A method for separating and purifying silica-coated magnetic particles in coal fly ash

Abstract

This invention provides a sample pretreatment method for separating and purifying silica-coated magnetic particles from coal fly ash. The method employs magnetic adsorption to separate the magnetic particles and hydrochloric acid digestion to effectively purify the silica-coated magnetic particles from the separated sample, thereby obtaining pure magnetic particles with a silica outer coating structure. This method avoids the limitations of traditional artificial synthesis methods, such as high energy consumption, high pollution, and complex procedures, and has advantages such as simple and environmentally friendly raw materials, simple and rapid process, high separation degree of target particles, and few interfering impurities.

Description

Technical Field

[0001] This invention relates to the field of sample pretreatment, specifically to a method for separating and purifying magnetic particles coated with silica in coal fly ash samples. Background Technology

[0002] Magnetic particles with Fe3O4 and γ-Fe2O3 as their main components can exhibit directional movement under the influence of an external magnetic field. Due to their unique magnetic properties, various novel synthetic magnetic materials have shown great application potential in many fields such as biomedicine, medical imaging, environmental remediation, bio-fermentation, special coatings, and industrial catalysis in recent years, and have therefore attracted widespread attention.

[0003] Exposed magnetic particles, due to their hydrophobic nature, are prone to aggregation in solution. Furthermore, their magnetic characteristics, combined with magnetic dipole interactions, can further promote aggregation. Under acidic conditions, iron oxides are susceptible to corrosion, resulting in low biocompatibility. In recent years, various materials have been used to modify exposed magnetic particles, such as various noble metals, polymeric organic materials, and silica. Among these, silica, due to its low biotoxicity and strong chemical stability, is considered the most promising composite magnetic material for biomedical applications. The silica coating on the surface of magnetic particles effectively shields the interaction of their magnetic dipoles, reducing particle aggregation and enhancing their dispersion performance. The silica coating also protects the iron oxide core, enhancing its stability under acidic conditions and improving its biocompatibility. In addition, the silica surface has numerous silanol groups, facilitating surface modification and functionalization to prepare composite magnetic particles with different functions. Due to the excellent magnetic response, biocompatibility, and ease of functionalization of silica-encapsulated magnetic particles, they have been widely used in targeted drugs, magnetic thermotherapy, and bioaccumulation.

[0004] Currently, silica-coated magnetic particles are mainly prepared through artificial synthesis. First, Fe3O4 or γ-Fe2O3 particles are prepared chemically. Then, silica is coated onto the surface of these magnetic particles using a complex process, resulting in magnetic particles with a silica coating. However, artificial synthesis is energy-intensive, requires various raw materials, and involves complex processes. The high economic cost and energy consumption significantly limit the widespread use of silica-coated magnetic particles. Therefore, developing a low-cost, low-energy-consumption, simple, and environmentally friendly process for preparing silica-coated magnetic particles could greatly expand their applications across various fields.

[0005] As a typical waste resource, coal-fired power plants, which primarily use coal as fuel, generate large amounts of fly ash during coal combustion. Simultaneously, fly ash is a major anthropogenic source of global fine particulate matter pollution, and prolonged exposure poses serious health hazards to humans. Therefore, in-depth development of the utilization value of specific components in fly ash can not only reduce the consumption of natural resources and energy but also help mitigate the health hazards caused by fly ash emissions. Thus, using fly ash as a raw material to separate and extract silica-encapsulated magnetic particles has several significant advantages. First, silica and magnetic particles are the main mineral components in fly ash, both exhibiting high abundance. Second, statistics show that global coal-fired power plants generate over 1 billion tons of fly ash annually. If silica-encapsulated magnetic nanoparticles can be extracted from fly ash, the economic cost of their preparation can be effectively reduced, while significant environmental and health benefits can be obtained. Third, due to the fully high-temperature combustion process, coal fly ash is a natural fine particulate powder, which is very beneficial for sample processing during the separation and extraction process; at the same time, due to the extremely high-temperature combustion process, the mineral element particles in coal fly ash usually have strong chemical stability.

[0006] Currently, due to the lack of effective sample pretreatment techniques, it is not possible to effectively and specifically extract silica-encapsulated magnetic particles from magnetically enriched and recovered magnetic particles. Summary of the Invention

[0007] This invention provides a sample pretreatment method for the specific recovery of magnetic particles coated with silica from coal fly ash. The method is simple, safe, and can effectively remove impurities.

[0008] This invention provides a method for separating and purifying silica-encapsulated magnetic particles from coal fly ash, comprising the following steps:

[0009] 1) Preliminary separation of magnetic components

[0010] The collected coal fly ash powder was dispersed in an aqueous solution to obtain a coal fly ash aqueous solution. The coal fly ash aqueous solution was further dispersed by ultrasound for 20 minutes. After ultrasonic dispersion, the coal fly ash aqueous solution underwent preliminary separation of magnetic components under the action of an external magnetic field.

[0011] 2) Preliminary separation and purification of magnetic components

[0012] The magnetic components obtained from the initial separation were added to a hydrochloric acid solution with a concentration of ≥2 mol / L and heated to digest at 60-100℃ for 12 h. After the digested magnetic component solution was cooled to room temperature, it was ultrasonically dispersed for 20 min.

[0013] 3) Separation of magnetic components after purification

[0014] The sample solution after hydrochloric acid digestion is subjected to magnetic component separation again under the action of an external magnetic field. The component enriched under the final magnetic field is collected to obtain silica-encapsulated magnetic particles.

[0015] Furthermore, the coal fly ash is in powder form.

[0016] Furthermore, the magnetic components in the silica-encapsulated magnetic core particles include iron(III) oxide (Fe3O4) and isometric iron(III) oxide (γ-Fe2O3).

[0017] Furthermore, the outer coating layer of the silica-encapsulated magnetic particles is mainly composed of silica.

[0018] Furthermore, in step 2), the concentration of hydrochloric acid used is 2 mol / L.

[0019] Furthermore, in step 2), the heating and digestion temperature is 60°C.

[0020] Furthermore, the particle size distribution of the silica-encapsulated magnetic particles is in the range of nanometers to micrometers.

[0021] This invention utilizes the magnetic properties of Fe3O4 and γ-Fe2O3 and the chemical stability of silica in hydrochloric acid to design a simple sample pretreatment technique for the specific separation of silica-coated magnetic particles from coal fly ash. This technique offers very low sample recovery costs. Testing demonstrates that the method is simple and safe to operate, exhibits high specificity for target particle recovery, and effectively removes complex matrices from samples. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Transmission electron microscopy results of silica-encapsulated magnetic particles extracted from coal fly ash;

[0024] Figure 2 Energy dispersive spectral analysis of the elemental distribution of silica-encapsulated magnetic particles extracted from coal fly ash. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0026] A method for separating and purifying silica-encapsulated magnetic particles from coal fly ash includes the following steps:

[0027] 1) Preliminary separation of magnetic components

[0028] The collected coal fly ash powder was dispersed in an aqueous solution to obtain a coal fly ash aqueous solution. The coal fly ash aqueous solution was further dispersed by ultrasound for 20 minutes. After ultrasonic dispersion, the coal fly ash aqueous solution underwent preliminary separation of magnetic components under the action of an external magnetic field.

[0029] 2) Preliminary separation and purification of magnetic components

[0030] The magnetic components obtained from the initial separation were added to a hydrochloric acid solution with a concentration of ≥2 mol / L and heated to digest at 60-100℃ for 12 h. After the digested magnetic component solution was cooled to room temperature, it was ultrasonically dispersed for 20 min.

[0031] 3) Separation of magnetic components after purification

[0032] The sample solution after hydrochloric acid digestion is subjected to magnetic component separation again under the action of an external magnetic field. The component enriched under the final magnetic field is collected to obtain silica-encapsulated magnetic particles.

[0033] In this application, magnetic components in coal fly ash are first separated using magnetic recovery. Taking advantage of the chemical stability of silica in hydrochloric acid solution, the magnetic components without silica coating are removed by hydrochloric acid digestion under heating conditions. This achieves specific purification and separation of silica-coated magnetic particles, without the need for any other chemical reagents throughout the process. Testing shows that this method is simple, efficient, environmentally friendly, easy and safe to operate, and has high efficiency in recovering the target particles.

[0034] The present application will be further described below through examples:

[0035] Example 1 of this invention provides a sample pretreatment method for separating and purifying silica-encapsulated magnetic particles from coal fly ash, comprising the following steps:

[0036] 1) Preliminary separation of samples

[0037] 100 mg of collected coal fly ash powder sample was dispersed in 30 mL of aqueous solution. The glass bottle containing the coal fly ash aqueous solution sample was ultrasonically dispersed in an ultrasonic instrument for 20 min. After ultrasonic dispersion, a 1 cm × 1 cm magnet was fixed on the outer wall of the sample glass bottle to apply an external magnetic field for preliminary separation of magnetic components in the sample solution.

[0038] 2) Purification of the initially separated samples

[0039] Remove the solution after magnetic enrichment, collect the magnetic components enriched by magnetic adsorption, transfer the sample obtained from the preliminary magnetic separation to 5 mL of 2 mol / L hydrochloric acid solution, heat and digest at 60℃ for 12 h, and after the digested sample solution is cooled to room temperature, it is ultrasonically dispersed for 20 min.

[0040] 3) Separation of purified samples

[0041] The sample solution after hydrochloric acid digestion is subjected to magnetic separation again under the action of an external magnetic field. The component enriched under the action of the final magnetic field is collected to obtain pure silica-encapsulated magnetic particles.

[0042] Example 2 of this invention provides a sample pretreatment method for separating and purifying silica-encapsulated magnetic particles from coal fly ash, comprising the following steps:

[0043] 1) Preliminary separation of samples

[0044] 200 mg of collected coal fly ash powder sample was dispersed in 50 mL of aqueous solution. The glass bottle containing the coal fly ash aqueous solution sample was ultrasonically dispersed in an ultrasonic instrument for 20 min. After ultrasonic dispersion, a 1 cm × 1 cm magnet was fixed on the outer wall of the sample glass bottle to apply an external magnetic field for preliminary separation of magnetic components in the sample solution.

[0045] 2) Purification of the initially separated samples

[0046] Remove the magnetically enriched solution, collect the magnetically adsorbed components, transfer the sample obtained from the preliminary magnetic separation to 10 mL of 2 mol / L hydrochloric acid solution, heat and digest at 60 °C for 12 h, and then sonicate the digested sample solution after cooling to room temperature for 20 min.

[0047] 3) Separation of purified samples

[0048] The sample solution after hydrochloric acid digestion is subjected to magnetic separation again under the action of an external magnetic field. The component enriched under the action of the final magnetic field is collected to obtain pure silica-encapsulated magnetic particles.

[0049] The above steps were used to pre-treat samples of silica-coated magnetic particles in coal fly ash. The mass percentage of silica-coated magnetic particles in fly ash samples collected from three different thermal power plants is shown in the table below. The results show that the method of this invention can effectively separate and extract silica-coated magnetic particles from coal fly ash.

[0050] Sample number Sample Name mass percentage 1 Sample 1 of fly ash from coal-fired power plant 1.4 2 Sample 2 of fly ash from coal-fired power plant 0.8 3 Sample 3 of fly ash from coal-fired power plant 1.1

[0051] The silica-encapsulated magnetic particles extracted from coal fly ash through the above steps were characterized by transmission electron microscopy. Figure 1 , Figure 2 The images show the transmission electron microscopy (TEM) characterization results and elemental distribution energy dispersive spectroscopy (EDS) results of silica-encapsulated magnetic particles extracted from coal fly ash. These results indicate that the separated particles have a typical silica coating layer composed of silicon and oxygen, and the particles contain a Fe3O4 and γ-Fe2O3 magnetic core composed of iron and oxygen.

[0052] The present invention can be well implemented according to the above embodiments. It is worth noting that, based on the above design principles, even if some non-substantial modifications or refinements are made to the content disclosed in the present invention to solve the same technical problem, the essence of the technical solution adopted is still the same as that of the present invention, and therefore it should also be within the protection scope of the present invention.

Claims

1. A method for separating and purifying silica-coated magnetic particles in coal fly ash, characterized by, Includes the following steps: 1) Preliminary separation of magnetic components The collected coal fly ash powder was dispersed in an aqueous solution to obtain a coal fly ash aqueous solution. The coal fly ash aqueous solution was further dispersed by ultrasound for 20 minutes. After ultrasonic dispersion, the coal fly ash aqueous solution underwent preliminary separation of magnetic components under the action of an external magnetic field. 2) Preliminary purification of separated magnetic components The magnetic components obtained from the initial separation were added to a 2 mol / L hydrochloric acid solution and heated at 60°C for 12 h for digestion. After the digestion, the magnetic component solution was cooled to room temperature and then ultrasonically dispersed for 20 min. 3) Separation of the purified magnetic components The sample solution after hydrochloric acid digestion is subjected to magnetic component separation again under the action of an external magnetic field. The component enriched under the final magnetic field is collected to obtain silica-encapsulated magnetic particles.

2. The method of claim 1, wherein, The coal fly ash is in powder form.

3. The method as described in claim 1, characterized in that, The magnetic components in the silica-encapsulated magnetic core particles include iron(II,III) oxide (Fe3O4) and isometric iron(II,III) oxide (γ-Fe2O3).

4. The method according to any one of claims 1-3, characterized in that, The outer coating layer of the silica-encapsulated magnetic particles is mainly composed of silica.

5. The method according to any one of claims 1-3, characterized in that, The particle size distribution of the silica-encapsulated magnetic particles ranges from nanometers to micrometers.

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