Method for repairing light rare earth and heavy metal composite contaminated soil

Abstract

The application discloses a method for repairing light rare earth and heavy metal composite contaminated soil, and adopts bacillus megaterium (Bacillus megaterium) to repair the composite contaminated soil. Oceanobacillus sp. The bacillus megaterium is preserved in the China General Microbiological Culture Collection Center, has a preservation number of CGMCC No.22085, and is preserved on March 29, 2021. The repairing process is as follows: mixing bacillus megaterium liquid and cementing liquid to obtain a mixed liquid; mixing the air-dried contaminated soil and the mixed liquid, and then loading the mixed liquid into a mold for reaction; connecting a grouting pipe to the mold to inject the mixed liquid, and performing multiple rounds of pumping; after the pumping is completed, the contaminated soil is maintained and air-dried naturally. The application adopts the advantage strain, combines biological adsorption and biological mineralization, and realizes the effective control of the light rare earth and heavy metal composite contaminated soil under the action of double biological repair.

Description

Technical Field

[0001] This invention relates to the field of contaminated soil remediation technology, specifically a method for remediating soil contaminated with a mixture of light rare earth elements and heavy metals. Background Technology

[0002] In mineral deposits containing rare earth elements (REEs), heavy metals are often associated with them. Microbial-induced carbonate precipitation (MICP) is a widely used immobilization and stabilization technology. This technology not only has advantages such as simple reaction process control, fast reaction rate, and high chemical conversion efficiency, but also saves energy and protects the ecological environment. Currently, this technology has been widely studied and applied to the treatment of heavy metal pollution such as strontium, cadmium, zinc, lead, copper, nickel, iron, and arsenic. Although numerous studies have shown that MICP is effective in treating heavy metals, in addition to heavy metal pollution, light rare earth element pollution also exists in the soils surrounding rare earth mining areas. Research on the control of light rare earth pollution is relatively limited. The application of MICP to soils with mixed light rare earth element pollution is still immature. However, how to effectively control the pollution from tailings dams containing rare earth elements from entering groundwater and surrounding waters has become a critical issue that urgently needs to be addressed. Summary of the Invention

[0003] The purpose of this invention is to provide a method for remediating soil contaminated with a mixture of light rare earth elements and heavy metals in the middle section from the tailings dam to the surrounding waters. This method utilizes dominant bacterial strains to combine biosorption and biomineralization, exploring the effective control of this dual bioremediation approach on soil contaminated with light rare earth elements and heavy metals. The light rare earth elements include: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu).

[0004] The objective of this invention is achieved through the following technical solution: A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals: using Bacillus subtilis (B. oryzae) Oceanobacillus sp. The method of remediation of soil contaminated with light rare earth and heavy metals based on MICP combined with biosorption was used. The Bacillus aquaticus was deposited in the China General Microbiological Culture Collection Center, with accession number CGMCC No. 22085 and deposit date of March 29, 2021.

[0005] Furthermore, the following steps are included: (1) Cultivate Bacillus aquaticus and prepare bacterial suspension, wherein the OD of the bacterial suspension is... 600The value is 1; Preparation of cementing solution: The cementing solution uses water as solvent, and the solutes are CaCl2 and urea, the concentrations of CaCl2 and urea are both 1 mol / L; The cementing solution is mixed with the bacterial solution to obtain a mixed solution; (2) Air dry the collected soil contaminated with light rare earth and heavy metals; (3) After the air-dried contaminated soil is mixed with the mixture, it is placed into a mold and reacted for 24 hours; (4) Connect the upper and lower ends of the mold to the grouting pipes, and inject the mixture into the grouting pipe at one end for multiple pumping cycles; (5) After pumping is completed, the contaminated soil is cured and air-dried.

[0006] As an optimization scheme, in step (1): the culture medium used to cultivate Bacillus aquaticus contains: 20 g / L yeast extract powder, 10 g / L ammonium sulfate, and 15.748 g / L trihydroxymethylaminotoluene (Tris).

[0007] Further optimization involves air-drying and sieving the contaminated soil in step (2). Sieving involves passing the contaminated soil through a sieve with a pore size of 2 mm, retaining contaminated particles smaller than 2 mm.

[0008] Furthermore, the mold described in step (3) is a cylindrical mold, with the upper and lower planes of the cylinder connected to grouting pipes. The formulas for the amounts of contaminated soil and mixed liquid used in the mold in step (3) are as follows: In the formula: m 混合液表示 The quality of the mixture; m 干土 This indicates the quality of air-dried contaminated soil, with a moisture content of less than 5%. ω L This indicates the liquid limit value of the soil.

[0009] Furthermore, in step (4), the amount of liquid pumped each time is based on the standard of saturating the contaminated soil inside the mold without any excess liquid flowing out; pumping is carried out at a rate of 1013 μl / min, and 7 rounds of pumping are carried out, with an interval of 24 hours between each round.

[0010] Furthermore, in step (5), after 7 days of curing, the product is naturally air-dried for 14 days; the curing temperature is 8-12℃ and the relative humidity is 19-21% during curing.

[0011] The beneficial effects of this invention are: This invention utilizes superior bacterial strains to combine biosorption and biomineralization, achieving effective control of soils contaminated with light rare earth elements and heavy metals through dual bioremediation.

[0012] In this invention, the average reduction rates of the exchangeable states of the four elements after adsorption, mineralization, and adsorption-mineralization treatments were 19.79%, 40.62%, and 52.02%, respectively. Compared with using biomineralization or bioadsorption alone to treat light rare earth composite contaminated soil, adsorption-mineralization is more effective. This invention combines multifunctional bacterial strains with long-term beneficial microbial mineralization technology, significantly reducing the exchangeable states of rare earth elements and their mixed pollutants in contaminated soil, thus significantly decreasing the bioavailability of pollutants. This provides a new method for the environmental protection of waters surrounding tailings dams.

[0013] Applying the remediation method of this invention to the composite contaminated soil of rare earth tailings dams can achieve the effect of solidification / stabilization, reduce the leaching concentration of rare earth and its mixed pollutants in the soil in exchangeable form, and enable the contaminated site to be redeveloped and utilized.

[0014] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0015] Figure 1 The results of screening orthogonal experimental conditions in the experimental examples; The numbers on the horizontal axis represent the group numbers of the evidence test.

[0016] Figure 2 This is the test sample of Comparative Example 1 in this invention; Figure 3 This is the test sample of Comparative Example 2 in this invention; Figure 4 This is the test sample from Example 1 of the present invention; Figure 5 The results of phase analysis of the soil samples retrieved in this invention are shown; where KT1, KT2, KT3, KT4-1, KT4-2, KT4-3, and KT5 are the sampling point numbers; the same applies below. Figure 6 This describes the changes in the exchangeable states of Zn, Pb, La, and Ce under the conditions of Comparative Example 1 (JD), Comparative Example 2 (BG), and Example 1 (DY) in this invention. Figure 7 This describes the changes in the carbonate binding states of Zn, Pb, La, and Ce under the conditions of Comparative Example 2 (BG) and Example 1 (DY) in this invention. Figure 8 This describes the changes in the exchangeable states of Nd, Pr, Sm, and Eu under the conditions of Comparative Example 1 (JD), Comparative Example 2 (BG), and Example 1 (DY) in this invention. Figure 9This diagram illustrates the changes in the carbonate binding states of Nd, Pr, Sm, and Eu under the conditions of Comparative Example 1 (JD), Comparative Example 2 (BG), and Example 1 (DY) in this invention. Detailed Implementation

[0017] Experimental example: The purpose of this experiment is to screen suitable conditions for the mineralization and adsorption of light rare earth elements and heavy metals by Bacillus aquatilis.

[0018] The Bacillus oryzae used ( Oceanobacillus sp. The accession number is CGMCC No. 22085, and the accession date is March 29, 2021.

[0019] First, lead, zinc, lanthanum, and cerium were added to distilled water at concentrations of 691.9 ng / ml, 1154 ng / ml, 4535 ng / ml, and 12050 ng / ml, respectively, as grouped into Pb, Zn; La, Ce and Pb, Zn, La, Ce groups. The prepared background solutions were then aliquoted into 50 ml centrifuge tubes for later use. Relevant influencing factors were established. Distilled water was used throughout the experiment. Centrifuge tubes were inverted every two days to ensure sufficient reaction. After 14 days, the exchangeable states of elements in the solution were measured using ICP-MS. The decrease rate of exchangeable states obtained by treating the background solutions was compared to determine the optimal technical solution.

[0020] The adsorption mineralization method involves sequentially adding a cementing solution composed of a calcium source and urea in a 1:1 ratio, along with 10 ml of *Bacillus cereus* bacterial solution, to the background solution for a biomineralization reaction. The experimental parameters for the adsorption mineralization method are detailed in Table 1. The calcium source concentration was divided into two groups: Group A (single calcium source to the left of the slash) and Group B (composite calcium source to the right of the slash). Sixteen orthogonal experiments were conducted on both Groups A and B, and the orthogonal design is shown in Table 2. During the orthogonal experimental design, the relationship between heavy metal elements and OD... 600 The item adopts the pseudo-level method, that is, under the factor of heavy metal elements, the blanks are filled in according to Pb, Zn, La, Ce; in OD 600 Under this factor, the blank level was filled according to 2.1, and the results were compared according to different background solutions. Among them, the calcium-magnesium ratio of the calcium source was designed as 2:1 when dolomite is in its most stable state. Since Bacillus aquaticus is a salt-tolerant species, the pH of the bacterial solution was not included in the settings of influencing factors for the adsorption mineralization method.

[0021] Table 1. Test parameters of adsorption mineralization method Table 2 Orthogonal experimental design table for adsorption mineralization method The procedure for the ICP-MS test solution is as follows: When testing, pipette 5 ml into a volumetric flask, add 3 ml (1:1) HNO3, distilled water to a final volume of 50 ml, shake well and wait for testing.

[0022] like Figure 1 The figure shows the changes in the contents of Pb, Zn, La, and Ce in wastewater before and after treatment with Bacillus aquatilis using an adsorption mineralization method, as well as the rate of decrease of each element. It can be seen that the experimental group was the adsorption mineralization method-A6 group (1 mol / L CaCl₂). 2， OD 600 The average decrease rate of elements was highest at a value of 1.4, at 94.27%. Example 1 A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals includes the following steps: (1) Cultivate Bacillus aquaticus and prepare bacterial suspension, wherein the OD of the bacterial suspension is... 600 The value is 1.4; a cementing solution is prepared, wherein the cementing solution contains 1 mol / L CaCl2 and urea; the cementing solution is mixed with the bacterial solution to obtain a mixture. The *Bacillus aquaticus* is classified and named as: *Bacillus aquaticus* (…). Oceanobacillus sp. It is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 22085 and deposit date of March 29, 2021.

[0023] The *Bacillus aquatilis* strain described is a non-pathogenic, aerobic, Gram-positive bacterium. This strain is a native, self-extracted bacterium from the Hetao Irrigation District of China. After isolation and purification, this strain possesses microbial mineralization capabilities (microbially induced carbonate precipitation, i.e., MICP ability) and the ability to produce extracellular polysaccharides (capable of biosorbing heavy metals and rare earth elements). Optimization using yeast extract and ammonium sulfate as the optimal nitrogen source further enhances both of these capabilities. It exhibits strong environmental adaptability, rapid growth and reproduction, and good tolerance.

[0024] The culture medium used to cultivate *Bacillus aquaponica* consisted of 20 g / L yeast extract, 10 g / L ammonium sulfate, and 15.748 g / L tris(hydroxymethyl)aminotoluene (Tris). The pH of the medium was adjusted to 6, and the medium was sterilized at 120°C for 20 minutes. A 2% bacterial culture was inoculated into the medium, and then cultured with shaking at 30°C and 200 rpm for 48 hours. The cultured bacterial culture was then inoculated into the medium at a 5% inoculation ratio, and the culture was expanded to a larger scale and incubated at a constant temperature for 12 hours to maintain optimal optical density (OD). 600 =1.

[0025] (2) The collected soil contaminated with light rare earth and heavy metals was air-dried and then sieved. The contaminated soil samples (soil to be remediated) were collected from near a tailings dam in Inner Mongolia. Taking the tailings dam as the starting point, seven typical sampling areas were selected along the shortest straight-line distance from the tailings dam to the water area to its southwest for soil sampling. Among them, there were five horizontal topsoil sampling areas (0-15 cm). At the random sampling point of the fourth horizontal sampling area, two vertical sampling areas (20-35 cm; 40-55 cm) were randomly sampled.

[0026] The collected soil samples were air-dried naturally, and after removing large stones, grass roots, and branches, they were thoroughly mixed. The contaminated soil was then sieved through a 2mm sieve, retaining particles smaller than 2mm for later use.

[0027] (3) The sieved contaminated soil is mixed with the mixture and then placed into a cylindrical mold. The mold has an inner diameter of 6.18 cm and a height of 2 cm. Three parallel samples are prepared for each specimen. The amounts of contaminated soil sample and mixture are shown in the formula: In the formula: m 混合液表示 The quality of the mixture; m 干土 This indicates the quality of air-dried contaminated soil, with a moisture content of less than 5%. ω L This indicates the liquid limit value of the soil.

[0028] (4) After 24 hours of reaction, connect the grouting pipes to the upper and lower ends of the mold, and inject the mixture into the grouting pipe at one end. Pump the mixture at a rate of 1013 μl / min for 7 rounds, with each round spaced 24 hours apart. The amount of liquid pumped each time is determined by thoroughly soaking the contaminated soil specimen in the mold without any excess liquid flowing out. The pumping is one method of injecting liquid in MICP: the pumping method. A multi-channel peristaltic pump BT100-1L from Baoding Lange Constant Flow Pump Co., Ltd. was used.

[0029] (5) After pumping, the product is cured for 7 days and then air-dried for 14 days. The curing temperature is 8-12℃ and the relative humidity is 19-21%. Concentration leaching test is then performed.

[0030] The leaching test used a five-step extraction method to determine the exchangeable state. The leaching test determined the concentration of leached metals in the leachate. The reference for the determination method is: Tessier A, Campbell PGC, Bisson M. "Sequential chemical extraction procedure for the speciation of particulate trace metals". Anal Chem, 1979, 51(7):844-850. Exchangeable state: Weigh (1.0000+0.0003)g of soil sample into a 50 mL plastic centrifuge tube, add 8 mL of 1 mol / L MgCl2 solution, and continuously shake at room temperature for 1 h (200 r / min). Centrifuge for 10 min (4000 r / min), remove the supernatant, filter, and dilute to volume with a 50 mL volumetric flask. Carbonate-bound state: Add 8 mL of 1 mol / L NaAc solution (pH=5.0) to the residue from the previous step, keep at room temperature and shake continuously for 5 h (200 r / min), centrifuge for 10 min, remove the supernatant and filter, and dilute to volume with a 50 mL volumetric flask; Iron and manganese oxidation state: Add 20 mL of 25% HAc solution (pH=2.0) of 0.04 mol / L NH2OH·HCl to the residue from the previous step, incubate in a water bath at 96±3 ℃ for 6 h with intermittent stirring; after standing and clarifying, separate the supernatant solution; Organically bound state: Add 3 mL of 0.02 mol / L HNO3 solution and 5 mL of 30% H2O2 solution (pH=2.0) to the residue from the previous step. Incubate in a water bath at 85±2℃ for 2 hours with intermittent stirring. Add another 3 mL of 30% H2O2 solution (pH=2.0) and incubate in a water bath at 85±2℃ for 3 hours with intermittent stirring. Add 5 mL of 20% HNO3 containing 3.2 mol / L NH Ac. Dilute the solution to 20 mL and incubate at 22±5℃ with constant temperature shaking for 30 minutes (200 r / min). After standing and clarifying, separate the supernatant solution. Residual state: The residue after the previous treatment was analyzed by digestion using the nitric acid-hydrofluoric acid-perchloric acid digestion method.

[0031] Example 2 A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals. The difference between this embodiment and Embodiment 1 is that: In step (3), the inner diameter of the mold is 13 cm and the height is 4 cm.

[0032] Step (4) Pumping is performed at a rate of 1650 μl / min for 14 rounds, with an interval of 24 hours between each round.

[0033] Example 3 A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals. The difference between this embodiment and Embodiment 1 is that: In step (3), the inner diameter of the mold is 25cm and the height is 8cm.

[0034] Step (4) Pumping is performed at a rate of 2500 μl / min for 28 rounds, with an interval of 12 hours between each round.

[0035] Comparative Example 1 A method for remediating soil contaminated with light rare earth elements and heavy metals is presented in this comparative example. The method involves directly adding Bacillus megaterium solution to the contaminated soil using the principle of biosorption. The experimental conditions used are the optimal experimental conditions for treating soil contaminated with light rare earth elements and heavy metals by this strain after preliminary screening.

[0036] The difference between this comparative example and Example 1 is as follows: The bacteria used were *Bacillus megaterium*, strain number BNCC336464, a non-pathogenic aerobic Gram-positive bacterium that can adsorb rare earth elements and heavy metals through the functional groups on its cell surface, thereby reducing their bioavailability. It was commercially available and purchased from Beina Chuanglian Biotechnology Co., Ltd. The optical density of the bacterial suspension was measured using a spectrophotometer (UV-1700 UV-Vis spectrophotometer), representing the absorbance at a wavelength of 600 nm, expressed as OD. 600 express.

[0037] Step (1) Prepare the bacterial culture medium, which is formulated with 10 g / L peptone, 3 g / L beef extract, and 5 g / L sodium chloride. After complete dissolution, adjust the pH of the culture medium to 7.3 ± 0.1, and sterilize the culture medium in a high-temperature autoclave at 120°C for 20 min. Inoculate 2% bacterial solution into the culture medium, and then incubate with shaking in a constant temperature incubator at 30°C and 200 rpm for 24 h. Then, inoculate the cultured bacterial solution into the culture medium at a 5% inoculation ratio. For scale-up culture, incubate at a constant temperature for 12 h to maintain the optimal optical density, i.e., OD. 600 =2.1. No bonding solution needs to be prepared.

[0038] In step (2), the sieved contaminated soil is mixed with the bacterial solution and then placed into a mold. The bacterial solution is used instead of the mixed solution.

[0039] Comparative Example 2 A method for remediating soil contaminated with light rare earth elements and heavy metals is proposed, using experimental conditions that are the optimal experimental conditions for treating soil contaminated with light rare earth elements and heavy metals after preliminary screening.

[0040] The difference between this comparative example and Comparative Example 1 is that: The *Pasteurella multocida* strain used, strain number ATCC 11859, is a non-pathogenic aerobic Gram-positive bacterium capable of hydrolyzing urea. It was commercially available from Beina Chuanglian Biotechnology Co., Ltd. This bacterium has advantages such as low cost and high urease production, making it a commonly used strain in microbial mineralization processes and exhibiting good immobilization properties for heavy metals.

[0041] Step (1) Adjust the pH of the culture medium to 6, and sterilize the culture medium in a high-temperature autoclave at 120℃ for 20 min. Inoculate 2% bacterial suspension into the culture medium, and then incubate with shaking in a constant temperature incubator at 30℃ and 200 rpm for 48 h. Then, inoculate the cultured bacterial suspension into the culture medium at a 5% inoculation ratio. For scale-up culture, incubate at a constant temperature for 12 h to maintain the optimal optical density, i.e., OD. 600 =1.5.

[0042] The added liquid is a mixture of cementing solution and bacterial solution. The cementing solution uses water as a solvent and CaCl₂ as the solute. 2、 The concentrations of MgCl2 and urea were as follows: CaCl2: 1.3 mol / L; MgCl2: 0.7 mol / L; urea: 2 mol / L; and the bacterial culture concentration was pH 6 and OD... 600 =1.5% Pasteurella multocida bacterial suspension.

[0043] right Figure 6 Further calculations showed that the exchangeable states of Zn decreased by an average of 9.68%, 32%, and 39.9% under JD, BG, and DY treatments, respectively. The exchangeable states of Pb decreased by an average of 29.78%, 47.01%, and 66.99% under JD, BG, and DY treatments, respectively. The exchangeable states of La decreased by an average of 23.88%, 42.21%, and 51.76% under JD, BG, and DY treatments, respectively. The exchangeable states of Ce decreased by an average of 15.82%, 41.28%, and 49.43% under JD, BG, and DY treatments, respectively. Therefore, considering the degree of reduction in the exchangeable states of Zn, Pb, La, and Ce, the best effect was achieved by the repair method in Example 1 (DY), and the worst was achieved by the repair method in the comparative example (JD). After adsorption, mineralization, and adsorption-mineralization treatments, the average decrease rates of exchangeable states of the four elements were 19.79%, 40.62%, and 52.02%, respectively. like Figure 7As shown, since no carbonate form was generated during the bioadsorption reaction in Comparative Example 1 (JD), only the forms of Comparative Example 2 (BG) and Example 1 (DY) were analyzed. In the carbonate-bound state, Zn increased by 17.48% and 22.05% under BG and DY treatments, respectively. Pb increased by 25.49% and 42.30% under BG and DY treatments, respectively. La increased by 28.77% and 24.58% under BG and DY treatments, respectively. Ce increased by 38.67% and 20.61% under BG and DY treatments, respectively. This indicates that in the carbonate-bound state, free metal ions in the exchangeable state are fixed into the carbonate-bound state. Therefore, considering both the exchangeable and bound state results, the scheme in Example 1 still shows the best performance.

[0044] Figure 8 , Figure 9 For the exchangeable and carbonate-bound states of several light rare earth elements that are present in relatively small amounts in the contaminated soil of this embodiment, the scheme in Example 1 is optimal.

[0045] The above embodiments are only a partial embodiment of the present invention and do not cover all of the present invention. Based on the above embodiments and the accompanying drawings, those skilled in the art can obtain more implementation methods without creative effort. Therefore, all implementation methods obtained without creative effort should be included within the protection scope of the present invention.

Claims

1. A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals, characterized in that: Using Bacillus subtilis ( Oceanobacillus sp. The *Bacillus oryzae* strain is used for the remediation of soil contaminated with a mixture of light rare earth elements and heavy metals. It is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 22085, dated March 29, 2021. The light rare earth elements are one or more of La, Ce, Pr, Nd, Pm, Sm, and Eu. Includes the following steps: (1) Cultivate Bacillus aquaticus and prepare bacterial suspension, wherein the OD of the bacterial suspension is... 600 The value is 1.4; Preparation of cementing solution: The cementing solution uses water as solvent and CaCl2 and urea as solutes. The cementing solution is mixed with the bacterial solution to obtain a mixed solution; The concentration of CaCl2 and urea in the mixed solution is 1 mol / L; (2) Air dry the collected soil contaminated with light rare earth and heavy metals; (3) After the air-dried contaminated soil is mixed with the mixture, it is placed into a mold and reacted for 24 hours; (4) Connect the upper and lower ends of the mold to the grouting pipes, and inject the mixture into the grouting pipe at one end for multiple pumping cycles; (5) After pumping is completed, the contaminated soil is cured and air-dried.

2. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: In step (1): the culture medium used to culture Bacillus aquaticus contains: 20 g / L yeast extract powder, 10 g / L ammonium sulfate, and 15.748 g / L trihydroxymethylaminotoluene.

3. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: In step (2), the contaminated soil is air-dried and sieved. Sieving involves passing the contaminated soil through a sieve with a pore size of 2 mm, retaining contaminated particles smaller than 2 mm.

4. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: The mold in step (3) is a cylindrical mold, with the upper and lower planes of the cylinder connected to the grouting pipe.

5. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: The formulas for the amount of contaminated soil and mixed liquid used in the mold in step (3) are as follows: ; In the formula: m 混合液 Indicates the mass of the mixture; m 干土 This indicates the quality of air-dried contaminated soil, with a moisture content of less than 5%. ω L This indicates the liquid limit value of the soil.

6. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: In step (4), the amount of liquid pumped each time is based on the standard of saturating the contaminated soil in the mold without any excess liquid flowing out; pumping is carried out at a rate of 1013 μl / min, and 7 rounds of pumping are carried out with an interval of 24 hours between each round.

7. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 1, characterized in that: Step (5) After 7 days of curing, air dry naturally for 14 days; the curing temperature is 8-12℃, and the relative humidity during curing is 19%-21%.

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