A method for microplastics extraction in high salt environments

Abstract

The application discloses a microplastic extraction method for high-salt environment. The microplastic extraction method comprises the following steps: pretreating salt crust sediments, then performing once density separation to obtain supernatant, filtering the supernatant to obtain a first filter membrane carrying microplastics; initially filtering brine to obtain a second filter membrane carrying microplastics; respectively performing organic matter digestion on the first filter membrane carrying microplastics and the second filter membrane carrying microplastics to remove organic matter; respectively performing secondary filtration and cleaning on the first filter membrane and the second filter membrane after organic matter digestion, respectively performing secondary density separation on the cleaned first filter membrane and the cleaned second filter membrane, and obtaining microplastic extracts through post-processing. The microplastic extraction method provided by the application realizes high recovery rate and optimal morphological preservation effect of microplastics in high-salt lake samples, and provides a thought for accurate extraction of microplastics in high-salt environment.

Description

Technical Field

[0001] This invention belongs to the field of microplastics technology, specifically relating to a method for extracting microplastics in high-salt environments. Background Technology

[0002] Microplastics (MPs) are plastic particles with a diameter of less than 5 mm. They have become a ubiquitous global environmental pollutant in the Anthropocene, posing potential risks to biodiversity, ecosystem function, and human health. Most research on microplastic pollution focuses on conventional ecosystems such as terrestrial, marine, and freshwater systems, while systematic studies on specific local environments such as high-salinity lakes remain relatively scarce. High-salinity lakes typically have salinity exceeding 15 g / L (often reaching 200-300 g / L), exhibiting extreme environmental characteristics such as high salinity, high mineralization, strong evaporation, and salt crystal encapsulation and ion-induced aggregation. This leads to the formation of co-precipitation complexes between microplastics and salt minerals (gypsum, rock salt, etc.). Furthermore, microplastics are easily encapsulated by salt crystals and undergo surface weathering, making it difficult for traditional extraction methods to efficiently separate microplastics from the complex matrix and fully preserve their original morphology (such as key parameters like roundness, density, aspect ratio, and fiber ratio). Existing extraction processes commonly suffer from severe loss of small-sized microplastics and significant morphological damage in these samples, directly affecting the accuracy of subsequent high-throughput characterization such as laser direct infrared imaging (LDIR), and thus restricting the scientific rigor of microplastic pollution level assessment and ecological risk research in high-salinity lakes.

[0003] The mainstream approach to microplastic extraction technology is to utilize the differences in density and chemical properties between plastic particles and the environmental matrix to achieve separation and purification. The main technical pathways include: (1) density separation method, which uses high-density salt solutions to make microplastics float while mineral particles sink; (2) organic matter digestion method, which uses oxidants, acids or alkalis to remove interfering organic residues; and (3) filtration / concentration steps, which enrich the extract to a state that is convenient for subsequent characterization.

[0004] For example, existing technical solutions mainly involve conventional density separation combined with organic matter digestion. Typical examples include density separation and H2O2 digestion based on NaCl solution, density separation based on NaI solution, cyclic extraction based on NaBr solution, and acid / base digestion based on HCl or NaOH. These methods are widely used in common environmental matrices, but their ability to destroy salt crystal encapsulation and ion aggregation in the complex matrices of high-salinity lakes is limited. They are significantly less applicable to the unique problems of salt crystal encapsulation, ion aggregation, and high mineralization interference in high-salinity lakes, and easily lead to low recovery rates of small-sized particles and damage to microplastic morphology.

[0005] Currently, existing technologies such as CN 121231113 A, CN 117554152 A, and CN 121190589 A have respectively implemented "NaBr density separation followed by H2O2 digestion" for sediment samples and "H2O2 digestion followed by NaBr density separation" for brine samples, thereby protecting the morphology of microplastic particles.

[0006] While the aforementioned existing technologies have achieved some success in conventional matrices, they all suffer from the following inherent technical defects, rendering them unsuitable for efficient extraction from high-salinity lake brine and salt crust sediments—specific environmental samples: First, existing technologies fail to address the core interference issue of salt crystal encapsulation and ion-induced aggregation in high-salinity lake environments. The main interference from microplastics in existing matrices comes from organic matter, waxy layers, or biofilms; there is no physical encapsulation or chemical co-precipitation effect of salt crystals on microplastics. Therefore, when directly applied to high-salinity lake samples, a large number of microplastics are trapped by salt crystals and cannot be effectively released, resulting in a significantly low recovery rate for small particles (<100 μm). Second, the multiple or secondary separation settings in existing technologies are simply repetitive extraction operations aimed at improving recovery rates rather than achieving specific purification functions. This leads to the easy adhesion of colloidal impurities to the surface of microplastics extracted using existing technologies, severely affecting the accuracy of subsequent characterization techniques such as laser direct infrared imaging (LDIR) in identifying small particles and obtaining morphological parameters. Third, existing technologies lack a systematic design for morphological protection. While existing technologies avoid strong acids and alkalis, the extraction process often involves mechanical operations, which may cause mechanical damage to the weathered and fragile microplastics, making it difficult to preserve the original morphological parameters of the microplastics to the greatest extent. Fourth, the process parameters of existing technical solutions are optimized for their respective conventional matrices and are not adaptable to high-salinity lake samples, thus they cannot be directly transferred to high-salinity lake samples.

[0007] In summary, existing technologies have not optimized the process sequence to address the unique challenges of salt crystal embedding, ion-induced aggregation, and high mineralization interference in high-salinity lakes, nor have they systematically considered the synergistic protection of small particle recovery rate and morphological integrity. Therefore, they exhibit significant limitations in high-salinity environmental samples. Summary of the Invention

[0008] The main objective of this invention is to provide a method for extracting microplastics in high-salt environments, thereby overcoming the shortcomings of existing technologies.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: A first aspect of the present invention provides a method for extracting microplastics in a high-salt environment, comprising: The salt crust deposits were pretreated, followed by a density separation to obtain a supernatant. The supernatant was then filtered to obtain a first filter membrane loaded with microplastics. The brine was initially filtered to obtain a second filter membrane loaded with microplastics. The first filter membrane carrying microplastics and the second filter membrane carrying microplastics are respectively subjected to organic matter digestion; The first and second filter membranes after organic matter digestion were subjected to secondary filtration and washing, and the washed first and second filter membranes were subjected to secondary density separation. After post-processing, microplastic extract was obtained.

[0010] In some embodiments, the pretreatment includes drying the salt crust deposit at 50-60°C and then pulverizing it to obtain salt crust deposit powder with a particle size of <5 mm.

[0011] In some embodiments, the first density separation specifically includes: mixing the salt crust sediment powder with a separating agent until uniform, ultrasonically treating it, allowing it to stand, taking the supernatant, and repeating the process 3 to 4 times to obtain the supernatant.

[0012] Furthermore, the separating agent is a saturated salt solution, including a saturated NaBr solution.

[0013] Furthermore, the ratio of the salt crust deposit powder to the saturated NaBr solution is 1 g: 10 mL to 1 g: 20 mL by mass-volume ratio.

[0014] Furthermore, the mass-to-volume ratio of the salt crust deposit powder to the saturated NaBr solution is 1 g : 12 mL to 1 g : 18 mL.

[0015] Furthermore, the mass-to-volume ratio of the salt crust deposit powder to the saturated NaBr solution is 1 g : 15 mL.

[0016] Furthermore, the ultrasonic treatment time is 5-10 minutes, and the power is 15-20W.

[0017] Furthermore, the settling time is 24~48h.

[0018] In some implementations, the organic matter digestion specifically includes: using a digesting agent to digest the organic matter in a first filter membrane and a second filter membrane carrying microplastics at 50-60°C for 24-48 hours to remove the organic matter.

[0019] In some preferred embodiments, the digesting agent is hydrogen peroxide. For example, the organic matter is digested in a 30wt% H₂O₂ solution at 50-60°C for 24-48 hours on the first and second filter membranes carrying microplastics to remove the organic matter. The amount of digesting agent used is until the organic matter is completely digested.

[0020] In some implementations, the extraction method specifically includes: performing secondary filtration on the first and second filter membranes after organic matter digestion, and washing them with a separating agent.

[0021] In some implementations, the secondary density separation specifically includes: mixing the washed first and second filter membranes with a separating agent, then ultrasonically treating and allowing them to stand to obtain a supernatant, repeating the process 3 to 4 times to complete the secondary density separation.

[0022] Furthermore, in the secondary density separation, each filter membrane is prepared with 100-200 mL of saturated NaBr solution.

[0023] Furthermore, in the secondary density separation, each filter membrane is supplied with 150 mL of saturated NaBr solution.

[0024] Furthermore, the ultrasonic treatment time is 5-10 minutes, and the power is 15-20W.

[0025] Furthermore, the settling time is 24~48h.

[0026] In some embodiments, the post-processing includes: filtering the supernatant obtained by secondary density separation, then drying, ultrasonically treating and washing the first and second filter membranes carrying microplastics, respectively, and then concentrating the resulting washing solutions to obtain the microplastic extract.

[0027] In some implementations, both the first and second filter membranes are 10 μm stainless steel filter membranes.

[0028] In some implementations, the microplastic extraction method achieves a recovery rate of over 80% for microplastics <100 μm.

[0029] In some more specific implementations, the method for extracting microplastics specifically includes the following steps: (I) Salt crust sediment sample extraction process Sample pretreatment: The collected salt crust sediment samples were placed in an oven and dried at 50~60℃ until constant weight was achieved; then crushed, thoroughly mixed and sieved through a 5 mm soil sieve.

[0030] Initial density separation: The pretreated sediment sample was placed in a glass beaker, and a saturated NaBr solution (ρ = 1.5 g / mL) was added, wherein the mass-to-volume ratio of the salt crust sediment powder to the saturated NaBr solution was 1 g : 10 mL to 1 g : 20 mL. The mixture was thoroughly stirred with a glass rod and sonicated at 15–20 W for 5–10 min. It was then stirred again, and the glass rod was rinsed with a small amount of NaBr solution. The mixture was allowed to stand for 24–48 h to allow the supernatant and sediment matrix to fully separate, enabling microplastics to float and disrupt the salt crystal embedding structure and ion-induced aggregation complexes. The supernatant was transferred to another clean large beaker. This initial density separation was repeated 3–4 times to obtain the supernatant. The combined supernatant was then vacuum filtered through a 10 µm stainless steel filter membrane, which contained microplastics.

[0031] H2O2 Organic Matter Digestion: Transfer a 10 μm stainless steel filter membrane containing microplastics to a clean small beaker or Erlenmeyer flask, add 30% H2O2 solution (20-60 mL per membrane, preferably 30-50 mL), and then place in a 50-60℃ constant temperature oven or shaker for 24-48 h until residual organic matter is removed. During digestion, add an appropriate amount of 30% H2O2 as needed based on the reaction. Digestion is considered complete when no obvious bubbles are produced after adding H2O2.

[0032] Secondary filtration and washing: After digestion, the digestate is filtered onto a 10 µm stainless steel filter membrane. The filter membrane is then placed in a beaker and thoroughly washed with a saturated NaBr solution.

[0033] Secondary density separation: Repeat the initial density separation step 3-4 times (stirring, sonication, settling, and supernatant collection) to effectively capture microplastic particles that still adhere to or remain after digestion. Use 100-200 mL of saturated NaBr solution for each filter membrane.

[0034] Final filtration, drying and concentration: The collected supernatant was filtered through a 10 μm stainless steel filter membrane, which was dried at 50 °C. The filter membrane was then placed in a 150 ml beaker, 10-20 mL of anhydrous ethanol was added, and the mixture was sonicated at 15-20 W for 5-10 min. The particulate matter on the filter membrane was then washed with anhydrous ethanol, and all particulate matter was transferred to the solution. Finally, the solution was concentrated into a 2 ml sample vial to obtain the microplastic extract.

[0035] In this invention, the first density separation aims to remove soluble salts and light impurities, and initially dissociate the salt crust. After digestion removes organic matter, the second density separation targets the recovery of released microplastics (especially particles <100 μm), avoiding recrystallization of salt crystals or secondary encapsulation of small particles by residual organic matter-salt crystal complexes during digestion. The two steps produce a synergistic effect. In high-salt environments, compared with the conventional "single density separation + digestion" method, the recovery rate of microplastic particles <100 μm is significantly improved and the breakage rate is significantly reduced.

[0036] (II) Brine Sample Extraction Procedure Initial filtration: The collected brine sample was directly vacuum filtered through a 10 μm stainless steel filter membrane to trap microplastics and related particles on the filter membrane, thereby enriching the particulate matter in the water sample.

[0037] H2O2 Organic Matter Digestion: Place the filter membrane carrying the particles in a 150 mL glass beaker / Eragonal flask, and add 30% H2O2 solution. The amount of 30% H2O2 solution used is 20-60 mL per filter membrane carrying the particles, preferably 30-50 mL. Digest in a constant temperature oven or shaker at 50-60℃ for 24-48 h. During the digestion process, add a small amount of 30% H2O2 to observe the reaction until no obvious bubbles are produced after adding H2O2, indicating that the organic matter is completely digested.

[0038] Filtration and density separation: After digestion, filter the sample and perform density separation 3-4 times with saturated NaBr solution. Collect the supernatant after each settling for 24-48 h.

[0039] Final filtration, drying and concentration: The supernatant was filtered through a 10 μm stainless steel filter membrane, which was dried at 50 °C. Then, it was placed in a small beaker, anhydrous ethanol was added, and the mixture was sonicated at 15-20 W for 5-10 min. The particulate matter on the filter membrane was rinsed off, and the resulting solution was concentrated into a 2 ml sample vial to obtain the microplastic extract.

[0040] In the above-described steps, this invention employs a processing sequence of "initial density separation, H2O2 digestion, and secondary density separation" for sediment samples. The initial NaBr density separation preferentially removes most high-density mineral particles and salt solids, disrupting some salt crystal embedding and mineral adhesion structures, thereby reducing the matrix load during subsequent digestion. Subsequently, H2O2 is used to remove residual organic matter and biofilm, further releasing mineral polymers (MPs) coated or adhered to by organic matter. The second NaBr density separation after digestion helps allow particles still retained on fine-grained minerals, organic residues, or the filter membrane surface to re-participate in the flotation process, reducing MP loss during filtration and transfer, and improving the integrity and stability of the entire extraction process.

[0041] Unlike sediments, brine in salt lakes typically contains relatively low levels of large-particle minerals. The main interferences come from high concentrations of dissolved salts, suspended particles, halophilic microorganisms, and their biofilms. Simultaneously, salt crystal precipitation occurs during filtration and concentration, leading to MP (mineral matrix) encapsulation, filter membrane clogging, or particle transfer loss. Therefore, in this invention, brine samples are first enriched by filtration to remove suspended MPs and related particulate matter. Then, the filter residue is digested with H2O2 to remove biofilms and organic coatings, reducing the impact of particle aggregation and organic residues on subsequent analysis. Subsequently, NaBr density separation is used to further remove inorganic suspended particles and precipitated salt crystals, achieving further purification and concentration of MPs. This processing sequence reflects the difference in process between brine samples, which focus on "filtration enrichment and control of salt crystal interference," and sediment samples, which focus on "removal of solid mineral matrix and release of encapsulated particles."

[0042] Therefore, this invention achieves precise synergy among functional modules through a "differentiated process sequence": sediment samples undergo multiple NaBr density separations to preferentially disrupt the salt crystal embedding and mineral co-precipitation structures in the high-salt environment, followed by gentle H2O2 digestion to remove residual organic matter, avoiding secondary agglomeration caused by mineral interference during digestion; brine samples are first digested with H2O2 to disrupt biofilm adhesion, followed by density separation to ensure efficient concentration of microplastics in large-volume samples. The secondary density separation step (sediment process only) forms a closed-loop extraction mechanism to further capture residual particles. Throughout the process, a 10 μm stainless steel filter membrane serves as the core filtration component, ensuring a high rejection rate for particles <100 μm while also possessing the advantages of chemical corrosion resistance and reusability; the 50~60℃ temperature control balances H2O2 oxidation efficiency with microplastic morphology protection; and an anhydrous ethanol ultrasonic cleaning step achieves final purification, avoiding the influence of residual moisture on subsequent laser direct infrared imaging (LDIR) characterization.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects: (1) A fundamental breakthrough in process sequence for addressing the problem of salt crystal embedding. This invention reveals for the first time the fundamental mechanism of microplastic extraction failure in high-salinity lakes, and designs a revolutionary differentiated process sequence based on this mechanism: for salt crust sediments, NaBr density separation is used first, followed by H2O2 digestion, combined with secondary density separation, prioritizing the physical destruction of the salt crystal structure with high-density NaBr solution to release the embedded microplastics in advance; for brine samples, a reverse process of H2O2 digestion followed by NaBr density separation is used, breaking down biofilm adhesion before density separation. This sequential design based on the microscopic mechanism of extreme environments enables the efficient recovery of small-sized microplastics that were originally bound by salt crystals and could not be released, fundamentally solving the problem of microplastic extraction failure in high-salinity matrices.

[0044] (2) In this invention, secondary density separation is explicitly set after the H2O2 digestion step, and it is given a completely new technical purpose. It is no longer a simple repeated extraction, but a chemical purification step after digestion, specifically used to remove nanoscale organic colloidal fragments generated during digestion. This innovative design effectively avoids heterogeneous aggregation of colloids and microplastics, so that the extracted microplastics retain their original environmental state to the greatest extent in terms of key morphological parameters such as roundness and aspect ratio, providing a reliable basis for subsequent morphology-based ecological risk assessment.

[0045] (3) This invention elevates morphological protection from simply avoiding chemical corrosion to a systematic level, achieved through multi-dimensional synergy: using mild 30% H2O2 and 50℃ low temperature to avoid thermal damage; avoiding physical breakage by eliminating mechanical shearing throughout the process (static settling, without centrifugation or mechanical pouring); using anhydrous ethanol ultrasonic cleaning as the final treatment to avoid agglomeration and deformation caused by residual moisture, while effectively dispersing potentially agglomerated microplastic particles, ensuring the accuracy of particle counting and the signal-to-noise ratio of spectral identification by subsequent characterization techniques such as LDIR.

[0046] (4) Through extensive comparative experiments, this invention has optimized a precise parameter range for the specific physicochemical properties of high-salinity lake matrix. This precise parameter system ensures the stability and repeatability of the process across different batches and laboratories, providing data support for the establishment of a standardized method for microplastic extraction from high-salinity lakes. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the process for extracting microplastics from sediment samples in a typical embodiment of the present invention; Figure 2 This is a schematic diagram of the process for extracting microplastics from brine samples in a typical embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the extraction of microplastics from a sediment sample in a typical embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the extraction of microplastics from a brine sample in a typical embodiment of the present invention; Figure 5 These are LDIR imaging results of MPs extracted from the blank group and the NaBr-H2O2 group of this invention. Figure 6 These are LDIR imaging results of MPs extracted from salt lake samples (A, B, C) using different control extraction methods of this invention. Detailed Implementation

[0049] In view of the problems existing in the prior art, after in-depth research, a method for microplastic extraction in high-salt environments is provided.

[0050] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0051] First, the terminology used in this invention will be explained.

[0052] Microplastics (MPs) refer to plastic particles with a diameter of less than 5 mm, including various forms such as fragments, fibers, granules, and films. This invention particularly emphasizes small-sized microplastics (particle size <100 μm), which are the focus of this invention.

[0053] High-salinity lakes: Inland lake ecosystems with salinity typically exceeding 15 g / L (often reaching 200–300 g / L), characterized by extreme environmental features such as high mineralization, high alkalinity, low dissolved oxygen, strong evaporation, salt crust formation, and stratified brine structure.

[0054] Salt sediments: mineral matrix embedded in salt crystals formed by intense evaporation in highly saline lakes.

[0055] Brine: A highly concentrated salt solution from a high-salinity lake.

[0056] Density separation: a separation technology that utilizes the density difference between plastic particles and the environmental matrix, using a high-density salt solution to make microplastics float while mineral particles sink.

[0057] Laser direct infrared imaging (LDIR) is a high-throughput microplastic characterization technique that combines infrared spectroscopy molecular recognition with automated high-speed imaging. It is used to quantitatively evaluate the particle size distribution, polymer type, and morphological parameters of extracted microplastics.

[0058] The technical solution of the present invention will be further described below with reference to the embodiments. Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally selected and do not involve the core technical means of the present invention.

[0059] For example, the equipment and instruments used in the embodiments and comparative examples of the present invention mainly include: vacuum filtration device, Erlenmeyer flask / beaker, ultrasonic cleaner, 50℃ constant temperature oven / shaker, 2 ml sample bottle, etc.

[0060] The salt lake sediment samples used in the embodiments and comparative examples of this invention were collected from the Qarhan Dabuxun Salt Lake area. To ensure representativeness, sediment samples were collected from the periphery of the lake area and adjacent developed salt fields. Sediment from 0 to 20 cm was collected at each location using a pre-cleaned stainless steel shovel, with each sample weighing approximately 1000 g. After collection, the samples were sealed on-site in clean aluminum foil self-sealing bags and stored at room temperature in the dark to minimize the impact of light and external contamination on the samples.

[0061] Furthermore, all comparative examples in this invention use salt lake sediment samples. Considering that the occurrence state of MPs in salt lake samples is not only controlled by their own density, but also affected by factors such as salt crystal embedding, mineral particle adhesion, ion-induced aggregation, and high aging; the standard MPs added in the laboratory are difficult to truly simulate the fragility and occurrence state of MPs in the field environment.

[0062] To reduce the impact of spatial differences in samples on method comparison, all samples were thoroughly mixed before the experiment and divided into equal portions of different treatment groups according to the same mass.

[0063] Example 1 like Figure 1 and Figure 2 As shown, the process is divided into two parallel paths: "water sample" and "sediment". The main operational steps are as follows: (a) Salt crust sediment sample extraction process, such as Figure 1 and Figure 3 As shown: Sample pretreatment: The collected salt crust sediment samples were placed in an oven and dried at 50°C until constant weight was achieved; then crushed, thoroughly mixed, and sieved through a 5 mm soil sieve to remove large particles. After sieving, the samples were thoroughly mixed and used for subsequent extraction experiments.

[0064] Initial density separation: Accurately weigh 10 g of the pretreated sediment sample and place it in a 200 ml glass beaker. Add 150 ml of saturated NaBr solution (ρ = 1.5 g / ml). Stir thoroughly with a glass rod, sonicate at 20 W for 10 min, stir again, and rinse the glass rod with a small amount of NaBr solution. Allow the mixture to stand for at least 24 h to allow the supernatant and sediment matrix to fully separate, enabling microplastics to float and disrupting the salt crystal embedding structure and ion-induced aggregation complexes. Then transfer the supernatant (approximately 100 ml) to another clean large beaker. Repeat the above separation steps three times.

[0065] Filtration: The combined supernatant was filtered through a vacuum filtration device using a 10 μm stainless steel filter membrane to trap microplastic particles on the filter membrane.

[0066] H2O2 organic matter digestion: Transfer a 10 μm stainless steel filter membrane containing microplastics to a clean small beaker / Eragonal flask, add 40 ml of 30% H2O2 solution, and place it in a 50℃ constant temperature oven or shaker for 24 hours for digestion. During the digestion process, an appropriate amount of 30% H2O2 needs to be added according to the reaction. When no obvious bubbles are produced after adding H2O2, the digestion is considered to be complete until all residual organic matter is completely removed.

[0067] Secondary filtration and cleaning: The digest solution was filtered onto a 10 µm stainless steel filter membrane, which was then placed in a beaker and cleaned with NaBr solution.

[0068] Secondary density separation: The initial density separation step was repeated three times (stirring, sonication, settling, and supernatant collection) to effectively capture microplastic particles that still adhered or remained after digestion. In the secondary density separation, each filter membrane was prepared with 150 mL of saturated NaBr solution.

[0069] Final filtration, drying and concentration: The obtained supernatant was filtered through a 10 μm stainless steel filter membrane, which was dried at 50 °C. Then, the filter membrane was placed in a 150 ml beaker, 15 mL of anhydrous ethanol was added, and the mixture was sonicated at 15 W for 10 min. The particulate matter on the filter membrane was then washed with anhydrous ethanol, and all particulate matter was transferred to the solution. Finally, the obtained solution was concentrated into a 2 ml sample vial to obtain the microplastic extract.

[0070] (ii) Brine sample extraction process, such as Figure 2 and Figure 4 As shown: Initial filtration: The collected brine sample was directly vacuum filtered through a 10 μm stainless steel filter membrane to trap microplastics and related particles on the filter membrane.

[0071] H2O2 organic matter digestion: Place the filter membrane carrying the particles in a 150 ml glass beaker / Eragonal flask, add an appropriate amount of 30% H2O2 solution, and digest in a 50℃ constant temperature oven or shaker for 24 h. During the digestion process, add a small amount of 30% H2O2 to observe the reaction. When no obvious bubbles are produced after adding H2O2, the digestion is considered complete until all residual organic matter is completely removed.

[0072] Filtration and density separation: After digestion, the sample was filtered and density separated three times with saturated NaBr solution. The supernatant was collected after each 24-hour settling period. 150 mL of saturated NaBr solution was used for each filter membrane.

[0073] Final filtration, drying and concentration: The supernatant was filtered through a 10 μm stainless steel filter membrane, which was dried at 50 °C. Then, it was placed in a small beaker, 15 mL of anhydrous ethanol was added, and the mixture was sonicated at 15 W for 10 min. The particulate matter on the filter membrane was rinsed off, and all particulate matter was transferred to the solution. Finally, the resulting solution was concentrated into a 2 mL sample vial to obtain the microplastic extract.

[0074] Control experiment (I) Experimental Design The control experiment of this invention was designed to compare the effects of different combinations of separating agents and digesting agents on the extraction results of MPs from salt lake sediments. A separation agent control experiment and a digesting agent control experiment were set up.

[0075] In the separation agent control experiment, NaBr, NaCl, NaI, and HCOOK were used for density separation, followed by digestion with H2O2. In the digestion agent control experiment, NaBr was used for density separation, followed by digestion with H2O2, HCl, and NaOH, respectively. The operating steps, method parameters, and amounts of substances used in each experimental group were the same as in Example 1, with the only difference being the type of separation agent or digestion agent.

[0076] To compare the effects of different combinations of separating and digesting agents on the extraction results of MPs from salt lake sediments, three sediment samples (A, B, and C) were used in each experiment.

[0077] All processing groups followed the same extraction, filtration, concentration, and LDIR analysis procedures.

[0078] (II) Characterization and Quantitative Analysis of Extracted MPs This study employed LDIR for MPs identification and morphological parameter extraction, using an Agilent 8700 LDIR system and Agilent Clarity software for Particle Analysis. The instrument used a quantum cascade laser as the infrared light source, with a spectral acquisition range of 1800-975 cm⁻¹. -1 Parameters such as particle size, roundness, aspect ratio, and fiber ratio are all automatically calculated and derived based on the particle profile. Considering the influence of factors such as diffraction limit, signal-to-noise ratio, and spectral matching quality on small-sized particles, the effective statistical lower limit is set at 20 μm.

[0079] For each extraction result, the detection rate and morphological parameters of small-sized MPs were statistically analyzed. The detection rate of small-sized MPs was defined as the percentage of particles ranging from 20 to 100 μm out of all particles. Morphological parameters included roundness, density, aspect ratio, and fiber ratio, which were used to characterize particle edge regularity, contour integrity, extension, and the preservation of fibrous particles, respectively. In method evaluation, the detection rate of small-sized particles was analyzed in conjunction with morphological parameters: if an increase in the proportion of small-sized particles was accompanied by a decrease in density, aspect ratio, or fiber ratio, the possibility of particle breakage or fiber loss due to pretreatment should be considered. A stable detection rate of small-sized particles coexisting with good morphology more comprehensively reflects the overall applicability of the extraction method.

[0080] (III) Statistical Analysis Statistical analysis was conducted based on the data of particles with a matching mass greater than 0.7 in the LDIR identification results. The Friedman nonparametric test was used to compare the overall differences in the detection ratio of small-sized MPs and morphological parameters of different extraction methods. The significance level was set at P<0.05, and Kendall's W was calculated as the effect size.

[0081] (iv) Quality Control / Quality Assurance To further control background contamination, a complete blank control was included in this study. The blank control consisted of the same volume and concentration of reagent (NaBr-H2O2) as the official sample, and was performed according to the complete sample preparation procedure. The blank control was used to assess potential background MP contamination from experimental containers, reagents, air settling, and the operational process. Plastic equipment was avoided as much as possible throughout the experiment. All glassware and metal tools were cleaned and rinsed with ultrapure water before use. Aluminum foil was used to cover the samples during preparation to reduce the risk of exogenous contamination.

[0082] To verify the background contamination level in MP extraction, LDIR analysis was performed on a concurrently set process blank group. Very few individual MP particles were detected in the process blank group, indicating good control of exogenous MP contamination during the experiment. The LDIR imaging results of MP extracted from the process blank group and the NaBr-H2O2 group are shown below. Figure 5 As shown. Among them, (1) is the process blank control, and (2)-(4) are samples A, B and C of the NaBr-H2O2 method, respectively.

[0083] (V) Experimental Results (1) Analysis of the detection ratio and relative extraction effect of small-sized MPs Considering that the high salinity and mineralization of salt lakes can promote the embedding, adhesion, and heterogeneous aggregation of mineral polymers (MPs) with salt crystals and mineral particles, increasing the loss of small-sized particles during separation, this invention uses the relative extraction efficiency of small-sized MPs as one of the evaluation indicators. The detection ratio and morphological parameters of MPs using different extraction methods are shown in Table 1. LDIR imaging results of MPs extracted from salt lake samples (A, B, C) using different control extraction methods are shown in Table 1. Figure 6 (1)-(5) correspond to sample A, (6)-(10) correspond to sample B, and (11)-(15) correspond to sample C. Figure 6 The corresponding extraction methods from top to bottom are: NaCl-H2O2, NaI-H2O2, HCOOK-H2O2, NaBr-HCl, and NaBr-NaOH.

[0084] Table 1. Comparison of detection rates and morphological parameters of small MPs using different extraction methods As shown in Table 1, the detection rates of small MPs varied among different extraction methods. The NaBr-H2O2 group exhibited relatively stable detection rates across the three sample groups, at 85.48%, 85.68%, and 88.16% respectively (samples A, B, and C; LDIR imaging results are shown in Table 1). Figure 6 In contrast, the detection rates of the NaCl-H2O2 group fluctuated significantly across the three sample groups, at 74.71%, 83.40%, and 71.48%, with an average of 76.53%. This indicates that the detection capability of NaCl solution for small-sized microplastics (MPs) is limited in the high-matrix environment of salt lakes. The NaI-H2O2 group showed a higher overall detection rate for small-sized MPs, at 90.13%, 96.30%, and 88.36%, respectively. This suggests that a high-density separating agent is beneficial for improving the detection rate. Although the detection results of the NaI-H2O2 group were better than those of the NaBr-H2O2 group, considering the special characteristics of microplastics in high-salt environments (severe aging and easy breakage), as well as the safety, environmental friendliness, and price of the reagents (NaI is toxic, difficult to treat waste liquid, and expensive), the NaBr-H2O2 group had the best overall performance. The detection rate of the HCOOK-H2O2 group was generally lower than that of the NaBr-H2O group. These results indicate that the density of the separating agent and matrix compatibility are important factors affecting the detection effect.

[0085] Among different digesting agents, the detection rates of small-sized MPs were all relatively high in the NaBr-H2O2, NaBr-HCl, and NaBr-NaOH groups. The results indicate that under the same NaBr density separation conditions, different digesting agents can achieve good detection results for small-sized MPs; however, their impact on particle morphology still needs further evaluation based on subsequent morphological parameters (LDIR imaging results are shown in [link to LDIR imaging results]). Figure 6Generally, P < 0.05 indicates a significant difference. Kendall's W is the effect size index; the closer the value is to 1, the greater the difference. The Friedman test results (Table 2) show that different extraction methods in the NaBr-H2O2, NaBr-HCl, and NaBr-NaOH groups have a significant impact on the detection rate of MPs. X 2 =12.33, df=5, P=0.03, Kendall's W=0.82), the NaBr-H2O2 combination showed a good detection rate in the sample.

[0086] Table 2. Friedman test results on the influence of extraction methods on the detection rate and morphological parameters of small-sized MPs. (2) Comparison of morphological integrity parameters Based on LDIR identification results, the morphological parameter characteristics of MPs processed by different extraction methods were studied and compared. Morphological parameter indicators can reflect the integrity of MP contours and the preservation status of fibrous particles.

[0087] Table 1 shows that the NaBr-H2O2 group performed better overall in terms of density, aspect ratio, and fiber ratio. The average density was 0.82, higher than the NaCl-H2O2, NaI-H2O2, HCOOK-H2O2, NaBr-HCl, and NaBr-NaOH groups, indicating that the extracted particles had a more complete outline. Furthermore, fibrous MPs are prone to breakage or loss during extraction; therefore, aspect ratio and fiber ratio are important references for evaluating morphology retention. The average aspect ratio of the NaBr-H2O2 groups (A, B, C) was 1.45, and the average fiber ratio was 4.12%, both higher than other extraction methods. Similarly, the extraction effects varied significantly among different digestion agents. The density and fiber ratio of MPs in the HCl and NaOH groups were lower than those in the H2O2 group. Reports indicate that acid and alkali treatments affect the structural stability of MPs, suggesting that the mild oxidative digestion with H2O2 reagent is more suitable for extracting MPs samples that have undergone natural aging.

[0088] In summary, the NaBr-H2O2 method did not show the highest performance in all indicators, and the effects of different extraction methods on morphological parameters were not significant (P>0.05, Table 2). However, the NaBr-H2O2 method demonstrated a good balance between the detection rate of small-sized MPs and morphological parameters, indicating that this extraction method can achieve both extraction and morphological preservation of small-sized MPs in the complex matrix of salt lakes.

[0089] Example 2 The difference between this embodiment and Embodiment 1 is that: (I) Salt crust sediment sample extraction procedure: The mass-to-volume ratio of the salt crust sediment powder to the saturated NaBr solution is 1 g: 10 mL. That is, 10 g of the pretreated sediment sample is weighed, placed in a 200 ml glass beaker, and 100 ml of saturated NaBr solution (ρ=1.5 g / ml) is added.

[0090] The remaining steps are the same as in Example 1.

[0091] In this embodiment, the recovery rate of microplastics with a particle size of less than 100 μm was approximately 87.03%.

[0092] Example 3 The difference between this embodiment and Embodiment 1 is that: (I) Salt crust sediment sample extraction procedure: The mass-to-volume ratio of the salt crust sediment powder to the saturated NaBr solution was 1 g: 20 mL. 10 g of the pretreated sediment sample was weighed and placed in a 200 ml glass beaker, and 200 ml of saturated NaBr solution (ρ=1.5 g / ml) was added.

[0093] The remaining steps are the same as in Example 1.

[0094] The recovery rate of microplastics with a particle size of less than 100 μm is approximately 85.56%.

[0095] In summary, this invention provides a method for extracting microplastics from brine and salt crust sediments in high-salinity lakes. The technical solution utilizes an optimized combination of NaBr density separation and H2O2 organic matter digestion, along with differentiated process sequences for sediment and brine matrices (sediments undergo "density separation followed by digestion + secondary density separation," while brine undergoes "digestion followed by density separation"). Key technologies such as 10 μm stainless steel membrane filtration and ultrasonic cleaning and concentration with anhydrous ethanol effectively overcome interference from high-salinity environments, such as salt crystal embedding and ion-induced aggregation, while maximizing the preservation of the original morphological integrity of the microplastics.

[0096] In addition, the present invention has also conducted experiments with other raw materials, process operations and process conditions described in this specification, with reference to the foregoing embodiments, and has obtained relatively ideal results in all cases.

[0097] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for extracting microplastics in high-salt environments, characterized in that, include: The salt crust deposits were pretreated, followed by a density separation to obtain a supernatant. The supernatant was then filtered to obtain a first filter membrane loaded with microplastics. The brine was initially filtered to obtain a second filter membrane loaded with microplastics. The first filter membrane carrying microplastics and the second filter membrane carrying microplastics are respectively subjected to organic matter digestion; The first and second filter membranes after organic matter digestion were subjected to secondary filtration and washing, and the washed first and second filter membranes were subjected to secondary density separation. After post-processing, microplastic extract was obtained.

2. The microplastic extraction method according to claim 1, characterized in that, The pretreatment includes drying the salt crust deposit at 50-60°C and then pulverizing it to obtain salt crust deposit powder with a particle size of <5 mm.

3. The microplastic extraction method according to claim 2, characterized in that, The first density separation specifically includes: mixing the salt crust sediment powder with the separating agent evenly, ultrasonically treating it, allowing it to stand, taking the supernatant, and repeating the process 3 to 4 times to obtain the supernatant.

4. The microplastic extraction method according to claim 3, characterized in that: The separating agent is a saturated salt solution, including a saturated NaBr solution; Preferably, the mass-to-volume ratio of the salt crust deposit powder to the saturated NaBr solution is 1 g : 10 mL to 1 g : 20 mL, and more preferably 1 g : 12 mL to 1 g : 18 mL; And / or, the ultrasonic treatment time is 5-10 min and the power is 15-20 W; And / or, the settling time is 24~48h.

5. The microplastic extraction method according to claim 1, characterized in that, The organic matter digestion specifically includes: using a digesting agent to digest the organic matter in the first and second filter membranes loaded with microplastics at 50-60°C for 24-48 hours; Preferably, the digestive agent comprises hydrogen peroxide, and the amount of the digestive agent is such that the organic matter is completely digested.

6. The microplastic extraction method according to claim 1, characterized in that, Specifically, it includes: The first and second filter membranes, after being digested by organic matter, are subjected to secondary filtration and then cleaned with a separating agent.

7. The microplastic extraction method according to claim 1, characterized in that, The secondary density separation specifically includes: mixing the washed first and second filter membranes with a separating agent, ultrasonically treating them, and allowing them to stand to obtain a supernatant. This process is repeated 3 to 4 times to complete the secondary density separation.

8. The microplastic extraction method according to claim 7, characterized in that: In the secondary density separation, each filter membrane is prepared with 100-200 mL of saturated NaBr solution; And / or, the ultrasonic treatment time is 5-10 min, and the power is 15-20W; And / or, the settling time is 24~48h.

9. The microplastic extraction method according to claim 1, characterized in that, The post-processing includes: filtering the supernatant obtained by secondary density separation, and then drying, ultrasonically treating and washing the first and second filter membranes carrying microplastics in sequence, and then concentrating the resulting washing solutions to obtain the microplastic extract.

10. The method for extracting microplastics according to any one of claims 1-9, characterized in that: Both the first and second filter membranes are stainless steel filter membranes with a pore size of 10 μm; And / or, the microplastic extraction method has a recovery rate of over 80% for microplastics with a particle size of less than 100 μm.

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