A method for recycling sealed sand by magnetic separation in the high-temperature annealing of steel coils

Abstract

The present invention discloses a method for magnetic separation and recycling of sealed sand in high-temperature annealing of steel coils, comprising: coarsely crushing the agglomerated sealed sand, screening and separating the unagglomerated original sand grains and the agglomerated mixture, where the agglomerated mixture includes: undissociated original sand grains, glass phase coatings, and sintered agglomerates; treating the agglomerated mixture by combining microwave heating and liquid nitrogen cooling to targetedly break the glass phase coatings, and then separating loose particles and undissociated blocks by air classification; the loose particles are first directly adsorbed with free iron oxide by primary magnetic separation, and then enter secondary magnetic separation to separate weakly magnetic iron oxide through combined dynamic fluidized classification and magnetic fluid enhanced separation; the undissociated blocks are acid-washed and dissociated, and the glass phase and undamaged original sand grains are separated by electric field classification; the surface of the loose particles and the undamaged original sand grains is melted and cooled to form, restoring the roundness of the sand grains. The present invention realizes the efficient purification and recycling of the sealed sand, significantly improving the magnetic separation efficiency and the quality of the sand grains.

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, and high-voltage electric field separation, in particular to the technical field of magnetic separation, and specifically to a method for magnetic separation and recycling of sealing sand for 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 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 sands mainly include fused silica sand, purple sand, etc., and their 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 scale (Fe3O4, Fe2O3, FeO) on the surface 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 such deteriorated sealing sand is to pour the sealing sand into a vibrating screen. The vibrating screen is equipped with magnets, and during the vibration process, the magnets adsorb and clean up the falling scale, thus purifying 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 for 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 for high-temperature annealing of steel coils, aiming to solve the problems in the existing technology that the iron oxide powder is encapsulated 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: a method for magnetic separation and recycling of sealing sand for high-temperature annealing of steel coils, including:

[0008] S1. Coarse-crush the caked sealed sand, and screen and separate the uncaked original sand grains and the caked mixture. The caked mixture includes: undissociated original sand grains, glass-phase coatings, and sintered aggregates.

[0009] S2. Treat the caked mixture by combining microwave heating and liquid nitrogen cooling to targetedly break the glass-phase coatings, and then separate the loose particles and undissociated blocks by air classification.

[0010] 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.

[0011] S4. Acid-wash and dissociate the undissociated blocks, and separate the glass phase and the undamaged original sand grains by electric field classification.

[0012] S5. Perform surface melting and cooling forming on the loose particles in S3 and the undamaged original sand grains in S4 to restore the roundness of the sand grains.

[0013] 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.

[0014] 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 evenly 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.

[0015] In a preferred embodiment of the present invention, in step S2, the quenched caked mixture is sent into a vortex classifier, a high-speed air flow forms a spiral upward flow field, and 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.

[0016] 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, an ultrasonic vibration plate is installed below the conveyor belt, and a high-frequency vibration of 30 - 40 kHz is applied; the surface magnetic induction intensity of the Halbach permanent magnet array is as high as 1.8 - 2.0 T, and the gradient field strength reaches 0.5 - 1.8 T / mm.

[0017] 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 material after the primary magnetic separation is injected into the bottom of the fluidized bed, with a nitrogen gas flow rate of 10 - 12 m / s; the height of the fluidized bed is 1.5 - 2 m, and the residence time of the material is 5 - 8 s; a magnetic fluid is added, and the magnetic fluid is a 10 wt% Fe3O4 nanofluid with a particle size of <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 switches 5 times per second.

[0018] In a preferred embodiment of the present invention, in step S4, the undissociated block is put into the pickling tank according to a solid-liquid ratio of 1:5 - 8, and the pickling solution uses a citric acid-oxalic acid mixed solution with a molar ratio of 1:1 - 1.5. 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.

[0019] 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.

[0020] 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 mixing ratio of the working gases Ar / H2 is 9:1, the gas flow rate is 15 - 20 L / min, and the depth is <5 μm.

[0021] In a preferred embodiment of the present invention, in step S5, the molten particles enter a centrifugal atomizer and achieve an ultrafast cooling rate of 10 7 °C / s at a rotational speed of 25000 - 30000 rpm.

[0022] The present invention solves the defects existing in the background technology, and the present invention has the following beneficial effects:

[0023] (1)The present invention proposes a method for recycling sealed sand by magnetic separation, which solves the problems of glass-phase coating hindering magnetic separation, weakening of the magnetic properties of iron oxide particles, and 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 oxide, uses a citric acid-oxalic acid system to selectively dissociate sintered aggregates, and restores the properties 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.

[0024] (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, realizing 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, the comprehensive removal effect of iron oxide impurities is further achieved.

[0025] (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 mixed acid solution of citric acid and oxalic acid 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 by utilizing the difference in dielectric constants between the glass phase and quartz sand. Compared with the prior art, the comprehensive removal of different forms of iron oxide and the efficient recovery of original sand grains are realized.

[0026] (4)The present invention combines coarse crushing and screening with thermal shock dissociation. First, mechanical crushing and screening are used to separate the agglomerated sealed sand into unagglomerated original sand grains and agglomerated mixtures, ensuring the uniformity of the particle size of the subsequent treatment materials. Subsequently, a 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, realizing the efficient dissociation of complex agglomerated 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, the effects of efficient dissociation and resource recovery are further achieved.

[0027] (5) By combining surface melting and thin film deposition, the present invention instantaneously melts the surface of the sand grains using plasma to eliminate edges and microcracks and restore the roundness of the sand grains. Subsequently, a corrosion-resistant thin film is deposited on the surface of the sand grains by magnetron sputtering to enhance their high-temperature resistance and corrosion resistance, realizing the performance restoration and enhancement of the recycled sand grains. The surface treatment not only optimizes the physical properties of the sand grains but also extends the service life of the sealing sand through film protection. Compared with the prior art, it further achieves the closed-loop design effect of sealing sand performance restoration and resource recycling. Description of the Drawings

[0028] In order 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 the description of the embodiments or the prior art. Obviously, the drawings described below 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.

[0029] Figure 1 is the flowchart of the steps of the preferred embodiment of the present invention;

[0030] Figure 2 is the classification diagram of the caked sealing sand to be recycled in the preferred embodiment of the present invention;

[0031] Figure 3 is the flowchart of the recycling of the sealing sand in the preferred embodiment of the present invention. Detailed Embodiments

[0032] 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 the embodiments. 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.

[0033] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention, but the present invention may be practiced 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.

[0034] In the description of this application, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "linkage" 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 this application can be understood according to specific circumstances.

[0035] Application Overview:

[0036] During the annealing process of the steel coil, the sealing sand is long-term exposed to a high-temperature environment of 650°C - 1150°C, and complex physical and chemical changes occur inside it. Under the action of high temperature, components such as silica in the sand grains gradually melt to form a glass phase. This viscous substance promotes sintering between the sand grains, forming a densified block structure. During this process, the flux components in the impurities inside the sand body significantly accelerate the formation of the glass phase, causing the surface of the sand grains to be wrapped by the molten substance, 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 means to effectively capture the encapsulated iron oxide particles.

[0037] With the gradual increase of the annealing temperature, the physical and chemical properties of the iron oxide powder undergo fundamental changes. The high-temperature environment promotes the crystal structure reorganization of iron oxide, and its magnetic characteristics are significantly weakened as the chemical form changes. At the same time, the intense thermal movement causes the iron oxide particles to continuously refine, forming sub-micron or even nano-scale ultra-fine powders. These fine particles are diffusely distributed inside the sintered body. The densified structure formed by the high-temperature sintering of the sand body further aggravates the consolidation of the iron oxide powder. Even through mechanical crushing treatment, there are still a large number of iron oxide fine 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 the fine particles, ultimately resulting in 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.

[0038] In view of the above situation, the present application proposes a method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils. Through coarse crushing and screening, preliminary separation of unagglomerated primary sand grains is achieved. Subsequently, a thermal shock technology combining microwave heating and rapid cooling with liquid nitrogen is adopted. Utilizing the significant difference in the thermal expansion coefficients of the glass phase and quartz sand, the glass phase coating is broken and the encapsulated iron oxide particles are released. Further, through primary magnetic separation with strong magnetic capture and ultrasonic-assisted dissociation, and secondary magnetic separation with dynamic fluidized bed separation combined with magnetic fluid enhanced separation, free iron oxide and weakly magnetic iron oxide in loose particles are efficiently removed. For the undissociated lumps, a mixed pickling system of citric acid-oxalic acid is used for selective dissociation, and then the glass phase and undamaged primary sand grains are separated by high-voltage pulsed electric field sorting. Finally, the recycled sand grains are subjected to plasma surface melting and ultra-rapid cooling to restore their roundness, and a corrosion-resistant thin film is deposited by magnetron sputtering. Ultimately, recycled sealed sand with excellent physical properties and surface characteristics is obtained. This method not only significantly improves the magnetic separation efficiency and the quality of sand grains, but also realizes the efficient recycling of resources.

[0039] As Figure 2 shown, the agglomerated sealed sand recycled in the present application is the sealed sand after high-temperature annealing of steel coils, and the sealed sand contains: primary sand grains, glass phase coatings, free iron oxide, and sintered aggregates;

[0040] The primary sand grains are the original quartz sand that has not participated in the melting reaction, maintaining a complete crystal structure and excellent physical properties, which is the main target for recycling;

[0041] The glass phase coatings are amorphous glass phase layers formed on the surface of sand grains due to high-temperature melting, which may encapsulate iron oxide particles. Although their magnetism is retained, it is shielded by the glass phase;

[0042] 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;

[0043] 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 with chemically bonded Si-Al-Fe-O.

[0044] Exemplary method:

[0045] As Figure 1 、 Figure 3 shown, a method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils includes the steps of:

[0046] S1. Coarsely crush the agglomerated sealed sand, and screen and separate the unagglomerated primary sand grains and the agglomerated mixture. The agglomerated mixture includes: undissociated primary sand grains, glass phase coatings, and sintered aggregates;

[0047] S2. Treat the caked mixture by combining microwave heating and liquid nitrogen cooling to targetedly break the glass phase coating, and then separate the loose particles and undissociated blocks by air classification;

[0048] S3. The loose particles are first directly adsorbed with free iron oxide by primary magnetic separation, and then enter the secondary magnetic separation to separate the weakly magnetic iron oxide through the combined dynamic fluidized classification and magnetic fluid enhanced separation;

[0049] S4. Acid wash and dissociate the undissociated blocks, and separate the glass phase and the undamaged original sand grains by electric field classification;

[0050] S5. Perform surface melting and cooling forming on the loose particles in S3 and the undamaged original sand grains in S4 to restore the roundness of the sand grains.

[0051] In view of the complex composition of the caked sealing sand, this method first adopts the combination of mechanical crushing and screening for preliminary separation.

[0052] In step S1, the caked sealing sand is batch-fed into the 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 original sand grains caused by excessive crushing; the compressive strength of quartz sand is 120 - 150 MPa, and 5 MPa pressure is sufficient to break the caked body without damaging the original 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 original sand grains of the caked sealing sand is 0.5 - 2 mm;

[0053] Use a double-layer vibrating screen with a screen aperture of 3 mm for the upper layer and 1 mm for the lower layer, a vibration frequency of 25 - 30 Hz, and an amplitude of 5 mm;

[0054] The product intercepted by the upper layer screen > 3 mm, mainly large caked materials that are not fully broken, is returned to the crusher for secondary crushing to ensure the full dissociation of the caked body.

[0055] The middle layer screen collects the caked mixture of 1 - 3 mm, including undissociated original sand grains, glass phase coatings, and sintered aggregates. This part of the material needs to enter step S2 to further dissociate the glass phase coating through thermal shock.

[0056] The product obtained by the bottom layer screen < 1 mm is mainly composed of un-caked original sand grains and fine free iron oxide powder. For this part of the product, a permanent magnet drum is directly used for magnetic separation, and the magnetic field strength is set to 0.3 - 0.5 T to effectively remove the fine free iron oxide powder and obtain pure original sand grains; the un-caked original sand particle size is 0.5 - 1 mm, the roundness > 0.85, and the crystal structure is complete.

[0057] Since the original sand grains did not participate in sintering, the crystal structure of the original quartz sand was maintained. The particle size was concentrated in the range of 0.5 - 2 mm, and the unagglomerated particles had not undergone sintering agglomeration, so the single particle size was smaller, resulting in a high proportion of the part less than 1 mm; the agglomerated mixture contained complex structures such as glass phase coatings and sintered agglomerates. Although these agglomerates were broken to less than 10 mm after coarse crushing, they still retained the agglomerated structure formed by the bonding of multiple particles, and the overall particle size was significantly larger than that of the original sand grains. Even if the agglomerated mixture might contain original sand grains, they could be further selected in subsequent steps.

[0058] Through the above-mentioned coarse crushing and screening pretreatment, the separation of undamaged original sand grains was initially achieved, laying a foundation for subsequent fine dissociation and purification.

[0059] During the high-temperature annealing process of the steel coil, a layer of amorphous glass phase coating will form on the surface of the quartz sand particles in the sealing sand. This coating not only wraps some original sand grains but also may embed iron oxide particles, seriously hindering the efficiency of subsequent magnetic separation purification.

[0060] This application adopts the 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 original 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.

[0061] 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 through rapid heating and liquid nitrogen quenching. Subsequently, using the air flow separation technology, according to the differences in particle density and shape, the loose particles after breaking are separated from the undissociated blocks.

[0062] The loose particles include: original sand grains and iron oxide; the undissociated blocks are mainly incompletely broken sintered agglomerates.

[0063] In step S2, the agglomerated mixture is fed into a microwave reactor, nitrogen is introduced for protection, the frequency is 2.45 GHz ± 50 Hz, and the power density is 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. This enables the glass phase to preferentially absorb microwave energy to rapidly soften 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 the destruction of the quartz sand crystal structure.

[0064] 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;

[0065] This is based on the coefficient of thermal expansion of quartz sand CTE = 0.5×10 -6 / °C and that of the glass phase (CTE = 9×10 -6 / °C), and the shrinkage rate difference during quenching reaches 18 times. Due to the large difference in the coefficients 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 an amorphous silicate with an irregular internal structure and lacks slip planes of crystals to release energy. When subjected to thermal shock, energy accumulates inside, leading to crack propagation and causing the glass phase coating to rupture.

[0066] In this state, the glass phase rapidly shrinks from the softened state and detaches from the quartz sand matrix, causing the glass phase coating to rupture and releasing the encapsulated iron oxide particles.

[0067] The quenched mixture is pneumatically conveyed into a vortex separator. A high-speed air flow forms a spiral upward flow field. Loose particles are carried to the top collector, and the undissociated blocks sink to the bottom under the action of centrifugal force; the air flow velocity is 12 - 18 m / s; the sorting time is 2 - 3 min / batch; the separation particle size threshold is 50 μm;

[0068] The density of the loose particles is 2.2 - 3.5 g / cm³, and the density of the undissociated blocks > 4.0 g / cm³, and they are separated by the action of centrifugal force in the air flow; in addition, the particle size of the undissociated blocks > 1 mm, and the particle size of the loose particles < 1 mm;

[0069] The loose particles are mainly composed of primary sand grains and iron oxide and enter step S3 for magnetic separation and purification;

[0070] The undissociated blocks are mainly incompletely broken sintered agglomerates and enter step S4 for acid pickling and dissociation.

[0071] 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 the loose particles and undissociated blocks using air classification technology. It not only achieves the targeted dissociation of the glass-phase coating but also avoids the thermal damage to the original sand grains, significantly improving the separation efficiency. The separated loose particles will enter step S3, where the original sand grains are further purified by magnetic separation technology to remove free iron oxide, while the undissociated blocks enter step S4 for pickling dissociation to recover more original sand grain resources.

[0072] Step S3 is to magnetically 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 original sand grains.

[0073] In step S3, the first-stage magnetic separation is strong magnetic capture. The loose particles obtained in step S2 are evenly laid on a non-magnetic conveyor belt to ensure that the particles are distributed in a single layer to maximize the magnetic separation efficiency. An ultrasonic vibration plate is installed below 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 glass-phase residue with a particle size < 10 μm, so that the encapsulated iron oxide particles are fully exposed, thereby improving their magnetic separation capture rate.

[0074] Below 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.

[0075] 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 original 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 process.

[0076] After the first-stage magnetic separation, the remaining materials enter the second-stage magnetic separation stage, adopting the dynamic fluidized bed separation combined with magnetic fluid technology to further remove the weakly magnetic iron oxide.

[0077] Inject the remaining materials after the first-stage magnetic separation into the bottom of the fluidized bed, and the nitrogen gas flow rate of 10 - 12 m / s makes it fully dispersed, so that the materials are fully dispersed in the fluidized bed to form a fluidized state; the height of the fluidized bed bed layer is 1.5 - 2 m, and the residence time of the materials is 5 - 8 s to ensure the full mixing and dispersion among the particles. Under the action of the fluidizing gas nitrogen, the particles are in a fluidized state, enhancing the dispersion of the particles.

[0078] During the fluidization process, a ferrofluid is added. The ferrofluid is atomized and sprayed into the bed through a nozzle, wrapping the weakly magnetic iron oxide and enhancing its apparent magnetic susceptibility. The ferrofluid is a 10 wt% Fe3O4 nanofluid with a particle size <50 nm.

[0079] An alternating magnetic field is applied outside the fluidized bed. The magnetic particles in the ferrofluid interact with the weakly magnetic iron oxide, further enhancing 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 causes the magnetized particles to move reciprocally, separating from the glass phase and quartz sand due to density differences. The magnetic particles are adsorbed onto the magnetic pole plates, and the non-magnetic particles are discharged from the top.

[0080] The frequency of the alternating magnetic field is 4 - 6 Hz, matching the particle relaxation time to prevent fine particles from escaping due to the magnetic hysteresis effect; nano-Fe3O4 adsorbs on the surface of iron oxide, forming a "magnetic shell layer" to enhance the magnetic susceptibility of the weakly magnetic particles.

[0081] Through the strong magnetic capture of the first-stage magnetic separation and ultrasonic-assisted dissociation, as well as the combined magnetic fluid-enhanced separation of the dynamic fluidization sorting 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 original sand grains.

[0082] In step S4, the undissociated blocks (including sintered aggregates) after the gas flow sorting in S2 are put into the pickling tank at 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.

[0083] The pickling system achieves directional dissolution through synergistic effects. Citrate anions preferentially form stable chelates with Fe 2+ while oxalate reduces Fe 3+ to Fe 2+ and destroys the Si-O-Fe chemical bond, selectively dissolving 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, and at the same time avoiding the abrasion of sand grains caused by traditional mechanical stirring.

[0084] The reason for choosing the citric acid-oxalic acid system lies in its chemical inertness to quartz sand. Under the weakly acidic condition of pH = 2 - 3, the corrosion rate of SiO2 is lower than 1×10 -8 g / (m 2·s), even after 30 minutes of treatment, the surface mass loss rate of quartz sand is still less than 0.02%. Acid 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.

[0085] After acid pickling, a vacuum filter is used to separate the solid residue and the filtrate containing Fe. 3+ Filtrate.

[0086] The solid residue is mixed with water at a ratio of 1:7 - 9 and pumped to a 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, glass-phase particles with a high dielectric constant migrate to the region with a higher electric field intensity due to the gradient force, while quartz sand particles with a low dielectric constant are separated by gravitational sedimentation due to their weaker polarization force.

[0087] The dielectric constant of the glass phase is 5.2, and the dielectric constant of quartz sand is 3.8. There are differences in their dielectric properties. The polarization force received by glass-phase particles in the electric field is significantly greater than that of quartz sand, so they are adsorbed to the surface of the positive electrode plate, while the undamaged original sand grains are efficiently recovered by gravitational sedimentation.

[0088] 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 a plasma torch through a vibrating feeder. The power is 80 - 100 kW, the mixing ratio of the working gases Ar / H2 is 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, with a depth of <5 μm. The edges and microcracks are eliminated by the action of surface tension.

[0089] The molten particles then enter a centrifugal atomizer and are rapidly cooled at a rate of 10 °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. 7 The reconstituted sealed sand and the original sand grains in S1 are evenly laid on a rotating substrate with a rotational speed of 10 - 20 rpm, and Cr target sputtering is carried out. A DC sputtering power of 5 - 6 kW is used, 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.

[0090] Finally, the unagglomerated original sand grains in S1 and the film-coated sand grains in S5 are refilled into the gaps of the high-temperature annealing hood of the steel coil to achieve the reuse and enhancement of the sealed sand.

[0091] Finally, the unagglomerated original sand grains in S1 and the film-coated sand grains in S5 are refilled into the gaps of the high-temperature annealing hood of the steel coil to achieve the reuse and enhancement of the sealed sand.

[0092] Exemplary device:

[0093] A device for recycling sealed sand in high-temperature annealing of steel coils, comprising:

[0094] A crusher, used for coarse crushing of agglomerated sealed sand, which is the starting part of the whole device; the discharge port of the crusher is connected to the feed port of a double-deck vibrating screen through a conveyor belt or a pipeline;

[0095] A double-deck vibrating screen, installed after the crusher, for screening the crushed materials; the upper screen of the double-deck vibrating screen is connected to a conveying device that returns to the crusher, the middle screen is connected to a microwave reactor, and the bottom screen is connected to a permanent magnetic drum;

[0096] A microwave reactor, receiving 1-3 mm agglomerated mixture from the middle screen of the vibrating screen, for rapid heating treatment; the outlet of the microwave reactor is connected to a quenching bin through a closed conveying pipeline;

[0097] A quenching bin, installed after the microwave reactor, 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;

[0098] A vortex separator, 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 an acid pickling tank;

[0099] 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;

[0100] A secondary magnetic separation device, for further magnetic separation of 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;

[0101] An acid pickling tank, receiving the undissociated blocks from the vortex separator, for acid pickling treatment; the acid pickling tank is connected to a dielectric separation tank through a corrosion-resistant pump;

[0102] A dielectric separation tank, used for separating the glass phase and quartz sand in the solid residue after acid pickling; the outlet of the dielectric separation tank is connected to a plasma torch;

[0103] A plasma torch, receiving the materials from the secondary magnetic separation device and the dielectric separation tank, for surface melting and cooling forming treatment; the outlet of the plasma torch is connected to a centrifugal atomizer;

[0104] A centrifugal atomizer, used for ultra-fast cooling of the molten particles; the outlet of the centrifugal atomizer is connected to a magnetron sputtering system;

[0105] A magnetron sputtering system is used to perform thin film deposition on the cooled particles. The outlet of the magnetron sputtering system is connected to a finished product collection device.

[0106] The finished product collection device is used to collect the processed sealed sand and prepare it for backfilling into the gaps of the high-temperature annealing hood of the steel coil.

[0107] Example 1:

[0108] A method for magnetic separation and recycling of sealed sand for high-temperature annealing of steel coils includes:

[0109] S1. The caked sealed sand is fed into a jaw crusher in batches. 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.

[0110] A double-layer vibrating screen is used, with the upper-layer screen aperture of 3 mm and the lower-layer screen aperture of 1 mm. The vibration frequency is set to 28 Hz and the amplitude is 5 mm.

[0111] The upper-layer screen intercepts large caked materials >3 mm and returns them to the crusher for secondary crushing.

[0112] The middle-layer screen collects the caked mixture of 1-3 mm: containing undissociated primary sand grains, glass-phase coatings, and sintered aggregates, and enters step S2.

[0113] The bottom-layer screen obtains the product <1 mm: un-caked primary sand grains and free iron oxide fine powder. Permanent magnetic drum magnetic separation is used 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).

[0114] S2. The 1-3 mm caked mixture is fed into a microwave reactor, nitrogen is introduced for protection, the frequency is 2.45 GHz, the power density is 22 W / cm 3 , the heating rate is 100 °C / min, and it is heated to 800 °C and held for 8 min to soften the glass phase but not melt it.

[0115] 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. Utilizing the difference in thermal expansion coefficients between quartz sand and the glass phase, the glass-phase coatings are broken.

[0116] 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.

[0117] The loose particles (density 2.2-3.5 g / cm 3 , particle size <1 mm) are carried to the top collector and enter step S3; the undissociated blocks (density >4.0 g / cm 3, particles with a particle size > 1 mm settle to the bottom and enter step S4;

[0118] S3. The loose particles are evenly laid on a non-magnetic conveyor belt, and a Halbach permanent magnet array is installed below. The surface magnetic induction intensity is 1.9 T, the gradient magnetic field strength is 1.2 T / mm, and an ultrasonic vibration plate is arranged below the conveyor belt with a frequency of 35 kHz to break the residual glass phase coating;

[0119] The remaining materials after the first magnetic separation 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; a magnetic fluid is added: a 10 wt% Fe3O4 nanofluid with a particle size < 50 nm. An alternating magnetic field is externally applied with a frequency of 5 Hz, a peak value of 1.3 T, and the direction is switched 5 times per second to increase the magnetic susceptibility of weakly magnetic iron oxide and adsorb it to the magnetic pole plate;

[0120] 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, pH = 2.5, at a constant temperature of 50 °C, ultrasonic oscillation, power density 500 W / cm³, frequency 35 kHz, and treatment time 35 min; after pickling, vacuum filtration is used to separate the solid residue and the Fe 3+ filtrate;

[0121] 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 glass phase particles are adsorbed to the positive electrode plate, and the original sand grains are recovered by gravity sedimentation;

[0122] S5. The loose particles after magnetic separation in S3 and the original sand grains recovered in S4 are mixed and sent into a plasma torch with a power of 90 kW, an Ar / H2 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, and the cooling rate is 10 7 °C / s to form a dense amorphous / nanocrystalline composite surface layer;

[0123] 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 sputtering is stopped after the film thickness reaches 5 nm.

[0124] The treated sealed sand is mixed with the non-agglomerated original sand grains in S1 and re-backfilled into the gaps of the steel coil high-temperature annealing hood to achieve the reuse and performance enhancement of the sealed sand.

[0125] Example 2:

[0126] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this example and Example 1 are as follows:

[0127] In S2, microwave heating is carried out to 750 °C.

[0128] Example 3:

[0129] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this example and Example 1 are as follows:

[0130] In S2, microwave heating is carried out to 780 °C.

[0131] Example 4:

[0132] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this example and Example 1 are as follows:

[0133] In S2, microwave heating is carried out to 820 °C.

[0134] Example 5:

[0135] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this example and Example 1 are as follows:

[0136] In S2, microwave heating is carried out to 850 °C.

[0137] Comparative Example 1:

[0138] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this comparative example and Example 1 are as follows:

[0139] Secondary magnetic separation is not carried out.

[0140] Comparative Example 2:

[0141] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this comparative example and Example 1 are as follows:

[0142] Pickling treatment is not carried out and the separated blocks are not connected.

[0143] Comparative Example 3:

[0144] A method for recycling sealed sand by magnetic separation in high-temperature annealing of steel coils, the same parts as in Example 1 will not be repeated. The differences between this comparative example and Example 1 are as follows:

[0145] After coarse crushing and screening, magnetic separation is directly carried out to adsorb iron oxide.

[0146] Experimental Example 1:

[0147] Examples 1 to 5 and Comparative Examples 1 to 3 were selected for experimental verification of the treated sealed sand to obtain the free iron oxide capture rate, weakly magnetic iron oxide capture, and virgin sand grain recovery rate;

[0148] 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%;

[0149] 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%;

[0150] The above evaluates the removal efficiency of the magnetic separation process for free iron oxide to ensure its effective removal of magnetic impurities;

[0151] Virgin sand grain recovery rate = (mass of recovered pure virgin sand grains / total mass of virgin sand grains in the initial material) × 100%;

[0152] The virgin sand grain recovery rate evaluates the recovery efficiency of the entire recycling method for virgin sand grains to ensure the efficient recycling of resources.

[0153] Table 1 Data of Experiment 1

[0154]

[0155] 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 free iron oxide capture rate and virgin sand recovery rate of Example 1 reach their peaks, 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.

[0156] In Comparative Example 1, secondary magnetic separation was not carried out, and the weakly magnetic iron oxide capture rate dropped sharply to 63.8%. Because primary magnetic separation can only capture free iron oxide, while secondary magnetic separation uses dynamic fluidized bed separation combined with magnetic fluid technology to increase the magnetic susceptibility of weakly magnetic particles, enabling them to be effectively separated.

[0157] In Comparative Example 2, pickling was not carried out, and the virgin sand grain recovery rate dropped to 69.7%. Because the sintered aggregates in the undissociated blocks contain Fe - Si - O chemical bonds, and the iron silicate phase needs to be selectively dissolved by mixed citric acid - oxalic acid pickling to release the encapsulated virgin sand grains.

[0158] 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 free iron oxide capture rate and recovery rate. Because the glass phase coating was not cracked, the iron oxide particles were shielded, and the sintered aggregates were not dissociated, and a large number of virgin sand grains could not be recovered.

[0159] Based on the inspiration of the ideal embodiments of the present invention, 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 recycling and magnetic separation of sealing sand in high-temperature annealing of steel coils, characterized in that, Including the steps: S1. Coarsely crush the agglomerated sealed sand, and screen and separate the unagglomerated original sand grains and the agglomerated mixture. The agglomerated mixture includes: undissociated original sand grains, glass phase coatings, and sintered aggregates; S2. Treat the agglomerated mixture by combining microwave heating and liquid nitrogen cooling to targetedly break the glass phase coatings, and then separate the 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 to separate weakly magnetic iron oxide through combined dynamic fluidized bed separation and magnetic fluid enhanced separation; S4. Acid wash and dissociate the undissociated blocks, and separate the glass phase and the undamaged original sand grains by electric field separation; S5. Perform surface melting and cooling forming on the loose particles in S3 and the undamaged original sand grains in S4 to restore the roundness of the sand grains; In step S2, the heating rate is 100 °C / min, heated to 750 - 850 °C, and held for 5 - 10 min; the heated agglomerated mixture enters the quenching bin, and liquid nitrogen is evenly sprayed onto the surface of the agglomerated 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 to reduce the surface temperature of the agglomerated mixture to -50 °C; In step S3, the secondary magnetic separation uses combined dynamic fluidized bed separation and magnetic fluid technology. The remaining material after primary magnetic separation is 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 bed layer is 1.5 - 2 m, and the residence time of the material is 5 - 8 s; magnetic fluid is added, and the magnetic fluid is a 10 wt% Fe3O4 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 switches 5 times per second; In step S5, the surface melting instantaneously melts the surface of the sand grains at 15000 - 18000 °C by plasma. The power of the plasma torch is 80 - 100 kW, the mixing ratio of the working gases Ar / H2 is 9:1, the gas flow rate is 15 - 20 L / min, and the depth < 5 μm.

2. A method for recycling sealed sand in high-temperature annealing of steel coils according to claim 1, characterized in that: In step S1, the agglomerated 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-layer vibrating screen is used, with the upper screen aperture of 3 mm and the lower screen aperture of 1 mm, the vibration frequency is 25 - 30 Hz, and the amplitude is 5 mm.

3. A method for recycling sealed sand by magnetic separation in the high-temperature annealing of steel coils according to claim 1, characterized in that: In step S2, the quenched agglomerated mixture is sent into a vortex classifier, and a high-speed air flow forms a spiral upward flow field. The air flow speed is 12 - 18 m / s; the separation time is 2 - 3 min / batch; the separation particle size threshold is 50 μm.

4. A method for recycling and magnetic separation of sealing sand in high-temperature annealing of steel coils according to claim 1, characterized in that: 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 vibration 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.

5. A method for recycling and magnetic separation of sealing sand in high-temperature annealing of steel coils according to claim 1, characterized in that: In step S4, the undissociated mass is put into the pickling tank at a solid-liquid ratio of 1:5-8. The pickling solution 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 through a pH buffer system; the acid solution is kept at a constant temperature of 60 °C, 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; and the solid residue and the Fe 3+ containing filtrate are separated.

6. A method for recycling and magnetic separation of sealed sand in high-temperature annealing of steel coils according to claim 5, 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 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.

7. A method for recycling and magnetic separation of sealing sand in high-temperature annealing of steel coils according to claim 1, characterized in that: In step S5, the molten particles enter the centrifugal atomizer and are rapidly cooled at a rate of 10 7 °C / s at a rotational speed of 25,000 - 30,000 rpm.

Images