Method for removing flocculant residues in wet-process sand making

Abstract

The invention relates to the technical field of building materials, in particular to a method for removing flocculant residues in wet-process sand making. The invention discloses a method for removing flocculant residues in wet-process sand making. The method comprises the following steps: S1, preparing a flocculant degradation agent; s2, using a flocculating agent degradation agent: mixing the flocculating agent degradation agent and machine-made sand which is washed by circulating wastewater and contains a polyacrylamide flocculating agent according to the mass part ratio, stirring and reacting for 10-20 minutes, and then performing coarse filtration and separation to obtain the machine-made sand and mixed wastewater; and S3, performing fine filtration treatment and reutilization. The invention provides an economical and effective method for treating the problem of residual polyacrylamide flocculants in the machine-made sand, and the method has important significance for improving the quality of concrete and mortar and also has relatively high practical value and environmental friendliness.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to a method for removing flocculant residues in wet sand making. Background Art

[0002] At present, my country mainly uses two sand-making processes, dry method (i.e., air separation to remove powder) and wet method (i.e., water washing to remove powder), to remove excess stone powder and mud powder in the machine-made sand to ensure that its quality indicators meet national standards. Compared with the dry method, the wet sand-making process can not only significantly reduce dust emissions, but also effectively control the fine powder content in the finished machine-made sand. However, this process requires a large amount of water resources and produces a large amount of high-concentration mud wastewater, which increases the difficulty and cost of treatment. In order to respond to the requirements of water conservation, cost reduction and environmental protection, enterprises that use wet sand making usually add flocculants to the mud wastewater to accelerate the sedimentation of suspended particles, thereby realizing the secondary utilization of the supernatant for subsequent sand washing processes. This method not only promotes the rapid and efficient recycling of sand washing wastewater, but also reduces dependence on external water sources, while reducing the cost and environmental impact of wastewater treatment.

[0003] In the wet sand making process, polyacrylamide flocculants (hereinafter referred to as PAM) are widely used due to their efficient mud powder and dust flocculation ability and relatively low price. However, in the circulating sand making process, PAM will not only remain in the treated upper clear water, but also be mixed into the machine-made sand along with the water. At present, the machine-made sand production enterprises generally pay insufficient attention to the types and dosages of flocculants, and their selection and use are often relatively extensive, which leads to large fluctuations in the PAM residue in the circulating wastewater, and thus makes the residual amount of flocculants in the machine-made sand unstable. It is worth noting that PAM residues have a significant negative impact on the performance of concrete mixtures, which is specifically manifested in the reduction of concrete slump and increased losses, which in turn affects the smooth progress of pumping construction. This adverse effect seriously restricts the application scope and development potential of machine-made sand. At present, in order to deal with this problem, the method of adjusting the dosage of water reducer or pumping agent is usually adopted to improve the performance of concrete. However, due to the instability of the residual amount of flocculants, it is difficult to accurately control the dosage of water reducer, which leads to large fluctuations in the working performance of machine-made sand concrete. This issue has become a common focus of attention for machine-made sand production companies, admixture manufacturers and concrete mixing plants, and there is an urgent need to find more effective solutions to ensure the stability of concrete quality and the smooth progress of construction.

[0004] In order to alleviate the above problems, future research directions should include exploring new flocculants, developing more sophisticated flocculant usage strategies, and studying how to better control and reduce the residual amount of flocculants in machine-made sand.

[0005] Chinese invention patent application CN113336462B provides a method for degrading residual flocculants in washed machine-made sand in concrete mixing, wherein machine-made sand with low residual flocculant content is selected by ultraviolet visible spectrophotometer for storage in sand bin, and then the stored machine-made sand is transported to a mixing bin made of wear-resistant steel for preparing concrete by conveyor belt, and the machine-made sand on the conveyor belt is irradiated by low-pressure mercury lamp during the transportation process, and cement, mineral powder, and fly ash are added to the mixer for dry mixing, and then water and 2%-2.4% of the degradable polycarboxylate water-reducing agent compounded with zinc sulfate are added for wet mixing to obtain the finished concrete product. Disadvantages: The machine-made sand is thickly accumulated, and the machine-made sand below the surface is difficult to be irradiated, which affects the degradation effect.

[0006] Chinese invention patent CN115594804A discloses a method for preparing a deflocculating amphoteric polycarboxylic acid water reducer, comprising the following steps: step 1, preparing a mixture A with an unsaturated polyether as a macromonomer; step 2, dissolving a chain transfer agent in a reducing agent to obtain a mixture B; step 3, removing the solvent by rotary evaporation under reduced pressure to obtain a light yellow transparent liquid; step 4, preparing a mixture C; step 5, simultaneously dropping mixture B and mixture C into mixture A, mechanically stirring for 26 hours, and obtaining a reactant of a deflocculating amphoteric water reducer; step 6, pouring the reactant into a beaker, cooling it to room temperature, and adjusting the pH value to 6-8 with an aqueous NaOH solution to obtain a deflocculating amphoteric water reducer. Disadvantages: complex preparation process, expensive raw materials, energy consumption: the process requires rotary evaporation, resulting in unnecessary energy consumption.

[0007] Chinese invention patent CN113773441A proposes a method for preparing and applying a deflocculant, using acrylamide as a raw material to prepare a cationic monomer with good polymerization activity, and using styrene as a raw material for the deflocculant. Styrene is a monomer with a positive charge, and the benzene ring and C=C form a conjugation, which causes the electrons to shift to the double bond. The benzene ring has a positive charge and can attract the flocculant with a different charge. The essence of this patent is to adsorb the flocculant through a low molecular polymer. Disadvantages: The technical cost is too high, which is not conducive to promotion.

[0008] Chinese invention patent CN114920509A provides a method and application for resisting the negative effects of flocculants in machine-made sand. The machine-made sand or concrete or mortar containing machine-made sand is treated with a degradation agent, wherein the degradation agent includes one or more of sodium hypochlorite, hypochlorous acid, chlorine, bromine, hypobromous acid, and sodium hypobromite, and the acrylamide unit in the polyacrylamide flocculant is degraded into ethyleneamine with one less carbon atom through the Hofmann degradation reaction. Disadvantages: Halogen ions will be introduced into the concrete, which will corrode the steel bars in the concrete and affect the durability of the concrete.

[0009] Chinese invention patent CN117924538A discloses a modified cyclodextrin deflocculant for concrete and its preparation method and application. The patent uses cyclodextrin, sulfonating agent, crosslinking agent, catalyst and water as raw materials, and forms a deflocculant in the form of a framework molecule with multiple cyclodextrins cross-linked with anionic sulfonic acid groups through the sulfonation and cross-linking composite reaction of cyclodextrin. Disadvantages: Heating above 100°C for synthesis generates unnecessary energy consumption.

[0010] The main deficiencies of the above invention patent application can be summarized as follows: ① Energy consumption problem: The existing technology generates unnecessary energy consumption in the process of processing machine-made sand, which not only increases production costs, but also runs counter to the environmental protection concept of energy conservation and emission reduction. ② Economic problem: The preparation process is complicated and the raw materials are expensive, resulting in high overall costs. The high cost limits the large-scale promotion and application of this technology, especially in the cost-sensitive building materials market. ③ Concrete performance problem: The existing technology may have a negative impact on other properties while improving the working performance of concrete. In view of the above challenges, there is an urgent need to develop a new method that can solve the negative impact of flocculant residues on concrete from the root, and at the same time have the following characteristics: low cost, low energy consumption and high performance. Summary of the invention

[0011] In view of the shortcomings of the prior art, the present application provides a method for removing residual flocculants in wet sand making. The flocculant degradation agent prepared in the present application cleverly combines the oxidative degradation effect of a strong oxidant and the flocculation degradation effect of an antiflocculant, wherein the metal ions in the antiflocculant can catalytically decompose the strong oxidant into strong oxidizing free radicals at room temperature, and the strong oxidizing free radicals can effectively reduce the molecular weight of the polyacrylamide flocculant PAM, breaking the long polymer chain into short chains, thereby significantly reducing the residual amount of polyacrylamide flocculants in machine-made sand, thereby reducing the negative impact on the performance of concrete and mortar, and improving the working performance and mechanical properties of machine-made sand concrete, such as slump and compressive strength.

[0012] In a first aspect, the present application provides a method for removing flocculant residues in wet sand making, using the following technical solution: A method for removing flocculant residues in wet sand making comprises the following steps: S1. preparing a flocculant degradation agent: mixing a strong oxidant, an antiflocculant and water according to parts by mass and stirring them sufficiently until they are completely dissolved to obtain a flocculant degradation agent; S2. Use of flocculant degradation agent: according to the mass ratio, mix the flocculant degradation agent and the machine-made sand containing polyacrylamide flocculants washed with circulating wastewater, stir and react for 10-20 minutes, and then roughly filter and separate to obtain machine-made sand and mixed wastewater; S3. Fine filtration treatment and reuse: fine filtration and separation of the mixed wastewater to remove the wastewater containing polyacrylamide flocculants and a small amount of flocculent precipitates generated by the reaction of flocculant degradation agent and polyacrylamide flocculants. The flocculant degradation agent can be added to the obtained wastewater, which can be used to repeatedly clean the machine-made sand to remove the polyacrylamide flocculant residues.

[0013] By adopting the above technical scheme, a flocculant degradation agent is prepared: a strong oxidant, a deflocculant and water are mixed and stirred until they are completely dissolved to form a flocculant degradation agent. This step provides the necessary chemical environment for the subsequent degradation of the flocculant. The strong oxidant and the deflocculant act on the flocculant together, and act on the flocculant molecules through two mechanisms of charge neutralization and oxidative degradation, causing them to lose their original structure and function. Use of flocculant degradation agent: the flocculant degradation agent is mixed with the machine-made sand containing polyacrylamide flocculants and stirred to react, and the flocculant is degraded by chemical reaction to reduce its residual amount in the machine-made sand. The strong oxidant and the deflocculant in the flocculant degradation agent interact with each other, and act on the flocculant molecules through two mechanisms of charge neutralization and oxidative degradation, causing them to degrade into small molecules or lose viscosity. Fine filtration treatment and reuse: a small amount of flocculent precipitate generated by the reaction of the polyacrylamide flocculant and the flocculant degradation agent is removed by fine filtration separation, and the obtained wastewater can be used for repeated cleaning of the machine-made sand. Fine filtration treatment ensures the reuse of wastewater and reduces pollution to the environment. In short, this application achieves effective removal of flocculant residues in wet sand making through the synergistic effect of three steps: preparing a flocculant degradation agent, using the degradation agent to treat machine-made sand containing flocculants, and fine filtration to treat wastewater. This method not only improves the quality of machine-made sand and reduces the impact on concrete performance, but also improves resource utilization efficiency and environmental sustainability.

[0014] Preferably, in step S1, the flocculant degradation agent comprises the following raw materials, calculated by weight: 20-50 parts of a strong oxidant, 10-30 parts of a deflocculant, and 100 parts of water.

[0015] By adopting the above technical scheme, when preparing the flocculant degradation agent in step S1, the mass fraction ratio of the strong oxidant and the anti-flocculant and the water ratio are carefully designed. The role of the strong oxidant is to oxidize and degrade the polyacrylamide flocculant into smaller molecular fragments or monomers, thereby reducing its impact on the subsequent treatment process and concrete performance. At the same time, the metal ions in the anti-flocculant play two key roles: one is the charge neutralization effect, which interferes with the bridging effect between flocculant molecules by reacting with the negative charge sites in the flocculant molecules, destroying the stable aggregation state of colloids or suspended particles; the other is to act as a catalyst to activate the strong oxidant to produce strong oxidizing free radicals, further promoting the degradation of polyacrylamide flocculants. This synergistic effect ensures that the flocculant degradation agent can effectively degrade the polyacrylamide flocculant while maintaining the economy of the treatment process and the simplicity of operation. In practical applications, this flocculant degradation agent can be used in the production process or pretreatment of machine-made sand. Through simple operation, the residual amount of polyacrylamide flocculants can be significantly reduced, and the working performance and mechanical properties of concrete can be improved.

[0016] The strong oxidant and the anti-flocculant are mixed together, and the two materials work synergistically to reduce the viscosity of PAM in a very short time. The degradation of the flocculant by the two materials includes the following principles: a. Charge neutralization (flocculation degradation) Deflocculants can inhibit the effectiveness of flocculants, and the mechanism involves the interaction between the metal ions contained in the deflocculants and the flocculant molecules. Specifically, these metal ions can react with the negatively charged sites in the flocculants to neutralize the charge, thereby interfering with the bridging effect between flocculant molecules, resulting in the destruction of the stable aggregation state of colloids or suspended particles originally promoted by the flocculants. This process weakens the integrity of the flocculant structure, reduces its solution viscosity, and forms flocculent precipitates.

[0017] This phenomenon is usually described as the "depolymerization" or "dispersion" effect of anti-flocculants on flocculants, that is, by changing the charge distribution and steric hindrance characteristics of the system, the particle aggregation caused by the flocculant is reversed, thereby achieving the regulation or control of the flocculation process. In addition, this process may be accompanied by changes in the conformation of the flocculant molecular chain, further affecting the rheological properties of the entire system.

[0018] b. Oxidative degradation PAM is a thin and long chain, the molecular chain stretches out and curls to form a dense network structure, the chains are intertwined and entangled. After being degraded by strong oxidants, the morphology of PAM changes significantly, the surface is smooth and relatively broken, unlike the network structure before oxidation, but the long chain breaks into small fragments. Metal ions can catalyze the decomposition of strong oxidants into strong oxidizing free radicals at room temperature, thereby further degrading PAM. The conditions required for this activation method are easy to obtain, its mechanism of action is simple, does not require any heat source or light source, and has low energy consumption. Fe 2+ Taking the activation to generate sulfate free radicals as an example, the specific reaction equation is shown in formula (1);

[0019] Strong oxidizing free radicals can effectively reduce the molecular weight of PAM, breaking the long polymer chain into short chains, thereby reducing the viscosity of the flocculant solution, resulting in a significant decrease in the viscosity of the solution. As the reaction time increases, PAM undergoes a chain breaking reaction, causing chain oxidation degradation, accompanied by deamidation and decarboxylation reactions, generating various oxidative degradation fragments, and finally breaking the CC, CH, and CN bonds in the fragments, which are eventually mineralized into small molecules. The flocculant is degraded through redox reactions, so that the flocculant molecules are degraded from large molecules to small molecules, reducing their impact on the workability of concrete.

[0020] Preferably, the strong oxidant comprises the following raw materials, calculated by weight: 10 parts of hydrogen peroxide and 30 parts of soluble salt of peroxydisulfate ion.

[0021] Preferably, the soluble salt of peroxodisulfate ion is at least one of potassium persulfate, ammonium persulfate and sodium persulfate.

[0022] By adopting the above technical solution, the strong oxidant is mainly composed of hydrogen peroxide and soluble salt of persulfate ion. Hydrogen peroxide is a common strong oxidant that can effectively oxidize and degrade polyacrylamide. 2+ ) in the presence of persulfate ions, soluble salts can catalyze the decomposition of hydrogen peroxide at room temperature to generate strong oxidizing free radicals (such as SO4· - and ·OH), thereby significantly enhancing the oxidative degradation ability of the system.

[0023] Preferably, the deflocculant comprises the following raw materials, calculated by weight: 20 parts of aminotrimethylenephosphonic acid, 20 parts of polyacrylate, 40 parts of polyethylene glycol, 25 parts of ferrous sulfate, and 300 parts of water.

[0024] By adopting the above technical scheme, aminotrimethylenephosphonic acid (ATMP) reacts with free metal ions (such as Ca 2+ Mg2+ ) to form a stable complex, reducing the competitive binding of metal ions with deflocculants, thereby protecting their dispersion properties. In the presence of ferrous sulfate, ATMP can complex Fe 2+ Delaying its oxidation to Fe 3+ , and inhibit Fe 3+ At appropriate concentrations, ATMP and ferrous sulfate can work synergistically to prolong the 2+ The catalytic life of the catalyst is prolonged, and oxidants such as persulfate are continuously decomposed to generate free radicals. Polyacrylate (PAAS) is a polymer dispersant that is adsorbed on the surface of particles and prevents particle aggregation through electrostatic repulsion and steric hindrance. It interferes with the bridging effect between polyacrylamide (PAM) molecules to prevent re-flocculation of short chains after degradation. Together with ATMP, it maintains the dispersion stability of the system and enhances the anti-flocculation effect. Polyethylene glycol reduces the surface tension of the solution and promotes uniform dispersion of the components of the anti-flocculating agent. It helps the anti-flocculating agent quickly penetrate into the PAM molecules and accelerates the degradation reaction. It improves the dispersion efficiency of PAAS and ATMP and ensures the uniformity of the reaction system. Ferrous sulfate: Fe 2+ Catalyzes the decomposition of persulfate (such as K2S2O8) to generate sulfate radicals (SO4· - ), or form a Fenton system with H2O2 to produce hydroxyl radicals (·OH). Charge neutralization: Fe 2+ Combines with negatively charged PAM molecules, neutralizes their charge, and destroys the flocculant structure. Combines with ATMP to prevent self-oxidation and inactivation, and cooperates with strong oxidants to achieve oxidative chain breakage of PAM. Synergistic mechanism: 1) Dual pathways of oxidative degradation and charge neutralization, oxidative degradation: Ferrous sulfate catalyzes strong oxidants (such as persulfate) to generate free radicals (SO4· - or ·OH), attacking the CC and CN bonds of the PAM molecular chain, breaking the chain into small molecular fragments. Charge neutralization: Fe 2+ Combined with the negatively charged groups (such as carboxylate) of PAM, it destroys its intermolecular bridging effect and reduces the viscosity of the solution. 2) Construction of dispersion and stabilization system: PAAS and ATMP: PAAS prevents degradation products from re-aggregating through steric hindrance, and ATMP chelates free metal ions to avoid system turbidity, jointly maintaining the stability of the reaction system. PHEE accelerates the penetration of deflocculants into PAM through wetting, improving degradation efficiency. 3) Recycling of deflocculants. The degraded wastewater can be finely filtered to remove flocculent precipitation, and can be reused for machine-made sand cleaning after adding a small amount of deflocculant, forming a closed-loop cycle and reducing costs. Through the synergistic effect of multiple components, taking into account both oxidative degradation and physical dispersion, PAM residues in machine-made sand can be efficiently removed, which has significant industrial application value.

[0025] Preferably, the preparation method of the deflocculant is as follows: aminotrimethylenephosphonic acid, polyacrylate, polyethylene glycol, ferrous sulfate and water are added to a reactor according to their mass fractions, mixed evenly, reacted at 45-50° C. for 2-2.5 hours, cooled to room temperature, adjusted the solution pH to 7, and finally concentrated using a rotary evaporator to obtain a deflocculant with a solid content of 45%.

[0026] Preferably, in step S2, the mass ratio of the flocculant degradation agent to the machine-made sand containing the polyacrylamide flocculant washed with the circulating wastewater is 1:8000-12000.

[0027] Preferably, in step S2, the polyacrylamide flocculant is one of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide.

[0028] Preferably, in step S2, the content of polyacrylamide flocculant in the machine-made sand containing polyacrylamide flocculant washed with the circulating wastewater is 0.0002%-0.0020%.

[0029] In summary, the beneficial technical effects of this application are: 1. Improve the quality of machine-made sand: By using flocculant degradation agents to treat machine-made sand containing polyacrylamide flocculants, the amount of flocculant residue in the machine-made sand can be significantly reduced. This helps to improve the quality of machine-made sand and reduce the negative impact on the performance of concrete and mortar.

[0030] 2. Improve concrete performance: Due to the reduction of the residual amount of flocculants in the machine-made sand, the workability and mechanical properties of concrete (such as slump and compressive strength) are improved. This is essential to ensure the stability and durability of the concrete structure.

[0031] 3. Simple operation and low cost: The treatment method provided in this application is simple to operate and easy to implement in actual production. The flocculant degradation agent and strong oxidant used at the same time are low in cost and easy to obtain, which makes the method highly economical.

[0032] 4. Environmentally friendly: The wastewater obtained through fine filtration treatment can be reused in the cleaning process of machine-made sand, which not only reduces the waste of resources but also contributes to environmental protection.

[0033] 5. High flexibility: This method is suitable for the production process and pretreatment of machine-made sand, and has greater flexibility and adaptability. At the same time, compared with the traditional method of adding admixtures to concrete or mortar, the method of this application is more flexible and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings used in the embodiments: Figure 1 This is a schematic diagram of the state of the anionic polyacrylamide flocculant solution in Example 1 after being treated with a degradation agent. DETAILED DESCRIPTION

[0035] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0036] In the following embodiments and preparation examples, 1 part represents 100 g, and the machine-made sand is machine-made sand produced by a dry process with zero flocculant residue.

[0037] Preparation Example 1 Preparation of strong oxidant The preparation method of the strong oxidant is as follows: 10 parts of hydrogen peroxide and 30 parts of potassium persulfate are uniformly mixed to obtain the strong oxidant.

[0038] Preparation Example 2 The antiflocculant comprises the following raw materials by weight: 20 parts of aminotrimethylene phosphonic acid, 20 parts of polyacrylate, 40 parts of polyethylene glycol, 25 parts of ferrous sulfate and 300 parts of water. The preparation method of the antiflocculant is as follows: according to the weight parts, aminotrimethylene phosphonic acid, polyacrylate, polyethylene glycol, ferrous sulfate and water are added into a reactor, mixed evenly, reacted at 48°C for 2.3h, cooled to room temperature, adjusted the solution pH to 7, and finally concentrated by a rotary evaporator to obtain an antiflocculant with a solid content of 45%.

[0039] Example 1 (1) Prepare 1 g / L anionic polyacrylamide solution (flocculant solution), use a rotational viscometer to estimate the viscosity of the flocculant solution, and record the data; (2) Weigh 20 parts of a strong oxidant, 15 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (3) The prepared degradation agent was added to the anionic polyacrylamide solution and stirred thoroughly. After standing for 1 hour, the viscosity of the treated flocculant solution was estimated using a rotational viscometer and the data was recorded. The results are shown in Table 1.

[0040] Example 2 (1) Prepare a 1 g / L cationic polyacrylamide solution (flocculant solution), use a rotational viscometer to estimate the viscosity of the flocculant solution, and record the data; (2) Weigh 30 parts of a strong oxidant, 10 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (3) The prepared degradation agent was added to the cationic polyacrylamide solution and stirred thoroughly. After standing for 1 hour, the viscosity of the treated flocculant solution was estimated using a rotational viscometer and the data was recorded. The results are shown in Table 1.

[0041] Example 3 (1) Prepare 1 g / L nonionic polyacrylamide solution (flocculant solution), use a rotational viscometer to estimate the viscosity of the flocculant solution, and record the data; (2) Weigh 20 parts of a strong oxidant, 10 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (3) The prepared degradation agent was added to the non-ionic polyacrylamide solution and stirred thoroughly. After standing for 1 hour, the viscosity of the treated flocculant solution was estimated using a rotational viscometer and the data was recorded. The results are shown in Table 1.

[0042] Example 4 (1) Prepare 5 mg / L anionic polyacrylamide solution and place it for 24 hours; (2) mixing the anionic polyacrylamide solution and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing anionic polyacrylamide and having a water content of 10%; (3) Weigh 20 parts of a strong oxidant, 15 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (4) According to the mass ratio, 100 parts of flocculant degradation agent were added to 10,000 parts of water, and after being fully stirred, 800,000 parts of machine-made sand containing anionic polyacrylamide were added and mixed. After stirring for 10 minutes, the machine-made sand was separated by coarse filtration to obtain purified machine-made sand, which was left to stand for 1 hour and then dried for use.

[0043] Example 5 (1) Prepare a 5 mg / L cationic polyacrylamide solution and place it for 24 hours; (2) mixing the cationic polyacrylamide solution and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing cationic polyacrylamide and having a water content of 10%; (3) Weigh 30 parts of a strong oxidant, 10 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (4) According to the mass ratio, 100 parts of flocculant degradation agent were added to 10,000 parts of water, and after being fully stirred, 800,000 parts of machine-made sand containing cationic polyacrylamide were added and mixed. After stirring and reacting for 20 minutes, the machine-made sand was separated by coarse filtration to obtain the purified machine-made sand, which was left to stand for 1 hour and then dried for use.

[0044] Example 6 (1) Prepare a 5 mg / L nonionic polyacrylamide solution and place it for 24 hours; (2) mixing the nonionic polyacrylamide and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing nonionic polyacrylamide and having a water content of 10%; (3) Weigh 20 parts of a strong oxidant, 10 parts of a deflocculant, and 100 parts of water, and stir them thoroughly to prepare a flocculant degradation agent; (4) According to the mass ratio, 100 parts of flocculant degradation agent were added to 10,000 parts of water, and after being fully stirred, 800,000 parts of machine-made sand containing non-ionic polyacrylamide were added and mixed. After stirring for 15 minutes, the machine-made sand was separated by coarse filtration to obtain the purified machine-made sand, which was left to stand for 1 hour and then dried for use.

[0045] Comparative Example 1: Blank Control Group Machine-made sand produced by dry process without any treatment (without flocculant).

[0046] Comparative Example 2: (Comparative to Example 4 without flocculant degradation agent treatment) (1) Prepare 5 mg / L anionic polyacrylamide solution and place it for 24 hours; (2) mixing the anionic polyacrylamide solution and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing anionic polyacrylamide and having a water content of 10%; (3) Let it stand for 1 hour and then dry it for later use.

[0047] Comparative Example 3: (Comparative to Example 5 without flocculant degradation agent treatment) (1) Prepare a 5 mg / L cationic polyacrylamide solution and place it for 24 hours; (2) mixing the cationic polyacrylamide solution and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing cationic polyacrylamide and having a water content of 10%; (3) Let it stand for 1 hour and then dry it for later use.

[0048] Comparative Example 4: (Comparative to Example 6 without flocculant degradation agent treatment) (1) Prepare a 5 mg / L nonionic polyacrylamide solution and place it for 24 hours; (2) mixing the nonionic polyacrylamide and the machine-made sand in a mass ratio of 1:10 to prepare machine-made sand containing nonionic polyacrylamide and having a water content of 10%; (3) Let it stand for 1 hour and then dry it for later use.

[0049] Performance Testing The viscosity of the flocculant solution before and after treatment is compared in Examples 1 to 3. The results are shown in Table 1. The state of the solution after treatment in Example 1 is shown in Table 1. Figure 1 .

[0050] The processed machine-made sand obtained in Examples 4 to 6 and Comparative Examples 1 to 4 were respectively subjected to concrete tests to test the slump and slump loss over time of the concrete and the compressive strength of the formed test blocks. The concrete mix ratio is shown in Table 2, and the test results are shown in Table 3.

[0051] Compressive strength: Tested in accordance with the relevant provisions of GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete"; Slump: The test is carried out in accordance with the slump determination method specified in GB / T50080-2002.

[0052] Table 1 Comparison of viscosity of flocculant solution before and after treatment Table 2 Concrete mix ratio (kg / m 3 ) cement Mineral powder Fly ash Machine-made sand stone water Water reducing agent 220 50 50 830 1020 164.2 6.4 Table 3 Concrete test results project Slump(mm) 1h slump (mm) 28d compressive strength (MPa) Comparative Example 1 230 200 52.2 Comparative Example 2 200 140 45.5 Comparative Example 3 200 130 46.2 Comparative Example 4 210 160 47.4 Example 4 230 200 52.0 Example 5 225 200 51.5 Example 6 230 200 52.3 Analyzing the data in Table 1, we can see that: The flocculant degradation agent prepared by the present application has a good degradation effect on anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide. The viscosity of the solution before and after the flocculant degradation agent is used is very different. The flocculant degradation agent can effectively reduce the viscosity of the flocculant solution. The flocculant degradation agent has the best degradation effect on anionic polyacrylamide, the second best effect on nonionic polyacrylamide, and the worst effect on cationic polyacrylamide, but it can still reach more than 85%.

[0053] Combined with Table 1, Figure 1 As shown, Example 1 shows that after adding the flocculant degradation agent and stirring evenly, flocculent precipitates are generated in the solution and the viscosity of the solution is reduced, indicating that the flocculant degradation agent has a good treatment effect on the flocculant.

[0054] Analyzing the data in Table 3, we can see that: 1) The manufactured sand concrete (such as Comparative Examples 2-4) prepared by using the manufactured sand containing flocculants without flocculant degradation agent treatment is significantly inferior to the manufactured sand concrete (such as Comparative Example 1) in terms of working performance and mechanical properties, which is specifically manifested in that the slump of the concrete is significantly reduced, the slump loss over time is increased, and the compressive strength after molding is reduced. These results clearly show that polyacrylamide flocculants have a significant negative impact on the working performance and mechanical properties of concrete, and compared with non-ionic polyacrylamide, the negative impact of ionic polyacrylamide on concrete performance is more significant.

[0055] 2) The machine-made sand treated with the flocculant degradation agent prepared by the present application, the obtained machine-made sand concrete (such as Example 4-Example 6) showed better slump and slump loss characteristics over time, and compared with the machine-made sand concrete (such as Comparative Example 2-Comparative Example 4) prepared by the machine-made sand not treated with the flocculant degradation agent, the slump was significantly improved, and the slump loss over time was also significantly reduced. In addition, the compressive strength of the machine-made sand concrete treated with the flocculant degradation agent after molding is basically consistent with that of the blank control group (such as Comparative Example 1), showing the effectiveness of the flocculant degradation agent treatment and ensuring the long-term stability of the concrete. These results not only prove that the flocculant degradation agent provided by the present application can effectively destroy the flocculant flocculation structure, weaken the bridging effect between flocculant molecules, and significantly reduce its adsorption on cement particles and water reducers. The method of the present application fundamentally solves the problem of flocculant residue and greatly reduces its negative impact on concrete performance.

[0056] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the protection scope of the present application.

Claims

1. A method for removing flocculant residues in wet sand making, characterized in that: The following steps are involved: S1. preparing a flocculant degradation agent: mixing a strong oxidant, an antiflocculant and water according to parts by mass and stirring them sufficiently until they are completely dissolved to obtain a flocculant degradation agent; S2. Use of flocculant degradation agent: according to the mass ratio, the flocculant degradation agent and the machine-made sand containing polyacrylamide flocculant washed with circulating wastewater are mixed, stirred for reaction for 10-20 minutes, and then coarsely filtered and separated to obtain machine-made sand and mixed wastewater; S3. Fine filtration treatment and reuse: The mixed wastewater is finely filtered and separated to remove the wastewater containing a small amount of flocculent precipitate generated by the reaction of polyacrylamide flocculants and flocculant degraders. The flocculant degrader can be added to the obtained wastewater and can be used for repeated cleaning of machine-made sand to remove polyacrylamide flocculant residues.

2. A method for removing flocculant residues in wet sand making according to claim 1, characterized in that: In step S1, the flocculant degradation agent includes the following raw materials by weight: 20-50 parts of a strong oxidant, 10-30 parts of an anti-flocculant, and 100 parts of water.

3. A method for removing flocculant residues in wet sand making according to claim 2, characterized in that: The strong oxidant comprises the following raw materials, calculated by weight: 10 parts of hydrogen peroxide and 30 parts of soluble salt of peroxydisulfate ion.

4. A method for removing flocculant residues in wet sand making according to claim 3, characterized in that: The soluble salt of persulfate ion is at least one of potassium persulfate, ammonium persulfate and sodium persulfate.

5. A method for removing flocculant residues in wet sand making according to claim 2, characterized in that: The antiflocculant comprises the following raw materials, calculated by weight: 20 parts of aminotrimethylenephosphonic acid, 20 parts of polyacrylate, 40 parts of polyethylene glycol, 25 parts of ferrous sulfate, and 300 parts of water.

6. A method for removing flocculant residues in wet sand making according to claim 4, characterized in that: The preparation method of the deflocculant is as follows: aminotrimethylenephosphonic acid, polyacrylate, polyethylene glycol, ferrous sulfate and water are added into a reactor according to their mass fractions, mixed evenly, reacted at 45-50° C. for 2-2.5 hours, cooled to room temperature, adjusted the solution pH to 7, and finally concentrated by a rotary evaporator to obtain a deflocculant with a solid content of 45%.

7. A method for removing flocculant residues in wet sand making according to claim 1, characterized in that: In step S2, the mass ratio of the flocculant degradation agent to the machine-made sand containing polyacrylamide flocculants washed with circulating wastewater is 1:8000-12000.

8. The method for removing flocculant residue in wet sand making according to claim 1, characterized in that: In step S2, the polyacrylamide flocculant is one of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide.

9. A method for removing flocculant residues in wet sand making according to claim 1, characterized in that: In step S2, the content of polyacrylamide flocculant in the machine-made sand containing polyacrylamide flocculant washed with the circulating wastewater is 0.0002%-0.0020%.

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