the secondary separator (203) are connected to an impurity collection tank (209) through valves.

5. A washing system for washing calcium fluoride granules produced by nucleation granulation according to claim 3 or 4, characterized in that, The extraction fluid feeding system includes a supercritical CO2 feeding system and an entrainer precision injection unit connected in parallel. The supercritical CO2 feeding system includes a CO2 storage tank (210), a high-pressure plunger pump (211), and a tubular preheater (212) connected in sequence. The entrainer precision injection unit includes multiple high-pressure micro-injection pumps (213) connected in parallel. The multiple high-pressure micro-injection pumps (213) are respectively connected to entrainer storage tanks (214) containing different entrainers.

6. The washing system for washing calcium fluoride granules produced by nucleation granulation according to claim 5, characterized in that, The first back pressure regulating valve (207) is configured to maintain the operating pressure of the high-pressure extraction vessel (201) at a preset first high pressure value; the second back pressure regulating valve (208) is configured to maintain the operating pressure of the primary separator (202) at a second medium pressure value lower than the first high pressure value; the first high pressure value is 15-35 MPa, the second medium pressure value is 8-15 MPa, and the operating pressure of the secondary separator (203) is 2-5 MPa; the system establishes and maintains a stable stepped pressure gradient between the extraction vessel (201), the primary separator (202), and the secondary separator (203) through the regulation of the first back pressure regulating valve (207) and the second back pressure regulating valve (208).

7. The washing system for calcium fluoride granules produced by nucleation granulation according to claim 1, characterized in that, The intelligent control and loop module includes: A laser-induced breakdown spectroscopy online component analyzer (301) has its probe set at the feed inlet of the plasma surface activation module (100) for real-time detection of the elemental composition spectrum of the granulation surface; A central controller that stores a preset database of "impurity spectra - process formulations"; The central controller is configured to receive spectral data from the laser-induced breakdown spectroscopy online component analyzer (301), automatically generate and issue a set of collaborative process parameters to the plasma surface activation module (100) and the supercritical fluid extraction and purification module (200) through algorithm matching with the database; the "collaborative process parameters" include at least the plasma working gas formula and discharge power for the plasma surface activation module (100), and the extraction temperature and pressure, entrainer type and injection procedure for the supercritical fluid extraction and purification module (200).

8. A method for washing calcium fluoride granules using the washing system of claim 6 or 7, characterized in that, Includes the following steps: S1: Input the calcium fluoride granules with a water content of less than 10% into the plasma surface activation module (100). S2: Start the laser-induced breakdown spectroscopy online component analyzer (301) to scan the granules. The central controller matches and calls the optimal synergistic process formula from the database according to the identified impurity characteristic spectrum. S3: According to the formula, the granules are subjected to pulsed discharge plasma treatment in the plasma surface activation module (100); the pulsed discharge plasma treatment is carried out under vibration fluidization conditions, and the treatment atmosphere is selected according to the type of impurities: when organic matter is the main impurity, a mixture of argon and oxygen is used; when metal compounds are the main impurities, pure argon is used. S4: The plasma-treated granules are transferred to the high-pressure extraction vessel (201) through the double gate airlock valve feeding system (105); S5: Based on the parameters set in the formula, start the supercritical fluid extraction and purification module (200) to make the supercritical CO2 fluid continuously circulate in the closed-loop system to dynamically extract the granules. S6: After extraction, the dried high-purity calcium fluoride granules are taken out from the high-pressure extraction vessel (201), and the separated impurities are collected from the bottom of the primary separator (202) and the secondary separator (203), respectively.

9. The washing method for calcium fluoride granules according to claim 8, characterized in that, In step S5, the supercritical CO2 fluid circulation extraction process is continuous, powered by a high-pressure plunger pump (211). The path is as follows: liquid CO2 is pressurized and heated by the pump to become a supercritical fluid, which enters from the bottom of the high-pressure extraction vessel (201), penetrates the solid material layer, and at the same time, the drive motor (2012) drives the rotatable material basket (2011) to rotate, and the stirring rod (2013) stirs the granulated material; the dissolved impurities flow out from the top, and flow sequentially through the first back pressure regulating valve (207), the primary separator (202), the second back pressure regulating valve (208), and the secondary separator (203), and finally, after compression and condensation, it becomes liquid CO2 again, completing the cycle; during the continuous cycle, the first back pressure regulating valve (207) adjusts its opening to control the pressure of the high-pressure extraction vessel (201). The pressure is constantly controlled at the first high pressure value; when the supercritical fluid loaded with impurities flows through the first back pressure regulating valve (207), adiabatic throttling expansion occurs, the pressure drops sharply to the second medium pressure value and enters the first-stage separator (202). At this time, most of the heavy component impurities precipitate and settle due to the sharp decrease in solubility; the fluid flowing out of the first-stage separator (202) continues to flow through the second back pressure regulating valve (208), the pressure drops further to the low pressure and enters the second-stage separator (203). The remaining entrainer and light component impurities are completely condensed into liquid here and separated from the gaseous CO2. The clean CO2 gas is drawn and recovered by the compressor (204); the entrainer precision injection unit injects a specific type and flow rate of entrainer into the main CO2 flow path according to the formula program. The entrainer includes ethanol, acetic acid or dilute nitric acid solution.

10. A calcium fluoride granule prepared using the washing method for calcium fluoride granules according to claim 9, characterized in that, The calcium fluoride granules have a surface impurity removal rate of ≥95%, a water content of ≤0.5%, and a micro-nano composite structure formed by plasma etching on their surface. The contact angle with water is ≥130°, exhibiting superhydrophobicity. Its BET specific surface area increased by 20%-60% compared to before treatment.

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