Application of celosia argentea combined with polyethylene microplastics in repairing tailings sandy soil

Abstract

The application relates to application of celosia argentea combined polyethylene microplastics in repairing tailing sandy soil and belongs to the technical field of biotechnology. By adding polyethylene microplastics in the soil and planting celosia argentea, the content of lead and cadmium in the soil can be effectively reduced, the physical and chemical properties of the soil can be improved, the soil fertility can be improved, the formation and stability of soil aggregates can be promoted, the anti-erosion capacity of the soil can be improved, the microbial diversity in the soil is not damaged, the purpose of repairing the tailing sandy soil is achieved. In addition, by adding the microplastics in the soil, the cumulative biomass of the celosia argentea can be increased, the growth of the celosia argentea is promoted, the repair efficiency of the celosia argentea on the tailing sandy soil is further improved, a synergistic repair effect is formed, and the ecological system can realize self-recovery and achieve benign circulation.

Description

Technical Field

[0001] This invention belongs to the field of biotechnology, and in particular relates to the application of Celosia argentea combined with polyethylene microplastics in the remediation of sandy soil in tailings. Background Technology

[0002] With the large-scale development of mineral resources, the amount of tailings sandy soil (tailings soil / tailings) produced is increasing year by year, resulting in a continuous rise in the number of tailings ponds. However, affected by factors such as structural instability of the pond body and aging of the anti-seepage system, tailings pond accidents such as dam failure and leakage occur frequently, causing serious problems of heavy metal diffusion and ecological degradation, becoming a focus of environmental governance. As typical mine waste sites, tailings ponds generally suffer from problems such as loose matrix structure, lack of organic matter, and enrichment of heavy metals; their surface soil development is hindered, the concentration of key nutrients such as nitrogen and phosphorus is less than 10% of that of natural soil, while the content of toxic elements such as cadmium and lead often exceeds the standard by dozens of times. Under the weathering and leaching of long-term stockpiled tailings, heavy metals are continuously released through surface runoff, dust migration, and other pathways, and the pollution range extends far beyond the stockpiling area itself, forming a large-scale "pollution diffusion circle". A single tailings pond can cause watershed-wide combined soil and water pollution. This pollution not only leads to the degradation of the surrounding soil-water system and a sharp decline in biodiversity, but also threatens residents' health through bioaccumulation in the food chain, inducing diseases such as cancer and nerve damage, and seriously restricting regional sustainable development. Against this backdrop, the development of tailings pond ecological restoration technologies has become a major challenge in the field of environmental science and engineering.

[0003] Traditional remediation technologies, such as topsoil replacement, chemical passivation, or single-plant remediation, have limitations such as high cost, significant risk of secondary pollution, or low efficiency. In recent years, phytoremediation technology has received considerable attention due to its eco-friendly nature; however, the biomass accumulation and tolerance of hyperaccumulating plants remain challenging due to extreme soil conditions in mining areas, such as infertility, acidification, and heavy metal toxicity. Meanwhile, microplastics, as an emerging global pollutant, are widely present in mining environments, primarily originating from wear and tear on mining equipment, aging of plastic geomembranes, and atmospheric deposition. Traditional views hold that microplastics exacerbate ecological risks and affect plant growth and development. Therefore, there are currently no reports on the combined use of microplastics and phytoremediation for tailings sandy soils. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide the application of Celosia argentea combined with polyethylene microplastics in the remediation of sandy tailings soil, which reduces the lead and cadmium content in the soil, improves soil fertility and erosion resistance, and promotes the growth of Celosia argentea without affecting the diversity of soil microorganisms.

[0005] This invention provides the application of celosia argentea combined with polyethylene microplastics in the remediation of sandy soil in tailings.

[0006] This invention provides the application of celosia argentea combined with polyethylene microplastics in reducing lead and / or cadmium pollution in tailings sandy soil.

[0007] This invention provides the application of Celosia argentea combined with polyethylene microplastics in improving the fertility of sandy soil in tailings.

[0008] This invention provides the application of celosia combined with polyethylene microplastics in improving the erosion resistance of tailings sandy soil.

[0009] The present invention also provides a method for remediating tailings sandy soil, the method comprising the following steps: mixing tailings sandy soil with polyethylene microplastics, and planting Celosia argentea in the soil containing polyethylene microplastics; wherein the mass ratio of the polyethylene microplastics to the tailings sandy soil is (1-10):100.

[0010] Preferably, the particle size of the polyethylene microplastics is 100-300 mesh.

[0011] Preferably, the Celosia argentea is a seedling that has been raised for 28 to 32 days; the ratio of Celosia argentea to soil containing polyethylene microplastics is 3 seedlings: (1.3 to 3) kg.

[0012] Preferably, after planting Celosia argentea, the soil containing polyethylene microplastics has a moisture content of 55% to 75%.

[0013] Preferably, the planting time is ≥100 days.

[0014] Preferably, the tailings sandy soil includes lead-zinc mine tailings soil.

[0015] The beneficial effects of this invention are:

[0016] This invention provides the application of *Celosia argentea* combined with polyethylene microplastics in the remediation of tailings sandy soil. By adding polyethylene microplastics to the soil and planting *Celosia argentea*, the content of lead and cadmium in the soil can be effectively reduced, the physical and chemical properties of the soil can be improved, and soil fertility can be enhanced without affecting soil microbial diversity. It can also promote the formation and stabilization of soil aggregates, improve the soil's resistance to erosion, and thus achieve the effect of remediating tailings sandy soil. Furthermore, the addition of polyethylene microplastics to the soil can further increase the cumulative biomass of *Celosia argentea*, especially the cumulative biomass of its aboveground parts. This indicates that the addition of polyethylene microplastics not only improves the tolerance of *Celosia argentea* to heavy metal pollution, but also promotes its growth, further improving the remediation efficiency of *Celosia argentea* in tailings sandy soil, achieving a synergistic remediation effect. This invention, using polyethylene microplastics and *Celosia argentea* in the joint remediation of tailings sandy soil, can not only remediate lead and cadmium contaminated soil and promote the evolution of the tailings sandy soil matrix, but also promote the growth of *Celosia argentea*, enabling the ecosystem to achieve self-recovery and a virtuous cycle.

[0017] This invention utilizes a combination of polyethylene microplastics and celosia to remediate sandy soil in tailings, enabling remediation to be completed in a relatively short time. It boasts advantages such as not damaging the site structure, simple operation, low investment, large-scale application, environmental friendliness, and safety, making it significant for the sustainable and efficient utilization of mining resources. Attached Figure Description

[0018] Figure 1 This is a characterization image of tailings sandy soil collected from a tailings pond of a lead-zinc mine in Guilin (Yangshuo Lead-Zinc Mine Tailings Pond) in Example 1. The upper left is a scanning electron microscope (SEM) image, the upper right is an EDS energy dispersive spectroscopy (EDS) image, and the lower left is an X-ray diffraction (XRD) image.

[0019] Figure 2 The graphs show the growth and cumulative biomass of Celosia argentea after 100 days of planting in each group. From left to right, the graphs show the root length measurement results, plant height measurement results, and biomass measurement results of different parts of Celosia argentea. In each bar chart, the presence of the same letter between different groups indicates no significant difference (P>0.05), while the absence of the same letter between different groups indicates a significant difference (P<0.05). The letters in the biomass measurement results of different parts of Celosia argentea indicate whether the difference in total biomass of the whole plant is significant.

[0020] Figure 3 This chart shows the lead and cadmium content in *Celosia argentea* and the soil, as well as the removal rates of lead and cadmium in the soil. The first row, from left to right, shows the lead and cadmium content in the aboveground and belowground parts of *Celosia argentea*. The second row, from left to right, shows the lead and cadmium residues in the soil. The third row, from left to right, shows the lead and cadmium removal rates in the soil. In each bar chart, the presence of the same letter between different groups indicates no significant difference (P > 0.05), while the absence of the same letter between different groups indicates a significant difference (P < 0.05). The letters in the first row indicate whether the differences in aboveground and belowground lead / cadmium content within the plant are significant between groups. The letters do not involve comparisons of aboveground and belowground lead / cadmium content within or between groups. Detailed Implementation

[0021] This invention provides the application of celosia argentea combined with polyethylene microplastics in the remediation of sandy soil in tailings.

[0022] This invention also provides the application of Celosia argentea combined with polyethylene microplastics in reducing lead and / or cadmium pollution in tailings sandy soil, improving the fertility of tailings sandy soil, and enhancing the erosion resistance of tailings sandy soil.

[0023] This invention involves adding polyethylene microplastics to tailings sandy soil, and then planting Celosia argentea in the soil containing polyethylene microplastics. The polyethylene microplastics influence the soil's pore structure and water retention capacity, reducing its permeability and promoting its growth. Simultaneously, they adsorb lead and cadmium. Through the combined effects of absorption by Celosia argentea during its growth, root exudates, and microbial degradation, the content of lead and cadmium in the soil is significantly reduced. This also improves the soil's physicochemical properties, promotes the formation and stability of soil aggregates, enhances soil fertility and erosion resistance, provides a favorable soil environment for Celosia argentea growth, increases its tolerance to heavy metals, promotes its growth, and further improves the remediation efficiency of tailings sandy soil by Celosia argentea, forming a synergistic remediation force, promoting the evolution of the tailings sandy soil matrix, and enabling the ecosystem to self-recover and achieve a virtuous cycle.

[0024] The present invention also provides a method for remediating tailings sandy soil, the method comprising the following steps: mixing tailings sandy soil with polyethylene microplastics, and planting Celosia argentea in the soil containing polyethylene microplastics.

[0025] In this invention, tailings sandy soil is mixed with polyethylene microplastics to obtain soil containing polyethylene microplastics. The particle size of the polyethylene microplastics is preferably 100-300 mesh, more preferably 100 mesh, 150 mesh, 200 mesh, or 300 mesh. The mass ratio of the polyethylene microplastics to the tailings sandy soil is (1-10):100, preferably 1:100, 3:100, 5:100, 8:100, or 10:100. The selection of the polyethylene microplastic particle size and its addition ratio in the tailings sandy soil allows the polyethylene microplastics to effectively remediate the tailings sandy soil without inhibiting the growth of *Celosia argentea*, and even promoting its growth. The polyethylene microplastics in this invention are preferably 100% polyethylene. This invention does not have a special limitation on the source of the polyethylene microplastics; conventional commercially available products in the art are acceptable.

[0026] In this invention, *Celosia argentea* is planted in the soil containing polyethylene microplastics obtained above. The *Celosia argentea* is preferably cultivated for 28-32 days, more preferably for 28, 29, 30, 31, or 32 days. The cultivation time is preferably calculated from the start of seed cultivation after seed soaking. This invention does not specifically limit the source of the *Celosia argentea*; commercially available products or self-cultivated varieties are acceptable. Self-cultivation is preferably achieved by soaking *Celosia argentea* seeds before seed cultivation. Soaking is preferably performed at 20℃-30℃ for 8-10 hours, more preferably at 20℃, 22℃, 25℃, 28℃, or 30℃ for 8 hours, 8.5 hours, 9 hours, 9.5 hours, or 10 hours. This invention does not specifically limit the source of the *Celosia argentea* seeds; conventional commercially available products are acceptable.

[0027] In this invention, when *Celosia argentea* seeds are soaked and then raised for 28-32 days before being planted in the aforementioned soil containing polyethylene microplastics, the preferred ratio of *Celosia argentea* to the soil containing polyethylene microplastics is 3 plants:(1.3-3) kg, more preferably 3 plants:1.3 kg, 3 plants:1.5 kg, 3 plants:2 kg, 3 plants:2.5 kg, or 3 plants:3 kg. This invention does not impose any special limitations on the planting steps; conventional planting steps in the art can be used. After planting *Celosia argentea*, it is preferable to maintain the soil moisture content containing polyethylene microplastics by controlling the irrigation frequency and amount. The preferred soil moisture content containing polyethylene microplastics is within the range of 55%-75% (55-75g of water per 100g of soil containing polyethylene microplastics), for example, 55%, 58%, 60%, 62%, 65%, 68%, 70%, or 75%. This invention relates to a method that improves the water retention capacity of tailings sandy soil by incorporating polyethylene microplastics, thereby promoting the synergistic remediation effect of Celosia argentea and polyethylene microplastics on tailings sandy soil. This invention does not impose special requirements on the post-planting growth environment of Celosia argentea, such as temperature and humidity; conventional conditions for Celosia argentea planting in this field can be followed.

[0028] In this invention, the first day is preferably taken as the day of planting Celosia argentea, and the planting time is ≥100 days. In one embodiment, 100 days, 105 days, 110 days, 115 days, 120 days or 150 days can be selected.

[0029] In this invention, the tailings sandy soil preferably includes lead-zinc mine tailings soil, and the tailings sandy soil is preferably sandy soil with excessive heavy metal pollution, low fertility and poor corrosion resistance. The preferred physicochemical properties of the tailings sandy soil are: pH 7.5–8.5, cation exchange capacity 7–8.2 cmol / kg, electrical conductivity 0.15–0.23 mS / cm, organic matter content 13–15 g / kg, available nitrogen content 85–89 mg / kg, available phosphorus content 3.4–3.8 mg / kg, cadmium 40–60 mg / kg, and lead 1250–1560 mg / kg; more preferably: pH 7.5, 7.6, 7.7, 7.89, 8.0, 8.2, 8.4, or 8.5, cation exchange capacity 7 cmol / kg, 7.2 cmol / kg, 7.5 cmol / kg, 7.73 cmol / kg, 8.0 cmol / kg, or 8.2 cmol / kg, electrical conductivity 0.15 mS / cm, 0.17 mS / cm, 0.19 mS / cm, or 0.23 mS / cm. 0.21mS / cm or 0.23mS / cm, organic matter content 13g / kg, 13.5g / kg, 13.96g / kg, 14.5g / kg or 15g / kg, alkaline nitrogen content 85mg / kg, 86mg / kg, 87mg / kg, 87.94mg / kg or 89mg / kg, available phosphorus content 3.4mg / kg, 3.5mg / kg, 3.62mg / kg, 3.7mg / kg or 3.8mg / kg, cadmium 40mg / kg, 42.85mg / kg, 45mg / kg, 50mg / kg, 55mg / kg or 60mg / kg, lead 1250mg / kg, 1300mg / kg, 1350mg / kg, 1400mg / kg, 1452mg / kg, 1500mg / kg or 1560mg / kg.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Unless otherwise specified, the following embodiments are all conventional methods.

[0032] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0033] The following examples, comparative examples, and test cases were conducted in the greenhouse of Guilin University of Technology.

[0034] Example 1

[0035] 1. The experiment used tailings sandy soil as potting soil. The tailings sandy soil was collected from a tailings pond of a lead-zinc mine in Guilin (Yangshuo lead-zinc mine tailings pond). Its basic physicochemical properties are as follows: pH value 7.89, cation exchange capacity 7.73 cmol / kg, electrical conductivity 0.19 mS / cm, organic matter content 13.96 g / kg, available nitrogen content 87.94 mg / kg, available phosphorus content 3.62 mg / kg. The background values ​​of heavy metals cadmium and lead in the tailings sandy soil are 42.85 mg / kg and 1452 mg / kg, respectively, which poses a significant ecological and health risk.

[0036] 2. After the potting soil from step 1 has dried, add 5% of 200-mesh polyethylene microplastics (5g of polyethylene microplastics per 100g of potting soil) and mix thoroughly to obtain soil containing polyethylene microplastics. Place the soil into round plastic pots with a diameter of 20cm and a height of 15cm, adding 1.5kg of the polyethylene microplastic-containing soil to each pot. Set up 5 pots in total for subsequent planting of Celosia argentea.

[0037] 3. Select plump, mature, and insect-free Celosia seeds and soak them in 25℃ water for 9 hours before raising seedlings. Then, after raising the seedlings for 30 days, plant them in soil containing polyethylene microplastics, with 3 seedlings per pot. During the growth period, irrigate with deionized water. Strictly control the irrigation frequency and amount during the experiment to maintain the water holding capacity of the potted soil within the range of 55%-75% (55-75g of water per 100g of soil containing polyethylene microplastics). The planting time is 100 days.

[0038] Example 2

[0039] The only difference from Example 1 is that 1% of 200-mesh polyethylene microplastics is added after the potting soil is air-dried in step 2; the rest is the same as in Example 1.

[0040] Example 3

[0041] The only difference from Example 1 is that in step 2, 10% of 200-mesh polyethylene microplastics are added after the potting soil has been air-dried; otherwise, the same as in Example 1.

[0042] Example 4

[0043] 1. The experiment used tailings sandy soil as potting soil, which was collected from a tailings pond of a lead-zinc mine in Guilin (Yangshuo lead-zinc mine tailings pond). The basic physicochemical properties of the tailings sandy soil were: pH 7.5, cation exchange capacity 7 cmol / kg, electrical conductivity 0.15 mS / cm, organic matter content 13 g / kg, available nitrogen content 85 mg / kg, and available phosphorus content 3.4 mg / kg. The background values ​​of heavy metals cadmium and lead in the tailings sandy soil were 40 mg / kg and 1250 mg / kg, respectively, posing significant ecological and health risks.

[0044] 2. After the potting soil from step 1 has dried, add 5% of 100-mesh polyethylene microplastics and mix thoroughly to obtain soil containing polyethylene microplastics. Place the soil into round plastic pots with a diameter of 18cm and a height of 12cm, adding 1.3kg of the polyethylene microplastic-containing soil to each pot. Set up 5 pots for subsequent planting of Celosia argentea.

[0045] 3. Select plump, mature, and insect-free Celosia seeds and soak them in 20℃ water for 10 hours before raising seedlings. Then, after raising the seedlings for 28 days, plant them in soil containing polyethylene microplastics, with 3 seedlings per pot. During the growth period, irrigate with deionized water. Strictly control the irrigation frequency and amount during the experiment to keep the water holding capacity of the potted soil within the range of 55%-75%. The planting time is 110 days.

[0046] Example 5

[0047] 1. The experiment used tailings sandy soil as potting soil, which was collected from a tailings pond of a lead-zinc mine in Guilin (Yangshuo Lead-Zinc Mine Tailings Pond). The basic physicochemical properties of the tailings sandy soil were: pH 8.5, cation exchange capacity 8.2 cmol / kg, electrical conductivity 0.23 mS / cm, organic matter content 15 g / kg, available nitrogen content 89 mg / kg, and available phosphorus content 3.8 mg / kg. The background values ​​of heavy metals cadmium and lead in the tailings sandy soil were 60 mg / kg and 1560 mg / kg, respectively, posing significant ecological and health risks.

[0048] 2. After the potting soil from step 1 has dried, add 5% of 300-mesh polyethylene microplastics and mix thoroughly to obtain soil containing polyethylene microplastics. Place the soil into round plastic pots with a diameter of 22cm and a height of 18cm, adding 3kg of the polyethylene microplastic-containing soil to each pot. Set up a total of 5 pots for subsequent planting of Celosia argentea.

[0049] 3. Select plump, mature, and insect-free Celosia seeds and soak them in 30℃ water for 8 hours before raising seedlings. Then, after raising the seedlings for 32 days, plant them in soil containing polyethylene microplastics, with 3 seedlings per pot. During the growth period, irrigate with deionized water. Strictly control the irrigation frequency and amount during the experiment to keep the water holding capacity of the potted soil within the range of 55%-75%. The planting time is 120 days.

[0050] Comparative Example 1

[0051] The only difference from Example 1 is that polyethylene microplastics are not added after the potting soil is air-dried in step 2; otherwise, they are the same as in Example 1.

[0052] Comparative Example 2

[0053] The only difference from Example 1 is that in step 2, "adding 5% of 200-mesh polyethylene microplastics after the potting soil has dried" is replaced with "adding 5% of 200-mesh polylactic acid microplastics after the potting soil has dried". All other steps are the same as in Example 1.

[0054] Comparative Example 3

[0055] The only difference from Example 1 is that in step 2, "adding 5% of 200-mesh polyethylene microplastics after the potting soil has dried" is replaced with "adding 1% of 200-mesh polylactic acid microplastics after the potting soil has dried". All other steps are the same as in Example 1.

[0056] Comparative Example 4

[0057] The only difference from Example 1 is that in step 2, "adding 5% of 200-mesh polyethylene microplastics after the potting soil has dried" is replaced with "adding 10% of 200-mesh polylactic acid microplastics after the potting soil has dried". All other steps are the same as in Example 1.

[0058] Experimental Example 1

[0059] Characterization of tailings sandy soil collected from the tailings pond of the Yangshuo lead-zinc mine in Example 1:

[0060] The characterization methods are as follows:

[0061] (1) Observation by scanning electron microscope

[0062] The morphological characteristics and elemental distribution of the tailings sandy soil were analyzed using a scanning electron microscope (SU-8010, Hitachi). The scanning electron microscope images are shown below. Figure 1 (Top left) As shown. The results show that the morphology of the tailings sandy soil conforms to that of sandy soil dominated by ore. The EDS spectrum of the elemental analysis results is shown below. Figure 1 As shown in the upper right, the results show that Pb, Zn, Cd and other metal elements are distributed in the tailings sandy soil, indicating that the tailings sandy soil is heavy metal contaminated soil.

[0063] (2) X-ray diffraction pattern (XRD)

[0064] The crystal structure of tailings sandy soil was analyzed using an X-ray diffractometer (SmartLab Rigaku) ​​with Cu-kα, 2θ ranging from 5° to 90°. The results are as follows: Figure 1 (Lower left) The results show that the characteristic diffraction peaks of this tailings sandy soil are the same as and overlap with those of quartz (pdfno. 46-1045) and albite (pdfno. 41-1480), which is consistent with the characteristics of tailings sandy soil.

[0065] Experimental Example 2

[0066] 1. Grouping

[0067] After 100 days of planting, the plants from Examples 1-3 and Comparative Example 1 were divided into groups: Example 1 (PE2), Example 2 (PE1), Example 3 (PE3), and Comparative Example 1 (CK). Soil samples were collected from each group 100 days after planting, and soil physicochemical indicators, aggregate-related indicators, and microbiological-related indicators were measured.

[0068] 2. Measurement methods and results

[0069] 2.1 Soil physicochemical properties:

[0070] pH: Soil pH was measured using an electrode; Electrical conductivity (EC): Measured using an EC electrode; Cation exchange capacity (CEC): Measured using the hexahydrate and cobalt chloride exchange method; Organic matter: Measured using the potassium dichromate capacity method with external heating; Alkaline nitrogen: Measured using the alkaline diffusion method. The results are shown in Table 1.

[0071] Table 1 Soil Physicochemical Indicators

[0072]

[0073] Note: For the same indicator, the presence of the same letter in different groups indicates no significant difference (P>0.05), while the absence of the same letter indicates a significant difference (P<0.05).

[0074] Table 1 shows that the tailings without added polyethylene microplastics (CK group) had the lowest organic matter content (14.23 g / kg), a neutral pH of 7.25, and an available nitrogen content of 98.16 mg / kg, indicating low soil fertility. After adding polyethylene microplastics, the soil's physical and chemical properties significantly improved. Among them, the PE2 group, with 5% polyethylene microplastics and planted with Celosia argentea, showed the best performance, with organic matter content increasing to 23.29 g / kg, pH moderately rising to 7.74, and available nitrogen content increasing to 102.16 mg / kg. These changes indicate that the synergistic effect of organic matter and the moderately increased pH promoted the improvement of soil fertility.

[0075] 2.2 Aggregate-related indicators

[0076] (1) Dry sieving method

[0077] Aggregates were separated using a dry sieving method. The dry sieving system was set to separate aggregates into five sizes: >5mm, 2–5mm, 1–2mm, 0.25–1mm, and <0.25mm. A 500g soil sample was placed in a soil sieve with mesh diameters of 5mm, 2mm (10 mesh), 1mm (18 mesh), and 0.25mm (65 mesh). The sample was shaken for approximately 15 minutes to separate the aggregates into the five sizes: >5mm, 2–5mm, 1–2mm, 0.25–1mm, and <0.25mm. The aggregates of each size were then weighed.

[0078] (2) Wet sieving method

[0079] Soil samples of aggregates at each level obtained by the dry sieving method were soaked in deionized water for 5 minutes. Then, the sieve immersed in water was carefully moved up and down with a movement range of 3 cm and a movement speed of about 25 times / min for 2 minutes. The water-soil mixture that passed through a 1.0 mm (pore size) sieve was then passed through 0.5 mm, 0.25 mm, 0.053 mm, and 0.02 mm sieves in the same manner. The soil retained in each sieve was collected, which is the weight of each level of water-stable aggregates.

[0080] (3) Stability index calculation

[0081] The stability of soil aggregates was evaluated using commonly used indices such as mean weight diameter (MWD), normalized mean weight diameter (NMWD), proportion of aggregates >5 mm (R2.5), structural stability index (SSI), and fractal dimension (D). The results of each index were calculated from dry and wet sieving results, as follows. The effects of polyethylene microplastic addition and Celosia argentea planting on soil aggregate stability were determined based on the differences in these indices.

[0082] a. Mean Weight Diameter (MWD)

[0083] The mean mass diameter (MWD) of soil aggregates reflects their average size and is an important indicator of soil aggregate stability. MWD is calculated by weighted summation, multiplying the mean diameter of each particle size group by its mass percentage and then summing the results. The formula is as follows:

[0084]

[0085] Where, x i Wi is the average diameter (mm) of the soil aggregates in the i-th particle size class after dry sieving, Wi is the percentage of the mass of the soil aggregates in this particle size class to the dry mass of the soil sample (%), and n represents the number of particle sizes.

[0086] b. Normalized Mean Weight Diameter (NMWD)

[0087] Standardized mean weight diameter (NMWD) is an important indicator for measuring the stability of soil aggregates. Its calculation formula is as follows:

[0088]

[0089] Where: MWD is the average weight diameter, rmax is the maximum aperture of the dry sieve, and rmin is the minimum aperture of the dry sieve. Using this formula, NMWD can standardize the stability of aggregates of different particle sizes, facilitating comparisons of aggregate stability in different soil samples.

[0090] c. Proportion of aggregates with a particle size >5mm (R2.5)

[0091] R2.5 represents the proportion of aggregates larger than 5 mm in soil aggregates, reflecting the content of large aggregates in the soil. This index is calculated directly by determining the mass of aggregates of each particle size using a dry sieving method. The formula for calculating R2.5 is:

[0092] R2.5 = (Total mass of aggregates larger than 5 mm / Total mass of soil sample) × 100%

[0093] d. Aggregate structural stability index (SSI)

[0094] SSI (Soil Aggregate Stability Index) is used to evaluate the stability of soil aggregates during wet sieving. This index is calculated by comparing the mass of aggregates >0.25 mm after dry and wet sieving. The formula for calculating SSI is:

[0095] SSI = (Mass of agglomerates >0.25mm after dry sieving / Mass of agglomerates >0.25mm after wet sieving) × 100%

[0096] e. Fractal dimension (D)

[0097] Fractal dimension is used to describe the distribution of soil aggregates. The formula for calculating fractal dimension is:

[0098]

[0099] in, Let be the average diameter of the i-th order aggregate, in mm; For diameter less than The mass of the aggregate, in g; W represents the maximum average diameter of the aggregates, in mm. T The total mass of the aggregate is expressed in grams. (The remaining text appears to be incomplete and requires further context.) and By fitting the x and y axes, the slope of the fitted curve is obtained, and thus the D value is obtained.

[0100] The calculation results for each indicator are shown in Table 2.

[0101] Table 2. Aggregate-related indicators

[0102] CK 70.66±5.2b 14.82±1.3b 0.67±0.03a 1.54±0.12b 2.29±0.02b PE1 120.15±8.7a 25.24±2.1a 0.67±0.02a 1.49±0.15b 2.38±0.03a PE2 128.44±9.1a 26.99±2.4a 0.68±0.04a 1.80±0.18a 2.31±0.04ab PE3 134.64±6.8b 28.29±1.8b 0.71±0.05a 1.54±0.13a 2.27±0.02b

[0103] Note: For the same indicator, the presence of the same letter in different groups indicates no significant difference (P>0.05), while the absence of the same letter indicates a significant difference (P<0.05).

[0104] Table 2 shows that the tailings aggregates without added polyethylene microplastics (CK group) exhibited poor aggregate stability, with a MWD of 70.66, NMWD of 14.82, R2.5 of 0.67, SSI of 1.54, and D of 2.29. This indicates that the soil aggregates had a loose structure and weak erosion resistance. The addition of polyethylene microplastics significantly improved the stability of the soil aggregates. When the addition amount of polyethylene microplastics was 5%, the MWD and NMWD increased to 128.44 and 26.99, respectively, and the SSI increased to 1.80. This indicates that the increase in organic matter and the moderately elevated pH synergistically promoted the formation of large aggregates, enhancing the soil's erosion resistance.

[0105] 2.3 Microorganisms: Soil microbial indicators: bacterial ace, bacterial shannon, fungal ace, and fungal shannon were obtained by Shanghai Meiji Biomedical Technology Co., Ltd. through DNA extraction, PCR amplification, and sequencing using the MiSeq platform.

[0106] Table 3 Microbial species-level index

[0107] CK 30086±359a 7.18±0.19a 1473±139ab 0.78±0.01a PE1 30084±63a 7.38±0.01a 1507±46a 0.77±0.01a PE2 29930±767a 7.22±0.08a 1507±73a 0.79±0.01a PE3 30438±420a 7.36±0.01a 1294±96c 0.79±0.02a

[0108] Note: For the same indicator, the presence of the same letter in different groups indicates no significant difference (P>0.05), while the absence of the same letter indicates a significant difference (P<0.05).

[0109] The results of the microbial level indices are shown in Table 3. In the tailings (CK group) without added polyethylene microplastics, the ACE index of the bacterial community was 30086 and the Shannon index was 7.18, while the ACE index of the fungal community was 1473 and the Shannon index was 0.78, indicating high soil microbial diversity but low fungal richness. After adding polyethylene microplastics, the ACE and Shannon indices of the bacterial community did not change significantly. When the polyethylene microplastic addition was 10%, the fungal ACE index decreased significantly to 1294, indicating that high concentrations of polyethylene microplastics may have inhibited fungal community richness. Overall, the PE treatment had a relatively small impact on the bacterial community, while high concentrations of PE had a certain inhibitory effect on fungal community richness.

[0110] Experimental Example 3

[0111] After 100 days of cultivation, the plants from Examples 1-3 and Comparative Examples 1-4 were grouped as follows: Example 1 (PE2), Example 2 (PE1), Example 3 (PE3), Comparative Example 1 (CK), Comparative Example 2 (PLA2), Comparative Example 3 (PLA1), and Comparative Example 4 (PLA3). After 100 days of cultivation, the aboveground stems, leaves, flowers, and underground roots of the plants were harvested, and soil samples were collected. Root length and plant height were measured, as well as the biomass of the plants and the content of heavy metals cadmium and lead in the plants and soil. The lead and cadmium removal rates in the soil were calculated.

[0112] Lead and cadmium content: detected using inductively coupled plasma mass spectrometry.

[0113] Determination of plant biomass: The flowers, stems, leaves and roots of a plant are dried to constant weight and then weighed to obtain the biomass of the corresponding parts.

[0114] The plant growth of each group after 100 days is as follows: Figure 2 As shown in the figure, the root length of *Celosia argentea* without added polyethylene microplastics was 9.8 cm, the plant height was 53.4 cm, and the total biomass was 12.26 g / plant. Adding polyethylene microplastics had no significant effect on root length, but significantly increased plant height and biomass. When the polyethylene microplastic addition was 5%, the biomass was 17.37 g / plant, an increase of 41.7%, and the plant height was 64.3 cm, an increase of 20.4%. When the polyethylene microplastic addition was 10%, the biomass was 16.64 g / plant, an increase of 35.7%, and the plant height was 68.5 cm, an increase of 28.3%. While adding polylactic acid (PLA) microplastics, although low amounts could increase plant height, it reduced root length, and the biomass of *Celosia argentea* in all addition groups was significantly reduced. Biomass levels represent plant growth and development and tolerance to pollutants. The addition of polyethylene microplastics increased plant biomass, indicating that the addition of polyethylene microplastics can promote the growth of Celosia argentea, while polylactic acid microplastics inhibit the growth of Celosia argentea.

[0115] The content of cadmium and lead in the aboveground and underground parts of Celosia argentea after 100 days in different treatment groups, as well as the residual amount and removal rate of cadmium and lead in the soil, are shown in the figure. Figure 3 .Depend on Figure 3 It can be seen that, except for groups CK, PE1, and PLA1, the cadmium and lead content in the roots of all other groups of *Celosia argentea* was no lower than that in the aboveground stems and leaves. This indicates that cadmium and lead mainly accumulate in the roots of *Celosia argentea*, thereby reducing the toxic effects on the aboveground organs. It also avoids the entry of soil pollutants into the food chain during phytoremediation, making it suitable for the remediation of mine-contaminated soil. However, the cadmium content in the aboveground parts of the group with 1% polylactic acid microplastics was approximately three times that in the underground parts, indicating that the addition of 1% polylactic acid microplastics easily caused toxic effects on the aboveground tissues and organs of *Celosia argentea*.

[0116] CK was the treatment with only *Celosia argentea* planted, and the removal rates of lead and cadmium in the soil after planting were 25.99% and 16.61%, respectively. Adding polyethylene microplastics to the soil after planting *Celosia argentea* reduced the residual levels of cadmium and lead. Specifically, the PE2 treatment (5% polyethylene microplastics + *Celosia argentea*) showed a cadmium removal rate of 33.62% and a lead removal rate of 32.11%; the PE3 treatment (10% polyethylene microplastics + *Celosia argentea*) showed a lead removal rate of 36.08% and a cadmium removal rate of 20.44%. The removal rates of lead and cadmium in the three treatment groups (PE1, PE2, and PE3) with polyethylene microplastics and *Celosia argentea* were significantly higher than those in the CK group (P < 0.05). Furthermore, the lead removal rate after polyethylene microplastic treatment was significantly higher than that after polylactic acid treatment (PLA1, PLA2, and PLA3) (P < 0.05). While polylactic acid microplastics also showed good cadmium removal performance, their effect on lead removal was poor. Compared with the control group (CK) without microplastics, the lead removal rates of the three treatment groups (PLA1, PLA2, and PLA3) with added polylactic acid were significantly lower (P < 0.05).

[0117] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. Application of Celosia argentea combined with polyethylene microplastics in the remediation of tailings sandy soil; the mass ratio of the polyethylene microplastics to the tailings sandy soil is 5:100; the tailings sandy soil is lead and cadmium contaminated soil; Celosia argentea combined with polyethylene microplastics can reduce the content of lead and cadmium in the soil, improve the soil fertility and erosion resistance, and promote the growth of Celosia argentea.

2. A method for remediating sandy soil from tailings, characterized in that, The method includes the following steps: mixing tailings sandy soil with polyethylene microplastics, and planting Celosia argentea in the soil containing polyethylene microplastics; the mass ratio of polyethylene microplastics to tailings sandy soil is 5:100; the combination of Celosia argentea and polyethylene microplastics can reduce the content of lead and cadmium in the soil, improve the soil fertility and erosion resistance, and promote the growth of Celosia argentea.

3. The method according to claim 2, characterized in that, The polyethylene microplastics have a particle size of 100–300 mesh.

4. The method according to claim 2, characterized in that, The *Celosia argentea* seedlings were cultivated for 28–32 days; the ratio of *Celosia argentea* to soil containing polyethylene microplastics was 3 seedlings: (1.3–3) kg.

5. The method according to claim 2, characterized in that, After planting Celosia, the soil containing polyethylene microplastics has a moisture content of 55% to 75%.

6. The method according to claim 2, characterized in that, The planting time is ≥100 days.

7. The application according to claim 1 or the method according to any one of claims 2 to 6, characterized in that, The tailings sandy soil includes lead-zinc mine tailings soil.

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