Modified fly ash buoyant microspheres and preparation and application thereof

Abstract

The application discloses a modified fly ash buoyancy microsphere and preparation and application thereof, and relates to the technical field of inorganic nonmetallic adsorption materials. The application selects fly ash hollow microspheres as the base of the buoyancy microspheres, utilizes the characteristics of the low density, large specific surface area, rich active groups on the surface and excellent self-floating performance of the fly ash hollow microspheres, introduces active amino groups on the surface of the microspheres through a silane coupling agent, and then makes chemical bonding with chitosan, so that the chitosan is stably grafted on the surface of the microspheres in the form of a covalent bond, and the chitosan modified buoyancy microspheres with high positive charge density are formed. The microspheres can efficiently capture negatively charged microalgae cells through electrostatic adsorption, and the formed aggregates can spontaneously float up to realize rapid separation; meanwhile, the application realizes resource utilization of solid waste, has low material cost, can be added in situ, does not need air flotation equipment, can complete microalgae flotation separation within several minutes, and is suitable for emergency treatment of blue-green algae in eutrophic water bodies.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic adsorbent materials technology, specifically to a modified fly ash buoyancy microsphere and its preparation and application. Background Technology

[0002] In recent years, with the rapid development of industry and agriculture and the continuous increase in urban sewage discharge, the eutrophication problem of freshwater bodies such as lakes and reservoirs has become increasingly serious. Excessive input of nutrients such as nitrogen and phosphorus has led to frequent outbreaks of cyanobacterial blooms. Among them, Microcystis, which can produce microcystin, seriously threatens drinking water safety and aquatic ecological stability, and has become a major problem that urgently needs to be solved in the field of water environment management.

[0003] Currently, the main technologies for treating cyanobacterial blooms include physical, chemical, and biological methods. Physical methods, such as mechanical harvesting and membrane filtration, suffer from low treatment efficiency and high equipment investment. Chemical methods, such as adding flocculants like copper salts and polyaluminum chloride, can quickly flocculate and settle algal cells, but they are prone to secondary pollution and pose a risk of endogenous release from the settled sediment. Biological methods have long treatment cycles and are constrained by environmental conditions. Traditional air flotation technology relies on external bubble generating equipment, resulting in complex systems, high operating costs, and unsuitability for rapid in-situ response to sudden cyanobacterial blooms.

[0004] Adsorption / flocculation technologies based on modified clay or magnetic particles have attracted attention in recent years. These materials enhance the electrostatic adsorption capacity of negatively charged algal cells through surface charge modification, but modified clay requires sedimentation and separation, which exacerbates sediment pollution; magnetic particles are costly to prepare and have uneven magnetic field distribution in large-scale water bodies. The above-mentioned materials generally suffer from problems such as large dosage and loose flocs, making it difficult to achieve both rapid capture and efficient separation.

[0005] Hollow microspheres made from fly ash are lightweight inorganic non-metallic materials extracted from the byproducts of pulverized coal combustion in thermal power plants. They are typical inorganic non-metallic adsorbents with low density, large specific surface area, rich silanol groups on the surface, and good self-floating properties. They are also widely available and inexpensive.

[0006] However, there are currently no reports on the direct use of fly ash hollow microspheres for the adsorption and removal of cyanobacteria in water. The inherent low charge density on their surface makes their electrostatic capture ability for negatively charged microalgae very limited. It is urgent to endow them with efficient algae-capturing performance through appropriate surface functionalization modification methods, so as to give full play to their application potential as a self-floating carrier in the emergency treatment of cyanobacteria.

[0007] Based on this, the present invention urgently needs to develop a novel functionalized hollow microsphere material that is low in cost, can be added in situ, does not require air flotation equipment, and has rapid flotation capability.

[0008] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a modified fly ash buoyancy microsphere, its preparation, and its application, thereby resolving the issues raised in the background section.

[0010] A modified fly ash buoyancy microsphere comprises: hollow fly ash microspheres, a silane coupling agent grafted onto the surface of the hollow fly ash microspheres, and chitosan combined with the silane coupling agent.

[0011] Preferably, the silane coupling agent is 3-aminopropyltriethoxysilane.

[0012] Preferably, the mass ratio of the fly ash hollow microspheres to chitosan is 8:1.

[0013] Preferably, the particle size of the fly ash hollow microspheres is 50±4 μm.

[0014] A method for preparing modified fly ash buoyancy microspheres according to the above-described method includes the following steps: (1) The fly ash hollow microspheres are cleaned and dried to obtain clean and dry fly ash hollow microspheres; (2) Hydrolyze the 3-aminopropyltriethoxysilane coupling agent in an aqueous ethanol solution to obtain a hydrolyzed coupling agent solution; (3) The dried fly ash hollow microspheres were added to the hydrolyzed coupling agent solution to carry out the silanization reaction and obtain silanized modified fly ash hollow microspheres. (4) Add the silanized modified fly ash hollow microspheres to the acetic acid solution of chitosan to carry out the coating reaction, and obtain chitosan-coated fly ash hollow microspheres; (5) The chitosan-coated fly ash hollow microspheres are washed and dried to obtain chitosan-modified fly ash hollow microspheres.

[0015] Preferably, in step (2), the mass ratio of the 3-aminopropyltriethoxysilane coupling agent to the 95% ethanol aqueous solution is 1:50, and the hydrolysis time is 1 h.

[0016] Preferably, in step (3), the mass ratio of the fly ash hollow microspheres to the hydrolyzed 3-aminopropyltriethoxysilane coupling agent solution is 1:20, the silanization reaction temperature is 60–80°C, and the reaction time is 2.0–4.0 h.

[0017] Preferably, the chitosan in step (4) is provided in the form of a 1% acetic acid solution with a concentration of 5 g / L, the coating reaction temperature is 50°C, and the reaction time is 3.0–5.0 h.

[0018] An application of modified fly ash buoyancy microspheres as described above in the in-situ capture and rapid flotation removal of Microcystis aeruginosa in water.

[0019] A type of modified fly ash buoyancy microsphere with a chitosan dosage of 45–55 mg chitosan / g dry algae.

[0020] The modified fly ash buoyancy microspheres provided in this invention, along with their preparation and application, have the following beneficial effects: (1) This invention is the first to use fly ash hollow microspheres as the matrix material, and introduces active amino groups on their surface through a silane coupling agent, which then chemically bonds with chitosan, successfully constructing modified buoyancy microspheres with high positive charge density. These microspheres retain the physical properties of low density and excellent self-floating performance of fly ash hollow microspheres, and at the same time, through the introduction of positive charge on the surface, they can efficiently capture negatively charged microalgal cells by means of electrostatic adsorption.

[0021] (2) In this invention, chitosan and fly ash hollow microspheres are stably bonded together by a coupling agent in the form of covalent bonds, which is different from the traditional physical mixing or simple coating modification method, effectively avoiding the problem of functional components falling off during use. At the same time, the amino functional groups of chitosan can also form multiple synergistic effects with the surface of algal cells, such as hydrogen bonds and van der Waals forces, which significantly enhances the capture ability of microalgae and the stability of flocs.

[0022] (3) This invention achieves rapid flotation separation of microalgae. Benefiting from the excellent buoyancy of the microspheres and the compact, low-density structure of the algae-microsphere aggregates, the flocs can spontaneously float to the water surface, and the flotation process can be completed within minutes, without relying on external air flotation equipment, significantly reducing energy consumption and operational complexity. Compared with traditional settling materials, this invention avoids the risk of endogenous pollution caused by algal sediment deposition.

[0023] (4) The raw materials for this invention are widely available and inexpensive, and the preparation process is simple, controllable, and easy to scale up. Fly ash hollow microspheres are solid waste from thermal power plants, and using them as a matrix material realizes the resource utilization of solid waste. The material dosage is small, the treatment efficiency is high, and it has both environmental and economic benefits. Attached image description: Figure 1 This is a flowchart of the preparation process for modified fly ash buoyancy microspheres; Figure 2 The flotation efficiency-time curves of microcystis aeruginosa modified with fly ash buoyancy microspheres of different particle sizes are shown. Figure 3 These are scanning electron microscope images of modified fly ash buoyancy microspheres and algae-microsphere aggregates; in, Figure 3 The left image is a SEM image of the modified fly ash buoyancy microspheres; Figure 3 The image on the right is a SEM image of algal-microsphere aggregates. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To address the aforementioned technical problems, this invention provides a modified fly ash buoyancy microsphere, its preparation, and its application, thereby resolving the issues raised in the background section.

[0026] Pretreatment of fly ash hollow microspheres: Fly ash hollow microspheres (FABC) produced by Henan Hengyuan New Material Technology Co., Ltd., China, were used as the flotation carrier with a particle size range of 50–120 μm to ensure stable flotation performance. The fly ash hollow microspheres were washed with distilled water to remove debris, and then dried at 105°C for surface modification.

[0027] Example 1: Preparation of silane coupling agent-grafted hollow fly ash microspheres 10.0 g of fly ash hollow microspheres were washed with deionized water and dried at 105°C for later use. 2 mL of 3-aminopropyltriethoxysilane was added to 100 mL of 95% ethanol and hydrolyzed for 1 h. Then, 5.0 g of fly ash hollow microspheres were added to the hydrolyzed 3-aminopropyltriethoxysilane solution and reacted at 80°C for 2 h. The modified fly ash hollow microspheres were washed with anhydrous ethanol and then dried at 50°C for 24 h to obtain silane coupling agent-grafted fly ash hollow microspheres.

[0028] Example 2: Effect of different mass ratios of fly ash hollow microspheres to chitosan on flotation performance 1.0 g of chitosan was dissolved in 200 mL of 1% acetic acid solution to prepare a 5 g / L solution. 2.0 g, 4.0 g, 6.0 g, 8.0 g, and 10.0 g of 50±4 μm silane coupling agent-grafted fly ash hollow microspheres were weighed and added to the chitosan solution, making the mass ratio of fly ash hollow microspheres to chitosan 2:1, 4:1, 6:1, 8:1, and 10:1, respectively. The mixture was stirred at 50°C for 3 h, and the resulting product was washed with anhydrous ethanol and dried at 50°C for 24 h to obtain modified buoyancy microspheres with different chitosan loadings.

[0029] In the Microcystis flotation experiment, 200 mL of 1×10^ 7 Modified fly ash buoyancy microspheres at different mass ratios were added to a Microcystis aeruginosa solution containing 55 mg / g of dry algae. The mixture was then rapidly stirred for 50 s, slowly stirred for 5 min, and allowed to stand for 5 min. The results showed that the optimal mass ratio was 8:1 (fly ash hollow microspheres to chitosan) for the highest algal cell removal rate, exceeding 95%.

[0030] Example 3: Effect of modified fly ash buoyancy microspheres of different particle sizes on flotation performance 1.0 g of chitosan was dissolved in 200 mL of 1% acetic acid solution to prepare a 5 g / L solution. 8.0 g of silane coupling agent-grafted hollow fly ash microspheres with particle sizes of 50±4 μm, 68±2 μm, 86±2 μm, and 108±3 μm were weighed and added to the chitosan solution. The mixture was stirred at 50°C for 3 h, washed with anhydrous ethanol, and dried at 50°C for 24 h to obtain modified fly ash buoyancy microspheres of different particle sizes.

[0031] In the Microcystis flotation experiment, 200 mL of 1×10^ 7 Modified fly ash buoyancy microspheres of different particle sizes were added to a Microcystis aeruginosa solution of cells / mL to make the chitosan dosage 55 mg / g dry algae. The mixture was stirred rapidly for 50 s, then slowly for 5 min, and then allowed to stand for 5 min.

[0032] Figure 2 The results showed that modified fly ash buoyancy microspheres with a particle size of 50±4 μm had the best flotation effect, achieving rapid flotation of more than 90% of algal cells within 1 minute and a removal rate of nearly 100% within 5 minutes; microspheres with particle sizes of 68±2 μm and 86±2 μm had moderate flotation rates and removal rates, with removal rates of approximately 88% and 83% respectively within 5 minutes; microspheres with a particle size of 108±3 μm had the worst flotation effect, with a removal rate of less than 80% within 5 minutes.

[0033] The flotation efficiency decreases gradually with increasing particle size. This is because the smaller the particle size, the larger the specific surface area of ​​the microspheres, the more positive charge sites are exposed on the surface, and the stronger the electrostatic adsorption and charge neutralization ability with negatively charged algal cells. At the same time, the algal-microsphere flocs formed are more compact and have lower density, resulting in a faster flotation rate.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A modified fly ash buoyancy microsphere, characterized in that, include: Hollow microspheres of fly ash, silane coupling agents grafted onto the surface of the hollow microspheres of fly ash, and chitosan combined with the silane coupling agents.

2. The modified fly ash buoyancy microspheres according to claim 1, characterized in that, The silane coupling agent is 3-aminopropyltriethoxysilane.

3. The modified fly ash buoyancy microspheres according to claim 1, characterized in that, The mass ratio of the fly ash hollow microspheres to chitosan is 8:

1.

4. The modified fly ash buoyancy microspheres according to claim 1, characterized in that, The particle size of the hollow fly ash microspheres is 50±4 μm.

5. A method for preparing modified fly ash buoyancy microspheres according to any one of claims 1-4, characterized in that, Includes the following steps: (1) The fly ash hollow microspheres are cleaned and dried to obtain clean and dry fly ash hollow microspheres; (2) Hydrolyze the 3-aminopropyltriethoxysilane coupling agent in an aqueous ethanol solution to obtain a hydrolyzed coupling agent solution; (3) The dried fly ash hollow microspheres were added to the hydrolyzed coupling agent solution to carry out the silanization reaction and obtain silanized modified fly ash hollow microspheres. (4) Add the silanized modified fly ash hollow microspheres to the acetic acid solution of chitosan to carry out the coating reaction, and obtain chitosan-coated fly ash hollow microspheres; (5) The chitosan-coated fly ash hollow microspheres are washed and dried to obtain chitosan-modified fly ash hollow microspheres.

6. The method for preparing modified fly ash buoyancy microspheres according to claim 5, characterized in that, In step (2), the mass ratio of the 3-aminopropyltriethoxysilane coupling agent to the 95% ethanol aqueous solution is 1:50, and the hydrolysis time is 1 h.

7. The method for preparing modified fly ash buoyancy microspheres according to claim 5, characterized in that, In step (3), the mass ratio of the fly ash hollow microspheres to the hydrolyzed 3-aminopropyltriethoxysilane coupling agent solution is 1:20, the silanization reaction temperature is 60–80°C, and the reaction time is 2.0–4.0 h.

8. The method for preparing modified fly ash buoyancy microspheres according to claim 5, characterized in that, The chitosan in step (4) is provided in the form of a 1% acetic acid solution with a concentration of 5 g / L, the coating reaction temperature is 50°C, and the reaction time is 3.0–5.0 h.

9. The application of the modified fly ash buoyancy microspheres according to any one of claims 1-4 in the in-situ capture and rapid flotation removal of Microcystis aeruginosa in water.

10. The application of the modified fly ash buoyancy microspheres according to claim 9 in the in-situ capture and rapid flotation removal of Microcystis aeruginosa in water, characterized in that, The modified fly ash buoyancy microspheres are calculated at a chitosan dosage of 45–55 mg chitosan / g dry algae.

Images