Composite flocculant for tunnel construction wastewater treatment and preparation method thereof

Abstract

This invention relates to the field of water treatment technology, specifically to a composite flocculant for treating tunnel construction wastewater and its preparation method. The method includes the following steps: preparing tertiary amine acrylate by reacting triethanolamine with isocyanate methacrylate; preparing polyethylene glycol-modified quaternary ammonium acrylate by reacting the tertiary amine acrylate with methoxy-polyethylene glycol-chloride; further preparing a modifier by reacting with methyldichlorosilane; and compounding the modifier with a mixed solution of hydrotalcite, sodium silicate, and iron-magnesium-calcium compounds to prepare the composite flocculant. This flocculant achieves efficient flocculation and pH adjustment through mechanisms such as charge neutralization and adsorption bridging. It features rapid aggregation of suspended particles, reduced sludge production, improved floc density, and enhanced dewatering performance. It is suitable for treating high-concentration suspended solids and alkaline wastewater, exhibiting comprehensive advantages of high efficiency, economy, and environmental friendliness, meeting the on-site treatment needs of tunnel construction wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a composite flocculant for tunnel construction wastewater treatment and a preparation method thereof. Background Art

[0002] A large amount of wastewater is generated during tunnel construction, which contains high concentrations of suspended matter, sediment particles and alkaline substances. If these wastewaters are discharged directly without treatment, they will not only cause serious pollution to the surrounding environment, but may also affect the ecological balance of water bodies and even endanger human health. Therefore, how to efficiently treat tunnel construction wastewater, reduce its suspended matter content, adjust the pH value and reduce sludge production has become an urgent problem to be solved in the current wastewater treatment field.

[0003] Traditional methods for treating tunnel construction wastewater mainly rely on inorganic flocculants (such as polyaluminium chloride, aluminium sulfate, etc.) or organic polymer flocculants (such as polyacrylamide). Although inorganic flocculants are low-cost, their flocculation effect is limited and they are prone to produce a large amount of sludge, which increases the cost of subsequent treatment. Although organic polymer flocculants have a good flocculation effect, they have a weak ability to adjust the pH of wastewater and are prone to floc instability in wastewater with high concentrations of suspended matter. In addition, a single type of flocculant is difficult to simultaneously meet the comprehensive needs of efficient flocculation, pH adjustment and reduction of sludge production.

[0004] In recent years, composite flocculants have gradually become a research hotspot. By combining inorganic flocculants, organic polymer flocculants and acid-base regulating components, the flocculation efficiency can be significantly improved by utilizing various mechanisms such as electrical neutralization and adsorption bridging. However, existing composite flocculants still have some shortcomings in practical applications, such as the treatment effect on high-concentration suspended solids wastewater is not ideal, the floc density and dewatering performance are poor, resulting in high sludge production. In addition, the preparation process of existing composite flocculants is relatively complicated and the cost is high, which makes it difficult to meet the needs of on-site treatment of tunnel construction wastewater. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose a composite flocculant for tunnel construction wastewater treatment and a preparation method thereof, so as to provide an efficient, economical and environmentally friendly composite flocculant to solve the problem of tunnel construction wastewater treatment.

[0006] Based on the above purpose, the present invention provides a method for preparing a composite flocculant for tunnel construction wastewater treatment, comprising the following steps:

[0007] (1) Add triethanolamine and isocyanoethyl methacrylate to dichloromethane, stir at room temperature for 10-14 hours, and then transfer to n-hexane to precipitate an oily substance, separate, wash, and rotary evaporate to obtain tertiary amine acrylate;

[0008] (2) Under nitrogen protection, tertiary amine acrylate and hydroquinone are added to dichloromethane, stirred for 20-40 minutes, and then methoxy-polyethylene glycol-chloride is added, the temperature is raised to 40-50°C, stirred and refluxed for 20-28 hours, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0009] (3) Under a nitrogen atmosphere, polyethylene glycol-modified quaternary ammonium acrylate, methyldichlorosilane and hydroquinone are added to xylene, stirred for 20-40 minutes, and then a palladium carbon catalyst is added, the temperature is raised to 115-125° C., stirred for reaction for 0.8-1.2 hours, washed, and vacuum dried to obtain a modifier;

[0010] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at 45-55° C. to obtain an iron-magnesium-calcium mixed solution;

[0011] (5) Add the modifier to a mixed solution of deionized water and anhydrous ethanol, adjust the pH to 3-4 with hydrochloric acid, stir for 20-40 min, then add hydrotalcite, raise the temperature to 70-80°C, stir and reflux for 5-7 h, then add sodium silicate, and dropwise add a mixed solution of iron, magnesium and calcium, continue stirring for 1.5-2.5 h, and finally dry at 110-130°C for 20-28 h and at 190-210°C for 2-4 h to obtain a composite flocculant for tunnel construction wastewater treatment.

[0012] Preferably, in step (1), the weight ratio of triethanolamine, isocyanoethyl methacrylate and dichloromethane is 0.5:1.5-1.8:8-12.

[0013] Preferably, in step (2), the weight ratio of tertiary amine acrylate, hydroquinone, dichloromethane and methoxy-polyethylene glycol-chloride is 1:0.03-0.08:8-12:0.1-0.9.

[0014] Preferably, the weight average molecular weight of methoxy-polyethylene glycol-chloride in step (2) is 350.

[0015] Preferably, in step (3), the weight ratio of polyethylene glycol-modified quaternary ammonium acrylate, methyldichlorosilane, hydroquinone and xylene is 1:0.6-1:0.03-0.08:8-12.

[0016] Preferably, the amount of palladium-carbon catalyst added in step (3) is 0.8%-1.2% of the weight of the polyethylene glycol-modified quaternary ammonium salt acrylate.

[0017] Preferably, in step (4), the molar mass ratio of ferric chloride, magnesium sulfate and calcium sulfate is 10:0.8-1.2:0.8-1.2.

[0018] Preferably, the hydrotalcite in step (5) is magnesium-aluminum hydrotalcite with an average particle size of 0.5-0.8 μm.

[0019] Preferably, in step (5), the weight ratio of the modifier, deionized water, anhydrous ethanol, hydrotalcite, sodium silicate and iron magnesium calcium mixed solution is 0.1-0.3:80-120:20-40:8-12:3-8:20-30.

[0020] Beneficial effects of the present invention:

[0021] The present invention provides a composite flocculant for treating wastewater from tunnel construction, which can effectively reduce the pH value of wastewater, the content of high-concentration suspended solids, and reduce the amount of slag produced. By optimizing the formula design, combining inorganic flocculants, organic polymer flocculants and acid-base adjustment components, and utilizing mechanisms such as electrical neutralization and adsorption bridging, efficient flocculation and pH adjustment are achieved. The characteristics include rapid aggregation of suspended particles, reduction of sludge production, and improvement of floc density and dehydration performance. It is particularly suitable for the treatment of high-concentration suspended solids and alkaline wastewater, reduces the dosage of agents and the cost of sludge treatment, has the characteristics of high efficiency, economy, and environmental protection, and meets the needs of on-site treatment of tunnel construction wastewater.

[0022] The present invention further improves the performance of the flocculant through the design of the modifier. The modifier is inserted between the hydrotalcite layers to increase the interlayer spacing, promote the cross-linking of sodium silicate to form a polysilane structure, enhance the adsorption capacity and flocculation performance, enable the flocculant to capture suspended particles more efficiently, form a tighter floc, and reduce the sludge volume and output. In addition, the polyethylene glycol molecular chain introduced into the modifier further expands the interlayer spacing and improves the hydrophilicity, promotes metal ion loading and sodium silicate cross-linking, significantly improves the flocculation effect and optimizes the pH adjustment ability.

[0023] At the same time, the addition of chlorosilane promotes the cross-linking of sodium silicate, generating a stable polysilane structure, further enhancing the interlayer stability and adsorption capacity, and improving the capture efficiency of suspended particles. The synergistic effect of sodium silicate and the mixed solution of iron, magnesium and calcium optimizes the density of flocs, reduces sludge production and improves the pH adjustment effect of wastewater, showing the comprehensive advantages of high efficiency and environmental protection. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0025] In a specific embodiment of the present invention, the hydrotalcite is magnesium aluminum hydrotalcite with an average particle size of 0.6 μm; methoxy-polyethylene glycol-chloride was purchased from Shenzhen Meiluo Technology Co., Ltd.

[0026] Embodiment 1:

[0027] (1) Add 0.5 g of triethanolamine and 1.5 g of isocyanoethyl methacrylate to 8 g of dichloromethane, stir at room temperature for 10 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0028] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.03 g of hydroquinone were added to 8 g of dichloromethane, stirred for 20 min, and then 0.7 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added. The temperature was raised to 40°C, stirred and refluxed for 20 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0029] (3) Under nitrogen atmosphere, add 1 g of polyethylene glycol modified quaternary ammonium acrylate, 0.6 g of methyldichlorosilane and 0.03 g of hydroquinone to 8 g of xylene, stir for 20 min, then add 0.008 g of palladium carbon catalyst, heat to 115 °C, stir for 0.8 h, wash, and vacuum dry to obtain a modifier;

[0030] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:0.8:0.8 at 45° C. to obtain an iron-magnesium-calcium mixed solution;

[0031] (5) Add 0.1 g of the modifier to a mixed solution of 80 g of deionized water and 20 g of anhydrous ethanol, adjust the pH to 3.1 with hydrochloric acid, stir for 20 min, add 8 g of hydrotalcite, raise the temperature to 70 °C, stir and reflux for 5 h, add 3 g of sodium silicate, and dropwise add 20 g of the iron-magnesium-calcium mixed solution, continue stirring for 1.5 h, and finally dry at 110 °C for 20 h and at 190 °C for 2 h to obtain a composite flocculant for tunnel construction wastewater treatment.

[0032] Embodiment 2:

[0033] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0034] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.05 g of hydroquinone were added to 10 g of dichloromethane, stirred for 30 min, and then 0.8 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added, the temperature was raised to 45°C, stirred and refluxed for 24 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0035] (3) Under nitrogen atmosphere, add 1 g of polyethylene glycol modified quaternary ammonium acrylate, 0.8 g of methyldichlorosilane and 0.05 g of hydroquinone to 10 g of xylene, stir for 30 min, then add 0.01 g of palladium carbon catalyst, heat to 120 °C, stir for 1 h, wash, and vacuum dry to obtain a modifier;

[0036] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50° C. to obtain an iron-magnesium-calcium mixed solution;

[0037] (5) Add 0.2 g of the modifier to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, add 10 g of hydrotalcite, heat to 75 °C, stir and reflux for 6 h, add 5 g of sodium silicate, and dropwise add 25 g of a mixed solution of iron, magnesium and calcium, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a composite flocculant for tunnel construction wastewater treatment.

[0038] Embodiment 3:

[0039] (1) Add 0.5 g of triethanolamine and 1.8 g of isocyanoethyl methacrylate to 12 g of dichloromethane, stir at room temperature for 14 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0040] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.08 g of hydroquinone were added to 12 g of dichloromethane, stirred for 40 min, and then 0.9 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added, the temperature was raised to 50°C, stirred and refluxed for 28 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0041] (3) Under nitrogen atmosphere, add 1 g of polyethylene glycol modified quaternary ammonium acrylate, 1 g of methyldichlorosilane and 0.08 g of hydroquinone to 12 g of xylene, stir for 40 min, then add 0.012 g of palladium carbon catalyst, heat to 125 °C, stir for 1.2 h, wash, and vacuum dry to obtain a modifier;

[0042] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1.2:1.2 at 55° C. to obtain an iron-magnesium-calcium mixed solution;

[0043] (5) Add 0.3 g of the modifier to a mixed solution of 120 g of deionized water and 40 g of anhydrous ethanol, adjust the pH to 3.8 with hydrochloric acid, stir for 40 min, add 12 g of hydrotalcite, heat to 80 °C, stir and reflux for 7 h, add 8 g of sodium silicate, and dropwise add 30 g of a mixed solution of iron, magnesium and calcium, continue stirring for 2.5 h, and finally dry at 130 °C for 28 h and at 210 °C for 4 h to obtain a composite flocculant for tunnel construction wastewater treatment.

[0044] Comparative Example 1:

[0045] The difference between Comparative Example 1 and Example 2 is that the modifier in step (5) is replaced by tertiary amine acrylate;

[0046] The specific steps are as follows:

[0047] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0048] (2) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50°C to obtain an iron-magnesium-calcium mixed solution;

[0049] (3) Add 0.2 g of tertiary amine acrylate to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, then add 10 g of hydrotalcite, raise the temperature to 75 °C, stir and reflux for 6 h, then add 5 g of sodium silicate, and dropwise add 25 g of a mixed solution of iron, magnesium and calcium, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a flocculant.

[0050] Comparative Example 2:

[0051] The difference between Comparative Example 2 and Example 2 is that the methoxy-polyethylene glycol-chloride in step (2) is replaced by ethyl bromide;

[0052] The specific steps are as follows:

[0053] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0054] (2) Under nitrogen protection, add 1 g of tertiary amine acrylate and 0.05 g of hydroquinone to 10 g of dichloromethane, stir for 30 min, then add 0.8 g of ethyl bromide, heat to 45 °C, stir and reflux for 24 h, wash, and vacuum dry to obtain quaternary ammonium acrylate;

[0055] (3) Under nitrogen atmosphere, add 1 g of quaternary ammonium acrylate, 0.8 g of methyldichlorosilane and 0.05 g of hydroquinone to 10 g of xylene, stir for 30 min, then add 0.01 g of palladium carbon catalyst, heat to 120 °C, stir for 1 h, wash, and vacuum dry to obtain a modifier;

[0056] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50° C. to obtain an iron-magnesium-calcium mixed solution;

[0057] (5) Add 0.2 g of the modifier to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, add 10 g of hydrotalcite, heat to 75 °C, stir and reflux for 6 h, add 5 g of sodium silicate, and dropwise add 25 g of a mixed solution of iron, magnesium and calcium, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a flocculant.

[0058] Comparative Example 3:

[0059] The difference between Comparative Example 3 and Example 2 is that the modifier in step (5) is replaced by polyethylene glycol modified quaternary ammonium salt acrylate;

[0060] The specific steps are as follows:

[0061] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0062] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.05 g of hydroquinone were added to 10 g of dichloromethane, stirred for 30 min, and then 0.8 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added, the temperature was raised to 45°C, stirred and refluxed for 24 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0063] (3) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50°C to obtain an iron-magnesium-calcium mixed solution;

[0064] (4) Add 0.2 g of polyethylene glycol-modified quaternary ammonium acrylate to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, add 10 g of hydrotalcite, raise the temperature to 75 °C, stir and reflux for 6 h, add 5 g of sodium silicate, and dropwise add 25 g of a mixed solution of iron, magnesium and calcium, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a flocculant.

[0065] Comparative Example 4:

[0066] The difference between Comparative Example 4 and Example 2 is that: sodium silicate is not added in step (5);

[0067] The specific steps are as follows:

[0068] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0069] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.05 g of hydroquinone were added to 10 g of dichloromethane, stirred for 30 min, and then 0.8 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added, the temperature was raised to 45°C, stirred and refluxed for 24 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0070] (3) Under nitrogen atmosphere, add 1 g of polyethylene glycol modified quaternary ammonium acrylate, 0.8 g of methyldichlorosilane and 0.05 g of hydroquinone to 10 g of xylene, stir for 30 min, then add 0.01 g of palladium carbon catalyst, heat to 120 °C, stir for 1 h, wash, and vacuum dry to obtain a modifier;

[0071] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50° C. to obtain an iron-magnesium-calcium mixed solution;

[0072] (5) Add 0.2 g of the modifier to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, add 10 g of hydrotalcite, raise the temperature to 75 °C, stir and reflux for 6 h, add 25 g of the iron-magnesium-calcium mixed solution dropwise, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a flocculant.

[0073] Comparative Example 5:

[0074] The difference between Comparative Example 5 and Example 2 is that no iron-magnesium-calcium mixed solution is added in step (5):

[0075] The specific steps are as follows:

[0076] (1) Add 0.5 g of triethanolamine and 1.6 g of isocyanoethyl methacrylate to 10 g of dichloromethane, stir at room temperature for 12 h, and then transfer to n-hexane to precipitate an oily substance, separate it, wash it with n-hexane, and rotary evaporate it to obtain tertiary amine acrylate;

[0077] (2) Under nitrogen protection, 1 g of tertiary amine acrylate and 0.05 g of hydroquinone were added to 10 g of dichloromethane, stirred for 30 min, and then 0.8 g of methoxy-polyethylene glycol-chloride with a weight average molecular weight of 350 was added, the temperature was raised to 45°C, stirred and refluxed for 24 h, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate;

[0078] (3) Under nitrogen atmosphere, add 1 g of polyethylene glycol modified quaternary ammonium acrylate, 0.8 g of methyldichlorosilane and 0.05 g of hydroquinone to 10 g of xylene, stir for 30 min, then add 0.01 g of palladium carbon catalyst, heat to 120 °C, stir for 1 h, wash, and vacuum dry to obtain a modifier;

[0079] (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at a molar mass ratio of Fe:Mg:Ca of 10:1:1 at 50° C. to obtain an iron-magnesium-calcium mixed solution;

[0080] (5) Add 0.2 g of the modifier to a mixed solution of 100 g of deionized water and 30 g of anhydrous ethanol, adjust the pH to 3.5 with hydrochloric acid, stir for 30 min, add 10 g of hydrotalcite, raise the temperature to 75 °C, stir and reflux for 6 h, add 5 g of sodium silicate, continue stirring for 2 h, and finally dry at 120 °C for 24 h and at 200 °C for 3 h to obtain a flocculant.

[0081] Performance Test:

[0082] Tunnel construction wastewater with a pH of 11.78 and a high concentration of suspended solids (SS) content of 132.14 mg / L was taken as the treatment object. The flocculants prepared in the embodiments and comparative examples were prepared into a slurry with a mass concentration of 10%, and stirred continuously to prevent sinking to the bottom. Under stirring conditions, 200 mg of flocculant was added to the tunnel construction wastewater per liter of wastewater, and the reaction was stirred for 2 minutes, and then allowed to stand and settle for 10 minutes. The pH, SS content and slag production of the treated wastewater were tested, and the results are shown in Table 1.

[0083] Table 1 Wastewater treatment results

[0084]

[0085] Note: The amount of slag produced is the amount of precipitated sludge. In tunnel construction wastewater treatment, the less the better, because the more slag produced, the more precipitated sludge will require further treatment.

[0086] Data Analysis:

[0087] From the data of Examples 1-3 in Table 1, it can be seen that the composite flocculant for tunnel construction wastewater treatment prepared by the present invention has significant advantages, and can effectively reduce the pH value of wastewater, the content of high-concentration suspended solids, and reduce the amount of slag produced. By optimizing the formula design, the flocculant combines inorganic flocculants, organic polymer flocculants and acid-base adjustment components, and utilizes mechanisms such as electrical neutralization and adsorption bridging to achieve efficient flocculation and pH adjustment. Its characteristics include rapid aggregation of suspended particles, reduction of sludge production, improvement of floc density and dehydration performance, and is suitable for the treatment of high-concentration suspended solids and alkaline wastewater. The flocculant reduces the dosage of chemicals and the cost of sludge treatment, has the characteristics of high efficiency, economy, and environmental protection, and is particularly suitable for on-site treatment needs of tunnel construction wastewater.

[0088] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that, compared with tertiary amine acrylate, the modifier prepared by the present invention can effectively improve the flocculation ability of the flocculant, because the modifier is inserted into the interlayer of the hydrotalcite, increases its interlayer spacing, and promotes the cross-linking reaction of sodium silicate between the layers to form a polysilane structure. The formation of this structure enhances the adsorption capacity and flocculation performance of the hydrotalcite, so that it can more efficiently capture suspended particles and form more compact flocs when treating wastewater, thereby reducing the volume and output of sludge.

[0089] It can be seen from the data of Example 2 and Comparative Example 2 in Table 1 that, relative to ethyl bromide, methoxy-polyethylene glycol-chloride as a quaternizing agent can further improve the flocculation ability and pH adjustment ability of the flocculant, and reduce the amount of slag produced. This is because methoxy-polyethylene glycol-chloride as a quaternizing agent can introduce polyethylene glycol molecular chains into the modifier, thereby further expanding the interlayer spacing of the hydrotalcite and improving the hydrophilicity of the interlayers, thereby promoting the loading of iron, magnesium and calcium metal ions between the layers and the cross-linking of sodium silicate. As a result, the flocculant can more efficiently capture suspended particles in the wastewater and form a tighter floc, thereby improving the flocculation effect and reducing the sludge output.

[0090] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that the chlorosilane on the modifier can effectively improve the flocculation ability of the flocculant, because the chlorosilane promotes the cross-linking of sodium silicate, thereby generating a stable polysilane structure. The cross-linking effect further enhances the interlayer stability and adsorption capacity of the hydrotalcite, while improving the capture efficiency of the flocculant for suspended particles, forming a more compact floc structure, thereby significantly improving the flocculation effect.

[0091] From the data of Example 2 and Comparative Examples 4-5 in Table 1, it can be seen that the addition of sodium silicate and iron-magnesium-calcium mixed solution can further improve the flocculation ability and pH adjustment ability of the flocculant and reduce the amount of slag produced. This is because the cross-linking reaction between sodium silicate and hydrotalcite occurs to generate a stable polysilane structure, which further enhances the adsorption capacity and flocculation effect of the flocculant. At the same time, the loading of iron, magnesium and calcium ions improves the interlayer stability and ion exchange capacity of the hydrotalcite and enhances the capture efficiency of suspended particles in the wastewater. In addition, this synergistic effect optimizes the density of the flocs, thereby reducing the sludge production and improving the pH adjustment effect of the wastewater.

[0092] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A method for preparing a composite flocculant for tunnel construction wastewater treatment, characterized in that: The following steps are involved: (1) Add triethanolamine and isocyanoethyl methacrylate to dichloromethane, stir at room temperature for 10-14 hours, and then transfer to n-hexane to precipitate an oily substance, separate, wash, and rotary evaporate to obtain tertiary amine acrylate; (2) Under nitrogen protection, tertiary amine acrylate and hydroquinone are added to dichloromethane, stirred for 20-40 minutes, and then methoxy-polyethylene glycol-chloride is added, the temperature is raised to 40-50°C, stirred and refluxed for 20-28 hours, washed, and vacuum dried to obtain polyethylene glycol-modified quaternary ammonium salt acrylate; (3) Under a nitrogen atmosphere, polyethylene glycol-modified quaternary ammonium acrylate, methyldichlorosilane and hydroquinone are added to xylene, stirred for 20-40 minutes, and then a palladium carbon catalyst is added, the temperature is raised to 115-125° C., stirred for reaction for 0.8-1.2 hours, washed, and vacuum dried to obtain a modifier; (4) preparing ferric chloride into a saturated solution, adding magnesium sulfate and calcium sulfate at 45-55° C. to obtain an iron-magnesium-calcium mixed solution; (5) Add the modifier to a mixed solution of deionized water and anhydrous ethanol, adjust the pH to 3-4 with hydrochloric acid, stir for 20-40 minutes, then add hydrotalcite, heat to 70-80°C, stir and reflux for 5-7 hours, then add sodium silicate, and dropwise add a mixed solution of iron, magnesium and calcium, continue stirring for 1.5-2.5 hours, and finally dry at 110-130°C for 20-28 hours and at 190-210°C for 2-4 hours to obtain a composite flocculant for tunnel construction wastewater treatment; The weight average molecular weight of methoxy-polyethylene glycol-chloride in step (2) is 350; In the step (5), the weight ratio of the modifier, deionized water, anhydrous ethanol, hydrotalcite, sodium silicate and iron magnesium calcium mixed solution is 0.1-0.3:80-120:20-40:8-12:3-8:20-30.

2. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: In the step (1), the weight ratio of triethanolamine, isocyanoethyl methacrylate and dichloromethane is 0.5:1.5-1.8:8-12.

3. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: In the step (2), the weight ratio of tertiary amine acrylate, hydroquinone, dichloromethane and methoxy-polyethylene glycol-chloride is 1:0.03-0.08:8-12:0.1-0.

9.

4. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: In the step (3), the weight ratio of polyethylene glycol modified quaternary ammonium acrylate, methyldichlorosilane, hydroquinone and xylene is 1:0.6-1:0.03-0.08:8-12.

5. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: The amount of palladium-carbon catalyst added in step (3) is 0.8%-1.2% of the weight of the polyethylene glycol-modified quaternary ammonium salt acrylate.

6. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: In the step (4), the molar mass ratio of ferric chloride, magnesium sulfate and calcium sulfate is 10:0.8-1.2:0.8-1.

2.

7. The method for preparing a composite flocculant for tunnel construction wastewater treatment according to claim 1, characterized in that: The hydrotalcite in step (5) is magnesium-aluminum hydrotalcite with an average particle size of 0.5-0.8 μm.

8. A composite flocculant for treating tunnel construction wastewater, characterized in that: The composite flocculant for tunnel construction wastewater treatment is obtained by the preparation method of any one of claims 1-7.

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