阅读说明：本技术 一种以废液为原料制备水化硅酸钙的方法 (Method for preparing calcium silicate hydrate by using waste liquid as raw material ) 是由 潘钢华 周飞飞 于 2020-12-22 设计创作，主要内容包括：本发明公开了一种以废液为原料制备水化硅酸钙的方法,包括如下步骤：1)以废弃水泥基材料为原料,获取钙源；2)以非木材制浆黑液为原料,获取硅源；3)取步骤1)所得钙源与步骤2)所得硅源,通过化学共沉淀法制备水化硅酸钙。本发明以酸处理废弃水泥基材料废液为钙源、非木材制浆黑液为硅源,大大降低了水化硅酸钙的原料成本,同时解决了废液的处理问题,减少了废液对环境的不利影响,提升了黑液碱回收领域的清洁度；而且,非木材制浆黑液含有的木质素发挥了分散剂和改性剂的作用,改性水化硅酸钙、防止其团聚,从而在无需额外添加分散剂的情况下降低了水化硅酸钙的粒径,进一步降低了细化水化硅酸钙粒径的成本。(The invention discloses a method for preparing calcium silicate hydrate by taking waste liquid as a raw material, which comprises the following steps: 1) taking waste cement-based materials as raw materials to obtain a calcium source; 2) taking non-wood pulping black liquor as a raw material to obtain a silicon source; 3) preparing calcium hydrate calcium silicate by a chemical coprecipitation method from the calcium source obtained in the step 1) and the silicon source obtained in the step 2). According to the invention, the waste cement-based material liquid after acid treatment is taken as a calcium source, and the non-wood pulping black liquor is taken as a silicon source, so that the raw material cost of calcium silicate hydrate is greatly reduced, the problem of waste liquid treatment is solved, the adverse effect of the waste liquid on the environment is reduced, and the cleanliness of the black liquor in the alkali recovery field is improved; in addition, lignin contained in the non-wood pulping black liquor plays the roles of a dispersant and a modifier, and modifies the calcium silicate hydrate and prevents the calcium silicate hydrate from agglomerating, so that the particle size of the calcium silicate hydrate is reduced under the condition of not additionally adding the dispersant, and the cost for refining the particle size of the calcium silicate hydrate is further reduced.)

1. A method for preparing calcium silicate hydrate by taking waste liquid as a raw material is characterized by comprising the following steps:

1) taking waste cement-based materials as raw materials to obtain a calcium source;

2) taking non-wood pulping black liquor as a raw material to obtain a silicon source;

3) preparing calcium hydrate calcium silicate by a chemical coprecipitation method from the calcium source obtained in the step 1) and the silicon source obtained in the step 2).

2. The method for preparing calcium silicate hydrate by using waste liquid as a raw material according to claim 1, wherein in the step 1), the method for obtaining the calcium source comprises the following steps: soaking the waste cement-based material in an acid solution, and filtering out the waste cement-based material after soaking to obtain waste liquid of the acid-treated waste cement-based material; and then adjusting the pH value of the waste liquid of the acid-treated waste cement-based material to be not less than 12, and filtering impurities in the waste liquid to obtain the calcium source.

3. The method for preparing calcium silicate hydrate by using waste liquid as raw material according to claim 2, wherein the acid solution is one or more of acetic acid, hydrochloric acid, sulfuric acid or nitric acid.

4. The method for preparing calcium silicate hydrate by using waste liquid as a raw material according to claim 1 or 2, wherein in the step 1), the waste cement-based material is recycled aggregate or waste foamed cement.

5. The method for preparing calcium silicate hydrate from waste liquid as raw material according to claim 1, wherein in the step 2), the silicon source is obtained by: and filtering solid impurities in the non-wood pulping black liquor to obtain a silicon source.

6. The method for preparing calcium silicate hydrate by using waste liquor as raw material according to claim 1 or 5, wherein in the step 2), the non-wood pulping black liquor is one or more of straw, bamboo or bagasse pulping black liquor.

7. The method for preparing calcium silicate hydrate by using waste liquid as a raw material according to claim 1, wherein in the step 3), the calcium source and the silicon source are weighed according to the molar ratio of calcium ions in the calcium source to silicate ions in the silicon source of 0.7-2: 1, the calcium source is slowly added into the silicon source while stirring, after the calcium source is added, the stirring reaction is continued, and then the resultant is washed and dried to obtain the calcium silicate hydrate.

8. The method for preparing calcium silicate hydrate from waste liquid as raw material according to claim 7, wherein the stirring speed is 300-900 rpm, and the stirring reaction is continued for 6-24 hours after the calcium source is added.

9. The method for preparing calcium silicate hydrate from waste liquid as raw material according to claim 7, wherein the adding speed of the calcium source is 1-60 ml/min.

10. The method for preparing calcium silicate hydrate by using the waste liquid as the raw material according to claim 7, wherein the product is washed by deionized water and absolute ethyl alcohol until the pH value of the washing liquid is less than 8, and then the product is freeze-dried to obtain calcium silicate hydrate powder.

Technical Field

The invention relates to a method for preparing calcium silicate hydrate by using waste liquid as a raw material, belonging to the technical field of nano-particle preparation.

Background

The hydrated calcium silicate as the main product of cement hydration can be used as a crystal embryo early strength agent to provide nucleation sites for cement hydration, thereby accelerating the cement hydration and promoting the development of the strength of cement-based materials. At present, the methods commonly used for preparing calcium silicate hydrate mainly comprise a chemical coprecipitation method, a hydrothermal method and a mechanochemical method. Among them, the chemical coprecipitation method is fast, efficient, low in energy consumption and more in application. However, calcium sources used for preparing calcium silicate hydrate by a chemical coprecipitation method are calcium nitrate, calcium chloride and calcium acetate, silicon sources are sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, and the raw materials have higher cost, so that the production cost of the calcium silicate hydrate is increased. Furthermore, the particle size of the hydrated calcium silicate particles significantly affects their early strength effect. Therefore, a dispersing agent is often added in the preparation process of the calcium silicate hydrate, so that the particles of the calcium silicate hydrate are refined, and the nano-scale calcium silicate hydrate is obtained. However, the use of dispersants further increases the cost of the calcium silicate hydrate. In order to reduce the production cost of calcium silicate hydrate and to refine calcium silicate hydrate particles, it is necessary to search for a more inexpensive calcium source, a silicon source, and a dispersant.

The Chinese patent application with the application number of 201710931406.5 discloses a preparation method of an early strength agent of calcium silicate hydrate, which takes acid treatment recycled aggregate waste liquid as a calcium source and sodium silicate and sodium metasilicate as silicon sources to prepare the calcium silicate hydrate by a chemical coprecipitation method. Although the method uses acid-treated recycled aggregate waste liquid as a calcium source, the silicon source is still sodium silicate or sodium metasilicate, the price is still higher, and the particle size of the prepared calcium silicate hydrate particles is larger, so that the early strength performance is not fully exerted. In order to further reduce the production cost of calcium silicate hydrate and refine calcium silicate hydrate particles, patent ZL 201711331837.4 discloses a preparation method of an early strength agent for calcium silicate hydrate, which takes rice hull ash as a silicon source, takes waste liquid for producing calcium lignosulfonate as a calcium source, and takes a gel dispersing agent and polyacrylamide as dispersing agents to prepare calcium silicate hydrate. The calcium silicate hydrate has the advantages of low cost, uniform dispersion and good application effect. However, the gel dispersing agent and polyacrylamide still increase the production cost of the hydrated calcium silicate to a certain extent, and may have negative effects on other properties of the cement-based material. In addition, the pretreatment of the rice hull ash consumes more alkali and requires more energy consumption.

On the other hand, in the field of paper making and pulping, pulping black liquor containing a large amount of organic matter and a small amount of inorganic matter is produced. Wherein the organic matter is mainly lignin, and also low molar mass polysaccharides and resinous compounds. The inorganic substances are mainly sodium hydroxide and sodium silicate. When non-wood materials such as straw, rice straw, bamboo, and bagasse are used for pulping, the silicon content in the black liquor is higher. However, the existence of silicon element can increase the viscosity of the black liquor, influence the incineration performance of the black liquor and be not beneficial to the alkali recovery of the black liquor.

Based on this, the applicant considers that silicon element in the black liquor is used as a silicon source to prepare hydrated calcium silicate, thereby forming the technology of the invention.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the problems of high cost of raw materials for preparing hydrated calcium silicate, larger particle size and poor early strength effect of the prepared hydrated calcium silicate by the existing chemical coprecipitation method, the invention provides a method for preparing hydrated calcium silicate by taking waste liquid as a raw material, silicate ions in black liquid are taken as a silicon source, the cost of the raw materials for hydrated calcium silicate is effectively reduced, the problem of alkali recovery of the black liquid is solved, and meanwhile, the particle size of the hydrated calcium silicate is reduced under the condition of not adding a dispersing agent.

The technical scheme is as follows: the method for preparing calcium silicate hydrate by using waste liquid as a raw material comprises the following steps:

1) taking waste cement-based materials as raw materials to obtain a calcium source;

2) taking non-wood pulping black liquor as a raw material to obtain a silicon source;

3) preparing calcium hydrate calcium silicate by a chemical coprecipitation method from the calcium source obtained in the step 1) and the silicon source obtained in the step 2).

In the step 1), the waste cement-based material can be recycled aggregate or waste foamed cement. Preferably, the method for obtaining the calcium source comprises the following steps: soaking the waste cement-based material in an acid solution, and filtering out the waste cement-based material after soaking to obtain waste liquid of the acid-treated waste cement-based material; and then adjusting the pH value of the waste liquid of the acid-treated waste cement-based material to be not less than 12, and filtering impurities in the waste liquid to obtain the calcium source. Wherein, the acid solution can be one or more of acetic acid, hydrochloric acid, sulfuric acid or nitric acid.

In step 2), the non-wood pulping black liquor can be one or a combination of straw, rice straw, bamboo or bagasse pulping black liquor. Preferably, the method for obtaining the silicon source comprises the following steps: and filtering solid impurities in the non-wood pulping black liquor to obtain a silicon source.

Specifically, in the step 3), the calcium source and the silicon source are weighed according to the designed stoichiometric ratio, the calcium source is slowly added into the silicon source while stirring, the stirring reaction is continued after the calcium source is added, and then the product is washed and dried to obtain the hydrated calcium silicate.

Wherein, the stoichiometric ratio of the calcium source to the silicon source is as follows: the molar ratio of calcium ions in the calcium source to silicate ions in the silicon source is 0.7-2: 1. Optionally, the molar concentration of calcium ions in the calcium source obtained in the step 1) is tested, and then the molar concentration of the calcium ions is adjusted to 0.01-0.2 mol/L; testing the concentration of silicate ions in the silicon source obtained in the step 2), and adjusting the molar concentration of the silicate ions to 0.01-0.2 mol/L; then weighing the silicon source and the calcium source according to the stoichiometric ratio.

Preferably, in the step 3), the adding speed of the calcium source is 1-60 ml/min. Further, the stirring speed of the mixing and reaction of the silicon source and the calcium source is controlled to be 300-900 rpm, and the stirring reaction is continued for 6-24 hours after the calcium source is added; during the process of forming calcium silicate hydrate particles through chemical coprecipitation reaction, lignin in the black liquor can be inserted into the layers of the calcium silicate hydrate, the reaction time is proper, the stability of the calcium silicate hydrate is improved, the reaction time is too short, the calcium silicate hydrate is difficult to form a stable interlayer structure, the lignin cannot be inserted into the layers of the calcium silicate hydrate, and the modification effect of the lignin can be greatly reduced. After stirring, standing for 24-48 h, and then washing and drying; preferably, the product is washed by deionized water and absolute ethyl alcohol until the pH value of the washing liquid is less than 8, and then the product is frozen and dried to obtain the calcium silicate hydrate powder.

The invention principle is as follows: the method takes acid-treated waste cement-based material liquid as a calcium source and non-wood pulping black liquor as a silicon source, and prepares calcium silicate hydrate through chemical coprecipitation reaction. The acid treatment of the waste cement-based material can dissolve out calcium ions in the waste cement-based material; by further adjusting the pH value of the acid-treated recycled aggregate waste liquid to be not less than 12, impurity ions such as magnesium ions, iron ions and the like in the recycled aggregate waste liquid can be removed, so that the recycled aggregate waste liquid can be used as a calcium source for preparing calcium silicate hydrate. The main organic matter in the non-wood pulping black liquor is lignin, the main inorganic matter is sodium hydroxide and sodium silicate, the strong alkaline black liquor is favorable for the growth of hydrated calcium silicate, and the sodium silicate can provide silicate ions and is used as a silicon source for preparing the hydrated calcium silicate.

The waste liquid of the acid-treated waste cement-based material is slowly added into the non-wood pulping black liquor, and calcium ions and silicate ions are subjected to chemical coprecipitation reaction to form calcium silicate hydrate particles. Meanwhile, lignin in the black liquor is inserted between the layers of the calcium silicate hydrate or adsorbed on the surface of the calcium silicate hydrate to modify and modify the calcium silicate hydrate and refine calcium silicate hydrate particles. Finally, the generated hydrated calcium silicate particles can be deposited, and further, nano-scale hydrated calcium silicate with fine particles can be obtained through solid-liquid separation, and the silicon content in the black liquor is greatly reduced.

Has the advantages that: compared with the prior art, the invention has the advantages that: (1) according to the invention, the waste liquid of the acid-treated waste cement-based material is used as a calcium source, and the non-wood pulping black liquid is used as a silicon source, so that the cost of the raw material of hydrated calcium silicate is greatly reduced, and the problem of waste liquid treatment is solved; (2) while providing a silicon source, the non-wood pulping black liquor contains lignin which plays the role of a dispersant and a modifier to modify calcium silicate hydrate and prevent the calcium silicate hydrate from agglomerating, so that the particle size of the calcium silicate hydrate is reduced under the condition of not additionally adding a dispersant, and the cost for refining the particle size of the calcium silicate hydrate is further reduced; (3) according to the invention, the waste liquid of the acid-treated waste cement-based material is used as a calcium source, so that the performance of the waste cement-based material is improved, and the adverse effect of the waste liquid on the environment is reduced; the non-wood pulping black liquor is used as a silicon source, so that the silicon content in the black liquor is greatly reduced, the cleanliness of the black liquor in the alkali recovery field is improved, and the clean production of the papermaking industry is facilitated.

Drawings

FIG. 1 is an X-ray diffraction pattern of calcium silicate hydrate obtained in example 1 and comparative example 1;

FIG. 2 is an SEM topography magnified 100000 times of calcium silicate hydrate obtained in example 1;

FIG. 3 is an SEM topography magnified 100000 times of calcium silicate hydrate obtained in comparative example 1;

FIG. 4 is a heat of hydration plot of the calcium silicate hydrate obtained in example 1 and comparative example 1 mixed with a cement slurry.

Detailed Description

The technical solution of the present invention is further explained with reference to the drawings and the embodiments.

Example 1

A method for preparing calcium silicate hydrate by using waste liquid as a main raw material comprises the following steps:

1) calcium source acquisition

(1.1) acid-treating the waste cement-based material: soaking the recycled aggregate in an acetic acid solution with the mass concentration of 1%, wherein the mass part of the recycled aggregate is 100, the mass part of the acetic acid solution is 300, and filtering out the recycled aggregate after 24h to obtain waste cement-based material liquid after acid treatment;

(1.2) pretreating waste cement-based material waste liquid by acid treatment: and (3) regulating the pH value of the waste liquid of the acid-treated waste cement-based material obtained in the step (1.1) to 12 by using a sodium hydroxide solution with the mass concentration of 10%, and then filtering impurities in the solution to obtain the calcium source.

2) Silicon source acquisition

And selecting straw pulping black liquor, and filtering impurities in the straw pulping black liquor to obtain a silicon source.

3) Synthesis of hydrated calcium silicate

(3.1) measuring and adjusting the concentration of calcium element in the calcium source: testing the molar concentration of calcium ions in the calcium source obtained in the step (1.2), and adjusting the molar concentration of the calcium ions to 0.05 mol/L;

(3.2) measuring and adjusting the concentration of silicon element in the silicon source: testing the molar concentration of silicate ions in the silicon source obtained in the step (2.2), and adjusting the molar concentration of the silicate ions to 0.05 mol/L;

(3.3) chemical coprecipitation reaction: respectively measuring the required calcium source and the silicon source according to the molar ratio of the calcium ions in the calcium source to the silicon ions in the silicon source of 1, wherein the volume part of the calcium source is 100, and the volume part of the silicon source is 100, and then slowly adding the calcium source into the calcium source while stirring the silicon source. The addition speed of the calcium source is 10ml/min, and the stirring speed of the silicon source is 300 rpm. And after the calcium source is completely added, continuously stirring for 24 hours. And then standing the reaction solution for 24 hours, filtering out precipitates in the reaction solution, washing and repeatedly washing by using deionized water and absolute ethyl alcohol until the pH value of the washing solution is less than 8, and then freeze-drying to obtain the calcium silicate hydrate powder.

Example 2

A method for preparing calcium silicate hydrate by using waste liquid as a main raw material comprises the following steps:

1) calcium source acquisition

(1.1) acid-treating the waste cement-based material: soaking the recycled aggregate in an acetic acid solution with the mass concentration of 1%, wherein the mass part of the recycled aggregate is 100, the mass part of the acetic acid solution is 300, and filtering out the recycled aggregate after 24h to obtain waste cement-based material liquid after acid treatment;

(1.2) pretreating waste cement-based material waste liquid by acid treatment: and (3) regulating the pH value of the waste liquid of the acid-treated waste cement-based material obtained in the step (1.1) to 12 by using a sodium hydroxide solution with the mass concentration of 10%, and then filtering impurities in the solution to obtain the calcium source.

2) Silicon source acquisition

And selecting straw pulping black liquor, and filtering impurities in the straw pulping black liquor to obtain a silicon source.

3) Synthesis of hydrated calcium silicate

(3.1) measuring and adjusting the concentration of calcium element in the calcium source: testing the molar concentration of calcium ions in the calcium source obtained in the step (1.2), and adjusting the molar concentration of the calcium ions to 0.05 mol/L;

(3.2) measuring and adjusting the concentration of silicon element in the silicon source: testing the molar concentration of silicate ions in the silicon source obtained in the step (2.2), and adjusting the molar concentration of the silicate ions to 0.05 mol/L;

(3.3) chemical coprecipitation reaction: respectively measuring the required calcium source and the silicon source according to the molar ratio of the calcium ions in the calcium source to the silicon ions in the silicon source of 1, wherein the volume part of the calcium source is 100, and the volume part of the silicon source is 100, and then slowly adding the calcium source into the calcium source while stirring the silicon source. The addition speed of the calcium source is 1ml/min, and the stirring speed of the silicon source is 600 rpm. And after the calcium source is completely added, continuously stirring for 6 hours. And then standing the reaction solution for 24 hours, filtering out precipitates in the reaction solution, washing the reaction solution by using deionized water and absolute ethyl alcohol repeatedly until the pH value of the washing solution is less than 8, and then freeze-drying the washing solution to obtain the calcium silicate hydrate powder.

Example 3

A method for preparing calcium silicate hydrate by using waste liquid as a main raw material comprises the following steps:

1) calcium source acquisition

(1.1) acid-treating the waste cement-based material: soaking the recycled aggregate in an acetic acid solution with the mass concentration of 1%, wherein the mass part of the recycled aggregate is 100, the mass part of the acetic acid solution is 300, and filtering out the recycled aggregate after 24h to obtain waste cement-based material liquid after acid treatment;

(1.2) pretreating waste cement-based material waste liquid by acid treatment: and (3) regulating the pH value of the waste liquid of the acid-treated waste cement-based material obtained in the step (1.1) to 12 by using a sodium hydroxide solution with the mass concentration of 10%, and then filtering impurities in the solution to obtain the calcium source.

2) Silicon source acquisition

And selecting straw pulping black liquor, and filtering impurities in the straw pulping black liquor to obtain a silicon source.

3) Synthesis of hydrated calcium silicate

(3.1) measuring and adjusting the concentration of calcium element in the calcium source: testing the molar concentration of calcium ions in the calcium source obtained in the step (1.2), and adjusting the molar concentration of the calcium ions to 0.05 mol/L;

(3.2) measuring and adjusting the concentration of silicon element in the silicon source: testing the molar concentration of silicate ions in the silicon source obtained in the step (2.2), and adjusting the molar concentration of the silicate ions to 0.05 mol/L;

(3.3) chemical coprecipitation reaction: respectively measuring the required calcium source and the silicon source according to the molar ratio of the calcium ions in the calcium source to the silicon ions in the silicon source of 1, wherein the volume part of the calcium source is 100, and the volume part of the silicon source is 100, and then slowly adding the calcium source into the calcium source while stirring the silicon source. The addition speed of the calcium source is 60ml/min, and the stirring speed of the silicon source is 900 rpm. After the calcium source is completely added, stirring is continued for 18 h. And then standing the reaction solution for 24 hours, filtering out precipitates in the reaction solution, washing and repeatedly washing by using deionized water and absolute ethyl alcohol until the pH value of the washing solution is less than 8, and then freeze-drying to obtain the calcium silicate hydrate powder.

Comparative example 1

A method for preparing calcium silicate hydrate by utilizing calcium acetate and sodium metasilicate pentahydrate comprises the following steps:

(1) calcium source acquisition

And (3) taking a calcium acetate water solution as a calcium source, wherein the calcium acetate is analytically pure, and the concentration of calcium element in the calcium source is 0.05 mol/L.

(2) Silicon source acquisition

Sodium metasilicate pentahydrate is used as a silicon source, wherein the sodium metasilicate pentahydrate is used as analytical pure, and the concentration of a silicon element in the silicon source is 0.05 mol/L.

(3) Synthesis of hydrated calcium silicate

Respectively measuring the required calcium source and silicon source according to the molar ratio of the calcium element in the calcium source to the silicon element in the silicon source of 1, wherein the volume part of the calcium source is 100, the volume part of the silicon source is 100, adding 200 parts of water into a reaction container, stirring the water in the reaction container at the stirring speed of 400rmp, slowly adding the calcium source and the silicon source into the reaction container at the adding speed of 10ml/min, continuing stirring for 3 hours after the calcium source and the silicon source are added, washing a product in the reaction container by using deionized water and absolute ethyl alcohol until a washing liquid is colorless and the pH value is less than 8, and then, carrying out cold freeze-drying to obtain the hydrated calcium silicate powder.

The calcium silicate hydrate obtained in example 1 and comparative example 1 was subjected to characterization analysis, as follows:

(1) the calcium silicate hydrate obtained in example 1 and comparative example 1 was subjected to X-ray diffraction analysis

FIG. 1 is an X-ray diffraction pattern of calcium silicate hydrate obtained in example 1 and comparative example 1, as can be seen from the figure: the X-ray diffraction pattern of the calcium silicate hydrate obtained in the example 1 is consistent with that of the calcium silicate hydrate obtained in the comparative example 1, the crystal diffraction peaks of the two are in one-to-one correspondence, and the intensity is substantially equivalent, which shows that: the method for preparing calcium silicate hydrate by using waste liquid provided by the invention can be used for preparing calcium silicate hydrate.

(2) The morphology of the calcium silicate hydrates obtained in example 1 and comparative example 1 was analyzed by SEM

Fig. 2 is an SEM image of the calcium silicate hydrate obtained in example 1 magnified 100000 times, and it can be seen from the figure that the calcium silicate hydrate particles obtained in example 1 are fine and have a particle size of nanometer order.

Fig. 3 is an SEM image of the calcium silicate hydrate obtained in comparative example 1 magnified 100000 times, and it can be seen from the figure that the calcium silicate hydrate obtained in comparative example 1 has serious agglomeration and large particle size.

By comparing and analyzing the SEM appearances of the calcium silicate hydrate obtained in the example 1 and the calcium silicate hydrate obtained in the comparative example 1, the method for preparing the calcium silicate hydrate by using the waste liquid can obviously refine calcium silicate hydrate particles. The calcium silicate hydrate particles prepared in the embodiments 2 to 3 are analyzed by X-ray diffraction analysis and SEM, the morphological characteristics of the calcium silicate hydrate particles are similar to those of the calcium silicate hydrate particles prepared in the embodiment 1, the particles are dispersed, and the particle size reaches the nanometer level.

The effect of the calcium silicate hydrate obtained in example 1 and comparative example 1 on the properties of cement-based materials was analyzed as follows:

(1) effect of calcium silicate hydrate obtained in example 1 and comparative example 1 on Cement hydration exotherm

The calcium silicate hydrate obtained in example 1 and comparative example 1 is added into cement slurry, wherein the adding amount of the calcium silicate hydrate is 0.5 percent of the mass of the cement. Thereafter, the cement paste was mixed in a water cement ratio of 0.5, and the hydration exotherm of the paste was tested. In addition, in order to further compare and analyze the early strength effect of the obtained calcium silicate hydrate, the invention also provides a blank group for comparison and analysis. The blank group is a pure cement system, no hydrated calcium silicate is doped, and cement slurry is mixed according to the water cement ratio of 0.5.

FIG. 4 is a graph showing the exothermic heat of hydration of the calcium silicate hydrate obtained in example 1 of the present invention and comparative example 1 when mixed with a cement paste, as can be seen from the graphs: compared with the blank group and the calcium silicate hydrate obtained in the comparative example 1, the calcium silicate hydrate obtained in the example 1 has a larger hydration heat release rate and a advanced hydration heat release peak, and can further shorten the induction period of cement hydration, accelerate cement hydration and promote setting and hardening of cement.

(2) Effect of calcium silicate hydrate obtained in example 1 and comparative example 1 on the development of Cement-based Material Strength

The calcium silicate hydrate obtained in example 1 and comparative example 1 were used to prepare mortar test pieces, and blank groups were set for comparative analysis. The formulation of the mortar is shown in table 1 below, wherein the cement used is P.O 42.5.5 cement, the sand is standard sand, the water is tap water, the molding of the mortar test piece is carried out according to the specification of JGJ/T70-2009 Standard test method for basic Performance of building mortar, and the molded mortar is subjected to standard curing (temperature: 20 + -2 ℃, relative humidity: 95%).

TABLE 1 mortar mixing ratio

The following table 2 is a result of the compressive strength test of the mortar test piece, and the result shows that: the calcium silicate hydrate prepared by the method for preparing the calcium silicate hydrate by using the waste liquid has a good early strength effect, and can remarkably promote the strength development of mortar.

TABLE 2 mortar test piece compression strength test results