Combined contaminated soil in-situ foam remediation method

Abstract

The invention discloses a compound contaminated soil in-situ foam remediation method, and relates to the technical field of soil remediation. According to the method, a foam injection structure is arranged on the composite contaminated soil, a surfactant and a repairing agent with oxidability are mixed to form a mixed solution, the mixed solution is injected into the soil after foaming treatment, organic pollutants are oxidized and degraded through the repairing agent, and stabilization of heavy metal is achieved through reaction products of the repairing agent. The foam carrier improves the mass transfer uniformity of the agent, synchronously solves the problem of combined pollution, does not need subsequent treatment, retains soil functions, and is suitable for efficient in-situ remediation of organic matter and heavy metal combined polluted soil.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology for soils contaminated with a combination of organic matter and heavy metals, and specifically to an in-situ foam remediation method for soils contaminated with a combination of organic matter and heavy metals. Background Technology

[0002] With the closure and relocation of industrial enterprises, my country has left behind over 500,000 contaminated sites, among which the problem of compound pollution caused by organic matter and heavy metals is prominent. Petroleum hydrocarbons and lead are representative pollutants in sites contaminated by industries such as machinery repair, processing and manufacturing, and electroplating. Petroleum hydrocarbons are complex mixtures composed of saturated hydrocarbons, aromatic hydrocarbons, colloids, and asphaltenes. After entering the soil, they tightly complex with organic matter and minerals, and their high viscosity and strong hydrophobicity make them difficult for organisms to utilize. Lead in the soil mainly exists in insoluble forms such as carbonates, phosphates, and sulfides, exhibiting strong accumulation and low mobility. The coexistence of these two pollutants poses a serious threat to the ecological environment and human health. For such complex contaminated soils, soil leaching is often used as a remediation method. This method uses an aqueous solution containing surfactants and chelating agents to remediate contaminated soil. However, in low-permeability areas and dead zones of the soil, this method causes preferential flow of the injected liquid agent, making it difficult for the agent to be uniformly transferred in the soil. To solve this problem, some have proposed using foam leaching for remediation. While foam rinsing can effectively address the problem of insufficient mass transfer, the foam is prone to collapse when treating soils contaminated with a mixture of organic matter and heavy metals, thus reducing rinsing efficiency. Furthermore, the residual pollutants after rinsing require subsequent treatment with solidifying and stabilizing agents, which can cause the soil to lose its original functions.

[0003] In summary, existing soil remediation methods are not yet effective in addressing soils contaminated with a combination of organic matter and heavy metals. To solve this problem, this invention utilizes surfactant-loaded ferrates to degrade petroleum hydrocarbons, and leverages the reaction products of the ferrates and petroleum hydrocarbons to stabilize lead. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ foam remediation method for complex contaminated soil, so as to solve the problems of low remediation efficiency, easy secondary pollution, and difficulty in removing multiple pollutants in the existing technology.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] An in-situ foam remediation method for complex contaminated soil includes the following steps:

[0007] S1: Install foam injection structures in areas of soil contaminated with a combination of organic matter and heavy metals;

[0008] S2: Perform a foaming process, the foaming process including:

[0009] S21: Prepare foaming water containing a surfactant, wherein the surfactant is a substance that can orient itself at the interface and reduce surface tension;

[0010] S22: Add an oxidizing iron-based repair agent to the foaming water and mix to form a surfactant-loaded repair agent mixture;

[0011] S23: The mixture is foamed to form foam that can be injected into the soil;

[0012] S3: Inject the foam into the foam injection structure to achieve the degradation of organic matter and the stabilization and remediation of heavy metals in the soil.

[0013] Further proposed solution: The organic matter includes petroleum hydrocarbons, the heavy metals include lead, and the composite contaminated soil is soil contaminated by a combination of petroleum hydrocarbons and lead.

[0014] Further options: The oxidizing iron-based remedial agent includes ferrates.

[0015] Further embodiment: In S1, the surfactant is an amphiphilic molecule, and the foaming water is prepared by mixing the surfactant with water, wherein the ratio of the mass (g) of the surfactant to the volume (mL) of the water is (1-10):50.

[0016] Further solution: In S3, the foaming process is as follows: after dissolving the gas in the mixture under high pressure, the mixture is stirred to form nano- or micron-sized foam; the pressure of the high pressure environment is 30 kPa or above.

[0017] Further details: The foam has a half-life of less than 60 minutes and an average particle size of less than 500 μm.

[0018] Further solution: In the injection step, the foam is prepared and injected immediately, and the injection frequency is once every three times the half-life of the foam.

[0019] Further details: The concentrations of petroleum hydrocarbons and lead in the soil are both below 6000 mg / kg; the ratio of petroleum hydrocarbon content (mg / kg) to the volume (L) of the injected mixed liquid per cubic meter of soil is 125:(1-50).

[0020] Further proposed solution: During the remediation process, the water-to-soil ratio of the soil to the injected mixture is 1 g:(0.1-1.0) mL.

[0021] Further embodiment: The ratio of the concentration (g / L) of the ferrate to the petroleum hydrocarbon content (mg / kg) in the soil is (50-100):(500-3000); the ratio of the concentration (g / L) of the ferrate to the lead content (mg / kg) in the soil is (50-100):(500-3000).

[0022] The present invention has the following advantages:

[0023] When surfactant foam carrying ferrates enters the soil, it promotes the desorption of petroleum hydrocarbons and lead from soil particles into the foam film. Ferrate and its self-decomposition-generated ·OH groups degrade petroleum hydrocarbons through hydrogen abstraction and electron transfer. During foaming in an air atmosphere, oxygen diffusion between foam particles promotes the generation of free radicals such as CH3C(O)O· (E0 = 2.24V) and CH3C(O)OO· (E0 = 1.60V) in a free radical chain reaction of petroleum hydrocarbons. The chain termination products of these free radicals protonate Fe(VI), enhancing its oxidizing properties. The reduction of ferrates by carboxyl, phenolic, and amino groups in soil organic matter to produce Fe(V) and Fe(IV) promotes the degradation of organic pollutants such as petroleum hydrocarbons. Minerals in the soil, such as montmorillonite, kaolinite, goethite, and ferrous sulfate, also enhance the degradation effect of Fe(VI) on petroleum hydrocarbons through electrostatic and surface adsorption. The products of ferrate oxidation of petroleum hydrocarbons and other organic pollutants can form co-precipitates with heavy metals such as lead through adsorption and surface complexation, promoting the transformation of lead in the soil to a stable storage form. This achieves synergistic remediation of combined organic and heavy metal pollution. The gases (small-molecule hydrocarbons, alcohols, aldehydes, acids, oxygen, and carbon dioxide) generated during the degradation of organic pollutants in the soil can extend the foam's lifespan, achieving continuous and effective remediation.

[0024] The ferrate compound used in this invention undergoes a self-decaying reaction in the system, generating ferric hydroxide colloids with high adsorption activity. These colloidal particles interact strongly with surfactant molecules in the system, significantly increasing the viscosity of the entire system through the formation of colloidal-surfactant complexes. This viscosity-enhancing effect is broad-spectrum, acting on various anionic, cationic, and nonionic surfactants. More importantly, this viscosity increase is not instantaneous but gradually strengthens with the continuous decay of the ferrate, thereby achieving dynamic control of the viscoelasticity of the foam system. This unique synergistic mechanism continuously improves the liquid film strength and drainage behavior of the foam, ultimately extending its lifespan. Attached Figure Description

[0025] Figure 1 Flowchart of foam-enhanced in-situ remediation process for petroleum-contaminated soil. Detailed Implementation

[0026] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0027] Experimental materials and equipment:

[0028] Materials: The contaminated soil was taken from an industrial site and tested to be contaminated with a combination of petroleum hydrocarbons and lead. Sodium dodecyl sulfate (surfactant), potassium ferrate (remediation agent), and other chemical reagents were all of analytical grade.

[0029] Equipment: Soil column (simulating soil remediation device), peristaltic pump (for foam injection), stirrer (for solution mixing and foam preparation), gas chromatograph (for detecting petroleum hydrocarbon content), atomic absorption spectrometer (for detecting lead content), etc.

[0030] Example 1

[0031] Experimental materials: The contaminated soil was taken from an industrial site and was a combination of petroleum hydrocarbon and lead contaminated soil, with a total petroleum hydrocarbon content of 1670 mg / kg and a lead content of 1855 mg / kg. Sodium dodecyl sulfate was used as the surfactant, and potassium ferrate was used as the remediation agent; both were of analytical grade.

[0032] Experimental equipment: soil column, peristaltic pump, stirrer, gas chromatograph, atomic absorption spectrometer, etc.

[0033] Procedure: Fill a soil column with 182.8g of contaminated soil, achieving a bulk density of 1.37g / cm³. 3 The porosity was 31.5%. 1 mL of sodium dodecyl sulfate was mixed with 50 mL of water to prepare foaming water. Potassium ferrate was added to the foaming water to achieve a ferrate concentration to petroleum hydrocarbon content ratio in the soil of 88:1670 and a lead concentration to lead content ratio in the soil of 88:1855. The mixture was stirred until homogeneous. The mixture was then placed under a 130 kPa high-pressure environment to dissolve gas, and foam with an average particle size of 40 μm and a half-life of 10 min was formed by stirring. The foam was injected into a soil column using a peristaltic pump at a flow rate of 100 mL / min, with an injection frequency of once every 5 min. The soil-to-water ratio was 1 g:0.27 mL, and the ratio of petroleum hydrocarbon content to injected mixture volume per cubic meter of soil was 125:28. Samples were taken for testing after standing for 24 hours.

[0034] Test results: The total petroleum hydrocarbon content in the soil decreased to 818 mg / kg; the proportion of exchangeable lead decreased from 5.2% to 0.5%, while the proportion of lead bound to iron and manganese oxides increased from 21.6% to 44.3%.

[0035] Example 2

[0036] Experimental materials: Same as in Example 1, with total petroleum hydrocarbon content of 2081 mg / kg and lead content in the contaminated soil. 1934 mg / kg.

[0037] Experimental equipment: Same as in Example 1.

[0038] Procedure: Fill a soil column with 180g of contaminated soil, with a bulk density of 1.35g / cm³. 3 The porosity was 32.5%. 2 mL of surfactant (amphiphilic molecule) was mixed with 50 mL of water to prepare foaming water. Ferrate was added to the foaming water to achieve a ferrate concentration to petroleum hydrocarbon content ratio of 88:2081 and a lead content ratio of 88:1934, and the mixture was stirred to form a solution. The solution was then dissolved in gas under 140 kPa high pressure, and stirred to form foam with an average particle size of 60 μm and a half-life of 11 min. The foam was prepared and injected immediately, with an injection frequency of once every 5 minutes. The soil-to-water ratio was 1 g:0.28 mL, and the petroleum hydrocarbon content to solution volume ratio per cubic meter of soil was 125:22.5. The solution was allowed to stand for 24 hours before testing.

[0039] Test results: The total petroleum hydrocarbon content in the soil decreased to 825 mg / kg; the proportion of exchangeable lead decreased from 6.9% to 0.4%, while the proportion of lead bound to iron and manganese oxides increased from 21% to 43.3%.

[0040]

[0041] Based on the test data from the two sets of embodiments, the in-situ foam remediation method for composite contaminated soil of the present invention has a significant and stable remediation effect on soil contaminated with petroleum hydrocarbons and lead, specifically as follows:

[0042] Petroleum hydrocarbon degradation effect: The total petroleum hydrocarbon content in the soil was significantly reduced after treatment, and all met the screening value requirements for Class I land use in GB36600-2018 (826 mg / kg), demonstrating the high efficiency of this method in degrading petroleum hydrocarbons.

[0043] Lead stabilization effect: The proportion of exchangeable lead (the form with high bioavailability) decreased significantly, from the initial 5.2%–6.9% to 0.5%–0.4%, indicating a significant reduction in the biotoxicity of lead.

[0044] The proportion of lead in the iron-manganese oxide bound state (a more stable form) increased significantly, from about 21% initially to about 44%, indicating that lead has transformed into a more stable occurrence form, achieving effective stabilization and repair.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for in-situ foam remediation of composite contaminated soil, characterized in that, Includes the following steps: S1: Install foam injection structures in areas of soil contaminated with a combination of organic matter and heavy metals; S2: Perform foaming treatment; The foaming process includes: S21: Prepare foaming water containing a surfactant, wherein the surfactant is a substance that can orient itself at the interface and reduce surface tension; S22: Add an oxidizing iron-based repair agent to the foaming water and mix to form a surfactant-loaded repair agent mixture; S23: The mixture is foamed to form foam that can be injected into the soil; S3: Inject the foam from step S23 into the foam injection structure described in step S1 to achieve the degradation of organic pollutants and the stabilization and remediation of heavy metals in the soil.

2. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, The organic matter includes petroleum hydrocarbons, the heavy metals include lead, and the composite contaminated soil is soil contaminated with both petroleum hydrocarbons and lead.

3. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, Iron-based remedial agents with oxidizing properties include ferrates.

4. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, In S1, the surfactant is an amphiphilic molecule, and the foaming water is prepared by mixing the surfactant with water, wherein the ratio of the mass of the surfactant (g) to the volume of the water (mL) is (1-10):

50.

5. The in-situ foam remediation method for composite contaminated soil according to claim 4, characterized in that, In S3, the foaming process is as follows: after dissolving the gas in the mixture under high pressure, the mixture is stirred to form nano- or micron-sized foam; the pressure of the high pressure environment is 30 kPa or above.

6. The in-situ foam remediation method for composite contaminated soil according to claim 5, characterized in that, The foam has a half-life of less than 60 minutes and an average particle size of less than 500 μm.

7. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, In the injection step, the foam is prepared and injected immediately, and the injection frequency is once every three times the half-life of the foam.

8. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, The concentrations of petroleum hydrocarbons and lead in the soil are both below 6000 mg / kg; the ratio of petroleum hydrocarbon content (mg / kg) to the injected mixed liquid volume (L) per cubic meter of soil is 125:(1-50).

9. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, The water-to-soil ratio of the soil to the injected mixture is 1 g:(0.1–1.0) mL.

10. The in-situ foam remediation method for composite contaminated soil according to claim 1, characterized in that, The ratio of the concentration of ferrate (g / L) to the petroleum hydrocarbon content (mg / kg) in the soil is (50-100):(500-3000); the ratio of the concentration of ferrate (g / L) to the lead content (mg / kg) in the soil is (50-100):(500-3000).

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