Magnetic separation and recycling method of sealing sand for high-temperature annealing of steel coil

Abstract

The invention discloses a steel coil high-temperature annealing sealing sand magnetic separation recycling method which comprises the following steps: caked sealing sand is coarsely crushed, uncaked raw sand grains and caked mixed materials are screened and separated, and the caked mixed materials comprise undissociated raw sand grains, glass phase coating bodies and sintered aggregates; microwave heating and liquid nitrogen cooling are combined to treat the caked mixture, so that a glass phase coating body is subjected to targeted fracture, and loose particles and undissociated blocks are separated through airflow separation; the loose particles directly adsorb free iron oxide through first-stage magnetic separation, and then enter second-stage magnetic separation, and weak magnetic iron oxide is separated through combination of dynamic fluidization separation and magnetofluid enhancement; the undissociated blocks are subjected to acid pickling dissociation, and a glass phase and undamaged raw sand grains are separated through electric field separation; and surface melting and cooling forming are conducted on the loose particles and undamaged original sand grains, and the roundness of the sand grains is recovered. Efficient purification and cyclic utilization of the sealing sand are achieved, and the magnetic separation efficiency and the sand grain quality are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic or electrostatic separation for separating solid materials from solid materials or fluids, high-voltage electric field separation, and particularly to the technical field of magnetic separation. Specifically, it is a method for magnetic separation and recycling of sealing sand in high-temperature annealing of steel coils. Background Art

[0002] In the iron and steel industry, high-temperature annealing of steel coils is a key process for optimizing material properties. For different steel grades, it usually involves heating the cold-rolled steel coils in an annealing furnace to about 650°C - 1150°C and holding for a certain period of time to achieve recrystallization, eliminate internal stress, and improve material toughness. To prevent the steel coils from sticking together due to close contact at high temperatures, a high-temperature resistant sealing material - sealing sand needs to be filled in the gaps between them.

[0003] Currently, the commonly used sealing sand mainly includes fused silica sand, purple sand, etc., and its particle size distribution and chemical composition need to be optimized according to the annealing process. Although the sealing sand plays a key role in the annealing process, there are still the following technical challenges in practical applications: when the steel coils are annealed at high temperatures, the surface scale (Fe 3 O 4 、Fe 2 O 3 、FeO) may break to form iron oxide powder, which adheres to the surface of the sealing sand. The iron oxide powder not only pollutes the sealing sand but may also reattach to the surface of the steel coils due to the flow of the protective gas or gravity, resulting in surface quality defects. In addition, the sealing sand is prone to caking after high-temperature annealing, leading to a decrease in the sealing performance of the hood, affecting normal production. The caked sand needs to be reprocessed to continue to be used, increasing production costs and time.

[0004] The existing technology for recycling this deteriorated sealing sand is to pour the sealing sand into a vibrating screen. The vibrating screen is equipped with magnets, and the magnets adsorb and clean up the falling scale during the vibration process to purify the sand. Subsequently, the caked sand is broken up and backfilled to its original position for continued use. However, this method is prone to incomplete removal of fine iron oxide powder, resulting in residues in the sand.

[0005] Therefore, it is necessary to improve a method for magnetic separation and recycling of sealing sand in high-temperature annealing of steel coils in the existing technology to solve the above problems. Summary of the Invention

[0006] The present invention overcomes the deficiencies of the existing technology and provides a method for magnetic separation and recycling of sealing sand in high-temperature annealing of steel coils, aiming to solve the problems in the existing technology that the iron oxide powder is wrapped by the glass phase and cannot be effectively magnetically separated due to high-temperature sintering, the physical properties of the recycled sand deteriorate, and the recycling rate is low.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, comprising: S1. Coarsely crush the caked sealed sand, and screen and separate the uncaked primary sand grains and the caked mixture. The caked mixture includes: undissociated primary sand grains, glass-phase coatings, and sintered aggregates; S2. Treat the caked mixture by combining microwave heating and liquid nitrogen cooling to targetedly break the glass-phase coatings, and then separate loose particles and undissociated blocks by air classification; S3. The loose particles are first directly adsorbed with free iron oxide by primary magnetic separation, and then enter secondary magnetic separation, and weakly magnetic iron oxide is separated by combining dynamic fluidized classification and magnetic fluid enhancement; S4. Acid-wash and dissociate the undissociated blocks, and separate the glass phase and the undamaged primary sand grains by electric field classification; S5. Perform surface melting and cooling forming on the loose particles in S3 and the undamaged primary sand grains in S4 to restore the roundness of the sand grains.

[0008] In a preferred embodiment of the present invention, in step S1, the caked sealed sand is batch-fed into a crusher for coarse crushing. The single-feed amount ≤ 500 kg, the biting pressure applied by the crusher ≤ 5 MPa, and the particle size of the crushed product < 10 mm; a double-deck vibrating screen is used, the upper screen aperture is 3 mm, the lower screen aperture is 1 mm, the vibration frequency is 25 - 30 Hz, and the amplitude is 5 mm.

[0009] In a preferred embodiment of the present invention, in step S2, the heating rate is 100 °C / min, heated to 750 - 850 °C, and held for 5 - 10 min; the heated caked mixture enters a quenching bin, and liquid nitrogen is uniformly sprayed onto the surface of the caked mixture through an annular nozzle array. The temperature of the liquid nitrogen is -196 °C, and the spraying flow rate is 7 - 10 L / min; the quenching time ≤ 30 s, so that the surface temperature of the caked mixture drops to -50 °C.

[0010] In a preferred embodiment of the present invention, in step S2, the quenched caked mixture is fed into a vortex classifier, and a high-speed air flow forms a spiral upward flow field. The air flow velocity is 12 - 18 m / s; the classification time is 2 - 3 min / batch; the separation particle size threshold is 50 μm.

[0011] In a preferred embodiment of the present invention, in step S3, the primary magnetic separation is strong magnetic capture. The loose particles are evenly laid on a non-magnetic conveyor belt, and an ultrasonic vibrating plate is installed below the conveyor belt to apply a high-frequency vibration of 30 - 40 kHz; the surface magnetic induction intensity of the Halbach permanent magnet array is as high as 1.8 - 2.0 T, and the gradient magnetic field strength reaches 0.5 - 1.8 T / mm.

[0012] In a preferred embodiment of the present invention, in step S3, the secondary magnetic separation adopts a dynamic fluidized bed separation combined with a magnetic fluid technology. The remaining materials after the primary magnetic separation are injected into the bottom of the fluidized bed, and the nitrogen gas flow rate is 10 - 12 m / s; the height of the fluidized bed is 1.5 - 2 m, and the residence time of the materials is 5 - 8 s; a magnetic fluid is added, and the magnetic fluid is a 10 wt% Fe 3 O 4 nanofluid with a particle size < 50 nm; an alternating magnetic field is applied outside the fluidized bed, with a frequency of 4 - 6 Hz, a peak value of 1.2 - 1.5 T, and the magnetic field direction is switched 5 times per second.

[0013] In a preferred embodiment of the present invention, in step S4, the undissociated blocks are put into the pickling tank according to a solid - liquid ratio of 1:5 - 8. The pickling solution uses a citric acid - oxalic acid mixed solution with a molar ratio of 1:1 - 1.5, and the pH of the acid solution is maintained at 2 - 3 through a pH buffer system; the acid solution is controlled at a constant temperature of 60 °C, supplemented with ultrasonic oscillation at 30 - 40 kHz and a power density of 400 - 600 W / cm³, and the treatment time is set to 30 - 40 min; and the solid residue and the Fe 3+ filtrate are separated.

[0014] In a preferred embodiment of the present invention, in step S4, the solid residue is mixed with water at a ratio of 1:7 - 9 and sent to a dielectric separation tank, and a high - voltage pulsed electric field is applied. The parameters are set as follows: the electrode spacing is 8 - 10 mm, the pulse width is 3 - 5 μs, the electric field strength is 80 - 100 kV / cm, and the pulse frequency is 100 - 150 Hz.

[0015] In a preferred embodiment of the present invention, in step S5, the surface melting instantaneously melts the surface of the sand grains at 15000 - 18000 °C through a plasma. The power of the plasma torch is 80 - 100 kW, the working gas Ar / H 2 mixing ratio is 9:1, the gas flow rate is 15 - 20 L / min, and the depth is < 5 μm.

[0016] In a preferred embodiment of the present invention, in step S5, the molten particles enter a centrifugal atomizer and achieve an ultrafast cooling of 10 7 °C / s at a rotational speed of 25000 - 30000 rpm.

[0017] The present invention solves the defects existing in the background technology, and the present invention has the following beneficial effects: (1)The present invention provides a method for recycling sealed sand by magnetic separation, which solves the problems of the glass phase coating hindering magnetic separation, the weakening of the magnetic properties of iron oxide particles, and the dispersion distribution of fine particles through coarse crushing and screening, thermal shock dissociation, magnetic separation purification, acid washing separation, surface treatment, and thin film deposition. The present invention uses a thermal shock technology of microwave heating and liquid nitrogen quenching to break the glass phase coating, uses strong magnetic capture and magnetic fluid enhanced separation to remove free and weakly magnetic iron oxides, uses a citric acid-oxalic acid system to selectively dissociate sintered aggregates, and restores the performance of sand grains and enhances corrosion resistance through plasma surface melting and magnetron sputtering. Finally, the efficient purification and recycling of sealed sand are realized, the magnetic separation efficiency and the quality of sand grains are significantly improved, and the surface quality of the steel coil and the recycling performance of the sealed sand are ensured.

[0018] (2)The present invention combines primary magnetic separation and secondary magnetic separation. The primary magnetic separation uses the strong magnetic field of the Halbach permanent magnet array to directly capture free iron oxide, while the secondary magnetic separation further removes weakly magnetic iron oxide through dynamic fluidized separation combined with magnetic fluid technology, achieving the efficient removal of different magnetic iron oxides in loose particles. The primary magnetic separation enhances the capture rate through ultrasonic-assisted dissociation, and the secondary magnetic separation enhances the separation of weakly magnetic iron oxide through magnetic fluid, significantly improving the purity of the original sand grains. Compared with the prior art, it further achieves the comprehensive removal effect of iron oxide impurities.

[0019] (3)The present invention combines multi-stage magnetic separation and acid washing dissociation. Multiple magnetic separations capture free iron oxide and weakly magnetic iron oxide in loose particles. Acid washing dissociation uses a citric acid-oxalic acid mixed acid solution to selectively dissolve the iron silicate phase in the sintered aggregates and release the undamaged original sand grains. Subsequently, high-voltage pulsed electric field separation is used to achieve efficient separation based on the difference in dielectric constants between the glass phase and quartz sand. Compared with the prior art, it realizes the comprehensive removal of different forms of iron oxide and the efficient recovery of original sand grains.

[0020] (4)The present invention combines coarse crushing and screening with thermal shock dissociation. First, mechanical crushing and screening are used to separate the caked sealed sand into uncaked original sand grains and caked mixtures, ensuring the uniformity of the particle size of the subsequent treatment materials. Subsequently, the thermal shock technology of microwave heating and liquid nitrogen quenching is used to break the glass phase coating and release the encapsulated iron oxide particles, achieving the efficient dissociation of complex caked sealed sand and avoiding damage to the original sand grains caused by excessive crushing. The particle size control of coarse crushing and screening provides a uniform material basis for thermal shock, and thermal shock further optimizes the dissociation effect, significantly improving the efficiency of subsequent magnetic separation and acid washing. Compared with the prior art, it further achieves the effects of efficient dissociation and resource recovery.

[0021] (5) By combining surface melting and thin film deposition, the present invention instantaneously melts the surface of sand grains by plasma to eliminate edges and microcracks and restore the roundness of sand grains. Subsequently, a corrosion-resistant thin film is deposited on the surface of sand grains by magnetron sputtering to enhance their high-temperature resistance and corrosion resistance, realizing the performance restoration and enhancement of recycled sand grains. The surface treatment not only optimizes the physical properties of sand grains but also extends the service life of sealed sand through film protection. Compared with the prior art, it further achieves the closed-loop design effect of sealed sand performance restoration and resource recycling. Brief Description of the Drawings

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Figure 1 is the flowchart of the steps of the preferred embodiment of the present invention; Figure 2 is the classification diagram of the agglomerated sealed sand to be recycled in the preferred embodiment of the present invention; Figure 3 is the flowchart of the recycling of sealed sand in the preferred embodiment of the present invention. Detailed Embodiments

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0024] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0025] In the description of the present application, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0026] Application Overview: During the annealing process of the steel coil, the sealing sand is exposed to a high temperature environment of 650℃-1150℃ for a long time, and complex physical and chemical changes occur inside it. Under the action of high temperature, the silicon dioxide and other components in the sand particles gradually melt to form a glass phase. This sticky substance promotes sintering between the sand particles, forming a densified block structure. In this process, the fluxing components in the impurities inside the sand body significantly accelerate the formation of the glass phase, so that the surface of the sand particles is coated with molten substances, resulting in the iron oxide powder particles being firmly embedded in the sintered body. The formation of the glass phase not only changes the pore structure of the sand body, but also forms a dense coating layer on the surface of the iron oxide powder, blocking the direct interaction between the magnetic material and the external magnetic field, making it difficult for traditional magnetic separation methods to effectively capture the coated iron oxide particles.

[0027] With the gradual increase of annealing temperature, the physical and chemical properties of iron oxide powder undergo fundamental changes. The high temperature environment causes the crystal structure of iron oxide to reorganize, and its magnetic characteristics are significantly weakened as the chemical form changes. At the same time, the violent thermal motion causes the iron oxide particles to be continuously refined, forming submicron or even nanometer ultrafine powders. These fine particles are dispersed inside the sintered body. The densified structure of the sand body formed by high-temperature sintering further intensifies the consolidation of the iron oxide powder. Even after mechanical crushing, there are still a large number of iron oxide powders tightly wrapped by the glass phase. Conventional magnetic separation processes are difficult to penetrate the glass phase coating layer to achieve effective adsorption, and the weakened magnetism greatly reduces the capture efficiency of fine particles, which ultimately leads to residual iron oxide impurities in the recycled sand body, seriously affecting the surface quality of the steel coil and the recycling performance of the sealing sand.

[0028] In view of the above situation, the present application proposes a method for magnetic separation and recycling of sealing sand for high-temperature annealing of steel coils, which realizes the preliminary separation of unagglomerated original sand particles by coarse crushing and screening, and then adopts a thermal shock technology combining microwave heating and liquid nitrogen quenching, and utilizes the significant difference in thermal expansion coefficients between the glass phase and quartz sand to break the glass phase coating and release the encapsulated iron oxide particles. Furthermore, through the first-level magnetic separation strong magnetic capture and ultrasonic assisted dissociation, and the second-level magnetic separation dynamic fluidization separation combined with magnetic fluid enhanced separation, the free iron oxide and weak magnetic iron oxide in the loose particles are efficiently removed. For the undissociated blocks, a citric acid-oxalic acid mixed pickling system is used for selective dissociation, and then the glass phase and the undamaged original sand particles are separated by high-voltage pulsed electric field sorting. Finally, the recovered sand particles are subjected to plasma surface melting and ultrafast cooling to restore their roundness, and a corrosion-resistant film is deposited by magnetron sputtering, and finally a recycled sealing sand with excellent physical properties and surface characteristics is obtained. This method not only significantly improves the magnetic separation efficiency and sand quality, but also realizes the efficient recycling of resources.

[0029] like Figure 2As shown, the caked sealing sand recycled in this application is the sealing sand after high-temperature annealing of the steel coil. The sealing sand contains: virgin sand grains, glass-phase coatings, free iron oxide, and sintered aggregates; The virgin sand grains are the original quartz sands that have not participated in the melting reaction, maintaining a complete crystal structure and excellent physical properties, which are the main targets for recycling; The glass-phase coatings are amorphous glass-phase layers formed on the surface of sand grains due to high-temperature melting. They may wrap iron oxide particles, and although their magnetism is retained, it is shielded by the glass phase; The free iron oxide is iron oxide particles attached to the surface of sand grains, with strong magnetism and easy to be removed by magnetic separation; The sintered aggregates are complex structures formed by the melting and bonding of multiple particles. Fe 2+ enters the silicate lattice to form a multiphase eutectic of chemically bonded Si-Al-Fe-O.

[0030] Exemplary method: Such as Figure 1 、 Figure 3 As shown, a method for magnetic separation and recycling of the sealing sand for high-temperature annealing of steel coils includes the steps of: S1. Coarsely crush the caked sealing sand, and screen and separate the uncaked virgin sand grains and the caked mixture. The caked mixture contains: undissociated virgin sand grains, glass-phase coatings, and sintered aggregates; S2. Treat the caked mixture by combining microwave heating and liquid nitrogen cooling to target the rupture of the glass-phase coatings, and then separate the loose particles and undissociated blocks by air classification; S3. The loose particles first directly adsorb free iron oxide through primary magnetic separation, and then enter secondary magnetic separation to jointly separate weak magnetic iron oxide through dynamic fluidized classification and magnetic fluid enhancement; S4. Pickle and dissociate the undissociated blocks, and separate the glass phase and the undamaged virgin sand grains by electric field classification; S5. Perform surface melting and cooling forming on the loose particles in S3 and the undamaged virgin sand grains in S4 to restore the roundness of the sand grains.

[0031] For the complex composition of the caked sealing sand, this method first uses a combination of mechanical crushing and screening for preliminary separation.

[0032] In step S1, the caked sealing sand is batch-fed into a crusher for coarse crushing. The single-feed amount ≤ 500 kg, and the coarse crushing is completed in batches. The biting pressure applied by the crusher ≤ 5 MPa to avoid damage to the virgin sand grains caused by excessive crushing; the compressive strength of quartz sand is 120 - 150 MPa, and 5 MPa pressure is sufficient to crush the caked body without damaging the virgin sand grains; the particle size of the crushed product < 10 mm to ensure the uniformity of the subsequent magnetic separation materials; the particle size range of the virgin sand grains in the caked sealing sand is 0.5 - 2 mm; Use a double - layer vibrating screen with an upper - layer screen aperture of 3 mm and a lower - layer screen aperture of 1 mm, a vibration frequency of 25 - 30 Hz, and an amplitude of 5 mm; The upper - layer screen intercepts products larger than 3 mm, mainly large lumps of incompletely broken materials, which are returned to the crusher for secondary crushing to ensure full dissociation of the lumps.

[0033] The middle - layer screen collects the lumpy mixture of 1 - 3 mm, which contains undissociated primary sand grains, glass - phase coatings, and sintered aggregates. This part of the material needs to enter step S2 to further dissociate the glass - phase coatings through thermal shock.

[0034] The bottom - layer screen obtains products smaller than 1 mm, mainly composed of un - lumped primary sand grains and free iron - oxide fine powder. For this part of the products, a permanent - magnet drum is directly used for magnetic separation, with the magnetic field strength set at 0.3 - 0.5 T to effectively remove the free iron - oxide fine powder and obtain pure primary sand grains; the un - lumped primary sand has a particle size of 0.5 - 1 mm, a roundness greater than 0.85, and a complete crystal structure.

[0035] Since the primary sand grains do not participate in sintering, they maintain the crystal structure of the original quartz sand, with the particle size concentrated in the range of 0.5 - 2 mm. And the un - lumped particles, due to not experiencing sintering agglomeration, have a smaller single - particle size, resulting in a high proportion of the part smaller than 1 mm; the lumpy mixture contains complex structures such as glass - phase coatings and sintered aggregates. Although these lumps are broken to less than 10 mm after coarse crushing, they still retain the agglomerated structure formed by the bonding of multiple particles, and the overall particle size is significantly larger than that of the primary sand grains. Even if the lumpy mixture may contain primary sand grains, they can be further separated in subsequent steps.

[0036] Through the above - mentioned coarse crushing and screening pretreatment, the separation of undamaged primary sand grains is initially achieved, laying a foundation for subsequent fine dissociation and purification.

[0037] During the high - temperature annealing of the steel coil, a non - crystalline glass - phase coating will form on the surface of the quartz sand particles in the sealing sand. This coating not only wraps some primary sand grains but also may embed iron - oxide particles, seriously hindering the efficiency of subsequent magnetic - separation purification.

[0038] This application adopts a thermal - shock dissociation technology. Utilizing the significant difference in the thermal expansion coefficients between the glass phase and quartz sand, through rapid heating and quenching, the glass - phase coating is broken, thereby releasing the wrapped primary sand grains and iron - oxide particles. Microwave heating has the advantages of selective heating, rapid temperature rise, and uniform heating, which can ensure that the glass - phase coating is fully softened without damaging the quartz - sand matrix. Liquid - nitrogen quenching uses extremely low - temperature liquid nitrogen to rapidly reduce the temperature of the material, causing the glass - phase coating to crack and finally break due to rapid contraction.

[0039] In step S2, the 1-3 mm agglomerated mixture screened in step S1 is subjected to thermal shock treatment. The glass phase coating is broken by rapid heating and sudden quenching with liquid nitrogen. Subsequently, using air classification technology, according to the differences in particle density and shape, the broken loose particles are separated from the undissociated blocks.

[0040] The loose particles include: primary sand grains and iron oxide; the undissociated blocks are mainly incompletely broken sintered aggregates.

[0041] In step S2, the agglomerated mixture is fed into a microwave reactor, protected by nitrogen injection, with a frequency of 2.45 GHz ± 50 Hz and a power density of 20-25 W / cm³; the heating rate is 100 °C / min, heated to 750-850 °C, and held for 5-10 min to soften the glass phase; the glass phase is amorphous silicate, and the dielectric loss factor tanδ of the glass phase = 0.05, which is higher than that of quartz sand (tanδ = 0.001), enabling the glass phase to preferentially absorb microwave energy, achieving rapid softening of the glass phase. And 750-850 °C is the softening point of the glass phase, which can ensure its full softening but not complete melting, avoiding damage to the crystal structure of quartz sand.

[0042] The heated agglomerated mixture enters the quenching bin through a closed conveying pipeline. Liquid nitrogen is evenly sprayed onto the surface of the agglomerated mixture through an annular nozzle array, covering all particles. The temperature of the liquid nitrogen is -196 °C, and the spraying flow rate is 7-10 L / min; the quenching time ≤ 30 s, so that the surface temperature of the agglomerated mixture drops to -50 °C; the material temperature is monitored in real time to ensure that the internal temperature difference after quenching > 800 °C; This is due to the difference in the coefficient of thermal expansion (CTE) of quartz sand (CTE = 0.5×10 -6 / °C) and the glass phase (CTE = 9×10 -6 / °C), with a difference in shrinkage rate of up to 18 times during quenching. Due to the large difference in the coefficient of thermal expansion between quartz sand and the glass phase, during quenching, the glass phase shrinks faster while quartz sand shrinks slower, resulting in shear stress between the two. The shear stress exceeds the strength limit of the glass phase; the glass phase is amorphous silicate, with an irregular internal structure and a lack of crystal slip layers to release energy. When subjected to thermal shock, energy accumulates inside, leading to crack propagation and causing the glass phase coating to break.

[0043] In this state, the glass phase rapidly shrinks from the softened state, detaches from the quartz sand matrix, causing the glass phase coating to break and releasing the encapsulated iron oxide particles.

[0044] The quenched mixture is pneumatically conveyed into a vortex separator. A high-speed air flow forms a spiral upward flow field. The loose particles are carried to the top collector, and the undissociated blocks settle to the bottom under the action of centrifugal force; the air flow velocity is 12-18 m / s; the separation time is 2-3 min / batch; the separation particle size threshold is 50 μm; The density of loose particles is 2.2 - 3.5 g / cm³, and the density of undissociated lumps is > 4.0 g / cm³. They are separated by centrifugal force in the air flow. In addition, the particle size of undissociated lumps is > 1 mm, and the particle size of loose particles is < 1 mm. Loose particles are mainly composed of primary sand grains and iron oxide, and enter step S3 for magnetic separation and purification. Undissociated lumps are mainly incompletely broken sintered aggregates and enter step S4 for pickling and dissociation.

[0045] Through the precisely controlled microwave heating and liquid nitrogen quenching process, step S2 effectively breaks the glass - phase coating, releases the encapsulated iron oxide particles, and successfully separates loose particles and undissociated lumps using air - flow sorting technology. It not only realizes the targeted dissociation of the glass - phase coating but also avoids the thermal damage of primary sand grains, significantly improving the separation efficiency. The separated loose particles will enter step S3, and the primary sand grains are further purified by magnetic separation technology to remove free iron oxide, while the undissociated lumps enter step S4 for pickling and dissociation to recover more primary sand grain resources.

[0046] Step S3 is to magnetically separate and purify the loose particles separated in step S2 to remove the free iron oxide and weakly magnetic iron oxide in them, so as to obtain pure primary sand grains.

[0047] In step S3, the first - stage magnetic separation is strong - magnetic capture. The loose particles obtained in step S2 are evenly spread on a non - magnetic conveyor belt to ensure that the particles are in a single - layer distribution to maximize the magnetic separation efficiency. An ultrasonic vibration plate is installed under the conveyor belt, applying a high - frequency vibration of 30 - 40 kHz. This high - frequency vibration can effectively break the residual glass - phase coating layer, especially break the residual glass - phase with a particle size < 10 μm, so that the encapsulated iron oxide particles are fully exposed, thereby improving their magnetic separation capture rate.

[0048] Under the conveyor belt, a Halbach permanent - magnet array is set up. This array is composed of high - performance neodymium - iron - boron permanent magnets to form a closed magnetic circuit. The surface magnetic induction intensity of the Halbach array is as high as 1.8 - 2.0 T, and the gradient magnetic field strength reaches 0.5 - 1.8 T / mm. This strong - magnetic - field design can ensure the efficient capture of magnetic particles.

[0049] When the loose particles pass through the Halbach array, the free iron oxide is captured by the gradient magnetic field due to its high magnetic susceptibility; while the weakly magnetic primary sand grains and glass - phase fragments are not affected and directly pass through the magnetic separation area and enter the subsequent second - stage magnetic separation link.

[0050] After the first - stage magnetic separation, the remaining materials enter the second - stage magnetic separation stage, adopting a dynamic fluidized - bed sorting combined with magnetic fluid technology to further remove weakly magnetic iron oxide.

[0051] Inject the remaining materials after the first-stage magnetic separation into the bottom of the fluidized bed, and use a nitrogen gas flow rate of 10 - 12 m / s to disperse them sufficiently, so that the materials are fully dispersed in the fluidized bed to form a fluidized state; the height of the fluidized bed is 1.5 - 2 m, and the residence time of the materials is 5 - 8 s to ensure sufficient mixing and dispersion among the particles. Under the action of the fluidizing gas nitrogen, the particles are in a fluidized state, enhancing the dispersibility of the particles.

[0052] During the fluidization process, magnetic fluid is added. The magnetic fluid is atomized and sprayed into the bed layer through a nozzle to coat the weakly magnetic iron oxide and enhance its apparent magnetic susceptibility. The magnetic fluid is a nanofluid with a concentration of 10 wt% Fe 3 O 4 with a particle size < 50 nm.

[0053] Apply an alternating magnetic field outside the fluidized bed. The magnetic particles in the magnetic fluid interact with the weakly magnetic iron oxide to further enhance the magnetic field strength, thereby improving the separation efficiency of the weakly magnetic iron oxide. The frequency of the alternating magnetic field is 4 - 6 Hz, the peak value is 1.2 - 1.5 T, and the magnetic field direction switches 5 times per second. The alternating magnetic field makes the magnetized particles move reciprocally and separate from the glass phase and quartz sand due to density differences. The magnetic particles are adsorbed to the magnetic pole plate, and the non-magnetic particles are discharged from the top.

[0054] The frequency of the alternating magnetic field is 4 - 6 Hz, which matches the particle relaxation time to avoid the escape of fine particles due to the magnetic hysteresis effect; nano Fe 3 O 4 is adsorbed on the surface of the iron oxide to form a "magnetic shell layer", increasing the magnetic susceptibility of the weakly magnetic particles.

[0055] Through the strong magnetic capture and ultrasonic-assisted dissociation in the first-stage magnetic separation, and the combined magnetic fluid-enhanced separation of dynamic fluidized bed separation in the second-stage magnetic separation, step S3 can efficiently remove the free iron oxide and weakly magnetic iron oxide in the loose particles, significantly improving the purity of the raw sand grains.

[0056] In step S4, the undissociated blocks (including sintered aggregates) after the gas flow separation in S2 are put into the pickling tank according to a solid-liquid ratio of 1:5 - 8. The pickling solution uses a citric acid-oxalic acid mixed solution with a molar ratio of 1:1 - 1.5, and the pH of the acid solution is maintained at 2 - 3 through a pH buffer system. The system uses an indirect heating method to keep the acid solution at a constant temperature of 40 - 60 °C, and is assisted by ultrasonic oscillation at 30 - 40 kHz with a power density of 400 - 600 W / cm³, and the treatment time is set to 30 - 40 min.

[0057] The pickling system achieves directional dissolution through synergistic effects. The citrate anions preferentially form stable chelates with Fe 2+ while the oxalate reduces Fe 3+ to Fe 2+It also breaks the Si-O-Fe chemical bond and selectively dissolves the iron silicate phase in the sintered body. The ultrasonic cavitation effect significantly accelerates the penetration of the acid solution, increasing the reaction interface renewal rate by 3 - 5 times, while avoiding the sand grain wear caused by traditional mechanical stirring.

[0058] The reason for choosing the citric acid - oxalic acid system lies in its chemical inertness to quartz sand. Under weakly acidic conditions with pH = 2 - 3, the corrosion rate of SiO 2 is lower than 1×10 -8 g / (m 2 ·s). Even after 30 minutes of treatment, the surface mass loss rate of the quartz sand is still less than 0.02%. Pickling effectively avoids damaging the Si-O-Si network structure by selectively attacking the Fe-Si-O bonding sites, ensuring the crystal integrity of the original sand grains.

[0059] After pickling, a vacuum filter is used to separate the solid residue from the Fe 3+ -containing filtrate.

[0060] The solid residue is mixed with water at a ratio of 1:7 - 9 and pumped to the dielectric separation tank through a corrosion-resistant pump. A high-voltage pulsed electric field is applied in the separation tank, and the parameters are set as follows: the electrode spacing is 8 - 10 mm, the pulse width is 3 - 5 μs, the electric field intensity is 80 - 100 kV / cm, and the pulse frequency is 100 - 150 Hz. Under the action of the non-uniform electric field, the glass phase particles with high dielectric constant migrate to the region with higher electric field intensity due to the gradient force, while the quartz sand particles with low dielectric constant are separated by gravitational sedimentation due to the weaker polarization force.

[0061] The dielectric constant of the glass phase is 5.2, and that of the quartz sand is 3.8. There are differences in their dielectric properties. The polarization force on the glass phase particles in the electric field is significantly greater than that on the quartz sand, causing them to be adsorbed to the surface of the positive electrode plate, while the undamaged original sand grains are efficiently recovered through gravitational sedimentation.

[0062] In step S5, the loose particles after magnetic separation in S3 and the undamaged original sand grains recovered in S4 are mixed and fed into the plasma torch through a vibrating feeder. The power is 80 - 100 kW, the working gas is Ar / H 2 with a mixing ratio of 9:1, the gas flow rate is 15 - 20 L / min, and the surface of the sand grains is instantaneously melted at 15000 - 18000 °C to a depth of <5 μm. The corners and microcracks are eliminated by the surface tension; The molten particles then enter the centrifugal atomizer and are rapidly cooled at a rate of 10 7 °C / s at a rotational speed of 25000 - 30000 rpm to form a dense amorphous / nanocrystalline composite surface layer. The high temperature of 15000 - 18000 °C only acts on the surface, avoiding damage to the internal crystal structure.

[0063] The reconstituted sealing sand after surface reconstruction and the virgin sand grains of S1 are evenly laid on a rotating substrate at a rotational speed of 10 - 20 rpm, and Cr target sputtering is carried out. A DC sputtering power of 5 - 6 kW is adopted, combined with an axial magnetic field of 0.5 - 1 T to confine the plasma, achieving a deposition rate of 0.1 - 0.2 nm / s. Sputtering is stopped when the film thickness reaches 5 nm.

[0064] Finally, the virgin sand grains of S1 that have not caked and the coated sand grains of S5 are re - backfilled into the gaps of the high - temperature annealing hood of the steel coil to achieve the reuse and enhancement of the sealing sand.

[0065] Exemplary device: A device for magnetic separation and reuse of sealing sand for high - temperature annealing of steel coils, comprising: A crusher, which is used for coarsely crushing the caked sealing sand and is the starting part of the whole device; the discharge port of the crusher is connected to the feed port of a double - layer vibrating screen through a conveyor belt or a pipeline; A double - layer vibrating screen, installed after the crusher, which is used for screening the crushed materials; the upper sieve of the double - layer vibrating screen is connected to the conveying device that returns to the crusher, the middle sieve is connected to a microwave reactor, and the bottom sieve is connected to a permanent - magnet drum; A microwave reactor, which receives the 1 - 3 mm caked mixture from the middle sieve of the vibrating screen and conducts rapid heating treatment; the outlet of the microwave reactor is connected to a quenching bin through a sealed conveying pipeline; A quenching bin, installed after the microwave reactor, which is used for quenching the heated materials with liquid nitrogen; the outlet of the quenching bin is connected to a vortex separator through a pneumatic conveying system; A vortex separator, which is used for separating loose particles and undissociated blocks; the top outlet of the vortex separator is connected to a primary magnetic separation device, and the bottom outlet is connected to a pickling tank; The primary magnetic separation device strongly magnetically captures the loose particles to remove free iron oxide; the outlet of the primary magnetic separation device is connected to a secondary magnetic separation device; A secondary magnetic separation device, which further magnetically separates the materials after primary magnetic separation to remove weakly magnetic iron oxide; the outlet of the secondary magnetic separation device is connected to a plasma torch; A pickling tank, which receives the undissociated blocks from the vortex separator and conducts pickling treatment; the pickling tank is connected to a dielectric separation tank through a corrosion - resistant pump; A dielectric separation tank, which is used for separating the glass phase and quartz sand in the solid residue after pickling; the outlet of the dielectric separation tank is connected to a plasma torch; A plasma torch, which receives the materials from the secondary magnetic separation device and the dielectric separation tank and conducts surface melting and cooling forming treatment; the outlet of the plasma torch is connected to a centrifugal atomizer; A centrifugal atomizer, which is used for ultra - fast cooling of the molten particles; the outlet of the centrifugal atomizer is connected to a magnetron sputtering system; A magnetron sputtering system is used to deposit a thin film on the cooled particles. The outlet of the magnetron sputtering system is connected to a finished product collection device. The finished product collection device is used to collect the treated sealing sand and prepare to backfill the gaps in the high-temperature annealing hood of the steel coil.

[0066] Example 1:

[0067] A method for magnetic separation and recycling of sealing sand for high-temperature annealing of steel coils includes: S1. Batch-feed the agglomerated sealing sand into a jaw crusher. The single-feed amount is set to 250 kg, the biting pressure applied by the crusher is controlled at 3 MPa, and the particle size of the crushed product is controlled to be <10 mm. Use a double-deck vibrating screen with a screen aperture of 3 mm for the upper layer and 1 mm for the lower layer. The vibration frequency is set to 28 Hz and the amplitude is 5 mm. The upper-layer screen intercepts large agglomerated materials >3 mm and returns them to the crusher for secondary crushing.

[0068] The middle-layer screen collects the agglomerated mixture of 1-3 mm: including undissociated primary sand grains, glass-phase coatings, and sintered aggregates, and enters step S2.

[0069] The bottom-layer screen obtains products <1 mm: unagglomerated primary sand grains and free iron oxide fine powder. Use a permanent magnet drum magnetic separator with a magnetic field strength of 0.4 T to remove the free iron oxide and obtain pure primary sand grains (particle size 0.5-1 mm, roundness >0.85). S2. Feed the 1-3 mm agglomerated mixture into a microwave reactor, introduce nitrogen for protection, with a frequency of 2.45 GHz and a power density of 22 W / cm 3 , a heating rate of 100 °C / min, heat to 800 °C, and keep warm for 8 min to soften but not melt the glass phase. After heating, the material enters the quenching chamber through a closed pipeline. The liquid nitrogen spraying flow rate is 8 L / min, and the quenching time is 20 s. The surface temperature of the material drops to -50 °C, and the internal temperature difference >800 °C. Utilize the difference in thermal expansion coefficients between quartz sand and the glass phase to break the glass-phase coatings. After quenching, the mixture passes through a vortex separator with an air flow velocity of 15 m / s and a separation time of 2.5 min / batch. Loose particles (density 2.2-3.5 g / cm 3 , particle size <1 mm) are carried to the top collector and enter step S3; undissociated blocks (density >4.0 g / cm 3 , particle size >1 mm) settle to the bottom and enter step S4. S3. The loose particles are evenly laid on a non-magnetic conveyor belt. A Halbach permanent magnet array is installed below, with a surface magnetic induction intensity of 1.9 T and a gradient magnetic field strength of 1.2 T / mm. An ultrasonic vibration plate is set below the conveyor belt, with a frequency of 35 kHz, to break the residual glassy phase coating; After the first-stage magnetic separation, the remaining materials are injected into a fluidized bed. The nitrogen gas flow rate is 11 m / s, the bed height is 1.8 m, and the residence time is 6 s; Magnetic fluid is added: with a concentration of 10 wt% Fe 3 O 4 nanofluid, with a particle size <50 nm. An alternating magnetic field is applied externally, with a frequency of 5 Hz, a peak value of 1.3 T, and the direction switching 5 times per second, to increase the magnetic susceptibility of weakly magnetic iron oxide and adsorb it to the magnetic pole plate; S4. The undissociated blocks are put into a pickling tank according to a solid-liquid ratio of 1:6. The pickling solution is a citric acid-oxalic acid mixed solution, with a molar ratio of 1:1.2 and a pH of 2.5. Keep the temperature constant at 50 °C and perform ultrasonic oscillation, with a power density of 500 W / cm³ and a frequency of 35 kHz. The treatment time is 35 min; After pickling, vacuum filtration is used to separate the solid residue and the Fe 3+ filtrate; The solid residue is mixed with water at a ratio of 1:8 and transported to a dielectric separation tank. A high-voltage pulsed electric field is applied, with an electrode spacing of 9 mm, a pulse width of 4 μs, an electric field strength of 90 kV / cm, and a frequency of 120 Hz; The glassy phase particles are adsorbed to the positive electrode plate, and the original sand grains are recovered by gravity sedimentation; S5. The loose particles after magnetic separation in S3 and the original sand grains recovered in S4 are mixed and fed into a plasma torch, with a power of 90 kW, an Ar / H 2 mixing ratio of 9:1, and a gas flow rate of 18 L / min. The surface is instantaneously melted at 16500 °C to a depth of <5 μm; The molten particles enter a centrifugal atomizer with a rotation speed of 28000 rpm to achieve ultra-fast cooling, with a cooling rate of 10 7 °C / s, forming a dense amorphous / nanocrystalline composite surface layer; The sealed sand after surface reconstruction is evenly laid on a rotating substrate with a rotation speed of 15 rpm. DC sputtering is used, with a power of 5.5 kW and an axial magnetic field of 0.8 T. The deposition rate is 0.15 nm / s, and sputtering is stopped after a film thickness of 5 nm.

[0070] The treated sealed sand is mixed with the non-caked original sand grains in S1 and re-backfilled into the gaps of the steel coil high-temperature annealing hood to realize the reuse and performance enhancement of the sealed sand.

[0071] Example 2:

[0072] A method for magnetic separation and reuse of sealed sand for high-temperature annealing of steel coils, the same parts as in Example 1 will not be elaborated. The differences between this example and Example 1 are as follows: In S2, microwave heating is carried out to 750 °C.

[0073] Example Three:

[0074] A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this example and Example One are as follows: In S2, microwave heating is carried out to 780 °C.

[0075] Example Four:

[0076] A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this example and Example One are as follows: In S2, microwave heating is carried out to 820 °C.

[0077] Example Five:

[0078] A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this example and Example One are as follows: In S2, microwave heating is carried out to 850 °C.

[0079] Comparative Example One: A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this comparative example and Example One are as follows: Secondary magnetic separation is not carried out.

[0080] Comparative Example Two: A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this comparative example and Example One are as follows: Pickling treatment is not carried out and the separated blocks are not connected.

[0081] Comparative Example Three: A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils, the same parts as in Example One will not be described in detail. The differences between this comparative example and Example One are as follows: After coarse crushing and screening, magnetic separation is directly carried out to adsorb iron oxide.

[0082] Experimental Example One: Select Examples One to Five and Comparative Examples One to Three to conduct experimental verification on the treated sealed sand to obtain the free iron oxide capture rate, weakly magnetic iron oxide capture, and primary sand grain recovery rate; Free iron oxide capture rate = (mass of free iron oxide removed by magnetic separation / total mass of free iron oxide in the initial material) × 100%; Weakly magnetic iron oxide capture rate = (mass of weakly magnetic iron oxide separated / total mass of weakly magnetic iron oxide in the initial material) × 100%; Evaluate the removal efficiency of the above magnetic separation process for free iron oxide to ensure its effective removal of magnetic impurities; Recovery rate of virgin sand grains = (mass of recovered pure virgin sand grains / total mass of virgin sand grains in the initial material) × 100%; The recovery rate of virgin sand grains evaluates the recovery efficiency of the entire recycling method for virgin sand grains to ensure the efficient recycling of resources.

[0083] Table 1 Data of Experiment 1

[0084] When the temperature is in the range of 750 - 850 °C, the glass phase is fully softened but not completely melted, and the cracking effect after thermal shock is the best. The capture rate of free iron oxide and the recovery rate of virgin sand in Example 1 reach the peak, indicating that this temperature can balance the softening of the glass phase and the protection of quartz sand. Too low a temperature results in insufficient softening of the glass phase and incomplete cracking; too high a temperature may cause damage to the quartz sand crystals and reduce the recovery rate.

[0085] In Comparative Example 1, secondary magnetic separation was not carried out, and the capture rate of weakly magnetic iron oxide dropped sharply to 63.8%. Because primary magnetic separation can only capture free iron oxide, while secondary magnetic separation uses dynamic fluidized separation combined with magnetic fluid technology to increase the magnetic susceptibility of weakly magnetic particles, so that they can be effectively separated.

[0086] In Comparative Example 2, pickling was not carried out, and the recovery rate of virgin sand grains dropped to 69.7%. Because the sintered aggregates in the undissociated blocks contain Fe - Si - O chemical bonds, it is necessary to selectively dissolve the iron silicate phase through mixed pickling with citric acid - oxalic acid to release the encapsulated virgin sand grains.

[0087] In Comparative Example 3, the thermal shock and pickling steps were skipped, and only magnetic separation was carried out after coarse crushing, resulting in the lowest capture rate and recovery rate of free iron oxide. Because the glass - phase coating was not cracked, the iron oxide particles were shielded, and the sintered aggregates were not dissociated, so a large amount of virgin sand grains could not be recovered.

[0088] Based on the ideal embodiments of the present invention as an inspiration, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of this invention.

Claims

1. A method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils, characterized in that: Includes steps: S1, coarsely crushing the agglomerated sealing sand, screening and separating the unagglomerated original sand particles and the agglomerated mixture, the agglomerated mixture comprising: undissociated original sand particles, glassy phase inclusions and sintered agglomerates; S2, treating the agglomerated mixture by combining microwave heating with liquid nitrogen cooling to achieve targeted rupture of the glassy coating, and then separating the loose particles and undissociated lumps by airflow sorting; S3, loose particles first directly adsorb free iron oxide through the first-stage magnetic separation, and then enter the second-stage magnetic separation through dynamic fluidization separation combined with magnetic fluid enhancement to separate weak magnetic iron oxide; S4, acid washing and dissociation of the undissociated block, and separation of the glass phase and the undamaged original sand particles by electric field sorting; S5: Surface melting and cooling of the loose particles of S3 and the undamaged original sand particles of S4 are performed to restore the roundness of the sand particles.

2. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S1, the agglomerated sealing sand is fed into a crusher in batches for coarse crushing, the single feed amount is ≤500kg, the bite pressure applied by the crusher is ≤5MPa, and the particle size of the crushed product is <10mm; a double-layer vibrating screen is used, the upper layer of the screen has an aperture of 3mm, the lower layer of the screen has an aperture of 1mm, the vibration frequency is 25-30Hz, and the amplitude is 5mm.

3. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S2, the heating rate is 100°C / min, heated to 750-850°C, and kept warm for 5-10min; the heated agglomerated mixture enters a quenching bin, and liquid nitrogen is evenly sprayed onto the surface of the agglomerated mixture through an annular nozzle array, the liquid nitrogen temperature is -196°C, and the spraying flow rate is 7-10L / min; the quenching time is ≤30s, so that the surface temperature of the agglomerated mixture drops to -50°C.

4. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 3, characterized in that: In step S2, the quenched agglomerated mixture is sent to a vortex separator, and a high-speed airflow forms a spiral upward flow field with an airflow velocity of 12-18 m / s; the separation time is 2-3 min / batch; and the separation particle size threshold is 50 μm.

5. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S3, the first-level magnetic separation is strong magnetic capture, and the loose particles are evenly laid on a non-magnetic conveyor belt. An ultrasonic vibration plate is installed under the conveyor belt to apply high-frequency vibration of 30-40kHz; the surface magnetic induction intensity of the Halbach permanent magnet array is as high as 1.8-2.0T, and the gradient field strength reaches 0.5-1.8T / mm.

6. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S3, the secondary magnetic separation adopts dynamic fluidization separation combined with magnetic fluid technology, and the remaining materials after the primary magnetic separation are injected into the bottom of the fluidized bed, with a nitrogen flow rate of 10-12m / s; the fluidized bed height is 1.5-2m, and the material residence time is 5-8s; a magnetic fluid is added, and the magnetic fluid is a 10wt% Fe3O4 nanofluid with a particle size of <50nm; an alternating magnetic field is applied to the outside of the fluidized bed, with a frequency of 4-6Hz, a peak value of 1.2-1.5T, and the direction of the magnetic field is switched 5 times per second.

7. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S4, the undissociated block is put into the pickling tank at a solid-liquid ratio of 1:5-8, the pickling liquid is a citric acid-oxalic acid mixed solution with a molar ratio of 1:1-1.5, and the pH of the acid solution is maintained at 2-3 by a pH buffer system; the acid solution is temperature controlled at 60°C, assisted by 30-40kHz ultrasonic oscillation, power density 400-600W / cm³, and the treatment time is set to 30-40min; and the solid residue and Fe-containing 3+ filtrate.

8. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 7, characterized in that: In step S4, the solid residue is mixed with water at a ratio of 1:7-9, sent to a dielectric separation tank and a high-voltage pulse electric field is applied, and the parameters are set as follows: electrode spacing 8-10 mm, pulse width 3-5 μs, electric field strength 80-100 kV / cm, and pulse frequency 100-150 Hz.

9. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 1, characterized in that: In step S5, the surface melting is achieved by instantaneously melting the sand surface at a plasma temperature of 15000-18000°C, a plasma torch power of 80-100kW, a working gas Ar / H2 mixing ratio of 9:1, a gas flow rate of 15-20L / min, and a depth of <5μm.

10. The method for magnetic separation and recycling of sealing sand for high temperature annealing of steel coils according to claim 9, characterized in that: In step S5, the molten particles enter the centrifugal atomizer and are atomized at a speed of 25000-30000 rpm for 10 7 ℃ / s ultra-fast cooling.

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