Preparation method of modified machine-made sand

Abstract

The invention relates to the technical field of machine-made sand, in particular to a preparation method of modified machine-made sand, surface activation and graft polymerization are synchronously completed in a single reaction system through the synergistic effect of a coupling agent and a hydrophilic monomer, and the effect of integrating an existing three-step method of hydroxylation, coupling agent modification and graft polymerization into a one-step method is achieved. Therefore, the technological process is simplified. Meanwhile, water is used as a solvent in the whole preparation process, organic reagents such as methylbenzene are avoided, and post-treatment steps and environmental protection pressure are reduced. In addition, the whole preparation process is carried out at room temperature, and a 80-110 DEG C high-temperature or ice-bath low-temperature environment does not need to be provided, so that the industrial application difficulty is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of machine-made sand, and more specifically, to a method for preparing modified machine-made sand. Background Art

[0002] Artificial sand is sand and gravel particles made from rocks, ores or tailings through mechanical crushing, screening and shaping. Particles with a diameter greater than 4.75mm are machine-made gravel, and those with a diameter less than 4.75mm are machine-made sand. It has a wide range of sources and can alleviate the shortage of natural sand resources. It is widely used in the construction field and is a key raw material for concrete and cement products. In recent years, the market scale of artificial sand has continued to expand, but there are problems such as high environmental pressure and uneven product quality in production. With the development of the industry, it is moving towards green and large-scale directions, and will continue to improve quality and expand the scope of application in the future.

[0003] The patent document with the prior art publication number CN114292042A discloses a method for preparing highly hydrophilic comb-shaped polymer grafted artificial sand, which improves the hydrophilicity and compatibility of artificial sand with cement-based materials through chemical modification, but still has some shortcomings: ① The process involves multiple steps such as hydroxylation, coupling agent modification and grafting polymerization, and the process is relatively complicated; ② Organic solvents such as toluene are used in the process, which may cause pollution to the environment; ③ Some reactions need to be carried out at high or low temperatures, which increases the difficulty of industrialization.

[0004] In summary, although the above preparation method improves the hydrophilicity of machine-made sand and its compatibility with cement-based materials, there are still problems such as complex process, poor environmental protection, and high difficulty in industrialization. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing modified machine-made sand, which is used to solve the technical problems of complex process, poor environmental protection and high difficulty in industrialization of the current highly hydrophilic machine-made sand.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions: A method for preparing modified machine-made sand comprises the following steps: (1) Mix machine-made sand, coupling agent and hydrophilic monomer; add water as solvent with a solid-liquid mass ratio of 1:(3-4) and stir to form a uniform slurry; (2) adding hydrogen peroxide-ascorbic acid initiation system to the slurry, stirring and reacting at 25-35°C for 2-3 hours, and adding pH adjuster during the reaction to maintain the pH of the system at 5-6; (3) After the reaction is completed, the reactants are filtered continuously through a continuous vacuum filter, washed in a multi-stage countercurrent washing tank, and dried in a fluidized bed dryer to finally obtain modified machine-made sand.

[0007] This preparation method uses the synergistic effect of the coupling agent and the hydrophilic monomer to simultaneously complete surface activation and graft polymerization in a single reaction system, which has the effect of integrating the existing three-step method of hydroxylation, coupling agent modification, and graft polymerization into a one-step method, thereby simplifying the process flow. At the same time, water is used as the solvent throughout the preparation process, avoiding organic reagents such as toluene, reducing post-processing steps and environmental pressure. In addition, the entire preparation process is carried out at room temperature, without the need to provide a high temperature of 80-110°C or a low temperature environment of an ice bath, thereby reducing the difficulty of industrial application.

[0008] The present invention uses mechanical stirring to evenly disperse the coupling agent and the hydrophilic monomer on the surface of the machine-made sand, thereby avoiding local uneven concentration in the subsequent reaction; the coupling agent directly reacts with the silanol group on the surface of the machine-made sand to form an active site, thereby eliminating the hydroxylation pretreatment step. The hydrogen peroxide-ascorbic acid initiation system generates free radicals under mild conditions, directly initiating the polymerization of the monomer on the surface of the machine-made sand without the need for high temperature or organic solvents, thereby reducing side reactions and increasing the conversion rate of the hydrophilic monomer. The pH adjustment optimizes the ionization state of the hydrophilic monomer, enhances the binding ability with the surface of the machine-made sand, and improves the grafting efficiency.

[0009] Preferably, in step (1), machine-made sand, coupling agent and hydrophilic monomer are mixed in a mass ratio of 1:(0.4-0.6):(1.5-2.5).

[0010] Preferably, in step (1), the particle size of the machine-made sand is 150-200 mesh; and the hydrophilic monomer is one or two of acrylic acid and hydroxyethyl methacrylate phosphate.

[0011] Preferably, in step (2), the hydrogen peroxide-ascorbic acid initiation system is composed of hydrogen peroxide and ascorbic acid mixed in a mass ratio of 1:(0.1-0.2).

[0012] Preferably, in step (2), the pH adjuster is a sodium hydroxide solution.

[0013] Preferably, in step (3), after the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid, and after the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration.

[0014] The present invention first uses gravity to settle solid particles in the reaction product, preliminarily reducing the amount of liquid and alleviating the burden on subsequent filtering equipment. By adopting a continuous vacuum filter and a multi-stage countercurrent washing process, it can effectively solve the challenges of centrifugal separation and multiple washing in the patent document of CN114292042A in industrial applications, realize efficient, energy-saving, environmentally friendly continuous production, and reduce equipment costs and operating difficulties.

[0015] Preferably, the machine-made sand in step (1) is made from any one of granite, basalt and limestone.

[0016] The present invention has the following beneficial effects: This preparation method simultaneously completes surface activation and graft polymerization in a single reaction system through the synergistic effect of the coupling agent and the hydrophilic monomer, which has the effect of integrating the existing three-step method of hydroxylation, coupling agent modification, and graft polymerization into a one-step method, thereby simplifying the process flow. At the same time, water is used as a solvent throughout the preparation process, avoiding organic reagents such as toluene, reducing post-processing steps and environmental pressure. In addition, the entire preparation process is carried out at room temperature, without the need to provide a high temperature of 80-110°C or a low temperature environment of an ice bath, thereby reducing the difficulty of industrial application. DETAILED DESCRIPTION

[0017] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation of the present invention is described in detail below in conjunction with the embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0018] The present invention is described in detail below in conjunction with embodiments. Example 1

[0019] A method for preparing modified machine-made sand comprises the following steps: (1) Mix machine-made sand (particle size 150-200 mesh), coupling agent (KH-570) and hydrophilic monomer (acrylic acid) in a mass ratio of 1:0.4:1.5; add water as a solvent with a solid-liquid mass ratio of 1:3, and stir to form a uniform slurry; (2) Add 1.5 g of hydrogen peroxide-ascorbic acid initiator system (mass ratio 30% H2O2:10% Vc =1:0.1) to 100 g of the slurry, and continue stirring at 25 °C for 3 hours. During the reaction, a pH adjuster (sodium hydroxide solution) was added dropwise to maintain the pH of the system at 5-6; (3) After the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid. After the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration. The filtered product is then transported to a multi-stage countercurrent washing tank for washing (for removing unreacted monomers and initiators). The washed product is then transported to a fluidized bed dryer for drying at 50-60°C to obtain modified machine-made sand. Example 2

[0020] A method for preparing modified machine-made sand comprises the following steps: (1) Mix machine-made sand (particle size 150-200 mesh), coupling agent (KH-570) and hydrophilic monomer (acrylic acid) in a mass ratio of 1:0.5:2; add water as a solvent with a solid-liquid mass ratio of 1:3, and stir to form a uniform slurry; (2) Add 1.5 g of hydrogen peroxide-ascorbic acid initiator system (mass ratio 30% H2O2:10% Vc =1:0.1) to 100 g of the slurry, and continue stirring at 35 °C for 3 hours. During the reaction, a pH adjuster (sodium hydroxide solution) was added dropwise to maintain the system pH at 5-6; (3) After the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid. After the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration. The filtered product is then transported to a multi-stage countercurrent washing tank for washing (for removing unreacted monomers and initiators). The washed product is then transported to a fluidized bed dryer for drying at 50-60°C to obtain modified machine-made sand. Example 3

[0021] A method for preparing modified machine-made sand comprises the following steps: (1) Mix machine-made sand (particle size 150-200 mesh), coupling agent (KH-570) and hydrophilic monomer (acrylic acid) in a mass ratio of 1:0.6:2.5; add water as a solvent with a solid-liquid mass ratio of 1:4, and stir to form a uniform slurry; (2) Add 2 g of hydrogen peroxide-ascorbic acid initiator system (mass ratio 30% H2O2:10% Vc = 1:0.1) to 100 g of the slurry, and continue stirring at 30 °C for 2.5 hours. During the reaction, a pH adjuster (sodium hydroxide solution) was added dropwise to maintain the pH of the system at 5-6; (3) After the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid. After the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration. The filtered product is then transported to a multi-stage countercurrent washing tank for washing (for removing unreacted monomers and initiators). The washed product is then transported to a fluidized bed dryer for drying at 50-60°C to obtain modified machine-made sand. Example 4

[0022] A method for preparing modified machine-made sand comprises the following steps: (1) Mix machine-made sand (particle size 150-200 mesh), coupling agent (KH-570) and hydrophilic monomer (acrylic acid and hydroxyethyl methacrylate phosphate in a mass ratio of 2:1) in a mass ratio of 1:0.5:2; add water as a solvent with a solid-liquid mass ratio of 1:3, and stir to form a uniform slurry; (2) Add 1.5 g of hydrogen peroxide-ascorbic acid initiator system (mass ratio 30% H2O2:10%Vc =1:0.2) to 100 g of the slurry, and continue stirring at 35 °C for 3 hours. During the reaction, a pH adjuster (sodium hydroxide solution) was added dropwise to maintain the system pH at 5-6; (3) After the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid. After the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration. The filtered product is then transported to a multi-stage countercurrent washing tank for washing (for removing unreacted monomers and initiators). The washed product is then transported to a fluidized bed dryer for drying at 50-60°C to obtain modified machine-made sand.

[0023] Comparative Example 1 A method for preparing modified machine-made sand, which differs from Example 2 in that the mass ratio of hydrogen peroxide to ascorbic acid in the hydrogen peroxide-ascorbic acid initiation system is 1:0.05.

[0024] Comparative Example 2 A method for preparing modified machine-made sand, which differs from Example 2 in that the mass ratio of hydrogen peroxide to ascorbic acid in the hydrogen peroxide-ascorbic acid initiation system is 1:0.3.

[0025] Comparative Example 3 A method for preparing modified machine-made sand, which differs from Example 2 in that a pH regulator is added dropwise to maintain the pH of the system at 3-4.

[0026] Comparative Example 4 A method for preparing modified machine-made sand, which differs from Example 2 in that a pH regulator is added dropwise to maintain the pH of the system at 7-8.

[0027] The organic matter content and grafting rate of the modified machine-made sand prepared in Examples 1-4 and Comparative Examples 1-4 were measured. The organic matter content refers to the ratio of the mass of the polymer grafted to the surface of the machine-made sand to the total mass of the modified machine-made sand. The weight of the machine-made sand after modification is recorded as m 改性砂 The weight of inorganic matter (SiO2) in the modified machine-made sand was determined by thermogravimetric analysis (TGA), recorded as m 无机物 , then the organic matter content = (m 改性砂 -m 无机物 ) / m 改性砂 *100%. The grafting rate refers to the proportion of the monomers (such as acrylic acid) involved in the grafting polymerization to the total monomers. Record the weight of the monomers added before the reaction, recorded as m 初始 After the reaction is completed, the weight of the unreacted monomer separated by filtration is measured by titration and recorded as m 未反应 , then the grafting rate = (m 初始 -m未反应 ) / m 初始 *100%. The results are shown in Table 1.

[0028] Table 1 Comparison of organic matter content and grafting rate in modified machine-made sand

[0029] As can be seen from Table 1, the organic matter content in the modified machine-made sand prepared in Examples 1-4 of the present invention is between 16.8% and 18.6%, and the grafting rate is between 85.1% and 86.3%. The grafting rate of Comparative Example 1 is reduced from 87.4% in Example 2 to 75.2%, and the reason may be that the proportion of hydrogen peroxide in the initiation system is increased, so that the free radicals are generated too quickly, resulting in self-polymerization of the monomers instead of grafting. The grafting rate of Comparative Example 2 is reduced from 87.4% in Example 2 to 64.7%, and the reason is that the ascorbic acid content in the initiation system is too large, so that the free radicals are insufficiently generated, and the grafting rate is significantly reduced. The grafting rate of Comparative Example 3 is reduced from 87.4% in Example 2 to 80.5%, and the reason is that too low pH will inhibit the reducing ability of ascorbic acid, thereby affecting the grafting rate of the monomer. The grafting rate of Comparative Example 4 is reduced from 87.4% in Example 2 to 76.8%, and the reason is that too high pH may cause hydrogen peroxide to decompose, thereby affecting the grafting rate of the monomer.

[0030] In order to detect the adaptability of modified machine-made sand and cement mortar, the experiment was carried out with reference to the mortar fluidity test method in "GB 8077-2000 Test method for homogeneity of concrete admixtures". The adaptability of modified machine-made sand and cement mortar was studied by adjusting the modified machine-made sand (the percentage of machine-made sand in the experimental sand). The cement used the reference cement specified in the standard "GB8076-2008 Concrete Admixtures", the machine-made sand was the machine-made sand used to prepare the modified machine-made sand of the present invention, the modified machine-made sand was the modified machine-made sand prepared in Example 2, and the mixing water was tap water. The results are shown in Table 2.

[0031] Table 2 Compatibility data of modified machine-made sand and cement mortar

[0032] It can be seen from Table 2 that when the modified machine-made sand prepared in the present invention is added to the mortar fluid, the fluidity of the mortar gradually increases with the addition of the modified machine-made sand, and the fluidity retention ability of the mortar also gradually increases. At the same time, it has good fluidity retention ability, which shows that the modified machine-made sand of the present invention has good compatibility with cement-based materials.

[0033] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing modified machine-made sand, characterized in that: The following steps are involved: (1) Mix machine-made sand, coupling agent and hydrophilic monomer; add water as solvent with a solid-liquid mass ratio of 1:(3-4) and stir to form a uniform slurry; (2) adding hydrogen peroxide-ascorbic acid initiation system to the slurry, stirring and reacting at 25-35°C for 2-3 hours, and adding pH adjuster during the reaction to maintain the pH of the system at 5-6; (3) After the reaction is completed, the reactants are filtered continuously through a continuous vacuum filter, washed in a multi-stage countercurrent washing tank, and dried in a fluidized bed dryer to finally obtain modified machine-made sand.

2. The method for preparing modified machine-made sand according to claim 1, characterized in that: In step (1), machine-made sand, coupling agent and hydrophilic monomer are mixed in a mass ratio of 1:(0.4-0.6):(1.5-2.5).

3. The method for preparing modified machine-made sand according to claim 2, characterized in that: In step (1), the particle size of the machine-made sand is 150-200 meshes; the hydrophilic monomer is one or two of acrylic acid and hydroxyethyl methacrylate phosphate.

4. The method for preparing modified machine-made sand according to claim 1, characterized in that: In step (2), the hydrogen peroxide-ascorbic acid initiation system is composed of hydrogen peroxide and ascorbic acid mixed in a mass ratio of 1:(0.1-0.2).

5. The method for preparing modified machine-made sand according to claim 1, characterized in that: In step (2), the pH adjuster is a sodium hydroxide solution.

6. The method for preparing modified machine-made sand according to claim 1, characterized in that: In step (3), after the reaction is completed, the reaction product is first transferred to a sedimentation tank for gravity sedimentation to initially separate most of the liquid from the solid. After the supernatant is discharged, the settled material is transported to a continuous vacuum filter for continuous filtration.

7. The method for preparing modified machine-made sand according to claim 1, characterized in that: The machine-made sand in step (1) is made from any one of granite, basalt and limestone.

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