Method for preparing multi-layer light spherical refractory aggregate from coal gangue-bauxite tailings

Abstract

The invention belongs to the technical field of refractory materials, and relates to a method for preparing multi-layer light spherical refractory aggregate from coal gangue-bauxite tailings. According to the preparation method of the multi-layer light spherical refractory aggregate, coal gangue powder is subjected to spray granulation to form inner core spherical particles, coal gangue-bauxite tailing composite powder and bauxite tailing powder are sequentially coated on the surfaces of the particles to form multi-layer spherical particles, and the mass ratio of the coal gangue powder to the composite powder is controlled to be (20-80): 100; and finally, drying, and calcining at 1250-1400 DEG C to obtain the multi-layer spherical refractory aggregate. According to the preparation method, the raw materials are easy to obtain, the cost is low, and the preparation process is simple; the multi-layer light spherical refractory aggregate disclosed by the invention is small in volume density, low in K2O and Na2O content on the surface of the aggregate, good in structural continuity and very good in application value.

Description

A method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to a method for preparing multi-layer lightweight spherical refractory aggregates from coal gangue-bauxite tailings. Background Technology

[0002] With the increasing demands for energy consumption control in high-temperature industries, the development of lightweight thermal insulation refractory materials is of significant application value for achieving lightweight, low heat capacity, and long service life in thermal insulation linings. Lightweight spherical refractory aggregates are one of the important raw materials for preparing lightweight thermal insulation refractory materials, characterized by low bulk density, low thermal conductivity, good mechanical properties, and excellent thermal shock stability. Currently, the raw materials used in the preparation of lightweight spherical refractory aggregates are still high-alumina bauxite and industrial alumina. Publication number CN104817328B discloses the successful preparation of an Al2O3-SiO2 spherical refractory aggregate using bauxite raw ore powder, clay raw ore powder, and industrial alumina powder as raw materials. Publication number CN119462098B discloses the successful preparation of a bauxite-based corundum mullite hollow sphere with a gradient structure using grade III high-alumina bauxite as raw material. However, the limited supply of high-grade high-alumina bauxite and industrial alumina raw materials leads to increased raw material costs and resource waste in spherical refractory aggregate preparation.

[0003] Coal gangue and bauxite tailings are both typical bulk solid wastes in my country. The former is generated during coal mining and washing, while the latter is generated during bauxite separation. my country has a large output of coal gangue and bauxite tailings, which are accumulated and dumped year-round, causing pollution to soil and water sources. To achieve high-value utilization of coal gangue and bauxite tailings and to replace high-alumina bauxite and industrial alumina as raw materials, research is being conducted on the preparation of lightweight spherical refractory aggregates. Most coal gangue has relatively few non-plastic impurities, and the loss of residual carbon after burning facilitates the formation of pores, making it suitable as a raw material for lightweight spherical aggregates. However, coal gangue has a low Al2O3 content and high K2O and Na2O content, resulting in a limited number of high-quality grades. At high temperatures, this type of low-grade coal gangue easily produces low-melting-point phases, leading to deterioration of the high-temperature mechanical properties of refractory materials and a decrease in the load softening temperature, thus making it difficult to apply low-grade coal gangue to refractory materials. Although bauxite tailings have low K2O and Na2O content, the loss of minerals such as metakaolinite during ignition also contributes to porosity formation. However, bauxite tailings have a high level of non-plastic impurities, making direct spheroidization difficult. Therefore, it is necessary to explore novel preparation methods that utilize the characteristics of coal gangue and bauxite tailings for spherical structure design and composition control. This could expand the application range of coal gangue and bauxite tailings in refractory materials and contribute to energy conservation and carbon reduction in high-temperature industries. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of high K2O and Na2O content in existing coal gangue and the difficulty in directly pelletizing bauxite tailings. This invention proposes a method for preparing multi-layered lightweight spherical refractory aggregates by using coal gangue as the core particle, coating the particle surface with coal gangue-bauxite tailings composite powder and bauxite tailings powder in sequence, and then spray granulating, drying and calcining.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] Step 1: Place the coal gangue powder in a disc granulator for spray granulation. The weight of the coal gangue powder is 10-50 parts, the particle size is 0.045-0.15mm, the spray liquid is water, and the mass of the spray liquid is 5-10% of the coal gangue powder. The rotation speed of the disc granulator is 50-100rpm to form core spherical particles.

[0007] Step 2: Mix coal gangue powder and bauxite tailings powder evenly in a mixer. The mass ratio of coal gangue powder to bauxite tailings powder is 20~80:100 to form a composite powder of coal gangue and bauxite tailings. The particle size of the resulting composite powder is 0.045~0.15mm.

[0008] Step 3: Add the composite powder of coal gangue and bauxite tailings to the disc granulator. The weight of the composite powder of coal gangue and bauxite tailings is 25 to 50 parts. The spray liquid is water, and the mass of the spray liquid is 5 to 10% of the composite powder of coal gangue and bauxite tailings. This makes the composite powder obtained in step 2 uniformly coat the core surface obtained in step 1, forming an intermediate layer, and finally forming spherical particles.

[0009] Step 4: Add bauxite tailings powder to a disc granulator. The weight of the bauxite tailings powder is 25-50 parts, and the particle size is 0.045-0.15mm. The spray liquid is water, and the mass of the spray liquid is 5-10% of the bauxite tailings powder. This will make the surface of the spherical particles obtained in Step 3 uniformly coated to form an outer layer, and finally form multi-layer spherical particles.

[0010] Step 5: Dry the multi-layered spherical particles obtained in Step 4 at a temperature of 80~120℃ for 12~24 hours.

[0011] Step 6: Calcine the dried product obtained in Step 5. The dried product is heated to 1250~1400℃ at a heating rate of 5℃ / min and the calcination time is 1.5~5h to obtain multi-layer lightweight spherical refractory aggregate.

[0012] The multi-layer lightweight spherical refractory aggregate obtained by this invention has a three-layer spherical structure. The core sphere is coal gangue powder, the middle layer that completely encloses the core is a sphere composed of coal gangue-bauxite tailings composite powder, and the outer shell that completely encloses the middle layer is a sphere formed by bauxite tailings powder.

[0013] In the above technical solution, the coal gangue powder has an Al2O3 content of 15~50 wt.%, a K2O content of 1~5 wt.%, a Na2O content of 1~5 wt.%, a residual carbon content of 0~10 wt.%, and a loss on ignition of 5~15 wt.%.

[0014] In the above steps, the rotation speed of the disc granulator is 50~100 rpm.

[0015] The bauxite tailings powder contains 30-45 wt.% Al2O3, 0-0.25 wt.% K2O, 0-0.25 wt.% Na2O, and 5-15 wt.% loss on ignition.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention uses coal gangue and bauxite tailings as raw materials. Coal gangue powder is spray-granulated to form a core with a certain strength, which is then coated with coal gangue-bauxite tailings composite powder and bauxite tailings powder in sequence to form a three-layer structure. After drying and calcination, lightweight spherical refractory aggregate is obtained.

[0018] Currently, high-alumina bauxite is an industrial raw material, especially Grade I or extra-grade high-alumina bauxite with an Al2O3 content ≥70wt.%, which is extremely scarce in my country. Furthermore, the price of imported high-alumina bauxite has been consistently high in recent years due to trade conflicts. Therefore, high-alumina bauxite with an Al2O3 content ≥70wt.% is already a high-priced and scarce raw material in the refractory materials field, resulting in poor economic viability. However, the coal gangue and bauxite tailings used in this invention are typical bulk solid wastes in my country, with abundant resources, readily available raw materials, and extremely low prices. Preparing them into multi-layered lightweight spherical refractory aggregates has a significant advantage in raw material costs, resulting in high economic efficiency. Simultaneously, it enables high-quality utilization of solid waste, alleviating the pressure on my country's high-alumina resources.

[0019] This invention uses coal gangue with high loss on ignition and low-grade bauxite as raw materials, and the bulk density of the spherical refractory aggregate is 0.68~1.02 g / cm³. 3 No additional pore-forming agents or foaming agents are required. The lightweight spherical refractory aggregate of this invention has a low bulk density and therefore a low thermal conductivity, making it more suitable for heat-insulating refractory materials. It can be applied to the insulation lining of high-temperature furnace linings and other parts, which is of great significance for the lightweight preparation of refractory materials.

[0020] For thermal insulation refractory materials such as thermal insulation linings, the service temperature should not exceed 1300℃. At this service temperature, lightweight spherical refractory aggregates should be developed towards low alumina content.

[0021] Therefore, when the Al2O3 content in this invention is 30~45wt.%, the large amount of mullite phase generated at the service temperature forms an interlocking structure, which can provide high high-temperature mechanical properties.

[0022] Therefore, the use of coal gangue and bauxite tailings as raw materials in this invention aligns perfectly with its application scenario. This invention uses coal gangue and bauxite tailings as raw materials. Bauxite tailings, due to the presence of numerous primary mineral phases with bound water, such as metakaolinite, exhibits low Al2O3 content and high loss on ignition. This allows the calcined spherical aggregate to retain its original lost-on-ignition porosity, resulting in a lightweight material.

[0023] To avoid dense granulation and compaction of the powder, the preparation of the lightweight spherical refractory aggregate of the present invention requires a relatively high rotation speed of 50-100 rpm. Furthermore, to prevent powder densification and sintering shrinkage, the calcination time is strictly controlled within 1.5-5 hours.

[0024] This invention uses water as the spray granulation liquid, eliminating the need for additional binders. It employs a coal gangue-bauxite tailings composite powder as the intermediate layer to coat the bauxite tailings, solving the problem of difficulty in pelletizing bauxite tailings without the need for additional plasticizers. The three-layer spherical structure of this invention is designed for lightweight spherical aggregates. The three-layer structure consists of a core sphere made of coal gangue powder, an intermediate layer completely enclosing the core composed of coal gangue-bauxite tailings composite powder, and an outer shell completely enclosing the intermediate layer, also composed of bauxite tailings powder. The intermediate layer, composed of coal gangue-bauxite tailings composite powder, serves to buffer compressive and tensile stresses generated by thermal expansion, reducing the damage to structures with low bulk density caused by thermal expansion mismatch—crucial for lightweight spherical aggregates. Furthermore, the three-layer structure of this invention is also designed for coal gangue with high K2O and Na2O phases. Coal gangue is a solid waste containing high K2O and Na2O, which easily produces low-melting-point phases such as feldspar during calcination and readily migrates to the hot end (surface of spherical aggregate), resulting in severe degradation of the high-temperature performance of the spherical aggregate. The design of the intermediate layer in this invention can hinder the migration of the liquid phase within the coal gangue, improving the resistance to element migration through structural design. During a relatively short calcination process, the liquid phase only accumulates within the intermediate layer and does not migrate to the surface of the spherical aggregate. After calcination, the multi-layer lightweight spherical refractory aggregate exhibits good structural continuity, improving its mechanical properties, with a room-temperature compressive strength of 4.5~10.3 MPa.

[0025] This invention employs a three-step process of granulation, drying, and calcination, which is simple, easy to operate, green, and efficient. It requires no complex manufacturing equipment, facilitates large-scale production, and further improves the reliability of the process. Attached Figure Description

[0026] Figure 1 is a SEM image of the multilayer lightweight spherical refractory aggregate prepared according to the present invention;

[0027] Figure 2 is a SEM image of the cross-section of the multi-layer lightweight spherical refractory aggregate shown in Figure 1;

[0028] Figure 3 shows the XRD pattern of the outer layer of the multilayer lightweight spherical refractory aggregate prepared in this invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0030] Example 1:

[0031] Step 1: Place the coal gangue powder in a disc granulator for spray granulation. The weight of the coal gangue powder is 10 parts, the particle size is 0.045~0.15mm, the spray liquid is water, and the mass of the spray liquid is 5% of the coal gangue powder. The rotation speed of the disc granulator is 50~100rpm; forming core spherical particles.

[0032] Step 2: Mix coal gangue powder and bauxite tailings powder evenly in a mixer. The mass ratio of coal gangue powder to bauxite tailings powder is 80:100 to form a composite powder of coal gangue and bauxite tailings. The particle size of the resulting composite powder is 0.045~0.15mm.

[0033] Step 3: Add the composite powder of coal gangue and bauxite tailings into the disc granulator. The weight of the composite powder of coal gangue and bauxite tailings is 50 parts. The spray liquid is water, and the mass of the spray liquid is 10% of the composite powder of coal gangue and bauxite tailings. This makes the composite powder obtained in step 2 evenly coat the core surface obtained in step 1, forming an intermediate layer, and finally forming spherical particles.

[0034] Step 4: Add bauxite tailings powder to the disc granulator. The weight of the bauxite tailings powder is 25 parts, and the particle size is 0.045~0.15mm. The spray liquid is water, and the mass of the spray liquid is 5% of the bauxite tailings powder. This will make the surface of the spherical particles obtained in Step 3 uniformly coated to form an outer layer, and finally form multi-layer spherical particles.

[0035] Step 5: Dry the multi-layered spherical particles obtained in Step 4 at a temperature of 80℃ for 12 hours.

[0036] Step 6: Calcine the dried product obtained in Step 5. The dried product is heated to 1400℃ at a heating rate of 5℃ / min and calcined for 1.5h to obtain multi-layered lightweight spherical refractory aggregate.

[0037] The chemical composition of coal gangue powder and bauxite tailings powder is shown in Table 1.

[0038] Table 1 Chemical composition of coal gangue powder and bauxite tailings powder

[0039]

[0040] The properties of this multi-layered lightweight spherical refractory aggregate, as tested, are as follows: bulk density is 1.02 g / cm³. 3 The compressive strength of the particles at room temperature is 10.3 MPa.

[0041] Example 2:

[0042] Step 1: Place the coal gangue powder in a disc granulator for spray granulation. The weight of the coal gangue powder is 50 parts, the particle size is 0.045~0.15mm, the spray liquid is water, and the mass of the spray liquid is 10% of the coal gangue powder. The rotation speed of the disc granulator is 50~100rpm; forming core spherical particles.

[0043] Step 2: Mix coal gangue powder and bauxite tailings powder evenly in a mixer. The mass ratio of coal gangue powder to bauxite tailings powder is 20:100 to form a composite powder of coal gangue and bauxite tailings. The particle size of the resulting composite powder is 0.045~0.15mm.

[0044] Step 3: Add the composite powder of coal gangue and bauxite tailings to the disc granulator. The weight of the composite powder of coal gangue and bauxite tailings is 25 parts. The spray liquid is water, and the mass of the spray liquid is 5% of the composite powder of coal gangue and bauxite tailings. This makes the composite powder obtained in step 2 uniformly coat the core surface obtained in step 1, forming an intermediate layer, and finally forming spherical particles.

[0045] Step 4: Add 50 parts by weight of bauxite tailings powder to the disc granulator. The particle size is 0.045~0.15mm. The spray liquid is water, and the mass of the spray liquid is 10% of the bauxite tailings powder. This will uniformly coat the surface of the spherical particles obtained in Step 3 to form an outer layer, and finally form multi-layer spherical particles.

[0046] Step 5: Dry the multi-layered spherical particles obtained in Step 4 at a temperature of 120℃ for 12 hours.

[0047] Step 6: Calcine the dried product obtained in Step 5. The dried product is heated to 1250℃ at a heating rate of 5℃ / min and calcined for 5 hours to obtain multi-layered lightweight spherical refractory aggregate.

[0048] The chemical composition of coal gangue powder and bauxite tailings powder is shown in Table 2.

[0049] Table 2 Chemical composition of coal gangue powder and bauxite tailings powder

[0050]

[0051] The properties of this multi-layered lightweight spherical refractory aggregate, as tested, are as follows: bulk density is 0.87 g / cm³. 3 The compressive strength of the particles at room temperature is 6.9 MPa.

[0052] Example 3:

[0053] Step 1: Place the coal gangue powder in a disc granulator for spray granulation. The weight of the coal gangue powder is 30 parts, the particle size is 0.045~0.15mm, the spray liquid is water, and the mass of the spray liquid is 15% of the coal gangue powder. The rotation speed of the disc granulator is 50~100rpm; forming core spherical particles.

[0054] Step 2: Mix coal gangue powder and bauxite tailings powder evenly in a mixer. The mass ratio of coal gangue powder to bauxite tailings powder is 60:100 to form a composite powder of coal gangue and bauxite tailings. The particle size of the resulting composite powder is 0.045~0.15mm.

[0055] Step 3: Add the composite powder of coal gangue and bauxite tailings into the disc granulator. The weight of the composite powder of coal gangue and bauxite tailings is 45 parts. The spray liquid is water, and the mass of the spray liquid is 5% of the composite powder of coal gangue and bauxite tailings. This makes the composite powder obtained in step 2 uniformly coat the core surface obtained in step 1, forming an intermediate layer and forming spherical particles.

[0056] Step 4: Add bauxite tailings powder to the disc granulator. The weight of the bauxite tailings powder is 35 parts, and the particle size is 0.045~0.15mm. The spray liquid is water, and the mass of the spray liquid is 8% of the bauxite tailings powder. This will make the surface of the spherical particles obtained in Step 3 uniformly coated to form an outer layer, and finally form multi-layer spherical particles.

[0057] Step 5: Dry the multi-layered spherical particles obtained in Step 4 at a temperature of 120℃ for 20 hours.

[0058] Step 6: Calcine the dried product obtained in Step 5. The dried product is heated to 1300℃ at a heating rate of 5℃ / min and calcined for 3 hours to obtain multi-layer lightweight spherical refractory aggregate.

[0059] The chemical compositions of coal gangue powder and bauxite tailings powder are shown in Table 3.

[0060] Table 3 Chemical composition of coal gangue powder and bauxite tailings powder / wt.%

[0061]

[0062] The properties of this multi-layered lightweight spherical refractory aggregate, as tested, are as follows: bulk density is 0.68 g / cm³. 3 The compressive strength of the particles at room temperature is 4.5 MPa.

[0063] Figure 1 is a SEM image of the multilayer lightweight spherical refractory aggregate prepared in Example 1 of the present invention. As can be seen from Figure 1, the refractory aggregate is spherical and has a complete structure.

[0064] Figure 2 is a SEM image of the cross-section of the multilayer lightweight spherical refractory aggregate prepared in Example 1 of the present invention. As can be seen from Figure 2, the cross-section of the refractory aggregate shows obvious differences in the inner and outer layer structures, but the aggregate structure has good continuity.

[0065] Figure 3 is the XRD pattern of the outer layer of the multilayer lightweight spherical refractory aggregate prepared in Example 1 of the present invention. As can be seen from Figure 3, the main phases of the outer layer of the refractory aggregate are mullite, corundum and cristobalite, and no low-melting-point phases containing K2O and Na2O were found.

Claims

1. A method for preparing multi-layered lightweight spherical refractory aggregate from coal gangue-bauxite tailings, characterized in that: Step 1: Place the coal gangue powder in a disc granulator for spray granulation. The weight percentage of the coal gangue powder is 10-50 parts, and the spray liquid is water, which accounts for 5-10% of the coal gangue powder mass. The disc granulator rotates at 50-100 rpm to form spherical particles with a core. Step 2: Mix the coal gangue powder and bauxite tailings powder evenly in a mixer. The mass ratio is 20~80:100 to form a composite powder of coal gangue and bauxite tailings; the particle size of the obtained composite powder is 0.045~0.15mm; Step 3: Add the composite powder of coal gangue and bauxite tailings to a disc granulator, the weight of the composite powder of coal gangue and bauxite tailings is 25~50 parts, the spray liquid is water, and the mass of the spray liquid is the composite powder of coal gangue and bauxite tailings. Step 2: 5-10% of the composite powder obtained in Step 2 is used to uniformly coat the core surface obtained in Step 1, forming an intermediate layer and ultimately forming spherical particles. Step 4: 25-50 parts by weight of bauxite tailings powder are added to a disc granulator. The spray liquid is water, and the mass of the spray liquid is 5-10% of the bauxite tailings powder, so that the bauxite tailings powder is uniformly coated on the surface of the spherical particles obtained in Step 3, forming an outer layer and ultimately forming multi-layered spherical particles. Step 5: The multi-layered spherical particles obtained in Step 4 are dried at a temperature of 80-120℃ for 12-24 hours. Step 6: The dried product obtained in Step 5 is calcined at a heating rate of 5℃ / min to 1250-1400℃ for 1.5-5 hours to obtain multi-layered lightweight spherical refractory aggregate.

2. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The coal gangue powder has an Al2O3 content of 15~50 wt.%, a K2O content of 1~5 wt.%, a Na2O content of 1~5 wt.%, a residual carbon content of 0~10 wt.%, and a loss on ignition of 5~15 wt.%.

3. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The bauxite tailings powder has an Al2O3 content of 30-45 wt.%, a K2O content of 0-0.25 wt.%, a Na2O content of 0-0.25 wt.%, and a loss on ignition of 5-15 wt.%.

4. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: During the process, the rotation speed of the disc granulator is 50~100 rpm.

5. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The particle size of coal gangue powder is 0.045~0.15mm.

6. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The bauxite tailings are 0.045~0.15mm.

7. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The multi-layered lightweight spherical refractory aggregate obtained in step six has a three-layer spherical structure. The core sphere is made of coal gangue powder, the middle layer that completely encloses the core is a sphere composed of coal gangue-bauxite tailings composite powder, and the outer shell that completely encloses the middle layer is a sphere formed by bauxite tailings powder.

8. The method for preparing multi-layer lightweight spherical refractory aggregate from coal gangue-bauxite tailings according to claim 1, characterized in that: The multi-layered lightweight spherical refractory aggregate obtained in step six has an Al2O3 content of 30~45wt.%, and at the service temperature, a large amount of mullite phase is generated to form an interlocking structure.

Images