A step-pore foamed ceramic based on sulfur-containing tailings and its preparation method

Abstract

The present invention relates to the technical field of porous ceramic preparation, and specifically to a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof. The raw materials include: 20 to 60 parts of sulfur-containing tailings, 30 to 70 parts of coal-based industrial solid waste, 3 to 15 parts of flux, 2 to 8 parts of foam stabilizer, 0.05 to 0.30 parts of foaming agent, and 0.05 to 0.50 parts of triethanolamine. The above raw materials are sequentially added to a ceramic ball mill, mixed by a wet method to form a uniform slurry, which is dried and crushed to form a powder and filled in a square refractory sagger. Subsequently, the slurry is foamed at high temperature, cooled and cut to prepare a foamed ceramic with a pore size that decreases stepwise along the height direction. The step-pore foamed ceramic prepared by the present invention not only has high mechanical properties, but also has good thermal insulation properties. This preparation method not only solves the problem of the difficulty in balancing the mechanical properties and thermal insulation properties of foamed ceramics, but also realizes high value-added utilization of industrial solid waste.

Description

Technical Field

[0001] The invention relates to the technical field of porous ceramic preparation, and in particular to a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof. Background Art

[0002] Foamed ceramics are a ceramic-based foam material with a closed pore structure. It is an inorganic thermal insulation material with excellent properties such as light weight and high strength, thermal insulation, fire retardant, waterproof and antifreeze, sound insulation, and aging resistance. It has been widely used in building insulation, pipeline insulation and other fields. Foamed ceramics are usually prepared by high-temperature powder foaming method, which mainly uses the gas produced by the high-temperature decomposition of the foaming agent to form closed bubbles in the molten and softened body to construct a porous ceramic with a foam structure. The number and pore size of the pores inside the foamed ceramic affect the density of the material, which in turn determines the mechanical properties and thermal insulation properties of the material. Due to the small pore size and high density (density 400-800kg / m 3 ) foam ceramics have high strength and are usually used as lightweight partition materials. However, their thermal conductivity is high. When used in walls with high thermal insulation requirements, they also need to be combined with insulation boards with low thermal conductivity (such as EPS boards), which seriously affects construction efficiency and cost. On the other hand, large pore size and low density (≤280kg / m 3 Although foamed ceramics (likely referring to a foamed ceramic) have low thermal conductivity, they suffer from poor compressive strength and impact resistance, limiting their use to exterior wall insulation panels. If foamed ceramics with a stepped pore size distribution could be produced, achieving both excellent thermal insulation and high strength, this would be of great significance for improving the overall performance of foamed ceramics and innovating the design of wall insulation structures.

[0003] Chinese invention patent CN202210755807.0 discloses a nickel slag-based aerogel multi-level porous foamed ceramic and its preparation method. This method prepares a multi-level porous structure foamed ceramic with macropores and mesopores by adding a chemical foaming agent and aerogel. However, the pores of different pore sizes are evenly distributed inside the foamed ceramic and a stepped distribution is not achieved. Therefore, the sample still cannot have both high strength and good thermal insulation performance.

[0004] In addition, Chinese invention application CN202310353193.8 discloses a method for preparing multi-level porous ceramics by hydrolysis self-foaming-gel integration. This method uses secondary aluminum ash as raw material and foaming agent, and adopts gel injection molding to prepare multi-level porous ceramics with a pore size distribution of 50μm to 2mm. Similarly, although the multi-level porous ceramics prepared by this method have a wide pore size distribution range, the pores of different pore sizes are not distributed in layers, and the gel injection molding process is complicated and costly, making it difficult to use on a large scale for wall insulation materials.

[0005] Sulfur-containing tailings are a type of metal tailings with a high sulfur content. Since pyrite is often accompanied by non-ferrous metals such as gold, silver, copper, and zinc, a variety of useless minerals including iron sulfide and calcium sulfate are discharged during the non-ferrous metal refining process, and the resulting residue is called sulfur-containing tailings.

[0006] Chinese invention patent CN201510416038.1 discloses a method for resource utilization of iron sulfide tailings. By adding microorganisms to iron sulfide tailings, a microbial fuel cell is prepared, which can effectively recover heavy metals and also recover electrical energy. However, this type of method has little effect on the huge consumption of sulfur-containing tailings. At present, a large amount of sulfur-containing tailings (such as gold tailings and copper tailings) are still disposed of in a stockpiling manner. Due to the high tailings dam body, there are safety hazards. At the same time, the tailings components and residual mineral processing agents seriously damage the ecological environment, especially those containing heavy metals and toxic CN - The cyanide tailings, when leached with rainwater, pose a serious threat to the entire ecological environment and human survival. Therefore, more effective methods for the resource utilization of sulfur-containing tailings are needed. Since sulfur-containing tailings contain not only aluminum-silicon minerals but also sulfur-containing minerals such as FeS2, FeS, and CaSO4, these substances decompose at high temperatures to produce SO2 gas. If sulfur-containing tailings are used to produce foamed ceramics, the SO2 gas generated at high temperatures can be used to create pores within the green body, reducing the amount of foaming agent used in the production of foamed ceramics.

[0007] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the Invention

[0008] The purpose of the present invention is to solve the problems that existing small-pore, high-density foamed ceramics have high strength but insufficient thermal insulation performance; large-pore, low-density foamed ceramics have good thermal insulation performance but low strength. The present invention discloses a stepped pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof.

[0009] In order to achieve the above-mentioned purpose, the present invention discloses a stepped pore foamed ceramic based on sulfur-containing tailings, which comprises the following raw materials, calculated by weight: 20 to 60 parts of sulfur-containing tailings, 30 to 70 parts of coal-based industrial solid waste, 3 to 15 parts of flux, 2 to 8 parts of foam stabilizer, 0.05 to 0.30 parts of foaming agent, and 0.05 to 0.50 parts of triethanolamine.

[0010] The sulfur-containing tailings include at least one of gold tailings, silver tailings, copper tailings, and cyanide tailings, and the sulfur content in the chemical composition thereof is 2-10 wt%.

[0011] The coal-based industrial solid waste includes at least one of fly ash, coal gangue powder, and coal-fired furnace slag powder, and its chemical composition includes Al2O3+SiO2: 60~95wt%, CaO+MgO: 0~10wt%, Na2O+K2O: 1~6wt%, Fe2O3: 0~8wt%, and loss on ignition 0~10%.

[0012] The flux includes at least one of feldspar powder, soda ash, borax, and glass powder.

[0013] The foam stabilizer includes at least one of trisodium phosphate, magnesite powder, light-burned magnesium oxide powder, and corundum powder.

[0014] The foaming agent includes at least one of carbon black, silicon carbide powder and silicon nitride powder.

[0015] The closed porosity of the stepped pore foamed ceramic is 60-95%, the apparent porosity is 0-2%, the pore size is 0.1-2.0 mm, and the pore size increases stepwise along the height direction. The average pore size of the top surface is 1.5-3.5 times that of the bottom surface, and the volume density is 200-600 kg / m 3 , compressive strength 1.0~12.5MPa, thermal conductivity 0.050~0.195W / (m·K).

[0016] The present invention also discloses a method for preparing the above-mentioned step-pore foamed ceramic based on sulfur-containing tailings, comprising the following steps:

[0017] S1, adding raw materials into a ceramic ball mill, adding water according to the material-water mass ratio of 1:0.7 and mixing for 4-8 hours, the ball mill rotation speed is 40-80 r / min, and the mill slurry is dried at 95℃-105℃ to obtain fine powder;

[0018] S2, evenly piling the powder obtained in step S1 in a square refractory sagger, flattening the surface, and pressing until the powder is dense;

[0019] S3, placing the refractory sagger filled with powder obtained in step S2 in a kiln, heating it to 1150-1250°C, keeping it warm for 30-90 minutes, then cooling it to room temperature at a rate of -3--10°C / min, taking it out and cutting the surface to obtain stepped pore foamed ceramics of specified size.

[0020] In step S2, the thickness of the powder is 5 to 10 cm, and the pressure to compact the powder is 5 to 10 N / cm 2 .

[0021] In step S3, the specific heating process is as follows: heating to 500-600°C at 3-5°C / min, keeping warm for 30 minutes, then heating to 800-1000°C at 6-10°C / min, and then heating to 1150-1200°C at 3-5°C / min.

[0022] The present invention uses sulfur-containing tailings in conjunction with coal-based solid waste to produce stepped pore foamed ceramics. The method utilizes the high-temperature decomposition properties of sulfur-containing tailings to produce SO₂ gas. By adding coal-based solid waste, flux, foam stabilizer, and foaming agent, the product is sintered and foamed at high temperatures to form a closed-cell foam structure. In this technical solution, since pyrite begins to gradually decompose at around 600°C and consumes a large amount of O₂ during decomposition, the oxygen concentration within the green body decreases. However, during the heating process, oxygen in the air penetrates from the surface of the green body to the bottom through the gaps between the powder particles, causing the oxygen concentration within the green body to gradually decrease from the surface to the bottom. When the green body is heated to the foaming temperature (1150-1250°C), the foaming agent (such as carbon black and SiC) begins to oxidatively decompose, producing gas. However, due to the different degrees of oxidative decomposition of the foaming agent in different oxygen concentration environments, the amount of CO₂ gas produced varies, resulting in the pores formed at the bottom of the sample being smaller than those at the surface. Therefore, a single firing process can be used to produce foamed ceramics with stepped pore sizes.

[0023] When using this technical solution to prepare stepped-pore foam ceramics, it is necessary not only to control the type and dosage of sulfur-containing tailings, but also the packing density, thickness, and heating rate of the blank. Otherwise, due to excessively high or low oxygen concentrations within the blank, stepped pores may not form, or degraded black-core macropores may form at the bottom of the sample. A detailed analysis is shown in the Examples.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. The foamed ceramic prepared by the present invention has a stepped pore structure, and the pore size gradually increases or decreases along the thickness direction of the foamed ceramic, so that the foamed ceramic not only has good thermal insulation performance, but also has high compressive strength and impact resistance;

[0026] 2. The raw materials used in the present invention are mainly solid wastes such as sulfur-containing tailings and coal-based solid waste, with a comprehensive utilization rate of 80% to 90%. The high-temperature sintering effect is used to promote the decomposition of harmful substances in the solid waste and the solidification of heavy metals, which not only achieves the harmless and high-value-added utilization of various solid wastes, but also reduces the preparation cost of foamed ceramics.

[0027] 3. The present invention uses sulfur-containing tailings as the main raw material, and utilizes the characteristics of sulfur-containing minerals (such as FeS2, CaSO4) to produce SO2 gas by high-temperature decomposition and consume O2, which not only reduces the amount of foaming agent added (when the amount of foaming agent is only 0.05% to 0.30%, a foaming agent with a volume density of 200 to 600 kg / m3 Foamed ceramics) and at the same time constructing foamed ceramics with a stepped pore structure;

[0028] 4. The present invention still uses the powder high-temperature foaming method commonly used in ordinary foamed ceramics. It only achieves the preparation of stepped pore foamed ceramics by optimizing the material formula composition, powder stacking method and firing system. The process equipment is mature, the production cost is low, and it is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The appearance, stepped pore structure morphology and pore size distribution of the foamed ceramic prepared in Example 1 of the present invention are shown;

[0030] Figure 2 This is a flow chart of the step-pore foamed ceramic based on sulfur-containing tailings and its preparation method in the present invention;

[0031] Figure 3 The appearance and structural morphology of the foamed ceramic prepared in Comparative Example 1;

[0032] Figure 4 The following are the appearance, structural morphology and pore size distribution of the foamed ceramic prepared in Comparative Example 2. DETAILED DESCRIPTION

[0033] The above and other technical features and advantages of the present invention are described in more detail below with reference to the accompanying drawings.

[0034] Example 1

[0035] This embodiment provides a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof, wherein the raw materials and the proportions are as follows:

[0036] 40 parts of cyanide tailings, 40 parts of fly ash, 10 parts of coal gangue powder, 12 parts of feldspar powder, 1 part of sodium carbonate, 4 parts of light-burned magnesium oxide, 0.15 parts of SiC powder, and 0.05 parts of triethanolamine.

[0037] The method for preparing stepped pore foam ceramics using the above raw materials is as follows: Figure 2 As shown, the following steps are included:

[0038] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 6 hours. The ball mill speed is 60 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0039] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 5 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 5 N / cm 2 Press lightly until the powder is dense.

[0040] 3) Place the refractory sagger filled with powder in the kiln, heat it to 500°C at 3°C / min, keep it warm for 30 minutes, then heat it to 900°C at 10°C / min, then heat it to 1150°C at 3°C / min, keep it warm for 45 minutes, and then cool it to room temperature at -3°C / min. After taking it out, cut the surface to obtain a stepped hole foamed ceramic sample with a size of 100*80*60mm.

[0041] The obtained stepped pore foam ceramic has a closed porosity of 86.5%, an apparent porosity of 1.1%, a pore size of 0.35 to 1.25 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 1.04 mm, the average pore size on the bottom surface is 0.52 mm, and the bulk density is 365 kg / m 3 , compressive strength 5.52MPa, thermal conductivity 0.106W / (m·K). The appearance, pore structure morphology and pore size distribution of the stepped pore foamed ceramics prepared in this embodiment are shown in the figure below. Figure 1 As shown by Figure 1 It can be seen that the pore size of the stepped pore foamed ceramic obtained in this embodiment decreases stepwise along the height direction.

[0042] Example 2

[0043] This embodiment provides a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof, wherein the raw materials and the proportions are as follows:

[0044] 20 parts of cyanide tailings, 60 parts of fly ash, 10 parts of coal gangue powder, 12 parts of feldspar powder, 1 part of sodium carbonate, 8 parts of magnesite powder, 0.2 parts of SiC powder, and 0.05 parts of triethanolamine.

[0045] The method for preparing stepped pore foam ceramics using the above raw materials comprises the following steps:

[0046] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 6 hours. The ball mill speed is 60 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0047] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 6 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 8 N / cm 2 Press lightly until the powder is dense.

[0048] 3) Place the refractory sagger filled with powder in the kiln, heat it to 500°C at 4°C / min, keep it warm for 30 minutes, then heat it to 900°C at 10°C / min, then heat it to 1180°C at 3°C / min, keep it warm for 60 minutes, and then cool it to room temperature at -3°C / min. After taking it out, cut the surface to obtain a stepped pore foamed ceramic sample.

[0049] The obtained stepped pore foam ceramic has a closed porosity of 85.6%, an apparent porosity of 0.9%, a pore size of 0.45 to 1.15 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 0.98 mm, the average pore size on the bottom surface is 0.60 mm, and the bulk density is 389 kg / m 3 , compressive strength 5.92MPa, thermal conductivity 0.115W / (m·K).

[0050] Example 3

[0051] This embodiment provides a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof, wherein the raw materials and the proportions are as follows:

[0052] 50 parts of gold tailings, 40 parts of fly ash, 10 parts of feldspar powder, 5 parts of corundum powder, 3 parts of light-burned magnesium oxide, 0.3 parts of SiC powder, and 0.05 parts of triethanolamine.

[0053] The method for preparing stepped pore foam ceramics using the above raw materials comprises the following steps:

[0054] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 8 hours. The ball mill speed is 80 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0055] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 5 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 8 N / cm 2 Press lightly until the powder is dense.

[0056] 3) Place the refractory sagger filled with powder in the kiln, heat it to 500°C at 3°C / min, keep it warm for 30 minutes, then heat it to 900°C at 8°C / min, then heat it to 1200°C at 3°C / min, keep it warm for 80 minutes, and then cool it to room temperature at -3°C / min. After taking it out, cut the surface to obtain a stepped pore foamed ceramic sample.

[0057] The obtained stepped pore foam ceramic has a closed porosity of 89.9%, an apparent porosity of 1.6%, a pore size of 0.45 to 1.68 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 1.49 mm, the average pore size on the bottom surface is 0.62 mm, and the bulk density is 273 kg / m 3 , compressive strength 2.68MPa, thermal conductivity 0.070W / (m·K).

[0058] Example 4

[0059] This embodiment provides a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof, wherein the raw materials and the proportions are as follows:

[0060] 30 parts of gold tailings, 20 parts of fly ash, 35 parts of slag powder, 10 parts of glass powder, 5 parts of soda ash, 5 parts of light-burned magnesium oxide, 0.3 parts of SiC powder, and 0.05 parts of triethanolamine.

[0061] The method for preparing stepped pore foam ceramics using the above raw materials comprises the following steps:

[0062] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 6 hours. The ball mill speed is 60 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0063] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 5 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 5 N / cm 2 Press lightly until the powder is dense.

[0064] 3) The refractory sagger filled with the powder is placed in a kiln, and the firing system is the same as the cooling system in Example 3. When the sample is cooled to room temperature, it is taken out and the surface is cut to obtain a stepped pore foamed ceramic sample.

[0065] The obtained stepped pore foam ceramic has a closed porosity of 90.2%, an apparent porosity of 1.8%, a pore size of 0.52 to 1.48 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 1.29 mm, the average pore size on the bottom surface is 0.75 mm, and the bulk density is 265 kg / m 3 , compressive strength 1.98MPa, thermal conductivity 0.068W / (m·K).

[0066] Example 5

[0067] This embodiment provides a step-pore foamed ceramic based on sulfur-containing tailings and a preparation method thereof, wherein the raw materials and the proportions are as follows:

[0068] 60 parts of copper tailings, 30 parts of fly ash, 10 parts of feldspar powder, 1 part of trisodium phosphate, 3 parts of light-burned magnesium oxide, 0.05 parts of SiC powder, and 0.1 parts of triethanolamine.

[0069] The method for preparing stepped pore foam ceramics using the above raw materials comprises the following steps:

[0070] 1) All raw materials were added to a ceramic ball mill and ball-milled. The mixing process parameters were the same as those in Example 4.

[0071] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 8 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 10 N / cm 2 Press lightly until the powder is dense.

[0072] 3) Place the refractory sagger filled with powder in the kiln, heat it to 600℃ at 3℃ / min, keep it warm for 30min, then heat it to 1000℃ at 10℃ / min, then heat it to 1160℃ at 3℃ / min, keep it warm for 40min, and then cool it to room temperature at -4℃ / min. After taking it out, cut the surface to obtain a stepped pore foamed ceramic sample.

[0073] The obtained stepped pore foam ceramic has a closed porosity of 78.4%, an apparent porosity of 0.5%, a pore size of 0.25 to 1.06 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 0.95 mm, the average pore size on the bottom surface is 0.42 mm, and the bulk density is 585 kg / m 3 , compressive strength 11.52MPa, thermal conductivity 0.185W / (m·K).

[0074] Comparative Example 1

[0075] This comparative example provides a comparative case that does not adopt the preferred parameters proposed in the present invention. The raw materials and proportions are:

[0076] 40 parts of cyanide tailings, 40 parts of fly ash, 10 parts of coal gangue powder, 12 parts of feldspar powder, 1 part of sodium carbonate, 4 parts of light-burned magnesium oxide, 0.15 parts of SiC powder, and 0.05 parts of triethanolamine.

[0077] The method for preparing stepped pore foam ceramics using the above raw materials is as follows: Figure 2 As shown, the following steps are included:

[0078] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 6 hours. The ball mill speed is 60 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0079] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 5 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 50 N / cm 2 Press until the powder is dense.

[0080] 3) Place the refractory sagger filled with powder in a kiln, heat it to 1150°C at 8°C / min, keep it warm for 45 minutes, and then cool it to room temperature at -3°C / min. After taking it out, cut the surface to obtain a foamed ceramic sample with a size of 100*80*60mm.

[0081] The obtained stepped pore foam ceramic has a closed porosity of 32.3%, an apparent porosity of 59.1%, a pore size of 0.55 to 15.51 mm, and a large number of degraded macropores with a size exceeding 10 mm at the bottom of the sample. The bulk density is 275 kg / m 3, compressive strength 0.53MPa. The appearance and pore structure of the foamed ceramic prepared in this comparative example are as follows Figure 3 shown.

[0082] Compared with Example 1, Comparative Example 1 uses the same raw material composition, but uses a higher molding pressure and a faster firing rate. The bottom of the foamed ceramic produced black-core macropores, and the apparent porosity increases rapidly, resulting in a compressive strength of the sample of only 0.53 MPa. This is because the powder density is too high. During the short firing time, the oxygen in the air cannot penetrate into the bottom of the green body in time to replenish the oxygen consumed by the decomposition of pyrite, resulting in a reducing atmosphere inside. Due to the high iron content in the green body, the viscosity of the green body is reduced during the foaming stage, and the pores grow abnormally. This also shows that powder molding pressure and firing rate are important factors affecting the preparation of step-hole foamed ceramics.

[0083] Comparative Example 2

[0084] This comparative example provides a comparative case that does not adopt the preferred parameters proposed in the present invention. The raw materials and proportions are:

[0085] 10 parts of cyanide tailings, 70 parts of fly ash, 10 parts of coal gangue powder, 12 parts of feldspar powder, 1 part of sodium carbonate, 4 parts of light-burned magnesium oxide, 0.15 parts of SiC powder, and 0.05 parts of triethanolamine.

[0086] The method for preparing stepped pore foam ceramics using the above raw materials is as follows: Figure 2 As shown, the following steps are included:

[0087] 1) Add all raw materials into a ceramic ball mill, add water at a material-water ratio of 1:0.7 and mix for 6 hours. The ball mill speed is 60 r / min. The mill slurry is dried at 100℃±5℃ to obtain a fine powder.

[0088] 2) The obtained powder is evenly piled in a square refractory sagger with a thickness of 5 cm. After the surface is smoothed, the powder is evenly piled with a pressure of 50 N / cm 2 Press until the powder is dense.

[0089] 3) Place the refractory sagger filled with powder in a kiln, heat it to 1150°C at 2°C / min, keep it warm for 45 minutes, and then cool it to room temperature at -3°C / min. After taking it out, cut the surface to obtain a foamed ceramic sample with a size of 100*80*60mm.

[0090] The obtained stepped pore foam ceramic has a closed porosity of 88.1%, an apparent porosity of 0.9%, a pore size of 0.86 to 1.15 mm, and the pore size increases stepwise along the height direction. The average pore size on the top surface is 1.09 mm, the average pore size on the bottom surface is 0.98 mm, and the bulk density is 322 kg / m 3, compressive strength 4.51MPa, thermal conductivity 0.102W / (m·K). The appearance, pore structure morphology and pore size distribution of the foamed ceramic prepared in this comparative example are shown in the figure below. Figure 4 shown.

[0091] Compared with Example 1, Comparative Example 2 uses less sulfur-containing tailings (cyanide tailings) as raw materials and uses a slower firing rate. The resulting foamed ceramic has a uniform bottom pore size and no obvious pore size step distribution phenomenon. This is because the decomposition of less sulfur-containing minerals consumes less oxygen, and the oxygen in the air can also penetrate into the body within a longer heating time. Therefore, the oxygen concentration inside the body is sufficient during the foaming stage, and the decomposition of the foaming agent is not restricted, so the pores can grow uniformly. This shows that the sulfur-containing tailings dosage and firing rate, as well as the mutual matching between the two parameters, are important factors affecting the preparation of stepped pore foamed ceramics.

[0092] The chemical compositions of the solid waste raw materials used in Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 1:

[0093] Table 1 Chemical composition of solid waste raw materials used in Examples 1 to 5

[0094]

[0095] The above description is merely a preferred embodiment of the present invention and is intended to be illustrative rather than restrictive of the present invention. Those skilled in the art will appreciate that many changes, modifications, and even equivalents may be made to the present invention within the spirit and scope of the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A step-pore foamed ceramic based on sulfur-containing tailings, characterized in that: The raw materials are as follows, calculated by weight: 20-60 parts of sulfur-containing tailings, 30-70 parts of coal-based industrial solid waste, 3-15 parts of flux, 2-8 parts of foam stabilizer, 0.05-0.30 parts of foaming agent, and 0.05-0.50 parts of triethanolamine. The sulfur-containing tailings include at least one of gold tailings, silver tailings, copper tailings, and cyanide tailings, and the sulfur content in the chemical composition is 2-10 wt%. The sulfur-containing tailings are decomposed at high temperature to produce SO2 gas and consume O2. The preparation method of the step-pore foamed ceramic based on sulfur-containing tailings comprises the following steps: S1, add raw materials into ceramic ball mill, add water according to the material-water mass ratio of 1:0.7 and mix for 4-8 hours, the ball mill rotation speed is 40-80r / min, and the mill slurry is dried at 95℃~105℃ to obtain fine powder; S2, evenly piling the powder obtained in step S1 in a square refractory sagger, flattening the surface, and pressing until the powder is dense; S3, placing the refractory sagger containing the powder obtained in step S2 in a kiln, heating it to 1150-1250°C, holding it for 30-90 minutes, then cooling it to room temperature at a rate of -3--10°C / min, taking it out and cutting the surface to produce a stepped pore foam ceramic of a specified size; In step S2, the thickness of the powder is 5-10 cm, and the pressure to compact the powder is 5-10 N / cm 2 ; In step S3, the specific heating process is as follows: heating to 500-600°C at 3-5°C / min, keeping warm for 30 minutes, then heating to 800-1000°C at 6-10°C / min, and then heating to 1150-1200°C at 3-5°C / min.

2. The step-pore foamed ceramic based on sulfur-containing tailings according to claim 1, characterized in that: The coal-based industrial solid waste includes at least one of fly ash, coal gangue powder, and coal-fired furnace slag powder, and its chemical composition includes Al2O3+SiO2: 60~95wt%, CaO+MgO: 0~10wt%, Na2O+K2O: 1~6wt%, Fe2O3: 0~8wt%, and loss on ignition 0~10%.

3. The step-pore foamed ceramic based on sulfur-containing tailings according to claim 1, characterized in that: The flux includes at least one of feldspar powder, soda ash, borax, and glass powder.

4. The step-pore foamed ceramic based on sulfur-containing tailings according to claim 1, characterized in that: The foam stabilizer includes at least one of trisodium phosphate, magnesite powder, light-burned magnesium oxide powder, and corundum powder.

5. The step-pore foamed ceramic based on sulfur-containing tailings according to claim 1, characterized in that: The foaming agent includes at least one of carbon black, silicon carbide powder and silicon nitride powder.

6. The step-pore foamed ceramic based on sulfur-containing tailings according to claim 1, characterized in that: The stepped pore foam ceramic has a closed porosity of 60-95%, an apparent porosity of 0-2%, a pore size of 0.1-2.0 mm, and the pore size increases stepwise along the height direction. The average pore size of the top surface is 1.5-3.5 times that of the bottom surface, and a bulk density of 200-600 kg / m 3 , compressive strength 1.0~12.5MPa, thermal conductivity 0.050~0.195W / (m·K).

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