Efficient soil micro-plastic separation and extraction method based on Fenton reaction

Abstract

The invention belongs to the technical field of environmental pollutant analysis and detection. The invention discloses a Fenton reaction-based efficient separation and extraction method for soil micro-plastics. The method comprises the following steps: preparing a micro-plastic soil sample; carrying out digestion and purification treatment on the micro-plastic; then separating the micro-plastics through a density flotation method; and finally, carrying out microscopic observation on the dried filter membrane by using a stereoscope so as to calculate the abundance of the micro-plastic and analyze the morphological characteristics of the micro-plastic. According to the method, the salt solution with lower cost and the organic matter digestion method with small influence on the micro-plastic particles are used, efficient removal of organic matter in the complex soil matrix and efficient extraction of the micro-plastic are achieved, the micro-plastic separation and extraction time is shortened, the micro-plastic recovery rate is increased, and the method is easy and convenient to operate, economical and practical.

Description

Technical Field

[0001] The invention relates to a method for efficiently separating and extracting soil microplastics based on improved Fenton reaction pretreatment, and belongs to the technical field of environmental pollutant analysis and detection. Background Art

[0002] As the foundation and core of agricultural production, soil not only provides sufficient nutrients and nutrients for the growth and development of crops, but also is an important natural resource to ensure the sustainable development of agriculture. However, with the advancement of modern industrialization, soil pollution has become increasingly serious. Among them, microplastics caused by the large-scale production and rapid consumption of plastic products, inadequate management of plastic waste recycling, and the widespread use of agricultural films have become a new soil pollutant. Microplastics refer to plastic particles with a size of less than 5 mm. They have a small particle size, are easy to migrate, are widely distributed, have a stable chemical structure, and are not easy to degrade. They can exist in the environment for a long time, and after being ingested by organisms, they are enriched and transmitted in the food chain, posing a major threat to the ecological environment and human health.

[0003] In recent years, microplastic pollution has become a hot topic of global concern. Microplastics in soil change the physical and chemical properties and biological functions of soil through complex physical and chemical reactions, causing potential impacts on plant growth and development. Soil microplastics enter the food chain through the ingestion of soil animals and microorganisms, further migrate and cause immeasurable impacts on a wider range of organisms. Therefore, it is of great significance to study and control the problem of microplastic pollution in soil.

[0004] The key to studying and controlling soil microplastics is to fully separate and extract them from the complex soil environment. However, soil properties, mineral composition, organic matter content, and microplastic types pose great limitations to the efficient separation and extraction of microplastics. At present, the methods used to analyze microplastics in soil are mostly based on research methods of microplastics in water bodies and sediments, but there are no standard and mature methods for separation, extraction and purification of microplastics. Different methods may lead to differences in results, limiting the precise analysis of soil microplastics. At present, the main methods for separating microplastics from soil include artificial separation, electrostatic separation, pressurized fluid extraction, and density flotation separation. Among them, the most commonly used is density flotation separation, because the density of microplastics detected in soil is usually 0.8-1.4g / cm 3 , while the density of natural soil samples is generally 2.6-2.7 g / cm 3. Density flotation separation uses the density difference between the two to add the pretreated soil samples into various high-density salt solutions, so that components with lower density such as microplastics float on the upper layer and are further separated. The use of different salt solutions results in different microplastic recovery rates. To obtain the best recovery rate, the most suitable salt solution must be selected. It is crucial to select a flotation solution of appropriate density based on the properties of the sample for microplastic separation. Commonly used salt solutions such as NaCl, due to their low density, can only float very few low-density polymers in the environment such as PP, PE, PS, etc.; in contrast, high-density salt solutions such as NaI and KI have high usage costs, but the amount of separated samples is not large, which limits the widespread use of this method. In addition, simple density separation methods cannot completely extract microplastics, and digestion and purification are required to remove organic matter. Most of the commonly used digestion methods are time-consuming, and long-term oxidative digestion may have a certain impact on the microplastics themselves.

[0005] Based on the team's existing invention CN116296672A for the efficient separation and extraction of microplastics in soil environments, the present invention improves the existing invention using Fenton's reagent, and uses density separation to achieve rapid removal of organic matter in complex soil matrices and efficient extraction of microplastics; compared with the existing invention, the digestion time of soil organic matter is greatly shortened by pre- and post-treatment with Fenton's reagent. Summary of the invention

[0006] The purpose of the present invention is to combine density flotation with Fenton reagent oxidation digestion, use a lower-cost salt solution and an organic matter digestion method that has less impact on microplastic particles, to achieve efficient removal of organic matter in complex soil matrices and efficient extraction of microplastics; compared with existing inventions, the present invention greatly shortens the digestion time of soil and plant organic matter by using Fenton reagent, and shortens the separation and extraction time to 8 hours. The present invention can shorten the separation and extraction time of microplastics, improve the recovery rate of microplastics, and is simple to operate, economical and practical.

[0007] The specific technical solutions are as follows:

[0008] A method for efficiently separating and extracting soil microplastics based on Fenton reaction mainly comprises the following steps:

[0009] Step 1: Preparation of soil samples containing microplastics:

[0010] (1) Soil sample acquisition: Deep soil samples were collected to minimize microplastic pollution; soil samples were ground using an extrusion soil crusher and a 5 mm sieve was used for preliminary particle size screening; soil samples were observed under a stereomicroscope to confirm that there was no microplastic pollution, and 10 g of soil samples were weighed for later use;

[0011] (2) Preparation of spiked microplastics: PP, PE and PET, three typical plastic polymers in farmland soil, were selected, among which the density of PET exceeded 1 g cm -3 , used as a representative of higher density materials; while the density is less than 1g·cm -3 PE and PP represent lower density materials. Two different types of microplastic samples were prepared: environmental samples and standard samples. Environmental microplastic samples come from residual films, flower pots and mineral water bottles in long-term film-covered farmland soil. After component identification, they are manually cut into 1-2mm microplastic samples; standard microplastic samples are 0.4-0.5mm granular commercial microplastics.

[0012] (3) Sample mixing: Weigh 6 blank soil samples (10 g each), add 10 environmental samples and 10 standard samples of PE, PP, and PET microplastics, respectively, and mix them manually until the microplastics are completely coated in the soil particles for later use;

[0013] Step 2: Density flotation separation of microplastics:

[0014] (1) Add 50 ml of Fenton's reagent to 10 g of soil sample with added microplastics, heat in a water bath, and control the temperature at 60°C; the reaction between Fenton's reagent and organic matter in the soil is an exothermic reaction. Use a thermometer to observe the temperature change during the reaction. When the temperature exceeds 60°C, use an ice-water mixture ice bath to maintain the temperature at 60°C;

[0015] (2) Pour the mixture into the sample sieve and rinse it with tap water to remove the soil; during the filtration process, gently stir it with a glass rod; at the same time, use tweezers to remove large pieces of plant residues that are easily identifiable on the sieve, rinse them under tap water and discard them;

[0016] (3) Use density 1.45-1.5g·cm -3 The residue is washed with ZnCl2 solution and transferred to a clean glass bottle. The ZnCl2 solution is added to 1L, stirred thoroughly, and allowed to stand to promote separation of the suspension and the soil. When separation is obvious, the upper suspension is gently poured out, the solution is filtered, and the filter membrane is collected.

[0017] Step 3: Digestion and purification of filtration residue: Fenton reagent is used as the digestion solution, and the microplastics on the two filter membranes together with a small amount of impurities are transferred to the digestion bottle for digestion and purification. During the reaction, Fe 2+ Oxidized to Fe 3+ , L-Ascorbic acid reducing agent was added to the reaction system for 0.5 h to reduce Fe 3+ Reduction to Fe 2+ To exclude Fe 3+ Color interference makes it easier to filter and observe; filter the solution and collect the filter membrane;

[0018] Step 4: Calculation of recovery rate: Use a stereo microscope to conduct detailed microscopic observation of the dried filter membrane, compare the number of microplastics on the filter membrane with the number of microplastics input and calculate the recovery rate, and use Fourier transform infrared spectroscopy ATR-FTIR to match and identify the polymer type to determine the type of recycled microplastics.

[0019] Preferably, the Fe in the Fenton reagent added in step 2 (1) 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2 + The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of a FeSO4 solution with a mass percentage concentration of 2.78%; the mass percentage of the H2O2 solution was 30%.

[0020] Preferably, Fe in Fenton's reagent in step 3 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of 2.78% FeSO4 solution; the mass fraction of the H2O2 solution was 30%, the digestion temperature was 60°C, the shaking speed was 115 rpm, and the digestion time was 8 h.

[0021] Preferably, the determination of the environmental microplastic components in step 1 (2) is performed by matching and identifying the polymer type through Fourier transform infrared spectroscopy ATR-FTIR, and the chemical composition of the polymer is determined based on a matching degree of >80%.

[0022] Preferably, the pH of the RO water in step 2 (1) is adjusted to 3; the sample separation sieve in step 2 (2) is a 600-mesh standard test sample separation sieve; and the pore size of the filter membrane in step 2 is 20 μm.

[0023] In the process of developing a method for efficiently separating and extracting soil microplastics based on Fenton reaction of the present invention, the applicant mainly did the following work:

[0024] 1. Preparation of spiked microplastics: In this invention, three typical plastic polymers of farmland soil, polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET) were selected (see Table 1). Among them, the density of PET exceeds 1g·cm -3 , is used as a representative of higher density materials; density below 1 g cm -3PE and PP represent lower density materials. Two different types of microplastic samples were prepared: environmental samples and standard samples; environmental microplastic samples came from residual films, flower pots and mineral water bottles in long-term film-covered farmland soil. After component identification, they were manually cut into 1-2mm microplastic samples; standard microplastic samples were 0.4-0.5mm granular commercial microplastics;

[0025] 2. Through the comparison of previous experiments, the density of ZnCl2 flotation solution was controlled at 1.45-1.5g·cm -3 Within this range, it can effectively achieve the common types of microplastics in the soil (density range: 0.8-1.4g cm -3 ), avoid the waste of ZnCl2 raw materials due to excessive density and prevent other interfering substances in the soil matrix from entering the flotation supernatant, which is beneficial to the subsequent analysis and identification of microplastics.

[0026] 3. Fenton's reagent, H2O2 oxidation, KOH and NaOH alkaline digestion have different effects on the integrity of microplastic particles when removing organic matter. Among them, Fenton's reagent digestion at 60°C has no effect on most microplastics. The present invention selects short-term (8h) digestion of Fenton's reagent to remove plant residues, which greatly reduces the impact of the digestion reagent on the microplastic particles themselves. In general, compared with traditional separation methods, this method is a simple, fast, efficient, low-cost experimental method for extracting various types of microplastics from complex soil matrices with relatively small environmental effects.

[0027] Table 1 Type, shape, size, source and density of spiked microplastics used in this method (g cm -3 )

[0028]

[0029] The advantages of the present invention are:

[0030] The present invention provides a method for rapid and efficient separation and extraction of soil microplastics, which has high working efficiency and high recovery rate. This method is economical and practical, and is suitable for removing organic matter from complex soil matrices and efficiently separating microplastics. The present invention combines density flotation with Fenton reagent oxidation digestion, and comprehensively evaluates the density, cost, environmental impact of different salt solutions and the impact of oxidation digestion agent treatment on microplastics. By rationally selecting a cost-effective salt solution and a digestion method with less impact on microplastic particles, combined with various soil sample pretreatment techniques, the present invention achieves efficient extraction of microplastics. This invention effectively solves the problems of cumbersome, time-consuming, low efficiency and low recovery rate in the soil microplastic extraction process in the prior art.

[0031] (1) The present invention demonstrates an advanced and efficient extraction technology for soil microplastics. Compared with the current conventional methods, this technology uses Fenton's reagent to dissolve soil samples in the pretreatment stage, combined with screen cleaning, to significantly optimize the traditional density flotation method. This innovative process allows the flotation of microplastics to be completed in ZnCl2 solution in just 1 hour. This method can achieve efficient separation and extraction of environmental microplastics and standard microplastics of different shapes (flakes or granules) and different sizes (ranging from 0.4-0.5 mm to 1-2 mm) in a variety of soil matrices (10 grams), with a recovery rate of more than 80%. It effectively ensures the efficient separation of microplastics in complex matrices. Some studies have mentioned that dirt and biofilms may affect the extraction efficiency of aged microplastics, and the present invention uses Fenton's reagent pretreatment and screen cleaning to successfully solve this problem and significantly shorten the flotation time.

[0032] (2) The reason why the present invention adds a 0.5h Fenton reagent short-term digestion experimental step before density flotation: the pores of microplastics that exist for a long time in the soil environment may be filled with organic substances such as plant residues, which may affect the density of microplastics. Therefore, the interference of these plant residues can be removed by using Fenton reagent. This process will not affect the microplastic particles themselves, thus avoiding the loss of microplastics in the subsequent density flotation process.

[0033] (3) The present invention precisely controls the density of the ZnCl2 flotation solution to 1.45-1.5 g·cm- 3 The full flotation of soil microplastics was achieved within the range of 1.5 wt % and 2.5 wt % respectively. This step not only reduced the amount of ZnCl2 used, but also simplified the subsequent digestion and purification steps and improved the extraction efficiency. While reducing the cost of microplastic separation and extraction, the extraction steps were also simplified, significantly shortening the experimental time. In addition, by filtering 2 / 3 of the flotation supernatant and fully rinsing the inner wall of the container, the loss caused by microplastic adhesion was greatly reduced.

[0034] (4) The present invention selects to digest the plant residues after separation and extraction with salt solution, and uses Fenton reagent at 60°C and 115 rpm to effectively remove the light organic matter remaining after flotation. Compared with the common organic matter removal methods, this oxidation digestion method has excellent applicability to complex soil matrices (recovery rate of various microplastics> 80%), and the digestion time is controlled to 8 hours by optimizing the pre-digestion steps, avoiding the impact of long-term oxidation digestion on microplastics.

[0035] The present invention combines density flotation with Fenton reagent oxidation digestion, uses a lower-cost salt solution and an organic matter digestion method that has less impact on microplastic particles, to achieve rapid removal of organic matter in complex soil matrices and efficient extraction of microplastics, shortens separation and extraction time, and improves the recovery rate of microplastics. It is easy to operate and is economical and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is an operation flow chart of the efficient separation and extraction experimental method in Example 1 of the present invention.

[0037] Figure 2 This is the plastic recovery rate in 6 soil samples in Example 1 of the present invention.

[0038] Figure 3 This is a microscopic image of polyethylene microplastics extracted from actual long-term film-covered farmland in Example 2 of the present invention.

[0039] Figure 4 It is a spectrum diagram of PE in Example 2 of the present invention, expressing the spectral information of PE microplastics under Fourier transform infrared spectroscopy ATR-FTIR. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with specific embodiments, but is not intended to limit the present invention.

[0041] The main instruments and reagents used in the examples are as follows:

[0042] (1) Reagents:

[0043] Ferrous acid (FeSO4·5H2O): purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd.;

[0044] Zinc chloride (ZnCl2): analytical grade, purchased from Tianjin Yongda Chemical Reagent Co., Ltd.;

[0045] Hydrogen peroxide (H2O2): 30% by mass, analytical grade, purchased from Tianjin Chemical Reagent Co., Ltd.;

[0046] L-Ascorbic acid:>99.0%(T), purchased from Shandong Keyuan Biochemical Co., Ltd.;

[0047] (2) Experimental instruments:

[0048] Glass mercury thermometer, manufacturer: Hongxing Instrument Factory, Wuqiang County, Hebei Province, China;

[0049] GZX-9140MBE drying oven, manufacturer: Shanghai Boxun Company, China;

[0050] HZ-9612K high temperature vertical oscillator, manufacturer: Taicang Science and Education Equipment Factory, China;

[0051] SHA-BA water bath constant temperature oscillator: Manufacturer: Changzhou Guowang Instrument Manufacturing Co., Ltd., China;

[0052] JL-UPR-Ⅲ-10T ultrapure water device: manufacturer Sichuan Jinlan Technology Co., Ltd., China;

[0053] GM-1.0A vacuum filtration device, manufacturer: Tianjin Jinteng Company, China;

[0054] Meilen MTB 200 electronic balance, manufacturer: Shenzhen Meifu Electronics Co., Ltd., China;

[0055] V 2.0 Zeiss stereo microscope, Germany;

[0056] Embodiment 1:

[0057] A method for efficiently separating and extracting soil microplastics based on Fenton reaction mainly includes the following steps:

[0058] Step 1: Preparation of soil samples containing microplastics:

[0059] (1) Blank soil sample: Obtaining blank soil sample: Collect deep soil samples to minimize microplastic pollution; grind soil samples with an extrusion soil crusher and use a 5 mm sieve for preliminary particle size screening; observe under a stereoscope to confirm that there is no microplastic pollution in the soil sample, and weigh 10 g of soil sample for later use;

[0060] (2) Preparation of spiked microplastics: Three typical farmland soil plastic polymers, polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET), were selected. The density of PET is more than 1 g cm -3 , used as a representative of higher density materials; while the density is less than 1g·cm -3 PE and PP represent lower density materials. Two different types of microplastic samples were prepared: environmental samples and standard samples. Environmental microplastic samples come from residual films, flower pots and mineral water bottles in long-term film-covered farmland soil. After component identification, they are manually cut into 1-2mm microplastic samples; standard microplastic samples are 0.4-0.5mm granular commercial microplastics.

[0061] (3) Sample mixing: Weigh 6 blank soil samples (10 g each), add 10 environmental samples and 10 standard samples of PE, PP, and PET microplastics, respectively, and mix them manually until the microplastics are completely coated in the soil particles for later use;

[0062] Step 2: Density flotation separation of microplastics:

[0063] (1) Add 50 ml of Fenton's reagent to 10 g of soil sample with added microplastics, heat in a water bath, and control the temperature at 60°C; the reaction between Fenton's reagent and organic matter in the soil is an exothermic reaction. Use a thermometer to observe the temperature change during the reaction. When the temperature exceeds 60°C, use an ice-water mixture to maintain the temperature at 60°C;

[0064] (2) Pour the reaction mixture into a sieve, rinse with tap water, and gently stir with a glass rod to remove soil organic matter;

[0065] (3) Use density 1.45-1.5g·cm -3 The ZnCl2 solution is used to rinse the filter residue and transfer it to a clean glass bottle, and the ZnCl2 solution is added to 1L, stirred thoroughly, and allowed to stand to promote the stratification of the suspension and the soil; after the stratification is obvious, the upper suspension is gently poured out, the solution is filtered, and the filter membrane is collected; the ZnCl2 solution is added to the bottom sediment after filtration to 1L again, and a second flotation is performed, and the filter membrane is collected after the solution is filtered using a 20μm filter membrane. In the present invention, the ZnCl2 solution is recycled for multiple times to achieve resource recycling. Before each use, a PET polymer material of known density is added to test the density of the ZnCl2 solution, and the ZnCl2 solution is filtered using a 1μm pore size filter membrane. At the same time, in order to maintain the cleanliness of the equipment and the accuracy of the experiment, the filter needs to be rinsed with clean water at least three times after each filtration, and the rinse liquid is filtered together.

[0066] Step 3: Digestion and purification of filtration residue: Use Fenton reagent as digestion solution, transfer the microplastics on the two filter membranes together with a small amount of impurities into a digestion bottle for digestion and purification; during the reaction, Fe2+ is oxidized to Fe3+, and L-Ascorbic acid reducing agent is added to the reaction system for 0.5h to reduce Fe3+ to Fe2+ to eliminate Fe3+ color interference, which is convenient for membrane filtration and observation; filter the solution and collect the filter membrane;

[0067] Step 4: Calculation of recovery rate: Use a stereo microscope to conduct detailed microscopic observation of the dried filter membrane, compare the number of microplastics on the filter membrane with the number of microplastics input and calculate the recovery rate, and use Fourier transform infrared spectroscopy ATR-FTIR to match and identify the polymer type to determine the type of recycled microplastics.

[0068] The Fe in the Fenton reagent added in step 2 (1) above 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to prepare 50 mL of a FeSO4 solution with a mass percentage concentration of 2.78%; the mass percentage of the H2O2 solution was 30%.

[0069] In the above step 3, Fe in Fenton's reagent 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of 2.78% FeSO4 solution; the mass fraction of the H2O2 solution was 30%, the digestion temperature was 60°C, the shaking speed was 115 rpm, and the digestion time was 8 h.

[0070] The determination of the environmental microplastic components in the above step 1 (2) is carried out by matching and identifying the polymer type through Fourier transform infrared spectroscopy ATR-FTIR, and the chemical composition of the polymer is determined based on a matching degree of >80%.

[0071] In the above step 2 (1), the pH of the RO water is adjusted to 3; the sieve in step 2 (2) is a 600-mesh standard test sample screening sieve; the pore size of the filter membrane in step 2 is 20 μm.

[0072] from Figure 2 It can be seen that this method can achieve a recovery rate of more than 80% for microplastics of different sources, different particle sizes and different shapes.

[0073] Embodiment 2:

[0074] Taking the actual planting field soil as the application object, a method for efficient separation and extraction of soil microplastics based on Fenton reaction was proposed. The main steps are as follows:

[0075] Step 1: Density flotation separation of microplastics:

[0076] (1) Weigh 10 g of environmental soil sample, add 50 ml of Fenton's reagent, heat in a water bath, and control the temperature at 60°C; the reaction between Fenton's reagent and organic matter in the soil is an exothermic reaction. Use a thermometer to observe the temperature change during the reaction. When the temperature exceeds 60°C, use an ice-water mixture ice bath to maintain the temperature at 60°C;

[0077] (2) Pour the reaction mixture into a sieve, rinse with tap water, and gently stir with a glass rod to remove soil organic matter;

[0078] (3) Use density 1.45-1.5g·cm -3The residue is washed with ZnCl2 solution and transferred to a clean glass bottle. The ZnCl2 solution is added to 1L, stirred thoroughly, and allowed to stand to promote separation of the suspension and the soil. When separation is obvious, the upper suspension is gently poured out, the solution is filtered, and the filter membrane is collected.

[0079] Step 2: Digestion and purification of filtration residue: Fenton reagent is used as the digestion solution, and the microplastics on the two filter membranes together with a small amount of impurities are transferred to the digestion bottle for digestion and purification. During the reaction, Fe 2+ Oxidized to Fe 3+ , L-Ascorbic acid reducing agent was added to the reaction system for 0.5 h to reduce Fe 3+ Reduction to Fe 2+ To exclude Fe 3+ Color interference makes it easier to filter and observe; filter the solution and collect the filter membrane;

[0080] Step 3: Calculation of recovery rate: Use a stereo microscope to conduct detailed microscopic observation of the dried filter membrane, compare the number of microplastics on the filter membrane with the number of microplastics input and calculate the recovery rate, and use Fourier transform infrared spectroscopy ATR-FTIR to match and identify the polymer type to determine the type of recycled microplastics.

[0081] The Fe in the Fenton reagent added in step 1 (1) above 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution is prepared as follows: 1.39 g of ferrous sulfate solid is added to 50 mL of RO water to obtain 50 mL of a FeSO4 solution with a mass percentage concentration of 2.78%; the mass percentage of the H2O2 solution is 30%; the pH of the RO water in step 1 (1) is adjusted to 3; the sieve described in step 1 (2) is a 600-mesh standard test sample screening sieve; the pore size of the filter membrane described in step 1 is 20 μm.

[0082] In the above step 2, Fe 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of 2.78% FeSO4 solution; the mass fraction of the H2O2 solution was 30%, the digestion temperature was 60°C, the shaking speed was 115 rpm, and the digestion time was 8 h.

[0083] Compared with Example 1, this example is different in that the high-efficiency separation and extraction application method of the present invention is used to specifically extract microplastics in real farmland soil environments. The specific operation is to weigh 10g of real soil sample, and then use the optimized separation and extraction technology of the present invention to separate and extract microplastics in farmland soil multiple times, and repeat the experimental process 3 times to collect microplastics in farmland soil. Use a stereoscope to observe the microplastic samples, focusing on the polyethylene (PE) microplastics from the ground film. Figure 3 As shown in the figure, the polyethylene microplastics from residual film are mainly in the form of transparent flakes with pores on the surface, which may be caused by the long-term environmental degradation of residual film fragments. Figure 4 This is the spectral information of PE microplastics under Fourier transform infrared spectroscopy ATR-FTIR.

[0084] from Figure 2 It can be seen that this method can achieve a recovery rate of more than 80% for the separation and extraction of microplastics from different sources with different particle sizes and shapes; at the same time, combined with Figure 3 It can be observed that the present invention successfully achieves efficient separation and extraction of microplastics in long-term film-covered farmland soil. Figure 3 The microscopic images of polyethylene microplastics from ground film are shown. This shows that the method can effectively separate microplastics from soil without damaging their surface morphology and chemical composition. There is no organic matter remaining in the pores of the observed aged microplastics, and the images are clear and clean, indicating that the method is simple and effective.

[0085] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that are not conceived through creative work should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined in the claims.

Claims

1. A method for efficiently separating and extracting soil microplastics based on Fenton reaction, characterized in that The main steps are as follows: Step 1: Preparation of soil samples containing microplastics: (1) Soil sample acquisition: Deep soil samples were collected to minimize microplastic pollution; soil samples were ground using an extrusion soil crusher and a 5 mm sieve was used for preliminary particle size screening; soil samples were observed under a stereomicroscope to confirm that there was no microplastic pollution, and 10 g of soil samples were weighed for later use; (2) Preparation of spiked microplastics: PP, PE and PET, three typical plastic polymers in farmland soil, were selected, among which the density of PET exceeded 1 g cm -3 , used as a representative of higher density materials; while the density is less than 1g·cm -3 PE and PP represent lower density materials. Two different types of microplastic samples were prepared: environmental samples and standard samples. Environmental microplastic samples come from residual films, flower pots and mineral water bottles in long-term film-covered farmland soil. After component identification, they were manually cut into 1-2mm microplastic samples. The standard microplastic samples are 0.4-0.5 mm granular commercial microplastics; (3) Sample mixing: Weigh 6 blank soil samples (10 g each), add 10 environmental samples and 10 standard samples of PE, PP, and PET microplastics, respectively, and mix them manually until the microplastics are completely coated in the soil particles for later use; Step 2: Density flotation separation of microplastics: (1) Add 50 ml of Fenton's reagent to the soil sample with microplastics added, heat it in a water bath, and control the temperature at 60°C; the reaction between Fenton's reagent and organic matter in the soil is an exothermic reaction. Use a thermometer to observe the temperature change during the reaction. When the temperature exceeds 60°C, use an ice-water mixture ice bath to maintain the temperature at 60°C; (2) Pour the reaction mixture into a sieve, rinse with tap water, and gently stir with a glass rod to remove soil organic matter; (3) Use density 1.45-1.5g·cm -3 The residue was rinsed with ZnCl2 solution and transferred to a clean glass bottle, and the ZnCl2 solution was added to 1L, stirred thoroughly, and allowed to stand to promote separation of the suspension and the soil; After the layers are clearly separated, pour out the upper suspension, filter the solution, and collect the filter membrane; Step 3: Digestion and purification of filtration residue: Fenton reagent is used as the digestion solution, and the microplastics on the two filter membranes together with a small amount of impurities are transferred to the digestion bottle for digestion and purification. During the reaction, Fe 2+ Oxidized to Fe 3+ , L-Ascorbic acid reducing agent was added to the reaction system for 0.5 h to reduce Fe 3+ Reduction to Fe 2+ To exclude Fe 3+ Color interference makes it easier to filter and observe; Filter the solution and collect the filter membrane; Step 4: Calculation of recovery rate: Use a stereo microscope to conduct detailed microscopic observation of the dried filter membrane, compare the number of microplastics on the filter membrane with the number of microplastics input and calculate the recovery rate, and use Fourier transform infrared spectroscopy ATR-FTIR to match and identify the polymer type to determine the type of recycled microplastics.

2. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 1, characterized in that Fe in Fenton's reagent added in step 2 (1) 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of a FeSO4 solution with a mass percentage concentration of 2.78%; the mass percentage of the H2O2 solution was 30%.

3. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 1 or 2, characterized in that Fe in Fenton's reagent in step 3 2+ The volume ratio of Fe to H2O2 solution is 50:1; 2+ The solution was prepared as follows: 1.39 g of ferrous sulfate solid was added to 50 mL of RO water to obtain 50 mL of 2.78% FeSO4 solution; the mass fraction of the H2O2 solution was 30%, the digestion temperature was 60°C, the shaking speed was 115 rpm, and the digestion time was 8 h.

4. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 3, characterized in that The determination of the environmental microplastic components in step 1 (2) is carried out by matching and identifying the polymer type through Fourier transform infrared spectroscopy ATR-FTIR, and determining the polymer chemical composition based on a matching degree of >80%.

5. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 4, characterized in that In step 2 (1), the pH of the RO water was adjusted to 3.

6. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 5, characterized in that The sieve described in step 2 (2) is a 600-mesh standard test sample screening sieve.

7. A method for efficiently separating and extracting soil microplastics based on Fenton reaction as claimed in claim 6, characterized in that The pore size of the filter membrane described in step 2 is 20 μm.

Images