Method for in-situ thermal desorption remediation of organic contaminated soil and kinetic evaluation system

Abstract

The application discloses a method for repairing organic contaminated soil in situ by thermal desorption and a dynamic evaluation system, and comprises the following steps: identifying organic pollutants in soil, initial water content of soil and soil texture type; judging the initial water content of soil according to the octanol / water partition coefficient of the organic pollutants determined in the step of identifying key factors and adjusting the water content of soil accordingly; arranging heating devices at intervals in the contaminated site area; and performing in-situ thermal desorption treatment on the contaminated soil according to the heating temperature and heating time determined in the step of gradient heating, so that the organic pollutants are separated and removed from the soil. The application realizes efficient, energy-saving and accurate soil repair by identifying key factors and establishing a water content regulation strategy based on the octanol / water partition coefficient.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation simulation technology, specifically relating to a method and kinetic assessment system for in-situ thermal desorption remediation of organically contaminated soil. Background Technology

[0002] Soil is a vital component of the ecological environment, playing crucial roles in agricultural production, resource utilization, and ecological balance. The remediation of organically contaminated soil is a key focus and challenge in the field of ecological environmental protection. Volatile and semi-volatile organic pollutants (such as nitrobenzene, naphthalene, and phenanthrene) pose a serious threat to the soil environment and human health due to their high toxicity, recalcitrant nature, and easy migration. In-situ thermal desorption technology, as a highly efficient remediation technique for organically contaminated soil, offers advantages such as short remediation cycles, wide applicability, and no secondary pollution. It involves in-situ heating of the contaminated soil to volatilize and separate the organic pollutants, thereby achieving their removal.

[0003] However, existing in-situ thermal desorption technologies still face numerous challenges in practical applications. First, thermal desorption process parameters, such as heating temperature and time, largely rely on empirical settings, lacking scientific kinetic theoretical support, leading to low remediation efficiency and excessive energy consumption. For example, CN120115525A discloses a low-temperature thermal desorption synergistic low-dose persulfate remediation method, which removes volatile pollutants through low-temperature thermal desorption and then utilizes residual heat to activate persulfate to degrade non-volatile pollutants. However, its heating temperature setting is only based on a rough classification of pollutant boiling points, failing to consider the influence of key factors such as soil moisture content. Second, the impact mechanism of soil conditions such as soil moisture content and soil texture on desorption efficiency is unclear, making targeted process optimization difficult. Third, the lack of a comprehensive kinetic evaluation system makes it impossible to accurately quantify the desorption process, predict remediation effects, or select appropriate enhancement methods based on pollutant type and soil conditions.

[0004] Therefore, in view of the problems of insufficient optimization of process parameters, unclear influence mechanism and imperfect evaluation system of existing in-situ thermal desorption technology, this paper proposes to provide a method and kinetic evaluation system for in-situ thermal desorption remediation of organic contaminated soil. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method and kinetic assessment system for in-situ thermal desorption remediation of organically contaminated soil. The method achieves efficient, energy-saving, and precise soil remediation by identifying key influencing factors, optimizing process parameters, revealing microscopic mechanisms, providing enhancement methods, and establishing an assessment system.

[0006] The first aspect of this invention provides a method for in-situ thermal desorption remediation of organically contaminated soil, comprising: The steps for identifying key factors are as follows: Soil samples are collected from the contaminated site area, and the key factors affecting the thermal desorption efficiency of organic pollutants are analyzed and determined; wherein the key factors include organic pollutants in the soil, initial soil moisture content, and soil texture type. Gradient heating steps: Based on the physicochemical properties of the organic pollutants, a gradient heating program is set, with a heating temperature of 50-350℃ and a heating time of 0-60 minutes; The steps for soil moisture regulation are as follows: Based on the octanol / water partition coefficients of organic pollutants determined in the key factor identification step, the initial soil moisture content is assessed and adjusted accordingly. When the octanol / water partition coefficient of the organic pollutant is <3.33, there is no need to adjust the soil moisture content; the thermal desorption treatment can be performed directly. When the octanol / water partition coefficient of the organic pollutant is ≤4.46, adjust the soil moisture content to 12-18% to promote pollutant desorption, and then perform the thermal desorption treatment step. When the octanol / water partition coefficient of the organic pollutant is >4.46, the soil is dried to adjust the soil moisture content to below 6%, and then thermal desorption treatment is performed. The steps of thermal desorption treatment are as follows: heating devices are arranged at intervals in the contaminated site area, and in-situ thermal desorption treatment is carried out on the contaminated soil according to the heating temperature and heating time determined in the gradient heating steps, so that organic pollutants are separated and removed from the soil.

[0007] Furthermore, the organic pollutants mentioned in the key factor identification step include volatile organic pollutants and semi-volatile organic pollutants, and the organic pollutants are selected from one or more of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene; the soil texture type includes sandy soil, loam, and clay.

[0008] Furthermore, in the gradient heating step, the heating temperature is set according to the boiling point and apparent activation energy of the pollutant: For organic pollutants with a boiling point below 250℃ or an apparent activation energy ≤15 kJ / mol, the heating temperature is 50-150℃; For organic pollutants with boiling points above 250℃ or apparent activation energies >20 kJ / mol, the heating temperature is 200-350℃.

[0009] Furthermore, in the gradient heating step, the heating time is set according to the two-stage kinetic characteristics of thermal desorption: The first stage is the surface desorption period, with a heating time of 0-10 minutes and a relatively fast desorption rate. The second stage: intraparticle desorption period, heating time is 10-60 minutes, and the desorption rate gradually slows down; For high-boiling-point pollutants, the heating time shall not be less than 30 minutes.

[0010] Furthermore, in the thermal desorption treatment step, the heating device is an electric heating rod, the depth of which is consistent with the depth of the contaminated soil layer, and extraction wells are arranged around the heating rod to extract and treat the vaporized pollutants.

[0011] Furthermore, the method for in-situ thermal desorption remediation of organically contaminated soil also includes an enhancement step: simultaneously with or before the thermal desorption treatment step, an electric field is applied for electric field enhancement, with a voltage gradient of 1-5 V / cm, an electrode spacing of 0.5-2 m, and a treatment time of 24-200 hours.

[0012] Furthermore, the method for in-situ thermal desorption remediation of organically contaminated soil also includes an enhancement step: simultaneously with or before the thermal desorption treatment step, a chemical oxidant or reducing agent, including one or more of persulfate and hydrogen peroxide, is injected into the contaminated soil at an injection amount of 0.5-5% (w / w, relative to dry soil mass), and the reaction conditions are a temperature of 50-120℃.

[0013] A second aspect of the present invention provides a system for in-situ thermal desorption remediation of organically contaminated soil, for implementing the above method, the system comprising: Key Factor Identification Module: Used to identify key factors affecting thermal desorption efficiency in soil samples within the contaminated site area; wherein the key factors include organic pollutants in the soil, initial soil moisture content, and soil texture type; Gradient heating module: used to set a gradient heating program based on the physicochemical properties of organic pollutants identified by the key factor identification module; Soil moisture content regulation module: Used to determine the initial soil moisture content based on the octanol / water partition coefficient (logKow) corresponding to organic pollutants identified in the key factor identification module, and adjust the soil moisture accordingly. Thermal desorption treatment module: Used to perform in-situ thermal desorption treatment on contaminated soil in the contaminated site area according to the heating temperature and heating time determined in the gradient heating module, so that organic pollutants are separated and removed from the soil.

[0014] A third aspect of this invention provides an analytical method for the microscopic mechanism of thermal desorption of organic pollutants, comprising: Step 1: Under different heating temperatures and soil conditions, determine the change in the residual rate of the target organic pollutant in the soil over time, and plot the thermal desorption kinetic curve; Step 2: Based on the slope of the thermal desorption kinetic curve plotted in Step 1, the thermal desorption process is divided into a surface desorption phase and an intraparticle desorption phase. The surface desorption phase is characterized by the evaporation and vaporization of pollutants on the surface of soil particles, while the intraparticle desorption phase is characterized by the outward diffusion and migration of pollutants inside soil particles. The evaporation phase refers to water evaporation, and the vaporization phase refers to the outward diffusion and migration of pollutants inside soil particles. Step 3: The experimental data of the target organic pollutant optimized in Step 4 are nonlinearly fitted using an exponential decay kinetic model. The formula is as follows: Ct = C0·e^(-kt n ); Where Ct represents the pollutant concentration at time t; C0 represents the initial pollutant concentration; n represents the model order; and k represents the desorption rate constant. Step 4: Calculate the apparent activation energy Ea of the pollutant based on the Arrhenius equation. The formula is: ln k = -Ea / (RT) + ln A.

[0015] Where R is the gas constant (8.314 J / mol·K), T is the thermodynamic temperature, k represents the desorption rate constant, A is the pre-exponential factor, i.e. the frequency factor, and Ea is the activation energy.

[0016] The beneficial effects of this invention are as follows: The method described in this invention identifies key factors and establishes a moisture content control strategy based on the octanol / water partition coefficient, thus providing a scientific basis for setting thermal desorption process parameters. It also clarifies the surface desorption and intraparticle desorption stages of thermal desorption and provides theoretical support for process optimization through kinetic models and activation energy calculations. Furthermore, it provides two additional enhancement methods: electric field enhancement and electrochemical enhancement, which can be used in conjunction with in-situ thermal desorption to significantly improve remediation efficiency and shorten the remediation cycle.

[0017] The method described in this invention optimizes the heating temperature and moisture content to avoid excessively high temperatures damaging the soil structure, while also reducing energy consumption. Attached Figure Description

[0018] Figure 1 This is a flowchart of the in-situ thermal desorption remediation method for organically contaminated soil described in Example 1; Figure 2a shows the residual rates of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene in brown soil at different initial moisture contents under different temperatures in Example 1; where... Figure 2a-1 This is the curve showing the change in residual nitrobenzene in brown soil at an initial moisture content of 6%; Figure 2a-2 This is the curve showing the change in the residual rate of nitrobenzene in brown soil with an initial moisture content of 12%; Figure 2a-3This is the curve showing the change in the residual rate of nitrobenzene in brown soil with an initial moisture content of 18%; Figure 2a-4 This is the curve showing the change in the residual rate of naphthalene in brown soil at an initial moisture content of 6%; Figure 2a-5 The curve shows the change in the residual rate of naphthalene in brown soil with an initial moisture content of 12%. Figure 2a-6 The curve shows the change in the residual rate of naphthalene in brown soil with an initial moisture content of 18%. Figure 2a-7 This is the curve showing the change in the residual rate of n-dodecane in brown soil with an initial moisture content of 6%; Figure 2a-8 This is the curve showing the change in the residual rate of n-dodecane in brown soil with an initial moisture content of 12%; Figure 2a-9 This is the curve showing the change in the residual rate of n-dodecane in brown soil with an initial moisture content of 18%; Figure 2a-10 This is the curve showing the change in the residual rate of 1-nitronaphthalene in brown soil with an initial moisture content of 6%; Figure 2a-11 This is the curve showing the change in the residual rate of 1-nitronaphthalene in brown soil with an initial moisture content of 12%; Figure 2a-12 This is the curve showing the change in the residual rate of 1-nitronaphthalene in brown soil with an initial moisture content of 18%; Figure 2a-13 The curve showing the change in residual rate of phytorelin in brown soil at an initial moisture content of 6%; Figure 2a-14 The curve showing the change in residual rate of phytorelin in brown soil with an initial moisture content of 12%; Figure 2a-15 The curve showing the change in residual rate of phytorelin in brown soil with an initial moisture content of 18%; Figure 2b shows the residual rates of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene in gray soil at different initial moisture contents under different temperatures; among them; Figure 2b-1 This is the curve showing the change in the residual rate of nitrobenzene in gray soil with an initial moisture content of 6%; Figure 2b-2 This is the curve showing the change in the residual rate of nitrobenzene in gray soil with an initial moisture content of 12%; Figure 2b-3 This is the curve showing the change in the residual rate of nitrobenzene in gray soil with an initial moisture content of 18%; Figure 2b-4 This is the curve showing the change in the residual rate of naphthalene in gray soil at an initial moisture content of 6%; Figure 2b-5 The curve shows the change in the residual rate of naphthalene in gray soil with an initial moisture content of 12%. Figure 2b-6 The curve shows the change in the residual rate of naphthalene in gray soil with an initial moisture content of 18%. Figure 2b-7 This is the curve showing the change in the residual rate of n-dodecane in gray soil with an initial moisture content of 6%; Figure 2b-8 This is the curve showing the change in the residual rate of n-dodecane in gray soil with an initial moisture content of 12%; Figure 2b-9 This is the curve showing the change in the residual rate of n-dodecane in gray soil with an initial moisture content of 18%; Figure 2b-10 This is the curve showing the change in the residual rate of 1-nitronaphthalene in gray soil with an initial moisture content of 6%; Figure 2b-11 This is the curve showing the change in the residual rate of 1-nitronaphthalene in gray soil with an initial moisture content of 12%; Figure 2b-12 This is the curve showing the change in the residual rate of 1-nitronaphthalene in gray soil with an initial moisture content of 18%; Figure 2b-13 The curve showing the change in residual rate of phytorelin in gray soil at an initial moisture content of 6%; Figure 2b-14 The curve showing the change in residual rate of phytorelin in gray soil with an initial moisture content of 12%; Figure 2b-15 The curve showing the change in residual rate of phytorelin in gray soil with an initial moisture content of 18%; Figure 3 This diagram illustrates the two-stage mechanism of the thermal desorption process of organic pollutants in step two of the in-situ thermal desorption remediation method for organically contaminated soil described in Example 1. Figure 4 shows the thermal desorption kinetic fitting curves of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene at 50-200℃, plotted in step one of the analytical method for the microscopic mechanism of thermal desorption of organic pollutants in Example 4; where... Figure 4a The fitted curve of thermal desorption kinetics of nitrobenzene with an initial water content of 6% is shown. Figure 4b The fitted curve of thermal desorption kinetics of nitrobenzene with an initial moisture content of 12% is shown. Figure 4c The fitted curve of thermal desorption kinetics of nitrobenzene with an initial moisture content of 18% is shown. Figure 4d The fitted curve of thermal desorption kinetics of naphthalene with an initial water content of 6% is shown. Figure 4e The fitted curve of thermal desorption kinetics of naphthalene with an initial water content of 12% is shown. Figure 4f The thermal desorption kinetics fitting curve of naphthalene with an initial water content of 18% is shown; Figure 4g The fitted curve of thermal desorption kinetics of n-dodecane with an initial water content of 6% is shown; Figure 4h The fitted curve of thermal desorption kinetics of n-dodecane with an initial water content of 12% is shown; Figure 4i The fitted curve of thermal desorption kinetics of n-dodecane with an initial water content of 18% is shown; Figure 4j The thermal desorption kinetics fitting curve of 1-nitronaphthalene with an initial water content of 6% is shown; Figure 4k The thermal desorption kinetics fitting curves of 1-nitronaphthalene with an initial water content of 12% are shown. Figure 4l The thermal desorption kinetics fitting curve of 1-nitronaphthalene with an initial water content of 18% is shown; Figure 4m The fitted curve of the thermal desorption kinetics of phenanthrene with an initial moisture content of 6% is shown. Figure 4n The fitted curve of thermal desorption kinetics of phenanthrene with an initial water content of 12% is shown. Figure 4o The fitted curve of the thermal desorption kinetics of phenanthrene with an initial moisture content of 18% is shown. Figure 5 shows the linear relationship between ln k and 1000 / T under different soil conditions in step four of the analytical method for the microscopic mechanism of thermal desorption of organic pollutants in Example 4; where Figure 5a The linear relationship of nitrobenzene is shown in the graph; Figure 5b The linear relationship graph of naphthalene is shown; Figure 5c The linear relationship of n-dodecane is shown in the graph; Figure 5dThe linear relationship of 1-nitronaphthalene is shown in the graph; Figure 5e The linear relationship of 1-nitronaphthalene is shown in the graph. Detailed Implementation

[0019] To make the objectives, technical solutions, beneficial effects, and significant advancements of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided in the examples of the present invention. Obviously, all the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this application, unless otherwise expressly specified and limited, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more; unless otherwise specified or explained, the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] Example 1 like Figure 1 As shown, an in-situ thermal desorption method for remediating organically contaminated soil is presented. This embodiment addresses a sandy contaminated site left over from the relocation of a chemical plant. The main pollutants at this site are nitrobenzene and naphthalene. The specific method includes: Step 1: Key factor identification.

[0022] First, a grid-based sampling method was used at the contaminated site (sampling depth 0-6m), and samples were collected according to the "Technical Specification for Soil Environmental Monitoring" (HJ / T 166-2004). The collected soil samples were analyzed using gas chromatography-mass spectrometry (GC-MS) to determine that nitrobenzene and naphthalene were the key factors affecting the thermal desorption efficiency of organic pollutants. Soil particle composition was determined using a pipette method, confirming the contaminated soil texture as sandy soil. The initial moisture content of the sandy soil was assessed to be 4.9%, with nitrobenzene having a boiling point of 210.9℃ and a logKow of 1.85-1.88; and naphthalene having a boiling point of 218℃ and a logKow of 3.01-3.59. The residual rates of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene at different initial moisture contents in brown and gray soils at different temperatures are shown in Figures 2a and 2b.

[0023] Step 2: Based on the physicochemical properties of the pollutants determined in Step 1, set the heating process parameters.

[0024] Since the boiling points of nitrobenzene and naphthalene are both below 250℃, and their apparent activation energies Ea, determined by thermogravimetric analysis-differential scanning calorimetry, are both less than 15 kJ / mol, the heating temperature gradients were set using a thermogravimetric analyzer (TGA) as follows: 50℃, 100℃, 150℃, 200℃, 250℃, 300℃, 350℃.

[0025] The heating time was set in two stages: the surface desorption stage, with a heating time of 10 minutes, during which pollutants mainly desorb and vaporize from the outer surface of soil particles, resulting in a relatively fast desorption rate; and the intraparticle desorption stage, with a heating time of 50 minutes, during which pollutants mainly diffuse from the micropores inside the soil particles to the surface, and the desorption rate gradually slows down. A schematic diagram of the two-stage desorption mechanism is shown below. Figure 3 As shown.

[0026] The total heating time is 60 minutes to ensure complete desorption of nitrobenzene and naphthalene.

[0027] Step 3: Soil moisture content regulation.

[0028] Based on the octanol / water partition coefficient (log Kow) of the pollutant nitrobenzene determined in step one, the initial soil moisture content is assessed and processed.

[0029] Since the log Kow of nitrobenzene (between 1.85 and 1.88) is less than 3.33, and the log Kow of naphthalene (between 3.01 and 3.59) is between 3.33 and 4.46, it falls within the range where soil moisture promotes desorption.

[0030] Based on the original soil moisture content of 4.9%, the soil moisture content was adjusted to 15% (w / w) by spraying deionized water to promote desorption.

[0031] Step 4: Thermal desorption treatment.

[0032] Electric heating rods are arranged in a grid pattern within the contaminated site area, with the depth of the heating rods matching the depth of the contaminated soil layer. Extraction wells and their connected vacuum pumps are arranged around the heating rods.

[0033] When working, start the heating rod and heat the soil for a total of 60 minutes according to the temperature gradient set in step two. At the same time, turn on the vacuum pump and control the vacuum degree in the extraction well to -50 kPa. During the heating process, nitrobenzene and naphthalene desorb from the surface of soil particles and vaporize, and are extracted and processed through the extraction well.

[0034] After heating, soil samples were collected again to test the pollutant concentration. The results showed that the removal rate of nitrobenzene was over 95% and the removal rate of naphthalene was over 90%, meeting the screening value for Class I land use in the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control" (GB36600-2018).

[0035] Example 2 A method for in-situ thermal desorption remediation of organically contaminated soil is provided. The method is basically the same as that in Example 1, except for step four. The same content will not be repeated. Only the differences will be described below.

[0036] Building upon step four of Example 1, an electric field is applied to the contaminated soil to enhance pollutant desorption efficiency through Joule heating, electroosmosis, and electromigration. The voltage gradient is set to 1-5 V / cm; the electrode spacing to 0.5-2 m; and the treatment time is determined based on the type of pollutant, generally 24-200 hours.

[0037] When the above-mentioned electric field enhancement is used in combination with the thermal desorption in step four, the heating rate is increased by more than 20% compared with the traditional external heating method.

[0038] Example 3 A method for in-situ thermal desorption remediation of organically contaminated soil is provided. The method is basically the same as that in Example 1, except for step four. The same content will not be repeated. Only the differences will be described below.

[0039] Based on step four of Example 1, a chemical oxidant or reducing agent, including one or more of persulfate and hydrogen peroxide, is injected into the contaminated soil. Injection amount: 0.5-5% (w / w, relative to dry soil mass); Reaction conditions: temperature 50-120℃.

[0040] When the above-mentioned electrochemical enhancement is combined with the thermal desorption in step four, the desorption rate of polycyclic aromatic hydrocarbons is increased by 3-5 times.

[0041] Example 4 An analytical method for the microscopic mechanism of thermal desorption of organic pollutants was presented in this embodiment. Sandy soil (sand content >85%) was collected, and five typical organic pollutants were selected as target compounds: nitrobenzene (volatile, logKow = 1.85), naphthalene (semi-volatile, logKow = 3.30), n-dodecane (low water solubility, logKow = 7.00), 1-nitronaphthalene (semi-volatile, logKow = 3.70), and phenanthrene (semi-volatile, logKow = 4.46). Nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene were loaded into the soil using a static adsorption method. The initial concentration of the contaminated soil was 29,000 to 31,000 mg / kg.

[0042] The method of step one in Example 1 is used for soil texture, and the same content will not be repeated.

[0043] The specific steps of the analysis method are as follows: Step 1: Set the heating temperature gradient using a thermogravimetric analyzer (TGA): 50℃, 100℃, 150℃, 200℃. At each set temperature and at each constant temperature, contaminated soil samples with initial moisture contents of 6%, 12%, and 18% were heated. The residual amount of the target pollutant at 0, 5, 10, 20, 30, 45, and 60 minutes of heating was determined using gas chromatography-mass spectrometry (GC-MS), and the residual rate was calculated. The thermogravimetric kinetic fitting curve of the residual rate versus desorption time was plotted, as shown in Figure 4.

[0044] Step 2: Observe the thermal desorption kinetic curve drawn in Step 1. Based on the change in the slope of the kinetic curve, divide the thermal desorption process into the surface desorption period and the intraparticle desorption period. The surface desorption period is 0-10 minutes: such as Figures 4a-4o As shown, the residual rate drops sharply, and the curve slope is large; the evaporation and vaporization of pollutants on the surface of soil particles and the desorption rate are relatively fast and are significantly affected by soil moisture. The intraparticle desorption period is 10-60 min: pollutants inside soil particles diffuse and migrate outward, the desorption rate decreases, and it is limited by the soil pore structure.

[0045] Step 3: An exponential decay kinetic model was used to perform nonlinear fitting on the experimental data of the five pollutants optimized in Step 4 at 150℃. The model formula is as follows: Ct = C0·e^(-kt n ); Where Ct represents the pollutant concentration at time t; C0 represents the initial pollutant concentration; n represents the model order; and k represents the desorption rate constant. The model order n is determined through fitting; the fitting method and evaluation criteria need to be explained. Additional information is required, such as n being obtained through nonlinear least squares fitting, with R0... 2 A score of >0.95 is the goodness-of-fit criterion.

[0046] Step 4: Calculate the apparent activation energy Ea of the pollutants based on the Arrhenius equation, using the following formula: ln k = -Ea / (RT) + ln A.

[0047] Where R is the gas constant (8.314 J / mol·K), T is the thermodynamic temperature, k represents the desorption rate constant, A is the pre-exponential factor, i.e., the frequency factor, and Ea is the activation energy. The relationship between the desorption rate constant k and the apparent activation energy Ea satisfies ln(k2 / k1) = Ea(T2- T1) / (RT1T2).

[0048] The above analysis shows that for pollutants with higher apparent activation energy (Ea), the increase in temperature has a greater effect on the desorption rate constant (k), meaning that high activation energy pollutants are more likely to have their desorption efficiency increased by raising the temperature. Therefore, for such high activation energy pollutants, higher heating temperatures should be prioritized to achieve efficient remediation.

[0049] Figure 5a , Figure 5b , Figure 5c , Figure 5d , Figure 5e The graph shows the linear relationship between the natural logarithm of the reaction rate constant (lnk) and the reciprocal of temperature (1000 / T) under different soil conditions. The graph shows that plotting lnk against temperature yields a series of well-fitting linear lines, all with negative slopes, consistent with the classical form of the Arrhenius equation in step four. This indicates that within the studied temperature range, the reaction process of the aforementioned pollutants in the soil follows Arrhenius kinetics. The slope (absolute value) is proportional to the apparent activation energy Ea of the reaction, while the intercept corresponds to the natural logarithm of the pre-exponential factor A.

[0050] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for in-situ thermal desorption remediation of organically contaminated soil, characterized in that... include: The steps for identifying key factors are as follows: Soil samples are collected from the contaminated site area, and the key factors affecting the thermal desorption efficiency of organic pollutants are analyzed and determined; wherein the key factors include organic pollutants in the soil, initial soil moisture content, and soil texture type. Gradient heating steps: Based on the physicochemical properties of the organic pollutants, a gradient heating program is set, with a heating temperature of 50-350℃ and a heating time of 0-60 minutes; The steps for soil moisture regulation are as follows: Based on the octanol / water partition coefficient (logKow) of the organic pollutants determined in the key factor identification step, the initial soil moisture content is judged and the soil moisture is adjusted accordingly. When the octanol / water partition coefficient of the organic pollutant is < 3.33, there is no need to adjust the soil moisture content; the thermal desorption treatment can be performed directly. When the octanol / water partition coefficient of the organic pollutant is ≤4.46, adjust the soil moisture content to 12-18% to promote pollutant desorption, and then perform the thermal desorption treatment step. When the octanol / water partition coefficient of the organic pollutant is >4.46, the soil is dried to adjust the soil moisture content to below 6%, and then thermal desorption treatment is performed. The steps of thermal desorption treatment are as follows: heating devices are arranged at intervals in the contaminated site area, and in-situ thermal desorption treatment is carried out on the contaminated soil according to the heating temperature and heating time determined in the gradient heating steps, so that organic pollutants are separated and removed from the soil.

2. The method for in-situ thermal desorption remediation of organically contaminated soil according to claim 1, characterized in that, The organic pollutants in the key factor identification step include volatile organic pollutants and semi-volatile organic pollutants, and the organic pollutants are selected from one or more of nitrobenzene, naphthalene, n-dodecane, 1-nitronaphthalene, and phenanthrene; the soil texture type includes sandy soil, loam and clay.

3. The method for in-situ thermal desorption remediation of organically contaminated soil according to claim 1, characterized in that, In the gradient heating step, the heating temperature is set based on the boiling point and apparent activation energy (Ea) of the pollutant: For organic pollutants with a boiling point below 250℃ or Ea ≤ 15 kJ / mol, the heating temperature is 50-150℃; For organic pollutants with boiling points above 250℃ or Ea > 20 kJ / mol, the heating temperature is 200-350℃.

4. The method for in-situ thermal desorption remediation of organically contaminated soil according to claim 1, characterized in that, In the thermal desorption process, the heating device is an electric heating rod, the depth of which is the same as the depth of the contaminated soil layer, and extraction wells are arranged around the heating rod to extract and treat the vaporized pollutants.

5. The method for in-situ thermal desorption remediation of organically contaminated soil according to claim 1, characterized in that, The method for in-situ thermal desorption remediation of organically contaminated soil further includes an enhancement step: simultaneously with or before the thermal desorption treatment step, an electric field is applied for electric field enhancement, with a voltage gradient of 1-5 V / cm, an electrode spacing of 0.5-2 m, and a treatment time of 24-200 hours.

6. The method for in-situ thermal desorption remediation of organically contaminated soil according to claim 1, characterized in that, The method for in-situ thermal desorption remediation of organically contaminated soil further includes an enhancement step: simultaneously with or before the thermal desorption treatment step, a chemical oxidant or reducing agent, including one or more of persulfate and hydrogen peroxide, is injected into the contaminated soil at an injection amount of 0.5-5% (w / w, relative to dry soil mass), and the reaction conditions are a temperature of 50-120℃.

7. A system for in-situ thermal desorption remediation of organically contaminated soil, used to implement the method according to any one of claims 1 to 6, characterized in that, The system includes: Key Factor Identification Module: Used to identify key factors affecting thermal desorption efficiency in soil samples within the contaminated site area; wherein the key factors include organic pollutants in the soil, initial soil moisture content, and soil texture type; Gradient heating module: used to set a gradient heating program based on the physicochemical properties of organic pollutants identified by the key factor identification module; Soil moisture content regulation module: Used to determine the initial soil moisture content based on the octanol / water partition coefficients of organic pollutants identified in the key factor identification module, and adjust the soil moisture accordingly. Thermal desorption treatment module: Used to perform in-situ thermal desorption treatment on contaminated soil in the contaminated site area according to the heating temperature and heating time determined in the gradient heating module, so that organic pollutants are separated and removed from the soil.

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