A method for preparing corundum-mullite composite refractory bricks by using graphite tailings

Abstract

The present application relates to the field of firebrick preparation, and discloses a method for preparing corundum-mullite composite firebrick from graphite tailings. The method comprises the following steps: ball-milling and sieving the graphite tailings, and then treating the graphite tailings with a hydrofluoric acid solution to obtain acid-leached graphite tailings; mixing the acid-leached graphite tailings with an aluminum source, adding a binder, and then sintering the mixture after compression molding to obtain the corundum-mullite composite firebrick. The method can effectively destroy the quartz phase in the graphite tailings and leach out impurities such as silicon dioxide, and can also introduce aluminum-, iron-, and calcium-containing fluorides as synthetic active components to promote the mullitization reaction during sintering, thereby forming a dense corundum-mullite composite structure and preparing a corundum-mullite composite firebrick with excellent comprehensive performance. The present application realizes the high-value utilization of graphite tailings and has good economic value and industrial promotion prospects.

Description

Technical Field

[0001] This invention belongs to the field of refractory brick preparation, specifically a method for preparing corundum-mullite multiphase refractory bricks using graphite tailings. Background Technology

[0002] Corundum-mullite multiphase materials are important high-temperature structural materials, widely used in high-temperature industrial fields such as iron and steel smelting, cement kilns, and glass melting furnaces due to their high refractoriness, good thermal shock resistance, excellent high-temperature strength, and chemical stability. Traditional corundum-mullite multiphase materials are typically prepared from natural minerals such as kaolin and bauxite through high-temperature sintering. Kaolin, as a silicon source material, is used in large quantities and is costly, and the increasing scarcity of high-quality kaolin resources has led to a continuous rise in the production cost of refractory bricks.

[0003] With the rapid development of my country's graphite industry, graphite tailings, as the main solid waste generated during graphite beneficiation, are showing a year-on-year increasing trend in their discharge. The main chemical components of graphite tailings are silicon dioxide and alumina, with a total content exceeding 70%, possessing potential value as silicon and alumina sources for refractory bricks. However, graphite tailings also contain high levels of impurity minerals such as quartz, hematite, and calcite. If directly used to prepare refractory bricks, these impurities will severely affect sintering performance, resulting in products with high porosity, low strength, and insufficient refractoriness, failing to meet the performance requirements of high-alumina bricks. Therefore, effectively removing harmful impurities from graphite tailings and activating their reactivity is a key technical challenge for achieving high-value utilization of graphite tailings in the refractory brick field.

[0004] In existing technologies, the utilization of graphite tailings is mainly focused on recovering valuable minerals or preparing low-value-added products such as ordinary ceramic bricks and sintered bricks, resulting in low utilization rates and limited economic benefits. When graphite tailings are directly used to prepare high-value-added refractory bricks, the high quartz content in the tailings makes it difficult for them to fully participate in the mullite formation reaction during sintering, leading to a large amount of residual quartz phase in the product, severely reducing the material's refractory and mechanical properties. Current technologies do not provide a feasible solution to effectively address these problems and achieve high-value utilization of graphite tailings for the preparation of high-performance corundum-mullite multiphase refractory bricks. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing corundum-mullite multiphase refractory bricks using graphite tailings. This method solves the problems in the prior art where the high quartz impurity content in graphite tailings makes it difficult to directly use them to prepare high-performance refractory bricks, resulting in severe quartz phase residue in the product, insufficient mullite formation reaction, and mechanical and refractory properties that fail to meet usage requirements.

[0006] A method for preparing corundum-mullite multiphase refractory bricks using graphite tailings as raw material includes the following steps:

[0007] S1. The graphite tailings are ball-milled and sieved to obtain fine graphite tailings powder;

[0008] S2. The graphite tailings fine powder obtained in step S1 is subjected to acid leaching with an acidic solution to obtain acid-leached graphite tailings pre-material; the acidic solution is a solution that can leach SiO2 from the graphite tailings and introduce aluminum, iron, and calcium fluoride.

[0009] S3. Mix the acid-leached graphite tailings pre-material obtained in step S2 with the aluminum source, add a binder, and press into shape to obtain a brick blank.

[0010] S4. Sinter the brick blanks obtained in step S3 to obtain corundum-mullite multiphase refractory bricks.

[0011] Preferably, the acidic solution in step S2 is a hydrofluoric acid solution.

[0012] Preferably, the concentration of the hydrofluoric acid solution is 5.65 mol / L to 22.6 mol / L, and the liquid-to-solid ratio of the acid leaching treatment is 0.9:1 to 2.7:1.

[0013] Preferably, the concentration of the hydrofluoric acid solution is 7.53 mol / L, and the liquid-to-solid ratio of the acid leaching treatment is 1.5:1.

[0014] Preferably, the mass ratio of the acid-leached graphite tailings pre-material to the aluminum source in step S3 is (50-60):(40-50).

[0015] Preferably, the mass ratio of the acid-leached graphite tailings pre-material to the aluminum source in step S3 is 55:45.

[0016] Preferably, the aluminum source in step S3 is α-Al2O3 powder, and the binder is aluminum dihydrogen phosphate solution.

[0017] Preferably, the sintering temperature in step S4 is 1300 ℃~1500 ℃, the holding time is 1 h~4 h, and the heating rate is 5 ℃ / min~15 ℃ / min.

[0018] This invention provides a corundum-mullite multiphase refractory brick, which is prepared by the above-described method.

[0019] Preferably, the bulk density of the corundum-mullite multiphase refractory brick is ≥2.45 g / cm³. 3 Apparent porosity ≤ 9.0%, room temperature compressive strength ≥ 50 MPa, refractoriness ≥ 1770 ℃.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] By using graphite tailings as raw material, acid leaching with hydrofluoric acid followed by compounding with α-Al2O3 powder, and then solid-state reaction sintering, corundum-mullite multiphase refractory bricks are prepared, realizing the high-value utilization of industrial solid waste. This method uses hydrofluoric acid to leach graphite tailings, which can effectively leach out the quartz components in the graphite tailings and reduce the impurity content. On the other hand, it can introduce aluminum-, iron-, and calcium-containing fluoride active components into the tailings. These fluorides can play a good fluxing role in the subsequent high-temperature sintering process, promote the formation of liquid phase, significantly reduce the solid-state reaction temperature, and accelerate the mass transfer process, thereby effectively promoting the transformation of the corundum phase to the mullite phase, so that the final product forms a dense multiphase structure with tight grain bonding.

[0022] This invention completely replaces traditional kaolin as the silicon source with graphite tailings and prepares corundum-mullite multiphase refractory bricks by compounding them with α-Al2O3 powder. The raw materials are widely available and inexpensive. Compared with the traditional high-alumina brick preparation process, this invention does not require complex equipment modification, has a simple process flow, and is easy to operate, and has excellent industrial promotion value. At the same time, this invention realizes the large-scale disposal of graphite tailings, effectively solving the environmental problems such as land occupation and water pollution caused by graphite tailings accumulation, which is in line with the development concept of green environmental protection and circular economy.

[0023] The corundum-mullite multiphase refractory brick prepared by this invention has excellent comprehensive performance, with low apparent porosity, high bulk density, high room temperature compressive strength, and excellent refractoriness. Its comprehensive performance is superior to similar commercially available high-alumina brick products, and it can be widely used in high-temperature industrial fields such as steel, metallurgy, and building materials, with broad market prospects and significant economic benefits. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: This example provides a method for preparing corundum-mullite multiphase refractory bricks using graphite tailings as raw material. The specific steps are as follows:

[0027] Step 1: Raw material ball milling treatment

[0028] Graphite tailings from a mine in Hegang, Heilongjiang Province, were crushed. Appropriate amounts of graphite tailings, zirconium oxide balls, and anhydrous ethanol were weighed and placed in a ceramic jar of a planetary ball mill at a mass ratio of 1:3:1. The mill was set to a speed of 2000 r / min and ground for 30 min. The powder was then passed through a 160-mesh standard sieve to obtain fine graphite tailings powder with a particle diameter ≤89 μm.

[0029] Step 2: Acid leaching for impurity removal and activation

[0030] In a fume hood, the fine graphite tailings powder obtained in step 1 was mixed with a 7.53 mol / L hydrofluoric acid (HF) solution at a liquid-to-solid ratio of 3:2 (i.e., 1.5 L of acid solution was used per kilogram of tailings), and placed in a plastic beaker. A plastic magnetic rotor was added. The beaker was placed on a heat-collecting constant-temperature magnetic stirrer and stirred for 30 min at a constant temperature of 40 ℃. After the exothermic acid leaching reaction was completed, the mixture was allowed to stand at room temperature of 20 ℃ for 30 min to separate the residual graphite floating on the upper layer. The lower solid product was placed in an electric heating forced-air drying oven and dried at 100 ℃ for 24 h. After drying, the mixture was ground again and passed through a 160-mesh standard sieve to obtain the prepared graphite tailings material after acid leaching.

[0031] Step 3: Mixing and Shaping

[0032] Weigh 550 g (55 wt%) of the acid-leached graphite tailings pre-material obtained in step 2 and mix it evenly with 450 g (45 wt%) of α-Al₂O₃ powder. Add 150 mL of a saturated solution of aluminum dihydrogen phosphate (Al(H₂PO₄)₃) at 20 °C as a binder to the mixture and continue stirring until homogeneous. Form the mixture into standard straight brick blanks with dimensions of 230 mm × 114 mm × 65 mm using a hydraulic press under a molding pressure of 150 MPa. The formed brick blanks are then aged and cured at 20 °C for 12 h to eliminate pseudo-agglomeration during molding and to ensure a tighter bond between the binder and the matrix. The mass of the refractory brick blank after demolding is approximately 1150 g.

[0033] Step 4: Sintering

[0034] The cured brick blanks were placed in a box-type gradient electric furnace and heated from room temperature of 20 ℃ to 1400 ℃ at a heating rate of 10 ℃ / min. The temperature was held at 1400 ℃ for 2 h, and then naturally cooled to room temperature of 20 ℃ with the furnace to obtain the finished corundum-mullite multiphase refractory brick.

[0035] Performance testing of the product obtained in this embodiment:

[0036] X-ray diffraction was used to analyze the phase composition of the product, and the results showed that the main phases of the product were corundum and mullite. Apparent porosity and bulk density were determined according to GB / T 2997-2015, room temperature compressive strength was determined according to GB / T 5072-2008, and refractoriness was determined according to GB / T 7322-2017.

[0037] The test results are as follows: bulk density 2.28 g / cm³, apparent porosity 8.52%, room temperature compressive strength 52.21 MPa, and refractoriness 1784 ℃. All of the above indicators are better than the performance requirements of commercially available LZ-55G type high alumina bricks (GB / T 2988—2012).

[0038] Example 2: The difference between this example and Example 1 is that the mass ratio of graphite tailings pre-material to α-Al2O3 powder in step 3 is 50:50, that is, 500 g of graphite tailings pre-material and 500 g of α-Al2O3 powder. The remaining steps and parameters are the same as in Example 1.

[0039]

[0040] Table 2-4 General Performance Indicators of Ordinary High Alumina Bricks (GB / T2988—2012)

[0041] The bulk density of the obtained refractory brick sample was 2.65 g / cm³. 3 It has an apparent porosity of 8.90%, a room temperature compressive strength of 50.15 MPa, and a refractoriness of 1770 ℃.

[0042] Example 3: The difference between this example and Example 1 is that the hydrofluoric acid leaching temperature in step 2 is 50 ℃, and the stirring time is 40 min; the remaining steps and parameters are the same as in Example 1; the bulk density of the obtained refractory brick sample is 2.26 g / cm³. 3 The apparent porosity is 8.75%, the room temperature compressive strength is 51.80 MPa, and the refractoriness is 1780 ℃ (all optimized performance data indicators meet or exceed those of commercially available LZ-55G type high alumina bricks (GB / T 2988—2012)).

[0043] Example 4: The difference between this example and Example 1 is that the sintering heating rate in step 4 is 5 ℃ / min, and the other steps and parameters are the same as in Example 1;

[0044] The bulk density of the obtained refractory brick sample was 2.27 g / cm³. 3 The apparent porosity is 8.68%, the room temperature compressive strength is 51.95 MPa, and the refractoriness is 1782 ℃. All of the above performance indicators meet or exceed the performance requirements of commercially available LZ-55G type high alumina bricks (GB / T2988—2012).

[0045] Example 5: The difference between this example and Example 1 is that the heating rate of sintering in step 4 is 15 ℃ / min, and the other steps and parameters are the same as in Example 1;

[0046] The bulk density of the obtained refractory brick sample was 2.26 g / cm³. 3 The apparent porosity is 8.82%, the room temperature compressive strength is 51.50 MPa, and the refractoriness is 1778 ℃. All of the above performance indicators meet or exceed the performance requirements of commercially available LZ-55G type high alumina bricks (GB / T2988—2012).

[0047] Comparative Example 1: The difference between this comparative example and Example 1 is that the graphite tailings were not subjected to any acid leaching treatment and were directly mixed with α-Al2O3 powder at a mass ratio of 55:45. A binder was added for molding and sintering. The remaining steps and parameters were the same as in Example 1. XRD analysis of the obtained product showed that the main phases were quartz and corundum, with no obvious mullite phase. The product's room temperature compressive strength was only 34.6 MPa, and its refractoriness was 1680 ℃, failing to meet the performance indicators of LZ-55G type high-alumina bricks in GB / T 2988—2012.

[0048] Comparative Example 2: The difference between this comparative example and Example 1 is that the hydrofluoric acid concentration in step 2 is 5.65 mol / L, while the remaining steps and parameters are the same as in Example 1. The amount of mullite phase formed in the obtained product is significantly reduced, the room temperature compressive strength is 45.2 MPa, and the refractoriness is 1720 ℃, which fails to meet the requirements of LZ-55G type high alumina bricks.

[0049] Comparative Example 3: This comparative example differs from Example 1 in that the liquid-to-solid ratio in step 2 is 1:1, while the remaining steps and parameters are the same as in Example 1. The resulting product exhibits obvious pores and a bulk density of 2.10 g / cm³. 3 The apparent porosity was 12.5%, and the room temperature compressive strength was 41.5 MPa, which failed to meet the target performance indicators.

[0050] Comparative Example 4: The difference between this comparative example and Example 1 is that the concentration of hydrofluoric acid in step 2 is 22.6 mol / L and the liquid-to-solid ratio is 2.7:1. The remaining steps and parameters are the same as in Example 1.

[0051] The product had an excessively high fluoride content and an excessive liquid phase during sintering, resulting in severe product deformation and a bulk density of 2.05 g / cm³. 3 The apparent porosity was 15.2%, the room temperature compressive strength was 38.5 MPa, and the refractoriness was 1650 ℃, which failed to meet the target performance indicators.

[0052] Technical effect analysis

[0053] As shown in Examples 1-5 and Comparative Examples 1-4, the present invention uses hydrofluoric acid of a specific concentration (5.65 mol / L to 22.6 mol / L) and a liquid-to-solid ratio (0.9:1 to 2.7:1) to leach graphite tailings, which can effectively leach out quartz components and introduce compounds such as AlF3, FeF3, and CaF2 that are beneficial to mullite formation, significantly promoting the transformation of corundum phase to mullite phase during high-temperature sintering. When the hydrofluoric acid concentration is below 5.65 mol / L, SiO2 leaching is incomplete, and the amount of mullite phase generated is insufficient (Comparative Example 2). When the hydrofluoric acid concentration is above 22.6 mol / L or the liquid-to-solid ratio is above 2.7:1, excessive fluoride is introduced, resulting in excessive liquid phase during sintering and product deformation (Comparative Example 4). When the liquid-to-solid ratio is below 0.9:1, the amount of acid is insufficient, SiO2 leaching is incomplete, and the porosity and strength of the product increase (Comparative Example 3).

[0054] The product obtained in Example 1, with a graphite tailings content as high as 55%, has a bulk density of 2.28 g / cm³. 3 The apparent porosity is 8.52%, the room temperature compressive strength is 52.21 MPa, and the refractoriness is 1784 ℃. All performance indicators are superior to those of commercially available LZ-55G type high alumina bricks (GB / T 2988—2012). Examples 4 and 5 further verified that high-performance products can be obtained within a heating rate range of 5 ℃ / min to 15 ℃ / min.

[0055] Furthermore, according to cost accounting, the cost of hydrofluoric acid (0.5 kg) required to prepare 1 kg of graphite tailings refractory bricks is approximately RMB 2.5, and the cost of α-Al2O3 powder (0.45 kg) is approximately RMB 1.35, with a comprehensive raw material cost of approximately RMB 4.3 / kg. This represents a cost saving of approximately 82.8% compared to commercially available high-alumina refractory bricks (approximately RMB 25 / kg). This invention achieves high-value utilization of industrial solid waste, and the acid leaching process does not require complex equipment or process modifications, demonstrating good economic viability and industrial promotion value.

[0056] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made by those skilled in the art to the above embodiments within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing corundum-mullite multiphase refractory bricks using graphite tailings as raw material, characterized in that, Includes the following steps: S1. The graphite tailings are ball-milled and sieved to obtain fine graphite tailings powder; S2. The graphite tailings fine powder obtained in step S1 is subjected to acid leaching with an acidic solution to obtain acid-leached graphite tailings pre-material; the acidic solution is a solution that can leach SiO2 from the graphite tailings and introduce aluminum, iron, and calcium fluoride. S3. Mix the acid-leached graphite tailings pre-material obtained in step S2 with the aluminum source, add a binder, and press into shape to obtain a brick blank. S4. Sinter the brick blanks obtained in step S3 to obtain corundum-mullite multiphase refractory bricks.

2. The method according to claim 1, characterized in that, The acidic solution mentioned in step S2 is a hydrofluoric acid solution.

3. The method according to claim 2, characterized in that, The concentration of the hydrofluoric acid solution is 5.65 mol / L to 22.6 mol / L, and the liquid-to-solid ratio of the acid leaching treatment is 0.9:1 to 2.7:

1.

4. The method according to claim 3, characterized in that, The concentration of the hydrofluoric acid solution is 7.53 mol / L, and the liquid-to-solid ratio of the acid leaching treatment is 1.5:

1.

5. The method according to claim 1, characterized in that, The mass ratio of the acid-leached graphite tailings pre-material to the aluminum source in step S3 is (50-60):(40-50).

6. The method according to claim 5, characterized in that, The mass ratio of the acid-leached graphite tailings pre-material to the aluminum source in step S3 is 55:

45.

7. The method according to claim 1, characterized in that, The aluminum source in step S3 is α-Al2O3 powder, and the binder is aluminum dihydrogen phosphate solution.

8. The method according to claim 1, characterized in that, The sintering temperature in step S4 is 1300 ℃~1500 ℃, the holding time is 1 h~4 h, and the heating rate is 5 ℃ / min~15 ℃ / min.

9. A corundum-mullite multiphase refractory brick, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The corundum-mullite multiphase refractory brick according to claim 9, characterized in that, The bulk density of the corundum-mullite multiphase refractory brick is ≥2.45 g / cm³. 3 Apparent porosity ≤ 9.0%, room temperature compressive strength ≥ 50 MPa, refractoriness ≥ 1770 ℃.

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