Method for repairing heavy rare earth and heavy metal mixed polluted soil

Abstract

The invention relates to a method for repairing heavy rare earth and heavy metal mixed polluted soil, which adopts bacillus pasteurii to repair heavy rare earth and heavy metal combined polluted soil, and the repairing process comprises the following steps: mixing a bacillus pasteurii bacterial solution with a calcium source and urea to obtain a mixed solution; 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, and effective control over the heavy rare earth and heavy metal mixed contaminated soil can be achieved through biomineralization.

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 heavy rare earth elements and heavy metals. Background Technology

[0002] Microbial-induced carbonate precipitation (MICP) is a widely used solidification and stabilization technology. The principle of MICP is that urease produced by microorganisms hydrolyzes urea, and the free carbonate ions combine with free metal cations in the environment to form carbonate precipitates. Currently, this technology has been extensively studied and applied to the treatment of heavy metal pollution such as zinc and lead.

[0003] In the soils surrounding rare earth mining areas, heavy metals and rare earth elements are often found together, necessitating the resolution of both heavy metal and rare earth pollution issues. Effectively controlling the entry of rare earth element-containing tailings dams into groundwater has become a critical and urgent problem. Although numerous studies have demonstrated the significant effectiveness of MICP in treating heavy metals, its application in solidifying and stabilizing heavy and rare earth element pollution, as well as mixed heavy and rare earth element pollution, is rarely reported. Summary of the Invention

[0004] The purpose of this invention is to provide a method for remediating soil contaminated with mixed heavy rare earth elements and heavy metals in the section from the tailings dam to the surrounding waters. A dominant bacterial strain is used to explore the effective control of soil contaminated with mixed heavy rare earth elements and heavy metals through biomineralization. The heavy rare earth elements include: gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).

[0005] The objective of this invention is achieved through the following technical solution: A method for remediating soil contaminated with a mixture of heavy rare earth elements and heavy metals, using Bacillus pasteurellii, includes the following steps: (1) Cultivate Bacillus pasteurellii and prepare bacterial suspension, wherein the OD of the bacterial suspension is... 600 The value is 1.5; (2) Preparation of mixed solution: CaCl2, MgCl2 and urea were added to the above bacterial solution to obtain a mixed solution; the total concentration of CaCl2 and MgCl2 in the mixed solution was 2 mol / L, the concentration of urea was 2 mol / L, the concentration ratio of CaCl2 to MgCl2 was 1.95~2.05:1, and the pH of the mixed solution was 6. (3) Air dry the collected soil contaminated with heavy rare earth elements and heavy metals; (4) the polluted soil after air-drying is mixed with the mixed solution and then is filled into a mold, and is reacted for 24 hours; (5) the upper end and the lower end of the mold are connected with grouting pipes, the mixed solution is injected into the grouting pipe at one end, and multiple rounds of pumping are carried out, and the interval between each round is 24 hours; (6) after the pumping is completed, the polluted soil is maintained and is naturally air-dried.

[0006] Further, in step (1), the culture medium used for culturing the bacillus pasteurii contains: yeast extract powder 20 g / L, ammonium sulfate 10 g / L, and trihydroxy methyl aminomethyl toluene 15.748 g / L, and the bacillus pasteurii is cultured for 48 hours.

[0007] Further, in step (2), the polluted soil is air-dried and is sieved, the sieving is that the polluted soil is passed through a sieve with a pore size of 2 mm, and the polluted 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.

[0009] Further, the length of the diameter of the bottom surface of the cylinder is greater than the height.

[0010] Further, in step (3), the amount of the polluted soil and the mixed solution in the mold is as follows: In the formula, m 混合液 represents the mass of the mixed solution; m 干土 represents the mass of the air-dried polluted soil, and the water content is less than 5%; ω L represents the liquid limit value of the soil.

[0011] Further, in step (4), the amount of the liquid pumped each time is taken as the standard that the polluted soil in the mold is soaked and no excess liquid flows out; the pumping is carried out at a rate of 1013 μl / min, and 7 rounds of pumping are carried out.

[0012] Further, in step (5), the maintenance is carried out for 7 days, and the natural air-drying is carried out for 14 days; the maintenance temperature is 8-12 DEG C, and the relative humidity during the maintenance is 19%-21%.

[0013] The beneficial effects of the present application are as follows: The present application uses the dominant strain, and realizes the effective control on the heavy rare earth and heavy metal composite mixed polluted soil by using the biomineralization reaction.

[0014] The exchangeable state average reduction rate of heavy metals and heavy rare earth elements after the bacillus pasteurii mineralization treatment is obviously better than single bacillus with adsorption and other bacillus with mineralization, the exchangeable state of heavy rare earth elements and mixed pollutants in the contaminated soil can be greatly reduced, and the bioavailability of pollutants is significantly reduced. A new method is provided for the surrounding water environment protection of tailing dam.

[0015] The application will be further described in detail below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The test samples in the application (from top to bottom in order are comparative example 5 (bio-adsorption), example 1 (biological mineralization-A), comparative example 6 (biological mineralization-B)).

[0017] Figure 2 The phase state analysis results of Cu before and after the treatment of the test samples in the application; Wherein JD represents the bio-adsorption result of comparative example 5, BG represents the biological mineralization-A result of example 1, DY represents the biological mineralization-B result of comparative example 6, and AK1 represents the soil without treatment, and the same below.

[0018] Figure 3 The phase state analysis results of Mn before and after the treatment of the test samples in the application.

[0019] Figure 4 The phase state analysis results of Gd before and after the treatment of the test samples in the application.

[0020] Figure 5 The phase state analysis results of Tb before and after the treatment of the test samples in the application.

[0021] Figure 6 The phase state analysis results of Dy before and after the treatment of the test samples in the application.

[0022] Figure 7 The phase state analysis results of Ho before and after the treatment of the test samples in the application.

[0023] Figure 8 The phase state analysis results of Er before and after the treatment of the test samples in the application.

[0024] Figure 9 The phase state analysis results of Tm before and after the treatment of the test samples in the application.

[0025] Figure 10 The phase state analysis results of Yb before and after the treatment of the test samples in the application.

[0026] Figure 11 The phase state analysis results of Lu before and after the treatment of the test samples in the application.

[0027] Figure 12 The phase analysis results of Y before and after the treatment of the test sample in the present application.

[0028] Figure 13 The exchangeable state reduction rates of heavy metals (Cu, Mn) and heavy rare earths (gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y)) in the case of Comparative Example 5, Example 1, and Comparative Example 6. DETAILED DESCRIPTION

[0029] Example 1 A method for repairing heavy rare earth and heavy metal composite contaminated soil, comprising the following steps: The adopted Bacillus pasteurii (Bacillus pasteurii) (Bacillus pasteurii) is a non-pathogenic aerobic gram-positive bacteria that can hydrolyze urea, and can be purchased through commercial channels. It is purchased from Beinaeliang Biotechnology Co., Ltd. Sporosarcina pasteurii The culture medium of the bacteria is prepared by the formula of 20 g / L of yeast extract powder, 10 g / L of ammonium sulfate, and 15.748 g / L of Tris, and the culture time of the bacteria is 48 hours.

[0030] (1) Cultivate Bacillus pasteurii and prepare a bacterial solution, wherein the OD value of the bacterial solution is 1.5; 600

[0031] (2) Prepare a mixed solution: add CaCl2, MgCl2 and urea to the above bacterial solution to obtain a mixed solution; the concentration of calcium source in the mixed solution is 2 mol / L, wherein the calcium source is composed of CaCl2 and MgCl2, and the concentrations of CaCl2 and MgCl2 are about 1.33 mol / L and 0.67 mol / L, respectively, and the concentration of urea is 2 mol / L, and the pH of the mixed solution is 6; (3) Dry and sieve the collected heavy rare earth and heavy metal composite contaminated soil; The contaminated soil sample (soil to be repaired) is collected from the vicinity of a tailings dam in Inner Mongolia. The returned soil sample is naturally air-dried, and after removing large stones and grass roots and branches, it is thoroughly mixed. Sieving is to pass the contaminated soil through a sieve with a pore size of 2 mm, and the particles below 2 mm are reserved for use. (4) Mix the sieved contaminated soil with the mixed solution and load it into a mold, and the mold is a cylindrical mold. The inner diameter of the mold is 6.18 cm, and the height is 2 cm. Each test piece is provided with 3 parallel samples. The amount of contaminated soil sample and mixed solution is shown in the formula:

[0032] ​​In the formula: m 混合液 represents the mass of the mixed solution; m 干土 represents the mass of the air-dried contaminated soil, with a water content of less than 5%; ω L represents the liquid limit value of the soil.

[0033] (5) After 24 h of reaction, the mold was connected with grouting pipes at the upper and lower ends, and the mixed solution was injected into the grouting pipe at one end, pumped at a rate of 1013 μl / min, and 7 rounds of pumping were performed with an interval of 24 h. The amount of liquid pumped each time was determined by the standard of soaking the contaminated soil sample 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. was used.

[0034] (6) After pumping, the samples were cured for 7 days and naturally air-dried for 14 days; the curing temperature was 8-12°C, and the relative humidity during curing was 19-21%. All the parallel samples prepared by the same method were mixed, crushed to below 200 mesh, and stirred uniformly for concentration leaching test.

[0035] The leaching test was tested and analyzed by using a seven-step form method, and the specific steps were as follows: 1) Water-soluble state: 5.00 g of sample was weighed and added with 50 mL of deionized water and shaken. After 2 h of oscillation at 200 r / min and 2 min of centrifugation at 8000 r / min, 2.5 mL of clear liquid was separated and added with 2.5 mL of 3% HNO3.

[0036] 2) Ion exchange state: 50 mL of MgCl2· 6H2O solution was added, shaken, and then oscillated at 200 r / min for 2 h and centrifuged at 8000 r / min for 2 min. 0.5 mL of clear liquid was taken and added with 3% HNO3 to 10 mL and shaken, and determined by ICP-MS.

[0037] 3) Carbonate-bound state: 50 mL of CH3COONa· 3H2O solution was added to the residue, shaken, and then oscillated at 200 r / min for 5 h and centrifuged at 8000 r / min for 2 min, and the remaining steps were the same as (2).

[0038] 4) Humic acid bound fraction 50 mL of 0.1 mol / L Na4PO7·10H2O solution was added to the residue, and after shaking, 200 r / min oscillation was performed for 3 h, and 8000 r / min centrifugation was performed for 2 min. 5 mL of supernatant was taken to a polytetrafluoroethylene beaker pre-added with 10 mL of concentrated HNO3, and heated for 10 min. After standing overnight, 8 mL of mixed acid (HCIO4: HNO3=1:3) was added, and heating was performed until HCIO4 white smoke was emitted. 5 mL of aqua regia was added, the beaker wall was washed with deionized water, and low-temperature heating was performed until the salts were dissolved. Water was added to 25 mL, and shaking was performed. After standing and clarification, 0.5 mL of solution was taken, 4.5 mL of 3% HNO3 was added, and ICP-MS determination was performed.

[0039] 5) Iron-manganese oxide bound fraction 50 mL of HONH3Cl+HCl mixed solution was added to the residue, and after shaking, 200 r / min oscillation was performed for 6 h, and 8000 r / min centrifugation was performed for 2 min. 0.5 mL of supernatant was taken, deionized water was added to 10 mL, and shaking was performed. ICP-MS determination was performed.

[0040] 6) Strong organic bound fraction 5 mL of 0.02 mol / L HNO3 and 10 mL of H2O2 were added to the residue, shaking was performed, and incubation was performed in a 83°C oven for 1.5 h. 5 mL of H2O2 was added, and incubation was continued in a 83°C oven for 70 min. After being taken out and cooled to room temperature, 30 mL of diluted CHCOONH4+HNO3 solution was added, shaking was performed, and standing was performed for 10 h. After shaking, 8000 r / min centrifugation was performed for 2 min, and the remaining steps were the same as (4).

[0041] 7) Residual fraction The residue of (6) was incubated in a 70°C oven for about 4 hours, and was dried and weighed. 0.2500 g of sample was taken to a polytetrafluoroethylene beaker, 10 mL of mixed acid (HCIO4: HNO3=1:3) and 6 mL of HF were added, heating was performed until HCIO4 white smoke was emitted, 10 mL of aqua regia was added, and the remaining steps were the same as (4).

[0042] Example 2 A method for repairing heavy rare earth and heavy metal mixed contaminated soil, the difference between this embodiment and example 1 is that the inner diameter of the mold in step (4) is 3.8 cm, and the height is 7.6 cm. The other operations are the same.

[0043] In the implementation process of this sample scale, when the inner diameter of the mold is smaller and the height is higher, the upper and lower surfaces and the near-surface layer of the sample will undergo more complete biomineralization reaction after the first few pumping. Since the outer connecting holes have been blocked most of the time, the internal biomineralization reaction of the sample will not be much, that is, the amount of pollution elements in the center of the sample will be less stable. Compared with Example 1, the degradation rate of pollutants obtained by the treatment method under the mold is not as high as that of Example 1.

[0044] Comparative Example 1: A method for repairing heavy rare earth and heavy metal mixed contaminated soil, the difference between this comparative example and Example 1 is that in step (5), the pumping interval is 12h.

[0045] Under the experimental conditions of setting the solidification period to 12 hours, the internal biochemical reaction process of the sample has not been fully carried out after the first solidification, and the soil body is still in a state of high water content. On this basis, when subsequent solidification cycles are carried out, due to the high soil humidity in the previous solidification stage, the amount of mixed liquid added in the new solidification process is relatively reduced.

[0046] After the mixed liquid contacts the soil, the precipitate generated by the chemical reaction cannot effectively penetrate into the internal soil, but is mainly enriched in the surface layer of the sample, and cannot realize the full filling of the soil pore structure. This phenomenon directly leads to the fact that the target pollution elements in the contaminated soil in the center of the sample cannot be effectively fixed by the physical wrapping or chemical adsorption of the precipitate, thereby causing the stabilization effect of the pollution elements to be less than expected.

[0047] Comparative Example 2: A method for repairing heavy rare earth and heavy metal mixed contaminated soil, the difference between this comparative example and Example 1 is that in step (5), the pumping interval is 48h.

[0048] Under the experimental conditions of setting the solidification period to 48 hours, the sample is in a low water content state when the next solidification is carried out, at this time the internal biochemical reaction has been carried out most of the time, the pore structure in the soil body decreases with the increase of the solidification times, therefore, in the subsequent several solidification processes, the mixed liquid added to the soil is less and less, the liquid is more likely to stay on the surface and make the surface solidify, under this method, not only the soil layer will be solidified unevenly, but also the pollution elements in the soil will not get the most optimal solidification effect.

[0049] Comparative Example 3: A method for repairing heavy rare earth and heavy metal mixed contaminated soil, this comparative example uses the soaking method for treatment.

[0050] The preparation of the bacterial solution is the same as that of Example 1. After the contaminated soil and the bacterial solution are mixed well, the mixture is placed in a cylindrical mold with an inner diameter of 38 mm and a height of 76 mm. After the soil column is formed, the soil column is removed from the mold and placed in a geotextile with the same size to form a test piece. The test piece is placed in a cementing solution containing CaCl2, MgCl2, and urea; the total concentration of CaCl2 and MgCl2 in the cementing solution is 2 mol / L, and the concentration of urea is 2 mol / L; the concentrations of CaCl2 and MgCl2 are 1.33 mol / L and 0.67 mol / L, respectively. The test piece is soaked in the cementing solution for a total of 7 days, and the test piece is turned over every 24 hours for the first three days and every 48 hours for the last four days. After 7 days, the test piece is removed from the cementing solution, the geotextile is removed, and the test piece is naturally air-dried for 14 days. Subsequently, the phase analysis method in step (6) of Example 1 is used for testing.

[0051] Compared with Example 1, the data value is smaller than the detection value in Example 1 (i.e., the exchangeable state reduction rate is higher than that of Example 1), but this is not accurate. The reason is that when the sample is soaked, the ions of the contaminant elements flow into the entire soaking liquid environment, and the flow of contaminant elements into the soaking liquid is not conducive to the environment. Therefore, this method is not practical and is not recommended.

[0052] Comparative Example 4: In this comparative example, the spray method is used for treatment.

[0053] The bacterial solution and the cementing solution of this comparative example are the same as those of Comparative Example 3.

[0054] The contaminated soil is placed in a 10 cm * 10 cm acrylic open box, and the mixed solution containing the bacterial solution and the cementing solution is sprayed on the contaminated soil 21 times in 7 days, with an interval of 8 hours each time. After 7 days, the phase analysis method in step (6) of Example 1 is used for testing. Compared with Example 1, the data value is larger than the detection value in Example 1 (i.e., the exchangeable state reduction rate is not as high as that of Example 1). The reason is that during the spraying process, the water in the soil sample slowly infiltrates into the lower layer of soil. Therefore, this method is not recommended.

[0055] Comparative Example 5: A method for repairing heavy rare earth and heavy metal mixed contaminated soil, this comparative example uses the principle of biosorption to add bacillus megaterium bacterial solution to the contaminated soil. The test conditions used are the optimal test conditions for treating heavy rare earth and heavy metal composite contaminated soil after preliminary screening of the bacterial strain.

[0056] The difference between this comparative example and Example 1 is: The bacteria used are bacillus megaterium ( Bacillus megaterium), and the strain number is BNCC336464. The non-pathogenic aerobic gram-positive bacteria can adsorb rare earth and heavy metals through the action of functional groups on the cell surface to reduce their bioavailability. The bacteria can be purchased through commercial channels from Beinaeliang Biotechnology Co., Ltd. The optical density of the bacterial solution is measured by a spectrophotometer (ultraviolet (UV)-1700 ultraviolet-visible spectrophotometer) and is represented by the absorbance at a wavelength of 600 nm, denoted as OD 600 .

[0057] Step (1) Prepare the culture medium of the bacteria. The culture medium is prepared from a 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. Inoculate 2% of the bacterial solution in the culture medium, then shake culture 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 ratio of 5%, and select constant-temperature culture for 12 h to maintain the optimal optical density, i.e., OD 600 =2.1. No cementing liquid is needed.

[0058] In step (2), the sieved contaminated soil is mixed with the bacterial solution and then loaded into the mold. The bacterial solution is used instead of the mixed liquid, and the other steps are the same as those in Example 1.

[0059] Comparative Example 6: A method for repairing heavy rare earth and heavy metal mixed contaminated soil, which adopts the optimal test conditions of the strain for treating heavy rare earth and heavy metal composite contaminated soil after preliminary screening.

[0060] The difference between this comparative example and Comparative Example 1 is that: (1) The bacteria are cultured and the bacterial solution is prepared, and the OD 600 value of the bacterial solution is 1.4; the cementing liquid is prepared, and the cementing liquid is 1 mol / L CaCl2 combined with 1 mol / L urea; the cementing liquid and the bacterial solution are mixed to obtain a mixed liquid. The bacteria are classified and named as Bacillus oceani (Bacillus oceani) Oceanobacillus sp. ), which is preserved in the China General Microbiological Culture Collection Center, and the preservation number is CGMCC No. 22085, and the preservation date is March 29, 2021.

[0061] The culture medium component for cultivating the Oceanospirillum sp. 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. 2% of the bacterial liquid is inoculated in the culture medium, and then the culture is cultured in a constant temperature incubator at 30°C, 200 rpm for 48 h. The cultured bacterial liquid is inoculated into the culture medium at a ratio of 5%, and the expansion culture is selected for constant temperature culture for 12 h to maintain the best optical density, i.e. OD 600 =1. The other steps are the same as those in Example 1.

[0062] Figures 3-12 The phase analysis results of the test samples before and after treatment in Example 1, Comparative Example 5 and Comparative Example 6 (determined after mixing 3 times of soil samples in parallel). Based on the results of Figures 3-12 , the further analysis results are shown in Figure 13 . The exchangeable state of Cu decreased by an average of -5.77%, 20.68% and 1.08% under the treatments of biosorption (Comparative Example 5), biological mineralization-A (Example 1) and biological mineralization-B (Comparative Example 6), respectively. The exchangeable state of Mn decreased by an average of 4.22%, 49.05% and 32.99% under the treatments of biosorption, biological mineralization-A and biological mineralization-B, respectively. The average decrease values of the exchangeable state of 9 kinds of heavy rare earth elements under the treatments of biosorption, biological mineralization-A and biological mineralization-B are shown in Figure 13 . From the decrease degree of the exchangeable state of Cu, Mn and heavy rare earth elements, the best effect is Example 1, i.e. the biological mineralization-A method, and the worst is Comparative Example 5, i.e. the biosorption method.

[0063] The above examples are only part of the embodiments of the present application and cannot cover all the embodiments of the present application. Based on the above examples and the accompanying drawings, those skilled in the art can obtain more embodiments without creative labor, and therefore the embodiments obtained without creative labor should be included in the protection scope of the present application.

Claims

1. A method for remediation of heavy rare earth and heavy metal mixed contaminated soil, characterized in that: The method for remediation of heavy rare earth and heavy metal mixed contaminated soil by using bacillus pasteurii comprises the following steps: Bacillus pasteurii was cultivated and a bacterial solution was prepared, the OD 600 value of which was 1.5; Preparation of mixed solution: adding CaCl2, MgCl2 and urea into the above-mentioned bacterial solution to obtain a mixed solution; the total concentration of CaCl2 and MgCl2 in the mixed solution is 2 mol / L, the concentration of urea is 2 mol / L, the concentration ratio of CaCl2 and MgCl2 is 1.95-2.05:1, and the pH value of the mixed solution is 6; Air-drying the collected heavy rare earth and heavy metal mixed contaminated soil; Mixing the air-dried contaminated soil with the mixed solution and then loading into a mold for reaction for 24 h; Connecting the upper and lower ends of the mold with grouting pipes, and injecting the mixed solution into the grouting pipe at one end, and performing multiple rounds of pumping with an interval of 24 h between each round; After pumping is completed, the contaminated soil is cured and naturally air-dried.

2. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: In step (1), the culture medium for culturing bacillus pasteurii contains: yeast extract powder 20 g / L, ammonium sulfate 10 g / L, and trihydroxy methyl aminomethyl benzene 15.748 g / L, and the culturing time of bacillus pasteurii is 48 h.

3. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: In step (2), the contaminated soil is air-dried and sieved, that is, the contaminated soil is passed through a sieve with a pore size of 2 mm, and the contaminated particles smaller than 2 mm are retained.

4. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: In step (3), the mold is a cylindrical mold, and the upper and lower planes of the cylinder are connected with grouting pipes.

5. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: The length of the diameter of the bottom surface of the cylinder is greater than the height.

6. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: In step (3), the amount of contaminated soil and mixed solution in the mold is calculated according to the following formula: wherein: m 混合液 represents the mass of the mixture liquid; m 干土 represents the mass of the air-dried contaminated soil, with a moisture content of less than 5%; ω L represents the liquid limit value of the soil.

7. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: 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 performed at a rate of 1013 μl / min, and 7 rounds of pumping are performed.

8. The method for remediation of heavy rare earth and heavy metal mixed contaminated soil according to claim 1, characterized in that: In step (5), the curing is performed for 7 days, and the natural air-drying is performed for 14 days; the curing temperature is 8-12℃, and the relative humidity during curing is 19%-21%.

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