Step-by-step leaching remediation method for chromium-contaminated soil

Abstract

The invention provides a step-by-step leaching remediation method for chromium-contaminated soil, which comprises the following steps: mixing the chromium-contaminated soil and a first leacheate, carrying out first oscillation, then adding a second leacheate into the mixture, and carrying out second oscillation to obtain the remediated soil, the first leacheate comprises sodium salt; the second leacheate comprises organic acid and ferric salt; the temperature of the second oscillation is 70 DEG C to 90 DEG C. The method comprises the following steps: desorbing and releasing hexavalent chromium adsorbed on the surfaces of soil particles by using a sodium salt eluting agent, dissolving the soil particles to promote release of insoluble hexavalent chromium, and dissolving the soil particles containing high-concentration insoluble hexavalent chromium by using a composite eluting agent of organic acid and ferric salt under a high-temperature condition. And when the hexavalent chromium is released, the hexavalent chromium is efficiently reduced and stabilized, so that the aim of removing the hexavalent chromium in the polluted soil is fulfilled.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology and relates to a stepwise leaching remediation method for chromium-contaminated soil. Background Technology

[0002] Hexavalent chromium (Cr(VI)) is classified as a Group 1 carcinogen by the International Agency for Research on Cancer due to its strong oxidizing properties, high water solubility, and biotoxicity. Cr(VI) in soil mainly originates from leaks and spills in industries such as chromium chemicals (chromium salts and oxides production), leather tanning (chromium tanning agents), and electroplating (chromium plating solutions), as well as seepage from chromium-containing waste dumps. With industrial restructuring and the relocation of industries from urban areas to industrial parks, my country has shut down or relocated a large number of chromium-related enterprises, leaving behind numerous high-risk chromium-contaminated sites. The Cr(VI) concentration in the soil at these sites generally reaches several thousand mg / kg, seriously threatening the surrounding ecological environment. Sites located in ecologically sensitive areas, in particular, urgently require remediation.

[0003] Currently, the mainstream approach to chromium-contaminated soil remediation both domestically and internationally is reduction stabilization technology, which uses chemical or biological methods to reduce highly toxic hexavalent chromium (Cr(VI)) to less toxic trivalent chromium (Cr(III)) precipitates. However, this method has limitations: firstly, chromium pollution is often accompanied by insoluble hexavalent chromium pollution, which is difficult to completely remove; secondly, existing technologies cannot reduce hexavalent chromium in soil to below the limits set in the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control" (GB 36600-2018); and finally, residual trivalent chromium in the soil poses a long-term risk of re-oxidation. Therefore, leaching remediation technology aimed at directly removing hexavalent chromium is receiving increasing attention.

[0004] CN111215441A discloses a stepwise leaching method for remediating chromium-contaminated soil, comprising the following steps: S1, oxidation stage; S2, alkaline leaching stage: adjusting the pH to greater than 10 and adding an alkaline leaching agent for removing chromium (VI) for leaching; S3, acid leaching stage: adjusting the pH to less than 4 and adding an acid leaching agent for removing chromium (III) for leaching; S4, reduction and neutralization stage. The alkaline leaching agent in step S2 includes at least one of a chelating agent and a dispersant; the chelating agent includes at least one of a phosphate and a cationic surfactant; the dispersant includes at least one of sodium lignosulfonate, maleic acid-acrylic acid copolymer, and sodium ethylenediamine di-o-phenylacetate; the acid leaching agent in step S3 is a low-molecular-weight organic acid; the low-molecular-weight organic acid includes at least one of citric acid, oxalic acid, and acetic acid.

[0005] Although the above methods can achieve efficient removal of total chromium and hexavalent chromium Cr(VI) from soil, they are complex to operate, and the use of alkaline leaching can easily leach out metal cations from the soil, causing soil fertility loss. Furthermore, the inorganic reducing agents used will remain in the soil for a long time, causing long-term effects on the soil.

[0006] Therefore, a non-toxic, low-cost, easy-to-operate, and efficient method for leaching chromium-contaminated soil is proposed to address the problem of chromium pollution in soil at its source. Summary of the Invention

[0007] The purpose of this invention is to provide a stepwise leaching remediation method for chromium-contaminated soil. The method employs a two-step leaching process, first using a sodium salt leaching agent to promote the dissolution / desorption of insoluble hexavalent chromium on the surface and between soil particles, and then using a composite leaching agent consisting of organic acid and iron salt to reduce and stabilize the dissolved hexavalent chromium, thereby achieving the goal of removing hexavalent chromium from contaminated soil.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a stepwise leaching remediation method for chromium-contaminated soil, the stepwise leaching remediation method comprising:

[0010] The chromium-contaminated soil and the first leaching solution were mixed and shaken for the first time. Then, the second leaching solution was added and shaken for the second time to obtain the remediated soil.

[0011] The first eluent comprises sodium salt; the second eluent comprises organic acid and iron salt;

[0012] The temperature of the second oscillation is 70°C-90°C, for example, it can be 72°C, 74°C, 75°C, 76°C, 78°C, 80°C, 82°C, 84°C, 85°C, 86°C or 88°C, etc.

[0013] In this invention, the solvent for both the first rinsing solution and the second rinsing solution is deionized water.

[0014] The stepwise leaching remediation method provided by this invention first uses a sodium salt leaching agent to desorb and release hexavalent chromium adsorbed on the surface of soil particles, and also dissolves soil particles to promote the release of insoluble hexavalent chromium. Then, a composite leaching agent of organic acid and iron salt is used to dissolve soil particles containing high concentrations of insoluble hexavalent chromium under high-temperature conditions, releasing the hexavalent chromium while simultaneously and efficiently reducing and stabilizing it, thus achieving the goal of removing hexavalent chromium from contaminated soil. This stepwise leaching remediation method is characterized by low cost, simple operation, and high efficiency, and the leaching agent can be recycled after treatment.

[0015] It should be noted that organic acids are a natural biodegradable material. Using natural organic acids for leaching can further dissolve soil particles and release hexavalent chromium. Furthermore, under the catalysis of iron salts, organic acids can efficiently reduce and stabilize the dissolved hexavalent chromium into trivalent chromium.

[0016] Preferably, the concentration of hexavalent chromium in the chromium-contaminated soil is >1500 mg / kg, for example, it can be 1600 mg / kg, 1700 mg / kg, 1800 mg / kg, 1900 mg / kg or 2000 mg / kg, etc.

[0017] Preferably, the chromium-contaminated soil is further subjected to drying, crushing, and sieving before mixing.

[0018] Preferably, the mesh size of the sieve is 10-40 mesh, for example, it can be 12 mesh, 15 mesh, 16 mesh, 18 mesh, 20 mesh, 22 mesh, 25 mesh, 26 mesh, 28 mesh, 30 mesh, 32 mesh, 35 mesh, 36 mesh or 38 mesh, etc.

[0019] In this invention, controlling the particle size of chromium-contaminated soil within the range of 10-40 mesh facilitates the leaching of hexavalent chromium from the contaminated soil.

[0020] Preferably, the liquid-to-solid ratio of the first leaching solution to the chromium-contaminated soil is (5-15):1mL / g, for example, it can be 6:1mL / g, 7:1mL / g, 8:1mL / g, 9:1mL / g, 10:1mL / g, 11:1mL / g, 12:1mL / g, 13:1mL / g or 14:1mL / g, etc.

[0021] Preferably, the concentration of the first eluent is 0.5 mol / L to 2 mol / L, for example, it can be 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L or 1.8 mol / L, etc.

[0022] It should be noted that by controlling the concentration range of the first leaching solution, the dissolution and release of contaminated soil particles and crystalline insoluble hexavalent chromium can be effectively promoted.

[0023] Preferably, the sodium salt comprises any one or a combination of at least two of sodium phosphate, sodium carbonate, sodium bicarbonate, or sodium sulfate.

[0024] Preferably, the rotational speed of the first oscillation is 100r / min-300r / min, for example, it can be 120r / min, 150r / min, 160r / min, 180r / min, 200r / min, 220r / min, 250r / min, 260r / min or 280r / min, etc.

[0025] Preferably, the temperature of the first oscillation is 20°C-30°C, for example, it can be 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C or 29°C.

[0026] Preferably, the duration of the first oscillation is 10-15 hours, for example, it can be 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours or 14.5 hours.

[0027] Preferably, the pH value of the second rinsing solution is 3.5-4.5, for example, it can be 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3 or 4.4, etc.

[0028] In this invention, the second rinsing solution can be adjusted to the required pH using acid or alkali. Any acid or alkali can be a conventional material in the art, and no specific limitation is made here.

[0029] It should be noted that pH value has a significant impact on the form of chromium in soil, the adsorption of chromium on the surface of soil particles, and the intensity of chromium binding inside the soil. By controlling the pH value of the second leaching solution within a specific range, the activation capacity of organic acids can be improved, ferrous ions can be protected from oxidation, and the catalytic reduction capacity of iron salts can be enhanced, thereby improving leaching efficiency.

[0030] Preferably, the liquid-to-solid ratio of the second leaching solution to the chromium-contaminated soil is (5-15):1mL / g, for example, it can be 6:1mL / g, 7:1mL / g, 8:1mL / g, 9:1mL / g, 10:1mL / g, 11:1mL / g, 12:1mL / g, 13:1mL / g or 14:1mL / g, etc.

[0031] Preferably, the organic acid includes any one or a combination of at least two of citric acid, oxalic acid, malic acid, or tartaric acid.

[0032] Preferably, the iron salt includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, ferrous acetate, or ferrous sulfide.

[0033] Preferably, the concentration of organic acid in the second eluent is 1 mol / L-4 mol / L, for example, it can be 1.2 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.6 mol / L, or 3.8 mol / L, etc.

[0034] Preferably, the concentration of iron salt in the second eluent is 0.05 mol / L to 1 mol / L, for example, it can be 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, or 0.9 mol / L, etc.

[0035] It should be noted that by controlling the concentration range of organic acids and iron salts in the second leaching solution, the iron salts mainly play a catalytic role in the reaction. By adding a small amount of iron salts, the removal effect of organic small molecule acids on hexavalent chromium in the soil can be improved. While achieving efficient removal of hexavalent chromium from the soil, it can effectively reduce the disturbance to the soil structure, which is conducive to the chemical leaching-reduction stabilization treatment of hexavalent chromium in the soil, thereby improving the remediation effect of chromium-contaminated soil.

[0036] Preferably, the rotational speed of the second oscillation is 100r / min-300r / min, for example, it can be 120r / min, 150r / min, 160r / min, 180r / min, 200r / min, 220r / min, 250r / min, 260r / min or 280r / min, etc.

[0037] Preferably, the second oscillation time is 30-60 minutes, for example, it can be 32 minutes, 35 minutes, 38 minutes, 40 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 50 minutes, 52 minutes, 55 minutes or 58 minutes.

[0038] In this invention, solid-liquid separation is performed after the second oscillation.

[0039] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The stepwise leaching remediation method provided by the present invention firstly uses sodium salt leaching agent to desorb and release hexavalent chromium adsorbed on the surface of soil particles, and can also dissolve soil particles to promote the release of insoluble hexavalent chromium. Then, a composite leaching agent of organic acid and iron salt can dissolve soil particles containing high concentration of insoluble hexavalent chromium under high temperature conditions, release hexavalent chromium and efficiently reduce and stabilize it, so as to remove hexavalent chromium from polluted soil.

[0042] (2) The stepwise leaching remediation method provided by the present invention uses a low-cost leaching agent that does not harm the soil environment. It effectively improves the contaminated soil through secondary remediation. Under preferred conditions, the hexavalent chromium content in chromium-contaminated soil can be reduced to below the control value specified in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard GB36600-2018". Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0044] All materials used in the specific embodiments of this invention are commercially available or prepared using conventional methods in the prior art. All methods employed are conventional techniques in the field.

[0045] In the following examples and comparative examples, the concentration of hexavalent chromium in the contaminated soil before remediation was 1956.2 mg / kg; the pH of the second leaching solution was adjusted to the required value using 25% sulfuric acid or 0.1 mol / L sodium hydroxide solution.

[0046] Example 1

[0047] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil, the stepwise leaching remediation method comprising:

[0048] After the chromium-contaminated soil was air-dried and crushed, it was passed through a 10-mesh sieve. Then, the sieved chromium-contaminated soil and the first leaching solution were mixed at a liquid-to-solid ratio of 10:1 mL / g. The mixture was subjected to a first shaking at room temperature and a rotation speed of 300 r / min for 12 hours, after which the shaking was stopped. Then, the second leaching solution was added, and the mixture was subjected to a second shaking at a temperature of 75°C and a rotation speed of 300 r / min for 30 minutes. After filtration, the remediated soil was obtained.

[0049] The concentration of the first rinsing solution is 1 mol / L, and the first rinsing solution includes sodium sulfate and deionized water.

[0050] The second leaching solution has a pH of 4.0, and the liquid-to-solid ratio of the second leaching solution to the chromium-contaminated soil is 10:1 mL / g. The second leaching solution includes citric acid, ferrous chloride, and deionized water. The concentrations of citric acid and ferrous chloride in the second leaching solution are 1 mol / L and 0.1 mol / L, respectively.

[0051] Example 2

[0052] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil, the stepwise leaching remediation method comprising:

[0053] After the chromium-contaminated soil was air-dried and crushed, it was passed through a 10-mesh sieve. Then, the sieved chromium-contaminated soil and the first leaching solution were mixed at a liquid-to-solid ratio of 10:1 mL / g. The mixture was subjected to a first shaking at room temperature and a rotation speed of 200 r / min for 12 hours, after which the shaking was stopped. Then, the second leaching solution was added, and the mixture was subjected to a second shaking at a temperature of 90°C and a rotation speed of 200 r / min for 30 minutes. After filtration, the remediated soil was obtained.

[0054] The concentration of the first eluent is 1 mol / L, and the first eluent includes sodium carbonate and deionized water.

[0055] The second leaching solution has a pH of 4.1 and a liquid-to-solid ratio of 10:1 mL / g between the second leaching solution and the chromium-contaminated soil. The second leaching solution includes tartaric acid, ferrous sulfate, and deionized water. The concentrations of tartaric acid and ferrous sulfate in the second leaching solution are 1 mol / L and 0.1 mol / L, respectively.

[0056] Example 3

[0057] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil, the stepwise leaching remediation method comprising:

[0058] After the chromium-contaminated soil was air-dried and crushed, it was passed through a 10-mesh sieve. Then, the sieved chromium-contaminated soil and the first leaching solution were mixed at a liquid-to-solid ratio of 10:1 mL / g. The mixture was subjected to a first shaking at room temperature and a rotation speed of 200 r / min for 12 hours, after which the shaking was stopped. Then, the second leaching solution was added, and the mixture was subjected to a second shaking at a temperature of 75°C and a rotation speed of 200 r / min for 30 minutes. After filtration, the remediated soil was obtained.

[0059] The concentration of the first rinsing solution is 1 mol / L, and the first rinsing solution includes sodium sulfate and deionized water.

[0060] The second leaching solution has a pH of 3.7 and a liquid-to-solid ratio of 10:1 mL / g between the second leaching solution and the chromium-contaminated soil. The second leaching solution includes tartaric acid, ferrous sulfate, and deionized water. The concentrations of tartaric acid and ferrous sulfate in the second leaching solution are 1 mol / L and 0.1 mol / L, respectively.

[0061] Example 4

[0062] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil, the stepwise leaching remediation method comprising:

[0063] After the chromium-contaminated soil was air-dried and crushed, it was passed through a 20-mesh sieve. Then, the sieved chromium-contaminated soil and the first leaching solution were mixed at a liquid-to-solid ratio of 10:1 mL / g. The mixture was subjected to a first shaking at room temperature and a rotation speed of 100 r / min for 14 hours, after which the shaking was stopped. Then, the second leaching solution was added, and the mixture was subjected to a second shaking at a temperature of 80°C and a rotation speed of 100 r / min for 60 minutes. After filtration, the remediated soil was obtained.

[0064] The concentration of the first eluent is 1.5 mol / L, and the first eluent includes sodium phosphate and deionized water;

[0065] The second leaching solution has a pH of 4.0, and the liquid-to-solid ratio of the second leaching solution to the chromium-contaminated soil is 10:1 mL / g. The second leaching solution includes malic acid, ferrous sulfate, and deionized water. The concentrations of malic acid and ferrous sulfate in the second leaching solution are 2 mol / L and 0.5 mol / L, respectively.

[0066] Example 5

[0067] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil. Except that the concentration of the first leaching solution is 0.1 mol / L, all other conditions are the same as in Example 1.

[0068] Example 6

[0069] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the pH value of the second leaching solution being 2, all other conditions are the same as in Example 1.

[0070] Example 7

[0071] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the pH value of the second leaching solution being 5.5, all other conditions are the same as in Example 1.

[0072] Example 8

[0073] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the concentration of citric acid in the second leaching solution being 0.5 mol / L, all other conditions are the same as in Example 1.

[0074] Example 9

[0075] This embodiment provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the concentration of ferrous chloride in the second leaching solution being 0.01 mol / L, all other conditions are the same as in Example 1.

[0076] Comparative Example 1

[0077] This comparative example provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the absence of a first leaching solution, all other conditions are the same as in Example 1.

[0078] Comparative Example 2

[0079] This comparative example provides a stepwise leaching remediation method for chromium-contaminated soil. Except that the second leaching solution does not contain citric acid, all other conditions are the same as in Example 1.

[0080] Comparative Example 3

[0081] This comparative example provides a stepwise leaching remediation method for chromium-contaminated soil. Except that the second leaching solution does not contain ferrous chloride, all other conditions are the same as in Example 1.

[0082] Comparative Example 4

[0083] This comparative example provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the temperature of the second oscillation being 50°C, all other conditions are the same as in Example 1.

[0084] Comparative Example 5

[0085] This comparative example provides a stepwise leaching remediation method for chromium-contaminated soil. Except for the temperature of the second oscillation being 100°C, all other conditions are the same as in Example 1.

[0086] The hexavalent chromium content in the remediated soils obtained from the above examples and comparative examples was determined using HJ 1082-2019, "Determination of Hexavalent Chromium in Soils and Sediments - Alkali Extraction-Flame Atomic Absorption Spectrophotometry," and the hexavalent chromium removal rate was calculated. The results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As shown in Table 1:

[0090] The stepwise leaching remediation method provided in Examples 1-4 of this invention uses a composite leaching agent consisting of sodium salt leaching agent, organic acid, and iron salt to remediate hexavalent chromium-contaminated soil with a concentration >1500 mg / kg, thereby achieving the purpose of removing hexavalent chromium from the contaminated soil. Among these methods, tartaric acid is used as the organic acid with superior removal efficiency, achieving a hexavalent chromium removal rate >90% in the contaminated soil.

[0091] A comparison of Examples 1 and 5 and Comparative Example 1 shows that if the concentration of the first leaching solution is low or if the first leaching solution is not used, the removal rate of hexavalent chromium in the contaminated soil will decrease due to insufficient dissolution and release of sparingly soluble hexavalent chromium in the soil.

[0092] A comparison of Examples 1 and 6-7 shows that if the pH of the second leaching solution is too low, the excessive acidity will dissolve other metal oxides in the soil, and the dissolved metal cations will compete to consume the reducing agent, thereby reducing the reduction efficiency of hexavalent chromium and resulting in a decrease in the removal rate of hexavalent chromium in the contaminated soil. If the pH of the second leaching solution is too high, the key acidic reduction environment will be weakened, causing the iron-based catalyst to deactivate and precipitate, resulting in a significant decrease in the removal rate of hexavalent chromium in the contaminated soil.

[0093] A comparison of Examples 1 and 8 and Comparative Example 2 shows that if the concentration of organic acid in the second leaching solution is low or no organic acid is used in the compounding, the reduction in the content of reducing agent will lead to a decrease in the removal rate of hexavalent chromium in the contaminated soil.

[0094] A comparison of Examples 1 and 9 and Comparative Example 3 shows that if the concentration of iron salt in the second leaching solution is low or iron salt is not used in the compound, the lack of catalytic effect of iron salt on organic acids will lead to a decrease in the removal rate of hexavalent chromium in the contaminated soil.

[0095] A comparison of Example 1 and Comparative Examples 4-5 shows that if the temperature of the second oscillation is too low, the removal rate of hexavalent chromium in the contaminated soil will decrease because the sparingly soluble hexavalent chromium cannot be completely dissolved and released; if the temperature of the second oscillation is too high, the removal rate of hexavalent chromium in the contaminated soil will decrease because the organic acid undergoes thermal decomposition at continuous high temperature.

[0096] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A stepwise leaching remediation method for chromium-contaminated soil, characterized in that, The stepwise rinsing repair method includes: The chromium-contaminated soil and the first leaching solution were mixed and shaken for the first time. Then, the second leaching solution was added and shaken for the second time to obtain the remediated soil. The first eluent comprises sodium salt; the second eluent comprises organic acid and iron salt; The temperature of the second oscillation is 70°C-90°C.

2. The stepwise rinsing repair method according to claim 1, characterized in that, The concentration of hexavalent chromium in the chromium-contaminated soil was >1500 mg / kg; Preferably, the chromium-contaminated soil is further subjected to drying, crushing, and sieving before mixing; Preferably, the mesh size of the sieve is 10-40 mesh.

3. The stepwise rinsing repair method according to claim 1, characterized in that, The liquid-to-solid ratio of the first leaching solution to the chromium-contaminated soil is (5-15):1mL / g.

4. The stepwise rinsing repair method according to claim 1, characterized in that, The concentration of the first eluent is 0.5 mol / L-2 mol / L.

5. The stepwise rinsing repair method according to claim 1, characterized in that, The sodium salt includes any one or a combination of at least two of sodium phosphate, sodium carbonate, sodium bicarbonate, or sodium sulfate.

6. The stepwise rinsing repair method according to claim 1, characterized in that, The rotational speed of the first oscillation is 100 r / min-300 r / min; Preferably, the temperature of the first oscillation is 20°C-30°C; Preferably, the duration of the first oscillation is 10-15 hours.

7. The stepwise rinsing repair method according to claim 1, characterized in that, The pH value of the second rinsing solution is 3.5-4.5; Preferably, the liquid-to-solid ratio of the second leaching solution to the chromium-contaminated soil is (5-15):1 mL / g.

8. The stepwise rinsing repair method according to claim 1, characterized in that, The organic acid includes any one or a combination of at least two of citric acid, oxalic acid, malic acid or tartaric acid; Preferably, the iron salt includes any one or a combination of at least two of ferrous sulfate, ferrous chloride, ferrous acetate, or ferrous sulfide.

9. The stepwise rinsing repair method according to claim 1, characterized in that, The concentration of organic acid in the second eluent is 1 mol / L-4 mol / L; Preferably, the concentration of iron salt in the second elution solution is 0.05 mol / L to 1 mol / L.

10. The stepwise rinsing repair method according to claim 1, characterized in that, The rotational speed of the second oscillation is 100 r / min - 300 r / min; Preferably, the second oscillation time is 30 min to 60 min.

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