A method for preparing binary ceramsite using coal gangue and the prepared binary ceramsite

Abstract

The present application relates to the field of ceramsite, and specifically discloses a method for preparing binary ceramsite using coal gangue and the obtained ceramsite. The method comprises the following steps: preparing the core: fully mixing carbon-free industrial waste slag with calcium phosphate solution at a ratio of 1kg: (0.4-0.8)L, pressurizing, and then granulating to obtain green balls, and uniformly spraying a binding solution on the surface of the green balls to obtain the core; preparing the coating material: fully mixing coal gangue with sodium alginate solution at a ratio of 1kg: (0.2-0.5)L to obtain the coating material; overmolding: uniformly coating the core with the coating material to form a binary green ball, wherein 0.15 < d / D < 0.75, d is the green ball diameter, and D is the binary green ball diameter; preparing the ceramsite: drying, pyrolyzing, decarbonizing, sintering, and cooling the binary green balls to form binary ceramsite. The obtained ceramsite product not only has no black core, excellent strength, but also good water absorption.

Description

Technical Field

[0001] The present application relates to the field of ceramsite, and more specifically, to a method for preparing binary ceramsite using coal gangue. Background Art

[0002] Gangue is an industrial solid waste generated during coal production and processing. Annually, it is emitted in large quantities, and its rate of emission continues to increase. It represents a significant amount of solid waste in my country. Gangue typically contains carbonaceous components, with a unit calorific value of approximately 2,000-4,000 kcal / kg. For a long time, gangue has primarily been stored in piles, which not only occupies significant land resources but also pollutes the local environment through the generation of large amounts of sulfur dioxide, carbon dioxide, and dust during spontaneous combustion. With the development of various industries, the emission of industrial waste has also increased annually, making the harmless treatment of gangue and industrial waste slag urgent.

[0003] The production of expanded clay is an important way to reuse coal gangue and industrial waste slag. In the production process of expanded clay, coal gangue and industrial waste slag are pelletized under moist conditions to form green balls that meet the feed particle size of the equipment, which are then decarbonized and sintered to form expanded clay. During decarbonization, the temperature reaches above 1000°C. At this time, a liquid phase appears on the surface of the green balls, blocking the contact between the fixed carbon inside the green balls and oxygen to produce an oxidation reaction. The carbon in the green balls cannot be fully utilized, and "black core" is easily produced. The expanded clay is severely compacted. The black core expanded clay not only causes a large amount of coal gangue heat to be unable to be utilized, resulting in energy waste, but also due to the difficulty in internal decarbonization, the pore structure of the expanded clay is not fully developed, affecting its water retention and strength. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a method for preparing binary ceramsite using coal gangue and the prepared binary ceramsite.

[0005] The present application provides a binary ceramsite prepared from coal gangue using the following technical solution:

[0006] In a first aspect, the present application provides a method for preparing binary ceramsite using coal gangue, which adopts the following technical solution:

[0007] A method for preparing binary ceramsite using coal gangue comprises the following steps:

[0008] Preparation of the inner core: Carbon-free industrial waste residue and calcium phosphate solution are thoroughly mixed at a ratio of 1 kg: (0.4-0.8) L, pressure treated, and then granulated to obtain green balls. The bonding solution is evenly sprayed on the surface of the green balls to obtain the inner core;

[0009] Preparation of coating material: Coal gangue and sodium alginate solution are fully mixed in a ratio of 1 kg: (0.2-0.5) L to obtain coating material;

[0010] Overmolding: Use coating material to evenly coat the core to form a binary green ball, where 0.15<d / D<0.75, d is the green ball diameter, and D is the binary green ball diameter;

[0011] Preparation of ceramsite: The binary green pellets are dried, pyrolyzed, decarbonized, sintered and cooled to form binary ceramsite.

[0012] Furthermore, the mass concentration of the calcium phosphate solution is 8-12%.

[0013] Furthermore, the mass concentration of the sodium alginate solution is 5-10%.

[0014] Furthermore, the diameter d of the green ball ranges from 5 to 25 mm.

[0015] In this field, if ceramsite is used as a supporting aggregate to play a structural supporting role, it only needs high strength. If ceramsite is used as a soilless cultivation medium in agriculture and horticulture, it only needs good water absorption and water retention. It is difficult to take both into account at the same time, which greatly limits the use scenarios of ceramsite and also weakens the recycling rate of coal gangue and industrial waste.

[0016] The present application uses a calcium phosphate solution to treat carbon-free industrial waste slag under pressurized conditions. Calcium phosphate is not easily soluble in pure water at room temperature, but its solubility can be effectively improved in an acidic environment. Therefore, the calcium phosphate solution actually used in the present application is acidic, and the acidic solution added to promote the dissolution of calcium phosphate is acetic acid. During the pressurized treatment process, the calcium phosphate solution is forced to quickly penetrate into the pores and surface cracks of the carbon-free industrial waste slag. The acidic environment not only improves the surface properties of the carbon-free industrial waste slag, but also gradually evaporates the acetic acid during the pressurized treatment process, without affecting the subsequent process. At high temperatures, oxides such as silicon, aluminum, and iron in the industrial waste slag react with phosphate to generate phosphate minerals, which play a fluxing role, reduce the energy required for sintering, and promote particle rearrangement and bonding between particles. The adhesive solution sprayed on the surface of the inner core can fill the gaps between the particles, increase the friction and bite force between the particles, and further promote the tightness of the connection between the coating material and the inner core. At the same time, when the coating material formed by fully mixing the coal gangue and the sodium alginate solution is coated on the inner core, the calcium ions in the carbon-free industrial waste slag can further cross-link with the sodium alginate solution to form a network structure, thereby improving the bonding effect between the green ball and the coating material, making the overall structure of the binary green ball more stable, and avoiding the separation of the core and the coating material or the product bursting in subsequent processes such as drying. At the same time, after the binary green ball is decarbonized and sintered, the water absorption rate of the product is further improved.

[0017] By strictly controlling the ratio of the green ball diameter to the binary green ball diameter, and combining specific raw material components to form the binary ceramsite structure of this application, the difficulty of decarbonizing the green balls in traditional processes is overcome. Incomplete decarbonization easily leads to the formation of a black core. Traditional coal gangue green balls have a low decarbonization rate and are prone to the black core phenomenon. The binary green ball structure of the present invention has a high decarbonization rate, which can effectively improve the calorific value utilization rate of coal gangue by more than 20%. It can also prevent the formation of a black core in the ceramsite, and the resulting ceramsite product not only has excellent strength but also good water absorption.

[0018] Preferably, the chemical composition of the coal gangue includes SiO2 content of 50%-60%, Al2O3 content of 15%-25%, fixed carbon content of 5%-20%, particle size of the coal gangue less than 200 mesh>50%, and moisture content of 8-15%.

[0019] Through the above technical solution, the selection of coal gangue is optimized and the comprehensive performance of the product is improved. If the particle size distribution of the raw materials is unreasonable, the moisture content is poor, there are too many impurities, etc., it will affect the bonding effect between the components, making the binary green ball structure uneven and prone to separation of the core and the coating material.

[0020] Preferably, the conditions for the pressure treatment are: pressure 1-3 MPa, temperature 60-85° C., and time 20-35 min.

[0021] Preferably, during the preparation of the inner core, 0.5-1 g of the binding solution is sprayed per 100 g of green balls.

[0022] Through the above technical solution, the spraying amount of the bonding solution sprayed on the surface of the green ball is optimized to facilitate the formation of an effective connection network between the core and the coating material. If the bonding solution is too little, it will lead to insufficient viscosity, and the core and the coating material will easily separate in the subsequent process. If the bonding solution is too much, the green ball will be too soft and too sticky, affecting the air permeability of the green ball and increasing the risk of bursting.

[0023] Preferably, the bonding solution includes one of a starch solution and a gelatin solution.

[0024] Furthermore, the mass concentration of the bonding solution is 8-12%, and the most preferred is an oxidized starch solution.

[0025] By adopting the above technical solution, the bonding solution can further cooperate with calcium ions and sodium alginate solution to form an effective connection network between the particles, play a good bonding role, avoid separation between the core and the coating material or product bursting, improve product strength and improve the water absorption rate of the expanded clay.

[0026] Preferably, the carbon-free industrial waste residue includes one or more of fly ash, silica fume, metakaolin, sludge, and shale.

[0027] Furthermore, the carbon-free industrial waste residue is preferably fly ash, specifically fly ash with a fineness of 80 μm and a sieve residue of no more than 15%, and its chemical composition has an SiO2 content of 45%-55% and an Al2O3 content of 25%-35%.

[0028] Through the above technical solution, the selection of carbon-free industrial waste slag is optimized, which helps improve the comprehensive performance of the product. If the particle size distribution of the carbon-free industrial waste slag is unreasonable and there are too many impurities, it will also affect the bonding effect between the components, making the binary green ball structure uneven, resulting in poor ball forming performance or no ball forming, and separation of the core and the coating material.

[0029] Preferably, the drying includes primary drying and secondary drying, the primary drying temperature is 120-150° C., and the primary drying time is 10-15 minutes; the secondary drying temperature is 220-260° C., and the secondary drying time is 10-15 minutes.

[0030] Preferably, the pyrolysis conditions are: temperature 320-450° C., time 15-20 min.

[0031] Preferably, the decarburization conditions are: temperature 500-700°C, time 20-45 minutes. As a preferred embodiment of the decarburization conditions, the decarburization conditions are: temperature 620-650°C, time 20-25 minutes.

[0032] Preferably, the sintering conditions are: temperature 1000-1200° C., and sintering time 20-30 min.

[0033] By adopting the above technical solutions, optimizing the process conditions of drying, sintering, pyrolysis and decarbonization, and combining the structural characteristics of binary green balls, it is more conducive to improving the comprehensive performance of binary ceramsite.

[0034] In a second aspect, the present application provides a binary ceramsite, which adopts the following technical solution:

[0035] A binary ceramsite is prepared by the above-mentioned method for preparing binary ceramsite by utilizing coal gangue.

[0036] By adopting the above technical solution, the binary ceramsite prepared has uniform shape, no black core, excellent strength and good water absorption.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. By strictly controlling the ratio of the green ball diameter to the binary green ball diameter and combining specific raw material components to form the binary ceramsite structure of this application, the problem of difficult decarbonization inside the green balls in traditional processes is overcome. If the decarbonization is not thorough, the problem of black core formation is easily formed. Traditional coal gangue green balls have a low decarbonization rate and are very prone to black core phenomenon. The binary green ball structure of the present invention has a high decarbonization rate, which can effectively improve the calorific value utilization rate of coal gangue by more than 20%. At the same time, it can also prevent the formation of black core in the ceramsite. The resulting ceramsite product not only has excellent strength but also good water absorption rate.

[0039] 2. The core and coating materials of the present application are combined with each other, and then combined with the corresponding process steps, which not only prevents the ceramsite from producing a black core, but also makes the obtained ceramsite product have excellent strength and good water absorption, solving the problem of balancing strength and water absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the binary ceramsite structure diagram for this application.

[0041] Figure 2 This is a picture of the product prepared in Example 8 of this application.

[0042] Figure 3 This is a product diagram obtained in Comparative Example 1.

[0043] Description of the accompanying drawings: 1. Core; 2. Coating material; d: green ball diameter, D: binary green ball diameter. DETAILED DESCRIPTION

[0044] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0045] Example 1

[0046] A method for preparing binary ceramsite using coal gangue comprises the following steps:

[0047] Raw material preparation: Fly ash is used as carbon-free industrial waste slag, with an 80μm sieve residue of 12%, a SiO2 content of 48%, and an Al2O3 content of 30%; coal gangue is crushed to a particle size of less than 2mm, with a moisture content of 10%, a SiO2 content of 55%, an Al2O3 content of 20%, a fixed carbon content of 15%, and a calorific value of 723Kcal;

[0048] Preparation of the inner core: Carbon-free industrial waste residue was thoroughly mixed with 8% calcium phosphate solution at a ratio of 1 kg:0.8 L. The mixture was stirred at a pressure of 1 MPa and a temperature of 85°C for 20 minutes. The pellets were pelletized in a disc pelletizer at a speed of 28 rpm for 12 minutes to obtain green pellets with a particle size of 9 mm. The bonding solution was evenly sprayed on the surface of the green pellets to obtain the inner core; 0.5 g of the bonding solution was sprayed on every 100 g of green pellets. The bonding solution was an 8% gelatin solution.

[0049] Preparation of coating material: Coal gangue and sodium alginate solution with a mass concentration of 5% were fully mixed in a ratio of 1 kg:0.2 L to obtain coating material;

[0050] Coating molding: Add coating material into the drum coating machine, rotate the drum at 18r / min, and coat for 6 minutes to ensure that the coating material evenly coats the core to form a binary green ball;

[0051] Binary green balls screening: The mesh size of the vibrating screen is 18mm. The balls below the screen are returned to the material bin, and the balls above the screen are qualified binary green balls.

[0052] Preparation of ceramsite: The binary green pellets are dried in a drying kiln at 120°C for 15 minutes, and then dried in a drying kiln at 260°C for 10 minutes; pyrolyzed at 350°C for 15 minutes; decarbonized at 620°C for 25 minutes; sintered at 1100°C for 30 minutes, and finally cooled to form binary ceramsite.

[0053] Example 2

[0054] The difference from Example 1 is that

[0055] Raw material preparation: Carbon-free industrial waste residue is metakaolin with an 80μm sieve residue of 10%, SiO2 content of 52%, and Al2O3 content of 28%; coal gangue is crushed to a particle size of less than 2mm, with a moisture content of 9%, SiO2 content of 58%, Al2O3 content of 18%, fixed carbon content of 7%, and a calorific value of 640kcal;

[0056] Preparation of the inner core: Carbon-free industrial waste residue was thoroughly mixed with a 12% calcium phosphate solution at a ratio of 1 kg:0.4 L. The mixture was stirred at a pressure of 3 MPa and a temperature of 60°C for 35 minutes. The pellets were pelletized in a disc pelletizer to obtain green pellets with a particle size of 5 mm. The surface of the green pellets was evenly sprayed with a binding solution to obtain the inner core; 1 g of the binding solution, a 12% gelatin solution, was sprayed on every 100 g of green pellets.

[0057] The rest are the same as in Example 1.

[0058] Example 3

[0059] The difference from Example 1 is that the inner core is prepared as follows: carbon-free industrial waste residue and a 10% calcium phosphate solution are thoroughly mixed in a ratio of 1 kg:0.6 L, stirred at a pressure of 2 MPa and a temperature of 70°C for 28 minutes, and pelletized in a disc pelletizer to obtain green balls with a particle size of 9 mm. A binding solution is evenly sprayed on the surface of the green balls to obtain the inner core; 1 g of the binding solution is sprayed for every 100 g of green balls, and the binding solution is a starch solution with a mass concentration of 8%;

[0060] The rest are the same as in Example 1.

[0061] Example 4

[0062] The difference from Example 3 is that, in the kernel preparation step, 0.8 g of binding solution is sprayed for every 100 g of raw balls, and the binding solution is an oxidized starch solution with a mass concentration of 10%; the rest is the same as Example 3.

[0063] Example 5

[0064] The difference from Example 3 is that, in the inner core preparation step, 2 g of a binding solution is sprayed on every 100 g of green balls, and the binding solution is water glass with a mass concentration of 10%; the rest is the same as Example 3.

[0065] Example 6

[0066] The difference from Example 4 is that the coating material is prepared by fully mixing coal gangue and a sodium alginate solution with a mass concentration of 10% at a ratio of 1 kg:0.5 L to obtain a coating material;

[0067] Coating molding: Add coating material into the drum coating machine, rotate the drum at 20r / min, and coat for 5 minutes to make the coating material evenly coat the core to form a binary green ball;

[0068] Binary green balls screening: The mesh size of the vibrating screen is 15mm. The balls below the screen are returned to the material bin, and the balls above the screen are qualified binary green balls.

[0069] The rest are the same as in Example 4.

[0070] Example 7

[0071] The difference from Example 6 is that, in the preparation of ceramsite, the binary green pellets are dried in a drying kiln at 200°C for 20 minutes; pyrolyzed at 420°C for 20 minutes; decarbonized at 500°C for 45 minutes; sintered at 1000°C for 30 minutes, and finally cooled to form binary ceramsite.

[0072] The rest are the same as in Example 6.

[0073] Example 8

[0074] The difference from Example 6 is that, in the preparation of ceramsite, the binary green balls are dried in a drying kiln at 130°C for an initial drying time of 12 minutes, and then dried in a drying kiln at 243°C for a secondary drying time of 15 minutes; pyrolyzed at a temperature of 375°C for 20 minutes; decarbonized at a temperature of 700°C for 30 minutes; sintered at a temperature of 1150°C for 22 minutes, and finally cooled to form binary ceramsite; the rest are the same as in Example 6.

[0075] Comparative Example 1

[0076] Single gangue was used to prepare ceramsite. The gangue raw material was the same as that in Example 8. The gangue was mixed with a starch solution with a mass fraction of 10% in a ratio of 9:1, stirred and pelletized to obtain gangue green balls. The gangue green balls were dried in a drying kiln at 130°C for an initial drying time of 12 min, and then dried in a drying kiln at 243°C for a secondary drying time of 15 min; pyrolyzed at 375°C for 20 min; decarbonized at 650°C for 30 min; sintered at 1150°C for 22 min, and finally cooled to form ceramsite.

[0077] Comparative Example 2

[0078] The difference from Example 8 is that the inner core is prepared by moistening the fly ash with water and then directly pelletizing it in a disc pelletizer to obtain green balls, and spraying the bonding solution evenly on the surface of the green balls to obtain the inner core; the rest is the same as Example 8.

[0079] Comparative Example 3

[0080] The difference from Example 8 is that coal gangue is directly used as the coating material, and the rest is the same as Example 8.

[0081] Comparative Example 4

[0082] The difference from Example 8 is that in the kernel preparation step, the fly ash and the calcium phosphate solution are fully mixed in a ratio of 1 kg:0.2 L;

[0083] In the coating material preparation step, the coal gangue and the sodium alginate solution are fully mixed in a ratio of 1 kg:1 L;

[0084] In the overmolding step, the value of green ball diameter d / binary green ball diameter D is 0.1;

[0085] The rest are the same as in Example 8.

[0086] The products prepared in Examples 1-8 and Comparative Examples 1-4 were tested for saturated water absorption, cylinder compressive strength, and calorific value according to GB / T 17431 "Lightweight aggregate and its test methods", and the calorific value utilization rate was calculated. The calorific value utilization rate = calorific value of coal gangue / calorific value of ceramsite. The results are shown in Table 1.

[0087] Table 1

[0088] Saturated water absorption / % Cylinder pressure strength / MPa Calorific value utilization / % Example 1 37.1 6.5 85.5 Example 2 35.5 6.7 87 Example 3 36.7 7 86.2 Example 4 37.6 7.2 88.1 Example 5 35.3 6.6 85.9 Example 6 38 7.5 89.5 Example 7 37 7.1 87.1 Example 8 38.4 8 92.5 Comparative Example 1 22 3.7 64 Comparative Example 2 30 4 78.7 Comparative Example 3 28 4.4 76.1 Comparative Example 4 24 4.1 75.3

[0089] Through Examples 1-8 and Table 1, it can be seen that the preparation method of the present application has a high decarbonization rate of coal gangue, the calorific value can be effectively utilized, the calorific value utilization rate is good, energy saving and emission reduction are achieved, and energy costs are saved for enterprises. The obtained binary ceramsite not only has excellent saturated water absorption rate, but also has good mechanical properties and good cylinder pressure strength. Figure 1 and Figure 2 It can be seen that the binary ceramsite structure of the present application is used, and the obtained ceramsite product has no black core and has a high product quality rate.

[0090] By comparing Example 1 and combining Figure 3 It can be seen from Table 1 that the ceramsite product obtained in Comparative Example 1 has a black core, is severely compacted, has a low decarbonization rate of coal gangue, and has a significantly decreased calorific value utilization rate. The water absorption performance and the strength of the ceramsite product are also poor. By way of Example 8 and Comparative Examples 2-4, and in conjunction with Table 1, it can be seen that in Comparative Example 2, the kernel preparation step is adjusted, fly ash is not pretreated using calcium phosphate solution, and in Comparative Example 3, only coal gangue is used directly as a coating material. In Comparative Example 4, the amount of fly ash and calcium phosphate solution, the amount of coal gangue and sodium alginate solution are adjusted, and the binary ceramsite structure is adjusted simultaneously, ultimately causing the overall performance of the ceramsite product to decline, and water absorption performance and mechanical properties cannot be achieved simultaneously.

[0091] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing binary ceramsite using coal gangue, characterized in that: The following steps are involved: Core preparation: Carbon-free industrial waste residue and calcium phosphate solution are thoroughly mixed at a ratio of 1 kg: (0.4-0.8) L, pressure treated, and then granulated to obtain green balls. The bonding solution is evenly sprayed on the surface of the green balls to obtain the core; the pressure treatment conditions are: pressure 1-3 MPa, temperature 60-85°C, and time 20-35 minutes; Preparation of coating material: Coal gangue and sodium alginate solution are fully mixed in a ratio of 1 kg: (0.2-0.5) L to obtain coating material; Overmolding: Use coating material to evenly coat the core to form a binary green ball, where 0.15<d / D<0.75, d is the green ball diameter, and D is the binary green ball diameter; Preparation of ceramsite: The binary green pellets are dried, pyrolyzed, decarbonized, sintered and cooled to form binary ceramsite.

2. The method for preparing binary ceramsite from coal gangue according to claim 1, wherein: The chemical composition of the coal gangue includes SiO2 content of 50%-60%, Al2O3 content of 15%-25%, fixed carbon content of 5%-20%, particle size of the coal gangue less than 200 mesh>50%, and moisture content of 8-15%.

3. The method for preparing binary ceramsite from coal gangue according to claim 1, wherein: During the preparation of the core, 0.5-1 g of the binding solution is sprayed per 100 g of the green pellets.

4. The method for preparing binary ceramsite from coal gangue according to claim 3, wherein: The bonding solution includes one of a starch solution and a gelatin solution.

5. The method for preparing binary ceramsite from coal gangue according to claim 1, wherein: The carbon-free industrial waste residue includes one or more of fly ash, silica fume, metakaolin, sludge, and shale.

6. The method for preparing binary ceramsite from coal gangue according to claim 1, wherein: The drying includes primary drying and secondary drying. The primary drying temperature is 120-150° C. and the primary drying time is 10-15 minutes. The secondary drying temperature is 220-260° C. and the secondary drying time is 10-15 minutes.

7. The method for preparing binary ceramsite from coal gangue according to claim 6, wherein: The pyrolysis conditions are: temperature 320-450° C., time 15-20 min.

8. The method for preparing binary ceramsite from coal gangue according to claim 7, wherein: The sintering conditions are: temperature 1000-1200° C., and sintering time 20-30 min.

9. A binary ceramsite, characterized in that: The binary ceramsite is prepared by the method for preparing binary ceramsite by using coal gangue as described in any one of claims 1 to 8.

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