Green low-carbon refractory material and preparation process thereof

Abstract

The application discloses a kind of green low-carbon refractory and preparation process thereof, belong to refractory technical field.The refractory includes recycled material, high-purity magnesia, ultra-high purity magnesia, magnesium-aluminum spinel, composite modifier, trace strengthening phase, composite binder and process aid agent;The recycled material is the regenerated raw material after three-stage gradient treatment of cement kiln waste refractory brick, and the total amount of harmful impurities is ≤0.15%.The application realizes the high-value-added regeneration of waste refractory brick by recycling material deep purification technology, composite modifier in-situ solidification technology, trace strengthening phase grain boundary pinning technology and multi-scale pore structure regulation technology, and the obtained product has better normal temperature compressive strength, high temperature bending strength, thermal shock resistance and corrosion resistance than traditional magnesium-aluminum spinel brick under the condition that the bulk density is reduced by 4%-6%, and the full life cycle carbon emission reduction reaches 52%-58%.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a green, low-carbon refractory material and its preparation process. Background Technology

[0002] The cement industry is a vital foundation of my country's national economy, but it is also a major consumer of resources and emitters of carbon. As the core equipment for clinker firing, the performance of the refractory lining material in the cement rotary kiln directly affects the stability, safety, and economy of production operations. Currently, high-performance refractory materials such as magnesia-alumina spinel bricks, widely used in the firing and transition zones of cement kilns, are primarily produced from the high-temperature sintering or electrofusion products of natural magnesite and bauxite.

[0003] However, this traditional method of obtaining raw materials suffers from the following insurmountable technical defects and industrial drawbacks: First, it is highly dependent on resources and causes severe ecological damage. Natural magnesite and bauxite are non-renewable resources. Long-term large-scale mining has led to the depletion of high-quality mineral resources, while causing irreparable ecological and environmental problems such as damage to surface vegetation, soil erosion, and decline in biodiversity in mining areas.

[0004] Second, it consumes a lot of energy and emits a lot of carbon. From ore mining and transportation to high-temperature calcination (usually requiring temperatures above 1700℃) or electrofusion (which consumes a huge amount of electricity), the entire process is extremely energy-intensive. It is estimated that producing one ton of traditional magnesia emits about 3-5 tons of carbon dioxide, which is seriously inconsistent with the current national strategic goal of "peaking carbon and achieving carbon neutrality".

[0005] Third, waste disposal has become a major pain point in the industry. Refractory materials used in cement kilns have a limited service life, resulting in a large amount of waste refractory bricks after they fail. Statistics show that my country generates over one million tons of waste cement kiln refractory bricks annually. These waste bricks are mainly composed of MgO and Al2O3, which should have high recycling value. However, during their service life, they absorb harmful components from cement raw materials and fuel flue gas, mainly including alkali metal oxides (K2O, Na2O), sulfides (SO3), and chlorides (Cl), with a total impurity content typically reaching 3%–6%. If simply crushed and reused, these impurities will form a low-melting-point liquid phase at high temperatures, severely deteriorating the high-temperature strength, erosion resistance, and volume stability of newly manufactured refractory materials. Therefore, for a long time, the vast majority of waste refractory bricks have only been landfilled or used at low value, not only occupying land resources but also potentially allowing harmful components to seep into the soil and groundwater, causing secondary pollution.

[0006] To address the aforementioned problems, various improvement solutions have been attempted in this field. For example, some studies have proposed using crushed waste bricks as aggregate to prepare low-end castables, but due to unresolved impurity issues, their performance falls far short of the stringent requirements of high-temperature sections in cement kilns. Other patents disclose methods for chemically cleaning waste bricks, but these suffer from high processing costs, difficult wastewater treatment, and limitations in industrial-scale application. Therefore, achieving high-value recycling of waste refractory bricks while ensuring that the performance of recycled materials is not lower than, and may even surpass, that of virgin materials has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a green and low-carbon refractory material and its preparation process. This technical solution uses high-content recycled waste refractory bricks as the core raw material. Through innovative impurity control technology, microstructure regulation technology and synergistic sintering technology, it achieves resource recycling and carbon emission reduction while obtaining refractory materials with comprehensive performance superior to traditional products.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A green, low-carbon refractory material, characterized in that it is composed of the following components in parts by weight: Recycled material: 50-80 parts; High-purity magnesia: 10-40 parts; Ultra-high purity magnesia: 1-8 parts, of which MgO content > 99%; Magnesium aluminum spinel: 2-8 parts; Composite modifier: 1-5 parts; Micro-enhancing phase: 0.1–1 part; Composite binder: 2.5–4.0 parts; Processing aids: 0.1 to 0.5 parts.

[0009] In this invention, the recycled material has a clear definition and strict processing standards. It refers to the recycled material obtained from waste magnesia or magnesia-alumina refractory bricks used in cement rotary kilns, processed through the following three-stage gradient treatment process: (1) Primary treatment (physical sorting): The waste bricks are crushed, screened and magnetically separated to remove iron inclusions and cement clinker layer adhering to the surface; (2) Secondary treatment (chemical purification): The physically sorted granules are placed in a specific reactor and circulated and washed with a composite acid solution at a temperature of 80-120℃ to selectively remove soluble harmful impurities such as K2O, Na2O, SO3 and Cl adsorbed inside and on the surface of the brick. (3) Tertiary treatment (thermal activation): The chemically purified raw materials are heat-treated at a temperature of 800-1100℃. On the one hand, the residual carbonates and hydroxides are completely decomposed, and on the other hand, the activity of the surface of the recycled material particles is activated, creating conditions for interfacial bonding in the subsequent high-temperature sintering process.

[0010] The chemical composition of the recycled material after the above three-stage treatment must meet the following strict control standards (mass percentage): MgO: 81%–86%; Al2O3: 10%–14%; SiO2: 0.5%~1.0%; CaO: 0.8%~1.8%; Fe2O3: 0.5%~0.9%; Total amount of harmful impurities (K2O+Na2O+SO3+Cl): ≤0.15%.

[0011] In this invention, the composite modifier refers to a mixture composed of specific mineral raw materials. Its function is to react with residual trace impurities in the recycled material during high-temperature calcination to generate a high-melting-point mineral phase, thereby achieving "in-situ solidification" of the impurities and avoiding the generation of a low-melting-point liquid phase. Preferably, the composite modifier is a mixture of kaolin, talc, and dolomite in a mass ratio of (3-5):(1-2):(1-2).

[0012] In this invention, the trace reinforcing phase is a nano- or submicron-sized composite of zirconium oxide (ZrO2) and cerium oxide (CeO2), with a mass ratio of (2-4):1. This reinforcing phase is mainly distributed at the grain boundaries in the material's microstructure. On the one hand, it improves the material's thermal shock resistance through a phase transformation toughening mechanism; on the other hand, it inhibits grain growth through a pinning effect, resulting in a uniform and fine microstructure.

[0013] In this invention, the composite binder is composed of organic and inorganic components, including 1-2 parts dextrin, 0.5-1.5 parts water glass, 0.5-1.5 parts clay, and 0.3-0.8 parts pulp waste liquor. This composite binder can exert a synergistic effect at different temperature stages: at low temperatures, the organic components provide molding strength; at medium temperatures, the carbonization of the pulp waste liquor forms a carbon network to strengthen the green body; and at high temperatures, the clay and water glass promote ceramic bonding.

[0014] 2.4 Particle size distribution design This invention systematically optimizes the particle size distribution of raw materials, adopting a design concept of "multi-grade distribution + micro powder filling": Coarse particles (3-5mm): accounting for 20% to 30% of the total granular material, mainly from recycled materials and high-purity magnesia; Medium-sized particles (1-3mm): accounting for 30% to 40% of the total particle size, mainly from recycled materials and magnesium aluminum spinel; Fine particles (0.1-1mm): accounting for 15% to 25% of the total granular material, mainly from high-purity magnesia and ultra-high-purity magnesia; Micro powder (<0.088mm): accounts for 60% to 80% of the total fine powder, including ultra-high purity magnesia micro powder, composite modifier micro powder, and micro powder of trace reinforcing phase, etc.

[0015] This invention also provides a preparation process for the aforementioned green and low-carbon refractory material, comprising the following steps: Step 1: Raw material pretreatment: (1) The recycled material is processed according to the aforementioned three-stage gradient processing technology to obtain recycled raw materials that meet the chemical composition requirements; (2) Crush and screen high-purity magnesia, ultra-high-purity magnesia, and magnesium aluminum spinel respectively to obtain granules and fine powders of the required particle size; (3) The composite modifier and the trace reinforcing phase are respectively subjected to ultrafine grinding so that their fineness reaches D50≤5μm.

[0016] Step 2: Ingredient Preparation and Mixing (1) Initial mixing: Weigh out coarse, medium and fine particles according to the formula ratio, add them to a high-power countercurrent mixer, and dry mix for 2-4 minutes; (2) Add binder: Add the pre-prepared composite binder and process aids, and wet mix for 3-5 minutes; (3) Add micro powder: Add composite modifier micro powder, trace amount of reinforcing phase micro powder and other fine powder, and continue wet mixing for 5-8 minutes; (4) The total mixing time is controlled at 12-15 minutes, the mixing temperature is controlled at 25-35℃, and the moisture content of the discharged mud is controlled at 2.5%-3.5%.

[0017] Step 3: Material Trapping and Molding The mixed clay is left to stand in a sealed container for 12-24 hours to allow the moisture and binder to be fully and evenly distributed. Then, a high-tonnage automatic hydraulic brick press is used for molding, with a molding pressure of not less than 1000 tons, 2-3 presses, and a holding time of 3-5 seconds, to obtain a dense green brick.

[0018] Step 4: Drying: The green body is placed in a temperature- and humidity-controlled drying kiln for step drying: Phase 1: Temperature 60-80℃, relative humidity 80%-90%, time 8-12 hours; Second stage: Temperature 100-120℃, relative humidity 50%-60%, time 10-15 hours; Phase 3: Temperature 140-160℃, forced ventilation, time 6-10 hours; The residual moisture content of the dried green body is ≤0.5%.

[0019] Step 5: Firing The dried green bodies are loaded into kiln cars according to a specific stacking method and pushed into a high-temperature tunnel kiln for firing. The firing process adopts a three-stage control: Preheating section (room temperature - 1000℃): heating rate ≤ 3℃ / min. This stage mainly completes the decomposition of the binder, the burn-off of organic matter, and the initial solid-phase reaction. High temperature section (1000-1650℃): Heating rate 1-2℃ / min, hold at 1650±20℃ for 8-12 hours. During this stage, the formation of the main mineral phases and densification sintering are completed. Cooling section: Control the cooling rate to 2-4℃ / min up to 800℃, and then allow it to cool naturally to avoid internal stress caused by excessive cooling.

[0020] Step Six: Post-processing: After firing, the products undergo appearance inspection, size sorting, and performance testing. Qualified products are then packaged with moisture-proof materials and put into storage.

[0021] Through the synergistic effect of the above-mentioned material composition and preparation process, the green and low-carbon refractory material obtained by this invention has unique microstructural characteristics: (1) Multi-scale pore structure: The material has a pore structure with a bimodal pore size distribution, including micron-sized pores with a diameter of 5-15 μm and submicron-sized pores with a diameter of 0.1-0.5 μm. This multi-scale pore structure not only ensures the thermal insulation performance of the material, but also gives it good strain tolerance.

[0022] (2) Grain boundary strengthening structure: The trace strengthening phase (ZrO2-CeO2 complex) is uniformly distributed at the grain boundaries of periclase and magnesium aluminum spinel, forming a continuous "grain boundary pinning network", which effectively hinders the abnormal growth of grains and the propagation of cracks at high temperature.

[0023] (3) In-situ reaction layer: The composite modifier reacts in-situ with the residual impurities in the recycled material at high temperature, forming a high-melting-point mineral reaction layer with a thickness of 2-5 μm at the particle interface. This reaction layer can both passivate the adverse effects of impurities and enhance the interfacial bonding strength between particles.

[0024] Beneficial effects Compared with the prior art, the present invention has the following outstanding advantages: 1. This invention, through an innovative three-stage gradient treatment process, successfully increases the utilization rate of waste refractory bricks from cement kilns to 50%–80%, far exceeding the less than 20% utilization rate of existing technologies. Based on an annual production of 10,000 tons of this invention's product, it can dispose of 5,000–8,000 tons of waste refractory bricks annually, reduce natural ore mining by 6,000–10,000 tons, and save 3,000–5,000 cubic meters of landfill space, resulting in significant economic and social benefits.

[0025] 2. The carbon footprint of this invention was calculated using the Life Cycle Assessment (LCA) method. The results show that compared with traditional magnesia-alumina spinel bricks, the product of this invention reduces carbon emissions by approximately 65% ​​in the raw material acquisition stage and approximately 35% in the manufacturing stage, achieving a comprehensive carbon emission reduction of 52%-58% over its entire life cycle. This effect stems from two aspects: firstly, the extensive use of recycled materials replaces the energy-intensive virgin magnesia sand; secondly, the low-temperature activation firing technology of this invention lowers the firing temperature by 50-80℃, directly reducing fuel consumption.

[0026] 3. While maintaining a low bulk density (which helps reduce the load on the kiln body), the product of this invention has achieved a comprehensive improvement in strength, thermal shock resistance and erosion resistance, especially the improvement in thermal shock resistance and erosion resistance, which is of great significance for extending the service life of cement kiln linings and improving operating rates.

[0027] 4. This invention achieves synergistic performance optimization through system composition design and process control. Specifically: Multi-scale porous structures reduce the thermal conductivity and elastic modulus of materials while retaining sufficient strength; Grain boundary pinning networks effectively suppress grain coarsening and crack propagation at high temperatures; The in-situ reaction layer passivates the harmful effects of impurities and enhances interfacial bonding.

[0028] The synergistic effect of these three microstructural mechanisms enables the product of this invention to achieve a comprehensive improvement in various performance characteristics despite a reduction in density. This breaks the traditional perception that "density and performance are positively correlated" in refractory materials, demonstrating the technological innovation and advancement of this invention.

[0029] 5. The preparation process of this invention is highly compatible with existing refractory material production lines; the main equipment can be reused, requiring only the addition of a recycled material pretreatment system. It has a short investment payback period, excellent technical and economic efficiency, and is suitable for large-scale industrialization. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] In the following implementation examples, the source and properties of the raw materials used are as follows: Recycled material: According to the method described in this invention, the recycled magnesium-aluminate spinel bricks used in cement kilns are sorted, crushed, and impurity removed to ensure that their final chemical composition meets the following requirements: MgO 82%, Al2O3 12%, SiO2 0.8%, CaO 1.5%, Fe2O3 0.8%, and the total of K2O+SO3+Na2O+Cl < 0.2%. The recycled material is then prepared into particles of 5-3mm, 3-1mm, and 1-0mm, and fine powder ≤ 0.088mm for later use.

[0032] Natural high-purity magnesia: commercially available, MgO≥97%, sintered or fused state.

[0033] Ultra-high purity magnesia: commercially available, MgO≥99.5%, fused state.

[0034] Magnesium aluminum spinel: Commercially available, Al2O3 content approximately 70-75%, sintered state.

[0035] Zirconia: Commercially available, monoclinic zirconium oxide, purity ≥99%.

[0036] Special raw materials A and B: Both are commercially available functional industrial raw materials that can decompose and induce the formation of micropores at high temperatures.

[0037] Binder: A liquid composite binder prepared by mixing dextrin and water glass in a 1:1 ratio and adding a small amount of special additives.

[0038] Additives: Commercially available molding aids.

[0039] Example 1. A green, low-carbon refractory material is provided, the raw material composition and weight parts of which are shown in Table 1: Table 1. Raw material ratio for Example 1

[0040] The preparation process is as follows: (1) Raw material pretreatment: Recycled material: According to the three-stage gradient treatment process described in this invention, firstly, waste magnesium-aluminum spinel bricks are crushed to ≤30mm and then magnetically separated to remove iron. Next, the crushed material is placed in a reaction vessel, and a 5% (by mass) composite acid solution (hydrochloric acid:nitric acid = 3:1) is added. The mixture is then circulated and washed for 3 hours at 95±5℃, with a solid-liquid ratio of 1:3. After filtration, the material is washed with water until neutral and dried at 150℃. Finally, it is heat-treated at 950℃ for 2 hours to obtain the required recycled material. This material is then crushed and sieved into granules of 5-3mm, 3-1mm, and 1-0mm, and fine powder ≤0.088mm for later use.

[0041] High-purity magnesia, ultra-high-purity magnesia, and magnesium aluminum spinel are crushed and screened into the required particle size.

[0042] After the composite modifiers are mixed in proportion, they are pulverized by air jet mill to D50=3.5μm.

[0043] After mixing the trace amounts of reinforcing phase in a certain proportion, the mixture was wet-milled using a stirred mill until D50 = 0.8 μm, and then spray-dried for later use.

[0044] (2) Mixing: A high-power countercurrent mixer (model R11, adjustable speed) was used. First, all granular materials (recycled material granules, high-purity magnesia granules, ultra-high-purity magnesia granules, and magnesium-aluminum spinel granules) were added, and the mixer was dry-mixed for 3 minutes at a speed of 280 rpm. Then, pre-mixed composite binder and process aids were added, and the mixer was wet-mixed for 4 minutes at a speed of 320 rpm. Finally, all micro-powders (recycled material fine powder, high-purity magnesia fine powder, ultra-high-purity magnesia fine powder, magnesium-aluminum spinel fine powder, composite modifier micro-powder, and trace reinforcing phase micro-powder) were added, and the mixer was wet-mixed for 6 minutes at a speed of 350 rpm. The total mixing time was 13 minutes, the discharge temperature was 32℃, and the moisture content of the slurry was 3.1%.

[0045] (3) Material trapping and molding: The mixed clay is placed in sealed plastic bags and left to stand for 18 hours in a curing chamber at 25°C and 80% humidity. It is then formed using a 1600-ton automatic hydraulic brick press, with a pressing pressure of 1200 tons, applied twice, and held for 4 seconds. After forming, the appearance of the green bricks is inspected, and any bricks with cracks, missing corners, or delamination are discarded.

[0046] (4) Drying: A tunnel drying kiln is used, and the drying process is carried out according to a stepped drying regime. Phase 1: Temperature 70℃, humidity 85%, time 10 hours; Second stage: Temperature 110℃, humidity 55%, time 12 hours; Phase 3: Temperature 150℃, forced ventilation, duration 8 hours.

[0047] The residual moisture content of the green body after drying was 0.3%.

[0048] (5) Firing: A 108-meter-long high-temperature tunnel kiln is used. The kiln car size is 1.5m × 1.6m, with 8 layers stacked on each car, and 12 bricks per layer. Firing procedure: Preheating section (parking spaces 1-20): The temperature rises from room temperature to 1000℃, with the heating rate controlled at 2.5℃ / min; Firing section (car bays 21-35): Temperature rises from 1000℃ to 1650℃ at a rate of 1.5℃ / min, and is held at 1650℃ for 10 hours; Cooling section (carriages 36-54): Control the cooling rate to 3℃ / min up to 800℃, then allow it to cool naturally until the kiln exit temperature is ≤80℃.

[0049] (6) Post-processing: After the fired products are removed from the kiln, they are inspected for appearance, graded according to dimensional deviations, and representative samples are selected for performance testing. Qualified products are wrapped in moisture-proof paper, packed on wooden pallets, and put into storage.

[0050] Example 2. A green, low-carbon refractory material is provided, the raw material composition and weight parts of which are shown in Table 2: Table 2. Raw material ratio for Example 2

[0051] The preparation process is the same as in Example 1.

[0052] Example 3. A green, low-carbon refractory material is provided, the raw material composition and weight parts of which are shown in Table 3: Table 3. Raw material ratio for Example 3

[0053] The preparation process is the same as in Example 1, except that the firing temperature is adjusted to 1620℃ and the holding time is 12 hours.

[0054] Comparative Example 1. Commercially available high-quality magnesium aluminum spinel bricks were used. The main raw materials were: 70% high-purity magnesia, 25% fused magnesium aluminum spinel, and 5% binder. The firing temperature was 1680℃ and the holding time was 8 hours.

[0055] Comparative Example 2. A recycled refractory material made from waste bricks prepared in accordance with the prior patent application No. 202410419523.3, entitled "A method for reusing waste refractory bricks and an unshaped refractory material", uses recycled material (total impurities of about 2.5%) that has not undergone deep impurity removal treatment to replace 50% of the magnesia, with the remainder being high-purity magnesia and spinel. The binder is waste pulp liquid, and the firing temperature is 1650℃.

[0056] The products obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to systematic performance tests. The test methods and results are as follows.

[0057] Table 4. Performance Test Results

[0058] It should be noted that the test method for resistance to alkali salt corrosion in Table 4 is as follows: the sample is processed into a 50mm×50mm×50mm block, dried at 110℃ to constant weight and the volume V0 is measured. Then the block is placed in a crucible filled with KCl and kept at 900℃ for 10 hours. After cooling, the surface is cleaned and dried again and the volume V1 is measured. The volume change rate ΔV=(V1-V0) / V0×100% is calculated.

[0059] The following conclusions can be drawn from the test results in Table 4: (1) Comparison of Examples 1-3 with Comparative Example 1 of traditional high-quality products: The bulk density is reduced by 4.4%-5.1%, which can significantly reduce the load on the kiln body; The compressive strength at room temperature is increased by 8.4%-21.1%, and the flexural strength at high temperature is increased by 21.4%-35.8%, exhibiting better mechanical properties; The thermal shock resistance is improved by 60%-80%, and the resistance to alkaline salt corrosion is improved by 72%-79%, indicating that the thermomechanical stability and chemical stability of the product of this invention are significantly better than those of traditional products. The coefficient of thermal expansion is reduced by 7.3%-11.5%, and the thermal conductivity is reduced by 8.5%-14.5%, which helps to improve the insulation effect of the kiln lining, reduce the temperature of the kiln shell, and reduce heat loss. The increase in load softening temperature by 20-40℃ indicates that the product of this invention has better high-temperature structural stability.

[0060] (2) Comparison of Examples 1-3 with Comparative Example 2 of existing technology recycled materials: It outperforms all other performance indicators by a wide margin, especially with room temperature compressive strength increased by 30%-45%, high temperature flexural strength increased by 60%-79%, thermal shock resistance increased by 167%-200%, and corrosion resistance increased by 88%-92%. The volume of the product in Comparative Example 2 expanded by 3.86% after corrosion resistance, indicating significant material deterioration. In contrast, the product of this invention showed minimal volume change and maintained its intact structure. The comparative results show that the present invention has successfully solved the technical bottleneck of waste brick recycling through systematic impurity control technology and microstructure regulation technology, and achieved the performance improvement and breakthrough of recycled materials.

[0061] (3) Comparison between embodiments: Example 2 (50% recycled material) showed the best overall performance, followed by Example 1 (65% recycled material), and then Example 3 (75% recycled material), but all three were far superior to the comparative example. This invention demonstrates that within the technical framework of the present invention, excellent performance can be obtained with a recycled material content ranging from 50% to 75%, which can be adjusted according to resource supply and has good process adaptability. In Example 3, the content of trace reinforcing phase was relatively high (0.8%), which played a positive role in improving high-temperature performance, enabling it to maintain good overall performance even with the highest recycled material content.

[0062] Industrial application trials: The green, low-carbon refractory material prepared in Example 1 was subjected to an industrial application test in the firing zone of a novel dry-process rotary kiln producing 5000 tons of cement clinker per day, and compared with conventional magnesia-alumina spinel bricks (Comparative Example 1). The test results are shown in Table 5 below: Table 5. Results of Industrial Application Tests

[0063] The results of industrial application tests fully verify the excellent performance and promising application prospects of the product of this invention.

[0064] In summary, this invention provides a green, low-carbon refractory material and its preparation process. Through innovative technologies such as deep purification of recycled materials, in-situ solidification of composite modifiers, micro-strengthening phase grain boundary pinning, and multi-scale pore structure control, it successfully achieves high-value-added recycling of waste refractory bricks. The prepared product exhibits improved mechanical, thermal, and erosion resistance despite reduced bulk density, demonstrating significant resource savings, carbon reduction, and excellent performance. It provides the cement industry with a high-performance refractory material solution that combines economic value and environmental benefits.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A green, low-carbon refractory material, characterized in that, The raw materials for preparation include, by weight: 50-80 parts recycled material, 10-40 parts high-purity magnesia, 1-8 parts ultra-high-purity magnesia, 2-8 parts magnesium aluminum spinel, 1-5 parts composite modifier, 0.1-1 parts trace reinforcing phase, 2.5-4.0 parts composite binder, and 0.1-0.5 parts process aids; The ultra-high purity magnesia contains >99% MgO. The recycled material is a recycled raw material from waste refractory bricks from cement kilns after three-stage gradient treatment, and its total amount of harmful impurities is: K2O+Na2O+SO3+Cl≤0.15%.

2. The green and low-carbon refractory material according to claim 1, characterized in that, The chemical composition of the recycled material, by weight percentage, is as follows: MgO 81%–86%, Al2O3 10%–14%, SiO2 0.5%–1.0%, CaO 0.8%–1.8%, Fe2O3 0.5%–0.9%, K2O+Na2O+SO3+Cl ≤0.15%.

3. The green and low-carbon refractory material according to claim 1, characterized in that, The three-stage gradient treatment includes: a first-stage physical sorting treatment, a second-stage chemical purification treatment, and a third-stage thermal activation treatment; the second-stage chemical purification treatment involves cyclic immersion in a composite acid solution at a temperature of 80-120℃; and the third-stage thermal activation treatment involves heat treatment at a temperature of 800-1100℃.

4. The green and low-carbon refractory material according to claim 1, characterized in that, The composite modifier is a mixture of kaolin, talc and dolomite in a mass ratio of (3-5):(1-2):(1-2).

5. The green and low-carbon refractory material according to claim 1, characterized in that, The trace reinforcing phase is a nano- or submicron-sized composite of zirconium oxide and cerium oxide, with a mass ratio of (2-4):1, and a particle size D50 ≤ 1 μm.

6. The green and low-carbon refractory material according to claim 1, characterized in that, The composite binder is composed of organic and inorganic components, including 1-2 parts dextrin, 0.5-1.5 parts water glass, 0.5-1.5 parts clay, and 0.3-0.8 parts pulp waste liquor.

7. The preparation process of the green low-carbon refractory material according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Raw material pretreatment: The recycled material is subjected to three-stage gradient treatment, and other raw materials are crushed, screened and ultra-finely pulverized respectively; (2) Ingredients and mixing: Weigh each raw material according to the formula, and then dry mix the granules, wet mix with binder, and mix with micro powder in sequence. The total mixing time is 12-15 minutes. (3) Curing and molding: Curing the mixed mud for 12-24 hours, and then pressing it into shape using an automatic hydraulic brick press; (4) Step drying: The green body is dried in three steps, and the residual moisture content after drying is ≤0.5%; (5) Three-stage firing: The dried green body is fired in three stages: preheating, high temperature and cooling. The temperature of the high temperature stage is 1600-1680℃ and the holding time is 8-12 hours. (6) Post-processing: Inspect, sort and package the fired products.

8. The preparation process according to claim 7, characterized in that, The stepped drying process includes: the first stage with a temperature of 60-80℃, relative humidity of 80%-90%, and a time of 8-12 hours; the second stage with a temperature of 100-120℃, relative humidity of 50%-60%, and a time of 10-15 hours; and the third stage with a temperature of 140-160℃, forced ventilation, and a time of 6-10 hours.

9. The preparation process according to claim 7, characterized in that, The three-stage firing process includes: a preheating stage where the temperature is raised from room temperature to 1000℃ at a rate of ≤3℃ / min; a high-temperature stage where the temperature is raised from 1000℃ to 1600-1680℃ at a rate of 1-2℃ / min, and the temperature is maintained in the high-temperature stage for 8-12 hours; and a cooling stage where the temperature is controlled at a rate of 2-4℃ / min until the temperature reaches 800℃, after which the temperature is allowed to cool naturally.

10. The application of the green and low-carbon refractory material according to any one of claims 1-6 in the firing zone or transition zone of a cement rotary kiln.

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