Method for recycling and reusing waste magnesium-carbon brick

Abstract

The present application belongs to the technical field of waste magnesium-carbon brick recycling, and particularly relates to a waste magnesium-carbon brick recycling method. The waste magnesium-carbon brick is crushed, sieved, ground and micro-adjusted in particle size to obtain a ground product; the ground product is placed into a microwave ashing furnace cavity for microwave thermal stress dissociation to obtain a dissociation product; the dissociation product is dried and then rapidly placed into a plasma jet system for plasma impurity removal to obtain regenerated magnesium-carbon powder; the regenerated magnesium-carbon powder is subjected to flotation to collect foam products and tank bottom products; the foam products and tank bottom products are respectively ultrasonically cleaned and then dried to obtain a magnesium-rich product and a carbon-rich product; the carbon-rich product is mixed with magnesium sand and metal silicon powder of different particle sizes, a binder is added, and then the mixture is pressed and molded and dried to obtain regenerated magnesium-carbon brick. The present application uses microwave dissociation and plasma impurity removal to more completely separate graphite from periclase, and can also effectively remove active aluminum impurities such as Al4C3 in the material, significantly improving the concentrate purity and effectively inhibiting false particle defects.

Description

Technical Field

[0001] This invention belongs to the field of refractory material recycling, specifically relating to a method for recycling and reusing waste magnesia-carbon bricks. Background Technology

[0002] Magnesia-carbon bricks (MgO-C bricks) are non-burning refractory materials composed of magnesium oxide and high-melting-point carbon materials (mainly graphite), formed under high pressure using phenolic resin and other binders. They combine the excellent resistance to alkaline slag erosion of magnesium oxide with the high thermal conductivity and low thermal expansion of graphite, exhibiting superior high-temperature resistance, thermal shock resistance, erosion resistance, and impermeability. They are widely used in furnace linings of converters, electric furnaces, and ladles, especially in demanding areas such as slag lines, hot spots, and tapholes, directly determining the lifespan and efficiency of smelting equipment. Globally, a large amount of used magnesia-carbon bricks (referred to as "waste magnesia-carbon bricks") are discarded annually, making their recycling and reuse significant. However, existing waste magnesia-carbon brick recycling processes have significant shortcomings, hindering their high-value and large-scale application. Firstly, there are defects in the quality of recycled materials: when waste magnesia-carbon bricks are crushed, a large number of "pseudo-particles" composed of loosely bound grains are generated. These particles have high porosity, low density, and poor strength, severely affecting the density and high-temperature performance of the recycled products. Secondly, additives such as aluminum in waste magnesia-carbon bricks generate non-oxides like Al4C3 during use. These non-oxides react with water to produce gases, causing the recycled products to expand, crack, or even pulverize. Therefore, the key issues in recycling waste magnesia-carbon bricks are solving the problem of pseudo-particle interface bonding and removing harmful impurities such as Al4C3.

[0003] Currently, the main methods for addressing the "fake particles" problem are simple crushing, iron removal, screening, and then mixing with new materials to form the final product. For example, patent CN101851103B involves selecting waste magnesia-carbon bricks, removing surface impurities, crushing and magnetically separating them, followed by pulverization, dehydration, and electromagnetic resonance homogenization. Patent CN112062581A involves crushing waste magnesia-carbon bricks into 3-6mm coarse particles using a jaw crusher or roller crusher, then mixing the coarse particles with alumina, followed by electromagnetic homogenization, holding at 300-400℃, then secondary crushing, impurity removal, magnetic separation, microwave heating, rapid cooling, and finally heating again to 100-200℃ and holding for 30 minutes before use. These existing technologies do not fundamentally separate magnesium oxide and graphite, leaving residual "fake particles."

[0004] For impurities such as Al4C3, the current common method is to remove them by prolonged water immersion followed by high-temperature drying. For example, patent CN103553690A describes a process where waste magnesia-carbon bricks are cleaned of impurities, then sprayed with water, and then placed in a semi-enclosed device. The temperature is raised to 500-800℃ and held for heat treatment. After heat treatment, the bricks are crushed and iron is removed to obtain magnesia-carbon powder. This patent uses a high-temperature "burn-off method" to promote the hydration of aluminum carbide in the recycled magnesia-carbon bricks. However, the high-temperature treatment also burns away valuable graphite, resulting in resource waste and affecting the performance of the recycled magnesia. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for recycling and reusing waste magnesia-carbon bricks. It employs microwave selective heating to generate significant thermal stress between the graphite and periclase phases, effectively disrupting the pseudo-particle interface and enabling more thorough separation of the two phases. Simultaneously, a plasma impurity removal process is introduced. This process effectively removes active aluminum impurities such as Al4C3 from the material, achieving highly efficient impurity removal while protecting the aggregate structure.

[0006] This invention is specifically achieved through the following technical solution: a method for recycling and reusing waste magnesia-carbon bricks proposed according to this invention includes the following steps: S1. After crushing the waste magnesia-carbon bricks, pass them through a 5 mm sieve. Grind the material under the sieve and sort it to collect intermediate grade material. Use an air jet mill to finely adjust the particle size of the collected intermediate grade material so that D50 is in the range of 120~150 μm, and obtain a grinding product with uniform particle size distribution. S2. Place the grinding product obtained in step S1 into the microwave ashing furnace cavity for microwave thermal stress dissociation. After dissociation, cool it in an environment of 15~30 ℃ to obtain the dissociated product. S3. After drying the dissociation product obtained in step S2, quickly place it into a plasma jet system for plasma impurity removal. After completion, turn off the plasma jet, cool to room temperature, and then discharge the material to obtain regenerated magnesium carbon powder. S4. Take a certain amount of the recycled magnesium-carbon powder obtained in step S3 and prepare a slurry with a mass fraction of 15-25%. Pour the slurry into a flotation machine, adjust the pH of the slurry to 9.5-10.5, and then add a modifier, collector, and frother. In the flotation machine, aerate and stir the slurry for flotation. After completion, collect the froth product and the bottom product separately. Clean the collected bottom product with deionized water using ultrasonic cleaning and then dry it to obtain a magnesium-rich product. Clean the collected froth product with deionized water using ultrasonic cleaning and then dry it to obtain a carbon-rich product. S5. The obtained carbon-rich product is mixed with magnesia of different particle sizes and metallic silicon powder with a particle size ≤100 μm at 20 ℃ and 25 rpm for 150 s to obtain a mixture. Then, phenolic resin is added to the mixture, and it is mixed again at 20 ℃ and 25 rpm for 150 s. Then, the mixture is allowed to stand for 24 h to obtain a compound. The compound is pressed into shape at 150~200 MPa and held for 10~20 s. After the pressed sample is dried, recycled magnesia-carbon bricks are obtained.

[0007] In the aforementioned method for recycling and reusing waste magnesia-carbon bricks, in step S1, the undersize material is ground using one or more of the following methods: ball mill, Raymond mill, vertical mill, and air jet mill. During ball milling, the mill speed is 200-400 r / min, the grinding balls are zirconia balls, the ball-to-material mass ratio is 4:1, the grinding medium is anhydrous ethanol, and the grinding medium to raw material mass ratio is (1.2-2):1. When using a Raymond mill or vertical mill, the roller mill pressure is 1.2-1.8 MPa. A double-layer high-frequency vibrating screen (200 mesh and 325 mesh) is used for separation, with a separator speed of 800-1200 r / min, to remove fine mud and coarse particles, and collect intermediate-grade material.

[0008] Preferably, in step S2, the microwave thermal stress dissociation operates at a frequency of 2.00~2.50 GHz, a power of 2~5 kW, a temperature of 300~400 ℃, and is continuously irradiated for 3~5 min.

[0009] Preferably, in step S3, after the dissociation product is dried at 110 °C for 2-4 h, it is subjected to plasma purification. The plasma source is a coupled low-temperature plasma processor with a power range of 0-5 kW. The working gas for plasma purification is high-purity oxygen with a flow rate of 10-30 L / min. The plasma treatment power is 200-400 W, the treatment time is 30-60 s, and the process is repeated 2-3 times. The temperature is controlled at 350-400 °C.

[0010] Preferably, the modifier is one or more of water glass, sodium silicate, and sodium metasilicate, and the amount added is 0.5~1.0 g / kg based on the mass of the recycled magnesium carbon powder; the collector is one or more of kerosene, diesel oil, and oxidized paraffin soap, and the amount added is 0.8~1.2 g / kg based on the mass of the recycled magnesium carbon powder; the foaming agent is one or more of pine oil and methyl isobutyl methanol, and the amount added is 0.2~0.4 g / kg based on the mass of the recycled magnesium carbon powder.

[0011] Preferably, in step S4, the flotation machine speed is 1800~2200 r / min, and the flotation time is 3~5 min; the bottom product is ultrasonically cleaned with deionized water 5~8 times, and then dried at 110℃ for 12 h to obtain a magnesium-rich product; the foam product is ultrasonically cleaned with deionized water 5~8 times, and then dried at 110℃ for 12 h to obtain a carbon-rich product.

[0012] Preferably, in the mixture described in step S5, the mass percentages of carbon-rich products, magnesia of different particle sizes, and metallic silicon powder are 80-92%, 3-15%, and 1-5%, respectively; the magnesia of different particle sizes includes fused magnesia with a particle size of 3-1 mm, fused magnesia with a particle size ≤1 mm, and fused magnesia with a particle size of 200 mesh; and the phenolic resin accounts for 2-6% of the total mass of the mixture.

[0013] Furthermore, the magnesia of different particle sizes includes fused magnesia with a particle size of 3~1 mm, fused magnesia with a particle size of ≤1 mm, and magnesium-rich products with a particle size of 200 mesh, wherein the magnesium-rich products are the magnesium-rich products obtained in step S4.

[0014] Preferably, in step S5, the pressed sample is first dried at 80 ℃ for 8 h, then dried at 120 ℃ for 8 h, and finally dried at 180 ℃ for 8 h to obtain recycled magnesia-carbon bricks.

[0015] The aforementioned method for recycling and reusing waste magnesia-carbon bricks produces recycled magnesia-carbon bricks with a room temperature flexural strength of 6-10 MPa, a room temperature compressive strength of 40-55 MPa, a bulk density of 2.6-3.0 g / cm³, and an apparent porosity of 10-15%.

[0016] Compared with the prior art, the present invention has at least the following advantages: This invention employs microwave selective dissociation, where microwave thermal stress generates significant thermal stress between the graphite and periclase phases, breaking down the bonded phases from within the material interface. This allows for a more thorough separation of the graphite and periclase phases, achieving true dissociation and yielding more complete recycled aggregate. Simultaneously, a plasma impurity removal process is used. This process effectively removes active aluminum impurities such as Al4C3 from the material, achieving high-efficiency impurity removal while protecting the aggregate structure. After microwave dissociation and plasma impurity removal, the impurity peak intensity in the carbon-rich product obtained from flotation is significantly reduced, and the periclase and magnesium aluminum spinel peaks nearly disappear. Therefore, microwave dissociation effectively disrupts the pseudo-particle interface bonding, allowing for complete dissociation of graphite and periclase, thereby effectively improving the purity of graphite in the flotation froth product.

[0017] This invention utilizes the differences in surface wettability of minerals, and through reagent regulation, it can enrich graphite in the foam product and magnesia in the bottom product, significantly improving the purity of both types of concentrates. The recycling method of this invention effectively removes impurities, suppresses pseudo-particle defects, and yields chemically stable concentrates that can be directly used to produce high-quality recycled magnesia-carbon bricks, accelerating resource recycling and enhancing the reuse value of waste magnesia-carbon bricks.

[0018] Instruction manual illustrations Figure 1 This is the XRD pattern of the carbon-rich product obtained in step S4 of Example 1.

[0019] Figure 2 This is the XRD pattern of the carbon-rich product obtained in step S2 of the comparative example. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Unless otherwise specified, all conditions in the following embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified are all commercially available products. Unless otherwise specified, the scientific and technical terms and experimental methods in this invention are based on the conventional understanding and existing standard methods of those skilled in the art. It should be understood that the parameters such as temperature and holding time involved in this invention are approximate values ​​and are used for illustrative purposes; those skilled in the art can make reasonable adjustments according to actual needs.

[0022] Example 1 S1. Waste Grinding: Take 1 kg of used magnesia-carbon brick waste (waste magnesia-carbon brick), coarsely crush it with a jaw crusher and pass it through a 5 mm sieve. The material under the sieve is then finely crushed in a ball mill. The grinding balls are zirconia balls (φ10 mm and φ5 mm zirconia balls are mixed at a mass ratio of 1:2), the ball-to-material mass ratio is 4:1, the grinding medium is anhydrous ethanol, and the mass ratio of grinding medium to raw material is 1.2:1. The ball mill speed is 300 rpm, and the grinding time is 12 h. After completion, the material is separated by a double-layer high-frequency vibrating screen of 200 mesh and 325 mesh. The intermediate grade material is collected and the particle size of the collected intermediate grade material is finely adjusted by an air jet mill so that D50 is in the range of 120~150 μm, resulting in a grinding product of 832 g with uniform particle size distribution.

[0023] S2. Microwave dissociation: The grinding product obtained in step S1 is spread evenly on a quartz tray and then placed in a microwave ashing furnace cavity for microwave thermal stress dissociation. The microwave frequency is 2.45 GHz, the power is 5 kW, the irradiation is continuous for 5 min, and the temperature is controlled at 350 ℃. After dissociation, the quartz tray is removed and cooled at room temperature of 20-25℃ to obtain the dissociated product.

[0024] S3. Plasma purification: The dissociation product obtained in step S2 is dried at 110 °C for 2 h, and then quickly placed into a plasma jet system. The plasma source is a coupled low-temperature plasma processor, the working gas is high-purity oxygen, the flow rate is 25 L / min, the plasma processing power is 400 W, the processing time is 45 s, and it is repeated twice. The temperature is controlled at 350~400 °C. After completion, the plasma jet is turned off, and the material is discharged after cooling to room temperature to obtain regenerated magnesium carbon powder.

[0025] S4. Flotation: Take 500 g of the regenerated magnesium-carbon powder obtained in step S3 and prepare a slurry with a mass fraction of 20%. Pour the slurry into the flotation machine, add NaOH solution to adjust the pH of the slurry to 10, then add 0.4 g of water glass (water glass modulus M = 2.0~3.4) and stir for 20 s. Then add 0.3 g of kerosene, 0.2 g of diesel oil and 0.15 g of pine oil. Aerate and stir at 2000 r / min for 5 min. Collect the froth product (rich in carbon) and the bottom product (rich in magnesium) separately. Ultrasonically wash the collected bottom product with deionized water 5 times, and then dry it at 110℃ for 12 h to obtain the magnesium-rich product. Ultrasonically wash the collected froth product with deionized water 5 times, and then dry it at 110℃ for 12 h to obtain the carbon-rich product.

[0026] Carbon-rich products were subjected to XRD analysis, such as... Figure 1 As shown, the carbon-rich products contain a large amount of graphite phase and only a small amount of brucite phase.

[0027] S5. Mixing: Take 50 g of the carbon-rich product obtained in step S4, add 350 g of fused magnesia with a particle size of 3~1 mm, 250 g of fused magnesia with a particle size of ≤1 mm, 300 g of fused magnesia with a particle size of 200 mesh, and 50 g of metallic silicon powder with a particle size of ≤100 μm. Mix in a mixer or blender at 20 ℃ and 25 rpm for 150 s to obtain a mixture. Then add phenolic resin to the mixture, with the phenolic resin accounting for 5% of the total mass of the mixture. Mix again at 20 ℃ and 25 rpm for 150 s, and then let it stand for 24 h to obtain a mixed material.

[0028] S6. Molding: Press the mixture obtained in step S5 at 150 MPa and hold the pressure for 15 s to obtain a strip sample of 25×25×150 mm. Make four strip samples of 25×25×150 mm in the same way.

[0029] S7. Regenerated Magnesia-Carbon Bricks: The four strip samples obtained in step S6 are first dried at 80 ℃ for 8 h, then dried at 120 ℃ for 8 h, and finally dried at 180 ℃ for 8 h to obtain recycled magnesia-carbon bricks.

[0030] The resulting recycled magnesia-carbon bricks were heat-treated at 1100℃ for 3 hours under carbon-embedded conditions. Their flexural strength, compressive strength, bulk density, and apparent porosity at room temperature were then tested. The flexural strength at room temperature was tested according to GB / T 3001-2017, and the compressive strength at room temperature was tested according to GB / T 5072-2008. The sample was placed in the center of a pressure plate and subjected to a pressure of 1 MPa·s⁻¹. -1 The load is applied at a rate until the specimen fails, and the maximum load is recorded. The calculation formula is: σ = Fmax / A0, where σ is the compressive strength (MPa), Fmax is the maximum load (N), and A0 is the area under pressure (mm). 2 Bulk density and apparent porosity were tested according to GB / T 2997-2015.

[0031] Tests showed that the recycled magnesia-carbon bricks produced in this embodiment have a room temperature flexural strength of 6.3 MPa, a room temperature compressive strength of 46.4 MPa, a bulk density of 2.75 g / cm³, and an apparent porosity of 14.6%.

[0032] Comparative Example S1. Waste material grinding: Same as step S1 in Example 1.

[0033] S2. Flotation: Take 500 g of the grinding product obtained in step S1 and prepare a 20% (w / w) slurry. Pour the slurry into the flotation machine. Perform the remaining operations as in step S4 of Example 1 to obtain a magnesium-rich product and a carbon-rich product. Perform XRD analysis on the carbon-rich product, such as... Figure 2 As shown.

[0034] S3. Mixing: The obtained carbon-rich product is processed according to step S5 of Example 1 to obtain mixture D.

[0035] S4. Molding: The obtained mixture D is pressed and shaped at 150 MPa and held for 15 s to obtain a strip sample D of 25×25×150 mm. Four strip samples D of 25×25×150 mm are made in this way.

[0036] S5. Regenerated Magnesia-Carbon Bricks: The strip sample D obtained in step S4 is first dried at 80 ℃ for 8 h, then dried at 120 ℃ for 8 h, and finally dried at 180 ℃ for 8 h to obtain recycled magnesia-carbon bricks D.

[0037] The obtained recycled magnesia-carbon brick D was heat-treated at 1100℃ for 3 hours under carbon embedding conditions, and its room temperature flexural strength, room temperature compressive strength, bulk density and apparent porosity were tested. The test methods were the same as in Example 1.

[0038] The recycled magnesia-carbon brick D obtained in this comparative example has a room temperature flexural strength of 3.6 MPa, a room temperature compressive strength of 23.2 MPa, a bulk density of 2.43 g / cm³, and an apparent porosity of 17.4%.

[0039] Figure 1 This is the XRD pattern of the carbon-rich product obtained in step S4 of Example 1. Figure 2 This is the XRD pattern of the carbon-rich product obtained in step S2 of the comparative example. Figure 1 and Figure 2 The comparison shows that, in the comparative example without microwave dissociation and plasma purification, the carbon-rich product obtained by flotation contained not only the main graphite peak but also strong periclase diffraction peaks, MgA spinel, and brucite impurity peaks. However, in Example 1, after microwave dissociation and plasma purification, the intensity of these impurity peaks in the carbon-rich product obtained by flotation was significantly reduced, and the periclase and MgA spinel peaks almost disappeared. This indicates that microwave selective thermal stress dissociation can effectively disrupt the pseudo-particle interface bonding, allowing for complete dissociation of graphite from periclase, and significantly improving the graphite purity in the flotation froth product.

[0040] Take 20 g each of the dissociation product obtained in step S2 of Example 1 (denoted as sample M) and the regenerated magnesium carbon powder obtained in step S3 of Example 1 (denoted as sample P), and place them in 250 mL beakers. Add 100 mL of deionized water to each beaker, and stir at 200 r / min for 2 h at 25 ℃, followed by standing for 22 h. After filtration, determine the Al content in the filtrate using ICP-OES. 3+ The concentration was determined, and the loss on ignition of the solid residue was measured according to GB / T 5069-2015. The results showed that the Al concentration in the filtrate of sample M was [missing value]. 3+ The concentration was 156.3 mg / L, and the Al in the filtrate of sample P was... 3+ The concentration was only 4.7 mg / L, a reduction of 97.0%; the loss on ignition decreased from 5.6% (sample M) to 3.3% (sample P). This fully demonstrates that plasma impurity removal can efficiently convert or remove active aluminum impurities such as Al4C3, achieving low-temperature and efficient impurity removal while protecting the aggregate structure.

[0041] The above comparison shows that the carbon-rich products obtained by grinding waste magnesia-carbon bricks through microwave dissociation, plasma purification, and flotation, and then adding magnesia sand and silicon powder of different particle sizes, result in significantly improved physical, chemical, and mechanical properties of the recycled magnesia-carbon bricks.

[0042] Example 2 S1. Waste Grinding: Take 1 kg of used magnesia-carbon brick waste (waste magnesia-carbon brick), coarsely crush it with a jaw crusher and pass it through a 5 mm sieve. The material under the sieve is then finely crushed in a ball mill. The grinding balls are zirconia balls (φ10 mm and φ5 mm zirconia balls mixed at a mass ratio of 1:2), the ball-to-material mass ratio is 4:1, the grinding medium is anhydrous ethanol, the grinding medium to raw material mass ratio is 1.2:1, the ball mill speed is 350 rpm, and the grinding time is 12 h. After completion, the material is sorted using a high-frequency vibrating screen (200 mesh and 325 mesh double layer) to collect the intermediate grade material. The collected intermediate grade material is then finely adjusted in particle size using an air jet mill to make D50 within the range of 120~150 μm, resulting in 827 g of grinding product with uniform particle size distribution.

[0043] S2. Microwave dissociation: The grinding product obtained in step S1 is spread evenly on a quartz tray and then placed in a microwave ashing furnace cavity for microwave thermal stress dissociation. The microwave frequency is 2.3 GHz, the power is 4 kW, the irradiation is continuous for 5 min, and the temperature is controlled at 350 ℃. After dissociation, the quartz tray is removed and placed at room temperature of 20-25℃ to cool, and the dissociated product is obtained.

[0044] S3. Plasma purification: The dissociation product obtained in step S2 is dried at 110 °C for 2 h, and then quickly placed into a plasma jet system. The plasma source is a coupled low-temperature plasma processor, the working gas is high-purity oxygen, the flow rate is 20 L / min, the plasma processing power is 400 W, the processing time is 50 s, and it is repeated twice. The temperature is controlled at 350~400 °C. After completion, the plasma jet is turned off, and the material is discharged after cooling to room temperature to obtain regenerated magnesium carbon powder.

[0045] S4. Flotation: Take 500 g of the regenerated magnesium-carbon powder obtained in step S3 and prepare a slurry with a mass fraction of 20%. Pour the slurry into the flotation machine, add NaOH solution to adjust the pH of the slurry to 10, then add 0.4 g of sodium silicate aqueous solution (sodium silicate aqueous solution mass fraction of 30%~50%) and stir for 20 s. Then add 0.3 g of kerosene, 0.3 g of diesel oil and 0.1 g of pine oil. Aerate and stir at 2000 r / min for 5 min. Collect the foam product (rich in carbon) and the bottom product (rich in magnesium) separately. Ultrasonically wash the collected bottom product with deionized water 5 times, and then dry it at 110℃ for 12 h to obtain the magnesium-rich product. Ultrasonically wash the collected foam product with deionized water 5 times, and then dry it at 110℃ for 12 h to obtain the carbon-rich product.

[0046] S5. Mixing: Take 50 g of the carbon-rich product obtained in step S4, add 350 g of fused magnesia with a particle size of 3~1 mm, 250 g of fused magnesia with a particle size of ≤1 mm, 300 g of the magnesium-rich product obtained in step S4 with a particle size of 200 mesh, and 50 g of metallic silicon powder with a particle size of ≤100 μm. Mix in a mixer or blender at 20 ℃ and 25 rpm for 150 s to obtain a mixture. Then add phenolic resin to the mixture, with the phenolic resin accounting for 4% of the total mass of the mixture. Mix again at 20 ℃ and 25 rpm for 150 s, and then let it stand for 24 h to obtain a mixed material.

[0047] S6. Molding: Press the mixture obtained in step S5 at 150 MPa and hold the pressure for 15 s to obtain a strip sample of 25×25×150 mm. Make four strip samples of 25×25×150 mm in the same way.

[0048] S7. Regenerated Magnesia-Carbon Bricks: The four strip samples obtained in step S6 are first dried at 80 ℃ for 8 h, then dried at 120 ℃ for 8 h, and finally dried at 180 ℃ for 8 h to obtain recycled magnesia-carbon bricks.

[0049] The obtained recycled magnesia-carbon bricks were heat-treated at 1100℃ for 3 hours under carbon embedding conditions, and their room temperature flexural strength, room temperature compressive strength, bulk density and apparent porosity were tested. The testing methods were the same as in Example 1.

[0050] The recycled magnesia-carbon bricks obtained in this embodiment have a room temperature flexural strength of 6.5 MPa, a room temperature compressive strength of 45.8 MPa, a bulk density of 2.77 g / cm³, and an apparent porosity of 12.8%.

[0051] Example 3 S1. Waste Grinding: Take 1 kg of used magnesia-carbon brick waste (waste magnesia-carbon brick), coarsely crush it with a jaw crusher and pass it through a 5 mm sieve. The material under the sieve is then finely crushed in a ball mill. The grinding balls are zirconia balls (φ10 mm and φ5 mm zirconia balls mixed at a mass ratio of 1:2), with a ball-to-material mass ratio of 4:1. The grinding medium is anhydrous ethanol, with a grinding medium to raw material mass ratio of 1.2:1. The ball mill speed is 400 rpm, and the grinding time is 12 h. After completion, the material is sorted using a high-frequency vibrating screen (200 mesh and 325 mesh double layer) to collect the intermediate grade material. The intermediate grade material is then surface modified and then finely adjusted in particle size using an air jet mill to make D50 within the range of 120~150 μm, resulting in a uniformly distributed grinding product of 814 g.

[0052] S2. Microwave dissociation: The grinding product obtained in step S1 is spread evenly on a quartz tray and then placed in a microwave ashing furnace cavity for microwave thermal stress dissociation. The microwave frequency is 2.00 GHz, the power is 4 kW, the irradiation is continuous for 5 min, and the temperature is controlled at 300 ℃. After dissociation, the quartz tray is removed and placed at room temperature of 20-25℃ to cool, and the dissociated product is obtained.

[0053] S3. Plasma purification: The dissociation product obtained in step S2 is dried at 110 °C for 2 h, and then quickly placed into a plasma jet system. The working gas is high-purity oxygen with a flow rate of 30 L / min, the plasma treatment power is 300 W, the treatment time is 60 s, and the process is repeated twice. The temperature is controlled at 350~400 °C. After completion, the plasma jet is turned off, and the material is discharged after cooling to room temperature to obtain regenerated magnesium carbon powder.

[0054] S4. Flotation: Take 500 g of the regenerated magnesium-carbon powder obtained in step S3 and prepare a slurry with a mass fraction of 25%. Pour the slurry into the flotation machine, add NaOH solution to adjust the pH of the slurry to 10.5, then add 0.5 g of water glass (water glass modulus M=2.0~3.4) and stir for 20 s. Then add 0.3 g of kerosene, 0.3 g of diesel oil and 0.2 g of pine oil. Aerate and stir at 2000 r / min for 5 min. Collect the foam product (rich in carbon) and the bottom product (rich in magnesium) separately. Ultrasonically wash the collected foam product and bottom product with deionized water 5 times, and then dry them at 110℃ for 12 h to obtain the carbon-rich product and the magnesium-rich product, respectively.

[0055] S5. Mixing: Take 70 g of the carbon-rich product obtained in step S4, add 340 g of fused magnesia with a particle size of 3~1 mm, 250 g of fused magnesia with a particle size of ≤1 mm, 300 g of fused magnesia with a particle size of 200 mesh, and 40 g of metallic silicon powder with a particle size of ≤100 μm. Mix in a mixer or blender at 20 ℃ and 25 rpm for 150 s to obtain a mixture. Then add phenolic resin to the mixture, with the phenolic resin accounting for 4% of the total mass of the mixture. Mix again at 20 ℃ and 25 rpm for 150 s, and then let it stand for 24 h to obtain a mixed material.

[0056] S6. Molding: Same as step S6 in Example 1.

[0057] S7. Regenerated magnesia-carbon bricks: Same as step S7 in Example 1.

[0058] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for recycling and reusing waste magnesia-carbon bricks, characterized in that, Includes the following steps: S1. After crushing the waste magnesia-carbon bricks, pass them through a 5 mm sieve. Grind the material under the sieve and sort it to collect intermediate grade material. Use an air jet mill to finely adjust the particle size of the collected intermediate grade material so that D50 is in the range of 120~150 μm, and obtain a grinding product with uniform particle size distribution. S2. Place the grinding product obtained in step S1 into the microwave ashing furnace cavity for microwave thermal stress dissociation. After dissociation, cool it in an environment of 15~30 ℃ to obtain the dissociated product. S3. After drying the dissociation product obtained in step S2, quickly place it into a plasma jet system for plasma impurity removal. After completion, turn off the plasma jet, cool to room temperature, and then discharge the material to obtain regenerated magnesium carbon powder. S4. Take a certain amount of the recycled magnesium-carbon powder obtained in step S3 and prepare a slurry with a mass fraction of 15-25%. Pour the slurry into a flotation machine, adjust the pH of the slurry to 9.5-10.5, and then add a modifier, collector, and frother. In the flotation machine, aerate and stir the slurry for flotation. After completion, collect the froth product and the bottom product separately. Clean the collected bottom product with deionized water using ultrasonic cleaning and then dry it to obtain a magnesium-rich product. Clean the collected froth product with deionized water using ultrasonic cleaning and then dry it to obtain a carbon-rich product. S5. The obtained carbon-rich product is mixed with magnesia of different particle sizes and metallic silicon powder with a particle size ≤100 μm at 20 ℃ and 25 rpm for 150 s to obtain a mixture. Then, phenolic resin is added to the mixture, and it is mixed again at 20 ℃ and 25 rpm for 150 s. Then, the mixture is allowed to stand for 24 h to obtain a compound. The compound is pressed into shape at 150~200 MPa and held for 10~20 s. After the pressed sample is dried, recycled magnesia-carbon bricks are obtained.

2. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S1, the undersize material is ground using one or more of the following methods: ball mill, Raymond mill, vertical mill, and air jet mill. When ball milling, the mill speed is 200~400 r / min, the grinding balls are zirconia balls, the ball-to-material mass ratio is 4:1, the grinding medium is anhydrous ethanol, and the grinding medium to raw material mass ratio is (1.2~2):

1. When using Raymond mill or vertical mill for grinding, the roller mill pressure is 1.2~1.8 MPa. A double-layer high-frequency vibrating screen with 200 mesh and 325 mesh is used for separation, and the separator speed is 800~1200 r / min to collect intermediate grade material.

3. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S2, the microwave thermal stress dissociation operates at a frequency of 2.00~2.50 GHz, a power of 2~5 kW, and a temperature of 300~400 ℃, with continuous irradiation for 3~5 min.

4. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S3, the dissociation products are dried at 110 °C for 2-4 h and then subjected to plasma purification. The working gas for plasma purification is high-purity oxygen with a flow rate of 10-30 L / min, a plasma treatment power of 200-400 W, a treatment time of 30-60 s, and the process is repeated 2-3 times. The temperature is controlled at 350-400 °C.

5. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S4, the modifier is one or more of water glass, sodium silicate, and sodium metasilicate, and the amount added is 0.5~1.0 g / kg based on the mass of the recycled magnesium carbon powder; the collector is one or more of kerosene, diesel oil, and oxidized paraffin soap, and the amount added is 0.8~1.2 g / kg based on the mass of the recycled magnesium carbon powder; the foaming agent is one or more of pine oil and methyl isobutyl methanol, and the amount added is 0.2~0.4 g / kg based on the mass of the recycled magnesium carbon powder.

6. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S4, the flotation machine speed is 1800~2200 r / min, and the flotation time is 3~5 min; the bottom product is ultrasonically cleaned with deionized water 5~8 times, and then dried at 110℃ for 12 h to obtain magnesium-rich product; the foam product is ultrasonically cleaned with deionized water 5~8 times, and then dried at 110℃ for 12 h to obtain carbon-rich product.

7. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In the mixture described in step S5, the mass percentages of carbon-rich products, magnesia of different particle sizes, and metallic silicon powder are 80-92%, 3-15%, and 1-5%, respectively; the magnesia of different particle sizes includes fused magnesia with a particle size of 3-1 mm, fused magnesia with a particle size ≤1 mm, and fused magnesia with a particle size of 200 mesh; the mass of phenolic resin added accounts for 2-6% of the total mass of the mixture.

8. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 7, characterized in that, The different particle size magnesia includes fused magnesia with a particle size of 3~1 mm, fused magnesia with a particle size of ≤1 mm, and magnesium-rich products with a particle size of 200 mesh. The magnesium-rich products are the magnesium-rich products obtained in step S4.

9. The method for recycling and reusing waste magnesia-carbon bricks as described in claim 1, characterized in that, In step S5, the pressed sample is first dried at 80 ℃ for 8 h, then dried at 120 ℃ for 8 h, and finally dried at 180 ℃ for 8 h to obtain recycled magnesia-carbon bricks.

10. The method for recycling and reusing waste magnesia-carbon bricks as described in any one of claims 1-9, characterized in that, The resulting recycled magnesia-carbon bricks have a room temperature flexural strength of 6~10 MPa, a room temperature compressive strength of 40~55 MPa, a bulk density of 2.6~3.0 g / cm³, and an apparent porosity of 10~15%.

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