Composite magnetic flocculant and preparation method thereof

Abstract

The invention discloses a composite magnetic flocculant, and belongs to the technical field of sewage treatment. The composite magnetic flocculant is prepared from the following components in parts by weight: 15 to 30 parts of fly ash, 5 to 10 parts of magnetic nanoparticles gamma-Fe2O3, 1 to 4 parts of poly L-cysteine, 3 to 6 parts of a calcium source and 0.5 to 1.5 parts of polyacrylamide. The fly ash is an industrial waste and is wide in source, the production cost can be remarkably reduced when the fly ash is applied to preparation of the flocculating agent, and the preparation method is simple and integrally green and economical. The composite magnetic flocculant is used for sewage treatment, has an excellent treatment effect, and can realize efficient flocculation and rapid sedimentation, and the sedimentation time is controlled within 3-8 min. The invention further discloses a preparation method of the flocculating agent, the raw materials are mixed step by step, then stirring is conducted under the heating condition, drying and smashing are conducted, and the preparation method is simple.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and relates to a composite magnetic flocculant and a preparation method thereof. Background Art

[0002] Flocculation sedimentation is the most commonly used method for treating high-turbidity wastewater. By adding coagulants and flocculants, the suspended particles are formed into larger flocs to accelerate the sedimentation of the particles. However, the flocs mainly rely on their own gravity to settle, and the sedimentation effect is not good. When the water quality of high-turbidity wastewater is very complex, it is often difficult to overcome the resistance of the fluid due to insufficient sedimentation force, and rapid sedimentation cannot be achieved. In order to improve the sedimentation power, people introduce magnetic, electrical, microwave and other effects into the sewage clarification process. Among them, magnetic flocculation technology uses the external magnetic field to act on the magnetic flocs to enhance the sedimentation power. It is simple to operate, has high separation efficiency, and rarely produces secondary pollution. It is very suitable for the treatment of high-turbidity wastewater.

[0003] Fly ash is the fine ash collected from the flue gas after coal combustion, and is the main solid waste discharged from coal-fired power plants. Its main components include inorganic minerals such as silicon dioxide, aluminum oxide, iron oxide, and calcium oxide. With the development of the power industry, the emission of fly ash has increased year by year, becoming one of the largest industrial waste residues in my country. As an industrial by-product, fly ash has a wide range of resource utilization potential, such as its application in the preparation of flocculants for sewage treatment. Fly ash is inexpensive and contains magnetic components such as magnetite and hematite. Using it as a magnetic seed can significantly reduce the preparation cost of flocculants, and can also remove heavy metal ions and organic matter from water through its porous structure and adsorption properties.

[0004] At present, there are many studies on the use of fly ash and other chemical reagents to prepare flocculants for treating sewage. Patent CN115947433B discloses a fly ash nano-magnetic bead flocculant, which uses fly ash, nano-silicon dioxide, polyacrylamide and other raw materials to prepare a flocculant for treating sewage. Although the flocculant adds fly ash waste, reduces production costs, and has a good overall flocculation effect, the flocculation sedimentation time is long. Patent CN104276643B discloses a method for preparing a magnetic flocculant using fly ash magnetic beads and polyacrylamide, including the selection of magnetic beads, ball milling and re-magnetic separation of fly ash, preparation of micro-magnetic bead suspension, micro-magnetic beads and polyacrylamide composite swelling and post-processing unit process. Compared with pure polyacrylamide, although the use of magnetic flocculant technology significantly improves the flocculation effect and sedimentation rate, the preparation process is relatively complicated, requires more instruments and equipment, and has a high cost.

[0005] Although new magnetic flocculants have their own advantages, there are problems in that it is difficult to achieve efficient flocculation, rapid sedimentation and low cost at the same time. Therefore, it is necessary to continuously provide new composite magnetic flocculants to achieve efficient and rapid flocculation and a flocculant with a green and economical preparation method. Summary of the Invention

[0006] Aiming at the defects of existing flocculants, the purpose of the present invention is to provide a composite magnetic flocculant. The composite magnetic flocculant takes fly ash, magnetic nanoparticles γ-Fe2O3, poly-L-cysteine, calcium source and polyacrylamide as core components. The calcium source is a modifier for fly ash, which enhances the magnetism and adsorption capacity of fly ash and reduces the production cost. At the same time, adding sulfate can further modify it; poly-L-cysteine contains thiol groups, amino groups, carboxyl groups and disulfide bonds, which can be used to modify the surface of magnetic nanoparticles γ-Fe2O3, giving it better dispersibility, biocompatibility and chemical stability; adding a small amount of polyacrylamide can enhance the flocculation effect. The composite magnetic flocculant prepared by compounding the above raw materials can achieve efficient and rapid flocculation and can significantly reduce the production cost. Another purpose is to provide a preparation method of the composite magnetic flocculant, with a simple process and being green and environmentally friendly.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: A composite magnetic flocculant, comprising the following components: 15-30 parts of fly ash, 5-10 parts of magnetic nanoparticles γ-Fe2O3, 1-4 parts of poly-L-cysteine, 3-6 parts of calcium source, and 0.5-1.5 parts of polyacrylamide.

[0008] Fly ash has a large specific surface area and a rich pore structure. Its surface also contains active groups such as aluminum, silicon, and iron, which can adsorb suspended particles, organic matter, and heavy metal ions in sewage to form flocs and precipitate. The calcium ions in the calcium source can react with silicates and aluminates in fly ash to generate hydrated products with cementitious properties. These hydrated products can further increase the adsorption capacity of fly ash and help encapsulate the pollutants in sewage. Polyacrylamide is a water-soluble polymer with a long-chain structure and a high molecular weight. Its long molecular chains can connect tiny particles in sewage like a bridge, connecting these particles into larger flocs through physical entanglement. This "bridging" effect enables the originally dispersed tiny particles to aggregate together, forming large flocculants that are easy to settle and filter. Fly ash also contains magnetic components such as magnetite and hematite, which can be used as magnetic seeds. After combining with the flocculant, through charge neutralization, adsorption bridging, compression of the double electric layer, and sweep flocculation, the colloidal particles in the water body can quickly aggregate to form relatively dense composite magnetic flocs with a larger specific gravity. However, the magnetic content in fly ash is relatively low, about between 1% and 5%, and the magnetism is weak. By adding magnetic nanoparticles, its magnetism can be enhanced, achieving the purpose of quickly aggregating and settling pollutants in sewage using magnetism. The addition of waste fly ash also reduces the use of strongly magnetic nanoparticle materials, greatly reducing production costs. Poly-L-cysteine has a unique chemical structure and various excellent properties. It contains thiol groups, amino groups, carboxyl groups, and disulfide bonds, which can effectively modify γ-Fe2O3 nanocomposites, endowing them with better dispersibility, biocompatibility, and chemical stability. It can form chemical bond coordination or chelation with heavy metal ions, thereby achieving an efficient adsorption effect.

[0009] Preferably, the composite magnetic flocculant is composed of the following raw materials in parts by weight: 20 - 25 parts of fly ash, 7 - 8 parts of magnetic nanoparticle γ-Fe2O3, 2 - 3 parts of poly-L-cysteine, 4 - 5 parts of calcium source, and 0.8 - 1.2 parts of polyacrylamide.

[0010] Preferably, the calcium source is one or both of calcium chloride and lime.

[0011] Lime is a modifier with low cost and easy availability, having a high cost performance in practical applications. Calcium chloride has stronger reaction activity and can achieve better modification effects under certain specific conditions.

[0012] Preferably, the polyacrylamide is anionic polyacrylamide with a molecular weight of 8 - 15 million, cationic polyacrylamide with a molecular weight of 5 - 12 million, and non-ionic polyacrylamide with a molecular weight of 9 - 12 million.

[0013] Polyacrylamide is an efficient flocculant. Adding a small amount of the flocculant can greatly enhance the flocculation effect of the system. The larger the molecular weight of polyacrylamide, the longer its molecular chain, and the more suspended particles it can adsorb. During the flocculation process, this polyacrylamide with a large molecular weight can more effectively capture and bridge tiny particles in water, improving the flocculation efficiency. However, when the molecular weight of polyacrylamide is too high, its molecular chain is too long, making it difficult to completely dissolve and disperse in water, which will instead affect the flocculation effect. Therefore, polyacrylamide with a molecular weight ranging from several hundred to over ten million is more suitable for sewage treatment.

[0014] Preferably, the composite magnetic flocculant further comprises, by weight: 2 - 5 parts of sulfate, 1 - 2 parts of dispersant, and 0.5 - 1 part of surfactant.

[0015] The dispersant can prevent the re - aggregation of modified fly ash particles and provide a uniform dispersion environment for the addition of subsequent components. The surfactant can modify the particle surface and enhance the adsorption capacity, further improving the performance of the flocculant.

[0016] Preferably, it further comprises, by weight: 3 - 4 parts of sulfate, 1.5 - 1.8 parts of dispersant, and 0.7 - 0.9 part of surfactant.

[0017] Preferably, the sulfate is one or both of sodium sulfate or gypsum, the dispersant is one or both of sodium hexametaphosphate or modified polyether dispersant, and the surfactant is one or both of oleic acid or Tween.

[0018] The sulfate ions in the sulfate can chemically react with the active components in the fly ash to form new chemical bonds. The formation of these chemical bonds helps to fix the pollutants in the sewage on the fly ash particles, thus achieving flocculation sedimentation. Sodium hexametaphosphate is a commonly used inorganic dispersant with relatively low production cost and wide sources, being easy to obtain. Using a small amount of modified polyether dispersant can significantly improve the efficiency and quality of the flocculant, thereby reducing the overall cost to a certain extent. Oleic acid has good wettability and dispersibility. Tween has excellent emulsifying, dispersing, and stabilizing properties.

[0019] The present invention also adopts another technical solution: A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add a calcium source and stir evenly, then slowly add sulfate and stir for 30 - 120 min, and finally remove the excess liquid by filtration or centrifugation to obtain modified fly ash; (2) Disperse the magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution, and stir for 6-12 h. Then, remove the unbound poly-L-cysteine by centrifugal separation and washing. (3) Mix the modified fly ash with a dispersant and stir evenly. Then, add the product obtained in step (2) and stir evenly. Finally, add the dispersant and surfactant and stir for 30-60 min to obtain a mixed solution. (4) Dry and crush the mixed solution to obtain a composite magnetic flocculant.

[0020] Fly ash particles are fine. Pre-dispersing fly ash in deionized water can prevent its agglomeration and ensure its uniform distribution. Then, adding a calcium source, which can undergo ion exchange or complexation reactions with components such as silicates in fly ash, can improve the surface properties of fly ash and make it more likely to combine with other components. Similarly, magnetic nanoparticles are extremely fine. They can be first dispersed evenly in deionized water to make their reaction with poly-L-cysteine more sufficient. The dispersant can prevent the re-agglomeration of modified fly ash particles and provide a uniform dispersion environment for the addition of subsequent components, namely, magnetic nanoparticles γ-Fe2O3 modified by poly-L-cysteine, and improve the stability and reaction efficiency of the flocculant. Polyacrylamide is a highly efficient flocculant. Adding a small amount of the flocculant can greatly enhance the flocculation effect of the system. The surfactant can adjust the surface tension of the system and further optimize the performance of the flocculant. The two are added last to avoid the agglomeration of nanoparticles and fly ash caused by premature addition.

[0021] Preferably, the stirring speed is 500-650 rpm.

[0022] Too slow stirring speed will result in uneven mixing of materials, leading to excessive local concentration, affecting product quality, and greatly increasing the reaction time. Too fast stirring speed will cause material splashing, damage the material structure, generate a large amount of heat, wear the instrument equipment, and reduce product quality.

[0023] Preferably, the stirring temperature in step (1) and step (2) is 30-60 °C, the stirring temperature in step (3) is 30-40 °C, and the drying temperature in step (4) is 60-80 °C.

[0024] When modifying fly ash and surface-modifying magnetic nanoparticles γ-Fe2O3, at 30-60 °C, the reaction rate is moderate and the reaction is relatively uniform. Lower temperatures can promote the reaction of sulfates and calcium sources with fly ash, while avoiding the destruction of chemical structures or organic ligands at high temperatures. At the same time, appropriate temperatures help break some of the glass network structure inside the fly ash to form more pores, thereby improving its adsorption performance. When adding substances such as dispersants and polyacrylamide, lower temperatures (30-40 °C) help the uniform dispersion of dispersants and surfactants, avoiding local overheating and agglomeration caused by high temperatures. High-molecular materials such as polyacrylamide can maintain chemical stability within this temperature range and avoid degradation. Finally, when drying, slightly higher temperatures can accelerate drying and also avoid degradation of the product and destruction of the chemical structure caused by too high temperatures.

[0025] The beneficial effects of the present invention are as follows: (1) It can effectively utilize fly ash industrial by-products, reduce waste of resources and recycle waste. (2) The raw materials have extremely low toxic and side effects. Only polyacrylamide has weak toxicity, but the dosage is small, which can reduce secondary pollution to the environment. (3) The fly ash used as the raw material is inexpensive. Although the prices of the strong magnetic material magnetic nanoparticles γ-Fe2O3 and polyacrylamide with good flocculation and adsorption effects are relatively high, the dosage is small, and the required price of the raw materials is relatively low. Moreover, the preparation method only includes the processes of heating, stirring, drying and pulverizing each component, so the preparation method is green and economical. (4) The combined use of each raw material can achieve efficient flocculation, with good flocculation effect, and by using magnetic and magnetic field effects, rapid sedimentation of flocs can be achieved. (5) It breaks through the defect that it is difficult for conventional flocculants to simultaneously achieve all advantages such as efficient flocculation, rapid sedimentation and low cost. Specific embodiments

[0026] The present invention will be further described below in conjunction with embodiments.

[0027] General embodiment This embodiment provides a composite magnetic flocculant, which includes the following components in parts by weight: 15-30 parts of fly ash, 5-10 parts of functionalized magnetic nanomaterial γ-Fe2O3, 1-4 parts of poly-L-cysteine, 3-6 parts of calcium source, 0.5-1.5 parts of polyacrylamide, 2-5 parts of sulfate, 1-2 parts of dispersant and 0.5-1 part of surfactant.

[0028] In some embodiments provided by the present invention, the calcium source is one or two of calcium chloride or lime.

[0029] In some embodiments provided by the present invention, the polyacrylamide is an anionic polyacrylamide with a molecular weight of 8 million - 15 million, a cationic polyacrylamide with a molecular weight of 5 million - 12 million, or a non - ionic polyacrylamide with a molecular weight of 9 million - 12 million.

[0030] In some embodiments provided by the present invention, the sulfate is one or both of sodium sulfate and gypsum.

[0031] In some embodiments provided by the present invention, the dispersant is one or both of sodium hexametaphosphate and modified polyether.

[0032] In some embodiments provided by the present invention, the surfactant is one or both of oleic acid and Tween.

[0033] This example also provides a method for preparing the above - mentioned composite magnetic flocculant, which includes the following steps: (1) Disperse fly ash in deionized water, add a calcium source and stir evenly, then slowly add sulfate and stir for 30 - 120 min. Finally, remove the excess liquid by filtration or centrifugation to obtain modified fly ash; (2) Disperse magnetic nanoparticles γ - Fe2O3 in deionized water, add a certain amount of poly - L - cysteine solution and stir for 6 - 12 h. Then, remove the unbound poly - L - cysteine by centrifugation and washing; (3) Mix the modified fly ash with the dispersant and stir evenly, then add the product obtained in step (2) and stir evenly. Finally, add the dispersant and surfactant and stir for 30 - 60 min to obtain a mixed solution; (4) Dry and crush the mixed solution to obtain the composite magnetic flocculant.

[0034] In some embodiments provided by the present invention, the stirring speed is 100 - 650 rpm.

[0035] In some embodiments provided by the present invention, the stirring temperature in step (1) and step (2) is 30 - 60 °C, the stirring temperature in step (3) is 30 - 40 °C, and the drying temperature in step (4) is 60 - 80 °C.

[0036] Example 1 A composite magnetic flocculant, comprising the following components in parts by weight: 22.5 parts of pulverized coal ash, 7.5 parts of magnetic nanoparticles γ - Fe2O3, 2.5 parts of poly - L - cysteine, 3.5 parts of sodium sulfate, 4.5 parts of calcium chloride, 1 part of anionic polyacrylamide, 1.5 parts of sodium hexametaphosphate, and 0.8 part of oleic acid.

[0037] A method for preparing a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add calcium chloride, with a stirring speed of 500 rpm and a temperature of 50 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min with a stirring speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugation to obtain modified fly ash; (2) Disperse magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution and stir for 8 h, with a stirring speed of 500 rpm and a temperature of 50 °C. Then, remove the unbound poly-L-cysteine by centrifugation and washing; (3) Mix the modified fly ash and sodium hexametaphosphate and stir evenly, with a stirring speed of 500 rpm and a temperature of 40 °C. Then, add the product obtained in step (2) and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixed solution; (4) Dry and crush the mixed solution at a drying temperature of 70 °C to obtain a composite magnetic flocculant.

[0038] Fly ash has a large specific surface area and a rich pore structure, and can adsorb suspended particles, organic matter and heavy metal ions in sewage. Moreover, its surface contains active groups such as aluminum, silicon and iron, and these groups can form charged active sites in water, which can combine with metal ions or organic matter in sewage to form flocs and precipitate. Modifying fly ash by combining a calcium source and sulfate can not only improve the chemical adsorption ability of fly ash, but also improve its physical structure and surface properties, so that it shows higher efficiency and better effect when treating sewage. These products not only improve the reaction activity of fly ash, but also enhance the flocculation effect by forming fibrous or network-like structures. Sodium hexametaphosphate is a commonly used inorganic dispersant, which can form stable complexes with multivalent metal ions such as calcium and magnesium, effectively prevent particle aggregation, and maintain the stability and uniformity of the system. Sodium sulfate and calcium chloride contain rich sulfate ions and calcium ions, and the modification effect is good. Anionic polyacrylamide is suitable for neutral or alkaline sewage and can effectively flocculate suspended particles in sewage.

[0039] Example 2 A composite magnetic flocculant, comprising the following components in parts by weight: 15 parts of pulverized coal ash, 5 parts of magnetic nanoparticles γ-Fe2O3, 3 parts of poly-L-cysteine, 4 parts of gypsum, 5 parts of lime, 1.2 parts of cationic polyacrylamide, 1.8 parts of modified polyether and 0.9 parts of Tween.

[0040] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add calcium chloride, with a stirring speed of 650 rpm and a temperature of 30 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min at a stirring speed of 650 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash; (2) Disperse magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution and stir for 8 h, with a stirring speed of 650 rpm and a temperature of 30 °C. Then, remove the unbound poly-L-cysteine by centrifugal separation and washing; (3) Mix the modified fly ash and sodium hexametaphosphate evenly, with a stirring speed of 650 rpm and a temperature of 40 °C. Then add the product obtained in step (2) and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixed solution; (4) Dry and crush the mixed solution at a drying temperature of 80 °C to obtain a composite magnetic flocculant.

[0041] Cationic polyacrylamide has a better flocculation effect on negatively charged suspended particles and is especially suitable for high-turbidity sewage containing a large amount of organic matter. The modified polyether dispersant realizes efficient dispersion in the medium through the combined action of hydrophilic groups and lipophilic groups in the molecular structure. The reaction between lime and water will release a large amount of heat, which can reduce the stirring temperature to avoid violent reactions caused by excessive temperature and protect the instrument. The main component of lime is calcium oxide, and these calcium ions can react with silicates, aluminates, etc. in fly ash to form hydrated products with gelling properties. Lime can also increase the alkalinity of fly ash and further stimulate its activity. The main component of gypsum is calcium sulfate, and sulfate ions can chemically react with the active components in fly ash to form hydrated products with gelling properties. These hydrated products can fill the gaps between fly ash particles, improve the compactness and strength of fly ash, and increase its adsorption capacity at the same time. At the same time, gypsum can also provide calcium ions to make the modification effect of fly ash better.

[0042] Example 3 A composite magnetic flocculant, comprising the following components in parts by weight: 30 parts of pulverized coal ash, 10 parts of magnetic nanoparticles γ-Fe2O3, 2 parts of poly-L-cysteine, 1.5 parts of sodium sulfate, 1.5 parts of gypsum, 4 parts of calcium chloride, 0.8 part of non-ionic polyacrylamide, 1.5 parts of sodium hexametaphosphate, and 0.7 part of oleic acid.

[0043] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add calcium chloride, with a stirring speed of 500 rpm and a temperature of 60 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min at a stirring speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash; (2) Disperse the magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution, stir for 8 h at a stirring speed of 650 rpm and a temperature of 60 °C, and then remove the unbound poly-L-cysteine by centrifugal separation and washing. (3) Mix the modified fly ash and sodium hexametaphosphate evenly by stirring at a stirring speed of 500 rpm and a temperature of 30 °C, then add the product obtained in step (2) and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixed solution. (4) Dry and crush the mixed solution at a drying temperature of 60 °C to obtain a composite magnetic flocculant.

[0044] Non-ionic polyacrylamide is suitable for neutral or weakly alkaline sewage and has good flocculation performance. The main component of gypsum is calcium sulfate, and sulfate ions can react with the active components in fly ash (such as silicon dioxide and alumina) to form hydrated products with gelling properties (such as silicon sulfate and aluminum sulfate). These hydrated products have better solubility and dispersibility in water, can fill the voids between fly ash particles, improve the density and strength of fly ash, and increase its adsorption capacity at the same time. At the same time, sulfate can destroy the original glass phase structure of fly ash, making its surface loose and porous, exposing more active sites. These active sites can more effectively adsorb impurities such as suspended solids and colloids in water, improving the flocculation efficiency.

[0045] Example 4 A composite magnetic flocculant, comprising the following components in parts by weight: 20 parts of pulverized coal ash, 7 parts of magnetic nanoparticles γ-Fe2O3, 1 part of poly-L-cysteine, 2 parts of sodium sulfate, 1.5 parts of calcium chloride, 1.5 parts of lime, 0.5 part of anionic polyacrylamide, 0.5 part of sodium hexametaphosphate, 0.5 part of modified polyether, and 0.5 part of oleic acid.

[0046] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add calcium chloride, stir at a stirring speed of 550 rpm and a temperature of 60 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min at a stirring speed of 550 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash. (2) Disperse the magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution, stir for 8 h at a stirring speed of 550 rpm and a temperature of 60 °C, and then remove the unbound poly-L-cysteine by centrifugal separation and washing. (3) Mix the modified fly ash and sodium hexametaphosphate evenly with a stirring speed of 550 rpm and a temperature of 40°C. Then add the product obtained in step (2) and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixed solution. (4) Dry and crush the mixed solution at a drying temperature of 70°C to obtain a composite magnetic flocculant.

[0047] The calcium ions (Ca 2+ ) in the calcium source may undergo chemical reactions with the active silicate ions and active aluminate ions in the fly ash to form compounds such as calcium silicate and calcium aluminate. These reactions may change the original structure of the fly ash, making its surface more porous and exposing more active sites, which is beneficial to the adsorption and flocculation processes. The addition of the calcium source may destroy the glassy phase structure of the fly ash and convert it into a crystalline phase structure with higher activity. This structural change may increase the specific surface area and porosity of the fly ash, thereby improving its adsorption performance and flocculation efficiency.

[0048] Example 5 A composite magnetic flocculant, comprising the following components in parts by weight: 25 parts of pulverized coal ash, 8 parts of magnetic nanoparticles γ-Fe2O3, 4 parts of poly-L-cysteine, 1 part of sodium sulfate, 1 part of gypsum, 1.5 parts of calcium chloride, 1.5 parts of lime, 1.5 parts of cationic polyacrylamide, 2 parts of sodium hexametaphosphate, 0.5 part of oleic acid, and 0.5 part of Tween.

[0049] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse the fly ash in deionized water, add calcium chloride, stir at a speed of 500 rpm and a temperature of 50°C. After stirring evenly, slowly add sodium sulfate and stir for 60 min at a speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugation to obtain modified fly ash. (2) Disperse the magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution and stir for 8 h at a speed of 500 rpm and a temperature of 50°C. Then remove the unbound poly-L-cysteine by centrifugation and washing. (3) Mix the modified fly ash and sodium hexametaphosphate evenly with a stirring speed of 500 rpm and a temperature of 35°C. Then add the product obtained in step (2) and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixed solution. (4) Dry and crush the mixed solution at a drying temperature of 70°C to obtain a composite magnetic flocculant.

[0050] The fly ash is modified by combining a calcium source and a sulfate. After modification, the surface of the fly ash may carry more positive or negative charges, and these charges can electrostatically adsorb impurity particles with opposite charges in water, thereby achieving chemical adsorption. The modified fly ash may have a higher density or better sedimentation performance, which enables the fly ash to settle faster in sewage, thus more effectively removing impurities such as suspended solids and colloids in water.

[0051] Comparative Example 1 A composite magnetic flocculant, comprising the following components in parts by weight: 22.5 parts of pulverized coal ash, 3.5 parts of sodium sulfate, 4.5 parts of calcium chloride, 1 part of anionic polyacrylamide, 1.5 parts of sodium hexametaphosphate, and 0.8 part of oleic acid.

[0052] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse the fly ash in deionized water, add calcium chloride, with a stirring speed of 500 rpm and a temperature of 50 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min, with a stirring speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash; (2) Mix the modified fly ash and sodium hexametaphosphate and stir evenly, with a stirring speed of 500 rpm and a temperature of 40 °C. Add anionic polyacrylamide and oleic acid and stir for 50 min to obtain a mixture; (3) Dry and crush the mixture, with a drying temperature of 70 °C, to obtain the composite magnetic flocculant.

[0053] The difference between this comparative example and Example 1 is that this comparative example does not add the modified nanoparticles γ-Fe2O3 and poly-L-cysteine.

[0054] Comparative Example 2 A composite magnetic flocculant, comprising the following components in parts by weight: 22.5 parts of pulverized coal ash, 7.5 parts of nanoparticles γ-Fe2O3, 3.5 parts of sodium sulfate, 4.5 parts of calcium chloride, 1 part of anionic polyacrylamide, 1.5 parts of sodium hexametaphosphate, and 0.8 part of oleic acid.

[0055] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse the fly ash in deionized water, add calcium chloride, with a stirring speed of 500 rpm and a temperature of 50 °C. After stirring evenly, slowly add sodium sulfate and stir for 60 min, with a stirring speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash; (2) Mix the modified fly ash and sodium hexametaphosphate evenly by stirring at a speed of 500 rpm and a temperature of 40°C. Then add the nano-particle γ-Fe2O3 and stir evenly. Finally, add anionic polyacrylamide and oleic acid and stir for 50 minutes to obtain a mixed solution. (3) Dry and crush the mixed solution at a drying temperature of 70°C to obtain a composite magnetic flocculant.

[0056] The difference between this comparative example and Example 1 is that poly-L-cysteine which can modify the nano-particle γ-Fe2O3 was not added in this comparative example.

[0057] Comparative Example 3 A composite magnetic flocculant, comprising the following components in parts by weight: 22.5 parts of coal fly ash, 7.5 parts of magnetic nano-particle γ-Fe2O3, 2.5 parts of poly-L-cysteine, 3.5 parts of sodium sulfate, 4.5 parts of calcium chloride, 1.5 parts of sodium hexametaphosphate, and 0.8 part of oleic acid.

[0058] A preparation method of a composite magnetic flocculant, comprising the following steps: (1) Disperse fly ash in deionized water, add calcium chloride, stir at a speed of 500 rpm and a temperature of 50°C. After stirring evenly, slowly add sodium sulfate and stir for 60 minutes at a speed of 500 rpm. Finally, remove the excess liquid by filtration or centrifugal separation to obtain modified fly ash. (2) Disperse the magnetic nano-particle γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution and stir for 8 hours at a speed of 500 rpm and a temperature of 50°C. Then remove the unbound poly-L-cysteine by centrifugal separation and washing. (3) Mix the modified fly ash and sodium hexametaphosphate evenly by stirring at a speed of 500 rpm and a temperature of 40°C. Then add the product obtained in step (2) and stir evenly to obtain a mixed solution. (4) Dry and crush the mixed solution at a drying temperature of 70°C to obtain a composite magnetic flocculant.

[0059] The difference between this comparative example and Example 1 is that the highly efficient flocculant anionic polyacrylamide was not added in this comparative example.

[0060] The summary table of the raw material ratios used in Examples 1-5 and Comparative Examples 1-3 is shown in Table 1.

[0061] Table 1 Raw material ratios used in Examples 1-5 and Comparative Examples 1-3.

[0062] Effect test The flocculation effects of Examples 1-5 and Comparative Examples 1-3 were tested. The test method was to use the flocculants obtained from Examples 1-5 and Comparative Examples 1-3 to treat oilfield wastewater under the action of an external magnetic field. Oilfield wastewater, also known as oil-based drilling wastewater, mainly comes from drilling operations, oilfield produced water, well washing water, etc. during the oil extraction process. Its characteristics are as follows: it contains various organic substances, inorganic substances, and microorganisms, etc. The organic substances are mainly petroleum hydrocarbons, and the inorganic substances mainly include various salts and heavy metals, etc. In addition, the wastewater may also contain suspended substances such as clay particles, silt, and fine sand. The composition is extremely complex, with extremely high oil content and suspended solid content, and the COD content is also extremely high, reaching several thousand or tens of thousands, making it extremely difficult to treat.

[0063] The test results obtained from Examples 1-5 and Comparative Examples 1-3 are shown in Table 2.

[0064] Table 2 Test results.

[0065] Test results.

[0066] It can be seen from Table 2 that the flocculation effect of the present invention is good and the sedimentation time is fast. In Examples 1-5, the total nitrogen removal rate and turbidity removal rate reached over 97%, and the total phosphorus removal rate, COD removal rate, heavy metal removal rate, and chromaticity removal rate all reached over 98%, all higher than those of the comparative examples, and the sedimentation time was controlled within 3-8 minutes. Compared with the comparative examples, the sedimentation time of the flocs was greatly accelerated. Therefore, the composite magnetic flocculant of the present invention can achieve beneficial effects such as efficient flocculation, rapid sedimentation, and effective removal of organic substances and heavy metals, can significantly reduce production costs, cause extremely little secondary pollution to the environment, and is green and economical.

Claims

1. A composite magnetic flocculant, characterized in that, By weight, it includes the following raw materials: 15 - 30 parts of fly ash, 5 - 10 parts of magnetic nanoparticles γ-Fe2O3, 1 - 4 parts of poly-L-cysteine, 3 - 6 parts of calcium source, and 0.5 - 1.5 parts of polyacrylamide.

2. The composite magnetic flocculant according to claim 1, characterized in that, By weight, it includes the following raw materials: 20 - 25 parts of fly ash, 7 - 8 parts of magnetic nanoparticles γ-Fe2O3, 2 - 3 parts of poly-L-cysteine, 4 - 5 parts of calcium source, and 0.8 - 1.2 parts of polyacrylamide.

3. The composite magnetic flocculant according to claim 1 or 2, characterized in that, The calcium source is one or both of calcium chloride and lime.

4. The composite magnetic flocculant according to claim 1, characterized in that, The polyacrylamide is anionic polyacrylamide with a molecular weight of 8 million - 15 million, cationic polyacrylamide with a molecular weight of 5 million - 12 million, or non-ionic polyacrylamide with a molecular weight of 9 million - 12 million.

5. The composite magnetic flocculant according to claim 1, wherein By weight, it also includes: 2 - 5 parts of sulfate, 1 - 2 parts of dispersant, and 0.5 - 1 part of surfactant.

6. The composite magnetic flocculant according to claim 5, wherein By weight, it also includes: 3 - 4 parts of sulfate, 1.5 - 1.8 parts of dispersant, and 0.7 - 0.9 part of surfactant.

7. The composite magnetic flocculant according to claim 5 or 6, characterized in that, The sulfate is one or both of sodium sulfate and gypsum, the dispersant is one or both of sodium hexametaphosphate and modified polyether dispersant, and the surfactant is one or both of oleic acid and Tween.

8. A preparation method of a composite magnetic flocculant, characterized in that, It includes the following steps: (1) Disperse fly ash in deionized water, add the calcium source and stir evenly, then slowly add the sulfate and stir for 30 - 120 min. Finally, remove the excess liquid by filtration or centrifugation to obtain modified fly ash. (2) Disperse magnetic nanoparticles γ-Fe2O3 in deionized water, add a certain amount of poly-L-cysteine solution and stir for 6 - 12 h. Then, remove the unbound poly-L-cysteine by centrifugation and washing. (3) Mix the modified fly ash with the dispersant and stir evenly, then add the product obtained in step (2) and stir evenly. Finally, add the dispersant and surfactant and stir for 30 - 60 min to obtain a mixed solution. (4) Dry and crush the mixed solution to obtain a composite magnetic flocculant.

9. The preparation method of the composite magnetic flocculant according to claim 8, characterized in that, The stirring speed is 500 - 650 rpm.

10. The preparation method of the composite magnetic flocculant according to claim 8, characterized in that, The stirring temperature in steps (1) and (2) is 30 - 60 °C, the stirring temperature in step (3) is 30 - 40 °C, and the drying temperature in step (4) is 60 - 80 °C.

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