A step-by-step method for synthesizing alumina-based lightweight high-strength mullite

Abstract

The present invention belongs to the field of refractory materials and relates to a step-by-step method for synthesizing bauxite-based lightweight, high-strength mullite. The method comprises: Step 1: homogenizing, crushing, and screening bauxite blocks larger than 8 mm. Bauxite blocks larger than 8 mm are melted at temperatures above 2000°C, and then a stream of air is applied to the molten liquid as it flows out, causing it to "atomize." The material rapidly cools as it falls, yielding a spherical, amorphous hollow intermediate. Step 2: Grinding bauxite blocks smaller than 8 mm to a fine powder comprising 10-25% by weight, with the remainder serving as intermediate ingredients, and adding 5-8% of a binder. The mixture is then rolled for 10-15 minutes to form the intermediate. The mixture is then dried, calcined at 1580-1650°C for 8-12 hours, and cooled naturally to yield the final product. The method can efficiently utilize low- and medium-grade bauxite to produce high-quality bauxite-based lightweight mullite. The production process is stable, and the resulting mullite has a high conversion rate, well-developed crystals, and high strength, achieving lightweight thermal insulation properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory materials, and in particular relates to a method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method. Background Art

[0002] Existing technologies mostly use extensive mining and simple processing methods to directly use downdraft kilns, vertical kilns, and rotary kilns to burn bauxite clinker. These process methods are limited by equipment capabilities and have high requirements on the grade and block size of the original ore. The A / S requirement is greater than 5.5, and fine particles cannot be processed and utilized. The crystal phase conversion rate of products with A / S less than 5.5 is relatively low, the quality of the burned bauxite clinker is poor, and resources cannot be reasonably and effectively utilized.

[0003] To address the issue of comprehensive utilization of bauxite, the technology of bauxite-based homogenized materials has received attention in the industry in recent years. Low- and medium-grade bauxite has been effectively utilized through processes such as homogenization, ball milling, molding, and high-temperature sintering. However, due to the primary mullitization, secondary mullitization, and liquid-phase sintering reactions that occur during the calcination of low- and medium-grade bauxite, the mass and volume change significantly at high temperatures. Existing process technologies and methods carry the risk of unstable production or product quality. For example, tunnel kiln calcination is prone to problems such as kiln tipping and kiln jamming, while rotary kiln calcination exhibits low mullite crystal conversion in the product due to the short high-temperature zone time and low temperature.

[0004] At present, the high-temperature industry has also put forward new requirements for energy-saving and heat-insulating materials. As an indispensable field for the high-temperature industry, the refractory material field is also actively seeking breakthroughs in lightweight and thermal insulation performance. Summary of the Invention

[0005] In order to solve the problems of unstable production or product quality in the existing technology and the demand for lightweight and heat-insulating products, the present invention provides a new method for synthesizing lightweight mullite using medium and low-grade bauxite distribution ores. The production process of the present invention is stable, and the prepared mullite has high strength, solid phase density, good uniformity, high mullite conversion rate, and can achieve lightweight and heat-insulating effects compared with ordinary mullite raw materials.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0007] A step-by-step method for synthesizing alumina-based lightweight high-strength mullite comprises the following steps:

[0008] Step 1: After homogenizing the lump bauxite, crushing and screening, the bauxite larger than 8mm is melted at above 2000℃, and then a strong air flow is applied to the molten liquid to "atomize" it. The material quickly forms balls during the falling process and cools to obtain the intermediate;

[0009] Step 2: According to the mass percentage of bauxite powder less than 8mm, 10-25% of the fine powder is ground, and the rest is the intermediate ingredients obtained in step 1, plus 5-8% of the binder, and the mixture is rolled by a wheel mill for 10-15 minutes, and then formed into bricks by a press, stacked on a kiln car, dried in a drying kiln, calcined at high temperature in a high-temperature kiln, and naturally cooled to obtain a bauxite-based lightweight high-strength mullite refractory raw material.

[0010] Among them, preferably, the aluminum-silicon ratio A / S of the bauxite after homogenization is 2-3, the Fe2O3 mass fraction is ≤2%, and the R2O (K2O+Na2O) mass fraction is ≤0.6%.

[0011] Preferably, the applied strong wind airflow has a wind speed of 250-300 km / h.

[0012] Among them, preferably, the obtained intermediate is a hollow amorphous phase intermediate, the phase composition is an amorphous phase, and the microstructure is a pseudo-spherical.

[0013] Among them, preferably, the fine powder particle size standard of the bauxite less than 8 mm after grinding is 325 mesh with a pass rate of more than 90%.

[0014] Among them, preferably, the added binder is one or more of drinking water, pulp waste liquid, and dextrin solution.

[0015] Wherein, preferably, the high temperature calcination temperature is 1580~1650℃, and the holding time is 8~12h.

[0016] The main crystal phase of the alumina-based lightweight high-strength mullite refractory raw material prepared by the above method is mullite phase, and the microstructure is well-developed mullite crystals cross-forming into clusters, forming a network between clusters, and pores distributed between clusters, such as Figure 3 As shown in the figure, the material is well sintered and has high solid phase density. Its bulk density is 15-30% lower than that of mullite of the same grade, and its true density is 2.95-3.10 g / cm 3 , the volume density is 2.15~2.35g / cm 3 , porosity is 25~30%, and compressive strength is ≥350MPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention breaks away from the existing technical thinking of the primary mullitization, secondary mullitization and liquid phase reaction in the process of calcining medium- and low-grade bauxite to produce bauxite-based mullite clinker. Through a step-by-step method, the process first melts and cools to form an amorphous intermediate, and then calcines the intermediate to produce mullite by a high-temperature liquid phase reaction. The intermediate prepared by high-temperature melting is amorphous, highly active, and has a relatively uniform and dense solid phase. The voids in the solid phase intermediate provide space for mullite growth, and the volume density of the finished mullite raw material is less than 2.35g / cm 3 , which is more than 15% lower than that of mullite of the same grade, thus providing a guarantee for lightweight and heat insulation of products; the calcination of the intermediate of the present invention bypasses the processes of large mass and volume changes such as dehydration of crystal water, primary mullitization, and secondary mullitization, and the linear change rate of the calcination process is less than 5%, which is much smaller than the linear shrinkage rate of more than 10% in other process methods, thus avoiding the risk of kiln collapse and jamming; therefore, the production process of the present invention is stable, the prepared mullite has high conversion rate, good crystal development, and high strength, and can achieve lightweight and heat insulation effects compared with ordinary mullite raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a microscopic photograph of the spherical intermediate synthesized in the preparation process of the present invention.

[0020] Figure 2 The XRD analysis diagram of the intermediate synthesized in the preparation process of the present invention shows that it is amorphous.

[0021] Figure 3 This is a microstructure photo of the alumina-based lightweight high-strength mullite prepared in the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in more detail below through specific implementation methods to facilitate understanding of the technical solution of the present invention, but is not intended to limit the scope of protection of the present invention.

[0023] Example 1

[0024] The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method in this embodiment includes the following steps:

[0025] Step 1: After homogenizing the bulk bauxite, crush it, and screen it. Bauxite larger than 8mm is melted at above 2000℃, and then a 250km / h airflow is applied to the melt as it flows out to "atomize" it. The material quickly forms balls and cools during the falling process to obtain an intermediate; the intermediate obtained is a hollow amorphous intermediate with an amorphous phase composition and a spherical microstructure. The microstructure photo of the spherical intermediate is shown in the figure. Figure 1 The XRD pattern of the intermediate is shown in Figure 2 shown.

[0026] Step 2: The bauxite powder (less than 8mm in size) from Step 1 is ground into fine powder and the intermediate in a ratio of 20% to 80% by mass, with 6% water added as a binder. The powder is then rolled on a roller mill for 15 minutes, then formed into bricks using a press. The bricks are then stacked on a kiln car, dried in a drying kiln, calcined in a high-temperature kiln at 1630°C for 8 hours, and cooled naturally to obtain a lightweight, high-strength bauxite refractory material. The water is drinking water.

[0027] The homogenized bauxite used in this example had an aluminum-silicon ratio (A / S) of 2.3, a Fe₂O₃ mass fraction of 1.35%, and a R₂O (K₂O + Na₂O) mass fraction of 0.53%. The 8mm bauxite ground in step 2 had a 325-mesh pass rate of 92%.

[0028] The technical indicators of the alumina-based lightweight high-strength mullite refractory raw material prepared in this embodiment are: mullite conversion rate is about 90%, the average crystal length is about 15 μm; the true density is 2.97 g / cm 3 , volume density 2.23g / cm 3 , porosity 26%, compressive strength 384MPa.

[0029] Example 2

[0030] The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method in this embodiment includes the following steps:

[0031] Step 1: After homogenizing the lump bauxite, crushing and screening, the bauxite larger than 8mm is melted at above 2000℃. The melt is then subjected to an airflow of 290km / h to atomize it as it flows out. The material quickly forms balls during the falling process and cools to obtain an intermediate.

[0032] Step 2: grind the bauxite powder smaller than 8 mm in step 1 into fine powder and mix the intermediate in a mass percentage of 25%:75%, add 7% pulp waste liquid diluent as a binder, use a wheel roller to roll for 14 minutes, and then use a press to form bricks, stack them on a kiln car, dry them in a drying kiln, calcine them at a high temperature of 1650℃ in a high temperature kiln, keep them warm for 10 hours, and then naturally cool them to obtain a bauxite-based lightweight high-strength mullite refractory raw material.

[0033] The homogenized bauxite used in this example had an aluminum-silicon ratio (A / S) of 2.9, a Fe₂O₃ mass fraction of 1.45%, and a R₂O (K₂O + Na₂O) mass fraction of 0.55%. The 8mm bauxite ground in step 2 had a 325-mesh pass rate of 95%. The pulp wastewater dilution solution was a mixture of pulp wastewater and water in a 1:1 ratio by mass.

[0034] The technical indicators of the alumina-based lightweight high-strength mullite refractory raw material prepared in this embodiment are: mullite conversion rate is about 95%, the average crystal length is about 16 μm; the true density is 3.08 g / cm 3 , volume density 2.33g / cm 3 , porosity 29%, compressive strength 468MPa.

[0035] Example 3

[0036] The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method in this embodiment includes the following steps:

[0037] Step 1: After homogenizing the lump bauxite, crushing and screening, the bauxite larger than 8mm is melted at above 2000℃. The melt is then subjected to an airflow of 300km / h to atomize it as it flows out. The material quickly forms balls during the falling process and cools to obtain an intermediate.

[0038] Step 2: Grind the bauxite powder smaller than 8mm in step 1 into fine powder and mix the intermediate in a mass percentage of 11%:89%, add 6% of pulp waste liquid as a binder, use a wheel roller to roll for 15 minutes, and then use a press to form bricks, stack them on a kiln car, dry them in a drying kiln, calcine them at a high temperature of 1600℃ in a high-temperature kiln, keep them warm for 12 hours, and then naturally cool them to obtain a bauxite-based lightweight high-strength mullite refractory raw material.

[0039] The homogenized bauxite used in this example had an aluminum-silicon ratio (A / S) of 2.1, a Fe₂O₃ mass fraction of 1.22%, and a R₂O (K₂O + Na₂O) mass fraction of 0.45%. The 8mm bauxite ground in step 2 had a 325-mesh pass rate of 96%.

[0040] The technical indicators of the alumina-based lightweight high-strength mullite refractory raw material prepared in this embodiment are: mullite conversion rate is about 93%, the average crystal length is about 18μm; the true density is 2.91 / cm 3 , volume density 2.18g / cm 3 , porosity 25%, compressive strength 451MPa.

[0041] Example 4

[0042] The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method in this embodiment includes the following steps:

[0043] Step 1: After homogenizing the lump bauxite, crushing and screening, the bauxite larger than 8mm is melted at above 2000℃. The melt is then subjected to an airflow of 285km / h to atomize it as it flows out. The material quickly forms balls during the falling process and cools to obtain an intermediate.

[0044] Step 2: Grind the bauxite powder smaller than 8mm in step 1 into fine powder and the intermediate in a mass percentage of 15%:85%, add 8% dextrin solution (dextrin is prepared with water, with a specific gravity of 1.1) as a binder, use a wheel roller to roll for 13 minutes, and then use a press to form bricks, stack them on a kiln car, dry them in a drying kiln, calcine them at a high temperature of 1600℃ in a high temperature kiln, keep them warm for 12 hours, and then naturally cool them to obtain a bauxite-based lightweight high-strength mullite refractory raw material.

[0045] The bauxite used in this example had an aluminum-silicon ratio (A / S) of 2.5 after homogenization, a Fe₂O₃ mass fraction of 1.35%, and a R₂O (K₂O + Na₂O) mass fraction of 0.51%. The 8mm bauxite ground in step 2 had a 325-mesh pass rate of 92%.

[0046] The technical indicators of the alumina-based lightweight high-strength mullite refractory raw material prepared in this embodiment are: mullite conversion rate is about 91%, the average crystal length is about 14 μm; the true density is 2.98 / cm 3 , volume density 2.23g / cm 3 , porosity 27%, compressive strength 420MPa.

[0047] The embodiments described above are only preferred embodiments of the present invention and do not limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structure, characteristics and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A step-by-step method for synthesizing alumina-based lightweight high-strength mullite, characterized in that: The steps include: Step 1: After homogenizing the lump bauxite, crushing and screening, the bauxite larger than 8mm is melted at above 2000℃, and then an air flow is applied to the molten liquid to atomize it. The material is pelletized and cooled during the falling process to obtain an intermediate; the air flow speed is 250~300km / h; Step 2: According to the mass percentage, the fine powder after grinding the bauxite with a particle size of less than 8 mm accounts for 10-25%, and the rest is the intermediate ingredients prepared in step 1, plus 5-8% of a binder, and the mixture is rolled for 10-15 minutes, formed, dried, calcined, and naturally cooled to obtain alumina-based lightweight high-strength mullite.

2. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: The aluminum-silicon ratio A / S of the bauxite after homogenization is 2-3, the mass fraction of Fe2O3 is ≤2%, and the mass fraction of R2O (K2O+Na2O) is ≤0.6%.

3. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: The intermediate obtained in step 1 is a hollow amorphous intermediate, the phase composition is an amorphous phase, and the microstructure is a pseudo-spherical body.

4. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: The standard for fine powder particle size of bauxite less than 8mm after grinding is 325 mesh with a pass rate of more than 90%.

5. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: The external binder in step 2 is one or more of water, pulp waste liquid, and dextrin solution.

6. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: In step 2, the calcination temperature is 1580-1650° C., and the holding time is 8-12 hours.

7. The method for synthesizing alumina-based lightweight high-strength mullite by a step-by-step method according to claim 1, characterized in that: The true density of the alumina-based lightweight high-strength mullite obtained in step 2 is 2.95~3.10g / cm 3 , the volume density is 2.15~2.35g / cm 3 , porosity is 25~30%, and compressive strength is ≥350MPa.

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