Fly ash-based hydrated calcium silicate, preparation method and use thereof

Abstract

The present invention provides a fly ash-based calcium silicate hydrate, a preparation method, and uses thereof. The preparation method comprises adding fly ash as a silicon source and a calcium-containing compound as a calcium source to water to produce a mixed slurry, then subjecting the mixture to thermal activation and hydrothermal reaction. After the reaction is complete, the liquid-solid separation and drying are performed to produce the fly ash-based calcium silicate hydrate. The present invention utilizes a pre-thermal activation process instead of the traditional alkaline activation process. The entire process does not require the addition of a caustic medium, the product does not require washing, and does not contain potassium or sodium metal ions, resulting in a simple process and low cost. The fly ash-based calcium silicate hydrate product produced by this method has a crystalline tobermorite content of up to 40%, a fibrous porous structure, and possesses the functions of water retention, heavy metal ion adsorption, heat insulation, and sound insulation. Furthermore, the fly ash-based calcium silicate hydrate product has a high content of citric acid-soluble silica and can be widely used in cement, concrete, adsorbents, soil conditioners, thermal insulation materials, sound insulation materials, and other fields.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and in particular to fly ash-based calcium silicate hydrate, a preparation method thereof, and uses thereof. Background Art

[0002] Calcium silicate hydrate (CSH) is composed of xCaO·SiO2·yH2O. Its composition is complex, with a calcium-silicon molar ratio ranging from 0.6 to 2.0. Calcium silicate hydrate is the primary hydration product of Portland cement and the primary contributor to the strength of cement concrete. Synthetic calcium silicate hydrate, when added to concrete along with water reducers and active admixtures, promotes cement hydration, improves the structure and strength of the cement paste, and ultimately enhances the strength and performance of the concrete. Synthetic calcium silicate hydrate is porous and rich in active calcium. It can not only adsorb and solidify some heavy metal ions but also absorb and recover phosphorus, ammonia, and nitrogen from wastewater. Consequently, research has recently begun exploring its potential applications in water treatment and ecological restoration. Furthermore, the silicon and calcium in CSH are largely citric acid-soluble, making them easily absorbed by plants. Both silicon and calcium are essential secondary elements for plant growth, making CSH a crucial raw material component in soil improvement materials.

[0003] CN107673362A discloses a method for preparing calcium silicate hydrate, comprising placing a mixture of sodium silicate solution, calcium nitrate solution, and water in a plastic container and ultrasonically mixing the mixture, then adding sodium hydroxide solution to adjust the pH of the mixed solution to greater than 13, thereby preparing calcium silicate hydrate of high purity. CN112250076A discloses a method for preparing nanometer calcium silicate hydrate, comprising using sodium silicate solution and calcium nitrate solution as raw materials and preparing nanometer-scale calcium silicate hydrate by gradual dropwise addition. CN106542551A discloses a method for extracting aluminum oxide from fly ash, comprising mixing quicklime, fly ash, and water, adding 5 g / L to 100 g / L of NaOH to adjust the pH of the slurry, reacting the mixture in a high-pressure sealed container at a temperature of 120°C to 260°C for 0.5 to 12 hours, and obtaining calcium silicate hydrate for cement concrete through solid-liquid separation.

[0004] Current methods for preparing calcium silicate hydrate from fly ash require the addition of potassium- or sodium-containing alkali solutions, which promote the dissolution of SiO2 in the fly ash, thereby achieving a relatively good reaction effect. However, the addition of potassium- or sodium-containing alkalis changes the morphology and chain length of the calcium silicate hydrate, resulting in potassium or sodium inclusions in the product. This is difficult to completely remove, even with large amounts of water washing. This can cause an alkali-aggregate effect in cement concrete applications, severely impacting performance. It can also easily cause alkali contamination when used in water treatment or ecological restoration.

[0005] Therefore, seeking a preparation method for calcium silicate hydrate with simple process, low cost, outstanding performance, especially one that does not contain potassium or sodium, is of great significance for its large-scale application as an industrial product. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a fly ash-based hydrated calcium silicate, a preparation method and use thereof. The preparation method has a relatively simple process, the raw material is derived from solid waste fly ash, and the preparation process does not require the addition of potassium or sodium-containing alkali solution. The product does not need to be washed, and no alkali return phenomenon will occur when used in cement or concrete. It is safe and harmless to soil and crops, has a short preparation time, high production capacity, and has very good application prospects.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing fly ash-based calcium silicate hydrate, the preparation method comprising the following steps:

[0009] (1) mixing a calcium source, fly ash, and water to obtain a mixed slurry;

[0010] (2) thermally activating the mixed slurry in step (1) to obtain an activated slurry;

[0011] (3) The activated slurry in step (2) is subjected to hydrothermal reaction, liquid-solid separation and drying in sequence to obtain the fly ash-based hydrated calcium silicate.

[0012] The fly ash-based calcium silicate hydrate preparation method of the present invention uses fly ash as a silicon source and a calcium-containing compound as a calcium source. The two are added to water in a certain proportion to form a mixed slurry. The fly ash is then converted into a highly active calcium silicate hydrate with a loose, porous structure through a special thermal activation (heating-maintaining temperature-cooling)-hydrothermal reaction process. The fly ash-based calcium silicate hydrate contains 10-40% crystalline tobermorite. The method uses solid waste as the raw material source, and the preparation process does not require the addition of potassium or sodium-containing alkali liquor. The process is simple, low-cost, safe, and efficient, making it a highly promising preparation method.

[0013] Preferably, the calcium source in step (1) is an industrial raw material with calcium oxide as the main component.

[0014] Preferably, the calcium source comprises any one or a combination of at least two of calcium hydroxide, lime, calcium phosphate or calcium sulfate, wherein typical but non-limiting combinations are: a combination of calcium hydroxide and lime, a combination of calcium phosphate and calcium sulfate, a combination of calcium hydroxide and calcium phosphate, or a combination of calcium sulfate, calcium hydroxide and lime.

[0015] The calcium source described in the present invention includes any one of calcium hydroxide, lime, calcium phosphate, or calcium sulfate, or a combination of at least two. While also alkaline, the calcium ions contained in these materials differ from the potassium- or sodium-containing lye used in prior art. The fly ash-based calcium silicate hydrate obtained in the present invention does not experience alkali reversion when used in cement or concrete, and is safe and harmless to soil and crops.

[0016] Preferably, the molar ratio of CaO in the calcium source to SiO2 in the fly ash in step (1) is (0.4-1.4):1, for example, it can be 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1 or 1.4:1, as well as other values ​​other than the above values, which are not exhaustively listed in the present invention due to space limitations and for the sake of simplicity. The molar ratio is preferably (0.8-1.1):1.

[0017] The present invention preferably has a molar ratio of CaO in the calcium source to SiO2 in the fly ash of (0.4-1.4):1, which can increase the content of citric acid-soluble silica in the product and also adjust the microscopic morphology of the product, such as the specific surface area and porosity.

[0018] Preferably, the solid-to-liquid ratio of the mixed slurry in step (1) is 1:(10-40) g / mL, for example, 1:10 g / mL, 1:15 g / mL, 1:20 g / mL, 1:25 g / mL, 1:30 g / mL, 1:35 g / mL or 1:40 g / mL, as well as other values ​​other than the above values, which are not exhaustively listed in the present invention due to space limitations and for the sake of simplicity. The mass-to-volume ratio is preferably 1:(15-25) g / mL.

[0019] The solid-liquid ratio of the mixed slurry of the present invention is very critical for the preparation of calcium silicate hydrate. When the mass-to-volume ratio is too high, the reactants in the mixed slurry are difficult to mix evenly and the reaction is insufficient. When the mass-to-volume ratio is too low, excessive energy consumption is caused.

[0020] Preferably, the thermal activation in step (2) includes a temperature rise section, a constant temperature section, and a temperature drop section, wherein the temperature drop section is a key step in the thermal activation and is essential. During the thermal activation process, the structural type of the silicon-oxygen tetrahedron in the fly ash changes and transforms into a structure that is more easily converted into calcium silicate hydrate, and the reaction activity is greatly enhanced, thereby laying a structural foundation for the next step of hydrothermal synthesis of calcium silicate hydrate. If the thermal activation is not performed in advance and the hydrothermal reaction is directly performed, the content of crystalline tobermorite in the calcium silicate hydrate will decrease under the same conditions, and the yield of calcium silicate hydrate will be significantly reduced.

[0021] Preferably, the heating rate of the heating section is 1-10°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, etc., as well as other values ​​other than the above values. Due to space limitations and for the sake of simplicity, the present invention will no longer list them exhaustively.

[0022] Preferably, the temperature of the constant temperature section is 150-250°C, for example, 150°C, 160°C, 180°C, 200°C, 220°C, 240°C or 250°C, as well as other values ​​other than the above values. Due to space limitations and for the sake of simplicity, the present invention does not list them all. The temperature is preferably 180-200°C.

[0023] If the temperature of the constant temperature section in the present invention is too low, the reaction rate of thermal activation is too slow, the conversion rate is too low, and the tobermorite crystal content and the citric acid-soluble silica content in the obtained fly ash-based hydrated calcium silicate are low; if the temperature of the constant temperature section is too high, the industrial cost of preparing the fly ash-based hydrated calcium silicate is high.

[0024] Preferably, the time of the constant temperature section is 0-1h, for example, it can be 0h, 0.1h, 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h, as well as other values ​​other than the above values. Due to space limitations and for the sake of simplicity, the present invention will no longer list them exhaustively.

[0025] Preferably, the terminal temperature of the cooling section is 25-80°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, as well as other values ​​other than the above values. Due to space limitations and for the sake of simplicity, the present invention will no longer list them all.

[0026] If the terminal temperature of the cooling section of the present invention is too high, activation is insufficient, the silicon-oxygen tetrahedron structure in the fly ash is not completely transformed, and the tobermorite crystal content and the citrate-soluble silica content in the obtained fly ash-based hydrated calcium silicate are low; if the terminal temperature of the cooling section is too low, the cooling time is too long, and the cost of preparing the fly ash-based hydrated calcium silicate increases.

[0027] Preferably, the cooling period is 0.1-3 h, for example, 0.1 h, 0.2 h, 0.3 h, 0.5 h, 0.7 h, 1 h, 1.5 h, 2 h, 2.5 or 3 h, as well as other values ​​other than the above values. Due to space limitations and for the sake of simplicity, the present invention will no longer list them exhaustively.

[0028] If the cooling period of the present invention is too short, the transformation of the silicon-oxygen tetrahedral structure in the fly ash is difficult to complete, which affects the activation effect. The tobermorite crystal content and the citrate-soluble silica content in the obtained fly ash-based hydrated calcium silicate are low. If the cooling period is too long, the cost of preparing the fly ash-based hydrated calcium silicate increases.

[0029] Preferably, the temperature of the hydrothermal reaction in step (3) is 150-250°C, for example, 150°C, 160°C, 180°C, 200°C, 220°C, 240°C, or 250°C, as well as other values ​​other than the above values, which are not exhaustively listed in the present invention due to space limitations and for the sake of brevity. The temperature is preferably 180-220°C.

[0030] Preferably, the hydrothermal reaction time in step (3) is 0.5-6 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h, as well as other values ​​other than the above values, which are not exhaustively listed in the present invention due to space limitations and for the sake of simplicity. The time is preferably 1-3 h.

[0031] The present invention will keep appropriate temperature in carrying out hydrothermal reaction process, when the temperature of hydrothermal reaction is too low, reaction can not fully be carried out, and crystalline state tobermorite and citric acid soluble silicon dioxide content are lower, and when the temperature of hydrothermal reaction is too high, energy consumption increases, and cost increases.When the time of hydrothermal reaction is too short, reaction is carried out incompletely, and crystalline state tobermorite and citric acid soluble silicon dioxide content are lower, and when the time of hydrothermal reaction is too long, energy consumption will be increased, and cost is improved.This preferred temperature and time can reduce energy consumption to greatest extent under the condition of guaranteeing crystalline state tobermorite and citric acid soluble silicon dioxide content, saves cost.

[0032] In the present invention, the calcium silicate hydrate product can be obtained by drying directly after the liquid-solid separation in step (3) without washing. Conventional equipment in the art can be used for liquid-solid separation and drying.

[0033] There is no limitation on the solid-liquid separation in the present invention, and any method for solid-liquid separation known to those skilled in the art may be used, such as filtration, sedimentation or centrifugation.

[0034] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0035] (1) mixing a calcium source, fly ash, and water to obtain a mixed slurry; the calcium source comprises any one of calcium hydroxide, lime, calcium phosphate, or calcium sulfate, or a combination of at least two thereof; the molar ratio of CaO in the calcium source to SiO2 in the fly ash is (0.4-1.4):1; and the solid-liquid ratio of the mixed slurry is 1:(10-40) g / mL;

[0036] (2) The mixed slurry of step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 1-10°C / min; the temperature of the constant temperature section is 150-250°C and the time is 0-1h; the terminal temperature of the cooling section is 25-80°C and the time is 0.1-3h;

[0037] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 150-250° C. for 0.5-6 h, liquid-solid separation and drying to obtain the fly ash-based hydrated calcium silicate.

[0038] In a second aspect, the present invention further provides a fly ash-based calcium silicate hydrate, which is prepared using the fly ash-based calcium silicate hydrate preparation method described above.

[0039] Preferably, the proportion of crystalline tobermorite in the fly ash-based calcium silicate hydrate is 10-40%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35% or 40%, as well as specific values ​​between the above values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific values ​​included in the range.

[0040] In a third aspect, the present invention further provides a use of the fly ash-based calcium silicate hydrate as described in the second aspect in building materials, adsorption materials, soil improvement materials, thermal insulation materials, and sound insulation materials.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] (1) The preparation method of fly ash-based calcium silicate hydrate provided by the present invention adopts a new method of pre-heat activation to stimulate the conversion of silicate structure in fly ash, which can greatly improve the reactivity of aluminum silicate in fly ash. This process can replace the role of alkali activators (caustic soda, water glass, etc.) in traditional processes. The overall process does not introduce alkali metal ions containing potassium or sodium, and does not require a washing process. It can eliminate the problems of alkali-aggregate reaction, efflorescence, and environmental pollution caused by alkali metal ions containing potassium or sodium from the source;

[0043] (2) The crystalline form of the fly ash-based hydrated calcium silicate provided by the present invention is tobermorite, accounting for more than 30%, and its microscopic morphology is a porous fibrous structure, which is similar to the structure after cement hydration. It has the application basis of being used as a cement hydration inducing crystal seed, accelerating cement hydration, and increasing cement strength. At the same time, the fly ash-based hydrated calcium silicate prepared by the present invention is rich in citric acid-soluble silica and has strong water retention capacity, and has the functions of adsorbing heavy metal ions, sound insulation, heat insulation, and air permeability. It can be widely used in the fields of adsorption materials, sound insulation and heat insulation materials, soil conditioners, etc., and is a calcium silicate hydrate product with great application prospects and strong practicality.

[0044] (3) The preparation method of fly ash-based calcium silicate hydrate provided by the present invention is simple and easy to carry out, has a short preparation time, low cost, and is easy to carry out large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention provides a process flow chart of a method for preparing fly ash-based calcium silicate hydrate.

[0046] Figure 2 This is the microscopic morphology of the fly ash-based hydrated calcium silicate prepared in Example 1. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0048] The present invention provides a method for preparing fly ash-based calcium silicate hydrate, the process flow chart of which is as follows: Figure 1 The preparation method comprises the following steps:

[0049] (1) mixing a calcium source, fly ash, and water to obtain a mixed slurry;

[0050] (2) thermally activating the mixed slurry in step (1) to obtain an activated slurry;

[0051] (3) The activated slurry in step (2) is subjected to hydrothermal reaction, liquid-solid separation and drying in sequence to obtain the fly ash-based hydrated calcium silicate.

[0052] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0053] Example 1

[0054] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0055] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:20 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 1.05:1;

[0056] (2) The mixed slurry in step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 5°C / min, the temperature is raised to 180°C, the constant temperature time is 0.5h, and after the constant temperature is completed, cooling water is passed to cool the slurry to 40°C, and the cooling time is 1h;

[0057] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 200° C. for 1 hour, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0058] The specific surface area of ​​the fly ash-based calcium silicate hydrate prepared in this example is 35.13 m 2 / g, the porosity is 92.51%, and its microstructure is as follows Figure 2 shown.

[0059] Example 2

[0060] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0061] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:20 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 1.05:1;

[0062] (2) The mixed slurry in step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 10°C / min, the temperature is raised to 200°C, the constant temperature time is 0h, and after the constant temperature is completed, cooling water is passed to cool the slurry to 25°C, and the cooling time is 3h;

[0063] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 200° C. for 1 hour, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0064] Example 3

[0065] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0066] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:20 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 1.05:1;

[0067] (2) The mixed slurry in step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 1°C / min, the temperature is raised to 180°C, the constant temperature time is 1 hour, and after the constant temperature is completed, cooling water is passed to cool the slurry to 80°C, and the cooling time is 3 hours;

[0068] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 200° C. for 0.1 h, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0069] Example 4

[0070] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0071] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:20 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 1.05:1;

[0072] (2) The mixed slurry in step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 7°C / min, the temperature is raised to 200°C, the constant temperature time is 1 hour, and after the constant temperature is completed, cooling water is passed to cool the slurry to 50°C, and the cooling time is 0.5 hour;

[0073] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 200° C. for 1 hour, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0074] Example 5

[0075] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0076] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:10 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 0.8:1;

[0077] (2) The mixed slurry of step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 10°C / min, the temperature is raised to 220°C, the constant temperature time is 1 hour, and after the constant temperature is completed, cooling water is passed to cool the slurry to 25°C, and the cooling time is 3 hours;

[0078] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 220° C. for 0.5 h, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0079] Example 6

[0080] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate, which comprises the following steps:

[0081] (1) mixing calcium hydroxide, fly ash from a power plant in Ximeng League, Inner Mongolia, and water, controlling the solid-liquid ratio to be 1:30 g / mL, to obtain a mixed slurry; the molar ratio of CaO in the calcium hydroxide to SiO2 in the fly ash is 1.2:1;

[0082] (2) The mixed slurry in step (1) is thermally activated to obtain an activated slurry; the thermal activation includes a heating section, a constant temperature section, and a cooling section; the heating rate of the heating section is 1°C / min, the temperature is raised to 160°C, the constant temperature time is 0h, and after the constant temperature is completed, cooling water is passed to cool the slurry to 80°C, and the cooling time is 0.5h;

[0083] (3) The activated slurry in step (2) is subjected to a hydrothermal reaction at a temperature of 160° C. for 6 hours, filtered and separated, and dried to obtain the fly ash-based hydrated calcium silicate.

[0084] Example 7

[0085] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate. The preparation method is the same as that of Example 1 except that the temperature of the constant temperature section in step (2) is 150°C.

[0086] Example 8

[0087] This embodiment provides a method for preparing fly ash-based calcium silicate hydrate. The preparation method is the same as that of Example 1, except that the terminal temperature of the cooling section in step (2) is 90° C. and the cooling time is 0.1 h.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing fly ash-based calcium silicate hydrate, which is the same as Example 2 except that the thermal activation in step (2) is not performed.

[0090] The fly ash-based calcium silicate hydrate prepared in this comparative example does not produce fibrous particles or particles with special morphology.

[0091] Comparative Example 2

[0092] This comparative example provides a method for preparing fly ash-based calcium silicate hydrate. The preparation method is the same as Example 2 except that the cooling stage in the thermal activation of step (2) is omitted and step (3) is directly performed.

[0093] The fly ash-based calcium silicate hydrate prepared in this comparative example does not produce fibrous particles or particles with special morphology.

[0094] The content of crystalline tobermorite in the fly ash-based calcium silicate hydrate prepared in the above examples and comparative examples was determined by adding an internal standard and using XRD Rietvel analysis.

[0095] The content of citric acid-soluble silicon dioxide in the fly ash-based calcium silicate hydrate prepared in the above examples and comparative examples was determined by dissolving the mixture in 1.5 mol / L hydrochloric acid using the ICP elemental quantitative method.

[0096] The particle morphology of the fly ash-based calcium silicate hydrate prepared in the above examples and comparative examples was observed and measured using a scanning electron microscope (SEM) test and analysis method. The results are shown in Table 1.

[0097] Table 1

[0098]

[0099] From Table 1 we can see that:

[0100] (1) Based on Examples 1 to 6, it can be seen that the method for preparing the fly ash-based calcium silicate hydrate provided by the present invention has a simple process. The prepared fly ash-based calcium silicate hydrate has a crystalline tobermorite content of up to 38%, a citric acid-soluble silica content of up to 25.32%, a porous structure in microstructure, a small particle size, and good adsorption effect.

[0101] (2) Combining Example 1 and Example 7, it can be seen that the temperature of the constant temperature section in Example 7 is 150°C, which is lower than the preferred temperature range of 180-200°C of the constant temperature section of the present invention. The content of crystalline tobermorite in the prepared fly ash-based hydrated calcium silicate is low, only 19%, and the content of citric acid-soluble silica is also reduced to 16.46%. In addition, the microscopic morphology is amorphous and the particle size is large. When it is subsequently used as a building material, the pore structure of the building material is large and the strength is low. When the temperature of the constant temperature section is high, it will result in high energy consumption and high preparation cost of the fly ash-based hydrated calcium silicate.

[0102] (3) Combining Example 1 and Example 8, it can be seen that the terminal temperature of the cooling section in Example 8 is 90°C, which is higher than the terminal temperature range of 25-80°C of the cooling section of the present invention. The content of crystalline tobermorite in the prepared fly ash-based hydrated calcium silicate is low, at 21%, and the content of citric acid-soluble silica is also reduced to 18.74%. In addition, the microscopic morphology is amorphous and the particle size is large. When used as a building material in the future, the pore structure of the building material is large and the strength is low. The terminal temperature of the constant temperature section in the present invention does not need to be lower.

[0103] (4) From Example 2 and Comparative Examples 1 and 2, it can be seen that the thermal activation in step (2) and the cooling stage in the thermal activation in step (2) of the present invention can greatly increase the content of crystalline tobermorite and the content of citric acid-soluble silica in the prepared fly ash-based hydrated calcium silicate, and the particle size is smaller.

[0104] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing fly ash-based calcium silicate hydrate, characterized in that: The preparation method comprises the following steps: (1) mixing a calcium source, fly ash, and water to obtain a mixed slurry; wherein the molar ratio of CaO in the calcium source to SiO2 in the fly ash is (0.4-1.4):1; (2) thermally activating the mixed slurry in step (1) to obtain an activated slurry; The thermal activation includes a temperature rising section, a constant temperature section and a temperature falling section; the temperature rising rate of the temperature rising section is 1-10°C / min; the temperature of the constant temperature section is 150-250°C; the time of the constant temperature section is 0-1h; the terminal temperature of the temperature falling section is 25-80°C; the time of the temperature falling section is 0.1-3h; (3) The activated slurry in step (2) is subjected to hydrothermal reaction, liquid-solid separation and drying in sequence to obtain the fly ash-based hydrated calcium silicate.

2. The preparation method according to claim 1, characterized in that The calcium source in step (1) is an industrial raw material with calcium oxide as the main component.

3. The preparation method according to claim 2, characterized in that The calcium source includes any one of calcium hydroxide, lime, calcium phosphate or calcium sulfate, or a combination of at least two thereof.

4. The preparation method according to claim 1, characterized in that The molar ratio of CaO in the calcium source and SiO2 in the fly ash in step (1) is (0.8-1.1):

1.

5. The preparation method according to claim 1, characterized in that The solid-to-liquid ratio of the mixed slurry in step (1) is 1:(10-40) g / mL.

6. The preparation method according to claim 5, characterized in that The solid-to-liquid ratio of the mixed slurry in step (1) is 1:(15-25) g / mL.

7. The preparation method according to claim 1, characterized in that The temperature of the constant temperature section in step (2) is 180-200°C.

8. The preparation method according to claim 1, characterized in that The temperature of the hydrothermal reaction in step (3) is 150-250°C.

9. The preparation method according to claim 8, characterized in that The temperature of the hydrothermal reaction in step (3) is 180-220°C.

10. The preparation method according to claim 1, characterized in that The hydrothermal reaction time in step (3) is 0.5-6h.

11. The preparation method according to claim 10, characterized in that: The hydrothermal reaction time in step (3) is 1-3 hours.

12. A fly ash-based calcium silicate hydrate, characterized in that: The fly ash-based calcium silicate hydrate is prepared by the preparation method of fly ash-based calcium silicate hydrate according to any one of claims 1 to 11.

13. The fly ash-based calcium silicate hydrate according to claim 12, characterized in that: The proportion of crystalline tobermorite in the fly ash-based hydrated calcium silicate is 10-40%.

14. Use of the fly ash-based calcium silicate hydrate according to claim 12 or 13 in building materials, adsorption materials, soil improvement materials, thermal insulation materials, and sound insulation materials.

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