CN114062071B - Method for quickly separating and detecting plastic from soil - Google Patents

Method for quickly separating and detecting plastic from soil Download PDF

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CN114062071B
CN114062071B CN202111196997.9A CN202111196997A CN114062071B CN 114062071 B CN114062071 B CN 114062071B CN 202111196997 A CN202111196997 A CN 202111196997A CN 114062071 B CN114062071 B CN 114062071B
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plastic
soil
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CN114062071A (en
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李�真
何文清
杨扬
严昌荣
崔吉晓
刘勤
刘琪
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Institute of Environment and Sustainable Development in Agriculturem of CAAS
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00Sampling; Preparing specimens for investigation
    • G01N1/28Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3577Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing liquids, e.g. polluted water
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64Fluorescence; Phosphorescence
    • G01N21/6402Atomic fluorescence; Laser induced fluorescence
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65Raman scattering
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00Technologies for solid waste management
    • Y02W30/50Reuse, recycling or recovery technologies
    • Y02W30/62Plastics recycling; Rubber recycling

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  • Health & Medical Sciences (AREA)
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  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
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  • Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
  • Separation Of Solids By Using Liquids Or Pneumatic Power (AREA)

Abstract

The invention relates to the technical field of material sorting, and discloses a method for quickly separating and detecting a mulching film source micro-plastic from soil. The method comprises the following steps: (1) Mixing the soil and the dispersion liquid to obtain a mixed liquid dispersed with the soil, and then carrying out ultrasonic treatment on the mixed liquid to release the micro plastic in the soil into a liquid phase; (2) Carrying out flotation on the material subjected to ultrasonic treatment in the step (1) to obtain target micro plastic; (3) And (3) detecting the target micro plastic obtained by separation in the step (2). The method can realize the rapid separation and detection of the mulching film source micro-plastic in the soil, and the obtained micro-plastic has high recovery rate, high product purity and small damage degree. The experimental operation is simple and convenient, and the cost is low.

Description

Method for quickly separating and detecting plastic from soil
Technical Field
The invention relates to the technical field of material sorting, in particular to a method for quickly separating and detecting a mulching film source micro-plastic from soil.
Background
The micro plastic is a general term of plastics with the maximum unilateral grain size of less than 5mm, and shows stronger and more durable environmental harmfulness due to the characteristics of small volume, strong penetrability, slow degradation and the like. In the early stage, the research on the micro-plastics is concentrated on water ecosystems such as oceans, soil, particularly farmland soil is taken as the most main place of agricultural production activities, and the research on the micro-plastics is just started. One of the important reasons is: the soil has high impurity content and various types, the soil micro-plastic separation process is complicated and inefficient, high-purity micro-plastic is difficult to obtain, and the like, and the research on the micro-plastic pollution of a land system is seriously hindered.
The mulching film is an important material for agricultural production in China. The application of the mulching film covering technology drives the change of agricultural production modes and the remarkable improvement of productivity in China. On the other hand, the mechanical strength of the mulching film after use is obviously reduced, the breakage degree is high, effective recovery is difficult, and a large amount of mulching film remains in farmland soil every year. Under the action of light, heat, oxygen, mechanical force, microbes and other factors in the farmland soil environment, the fertilizer is continuously aged and degraded. The data show that each plastic with a diameter of 200mm and a thickness of 0.2mm can be gradually disintegrated into 62500 micro-plastics with a particle size of about 0.8mm under the action of ultraviolet rays, organisms and the like, and serious plastic (micro-plastic) pollution in the environment is caused. The establishment of a simple and efficient method for separating and detecting the mulching film source micro-plastic is an important foundation and guarantee for deeply developing researches on aspects such as mulching film source micro-plastic soil environment safety and the like.
The method for separating the micro-plastic from the soil adopted at present is mainly a salt solution flotation method, and particularly, the plastic with the density smaller than that of the solution floats on the solution by water or salt solutions with different concentrations, such as NaCl, naI, znI and the like, and is separated from impurities with larger density; and further selecting and identifying the micro plastic by means of a microscope, an infrared spectrum, a Raman spectrum and the like. This method can remove impurities with high density. And for a large amount of low-density impurities such as plant residues, animal residues, paper scraps and the like contained in soil, strong acid, strong alkali, a strong oxidant, enzyme liquid and the like are used for digestion in a matching manner, but the problems of high cost, unsatisfactory digestion effect and the like exist, micro-plastics can be greatly damaged while the impurities are digested, and the original state of the soil micro-plastics is difficult to detect. More importantly, researches show that a large amount of micro-plastics can exist in the soil aggregate, and the traditional separation method is difficult to detect the micro-plastics in the water-stable soil aggregate, so that the detection result of the micro-plastics is seriously low, and the understanding and judgment of the current soil micro-plastic pollution condition are influenced.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provide a method for quickly separating and detecting the mulching film source micro-plastic from the soil, which does not need strong destructive digestion conditions such as strong acid, strong alkali and the like to remove low-density impurities and does not need manual selection or multiple flotation and other operation processes to realize quick separation and detection of the mulching film source micro-plastic in the soil, and the obtained micro-plastic has high recovery rate, high purity and small damage degree.
In order to achieve the above object, the present invention provides a method for rapidly separating and detecting a plastic from a soil, the method comprising:
(1) Mixing the soil and the dispersion liquid to obtain a mixed liquid dispersed with the soil, and then carrying out ultrasonic treatment on the mixed liquid to release the micro-plastics in the soil into a liquid phase;
(2) Performing flotation on the material subjected to ultrasonic treatment in the step (1) to obtain target micro plastic;
(3) And (3) detecting the target micro plastic obtained by separation in the step (2).
According to the invention, before the membrane source micro-plastic in the soil is separated, the soil is subjected to ultrasonic treatment, so that low-density pollutants in the soil can be decomposed, the micro-plastic is obtained through subsequent flotation separation, manual selection by means of a microscope is not needed for removing the low-density pollutants, strong corrosive agents such as strong acid and strong base are also not needed, the target micro-plastic is rapidly separated, and the purity of the target micro-plastic is improved. In addition, the water-stable soil aggregate can be dispersed through ultrasonic treatment, the micro-plastic wrapped in the water-stable soil aggregate is released, and the recovery rate of the soil micro-plastic is obviously improved. Furthermore, because the invention does not need to carry out multiple flotation to remove low-density pollutants, the accumulated loss of samples can not be caused, the high-rate recovery can be realized, the waste of the flotation solution is reduced, the complexity of multiple flotation is avoided, and the micro-plastic separation can be efficiently and quickly realized. Therefore, the method provided by the invention can realize the rapid separation of the soil film source micro-plastic, can be completed within 24 hours from the mixing of the soil and the dispersion liquid to the final detection, shortens the separation time, and simultaneously obtains the micro-plastic product with high purity, high recovery rate, small damage degree and reduces the use of the flotation liquid. The method has the advantages of simple and convenient experiment operation, low cost and suitability for popularization.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In the invention, the soil aggregate is a basic composition unit of soil, namely, an individual formed by soil particles after coagulation and cementation comprises water-stable aggregate and non-water-stable aggregate, wherein the water-stable aggregate is aggregate which is not immediately dispersed after a soil structure body is soaked in water and keeps the shape of the soil structure body from being broken.
The invention provides a method for quickly separating and detecting a mulching film source micro-plastic from soil, which comprises the following steps:
(1) Mixing the soil and the dispersion liquid to obtain a mixed liquid dispersed with the soil, and then carrying out ultrasonic treatment on the mixed liquid to release the micro plastic in the soil into a liquid phase;
(2) Carrying out flotation on the material subjected to ultrasonic treatment in the step (1) to obtain target micro plastic;
(3) And (3) detecting the target micro plastic obtained by separation in the step (2).
The inventor of the invention finds in the process of research that the soil is subjected to ultrasonic treatment in the presence of a dispersion liquid, so that the low-density impurities contained in the soil can be decomposed and softened in structure, the structure is destroyed, the soil is more hydrophilic and more easily settled, and the soil can be effectively separated by a flotation method and target micro-plastics. The low-density impurities mainly refer to impurities contained in soil and having density lower than that of micro-plastics (particularly target micro-plastics), and mainly comprise plant residues such as straw residues and paper scraps. The soil also includes impurities having a density greater than the higher density of the dispersion, which can settle after the soil and dispersion are mixed.
In the process of research, the inventor of the invention also finds that the soil is subjected to ultrasonic treatment in the presence of the dispersion liquid, so that the water-stable soil aggregate can be decomposed, the micro plastic wrapped in the water-stable soil aggregate is released as far as possible, and the complete separation of the target micro plastic in the soil is realized by a flotation method.
According to the present invention, in order to deeply study the content, morphology and other characteristics of the micro-plastics in soil aggregates with different size fractions, so as to further clarify the distribution and migration transformation characteristics of the micro-plastics in the soil, preferably, before mixing the soil and the dispersion, the method further comprises: and (3) carrying out particle size classification on the soil aggregates in the soil so as to separate and obtain the soil aggregates with different particle sizes and the target micro-plastics in soil pores. It can be understood that after the soil aggregates are classified, soil aggregates with different particle sizes are obtained, and then the extraction or detection of the micro-plastic is respectively carried out on the soil aggregates with different particle sizes, so that the difference of the micro-plastic conditions in the soil aggregates with different particle sizes can be known. The method of the particle size classification is not particularly limited, and for example, a dry screening method or a wet screening method may be used. The wet screening method is that the soil is cured in water for 3-8min, then sequentially passes through the screen columns with screen holes of 2.00mm, 0.25mm and 0.05mm (the screen columns are immersed in distilled water), and is driven up and down at the speed of 30-40 times per minute within 5 min; after sieving, slowly taking out the set sieve from water, standing, slightly drying, respectively washing aggregates in each sieve layer into an aluminum box, and drying at 40-60 ℃ for 24-48h to constant weight.
According to the present invention, it is preferable that the method further comprises pulverizing the soil before mixing the soil and the dispersion liquid. More preferably, the pulverization is carried out so that the particle size of the pulverized material is less than or equal to 2cm.
It will be appreciated that if the soil contains large pieces of impurities, such as stones, it may be necessary to remove the large pieces of impurities prior to comminution.
According to the present invention, the kind of the dispersion is not particularly limited as long as the dispersion does not cause dissolution of the target microplastic. For example, the dispersion may be a liquid having a density that is both greater than or less than the density of the low-density impurities after sonication and the density of the target microplastic, or a liquid having a density that is greater than the density of the target microplastic but less than the density of the low-density impurities after sonication. When the density of the dispersion liquid is the former, after the ultrasonic treatment is finished, putting the product into a flotation liquid with the density larger than that of the target micro-plastic but smaller than that of the low-density impurities after the ultrasonic decomposition to perform flotation on the target micro-plastic; when the density of the dispersion liquid is the latter, after the ultrasonic treatment is finished, the dispersion liquid can be directly used as a flotation liquid to carry out flotation on the target micro plastic.
However, for the purpose of simplifying the operation, the dispersion is a flotation solution used for flotation, and in order to make the dispersion function as a flotation solution at the same time, the density of the dispersion is preferably higher than that of the target micro plastic. The specific choice of the dispersion can be determined according to the density of the target micro-plastic and the low-density impurities after ultrasonic treatment, as long as the target micro-plastic can float and be separated from other impurities with higher density. Preferably, when the target micro-plastic is a polyethylene film source micro-plastic, the dispersion is selected from water or a saturated sodium chloride solution; when the target micro-plastic is a biodegradable film-derived micro-plastic or an oxidative biodegradable film-derived micro-plastic, the dispersion is selected from a sodium iodide solution or a zinc iodide solution. For example, the dispersion may be a saturated sodium iodide solution or a saturated zinc iodide solution.
According to the present invention, it is preferred that the dispersion further comprises a density gradient dispersion. It can be understood that the density gradient dispersion is a solution obtained by mixing several kinds of dispersions with different densities and capable of being layered, and the dispersions can not only better remove impurities, but also obtain target micro-plastics with different densities through one separation step, thereby avoiding complex multiple operations.
According to the present invention, the amount of the dispersion liquid is not particularly limited as long as it is sufficient to disperse the soil. When the dispersion is a flotation solution, the amount of the dispersion is also required to enable enough space for impurities to sink, and enough space for the target micro-plastic to float. In order to allow the dispersion to also function as a flotation solution, it is preferable that the ratio of the amount of the dispersion to the amount of soil is 60 to 150 (for example, can be 60. Wherein, after the soil and the dispersion liquid are mixed, the mixed materials can be stirred to ensure that the soil is uniformly dispersed in the dispersion liquid as much as possible, the stirring speed can be 230-280rpm, and the time can be 20-40min.
According to the present invention, in order to obtain the target micro-plastic in soil aggregates of different particle size grades, preferably, the method of the present invention may comprise performing a fractional flotation, wherein the fractional flotation may be accomplished by any one of the following:
the first method is as follows: the dispersion liquid is density gradient dispersion liquid (similar to density layering cocktail), and is subjected to ultrasonic treatment, stirring and standing for layering flotation to obtain micro-plastics with different densities; with the dispersion, micro-plastics with different densities can be obtained by one operation.
The second method comprises the following steps: using the dispersion liquid with the maximum density as a first flotation liquid, and sequentially carrying out flotation on the suspended substances obtained by flotation by using the flotation liquids with the densities from large to small to obtain the micro-plastics with different densities;
the third method comprises the following steps: and (3) taking the dispersion liquid with the minimum density as a first flotation liquid, and sequentially performing flotation on the substances remained after the flotation by using the flotation liquids with the densities from small to large to obtain the micro-plastics with different densities.
It will be appreciated that in both modes two and three, the first flotation solution needs to be mixed with the soil, and therefore, preferably, the first flotation solution and the soil are used in a ratio of 60 to 150 by weight. The later used flotation solutions with a density from large to small or flotation solutions with a density from small to large do not need to be mixed with the soil as the suspended matter obtained by flotation is subjected to flotation, so their amount can be determined according to the amount of suspended matter or suspension obtained by flotation in the first flotation solution, which can be, for example, 8-13 times the amount of suspension.
And, if the skilled person does not need to finely distinguish the separated microplastic according to the density range, one-stage flotation can be performed by selection of the dispersion, and if fine separation according to a specific density range is required for the microplastic, multi-stage flotation can be performed by the above two or three ways.
According to the present invention, the conditions of the ultrasound are not particularly limited as long as the soil and soil aggregate structure can be dispersed, the low-density impurities are decomposed and precipitated, and the target micro plastic is not affected. According to a preferred embodiment of the present invention, the ultrasonic treatment conditions include: the frequency is 20-60kHz (for example, 20kHz,25kHz,30kHz,35kHz,38kHz,40kHz,43kHz,45kHz,50kHz,55kHz, 60kHz), the temperature is 20-30 ℃ (for example, 20 ℃,21 ℃,22 ℃,23 ℃,24 ℃,25 ℃,26 ℃,27 ℃,28 ℃,29 ℃,30 ℃) and the time is 20-40min (for example, 20min,25min,30min,35min, 40min). More preferably, the ultrasonic treatment conditions include: the frequency is 35-45kHz, the temperature is 23-27 ℃, and the time is 25-35min.
The device for ultrasound may be any device capable of achieving the above purpose, and those skilled in the art may make specific selections according to actual situations, for example, at a laboratory level, the above operation may be accomplished by using a numerical control ultrasonic cleaner.
According to the present invention, in order to further promote the separation of low-density impurities and other impurities encapsulated in or encapsulated by the micro-plastic, thereby further improving the purity of the obtained target micro-plastic, preferably, after the ultrasonic treatment, the method further comprises: the materials are stirred and kept stand in sequence.
Wherein the conditions of the stirring are not particularly limited as long as the further separation of the impurities from the target microplastic can be achieved. Preferably, the stirring conditions include: the rotation speed is 230-280rpm (for example, 230rpm,240rpm,250rpm,260rpm,270rpm,280rpm can be selected), and the time is 20-40min (for example, 20min,25min,30min,35min, 40min). Among them, the device for accomplishing the stirring may not be particularly limited as long as the above object can be achieved, and for example, at a laboratory level, the device may be a magnetic stirrer.
According to the present invention, it is preferable that the standing time is 4 to 12h (for example, 4h,5h,6h,7h,8h,9h,10h,11h,12h may be mentioned).
According to the present invention, preferably, the dyeing method comprises: dyeing the target micro-plastic by adopting a fluorescent dye, and collecting the target micro-plastic; wherein the fluorescent dye is a hydrophobic fluorescent dye. For example, a solution containing a hydrophobic fluorescent dye can be added to the ultrasonically treated material, and the material is allowed to stand for 20-40min after stirring to dye the target micro-plastic as much as possible.
It can be understood that the material after ultrasonic treatment contains target micro-plastics and impurities, and the target micro-plastics has higher molecular weight and stronger hydrophobicity, so that the target micro-plastics can be combined as much as possible by adopting the hydrophobic fluorescent dye, and other impurities can be prevented from being dyed as much as possible. After the target micro plastic is dyed, the detection in the subsequent step (3) is facilitated.
According to the present invention, it is preferable that the hydrophobic fluorescent dye is selected from at least one of a nile red dye and a nile blue dye.
The method for collecting the target micro-plastic can be that a vacuum filtration device is adopted to carry out suction filtration on the dyed material, so that the micro-plastic is collected on the filter membrane. The filter membrane can be a glass fiber filter membrane with the pore size of 0.22 μm or 0.45 μm.
According to the present invention, in the step (3), the method for detecting the composition, content and morphology of the target micro plastic is not particularly limited as long as the object can be achieved. Preferably, however, the method of detection comprises: detecting the target micro plastic by adopting at least one of a fluorescence microscope, a Fourier infrared micro spectrum, a Raman spectrum and a scanning electron microscope; more preferably, the number, particle size and area of the target microplastic are counted by using Image analysis software such as Image J. It can be understood that the separated target micro-plastic can be counted, photographed, etc. using a fluorescence microscope, and the area, side length, number, etc. of the target micro-plastic sample can be counted using Image J software. The chemical components of the target micro-plastic can be detected by Fourier infrared micro-spectroscopy and Raman spectroscopy; the surface appearance of the target micro plastic can be observed by adopting a scanning electron microscope. By adopting the method, various data such as the composition, the morphology, the content and the like of the target micro plastic can be obtained.
According to the present invention, preferably, the recovery of the process is greater than 90%. Also, the particle size range by the method of the present invention may be 0.2 μm to 5mm.
The present invention will be described in detail below by way of examples. In the following examples of the present invention,
the purity calculation method of the target micro plastic comprises the following steps: the amount of separated microplastic/the sum of the amounts of separated microplastic and impurities;
the calculation method of the recovery rate of the target micro-plastic comprises the following steps: the sum of the amount of separated micro-plastic/the amount of micro-plastic known to be added.
Example 1
The method for rapidly separating and detecting the geomembrane-derived micro-plastic from the soil provided by the invention is illustrated
S1: collecting the soil polluted by the polyethylene film source micro-plastics according to a five-point sampling method; drying the collected soil in the air, removing large impurities, then crushing, and sieving to further ensure that the particle size of the crushed material is less than or equal to 2cm;
s2: and (3) taking the material obtained in the step (S1), putting the material into a glass beaker, adding a saturated sodium chloride solution according to the weight ratio of the dispersion liquid to the soil of 125.
S3: placing the mixed solution dispersed with the soil in an ultrasonic cleaner for ultrasonic treatment, wherein the ultrasonic treatment conditions comprise: the frequency is 40KHz, the temperature is 25 deg.C, and the time is 30min.
After the ultrasonic treatment is finished, the materials are placed in a multi-connected magnetic stirrer for stirring. Wherein, the stirring conditions comprise: the rotation speed was 280rpm and the time was 30min.
And after stirring, taking down the material from the multi-linkage magnetic stirrer, and standing for 12 hours.
S4: after standing, the material floating above the solution was transferred to a clean glass beaker. And then adding a nile red dye into the mixture, stirring the mixture, and standing the mixture for 30min to dye the target micro plastic as much as possible.
S5: after dyeing is finished, a vacuum filtration device is adopted to carry out suction filtration on the dyed materials, so that the micro-plastics are collected on a glass fiber filter membrane with the aperture of 0.22 mu m and the diameter of 50 mm.
S6: taking the target micro plastic collected in the step S5, and taking a picture of the separated target micro plastic by using a fluorescence microscope; image J software is adopted to count the area, side length, quantity and the like of the target micro-plastic sample, so as to obtain the content and the like of the target micro-plastic; detecting chemical components of the target micro-plastic by Fourier infrared micro-spectroscopy and the like; and observing the surface morphology of the target micro plastic by adopting a scanning electron microscope.
Example 2
The method for rapidly separating and detecting the geomembrane-derived micro-plastics from the soil provided by the invention is explained
S1: collecting soil polluted by the biodegradable plastic source micro-plastics according to a five-point sampling method; drying the collected soil in the air, removing large impurities, then crushing, and sieving to further ensure that the particle size of the crushed material is less than or equal to 2cm;
s2: and (3) taking the material obtained in the step (S1), putting the material into a glass beaker, adding a saturated sodium iodide solution according to the weight ratio of the dispersion liquid to the soil being 100.
S3: placing the mixed solution dispersed with the soil in an ultrasonic cleaner for ultrasonic treatment, wherein the ultrasonic treatment conditions comprise: the frequency is 35KHz, the temperature is 23 ℃, and the time is 35min.
And after the ultrasonic treatment is finished, placing the materials in a multi-connected magnetic stirrer for stirring. Wherein, the stirring conditions comprise: the rotation speed was 230rpm and the time was 20min.
And after stirring, taking the material from the multi-linkage magnetic stirrer, and standing for 4 hours.
S4: after standing, the material floating above the solution was transferred to a clean glass beaker. And adding a nile blue dye into the mixture, stirring the mixture, and standing the mixture for 20min to dye the target micro plastic as much as possible.
S5: after dyeing is finished, a vacuum filtration device is adopted to carry out suction filtration on the dyed material, so that the micro plastic is collected on a glass fiber filter membrane with the aperture of 0.22 mu m and the diameter of 50 mm.
S6: taking the target micro-plastic collected in the step S5, and taking a picture of the target micro-plastic obtained by separation by using a fluorescence microscope; image J software is adopted to count the area, side length, quantity and the like of the target micro-plastic sample, so as to obtain the content and the like of the target micro-plastic; detecting chemical components of the target micro-plastic by Fourier infrared micro-spectroscopy and the like; and observing the surface appearance of the target micro plastic by adopting a scanning electron microscope.
Example 3
The method for rapidly separating and detecting the geomembrane-derived micro-plastic from the soil provided by the invention is illustrated
S1: collecting the soil polluted by the oxidized and biodegradable plastic-sourced micro-plastics according to a five-point sampling method; drying the collected soil in the air, removing large impurities, then crushing, and sieving to further ensure that the particle size of the crushed material is less than or equal to 2cm;
s2: and (3) taking the material obtained in the step (S1), putting the material into a glass beaker, adding a saturated sodium iodide solution according to the weight ratio of the dispersion liquid to the soil of 150.
S3: placing the mixed solution dispersed with the soil in an ultrasonic cleaner for ultrasonic treatment, wherein the ultrasonic treatment conditions comprise: the frequency is 45KHz, the temperature is 27 deg.C, and the time is 25min.
And after the ultrasonic treatment is finished, placing the materials in a multi-connected magnetic stirrer for stirring. Wherein, the stirring conditions comprise: the rotation speed was 255rpm and the time was 40min.
And after stirring, taking the material from the multi-linkage magnetic stirrer, and standing for 6 hours.
S4: after standing, the material floating above the solution was transferred to a clean glass beaker. And adding a saturated sodium chloride solution into the floated micro plastic and the sodium iodide solution, wherein the volume of the saturated sodium chloride solution is 10 times of that of the floated micro plastic and the sodium iodide solution. And (5) placing the materials in a multi-connected magnetic stirrer for stirring and standing. Wherein, the stirring conditions comprise: the rotation speed was 255rpm and the time was 30min. And after stirring, taking down the material from the multi-linkage magnetic stirrer, and standing for 6 hours.
S5: after standing, the material floating above the solution was transferred to a clean glass beaker. And adding a nile red dye into the mixture, stirring the mixture, and standing the mixture for 40min to dye the target micro plastic as much as possible. The micro-plastics in the flotation solution obtained in the step S4 can be components such as polyethylene micro-plastics which are difficult to biodegrade in the oxidative biodegradation mulch film, and the micro-plastics in the sediment obtained in the step S4 can be components such as polyester which are easy to biodegrade in the oxidative biodegradation mulch film.
S6: after dyeing is finished, a vacuum filtration device is adopted to carry out suction filtration on the dyed material, so that the micro plastic is collected on a glass fiber filter membrane with the aperture of 0.22 mu m and the diameter of 50 mm.
S7: taking the target micro-plastic collected in the step S5, and counting and photographing the separated target micro-plastic by using a fluorescent body type microscope; image J software is adopted to count the area, side length, quantity and the like of the target micro-plastic sample, so as to obtain the content and the like of the target micro-plastic; detecting chemical components of the target micro plastic by adopting Fourier infrared micro spectroscopy and the like; and observing the surface appearance of the target micro plastic by adopting a scanning electron microscope.
Example 4
Illustrating the method for separating the polyethylene film source micro-plastic in the soil aggregate with different size fractions provided by the invention
S1: collecting the soil polluted by the polyethylene film source micro-plastics according to a five-point sampling method; and (3) drying the collected soil in the air, removing large impurities, crushing, and sieving to further ensure that the particle size of the crushed material is less than or equal to 2cm.
Weighing the obtained materials, curing the materials in water for 5min, then carrying out wet screening through a screen column with screen holes of 2.00mm, 0.25mm and 0.05mm, immersing the screen column in distilled water, and driving the screen column up and down at a speed of 30-40 times per minute within 5 min; after sieving, the set sieve is slowly taken out from the water, kept stand, slightly dried, and then the soil aggregate in each level of sieve layer is respectively washed into an aluminum box and dried for 48 hours at 50 ℃ until the weight is constant.
And respectively carrying out the following operations on the soil aggregate in each grade of sieve layer to obtain polyethylene mulch source micro-plastic in soil aggregate of different grades:
s2: and (3) taking the material obtained in the step (S1), putting the material into a glass beaker, adding a saturated sodium chloride solution according to the weight ratio of the dispersion liquid to the soil of 125.
S3: placing the mixed solution dispersed with the soil in an ultrasonic cleaner for ultrasonic treatment, wherein the ultrasonic treatment conditions comprise: the frequency is 40KHz, the temperature is 25 ℃, and the time is 30min.
And after the ultrasonic treatment is finished, placing the materials in a multi-connected magnetic stirrer for stirring. Wherein, the stirring conditions comprise: the rotation speed was 255rpm and the time was 30min.
And after stirring, taking the material from the multi-linkage magnetic stirrer, and standing for 8 hours.
S4: after standing, the material floating above the solution was transferred to a clean glass beaker. And adding a nile red dye into the mixture, stirring, and standing for 30min to dye the target micro plastic as much as possible.
S5: after dyeing is finished, a vacuum filtration device is adopted to carry out suction filtration on the dyed material, so that the micro plastic is collected on a glass fiber filter membrane with the aperture of 0.2 mu m and the diameter of 50 mm.
S6: taking the target micro-plastic collected in the step S5, and counting and photographing the separated target micro-plastic by using a fluorescent body type microscope; image J software is adopted to count the area, side length, quantity and the like of the target micro-plastic sample, so as to obtain the content and the like of the target micro-plastic; detecting chemical components of the target micro-plastic by Fourier infrared micro-spectroscopy and the like; and observing the surface appearance of the target micro plastic by adopting a scanning electron microscope.
Through the operation, the polyethylene mulch source micro-plastic in the soil aggregate with different particle sizes is obtained respectively, and the detection is realized.
Example 5
The membrane-derived micro-plastic was isolated and detected according to the method of example 1, except that the ultrasonic treatment conditions included: the frequency is 20KHz, the temperature is 20 ℃, and the time is 40min.
Example 6
The membrane-derived micro-plastic was isolated and detected according to the method of example 1, except that the ultrasonic treatment conditions included: the frequency is 60KHz, the temperature is 30 deg.C, and the time is 20min.
Comparative example 1
The detection of the separation of the geo-sourced micro-plastics was performed as in example 1, except that the sonication was not performed.
Test example
The detection times of examples 1 to 6 and comparative example 1 were recorded and the purities of the objective microplastics obtained were determined. The results are shown in Table 1.
TABLE 1
Figure BDA0003303531560000141
The recovery rate of each method was calculated as follows:
and adding 0.01g of micro-plastic into 5g of soil, and uniformly mixing to prepare the self-prepared soil containing the micro-plastic. Then, the prepared soil is taken, the method of examples 1 to 6 and the method of comparative example 1 are respectively adopted, the mulching film source micro-plastic is separated and detected, and the recovery rate of each method of examples 1 to 6 and comparative example 1 is calculated according to the obtained mulching film source micro-plastic. The results are shown in Table 2.
TABLE 2
Figure BDA0003303531560000142
Figure BDA0003303531560000151
In tables 1 and 2, 2.00mm, 0.25mm and 0.05mm in example 4 refer to the target microplastics in the soil aggregate obtained through 2.00, 0.25 and 0.05mm screens, respectively.
The results show that the method provided by the invention realizes the rapid separation and detection of the plastic from the mulching film in the soil, and the obtained micro plastic product has high purity and high recovery rate.
In addition, the speed is the target obtained by adopting the technical scheme of the invention, and the particle size range is between 0.2 mu m and 5mm. Because strong destructive substances such as strong acid, strong base, strong oxidizer, enzyme liquid and the like are not used, the original state of the micro plastic can be kept to a greater extent.
In addition, the method of the invention does not need manual selection or multiple times of flotation, shortens the separation time, can be completed within 24 hours from mixing the soil and the dispersion liquid to the final detection, has simple and convenient experimental operation and low cost, and is suitable for popularization.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (6)

1. A method for rapidly separating and detecting a mulching film source micro-plastic from soil is used for realizing rapid and nondestructive separation and detection of the mulching film source micro-plastic through simple operation, and the mulching film source micro-plastic with high recovery rate and high purity is obtained, and is characterized by comprising the following steps:
(1) Suspending, namely mixing the soil and the dispersion liquid to obtain a mixed liquid dispersed with the soil, wherein the density of the dispersion liquid is greater than that of the target micro plastic; wherein prior to mixing the soil and the dispersion, the method further comprises: grading the particle size of soil aggregates in the soil to separate and obtain the soil aggregates with different particle sizes and target micro-plastics in soil pores;
when the target micro-plastic is polyethylene film source micro-plastic, the dispersion liquid is selected from water or saturated sodium chloride solution; when the target micro-plastic is a biodegradable plastic from a ground film or an oxidative biodegradable plastic from a ground film, the dispersion liquid is selected from a sodium iodide solution or a zinc iodide solution;
(2) Performing ultrasonic treatment on the mixed solution dispersed with the soil to release the micro-plastics in the soil into a liquid phase and soften and settle low-density impurities; dyeing the target micro-plastic by adopting a fluorescent dye, and collecting the target micro-plastic; wherein the fluorescent dye is a hydrophobic fluorescent dye;
(3) Sorting, namely performing flotation and suction filtration on the ultrasonically treated material to obtain thin glass fiber buns so as to obtain target micro-plastics;
(4) Detecting, namely sequentially placing the filter membrane collected with the target micro-plastic in a fluorescent body microscope and a Fourier infrared micro-spectrum to detect the quantity, the morphology and the chemical components of the target micro-plastic;
(5) Counting, namely counting the quantity, the grain diameter and the area of the target micro plastic by adopting ImageJ image analysis software;
(6) The recovery rate of the method is more than 90%, the grain size range of the recovered micro-plastic is 0.22-5 mm, and the whole process of separating and detecting the soil film source micro-plastic can be completed within 24 hours.
2. The method of claim 1, wherein the dispersion further comprises a density gradient dispersion.
3. The method of claim 1, wherein the dispersion and soil are used in a weight ratio of 60-150:1.
4. the method of claim 1, wherein the sonication conditions include: the frequency is 20-60kHz, the temperature is 20-30 ℃, and the time is 20-40min.
5. The method of claim 1, wherein the hydrophobic fluorescent dye is selected from at least one of a nile red dye and a nile blue dye.
6. The method of claim 1, wherein the glass fiber filter is a 0.22um or 0.45um aperture smooth filter.
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