A system and method for purifying and recovering silicon nitride from dust recovered by bag filter

Abstract

The present invention provides a system and method for purifying and recovering silicon nitride from dust recovered by a bag dust collector, and relates to the technical field of silicon nitride powder recovery; the system comprises a slurrying device, an ultrasonic vibrating screen, a strong magnetic impurity removal device and a reaction tank connected in sequence. Among them, the slurrying device comprises a mixing tank for mixing dust and pure water into slurry. The input port of the ultrasonic vibrating screen is connected to the output end of the mixing tank, and is used to form a screening of the slurry. The strong magnetic impurity removal device comprises a flow channel connected to the output port of the ultrasonic vibrating screen for the flow of slurry, and a ferromagnetic rod arranged on the flow channel; the reaction tank comprises a reaction tank, the reaction tank comprises a slurry inlet connected to the end of the flow channel, and the reaction tank is also provided with a liquid inlet for the entry of impurity removal liquid, a water inlet for the entry of pure water, and an outflow port for the outflow of treatment liquid, and the reaction tank is also provided with a stirring unit for stirring the liquid in the reaction tank. The system for purifying and recovering silicon nitride from dust recovered by a bag dust collector of the present invention can better recover silicon nitride powder and avoid waste of resources.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride recovery, and in particular to a system and method for purifying and recovering silicon nitride from dust recovered by a bag filter. Background Art

[0002] Bag filter is one of the important equipment for industrial dust control. It is widely used in various industries such as steel, cement, power chemical industry, food, etc. It is also an important equipment / device in the production process of silicon nitride powder. The working principle of bag filter is that when the dust-containing gas enters the bag filter, the large particles of dust will fall directly into the ash hopper due to gravity, while the small particles of dust will enter the filter bag with the airflow. The bag is the core component of the bag filter. It is made of special fiber material and covered with a layer of fine mesh on the surface. The size of these meshes is just enough to prevent dust from passing through, but at the same time allow the gas to pass smoothly. When the dust-containing gas passes through the filter bag, the dust will be adsorbed by the surface of the filter bag, thereby separating the dust from the gas. As time goes by, the dust on the surface of the filter bag will increase, and then it is necessary to clean the dust. Cleaning is to use a pulse jet device to spray high-pressure airflow into the inside of the filter bag to shake the dust on the surface of the filter bag off and fall into the ash hopper. The materials collected in the dust collector contain a variety of impurities, such as metal fines caused by equipment wear, filter cloth debris, and unreacted silicon-containing fine particles. For high-purity and high-value-added silicon nitride products, if high-purity silicon nitride that meets the requirements can be obtained through purification and recovery, each ton of dust removal material can create an economic value of about 300,000 to 500,000 for the enterprise. However, the silicon nitride in the dust filtered by the bag filter has not yet been recovered, resulting in a waste of resources. Summary of the invention

[0003] To this end, the present invention proposes a system and method for purifying and recovering silicon nitride from dust recovered by a bag filter, so as to effectively recover silicon nitride from dust filtered by the bag filter.

[0004] The technical solution of the present invention is as follows: In the first aspect, the present invention provides a system for purifying and recovering silicon nitride from dust recovered by a bag filter, comprising a slurrying device, an ultrasonic vibrating screen, a strong magnetic impurity removal device and a reaction tank connected in sequence; the slurrying device comprises a mixing tank for mixing dust and pure water into slurry; the ultrasonic vibrating screen is used to screen the slurry; the strong magnetic impurity removal device comprises a flow channel for the slurry to flow, and a ferromagnetic rod arranged in the flow channel; the reaction tank has a slurry inlet for the slurry to flow in, and the reaction tank is also provided with a liquid inlet for the impurity removal liquid to enter, a water inlet for the pure water to enter, and an outflow port for the slurry to flow out, and the reaction tank is also provided with a stirring unit for stirring the liquid in the reaction tank.

[0005] Furthermore, the inner cavity of the reaction tank includes a cylindrical section and a conical section connected in series, the conical section is arranged below the cylindrical section, and the outflow port is located at the bottom end of the conical section.

[0006] Furthermore, two filtering mechanisms are provided on the side wall of the conical section, and the two filtering mechanisms respectively include a base block fixed on the reaction tank, and the two base blocks are also respectively provided with water pumping holes, the water outlet of each water pumping hole is located outside the reaction tank and connected to the input end of the water pump, the water inlet of each water pumping hole is located inside the reaction tank, and a filter net covering the water inlet is provided on the base block.

[0007] Furthermore, the base block is provided with an air supply hole group, which includes an air inlet located outside the reaction tank and connected to an external air supply device, and a plurality of exhaust ports provided on the side of the base block and located inside the reaction tank.

[0008] Furthermore, the base block is provided with a plurality of air blowing pipes connected with the air supply hole group, each of the air blowing pipes is arranged at intervals on the outside of the filter net, and each of the air blowing pipes is provided with a plurality of air blowing holes facing the filter net, and each of the air blowing holes is arranged at intervals along the length direction of the air blowing pipe.

[0009] Furthermore, the air supply hole group includes a main hole extending radially along the reaction tank, and a first branch and a second branch respectively perpendicular to and intersecting the main hole, and each exhaust port is connected to the second branch, and each air blowing pipe is connected to the first branch.

[0010] Furthermore, a blocking block is slidably provided in the main channel, and an elastic member is provided between the blocking block and the bottom end surface of the main channel, an annular groove is provided in the middle of the blocking block, and an air inlet hole connected to the annular groove is provided on the end surface of the blocking block, and the blocking block can be blown by the air intake from the air inlet and slide until the annular groove is opposite to the first branch, and when the air intake pressure at the air inlet increases, the blocking block can slide until the annular groove is opposite to the second branch, and the blocking block blocks the first branch.

[0011] Furthermore, the flow channel includes a bottom plate and two side plates, the two side plates are arranged on two opposite sides of the bottom plate and extend upward; and a first motor is fixedly arranged relative to the flow channel, a connecting piece is fixedly arranged on the motor shaft of the first motor, and the ferromagnetic rod is fixedly arranged on the connecting piece, and the ferromagnetic rod can be driven by the motor shaft to rotate between a horizontal state placed in the flow channel and a vertical state located outside the flow channel.

[0012] Furthermore, it also includes a scraper that can be raised and lowered by a cylinder, and the scraper is provided with a through hole. When the ferromagnetic rod is in the vertical state, the scraper can descend and allow the through hole to be mounted on the ferromagnetic rod to scrape off impurities on the ferromagnetic rod.

[0013] On the other hand, the present invention provides a method for purifying and recovering silicon nitride powder in a bag filter, using the above-mentioned bag filter to recover silicon nitride from dust, and comprising the following steps: S1. Add water to the dust and disperse it into slurry; S2, passing the slurry treated in step S1 through an ultrasonic vibrating screen to screen out filter cloth debris; S3, passing the slurry treated in step S2 through a ferromagnetic rod to remove metal chips; S4, adding the slurry treated in step S3 into a reaction tank, and performing the following treatment in the reaction tank: S41, injecting alkaline liquid into the reaction tank to remove elemental silicon; S42, injecting an acidic liquid into the reaction tank to remove metal impurities and oxides; S43, washing the material in the reaction tank with water; S5, drying the slurry after being processed in step S4.

[0014] The working principle and beneficial effects of the present invention are: In the system and method for purifying and recovering silicon nitride from dust recovered by a bag filter provided by the present invention, the recovery system can effectively remove impurities in the dust and recover silicon nitride through a slurrying device, an ultrasonic vibrating screen, a strong magnetic impurity removal device and a reaction tank connected in sequence. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0016] Figure 1 A simplified connection diagram of the components of a system for purifying and recovering silicon nitride from dust recovered by a bag filter according to an embodiment of the present invention; Figure 2 A three-dimensional diagram of a strong magnetic impurity removal device according to an embodiment of the present invention; Figure 3 is a cross-sectional view of a reaction tank according to an embodiment of the present invention; Figure 4 An exploded view of a filter mechanism according to an embodiment of the present invention; Figure 5 A schematic diagram of the internal structure of a filtering mechanism according to an embodiment of the present invention; Figure 6 for Figure 5 A partial enlarged view of point A in the middle.

[0017] In the figure: 100, pulping device; 200, ultrasonic vibration screen; 300, strong magnetic impurity removal device; 310, frame; 320, bottom plate; 330, side plate; 340, first motor; 350, connecting piece; 351, first connecting rod; 352, second connecting rod; 360, ferromagnetic rod; 370, cylinder; 371, scraper; 372, through hole; 400, reaction tank; 410, cylindrical section; 420, conical section; 421, outflow port; 430, inlet Slurry port; 440, liquid inlet; 500, filtering mechanism; 510, base block; 511, water outlet; 520, filter screen; 531, air inlet; 532, air outlet; 501, water extraction hole; 540, air blowing pipe; 541, air blowing hole; 600, main channel; 610, first branch; 620, second branch; 700, blocking block; 710, elastic member; 701, annular groove; 702, air inlet; 800, stirring unit; 810, stirring blade. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] This embodiment provides a system for purifying and recovering silicon nitride from dust recovered by a bag filter, which will be referred to as a recovery system in the following text. Figure 1 As shown, it includes a slurrying device 100, an ultrasonic vibrating screen 200, a strong magnetic impurity removal device 300 and a reaction tank 400 connected in sequence. Among them, the slurrying device 100 includes a mixing tank for mixing dust and pure water into slurry. The ultrasonic vibrating screen 200 is used to screen the slurry. The strong magnetic impurity removal device 300 includes a flow channel for the flow of slurry, and a ferromagnetic rod 360 arranged on the flow channel. The reaction tank 400 is provided with a slurry inlet 430, and the reaction tank 400 is also provided with a liquid inlet 440 for the impurity removal liquid to enter, a water inlet for the pure water to enter, and an outflow port 421 for the treated liquid to flow out, and the reaction tank 400 is also provided with a stirring unit for stirring the liquid in the reaction tank 400.

[0020] In general, in the recovery system of this embodiment, the powder collected by the bag filter will first be mixed with pure water in a mixing tank to form a slurry for subsequent processing. The slurry then passes through an ultrasonic vibrating screen 200 to screen out impurities such as fibers or filter cloth debris in the slurry; the slurry then passes through a strong magnetic impurity removal device 300, and the ferromagnetic impurities in the slurry are adsorbed by the ferromagnetic rod 360 during the flow of the slurry in the flow channel. The slurry then enters a reaction tank 400, and is sequentially alkali washed, acid washed, and water washed to remove the residual elemental silicon, as well as metal impurities and oxygen-containing substances in the silicon nitride powder, and then the slurry is dried to obtain silicon nitride powder with a higher purity.

[0021] Among them, one way of connecting the slurry device 100, the ultrasonic vibration screen 200, the strong magnetic impurity removal device 300 and the reaction tank 400 in sequence is: a recovery tank is set at the output end of the slurry device 100, and the slurry is pumped from the recovery tank to the ultrasonic vibration screen 200 by a pump body; this method can be used for the slurry from the ultrasonic vibration screen 200 to the strong magnetic impurity removal device 300, and from the strong magnetic impurity removal device 300 to the reaction tank 400.

[0022] The mixing tank of this embodiment is used to mix dust and water to form slurry, which can refer to the existing technology; the ultrasonic vibration screen 200 of this embodiment can also adopt existing products, which will not be described in detail in this embodiment. Since it does not affect the understanding, the specific structures of the reaction tank 400 and the ultrasonic vibration screen 200 are not shown in the drawings of this embodiment.

[0023] refer to Figure 2 As shown, the flow channel of this embodiment includes a frame 310, and a bottom plate 320 and two side plates 330 respectively arranged on the frame 310, and the two side plates 330 are respectively arranged on two opposite sides of the bottom plate 320 and extend upward, or in other words, the cross section of the flow channel is a square with an open top. In this embodiment, a first motor 340 is also arranged on the frame 310, and a connecting member 350 is fixed on the motor shaft of the first motor 340. The ferromagnetic rod 360 is fixed on the connecting member 350, and the ferromagnetic rod 360 can be driven by the motor shaft to rotate between a horizontal state placed in the flow channel and a vertical state located outside the flow channel.

[0024] Among them, Figure 2 As shown, when the ferromagnetic rod 360 is placed in the flow channel and is in a horizontal state, the connecting member 350 includes a first connecting rod 351 fixed on the motor shaft and extending horizontally to the flow channel, and a second connecting rod 352 connected to the free end of the first connecting rod 351 and extending downward, and the ferromagnetic rod 360 is fixed on the free end of the second connecting rod 352 and extends along the width direction of the flow channel. Based on this structure, when the motor shaft drives the connecting member 350 to rotate 90°, the ferromagnetic rod 360 rotates to a vertical state.

[0025] In this embodiment, reference Figure 2 As shown, a cylinder 370 is further provided on the frame 310 , and a scraper 371 is fixedly provided on the output rod of the cylinder 370 . The cylinder 370 can drive the scraper 371 to rise or fall, and a through hole 372 is provided on the scraper 371 .

[0026] When the ferromagnetic rod 360 is in a vertical state, the cylinder 370 can drive the scraper 371 to descend, and the through hole 372 is sleeved on the ferromagnetic rod 360. As the scraper 371 descends, the scraper 371 can scrape off the ferromagnetic impurities adsorbed on the ferromagnetic rod 360. Subsequently, the scraper 371 rises and detaches from the ferromagnetic rod 360, and the ferromagnetic rod 360 can be driven by the first motor 340 to rotate to a horizontal state again and be placed in the flow channel to re-absorb the ferromagnetic impurities in the slurry.

[0027] refer to Figure 3 As shown, the inner cavity of the reaction tank 400 of this embodiment includes a cylindrical section 410 and a conical section 420 connected in series, the conical section 420 is arranged below the cylindrical section 410, and the outflow port 421 is located at the bottom end of the conical section 420. In this embodiment, by setting the inner cavity to include the cylindrical section 410 and the conical section 420, and setting the outflow port 421 for the slurry to flow out at the bottom end of the conical section 420, it is convenient for all the slurry to flow out.

[0028] In this embodiment, reference Figure 3 and Figure 4 As shown, two filtering mechanisms 500 are provided on the side wall of the conical section 420, and the two filtering mechanisms 500 respectively include a base block 510 fixed on the reaction tank 400, and the two base blocks 510 are also provided with water pumping holes 501 respectively, and the water outlet 511 of the water pumping hole 501 is located outside the reaction tank 400 for connecting with the input end of the water pump, and the water inlet of each water pumping hole 501 is located in the reaction tank 400, and a filter net 520 covering the water inlet is provided on the base block 510.

[0029] In this embodiment, by setting the above-mentioned filtering mechanism 500, after the slurry is subjected to alkali washing, acid washing or water washing, the liquid in the reaction tank 400 can be extracted by a water pump through the pumping hole 501, and the solid particles are filtered through the filter net 520 to remain in the reaction tank 400, thereby quickly and conveniently performing alkali washing, acid washing and water washing on the solid particles.

[0030] In this embodiment, reference Figure 4As shown, a gas supply hole group is provided on the base block 510, and the gas supply hole group includes an air inlet 531 located outside the reaction tank 400 and connected to an external gas supply device, and a plurality of exhaust ports 532 provided on the side of the base block 510 and located inside the reaction tank 400. In this embodiment, by providing the gas supply hole group and providing the exhaust ports 532 on the side of the base block 510, the gas discharged from the exhaust ports 532 can drive the liquid in the reaction tank 400 to rotate around the circumference of the reaction tank 400, so that the gas in the reaction tank 400 is better mixed with the fixed particles. Among them, the surface of the base block 510 facing the center of the reaction tank 400 is the inner end surface, and the surface of the base block 510 adjacent to the inner end surface is the side surface of the base block 510. The gas is discharged from the side surface of the base block 510, which will blow the liquid in the reaction tank 400, thereby rotating the liquid in the reaction tank 400.

[0031] In this embodiment, reference Figure 4 As shown, a plurality of air blowing pipes 540 connected to the air supply hole group are further provided on the base block 510, and each air blowing pipe 540 is arranged at intervals on the outside of the filter net 520, and each air blowing pipe 540 is respectively provided with a plurality of air blowing holes 541 facing the filter net 520, and each air blowing hole 541 is arranged at intervals along the length direction of the air blowing pipe 540.

[0032] In this embodiment, by providing the above-mentioned blowing pipes 540, it is possible to prevent solid particles from accumulating outside the filter 520 and affecting the discharge of liquid. Specifically, in the recovery system of this embodiment, after adding alkali solution, acid solution or pure water into the reaction tank 400 for corresponding cleaning, the liquid in the reaction tank 400 can be quickly discharged, and the filter 520 can block the solid particles in the reaction tank 400; however, the solid particles will accumulate on the outside of the filter 520, blocking the filter 520 and affecting the discharge of liquid. In this embodiment, by providing the above-mentioned blowing pipes 540 and blowing holes 541, the solid particles on the outside of the filter 520 can be blown away, thereby preventing the solid particles from clogging the filter 520.

[0033] In this embodiment, reference Figure 5 and Figure 6 As shown, the air supply hole group includes a main hole path 600 extending radially along the reaction tank 400, and a first branch 610 and a second branch 620 which are respectively perpendicular to and intersecting the main hole path 600, and each exhaust port 532 is connected to the second branch 620, and each blowing pipe 540 is connected to the first branch 610.

[0034] refer to Figure 5 and Figure 6As shown, in this embodiment, a blocking block 700 is slidably provided in the main channel 600, and an elastic member 710 is provided between the blocking block 700 and the bottom end surface of the main channel 600, an annular groove 701 is provided in the middle of the blocking block 700, and an air inlet hole 702 connected with the annular groove 701 is provided on the end surface of the blocking block 700, and the blocking block 700 can be blown by the intake air from the air inlet 531 and slide until the annular groove 701 is opposite to the first branch 610; and when the intake pressure of the air inlet 531 increases, the blocking block 700 can slide until the annular groove 701 is opposite to the second branch 620, and the blocking block 700 blocks the first branch 610.

[0035] In this embodiment, by setting the above-mentioned blocking block 700, each exhaust port 532 or blowing pipe 540 can be selectively operated by different air supply pressures. Specifically, when the air supply pressure is within a certain range, the blocking block 700 slides until the annular groove 701 is opposite to the first branch 610. At this time, the gas can enter the annular groove 701 through the air inlet hole 702 on the blocking block 700, and then enter each air outlet pipe through the first branch 610 and be blown out to avoid clogging of the filter screen 520; when the air supply pressure increases, the blocking block 700 can continue to be pushed to slide until the annular groove 701 is opposite to the second branch 620. At this time, the gas can enter the annular groove 701 through the air inlet hole 702, and then pass through the second branch 620 and be discharged through the exhaust port 532 to promote the rotation of the liquid in the reaction tank 400, so that the solid particles are better mixed with the liquid.

[0036] That is, when the liquid in the reaction tank 400 needs to be extracted, gas of corresponding pressure can be provided to the gas inlet 531; when the liquid in the reaction tank 400 needs to be mixed with solid particles for reaction, the pressure of the gas supply can be increased.

[0037] In this embodiment, the stirring unit includes a second motor fixedly mounted on the reaction tank 400, and a stirring blade disposed in the reaction tank 400 and fixedly mounted on the motor shaft of the second motor. When it is necessary to explain, the stirring unit can adopt an existing product. The structure of this product will not be described in detail here.

[0038] Based on the above recovery system, this embodiment also provides a method for purifying and recovering silicon nitride powder in a bag filter, which comprises the following steps: S1. Add water to the dust and disperse it into slurry; S2, passing the slurry treated in step S1 through an ultrasonic vibration screen 200 to screen out filter cloth debris; S3, passing the slurry processed in step S2 through the ferromagnetic rod 360 to remove metal chips; S4, adding the slurry treated in step S3 into the reaction tank 400, and performing the following treatment in the reaction tank 400: S41, injecting alkaline liquid into the reaction tank 400 to remove elemental silicon; S42, injecting an acidic liquid into the reaction tank 400 to remove metal impurities and oxides; S43, washing the material in the reaction tank 400; S5, drying the slurry after being processed in step S4.

[0039] The alkaline liquid is, for example, a sodium hydroxide solution, and the acidic liquid is a hydrofluoric acid solution.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A system for purifying and recovering silicon nitride from dust recovered by a bag filter, characterized in that: It includes a slurrying device, an ultrasonic vibrating screen, a strong magnetic impurity removal device and a reaction tank which are connected in sequence; the slurrying device includes a mixing tank for mixing dust and pure water into slurry; the ultrasonic vibrating screen is used to screen the slurry; the strong magnetic impurity removal device includes a flow channel for the slurry to flow, and a ferromagnetic rod arranged in the flow channel; the reaction tank has a slurry inlet for the slurry to flow in, and the reaction tank is also provided with a liquid inlet for the impurity removal liquid to enter, a water inlet for the pure water to enter, and an outflow outlet for the slurry to flow out, and the reaction tank is also provided with a stirring unit for stirring the liquid in the reaction tank.

2. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 1, characterized in that: The inner cavity of the reaction tank comprises a cylindrical section and a conical section connected in series, the conical section is arranged below the cylindrical section, and the outflow port is located at the bottom end of the conical section.

3. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 2, characterized in that: Two filtering mechanisms are provided on the side wall of the conical section, and the two filtering mechanisms respectively include a base block fixed on the reaction tank, and the two base blocks are also respectively provided with a water pumping hole, the water outlet of each water pumping hole is located outside the reaction tank and connected to the input end of the water pump, the water inlet of each water pumping hole is located in the reaction tank, and a filter net covering the water inlet is provided on the base block.

4. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 3 is characterized in that: The base block is provided with an air supply hole group, which includes an air inlet located outside the reaction tank and connected to an external air supply device, and a plurality of exhaust ports arranged on the side of the base block and located in the reaction tank.

5. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 4, characterized in that: The base block is also provided with a plurality of air blowing pipes connected with the air supply hole group, each of the air blowing pipes is arranged at intervals on the outside of the filter screen, and each of the air blowing pipes is respectively provided with a plurality of air blowing holes facing the filter screen, and each of the air blowing holes is arranged at intervals along the length direction of the air blowing pipe.

6. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 5, characterized in that: The air supply hole group includes a main hole extending radially along the reaction tank, and a first branch and a second branch respectively perpendicular to and intersecting the main hole, and each exhaust port is connected to the second branch, and each air blowing pipe is connected to the first branch.

7. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 6, characterized in that: A blocking block is slidably provided in the main aperture, and an elastic member is provided between the blocking block and the bottom end surface of the main aperture, an annular groove is provided in the middle of the blocking block, and an air inlet hole connected with the annular groove is provided on the end surface of the blocking block, and the blocking block can be blown by the air intake from the air inlet and slide until the annular groove is opposite to the first branch, and when the air intake pressure at the air inlet increases, the blocking block can slide until the annular groove is opposite to the second branch, and the blocking block blocks the first branch.

8. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 1, characterized in that: The flow channel includes a bottom plate and two side plates, the two side plates are arranged on two opposite sides of the bottom plate and extend upward; and a first motor is fixedly arranged relative to the flow channel, a connecting piece is fixedly arranged on the motor shaft of the first motor, and the ferromagnetic rod is fixedly arranged on the connecting piece, and the ferromagnetic rod can be driven by the motor shaft to rotate between a horizontal state placed in the flow channel and a vertical state located outside the flow channel.

9. The system for purifying and recovering silicon nitride from dust recovered by a bag filter according to claim 8, characterized in that: It also includes a scraper driven by a cylinder to be raised and lowered, and the scraper is provided with a through hole. When the ferromagnetic rod is in the vertical state, the scraper can descend and allow the through hole to be sleeved on the ferromagnetic rod to scrape off impurities on the ferromagnetic rod.

10. A method for purifying and recovering silicon nitride powder in a bag filter, characterized in that: A system for purifying and recovering silicon nitride from dust using a bag filter as described in any one of claims 1 to 9, comprising the following steps: S1. Add water to the dust and disperse it into slurry; S2, passing the slurry treated in step S1 through an ultrasonic vibrating screen to screen out filter cloth debris; S3, passing the slurry treated in step S2 through a ferromagnetic rod to remove metal chips; S4, adding the slurry treated in step S3 into a reaction tank, and performing the following treatment in the reaction tank: S41, injecting alkaline liquid into the reaction tank to remove elemental silicon; S42, injecting an acidic liquid into the reaction tank to remove metal impurities and oxides; S43, washing the material in the reaction tank with water; S5, drying the slurry after being processed in step S4.

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