Modified fly ash composite flocculant and preparation method thereof

Abstract

The invention relates to a modified fly ash composite flocculant and a preparation method thereof, the modified fly ash composite flocculant comprises a flocculant carrier and a polysilicate aluminum ferric flocculant, the fly ash is subjected to alkaline calcination and acid leaching to prepare the polysilicate aluminum ferric flocculant, the fly ash is subjected to microwave modification and acid modification to prepare the flocculant carrier, and the flocculant carrier is added to the fly ash to prepare the polysilicate aluminum ferric flocculant. And finally, preparing the modified fly ash composite flocculant by using the prepared polysilicate aluminum ferric flocculant and a flocculant carrier. The method is easy to operate and suitable for industrial production, aluminum, iron, silicon and other components in the fly ash are fully utilized, effective utilization of waste is promoted, and compared with an existing water treatment flocculant, the cost is low, and the comprehensive effect is better.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment or wastewater treatment, in particular to the technical field of flocculants for water treatment or wastewater treatment, and specifically relates to a modified fly ash composite flocculant and a preparation method thereof. BACKGROUND

[0002] Fly ash is a common solid waste produced by high-temperature combustion of coal in thermal power plants, which is a mineral mixture composed of various alkali metals and metal oxides. At present, the annual discharge of fly ash in China reaches 600 million tons, and the subsequent storage exceeds 3 billion tons, with an annual increase of 200 million tons, which has caused great pressure on the ecological environment. With the formal proposal of the "double carbon" goal in China, the resource utilization of fly ash has gradually been valued. Foreign research on fly ash can be traced back to the 1920s, especially after the oil crisis in the 1970s, the fuel of many power plants was mainly coal, and the discharge of a large amount of fly ash waste slag had a negative impact on the surrounding environment and people's life, which prompted more people to pay attention to the comprehensive utilization of fly ash resources.

[0003] Fly ash is mainly composed of SiO2, Al2O3, Fe2O3 and other oxides, as well as valuable metals such as germanium, silver, gallium and zinc. Fly ash, modified fly ash and fly ash derivatives have been widely used as wastewater treatment reagents in the treatment and purification process of industrial wastewater, municipal wastewater, heavy metal ion wastewater and dye wastewater.

[0004] A method for preparing an inorganic polymer flocculant from fly ash is disclosed in Chinese patent CN107934978B. The method uses fly ash alkaline calcination, sodium hydroxide solution leaching to separate SiO2 and aluminum, acidification of the leaching solution to adjust the pH value, separation of polysilicate aluminum, acid leaching of the sodium hydroxide solution leaching residue, evaporation and concentration of the acid leaching solution, adjustment of the pH value, and polymerization to obtain a liquid iron sulfate product. However, the effective ingredient purity of the product is not high, and the liquid product is not convenient for long-distance transportation.

[0005] A method for treating urban domestic sewage and a flocculant using modified fly ash are disclosed in Chinese patent CN101134614B. The acid-modified fly ash flocculates urban domestic sewage impurities and adsorbs nitrogen and phosphorus, and then the magnetic response of the magnetic powder is used to rapidly enrich the impurities under the action of an external magnetic field, which is then transported out of the sewage reaction tank to effectively reduce the concentration of organic matter in the sewage. However, the hydrochloric acid modification method cannot extract a large amount of aluminum and iron ions with flocculating effect from the fly ash, resulting in poor flocculating effect and the need for a large amount of dosage; the subsequent addition of magnetic powder is beneficial to the separation of flocculation, but long-term use is toxic to the activated sludge in domestic sewage.

[0006] Although the literatures at home and abroad have studied the modification of fly ash and obtained excellent water treatment effect, the product has high purity and good water treatment effect, but the modification process is complex and cumbersome, the material consumption is high, and the cost is high, which limits the industrial application. SUMMARY

[0007] One technical problem to be solved by the present application is that the existing preparation method of the flocculant using fly ash as raw material cannot fully utilize fly ash. Another technical problem to be solved by the present application is that the existing preparation method of the flocculant has complex process, high material consumption and high cost. To solve at least one of the above technical problems, the present application provides a modified fly ash composite flocculant, which comprises a flocculant carrier and a polysilicate aluminum iron flocculant, the flocculant carrier is made of fly ash modified by microwave and acid, and the polysilicate aluminum iron flocculant is made of fly ash by alkaline calcination and acid leaching.

[0008] According to a preferred embodiment of the present application, the polysilicate aluminum iron flocculant and the flocculant carrier are both solid, and the weight ratio of the two is 1:2.6-1:12.5.

[0009] According to a preferred embodiment of the present application, the molar ratio of aluminum and iron elements in the polysilicate aluminum iron flocculant is 13-16, and the molar ratio of the sum of aluminum and iron elements to silicon element is 1.038-3.538.

[0010] In another aspect of the present application, a preparation method of the modified fly ash composite flocculant is provided, which comprises the following steps S1-S3, wherein steps S1 and S2 are not in sequence, but both are prior to step S3:

[0011] Step S1, alkaline calcination and acid leaching of fly ash to prepare polysilicate aluminum iron flocculant;

[0012] Step S2, microwave modification and acid modification of fly ash to prepare a flocculant carrier;

[0013] Step S3, using the polysilicate aluminum iron flocculant and the flocculant carrier prepared in steps S1 and S2 to prepare the modified fly ash composite flocculant.

[0014] According to a preferred embodiment of the present application, the step S1 comprises:

[0015] S1.1, alkaline calcination of fly ash to obtain an activated fly ash mixture;

[0016] S1.2, acid leaching process of the activated fly ash mixture to obtain an activated fly ash mixture leaching solution;

[0017] S1.3, extraction of the activated fly ash mixture leaching solution and maturation and heating evaporation to obtain a polysilicate aluminum iron flocculant.

[0018] According to the preferred embodiment of the present application, in the step S1.1, sodium carbonate is used as the alkaline material, and the fly ash and the alkaline material are mixed and calcined.

[0019] According to the preferred embodiment of the present application, in the step S1.2, the acid used in the acid leaching process is hydrochloric acid, the concentration of the hydrochloric acid is 0.5-5 mol / L, and the ratio between the volume value of the hydrochloric acid in milliliter and the mass value of the activated fly ash mixture in gram is 30:1-10:1.

[0020] According to the preferred embodiment of the present application, the step S2 comprises:

[0021] S2.1, microwave irradiation and heating are performed on the fly ash to perform microwave modification;

[0022] S2.2, acid modification is performed on the microwave-modified fly ash.

[0023] According to the preferred embodiment of the present application, in the step S2.2, a composite inorganic acid of sulfuric acid and nitric acid with a volume ratio of 1:1 is used for acid modification, and the ratio between the volume value of the composite inorganic acid of sulfuric acid and nitric acid in milliliter and the mass value of the fly ash in gram is 4-10.

[0024] The present application also provides a modified fly ash composite flocculant prepared by the preparation method of the modified fly ash composite flocculant.

[0025] The present application has the following beneficial effects:

[0026] (1) The preparation method of the present application uses fly ash as the principle in the preparation of the flocculant carrier and the polyaluminum silicate iron flocculant, which fully utilizes the aluminum, iron, silicon and other components in the fly ash, and greatly promotes the effective utilization of waste.

[0027] (2) The process of the present application is simple, and can efficiently prepare the modified fly ash composite flocculant, has high aluminum, iron and silicon ion leaching rate, low “three wastes” emission, saves resources, has low cost, and is convenient for large-scale industrial production.

[0028] (3) The product of the present application is solid, has fast flocculation and precipitation in the water treatment process, has good COD removal effect compared to the existing water treatment flocculant, and has a more excellent comprehensive removal rate. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a flow chart of the preparation of the modified fly ash composite flocculant of the present application.

[0030] Figure 2 The figure is a flow chart of the preparation of the polyaluminum silicate iron flocculant of an embodiment of the present application.

[0031] Figure 3 is a flow chart of preparing the flocculant carrier of an embodiment of the present application.

[0032] Figure 4 is a microstructure diagram of the modified fly ash composite flocculant prepared for an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to solve the above problems of the prior art, the present application improves the preparation method of the modified fly ash composite flocculant. Specifically, the modified fly ash composite flocculant of the present application comprises a flocculant carrier and a polysilicate aluminum iron flocculant, the flocculant carrier is modified fly ash, in particular, fly ash modified by acid modification and microwave compounding, and the polysilicate aluminum iron flocculant is an inorganic flocculant prepared by alkaline calcination and acid leaching of fly ash, and the main component of the inorganic flocculant is polysilicate aluminum iron.

[0034] Moreover, according to the actual measurement of the present application, the finished products of the polysilicate aluminum iron flocculant and the flocculant carrier are both solid, and the preferred weight ratio of the two is 1:2.6-1:12.5, and more preferably 1:3-1:10.

[0035] As the most preferred embodiment, in order to achieve the best effect of water treatment, the turbidity removal rate is >95%, the molar ratio of aluminum and iron elements in the flocculant, i.e. C Al :C Fe , is 13-16; and the molar ratio of the sum of aluminum and iron elements to silicon element, i.e. C Al+Fe :C Si , is 1.038-3.538. The content of aluminum, iron and silicon elements in the flocculant is obtained by actual measurement of ICP (inductively coupled plasma test).

[0036] Figure 1 is a flow chart of preparing the modified fly ash composite flocculant of the present application. As shown in Figure 1 , in order to prepare the modified fly ash composite flocculant of the present application, the preparation method of the modified fly ash composite flocculant proposed by the present application comprises the following steps:

[0037] S1, alkaline calcination and acid leaching of fly ash to prepare polysilicate aluminum iron flocculant.

[0038] Figure 2 is a flow chart of preparing the polysilicate aluminum iron flocculant of an embodiment of the present application. As shown in Figure 2 , the process of preparing the polysilicate aluminum iron flocculant comprises the following steps:

[0039] S1.1, alkaline calcination of fly ash to activate the fly ash and obtain an activated fly ash mixture.

[0040] This step involves activating the fly ash so that the aluminosilicate glass (Al₂O₃·2SiO₂) in the fly ash reacts with the activator under high temperature conditions and dissolves to form soluble sodium silicate (Na₂SiO₃) and sodium aluminate (NaAlO₂), breaking the Si-Al bonds and promoting the dissolution rate. This invention preferentially employs alkaline calcination for activation, that is, mixing the pulverized coal and alkaline materials before calcination. To reduce the cost of the activator while ensuring the breaking of Si-Al bonds, this invention preferably uses sodium carbonate as the alkaline material. Based on theoretical calculations and experimental verification, this invention controls the molar ratio of sodium carbonate to SiO₂ in the fly ash to be between 1:4 and 2:1.

[0041] As a specific implementation method, fly ash and sodium carbonate can be calcined in a box-type resistance furnace, with the temperature set at 650-1050℃ and the holding time at 0.5-3.0h, to obtain an activated fly ash mixture.

[0042] Preferably, the activated fly ash mixture after alkaline calcination and activation is ground to reduce the fly ash particle size and increase the surface area for subsequent chemical reactions. For example, the grinding time is 5–60 min to obtain an activated fly ash mixture (fine ash). The longer the grinding time, the finer the fly ash particles and the smaller the particle size D. 50 The size decreased from 102.1 μm to 19.7 μm.

[0043] S1.2. The activated fly ash mixture is subjected to an acid leaching process to obtain an activated fly ash mixture leachate.

[0044] The step of acid leaching the activated fly ash mixture involves adding the activated fly ash mixture (fine ash) to an aqueous acid solution for leaching. As an exemplary embodiment, a certain amount of the activated fly ash mixture can be added to a container, connected to a condensation device, and a certain volume of acid solution can be added for acid leaching.

[0045] According to a preferred embodiment of the present invention, the acid solution is preferably hydrochloric acid, and the concentration of hydrochloric acid is preferably 0.5 to 5 mol / L. More preferably, the ratio between the volume of hydrochloric acid in milliliters and the mass of the activated fly ash mixture in grams is 30:1 to 10:1.

[0046] According to the present invention, the above-mentioned acid leaching step is carried out at a constant temperature, for example in a water bath, and the water bath temperature is controlled to be constant at 30-90°C for 10-80 minutes.

[0047] Furthermore, stirring is performed during the acid leaching process of the present invention. Preferably, in order to promote a full redox reaction during acid leaching, accelerate ion transport, and shorten the reaction time, the stirring speed is preferably 100-500 r / min.

[0048] S1.3 Extract the leachate from the activated fly ash mixture and then mature and heat it to evaporate, to obtain polyaluminum silicate iron flocculant.

[0049] After acid leaching, to prevent the leachate from coagulating, add 0.2–3.0 times the amount of pure water, mix well, and collect the supernatant. Place the supernatant in a glass container, cover with plastic wrap, and allow it to mature at room temperature for 2–24 hours to obtain polyaluminum-iron silicate flocculant. Heating and evaporating this polyaluminum-iron silicate flocculant will yield a solid powder.

[0050] S2. Microwave and acid modification of fly ash to prepare flocculant carriers.

[0051] Figure 3 This is a flowchart illustrating the preparation of a flocculant carrier according to an embodiment of the present invention. Figure 3 As shown, the process of preparing flocculant carriers by microwave modification and acid modification of fly ash includes the following steps:

[0052] S2.1 Microwave modification of fly ash.

[0053] Microwave modification of fly ash refers to subjecting fly ash to microwave radiation and heating. In this invention, the preferred microwave power for microwave modification of fly ash is 300–600 W, and the microwave duration is 5–20 min. After microwave and high-temperature treatment, the number of active sites on the fly ash surface increases, the surface micro- and nano-pores enlarge, the surface area of ​​the fly ash increases, and the adsorption capacity is improved.

[0054] S2.2, Acid modification of the microwave-modified fly ash.

[0055] The pore size distribution, spacing, and other structural factors of fly ash all affect its adsorption performance. Acid modification of fly ash refers to acid treatment of the fly ash. This invention preferably uses sulfuric acid or nitric acid, or a composite inorganic acid prepared in a certain proportion. In a preferred embodiment, a composite inorganic acid of sulfuric acid and nitric acid in a volume ratio of 1:1 (sulfuric acid concentration of 70% and nitric acid concentration of 65%) is used, and the ratio of the volume of the composite inorganic acid (in milliliters) to the mass of the fly ash (in grams) is 4.0–10.0.

[0056] As a specific example, a mixture of fly ash and composite inorganic acid can be stirred at room temperature for 40–80 minutes at a stirrer speed of 100–500 r / min. Then, it can be allowed to stand for 0.5–1.0 h to remove the supernatant.

[0057] Next, the fly ash is washed until neutral, filtered and dried, for example at 120°C, to obtain acid-modified fly ash, which is then placed in a desiccator for later use.

[0058] After being etched with composite inorganic acids, fly ash has an increased surface and internal pore structure, which directly improves its adsorption performance.

[0059] S3. Using the polyaluminum silicate iron flocculant and flocculant carrier prepared in the above steps, a modified fly ash composite flocculant is prepared.

[0060] This step involves mixing an appropriate amount of modified fly ash, which serves as a flocculant carrier, with polyaluminum ferric silicate flocculant made from fly ash, and then heating and stirring the mixture to generate a modified fly ash composite flocculant.

[0061] According to the present invention, the ratio of the mass value of the flocculant carrier in grams to the volume value of the polyaluminum ferric silicate flocculant in milliliters is preferably 0.15 to 0.7 g / mL.

[0062] Preferably, the heating and stirring temperature is maintained between 40℃ and 70℃, and the time is between 2h and 24h. The rotation speed of the magnetic rotor at the bottom of the container is controlled between 100 and 500 r / min.

[0063] This step completes the surface physical and chemical adsorption, forming a polysilicate colloidal structure on the fly ash surface, and generating a modified fly ash composite flocculant.

[0064] The polyaluminum silicate iron flocculant and modified fly ash prepared by the above methods are both solids, and the optimal weight ratio between the two is 1:2.6 to 1:12.5.

[0065] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0066] The chemical composition (wt.%) of the fly ash used in the embodiments of the present invention is as follows.

[0067] CaO Fe2O3 Al2O3 SiO2 MgO TiO2 [K2O] Other 4.52 4.34 31.7 52.18 0.21 1.20 1.68 4.17

[0068] Example 1: Preparation of modified fly ash composite flocculant with low proportion fly ash carrier.

[0069] Sodium carbonate and fly ash were thoroughly mixed at a alkali-ash molar ratio of nNa2CO3:nSiO2 = 1:4, and calcined in a box-type resistance furnace at a set temperature of 800℃ for 1.5 hours. After calcination and activation, an activated fly ash mixture was obtained. This mixture was then ground for 10.0 minutes to obtain an activated fly ash mixture (fine ash). Hydrochloric acid with a concentration of 2.0 mol / L was added to the activated fly ash mixture (fine ash), and the temperature was maintained constant. A water bath was used for constant temperature control at 40℃. The ratio of the volume of hydrochloric acid (mL) to the mass of the activated fly ash mixture (g), i.e., the acid-ash ratio (mL / g), was 15:1. The constant temperature time was 30.0 minutes, and the bottom magnetic rotor speed was 300 r / min. Then, 1.0 times the amount of pure water was added, and the mixture was mixed to precipitate. The supernatant was collected. The supernatant was placed in a glass container, covered with plastic wrap, and allowed to mature at room temperature for 2 hours to obtain polyaluminum silicate iron flocculant A1.

[0070] In this embodiment, polyaluminum silicate iron flocculant A1 is a solid-liquid mixture, which can be directly used in subsequent steps during the laboratory stage. In actual production, the polyaluminum silicate iron flocculant solid-liquid mixture can be heated and evaporated to obtain polyaluminum silicate iron flocculant solid powder, which is used as the finished polyaluminum silicate iron flocculant product.

[0071] Separately, fly ash was subjected to microwave modification at a power of 300W for 10 minutes. Then, acid modification was performed. During acid modification, the amount of sulfuric acid and nitric acid (in a 1:1 ratio) used with fly ash was 5.0 mL / g, meaning the ratio of the volume of the combined inorganic acid (sulfuric acid and nitric acid) in milliliters to the mass of the fly ash in grams was 5.0. During this process, the mixture was stirred at room temperature for 50 minutes, allowed to stand for 0.5 hours, the supernatant was removed, the fly ash was washed until neutral, filtered, and dried at 120℃ to obtain modified fly ash flocculant carrier B1, which was then placed in a desiccator for later use.

[0072] Finally, a suitable amount of modified fly ash flocculant carrier B1 and polyaluminum-iron silicate flocculant A1 were mixed at a ratio of 0.15 g / mL, meaning the ratio of the mass of modified fly ash B1 (as flocculant carrier) to the volume of polyaluminum-iron silicate flocculant A1 (as milliliters) was 0.15. At this point, the weight ratio of solid polyaluminum-iron silicate flocculant to flocculant carrier was 1:3. The mixture was heated to 70°C and stirred for 4 hours, with the magnetic rotor speed at the bottom of the container controlled at 300 r / min, to obtain modified fly ash composite flocculant C1.

[0073] Example 2: Preparation of modified fly ash composite flocculant with high proportion fly ash carrier.

[0074] Sodium carbonate and fly ash were thoroughly mixed at a alkali-ash molar ratio of nNa2CO3:nSiO2 = 1:2, and then calcined in a box-type resistance furnace at a set temperature of 900℃ for 2.5 hours. After calcination and activation, an activated fly ash mixture was obtained. This mixture was then ground for 15.0 minutes to obtain an activated fly ash mixture (fine ash). Hydrochloric acid with a concentration of 3.0 mol / L was added to the activated fly ash mixture (fine ash), and the temperature was maintained constant. A water bath was used for temperature control at 50℃. The ratio of the volume of hydrochloric acid (mL) to the mass of the activated fly ash mixture (g), i.e., the acid-ash ratio (mL / g), was 20:1. The temperature control time was 40.0 minutes, and the bottom magnetic rotor speed was 400 r / min. Then, 1.5 times the volume of pure water was added, the mixture was stirred to precipitate, and the supernatant was collected. Place the supernatant into a glass container, cover with plastic wrap, and let it mature at room temperature for 20 hours to obtain polyaluminum silicate iron flocculant product A2.

[0075] In this embodiment, polyaluminum silicate iron flocculant A2 is a solid-liquid mixture, which can be directly used in subsequent steps during the laboratory stage. In actual production, the polyaluminum silicate iron flocculant solid-liquid mixture can be heated and evaporated to obtain polyaluminum silicate iron flocculant solid powder, which is used as the finished polyaluminum silicate iron flocculant product.

[0076] Separately, fly ash was subjected to microwave modification at a power of 350W for 10 minutes. Then, acid modification was performed. During acid modification, the amount of sulfuric acid and nitric acid (in a 1:1 ratio) used with fly ash was 7.0 mL / g, meaning the ratio of the volume of the combined inorganic acid (sulfuric acid and nitric acid) in milliliters to the mass of the fly ash in grams was 7.0. The mixture was stirred at room temperature for 60 minutes, allowed to stand for 1 hour, the supernatant was removed, the fly ash was washed until neutral, filtered, and dried at 120℃ to obtain modified fly ash flocculant carrier B2, which was then placed in a desiccator for later use.

[0077] Finally, a suitable amount of modified fly ash flocculant carrier B2 and polyaluminum-iron silicate flocculant A2 were mixed at a ratio of 0.5 g / mL, meaning the ratio of the mass value of modified fly ash B1 (as flocculant carrier) to the volume value of polyaluminum-iron silicate flocculant A2 (as milliliters) was 0.5. At this point, the weight ratio of solid polyaluminum-iron silicate flocculant to flocculant carrier was 1:10. The mixture was heated to 40℃ and stirred for 14 hours, with the rotation speed of the magnetic rotor at the bottom of the container controlled at 200 r / min, to obtain modified fly ash composite flocculant C2.

[0078] Example 3: Preparation of modified fly ash composite flocculant with optimal fly ash carrier ratio.

[0079] Sodium carbonate and fly ash were thoroughly mixed at a alkali-ash molar ratio of nNa2CO3:nSiO2 = 2:1, and then calcined in a box-type resistance furnace at a set temperature of 1000℃ for 2.0 h. After calcination and activation, an activated fly ash mixture was obtained, which was then ground for 30.0 min to obtain an activated fly ash mixture (fine ash). Hydrochloric acid with a concentration of 4.0 mol / L was added to the activated fly ash mixture (fine ash), and the temperature was maintained constant. A water bath was used for constant temperature control at 70℃, and the ratio of the volume of hydrochloric acid (mL) to the mass of the activated fly ash mixture (g), i.e., the acid-ash ratio (mL / g), was 25:1. The constant temperature time was 60.0 min, and the bottom magnetic rotor speed was 450 r / min. Then, 2.5 times the volume of pure water was added, the mixture was stirred to precipitate, and the supernatant was collected. Place the supernatant taken out into a glass container, cover it with plastic wrap, and let it mature at room temperature for 15 hours to obtain polyaluminum silicate iron flocculant product A3.

[0080] In this embodiment, polyaluminum silicate iron flocculant A3 is a solid-liquid mixture, which can be directly used in subsequent steps during the laboratory stage. In actual production, the polyaluminum silicate iron flocculant solid-liquid mixture can be heated and evaporated to obtain polyaluminum silicate iron flocculant solid powder, which is used as the finished polyaluminum silicate iron flocculant product.

[0081] Separately, fly ash was subjected to microwave modification at a power of 500W for 12.0 min. Then, acid modification was performed. During acid modification, the amount of sulfuric acid and nitric acid (in a 1:1 ratio) used with fly ash was 9.0 mL / g, meaning the ratio of the volume of the combined inorganic acid (sulfuric acid and nitric acid) in milliliters to the mass of the fly ash in grams was 9.0. The mixture was stirred at room temperature for 70.0 min, allowed to stand for 0.8 h, the supernatant was removed, the fly ash was washed until neutral, filtered, and dried at 120℃ to obtain modified fly ash flocculant carrier B3, which was then placed in a desiccator for later use.

[0082] Finally, a suitable amount of modified fly ash flocculant carrier B3 was mixed with polyaluminum silicate ferric flocculant A3 at a ratio of 0.35 g / mL. This means the ratio of the mass of modified fly ash B1 (as flocculant carrier) to the volume of polyaluminum silicate ferric flocculant A3 (as milliliters) was 0.35, resulting in a weight ratio of solid polyaluminum silicate ferric flocculant to flocculant carrier of 1:7. The mixture was heated to 60°C and stirred for 18 hours, with the magnetic rotor speed at the bottom of the container controlled at 400 r / min, to obtain modified fly ash composite flocculant C3.

[0083] Figure 4 This is a microstructure diagram of the modified fly ash composite flocculant prepared according to Example 2 of the present invention. From... Figure 4As can be seen, the surface of the sample powder is regularly spherical, with each sphere containing a high-density fly ash particle core. The particle surface is uneven, with a particle size of approximately 5–80 μm. The sphere surface is composed of numerous long chains. The high specific surface area and porous structure, along with the uniform dispersion of the polymer chain structure on the particle surface, promote the adsorption, bridging, and entrapment of pollutants, thereby accelerating the flocculation and sedimentation rate.

[0084] Preparation of a composite flocculant combining the polyaluminum-iron silicate flocculant synthesized in Comparative Example 1 with the flocculant carrier of the present invention.

[0085] Polyaluminum ferric silicate flocculant was synthesized using chemically pure reagents. 11.85 g of sodium silicate nonahydrate was weighed and added to 80 mL of water to prepare a water glass solution. 5 mL of concentrated sulfuric acid was measured and diluted to 10 mL. After cooling, the water glass solution was added and stirred, maintaining a total volume of 100 mL. At this point, the pH was approximately 5.5. The solution was allowed to stand for 6–7 minutes. Subsequently, 5.3 g of AlCl3·6H2O and 0.4 g of FeCl3·6H2O were added while stirring, and the solution was allowed to mature for 2 hours to obtain polyaluminum ferric silicate solution A4. The concentration of the effective component in this solution was consistent with the aluminum-iron-silicon ratio of product A3 in Example 3.

[0086] Separately, fly ash was subjected to microwave modification at a power of 500W for 12.0 min. Then, acid modification was performed. During acid modification, the amount of sulfuric acid and nitric acid (in a 1:1 ratio) used with fly ash was 9.0 mL / g, meaning the ratio of the volume of the combined inorganic acid (sulfuric acid and nitric acid) in milliliters to the mass of the fly ash in grams was 9.0. The mixture was stirred at room temperature for 70.0 min, allowed to stand for 0.8 h, the supernatant was removed, the fly ash was washed until neutral, filtered, and dried at 120℃ to obtain modified fly ash flocculant carrier B3, which was then placed in a desiccator for later use.

[0087] Finally, an appropriate amount of modified fly ash flocculant carrier B3 was mixed with the synthesized polyaluminum ferric silicate flocculant A4 at a ratio of 0.35 g / mL, meaning the ratio of the mass value of the modified fly ash B1 (as flocculant carrier) to the volume value of the flocculant A4 (in milliliters) was 0.35. The mixture was heated to 60°C and stirred for 18 hours with a magnetic rotor speed of 400 r / min at the bottom of the container to obtain composite flocculant C4.

[0088] Comparative Example 2: Flocculant without fly ash as a carrier.

[0089] Polyaluminum silicate iron flocculant A3 was prepared as the product of Comparative Example 2 using the method of Example 3.

[0090] Comparative Example 3: Commercial flocculant.

[0091] Three commercially available flocculants—polyaluminum silicate flocculant, polyaluminum chloride flocculant, and polyferric chloride flocculant—were used to conduct a comparative water treatment flocculation experiment.

[0092] The results of the water treatment flocculation experiment are shown in the table below.

[0093] Table 1 Comparison of the effects of three flocculants

[0094]

[0095] The comparison of actual water treatment effects above shows that the modified fly ash composite flocculant of this invention significantly improves the COD removal rate compared to existing commercially available flocculants, by approximately 11 to 38 percentage points. Its turbidity removal rate is comparable to or better than that of commercially available flocculants, and it also shows a certain improvement in color removal rate, while slightly shortening the settling time. Therefore, the modified fly ash composite flocculant of this invention exhibits excellent overall performance.

[0096] Secondly, as can be seen from the comparison with Comparative Example 1, the fly ash microwave acid-modified flocculant carrier of the present invention can also be used in combination with the synthetic polyaluminum ferric silicate flocculant to achieve the same excellent effect. Therefore, the intermediate product of the present invention also has a wide range of application scenarios.

[0097] Furthermore, a comparison with Comparative Example 2 shows that the fly ash modified polyaluminum silicate iron flocculant of the present invention without flocculant carrier also has excellent removal rate, only the sedimentation time is slightly longer.

[0098] In summary, this invention proposes a modified fly ash composite flocculant, which is a product obtained by reacting an inorganic flocculant prepared from fly ash with modified fly ash. The preparation method of the modified fly ash composite flocculant consists of three parts: preparation of modified fly ash polyaluminum-iron silicate flocculant, preparation of modified fly ash flocculant carrier, and composite reaction, forming a novel composite flocculant that possesses both highly efficient flocculation and adsorption properties.

[0099] The above examples also demonstrate that when the mass ratio of polyaluminum silicate iron flocculant to flocculant carrier (in solidified powder state) is between 1:3 and 1:10, the flocculant of the present invention exhibits excellent comprehensive treatment effects in treating wastewater with high color intensity, high concentration, and high COD from industries such as printing and dyeing, papermaking, and municipal processes. Further experiments of the present invention confirm that this numerical range can be appropriately extended to both ends; when the mass ratio of polyaluminum silicate iron flocculant to flocculant carrier (in solidified powder state) is between 1:2.6 and 1:12.5, it also exhibits better comprehensive treatment effects compared to existing technologies.

[0100] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified fly ash composite flocculant, comprising a flocculant carrier and polyaluminum ferric silicate flocculant, characterized in that: The flocculant carrier is made from fly ash that has been modified by microwave and acid. The polyaluminum ferric silicate flocculant is made by alkaline calcination and acid leaching of fly ash.

2. The modified fly ash composite flocculant as described in claim 1, characterized in that: Both the polyaluminum silicate iron flocculant and the flocculant carrier are solids, and their weight ratio is 1:2.6 to 1:12.

5.

3. The modified fly ash composite flocculant as described in claim 2, characterized in that: The polyaluminum silicate iron flocculant has a molar ratio of aluminum to iron of 13 to 16, and a molar ratio of the sum of aluminum and iron to silicon of 1.038 to 3.

538.

4. A method for preparing a modified fly ash composite flocculant, characterized in that, The steps S1 to S3 are as follows, wherein steps S1 and S2 are not sequential, but both precede step S3: Step S1: Alkaline calcination and acid leaching of fly ash to prepare polyaluminum silicate iron flocculant; Step S2: Microwave-modified and acid-modified fly ash to prepare flocculant carrier; Step S3: Prepare modified fly ash composite flocculant using the polyaluminum silicate flocculant and flocculant carrier prepared in steps S1 and S2.

5. The preparation method of the modified fly ash composite flocculant as described in claim 4, characterized in that, Step S1 includes: S1.

1. Alkaline calcination of fly ash to obtain activated fly ash mixture; S1.

2. The activated fly ash mixture is subjected to an acid leaching process to obtain an activated fly ash mixture leachate; S1.3 Extract the leachate from the activated fly ash mixture and perform aging and heating evaporation to obtain polyaluminum silicate iron flocculant.

6. The preparation method of the modified fly ash composite flocculant as described in claim 5, characterized in that, In step S1.1, sodium carbonate is used as an alkaline material, and the pulverized coal and the alkaline material are mixed and then calcined.

7. The preparation method of the modified fly ash composite flocculant as described in claim 5, characterized in that, In step S1.2, the acid used in the acid leaching process is hydrochloric acid, the concentration of which is 0.5 to 5 mol / L, and the ratio between the volume of hydrochloric acid in milliliters and the mass of the activated fly ash mixture in grams is 30:1 to 10:

1.

8. The preparation method of the modified fly ash composite flocculant as described in claim 4, characterized in that, Step S2 includes: S2.1 Microwave modification of fly ash by microwave radiation and heating; S2.2, Acid modification of the microwave-modified fly ash.

9. The preparation method of the modified fly ash composite flocculant as described in claim 5, characterized in that, In step S2.2, a composite inorganic acid of sulfuric acid and nitric acid with a volume ratio of 1:1 is used for acid modification, and the ratio of the volume value of the composite inorganic acid of sulfuric acid and nitric acid in milliliters to the mass value of fly ash in grams is 4 to 10.

10. A modified fly ash composite flocculant, characterized in that, It is prepared by the method described in any one of claims 4 to 9 for the preparation of the modified fly ash composite flocculant.

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