Production process of ultra-pure thorium fluoride

Abstract

The invention provides an ultra-pure thorium fluoride production process which comprises the following steps: preparing a nanoscale ThF4.xNH4F precursor through a gas-liquid-solid three-phase reaction, atomizing an ammonium fluoride solution into microdroplets by adopting ultrasonic atomization, and carrying out synergistic reaction with gaseous ammonium fluoride and a liquid-phase thorium nitrate solution; a microwave-plasma synergistic fluorination reaction is adopted, and the precursor is heated in a high-purity inert atmosphere to generate crude thorium fluoride; according to the ultra-pure thorium fluoride production process provided by the invention, the purity of thorium fluoride is remarkably improved through the technical means of preparation of a nanoscale precursor through a gas-liquid-solid three-phase reaction, microwave-plasma synergistic fluorination, multi-stage sublimation combined with graphene-based nano trapping membrane purification, intelligent process control, by-product closed-loop recovery and the like; the impurity content is low, and the requirements of nuclear reactor fuel substrates and high-end optical coatings on ultra-high purity are met. The method has the advantages of high yield, high process stability and small purity fluctuation among batches, and the production efficiency and the product consistency are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic compounds, and particularly to a production process of ultra-pure thorium fluoride. Background Art

[0002] Thorium fluoride (ThF4) is an important inorganic compound. Due to its high melting point, low volatility, and excellent optical properties, it has wide applications in fields such as nuclear reactor fuel matrices, optical coatings, and infrared transmission materials. Existing methods for preparing thorium fluoride mainly include gas-phase fluorination, wet precipitation-fluorination, and electrochemical fluorination. Among them, in the gas-phase fluorination method, thorium oxide (ThO2) reacts with hydrogen fluoride (HF) at high temperature (usually >600 °C) to produce ThF4. However, the reaction conditions are harsh, oxygen impurities are easily introduced, and the product purity is usually lower than 99.9%, making it difficult to meet the requirements for ultra-high purity (≥99.999%) in the nuclear energy and optical fields. In addition, the high-temperature reaction results in high energy consumption, and the equipment needs to use expensive corrosion-resistant materials, increasing the production cost.

[0003] In the wet precipitation-fluorination method, a thorium salt solution (such as thorium nitrate) reacts with a fluoride (such as NH4F) to form a ThF4 precipitate, which is then obtained as a product through high-temperature roasting. This method has a simple process, but anions (such as NO3 - 、SO4 2- ) and metal impurities (such as Fe, Al) are easily incorporated during the precipitation process. The roasting process may lead to uneven crystal forms, and the purity usually does not exceed 99.8%. At the same time, the wet process generates a large amount of fluorine-containing wastewater and by-products (such as HF, NH3), with high treatment costs and environmental pollution risks. The electrochemical fluorination method uses electrolysis to generate fluorine gas to react with thorium compounds. The equipment is complex, the process control is difficult, and the problems of by-product treatment and waste gas emission are also prominent, restricting its industrial application.

[0004] The purification processes of the existing technologies usually rely on single roasting or simple sublimation, which are difficult to effectively remove trace metal impurities and non-volatile oxides, resulting in the product purity being difficult to exceed 99.9%. In addition, the existing processes lack intelligent process control, the reaction parameters rely on manual adjustment, and the product consistency between batches is poor, making it difficult to meet the stability requirements of large-scale production. The treatment of by-products and wastewater mostly adopts neutralization and discharge, with low resource utilization rate and failure to achieve green production. These problems limit the application of ultra-pure thorium fluoride in high-precision fields, and there is an urgent need for a process that is efficient, environmentally friendly, and can stably prepare ultra-high purity products. Summary of the Invention

[0005] The object of the present invention is to propose a production process of ultra-pure thorium fluoride. By means of gas-liquid-solid three-phase reaction to prepare nano-level precursors, microwave-plasma synergistic fluorination, multi-stage sublimation combined with graphene-based nano-trapping membrane purification, intelligent process control, and closed-loop recycling of by-products, the purity of the product is significantly improved, energy consumption and environmental pollution are reduced, the deficiencies of the existing technology are overcome, and it has significant technical advantages and industrialization potential.

[0006] To achieve the above object, the present invention proposes the following technical solution: A production process of ultra-pure thorium fluoride, comprising the following steps:

[0007] (1) Prepare nano-level ThF4·xNH4F precursors through gas-liquid-solid three-phase reaction, wherein ammonium fluoride solution is atomized into micro-droplets by ultrasonic atomization and reacts synergistically with gaseous ammonium fluoride and liquid-phase thorium nitrate solution;

[0008] (2) Carry out microwave-plasma synergistic fluorination reaction, and heat the precursor in a high-purity inert atmosphere to generate crude thorium fluoride;

[0009] (3) Purify the crude thorium fluoride through multi-stage sublimation combined with graphene-based nano-trapping membrane to obtain ultra-pure thorium fluoride with a purity ≥ 99.9995%;

[0010] (4) Utilize an intelligent control system to dynamically adjust the parameters of the reaction and purification processes through multi-sensor monitoring and artificial intelligence algorithms;

[0011] (5) Carry out closed-loop recycling of reaction by-products, and carry out ion exchange and electrolysis treatment on wastewater to achieve green production.

[0012] Further, in the present invention, the specific operation of the gas-liquid-solid three-phase reaction in step (1) includes:

[0013] (a) Dissolve high-purity thorium nitrate in ultrapure water to prepare a solution with a concentration of 0.2 - 0.5 mol / L;

[0014] (b) Atomize ammonium fluoride solution with a concentration of 0.3 - 0.6 mol / L into micro-droplets with a diameter of 10 - 20 μm through an ultrasonic atomization device, spray them into the reaction kettle, and simultaneously introduce gaseous ammonium fluoride. The molar ratio of thorium nitrate to ammonium fluoride is 1:4.5 - 5.0;

[0015] (c) Control the reaction temperature at 35 - 45 °C, the ultrasonic frequency at 30 - 50 kHz, the stirring speed at 150 - 250 rpm, react for 2 - 4 hours, and generate ThF4·xNH4F precursors with a particle size of 50 - 100 nm;

[0016] (d) Separate the precursor by centrifugation, wash it alternately with absolute ethanol and ultrapure water for 3 - 5 times, and vacuum dry it at 40 - 60 °C for 8 - 12 hours.

[0017] Further, in the present invention, the specific operation of the microwave-plasma synergistic fluorination reaction in step (2) includes:

[0018] (a) Place the precursor in a high-purity quartz reactor and react in a microwave-plasma composite reaction furnace. The working atmosphere is high-purity argon with a flow rate of 100 - 200 mL / min;

[0019] (b) Adopt a gradient heating program: in the initial stage, the microwave power is 200 - 400 W, the plasma power is 30 - 60 W, the temperature is raised to 180 - 220 °C, and keep warm for 20 - 40 minutes; in the middle stage, the microwave power is 500 - 700 W, the plasma power is 80 - 120 W, the temperature is raised to 300 - 350 °C, and keep warm for 60 - 90 minutes; in the final stage, the microwave power is 300 - 500 W, the temperature is maintained at 280 - 320 °C, and keep warm for 20 - 40 minutes;

[0020] (c) Real-time monitor NH3 and HF in the tail gas through an on-line mass spectrometer and collect crude thorium fluoride.

[0021] Further, in the present invention, the purification process of the multi-stage sublimation combined with the graphene-based nano-trapping film in step (3) includes:

[0022] (a) Place the crude thorium fluoride in a vacuum sublimation furnace, with a pressure < 10 -3 Pa, the primary sublimation temperature is 800 - 850 °C, the temperature in the condensation zone is 180 - 220 °C, and the sublimation time is 2 - 4 hours;

[0023] (b) Set a graphene-based nano-trapping film above the condensation zone. The membrane pore size is 5 - 10 nm, the thickness is 30 - 60 μm, and the surface is modified with fluorination functional groups to trap trace metal impurities and oxides;

[0024] (c) Collect the primary sublimation product and conduct secondary sublimation. The temperature is 850 - 900 °C, the temperature in the condensation zone is 220 - 260 °C, and the time is 1 - 3 hours to obtain thorium fluoride with a purity ≥ 99.9995%;

[0025] (d) The trapping film is regenerated by purging with high-purity argon at 500 - 600 °C and can be recycled.

[0026] Further, in the present invention, the impurity content of the ultra-pure thorium fluoride in step (3) is: Fe < 0.2 ppm, Al < 0.1 ppm, O < 5 ppm, and the crystal form is monoclinic, with an average particle size of 1 - 2 μm.

[0027] Further, in the present invention, the specific operation of the intelligent control system in step (4) includes:

[0028] (a) An integrated temperature sensor, pressure sensor, infrared spectrometer and mass spectrometer are used to monitor the reaction temperature, pressure and tail gas composition in real time;

[0029] (b) Through an artificial intelligence control platform, based on a neural network model, the reaction process and the risk of impurity generation are predicted, and the microwave power, plasma intensity and sublimation temperature are dynamically adjusted, with the temperature fluctuation controlled within ±2°C;

[0030] (c) The process parameters and monitoring data are automatically stored for process optimization and quality traceability.

[0031] Furthermore, in the present invention, the specific operations of the closed-loop recycling and wastewater treatment in step (5) include:

[0032] (a) NH3 and HF in the reaction tail gas are treated by a two-stage absorption system. The first stage is an 8-12% NaOH solution to generate NH4OH and NaF, and the second stage is activated carbon adsorption with a capture efficiency > 99.9%;

[0033] (b) NH4OH is distilled and concentrated for recycling in the preparation of the precursor, and NaF is recrystallized and purified as an industrial raw material;

[0034] (c) The wastewater is passed through a strong acid cation exchange resin to remove trace amounts of Th 4+ , and the Th content in the discharged water is 4+ <0.01 mg / L. The resin regeneration solution is used to recover thorium by electrolysis.

[0035] Furthermore, in the present invention, the reaction device of the process includes:

[0036] (a) A multiphase reaction module, including an ultrasonic atomization device, a gaseous ammonium fluoride supply system and a high-purity polytetrafluoroethylene reaction kettle;

[0037] (b) A microwave-plasma reaction module, including a microwave heater, a low-temperature plasma generator and an on-line mass spectrometry monitoring system;

[0038] (c) A purification module, including a vacuum sublimation furnace and a graphene-based nano-capture membrane;

[0039] (d) An intelligent control module, including a multi-sensor system and an artificial intelligence control platform;

[0040] (e) A green by-product treatment module, including a two-stage absorption system, an ion exchange resin and an electrolytic recovery device.

[0041] Furthermore, in the present invention, the ultra-pure thorium fluoride is used for nuclear reactor fuel matrix, optical coating or infrared transmission material.

[0042] The production process of ultra-pure thorium fluoride in the present invention realizes synergistic effect at the underlying mechanism through the organic combination of technical features such as multiphase reaction, microwave-plasma synergy, nano-scale impurity trapping, intelligent control, and green treatment, and produces a number of unexpected technical effects.

[0043] Ultrasonic atomization converts ammonium fluoride solution into 10-20μm droplets, forming a multiphase reaction system with gaseous ammonium fluoride and liquid thorium nitrate, significantly increasing the reaction interface area (about 10 3 -10 4 m 2 / m 3 ). The cavitation effect induced by ultrasound promotes molecular collision and reduces the reaction activation energy (E a ), enabling the reaction to proceed efficiently at a low temperature of 35-45°C.

[0044] The multiphase system generates ThF4·xNH4F precursors with a particle size of 50-100nm. Their high specific surface area (>50m 2 / g) and uniformity enhance the kinetic efficiency of the subsequent fluorination reaction and reduce the inclusion of oxygen impurities and anions (such as NO3 - ).

[0045] Introduction of ultra-low impurities. The uniform crystal structure of the nano-scale precursors and the low-temperature reaction conditions reduce the oxygen impurity content to <5ppm, which is one order of magnitude lower than that of the traditional wet method (O>50ppm), breaking through the bottleneck of the existing technology in trace impurity control.

[0046] Crystal form control ability. The monoclinic crystal structure of the nano-precursors is retained in the subsequent fluorination. XRD analysis shows that the content of impurity phases is <0.1%, significantly improving the transmission performance of the optical coating application (infrared transmittance >95%).

[0047] Improvement of reaction efficiency: The multiphase system shortens the precursor preparation time to 2-3 hours and increases the yield to >90%, which is more efficient than the traditional wet method (6-8 hours, yield <80%), reducing the difficulty of process scale-up.

[0048] Microwave heating (2.45GHz) provides uniform volumetric heating, activates the vibration of precursor molecules, and reduces the fluorination reaction temperature to 300-350°C. Low-temperature plasma (argon, 100W) generates highly active F-radicals and electrons, catalyzes the decomposition of NH4F and the formation of Th-F bonds, and further reduces the reaction activation energy by about 20-30kJ / mol.

[0049] Gradient heating program (initial 200°C, intermediate 320°C, final 300°C) optimizes the energy distribution, suppresses side reactions (such as oxide formation), and ensures the regularity of the ThF4 crystal structure.

[0050] The synergistic effect reduces the reaction temperature by 200 - 300 °C, shortens the reaction time to 2 hours, saves more than 40% energy compared with the traditional gas phase method (600 °C, 4 - 6 hours), and maintains a high yield (88%).

[0051] Crystal defects are reduced, and plasma - catalyzed selective fluorination reduces lattice defects (defect density < 10 8 cm -2 ), improves the mechanical strength and optical uniformity of ThF4, and is suitable for high - precision optical devices.

[0052] By - product control, on - line mass spectrometry monitoring shows that the release rates of NH3 and HF are more controllable, the by - product generation is reduced by about 50%, and the load of the subsequent recovery system is reduced.

[0053] The graphene - based trapping membrane (pore size 5 - 10 nm) traps trace metal impurities (such as Fe 2+ 、Al 3+ ) and oxides through physical sieving and chemical chelation. The surface - modified - CF3 groups form stable coordination bonds with metal ions, and the selective adsorption coefficient reaches 10 4 -10 5 , significantly superior to traditional activated carbon (10 2 -10 3 ).

[0054] Multi - stage sublimation (850 °C + 900 °C) uses the high volatility of ThF4 (vapor pressure ~ 10 Pa at 900 °C) to separate non - volatile impurities, and the trapping membrane further enhances the removal efficiency of trace impurities.

[0055] Ultra - high purity breakthrough, with a purity of 99.9997%, and the impurity content (Fe 0.12 ppm, Al 0.06 ppm) is reduced by two orders of magnitude compared with the traditional sublimation method (Fe > 5 ppm), meeting the stringent impurity requirements of nuclear fuel (< 0.5 ppm).

[0056] Membrane regeneration efficiency, the trapping membrane is regenerated by argon purging at 500 °C, can be recycled > 50 times, and the adsorption efficiency decay < 5%, significantly reducing the purification cost.

[0057] Impurity separation selectivity, the low adsorption of the membrane to heavy metals (such as Th 4+ ) (adsorption rate < 0.1%) ensures a high recovery rate of ThF4 (> 95%) and avoids the problem of product loss in traditional filtration methods.

[0058] The multi - sensor system (FTIR, QMS) monitors the concentrations of reactants and by - products in real - time, generating high - dimensional data streams (~ 10 4Data points per minute). The neural network model predicts the reaction process and the risk of impurity generation through deep learning (LSTM algorithm), and dynamically adjusts the microwave power (±10 W), plasma intensity (±5 W), and sublimation temperature (±2 °C).

[0059] The closed-loop control system controls the process parameter fluctuations within ±0.5%, significantly improving the reaction stability.

[0060] Batch consistency, the purity fluctuation between batches is <0.0001%, and the crystal form consistency is >99.9%. It is two orders of magnitude higher than the traditional manual control (fluctuation ~0.01%), meeting the quality requirements of large-scale production.

[0061] Energy consumption optimization, the AI prediction model reduces the ineffective heating time, and the energy consumption is reduced by about 10% (in addition to the 40% energy saving of microwave - plasma), achieving ultra-high efficiency operation of the process.

[0062] Fault warning, the system identifies abnormal reaction trends (such as excessive release of HF), adjusts parameters in advance, reduces the equipment failure rate by >80%, and extends the equipment life.

[0063] The two-stage absorption system (NaOH + activated carbon) captures NH3 and HF through chemical neutralization and physical adsorption, and the capture efficiency is >99.9%. The ion exchange resin (strong acid type) removes Th in the wastewater through cation exchange (K e ~10 6 L / mol), and electrolytic recovery further improves the thorium utilization rate (>90%). 4+

[0064] The closed-loop cycle converts NH4OH and NaF into reusable raw materials, reducing resource waste.

[0065] Zero emission is achieved, the Th in the wastewater 4+ <0.01 mg / L, and the tail gas emission is better than the GB16297 - 1996 standard, achieving ultra-low emissions of radioactive substances and hazardous chemicals, and complying with the "Law on the Prevention and Control of Radioactive Pollution".

[0066] The by-product recovery rate is >99.9%. The recycling of NH4OH reduces the raw material cost by about 20%, and the purified NaF generates additional income as an industrial raw material.

[0067] Environmental adaptability, the process has the same by-product treatment efficiency for different scales of production (from laboratory to ton level). No additional adjustment of the system is required during the scale-up process, reducing the industrialization threshold.

[0068] Beneficial effects, the technical solution of this application has the following technical effects:

[0069] 1. The present invention provides a production process for ultra-pure thorium fluoride. By means of techniques such as gas-liquid-solid three-phase reaction to prepare nano-scale precursors, microwave-plasma synergistic fluorination, multi-stage sublimation combined with graphene-based nano-trapping membranes for purification, intelligent process control, and closed-loop recycling of by-products, the purity of thorium fluoride is significantly improved, with low impurity content, meeting the requirements of ultra-high purity for nuclear reactor fuel matrices and high-end optical coatings. Compared with traditional gas-phase fluorination methods and wet precipitation methods, the present invention uses low-temperature reactions to reduce energy consumption by about 40%, has a high yield, high process stability, and small fluctuations in purity between batches, significantly improving production efficiency and product consistency.

[0070] 2. The present invention realizes the precise separation of trace impurities through graphene-based nano-trapping membranes, breaking through the purity bottleneck of traditional purification methods; the intelligent control system dynamically optimizes reaction parameters based on artificial intelligence algorithms, reduces operation errors, and improves process repeatability; the closed-loop by-product recycling system increases the recovery rates of NH3 and HF to >99.9%, and the Th in wastewater discharge 4+ <0.01 mg / L, meeting the Integrated Emission Standard for Air Pollutants (GB16297-1996) and the Law on Prevention and Control of Radioactive Pollution. These technical features together achieve green production, reduce environmental pollution risks and production costs, and the process modular design facilitates industrial scale-up, being applicable to large-scale applications in fields such as nuclear energy, optics, and infrared transmission materials, with significant economic and environmental benefits.

[0071] It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be regarded as part of the inventive subject matter of the present disclosure as long as such concepts do not conflict with each other.

[0072] The foregoing and other aspects, embodiments, and features of the teachings of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of exemplary embodiments, will be apparent from the following description or learned through the practice of specific embodiments in accordance with the teachings of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in each figure may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Now, embodiments of various aspects of the present invention will be described by way of example and with reference to the drawings, where:

[0074] Figure 1 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0075] To better understand the technical content of the present invention, specific embodiments are hereby provided and described in conjunction with the accompanying drawings as follows. In the present disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure do not necessarily define all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of a number of ways, because the concepts and embodiments disclosed in the present invention are not limited to any implementation manner. In addition, some aspects of the present invention can be used alone, or in any suitable combination with other aspects of the present invention.

[0076] Experimental Equipment and Materials

[0077] Equipment: High-purity polytetrafluoroethylene reaction kettle (500 mL), ultrasonic nebulizer (40 kHz), microwave-plasma composite reaction furnace (2.45 GHz, maximum power 1000 W; plasma power 150 W), vacuum sublimation furnace (pressure < 10 -3 Pa), graphene-based nano-trapping membrane (pore size 5 - 10 nm, thickness 50 μm), ICP-MS (Agilent 7900), XRD (Bruker D8 Advance), laser particle size analyzer (Malvern Mastersizer 3000), online mass spectrometer (QMS, Hiden Analytical), infrared spectrometer (FTIR, Thermo Nicoleti S50), ion exchange system (strong acid cation resin), electrolytic recovery device.

[0078] Materials: High-purity thorium nitrate (Th(NO3)4, purity 99.995%), anhydrous ammonium fluoride (NH4F, purity 99.99%), ultrapure water (resistivity 18.2 MΩ·cm), high-purity argon gas (purity 99.9999%), 10% NaOH solution, activated carbon (BET specific surface area 1200 m 2 / g)

[0079] Example 1: Standard Process Verification

[0080] Experimental Steps, Preparation of Precursors:

[0081] Weigh 100 g of high-purity thorium nitrate, dissolve it in 300 mL of ultrapure water to prepare a 0.33 mol / L solution, and place it in a polytetrafluoroethylene reaction kettle.

[0082] Prepare a 0.5 mol / L ammonium fluoride solution (180 g of NH4F dissolved in 1 L of ultrapure water), atomize it into 10 - 15 μm droplets through an ultrasonic nebulizer (40 kHz, power 100 W), spray it into the reaction kettle, and the spraying rate is 5 mL / min.

[0083] Meanwhile, gaseous NH4F is generated by heating solid NH4F at 80 °C and introduced into the reaction kettle at a flow rate of 50 mL / min. The molar ratio of thorium nitrate to ammonium fluoride is 1:4.8.

[0084] Control the reaction temperature at 40 °C, the stirring speed at 200 rpm, and react for 3 hours to produce the ThF4·xNH4F precursor.

[0085] Centrifuge (8000 rpm, 10 min) to separate the precipitate, wash it alternately 4 times with 100 mL of absolute ethanol and 100 mL of ultrapure water, and vacuum dry it at 50 °C (pressure < 10 Pa) for 12 hours to obtain 92 g of the precursor.

[0086] Microwave-plasma synergistic fluorination: Place the precursor in a high-purity quartz reactor, place it in a microwave-plasma composite reaction furnace, and introduce high-purity argon gas (150 mL / min).

[0087] Gradient heating: 0 - 30 min, microwave power 300 W, plasma power 50 W, temperature 200 °C; 30 - 90 min, microwave power 600 W, plasma power 100 W, temperature 320 °C; 90 - 120 min, microwave power 400 W, temperature 300 °C.

[0088] Monitor the tail gas (NH3, HF) through QMS and collect 90 g of crude ThF4.

[0089] Multi-stage sublimation and nano-trapping: Place the crude ThF4 in a vacuum sublimation furnace (pressure 10-4 Pa). Primary sublimation: temperature 850 °C, condensation zone 200 °C, for 3 hours. Install a graphene-based nano-trapping membrane (pore size 8 nm) above the condensation zone to trap trace impurities.

[0090] Collect the primary product and perform secondary sublimation: temperature 900 °C, condensation zone 240 °C, for 2 hours to obtain 88 g of ultra-pure ThF4.

[0091] The trapping membrane is regenerated by purging with argon at 550 °C for 30 min.

[0092] Intelligent control:

[0093] Use FTIR and QMS to monitor the reaction tail gas, and temperature and pressure sensors (accuracy ±0.1 °C, ±0.1 kPa) to record parameters.

[0094] The AI platform (based on the LSTM neural network) dynamically adjusts the microwave power (±10 W) and sublimation temperature (±2 °C), and the data is stored in the cloud.

[0095] By-product recovery and wastewater treatment: The tail gas is absorbed by 10% NaOH solution to generate NH4OH and NaF, and activated carbon adsorbs the residual HF, with a trapping efficiency of 99.95%.

[0096] The NH4OH is distilled and concentrated and recycled for the next batch; the NaF is purified by recrystallization.

[0097] The wastewater removes Th through ion exchange resin 4+ , thorium is recovered by electrolysis, and Th in the discharged water 4+ < 0.01 mg / L

[0098] Product testing:

[0099] Purity: determined by ICP-MS.

[0100] Crystal form: analyzed by XRD.

[0101] Particle size: determined by a laser particle size analyzer.

[0102] Energy consumption: record the power of the reaction furnace and the running time, and calculate the total energy consumption.

[0103] Results: see the following table.

[0104] Example 2: Optimize process parameters

[0105] Experimental procedure:

[0106] Basically the same as Example 1, adjust the following parameters:

[0107] Step 1: The reaction temperature is 42 °C, the concentration of ammonium fluoride solution is 0.4 mol / L, the molar ratio is 1:5.0, the ultrasonic frequency is 45 kHz, and 90 g of the precursor is obtained.

[0108] Step 2: The intermediate stage temperature is 310 °C, the microwave power is 550 W, the plasma power is 90 W, and 89 g of crude ThF4 is obtained.

[0109] Step 3: The pore diameter of the capture membrane is 6 nm, the secondary sublimation temperature is 880 °C, and 86 g of ultrapure ThF4 is obtained.

[0110] Other steps are the same as in Example 1.

[0111] Results: see the following table.

[0112] Comparative example: Traditional gas-phase fluorination method

[0113] Experimental procedure: Weigh 100 g of thorium oxide (ThO2, purity 99.9%), and place it in a high-purity quartz reactor. Introduce hydrogen fluoride gas (HF, purity 99.9%, flow rate 200 mL / min), the reaction temperature is 650 °C, and keep it warm for 6 hours. Collect the crude ThF4 and place it in a vacuum sublimation furnace (900 °C, pressure 10 -3Pa, condensation zone (250 °C), sublimation for 4 hours, obtaining 78 g of ThF4. Without a nano-trapping film, intelligent control, and by-product recovery, the tail gas is absorbed by NaOH, and the wastewater is directly neutralized and discharged. The detection method is the same as in the example. Results: See the table below.

[0114] Data table

[0115]

[0116] Comparison conclusion:

[0117] The purity of Examples 1 and 2 (99.9996 - 99.9997%) is significantly higher than that of the comparative example (99.89%), and the impurity content is reduced by 1 - 2 orders of magnitude (Fe: 0.12 - 0.15 ppm vs. 5 ppm; O: 3 - 4 ppm vs. 50 ppm), verifying the technical effect of ultra-high purity.

[0118] The yield of the examples (86 - 88%) is higher than that of the comparative example (78%), and the reaction time is shortened to 2 hours (6 hours for the comparative example), demonstrating high efficiency.

[0119] The energy consumption of the examples (11.5 - 12 kWh / kg) is reduced by 40 - 42.5% compared to the comparative example (20 kWh / kg), verifying the advantage of low energy consumption.

[0120] The by-product recovery rate of the examples > 99.95%, and the Th in the wastewater 4+ < 0.01 mg / L. There is no recovery in the comparative example and the wastewater pollution is serious, proving the greening effect.

[0121] The purity fluctuation of the examples in batches < 0.0001%, and that of the comparative example is 0.01%, verifying high consistency.

[0122] The crystal form of the examples is pure (heterophase < 0.1%), and the particle size is smaller (1.3 - 1.5 μm vs. 3.2 μm), which is suitable for optical applications.

[0123] High purity is consistent with low impurity content, short reaction time corresponds to high yield, low energy consumption and green recovery complement each other, and XRD and particle size data support the improvement of optical performance.

[0124] Combined with the experimental data, the following analyzes from the underlying mechanism why the present invention can achieve the stated technical effects, and explains the synergistic effects of each technical feature and its unexpected effects.

[0125] 1. Ultra-high purity (99.9996 - 99.9997%) and low impurities (Fe < 0.15 ppm, O < 3 - 4 ppm)

[0126] Mechanism: Heterogeneous reaction: In the gas-liquid-solid three-phase system, ultrasonic atomization (40 - 45 kHz) generates micro-droplets of 10 - 15 μm, increasing the reaction interface area to 10 4 m 2 / m 3 , increasing the molecular collision frequency by 10 2 times and reducing the activation energy by 15 kJ / mol. Low temperature (40 - 42 °C) inhibits the adsorption of oxygen impurities, and the high specific surface area (>50 m 2 / g) of the nano-precursor (50 - 100 nm) reduces anion inclusions (such as NO3 - ).

[0127] Microwave-plasma synergy: Microwave uniform heating (320 °C) activates molecular vibration, and the plasma (90 - 100 W) generates F - radicals (concentration ~10 16 cm -3 ), catalyzing the formation of Th-F bonds and inhibiting the oxidation side reaction (O2 adsorption rate < 0.01%). Gradient heating (200 - 320 °C) optimizes crystal growth and reduces lattice defects (<10 8 cm -2 ).

[0128] Nano-trapping membrane: The graphene membrane (pore size 6 - 8 nm) forms coordination bonds (binding energy 200 kJ / mol) with Fe 2+ , Al 3+ with a selective adsorption coefficient of 10 5 , and the trapping efficiency > 99.99%. Multi-stage sublimation (850 - 900 °C) utilizes the high volatility of ThF4 (vapor pressure 10 Pa) to separate non-volatile oxides (O content < 5 ppm)

[0129] Effect cause:

[0130] Data (Fe: 0.12 - 0.15 ppm, O: 3 - 4 ppm) show that the nano-precursor prepared by heterogeneous reaction at low temperature reduces the introduction of initial impurities, plasma catalysis ensures high selectivity in the fluorination process, and the nano-trapping membrane breaks through the bottleneck of trace metal separation. Compared with the comparative example (Fe: 5 ppm, O: 50 ppm), the purity of the present invention is improved by two orders of magnitude, unexpectedly meeting the ultra-high purity requirements of nuclear fuel and optical coatings.

[0131] 2. High yield (86 - 88%) and short reaction time (2 hours)

[0132] Mechanism: Heterogeneous reaction: The ultrasonic cavitation effect (local pressure 10 5 Pa) promotes the reaction between NH4F and Th 4+The rapid complexation of the pyrolysis product increases the reaction rate constant k by 50 times, and a high yield of the precursor (>90%) is generated within 3 hours.

[0133] Microwave-plasma: Microwave volumetric heating (thermal efficiency > 90%) and plasma catalysis (F-free radicals accelerate the reaction 10 2 times) shortens the fluorination time to 2 hours, ThF4 generation mechanism: microwave stereo heating (thermal efficiency> 90%) and plasma catalysis (F - Free radicals accelerate reactions10 2 times) shortened the fluorination time to 2 hours, and the ThF4 generation rate reached 0.5 mol / h, which was much higher than that of the comparative example (0.2 mol / h).

[0134] Intelligent control: AI dynamically adjusts power (±10W) and temperature (±2°C), optimizes reaction paths, and reduces by-product loss (NH3 generation reduced by 50%).

[0135] Reasons for this effect: The data (yield 86-88% in 2 hours) demonstrates the synergistic effect of multiphase reaction and microwave-plasma, and AI control further improves reaction efficiency. The comparative example (yield 78% in 6 hours) had a lower yield due to high temperature (650°C) and slow reaction rate. The present invention unexpectedly achieves a balance between high yield and rapid reaction, reducing production cycle time.

[0136] 3. Low energy consumption (11.5-12kWh / kg)

[0137] Mechanism: Low-temperature reaction: Microwave-plasma synergy reduces the reaction temperature to 310-320°C (650°C for comparative example). Thermodynamic analysis shows that the enthalpy change (ΔH) is reduced by ∼30% and the energy requirement is reduced by 40%.

[0138] AI optimization: Neural networks predict reaction progress, reducing ineffective heating (accounting for 10% of total energy consumption), controlling power fluctuations to ±0.5%, and increasing thermal efficiency to 95%.

[0139] Gradient heating: Phased power distribution (300-600-400W) matches reaction kinetics and reduces overheating losses (<5%).

[0140] Reasons for this effect: The data (11.5-12 kWh / kg vs. 20 kWh / kg) demonstrates that low-temperature reaction and AI optimization significantly reduce energy consumption. Example 2 (11.5 kWh / kg) achieves further energy savings due to a lower temperature (310°C) and optimized power (550W). This unexpected result is a 42.5% reduction in energy consumption while maintaining high yields, breaking through the energy efficiency bottleneck of traditional processes.

[0141] 4. Green (recovery rate> 99.95%, Th4+ (<0.01 mg / L)

[0142] Mechanism: By-product recovery: Double-stage absorption (NaOH + activated carbon) captures NH3 and HF through chemical neutralization (ΔG < 0) and physical adsorption (BET surface area 1200 m 2 / g), and the adsorption equilibrium constant K ~ 10 6 . The distillation recovery rate of NH4OH > 99%, and the recrystallization purity of NaF > 98%.

[0143] Wastewater treatment: Ion exchange resin (exchange capacity 2 meq / g) selectively adsorbs Th 4+ (K e ~10 6 L / mol), electrolytic recovery of thorium (current efficiency > 90%), and Th in the discharged water 4+ <0.01 mg / L.

[0144] Cause of the effect: Data (recovery rate 99.95 - 99.98%, Th 4+ <0.01 mg / L) verifies the ultra-high efficiency of the closed-loop system. There is no recovery in the comparative example, and the Th in the wastewater 4+ reaches 0.5 mg / L, causing pollution. The present invention unexpectedly achieves zero discharge, and the resource recycling reduces the raw material cost by 20%, meeting the "Law on the Prevention and Control of Radioactive Pollution".

[0145] 5. High stability (batch fluctuation < 0.0001%)

[0146] Mechanism: AI control: The LSTM model analyzes 10 4 data points per minute, predicts the probability of impurity generation (error < 1%), dynamically adjusts parameters to make the temperature fluctuation < ±2 °C, and the reaction rate is stable at ±0.01 mol / h. Nano-precursor: Uniform particle size (50 - 100 nm) ensures the consistency of the fluorination process, and the crystal phase heterophase < 0.1%. Trapping membrane: High-selectivity adsorption (> 99.99%) stabilizes the purification effect, and the impurity fluctuation between batches < 0.01 ppm.

[0147] Cause of the effect: Data (fluctuation < 0.0001% vs. 0.01%) shows that AI control and nano-scale processes significantly improve stability. Example 2 (fluctuation < 0.00008%) performs better due to finer parameter optimization (membrane pore size 6 nm). The unexpected effect is that the batch consistency reaches the industrial level, reducing the quality risk of scale-up production.

[0148] 6. Excellent crystal form and particle size (heterophase < 0.1%, particle size 1.3 - 1.5 μm)

[0149] Mechanism: Nano-precursor: Small particle size (50 - 100 nm) provides high surface energy (~100 mJ / m2 ), promoting the growth of monoclinic crystals and suppressing the formation of impurity phases (<0.1%).

[0150] Gradient fluorination: at low temperature (310 - 320 °C) and plasma catalysis to control the crystal nucleation rate (~10 10 cm -3 ·s -1 ), generating uniform crystals (particle size 1.3 - 1.5 μm).

[0151] Purification process: multi - stage sublimation and trapping membranes are used to remove amorphous phases and impurities, and the crystal form purity > 99.9%.

[0152] Reasons for the effect: Data (impurity phase <0.05 - 0.1%, particle size 1.3 - 1.5 μm) verifies the excellent performance of crystal form and particle size. In the comparative example (impurity phase ~2%, particle size 3.2 μm), the performance decreased due to out - of - control crystal growth at high temperature. The present invention unexpectedly improves the infrared transmittance (>95%), which is suitable for high - end optical applications.

[0153] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by what is defined in the claims.

Claims

1. A production process for ultra-pure thorium fluoride, characterized in that, It includes the following steps: (1) Prepare a nanoscale ThF4·xNH4F precursor through a gas-liquid-solid three-phase reaction, in which an ammonium fluoride solution is atomized into microdroplets by ultrasonic atomization and reacts synergistically with gaseous ammonium fluoride and a liquid-phase thorium nitrate solution; (2) Use a microwave-plasma synergistic fluorination reaction to heat the precursor in a high-purity inert atmosphere to generate crude thorium fluoride; (3) Purify the crude thorium fluoride through multi-stage sublimation combined with a graphene-based nano-trapping membrane to obtain ultra-pure thorium fluoride with a purity ≥ 99.9995%; (4) Utilize an intelligent control system to dynamically adjust the parameters of the reaction and purification processes through multi-sensor monitoring and artificial intelligence algorithms; (5) Carry out closed-loop recycling of reaction by-products and perform ion exchange and electrolysis treatment on wastewater to achieve green production.

2. The ultra-pure thorium fluoride production process according to claim 1, characterized in that, The specific operations of the gas-liquid-solid three-phase reaction in step (1) include: (a) Dissolve high-purity thorium nitrate in ultrapure water to prepare a solution with a concentration of 0.2 - 0.5 mol / L; (b) Atomize an ammonium fluoride solution with a concentration of 0.3 - 0.6 mol / L into microdroplets with a size of 10 - 20 μm through an ultrasonic atomization device, spray them into the reaction kettle, and simultaneously introduce gaseous ammonium fluoride. The molar ratio of thorium nitrate to ammonium fluoride is 1:4.5 - 5.0; (c) Control the reaction temperature at 35 - 45 °C, the ultrasonic frequency at 30 - 50 kHz, the stirring speed at 150 - 250 rpm, and react for 2 - 4 hours to generate a ThF4·xNH4F precursor with a particle size of 50 - 100 nm; (d) Separate the precursor by centrifugation, wash it alternately with absolute ethanol and ultrapure water 3 - 5 times, and vacuum dry it at 40 - 60 °C for 8 - 12 hours.

3. The ultra-pure thorium fluoride production process according to claim 1 or 2, characterized in that, The specific operations of the microwave-plasma synergistic fluorination reaction in step (2) include: (a) Place the precursor in a high-purity quartz reactor and carry out the reaction in a microwave-plasma composite reaction furnace. The working atmosphere is high-purity argon with a flow rate of 100 - 200 mL / min; (b) Adopt a gradient heating program: in the initial stage, the microwave power is 200 - 400 W, the plasma power is 30 - 60 W, the temperature is raised to 180 - 220 °C, and keep it warm for 20 - 40 minutes; in the middle stage, the microwave power is 500 - 700 W, the plasma power is 80 - 120 W, the temperature is raised to 300 - 350 °C, and keep it warm for 60 - 90 minutes; in the final stage, the microwave power is 300 - 500 W, the temperature is maintained at 280 - 320 °C, and keep it warm for 20 - 40 minutes; (c) Real-time monitor NH3 and HF in the tail gas through an on-line mass spectrometer and collect the crude thorium fluoride.

4. The ultra-pure thorium fluoride production process according to claim 1, characterized in that, The purification process of the multi-stage sublimation combined with the graphene-based nano-trapping membrane in step (3) includes: (a) Place the crude thorium fluoride in a vacuum sublimation furnace, with a pressure < 10 -3 Pa, a primary sublimation temperature of 800 - 850 °C, a condensation zone temperature of 180 - 220 °C, and a sublimation time of 2 - 4 hours; (b) Set a graphene-based nano-trapping membrane above the condensation zone. The membrane pore size is 5 - 10 nm, the thickness is 30 - 60 μm, and the surface is modified with fluorination functional groups to trap trace metal impurities and oxides; (c) Collect the primary sublimation product, carry out secondary sublimation at a temperature of 850 - 900 °C, the temperature of the condensation zone is 220 - 260 °C, and the time is 1 - 3 hours to obtain thorium fluoride with a purity ≥ 99.9995%; (d) The capture membrane is regenerated by purging with high-purity argon at 500 - 600 °C and reused cyclically.

5. The ultra-pure thorium fluoride production process according to claim 1 or 4, characterized in that, The impurity content of the ultra-pure thorium fluoride described in step (3) is: Fe < 0.2 ppm, Al < 0.1 ppm, O < 5 ppm, and its crystal form is monoclinic system, with an average particle size of 1 - 2 μm.

6. The ultra-pure thorium fluoride production process according to claim 1, wherein The specific operations of the intelligent control system described in step (4) include: (a) Integrating a temperature sensor, a pressure sensor, an infrared spectrometer, and a mass spectrometer to monitor the reaction temperature, pressure, and tail gas composition in real time; (b) Through an artificial intelligence control platform, predicting the reaction process and the risk of impurity generation based on a neural network model, and dynamically adjusting the microwave power, plasma intensity, and sublimation temperature, with the temperature fluctuation controlled within ±2 °C; (c) Automatically storing process parameters and monitoring data for process optimization and quality traceability.

7. The ultra-pure thorium fluoride production process according to claim 1, characterized in that, The specific operations of the closed-loop recycling and wastewater treatment described in step (5) include: (a) NH3 and HF in the reaction tail gas are treated by a two-stage absorption system. The first stage is an 8 - 12% NaOH solution to generate NH4OH and NaF, and the second stage is activated carbon adsorption, with a capture efficiency > 99.9%; (b) NH4OH is distilled and concentrated for recycling in the preparation of the precursor, and NaF is purified by recrystallization as an industrial raw material; (c) Trace Th is removed from the wastewater by strong acid cation exchange resin 4+ , and Th in the discharged water 4+ is less than 0.01 mg / L. Thorium is recovered from the resin regeneration liquid by electrolysis.

8. The ultra-pure thorium fluoride production process according to claim 1, characterized in that, The reaction device of the process includes: (a) A multiphase reaction module, including an ultrasonic atomization device, a gaseous ammonium fluoride supply system, and a high-purity polytetrafluoroethylene reaction kettle; (b) A microwave-plasma reaction module, including a microwave heater, a low-temperature plasma generator, and an on-line mass spectrometry monitoring system; (c) A purification module, including a vacuum sublimation furnace and a graphene-based nano capture membrane; (d) An intelligent control module, including a multi-sensor system and an artificial intelligence control platform; (e) A green by-product treatment module, including a two-stage absorption system, ion exchange resin, and an electrolytic recovery device.

9. The ultra-pure thorium fluoride production process according to any one of claims 1-8, characterized in that, The ultra-pure thorium fluoride is used for nuclear reactor fuel matrix, optical coating, or infrared transmission material.

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