Method for evaluating long-term effectiveness of heavy metal stabilized material based on high-temperature accelerated aging

Abstract

The invention provides a heavy metal stabilized material long-term effectiveness evaluation method based on high-temperature accelerated aging, which comprises the following steps: mixing a chitosan loaded scrap iron composite material with arsenic and antimony polluted soil, then carrying out short-term stabilization treatment, and then setting high-temperature accelerated aging parameters by adopting a heat conservation algorithm in combination with annual mean temperature difference. The long-term stability mechanism of the material in an extreme environment is disclosed by utilizing RAC risk assessment index, BCR continuous extraction morphological analysis and mung bean germination toxicity experiment synchronous monitoring. Experiments show that after simulation for 100 years, the TCLP leaching concentration of arsenic / antimony is always below a safety limit value, the residue state proportion is increased to 14.84-36.51%, the RAC value is always at a risk-free level, and the germination rate of mung beans can reach 100%. According to the invention, regional differentiation aging simulation and ecological toxicity joint evaluation are realized for the first time, and an accurate prediction tool is provided for engineering application of heavy metal stabilized materials.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and more specifically, to a method for evaluating the long-term effectiveness of heavy metal stabilization materials based on high-temperature accelerated aging. Background Technology

[0002] For heavy metal pollution in soil, chemical remediation technology is currently the most commonly used method in the market. Among them, solidification / stabilization technology stands out as a popular choice for heavy metal contaminated soil remediation due to its advantages such as speed, simplicity, economy, low secondary pollution, abundant reagent sources, wide applicability, and minimal site restrictions. However, the challenges faced by solidification / stabilization materials in long-term application cannot be ignored, as these challenges often stem from complex and diverse environmental factors. With increasing stabilization time, solidification / stabilization materials gradually age naturally in contaminated soil. In addition, natural phenomena such as acid rain erosion, microbial activity, and temperature changes can also subtly affect the physicochemical properties of materials, such as specific surface area, surface microstructure, acidity, elemental composition, functional groups, and structural morphology. These changes may cause drastic fluctuations in the performance of solidification / stabilization materials, potentially damaging their effectiveness in field applications and long-term solidification / stabilization of heavy metals. Therefore, to ensure the long-term effectiveness and environmental safety of solidification / stabilization technology, it is necessary to conduct in-depth research on the stabilization performance of materials on arsenic and antimony in soil after aging, and to understand the long-term fixation performance of materials for heavy metals while improving the remediation effect of soil heavy metals.

[0003] Traditional long-term assessments of soil remediation effectiveness primarily rely on long-term in-situ monitoring strategies. For example, Antemir et al. conducted continuous monitoring of solidified / stabilized remediation sites for over a decade, verifying the sustainability of the technology by tracking the migration patterns of pollutants (ANTEMIR A. Performance assessment of stabilized / solidified waste-forms[D]. Greenwich: University of Greenwich, 2010). Meanwhile, Wang Fei et al. also conducted monitoring of sites remediated using solidification / stabilization technology for up to 17 years (Wang Fei, Shen Zhengtao, Wang Hailing. Effect analysis of cement solidification / stabilization of contaminated soil in sites[J]. Chinese Journal of Geotechnical Engineering, 2018, 040(003):540-545.). While these empirical studies are highly persuasive, they suffer from significant drawbacks such as lengthy cycles, high costs, and the inability to predict the risk of technology failure. In recent years, simulating high-temperature aging using physical methods has provided an important reference for evaluating the long-term effectiveness of solidification / stabilization technologies. In most studies, the aging temperature is usually set at around 60-120℃ (WANG H, FENG M, ZHOU F, et al. Effects of atmospheric ageing under different temperatures on surface properties of sludge-derived biochar and metal / metalloid stabilization [J]. Chemosphere, 2017, 184: 176-184.). Hale et al. speculated that maintaining biochar at 60℃ for two months through high-temperature aging can simulate the aging process of biochar in the natural environment at 10℃ for 100 years (HALE S, HANLEY K, LEHMANN J, et al. Effects of Chemical, Biological, and Physical Aging As Well As Soil Addition on the Sorption of Pyrene to Activated Carbon and Biochar [J]. Environmental Science & Technology, 2011, 45(24): 10445-10453.). However, these accelerated aging methods do not consider the impact of regional climate differences on simulation parameters, leading to significant deviations between the assessment results and actual environmental conditions. Therefore, designing a method that can rapidly and effectively evaluate the long-term performance of heavy metal stabilized materials based on high-temperature accelerated aging is of great significance.

[0004] Patent document CN111562354A (application number: 202010258658.8) discloses a method and device for evaluating the long-term effectiveness of solidified / stabilized heavy metal contaminated soil remediation agents, including the following steps: taking soil samples that meet the requirements after solidification / stabilization remediation to prepare soil simulation samples, rinsing the soil simulation samples with simulated acid rain until the rinsing liquid does not meet the requirements of the groundwater functional zone of the original soil location, recording the total amount of simulated acid rain rinsing before it does not meet the requirements, and calculating the long-term effectiveness period of the remediation technology based on the total amount of simulated acid rain rinsing. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging.

[0006] The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging, comprising: Step S1: Mix chitosan-loaded waste iron scrap with arsenic-antimony contaminated soil and perform short-term stabilization treatment for a preset number of days; Step S2: Accelerated aging simulation of the mixed soil after short-term stability treatment; Step S3: Monitor the transformation of arsenic and antimony speciation in the soil and assess the long-term stability of the soil in conjunction with phytotoxicity experiments.

[0007] Preferably, step S2 includes: The mixed soil after short-term stability treatment was placed in an environment that met the preset requirements for multi-cycle aging treatment. Each aging cycle includes: a high-temperature phase and a room-temperature recovery phase; The duration t of the high-temperature phase in each aging cycle is calculated based on the simulated years in the target area using the heat conservation equation and the average temperature difference. Each aging cycle room temperature recovery phase: Place the soil in a room temperature environment for a preset time.

[0008] Preferably, the single-cycle high-temperature duration t includes: t=(80-T ref ) / (40-T)× t1×n; Where Δt1×n represents the number of days within n years when the average summer temperature in the polluted soil area reaches the preset requirement of extreme high temperature; T ref The value represents the average annual temperature of the area with polluted soil; T represents the average annual temperature of the area.

[0009] Preferably, step S3 includes: Step S3.1: Obtain the content of heavy metals in the soil, including weakly acid extractable, reducible, oxidizable and residual states, by means of BCR continuous extraction method; Step S3.2: Calculate the RAC risk assessment index based on the obtained heavy metal content, including the weakly acid extractable state, reducible state, oxidizable state, and residue state; Step S3.3: Determine soil stability using the calculated RAC risk assessment index.

[0010] Preferably, step S3.2 includes:

[0011] Among them, F1, F2, F3, and F4 correspond to the contents of heavy metals in the weak acid extractable state, the reducible state, the oxidizable state, and the residue state, respectively.

[0012] Preferably, step S3.3 includes: when the RAC risk assessment index If the percentage is 1%, the current soil is considered to be without risk; when 1% RAC Risk Assessment Index If the percentage is 10%, the current soil risk is considered low; when 10%... RAC Risk Assessment Index If the percentage is 30%, then the current soil condition is considered risky; when 30%... RAC Risk Assessment Index If the RAC risk assessment index is 50%, the current soil is considered to be at high risk; If the percentage is 50%, then the current soil is considered to be at extremely high risk.

[0013] Preferably, the phytotoxicity test to assess long-term stability includes: assessing soil long-term stability based on phytotoxicity tests using plant germination rate and seed germination index.

[0014] Preferably, the higher the plant germination rate and seed germination index, the more stable the soil.

[0015] Preferably, the plant germination rate includes:

[0016] Where n represents the number of plant seeds that have germinated after cultivation; N represents the initial number of plant seeds placed in the petri dish.

[0017] Preferably, the seed germination index includes:

[0018] in, This indicates the percentage of germinated seeds in plant seeds cultured from soil sample extracts out of the total number of seeds. This represents the average root length of all seeds cultured in the soil sample extract. This indicates the percentage of germinated seeds out of the total number of seeds in hydroponically grown plants. This represents the average root length of all seeds grown hydroponically.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses simulated high-temperature aging soil in a target area to detect the leaching toxicity of heavy metals using the TCLP method. Combined with the RAC risk assessment index and phytotoxicity experiments, it extrapolates the long-term effectiveness of solidification / stabilization materials. By minimizing the external environment, the evaluation time is significantly shortened. This invention can be used to quickly evaluate the long-term effectiveness of solidification / stabilization materials for remediating heavy metal contaminated soil, obtain key data such as effective time and remediation effect, and facilitate engineering application research.

[0020] 2. This invention considers the impact of regional climate differences on simulation parameters and reduces the deviation between simulation results and actual environment through heat calculation; 3. This invention combines plant toxicity test results to determine the long-term effectiveness of solidified / stabilized materials, and for the first time realizes regionally differentiated aging simulation and ecotoxicity joint assessment, providing an accurate prediction tool for the engineering application of heavy metal stabilized materials. Attached Figure Description

[0021] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart of a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging.

[0022] Figures 2a to 2b This is a schematic diagram illustrating the effects of high-temperature aging on As and Sb in contaminated soil in Guangxi.

[0023] Figures 3a to 3b This is a schematic diagram illustrating the effects of high-temperature aging on the stabilization rates of As and Sb in contaminated soil in Guangxi.

[0024] Figures 4a to 4d This is a schematic diagram illustrating the effects of high-temperature aging on As and Sb speciation in contaminated soils in Guangxi, as well as on As and Sb speciation in stabilized soils.

[0025] Figures 5a to 5b This diagram illustrates the changes in available arsenic and available antimony content in contaminated soil in Guangxi under high-temperature aging conditions.

[0026] Figures 6a to 6b This is a schematic diagram illustrating the effects of high-temperature aging on As and Sb in contaminated soil in Yunnan.

[0027] Figures 7a to 7b This is a schematic diagram illustrating the effects of high-temperature aging on the stabilization rates of As and Sb in contaminated soil in Yunnan.

[0028] Figures 8a to 8d This is a schematic diagram illustrating the effects of high-temperature aging on the As and Sb speciation components in contaminated soils in Yunnan, as well as the As and Sb speciation components in stabilized soils.

[0029] Figures 9a to 9b This is a schematic diagram showing the changes in available arsenic and available antimony content in contaminated soil in Yunnan under high-temperature aging conditions. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0031] Example 1 According to the present invention, a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging is provided, such as... Figure 1 As shown, it includes: Step S1: Mix chitosan-loaded waste iron scrap with arsenic-antimony contaminated soil and perform short-term stabilization treatment for a preset number of days; Step S2: Accelerated aging simulation of the mixed soil after short-term stability treatment; Step S3: Monitor the transformation of arsenic and antimony speciation in the soil and assess the long-term stability of the soil in conjunction with phytotoxicity experiments.

[0032] Specifically, step S2 includes: The mixed soil after short-term stability treatment was placed in an environment that met the preset requirements for multi-cycle aging treatment. Each aging cycle includes: a high-temperature phase and a room-temperature recovery phase; The duration t of the high-temperature phase in each aging cycle is calculated based on the simulated years in the target area using the heat conservation equation and the average temperature difference. Each aging cycle room temperature recovery phase: Place the soil in a room temperature environment for a preset time.

[0033] Specifically, the single-cycle high-temperature duration t includes: t=(80-T ref ) / (40-T)× t1×n; Where Δt1×n represents the number of days within n years when the average summer temperature in the polluted soil area reaches the preset requirement of extreme high temperature; T ref The value represents the average annual temperature of the area with polluted soil; T represents the average annual temperature of the area.

[0034] Specifically, step S3 includes: Step S3.1: Obtain the content of heavy metals in the soil, including weakly acid extractable, reducible, oxidizable and residual states, by means of BCR continuous extraction method; Step S3.2: Calculate the RAC risk assessment index based on the obtained heavy metal content, including the weakly acid extractable state, reducible state, oxidizable state, and residue state; Step S3.3: Determine soil stability using the calculated RAC risk assessment index.

[0035] Specifically, step S3.2 includes:

[0036] Among them, F1, F2, F3, and F4 correspond to the contents of heavy metals in the weak acid extractable state, the reducible state, the oxidizable state, and the residue state, respectively.

[0037] Specifically, step S3.3 includes: when the RAC risk assessment index... If the percentage is 1%, the current soil is considered to be without risk; when 1% RAC Risk Assessment Index If the percentage is 10%, the current soil risk is considered low; when 10%... RAC Risk Assessment Index If the percentage is 30%, then the current soil condition is considered risky; when 30%... RAC Risk Assessment Index If the RAC risk assessment index is 50%, the current soil is considered to be at high risk; If the percentage is 50%, then the current soil is considered to be at extremely high risk.

[0038] Specifically, the plant toxicity test assessment of long-term stability includes: assessing soil long-term stability based on plant toxicity tests using plant germination rate and seed germination index.

[0039] Specifically, the higher the plant germination rate and seed germination index, the more stable the soil.

[0040] Specifically, the plant germination rate includes:

[0041] Where n represents the number of plant seeds that have germinated after cultivation; N represents the initial number of plant seeds placed in the petri dish.

[0042] Specifically, the seed germination index includes:

[0043] in, This indicates the percentage of germinated seeds in plant seeds cultured from soil sample extracts out of the total number of seeds. This represents the average root length of all seeds cultured in the soil sample extract. This indicates the percentage of germinated seeds out of the total number of seeds in hydroponically grown plants. This represents the average root length of all seeds grown hydroponically.

[0044] Example 2 Example 2 is a preferred example of Example 1. The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilization materials based on high-temperature accelerated aging, specifically a chitosan-supported waste iron scrap material repair agent. This method can quickly and effectively evaluate the long-term effectiveness of the curing / stabilization repair agent.

[0045] The method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging includes: Step 1: Mix chitosan-loaded waste iron scrap with arsenic-antimony contaminated soil and carry out short-term stabilization treatment for 7-35 days; Step 2: Accelerated aging simulation of the treated soil is conducted, specifically: the soil moisture content is maintained at 30%±2% under a high temperature environment of 80±2℃, and multiple aging cycles are performed; each aging cycle includes: a) High-temperature stage: Based on the simulated years for the target region, the heat conservation equation is used. Q=cm T is used to calculate the duration t of a single-cycle high temperature. b) Room temperature recovery stage: Place the soil in a room temperature environment and let it stand for 24 hours; Step 3: Monitor the transformation of arsenic and antimony speciation in soil using the RAC risk assessment index and BCR continuous extraction method, and assess long-term stability in conjunction with phytotoxicity experiments; Specifically, the total number of accelerated aging simulation cycles is 20, and the duration t of the high-temperature stage in a single cycle satisfies: a)t=(80-T ref ) / (40-T)× t1×5; Δt1×5 is the number of days in the 5-year period when the average summer temperature in the polluted soil area reaches an extreme high of 40°C; T ref The average annual temperature of the area with polluted soil is expressed in °C. b) Each cycle corresponds to 5 years of actual environmental time, with a total simulation life of 100 years.

[0046] Specifically, the contaminated soil is randomly sampled according to the actual area, with a sampling depth of 20±2cm. After sampling, large stones, plant roots, plastic fragments and other impurities in the soil sample are picked out. Then, it is laid flat in an outdoor rain-sheltered and ventilated place to air dry naturally. The air-dried contaminated soil is then sieved, and the sieved contaminated soil is uniform in size and texture.

[0047] Example 3 Example 3 is a preferred example of Example 1. The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging, comprising: The ratio of solidification / stabilization material to soil mass is 1%-6% (w / w); An 80℃ constant temperature chamber and a moisture content maintenance device were used to simulate accelerated aging. Risk monitoring is achieved by integrating TCLP leaching detection, BCR morphology analysis, and plant germination rate testing units.

[0048] Differentiated high-temperature periods are set for different climate regions: the single-cycle high-temperature period t=13.64 days for regions with an average annual temperature of 22℃; and the single-cycle high-temperature period t=5.32 days for regions with an average annual temperature of 18℃.

[0049] The phytotoxicity test used two indicators to evaluate the germination rate and root length inhibition rate of mung bean seeds. When the GI index was ≥80%, it was determined that there was no risk of phytotoxicity.

[0050] In the high-temperature accelerated aging simulation, the soil moisture content was maintained by a moisture-permeable plastic wrap (water vapor transmission rate 2000-2500 g / m²·24h), with a fluctuation range of ≤±2%.

[0051] Example 2 Example 2 is a preferred example of Example 1. The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging, comprising: Soil samples were collected from the simulated area. During the collection process, random sampling was carried out according to the actual area zoning. The sampling depth was set to 20cm. After sampling, large stones, plant roots, plastic fragments and other impurities in the soil sample were picked out and spread out in an outdoor rain-sheltered and ventilated place to air dry naturally. After grinding, the samples were passed through a 20-mesh sieve, mixed evenly and collected into sample bags, and placed in an indoor dry and ventilated place for later use.

[0052] Take soil samples from the simulated area, add solidification / stabilization material at 3wt%, apply solution pH=7, adjust soil moisture content to 30%, and cure at 25℃ for 35 days, stirring once every 7 days.

[0053] Based on the simulated regional average annual temperature, the single-cycle high-temperature time is calculated using the heat conservation equation: t = (80 - T) ref ) / (40-T)× t1×5.

[0054] The soil after short-term stabilization was placed in a constant temperature chamber at 80±1℃ and covered with a moisture-permeable plastic wrap (water vapor transmission rate 2200g / m²·24h) to maintain a moisture content of 30±2%. After each high-temperature treatment cycle, the soil was transferred to a 25℃ environment and left to stand for 24 hours to complete one cycle. The cycle was repeated 20 times, with a total simulation duration of 100 years.

[0055] Sampling time points were: 0 years, 5 years, 25 years, 50 years, 75 years, and 100 years. 1g of soil was taken at each time to determine the TCLP leaching concentration of arsenic and antimony, the speciation of arsenic and antimony, and other indicators. After the experiment, the germination rate of the planted mung beans was used to determine the plant toxicity.

[0056] Example 3 Example 3 is a preferred example of Example 1. The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging, comprising: Arsenic-antimony co-contaminated soil (As=297.49 mg / kg, Sb=187.59 mg / kg, pH=7.67) was collected from tailings in the mining area of ​​Hechi City, Guangxi Zhuang Autonomous Region. During the collection process, random sampling was conducted according to the actual area zones, with a sampling depth of 20 cm. After sampling, large stones, plant roots, plastic fragments, and other impurities were removed from the soil samples, which were then spread out in a sheltered and well-ventilated outdoor location to air dry naturally. Subsequently, the samples were ground, passed through a 20-mesh sieve, mixed thoroughly, and collected into sample bags, which were then stored indoors in a dry and well-ventilated place for later use.

[0057] Add the solidification / stabilization material at a dosage of 3 wt% to the arsenic and antimony contaminated soil, stir evenly, apply a solution with pH=7, adjust the soil moisture content to 30%, and cure at 25℃ for 35 days, stirring once every 7 days.

[0058] The average annual temperature in Guangxi is approximately 22℃, with summer highs reaching 40℃. Accelerated aging at 80℃ was employed, with a calculated t=13.64 days. The solidified / stabilized soil material was placed in an 80℃ high-temperature oven, its moisture content maintained using plastic wrap and other tools, and left for 13.64 days. Subsequently, it was placed at room temperature for 24 hours, simulating a 5-year high-temperature aging process—this constitutes one high-temperature aging cycle. A total of 20 cycles were performed, with a total simulation duration of 100 years.

[0059] At the simulated years 0 (0th time), 5th time (1st time), 25th time (5th time), 50th time (10th time), 75th time (15th time), and 100th time (20th time), 1.00g soil samples were taken to determine the TCLP leaching concentration of arsenic and antimony, the speciation of arsenic and antimony, and other indicators. After the experiment, the germination rate of the planted mung beans was used to determine the plant toxicity.

[0060] Example 4 Example 4 is a preferred example of Example 1. The present invention provides a method for evaluating the long-term effectiveness of heavy metal stabilized materials based on high-temperature accelerated aging, comprising: Arsenic-antimony co-contaminated soil (As=297.49 mg / kg, Sb=187.59 mg / kg, pH=7.67) was collected from tailings in the mining area of ​​Wenshan City, Yunnan Province. During the collection process, random sampling was conducted according to the actual area zones, with a sampling depth of 20 cm. After sampling, large stones, plant roots, plastic fragments, and other impurities were removed from the soil samples, which were then spread out in a sheltered and well-ventilated outdoor location to air dry naturally. Subsequently, the samples were ground, passed through a 20-mesh sieve, mixed thoroughly, collected in sample bags, and stored in a dry and well-ventilated indoor location for later use.

[0061] Add the solidification / stabilization material at a dosage of 3wt% to the arsenic and antimony contaminated soil, stir evenly, apply a solution with pH=7, adjust the soil moisture content to 30%, and cure at 25℃ for 35 days, stirring once every 7 days.

[0062] Yunnan Province has an average annual temperature of approximately 18℃, with summer highs reaching 40℃. Accelerated aging at 80℃ was employed, with a calculated t=5.32 days. The solidified / stabilized soil material was placed in an 80℃ high-temperature oven, its moisture content maintained using plastic wrap and other tools, and left for 5.32 days. Subsequently, it was placed at room temperature for 24 hours, simulating a 5-year high-temperature aging process—this constitutes one high-temperature aging cycle. A total of 20 cycles were performed, with a total simulation duration of 100 years.

[0063] At the simulated years 0 (0th time), 5th time (1st time), 25th time (5th time), 50th time (10th time), 75th time (15th time), and 100th time (20th time), 1.00g soil samples were taken to determine the TCLP leaching concentration of arsenic and antimony, the speciation of arsenic and antimony, and other indicators. After the experiment, the germination rate of the planted mung beans was used to determine the plant toxicity.

[0064] Table 1. Evaluation of the long-term effectiveness of soil heavy metal solidification / stabilization materials

[0065] As shown in the table, using the principle of heat conservation, under high-temperature aging conditions, the stabilization rates of arsenic and antimony in the contaminated soils of Guangxi and Yunnan provinces with added chitosan-loaded waste iron filings remained above 90%. The leaching concentrations of arsenic and antimony were both below safe limits, and the soil RAC values ​​remained at a risk-free level. The GI indices were 133.86% and 159.06%, respectively. This indicates that the long-term effectiveness of chitosan-loaded waste iron filings in solidifying / stabilizing arsenic and antimony in the contaminated soils of Guangxi and Yunnan provinces under high-temperature aging conditions can reach 100 years. Through this method, the stabilization effect of the material on heavy metals can be scientifically quantified, providing data support for the technical effects in the patent claims.

[0066] like Figures 2a to 2b This study compares the changes in TCLP leaching concentrations of arsenic and antimony in contaminated soil from a mining area in Guangxi under simulated high-temperature aging conditions, comparing a blank control group with a treatment using chitosan-loaded waste iron scrap. Figure 2a This indicates that chitosan-supported waste iron scrap material can effectively stabilize arsenic in Guangxi soil under high temperature conditions for a long period of time; Figure 2b This indicates that chitosan-supported waste iron scrap material can effectively stabilize antimony in Guangxi soil under high temperature conditions for a long period of time, and the impact of high temperature conditions on antimony in the soil is smaller than that on arsenic.

[0067] Figures 3a to 3b This study investigated the changes in the average stabilization rates of arsenic and antimony in contaminated soil from a mining area in Guangxi after treatment with chitosan-loaded waste iron scrap material under high-temperature aging conditions. The results showed that under these conditions, the stabilization rate of arsenic in the contaminated soil remained above 95%, while the stabilization rate of antimony remained above 99%. These findings indicate that the chitosan-loaded waste iron scrap material exhibits strong thermal stability at high temperatures and is not easily decomposed or melted at high temperatures, thus preventing a decrease in the stabilization rates of arsenic and antimony.

[0068] Figures 4a to 4b The study investigated the changes in arsenic and antimony speciation in contaminated soil from a mining area in Guangxi under simulated high-temperature aging conditions, comparing the results with those from a control group treated with chitosan-loaded waste iron scrap. Figure 4a With increasing high-temperature aging time, the proportions of weakly acid-extractable (F1) and reducible (F2) arsenic in the Guangxi contaminated soil of the blank control group increased, while the proportions of oxidizable (F3) and residual (F4) arsenic decreased. This indicates that arsenic gradually transforms from a more stable form to a less stable form, meaning that high-temperature conditions promote the release of arsenic from Guangxi soil. Figure 4bWith increasing high-temperature aging time, the content of weakly acid-extractable antimony (F1) in Guangxi contaminated soil fluctuated to some extent, while the content of reducible antimony (F2) increased, and the proportions of oxidizable antimony (F3) and residual antimony (F4) decreased. Among these, the reducible (F2) and oxidizable (F3) forms of antimony showed the greatest variation, indicating that under high-temperature conditions, antimony in Guangxi contaminated soil mainly transforms from oxidizable (F3) to reducible (F2). Figure 4c With increasing high-temperature aging time, the content of arsenic in the weakly acid extractable form (F1) of arsenic in the contaminated soil of Guangxi mining area treated with chitosan-loaded waste iron scrap remained basically unchanged, while the proportion of reducible (F2) and oxidizable (F3) forms decreased, and the proportion of residual (F4) forms increased. At the 100th year, the content of arsenic in the weakly acid extractable form (F1) decreased by 5.87% compared to the control group, while the content of residual (F4) forms increased by 14.84%. The reason why the content of arsenic in the weakly acid extractable form (F1) remained almost unchanged may be that after the chitosan-loaded waste iron scrap material was applied to the soil and reacted, F1 had already reached a low value and could not be further reduced. Figure 4d With increasing high-temperature aging time, the changes in the content of the four forms of antimony in the contaminated soil of Guangxi mining area after treatment with chitosan-loaded waste iron scrap material were basically consistent with those of arsenic. When the 100th simulated year was reached, the content of the weakly acid extractable form of antimony (F1) decreased by 9.68% compared with the blank control group, while the content of the residual form (F4) increased by 30.96% compared with the blank control group. However, the content of the stable form of antimony was lower than that of arsenic, indicating that under high-temperature aging conditions, the solidification / stabilization effect of chitosan-loaded waste iron scrap on antimony was better than that of arsenic. This may be due to the weak mobility of antimony in the soil, thus making it easier to transform into the more stable residual form.

[0069] Figures 5a to 5b The study compared the available arsenic and available antimony content in contaminated soil from a Guangxi mining area under simulated high-temperature aging conditions with that of a blank control group and a treatment group treated with chitosan-loaded waste iron scraps. Figure 5a As the simulation time increased, the effective arsenic content in the blank control group showed an upward trend; the effective arsenic content in the experimental group with chitosan-loaded waste iron scraps did not fluctuate significantly. Figure 5b During the 100 simulated years of high-temperature aging, the effective antimony content in the blank control group showed some fluctuations and was relatively high; the effective antimony content in the experimental group with chitosan-loaded waste iron scraps did not differ significantly with the increase of the simulated years.

[0070] Figures 6a to 6b This study compares the changes in TCLP leaching concentrations of arsenic and antimony in contaminated soil from a mining area in Yunnan Province under simulated high-temperature aging conditions, comparing the control group with that treated with chitosan-loaded waste iron scrap. Figure 6aUnder high-temperature aging conditions, the TCLP leaching concentration of arsenic in contaminated soil in Yunnan without chitosan-supported waste iron scrap material first decreased and then slowly increased with increasing high-temperature aging cycles, consistent with the changes in arsenic in Guangxi soil. However, the TCLP leaching concentration of arsenic after stabilization treatment showed a continuous decreasing trend during accelerated high-temperature aging, with a small change range, and remained below the TCLP safety limit for arsenic (5 mg / kg). These results indicate that chitosan-supported waste iron scrap material can effectively stabilize arsenic in Yunnan soil under long-term high-temperature conditions, and high temperature can promote the stabilization of soil arsenic by the material. Figure 6b With increasing high-temperature aging time, the TCLP leaching concentration of antimony in untreated soil decreased, indicating that high temperature facilitates the solidification of antimony in Yunnan soil. However, the lowest concentration still exceeded the TCLP safety limit (1.5 mg / kg). In soil treated with chitosan-loaded waste iron scrap, the TCLP leaching concentration of antimony showed an increasing trend, but the highest concentration was only 0.12 mg / kg, far below the safety limit. Therefore, it can be concluded that chitosan-loaded waste iron scrap can effectively stabilize antimony in Yunnan soil under high-temperature conditions for a long period.

[0071] Figures 7a to 7b This study investigated the changes in the average stabilization rates of arsenic and antimony in contaminated soil from a mining area in Yunnan Province after treatment with chitosan-supported waste iron scrap material under simulated high-temperature aging conditions. Under these conditions, the stabilization rate of arsenic in the contaminated soil increased with increasing cycle time, reaching a maximum of 93.60%. While the stabilization rate of antimony decreased slightly, it remained above 97%. This phenomenon indicates that the addition of chitosan-supported waste iron scrap material can efficiently solidify / stabilize arsenic and antimony in contaminated soil, and that under high-temperature aging conditions, the stabilization effect on antimony is superior to that on arsenic.

[0072] Figures 8a to 8d To investigate the changes in the speciation of arsenic and antimony in contaminated soil from Yunnan mining areas under simulated high-temperature aging conditions, comparing the blank control group with that treated with chitosan-loaded waste iron scrap. Figure 8a With the increase of high-temperature aging time, the changes in the speciation of arsenic in untreated contaminated soil in Yunnan and Guangxi were similar, showing an increase in the proportion of weakly acid extractable (F1) and reducible (F2) forms, and a decrease in the proportion of oxidizable (F3) and residual (F4) forms. Figure 8b With increasing high-temperature aging time, the weakly acid-extractable (F1) and reducible (F2) forms of antimony in Yunnan contaminated soil showed no significant changes, while the oxidizable (F3) form increased and the residual (F4) form decreased. This indicates that under high-temperature conditions, antimony in Yunnan contaminated soil mainly transforms from the residual (F4) form to the oxidizable (F3) form. Figure 8cWith increasing high-temperature aging time, the proportions of arsenic in the Yunnan mining area's contaminated soil after treatment with chitosan-supported waste iron scrap material decreased, as did the proportions of the weakly acid-extractable (F1), reducible (F2), and oxidizable (F3) forms, while the proportion of the residual (F4) form increased. After 100 simulated years, the proportion of the weakly acid-extractable (F1) form of arsenic decreased by 2.93% compared to the control group, while the proportion of the residual (F4) form increased by 17.73%. This phenomenon indicates that high temperature can further promote the solidification and stabilization of arsenic in the material, possibly because high temperature promotes the transformation of iron in the material into a stable mineral form. Figure 8d With increasing high-temperature aging time, the proportions of antimony in the Yunnan mining area's contaminated soil—specifically, the extractable (F1), reducible (F2), and oxidizable (F3) forms—decreased after treatment with chitosan-supported waste iron scrap, while the proportion of the residual (F4) form increased. At 100 pseudo-years, the extractable (F1) form of antimony decreased by 3.29% compared to the control group, while the residual (F4) form increased by 36.51%. Furthermore, the increase in the residual antimony form was higher than that of arsenic, but the proportion of the residual antimony form was lower than that of arsenic.

[0073] Figures 9a to 9b To determine the available arsenic and available antimony content in contaminated soil from Yunnan mining areas under simulated high-temperature aging conditions, comparing the blank control group with the treated soil containing chitosan-loaded waste iron scrap. Figure 9a With increasing cycle time, the available arsenic content in untreated soil showed a slow increasing trend; after material treatment, the available arsenic concentration decreased significantly. Figure 9b With increasing aging time, the concentration of available antimony in the soil without the applied material fluctuated within a small range; the content of available antimony in the experimental group with chitosan-loaded scrap iron material did not change significantly.

[0074] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging, characterized by, The method comprises the following steps: Step S1: mixing chitosan-loaded scrap iron material with arsenic-antimony contaminated soil and performing short-term stabilization treatment for a preset number of days; Step S2: performing accelerated aging simulation on the mixed soil after short-term stabilization treatment; Step S3: monitoring the form transformation of arsenic and antimony in the soil and evaluating the long-term stability of the soil in combination with a plant toxicity experiment.

2. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 1, characterized by, The step S2 comprises: placing the mixed soil after short-term stabilization treatment in an environment meeting preset requirements to perform multi-cycle aging cycle treatment; each aging cycle comprises a high-temperature stage and a room temperature recovery stage; the duration t of the high-temperature stage of each aging cycle is calculated according to the target region simulation years by a heat conservation equation combined with average temperature difference; the room temperature recovery stage of each aging cycle: placing the soil in a room temperature environment for a preset time.

3. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 2, characterized by, The single-cycle high-temperature duration t comprises: t = (80 - T ref ) / (40 - T) x t1 x n; wherein Δti x n represents the number of days in n years in which the average summer temperature of the contaminated soil area reaches an extreme high temperature that meets preset requirements; T ref represents the average temperature of the contaminated soil area throughout the year; T represents the annual average temperature of the area.

4. The long-term evaluation method of high-temperature accelerated aging-based heavy metal stabilization material according to claim 1, characterized by, The step S3 comprises: Step S3.1: obtaining the heavy metal content in the soil including weak acid extractable state, reducible state, oxidizable state and residual state by BCR sequential extraction method respectively; Step S3.2: calculating RAC risk assessment index based on the obtained heavy metal content including weak acid extractable state, reducible state, oxidizable state and residual state; Step S3.3: judging the stability of the soil by the calculated RAC risk assessment index.

5. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 4, characterized by, The step S3.2 comprises: F1, F2, F3 and F4 respectively correspond to the content of heavy metals in weak acid extractable state, reducible state, oxidizable state and residual state.

6. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 4, characterized by, The step S3.3 comprises: when the RAC risk assessment index 1%, the current soil is considered to be no risk; when 1% RAC risk assessment index 10%, the current soil is considered to be low risk; when 10% RAC risk assessment index 30%, the current soil is considered to be medium risk; when 30% RAC risk assessment index 50%, the current soil is considered to be high risk; when the RAC risk assessment index 50%, the current soil is considered to be extremely high risk.

7. The long-term evaluation method of high-temperature accelerated aging-based heavy metal stabilization material according to claim 1, characterized by, The plant toxicity experiment for evaluating long-term stability comprises evaluating the long-term stability of the soil based on the plant toxicity experiment by including plant germination rate and seed germination index.

8. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 7, characterized by, The higher the values of plant germination rate and seed germination index, the more stable the soil.

9. The method for evaluating long-term stability of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 7, characterized by, The plant germination rate comprises: wherein n represents the number of plant seeds germinated after cultivation; N represents the initial number of plant seeds placed in the culture dish.

10. The long-term stability evaluation method of a heavy metal-stabilized material based on high-temperature accelerated aging according to claim 7, characterized by, The seed germination index comprises: wherein, represents the percentage of germinated seeds to total seeds in the plant seeds incubated with the soil sample extract; represents the average root length value of all seeds incubated with the soil sample extract; represents the percentage of germinated seeds to total seeds in the plant seeds incubated in water; represents the average root length value of all seeds incubated in water.

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