A kind of foamed ceramic prepared by spontaneous foaming of contaminated soil and red mud

Abstract

The application belongs to the technical field of building material preparation, and provides a foamed ceramic prepared by self-foaming of contaminated soil and red mud. The contaminated soil and the red mud are dried, crushed, sieved, mixed, and then raw materials are obtained; the raw materials are added with a reducing agent and a catalyst and are ball milled to obtain a mixture; the mixture is stacked and placed in a mold, calcined in a furnace, and then cooled to obtain the foamed ceramic. By changing the ratio of the contaminated soil and the red mud, the amount of gas generation is regulated, self-foaming is realized, and the foamed ceramic is prepared by using all solid wastes; by matching the use of the reducing agent, the catalyst and the all solid waste raw materials, the reaction of the difficult-to-reduce compounds in the red mud is promoted, and then the easy-to-reduce iron-containing compounds are separated out, so that the reduction is sufficient, the gas production efficiency is improved, and the gas production temperature is reduced.

Description

Technical Field

[0001] This invention belongs to the field of building material preparation technology, and relates to a foamed ceramic prepared by self-foaming using contaminated soil and red mud. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Contaminated soil is primarily caused by the unorganized discharge of pollutants or the failure of discharge systems, allowing pollutants to seep into the soil layer. This leads to changes in the physical, mechanical, and chemical properties of the soil, directly affecting engineering activities or harming human health, animal reproduction, and plant growth. It is a waste product generated from modern industrial production. The complex composition and high heavy metal content of contaminated soil limit its widespread application. Currently, remediation remains the main treatment method, but its complexity and high cost limit large-scale remediation. A few researchers have conducted research on the reuse of contaminated soil by preparing ceramsite. For example, CN114538892A discloses a low-cost ceramsite preparation process based on the harmless treatment of contaminated soil. This process involves multiple steps, including primary purification, secondary purification, complexation, and adsorption treatment of the contaminated soil. The resulting mixture needs to be covered and cured for 60-100 days. The process is complex, costly, and time-consuming, affecting efficiency and hindering the large-scale application of contaminated soil. Patent CN116177992A discloses a high-temperature sintering method for preparing ceramsite from heavy metal contaminated soil in conjunction with fly ash. This preparation method requires the addition of alkaline water for aging and then drying, making the preparation method equally complex.

[0004] Red mud is a polluting waste residue discharged after refining alumina from bauxite. For every ton of alumina produced, 0.8-1.5 tons of red mud are generated as a byproduct. Its accumulation is increasing year by year, and the comprehensive utilization of red mud has become one of the limiting factors for the development of the aluminum industry. How to effectively utilize red mud is an urgent problem to be solved.

[0005] Foamed ceramics are high-porosity ceramic materials with a three-dimensional spatial network structure. SiO2 and Al2O3 are the main components constituting the material's skeleton. Foamed ceramics possess high porosity, low water absorption, low bulk density, and a certain compressive strength, thus showing broad application prospects in fireproofing, thermal insulation, sound insulation, and sound absorption. Contaminated soil and red mud are rich in silica-alumina oxides, which can provide the skeleton structure for foamed ceramics; they also contain a certain amount of alkali metal and alkaline earth metal oxides as fluxes during the sintering process. The iron oxides in red mud exist in complex forms. Although the iron oxides in red mud may undergo redox reactions to generate gas during sintering, they usually form difficult-to-reduc compounds with SiO2 and Al2O3 (such as fir olivine (2FeO·SiO2) and iron-aluminum spinel (FeO·Al2O3), which are unfavorable for gas production.

[0006] The characteristics of contaminated soil and red mud provide a feasibility for the self-foaming preparation of foamed ceramics using both as raw materials from solid waste. Patent CN105198481A discloses a method for preparing foamed ceramic thermal insulation boards using Yellow River silt and red mud, wherein the red mud content is 10%-50%, the high-temperature flux content is 9.95%-50%, and the foaming agent content is 0.05%-5%. Patent CN108503336A uses red mud as raw material, supplemented with a foam stabilizer and a foaming agent, to prepare foamed ceramics, wherein the red mud content is 33%-40%, and the total solid waste content is up to 70%. None of the above-mentioned prior art can achieve the preparation of foamed ceramics from all solid waste, and all require the addition of a foaming agent, increasing the preparation cost. Summary of the Invention

[0007] To address the problem of high production costs and the need for large amounts of foaming agents in the current preparation of foamed ceramics using contaminated soil and red mud as raw materials, this invention provides a method for preparing foamed ceramics using contaminated soil and red mud as entirely solid waste raw materials, supplemented with reducing agents and catalysts, through self-foaming. The method achieves self-foaming by regulating pore size through the synergistic effect of the reducing agent, catalyst, and red mud. This method offers efficient utilization of solid waste, and its simple preparation method facilitates widespread adoption.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A method for preparing self-foaming ceramics using contaminated soil and red mud as raw materials includes the following steps:

[0010] (1) The contaminated soil and red mud are dried, crushed, sieved, and mixed to obtain the raw materials;

[0011] (2) Selectively add reducing agent and catalyst to the raw materials and ball mill them to obtain a mixture;

[0012] (3) The mixture is piled into a mold, placed in a furnace for calcination, and cooled to obtain foamed ceramic.

[0013] The raw material comprises 40%-90% contaminated soil by mass, with the remainder being red mud. Preferably, the contaminated soil is organically contaminated soil. Preferably, the red mud is high-iron red mud obtained through magnetic separation.

[0014] In step (1), the sieve fineness is 200 mesh.

[0015] In step (2), the fineness of the mixture is 200 mesh.

[0016] The reducing agent is at least one selected from pulverized coal, carbon powder, graphite powder, and activated carbon. The amount of reducing agent added is 0-15% of the red mud mass; preferably 5-10% of the red mud mass.

[0017] The catalyst is at least one selected from sodium carbonate, sodium fluoride, and calcium fluoride. The amount of catalyst added is 0-10% of the red mud mass; preferably 2-6% of the red mud mass.

[0018] The calcination temperature is 1200℃-1260℃; preferably 1230℃-1250℃. In some embodiments, the calcination process is as follows: the temperature is increased to the calcination temperature at a heating rate of 3℃ / min-11℃ / min, and held at the calcination temperature for 0-60 min.

[0019] The mechanism and synergistic effects of this invention are as follows:

[0020] The reducing agent added in this invention can undergo a redox reaction with iron oxides (Fe2O3) in red mud through a carbothermic reduction process to generate gas. The added catalyst can react with difficult-to-reduc compounds such as fir olivine and iron-aluminum spinel in red mud, thereby separating easily reduced iron compounds (Fe2O3) to ensure complete reduction and improve gas production efficiency. In addition, the red mud pretreated with high-gradient magnetic separation increases the Fe2O3 content, thereby increasing gas production. At the same time, the pretreatment removes some minerals that hinder the reduction reaction and also lowers the gas production temperature.

[0021] Specifically,

[0022] The skeletal structure of foamed ceramics is mainly formed by silica-alumina oxides. The contaminated soil is rich in SiO2 and Al2O3, which lays the foundation for the successful sintering of foamed ceramics. Another major component of the contaminated soil, CaO, is an alkaline earth metal oxide. During high-temperature sintering, it can break the Si-O bonds in the silicate melt, reduce the viscosity of the high-temperature liquid phase, and significantly lower the sintering temperature, making it an effective flux. Furthermore, Ca... 2+It also has the function of regulating pore structure, and has a significant effect on regulating the balance between liquid phase surface tension and pore expansion growth force, which is beneficial to the preparation of foamed ceramics with uniform and full pores.

[0023] Red mud is rich in Fe2O3, which can undergo redox reactions during sintering:

[0024] Fe2O3→FeO+O2

[0025] The gas released from Fe2O3 in red mud is sufficient to cause the green body to expand, thus eliminating the need for additional foaming agents. The Na2O and TiO2 abundant in red mud are both alkaline oxides and also act as fluxing agents. Furthermore, altering the mixing ratio of contaminated soil and red mud can change the Fe2O3 content, regulate the gas generation, and adjust the content of other fluxing components, which helps improve the pore structure and is more conducive to obtaining foamed ceramics with uniform and stable structure and properties.

[0026] The uniformity of pore structure can be adjusted by changing the sintering temperature and holding time: changing the sintering temperature can affect the viscosity of the liquid phase, thereby reducing the activation energy of flow and decreasing the resistance to pore growth. Changing the holding time can change the amount of Fe2O3 reaction, thereby affecting the driving force for bubble growth. In this way, foamed ceramics with different pore sizes can also be obtained.

[0027] The present invention has the following advantages:

[0028] (1) This invention effectively adjusts the skeleton components and fluxing components of the mixed raw materials by changing the mixing ratio of contaminated soil and red mud, thus realizing the feasibility of preparing foamed ceramics from all solid waste.

[0029] (2) This invention controls the amount of gas generated by changing the amount of red mud and thus the Fe2O3 content in the mixed raw materials, thereby controlling the pore structure of the self-foaming ceramic.

[0030] (3) The matching use of reducing agents, catalysts and solid waste raw materials promotes the reaction of difficult-to-reducible compounds in red mud, thereby separating easily reduced iron-containing compounds Fe2O3, so that they are fully reduced and the gas production efficiency is improved.

[0031] (4) The red mud pretreated by high gradient magnetic separation increases the Fe2O3 content, which increases the gas production while removing some minerals that hinder the reduction reaction and also lowers the gas production temperature. Attached Figure Description

[0032] Figure 1 These are cross-sectional photographs of the foamed ceramic prepared in Example 1;

[0033] Figure 2 These are cross-sectional photographs of the foamed ceramic prepared in Example 2;

[0034] Figure 3 This is a cross-sectional photograph of the foamed ceramic prepared in Comparative Example 1;

[0035] Figure 4 This is a cross-sectional photograph of the foamed ceramic prepared in Example 3.

[0036] Figure 5 This is a cross-sectional photograph of the foamed ceramic prepared in Example 4. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments and accompanying drawings, but the present invention is not limited to the embodiments described below. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] Example 1: Preparation of foamed ceramics using carbon powder as a reducing agent, sodium fluoride as a catalyst, and contaminated soil and red mud as all-solid waste raw materials.

[0039] (1) The mass ratio of contaminated soil to red mud is 9:1. The amount of reducing agent added is 10% of the mass of red mud, and the amount of catalyst added is 2% of the mass of red mud. After mixing, the mixture is ball-milled and passed through a 200-mesh sieve to obtain the mixture.

[0040] (2) The mixture is piled into a mold and placed in a furnace for calcination. The firing temperature is 1260℃, the heating rate is 3℃ / min, the holding time is 30min, and the foamed ceramic is obtained after cooling.

[0041] The obtained cross-sectional photographs of the foamed ceramic are as follows Figure 1 As shown, its pore structure is closed-cell, but the upper pores are larger and the lower pores are smaller. Its porosity is 71% and its bulk density is 516 kg / m³. 3 The compressive strength is 6.21 MPa.

[0042] Example 2: Preparation of foamed ceramics using pulverized coal as a reducing agent, calcium carbonate as a catalyst, and contaminated soil and red mud as all-solid waste raw materials.

[0043] (1) The mass ratio of contaminated soil to red mud is 6:4. The amount of coal powder added is 10% of the mass of red mud, and the amount of calcium carbonate added is 5% of the mass of red mud. After mixing, the mixture is ball-milled and passed through a 200-mesh sieve to obtain the mixture.

[0044] (2) The mixture is piled into a mold and placed in a furnace for calcination. The firing temperature is 1230℃, the heating rate is 5℃ / min, the holding time is 30min, and the foamed ceramic is obtained after cooling.

[0045] The obtained cross-sectional photographs of the foamed ceramic are as follows Figure 2 As shown, its pore structure is a uniform closed-cell morphology, with a porosity of 87.6% and a bulk density of 355 kg / m³.3 The compressive strength is 4.13 MPa.

[0046] Comparative Example 1: Preparation of foamed ceramics using contaminated soil and red mud as raw materials from all solid waste.

[0047] (1) The mass ratio of contaminated soil to red mud is 6:4. No reducing agent or catalyst is added. The mixture is ball-milled and passed through a 200-mesh sieve to obtain the mixture.

[0048] (2) The mixture is piled into a mold and placed in a furnace for calcination. The firing temperature is 1230℃, the heating rate is 5℃ / min, the holding time is 30min, and the foamed ceramic is obtained after cooling.

[0049] The obtained cross-sectional photographs of the foamed ceramic are as follows Figure 3 As shown, its pore structure is uneven, exhibiting stratification. The upper layer has more pores than the lower layer, with a porosity of 63% and a bulk density of 585 kg / m³. 3 Its compressive strength is 7.24 MPa.

[0050] Example 3: Preparation of foamed ceramics using graphite powder as a reducing agent, calcium fluoride as a catalyst, and contaminated soil and red mud as all-solid waste raw materials.

[0051] (1) The mass ratio of contaminated soil to red mud is 4:6. The amount of reducing agent added is 5% of the mass of red mud, and the amount of catalyst added is 6% of the mass of red mud. After mixing, the mixture is ball-milled and passed through a 200-mesh sieve to obtain the mixture.

[0052] (2) The mixture is piled into a mold and placed in a furnace for calcination. The firing temperature is 1250℃, the heating rate is 10℃ / min, the holding time is 60min, and the foamed ceramic is obtained after cooling.

[0053] The obtained cross-sectional photographs of the foamed ceramic are as follows Figure 4 As shown, its pore structure exhibits large-sized pores with interconnected pores, a porosity of 91.88%, and a bulk density of 332 kg / m³. 3 The compressive strength is 2.15 MPa.

[0054] Example 4: Preparation of foamed ceramics using activated carbon as a reducing agent, calcium fluoride as a catalyst, and contaminated soil and magnetically separated red mud as all-solid waste raw materials.

[0055] (1) The mass ratio of contaminated soil and magnetically separated high-iron red mud is 4:6. The amount of reducing agent added is 5% of the mass of red mud, and the amount of catalyst added is 6% of the mass of red mud. After mixing, the mixture is ball-milled and passed through a 200-mesh sieve to obtain the mixture.

[0056] (2) The mixture is piled into a mold and placed in a furnace for calcination. The firing temperature is 1250℃, the heating rate is 10℃ / min, the holding time is 30min, and the foamed ceramic is obtained after cooling.

[0057] The obtained cross-sectional photographs of the foamed ceramic are as follows Figure 5 As shown, its pore structure exhibits large-sized pores with interconnected pores, a porosity of 89.69%, and a bulk density of 367 kg / m³. 3 Its compressive strength is 2.66 MPa.

Claims

1. A method for preparing self-foaming ceramics using contaminated soil and red mud as raw materials, characterized in that, Includes the following steps: (1) The contaminated soil and red mud are dried, crushed, sieved, and mixed to obtain the raw materials; (2) Add reducing agent and catalyst to the raw materials and ball mill them to obtain a mixture; (3) The mixture is piled into a mold, placed in a furnace for calcination, and cooled to obtain foamed ceramics; The raw materials contain 40%-90% contaminated soil by mass, with the remainder being red mud; The reducing agent is selected from at least one of pulverized coal, carbon powder, graphite powder, and activated carbon; The catalyst is at least one of calcium carbonate, sodium fluoride, and calcium fluoride. The calcination temperature is 1200℃-1260℃; the calcination process is as follows: the temperature is increased to the calcination temperature at a heating rate of 3℃ / min-11℃ / min, and then held at the calcination temperature for 0-60 minutes.

2. The preparation method according to claim 1, characterized in that, The contaminated soil is organic contaminated soil; the red mud is high-iron red mud after magnetic separation.

3. The preparation method according to claim 1, characterized in that, In step (1), the sieve fineness is 200 mesh; in step (2), the fineness of the mixture is 200 mesh.

4. The preparation method according to claim 1, characterized in that, The amount of the reducing agent added is 5%-15% of the mass of the red mud; the amount of the catalyst added is 2%-10% of the mass of the red mud.

5. The preparation method according to claim 1, characterized in that, The amount of the reducing agent added is 5-10% of the mass of the red mud; the amount of the catalyst added is 2-6% of the mass of the red mud.

6. The preparation method according to claim 1, characterized in that, The calcination temperature is 1230℃-1250℃.

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