A method for preparing 45 molecate from solid waste coal gangue

Abstract

This application relates to the field of coal gangue treatment technology, specifically to a method for preparing 45 molecate from solid waste coal gangue, comprising the following steps: crushing and screening the solid waste coal gangue, followed by microwave irradiation; then grinding and drying in a planetary ball mill; adding a composite alkali solution (an aqueous solution of NaOH and Na2CO3) for stirring and activation; adding an interface modifier and composite nanoparticles to the activated coal gangue powder to obtain modified powder; mixing with water, kneading, aging, followed by static pressing and pressure holding to obtain a green body; uniformly spraying an aqueous solution of a mineralizer onto the surface of the green body; pre-drying after spraying; then performing segmented calcination; and finally cooling to room temperature to obtain 45 molecate. By synergistically treating coal gangue through microwave irradiation, composite alkali activation, interface modification, and composite mineralizer, the problems of inertness and poor interfacial compatibility of the silicon-aluminum components in coal gangue are solved, while also achieving the resource utilization of solid waste.

Description

Technical Field

[0001] This application relates to the field of coal gangue treatment technology, specifically to a method for preparing 45 molecate from solid waste coal gangue. Background Technology

[0002] Mullite, a material with a high temperature stability, combines the properties of mullite with the low expansion coefficient of cordierite, making it widely used in metallurgy, building materials, and environmental protection. Traditional preparation processes rely on high-purity bauxite, kaolin, and other high-quality mineral raw materials, resulting in high resource consumption and production costs.

[0003] Coal gangue, a solid waste generated during coal mining and washing, has an annual discharge exceeding 300 million tons. Its stockpiling not only occupies vast amounts of land but also easily leads to environmental problems such as spontaneous combustion and groundwater pollution. Of particular note is that the main components of coal gangue are SiO2 and Al2O3, which highly match the silicon-aluminum composition requirements of 45 Mullate, making it an ideal low-cost raw material for preparing this material. However, when using coal gangue as a base material directly in the preparation process, a key technical bottleneck exists: its silicon-aluminum components exist as inert mineral phases, lacking effective bonding sites with the generated mullite crystals, resulting in poor interfacial compatibility and weak bonding between the two phases, forming obvious interfacial gaps. This interfacial defect directly causes low product density and insufficient mechanical properties. Especially under corrosive conditions, the medium easily penetrates along the interface, significantly reducing corrosion resistance and limiting the high-value utilization of coal gangue.

[0004] Therefore, there is an urgent need to develop interface bonding modification technology to strengthen the bonding force between the two by constructing a silicon-aluminum component-mullite transition layer, thereby improving the overall performance of the product and promoting the resource utilization of coal gangue and the low-cost industrialization of 45 mullite materials. Summary of the Invention

[0005] This application provides a method for preparing 45 molecate from solid waste coal gangue. The method involves microwave irradiation, compound alkali activation, interface modification, and synergistic treatment of coal gangue with compound mineralizers. This not only solves the problems of inertness and poor interfacial compatibility of the silicon and aluminum components in coal gangue, but also realizes the resource utilization of solid waste.

[0006] To achieve the above objectives, one technical solution adopted by the present invention is:

[0007] This application provides a method for preparing 45 molecate from solid waste coal gangue, comprising the following steps:

[0008] Step 1. The solid waste coal gangue is crushed by a jaw crusher, screened, and then microwave irradiated. After irradiation, it is fed into a planetary ball mill for grinding and then dried to obtain homogeneous coal gangue powder.

[0009] Step 2. Add the homogeneous coal gangue powder to the composite alkaline solution, stir and activate to obtain activated coal gangue powder.

[0010] Step 3. Add an interface modifier to the activated coal gangue powder, stir, and then add composite nanoparticles to obtain modified powder.

[0011] Step 4. Add water to the modified powder, mix and knead, then age, followed by static pressing and pressing to obtain a green body.

[0012] Step 5. The aqueous solution of the mineralizer is evenly sprayed onto the surface of the billet, pre-dried after spraying, then calcined in stages, and cooled to room temperature to obtain 45 Molecate.

[0013] In this application, after the coarse coal gangue particles in step 1 are irradiated with microwaves, the different mineral phases inside them undergo selective heating due to differences in dielectric properties, resulting in uneven thermal expansion and the formation of thermal stress. This can induce lattice distortion and grain boundary microcracks, reducing the hardness and toughness of the material. The non-thermal effects of microwaves can also disrupt the stable Si-O and Al-O bonds in the coal gangue, providing a pre-fabricated fracture path for subsequent alkali penetration and ultrafine grinding. After grinding in a planetary ball mill, the specific surface area of ​​the powder increases, exposing more fresh active surfaces and providing conditions for alkali activation.

[0014] In step 2, the NaOH in the composite alkaline solution provides a strongly alkaline environment, and its OH... - As a nucleophile, Na₂CO₃ attacks the bridging oxygen bonds of silicon-oxygen tetrahedra and aluminum-oxygen octahedra in coal gangue, efficiently breaking Si-O and Al-O bonds. Na₂CO₃ regulates the reaction intensity through pH buffering, avoiding the loss of active components due to local over-alkaliness, and forms aluminum carbonate intermediates with dissolved aluminum ions, achieving directional activation and efficient retention of silicon-aluminum components.

[0015] In step 3, adding water to the clay causes the modified powder particles to rearrange themselves through the liquid film effect. During aging, the moisture distribution tends to be uniform, and the particles undergo plastic deformation under humidity and temperature control, initially eliminating internal stress. High-pressure static pressing ensures close contact between the particles, forming a dense green body structure with nanoparticles as the framework, providing a foundation for high-temperature sintering.

[0016] In step 4, adding water to the clay causes the modified powder particles to rearrange themselves through the liquid film effect. During aging, the moisture distribution tends to be uniform, and the particles undergo plastic deformation under humidity and temperature control, initially eliminating internal stress. High-pressure static pressing ensures close contact between the particles, forming a dense green body structure with nanoparticles as the framework, providing a foundation for high-temperature sintering.

[0017] In step 5, surface mineralization and crystal growth occur: the mineralizer sprayed onto the surface of the billet decomposes during calcination; the fluoride ions generated by sodium fluorosilicate lower the melting temperature of the system; and the borosilicate glass phase generated by boric acid fills the micropores, providing channels for the migration of active silicon-aluminum units. During segmented calcination, residual moisture and organic matter are removed at low temperatures, while at high temperatures, guided by the mineralizer and nano-heterogeneous crystal nuclei, the active units rearrange in an orderly manner into the mullite crystal phase, forming continuous bonds with the matrix, eliminating interfacial gaps, and yielding high-density, corrosion-resistant 45 mullite.

[0018] Preferably, in step 1, the jaw crusher crushes the particles to a size ≤ 5mm; the microwave irradiation power is 700-900W, and the time is 20-30min.

[0019] Preferably, in step 1, the planetary ball mill rotates at a speed of 300-500 r / min, and the powder after grinding has a D50 ≤ 5 μm; the drying temperature is 100-120℃, and the drying time is 2-3 h.

[0020] Preferably, the stirring activation temperature in step 2 is 25-35℃, and the time is 20-30 min; the composite alkaline solution is an aqueous solution formed by mixing NaOH and Na2CO3; the mass ratio of NaOH to Na2CO3 is (1-3):1; the mass fraction of the composite alkaline solution is 4wt%-6wt%; and the mass-volume ratio of the homogeneous coal gangue powder to the composite alkaline solution is 1g:(8-12)mL.

[0021] Preferably, in step 3, the interface modifier includes either KH550 or KH560.

[0022] Preferably, in step 3, the composite nanoparticles include any two of nano-Al2O3, nano-SiO2, nano-ZrO2, and nano-TiO2.

[0023] Preferably, in step 3, the mass ratio of the activated coal gangue powder, the interface modifier, and the composite nanoparticles is 100:(0.3-0.8):(2-4).

[0024] Preferably, the kneading time in step 4 is 15-30 min; the amount of water added is 5wt%-8wt% of the mass of the modified powder; the aging temperature is 23-27℃, the humidity is 60%-70%, and the time is 12-24 h; the static pressing pressure is 150-200 MPa; and the holding time is 30-60 s.

[0025] Preferably, in step 5, the mineralizing agent is a mixture of sodium fluorosilicate and boric acid; the mass ratio of sodium fluorosilicate to boric acid is (0.8-1.2):1; the mass fraction of the aqueous solution prepared by the mineralizing agent is 10%-15%, and the spraying amount is 2wt%-3wt% of the mass of the green body.

[0026] Preferably, in step 5, the pre-baking temperature is 60-100℃ and the time is 0.5-2h; the segmented calcination includes a first stage calcination and a second stage calcination; the first stage calcination temperature is 600-800℃ and the time is 1-2h; the second stage calcination temperature is 1550-1600℃ and the time is 3-5h.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This application provides a method for preparing 45 mullicat from solid waste coal gangue. In this application, after microwave irradiation, the coarse coal gangue particles generate thermal stress due to the difference in thermal expansion between different mineral phases such as quartz and kaolinite, inducing microcracks at grain boundaries. Subsequent ball milling preserves the active surface, providing conditions for the penetration of the alkaline system. NaOH in the composite alkaline solution provides a strongly alkaline environment, with its hydroxide ions acting as nucleophiles, rapidly attacking the bridging oxygen bonds between silicon-oxygen tetrahedra and aluminum-oxygen octahedra, efficiently breaking Si-O and Al-O bonds. Na₂CO₃ regulates the reaction intensity through the pH buffering effect, while simultaneously forming a stable aluminum carbonate intermediate with dissolved aluminum ions, preventing the loss of active components. The coupling of these two processes achieves directional activation and efficient retention of the silicon-aluminum components. The hydroxyl groups at the ends of the interface modifier molecular chains form hydrogen bonds and covalent bonds with the residual hydroxyl groups on the coal gangue surface, while the hydrophobic groups at the other end adsorb composite nanoparticles through van der Waals forces or coordination interactions, forming a transition layer framework. The nanoparticles act as heterogeneous nuclei, reducing the nucleation activation energy of the mullite phase. Fluoride ions generated from the decomposition of the mineralizer can lower the melting temperature of the system. Boron oxide generated from the decomposition of boric acid fills the micropores in the green body in the form of a glassy phase, building migration channels for active silicon-aluminum units and promoting their aggregation to the transition layer. The two work synergistically to accelerate component diffusion. During calcination, the active units in the transition layer, guided by nanocrystal nuclei and the mineralizer, orderly recombine into the mullite crystal phase, forming a continuous bonding region with the silicon-aluminum components of the base material, eliminating interfacial gaps, thereby improving the density and corrosion resistance of 45 mullite. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow for preparing 45 molecate from solid waste coal gangue provided in this application. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0031] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0032] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0033] Furthermore, the terms "first" and "second" appearing in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] The following describes in detail, with reference to different embodiments, a method for preparing 45 molecate from solid waste coal gangue provided in this application.

[0035] Example 1

[0036] like Figure 1 As shown, a method for preparing 45 molecate using solid waste coal gangue includes the following steps:

[0037] Step 1. The solid waste coal gangue is crushed to a particle size ≤5mm by a jaw crusher, screened, and then microwave irradiated for 20min at a power of 700W. After irradiation, it is fed into a planetary ball mill and ground at a speed of 300r / min until the powder D50≤5μm. Then it is dried at 110℃ for 2h to obtain homogeneous coal gangue powder.

[0038] Step 2. Add the homogeneous coal gangue powder to a 4% (w / w) composite alkali solution and stir and activate it at 25°C for 20 min to obtain activated coal gangue powder. The composite alkali solution is an aqueous solution formed by mixing NaOH and Na2CO3, with a mass ratio of NaOH to Na2CO3 of 1:1 and a mass fraction of 4wt%. The mass-volume ratio of the homogeneous coal gangue powder to the composite alkali solution is 1g:8 / mL.

[0039] Step 3. Add KH550 to the activated coal gangue powder, stir, and then add composite nanoparticles. The composite nanoparticles are composed of nano Al2O3 and nano SiO2, wherein the mass ratio of nano Al2O3 to nano SiO2 is 1:1, to obtain modified powder. The mass ratio of activated coal gangue powder, KH550 and composite nanoparticles is 100:0.3:2.

[0040] Step 4. Add water to the modified powder, the amount of water added is 5wt% of the mass of the modified powder, mix and knead for 15 minutes, then age for 12 hours at a temperature of 23℃ and a humidity of 60%, and then use 150MPa pressure for static pressing and hold for 30 seconds to obtain the green body.

[0041] Step 5. Prepare a 10% (w / w) aqueous solution of the mineralizer, wherein the mass ratio of sodium fluorosilicate to boric acid in the mineralizer is 0.8:1. Spray the solution evenly onto the surface of the billet, with the amount of the aqueous solution being 2% of the billet mass. After spraying, pre-dry at 60°C for 0.5 hours, and then perform segmented calcination, including a first stage calcination and a second stage calcination. The first stage calcination is performed at 600°C for 1 hour, and the second stage calcination is performed at 1550°C for 3 hours. After cooling to room temperature, 45 Molecate is obtained.

[0042] Example 2

[0043] like Figure 1 As shown, a method for preparing 45 molecate using solid waste coal gangue includes the following steps:

[0044] Step 1. The solid waste coal gangue is crushed to a particle size ≤5mm by a jaw crusher, screened, and then microwave irradiated for 25min at a power of 800W. After irradiation, it is fed into a planetary ball mill and ground at a speed of 400r / min. The powder D50 after grinding is ≤5μm. Then it is dried at 120℃ for 2.5h to obtain homogeneous coal gangue powder.

[0045] Step 2. Add the homogeneous coal gangue powder to a 5% (w / w) composite alkali solution and stir and activate it at 30°C for 25 min to obtain activated coal gangue powder. The composite alkali solution is an aqueous solution formed by mixing NaOH and Na2CO3, with a mass ratio of NaOH to Na2CO3 of 2:1 and a mass fraction of 5wt%. The mass-volume ratio of the homogeneous coal gangue powder to the composite alkali solution is 1g:10mL.

[0046] Step 3. Add interface modifier KH560 to the activated coal gangue powder, stir, and then add composite nanoparticles. The composite nanoparticles are composed of nano Al2O3 and nano ZrO2, wherein the mass ratio of nano Al2O3 to nano ZrO2 is 1:1, to obtain modified powder. The mass ratio of the activated coal gangue powder, KH560 and composite nanoparticles is 100:0.5:3.

[0047] Step 4. Add water to the modified powder, the amount of water added is 6wt% of the mass of the modified powder, mix and knead for 22 minutes, then age for 18 hours at a temperature of 25℃ and a humidity of 65%, and then use 180MPa pressure for static pressing molding, hold pressure for 45 seconds to obtain the green body.

[0048] Step 5. Prepare a 12% (w / w) aqueous solution of the mineralizer, wherein the mass ratio of sodium fluorosilicate to boric acid in the mineralizer is 1:1. Spray the solution evenly onto the surface of the billet, with the amount of the aqueous solution being 2.5% of the billet mass. After spraying, pre-dry at 80°C for 1.8 hours, and then perform segmented calcination, including a first stage calcination and a second stage calcination. The first stage calcination is performed at 700°C for 1.5 hours, and the second stage calcination is performed at 1580°C for 4 hours. After cooling to room temperature, 45 Molecate is obtained.

[0049] Example 3

[0050] like Figure 1 As shown, a method for preparing 45 molecate using solid waste coal gangue includes the following steps:

[0051] Step 1. The solid waste coal gangue is crushed to a particle size ≤5mm by a jaw crusher, screened, and then microwave irradiated for 30min at a power of 900W. After irradiation, it is fed into a planetary ball mill and ground at a speed of 500r / min. The powder D50 after grinding is ≤5μm. Then it is dried at 130℃ for 3h to obtain homogeneous coal gangue powder.

[0052] Step 2. Add the homogeneous coal gangue powder to a 6% (w / w) composite alkali solution and stir and activate at 35°C for 30 min to obtain activated coal gangue powder. The composite alkali solution is an aqueous solution formed by mixing NaOH and Na2CO3, with a mass ratio of NaOH to Na2CO3 of 3:1 and a mass fraction of 6wt%. The mass-volume ratio of the homogeneous coal gangue powder to the composite alkali solution is 1g:12mL.

[0053] Step 3. Add interface modifier KH560 to the activated coal gangue powder, stir, and then add composite nanoparticles. The composite nanoparticles are composed of nano-SiO2 and nano-TiO2, wherein the mass ratio of nano-SiO2 to nano-TiO2 is 1:1, to obtain modified powder. The mass ratio of the activated coal gangue powder, KH560 and composite nanoparticles is 100:0.8:4.

[0054] Step 4. Add water to the modified powder, the amount of water being 8wt% of the mass of the modified powder. After mixing and kneading for 30 minutes, age for 24 hours at a temperature of 27℃ and a humidity of 70%. Then, use 200MPa pressure for static pressing and hold for 60 seconds to obtain the green body.

[0055] Step 5. Prepare a 15% (w / w) aqueous solution of the mineralizer, wherein the mass ratio of sodium fluorosilicate to boric acid in the mineralizer is 1.2:1. Spray the solution evenly onto the surface of the billet, with the amount of the aqueous solution being 3% of the billet mass. After spraying, pre-dry at 100°C for 2 hours, and then perform segmented calcination, including a first stage calcination and a second stage calcination. The first stage calcination is performed at 800°C for 2 hours, and the second stage calcination is performed at 1600°C for 5 hours. After cooling to room temperature, 45 Molecate is obtained.

[0056] Comparative Example 1

[0057] A method for preparing 45 molecate using solid waste coal gangue, which differs from Example 3 in that microwave irradiation is not performed in step 1.

[0058] Comparative Example 2

[0059] A method for preparing 45 molecate using solid waste coal gangue, which differs from Example 3 in that in step 2, an equal mass and concentration of NaOH solution is added instead of the composite alkali solution.

[0060] Comparative Example 3

[0061] A method for preparing 45 molecate using solid waste coal gangue, which differs from Example 3 in that step 3 is omitted and no interface modifier or composite nanoparticles are added in the entire process.

[0062] Comparative Example 4

[0063] A method for preparing 45 molecate using solid waste coal gangue, which differs from Example 3 in that the mineralizing agent in step 5 is sodium fluorosilicate.

[0064] Performance tests are as follows:

[0065] 1. Bulk density and apparent porosity: 50mm×50mm×50mm samples of 45 Molecate prepared in Examples 1-3 and Comparative Examples 1-4 were made. After drying at 110℃ to constant weight, the dry mass (m0) was measured. After boiling in water for 2 hours until fully saturated, the saturated mass (m1) was measured. The submerged mass (m2) was measured. Finally, the results were calculated using the following formulas: Bulk density = m0 / (m1-m2); Apparent porosity = [(m1-m0) / (m1-m2)]×100%.

[0066] 2. Compressive strength: 50mm×50mm×50mm specimens were made from 45 Moleculecate prepared in Examples 1-3 and Comparative Examples 1-4, respectively. The specimens were loaded at a rate of 0.5MPa / s at room temperature using a universal testing machine until fracture. The strength was calculated based on the maximum load and the area under pressure.

[0067] 3. Acid corrosion resistance: 50mm×50mm×50mm samples of 45 Molecate prepared in Examples 1-3 and Comparative Examples 1-4 were dried and weighed. They were then immersed in 5% hydrochloric acid solution at room temperature for 72 hours, rinsed, dried and weighed again. The mass corrosion rate was calculated.

[0068] 4. Alkali corrosion resistance: 50mm×50mm×50mm samples of 45 Molecate prepared in Examples 1-3 and Comparative Examples 1-4 were dried and weighed. They were then immersed in 5% sodium hydroxide solution at room temperature for 72 hours, rinsed, dried and weighed again. The mass corrosion rate was calculated.

[0069] 5. Coefficient of thermal expansion: φ5mm×50mm cylindrical samples were made from 45 Molexate prepared in Examples 1-3 and Comparative Examples 1-4, respectively. The thermal expansion instrument was used to heat the sample to 1000℃ at a rate of 5℃ / min. The length change was recorded at different temperatures, and the coefficient of thermal expansion from 20 to 1000℃ was calculated.

[0070] Table 1. Performance test data of 45 Molexate prepared in Examples 1-3 and Comparative Examples 1-3

[0071] Group <![CDATA[Volume density (g / cm 3 )]]> Apparent porosity (%) Compressive strength (MPa) Acid corrosion resistance rate (%) Alkali corrosion resistance rate (%) <![CDATA[Coefficient of thermal expansion (10 -6 °C -1 ).]]> Example 1 2.62 4.7 121 0.27 0.29 5.8 Example 2 2.71 4.1 136 0.21 0.23 5.2 Example 3 2.83 3.4 152 0.17 0.19 4.7 Comparative Example 1 2.31 8.6 74 0.66 0.68 6.9 Comparative Example 2 2.25 9.3 69 0.73 0.75 7.1 Comparative Example 3 2.04 12.8 53 0.98 1.02 7.5 Comparative Example 4 2.42 7.7 86 0.57 0.59 6.5

[0072] According to the data in Table 1, the performance differences between Examples 1-3 and Comparative Examples 1-4 are mainly due to the synergistic effect of the four core technical links in the preparation process: microwave irradiation pretreatment, composite alkali synergistic activation, interface modifier and composite nanoparticles to construct a transition layer, and sodium fluorosilicate-boric acid composite mineralizer synergistic effect.

[0073] In terms of bulk density and apparent porosity, the bulk density of Examples 1-3 reached 2.62~2.83 g / cm³, and the apparent porosity was as low as 3.4%-4.7%, which was significantly better than the comparative examples (bulk density 2.04~2.42 g / cm³, apparent porosity 7.7%~12.8%). This was due to the coupling effect of four major steps: microwave irradiation beforehand caused grain boundary microcracks in the coarse coal gangue particles, and the powder retained active surfaces and lattice defects after ball milling, providing channels for rapid penetration of the composite alkaline solution. NaOH efficiently breaks Si-O and Al-O bonds to release active silicon and aluminum components, while Na2CO3 prevents excessive loss of active components through pH buffering. The two work together to generate a stable active intermediate. An interface modifier builds a transition layer between coal gangue and composite nanoparticles. The nanoparticles act as heterogeneous nuclei to promote the directional growth of mullite crystal phase and fill internal pores. In the sodium fluorosilicate-boric acid composite mineralizer, fluoride ions lower the melting temperature of the system, and the borosilicate glass phase generated by boric acid builds diffusion channels and accelerates sintering and densification. Comparative Example 1, lacking microwave irradiation, had no grain boundary microcracks in the coal gangue, resulting in insufficient powder activity after ball milling and decreased composite alkali penetration and activation efficiency, leading to a volumetric density of only 2.31 g / cm³ and an apparent porosity of 8.6%. Comparative Example 2, using a single NaOH solution instead of the composite alkali solution, resulted in a violent reaction leading to excessive dissolution and precipitation of aluminum components, reduced formation of active intermediates, hindered sintering densification, and increased apparent porosity to 9.3%. Comparative Example 3, lacking an interface modifier and composite nanoparticles, lacked a transition layer, resulting in numerous interfacial gaps between the coal gangue matrix and the mullite crystal phase, leading to an apparent porosity as high as 12.8% and a volumetric density reduced to 2.04 g / cm³. Comparative Example 4, using a single sodium fluorosilicate mineralizer, lacked the diffusion channel effect of the borosilicate glass phase, hindering the migration of silicon-aluminum active units, resulting in insufficient sintering, an apparent porosity of 7.7%, and a volumetric density of 2.42 g / cm³, all inferior to the examples.

[0074] In terms of compressive strength, Examples 1-3 achieved strengths of 121-152 MPa, significantly higher than the 53-86 MPa of the comparative examples. This is primarily due to the dual effect of "transition layer construction and densification enhancement": the continuous transition layer formed by the interface modifier and composite nanoparticles eliminated interfacial gaps between the matrix and the crystalline phase; the composite mineralizer promoted the orderly growth of the mullite crystalline phase and its tight bonding with the matrix, resulting in a coherent internal structure and significantly improved load-bearing capacity. Comparative Example 1, lacking microwave pretreatment, suffered from insufficient activity, numerous internal pores and defects, and a strength of only 74 MPa. Comparative Example 2, with single-alkali activation, resulted in the loss of active components and loose crystal bonding, reducing its strength to 69 MPa. Comparative Example 3, lacking a transition layer, saw interfacial gaps become stress concentration points, making it prone to fracture under pressure, resulting in the lowest strength of only 53 MPa. Comparative Example 4, with a single mineralizer, suffered from incomplete sintering, with internal pores affecting stress transmission, resulting in a strength of 86 MPa, lower than all other examples.

[0075] Regarding acid and alkali corrosion resistance, the corrosion rates of the 45 Molexate materials in Examples 1-3 were as low as 0.17%-0.29%, while the comparative examples were as high as 0.57%-1.02%. The key factor is the "barrier" effect of the transition layer: the dense structure of the transition layer constructed by the interface modifier and composite nanoparticles can effectively prevent acidic (H⁺) and alkaline (OH⁻) corrosive media from penetrating into the material, thus avoiding the reaction between the base material and the corrosive media. Comparative Example 1: The lack of microwave pretreatment resulted in insufficient material density, with pores becoming penetration channels for corrosive media, leading to acid / alkali corrosion rates of 0.66%-0.68%, respectively. Comparative Example 2: Single alkali activation caused the loss of active components, resulting in insufficient material basis for the transition layer construction, making it easy for corrosive media to break through the interface, with corrosion rates rising to 0.73% / 0.75%. Comparative Example 3: The absence of a transition layer allowed interface gaps to directly provide penetration paths for corrosive media, resulting in corrosion rates as high as 0.98% / 1.02%. Comparative Example 4: The use of a single mineralizer led to discontinuous growth of the mullite crystal phase and poor integrity of the transition layer, with corrosion rates of 0.57% / 0.59%, still significantly higher than the examples.

[0076] Regarding the coefficient of thermal expansion, the coefficients of thermal expansion for Examples 1-3 are 4.7-5.8 × 10⁻ 6 ℃ -1 It meets the high-temperature dimensional stability requirements of Moleculecate materials, while the comparative example is 6.5~7.5×10⁻ 6 ℃ -1 The deviation from the reasonable range is due to the synergistic effect of the composite mineralizer and composite nanoparticles in guiding the ordered growth of mullite crystal phases: mullite itself has a low coefficient of thermal expansion, and its ordered arrangement ensures uniform thermal deformation of the material as a whole, while the composite mineralizer promotes the continuity of crystal phase growth, further optimizing thermal stability. Comparative Example 1, without microwave pretreatment, resulted in low mullite crystal phase transformation efficiency, an increased proportion of disordered crystal phases, and a thermal expansion coefficient rising to 6.9 × 10⁻⁻⁻⁶. 6 ℃ -1 Comparative Example 2: Single-alkali activation resulted in the loss of active components, insufficient mullite crystalline phase content, and a thermal expansion coefficient of 7.1 × 10⁻⁻⁻⁶. 6 ℃ -1 Comparative Example 3 lacks a transition layer and nanocrystal nuclei, exhibits disordered mullite crystal phase growth, uneven thermal deformation, and has the highest coefficient of thermal expansion at 7.5 × 10⁻⁻⁻⁶. 6 ℃ -1 Comparative Example 4: A single mineralizer caused discontinuous growth of the mullite crystal phase, decreased thermal stability, and a thermal expansion coefficient of 6.5 × 10⁻⁻⁶. 6 ℃ -1 This is higher than the previous example.

[0077] In summary, the superior performance of Examples 1-3 stems from the synergistic effect of the entire process of "microwave pretreatment - composite alkali activation - transition layer construction - composite mineralizer sintering", with each step supporting each other and none being dispensable. In contrast, the comparative example, due to the absence of any core step, resulted in insufficient activation of coal gangue, interface bonding defects, and insufficient sintering densification, ultimately leading to significantly inferior performance compared to the examples.

[0078] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0079] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing 45Mocaite using solid waste coal gangue, characterized in that, The method comprises the following steps: Step 1. The solid waste coal gangue is crushed by a jaw crusher, screened, subjected to microwave irradiation, and then ground in a planetary ball mill, followed by drying to obtain a homogeneous coal gangue powder; Step 2. The homogeneous coal gangue powder is added to a composite alkali solution, stirred and activated to obtain an activated coal gangue powder; the composite alkali solution is an aqueous solution formed by mixing NaOH and Na2CO3; Step 3. An interfacial modifier is added to the activated coal gangue powder, stirred, and then composite nanoparticles are added to obtain a modified powder; the interfacial modifier comprises any one of KH550 and KH560; the composite nanoparticles comprise any two of nano-Al2O3, nano-SiO2, nano-ZrO2 and nano-TiO2; Step 4. Water is added to the modified powder, mixed and aged, and then isostatically formed and pressure-maintained to obtain a green body; Step 5. An aqueous solution of a mineralizing agent, which is a mixture of sodium fluorosilicate and boric acid, is uniformly sprayed on the surface of the green body, the green body is pre-dried, then is subjected to staged calcination, and is cooled to room temperature to obtain a 45-mor carat.

2. The method for preparing 45Mocaite from solid waste coal gangue according to claim 1, characterized in that, In step 1, the jaw crusher is crushed to a particle size of ≤5 mm; the microwave irradiation power is 700-900 W, and the time is 20-30 min.

3. The method for preparing 45Mocaite from solid waste coal gangue according to claim 1, characterized in that, In step 1, the planetary ball mill rotates at a speed of 300-500 r / min, and the ground powder has a D50 of ≤5 μm; the drying temperature is 100-120 ℃, and the drying time is 2-3 h.

4. The method for preparing 45Mocaite from solid waste coal gangue according to claim 1, characterized in that, In step 2, the stirring and activation temperature is 25-35 ℃, and the time is 20-30 min; the mass ratio of NaOH to Na2CO3 is (1-3) : 1; the mass fraction of the composite alkali solution is 4wt%-6wt%; the mass-volume ratio of the homogeneous coal gangue powder to the composite alkali solution is 1g:(8-12)mL.

5. The method of claim 1, wherein the method of preparing 45Mocaite using solid waste coal gangue is characterized by, In step 3, the mass ratio of the activated coal gangue powder, the interfacial modifier and the composite nanoparticles is 100:(0.3-0.8):(2-4).

6. The method of claim 1, wherein the method of preparing 45Mocaite using solid waste coal gangue is characterized by, In step 4, the kneading time is 15-30 min; the amount of water added is 5wt%-8wt% of the mass of the modified powder; the aging temperature is 23-27 ℃, the humidity is 60%-70%, and the time is 12-24 h; the isostatic forming pressure is 150-200 MPa; and the pressure-maintaining time is 30-60 s.

7. The method of claim 1, wherein the method of preparing 45Mocaite using solid waste coal gangue is characterized by, In step 5, the mass ratio of sodium fluorosilicate to boric acid is (0.8-1.2) : 1; the mass fraction of the aqueous solution of the mineralizing agent is 10%-15%, and the spraying amount is 2wt%-3wt% of the mass of the green body.

8. The method of claim 1, wherein the method of preparing 45Mocaite using solid waste coal gangue is characterized by, In step 5, the pre-drying temperature is 60-100 ℃, and the time is 0.5-2 h; the staged calcination comprises first-stage calcination and second-stage calcination; the first-stage calcination temperature is 600-800 ℃, and the time is 1-2 h; the second-stage calcination temperature is 1550-1600 ℃, and the time is 3-5 h.

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