Method for repairing light rare earth and heavy metal compound polluted soil

Abstract

The invention relates to a method for repairing light rare earth and heavy metal compound polluted soil, which is characterized in that the compound polluted soil is repaired by adopting bacillus sp., the bacillus sp. Is preserved in the China General Microbiological Culture Collection Center (CGMCC), the preservation number is CGMCC No.22085, and the preservation date is March 29, 2021. The repairing process comprises the following steps: mixing the bacillus subtilis bacterial liquid with the cementing liquid to obtain a mixed liquid; mixing the air-dried polluted soil with the mixed solution, and filling the mixture into a mold for reaction; the mold is communicated with a grouting pipe to inject the mixed liquid, and multi-round pumping is carried out; and after pumping is completed, the polluted soil is maintained and naturally air-dried. According to the method, dominant strains are adopted, biological adsorption and biological mineralization are combined, and effective control over the light rare earth and heavy metal compound contaminated soil is achieved under the action of dual bioremediation.

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] Mineral resources are closely related to global economic development, but the environmental pollution caused by mining development is an undeniable fact. Large-scale mining activities and tailings dam accumulation lead to pollution of the surrounding environment, triggering ecological crises and even endangering human health. Similarly, the development of metal deposits presents similar problems. However, in deposits containing rare earth elements (REEs), heavy metals are often associated. 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 in soils contaminated with mixed rare earth elements is still in its early stages. However, effectively controlling the contamination from tailings dams containing rare earth elements from entering groundwater and surrounding water bodies 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] Further, comprising the following steps: (1) culture of ocean bacillus and preparation of bacterial liquid, the OD value of the bacterial liquid is 1; preparation of cementing liquid: the cementing liquid takes water as solvent, and the solute is CaCl2 and urea, the concentration of CaCl2 and urea is 1 mol / L; the cementing liquid is mixed with the bacterial liquid to obtain a mixed liquid; 600 (1) culture of ocean bacillus and preparation of bacterial liquid, the OD value of the bacterial liquid is 1; preparation of cementing liquid: the cementing liquid takes water as solvent, and the solute is CaCl2 and urea, the concentration of CaCl2 and urea is 1 mol / L; the cementing liquid is mixed with the bacterial liquid to obtain a mixed liquid; (2) the collected light rare earth and heavy metal composite contaminated soil is dried; (3) the dried contaminated soil is mixed with the mixed liquid and then loaded into a mold for reaction for 24 h; (4) the upper and lower ends of the mold are connected with grouting pipes, and the mixed liquid is injected into the grouting pipe at one end for multi-round pumping; (5) after pumping, the contaminated soil is maintained and naturally dried.

[0006] As an optimization scheme, in step (1), the culture medium for culturing ocean bacillus contains: yeast extract powder 20 g / L, ammonium sulfate 10 g / L, and Tris 15.748 g / L.

[0007] Further optimization, in step (2), the contaminated soil is dried and sieved, the sieving is to pass the contaminated soil through a sieve with a pore size of 2 mm, and the contaminated particles smaller than 2 mm are retained.

[0008] Further, in step (3), the mold is a cylindrical mold, and the upper and lower planes of the cylinder are connected with grouting pipes. In step (3), the amount of contaminated soil and mixed liquid in the mold is calculated according to the following formula: In the formula: m 混合液表示 The mass of the mixed liquid; m 干土 The mass of the dried contaminated soil, with a water content of less than 5%; omega L The liquid limit value of the soil.

[0009] Further, in step (4), the amount of liquid pumped each time is determined by the standard of soaking the contaminated soil in the mold without excess liquid flowing out; the pumping is carried out at a rate of 1013 μl / min, and 7 rounds of pumping are carried out, with an interval of 24 h between each round.

[0010] Further, in step (5), the maintenance is carried out for 7 days, and the natural drying is carried out for 14 days; the maintenance temperature is 8-12℃, and the relative humidity during maintenance is 19-21%.

[0011] The beneficial effects of the present application are: The application adopts the advantage strain, combines biological adsorption and biological mineralization, and realizes effective control of light rare earth and heavy metal compound contaminated soil under the action of double biological repair.

[0012] In the application, the average exchangeable state reduction rates of the four elements after adsorption, mineralization and adsorption-mineralization treatment are 19.79%, 40.62% and 52.02% respectively. Compared with the single use of the biological mineralization method and the single use of the biological adsorption method for treating light rare earth compound contaminated soil, the adsorption-mineralization is more effective. The method can combine the multifunctional strain with the long-term benefit microbial mineralization technology, can greatly reduce the exchangeable state of rare earth elements and mixed pollutants in the contaminated soil, and significantly reduces the biological availability of the pollutants. A new method is provided for the surrounding water environment protection of the tailing dam.

[0013] The repair method can be applied to the compound contaminated soil in the rare earth tailing dam, can achieve the solidification / stabilization effect, can reduce the leaching concentration of the exchangeable state of rare earth and mixed pollution elements in the contaminated soil, and can make the contaminated site be secondarily developed and utilized.

[0014] The application will be further described in detail in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The orthogonal test condition screening results in the test example are shown in Table 1. The numbers on the horizontal coordinates are the numbers of each group of the evidence test.

[0016] Figure 2 The test sample of the comparative example 1 in the application is shown in Table 2. Figure 3 The test sample of the comparative example 2 in the application is shown in Table 3. Figure 4 The test sample of the example 1 in the application is shown in Table 4. Figure 5 The phase state analysis results of the retrieved soil sample in the application are shown in Table 5; wherein KT1, KT2, KT3, KT4-1, KT4-2, KT4-3 and KT5 are the numbers of the sampling points; the same below. Figure 6 The exchangeable state changes of Zn, Pb, La and Ce under the conditions of the comparative example 1 (JD), the comparative example 2 (BG) and the example 1 (DY) in the application are shown in Table 6. Figure 7 The carbonate bound state changes of Zn, Pb, La and Ce under the conditions of the comparative example 2 (BG) and the example 1 (DY) in the application are shown in Table 7. Figure 8This 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 9 This 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 component for cultivating the B. oceanospirans is: yeast extract powder 20 g / L, ammonium sulfate 10 g / L, Tris 15.748 g / L. The pH value of the culture medium is adjusted to 6, and the culture medium is sterilized in a high-temperature sterilization pot at 120°C for 20 min. Inoculate 2% of the bacterial liquid in the culture medium, then shake culture in a constant temperature incubator at 30°C, 200 rpm for 48 h, then inoculate the cultured bacterial liquid into the culture medium at a ratio of 5%, and select constant temperature culture for 12 h when expanding the culture to maintain the best optical density, i.e. OD 600 =1.

[0025] (2) The collected light rare earth and heavy metal composite contaminated soil is dried and sieved; The contaminated soil sample (soil to be repaired) is collected from the vicinity of a tailings dam in Inner Mongolia. Starting from the tailings dam, along the shortest straight line from the tailings dam to the water area in the southwest direction, 7 typical sample collection areas are selected for soil sampling, including 5 horizontal tillage layer sample areas (0-15 cm), and 2 vertical sample areas are divided at the random sampling point of the fourth horizontal sample area in the vertical direction (20-35 cm; 40-55 cm).

[0026] The returned soil samples are naturally dried, and after removing large stones and grass roots and branches, they are thoroughly mixed. Sieving is performed by passing the contaminated soil through a sieve with a pore size of 2 mm, and the particles below 2 mm are retained for use.

[0027] (3) The sieved contaminated soil is mixed with the mixed solution and then loaded into a mold. The mold is a cylindrical mold with an inner diameter of 6.18 cm and a height of 2 cm. Three parallel samples are provided for each test piece. The amount of contaminated soil sample and mixed solution is shown in the formula: In the formula: m 混合液表示 The mass of the mixed solution; m 干土 The mass of the dried contaminated soil, with a water content of less than 5%; omega L The liquid limit value of the soil.

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

[0029] (5) After pumping, after 7 days of maintenance, 14 days of natural air drying; maintenance temperature 8-12℃, relative humidity during maintenance 19-21%. Concentration leaching test is carried out.

[0030] Among them, the leaching test uses five-step extraction method to determine the exchangeable state. The leaching test measures the leaching metal concentration in the leachate. The reference for the determination method is: Tessier A, Campbell P G C, Bisson M. Sequential chemical extraction procedure for the speciation of particular trace metals]. Anal Chem, 1979, 51(7): 844-850 Exchangeable state: weigh (1.0000+0.0003) g of soil sample in a 50 mL plastic centrifuge tube, add 8 mL of 1 mol / L MgCl2 solution, continuously oscillate at room temperature for 1 h (200 r / min), centrifuge for 10 min (4000 r / min), remove the supernatant and filter, and dilute to 50 ml with a volumetric flask; Carbonate-bound state: add 8 mL of 1 mol / L NaAc solution (pH=5.0) to the residue in the previous step, continuously oscillate at room temperature for 5 h (200 r / min), centrifuge for 10 min, remove the supernatant and filter, and dilute to 50 ml with a volumetric flask; Iron-manganese oxide state: add 20 mL of 0.04 mol / L NH2OH·HCl in 25% HAc solution (pH=2.0) to the residue in the previous step, and place in a water bath at 96±3 ℃ for 6 h with intermittent stirring; after standing and clarifying, take the supernatant solution; Organic-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 in the previous step, place in a water bath at (85±2) ℃ for 2 h with intermittent stirring, add 3 mL of 30% H2O2 solution (pH=2.0), place in a water bath at (85±2) ℃ for 3 h with intermittent stirring, add 5 mL of 3.2 mol / L NH Ac in 20% HNO3 solution, dilute to 20 mL, and oscillate at 22±5 ℃ for 30 min (200 r / min); after standing and clarifying, take the supernatant solution; Residual state: the residue after the previous treatment is digested and analyzed by nitric acid-hydrofluoric acid-perchloric acid digestion method.

[0031] Example 2 A method for repairing light rare earth and heavy metal composite contaminated soil The difference between this example and example 1 is that: The inner diameter of the mold in step (3) is 13 cm and the height is 4 cm.

[0032] Step (4) is pumped at a rate of 1650 μl / min, 14 rounds of pumping, each round interval of 24h.

[0033] Example 3 A method for repairing light rare earth and heavy metal composite contaminated soil The difference between this example and example 1 is that: The inner diameter of the mold in step (3) is 25 cm and the height is 8 cm.

[0034] Step (4) is pumped at a rate of 2500 μl / min, 28 rounds of pumping, each round interval of 12h.

[0035] Comparative Example 1 A method for repairing light rare earth and heavy metal composite contaminated soil, this comparative example is to use the principle of biosorption to directly add bacillus megaterium bacterial solution to the contaminated soil, and the optimal test conditions for treating light rare earth and heavy metal composite contaminated soil after preliminary screening are adopted.

[0036] The difference between this example and example 1 is that: The bacteria used is bacillus megaterium, strain number: BNCC336464, which is a non-pathogenic aerobic gram-positive bacteria, can adsorb rare earth and heavy metals through the functional groups on the cell surface to reduce their bioavailability, and can be purchased through commercial channels, purchased from Shangcheng Beinaeliang Biotechnology Co., Ltd. The optical density of the bacterial solution is measured by a spectrophotometer (ultraviolet (UV)-1700 ultraviolet-visible spectrophotometer), and the absorbance at a wavelength of 600 nm is expressed as OD 600 .

[0037] Step (1) prepares the culture medium of the bacteria, and the culture medium is prepared by the formula of 10 g / L of proteose peptone, 3 g / L of beef extract, and 5 g / L of sodium chloride. After complete dissolution, the pH value of the culture medium is adjusted to 7.3±0.1, and the culture medium is sterilized in a high-temperature sterilization pot at 120°C for 20 min. 2% of the bacterial solution is inoculated in the culture medium, and then cultured in a constant temperature incubator at 30°C and 200 rpm for 24h. The cultured bacterial solution is inoculated into the culture medium at a ratio of 5%, and the culture is selected for 12h to maintain the best optical density, i.e. OD 600 =2.1. No cementing fluid needs to be prepared.

[0038] In step (2), the screened contaminated soil is mixed with the bacterial solution and then loaded into the mold. The bacterial solution is used to replace the mixed solution.

[0039] Comparative Example 2 A method for repairing light rare earth and heavy metal composite contaminated soil, the test conditions are the optimal test conditions for treating light rare earth and heavy metal composite contaminated soil by the strain after preliminary screening.

[0040] The difference between the present comparative example and Comparative Example 1 is that: The Bacillus pasteurii used has the strain number ATCC 11859, is a non-pathogenic aerobic gram-positive bacteria, is a kind of bacteria that can hydrolyze urea, can be purchased through commercial channels, and is purchased from Shangcheng Beina Chuanglian Biotechnology Co., Ltd. The bacteria have the advantages of low cost, high urease yield, etc., are commonly used strains in microbial mineralization process, and have good fixation of heavy metal elements.

[0041] In step (1), the pH value of the culture medium is adjusted to 6, and the culture medium is sterilized in a high-temperature sterilization pot at 120℃ for 20min. 2% of the bacterial solution is inoculated in the culture medium, then the culture is shaken in a constant temperature incubator at 30℃ and 200rpm for 48h, and then the cultured bacterial solution is inoculated into the culture medium at a ratio of 5%, and the constant temperature culture is selected for 12h to maintain the best optical density, i.e. OD 600 =1.5.

[0042] The added liquid is a mixed solution of cementing liquid and bacterial solution. The cementing liquid uses water as solvent and CaCl 2、 , MgCl2 and urea as solutes. The concentration of CaCl2 is 1.3mol / L, the concentration of MgCl2 is 0.7mol / L, and the concentration of urea is 2mol / L. The bacterial solution is Bacillus pasteurii bacterial solution with pH=6 and OD 600 =1.5.

[0043] Comparative Example 2 Figure 6The results further calculate that the exchangeable state of Zn is averagely decreased by 9.68%, 32% and 39.9% under the treatments of JD, BG and DY respectively. The exchangeable state of Pb is averagely decreased by 29.78%, 47.01% and 66.99% under the treatments of JD, BG and DY respectively. The exchangeable state of La is averagely decreased by 23.88%, 42.21% and 51.76% under the treatments of JD, BG and DY respectively. The exchangeable state of Ce is averagely decreased by 15.82%, 41.28% and 49.43% under the treatments of JD, BG and DY respectively. Therefore, from the decreasing degree of the exchangeable state of Zn, Pb, La and Ce, the repair method of Example 1 (DY) is the best, and the repair method of Comparative Example (JD) is the worst. The average decreasing rates of the exchangeable state of the four elements after adsorption, mineralization and adsorption-mineralization are 19.79%, 40.62% and 52.02% respectively As shown in Figure 7 Since Comparative Example 1 (JD) does not generate carbonate form substances in the reaction process of biosorption, only the forms of Comparative Example 2 (BG) and Example 1 (DY) are analyzed. In the carbonate-bound state, Zn is increased by 17.48% and 22.05% under the treatments of BG and DY respectively. Pb is increased by 25.49% and 42.30% under the treatments of BG and DY respectively. La is increased by 28.77% and 24.58% under the treatments of BG and DY respectively. Ce is increased by 38.67% and 20.61% under the treatments of BG and DY respectively. It is indicated that the free metal ions in the exchangeable state are fixed into the carbonate-bound state. Therefore, from the results of the exchangeable state and the bound state, the effect of Example 1 is still the best.

[0044] Figure 8 、 Figure 9 For the exchangeable state and the carbonate-bound state of several light rare earths with relatively small content in the contaminated soil of the present embodiment, the scheme of Example 1 is the best.

[0045] The above embodiments are only part of the embodiments of the present application and cannot cover all the embodiments of the present application. Based on the above embodiments and the accompanying drawings, more embodiments can be obtained by those skilled in the art without creative labor, and therefore these embodiments obtained without creative labor should be included in the protection scope of the present application.

Claims

1. A method for remediating soil contaminated with a combination of light rare earth elements and heavy metals, characterized in that: Using Bacillus cereus ( Oceanobacillus sp. The *Bacillus oryzae* strain was deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 22085 and accession date of March 29, 2021, for the remediation of soil contaminated with light rare earth elements and heavy metals.

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: Includes the following steps: Cultivating Bacillus aquaticus and preparing 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 a 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. The collected soil contaminated with light rare earth elements and heavy metals was air-dried. The air-dried contaminated soil was mixed with the mixture and then placed into a mold for reaction for 24 hours. 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; After pumping is completed, the contaminated soil is cured and allowed to air dry naturally.

3. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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.

4. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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.

5. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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.

6. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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.

7. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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.

8. The method for remediating soil contaminated with a combination of light rare earth elements and heavy metals according to claim 2, 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 is 19%-21% during curing.

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