A method for producing sintered bricks using bauxite tailings and its products and applications

Abstract

This invention discloses a method for producing sintered bricks using bauxite tailings, along with its products and applications, belonging to the field of building materials production from industrial solid waste. The method comprises the following steps: (1) mixing 50-70 parts by weight of bauxite tailings, 30-40 parts of fly ash, and 0-10 parts of expanded perlite to obtain a mixture; controlling the moisture content of the mixture within a certain range, and then aging it to obtain aged raw materials; (2) preparing the aged raw materials into wet brick blanks; (3) drying the wet brick blanks to control their moisture content within a certain range, obtaining dry brick blanks; (4) firing the dry brick blanks, followed by natural cooling, to obtain sintered bricks. This method features simple raw material proportions, easily controllable production process parameters, and significantly reduces the drying shrinkage rate and sintering shrinkage rate of the brick blanks. The resulting sintered bricks possess excellent mechanical and thermal insulation properties, showing promising application prospects as building materials in construction.

Description

Technical Field

[0001] This invention relates to the field of producing building materials from industrial solid waste, and more particularly to a method for producing sintered bricks from bauxite tailings, the products thereof, and their applications. Background Technology

[0002] Bauxite resources are mainly monohydrate gibbsite type bauxite, characterized by high aluminum and high silicon content. The vast majority are low- to medium-grade bauxite with an aluminum-to-silicon ratio (the percentage of aluminum oxide to silicon dioxide, the same below) of less than 7. Desilication through flotation to improve the grade of bauxite, followed by the economical Bayer process for alumina production, has become an effective way to improve the utilization rate of low- to medium-grade bauxite resources. The tailings generated after bauxite beneficiation are generally discharged directly into tailings dams by increasing the slurry concentration. This will bring the following problems: (1) A large amount of tailings are piled up in tailings ponds, polluting the surrounding environment; (2) The investment, management, and maintenance costs of tailings ponds are large, and the potential safety threats are also quite prominent; (3) A large amount of useful minerals in the tailings are discarded and not effectively utilized, resulting in extreme waste of resources. Therefore, the comprehensive utilization of bauxite beneficiation tailings urgently needs to be addressed.

[0003] For example, Chinese invention patent CN108530015A discloses a method for preparing autoclaved bricks using bauxite tailings. The autoclaved bricks of this invention are made from bauxite tailings, fly ash, lime, desulfurized gypsum, additives, and water. The preparation steps involve first mixing the bauxite tailings, fly ash, lime, and desulfurized gypsum evenly, then adding water and additives and continuing stirring; subsequently, the evenly mixed slurry is poured into a mold and cured in a humid environment at 45-60 ℃ for 3-4 hours; after cleaning off excess slurry from the mold, the mold is placed in an autoclaving tank or chamber and cured at 70-100 ℃ for 20-24 hours. After natural cooling, the mold is removed to obtain the final product. In this invention, the bauxite tailings, fly ash, and desulfurized gypsum are all solid wastes, thus achieving waste resource utilization. However, bauxite tailings require calcination at 800°C to increase the material's activity. Uncalcined bauxite tailings cannot react with additives like lime and gypsum under steam curing conditions. Calcination adds to the processing steps, and the calcined tailings still need further crushing into bauxite powder before they can be used for brick making. Furthermore, steam-cured bricks have a relatively complex raw material composition and manufacturing process, and their compressive strength is generally lower than that of sintered bricks. This limits their applicability in applications requiring high resistance to weathering, frost resistance, and durability.

[0004] For example, Chinese invention patent CN108395178A discloses a non-autoclaved aerated concrete containing bauxite tailings and its preparation method. This invention's non-autoclaved aerated concrete is prepared from bauxite tailings powder, fly ash, lime, gypsum, cement, water, aluminum powder paste, and admixtures. The preparation method involves high-temperature treatment of bauxite tailings to transform their inactive minerals into highly active alumina and silica. Then, under non-autoclaved conditions, the alumina and silica generate new products that can exist stably, thereby improving the specific strength of the aerated concrete. This invention realizes the resource utilization of industrial solid waste and has profound environmental and social benefits. However, the bauxite tailings powder of this invention requires calcination of the bauxite tailings at 800°C, and its formula has a low amount of bauxite tailings added, resulting in a lower treatment effect on bauxite tailings per unit dosage. The raw material composition and process are also relatively complex.

[0005] In summary, this paper provides a method for producing sintered bricks using bauxite tailings to solve the problems existing in the prior art, which is of positive significance for expanding the comprehensive utilization of bauxite tailings. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for producing sintered bricks from bauxite tailings is provided, which features high utilization rate, convenient process, and high production flexibility, comprising the following steps:

[0007] (1) By weight, 50-70 parts of bauxite tailings, 30-40 parts of fly ash and 0-10 parts of expanded perlite are mixed to obtain a mixture; the moisture content of the mixture is controlled within a certain range and aged to obtain aged raw materials.

[0008] (2) The aged raw materials are made into wet brick blanks;

[0009] (3) The wet brick blanks are dried to control their moisture content within a certain range to obtain dry brick blanks;

[0010] (4) The dry brick blanks are fired and then cooled naturally to obtain sintered bricks.

[0011] Alumina is difficult to form glassy and crystalline phases with other components at 950-1050 °C, but it can form mullite crystalline phases with silicon dioxide above 1200 °C. The main purpose of limiting the aluminum-silicon ratio is to limit the alumina content; a high aluminum-silicon ratio results in a high alumina content and a high sintering temperature. Therefore, this invention is suitable for controlling the aluminum-silicon ratio in the raw materials within a certain range to reduce the difficulty of sintering, optimize the surface pulverization of the brick, and improve the product strength.

[0012] Preferably, in step (1), the aluminum-silicon ratio of the bauxite tailings is <1.3; and the aluminum-silicon ratio of the fly ash is <0.7.

[0013] Preferably, in step (1), the moisture content of the mixture is controlled to be between 15% and 20%.

[0014] Aging promotes the disintegration of raw material particles, loosens the clay clumps, and homogenizes moisture. Raw materials that have undergone appropriate aging are easier to shape, exhibiting better plasticity, easier molding, fewer cracks, and lower extrusion pressure. Simultaneously, the quality of the brick blanks is improved, such as a smoother surface, higher density, and less susceptibility to cracking, resulting in a higher success rate in forming the finished bricks.

[0015] Preferably, in step (1), the aging process lasts for 48-72 hours.

[0016] Preferably, in step (2), the aged raw materials are extruded and cut into blanks to form wet brick blanks of the target shape.

[0017] Maintaining the moisture content of dry brick blanks within a suitable range helps optimize the quality of the finished product. If the moisture content is too high, defects such as micro-cracks, dull bricks, and white-spotted bricks may appear on the surface of the product. Furthermore, high moisture content is detrimental to the development of brick strength and can easily cause deformation and tilting during the firing process.

[0018] Preferably, in step (3), the moisture content of the dry brick blank is <6%.

[0019] Preferably, in step (4), the roasting temperature is 950-1050 ℃ and the holding time is 1-2 h.

[0020] A tunnel kiln is a modern, continuous firing thermal equipment constructed from refractory, insulation, and building materials. It contains kiln cars and other transport vehicles, and its shape resembles a tunnel. The tunnel kiln operates on a counter-current principle, divided into three zones along its length: preheating, firing, and cooling. The products move in opposite directions to the airflow, completing the preheating, firing, and cooling processes sequentially within these three zones. The drying and firing processes of the sintered bricks described in this invention can be completed using a tunnel kiln commonly used in this field, eliminating the need for specialized equipment and offering advantages such as wide applicability and automated production.

[0021] Preferably, in steps (3) and (4), the drying and calcining operations are carried out in a tunnel kiln.

[0022] In a second aspect of the present invention, a sintered brick with excellent mechanical properties and good thermal insulation properties is provided, which is prepared by the preparation method of the first aspect of the present invention.

[0023] In a third aspect of the invention, the application of the sintered bricks of the second aspect of the invention is provided, specifically, the sintered bricks are used as building materials in building construction.

[0024] Based on the above technical solutions, the design concept and principle of this invention are as follows: using simpler raw materials such as bauxite tailings, fly ash, and expanded perlite, and producing sintered bricks using a common brick-making process. The technical difficulty this invention needs to overcome is that the bauxite tailings particles are extremely fine, with over 50% being below -0.010mm. When using high amounts of bauxite tailings to make bricks, the drying shrinkage and firing shrinkage rates of the brick blanks are both large, and if not properly controlled during drying and sintering, the brick blanks are prone to cracking. Furthermore, when using only bauxite tailings to make bricks, the brick blanks have too high viscosity, making extrusion molding difficult, and both drying and firing shrinkage are relatively large. When the brick blanks are stacked in the kiln car, they are prone to collapse during drying and sintering due to the large shrinkage.

[0025] Therefore, this invention adds fly ash and expanded perlite to significantly reduce the drying and sintering shrinkage of brick blanks, making them less prone to cracking during drying and sintering. The addition of fly ash primarily aims to increase the plasticity of the brick blanks and reduce their drying and sintering shrinkage. Fly ash contains a large amount of amorphous silica, which can react at certain temperatures to form stable compounds. The reaction is relatively slow in the initial stage; this delayed reaction reduces the drastic volume changes caused by rapid water loss, thereby reducing the shrinkage rate during drying and sintering. Fly ash particles have a glass microsphere structure; these microspheres fill the micropores in the mixture and contain numerous closed pores. The presence of pores reduces the overall material density, making the stress distribution caused by moisture evaporation during drying more uniform, thus reducing the tendency for shrinkage deformation. Expanded perlite is a powdered granular product formed after expansion at high temperatures. During the production of sintered bricks, the porosity of expanded perlite allows it to act as a buffer in the mixture, absorbing some of the stress generated by thermal expansion and contraction, preventing large cracks and deformations within the material, and further reducing the shrinkage rate. In addition, the porous structure of expanded perlite can improve the thermal insulation performance of bricks, and its addition amount can be appropriately controlled to produce load-bearing thermal insulation bricks.

[0026] During the calcination process, SiO2, Fe2O3, K2O, CaO, and other components in the raw materials form a glassy phase at high temperatures, filling the spaces between insoluble particles and optimizing strength development. Fly ash and expanded perlite are themselves formed at high temperatures and contain a large amount of glassy phase. At high temperatures, components of bauxite tailings can react with fly ash and expanded perlite to form new glassy phases, optimizing the overall performance of sintered bricks.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] This invention provides a method for producing sintered bricks using bauxite tailings. The method has a simple raw material ratio, easy-to-control production process parameters, and significantly reduces the drying shrinkage rate and sintering shrinkage rate of the brick blanks. It can utilize industrial solid waste bauxite tailings on a large scale, realize automated production, save the construction and maintenance costs of bauxite tailings ponds, and generate certain economic benefits.

[0029] This invention provides a sintered brick with good mechanical properties and thermal insulation properties.

[0030] This invention provides an application of sintered bricks, which have good application prospects as building materials in construction. Attached Figure Description

[0031] Figure 1 This is a photograph of the sintered bricks prepared in Example 2;

[0032] Figure 2 This is a photograph of the sintered bricks prepared in Example 4. Detailed Implementation

[0033] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0034] In the following embodiments:

[0035] The bauxite tailings were taken from a bauxite beneficiation plant in China. The particle size distribution characteristics, chemical composition, and mineral composition are shown in Tables 1, 2, and 3, respectively.

[0036] Table 1: Particle size distribution characteristics of bauxite tailings

[0037]

[0038] Table 2: Main chemical composition of bauxite tailings (wt.%)

[0039]

[0040] Table 3: Bauxite tailings mineral phase analysis results (wt.%)

[0041]

[0042] The fly ash was taken from a coal-fired power plant in China, and its chemical composition is shown in Table 4.

[0043] Table 4: Main chemical components of fly ash (wt.%)

[0044]

[0045] Example 1

[0046] A method for producing sintered bricks using bauxite tailings includes the following steps:

[0047] (1) By weight, 70 parts of bauxite tailings and 30 parts of fly ash are mixed to obtain a mixture; the moisture content of the mixture is controlled at 15%-20%, and the mixture is aged in an aging chamber for 48 hours to obtain aged raw materials;

[0048] (2) Extruding and cutting the aged raw materials into wet brick blanks of the target shape;

[0049] (3) The wet brick blanks are placed on the kiln cars of the tunnel kiln for drying, so that the moisture content of the dried brick blanks is reduced to below 6% to obtain dry brick blanks;

[0050] (4) The dry brick blanks are sent into the tunnel kiln for firing. The firing temperature is controlled at 950℃ and held for 1 hour. Then the bricks are naturally cooled to obtain sintered bricks.

[0051] Example 2

[0052] A method for producing sintered bricks using bauxite tailings includes the following steps:

[0053] (1) By weight, 60 parts of bauxite tailings and 40 parts of fly ash are mixed to obtain a mixture; the moisture content of the mixture is controlled at 15%-20%, and the mixture is aged in an aging chamber for 48 hours to obtain aged raw materials;

[0054] (2) Extruding and cutting the aged raw materials into wet brick blanks of the target shape;

[0055] (3) The wet brick blanks are placed on the kiln cars of the tunnel kiln for drying, so that the moisture content of the dried brick blanks is reduced to below 6% to obtain dry brick blanks;

[0056] (4) The dry brick blanks are fed into a tunnel kiln for firing at a temperature of 1000℃ for 1 hour, followed by natural cooling to obtain sintered bricks. The actual product is shown in the figure. Figure 1 As shown.

[0057] Example 3

[0058] A method for producing sintered bricks using bauxite tailings includes the following steps:

[0059] (1) By weight, 55 parts of bauxite tailings, 40 parts of fly ash and 5 parts of expanded perlite are mixed to obtain a mixture; the moisture content of the mixture is controlled at 15%-20%, and it is aged in an aging chamber for 48 hours to obtain aged raw materials.

[0060] (2) Extruding and cutting the aged raw materials into wet brick blanks of the target shape;

[0061] (3) The wet brick blanks are placed on the kiln cars of the tunnel kiln for drying, so that the moisture content of the dried brick blanks is reduced to below 6% to obtain dry brick blanks;

[0062] (4) The dry brick blanks are sent into the tunnel kiln for firing. The firing temperature is controlled at 1050℃ and held for 1 hour. Then, they are naturally cooled to obtain sintered bricks.

[0063] Example 4

[0064] A method for producing sintered bricks using bauxite tailings includes the following steps:

[0065] (1) By weight, 50 parts of bauxite tailings, 40 parts of fly ash and 10 parts of expanded perlite are mixed to obtain a mixture; the moisture content of the mixture is controlled at 15%-20%, and it is aged in an aging chamber for 72 hours to obtain aged raw materials.

[0066] (2) Extruding and cutting the aged raw materials into wet brick blanks of the target shape;

[0067] (3) The wet brick blanks are placed on the kiln cars of the tunnel kiln for drying, so that the moisture content of the dried brick blanks is reduced to below 6% to obtain dry brick blanks;

[0068] (4) The dry brick blanks are fed into a tunnel kiln for firing at a temperature of 1000℃ for 2 hours, followed by natural cooling to obtain sintered bricks. The actual product is shown in the figure. Figure 2 As shown.

[0069] Example 5

[0070] This embodiment tested the comprehensive performance of the sintered bricks prepared in Examples 1-3 to study their effectiveness in practical applications. Performance test indicators included compressive strength, density, water absorption, porosity, and thermal conductivity. The above tests were conducted using standard testing methods commonly used in the field. The performance test results for each sintered brick are shown in Table 5.

[0071] Table 5: Performance Test Results of Sintered Bricks

[0072]

[0073] In the thermal conductivity test, commercially available ordinary sintered bricks and bauxite tailings sintered bricks made at a sintering temperature of 1000 ℃ without the addition of other ingredients (fly ash, expanded perlite) were used as comparisons. Their thermal conductivity was measured to be 0.80 W / m·K and 0.83 W / m·K, respectively. The thermal conductivity of the sintered brick in Example 4 could be reduced to 0.34 W / m·K, indicating that the addition of fly ash and expanded perlite significantly improved the thermal insulation performance of the bauxite tailings sintered bricks. Furthermore, sintered bricks made solely from bauxite tailings (e.g., bauxite tailings sintered at 1000 ℃) had a compressive strength of 35 MPa and a density of 2.02 g / cm³. 3 Even with the method of this invention to prepare sintered bricks (with a water absorption rate of 8.50% and a porosity of 20.08%), under the control of other optional parameters, there are still difficulties in extruding and molding the brick blanks, and cracking and deformation are prone to occur during drying and sintering due to large drying shrinkage and sintering shrinkage.

[0074] This invention adds fly ash and expanded perlite to significantly reduce the drying and sintering shrinkage of brick blanks, making them less prone to cracking during drying and sintering. No cracking was observed in the sintered bricks produced in the examples. Adding fly ash increases the plasticity of the brick blanks and reduces their drying and sintering shrinkage. Fly ash contains a large amount of amorphous silica, which can react at certain temperatures to form stable compounds. The reaction is relatively slow in the initial stage; this delayed reaction reduces the drastic volume changes caused by rapid water loss, thereby reducing the shrinkage rate during drying and sintering. Fly ash particles have a glass microsphere structure; these microspheres fill the micropores in the mixture and contain many closed pores. The presence of pores reduces the overall material density, making the stress distribution caused by moisture evaporation during drying more uniform, thus reducing the tendency for shrinkage deformation. Expanded perlite is a powdered granular product formed after expansion at high temperatures. During the production of sintered bricks, the porosity of expanded perlite allows it to act as a buffer in the mixture, absorbing some of the stress generated by thermal expansion and contraction, thus preventing large cracks and deformation within the material. Therefore, the sintered bricks of this invention overcome the defect of cracking as a whole.

[0075] The sintered bricks of this invention also possess excellent mechanical properties. During the firing process, the components in the raw materials form a glassy phase at high temperatures, filling the spaces between insoluble particles and optimizing strength development. Fly ash and expanded perlite are themselves formed at high temperatures and contain a large amount of glassy phase. At high temperatures, the components of bauxite tailings can react with fly ash and expanded perlite to form a new glassy phase, optimizing the overall performance of the sintered bricks. Example 2 exhibited the highest compressive strength in the test. Although the compressive strength decreased after adding expanded perlite, it still met the general requirements for bricks, and its thermal insulation performance was further improved, making it suitable for applications with high thermal insulation requirements. Therefore, this invention can adjust the raw material ratio as needed to produce a series of products with different strengths and thermal insulation properties. The raw material ratio of this invention is simple, the production process parameters are easy to control, and automated production can be achieved, indicating a promising industrialization prospect.

[0076] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for producing sintered bricks using bauxite tailings, characterized in that, The steps include: (1) By weight, 50-70 parts of bauxite tailings, 30-40 parts of fly ash, and 0 parts <expanded perlite ≤ 10 parts are mixed to obtain a mixture; the moisture content of the mixture is controlled within a certain range, and the mixture is aged to obtain aged raw material; the aluminum-silicon ratio of the bauxite tailings is <1.3; the aluminum-silicon ratio of the fly ash is <0.7; the moisture content of the mixture is controlled within 15%-20%; (2) The aged raw materials are made into wet brick blanks; (3) The wet brick blanks are dried to control their moisture content within a certain range to obtain dry brick blanks; the moisture content of the dry brick blanks is <6%; (4) The dry brick blanks are fired and then naturally cooled to obtain sintered bricks; the firing temperature is 950-1050 ℃ and the holding time is 1-2 h.

2. The method for producing sintered bricks from bauxite tailings according to claim 1, characterized in that: In step (1), the aging process lasts for 48-72 hours.

3. The method for producing sintered bricks from bauxite tailings according to claim 1, characterized in that: In step (2), the aged raw materials are extruded and cut into blanks to form wet brick blanks of the target shape.

4. The method for producing sintered bricks from bauxite tailings according to claim 1, characterized in that: In steps (3) and (4), the drying and calcining operations are carried out in a tunnel kiln.

5. A sintered brick, characterized in that: It is prepared by the method described in any one of claims 1-4.

6. An application of the sintered brick as described in claim 5, characterized in that: Sintered bricks are used as building materials in building construction.

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