An in-situ dynamic soil and groundwater arsenic pollution remediation technology based on ferric arsenate-based material

Abstract

The present application relates to a kind of in-situ dynamic soil and groundwater arsenic pollution remediation technology based on arsenate iron-based material.The technology is synergized with persulfate and other oxidants by the slow-release ferrous salt capsule of innovative design, to generate arsenate in-situ in the contaminated area, to realize the efficient immobilization of arsenic. At the same time, the electrochemical regulation technology and intelligent monitoring feedback system are combined, the redox conditions of groundwater are dynamically optimized, the remediation process is accurately controlled, and the complex pollution environment is adapted. The technology has the advantages of high efficiency, economy, environmental protection, high intelligent degree, etc., and can effectively remediate arsenic pollution in soil and groundwater.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to an in-situ dynamic remediation technology for arsenic contamination in soil or groundwater. Background Technology

[0002] Arsenic pollution in soil and groundwater has become a global environmental problem, primarily originating from human activities such as mining, metal smelting, pesticide and fertilizer application, and industrial wastewater discharge, as well as natural processes like volcanic activity and rock weathering. Arsenic is a metalloid element with multiple valence states and forms, with trivalent and pentavalent arsenic being the two most common forms in the environment. Arsenic and its compounds are highly toxic and can accumulate in organisms through bioaccumulation in the food chain, posing a serious threat to ecosystem balance and human health. Long-term exposure to arsenic-containing environments may lead to various health problems, including skin lesions, cancer, cardiovascular disease, and neurological disorders. The World Health Organization has classified arsenic as a Group 1 carcinogen.

[0003] Traditional soil and groundwater arsenic contamination remediation technologies have many limitations. For example, while excavation-treatment-backfilling (EPR) techniques can effectively remove contaminated soil, they are costly and cause severe damage to soil structure. The dust and noise generated during construction can also cause secondary pollution to the surrounding environment. Ex-situ treatment technologies such as chemical precipitation and ion exchange also require large-scale excavation and extraction of contaminated soil and groundwater, resulting in high energy consumption and a high risk of secondary pollution. Phytoremediation, while environmentally friendly, has a long remediation cycle, is highly dependent on plant growth conditions, and is ineffective in heavily polluted areas. These traditional technologies are significantly inadequate in addressing complex and changing polluted environments, achieving efficient and precise remediation, and avoiding secondary pollution, making it difficult to meet the current needs of environmental protection and sustainable development. Summary of the Invention

[0004] An in-situ dynamic soil and groundwater arsenic contamination remediation technology based on ferric arsenate-based materials includes the following steps:

[0005] (1) Preparation of sustained-release ferrous salt capsules: Ferrous salt is coated onto a modified biochar carrier using a specific process to form a composite material with a core-shell structure and precise sustained-release properties; the initial ferrous salt loading of the sustained-release ferrous salt capsules is 0.2-0.7 g Fe. 2+ / g biochar, ferrous salt release rate is 0.01-0.05 mg / (g·d), release period is 60-180 days or more;

[0006] (2) The slow-release ferrous salt capsules are precisely added to the soil or groundwater area contaminated with arsenic, and the capsules are made to come into full contact with the contaminated medium through external force or gravity diffusion.

[0007] (3) Inject persulfate or other oxidants into the contaminated area, and dynamically adjust the type, concentration and injection method of the oxidant according to the characteristics of the contaminated medium and the remediation process;

[0008] (4) Using electrochemical control technology, a directional electric field is generated by electrodes arranged in the polluted area. The voltage range of the electrochemical control is 0.5-3.5 V, and the current density range is 0.1-1.5 mA / cm². 2 The energizing timing can be adjusted to include multiple modes such as continuous energizing, intermittent energizing, or pulsed energizing, thereby changing the redox conditions of the microenvironment of the polluting medium, promoting the formation of the stable phase of ferric arsenate and inducing its crystal transformation.

[0009] (5) Use multi-parameter sensors to monitor key parameters such as arsenic concentration, redox potential, pH, temperature, groundwater level and flow rate in the polluted area in real time, and transmit the data to the central control system;

[0010] (6) The central control system dynamically adjusts electrochemical parameters, including voltage, current density, and energizing sequence, based on sensor feedback data and using intelligent algorithms. At the same time, it intelligently decides the dosage and location of the slow-release ferrous salt capsules and oxidant to ensure the efficiency, stability and adaptability of the remediation process.

[0011] Further, the preparation method of the sustained-release ferrous salt capsule is as follows: (1) Select biochar material with high specific surface area, rich pore structure and active surface functional groups, and pre-oxidize, activate, acid-base treat or surface functionalization modification to enhance its interaction with ferrous salt and sustained-release performance; (2) Dissolve ferrous salt in deionized water or a specific solvent to prepare a mixed solution containing stabilizer, crystal form regulator and anti-interference additive, with a solution concentration range of 0.1-2 mol / L; (3) Use impregnation-heat treatment, impregnation-freeze drying, impregnation-microwave assisted drying or ultrasonic assisted impregnation-vacuum drying process to treat the mixed solution of biochar and ferrous salt under specific temperature, pressure, stirring rate and time conditions so that ferrous salt is uniformly coated inside and on the surface of biochar; (4) After drying, curing and post-treatment processes, a core-shell structure sustained-release ferrous salt capsule is formed.

[0012] Furthermore, the ferrous salt is one or a mixture of ferrous sulfate, ferrous chloride, and ferrous oxalate, and the purity of the ferrous salt is not less than 98% and the particle size is less than 0.1 mm, to ensure its uniform dispersion and good coating performance in the biochar carrier.

[0013] Furthermore, the oxidant is one or more of persulfate, hydrogen peroxide, ozone, and potassium permanganate, and the purity of the oxidant is not less than 95%. The injection concentration range is 0.05-0.3 mol / L, which can be dynamically adjusted according to the degree of pollution and the remediation process. At the same time, the oxidant injection method includes one-time injection, multi-stage injection, continuous injection, or pulse injection to achieve the best oxidation reaction effect and economic balance.

[0014] Furthermore, the electrode material is a composite structure of one or more of stainless steel, graphite, titanium, and zinc. The shape and size of the electrode are customized according to the geological conditions and remediation requirements of the contaminated area, including rod-shaped, mesh-shaped, sheet-shaped, or tubular. The electrode can be arranged vertically, horizontally, inclinedly, or in combination, with a spacing range of 1-5 m. The depth is determined according to the contamination depth and the location of the groundwater aquifer, ensuring that the electrode can effectively cover the contaminated area and generate a uniform electric field distribution, promoting the formation of the stable phase of ferric arsenate and the efficient progress of the remediation reaction.

[0015] Furthermore, the multi-parameter sensor includes one or more combinations of high-precision arsenic concentration sensors, redox potential sensors, pH sensors, temperature sensors, groundwater level and flow rate sensors, heavy metal ion sensors, and other parameter sensors related to environmental remediation. The sensor accuracy is not less than 5%, the response time is not greater than 30 minutes, and the data acquisition frequency ranges from once per minute to once every 24 hours. It is reasonably set according to the remediation process and pollution change characteristics, and has data storage, wireless transmission, and self-diagnostic functions to ensure the accuracy and reliability of the data, providing comprehensive and real-time environmental monitoring data support for the intelligent control system.

[0016] Furthermore, the central control system is a distributed intelligent control system based on a computer or microprocessor, possessing modules for data reception, storage, processing, analysis, modeling and prediction, and intelligent decision-making. It can perform real-time analysis and in-depth mining of data fed back from multi-parameter sensors, and dynamically establish mathematical models of the pollution remediation process using machine learning, neural networks, and fuzzy control algorithms. It can predict the remediation process and effects, automatically generate optimal electrochemical parameter adjustment schemes and supplementary dosing strategies for slow-release ferrous salt capsules and oxidants, and send instructions to the automated control interface of the remediation equipment to achieve precise, efficient, and intelligent control of the remediation process. At the same time, the system has remote monitoring, fault alarm, and data visualization display functions, which facilitates operators to grasp the remediation status in real time and manage it effectively.

[0017] Furthermore, the precise dosage of the slow-release ferrous salt capsules in the soil is 0.5-3.0 kg / m³. 2 The precise dosage for application in groundwater aquifers is 1.0-4.0 kg / m³.3 The application method is selected based on soil texture, groundwater flow characteristics and pollution distribution characteristics, using different technical means such as mechanical mixing, grouting, planting, high-pressure grouting, and directional drilling injection to ensure the uniform distribution and effective contact of the slow-release ferrous salt capsules in the polluted medium, thereby improving the uniformity and stability of the remediation effect.

[0018] Furthermore, the initial concentration of the persulfate or other oxidant is 0.05-0.3 mol / L. The dosage is precisely calculated and dynamically adjusted according to the volume of the contaminated area, the degree of contamination, the groundwater flow rate, and the remediation cycle. At the same time, the stoichiometric relationship and synergistic effect of the chemical reaction between the oxidant and the slow-release ferrous salt capsules are considered to achieve efficient and economical remediation results and avoid the risk of secondary pollution caused by excessive use of oxidants.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Intelligent slow-release material design and synergistic reaction mechanism: The slow-release ferrous salt capsule developed in this invention has a specially optimized internal structure. The unique pore structure and surface functional groups of the biochar carrier not only provide a stable loading environment for the ferrous salt, but also effectively regulate the release kinetics of the ferrous salt, enabling it to be released slowly and continuously within the polluted area. When it encounters oxidants such as persulfate, a complex chemical reaction occurs between the ferrous salt and the oxidant, generating ferric arsenate precipitate with a three-dimensional network structure. This structure has strong adsorption sites and encapsulation effects for arsenic ions, which can efficiently capture and fix arsenic in soil and groundwater, transforming it into a stable form with extremely low environmental risk. At the same time, the intermediate products generated during the reaction can further promote the synergistic degradation of other pollutants in the soil, demonstrating a good synergistic effect in environmental remediation and broadening the application scope and depth of remediation technology.

[0021] (2) Integration of Dynamic Electrochemical Regulation and Intelligent Feedback System: This invention innovatively integrates electrochemical regulation technology with an intelligent monitoring and feedback system. Electrochemical regulation not only breaks through the limitations of traditional remediation technologies that passively adapt to groundwater redox conditions, but also actively shapes a microenvironment conducive to the formation and survival of the stable phase of ferric arsenate through precise voltage and current control, thereby improving the performance and environmental adaptability of remediation materials from the source. The supporting real-time monitoring system can accurately capture minute changes in multiple key indicators such as arsenic concentration, redox potential, and pH, and transmit these data to the intelligent control system in real time. The control system uses advanced data processing algorithms and model prediction technology to dynamically evaluate and make decisions on the remediation process, automatically regulate electrochemical parameters and remediation material replenishment strategies, and ensure that the remediation process always proceeds along an efficient and stable trajectory. Even in the face of sudden changes in pollution load or fluctuations in environmental conditions, it can quickly and accurately respond to ensure the high-quality achievement of remediation goals. Attached Figure Description

[0022] Figure 1 This is a structural diagram of a sustained-release ferrous salt capsule, where 1 represents the biochar shell and 2 represents the encapsulated ferrous salt core.

[0023] Figure 2 This is a schematic diagram of the overall layout of the in-situ dynamic soil remediation system, where 3 represents the contaminated soil area, 4 represents the added slow-release ferrous salt capsules, 5 represents the electrode, 6 represents the sensor, 7 represents the control system, and 8 represents the oxidant injection device. Detailed Implementation

[0024] 1. Preparation of sustained-release ferrous salt capsules

[0025] High-quality biochar materials are selected, possessing characteristics such as high specific surface area, abundant pore structure, and active surface functional groups. Through fine pulverization, the particle size is precisely controlled within the range of 0.2-2 mm to balance mechanical strength and reactivity. High-purity ferrous salts, such as ferrous sulfate or ferrous chloride, are selected and dissolved in ultrapure water to prepare a homogeneous solution with a concentration between 0.1-2 mol / L. Appropriate amounts of stabilizers and crystal form modifiers are added to optimize the subsequent coating effect and the crystal morphology of the ferrous salts.

[0026] An advanced impregnation-heat treatment coating process is employed, in which biochar and ferrous salt solution are mixed at a precise solid-liquid ratio and impregnated under specific temperature, pressure, and stirring conditions. This allows the ferrous salt solution to fully penetrate the internal pores and surface micro / nano structures of the biochar. Subsequently, the impregnated biochar is placed in a temperature-controlled drying device and dried according to a preset heating rate and holding time. During this process, ferrous salt gradually forms a stable crystalline structure within the biochar and undergoes weak chemical bonding with the biochar carrier, ultimately forming a core-shell structured, sustained-release ferrous salt capsule. By precisely controlling various parameters in the preparation process, the ferrous salt loading, release rate, and structural stability of the capsules can be accurately regulated to meet the remediation needs of different pollution scenarios.

[0027] 2. Construction and Operation of In-situ Remediation System

[0028] In the preliminary investigation phase of the contaminated site, advanced geophysical exploration technologies and environmental monitoring methods are used to conduct a comprehensive and accurate assessment of the extent, depth, concentration distribution, and hydrogeological conditions of the contaminated soil and groundwater. Detailed three-dimensional maps and hydrogeological profiles of the contaminated area are generated, providing a scientific basis for the rational layout of the remediation system. Based on the investigation results, high-performance electrodes are implanted within the contaminated area according to an optimized grid spacing and depth. The electrode material is a novel composite material with good conductivity, strong corrosion resistance, and no risk of introducing secondary pollution. Its surface undergoes special treatment to enhance electrochemical reactivity with the surrounding medium and the uniformity of current distribution. Simultaneously, a multi-parameter sensor network is deployed at key locations. These sensors can monitor multiple environmental parameters in real time and in situ, including arsenic concentration, redox potential, pH, temperature, groundwater level, and flow velocity, and transmit the data to the central control system via a wireless transmission module.

[0029] The prepared slow-release ferrous salt capsules were precisely administered into contaminated soil and groundwater aquifers using specialized equipment, according to pre-calculated dosage and spatial distribution patterns. For soil remediation, mechanical stirring, grouting, or planting methods were employed to ensure full contact and uniform mixing between the capsules and soil particles. For groundwater remediation, precise water injection and flow field control technologies were used to ensure the capsules diffused systematically and adsorbed onto the aquifer within the groundwater flow field. Simultaneously, an appropriate amount of persulfate or other oxidants was injected into the contaminated area using an oxidant injection device. The injection method and flow rate were dynamically adjusted based on the characteristics of the contaminated medium, groundwater flow characteristics, and real-time feedback on the remediation progress to ensure an efficient and complete chemical reaction between the oxidant and the slow-release ferrous salt capsules.

[0030] The electrochemical control system is activated. Based on real-time environmental parameters fed back by sensors, the central control system dynamically calculates and sets optimal electrochemical parameters, such as voltage, current density, and energizing sequence, using intelligent algorithms. Under electrochemical action, the redox environment of groundwater undergoes a directional change, promoting the in-situ formation of ferrous arsenate around the slow-release ferrous salt capsules and on the surface of the contaminated medium. This continuously induces ferrous arsenate to transform into a more thermodynamically stable crystal form, enhancing the fixation effect and long-term stability of arsenic. Throughout the remediation process, the system continuously collects sensor data, assessing the remediation progress and effectiveness in real time. If any local remediation anomalies or signs of pollution rebound are detected, the system immediately and automatically adjusts the electrochemical parameters, replenishes the slow-release ferrous salt capsules, and adjusts the dosage and location of the oxidant to ensure the comprehensive and stable achievement of the remediation goals until the arsenic concentration in the soil and groundwater drops below the predetermined safety standard, and undergoes rigorous environmental quality acceptance monitoring and ecological risk assessment.

[0031] Example

[0032] Example 1

[0033] Site Overview: Due to long-term application of arsenic-containing pesticides, the average arsenic content in the soil of a certain farmland is as high as 50 mg / kg. The contamination depth is concentrated in the range of 0-1 m. The soil texture is mainly loam, and the groundwater level is relatively deep. The relatively independent shallow soil contamination environment provides convenient conditions for remediation.

[0034] Preparation of sustained-release ferrous salt capsules: Biochar derived from agricultural waste straw was selected, pre-oxidized and activated, and then pulverized to a particle size of 0.5-1 mm. A 0.5 mol / L ferrous sulfate solution was prepared, and 2% (mass fraction) of a crystal form regulator was added. An impregnation-heat treatment process was used: impregnation at 25℃ and atmospheric pressure for 24 hours, followed by heating to 80℃ at a rate of 5℃ / h and drying at that temperature for 12 hours to obtain sustained-release ferrous salt capsules. The initial ferrous salt loading of the capsules was determined to be 0.35 g Fe. 2+ / g biochar has excellent slow-release properties. Under simulated soil environmental conditions, the ferrous salt release rate is 0.02 mg / (g·d), and it can be released continuously for more than 60 days.

[0035] Remediation System Construction and Operation: Within the contaminated farmland area, stainless steel electrodes were vertically driven into the soil at 2 m × 2 m intervals, with an effective depth of 1.2 m, ensuring complete coverage of the contaminated soil layer. Multilayer arsenic concentration sensors, redox potential sensors, and pH sensors were deployed on the soil surface and at depths of 0.5 m and 1 m, respectively, forming a three-dimensional monitoring network. All sensors were connected to the control system via wireless modules. Using a small rotary tillage device, slow-release ferrous salt capsules were evenly mixed into the soil at a precise dosage of 1.2 kg per square meter. Simultaneously, persulfate solution was uniformly injected into the soil at an initial concentration of 0.12 mol / kg, representing 10% of the soil volume, via a soil injection device. The electrochemical control system was activated, with the initial electrode voltage set at 1.2 V and the current density at 0.5 mA / cm². 2 The control system automatically optimizes electrochemical parameters every 24 hours based on real-time sensor feedback data, and replenishes slow-release ferrous salt capsules and persulfate as needed according to soil moisture and remediation progress. After a 90-day remediation period, the average arsenic content in the soil decreased to 4.2 mg / kg, reaching the Class II land use screening value (30 mg / kg) in the National Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard. Furthermore, the remediated soil structure was not significantly damaged, crop growth was good, and field trials showed that the arsenic content in agricultural products met food safety standards.

[0036] Key technical indicators: The initial ferrous salt loading of the sustained-release ferrous salt capsules is 0.35 g Fe. 2+ / g biochar, precise dosage 1.2 kg / m³ 2 The initial concentration of persulfate was 0.12 mol / kg, the electrode voltage was 1.2 V, and the current density was 0.5 mA / cm². 2 The remediation period was 90 days, and the average arsenic content in the soil after remediation was 4.2 mg / kg.

[0037] Example 2

[0038] Site Overview: Groundwater surrounding a former electronics industrial plant has been contaminated by long-term leakage of arsenic-containing cleaning wastewater. The average arsenic concentration in the groundwater is 1.8 mg / L, and the contamination extends to a 500-meter radius around the plant. 2 In this area, the groundwater level is between 2 and 3 meters deep, and the groundwater is mainly pore water with an aquifer thickness of about 5 meters. The water flow is slow and is affected by municipal water supply pipelines and underground structures around the factory area. The restoration process must fully consider the utilization of underground space and the protection of the surrounding environment.

[0039] Preparation of sustained-release ferrous salt capsules: Wood-based biochar was used as a carrier, and after high-temperature pyrolysis and surface modification, the particle size was controlled to be 0.8-1.2 mm. A 0.7 mol / L mixed solution of ferrous sulfate and ferrous chloride (molar ratio 4:1) was prepared, and 3% (mass fraction) of stabilizer was added. A dynamic impregnation-microwave-assisted drying process was used, with impregnation at 30℃ and microwave power 300 W for 12 hours, followed by drying for 8 hours to obtain sustained-release ferrous salt capsules. Performance testing showed that the initial ferrous salt loading of the capsules was 0.5 g Fe. 2+ / g biochar, under simulated groundwater environment conditions, has a ferrous salt release rate of 0.03 mg / (g·d) and a release cycle of 120 days or more. The release process is less affected by groundwater flow and pH changes, and has good slow-release stability and environmental adaptability.

[0040] Remediation System Construction and Operation: Titanium alloy electrodes were deployed upstream and downstream of the groundwater flow direction at a spacing of 3 m × 3 m, with a depth of 7 m, penetrating the entire aquifer. Arsenic concentration sensors, redox potential sensors, and flow velocity and direction sensors were installed at depths of 2.5 m, 3.5 m, and 4.5 m within the aquifer, respectively, constructing a comprehensive groundwater monitoring system. Monitoring data was transmitted to the central control system in real time. Using high-pressure grouting technology, slow-release ferrous salt capsules were precisely injected into the contaminated aquifer at a dosage of 2.2 kg per cubic meter, ensuring that the capsules formed an effective arsenic adsorption and fixation barrier along the groundwater flow path. Simultaneously, persulfate solution was injected into the aquifer through decentralized injection wells, achieving a persulfate concentration of 0.16 mol / L in the groundwater, with the injection area covering the entire contamination plume. The electrochemical control system was activated, with the initial electrode current set at 0.6 A and the upper limit of voltage at 2.0 V. Based on real-time groundwater parameters fed back by sensors, the control system dynamically adjusted the electrochemical parameters every 12 hours using an intelligent algorithm. It also adjusted the replenishment location and dosage of slow-release ferrous salt capsules and persulfate according to groundwater flow and pollutant plume migration. After 180 days of remediation operation, the average concentration of arsenic in the groundwater decreased to 0.03 mg / L, far below the Class III standard (0.05 mg / L) in the national groundwater quality standards. Furthermore, the groundwater quality remained stable after remediation, and surrounding municipal water supply pipelines and underground structures were not affected by construction. Ecological environment monitoring showed that the surrounding soil and surface water environmental quality remained stable.

[0041] Key technical indicators: The initial ferrous salt loading of the sustained-release ferrous salt capsules is 0.5 g Fe. 2+ / g biochar, precise dosage 2.2 kg / m³ 3The initial persulfate concentration was 0.16 mol / L, the electrode current was 0.6 A, the upper limit of voltage was 2.0 V, the remediation period was 180 days, and the average arsenic concentration in the groundwater after remediation was 0.03 mg / L.

[0042] Example 3

[0043] Site Overview: A tailings dam in a mining area experienced a leakage accident, resulting in severe arsenic contamination of the surrounding soil and groundwater. The arsenic content in the soil reached 100-150 mg / kg, while the arsenic concentration in the groundwater was 4-6 mg / L. The contamination depth reached 0-5 m. Furthermore, the soil texture in the contaminated area was uneven, with an upper layer of gravel and a lower layer of clay. The groundwater flow was complex, containing various heavy metal ions and acidic substances, making remediation extremely difficult. Simultaneously, the mining area was still operational, requiring the remediation process to be coordinated with mining production activities, placing extremely high demands on the efficiency, safety, and flexibility of the remediation technology.

[0044] Preparation of sustained-release ferrous salt capsules: Biochar prepared from plant residues around the mining area was modified to enhance its acid and alkali resistance and selective adsorption of heavy metal ions, with a particle size of 0.3-0.6 mm. A 0.9 mol / L mixed solution of ferrous sulfate and ferrous chloride (molar ratio 3:2) was prepared, with 4% (mass fraction) of a special crystal form regulator added. An ultrasonic-assisted impregnation-vacuum drying process was used, with impregnation at 40℃ and 40 kHz for 8 hours, followed by drying under a vacuum of -0.08 MPa for 10 hours to obtain sustained-release ferrous salt capsules. Performance evaluation showed that the initial ferrous salt loading of the capsules was as high as 0.6 g Fe. 2+ / g biochar, under the complex simulated pollution environment of the mining area, the ferrous salt release rate is stable at 0.04 mg / (g·d), and it can synergistically form a composite precipitate with a variety of heavy metal ions, which broadens the application range of remediation materials and shows good multifunctional remediation potential and environmental adaptability.

[0045] System Construction and Operation: In the contaminated area surrounding the tailings dam, considering soil stratification and groundwater flow characteristics, a layered electrode arrangement was adopted. Graphite electrodes were implanted in the gravel layer at 1.5 m × 1.5 m intervals to a depth of 2 m; stainless steel electrodes were implanted in the clay layer at 2.5 m × 2.5 m intervals to a depth of 3 m, forming a vertically integrated electrode network. Multi-parameter sensor combinations, including high-precision arsenic concentration sensors, redox potential sensors, pH sensors, temperature sensors, and heavy metal ion sensors, were deployed at the soil-groundwater interface and key locations within the groundwater aquifer. This enabled comprehensive and detailed monitoring and data acquisition of the contaminated environment. All sensor data was transmitted to the central control system via fiber optic cable, ensuring high-speed, stable, and interference-resistant data transmission. Using a zoned dosing technique, slow-release ferrous salt capsules were precisely added at 2.5 kg per cubic meter in the upper gravel layer and 1.8 kg per cubic meter in the lower clay layer. These capsules were then injected into the corresponding soil layers through different inlets. Soil mixing equipment ensured uniform distribution of the capsules in the gravel layer, while in the clay layer, they diffused slowly due to their own weight and groundwater seepage. Simultaneously, a layered injection system injected a persulfate solution (initial concentration 0.2 mol / L) into the gravel layer and a composite oxidant solution (persulfate to hydrogen peroxide molar ratio 1:1, initial concentration 0.18 mol / L) into the clay layer. The injection volume was dynamically adjusted based on soil characteristics and real-time monitoring data. An electrochemical control system was activated, setting electrochemical parameters for different soil layers and electrode combinations. The initial electrode voltage for the gravel layer was 1.5V, and the current density was 0.8 mA / cm². 2 The initial voltage of the clay layer electrode was 2.2 V, and the current density was 0.4 mA / cm². 2 The central control system, based on real-time feedback data from sensors, intelligently optimizes electrochemical parameters every 6 hours using a multi-layer neural network algorithm. It also flexibly adjusts the replenishment strategies for slow-release ferrous salt capsules and oxidants, electrode operating status, and zoning control measures for the remediation area based on the migration and diffusion trends of the pollution plume and the impact of mining activities. After 120 days of intensive remediation, the arsenic content in the soil decreased to 12-18 mg / kg, and the arsenic concentration in groundwater decreased to 0.02-0.04 mg / L. Simultaneously, the concentrations of other heavy metal ions in the soil and groundwater also significantly decreased, meeting the corresponding national environmental quality standards and mining area remediation targets. Furthermore, the remediation process did not significantly interfere with normal production activities in the mining area, achieving coordinated development between pollution remediation and industrial production.

[0046] Key technical indicators: The initial ferrous salt loading of the sustained-release ferrous salt capsules is 0.6 g Fe. 2+ / g biochar, precise dosage 2.5 kg / m² for gravel layer 3 Clay layer 1.8 kg / m3 The initial concentration of persulfate in the gravel layer was 0.2 mol / L, and the concentration of the composite oxidant in the clay layer was 0.18 mol / L (persulfate to hydrogen peroxide molar ratio 1:1). The electrode voltage in the gravel layer was 1.5 V, and the current density was 0.8 mA / cm². 2 The clay layer electrode voltage is 2.2 V, and the current density is 0.4 mA / cm². 2 The remediation period is 120 days. After remediation, the arsenic content in the soil is 12-18 mg / kg, and the arsenic concentration in the groundwater is 0.02-0.04 mg / L.

[0047] Example 4

[0048] Site Overview: The soil and groundwater of reclaimed land in a coastal chemical industrial park are contaminated with arsenic from historical sources of surrounding chemical enterprises. The arsenic content in the soil is 40-80 mg / kg, and the arsenic concentration in the groundwater is 1.2-2.5 mg / L. The contamination depth is 0-3 m. The soil is alkaline and salinized, and the groundwater is affected by seawater intrusion, exhibiting high mineralization and a complex and variable hydrochemical environment. The remediation process must also consider the special meteorological conditions and ecological sensitivity of the coastal area to ensure the friendliness of the remediation technology to the marine ecological environment and the stability of the remediation process.

[0049] Preparation of sustained-release ferrous salt capsules: Biochar prepared from seaweed processing waste was desalinated, washed, and surface functionalized to adapt to saline-alkali environments, with a particle size of 0.4-0.8 mm. A 0.6 mol / L ferrous sulfate solution was prepared, and 3.5% (mass fraction) of a salt-tolerant crystal form regulator was added. An impregnation-freeze-drying process was used: impregnation at 2℃ for 16 hours, followed by freeze-drying at -50℃ and -0.1 MPa for 24 hours to obtain sustained-release ferrous salt capsules. Performance testing showed that the initial ferrous salt loading of the capsules was 0.45 g Fe. 2+ / g biochar, in simulated saline-alkali soil and highly mineralized groundwater environments, showed a stable ferrous salt release rate of 0.025 mg / (g·d), and could effectively resist the competitive adsorption interference of salt ions, ensuring the stable generation of ferric arsenate and the efficient fixation of arsenic, demonstrating good salt and alkali resistance and marine environmental adaptability.

[0050] System Construction and Operation: Within the contaminated area of ​​the coastal chemical industrial park, based on the topography of the reclaimed soil and the characteristics of groundwater flow, corrosion-resistant fiberglass electrodes are arranged at 2.5 m × 2.5 m intervals on the inner side of the seawall. The electrodes reach a depth of 3.5 m, penetrating the entire contaminated soil layer and partially extending into the underlying stable silty clay layer. Specialized arsenic concentration sensors, redox potential sensors, and conductivity sensors suitable for saline-alkali environments and highly mineralized water bodies are installed at the soil surface, at a depth of 1.5 m, and within the groundwater aquifer, respectively, constructing a multi-layered, three-dimensional monitoring network. Sensor data is transmitted via waterproof and moisture-proof transmission lines to a moisture-proof central control system, ensuring the reliability of data acquisition and transmission under harsh coastal weather conditions. Using precise mechanical mixing equipment, slow-release ferrous salt capsules were uniformly mixed into saline-alkali soil at a precise dosage of 1.6 kg per square meter at a depth of 0-1.5 m. For soil and groundwater aquifers at a depth of 1.5-3 m, capsules were injected into the target area at a dosage of 2.0 kg per cubic meter using directional drilling injection technology. Simultaneously, persulfate solution was injected into the soil and groundwater through corrosion-resistant injection pipes, achieving a persulfate concentration of 0.14 mol / kg in the soil and 0.13 mol / L in the groundwater, covering the entire contaminated area. The electrochemical control system was activated, with the initial electrode voltage set at 1.6 V and the current density at 0.7 mA / cm². 2 The control system, based on real-time feedback from sensors regarding saline-alkali soil and highly mineralized groundwater parameters, intelligently adjusts electrochemical parameters every 18 hours using an adaptive control algorithm. It also optimizes the replenishment scheme of slow-release ferrous salt capsules and persulfate, electrode operating modes, and monitoring frequency in a timely manner according to the impact of coastal meteorological factors such as tidal changes and rainfall on groundwater levels and quality. After a 150-day remediation period, the arsenic content in the soil decreased to 8-12 mg / kg, and the arsenic concentration in the groundwater decreased to 0.03-0.05 mg / L. Furthermore, the salinity of the remediated soil and the mineralization of the groundwater were effectively regulated. Monitoring of the surrounding marine ecological environment showed that marine biodiversity and water quality remained stable, without significant disturbance from the remediation process. The remediation target for arsenic pollution in soil and groundwater under complex coastal conditions was successfully achieved.

[0051] Key technical indicators: The initial ferrous salt loading of the sustained-release ferrous salt capsules is 0.45 g Fe. 2+ / g biochar, precise application rate: 1.6 kg / m² in the soil layer 2 Aquifer 2.0 kg / m 3 The initial persulfate concentrations were 0.14 mol / kg in soil and 0.13 mol / L in groundwater. The electrode voltage was 1.6 V, and the current density was 0.7 mA / cm². 2The remediation period is 150 days. After remediation, the arsenic content in the soil is 8-12 mg / kg, and the arsenic concentration in the groundwater is 0.03-0.05 mg / L.

Claims

1. A method for in-situ dynamic remediation of arsenic contamination in soil and groundwater based on ferric arsenate-based materials, characterized in that, Includes the following steps: (1) Preparation of sustained-release ferrous salt capsules: Ferrous salt is coated into a modified biochar carrier using a specific process to form a composite material with a core-shell structure and precise sustained-release performance; The preparation method of the sustained-release ferrous salt capsules is as follows: Biochar material with high specific surface area, abundant pore structure, and active surface functional groups is selected and subjected to pre-oxidation, activation, acid-base treatment, or surface functionalization modification to enhance its interaction with ferrous salt and its sustained-release performance. Ferrous salt is dissolved in deionized water to prepare a mixed solution containing stabilizers, crystal form regulators, and anti-interference additives, with a concentration range of 0.1-2 mol / L. The mixed solution of biochar and ferrous salt is treated under specific temperature, pressure, stirring rate, and time conditions using impregnation-heat treatment, impregnation-freeze-drying, impregnation-microwave-assisted drying, or ultrasonic-assisted impregnation-vacuum drying processes to uniformly coat the inside and surface of the biochar with ferrous salt. After drying, curing, and post-treatment processes, a core-shell structured sustained-release ferrous salt capsule is formed. The initial ferrous salt loading of the sustained-release ferrous salt capsule is 0.2-0.7 g Fe. 2+ / g biochar, ferrous salt release rate is 0.01-0.05 mg / (g·d), release period is 60-180 days or more; (2) The slow-release ferrous salt capsules are precisely added to the soil or groundwater area contaminated with arsenic, and the capsules are made to come into full contact with the contaminated medium through external force or gravity diffusion. (3) Inject persulfate or other oxidants into the contaminated area, and dynamically adjust the type, concentration and injection method of the oxidant according to the characteristics of the contaminated medium and the remediation process; (4) Using an electrochemical control method, a directional electric field is generated by electrodes arranged in the polluted area. The voltage range of the electrochemical control is 0.5-3.5 V, and the current density range is 0.1-1.5 mA / cm². 2 The energizing sequence can be continuous, intermittent, or pulsed, thereby altering the redox environment of groundwater and promoting the formation of stable phases and crystal transformation of ferric arsenate. (5) Use multi-parameter sensors to monitor the arsenic concentration, redox potential, pH, temperature, groundwater level and flow rate in the polluted area in real time, and transmit the data to the central control system; (6) The central control system dynamically adjusts electrochemical parameters, including voltage, current density, and energizing sequence, based on feedback data from multi-parameter sensors and using intelligent algorithms. At the same time, it intelligently decides the dosage and location of the slow-release ferrous salt capsules and oxidant to ensure the efficiency, stability and adaptability of the remediation process.

2. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The ferrous salt is one or a mixture of ferrous sulfate, ferrous chloride, and ferrous oxalate, and the purity of the ferrous salt is not less than 98% and the particle size is less than 0.1 mm to ensure its uniform dispersion and good coating performance in the biochar carrier.

3. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The oxidant is one or more of persulfate, hydrogen peroxide, ozone, and potassium permanganate, and the purity of the oxidant is not less than 95%. The injection concentration range is 0.05-0.3 mol / L, which is dynamically adjusted according to the degree of pollution and the remediation process. The oxidant can be injected in one go, in multiple injections, continuously, or in a pulse to achieve the best oxidation reaction effect and economic balance.

4. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The electrode material is a composite structure of one or more of stainless steel, graphite, titanium, and zinc. The shape and size of the electrode are customized according to the geological conditions and remediation requirements of the contaminated area, including rod-shaped, mesh-shaped, sheet-shaped, or tubular. The electrode can be arranged vertically, horizontally, inclinedly, or in combination, with a spacing of 1-5 m. The depth is determined according to the contamination depth and the location of the groundwater aquifer, ensuring that the electrode can effectively cover the contaminated area and generate a uniform electric field distribution, promoting the formation of the stable phase of ferric arsenate and the efficient progress of the remediation reaction.

5. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The multi-parameter sensor includes one or more combinations of high-precision arsenic concentration sensors, redox potential sensors, pH sensors, temperature sensors, groundwater level and flow rate sensors, heavy metal ion sensors, and other parameter sensors related to environmental remediation. The sensor accuracy is not less than 5%, the response time is not greater than 30 minutes, and the data acquisition frequency is once per minute to once every 24 hours. The sensor is reasonably set according to the remediation process and pollution change characteristics, and has data storage, wireless transmission, and self-diagnostic functions to ensure the accuracy and reliability of the data, providing comprehensive and real-time environmental monitoring data support for the intelligent control system.

6. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The central control system is a distributed intelligent control system based on a computer or microprocessor. It has modules for data reception, storage, processing, analysis, modeling and prediction, and intelligent decision-making. It can perform real-time analysis and in-depth mining of data fed back by multi-parameter sensors. Using machine learning, neural networks, and fuzzy control algorithms, it dynamically establishes a mathematical model of the pollution remediation process, predicts the remediation progress and effect, automatically generates the optimal electrochemical parameter adjustment scheme and the supplementary dosing strategy of slow-release ferrous salt capsules and oxidants, and sends instructions to the automated control interface of the remediation equipment to achieve precise, efficient, and intelligent control of the remediation process. At the same time, the system has remote monitoring, fault alarm, and data visualization display functions, which facilitates operators to grasp the remediation status in real time and manage it effectively.

7. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The precise dosage of the slow-release ferrous salt capsules in the soil is 0.5-3.0 kg / m³. 2 The precise dosage for application in groundwater aquifers is 1.0-4.0 kg / m³. 3 The application method is selected based on soil texture, groundwater flow characteristics, and pollution distribution characteristics, including mechanical stirring, grouting, and directional drilling injection, to ensure uniform distribution and effective contact of the slow-release ferrous salt capsules in the polluted medium, thereby improving the uniformity and stability of the remediation effect.

8. The in-situ dynamic soil and groundwater arsenic contamination remediation method according to claim 1, characterized in that, The initial concentration of the persulfate or other oxidant is 0.05-0.3 mol / L. The dosage is precisely calculated and dynamically adjusted according to the volume of the contaminated area, the degree of contamination, the groundwater flow rate, and the remediation cycle. At the same time, the stoichiometric relationship and synergistic effect of the chemical reaction between the oxidant and the slow-release ferrous salt capsules are considered to achieve efficient and economical remediation results and avoid the risk of secondary pollution caused by excessive use of oxidants.

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