CVD fluorine-containing powder recovery treatment method

Abstract

The application relates to the technical field of fluorine-containing waste resource recycling, and particularly discloses a CVD fluorine-containing powder recycling method which comprises eight steps of CVD fluorine-containing dust dissolving, water washing, pressure filtration, secondary water washing, evaporation concentration, cooling crystallization, centrifugation and drying. The CVD fluorine-containing dust is dissolved into a solution, waste gas in the solution is removed through water washing, and solid impurities and harmful substances in the solution are removed through pressure filtration, so that the solution is purified. After the purified solution is subjected to secondary water washing, evaporation concentration, cooling crystallization, centrifugation and drying, ammonium fluorosilicate products are obtained. The ammonium fluorosilicate is a chemical product with wide application, is mainly used for manufacturing ammonium silicate and potassium fluorosilicate, and is also an important raw material for smelting, fireworks, coating, electronic material and other industries. The extraction process does not need to add any additional materials, can save cost, and does not need to worry about causing secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of fluorine-containing waste resource recovery technology, specifically to a method for recovering and processing CVD fluorine-containing powder. Background Technology

[0002] Chemical vapor deposition (CVD) is a new technology for preparing inorganic materials that has developed in recent decades. It utilizes various energy sources such as heating, plasma excitation, or light radiation to allow gaseous or vaporous chemical substances to react at the gas phase or gas-solid interface within a reactor, forming solid deposits. The raw materials used in CVD vary greatly depending on its application and uses. In the semiconductor industry, CVD processes often use gases such as silane (SiH4), borane (B2H6), tetraethyl orthosilicate, N2O, NH3, C2F6, NF3, and He. After high-temperature incineration, these waste gases often produce large amounts of silicon- and fluorine-containing dust. The semiconductor industry, in particular, generates large quantities of ammonium fluoride, ammonium fluoride, and silica dust annually. These dust particles are fine, have a large specific surface area, and are porous, making it difficult to separate and recover valuable components.

[0003] Without proper recycling, these fluoride-containing dust particles will settle or be leached by rainwater, polluting soil and groundwater, causing environmental pollution and ecological damage. Currently, industrial treatment of such fluoride-containing dust mainly uses lime neutralization for fluoride removal. However, this generates large amounts of calcium fluoride slag and silica slag, resulting in large quantities of sludge and high treatment costs. Furthermore, to ensure effective fluoride removal, excessive lime is often added, which not only increases treatment costs but also generates large amounts of solid waste. If this solid waste is not properly treated, it can easily cause secondary pollution. Since fluoride is a cumulative toxic substance and readily soluble in water, how to effectively and rationally dispose of fluoride-containing dust, reduce unnecessary emissions and the environmental pollution and ecological damage caused by its accumulation, and how to effectively recycle and reuse fluoride-containing dust to turn waste into treasure, reduce environmental pollution, and obtain certain social value are urgent problems that need to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for recovering and treating fluorine-containing powder from CVD, so as to solve the problems of large sludge volume, high treatment cost, and easy secondary pollution caused by fluorine-containing dust recovery.

[0005] To address the above issues, the following technical solution is provided:

[0006] A method for recovering and processing CVD fluorine-containing powder includes the following steps:

[0007] S1: Dissolution: Mix CVD fluorine-containing dust with process water and stir continuously for 0.5-1h to dissolve the CVD fluorine-containing dust;

[0008] S2: Water washing: The dissolved CVD fluorine-containing solution is pumped into the first water washing tank for stirring and water washing;

[0009] S3: Filtration: The washed solution is pumped into a filter press for filtration.

[0010] S4: Secondary water washing: The filtrate from the pressure filter is pumped into the second water washing tank for secondary stirring and water washing, and the filter mud from the pressure filter is disposed of in landfill.

[0011] S5: Evaporation and Concentration: The filtrate after the second water washing is pumped into the evaporation raw water tank for evaporation and concentration;

[0012] S6: Cooling and crystallization: Drain the concentrated liquid into the crystallization kettle for cooling and crystallization until it reaches below 25°C, then start timing and let it stand for 1.5-2.5 hours;

[0013] S7: Centrifugation: The crystallized liquid after standing is pumped into a centrifuge for separation. The separated mother liquor is pumped into step S5, and the solid is dried.

[0014] S8: Drying: Dry the crude salt product obtained by centrifugation at a temperature of 80-120℃ for 2-3 hours. After drying, sample the ammonium fluorosilicate of the finished product and test it. Products that pass the test can be stored or sold, while products that fail the test are returned to step S1 for further processing.

[0015] Preferred Option 1: As a further optimization of the basic option, the process water used in step S1 is composed of one or more of the following: condensate, distilled water, recycled water, and tap water.

[0016] Preferred Scheme 2: As a further optimization of Preferred Scheme 1, in step S2, the solution in the first water washing mixing tank is pumped into the filter press for filtration only after the storage volume in the first water washing mixing tank is greater than 50%.

[0017] Preferred Scheme 3: As a further optimization of Preferred Scheme 2, the solid-liquid ratio of the CVD fluorine-containing dust and process water in step S1 is 0.18 to 0.24.

[0018] Preferred Option 4: As a further optimization of Preferred Option 3, the evaporation raw water tank in step S5 is equipped with a triple-effect evaporation device for evaporation and concentration. The triple-effect evaporation and concentration process heats the concentrated liquid until crystals are generated on the surface.

[0019] Preferred Option 5: As a further optimization of Preferred Option 4, the condensate produced by evaporation in step S5 is sampled and tested for its pH, salinity, total phosphorus, ammonia nitrogen, heavy metal content, etc.; after each indicator is qualified, it is directly injected into the biological collection tank, and after passing the biological treatment, it is discharged.

[0020] Preferred Option Six: As a further optimization of Preferred Option Five, the mother liquor generated by centrifugation in step S7 is pumped back to S5 for further concentration.

[0021] The beneficial effects of this technical solution are as follows: Compared to the method of neutralizing fluoride-containing dust with lime, this solution dissolves CVD fluoride-containing dust into a solution, removes waste gas from the solution by water washing, and then removes solid impurities and harmful substances from the solution by pressure filtration, thus purifying the solution. The purified solution undergoes secondary water washing, evaporation and concentration, cooling crystallization, centrifugation, and drying to obtain the finished ammonium fluorosilicate. Ammonium fluorosilicate is a widely used chemical, mainly used in the manufacture of ammonium silicate and potassium fluorosilicate, and is also an important raw material in industries such as smelting, fireworks, coatings, and electronic materials. The extraction process does not require the addition of any external materials, which not only saves costs but also eliminates concerns about secondary pollution.

[0022] The disposal cost for CVD fluorine-containing dust is 1500 yuan / ton, while the market price of ammonium fluorosilicate (98%) is at least 6000 yuan / ton; the market price of ammonium fluorosilicate (99%) is at least 15000 yuan / ton. Assuming a 70% recovery rate, it takes approximately 15 days to dispose of 50 tons of CVD fluorine-containing dust, disposing of 3 tons per day. The product price is calculated based on ammonium fluorosilicate (98%) at 6000 yuan / ton. The net profit per ton of fluorine-containing dust treated using this method is 5405.73 yuan. This not only avoids environmental pollution from fluorine-containing dust accumulation but also effectively realizes the resource utilization of fluorine-containing dust and yields considerable economic benefits. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention;

[0024] Figure 2 The images show the products numbered 1 and 2, which were evaporated once.

[0025] Figure 3 The images show the products numbered 3 and 4, which were evaporated once.

[0026] Figure 4 The images show samples numbered 5 and 6, which underwent secondary evaporation.

[0027] Figure 5 The images show the products numbered 7 and 8, which were evaporated twice.

[0028] Figure 6 The images show the products numbered 9 and 10, which were evaporated once.

[0029] Figure 7 The product images are of samples numbered 11 and 12, which were evaporated once.

[0030] Figure 8 This is a picture of a product that has been evaporated to 0°C and then cooled to room temperature.

[0031] Figure 9 This is a schematic diagram of a dissolving tank. Detailed Implementation

[0032] The following detailed description illustrates the specific implementation method:

[0033] The reference numerals in the accompanying drawings of the instruction manual include: tank body 1, stirring shaft 2, reciprocating screw 20, fixed cylinder 21, first one-way valve 211, slider 212, third one-way valve 213, rotating cylinder 22, second one-way valve 221, stirring blade 222, float 223, discharge pipe 3, scraper blade 31, float plate 32, collar 33, rotating shaft 34, conveyor belt 35, motor 4, switch 5, controller 6, LED light 61, light intensity sensor 62, and discharge valve 63.

[0034] Example 1 is basically as shown in the appendix. Figure 1 As shown:

[0035] A method for recovering and processing CVD fluorine-containing powder includes the following steps:

[0036] S1: Inspection: Check that the required dissolving tank, water washing mixing tank, and filter press have been cleaned and are free of other contaminants; check that all valves, pipes, etc. can be opened normally and are free from damage or leaks; check that the exhaust fan is running normally and the air duct is in the open position.

[0037] S2: Dissolving: Transfer the CVD fluorine-containing dust to the unloading area of ​​the dissolving tank. Turn on the agitator and first use the pump to inject process water into the dissolving tank (preferably use condensate, distilled water, or recycled water; add tap water if necessary). Then slowly add the CVD fluorine-containing dust into the dissolving tank. [The solid-liquid ratio of the added process water to the CVD fluorine-containing dust is 1:4.78 (if the added water volume is 4.78 cubic meters, then the weight of the CVD fluorine-containing dust is 1 ton). The total volume of the added material and water should not exceed 85% of the volume of the dissolving tank. Continue stirring for 45 minutes to allow the CVD fluorine-containing dust to dissolve completely.

[0038] S3: Water washing: Observe the dissolution status of CVD fluorine-containing dust in the dissolution tank. After ensuring that the CVD fluorine-containing dust has been completely dissolved, turn on the transfer pump to pump the completely dissolved solution into the first water washing mixing tank, and at the same time turn on the stirring device of the first water washing mixing tank.

[0039] S4: Filtration: After the storage capacity of the first water washing mixing tank is greater than 50%, turn on the filter press pump to pump the solution into the filter press for filtration; when there is no filtration water, remove all the filter mud from the filter plate, put it into a woven bag, tie it with a rope, put it into the secondary hazardous waste warehouse of the material control, and then landfill it for disposal.

[0040] S5: Secondary water washing: The filtrate enters the second water washing mixing tank, and the stirring device of the second water washing mixing tank is turned on at the same time, and it is ready for evaporation.

[0041] S6: Evaporation and concentration: The filtrate in the second water washing mixing tank is pumped into the reserved empty evaporation raw water tank using a filtrate pump. The CVD fluorine-containing dust filtrate in the evaporation raw water tank is sent to a triple-effect evaporator for evaporation and concentration. The solution is heated until a crystal film is formed on the liquid surface, i.e., the Baume degree of the solution is measured to be 20-26. In this embodiment, the preferred Baume degree is 25.

[0042] S7: Cooling and crystallization: When the evaporation system reaches the concentration discharge standard, that is, when the detected solution Baume degree is 25, the discharge valve of the second-effect separator will automatically open to discharge the concentrate into the crystallization kettle for cooling and crystallization. When the liquid temperature in the crystallization kettle drops below 25°C, the timer will start and the solution will stand for 2 hours.

[0043] S8: Centrifugation: After settling, the solution is pumped into a centrifuge. The piston centrifuge is turned on to perform coarse salt separation. The mother liquor produced by centrifugation enters the mother liquor tank. The mother liquor pump can be turned on to return the mother liquor to the triple-effect evaporator in step S6 for further concentration or discharge.

[0044] S9: Drying: The product obtained by centrifugation is dried at 100°C for 2 hours. After drying, the sample is packaged and sent for testing. If the fluorosilicic acid content of the product meets the production index, it is packaged and stored in the warehouse. Unqualified products are returned to step S1 for re-dissolving.

[0045] S10: Biochemical treatment: The condensate produced by evaporation is sampled and tested for pH, salinity, total phosphorus, ammonia nitrogen, heavy metals, etc. After each indicator is evaluated and qualified, it is directly injected into the biochemical collection tank. That is, the condensate meets the relevant industry and local standards for pH, salinity, total phosphorus, ammonia nitrogen, heavy metals, etc. required for biochemical treatment. After passing the biochemical treatment, it is discharged into the environment, which meets the relevant standards for sewage treatment discharge.

[0046] High concentrations of salt, heavy metals, or other toxic and harmful substances may inhibit microbial activity and affect the effectiveness of biological treatment; excessively high ammonia nitrogen may hinder the nitrification process in the biological system, affecting the overall nitrogen removal efficiency; excessively high total phosphorus concentrations will affect the eutrophication level of the water body and must be controlled within a reasonable range in advance to be effectively removed by biological means; ensuring that all indicators are within the range suitable for biological treatment can improve the stability and economy of the entire wastewater treatment process; at the same time, it can also ensure that the final effluent meets the standards and environmental protection regulations.

[0047] Wastewater condensate that does not meet the biochemical treatment standards will be further treated using methods such as chemical precipitation, oxidation, and ion exchange, based on the measured data.

[0048] Fluorine-containing dust obtained from the exhaust gas treatment of the CVD coating process at a Chongqing company (Chongqing Huike Jinyu Optoelectronic Technology Co., Ltd.) was used as the experimental raw material. The material was light beige, very loose, with extremely low bulk density, and easily generated. Analysis revealed that it mainly consisted of ammonium fluorosilicate and amorphous silicon dioxide. The heavy metal content was determined by ICP, and the results are shown in Table 1 below:

[0049] Table 1. Analysis results of metal content in CVD fluorine-containing dust

[0050] element Ag AL As Ba Ca Cr Cu Concentration (mg / L) 0.004 26.695 0.008 0.058 4.947 0.157 0.014 element Fe Li Mg Mn Ni Pb Zn Concentration (mg / L) 3.208 0.100 1.287 0.058 0.247 0.017 0.143

[0051] Experimental testing - Detection of ammonium fluorosilicate: The sample content was tested according to HG / T 4692-2014 Industrial Ammonium Fluorosilicate.

[0052] Experiment 1: Single Evaporation Experiment

[0053] Samples with solid-liquid ratios of 0.18, 0.20, 0.22, and 0.24 were dissolved in 200 mL of pure water. The process involved dissolution, filtration, evaporation, concentration, cooling, and crystallization. Detailed experimental data are shown in Table 2 below.

[0054] Table 2 Data from a single evaporation experiment

[0055]

[0056]

[0057] The product images of samples 1 and 2, which were evaporated once, are shown below. Figure 2 As shown;

[0058] The product images of samples numbered 3 and 4 from the single evaporation are shown below. Figure 3 As shown.

[0059] Experiment 2: Secondary Evaporation Experiment

[0060] The secondary evaporation experiment involved continuing the evaporation-concentration-cooling-crystallization process on the remaining mother liquor after centrifugation and filtration in step S8 during continuous production. The crystallization phenomenon was observed, and the experimental data are shown in Table 3 below.

[0061] Table 3. Experimental Data for Secondary Evaporation

[0062]

[0063] The product images of samples numbered 5 and 6 from the secondary evaporation are shown below. Figure 4 As shown;

[0064] The product images of samples numbered 7 and 8 from the secondary evaporation are shown below. Figure 5 As shown.

[0065] Experiment 3: Single Evaporation and Room Temperature Cooling Experiment

[0066] Samples with solid-liquid ratios of 0.26, 0.28, 0.30, and 0.32 were weighed and dissolved in 200 mL of pure water. The process involved heating to dissolve, filtering, evaporation, concentration, cooling, and crystallization. Detailed experimental data are shown in Table 4 below.

[0067] Table 4. Experimental Data for Single Evaporation and Room Temperature Cooling

[0068]

[0069] Product images of samples numbered 9 and 10, which underwent single evaporation and were cooled at room temperature, are shown below. Figure 6 As shown;

[0070] Product images of samples numbered 11 and 12, which underwent single evaporation and were cooled at room temperature, are shown below. Figure 7 As shown.

[0071] Experiment 4: Comparison Experiment of Single Evaporation at Room Temperature and Cooling to 0℃

[0072] After comparing appearance and content, and considering process aspects, a sample with a solid-liquid ratio of 0.22 was selected and dissolved in 200mL of pure water at room temperature. The sample underwent processes such as heating to dissolve, filtration, evaporation, concentration, cooling, and crystallization. However, during crystallization, the experimental conditions were changed: cooling and crystallization were carried out at room temperature and at 0℃, and the appearance was compared.

[0073] Product image shown: A product cooled to -0°C after single evaporation. Figure 8 As shown.

[0074] Summary of experimental results:

[0075] I. As shown in Table 1, when the solid-liquid ratio of fluorine-containing dust to water increases to 0.24, it becomes impossible for the dust to completely dissolve at room temperature. However, upon increasing the temperature, the undissolved fluorine-containing dust in the solution continues to dissolve, making this dissolution reaction endothermic. Therefore, a solid-liquid ratio of approximately 0.22 is preferable for dissolution at room temperature.

[0076] II. As shown in Tables 1 and 2, with the increase of the solid-liquid ratio of fluorine-containing dust to water, the specific gravity of the dissolved solution gradually increases. After one evaporation, the Baumé degree of the crystal film formed on the solution surface is 24-25, and the detected purity meets the product indicators of first-grade ammonium fluorosilicate. After the second evaporation, once the crystal film is fully formed, the Baumé degree is also between 24 and 25, and the total product yield increases to 85%-90%. That is, the concentration of the evaporated solution is suitable when the Baumé degree is detected to be around 25, and the calculated specific gravity is 1.21, i.e., the relative density is 1.21.

[0077] 3. Observe the appearance of the samples: In terms of whiteness and particle size, samples 1 to 4 are whiter than samples 9 to 12, and the particle sizes are similar; however, samples 9 to 12 have poor dispersibility and show signs of adhesion. Therefore, the solid-liquid ratio should be selected between 0.18 and 0.24.

[0078] IV. Samples cooled at room temperature generally have a purity of around 98%, while samples cooled at 0°C have a purity of approximately 100%. To reduce energy consumption, room temperature cooling is sufficient in the cooling process. Figure 8 It can be observed that the sample cooled at room temperature has a more uniform particle size, more even particle size dispersion, and better whiteness.

[0079] Experimental conclusion: Weigh out CVD fluorine-containing dust with a solid-liquid ratio of 0.22 and dissolve it. After dissolution, filter out water-insoluble matter. Evaporate and concentrate the filtrate until the density of the solution is 1.21 times that of pure water at the same temperature, i.e., the relative density is 1.21. Then cool it to room temperature, cool and crystallize for 2 hours, then centrifuge, filter and dry completely to obtain ammonium fluorosilicate with a product content of not less than 98%.

[0080] The economic analysis of recycling CVD fluorine-containing dust is as follows:

[0081] The disposal cost for CVD fluorine-containing dust is 1500 yuan / ton, and the lowest market price for ammonium fluorosilicate (98%) is 6000 yuan / ton; the lowest market price for ammonium fluorosilicate (99%) is 15000 yuan / ton. Assuming a 70% recovery rate, it takes approximately 15 days to dispose of 50 tons of CVD fluorine-containing dust, disposing of 3 tons per day. The cost analysis, based on an ammonium fluorosilicate (98%) price of 6000 yuan / ton, is shown in Table 5 below.

[0082] Table 5: Cost Analysis of CVD Fluorine-Containing Dust Recovery

[0083]

[0084] As shown in the table above, the above-mentioned process for recycling and reusing CVD fluorine-containing dust can bring economic benefits to enterprises.

[0085] In summary, ammonium fluorosilicate is a widely used chemical, mainly used in the manufacture of ammonium silicate and potassium fluorosilicate. It is also an important raw material for industries such as smelting, fireworks, coatings, and electronic materials. The above-mentioned process for extracting potassium fluorosilicate from CVD fluorine-containing dust not only eliminates the need for any external materials during the extraction process, saving costs, but also avoids secondary pollution and enables the recycling of CVD fluorine-containing dust, creating economic value while avoiding environmental pollution.

[0086] Example 2 is identical to Example 1 and will not be repeated. The difference is that the dissolving tank in step S1 includes a tank body 1, and a stirring mechanism and a feeding mechanism disposed within the tank body 1. The stirring mechanism includes a motor 4, a stirring shaft 2, a fixed cylinder 21, and a rotating cylinder 22. The upper end of the stirring shaft 2 is fixedly connected to the output shaft of the motor 4, and the lower end of the stirring shaft 2 extends to the bottom of the fixed cylinder 21 and is rotatably connected to the fixed cylinder 21 via a bearing. The upper end of the fixed cylinder 21 is open, and the bottom of the fixed cylinder 21 is fixed to the bottom of the tank body 1. A first one-way valve 211 is provided on the lower side wall of the fixed cylinder 21, allowing only material to enter the interior of the fixed cylinder 21. The upper end of the rotating cylinder 22 is splinedly connected to the rotating shaft 34. In this example, it is a hexagonal spline. The connection allows the rotating cylinder 22 to slide up and down along the stirring shaft 2, and the stirring shaft 2 can drive the rotating cylinder 22 to rotate. The lower end of the rotating cylinder 22 is open and in contact with the outer wall of the fixed cylinder 21. The stirring blade 222 is bolted to the outer wall of the rotating cylinder 22, and a float 223 is fixed to the upper end of the outer wall of the rotating cylinder 22. The side wall of the rotating cylinder 22 has a second one-way valve 221 for material to flow out of the rotating cylinder 22. The part of the stirring shaft 2 located inside the fixed cylinder 21 is provided with a reciprocating screw 20. The reciprocating screw 20 is threadedly connected to a slider 212. The slider 212 is provided with a third one-way valve 213 for material to flow from below the slider 212 to above the slider 212, and the slider 212 is slidably connected to the inner side wall of the fixed cylinder 21.

[0087] In use, the motor 4 is started, which drives the stirring shaft 2 to rotate, thereby driving the rotating cylinder 22 to rotate. The rotating cylinder 22 drives the stirring blades 222 to rotate, thus stirring the solution and promoting the accelerated dissolution of fluoride-containing dust in the solution. As the solution level gradually rises, due to the spline connection between the rotating cylinder 22 and the stirring shaft 2, the floating block 223 causes the rotating cylinder 22 to float upward along the stirring shaft 2, allowing the stirring blades 222 to stir the solution at different liquid levels as the liquid level rises, promoting uniform stirring. At the same time, the reciprocating screw 20 inside the fixed cylinder 21 rotates, causing the slider 212 to move up and down along the side wall of the fixed cylinder 21. When the slider 21... When the slider 21 moves upward, it enters the fixed cylinder 21 through the first one-way valve 211 on the side wall of the fixed cylinder 21. When the slider 212 moves upward, the solution in the fixed cylinder 21 flows from below the slider 212 to the space above the slider 212 through the third one-way valve 213. When the slider 212 moves upward again, the solution above the slider 212 is squeezed and flows back to the dissolving tank through the second one-way valve 221 of the rotating cylinder 22. This allows the solution to complete a bottom-to-top cycle, raising the solution at the bottom of the dissolving tank to the upper part of the water body, promoting the mixing of the bottom solution, improving the dissolution efficiency of fluorine-containing dust, and preventing the accumulation of fluorine-containing dust at the bottom of the tank 1.

[0088] The feeding mechanism includes a feeding pipe 3, a rotating shaft 34, and a scraper 31. The feeding pipe 3 is a telescopic corrugated pipe, and a float plate 32 is fixed at the discharge end of the feeding pipe 3. The rotating shaft 34 is arranged vertically and one end passes through the float plate 32. It is connected to the stirring shaft 2 via a conveyor belt 35. The conveyor belt 35 can be a toothed belt, and gears are fixed on the rotating shaft 34 and the stirring shaft 2 respectively. A collar 33 is splined to the rotating shaft 34, and the upper end of the collar 33 is rotatably connected to the lower end of the float plate 32. The scraper 31 is fixed to the side wall of the collar 33, and the upper end of the scraper 31 is connected to the discharge end of the feeding pipe 3. The scraper blades 31 are arranged in multiple directions around the collar 33, with four in this embodiment. When the float plate 32 floats, it drives the collar 33 to move upward, so that the outlet of the feed pipe 3 is always located on the solution surface. This allows the fluorine-containing dust to enter the solution directly through the feed pipe 3, preventing the product dust from being released into the workshop air. The scraper blades 31 throw the fluorine-containing dust discharged from the feed pipe 3 towards the stirring mechanism in the water, so that the fluorine-containing dust falling into the solution is quickly dispersed. At the same time, the material attached to the outlet can be scraped off to prevent dust from accumulating at the feed pipe.

[0089] A switch 5 is installed at the 185% water level of the tank, and a feeder is installed at the inlet end of the discharge pipe 3. The feeder is a belt feeder or a screw feeder, and the switch 5 is electrically connected to the feeder. When the float 32 floats to the 85% water level under the buoyancy of the mixed solution of process water and CVD fluorine dust, the float 32 presses the switch 5, and the switch 5 shuts off the feeder.

[0090] The tank 1 has two symmetrical inner walls equipped with LED lights 61 and light intensity sensors 62, respectively. A controller 6 is located outside the tank 1. The LED lights 61 are electrically connected to the output of the controller 6, and the controller 6 controls the opening and closing of the LED lights 61. The tank 1 has a discharge port at the lower end, and a discharge valve 63 is located at the discharge port. The discharge valve 63 is an electrically controlled valve. The input of the controller 6 is electrically connected to the light intensity sensor 62, and the output of the controller 6 is electrically connected to the discharge valve 63. The light intensity sensor 62 is used to measure the light intensity of the LED passing through the solution to reach the sensor location, and converts the light signal into an electrical signal and sends it to the controller 6. The controller 6 controls the opening and closing of the discharge valve 63 according to the light intensity value. When the dissolution tank is working, the controller 6 controls the LED light 61 to light up. When the CVD fluorine-containing dust is not completely dissolved, there is still a large amount of solid dust in the solution, and the light intensity received by the light intensity sensor 62 does not reach the set standard for opening the discharge valve 63. Therefore, the stirring mechanism continues to stir the solution to promote the dissolution of the fluorine-containing dust. When the CVD fluorine-containing dust has been completely dissolved, the light emitted by the LED light 61 passes through the solution and shines on the light intensity sensor 62. At this time, the light intensity received by the light intensity sensor 62 reaches the set standard. The controller 6 judges that the electrical signal of the received light intensity is greater than the set value and controls the discharge valve 63 to open, pumping the completely dissolved solution into the first water washing stirring tank.

[0091] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for recovering and treating fluorine-containing powder from CVD (Continuous Fluorescent Vapor Deposition) processes, characterized in that: Includes the following steps: S1: Dissolution: In the dissolution tank, CVD fluorine-containing dust is mixed with process water and stirred continuously for 0.5-1h to dissolve the CVD fluorine-containing dust. The solid-liquid ratio of the CVD fluorine-containing dust to the process water is 0.18-0.24 g / ml. S2: Water washing: The dissolved CVD fluorine-containing solution is pumped into the first water washing tank for stirring and water washing; S3: Filtration: The washed solution is pumped into a filter press for filtration. S4: Secondary water washing: The filtrate from the pressure filter is pumped into the second water washing tank for secondary stirring and water washing, and the filter mud from the pressure filter is disposed of in landfill. S5: Evaporation and Concentration: The filtrate after the second water washing is pumped into the evaporation raw water tank for a first evaporation and concentration; Stop heating when the solution's Baume degree is measured to be 20-26. S6: Cooling and crystallization: Drain the concentrated liquid into the crystallization kettle for cooling and crystallization until it reaches below 25°C, then start timing and let it stand for 1.5-2.5 hours; S7: Centrifugation: The crystallized liquid after standing is fed into a centrifuge for separation; S8: Drying: Dry the crude salt product obtained by centrifugation at a temperature of 80-120℃ for 2-3 hours. After drying, sample the ammonium fluorosilicate of the finished product and test it. Products that pass the test are stored or sold, and products that fail the test are returned to step S1 for further processing. The dissolving tank in step S1 includes a tank body, and a stirring mechanism and a feeding mechanism disposed within the tank body. The stirring mechanism includes a motor, a stirring shaft, a fixed cylinder, and a rotating cylinder. The upper end of the stirring shaft is fixedly connected to the output shaft of the motor, and the lower end of the stirring shaft extends to the bottom of the fixed cylinder and is rotatably connected to the fixed cylinder via a bearing. The upper end of the fixed cylinder is open, and the bottom of the fixed cylinder is fixed to the bottom of the tank body. A first one-way valve is provided on the lower side wall of the fixed cylinder, allowing only material to enter the interior of the fixed cylinder. The upper end of the rotating cylinder is splinedly connected to the rotating shaft, and the rotating cylinder can slide up and down along the stirring shaft, and the stirring shaft can drive the rotating cylinder to rotate. The lower end of the rotating cylinder is open and in contact with the wall of the fixed cylinder. A stirring blade is bolted to the outer wall of the rotating cylinder, and a float is fixed to the upper end of the outer wall of the rotating cylinder. A second one-way valve is provided on the side wall of the rotating cylinder, allowing only material to flow out of the rotating cylinder. The part of the stirring shaft located inside the fixed cylinder is provided with a reciprocating screw, and the reciprocating screw is threadedly connected to a slider. The slider is provided with a third one-way valve, allowing only material to flow from below the slider to above the slider, and the slider is slidably connected to the inner side wall of the fixed cylinder.

2. The method for recovering and treating CVD fluorine-containing powder according to claim 1, characterized in that: The process water used in step S1 is composed of one or more of the following: condensate, distilled water, and tap water.

3. The method for recovering and treating CVD fluorine-containing powder according to claim 1, characterized in that: In step S2, after the storage volume in the first water washing mixing tank is greater than 50%, the solution in the first water washing mixing tank is pumped into a filter press for filter pressing.

4. The method for recovering and treating CVD fluorine-containing powder according to claim 1, characterized in that: In step S5, the raw water tank is evaporated using a triple-effect evaporator for evaporation and concentration. The triple-effect evaporator heats the concentrated liquid until a crystal film is formed on the surface of the liquid.

5. The method for recovering and treating CVD fluorine-containing powder according to claim 4, characterized in that: The wastewater condensate generated during evaporation in step S5 is sampled for testing of its pH, salinity, total phosphorus, ammonia nitrogen, and heavy metal content. Once all indicators are qualified, it is directly pumped into the biological collection tank and discharged after passing biological treatment.

6. The method for recovering and treating CVD fluorine-containing powder according to claim 1, characterized in that: In step S7, the mother liquor generated by centrifugation is pumped back to S5 for further concentration.

7. The method for recovering and treating CVD fluorine-containing powder according to claim 1, characterized in that: The process water used in step S1 is recycled water.

Images