A novel flocculant for washed sand and its preparation and application methods

Abstract

This invention relates to the field of concrete, and more particularly to a novel flocculant specifically for washed sand and its preparation and application methods. The flocculant is prepared via free radical polymerization using unsaturated acids, amide monomers, polyether macromonomers, and asymmetric crosslinking agents as reactants. Based on its pH-responsive characteristics, this flocculant can intelligently switch between flocculant and water-reducing agent: during sand washing, it efficiently flocculates mud and fine powder in wastewater, promoting wastewater recycling; when it remains in manufactured sand and enters the alkaline environment of concrete, the ester bonds in the molecule can hydrolyze and break, degrading the flocculant into polycarboxylic acid fragments with a comb-like structure. This novel flocculant not only eliminates the problems of high water-reducing agent dosage and large slump loss caused by traditional flocculant residues, but the degradation products themselves can also play a dispersing role, helping to reduce the water-reducing agent dosage and improve the slump retention performance of concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete, and in particular to a novel flocculant for washed sand and its preparation and application methods. Background Technology

[0002] In the concrete industry, manufactured sand has gradually become an important substitute for natural sand. Water washing is a common pretreatment process to remove excess stone powder and soil from manufactured sand. In this process, anionic polyacrylamide (APAM) is widely used as a highly efficient flocculant. Through charge neutralization and adsorption bridging, it can rapidly promote the flocculation and sedimentation of fine particles, thereby improving sand washing efficiency.

[0003] However, traditional flocculants are difficult to completely remove after sand washing, and their residues adhere to the surface of sand particles. When such washed sand is used to mix concrete, it triggers a series of significant negative effects. The research by Fu Huiling et al. ("The Influence of Residual Flocculant in Machine-Made Sand on Concrete Performance," Guangdong Building Materials) directly confirms this problem, pointing out that residual APAM in manufactured sand leads to poorer concrete fluidity and accelerated loss over time. The research results of Yin Jianli ("Research on the Influence of Flocculants in Washed Machine-Made Sand on Concrete Performance," Concrete World) show that polyacrylamide flocculants have a significant impact on the slump and spread of concrete, with a 1-hour loss rate mainly concentrated between 10% and 50%. Tan Junfeng et al. ("The Influence of Nonionic Polyacrylamide Flocculant on the Dispersion Performance of Water-Reducing Agents," Railway Construction Technology) found that polycarboxylate superplasticizers first adsorb onto cement particles, and then their side chains interact and entangle with polyacrylamide through hydrogen bonds. This reduces the steric hindrance effect of the superplasticizer, resulting in a decrease in its initial dispersion performance. As the cement hydrates, the superplasticizer is more easily covered by hydration products, leading to a decline in its retention performance. Therefore, traditional flocculants have adverse effects on both the performance of polycarboxylate superplasticizers and the performance of concrete.

[0004] Currently, industrial practices for addressing flocculant residue issues primarily rely on physical rinsing. For example, Chinese invention patent CN202210331363.8 (title: Method for controlling residual flocculant in water-washed manufactured sand) discloses a process for reducing residual concentration by optimizing a "multi-stage rinsing" process. While effective, this method inherently consumes large amounts of clean water and generates more wastewater requiring treatment, increasing production costs and environmental burden.

[0005] Therefore, developing a new type of flocculant that can efficiently wash sand, whose residues do not have adverse effects on concrete performance, and can even be transformed into beneficial components through intelligent response to the concrete environment, has become an urgent technical need to break through the current industry bottleneck. Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the purpose of this invention is to provide a novel flocculant for water-washed sand and its preparation and application methods to solve the above-mentioned technical problems.

[0007] The novel flocculant for washed sand provided by this invention has multiple functions: on the one hand, it can be used in the washing sand process to accelerate the settling rate of mud and fine powder in the washed sand; even if the flocculant of this invention remains in the washed sand, it will not have a negative impact on the dispersion performance of polycarboxylate superplasticizer, the workability of concrete, or the performance of hardened concrete; unlike traditional flocculants, the flocculant of this invention can also reduce the dosage of polycarboxylate superplasticizer and improve the workability of concrete.

[0008] According to a first aspect of the present invention, a novel flocculant for washed sand is provided, which is prepared by means of the following raw materials in parts by weight:

[0009] 20-25 parts of unsaturated acids;

[0010] 25-30 parts of amide monomer;

[0011] 100-125 parts of polyether macromonomer;

[0012] 3.3-3.5 parts of asymmetric crosslinking agent;

[0013] Initiator 0.05~0.1 parts;

[0014] Chain transfer agent 0.05~0.1 parts.

[0015] In some embodiments, the unsaturated acid is at least one of acrylic acid and methacrylic acid; the amide monomer is at least one of acrylamide, methacrylamide, and N-propylacrylamide; the polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and ethylene glycol monovinyl polyethylene glycol ether; the relative molecular weight of the methyl allyl polyoxyethylene ether is 2400-3000, and the relative molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 2400-3000; the initiator is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; and the chain transfer agent is at least one of mercaptopropanol and mercaptopropionic acid.

[0016] In some embodiments, the preparation of the asymmetric crosslinking agent includes the following steps:

[0017] The polyether macromonomer and organic solvent were mixed to obtain a bottom solution; acryloyl chloride solution and triethylamine solution were added dropwise to the bottom solution (the temperature was controlled at 0~5℃ during the dropwise addition process), and the reaction was allowed to mature. After filtration, the filtrate was collected, washed, and the asymmetric crosslinking agent was obtained.

[0018] In some embodiments, during the preparation of the asymmetric crosslinking agent, the polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and ethylene glycol monovinyl polyethylene glycol ether; the organic solvent is dichloromethane; and the mass ratio of the polyether macromonomer to the organic solvent is 0.9:1 to 1:1.

[0019] In some embodiments, the acryloyl chloride solution is a mixture of acryloyl chloride and dichloromethane, wherein the mass ratio of acryloyl chloride to dichloromethane in the acryloyl chloride solution is 9.5 to 11:12; the triethylamine solution is a mixture of triethylamine and dichloromethane, wherein the mass ratio of triethylamine to dichloromethane in the triethylamine solution is 14:15 to 14:18.

[0020] In some embodiments, the addition of acryloyl chloride solution and triethylamine solution to the bottom liquid includes: adding acryloyl chloride solution and triethylamine solution to the bottom liquid at a temperature of 0~5℃, a stirring speed of 250~350 rpm, and under a protective atmosphere, with a dropping rate of 1 drop every 2~4 seconds; the ripening reaction temperature is 29~31℃, and the ripening reaction time is 1.9~2.1 h.

[0021] In some embodiments, the washing method is separation washing.

[0022] In some embodiments, the washing includes: washing the filtrate twice with a 10 wt% sodium bicarbonate solution, then twice with a saturated sodium chloride solution, allowing it to stand and separating the organic phase, and then removing the solvent from the organic phase at 40°C. Excess reactants and other impurities are removed by this separation and washing method.

[0023] The novel flocculant for washed sand provided by this invention has a relative molecular weight of 7.5 million to 8.5 million.

[0024] According to a second aspect of the present invention, the present invention provides a method for preparing a novel flocculant for washed sand, comprising the following steps:

[0025] Unsaturated acid, amide monomer, and asymmetric crosslinking agent are dissolved in deionized water and mixed to obtain a monomer mixture. The monomer mixture, initiator solution, and chain transfer agent solution are added dropwise to a polyether macromonomer solution to carry out a copolymerization reaction and aging treatment to obtain an aging mixture. After cooling to room temperature, the pH of the aging mixture is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0026] In some embodiments, the mass ratio of unsaturated acid to water in the monomer mixture is 20-25:50-60;

[0027] In some embodiments, the polyether macromonomer solution is a mixture of polyether macromonomer and water; in the polyether macromonomer solution, the mass ratio of polyether macromonomer to water is 100~125:5~60.

[0028] In some embodiments, the initiator solution is a mixture of initiator and water, wherein the mass ratio of initiator to water in the initiator solution is 0.05~0.1:20;

[0029] In some embodiments, the chain transfer agent solution is a mixture of chain transfer agent and water, wherein the mass ratio of chain transfer agent to water in the chain transfer agent solution is 0.05~0.1:20;

[0030] In some embodiments, the copolymerization reaction is carried out at a temperature of 70-80°C, and the monomer mixture and chain transfer agent solution are added dropwise over a time of 3.5-4 hours; the initiator solution is added dropwise over a time of 3.0-3.5 hours.

[0031] In some embodiments, the aging process is carried out at a temperature of 70-80°C for 1-2 hours.

[0032] According to a third aspect of the present invention, the present invention provides the application of a novel flocculant for washed sand in washed sand.

[0033] This invention provides the application of a novel flocculant specifically for washed sand in the production of washed manufactured sand, comprising the following steps:

[0034] (1) Wash the machined sand with water to obtain sand washing wastewater. Add the new type of sand washing flocculant to the sand washing wastewater. The mass of the new type of sand washing flocculant is 0.02~0.05% of the mass of the sand washing wastewater. After stirring and mixing, let it stand and settle for 3~10 minutes to achieve mud-water separation and obtain dewatered machined sand.

[0035] (2) When using the manufactured sand described in step (1) as fine aggregate to prepare concrete, the conventional dosage of polycarboxylate superplasticizer can be reduced by 5% to 10% when calculating the dosage of concrete admixture.

[0036] The novel flocculant for washed sand provided by this invention can be used in the fields of washed sand and concrete.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The novel flocculant for washed sand provided by this invention introduces a specific asymmetric crosslinking agent to bridge the polyether backbone with ether bonds and ester bonds respectively, thereby constructing a relatively stable three-dimensional network structure, which greatly increases the molecular weight of the flocculant and makes it exhibit excellent flocculation efficiency in the process of washing sand. More importantly, when the flocculant remains in the alkaline environment of concrete, the ester groups in the crosslinking agent can be rapidly hydrolyzed as "preset breakpoints", which promotes the degradation of the entire network structure into a comb-shaped polycarboxylate superplasticizer containing carboxyl groups and polyether side chains, realizing the intelligent transformation from flocculant to superplasticizer.

[0039] (2) One agent with dual effects, taking into account both sand washing performance and concrete workability. This invention achieves the unity of sand washing flocculation and concrete dispersion functions; in the sand washing process, its flocculation and settling efficiency is no less than that of traditional polyacrylamide; in the concrete mixing stage, its degradation products not only avoid competitive adsorption of polycarboxylate superplasticizer, but its own carboxyl group and long-chain polyether structure can also play a dispersing role, providing additional electrostatic repulsion and steric hindrance effects; therefore, using water-washed manufactured sand treated with this product to prepare concrete can not only effectively maintain the workability of concrete, but also reduce the amount of superplasticizer by 5%–10%, and improve the slump retention over time.

[0040] (3) Balancing environmental friendliness and economic efficiency. This invention solves the problem of flocculant residue from the molecular design stage, eliminating the need for high-water-consumption multi-stage rinsing processes and significantly reducing water consumption and wastewater treatment costs during sand washing. Simultaneously, its functional transformation in concrete reduces reliance on additional chemical admixtures, helping to lower concrete production costs and aligning with the development direction of green and sustainable building materials technology. Detailed Implementation

[0041] To better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below. It should be understood that the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] The synthesis of asymmetric crosslinking agents includes the following steps:

[0044] (1) Preparation of bottom liquid: Add 300 g of ethylene glycol monovinyl polyethylene glycol ether and an equal mass of dichloromethane solvent to the reactor, mix well, maintain the stirring speed of the reactor at 250 rpm and control the temperature of the reactor at 0℃ under nitrogen protection;

[0045] (2) Preparation of dropping solutions: Dropping solution A is an acryloyl chloride solution after mixing 9.5 g of acryloyl chloride and 12 g of dichloromethane solvent; Dropping solution B is a triethylamine solution after mixing 14 g of triethylamine and 15 g of dichloromethane solvent.

[0046] (3) Drop addition: Under the condition of maintaining the stirring speed of the reactor at 250 rpm and nitrogen protection, and controlling the temperature of the reactor at 0℃, the drop liquid A and drop liquid B are added dropwise to the reactor. The drop rate of drop liquid A and drop liquid B is 1 drop every 3 seconds to obtain a mixture.

[0047] (4) Curing reaction: After the dripping is completed, the mixture is heated to 30°C for curing reaction. The curing reaction time is 2 h to obtain the cured mixture.

[0048] (5) Post-treatment: First, filter the matured mixture with neutral filter paper (to remove the filter residue: triethylamine hydrochloride). After filtration, take the filtrate and wash it twice with 100g of 10wt% sodium bicarbonate solution. Let it stand to separate the layers and take the organic phase. Then wash it twice with 200g of saturated sodium chloride solution, let it stand to separate the layers and take the organic phase again. Finally, remove the solvent from the organic phase by rotary evaporation at 40℃ to obtain the asymmetric crosslinking agent.

[0049] The preparation of a novel flocculant specifically for washed sand includes the following steps:

[0050] S1. Preparation of the base solution: Add 50g of deionized water and 125g of ethylene glycol monovinyl polyethylene glycol ether (relative molecular weight of 3000) to the reactor, mix well to obtain the base solution, heat the reactor to 70℃ and start the stirrer.

[0051] S2. Preparation of the dropping solution: Dissolve 25 g of acrylic acid, 25 g of acrylamide, and 3.3 g of asymmetric crosslinking agent in 60 g of deionized water and mix well to prepare a monomer mixture (labeled M1); dissolve 0.05 g of initiator (ammonium persulfate is used here) in 20 g of deionized water and mix well to prepare an initiator solution (labeled M2); dissolve 0.1 g of mercaptopropanol in 20 g of deionized water and mix well to prepare a mercaptopropanol solution (labeled M3).

[0052] S3. Droplet addition copolymerization reaction: The temperature of the reaction system in the reactor is kept constant at 70℃, the stirring speed of the reactor is 250 rpm, and M1, M2 and M3 are added dropwise to the reactor. The droplet addition time of M1 and M3 is 3.5 h, and the droplet addition time of M2 is 3 h.

[0053] S4. Incubation and ripening: After the addition is completed, the reaction solution is obtained. The stirring speed of the reaction vessel is reduced to 50 rpm, and the reaction solution is incubated at 70°C for 1 hour to obtain the ripened reaction solution.

[0054] S5. Post-treatment: After the matured reaction solution is cooled to room temperature, the pH of the matured reaction solution is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0055] Example 2

[0056] The synthesis of asymmetric crosslinking agents includes the following steps:

[0057] (1) Preparation of bottom liquid: 240 g of methyl allyl polyoxyethylene ether and an equal mass of dichloromethane solvent are added to the reactor, mixed well, and the reactor is kept at a stirring speed of 250 rpm and under nitrogen protection, the reactor temperature is controlled at 5℃.

[0058] (2) Preparation of dropping solutions: Dropping solution A is an acryloyl chloride solution after mixing 11 g of acryloyl chloride and 12 g of dichloromethane solvent; Dropping solution B is a triethylamine solution after mixing 14 g of triethylamine and 15 g of dichloromethane solvent.

[0059] (3) Drop addition: Under the conditions of maintaining the stirring speed of the reactor at 250 rpm and nitrogen protection, and controlling the reactor temperature at 5℃, the drop liquid A and drop liquid B are added dropwise to the reactor. The drop rate of drop liquid A and drop liquid B is 1 drop every 3 seconds to obtain a mixture.

[0060] (4) Curing reaction: After the dripping is completed, the mixture is heated to 30°C for curing reaction. The curing reaction time is 2 h to obtain the cured mixture.

[0061] (5) Post-treatment: First, filter the matured mixture with neutral filter paper (to remove triethylamine hydrochloride). After filtration, take the filtrate and wash it twice with 100g of 10wt% sodium bicarbonate solution. Let it stand to separate the layers and take the organic phase. Then wash it twice with 200g of saturated sodium chloride solution, let it stand to separate the layers and take the organic phase again. Finally, remove the solvent from the organic phase by rotary evaporation at 40℃ to obtain the asymmetric crosslinking agent.

[0062] The preparation of a novel flocculant specifically for washed sand includes the following steps:

[0063] S1. Preparation of base solution: Add 55 g of deionized water and 100 g of methyl allyl polyoxyethylene ether (relative molecular weight of 2400) to the reactor, mix well to obtain the base solution, heat the reactor to 75°C and start the stirrer.

[0064] S2. Preparation of the dropping solution: Dissolve 20 g of acrylic acid, 27.5 g of methacrylamide, and 3.5 g of asymmetric crosslinking agent in 50 g of deionized water and mix well to prepare a monomer mixture (labeled M1); dissolve 0.1 g of initiator (potassium persulfate is used here) in 20 g of deionized water and mix well to prepare an initiator solution (labeled M2); dissolve 0.05 g of mercaptopropanol in 20 g of deionized water and mix well to prepare a mercaptopropanol solution (labeled M3).

[0065] S3. Droplet addition copolymerization reaction: The temperature of the reaction system in the reactor is kept constant at 75℃, the stirring speed of the reactor is 250 rpm, and M1, M2 and M3 are added dropwise to the reactor. The droplet addition time of M1 and M3 is 4 h, and the droplet addition time of M2 is 3.5 h.

[0066] S4. Incubation and ripening: After the addition is completed, the reaction solution is obtained. The stirring speed of the reactor is reduced to 50 rpm, and the reaction solution is incubated at 75°C for 1.5 hours to obtain the ripened reaction solution.

[0067] S5. Post-treatment: After the matured reaction solution is cooled to room temperature, the pH of the matured reaction solution is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0068] Example 3

[0069] The synthesis of asymmetric crosslinking agents includes the following steps:

[0070] (1) Preparation of bottom liquid: 240 g of methyl allyl polyoxyethylene ether and an equal mass of dichloromethane solvent are added to the reactor, mixed well, and the reactor is kept at a stirring speed of 250 rpm and under nitrogen protection, the reactor temperature is controlled at 3℃.

[0071] (2) Preparation of dropping solutions: Dropping solution A is an acryloyl chloride solution after mixing 11 g of acryloyl chloride and 12 g of dichloromethane solvent; Dropping solution B is a triethylamine solution after mixing 14 g of triethylamine and 15 g of dichloromethane solvent.

[0072] (3) Drop addition: Under the condition of maintaining the stirring speed of the reactor at 250 rpm and nitrogen protection, and controlling the temperature of the reactor at 0℃, the drop liquid A and drop liquid B are added dropwise to the reactor. The drop rate of drop liquid A and drop liquid B is 1 drop every 3 seconds to obtain a mixture.

[0073] (4) Curing reaction: After the dripping is completed, the mixture is heated to 30°C for curing reaction. The curing reaction time is 2 h to obtain the cured mixture.

[0074] (5) Post-treatment: First, filter the matured mixture with neutral filter paper (to remove triethylamine hydrochloride). After filtration, take the filtrate and wash it twice with 100 g of 10 wt% sodium bicarbonate solution. Let it stand to separate the layers and take the organic phase. Then wash it twice with 200 g of saturated sodium chloride solution, let it stand to separate the layers and take the organic phase again. Finally, remove the solvent from the organic phase by rotary evaporation at 40°C to obtain the asymmetric crosslinking agent.

[0075] The preparation of a novel flocculant specifically for washed sand includes the following steps:

[0076] S1. Preparation of base solution: Add 60 g of deionized water and 100 g of methyl allyl polyoxyethylene ether (relative molecular weight of 2400) to the reactor, mix well to obtain the base solution, heat the reactor to 75°C and start the stirrer.

[0077] S2. Preparation of the dropping solution: Dissolve 22.5 g of acrylic acid, 30 g of N-propylacrylamide, and 3.4 g of asymmetric crosslinking agent in 55 g of deionized water and mix well to prepare a monomer mixture (labeled M1); dissolve 0.075 g of initiator (sodium persulfate is used here) in 20 g of deionized water and mix well to prepare an initiator solution (labeled M2); dissolve 0.075 g of mercaptopropionic acid in 20 g of deionized water and mix well to prepare a mercaptopropionic acid solution (labeled M3).

[0078] S3. Droplet addition copolymerization reaction: The temperature of the reaction system in the reactor is kept constant at 80℃, the stirring speed of the reactor is 250 rpm, and M1, M2 and M3 are added dropwise to the reactor. The droplet addition time of M1 and M3 is 3.5 h, and the droplet addition time of M2 is 3 h.

[0079] S4. Incubation and ripening: After the addition is completed, the reaction solution is obtained. The stirring speed of the reactor is reduced to 50 rpm, and the reaction solution is incubated at 80°C for 2 hours to obtain the ripened reaction solution.

[0080] S5. Post-treatment: After the matured reaction solution is cooled to room temperature, the pH of the matured reaction solution is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0081] Example 4

[0082] The asymmetric crosslinking agent used in this embodiment is the asymmetric crosslinking agent synthesized in Example 3.

[0083] The preparation of a novel flocculant specifically for washed sand includes the following steps:

[0084] S1. Preparation of the base solution: Add 60 g of deionized water and 100 g of methyl allyl polyoxyethylene ether (relative molecular weight of 2400) to the reactor, heat to 75°C and stir to mix well to obtain the base solution. Keep the reactor temperature at 75°C.

[0085] S2. Preparation of the dropping solution: Dissolve 22.5 g of acrylic acid, 30 g of N-propylacrylamide, and 3.4 g of asymmetric crosslinking agent in 55 g of deionized water and mix well to prepare a monomer mixture (labeled M1); dissolve 0.075 g of initiator (sodium persulfate is used here) in 20 g of deionized water and mix well to prepare an initiator solution (labeled M2); dissolve 0.075 g of mercaptopropionic acid in 20 g of deionized water and mix well to prepare a mercaptopropionic acid solution (labeled M3).

[0086] S3. Droplet addition copolymerization reaction: The temperature of the reaction system in the reactor is kept constant at 80℃, the stirring speed of the reactor is 250 rpm, and M1, M2 and M3 are added dropwise to the reactor. The droplet addition time of M1 and M3 is 3.5 h, and the droplet addition time of M2 is 3 h.

[0087] S4. Incubation and ripening: After the addition is completed, the reaction solution is obtained. The stirring speed of the reactor is reduced to 50 rpm, and the reaction solution is incubated at 80℃ for 2.0 h to obtain the ripened reaction solution.

[0088] S5. Post-treatment: After the matured reaction solution is cooled to room temperature, the pH of the matured reaction solution is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0089] Example 5

[0090] The asymmetric crosslinking agent used in this embodiment is the asymmetric crosslinking agent synthesized in Example 3.

[0091] The preparation of a novel flocculant specifically for washed sand includes the following steps:

[0092] S1. Preparation of the base solution: Add 55 g of deionized water and 125 g of ethylene glycol monovinyl polyethylene glycol ether (relative molecular weight of 3000) to the reactor, heat to 75°C and stir to mix well to obtain the base solution. Maintain the reactor temperature at 75°C.

[0093] S2. Preparation of the dropping solution: Dissolve 22.5 g of acrylic acid, 30 g of N-propylacrylamide, and 3.4 g of asymmetric crosslinking agent in 55 g of deionized water and mix well to prepare a monomer mixture (labeled M1); dissolve 0.075 g of initiator (sodium persulfate is used here) in 20 g of deionized water and mix well to prepare an initiator solution (labeled M2); dissolve 0.075 g of mercaptopropanol in 20 g of deionized water and mix well to prepare a mercaptopropanol solution (labeled M3).

[0094] S3. Droplet addition copolymerization reaction: The temperature of the reaction system in the reactor is kept constant at 80℃, the stirring speed of the reactor is 250 rpm, and M1, M2 and M3 are added dropwise to the reactor. The droplet addition time of M1 and M3 is 3.5 h, and the droplet addition time of M2 is 3 h.

[0095] S4. Incubation and ripening: After the addition is completed, the reaction solution is obtained. The stirring speed of the reactor is reduced to 50 rpm, and the reaction solution is incubated at 80℃ for 2.0 h to obtain the ripened reaction solution.

[0096] S5. Post-treatment: After the matured reaction solution is cooled to room temperature, the pH of the matured reaction solution is adjusted to 6.0~7.0 with 30wt% sodium hydroxide solution to obtain the novel flocculant for water-washed sand.

[0097] Comparative Example 1

[0098] Except for the absence of an asymmetric crosslinking agent in S2, everything else is the same as in Example 5.

[0099] Comparative Example 2

[0100] Except for the crosslinking agent being changed to ethylene glycol dimethacrylate in S2, everything else was the same as in Example 5. The results showed that the gel, during the subsequent copolymerization reaction in S3, could not dissolve in water and therefore could not be used as a flocculant.

[0101] Comparative Example 3

[0102] Except for the absence of unsaturated acid (acrylic acid) in S2, everything else is the same as in Example 5.

[0103] Comparative Example 4

[0104] Except for the absence of the amide monomer (N-propylacrylamide) in S2, everything else is the same as in Example 5.

[0105] Comparative Example 5

[0106] Anionic polyacrylamide with a molecular weight of 8 million was used as a flocculant.

[0107] Effect verification

[0108] The method for determining the sedimentation effect of flocculants is as follows:

[0109] The flocculants prepared in each embodiment and comparative example were used as the test samples;

[0110] Using 400-mesh granite powder, water was added to prepare a 500 ml suspension with a concentration of 50 g / L. Flocculant was added to each group (no substance was added to the blank group, while the flocculant added to the other groups is shown in Table 1, where the flocculant dosage is expressed as the mass ratio of flocculant to water in each group). The mixture was stirred evenly at 300 rpm for 5 min. After stirring was stopped, the timer was started for 5 min. After standing, the supernatant was carefully aspirated with a pipette at a depth of 2 cm below the liquid surface, avoiding disturbing the sediment. The turbidity of the suspension was measured (instrument: WZS-185A turbidity analyzer, ≤1000 NTU, Shanghai Leici Instrument & Electronic Scientific Instrument Co., Ltd.).

[0111] To investigate the effects of each group of flocculants on the performance of subsequent concrete, each group of flocculants was added to the concrete formulation, and then each group of concrete was prepared and tested as follows.

[0112] The test methods for workability and mechanical properties of concrete refer to GB / T 50080 and GB / T 50081. The dosage of flocculant in each group is uniformly 0.005% (residual amount) of sand mass. The mass mix ratio of concrete test is m (cement):m (mineral powder):m (fly ash):m (sand):m (stone):m (water) = 200:90:50:50:790:1040:165.

[0113] The results are shown in Tables 1, 2 and 3 below.

[0114] Table 1 Comparison of sedimentation effects of flocculants

[0115]

[0116] As shown in Table 1, the turbidity of the blank sample was significantly higher than that of Examples 1-5 and Comparative Example 5, indicating that gravity sedimentation alone could not clarify the suspension under the experimental conditions. Examples 1-6 showed good sedimentation effects at dosages of 0.02% and 0.05%. Compared with Example 5, the turbidity of Comparative Example 1 was approximately 10 times that of Example 5, indicating that the synthesized flocculant had too small a molecular weight due to the absence of asymmetric crosslinking monomers, making it difficult to achieve flocculation. Compared with Example 5, Comparative Example 2 showed that the asymmetric crosslinking monomers of the present invention have long-chain structures, thus avoiding the formation of polymeric gels due to excessively dense crosslinking structures. Compared with Example 5, Comparative Example 3 showed that the lack of anionic groups resulted in a poorer flocculant effect. Comparative Example 3 also showed that the lack of neutral groups and excessively high anionic group density significantly reduced the flocculation effect of the flocculant. Compared with Example 5, Comparative Example 5 showed that the flocculant of the present invention was similar in effect to commercially available flocculants.

[0117] Table 2 Comparison of Concrete Performance

[0118]

[0119] Note: The dosage of water-reducing agent is 2.0% of the adhesive material.

[0120] Table 3 Comparison of Concrete Performance

[0121]

[0122] Note: The water-reducing agent dosage in the blank group was 2.0% of the adhesive material; the water-reducing agent dosage in the examples and comparative examples was 1.8%.

[0123] As shown in Table 2, the initial spread of concrete in Examples 1-5 was close to that of the control group, and its 1.5-hour spread loss was less than that of the control group. This indicates that the flocculant of the present invention has little impact on the water-reducing effect of the water-reducing agent and helps to improve the 1.5-hour spread of concrete. This shows that when the concrete with the flocculant of the present invention is in an alkaline environment, the ester group in the crosslinking agent can be rapidly hydrolyzed as a "preset breakpoint," promoting the degradation of the entire network structure into a comb-like polycarboxylate water-reducing agent containing carboxyl groups and polyether side chains. In addition, the examples had no negative impact on the compressive strength of concrete. Although Comparative Example 1 had no negative impact on the workability of concrete, it also lacked the flocculation and settling effect of the flocculant (see Table 1). Comparative Examples 3 and 5 showed extremely large slump losses, which affected the density of the concrete during molding and ultimately reduced the strength of the concrete.

[0124] As shown in Table 3, reducing the dosage of water-reducing agent reduced the initial expansion of both the control group and the examples to some extent; however, the examples still exhibited better slump retention performance than the control group, and had no negative impact on the compressive strength of the concrete. The overall performance of Comparative Examples 1 and 3-5 was also inferior to that of the examples.

[0125] The comparative example of this invention cannot simultaneously achieve the flocculation and sedimentation function of the flocculant and the functions of improving the slump retention performance of concrete or reducing the dosage of water-reducing agent. However, the embodiments of this invention introduce a specific asymmetric crosslinking agent to bridge the polyether backbone with ether bonds and ester bonds at both ends, constructing a relatively stable three-dimensional network structure. This significantly increases the molecular weight of the flocculant, enabling it to exhibit excellent flocculation efficiency during sand washing. Furthermore, when the flocculant remains in the alkaline environment of concrete, the ester groups in the crosslinking agent act as "pre-set breakpoints" and can rapidly hydrolyze, causing the entire network structure to degrade into a comb-like polycarboxylate water-reducing agent containing carboxyl groups and polyether side chains, thus achieving an intelligent transformation from flocculant to water-reducing agent.

[0126] In summary, the flocculant provided in this invention is prepared by free radical polymerization using unsaturated acids, amide monomers, polyether macromonomers, and asymmetric crosslinking agents as reactants. Based on its pH-responsive characteristics, this flocculant can intelligently switch from flocculant to water-reducing agent: during sand washing, it can efficiently flocculate mud and fine powder in wastewater, promoting wastewater circulation; when it remains in manufactured sand and enters the alkaline environment of concrete, the ester group bridges in the molecule can be hydrolyzed and broken, causing the flocculant to degrade into polycarboxylic acid fragments with a comb-like structure, which can play a dispersing role, helping to reduce the dosage of water-reducing agent and improve the slump retention performance of concrete, eliminating problems such as high water-reducing agent dosage and large slump loss caused by traditional flocculant residues.

[0127] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A flocculant specifically for washed sand, characterized in that, The preparation comprises the following raw materials in parts by weight: 20-25 parts of unsaturated acids; 25-30 parts of amide monomer; 100-125 parts of polyether macromonomer; 3.3-3.5 parts of asymmetric crosslinking agent; Initiator 0.05~0.1 parts; Chain transfer agent 0.05~0.1 parts; The amide monomer is at least one selected from acrylamide, methacrylamide, and N-propylacrylamide; The preparation of the asymmetric crosslinking agent includes the following steps: The polyether macromonomer and organic solvent were mixed to obtain the bottom liquid; acryloyl chloride solution and triethylamine solution were added dropwise to the bottom liquid, and the reaction was allowed to mature. After filtration, the filtrate was collected, washed, and the asymmetric crosslinking agent was obtained. The polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and ethylene glycol monovinyl polyethylene glycol ether.

2. The flocculant for washed sand according to claim 1, characterized in that, The unsaturated acid is at least one of acrylic acid and methacrylic acid; the relative molecular weight of the methyl allyl polyoxyethylene ether is 2400-3000, and the relative molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 2400-3000; the initiator is at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; and the chain transfer agent is at least one of mercaptopropanol and mercaptopropionic acid.

3. The flocculant for washed sand according to claim 1, characterized in that, The organic solvent is dichloromethane; the mass ratio of the polyether macromonomer to the organic solvent is 0.9:1 to 1:

1.

4. The flocculant for washed sand according to claim 1, characterized in that, The acryloyl chloride solution is a mixture of acryloyl chloride and dichloromethane, wherein the mass ratio of acryloyl chloride to dichloromethane in the acryloyl chloride solution is 9.5~11:12; the triethylamine solution is a mixture of triethylamine and dichloromethane, wherein the mass ratio of triethylamine to dichloromethane in the triethylamine solution is 14:15~14:

18.

5. The flocculant for washed sand according to claim 1, characterized in that, The addition of acryloyl chloride solution and triethylamine solution to the bottom liquid includes: adding acryloyl chloride solution and triethylamine solution dropwise to the bottom liquid at a temperature of 0~5℃, a stirring speed of 250~350 rpm, and under a protective atmosphere, with a drop rate of 1 drop every 2~4 seconds; the ripening reaction temperature is 29~31℃, and the ripening reaction time is 1.9~2.1 h.

6. The flocculant for washed sand according to any one of claims 1-5, characterized in that, The relative molecular weight of the flocculant specifically for washed sand is 7.5 million to 8.5 million.

7. The method for preparing the flocculant for washed sand according to any one of claims 1-6, characterized in that, Includes the following steps: Unsaturated acid, amide monomer, and asymmetric crosslinking agent are dissolved in water and mixed to obtain a monomer mixture. The monomer mixture, initiator solution, and chain transfer agent solution are added dropwise to a polyether macromonomer solution to carry out a copolymerization reaction and aging treatment to obtain an aging mixture. The pH of the aging mixture is adjusted to 6.0~7.0 to obtain the flocculant for water-washed sand.

8. The preparation method according to claim 7, characterized in that, In the monomer mixture, the mass ratio of unsaturated acid to water is 20~25:50~60; the initiator solution is a mixture of initiator and water, with a mass ratio of initiator to water of 0.05~0.1:20; the chain transfer agent solution is a mixture of chain transfer agent and water, with a mass ratio of chain transfer agent to water of 0.05~0.1:20; the copolymerization temperature is 70~80℃, and the dropping time of the monomer mixture and chain transfer agent solution is 3.5~4h; the dropping time of the initiator solution is 3.0~3.5h; the aging treatment temperature is 70~80℃, and the aging treatment time is 1~2h.

9. The application of the flocculant for washed sand according to any one of claims 1-6 in washed sand.

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