A medium-temperature oxidized sludge ash-red mud-regenerated glass powder ternary composite lightweight ceramsite and a preparation method and application thereof

Abstract

The present application belongs to the technical field of solid waste resource utilization and ceramsite preparation, and specifically relates to a medium-temperature oxidized sludge ash-red mud-regenerated glass powder ternary composite lightweight ceramsite as well as a preparation method and application thereof. The existing sludge-based ceramsite has a high firing temperature, and it is difficult to balance the lightweight performance and particle strength, and it is difficult to simultaneously resourcefully dispose of solid wastes such as sludge, red mud and waste glass. The lightweight ceramsite is prepared from a base material and an additional pore-forming agent. The base material includes, in mass parts, 100 parts of medium-temperature oxidized sludge ash, 6-14 parts of red mud and 68-72 parts of glass powder, and the additional pore-forming agent is silicon carbide powder, and the addition amount is 0.3%-0.7% of the total mass of the base material. The preparation method includes the steps of raw material pretreatment, mixing granulation, drying, preheating, calcination and cooling. The obtained lightweight ceramsite has a bulk density of 453-700 kg / m3, a single-particle compressive strength of 3-6.5 MPa and a 1 h water absorption of less than or equal to 2.1%, and can be used for building lightweight aggregate, lightweight backfill material, thermal insulation lightweight aggregate or permeable pavement aggregate.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and ceramsite preparation technology, specifically involving a medium-temperature oxidized sludge ash-red mud-recycled glass powder ternary composite lightweight ceramsite, its preparation method and application. Background Technology

[0002] With the increasing demands for resource utilization of solid waste and energy conservation and emission reduction, the synergistic utilization of multi-source solid waste such as municipal sludge, red mud, and glass-like solid waste has gradually attracted attention. Municipal sludge has a high water content and high organic matter content. If used directly as raw material for ceramsite, it is prone to problems such as cracking of the green body, poor uniformity of pore distribution, or decreased particle strength during drying, preheating, and firing due to water evaporation, drying shrinkage, and concentrated volatilization of organic matter. After municipal sludge undergoes thermal oxidation treatment at 550-650 ℃ in air or an oxygen-containing atmosphere, its water content and organic matter content are significantly reduced, and the inorganic components such as SiO2, Al2O3, and Fe2O3 are relatively enriched, making it easier to control the batching with raw materials such as red mud and glass powder, thereby improving the stability of the ceramsite firing process and pore structure formation.

[0003] In existing sludge ash preparation processes, sludge is mostly incinerated at high temperatures to form ash. Referring to GB 18485-2014, "Standard for Pollution Control of Municipal Solid Waste Incineration," the main technical performance indicators for municipal solid waste incinerators stipulate that the incineration temperature inside the furnace should not be lower than 850 ℃. Pollution control for sludge incinerators specifically designed for municipal wastewater treatment facilities can also be implemented with reference to this standard. Besides high-temperature incineration to form sludge ash, for treatments that emphasize sludge reduction and stabilization rather than complete high-temperature incineration, lower-temperature thermal oxidation treatment can be used to dehydrate the sludge and promote a certain degree of oxidation or decomposition of organic components, thereby forming medium-temperature oxidized sludge ash. Currently, the existing utilization methods for this type of medium-temperature oxidized sludge ash are relatively limited, usually relying on stockpiling, landfilling, or low-proportion blending in ordinary filling materials for disposal. High-value building material resource utilization pathways are limited. Among existing technologies, several techniques for preparing ceramsite or ceramic granules from sludge-type solid waste have been disclosed. For example, patent CN111517820A discloses a high-strength ceramsite containing sludge ash and its preparation method. It uses sludge ash and engineering waste soil as raw materials, granulates them, and then fires them at 1080-1200 ℃ to prepare high-strength ceramsite. Another example is patent CN114605163A, which discloses ceramsite based on sludge incineration ash, its preparation method, and its application. It uses sludge incineration ash, fly ash, clay, and other auxiliary materials as raw materials, and obtains ceramsite after mixing, granulation, drying, pre-firing, and firing at 1050-1250 ℃. Furthermore, patent CN110282996A discloses a method for co-processing red mud and sludge to produce ceramsite, which obtains ceramsite by mixing, granulating, calcining, and cooling red mud and sludge.

[0004] However, existing technologies still have certain shortcomings: First, they mostly rely on high-temperature incineration to process municipal sludge into ash before further producing ceramsite. Although this is a resource utilization of municipal sludge, high-temperature incineration does not meet the requirements of energy conservation and emission reduction. Second, some technologies still rely heavily on conventional silica-alumina auxiliary materials such as engineering waste soil, clay, and fly ash. On the other hand, some technologies require high firing temperatures, which can easily lead to increased energy consumption and excessive densification of the ceramsite surface, which is not conducive to the formation of a uniform internal pore structure and the improvement of lightweight performance. Summary of the Invention

[0005] This invention addresses the problems in existing sludge-based ceramsite preparation processes, which rely solely on high-temperature incinerated sludge ash, use conventional aluminosilicate additives, have low utilization rates of other solid wastes, require high firing temperatures, and struggle to balance lightweighting with particle strength. It provides a method for preparing medium-temperature oxidized sludge ash-based lightweight ceramsite. This invention uses sludge ash as the main raw material, red mud to regulate aluminum, iron, and fluxing components, glass powder to promote liquid phase formation, and SiC to assist in pore formation. Ultimately, lightweight ceramsite with a certain strength can be obtained at approximately 1060 °C. The synergistic combination of the three solid wastes in composition and function not only achieves a lightweight ceramsite preparation technology that balances lightweighting and mechanical properties at relatively low firing temperatures, but also provides a feasible approach for the reduction, harmlessness, and resource utilization of municipal sludge, red mud, and waste glass.

[0006] To achieve the above objectives, the present invention provides a medium-temperature oxidizing sludge ash-based lightweight ceramsite, wherein the lightweight ceramsite is prepared from matrix raw materials and an added pore-forming agent; the matrix raw materials, by dry weight, include 100 parts of medium-temperature oxidizing sludge ash, 6-14 parts of red mud, and 68-72 parts of glass powder; the glass powder includes waste glass powder and recycled glass powder; the added pore-forming agent is silicon carbide powder, and the added amount is 0.3%-0.7% of the total mass of the matrix raw materials.

[0007] The intermediate-temperature oxidation sludge ash is a solid residue obtained by thermally oxidizing sludge in air or an oxygen-containing atmosphere at 500-700 °C, preferably at 550-650 °C; the sludge includes municipal sludge. The chemical composition of the intermediate-temperature oxidation sludge ash, by mass percentage, is: SiO2 25-30%, Al2O3 28-32%, Fe2O3 10-14%, P2O5 15-19%, CaO 2-4%, Na2O 1-3%, K2O 2-4%, MgO 1-3%, with the remainder being unavoidable impurities. The red mud is an industrial solid waste generated during alumina production, and its chemical composition, by mass percentage, is: Fe2O3 34-40%, Al2O3 17-22%, SiO2 8-12%, TiO2 5-8%, CaO 4-7%, Na2O 2-5%, with the remainder being unavoidable impurities. The glass powder comprises waste glass powder and recycled glass powder, and its chemical composition, by mass percentage, is: SiO2 89-92%, Na2O 4-6%, Al2O3 2-4%, CaO 0.1-1%, with the remainder being unavoidable impurities. The silicon carbide powder is an added pore-forming agent, with a purity ≥98% and an average particle size D. 50 The range is 1-10 μm.

[0008] The present invention also provides a method for preparing the above-mentioned lightweight ceramsite, comprising the following steps: drying, crushing and sieving medium-temperature oxidized sludge ash, red mud and glass powder, preferably, passing the crushed raw materials through a 100-mesh sieve to make the raw material particle size less than 150 μm; mixing the treated medium-temperature oxidized sludge ash, red mud and glass powder in a certain proportion to form a matrix raw material, and then adding silicon carbide powder accounting for 0.3%-0.7% of the total mass of the matrix raw material as a pore-forming agent, mixing evenly and then adding water accounting for 5%-10% of the total mass of the matrix raw material and the pore-forming agent to make raw material granules; drying the raw material granules at 105 ℃ for 2-3 h; then placing them in a firing furnace, first heating to 350-450 ℃ and holding for 8-20 min for preheating, then continuing to heat to 1020-1070 ℃ and holding for 5-20 min for calcination, and cooling to room temperature after calcination to obtain the lightweight ceramsite. Preferably, preheating and calcination are completed continuously in the same calcining furnace. After preheating, the raw material particles are not cooled in the middle, but are heated to the calcination temperature.

[0009] Preferably, the preheating temperature is 400-420 ℃, and the preheating time is 8-12 min; the calcination temperature is 1050-1060 ℃, and the calcination time is 10-15 min.

[0010] More preferably, the preheating temperature is 415 ℃, and the preheating time is 10 min; the calcination temperature is 1060 ℃, and the calcination time is 15 min. These further preferred parameters are merely optimal implementation points in a specific embodiment and do not constitute the sole limitation on the scope of protection of this invention.

[0011] The resulting lightweight ceramsite has a bulk density of 453-700 kg / m³, a single particle compressive strength of 3-6.5 MPa, and a water absorption rate of no more than 2.1% in 1 h.

[0012] The lightweight ceramsite produced by this invention can be used as lightweight building aggregate, lightweight backfill material, thermal insulation lightweight aggregate, or permeable pavement aggregate.

[0013] The principle of this invention: Based on the compositional characteristics of medium-temperature oxidized sludge ash, red mud, and glass powder, this invention performs normalization calculations on the silica, alumina, and fluxing components in the formulation and plots Riley three-phase diagrams (e.g., Figure 2 (As shown). The results show that the composition points of the ternary formulation of medium-temperature oxidized sludge ash-red mud-waste glass powder used in this invention are all located in the suitable expansion zone. The medium-temperature oxidized sludge ash mainly provides the silicon-aluminum skeleton components. The red mud contains Al2O3, Fe2O3 and some fluxing oxides, which are used to supplement aluminum, iron and other components and adjust the sintering system, such as adjusting the relative proportion of each major oxide in the sintered billet. The glass powder provides a high content of SiO2 and Na2O, CaO and other components, mainly supplementing the siliceous components. Its glassy structure is conducive to the formation of liquid phase and particle bonding during the calcination process. Therefore, by combining the three raw materials, a suitable chemical composition basis can be provided for subsequent sintering, gas generation and pore structure formation. For example, by controlling the amount of red mud to 6-14 parts by mass and the amount of glass powder to 68-72 parts by mass, and adding an appropriate amount of silicon carbide and a corresponding calcination regime, the liquid phase formation, gas generation and skeleton solidification processes are coordinated with each other, thereby forming a porous structure.

[0014] Because the intermediate-temperature oxidized sludge ash does not undergo sufficient mineral crystallization during high-temperature incineration above 850 ℃, its mineral phase transformation is relatively incomplete, and its inorganic components still have the potential to participate in subsequent sintering reactions, liquid phase formation, and framework construction. Therefore, using intermediate-temperature oxidized sludge ash as the main raw material for the preparation of lightweight ceramsite can transform it from low-value landfill and filling disposal to high-value sintered building material utilization. At the same time, combined with the supplementary and regulating effects of red mud on components such as iron, aluminum, and calcium, the improving effects of glass powder on liquid phase formation and green body sintering state, and the pore structure regulating effects of pore-forming agents, it is beneficial to prepare lightweight ceramsite with low bulk density and certain particle strength, which has good resource utilization value and application prospects.

[0015] Regarding the role of red mud in the ceramsite system: Red mud is mainly used in this system to supplement components such as Al and Fe, and participates in adjusting the composition of the sintered matrix and the high-temperature liquid phase state.

[0016] Regarding the role of silicon carbide (SiC) pore-forming agent in the ceramsite system: The addition of SiC enables the ceramsite of this invention to achieve significant expansion and reduce bulk density. However, the overall performance of the resulting ceramsite is not solely determined by the gas-generating effect of SiC. SiC is only responsible for providing gas at high temperatures. Whether the gas can be effectively encapsulated and whether a uniform and stable closed-cell structure can be formed also depends on the softening state, liquid phase generation amount, and high-temperature viscosity of the matrix composed of medium-temperature oxidized sludge ash, red mud, and glass powder. If the matrix is ​​not sufficiently softened, SiC gas generation will be difficult to achieve effective expansion; if there is too much liquid phase or the viscosity is too low, it is easy to over-expand, deform, adhere, or lead to a decrease in pore wall strength. Therefore, the technical effect of this application comes from the combined effect of the ternary matrix composition, the amount of SiC used, and the firing process, rather than simply adding a pore-forming agent.

[0017] The role of glass powder in the ceramsite system is explained as follows: Glass powder is mainly used to supplement the siliceous components and adjust the proportions of SiO2, Al2O3, and fluxing components in the raw material system, ensuring a suitable composition for sintering expansion. During calcination, the amorphous silicate components in the glass powder soften, while fluxing components such as Na2O promote the formation of a liquid phase, which is beneficial for the sintering bonding between sludge ash and red mud particles. The resulting viscous liquid phase can encapsulate the gases generated by SiC oxidation, promoting pore expansion and the formation of a porous structure. After cooling, it solidifies to form the pore walls and outer shell of the ceramsite, providing support for maintaining a certain strength. Simultaneously, glass powder facilitates the formation of a suitable liquid phase and the achievement of sintering and foaming at relatively low calcination temperatures.

[0018] The beneficial effects of this invention are: 1. Compared with the prior art, the present invention uses medium-temperature oxidized sludge ash, red mud and glass powder as the main raw materials, wherein the glass powder can be waste glass powder, which is conducive to realizing the synergistic resource utilization of a variety of solid wastes.

[0019] 2. This invention uses medium-temperature oxidized sludge ash as the main raw material. Compared with sludge ash obtained by high-temperature incineration above 850 ℃, its heat treatment temperature is relatively low, and the inorganic components such as silicon, aluminum, and iron can still participate in subsequent sintering reactions and framework construction.

[0020] 3. Using medium-temperature oxidized sludge ash as the main component, red mud and glass powder are introduced to address its chemical composition and sintering characteristics. Red mud is used to adjust the overall chemical composition of the billet, while glass powder promotes liquid phase formation during firing. SiC content is controlled within a low range of 0.3%–0.7%, and a firing regime of 1020–1070 °C ensures that liquid phase formation, SiC gas expansion, and pore wall solidification are coordinated in terms of temperature and time. This combination solves the problems of insufficient expansion of the ternary base material itself, insufficient lightweighting due to insufficient SiC, and thinning of pore walls and decreased strength due to excessive SiC, ultimately achieving a balance between low bulk density and a certain particle strength.

[0021] 4. By combining the raw material composition with the firing process, the present invention can complete the sintering and pore formation of ceramsite in the range of 1020 to 1070 ℃. Compared with sintering systems that require higher firing temperatures, this invention is beneficial for reducing the firing temperature and high-temperature heat treatment requirements.

[0022] 5. Furthermore, SEM observation results show that the lightweight ceramsite cross-section forms a relatively obvious porous structure with pores distributed in the sintered matrix; XRD analysis results show that the calcined products mainly contain quartz, hematite and cristobalite crystal phases, indicating that the calcination process is accompanied by crystal phase transformation and sintered matrix formation, which is beneficial to the formation of ceramsite pore walls and solid phase skeleton.

[0023] 6. Compared with technical solutions that use a higher amount of pore-forming agent to achieve a lightweight effect, the present invention combines a sintering system composed of medium-temperature oxidized sludge ash, red mud, and glass powder. Only 0.3% to 0.7% of SiC, accounting for the total dry mass of the matrix raw materials, needs to be added. During the calcination process at 1020 to 1070 °C, an appropriate amount of gas can be generated and a porous structure can be formed, which is beneficial to reduce the consumption of pore-forming agent. At the same time, it avoids excessive gas production, pore merging and coarsening, thinning of pore walls, and decrease in particle strength caused by excessive SiC dosage. This allows the ceramsite to achieve a balance between low bulk density, low water absorption rate, and a certain particle strength.

[0024] 7. The lightweight ceramsite prepared by this invention has both an internal porous structure and a relatively dense outer shell. It has a low water absorption rate of 1 hour. While achieving lightweighting, it can reduce the weight gain due to water absorption during use, which is beneficial for its use as a lightweight building aggregate or lightweight backfill material. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of lightweight ceramsite according to the present invention. Figure 2 The distribution of the lightweight ceramsite basic formulation of this invention in the Riley ternary diagram; Figure 3 XRD patterns of lightweight ceramsite at calcination temperatures of 1005℃-1085℃; Figure 4 This is a SEM image of the cross-section of lightweight ceramsite obtained in Example 1 of the present invention, wherein... Figure 4 (a) is a SEM image of the cross-section of the ceramsite at a magnification of 100×. Figure 4 (b) is a SEM image of the cross-section of the ceramsite at a magnification of 200×; Figure 5 The XRD pattern of the lightweight ceramsite prepared in Example 1 of this invention; Figure 6 The image shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Example 1 of this invention. Figure 7 The image shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Example 9 of this invention. Figure 8 The image shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Example 10 of this invention. Figure 9 The images show the appearance and cross-sectional views of the three products obtained in Comparative Example 1. Figure 9 (a) shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Group A of Comparative Example 1. Figure 9 (b) shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Group B of Comparative Example 1. Figure 9 (c) is an image of the lightweight ceramsite prepared in Group C of Comparative Example 1. Figure 10 The images show the appearance and cross-sectional views of the two types of lightweight ceramsite prepared in Comparative Example 2. Figure 10 (a) is an image of the lightweight ceramsite prepared in Group A of Comparative Example 2. Figure 10 (b) shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Group B of Comparative Example 2. Figure 11 The images show the appearance and cross-sectional views of the two types of lightweight ceramsite prepared in Comparative Example 3. Figure 11 (a) shows the appearance and cross-sectional view of the lightweight ceramsite prepared in Group A of Comparative Example 3. Figure 11 (b) shows the appearance and cross-sectional view of the lightweight ceramsite prepared by group C of Comparative Example 3. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments and comparative examples, but the scope of protection of the present invention is not limited to the following embodiments. Equivalent substitutions or conventional modifications made by those skilled in the art based on the disclosure of the present invention without departing from the technical concept of the present invention should all fall within the scope of protection of the present invention.

[0027] The medium-temperature oxidation sludge ash used in this embodiment is taken from the wastewater treatment plant of Guangxi Beitou Environmental Protection and Water Group Co., Ltd. It is a solid residue obtained by thermal oxidation treatment of municipal sludge in air or an oxygen-containing atmosphere. The composition by mass percentage is: SiO2 25-30%, Al2O3 28-32%, Fe2O3 10-14%, P2O5 15-19%, CaO 2-4%, Na2O 1-3%, K2O 2-4%, MgO 1-3%, and the remainder is unavoidable impurities; the preferred thermal oxidation treatment temperature is 550-650 ℃. The red mud used was obtained from Guangxi Pingguo Aluminum Industry Company. It is a solid by-product generated during the Bayer process of alumina production. The composition, by mass percentage, is: Fe2O3 34-40%, Al2O3 17-22%, SiO2 8-12%, TiO2 5-8%, CaO 4-7%, Na2O 2-5%, with the remainder being unavoidable impurities. The glass powder used was waste glass powder, obtained from discarded laboratory glassware. It was used after being cleaned, dried, and crushed. The composition, by mass percentage, is: SiO2 89-92%, Na2O 4-6%, Al2O3 2-4%, CaO 0.1-1%, with the remainder being unavoidable impurities. The pore-forming agent was silicon carbide powder, purchased from Qinghe County Hangzhuo Co., Ltd., with a purity of 99.999% and a nominal fineness of 400-500 mesh. It was used as an external pore-forming agent.

[0028] Before use, the medium-temperature oxidized sludge ash, red mud, and glass powder are pretreated, specifically including drying, crushing, and sieving. The raw material drying temperature is 100-110 ℃, and after crushing, it is passed through a 100-mesh sieve for later use. Unless otherwise specified, the amount of water added for granulation in each embodiment and comparative example is 8% of the total mass of the matrix raw material and pore-forming agent. In the actual preparation process, the amount of water added can be adjusted within the range of 5%-10% according to the moisture content of the raw material and the granulation state. Near-spherical raw material particles with a diameter of 5-10 mm are obtained using a disc granulator. The raw material particles are dried at 105 ℃ for 2 h and then subjected to heat preservation preheating and heat preservation calcination. After calcination, they are cooled to room temperature to obtain lightweight ceramsite.

[0029] The preparation process flow chart of this invention is as follows: Figure 1 As shown.

[0030] Example 1 Lightweight ceramsite was prepared according to the following steps: (1) Medium-temperature oxidized sludge ash, red mud and glass powder were dried at 100-110 ℃ to constant weight, crushed and passed through a 100-mesh sieve; (2) 100 parts of medium-temperature oxidized sludge ash, 6 parts of red mud and 70 parts of glass powder were weighed according to the mass ratio, and silicon carbide pore-forming agent was weighed according to 0.5% of the total mass of matrix raw materials; (3) After the raw materials obtained in step (2) were mixed evenly, water accounting for 8% of the total mass of matrix raw materials and pore-forming agent was added, and after mixing evenly, it was formed into near-spherical raw material balls with a diameter of 5-10 mm by a disc granulator; (4) The raw material balls obtained in step (3) were placed at 105 ℃ and dried for 2 h; in step (5), the dried raw material balls were placed in a muffle furnace, preheated at 415 ℃ for 10 min, and then calcined at 1060 ℃ for 15 min, and then cooled to room temperature with the furnace to obtain lightweight ceramsite.

[0031] The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure. Figure 6 As shown.

[0032] Example 2 The lightweight ceramsite was prepared according to the method of Example 1, except that in step (5), the dried raw material balls were placed in a muffle furnace, preheated at 350 °C for 10 min, and then calcined at 1060 °C for 10 min; the remaining steps were the same as in Example 1.

[0033] Example 3

[0034] Lightweight ceramsite was prepared according to the method of Example 1, except that: (5) the dried raw material balls were placed in a muffle furnace, preheated at 400 °C for 10 min, and then calcined at 1040 °C for 10 min; the remaining steps were the same as in Example 1.

[0035] Example 4

[0036] The lightweight ceramsite was prepared according to the method of Example 1, except that in step (5), the dried raw material balls were placed in a muffle furnace, preheated at 400 °C for 10 min, and then calcined at 1045 °C for 10 min; the remaining steps were the same as in Example 1.

[0037] Example 5

[0038] The lightweight ceramsite was prepared according to the method of Example 1, except that in step (5), the dried raw material balls were placed in a muffle furnace, preheated at 400 °C for 10 min, and then calcined at 1030 °C for 5 min; the remaining steps were the same as in Example 1.

[0039] Example 6

[0040] The lightweight ceramsite was prepared according to the method of Example 1, except that in step (5), the dried raw material balls were placed in a muffle furnace, preheated at 400 °C for 10 min, and then calcined at 1030 °C for 15 min; the remaining steps were the same as in Example 1.

[0041] Example 7

[0042] The lightweight ceramsite was prepared according to the method of Example 1, except that: in step (2), 100 parts of medium-temperature oxidized sludge ash, 10 parts of red mud, and 68 parts of glass powder were weighed by mass, and silicon carbide pore-forming agent was weighed at 0.5% of the total mass of matrix raw materials; in step (5), after preheating at 400 ℃ for 10 min, it was calcined at 1040 ℃ for 10 min; the remaining steps were the same as in Example 1.

[0043] Example 8

[0044] The lightweight ceramsite was prepared according to the method of Example 1, except that: in step (2), 100 parts of medium-temperature oxidized sludge ash, 14 parts of red mud, and 72 parts of glass powder were weighed by mass, and silicon carbide pore-forming agent was weighed at 0.5% of the total mass of matrix raw materials; in step (5), after preheating at 400 ℃ for 10 min, it was calcined at 1040 ℃ for 10 min; the remaining steps were the same as in Example 1.

[0045] Example 9

[0046] The lightweight ceramsite was prepared according to the method of Example 1, except that in step (2), 100 parts of medium-temperature oxidized sludge ash, 10 parts of red mud, and 70 parts of glass powder were weighed by mass, and silicon carbide pore-forming agent was weighed by 0.3% of the total mass of matrix raw materials; the remaining steps were the same as in Example 1.

[0047] The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure below. Figure 7 As shown.

[0048] Example 10

[0049] The lightweight ceramsite was prepared according to the method of Example 1, except that in step (2), 100 parts of medium-temperature oxidized sludge ash, 10 parts of red mud, and 70 parts of glass powder were weighed by mass, and silicon carbide pore-forming agent was weighed at 0.7% of the total mass of the matrix raw materials; the remaining steps were the same as in Example 1.

[0050] The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure below. Figure 8 As shown.

[0051] Example 11 The products obtained in Examples 1-10 were tested according to the aforementioned test standards and methods. The bulk density and 1-hour water absorption rate of the obtained ceramsite were tested according to GB / T 17431.2 "Lightweight aggregates and their test methods Part 2: Lightweight aggregates test methods". The compressive strength of a single particle was measured using a digital compression testing machine.

[0052] During the bulk density test, the ceramsite is loaded into a graduated cylinder, leveled, weighed, and the volume is recorded. The bulk density is then calculated.

[0053] For the 1-hour water absorption rate test, the ceramsite was dried at 105 ℃ for 4 hours to constant weight, and then the dried mass was weighed after cooling. Subsequently, the ceramsite was soaked in water for 1 hour, and after being taken out, the surface moisture was wiped off to make it reach a saturated surface-dry state. The 1-hour water absorption rate was then weighed and calculated.

[0054] The compressive strength test adopts the single-particle compressive strength test method: using a digital pressure testing machine, at least 15 uniform ceramsite samples are randomly selected, and each sample is placed on the load platform. Vertical pressure is applied at a loading rate of 2 mm / min, and the load value (i.e., crushing force) at the moment of particle breakage is recorded.

[0055] The compressive strength of a single particle of expanded clay aggregate is calculated according to formula (1):

[0056] In the formula: σ is the measured compressive strength of a single ceramsite particle, in MPa; P is the load at the moment of crushing of the ceramsite, in N; and D is the particle size of the ceramsite, in mm.

[0057] The test results are shown in Table 1.

[0058] Table 1. Test results of products obtained in Examples 1-10

[0059] As shown in Table 1, lightweight ceramsite can be prepared in Examples 1 to 10 within the range of raw material ratio, SiC dosage and firing regime defined in this invention. The products obtained show different degrees of difference in bulk density, single particle compressive strength and 1-hour water absorption rate, indicating that the raw material composition, SiC dosage and firing conditions will affect the performance of ceramsite.

[0060] Examples 1-6 used the same raw material ratio and SiC dosage, and the effects of the firing regime were investigated by changing the preheating temperature, calcination temperature, and calcination time. The resulting ceramsite had a bulk density of 490-652 kg / m³, a single-particle compressive strength of 3.2-6.1 MPa, and a 1-hour water absorption rate of 0.8%-2.0%, indicating that lightweight ceramsite with low bulk density and certain particle strength can be obtained within the firing regime range defined by this invention. Example 1 used the preferred firing conditions, namely preheating at 415℃ for 10 min and calcining at 1060℃ for 15 min, resulting in ceramsite with a bulk density of 507 kg / m³, a single-particle compressive strength of 4.3 MPa, and a 1-hour water absorption rate of 1.1%, achieving a good balance between lightweighting, particle strength, and water absorption.

[0061] Examples 7 and 8, while maintaining the SiC dosage and firing regime unchanged, respectively selected different amounts of red mud and glass powder within the scope defined by this invention. Combined with the results of Example 1, it can be seen that when using different representative compositions within the specified red mud and glass powder ratio range, lightweight ceramsite with low bulk density and certain particle strength can be obtained, indicating that the raw material ratio of this invention is not limited to a single composition point and is feasible within the defined scope.

[0062] Examples 9 and 10 used 0.3% and 0.7% SiC, respectively, which, together with Example 1 using 0.5% SiC, cover the low, middle, and high values ​​of the SiC dosage range defined in this invention. The results show that when the SiC dosage is 0.3%, 0.5%, and 0.7%, the ceramsite can be sintered normally to form pores. As the SiC dosage increases, the overall bulk density of the ceramsite decreases, while the particle strength and water absorption properties change accordingly, indicating that the SiC dosage can regulate the degree of pore formation and its structure-property relationship. Therefore, limiting the SiC dosage to a lower range of 0.3% to 0.7% allows for different degrees of lightweighting effects while maintaining the particle strength and water absorption properties of the ceramsite.

[0063] In summary, the raw material ratio, SiC dosage, and firing regime specified in this invention do not correspond to a single optimal implementation point, but are all practically feasible within the specified range; through the combination of the three, the degree of sintering porosity and the lightweight-strength properties of the ceramsite can be controlled.

[0064] Example 12 Lightweight ceramsite was prepared according to the method in Example 1, except that in step (5), the calcination temperature was changed to 1005℃, 1030℃, 1060℃, and 1085℃, and XRD pattern analysis was performed. Figure 3As shown in the figure, this is the XRD pattern of ceramsite samples at different calcination temperatures. The figure shows that the main diffraction peaks of the samples at 1005 ℃, 1030 ℃, 1060 ℃, and 1085 ℃ are basically consistent, indicating that increasing the calcination temperature did not cause a significant change in the main crystal phase type. The main crystal phases in the samples are quartz (SiO2) and hematite (Fe2O3), possibly accompanied by a small amount of cristobalite (SiO2). The quartz mainly originates from unreacted siliceous components in the raw materials, while the hematite is related to the iron oxides abundant in red mud.

[0065] As the calcination temperature increased, the intensity of diffraction peaks of quartz and other crystalline phases generally weakened, indicating that some crystalline phases gradually participated in the melting reaction or were encapsulated by the generated liquid / amorphous glass phase. Simultaneously, all samples exhibited a broad diffuse diffraction background within the 15°–35° range, indicating the formation of a certain amount of amorphous glass phase in the ceramic particles. This glass phase mainly originated from the softening and melting of waste glass powder, as well as the reaction of components such as SiO2, Al2O3, Fe2O3, and Na2O at high temperatures.

[0066] At a comparative temperature of 1005 °C, quartz and hematite crystalline phases were more prominent in the sample, indicating a lower degree of raw material reaction and limited liquid phase formation at lower temperatures. When the calcination temperature increased to 1030 °C (within the range of this invention), some crystalline phase diffraction peaks began to weaken, indicating an improvement in the sintering reaction and liquid phase formation. At this point, sintering of the ceramic particles was achieved, but the degree of liquid phase formation and sintering was still lower than at 1060 °C. Further increasing the temperature to 1060 °C, some crystalline phase diffraction peaks weakened further, while the amorphous glass phase characteristics strengthened, indicating further development of the sintering reaction and liquid phase formation, which is beneficial to the formation and stability of the ceramic particle pore walls. Further increasing the temperature to 1085 °C, the crystalline phase diffraction peaks continued to weaken, and the degree of glassization further increased. Combined with the sintered morphology of the particles at this temperature, it can be seen that excessively high temperatures easily cause the particles to soften and deform, and tend to over-fire.

[0067] In summary, the phase changes of ceramsite in the range of 1005–1085 ℃ are mainly characterized by a weakening of the crystalline phase peak and an enhancement of the amorphous glass phase. The good match between crystalline phase retention and liquid phase formation at 1060 ℃ is an important reason for the formation of a stable porous structure and the achievement of good comprehensive performance in ceramsite.

[0068] Example 13 Results Analysis The lightweight ceramsite prepared in Example 1 was subjected to cross-sectional SEM observation and XRD analysis, and the results are as follows: Figure 4 and Figure 5 As shown. By Figure 4 (a) SEM image of the cross-section of ceramsite at 100× magnification, and Figure 4(b) The SEM image of the ceramsite cross-section at 200× magnification shows a relatively obvious porous structure inside the ceramsite cross-section. The pores are distributed within the sintered matrix, with some pores being nearly circular or elliptical. Continuous sintered phase is visible around the pore walls, indicating that under the firing regime of preheating at 415 ℃ for 10 min and calcining at 1060 ℃ for 15 min, the silicon carbide oxidation gas generation process and the glass powder softening to form a liquid phase process have a good matching relationship, which is beneficial for gas retention and pore formation within the green body. Figure 5 As can be seen, quartz and hematite were mainly detected in the ceramsite, accompanied by a small amount of cristobalite and other crystalline phases. With increasing calcination temperature, the diffraction peaks of some crystalline phases gradually weakened, while the diffuse diffraction background increased, indicating that a crystalline phase transformation occurred during calcination, forming a certain amount of amorphous glassy phase. Combined with SEM and XRD results, it can be seen that this invention, by adding an appropriate amount of silicon carbide pore-forming agent, combined with the formation of the glass powder liquid phase and the adjustment of red mud components, can promote pore formation and sintering framework construction, thus enabling the ceramsite to possess both low bulk density and certain particle strength.

[0069] Comparative Example 1 Effect of formulation on the properties of lightweight ceramsite Lightweight ceramsite was prepared according to the method in Example 1, with the difference that in step (2), three experimental groups were set up, with raw materials added in the following proportions: Group A (red mud deficiency group): medium-temperature oxidized sludge ash: red mud: glass powder = 100:0:70, Group B (glass powder deficiency group): medium-temperature oxidized sludge ash: red mud: glass powder = 100:10:0, and Group C (sludge ash deficiency group): medium-temperature oxidized sludge ash: red mud: glass powder = 0:10:70. The experimental results are shown in Table 2. The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in Table 2. Figure 9 As shown; Table 2 shows the test results of the product prepared in Comparative Example 1.

[0070] The results of Group A (red mud-deficient group) indicate that, under the representative firing condition of 1060 ℃, the main ceramsite properties of the red mud-deficient group and the ternary reference group are relatively similar, suggesting that red mud is not the primary factor determining the lightweight and strength of the ceramsite under these conditions. However, based on the chemical composition of the raw materials, Riley three-phase diagrams (such as...) were performed... Figure 2As shown in the figure, calculations show that after adding an appropriate amount of red mud, the S, A, and F composition of the sintered matrix is ​​further corrected, and the formula enters or is closer to the suitable expansion range. Red mud mainly adjusts the overall chemical composition and high-temperature liquid phase state of the sintered matrix by supplementing Al, Fe, and some fluxing components, so that the formula has a more reasonable theoretical composition margin when the raw material composition fluctuates and the firing conditions change. Therefore, this application positions red mud as a composition adjustment component in the sintered matrix. The comparison ratio without red mud can still produce ceramsite under representative firing conditions, indicating that its impact on the performance of the representative firing point is limited, and its main physical properties are not significantly different from the ternary reference group. This further shows that red mud and limiting its dosage have corresponding formula design basis, and the technical role of red mud is mainly reflected in the adjustment of the overall chemical composition, rather than solely determining the lightweighting, expansion, or strength properties of the ceramsite. The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure. Figure 9 As shown in (a).

[0071] The results of Group B (glass powder deficient group) show that without waste glass powder, the ceramsite basically did not achieve sintering expansion and lightweighting. Waste glass powder plays an important role in the formation of the low-temperature liquid phase and complete sintering. The appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure below. Figure 9 As shown in (b).

[0072] Although group C (lacking sludge ash) managed to granulate, it completely melted at 1060 °C, losing its granular shape and adhering to the crucible, making it impossible to obtain intact ceramsite. Therefore, the bulk density, particle strength, and water absorption could not be determined. The results indicate that removing the medium-temperature oxidized sludge ash, the main raw material, significantly increased the relative content of waste glass powder in the system, and markedly altered the composition of the sintered matrix and the high-temperature liquid phase state. Excessive liquid phase or excessively low viscosity at 1060 °C caused the green body to fail to maintain its granular shape and melt and collapse. Therefore, medium-temperature oxidized sludge ash is not only a major resource-based raw material but also participates in the composition and construction of the sintered matrix, playing a crucial role in maintaining the structural stability of the ceramsite during molding and firing. The appearance and cross-sectional view of the obtained lightweight ceramsite are shown below. Figure 9 As shown in (c).

[0073] The missing component comparison shows that each raw material plays a different role in the system. Medium-temperature oxidized sludge ash mainly constructs the sintering framework and maintains the high-temperature morphology of the particles; waste glass powder promotes liquid phase formation, full sintering, and expansion at 1060 ℃; red mud has a relatively limited impact on bulk density and compressive strength, mainly used to adjust the chemical composition of the matrix, and may improve sintering density and water absorption. Although the ternary reference group is not the best in any single indicator, it achieves a good overall balance between lightweighting, particle strength, low water absorption, and sintering stability.

[0074] Comparative Example 2 Effect of calcination temperature on the properties of lightweight ceramsite Lightweight ceramsite was prepared according to the method in Example 1, with the difference that in step (5), two experimental groups were set up, with calcination temperatures of Group A: 1010℃ and Group B: 1080℃ respectively; the experimental results are shown in Table 3; the appearance and cross-sectional view of the obtained lightweight ceramsite are shown in the figure. Figure 10 As shown; Table 3. Test results of the products prepared in Comparative Example 2

[0075] Group A (1010℃) results show that when the calcination temperature is 1010℃, the sintering degree of the ceramsite is insufficient. The particle surface is rough, without an obvious glaze layer, and the internal structure is relatively loose, with some areas still exhibiting a powdery or incompletely sintered state. This indicates that at this temperature, the matrix has not yet formed a sufficient amount of liquid phase with suitable viscosity, the bonding between particles is insufficient, and the SiC gas generation is difficult to be effectively encapsulated. Therefore, the ceramsite does not expand significantly during calcination and does not form a complete and stable porous structure. The appearance and cross-sectional view of the obtained lightweight ceramsite are shown below. Figure 10 As shown in (a).

[0076] The results for Group B (1080℃) indicate that while increasing the calcination temperature further promotes expansion and lightweighting at 1080℃, it also leads to excessive pore development, thinning of pore walls, or loosening of the structure, resulting in decreased strength and surface density. The table shows that the bulk density of the ceramsite in the 1080℃ group decreased to 376 kg / m³, but the compressive strength decreased to 2.3 MPa, the 1-hour water absorption rate increased to 2.1%, and excessive expansion, deformation, and adhesion occurred. This indicates that while further increasing the calcination temperature can promote expansion and reduce density, it also increases the amount of high-temperature liquid phase, reduces viscosity, causes excessive pore expansion, thinning of pore walls, and a decrease in surface structural integrity. Furthermore, the lowest density does not necessarily represent the best overall performance. The appearance and cross-sectional images of the obtained lightweight ceramsite are shown below. Figure 10 As shown in (b). Therefore, 1080 °C is beyond the suitable firing temperature range, and the upper limit of the firing temperature is set at 1070 °C to support it.

[0077] Comparative Example 3 Effect of silicon carbide addition on the properties of lightweight ceramsite Lightweight ceramsite was prepared according to the method in Example 1, with the difference that: the silicon carbide addition amounts were set to 0%, 0.8%, and 1.0%, and three experimental groups (A, B, and C) were set up; the experimental results are shown in Table 4; the appearance and cross-sectional views of the obtained lightweight ceramsite are shown in the figure. Figure 11 As shown; Table 4. Test results of the product prepared in Comparative Example 3

[0078] Table 4 shows that, under the same matrix raw material ratio and firing regime, the SiC addition amount has a significant impact on the bulk density, single-particle compressive strength, and water absorption rate of the ceramsite. Group A, without SiC, has a bulk density of 929 kg / m³, a single-particle compressive strength of 13.7 MPa, and a water absorption rate of only 0.2% after 1 h. This indicates that the ceramsite is relatively densely sintered without the addition of a pore-forming agent. Although it has high particle strength and low water absorption, its lightweight nature is insufficient. The appearance and cross-sectional view of the resulting lightweight ceramsite are shown in the figure. Figure 11 As shown in (a). After adding 0.5% SiC, the bulk density of Example 1 decreased to 507 kg / m³, while still maintaining a single-particle compressive strength of 4.3 MPa and a 1-h water absorption rate of 1.1%. This indicates that an appropriate amount of SiC can promote gas generation and pore formation during the sintering process, and maintain a certain particle strength and a low water absorption rate while significantly reducing the bulk density of the ceramic particles.

[0079] When the SiC addition was further increased to 0.8% and 1.0%, the bulk density of the ceramsite further decreased to 390 kg / m³ and 380 kg / m³, respectively, but the compressive strength of a single particle decreased to 2.0 MPa and 1.8 MPa, respectively, and the water absorption rate after 1 h increased to 2.7% and 2.5%, respectively. The appearance and cross-sectional profile of the lightweight ceramsite obtained when the SiC addition was 1.0% are shown in the figure below. Figure 11 As shown in (b), while a higher SiC content can further enhance gas generation and pore formation and reduce the bulk density of the ceramsite, it also leads to an increase in the porosity of the ceramsite structure, resulting in a significant decrease in particle strength and an increase in water absorption. Therefore, a higher SiC content is not necessarily more beneficial; a reasonable balance needs to be struck between lightweighting, particle strength, and water absorption performance.

Claims

1. A ternary composite lightweight ceramsite of medium-temperature oxidized sludge ash-red mud-recycled glass powder, characterized in that, The lightweight ceramic particles are prepared by sintering a matrix raw material with an added silicon carbide pore-forming agent; The matrix raw materials, by dry weight, include 100 parts of medium-temperature oxidized sludge ash, 6-14 parts of red mud, and 68-72 parts of glass powder; The amount of silicon carbide pore-forming agent added is 0.3%-0.7% of the total mass of the matrix raw materials.

2. The lightweight ceramsite according to claim 1, characterized in that, The medium-temperature oxidation sludge ash is a solid residue obtained after sludge is thermally oxidized in air or an oxygen-containing atmosphere at 550-650 ℃. The chemical composition of the medium-temperature oxidized sludge ash is as follows: by mass percentage, SiO2 is 25-30%, Al2O3 is 28-32%, Fe2O3 is 10-14%, P2O5 is 15-19%, CaO is 2-4%, Na2O is 1-3%, K2O is 2-4%, MgO is 1-3%, and the remainder is unavoidable impurities.

3. The lightweight ceramsite according to claim 1, characterized in that, The purity of the silicon carbide pore-forming agent is ≥98%, and the average particle size D is... 50 The range is 1-10 μm.

4. The lightweight ceramsite according to claim 1, characterized in that, The lightweight ceramsite has a bulk density of 453-700 kg / m³, a single particle compressive strength of 3-6.5 MPa, and a water absorption rate of ≤2.1% over 1 hour.

5. The application of the lightweight ceramsite as described in any one of claims 1-4 in lightweight building aggregates, lightweight backfill materials, thermal insulation lightweight aggregates, and permeable pavement aggregates.

6. A method for preparing a ternary composite lightweight ceramsite of medium-temperature oxidized sludge ash-red mud-recycled glass powder, characterized in that, Includes the following steps: (1) Raw material pretreatment: The medium-temperature oxidized sludge ash, red mud and glass powder are dried, crushed and sieved; (2) Mixed granulation: By mass, 100 parts of medium-temperature oxidized sludge ash, 6-14 parts of red mud, and 68-72 parts of glass powder are mixed to form matrix raw materials. Then, 0.3%-0.7% of silicon carbide pore-forming agent is added to the above matrix raw materials and mixed evenly. Water is then added to make raw material granules. (3) Drying: The raw material particles are dried. (4) Preheating: Place the dried raw material pellets in the firing furnace, heat to 350-450 ℃ and keep warm for 8-20 min; (5) Calcination: After preheating, continue to raise the temperature to 1020-1070 ℃ and hold for 5-20 min for calcination; (6) Cooling: After calcination, cool to room temperature to obtain the lightweight ceramsite.

7. The preparation method according to claim 6, characterized in that, In step (1), the medium-temperature oxidized sludge ash, red mud and glass powder are dried to constant weight, crushed and sieved so that the particle size of the raw materials is less than 150 μm; in step (2), the amount of water added is 5%-10% of the total mass of the matrix raw materials and silicon carbide pore-forming agent.

8. The preparation method according to claim 6, characterized in that, In step (3), the drying process is to dry at 105 °C for 2-3 h.

9. The preparation method according to claim 6, characterized in that, In step (4), the preheating temperature is 400-420 ℃ and the holding time is 8-12 min.

10. The preparation method according to claim 6, characterized in that, In step (5), the roasting temperature is 1050-1060 ℃ and the roasting time is 10-15 min.

Images