Method for removing residual polyacrylamide flocculants in circulating water of wet sand making

Abstract

The present application relates to the field of building sand, mortar and concrete, and particularly relates to a method for removing residual polyacrylamide flocculants in wet sand making circulating water. The method comprises the following steps: adding layered reagent solution into the wet sand making circulating water, stirring, standing, taking the upper liquid, adding oxidizing agent solution and first reducing agent solution, stirring to obtain a mixed solution, adjusting the pH of the mixed solution to be acidic, stirring, taking the upper floating matter, standing, and obtaining the wet sand making circulating water after removing the polyacrylamide flocculants. The present application uses layered reagents to flocculate, stratify and concentrate the polyacrylamide flocculants with different charge properties, and then carries out a ternary catalytic oxidation-reduction reaction in the concentrated solution. In this way, the polyacrylamide flocculants can be degraded and separated quickly and at low cost under mild conditions, the content of the flocculants in the circulating water is effectively reduced, and the problem of residual flocculants in the sand is fundamentally solved.

Description

Technical Field

[0001] This invention relates to the fields of building sand, mortar, and concrete, and particularly to a method for removing residual polyacrylamide flocculant from circulating water in wet sand production. Background Technology

[0002] With increasingly stringent environmental regulations, wet sand-making processes can only use circulating water for sand washing. To improve the utilization rate of circulating water, charged polyacrylamide (PAM) flocculants are generally used to accelerate the sedimentation of suspended solids in the wastewater. However, the circulating water after flocculation and sedimentation typically retains 0-0.05% flocculant. If this flocculant is used again for sand washing, it inevitably adheres to the sand surface. Many researchers have found that the residual flocculant in washed sand negatively impacts the fluidity and slump retention of concrete, and also reduces compressive strength.

[0003] To mitigate the side effects of flocculant residue on sand, many researchers have conducted studies on: (1) Direct washing method: This method uses water to physically wash the sand, but it can only remove free PAM, and the washing process introduces a large amount of water, which does not meet the requirements of water conservation and environmental protection. (2) Low-pressure mercury lamp irradiation method: The sand with flocculant is conveyed to a mixing chamber made of wear-resistant steel. During the conveying process, a low-temperature mercury lamp is turned on to irradiate the manufactured sand on the conveyor belt. This method is used to treat sand entering the construction site. This method is simple to operate, but it is not completely removed due to the influence of the intensity of mercury lamp irradiation and the conveying speed. (3) Strong oxidant oxygen decomposition method: Under the chemical action of strong oxidants such as ozone, the flocculant gradually separates and decomposes from the surface of the sand. However, this method requires the use of a lot of strong oxidizing substances, which has adverse effects on instruments, equipment and environment. In summary, existing methods for removing residual flocculants in wet sand making have drawbacks such as low efficiency, incomplete removal, and involvement of strong oxidizing substances. Therefore, it is necessary to develop a new method for removing residual polyacrylamide flocculants from circulating water in wet sand making. Summary of the Invention

[0004] In order to solve the technical problems existing in the prior art, the purpose of this invention is to provide a method for removing residual polyacrylamide flocculant in the circulating water of wet sand making to solve the above-mentioned technical problems.

[0005] This invention addresses the aforementioned problems by providing a method for removing residual polyacrylamide flocculants from circulating water in wet sand production. This method effectively separates and degrades residual flocculants in the circulating water. First, a stratification reagent is used to concentrate the flocculants in the circulating water. While rapidly releasing over 90% of the circulating water for production, the flocculant concentration is concentrated, significantly reducing the amount of degradation reagent used and improving the efficiency of degradation and separation. After adding the flocculant concentrate to a ternary catalytic redox system, the polyacrylamide flocculants are rapidly degraded and separated. Circulating water treated by this method can be used normally for sand production, and the sand produced does not exhibit the side effects of decreased concrete workability and deteriorated mechanical properties caused by flocculants.

[0006] According to a first aspect of the present invention, the present invention provides a method for removing residual polyacrylamide flocculant from circulating water in wet sand making; the method includes the following steps: (1) Preparation of flocculant concentrate: Add a layering reagent solution to the wet sand making circulating water containing residual polyacrylamide flocculant, stir and treat, stop stirring and let stand, take the upper layer liquid (the upper layer of clear water can be discharged through a separating funnel, separating tank or other separating device) to obtain flocculant concentrate. (2) Flocculant separation and degradation: The oxidant is prepared into a solution to obtain an oxidant solution; the first reducing agent is prepared into a solution to obtain a first reducing agent solution; the oxidant solution and the first reducing agent solution are added to the flocculant concentrate in step (1), and a first stirring treatment is performed to obtain a mixed solution; the second reducing agent is added to adjust the pH of the mixed solution to acidity, and a second stirring treatment is performed; after using a mesh with a pore size of 100-400 mesh to remove the floating matter on the upper layer of the mixed solution, a third stirring treatment is performed to obtain wet sand making circulating water after removing polyacrylamide flocculant.

[0007] In some embodiments, the polyacrylamide flocculant in step (1) is an anionic polyacrylamide flocculant or a cationic polyacrylamide flocculant, and the relative molecular mass of the polyacrylamide flocculant is 1 million to 20 million.

[0008] In some embodiments, the stratification reagent in step (1) is at least one of sodium polyacrylate, polydiallyldimethylammonium chloride and polyethyleneimine; the mass percentage concentration of the stratification reagent solution is 0.3-0.5 wt%; and the dosage of the stratification reagent solution is 0.2-1 wt% of the mass of the wet sand making circulating water containing residual polyacrylamide flocculant.

[0009] In some embodiments, when the polyacrylamide flocculant in the wet sand making circulating water containing residual polyacrylamide flocculant is cationic polyacrylamide, sodium polyacrylate is selected as the stratification agent; when the polyacrylamide flocculant in the wet sand making circulating water containing residual polyacrylamide flocculant is anionic polyacrylamide, polydiallyldimethylammonium chloride and / or polyethyleneimine are selected as the stratification agent. In some embodiments, when the polyacrylamide flocculant in the wet sand-making circulating water containing residual polyacrylamide flocculant is anionic polyacrylamide, polydiallyldimethylammonium chloride is selected as the stratification agent. Polydiallyldimethylammonium chloride has a better stratification effect.

[0010] Furthermore, to ensure the effectiveness of the stratification reagent, it is advisable to dissolve it in advance into a solution with a mass concentration of 0.3% to 0.5%. Adding the stratification reagent to the sand washing circulating water containing flocculant can, on the one hand, directly further concentrate the flocculant content in the solution, quickly obtaining clean water suitable for manufactured sand production and improving production efficiency; on the other hand, the concentrated flocculant solution requires less degradation material under high concentration conditions, resulting in lower cost and higher efficiency in flocculant separation and degradation.

[0011] In some embodiments, the sodium polyacrylate has a relative molecular weight of 1 million to 10 million; the polydiallyldimethylammonium chloride has a relative molecular weight of not less than 400,000; and the polyethyleneimine has a relative molecular weight of 5,000 to 10,000.

[0012] In some embodiments, the stirring time in step (1) is 30-60s, the stirring speed is 200-300 r / min, and the settling time is 5-10min.

[0013] In some embodiments, the oxidant solution in step (2) is at least one of hydrogen peroxide solution, ammonium persulfate solution, sodium persulfate solution, potassium permanganate solution, and potassium persulfate solution; the mass percentage concentration of the oxidant solution is 6-8 wt%; the oxidant solution has a strong oxidizing effect and can generate active free radicals to decompose the flocculant molecules in the aqueous solution.

[0014] In some embodiments, the amount of oxidant solution added in step (2) is 0.5-1 wt% of the mass of the wet sand making circulating water containing the residual polyacrylamide flocculant in step (1).

[0015] In some embodiments, in step (2), the first reducing agent solution is at least one of vitamin C solution, sodium sulfite solution, sodium thiosulfate solution, and sodium dithionite solution; the mass percentage concentration of the first reducing agent solution is 6-8 wt%; and the mass ratio of the oxidant solution to the first reducing agent solution is 1:07-1:1. The first reducing agent solution can enhance the activity of the oxidant, enabling it to decompose into highly active free radicals under normal temperature (0℃~40℃) and low concentration conditions.

[0016] In some embodiments, the rotation speed of the first stirring treatment in step (2) is 200~400 r / min, and the time of the first stirring treatment is 1-3 min.

[0017] In some embodiments, in step (2), the second reducing agent is at least one of ferrous sulfate, ferrous chloride and ferrous ammonium sulfate; after adding the second reducing agent, the pH of the mixture is adjusted to 5.0-6.5.

[0018] In some embodiments, the second reducing agent in step (2) is one or two of ferrous sulfate, ferrous chloride, and ferrous ammonium sulfate. The second reducing agent has catalytic, pH adjustment, and flocculation effects. On the one hand, it can further enhance the oxidation activity of degradation component A. On the other hand, it can lower the pH in the solution system, further enhancing the oxidation activity of degradation component A and significantly improving its efficiency in decomposing polyacrylamide flocculant. In addition, the second reducing agent has the function of agglomerating polyacrylamide.

[0019] In some embodiments, the rotation speed of the second stirring process in step (2) is 5~100 r / min, and the stirring time is 3-10 min.

[0020] In some embodiments, the rotation speed of the third stirring process in step (2) is 5~100 r / min, and the time of the third stirring process is 15-30 min.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The method provided by the present invention has significant effects on improving processing and production efficiency: The method of the present invention uses a stratification reagent to quickly flocculate and stratify polyacrylamide in circulating water, and can quickly put more than 90% of the circulating water into the production process within half an hour, which helps to improve production efficiency.

[0022] 2) The method provided by this invention uses low reagent dosage and mild reaction conditions: Compared with direct degradation, the flocculant is concentrated first and then separated and degraded. A low-concentration ternary redox system is used to rapidly separate and decompose the concentrate, which can significantly reduce the amount of decomposition reagent. The reaction can be carried out at room temperature (0℃~40℃), normal pressure and weak acid pH conditions without the need for high temperature and high pressure equipment.

[0023] 3) The ternary catalytic redox system used in the method provided in this embodiment of the invention has high selectivity of components: degradation component A can be selected from hydrogen peroxide, ammonium sulfate, etc., degradation component B can use a variety of inexpensive and readily available reagents such as vitamin C and sodium thiosulfate, and degradation component C can be ferrous sulfate, ferrous chloride, and ferrous ammonium sulfate. The system has wide adaptability to raw materials and can flexibly combine different redox pairs according to the water quality characteristics. Detailed Implementation

[0024] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below.

[0025] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] In some embodiments, before determining the charge properties of the polyacrylamide flocculant in the wet sand-making circulating water containing residual polyacrylamide flocculant, two 100 g cups of wet sand-making circulating water containing residual polyacrylamide flocculant are weighed simultaneously, and 5 g of 1wt% sodium polyacrylate and polydiallyldimethylammonium chloride (or polyethyleneimine) solution are added respectively. If the former shows a stratification reaction, the flocculant is cationic; if the addition of the other two reagents (polydiallyldimethylammonium chloride and / or polyethyleneimine) causes stratification, the flocculant is anionic.

[0027] In order to ensure the actual effect and the accuracy of the data, the following examples and comparative examples took water that had been soaked in sand for 24 hours, added a precisely prepared flocculant solution, mixed it evenly, and treated the resulting mixture as a wet sand making circulating water sample with residual polyacrylamide flocculant to simulate real wet sand making circulating water.

[0028] Example 1 S1. Preparation of flocculant concentrate: Take 10 kg of wet sand-making circulating water containing residual polyacrylamide flocculant (anionic polyacrylamide with a molecular weight of 1 million and a mass percentage concentration of 0.05 wt%), add 20 g of polydiallyldimethylammonium chloride solution with a mass percentage concentration of 0.3 wt% (molecular weight of 400,000), stir, and let stand for 6 min at a speed of 200 r / min for 30 s to allow the liquid to separate into layers; S2. Separation of flocculant concentrate: Take the upper layer of clear water to obtain 0.83 kg of flocculant concentrate; S3. Preparation of degradation components: Hydrogen peroxide is prepared into a 6 wt% solution as the oxidant solution (degradation component A); Vitamin C is prepared into a 6 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 50 g of degradation component A and 50 g of degradation component B to 0.83 kg of flocculant concentrate. Stir for 3 min at a stirring speed of 200 r / min. Then add 5 g of ferrous sulfate solid (degradation component C). Continue stirring for 3 min at a stirring speed of 50 r / min. Use a 100-mesh screen to remove the floating matter from the upper layer of the suspension. Continue stirring for 15 min at a stirring speed of 50 r / min to complete the separation and degradation of the flocculant, obtaining wet sand making circulating water after removing polyacrylamide flocculant.

[0029] Example 2 S1. Preparation of flocculant concentrate: Take 10 kg of wet sand-making circulating water containing residual polyacrylamide flocculant (anionic polyacrylamide with a molecular weight of 10 million and a mass percentage concentration of 0.03 wt%), add 100 g of polyethyleneimine (molecular weight of 5000) solution with a mass percentage concentration of 0.5 wt%, stir at a speed of 250 r / min for 45 s, and let stand for 8 min to allow the liquid to separate into layers; S2. Separation of flocculant concentrate: Take the upper layer of clear water to obtain 0.93 kg of flocculant concentrate; S3. Preparation of degradation components: Ammonium persulfate is prepared into a 10 wt% solution as the oxidant solution (degradation component A); sodium sulfite is prepared into a 7 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 60g of degradation component A and 60g of degradation component B to 0.93kg of flocculant concentrate. After stirring for 2 minutes at a stirring speed of 300 r / min, add 6g of ferrous chloride solid (degradation component C). Continue stirring for 5 minutes at a stirring speed of 75 r / min. After using a 300-mesh screen to remove the floating matter on the upper layer of the suspension, continue stirring for 20 minutes at a stirring speed of 75 r / min. This completes the separation and degradation of the flocculant, yielding wet sand making circulating water after removing the polyacrylamide flocculant.

[0030] Example 3 S1. Preparation of flocculant concentrate: Take 10 kg of wet sand-making circulating water containing residual polyacrylamide flocculant (anionic polyacrylamide with a molecular weight of 2 million and a mass percentage concentration of 0.01 wt%), add 50 g of polyethyleneimine (molecular weight of 10000) solution with a mass percentage concentration of 0.5%, stir for 60 s at a speed of 300 r / min, and let stand for 10 min to allow the liquid to separate into layers; S2. Separation of flocculant concentrate: The upper layer of clear water is discharged to obtain 0.90 kg of flocculant concentrate; S3. Preparation of degradation components: Potassium permanganate was prepared into a 7 wt% solution as the oxidant solution (degradation component A); sodium thiosulfate was prepared into a 7 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 70 g of degradation component A and 70 g of degradation component B to 0.90 kg of flocculant concentrate. After stirring for 3 min at a stirring speed of 400 r / min, add 5 g of ferrous ammonium sulfate solid (degradation component C). Continue stirring for 10 min at a stirring speed of 100 r / min. After using a 400-mesh screen to remove the floating matter on the upper layer of the suspension, continue stirring for 30 min at a stirring speed of 100 r / min. This completes the separation and degradation of the flocculant, yielding wet sand making circulating water after removing the polyacrylamide flocculant.

[0031] Example 4 S1. Preparation of flocculant concentrate: Take 10 kg of residual polyacrylamide flocculant in wet sand making circulating water (cationic polyacrylamide with a molecular weight of 1 million and a mass percentage concentration of 0.04 wt%), add 60 g of sodium polyacrylate (1 million) solution with a mass percentage concentration of 0.5%, stir for 45 s at a speed of 250 r / min, and let stand for 8 min to allow the liquid to separate into layers; S2. Separation of flocculant concentrate: Take the upper layer of clear water to obtain 0.91 kg of flocculant concentrate; S3. Preparation of degradation components: Hydrogen peroxide is prepared into a 7 wt% solution as the oxidant solution (degradation component A); Vitamin C is prepared into a 7 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 50 g of degradation component A and 45 g of degradation component B to 0.91 kg of flocculant concentrate. After stirring for 2 min at a stirring speed of 300 r / min, add 5 g of ferrous sulfate solid (degradation component C). Continue stirring for 5 min at a stirring speed of 75 r / min. After using a 300-mesh screen to remove the floating matter on the upper layer of the suspension, continue stirring for 20 min at a stirring speed of 75 r / min. This completes the separation and degradation of the flocculant, yielding wet sand making circulating water after removing the polyacrylamide flocculant.

[0032] Example 5 S1. Preparation of flocculant concentrate: Take 10 kg of residual polyacrylamide flocculant in wet sand making circulating water (cationic polyacrylamide with a molecular weight of 20 million and a mass percentage concentration of 0.01 wt%), add 50 g of sodium polyacrylate (5 million) solution with a mass percentage concentration of 0.3%, stir at a speed of 250 r / min for 45 s, and let stand for 8 min to allow the liquid to separate into layers; S2. Separation of flocculant concentrate: Take the upper layer of clear water to obtain 0.92 kg of flocculant concentrate; S3. Preparation of degradation components: Hydrogen peroxide is prepared into a 7 wt% solution as the oxidant solution (degradation component A); Vitamin C is prepared into a 7 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 50 g of degradation component A and 45 g of degradation component B to 0.92 kg of flocculant concentrate. After stirring for 2 min at a stirring speed of 300 r / min, add 7 g of ferrous sulfate solid (degradation component C). Continue stirring for 5 min at a stirring speed of 75 r / min. After using a 300-mesh screen to remove the floating matter on the upper layer of the suspension, continue stirring for 20 min at a stirring speed of 75 r / min. This completes the separation and degradation of the flocculant, yielding wet sand making circulating water after removing the polyacrylamide flocculant.

[0033] Example 6 S1. Preparation of flocculant concentrate: Take 10 kg of wet sand-making circulating water containing residual polyacrylamide flocculant (cationic polyacrylamide with a molecular weight of 20 million and a mass percentage concentration of 0.01 wt%), add 50 g of sodium polyacrylate (20 million) solution with a mass percentage concentration of 0.3 wt%, and stir. Stir at 250 r / min for 45 s and let stand for 8 min to allow the liquid to separate into layers. S2. Separation of flocculant concentrate: Take the upper layer of clear water to obtain 0.89 kg of flocculant concentrate; S3. Preparation of degradation components: Hydrogen peroxide is prepared into a 7 wt% solution as the oxidant solution (degradation component A); Vitamin C is prepared into a 7 wt% solution as the first reducing agent solution (degradation component B). S4. Flocculant Separation and Degradation: Add 55 g of degradation component A and 45 g of degradation component B to 0.89 kg of flocculant concentrate. After stirring for 2 min at a stirring speed of 300 r / min, add 10 g of ferrous sulfate solid (degradation component C). Continue stirring for 5 min at a stirring speed of 75 r / min. After using a 300-mesh screen to remove the floating matter on the upper layer of the suspension, continue stirring for 20 min at a stirring speed of 75 r / min. This completes the separation and degradation of the flocculant, yielding wet sand making circulating water after removing the polyacrylamide flocculant.

[0034] Comparative Example 1 Except for the absence of the flocculant concentrate preparation process in S1, everything else is the same as in Example 2.

[0035] Comparative Example 2 Except for the absence of step S1 and the difference in step S4, it is the same as in Example 2. Step S4 of Comparative Example 2 is described below.

[0036] S4. Flocculant Separation and Degradation: Add 420g of degradation component A and 420g of degradation component B to 10kg of flocculant concentrate. Stir for 2 minutes at a stirring speed of 300 r / min. Then add 48g of ferrous chloride solid and continue stirring for 5 minutes at a stirring speed of 75 r / min. After removing the floating matter on the upper layer of the suspension using a 300-mesh screen, continue stirring for 20 minutes at a stirring speed of 75 r / min to complete the separation and degradation of the flocculant.

[0037] Comparative Example 3 Except for the absence of degradation component A, it is the same as in Example 2.

[0038] Comparative Example 4 Except for the absence of degradation component B, it is the same as in Example 2.

[0039] Comparative Example 5 Except for the absence of degradation component C, it is the same as in Example 2.

[0040] Effect verification The above embodiments and comparative examples underwent performance testing, and the testing methods are as follows: The viscosity of the aqueous solution containing flocculant was measured using a rotational viscometer.

[0041] Before the concrete test, sand was soaked in different circulating water for 24 hours, then filtered and allowed to air dry naturally before being used as samples for testing. The mix proportion (mass ratio) for the C30 concrete test was m(cement):m(mineral powder):m(fly ash):m(sand):m(aggregate):m(water):m(admixture) = 210:60:60:780:1040:165:6.5. The admixture was WIN-105 polycarboxylate high-performance water-reducing agent produced by Guangzhou Academy of Building Research Group Co., Ltd. The slump and spread of the concrete were determined according to GB / T 50080 "Test Method for Performance of Ordinary Concrete Mixtures"; the compressive strength test was conducted according to GB / T 50081 "Standard for Test Method for Mechanical Properties of Ordinary Concrete". The results are shown in Table 1 below. The blank group in Table 1 used sand that had been soaked in pure water for 24 hours, filtered, and then air-dried as samples for testing.

[0042] Table 1 Table 1 shows that in Example 1, the viscosity of the circulating water before and after treatment was 38 mPa·s and 1.1 mPa·s, respectively, indicating that the water contained a large amount of flocculant before treatment, hence the higher viscosity. The slump of the concrete before and after treatment was 210 mm and 215 mm, respectively, and the 28-day compressive strength was 36.2 MPa and 38.3 MPa, respectively, indicating that not treating the circulating water would lead to a decrease in the slump and compressive strength of the concrete. In Example 2, the viscosity of the circulating water before and after treatment was 460 mPa·s and 1.2 mPa·s, respectively, showing a greater difference in viscosity and a more significant treatment effect. The corresponding concrete slump was 160 mm and 215 mm, respectively, and the 28-day compressive strength was 28.4 MPa and 37.9 MPa, respectively. This indicates that the viscosity of the circulating water was very high before treatment, indicating a high flocculant content, while the viscosity of the treated circulating water decreased significantly, indicating a low flocculant content. In terms of concrete performance, not treating the circulating water would lead to a significant decrease in the slump and a sharp decrease in the compressive strength of the concrete. Similarly, the data comparison of Examples 3-6 also shows a significant decrease in the viscosity of the treated circulating water, indicating a substantial reduction in flocculant content. Consequently, the concrete performance also recovers to near the level of the control group. Comparing Comparative Example 1 with Example 2 demonstrates that the absence of S1 in the flocculant concentrate preparation process affects the flocculant separation and degradation, ultimately failing to effectively improve the workability and mechanical properties of the concrete. Comparing Comparative Example 2 with Example 2 shows that without the addition of the stratification reagent to the circulating water, 6 times the amount of degradation components A and B, and 8 times the amount of degradation component C, are required to achieve the same treatment effect as in Example 2. This further illustrates that the addition of the stratification reagent can significantly reduce the amount of degradation components used, making the separation and degradation of flocculants more cost-effective and efficient. Comparing Comparative Examples 3-4 with Example 2 reveals that the absence of degradation components A, B, and C all affect the flocculant separation and degradation, causing the circulating water content to remain at a high level, ultimately leading to poor concrete workability and a decline in the performance of hardened concrete.

[0043] In summary, the method of this invention directly separates and degrades residual flocculants in circulating water. By using a stratification reagent to concentrate the flocculants in the circulating water, over 90% of the circulating water is rapidly released for production while simultaneously concentrating the flocculant concentration, significantly reducing the amount of degradation components required and improving the efficiency of degradation and separation. After adding the flocculant concentrate to the ternary catalytic redox system, the polyacrylamide flocculant is rapidly degraded and separated. Circulating water treated by this method can be used normally for sand production, and the produced sand does not exhibit the side effects of decreased concrete workability and deterioration of mechanical properties caused by flocculants.

[0044] 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 method for removing residual polyacrylamide flocculant from circulating water in wet sand making, characterized in that, Includes the following steps: (1) Add a layering reagent solution to the wet sand making circulating water containing residual polyacrylamide flocculant, stir and let stand, take the upper liquid to obtain flocculant concentrate. (2) Add an oxidant solution and a first reducing agent solution to the flocculant concentrate in step (1), perform a first stirring treatment to obtain a mixture, add a second reducing agent to adjust the pH of the mixture to acidic, perform a second stirring treatment, remove the floating matter on the upper layer of the mixture, and perform a third stirring treatment to obtain wet sand making circulating water after removing polyacrylamide flocculant. The stratification reagent in step (1) is at least one of sodium polyacrylate, polydiallyldimethylammonium chloride, and polyethyleneimine; the mass percentage concentration of the stratification reagent solution is 0.3-0.5 wt%; the dosage of the stratification reagent solution is 0.2-1 wt% of the mass of the wet sand-making circulating water containing residual polyacrylamide flocculant. The oxidant solution in step (2) is at least one of hydrogen peroxide solution, ammonium persulfate solution, sodium persulfate solution, potassium permanganate solution, and potassium persulfate solution; the mass percentage concentration of the oxidant solution is 6-8 wt%; the dosage of the oxidant solution in step (2) is 0.5-1 wt% of the mass of the wet sand making circulating water containing the residual polyacrylamide flocculant in step (1); Step (2) The first reducing agent solution is at least one of vitamin C solution, sodium sulfite solution, sodium thiosulfate solution and sodium dithionite solution; the mass percentage concentration of the first reducing agent solution is 6-8 wt%; the mass ratio of the oxidizing agent solution to the first reducing agent solution is 1:0.7-1:1; Step (2) The second reducing agent is at least one of ferrous sulfate, ferrous chloride and ferrous ammonium sulfate.

2. The method for removing residual polyacrylamide flocculant in circulating water during wet sand making according to claim 1, characterized in that, The polyacrylamide flocculant in step (1) is an anionic polyacrylamide flocculant or a cationic polyacrylamide flocculant, and the relative molecular mass of the polyacrylamide flocculant is 1 million to 20 million.

3. The method for removing residual polyacrylamide flocculant in circulating water during wet sand making according to claim 1, characterized in that, The sodium polyacrylate has a relative molecular weight of 1 million to 10 million; the polydiallyldimethylammonium chloride has a relative molecular weight of not less than 400,000; and the polyethyleneimine has a relative molecular weight of 5,000 to 10,000.

4. The method for removing residual polyacrylamide flocculant in circulating water during wet sand making according to claim 1, characterized in that, The stirring time in step (1) is 30-60s, the stirring speed is 200-300 r / min, and the settling time is 5-10min.

5. The method for removing residual polyacrylamide flocculant in circulating water during wet sand making according to claim 1, characterized in that, After adding the second reducing agent in step (2), the pH of the mixture is adjusted to 5.0-6.

5.

6. The method for removing residual polyacrylamide flocculant in circulating water during wet sand making according to claim 1, characterized in that, In step (2), the speed of the first stirring treatment is 200~400 r / min, and the time of the first stirring treatment is 1-3 min.

7. The method for removing residual polyacrylamide flocculant from circulating water in wet sand making according to any one of claims 1-6, characterized in that, In step (2), the second stirring treatment has a rotation speed of 5~100 r / min and a stirring time of 3-10 min; the third stirring treatment has a rotation speed of 5~100 r / min and a stirring time of 15-30 min.

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