Method for rapid separation and identification of microplastics in soil

Abstract

The present invention relates to the technical field of detection of microplastics in soil, and disclosed is a method for rapid separation and identification of microplastics in soil. The present invention comprises the following steps: step 1), first drying a soil sample, sieving the soil sample by means of a sieve to remove particles and impurities in the soil, and carrying out microwave treatment on the resulting soil sample. In the present invention, by gradually adding nano silicon dioxide, a surfactant, and citric acid during the microwave treatment, rapid separation of microplastics is successfully achieved. Firstly, the addition of the nano silicon dioxide increases the contact area between microplastics and soil aggregates, effectively promoting the release of microplastics. Secondly, the action of the surfactant reduces the adhesion of microplastics to soil particles, further improving the separation efficiency of microplastics. Finally, the addition of the citric acid accelerates the breakdown of soil aggregates, facilitating the release of microplastics.

Description

A rapid separation and identification method of soil microplastics TECHNICAL FIELD

[0001] The present application belongs to the field of soil microplastic detection, and particularly relates to a rapid separation and identification method of soil microplastics. BACKGROUND

[0002] Microplastics, i.e. plastic particles with a maximum single-side particle size of less than 5 mm, cause more persistent and more intense harm to the environment due to their small volume, strong permeability and slow degradation. Although early research mainly focused on marine and other water ecological systems, the research on soil microplastics is still in its initial stage. This is mainly due to the high content and variety of impurities in soil, which leads to a complex and inefficient separation process of microplastics, making it difficult to obtain high-purity microplastic samples, thereby seriously restricting the research on microplastic pollution in land systems.

[0003] Traditional methods usually use ultrasonic vibration and dispersion liquid for microplastic separation, but there are some problems. First, this method is low in efficiency and easy to cause the combination of microplastics and soil aggregates, resulting in the loss of part of the microplastics or the attachment of the microplastics on the soil particles, which is difficult to effectively separate. Second, the existing technology has a slow release speed of microplastics, and a long time is needed to achieve the complete separation of microplastics, and the operation is complex, which needs to frequently adjust the processing conditions. In addition, the existing technology often cannot effectively control the adhesion between microplastics and soil aggregates, further reducing the separation efficiency.

[0004] Therefore, the present application is proposed.

[0005] Content of the utility model

[0006] The technical problem to be solved by the present application is to overcome the deficiencies of the prior art and provide a dry rice method.

[0007] To solve the above technical problems, the basic idea of the technical scheme of the present application is:

[0008] To solve the above technical problems, the basic idea of the technical scheme of the present application is:

[0009] A rapid separation and identification method of soil microplastics, comprising the following steps:

[0010] Step 1), first dry the soil sample, and screen through a screen mesh to remove particles and impurities in the soil, and then microwave treat the obtained soil sample, dry and screen the soil sample, and then microwave treat, which can effectively remove impurities and particles in the soil, and at the same time, rapidly destroy soil aggregates through microwave heating, thereby creating conditions for effective extraction of microplastics and subsequent analysis;

[0011] Step 2), citric acid, surfactant and nano-silica are added to the soil sample during the microwave treatment to release the microplastics in the soil sample during the decomposition of soil aggregates, obtaining a mixture of soil sample and microplastics, and the microwave treatment is used to accelerate the decomposition of soil aggregates, and the nano-silica and surfactant are used to enhance the release of microplastics;

[0012] Step 3), a composition with a density gradient is prepared by preparing a plurality of liquids with different densities, and the mixture obtained in step 2) is mixed with the composition, and the sample is placed in a centrifuge for centrifugal separation, and according to the density difference of the liquids with different densities, the microplastics will be deposited at different positions to form layers, and the layered liquids formed after centrifugation are collected, and the samples containing microplastics are collected layer by layer, and the density gradient is constructed by using liquids with different densities, and centrifugal separation is performed, so that the microplastics are layered according to the density difference. The density of the substance can be accurately separated, and the purity and recovery rate of the microplastics are improved;

[0013] Step 4), the screened microplastic samples are analyzed by FTIR to identify and confirm the chemical composition of the microplastics, and the thermal properties of the microplastics are analyzed.

[0014] Optionally, the process temperature of step 1) is 40-60℃, and the dried soil sample contains 15%-30% of water, and the temperature of the microwave treatment in step 1) is 30-50℃, and the water in the soil is completely evaporated during the microwave treatment. During heating, the water in the soil gradually evaporates, the citric acid can help to adjust the pH value, and the surfactant can reduce the adhesion, so that the microplastics are more easily released from the soil aggregates. Secondly, heating makes nano-silica more uniformly dispersed in the soil mixture, improving its effect as a filter aid, helping to more effectively filter and collect microplastics in subsequent steps. Finally, the reciprocating heating process ensures that the entire soil sample is uniformly heated, which helps to uniformly decompose soil organic matter and aggregates at the microscopic level.

[0015] Optionally, the surfactant in step 2) includes but is not limited to Tween 80, Tween 20, and the weight ratio of soil sample, citric acid, Tween 20, and nano-silica in step 2) is 100:(0.5-2):(0.01-0.1):(1-2). The order of adding citric acid, Tween 20, and nano-silica to the soil sample in step 2) is: first add citric acid, then add Tween 20, and finally add nano-silica. According to the order of first adding citric acid, then adding Tween 20, and finally adding nano-silica, the pH value of the soil sample can be effectively adjusted, the surface tension can be reduced, and ultimately the effective separation and recovery of microplastics can be facilitated. Tween 20 as a surfactant can reduce the adhesion between soil particles and microplastics, while nano-silica can increase the dispersibility of microplastics, which helps to improve the release and layering effect of microplastics in the separation process.

[0016] Optionally, the liquid in step 3) includes but is not limited to the following concentrations of raw materials: water 1 g / cm 3 , sodium chloride solution 1.2 g / cm 3 , sucrose solution 1.4 g / cm 3 , potassium iodide solution 1.6 g / cm 3 . The liquids in step 3) are prepared in order of density from high to low, starting with potassium iodide solution, adding sucrose solution, sodium chloride solution, and water layer by layer, so that the mixture forms a smooth density gradient. By forming a density gradient, it can be ensured that microplastics can be uniformly layered in the centrifuge tube according to their density differences, thereby improving the efficiency and accuracy of centrifugal separation, and facilitating the purity and recovery rate of microplastics.

[0017] Optionally, the centrifuge speed in step 3) is 1000-5000 RPM, and the weight ratio of water, sodium chloride solution, sucrose solution, potassium iodide solution, and soil is 10:30:30:20:1.

[0018] After adopting the above technical solutions, the present application has the following advantages compared with the prior art. Of course, any product implementing the present application does not necessarily need to achieve all the advantages described below:

[0019] By gradually adding nano-silica, surfactant, and citric acid during the microwave treatment process, we successfully achieved the rapid separation of microplastics. First, the addition of nano-silica increases the contact area between microplastics and soil aggregates, effectively promoting the release of microplastics. Second, the role of the surfactant reduces the adhesion between microplastics and soil particles, further improving the separation efficiency of microplastics. Finally, the addition of citric acid accelerates the decomposition of soil aggregates, which helps to release microplastics.

[0020] The specific embodiments of the present application are described in further detail below. DETAILED DESCRIPTION

[0021] The present application is now described in further detail.

[0022] Example 1: In this embodiment, a rapid separation and identification method of soil microplastics is provided, which is used for separating microplastics in loam soil, including the following steps:

[0023] Step 1), dry the soil sample, so that the moisture in the soil sample is 15%, and use a screen to screen the dried soil sample to remove particles and impurities with a diameter greater than 0.05 mm. This can be done by gradually pouring the soil sample onto the screen and gently shaking the screen so that smaller particles of soil pass through the screen, while larger particles are left on the screen. The soil sample obtained by screening is subjected to microwave treatment. In this step, the soil sample is placed in a microwave treatment device and set to a microwave treatment condition of 30 degrees Celsius, and the soil sample is heated for 10 minutes to complete the microwave treatment process.

[0024] Step 2), during the microwave treatment of step 1), add citric acid, Tween 20, and nano-silicon dioxide in sequence, with a weight ratio of citric acid, Tween 20, and nano-silicon dioxide of 0.8:0.06:1.2, to release microplastics from the soil aggregates during their decomposition, obtaining a mixture of soil sample and microplastics together, using microwave treatment to accelerate the decomposition of soil aggregates, and using nano-silicon dioxide and surfactant to enhance the release of microplastics. By adding citric acid, Tween 20, and nano-silicon dioxide in sequence and using a specific weight ratio, the additives are uniformly dispersed and effectively act during microwave treatment, improving the efficiency of microplastic release. Using microwave treatment to accelerate the decomposition of soil aggregates allows faster release of microplastics, shortening the experimental time and improving work efficiency. Nano-silicon dioxide alone can increase the contact area between microplastics and soil aggregates, and the system of nano-silicon dioxide and surfactant can enhance the release of microplastics. The surfactant can reduce the adhesion of microplastics to soil particles, thereby further promoting the release of microplastics.

[0025] Step 3), prepare water, sodium chloride solution, sucrose solution, and potassium iodide solution in order of decreasing density to create a smooth density gradient. First, prepare the potassium iodide solution with a concentration of 1.6 g / cm 3 , as the highest density liquid. Then add sucrose solution, sodium chloride solution, and water in layers to reduce the density, forming a liquid gradient with gradually decreasing density. The concentration of each liquid is: water 1 g / cm3 sodium chloride solution is 1.2 g / cm 3 sucrose solution is 1.4 g / cm 3 potassium iodide solution is 1.6 g / cm 3 to ensure the accuracy of the density gradient. Specifically, the weight ratio of water, sodium chloride solution, sucrose solution, potassium iodide solution and soil is 10:30:30:20:1.

[0026] The mixture obtained in step 2 is mixed with the previously prepared density gradient liquid composition, ensuring uniform mixing, so as to perform centrifugal separation. The mixture sample is placed in a centrifuge, and the centrifugal speed is set to 3000 RPM for centrifugal separation. During centrifugation, microplastics will be deposited at different positions to form layers according to the density difference of different density liquids. The mixture sample is placed in a centrifuge, and the centrifugal speed is set to 3000 RPM for centrifugal separation. During centrifugation, microplastics will be deposited at different positions to form layers according to the density difference of different density liquids.

[0027] Step 4), the microplastic sample obtained by screening is subjected to Fourier transform infrared spectroscopy analysis to determine the chemical composition and structure of the microplastic. The FTIR instrument is used to measure the infrared spectrum of the sample, and compared with the known standard spectrum to identify the polymers and other compounds that may exist in the microplastic. The thermal properties of the microplastic sample are analyzed by thermogravimetric analysis or differential scanning calorimetry method.

[0028] In this embodiment, a method for rapid separation and identification of soil microplastics is provided. When separating microplastics in loam soil, the order and mass ratio of citric acid, Tween 20 and nano-silicon dioxide are adjusted compared to example one. Specifically, Tween 20 is added first, followed by nano-silicon dioxide, and finally citric acid, and the mass ratio of Tween 20, nano-silicon dioxide and citric acid is 0.04:1.8:1.3. Adding Tween 20 first helps to reduce the adhesion of microplastics to soil particles and improves the release efficiency of microplastics; adding nano-silicon dioxide second can increase the contact area of microplastics with soil aggregates, further promoting the release of microplastics; and adding citric acid last helps to decompose microplastics and soil aggregates, enhancing the release effect of microplastics.

[0029] In this embodiment, a rapid separation and identification method for soil microplastics is provided for separating microplastics in loam soil. When separating microplastics in loam soil, the order and mass ratio of adding citric acid, Tween 20, and nano-silicon dioxide are adjusted compared to Example One. Specifically, nano-silicon dioxide is added first, followed by citric acid, and then Tween 20, and the mass ratio of nano-silicon dioxide, citric acid, and Tween 20 is 1.6:0.9:0.089. Adding nano-silicon dioxide first helps to increase the contact area between microplastics and soil aggregates, promoting the release of microplastics. Adding citric acid next can promote the decomposition of soil aggregates, further releasing microplastics. Finally, adding Tween 20 helps to reduce the adhesion of microplastics to soil particles, improving the release efficiency of microplastics.

[0030] Comparative Example 1

[0031] In this embodiment, a rapid separation and identification method for soil microplastics is provided for separating microplastics in loam soil. In the process of separation, the use of nano-silicon dioxide, citric acid, and Tween 20 is cancelled, and conventional ultrasonic vibration and dispersion liquid in the prior art are used to separate microplastics.

[0032] Experimental Example

[0033] Five soil samples with a weight of 5 grams were taken, and 1 gram of microplastics was added to each soil sample for microplastic separation. The data of recovery rate and purity during microplastic separation were obtained according to the analysis data. Each experimental group and control group was repeated for 5 times, and the average value was taken. The calculation formula of recovery rate is (recovery rate = actual separation and recovery of microplastic mass / added microplastic mass x 100%), and the calculation formula of purity is (purity = microplastic mass / total mass x 100%)

[0034] In Example 1 and Example 3, the order and proportion of adding citric acid, Tween 20, and nano-silicon dioxide are optimized. First, the addition of nano-silicon dioxide increases the contact surface area between microplastics and soil aggregates, which is beneficial to the release of microplastics. Second, the addition of surfactant Tween 20 helps to reduce the adhesion of microplastics to soil particles, thereby promoting the effective release of microplastics. Finally, the addition of citric acid promotes the decomposition of soil aggregates, further enhancing the release effect of microplastics. This fine adjustment of the addition order and proportion helps to improve the separation efficiency of microplastics.

[0035] The control example 1 adopts a traditional method to process the soil sample, without adding auxiliary agents such as nano-silicon dioxide and surfactants. This results in that the adhesion between the microplastics and the soil aggregates is not effectively reduced, the release efficiency of the microplastics is relatively low, and the recovery rate of the separated microplastics and the purity of the microplastics are affected.

[0036] The present application is not limited to the above-mentioned embodiments, and any person should know that the structural changes made under the inspiration of the present application, any technical solutions with the same or similar to the present application, fall within the protection scope of the present application. The technical, shape, and structure parts not described in detail in the present application are well-known technologies.

Claims

1. A method for rapid isolation and identification of soil microplastics, characterized in that, The method comprises the following steps: Step 1), first dry the soil sample, and remove the particles and impurities in the soil by sieving, and then microwave the obtained soil sample; Step 2), add citric acid, a surfactant and nano-silicon dioxide to the soil sample during the microwave treatment, so that the microplastics in the soil sample are released during the decomposition of the soil aggregates, and a mixture of the soil sample and the microplastics is obtained; Step 3), prepare a composition with a density gradient by using liquids with different densities, mix the mixture obtained in step 2) with the composition, and then centrifuge the sample in a centrifuge, so that the microplastics are deposited in different positions to form layers according to the density difference of the liquids with different densities, and the sample containing the microplastics is collected layer by layer after the centrifugation; Step 4), analyze the screened microplastic sample by FTIR to identify and confirm the chemical composition of the microplastics, and analyze the thermal properties of the microplastics.

2. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The process temperature of the drying in step 1) is 40-60℃, and the soil sample after drying contains 15%-30% of water, and the temperature of the microwave treatment in step 1) is 30-50℃, and the water in the soil is completely evaporated during the microwave treatment.

3. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The surfactant in step 2) includes but is not limited to Tween 80 and Tween 20, and the weight ratio of the soil sample, citric acid, Tween 20, nano-silicon dioxide in step 2) is 100:(0.5-2):(0.01-0.1):(1-2).

4. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The order of adding citric acid, Tween 20 and nano-silicon dioxide to the soil sample in step 2) is: first add citric acid, then add Tween 20, and finally add nano-silicon dioxide.

5. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The liquid in step 3) includes, but is not limited to, the following concentrations of raw materials: water 1 g / cm 3 , sodium chloride solution 1.2 g / cm 3 , sucrose solution 1.4 g / cm 3 , potassium iodide solution 1.6 g / cm 3 .

6. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The liquids in step 3) are prepared in order from high to low density, starting with a potassium iodide solution, and then adding sucrose solution, sodium chloride solution and water layer by layer, so that the mixture forms a smooth density gradient.

7. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The centrifuge speed of the centrifuge in step 3) is 1000-5000 RPM, and the weight ratio of water, sodium chloride solution, sucrose solution, potassium iodide solution and soil is 10:30:30:20:

1.

8. The method for rapid separation and identification of soil microplastics according to claim 1, characterized in that, The diameter of the sieve hole when sieving the soil in step 1) is 0.05-2 mm.

Images