A cement kiln dust-based lightweight carbonized article and method of making the same

Abstract

The application discloses a kind of light carbonized products based on cement kiln dust, each raw material and the weight percentage it occupies include: kiln dust 100 parts, fly ash 20~40 parts, reinforcing fiber 4~8 parts, lightweight aggregate 10~30 parts, stabilizer 0.05~2 parts, dispersing agent 0.2~0.8 parts;Water solid ratio 0.4~0.6;Among them, lightweight aggregate is obtained by using kiln dust and fly ash with water roller compaction granulation, aging, carbonization, screening.The application can dispose kiln dust harmlessly, reduce carbon emissions in the process of cement production, improve cement kiln energy utilization rate;And can take into account light weight, high strength and other performance;And the preparation method and process involved are simple, with good economic benefit and environmental benefit, suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a lightweight carbonized product based on cement kiln ash and its preparation method. Background Technology

[0002] Cement kiln ash is a dry powder collected from the exhaust gas at the kiln tail during the production of silicate cement clinker in a rotary kiln. With the continuous exploration and research of kiln ash application technology, the uses and treatment technologies of kiln ash are becoming more and more diverse, such as: producing potassium fertilizer, using it as an admixture for masonry and plastering mortar, forming bio-cement with slag, using it as a cement admixture, recycling it back into the kiln, using it for roadbed solidification, and agricultural soil improvement.

[0003] With societal development, environmental protection has placed higher demands on the cement industry. One of the important energy-saving and carbon-reducing measures in cement production is the use of alternative and derivative fuels, and the co-processing of solid waste and municipal solid waste in cement kilns. However, alternative fuels can easily lead to increased levels of potassium, sodium, chlorine, sulfur, and heavy metals such as Fe, Hg, Ti, Se, Mo, Pb, and Cd in kiln ash. This poses new challenges to the harmless and resource-based treatment of cement kiln ash, resulting in increased landfill disposal of kiln ash and impacting the ecological environment.

[0004] Currently, the main challenges in applying kiln ash in the field of building materials are: 1. How to address the harmful effects of heavy metal elements; 2. The negative effects of potassium, sodium, chlorine, and sulfur on cement products; 3. The free calcium oxide from over-burning and sintering in kiln ash can easily cause poor volume stability of the products. Summary of the Invention

[0005] The main objective of this invention is to provide a lightweight carbonized product based on cement kiln ash, which can harmlessly and resourcefully dispose of kiln ash, reduce carbon emissions in the cement production process, improve the energy utilization rate of cement kilns, and take into account the characteristics of being lightweight, high-strength, and having good thermal insulation performance; moreover, the preparation method and process involved are simple, and have good economic and environmental benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A lightweight carbonized product based on cement kiln ash, comprising the following raw materials and their respective weight proportions: 100 parts kiln ash, 20-40 parts fly ash, 4-8 parts reinforcing fiber, 10-30 parts lightweight aggregate, 0.05-2 parts stabilizer, and 0.2-0.8 parts dispersant; with a water-to-solid ratio of 0.4-0.6; wherein the lightweight aggregate is obtained by roller pressing, aging, carbonizing, and sieving of kiln ash and fly ash with water.

[0008] In the above scheme, the kiln ash is ordinary kiln ash or co-existing kiln ash from cement kilns, with a particle size of 0-40 μm and a specific surface area greater than 350 m².2 / The main chemical components and their mass percentages (kg) include: SiO2 5–15%, Al2O3 2–4%, Fe2O3 0–3%, CaO 25–55%, MgO 0–3%, K2O 3–20%, Cl - It contains 8-25%; it may also contain heavy metal oxides such as Ti, Se, Mo, Pb, and Cd.

[0009] In the above scheme, the fly ash is a high-quality ash of grade II or above, and its CaO content in its chemical composition is less than 5 wt%.

[0010] In the above scheme, the reinforcing fiber is an acidified pulp fiber (one or more of bamboo pulp, straw pulp, and wood pulp); its length is 1-3 mm and its aspect ratio is 60-100.

[0011] Furthermore, the pulp fiber can be compounded with alkali-resistant glass fiber or carbon fiber of the same specifications.

[0012] In the above scheme, the carbon fiber has a diameter of 5-10 μm and a length of 0.8-1.2 mm; the alkali-resistant glass fiber has an average length of 3 mm and a diameter of 9-13 μm.

[0013] The specific preparation steps of the lightweight aggregate in the above scheme include: adding 20-35% fly ash to kiln ash (the additional fly ash is not included in the fly ash weight percentage of the lightweight carbonized product), mixing with water (moisture content controlled at 12-25%), and rapidly reacting the fly ash under the activation of the kiln ash to generate porous gel as a binder; granulating with a roller press (pressure 0.5-5.0 MPa) to form porous and loose particles, aging for 24-48 hours to improve the f-CaO reaction degree; then carbonizing for 8-20 hours under a gauge pressure of 0-0.3 MPa (relative to standard atmospheric pressure), CO2 concentration of 10-30 vol%, and temperature of 30-70℃, followed by drying after carbonization enhancement, and sieving out 2-5 mm particles as lightweight aggregate, with a bulk density of 640-850 kg / m³. 3 .

[0014] In the above scheme, the stabilizer can be one or more of cellulose ether, xanthan gum, styrax, polyacrylamide, etc., and its main function is to disperse solids and maintain the suspension of slurry.

[0015] In the above scheme, the dispersant is one or more of sodium polycarboxylate, sodium polyacrylate, and polyols (ethylene glycol or diethylene glycol, etc.). Its main functions are: first, to disperse calcium hydroxide. The calcium hydroxide produced by the surface dissolution of free calcium oxide particles sintered in kiln ash will hinder its further digestion. After adding the dispersant, the calcium hydroxide covering the surface of free calcium oxide can be effectively dispersed and removed, preventing agglomeration and thus improving the degree of dissolution of free calcium oxide and improving the volume stability of lightweight plates; second, it can effectively prevent calcium hydroxide agglomeration and further crystal growth, reduce the crystal size of calcium hydroxide, increase the specific surface area of ​​calcium hydroxide, and thus improve the carbonization activity of calcium hydroxide.

[0016] Furthermore, the dispersant is composed of sodium polycarboxylate and ethylene glycol, with a mass ratio of sodium polycarboxylate to ethylene glycol of 1:1.6 to 2.0.

[0017] The above-mentioned method for preparing lightweight carbonized products based on cement kiln ash includes the following steps:

[0018] 1) Weigh each ingredient according to the proportions;

[0019] 2) Add dispersant and mixing water to the kiln ash, stir evenly, and seal for aging;

[0020] 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir evenly to obtain molding slurry, then mold, and demold to obtain blank;

[0021] 4) Place the obtained green body in a standard humidity curing environment for pre-curing, and then adjust the moisture content of the green body to 10-18%;

[0022] 5) The blank obtained in step 4) is carbonized and cured to obtain a lightweight carbonized product.

[0023] In the above scheme, the sealing and aging process takes 24 to 48 hours.

[0024] In the above scheme, the mixing water temperature in step 2) is 50-80℃. A higher digestion temperature can increase the degree of dissolution of free calcium oxide in the kiln ash, improving the volume stability of the board; and it can reduce the crystal particle size and specific surface area of ​​calcium oxide, thereby increasing its carbonization activity, increasing the amount of carbonization, and improving the strength of the board. The mixing water can be heated using waste heat from the cement kiln, improving energy utilization and reducing carbon dioxide emissions.

[0025] In the above scheme, the molding step in step 3) uses a pressure of 0 to 20 MPa. It can be cast or pressurized. Different pressures result in different molding properties of the final carbonized products, which can be adjusted according to requirements and have different uses and applications.

[0026] In the above scheme, in step 4), the green body is pre-cured for 48-72 hours to initially obtain a certain strength, preventing damage to the green body during the carbonization process. The gel generated by the hydration of kiln ash and fly ash after curing can improve the water retention capacity of the green body and ensure the amount of carbonization water during the carbonization process.

[0027] In the above scheme, in step 4), since carbon dioxide needs to be dissolved in water before carbonization, the moisture content of the slab needs to be controlled within a certain range. Too high or too low a moisture content during carbonization will reduce the carbonization effect and affect the carbonization strength. Different carbonization environments, especially environmental conditions that affect moisture loss, such as gas flow and temperature, will influence the required moisture content of the slab.

[0028] In the above scheme, in step 5), the carbonation curing temperature is 30–70℃, the gauge pressure (relative to standard atmospheric pressure) is 0–0.3 MPa, the CO2 concentration is 10–30 vol%, and the carbonation time is 8–20 h. The CO2 gas used can be directly used from the cement kiln tail gas, reducing CO2 emissions from cement production and making it a resource.

[0029] Furthermore, the lightweight carbonized product can be further processed by cutting, drying, chamfering, and edge grinding to obtain the finished lightweight carbonized product.

[0030] The lightweight carbonized products based on kiln ash prepared according to the above technical solution have a dry flexural strength of 5–10 MPa and a dry bulk density of 900–1400 kg / m³. 3 It has a water absorption rate of 8–14.5% and a thermal conductivity of 0.10–0.25 W / (m·K).

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) This invention uses kiln ash as the main raw material and fly ash as an auxiliary material, which can realize the harmless and resource-based disposal of kiln ash. Kiln ash can be used directly in large quantities without complicated treatment methods, and also provides a new use for fly ash. At the same time, the carbonization process can effectively utilize CO2 in the kiln tail flue gas, reduce carbon emissions in the cement production process, and has good economic and environmental benefits.

[0033] 2) Kiln ash itself possesses certain hydration and carbonization activity, and is characterized by high alkalinity, which can effectively stimulate the potential activity of fly ash. At higher temperatures, the reaction rate is increased. Aluminum and silicon in fly ash can react with calcium, sulfur, and chlorine in kiln ash to form hydrated calcium sulfoaluminate, hydrated calcium chloroaluminate, and hydrated calcium aluminate. Simultaneously, the reaction products of fly ash and kiln ash have strong adsorption properties, effectively absorbing and solidifying harmful alkaline ions and most heavy metal elements in the kiln ash, thus achieving the goal of rendering the kiln ash harmless.

[0034] 3) This invention addresses the high calcium oxide content in kiln ash by increasing the digestion water temperature and adding dispersants. This improves the degree of calcium oxide digestion, reduces the risk of cracking in the boards, reduces the crystal size of calcium hydroxide, enhances carbonization activity and degree, and improves the strength of the boards. Through the hydration and carbonization reactions of kiln ash and fly ash, carbonized products with certain adsorption properties, lightweight, and high strength are prepared, which can be widely used in sound insulation filling, fireproof and heat insulation filling, building decoration, and buried insulation layers. Detailed Implementation

[0035] The present invention will be further described in detail below through specific implementation examples. These implementation examples are based on the technology of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the implementation examples given below.

[0036] In the following examples, the kiln ash used is cement kiln fly ash from Huaxin Wuxue Cement Company, containing 12.4% SiO2, 2.8% Al2O3, 2.3% Fe2O3, approximately 47.4% CaO, and Cl... - It contains approximately 12.6% minerals, 3.2% K₂O, and 6.1% SO₃; its particle size ranges from 0 to 40 μm, and its specific surface area is 450 m². 2 / kg.

[0037] The fly ash is classified as Grade I ash, with a residue of less than 12% on a 45μm sieve and a CaO content of 2.1wt%.

[0038] The reinforcing fiber is pulp fiber, or it can be used together with carbon fiber, with a carbon fiber content of 0.01 to 0.05 wt%. The pulp fiber has a length of 1 to 3 mm and an aspect ratio of 60 to 100. The carbon fiber has a diameter of 5 to 10 μm and a length of 0.8 to 1.2 mm.

[0039] The stabilizer is sorbitol; the dispersant consists of sodium polycarboxylate and ethylene glycol.

[0040] The preparation method of lightweight aggregate includes: adding 30% fly ash by mass to kiln ash, adding water and mixing, controlling the moisture content of the resulting mixture to 18%, granulating it using a roller press to form porous and loose particles, aging it at a roller press pressure of 3.5 MPa for 48 hours, carbonizing it for 20 hours under conditions of 0.2 MPa gauge pressure (relative to standard atmospheric pressure, the same below), CO2 concentration of 25%, and temperature of 50℃, drying it after carbonization enhancement, and sieving out particles of 2-5 mm as lightweight aggregate. The bulk density of the lightweight aggregate is approximately 767 kg / m³. 3 .

[0041] Example 1

[0042] A lightweight carbonized product based on kiln ash is prepared by the following steps:

[0043] 1) Weigh out the raw materials according to the weight parts of each material in the slurry of lightweight carbonized products: 100 parts kiln ash, 20 parts fly ash, 6 parts reinforcing fiber (acid-treated pulp fiber), 20 parts lightweight aggregate, 0.1 parts warm wheel rubber, 0.2 parts sodium polycarboxylate, 0.36 parts ethylene glycol, and water-to-solid ratio of 0.5.

[0044] 2) Add dispersant to the weighed kiln ash, add weighed mixing water at 50℃, stir evenly, seal and age for 24 hours.

[0045] 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir thoroughly to obtain the molding slurry;

[0046] 4) Place the molding slurry into the filter press molding mold, spread it evenly, and use the molding method to filter press the material at a pressure of 10MPa. Demold the material to obtain the blank.

[0047] 5) The green body is placed in a standard humid curing environment for pre-curing for 3 days, and the moisture content of the green body is controlled to 14% by blowing with a fan or adding water.

[0048] 6) Carbonize the blank obtained in step 5) at 30°C, with a CO2 concentration of 10%, a gauge pressure of 0.1 MPa, and a carbonization time of 20 h.

[0049] The obtained carbonized products were cut, dried, and their physical properties were tested. The specific test results are shown in Table 1.

[0050] Example 2

[0051] A lightweight carbonized product based on kiln ash is prepared by the following steps:

[0052] 1) Weigh the raw materials according to the weight parts of each material in the slurry of lightweight carbonized products: 100 parts kiln ash, 35 parts fly ash, 6 parts reinforcing fiber (acid-treated pulp fiber), 20 parts lightweight aggregate, 0.2 parts xanthan gum, 0.2 parts sodium polycarboxylate, 0.36 parts ethylene glycol, and water-to-solid ratio of 0.5.

[0053] 2) Add dispersant to the weighed kiln ash, add weighed mixing water at 70℃, stir evenly, seal and age for 24 hours.

[0054] 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir thoroughly to obtain the molding slurry;

[0055] 4) Place the molding slurry into the filter press molding mold, spread it evenly, and use the molding method to press and filter the material at a pressure of 20MPa. Demold the material to obtain the blank.

[0056] 5) The green body is placed in a standard humidity curing environment for pre-curing for 3 days, and the moisture content of the green body is controlled at 18%.

[0057] 6) Carbonize the green body obtained in step 5) at a temperature of 70°C, a CO2 concentration of 20%, a gauge pressure of 0.3 MPa, and a carbonization time of 20 h.

[0058] The obtained carbonized products were cut, dried, and their physical properties were tested. The specific test results are shown in Table 1.

[0059] Example 3

[0060] A lightweight carbonized product based on kiln ash is prepared by the following steps:

[0061] 1) Weigh out each raw material in the following proportions according to the weight of the slurry for lightweight carbonized products: 100 parts kiln ash, 35 parts fly ash, 6 parts reinforcing fiber (acid-treated pulp fiber), 18 parts lightweight aggregate, 0.08 parts xanthan gum, 0.2 parts sodium polycarboxylate, 0.36 parts ethylene glycol, and a water-to-solid ratio of 0.55.

[0062] 2) Add dispersant to the weighed kiln ash, add weighed mixing water at 65℃, stir evenly, seal and age for 24 hours.

[0063] 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir thoroughly to obtain the molding slurry;

[0064] 4) Pour the molding slurry into the molding mold, place the mold in a standard moisture curing environment for 3 days, and then remove the mold to obtain the green body;

[0065] 5) Control the moisture content of the billet to 16%;

[0066] 6) Carbonize the green body obtained in step 5) at a carbonization environment of 50°C, CO2 concentration of 30%, gauge pressure of 0.3 MPa, and carbonization time of 20 h.

[0067] The obtained carbonized products were cut, dried, and their physical properties were tested. The specific test results are shown in Table 1.

[0068] Example 4

[0069] A lightweight carbonized product based on kiln ash is prepared by the following steps:

[0070] 1) Weigh the raw materials according to the weight parts of each material in the slurry for lightweight carbonized products: 100 parts kiln ash, 30 parts fly ash, 6.02 parts reinforcing fiber (6 parts acid-treated pulp fiber, 0.02 parts carbon fiber), 23 parts lightweight aggregate, 1.2 parts 400 viscosity cellulose ether, 0.2 parts sodium polycarboxylate, 0.36 parts ethylene glycol, and water-to-solid ratio of 0.52.

[0071] 2) Add dispersant to the weighed kiln ash, add weighed mixing water at 58℃, stir evenly, seal and age for 24 hours.

[0072] 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir thoroughly to obtain the molding slurry;

[0073] 4) Place the molding slurry into the filter press molding mold, spread it evenly, and use the molding method to filter press the material at a pressure of 15MPa. Demold the material to obtain the blank.

[0074] 5) The green body is placed in a standard humidity curing environment for pre-curing for 3 days, and the moisture content of the green body is controlled at 17%;

[0075] 6) Carbonize the blank obtained in step 5) at 60°C, with a CO2 concentration of 25%, a gauge pressure of 0.3 MPa, and a carbonization time of 20 h.

[0076] The obtained carbonized products were cut, dried, and their physical properties were tested. The specific test results are shown in Table 1.

[0077] Comparative Example 1

[0078] The preparation methods of Comparative Example 1 and Example 2 are roughly the same, except that the moisture content of the green body in step 5) is controlled to be about 8%.

[0079] Comparative Example 2

[0080] The preparation methods of Comparative Example 2 and Example 2 are roughly the same, except that the moisture content of the green body in step 5) is controlled to be about 22%.

[0081] Comparative Example 3

[0082] The preparation methods of Comparative Example 3 and Example 2 are roughly the same, except that in step 1), 60 parts of fly ash are weighed.

[0083] Comparative Example 4

[0084] The preparation methods of Comparative Example 4 and Example 2 are roughly the same, except that in step 1), 10 parts of fly ash are weighed.

[0085] Comparative Example 5

[0086] The preparation method of Comparative Example 5 is roughly the same as that of Example 2, except that the molding pressure in step 4) is 35 MPa.

[0087] Comparative Example 6

[0088] The preparation methods of Comparative Example 6 and Example 2 are roughly the same, except that no dispersant is added in step 2), and the temperature of the mixing water is room temperature.

[0089] Comparative Example 7

[0090] The preparation methods of Comparative Example 7 and Example 2 are roughly the same, except that in the preparation method of lightweight aggregate, 30% of fly ash by mass is added to kiln ash, water is added and mixed, the moisture content of the resulting mixture is controlled at 5%, and the roll forming pressure is 3.5 MPa; the resulting lightweight aggregate is difficult to achieve the target particle size, and cannot effectively reduce the bulk density of the product and ensure its strength.

[0091] The physical properties of the lightweight carbonized products based on kiln ash prepared in the examples and comparative examples were tested, including the dry flexural strength and dry bulk density. The results are shown in Table 1.

[0092] Table 1. Performance test results of the carbonized products obtained in the examples and comparative examples.

[0093]

[0094] The physical properties of the lightweight carbonized products based on cement kiln ash described in this invention are influenced by a multitude of factors. The most significant factors are material ratio, molding pressure, green body moisture content, and carbonization temperature. Insufficient fly ash reduces hydration products and strength, while excessive fly ash, due to its low density, results in numerous pores in the product, further reducing strength. Molding pressure can significantly improve product strength, but it also greatly increases the product's bulk density. Green body moisture content has the greatest and most sensitive impact on carbonization strength; both excessively low and high moisture content significantly affect the carbonization effect, resulting in lower strength. Increasing the carbonization temperature can accelerate the hydration reaction, but it can also cause excessively rapid water loss from the green body, leading to insufficient carbonization water and difficulty in carbonization. Simultaneously, increased temperature reduces CO2 solubility, further decreasing the carbonization effect. Free calcium oxide in the kiln ash, without adequate treatment with dispersants and high-temperature water, can cause defects in the slabs, affecting both strength and appearance.

[0095] For researchers and those skilled in the art, improvements and modifications can be easily made to this invention without departing from the technical aspects thereof, and such improvements and modifications also fall within the protection scope of this invention. This invention is not limited to the above-described embodiments; any changes made without departing from the claims of this invention are covered within the protection scope.

Claims

1. A lightweight carbonized product based on cement kiln ash, characterized in that, The raw materials and their respective weight percentages include: 100 parts kiln ash, 20-40 parts fly ash, 4-8 parts reinforcing fiber, 10-30 parts lightweight aggregate, 0.05-2 parts stabilizer, and 0.2-0.8 parts dispersant; the water-to-solid ratio is 0.4-0.

6. The specific preparation steps for the lightweight aggregate include: adding fly ash to the kiln ash and mixing with water; then granulating using a roller press to form porous and loose particles, followed by aging; then carbonizing for 8-20 hours under a gauge pressure of 0-0.3 MPa, a CO2 concentration of 10-30 vol%, and a temperature of 30-70℃; after carbonization and strengthening, drying is performed, and 2-5 mm particles are sieved out. The preparation method of the lightweight carbonized product includes the following steps: 1) Weigh each ingredient according to the proportions; 2) Add dispersant and mixing water to the kiln ash, stir evenly, and seal for aging; the temperature of the mixing water should be 50~80℃; 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir evenly to obtain molding slurry, mold, demold, and obtain green body; the pressure used in the molding step is 0~20MPa; 4) Place the obtained green body in a standard humidity curing environment for pre-curing, and then adjust the moisture content of the green body to 10~18%; 5) Carbonize and cure the blank obtained in step 4) to obtain a lightweight carbonized product.

2. The lightweight carbonized product according to claim 1, characterized in that, The kiln ash has a particle size of 0~40μm and a specific surface area greater than 350m². 2 / kg; the main chemical components and their mass percentages include: SiO2 5~15%, Al2O3 2~4%, Fe2O3 0~3%, CaO 25~55%, MgO 0~3%, K2O 3~20%, Cl - 8~25%.

3. The lightweight carbonized product according to claim 1, characterized in that, The fly ash is a high-quality ash of grade II or above, and its CaO content in its chemical composition is less than 5wt%.

4. The lightweight carbonized product according to claim 1, characterized in that, The reinforcing fiber is an acidified pulp fiber, or a composite fiber of it with alkali-resistant glass fiber or carbon fiber; wherein the pulp fiber has a length of 1~3mm and an aspect ratio of 60~100.

5. The lightweight carbonized product according to claim 1, characterized in that, The bulk density of the lightweight aggregate is 640~850 kg / m³. 3 .

6. The lightweight carbonized product according to claim 1, characterized in that, The stabilizer is one or more of cellulose ether, xanthan gum, vinyl gum, and polyacrylamide.

7. The lightweight carbonized product according to claim 1, characterized in that, The dispersant is one or more of sodium polycarboxylate, sodium polyacrylate, and polyol.

8. The method for preparing lightweight carbonized products based on cement kiln ash according to any one of claims 1 to 7, characterized in that, Includes the following steps: 1) Weigh each ingredient according to the proportions; 2) Add dispersant and mixing water to the kiln ash, stir evenly, and seal for aging; 3) Add the remaining material weighed in step 1) to the slurry obtained in step 2), stir evenly to obtain molding slurry, mold, demold, and obtain blank; 4) Place the obtained green body in a standard humidity curing environment for pre-curing, and then adjust the moisture content of the green body to 10~18%; 5) Carbonize and cure the blank obtained in step 4) to obtain a lightweight carbonized product.

9. The preparation method according to claim 8, characterized in that, In step 5), the carbonization curing temperature is 30~70℃, the gauge pressure is 0~0.3MPa, the CO2 concentration is 10~30vol%, and the carbonization time is 8~20h.

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