Sodium alginate embedded iron-carbon microcapsule material for remediation of cadmium and arsenic polluted soil and preparation method of sodium alginate embedded iron-carbon microcapsule material

Abstract

The invention discloses a sodium alginate embedded iron-carbon microcapsule material for repairing cadmium and arsenic polluted soil and a preparation method of the sodium alginate embedded iron-carbon microcapsule material, and belongs to the technical field of soil heavy metal pollution repairing materials. The material comprises straw biochar, high-iron steel slag powder, a sulfydryl acetylated chitosan-iron monatomic cluster compound, a boron-doped graphitized carbon coated cobalt ferrite nanosheet, sodium alginate, calcium chloride and sodium carbonate. Wherein the sulfydryl acetylated chitosan is prepared by reacting chitosan with sulfydryl acetic anhydride, dialyzing and drying, and performing solvothermal reaction with ferric nitrate under high pressure. The preparation method comprises the following steps: pyrolyzing and drying the straw biochar, reacting the high-iron steel slag with sulfuric acid, adding the biochar, adjusting the pH value, adding sodium carbonate, mixing to obtain an iron-carbon-based passivation material, mixing with two modified compounds, mixing with a sodium alginate solution, dropwise adding a calcium chloride solution, and stirring and curing. The material can be applied to remediation of cadmium and arsenic polluted soil.

Description

Technical Field

[0001] This invention relates to the field of soil heavy metal pollution remediation materials, specifically to a sodium alginate-encapsulated iron-carbon microcapsule material for the remediation of cadmium and arsenic contaminated soil and its preparation method. Background Technology

[0002] Cadmium, a highly bioaccumulative heavy metal, can be absorbed by plant roots and accumulate in grains, remaining in the human body for a long time and causing damage to multiple organs. Arsenic, on the other hand, exists in the soil in a highly toxic form and easily migrates through groundwater or is absorbed into the human metabolic system through crops, interfering with enzyme activity, damaging cell structure, and causing irreversible effects on children's development and adults' health. The combined pollution of cadmium and arsenic is further complicated by the differences in their migration and chemical forms in the soil. Cadmium easily combines with minerals in the soil but is easily lost due to acidic or alkaline environments, while arsenic exists in an adsorbed or covalent state but is easily reduced to a more toxic form. Traditional remediation technologies struggle to simultaneously achieve the stable immobilization of both.

[0003] Existing soil heavy metal remediation technologies are mainly divided into three categories: physical remediation, chemical remediation, and bioremediation. Physical remediation methods, such as soil replacement and water management, can directly reduce pollutant exposure, but they are costly, complex to operate, and prone to damaging soil structure. Chemical remediation techniques, such as chemical leaching and solvent extraction, can rapidly reduce heavy metal concentrations, but they are prone to secondary pollution and difficult to apply on a large scale. Bioremediation, including phytoremediation and microbial remediation, is environmentally friendly but has a long cycle and low efficiency. Among these, in-situ passivation technology has become the preferred solution for large-scale contaminated soil remediation due to its advantages such as low investment, high efficiency, simple operation, and simultaneous improvement of soil physicochemical properties. Biochar, as a typical passivation material, has a certain adsorption capacity for heavy metal cations such as cadmium and lead due to its rich porous structure and surface functional groups, but its adsorption effect on arsenic is limited. Although iron-based materials can bind with arsenic through redox reactions or co-precipitation, they are easily affected by environmental factors such as alternating soil moisture and freezing-thaw cycles, leading to insufficient exposure of active sites, and they are prone to loss of passivation capacity due to oxidation after long-term use. Furthermore, traditional passivation materials are mostly single-component or simple compound formulations, lacking targeted designs for the synergistic effects of cadmium and arsenic, making it difficult to meet the remediation needs of complex contaminated soils. For example, in a simple mixture of biochar and iron-based materials, the interfacial interaction between the two is weak, failing to form a stable composite structure, resulting in both cadmium adsorption capacity and arsenic fixation efficiency falling short of expectations. While single iron-based materials have some arsenic fixation capacity, their complexation capacity for cadmium is insufficient, and they are prone to releasing iron ions due to soil pH fluctuations, posing a risk of secondary pollution.

[0004] To address the aforementioned technical bottlenecks, researchers have recently attempted to improve passivation efficiency through material modification or composite technologies. For example, some studies have introduced organic modifiers into biochar to enhance its complexation capacity for cadmium; others have improved iron-based materials by loading nano-iron or metal oxides to enhance their antioxidant capacity and arsenic fixation efficiency. However, these modified materials still face many challenges in practical applications: organic modifiers are easily lost due to soil microbial degradation, nanomaterials are prone to aggregation due to their small particle size, and most materials lack slow-release functions, leading to a significant decline in remediation effectiveness over time. Sodium alginate encapsulation technology can effectively slow the loss of active components and improve the stability of materials in soil by forming a semi-permeable membrane structure, but its encapsulated core material is mostly unmodified biochar or ordinary iron source, without designing functionalized components to meet the chemical transformation requirements of cadmium and arsenic co-polluted soils. Therefore, developing a novel iron-carbon-based microcapsule material with high adsorption capacity, synergistic passivation mechanism, and environmental adaptability has become an important research direction in the field of cadmium and arsenic co-polluted soil remediation. This invention, by introducing two functionalized modified components and combining them with sodium alginate encapsulation technology, is expected to achieve efficient synergistic fixation of cadmium and arsenic and long-term stable release of materials, providing a new technical approach for solving the problem of remediation of soils with complex pollution. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium alginate-encapsulated iron-carbon microcapsule material for the remediation of cadmium and arsenic contaminated soil and its preparation method, which solves the technical problems of low synergistic passivation efficiency, easy loss of materials due to environmental factors, and long remediation cycle in existing cadmium and arsenic combined contaminated soil remediation technologies.

[0006] The present invention achieves the above objectives through the following technical solutions: A sodium alginate-encapsulated iron-carbon microcapsule material comprises the following raw materials in parts by weight: Straw biochar: 120-180 parts by weight; High-speed rail steel slag powder: 450-550 parts by weight; Thiothioacetylated chitosan-iron monoatomic cluster compound: 30-60 parts by weight; Boron-doped graphitized carbon-coated cobalt ferrite nanosheets: 30-60 parts by weight; Sodium alginate: 20-40 parts by weight; Calcium chloride: 420-580 parts by weight; Na2CO3: 40-45 parts by weight; The preparation method of the thiol acetylated chitosan-iron single-atom cluster compound includes: A1, dissolving chitosan obtained after decalcification and deproteinization of shrimp shells in acetic acid solution, stirring and dissolving at 40-42℃, adding mercaptoacetic anhydride, reacting at 60-64℃ under nitrogen protection, adjusting the pH to 6.8-7.2 with NaOH solution after the reaction, dialyzing the precipitate with deionized water, and freeze-drying to obtain thiol acetylated chitosan; A2, dissolving thiol acetylated chitosan in deionized water, adding ferric nitrate nonahydrate, ultrasonically dispersing and transferring to a high-pressure reactor, solvothermal reaction at 180-184℃, the solvent being a mixture of deionized water and ethanol, and simultaneously adding ascorbic acid, naturally cooling to room temperature after the reaction, collecting the precipitate by centrifugation and washing with deionized water and ethanol, and vacuum drying.

[0007] In this invention, the preparation process of the thiol-acetylated chitosan-iron single-atom cluster compound is divided into two steps. The core is to construct a functionalized carrier with high coordination ability through chemical modification and loading reaction. The first step is the thiol acetylation modification of chitosan: natural chitosan is obtained after decalcification and deproteinization of shrimp shells. Its molecular chain is rich in amino groups (-NH2) and hydroxyl groups (-OH). Chitosan is dissolved in acetic acid solution (providing a weakly acidic environment) and stirred at 40-42°C for 2-4 hours to allow the chitosan molecules to fully expand. Then, thioacetic anhydride (an unsaturated acid anhydride containing thiol groups (-SH)) is added, and the reaction is carried out at 60-64°C for 12-14 hours under nitrogen protection. Nitrogen protection can prevent the thiol groups from being oxidized and deactivated by oxygen in the air. The anhydride group (-CO-O-CO-) of thioacetic anhydride undergoes a ring-opening reaction with the amino groups of chitosan to generate derivatives containing thiol groups (-SH), while retaining some unreacted amino and hydroxyl groups. After the reaction, the pH was adjusted to 6.8-7.2 (close to the isoelectric point of chitosan) with sodium hydroxide solution to promote slight aggregation between chitosan molecules. Unreacted small molecule impurities were removed by dialysis with deionized water (molecular weight cutoff 3500 Da), and finally, freeze-drying yielded thioacetylated chitosan. The key to this step is that thiolation modification provides coordination sites for subsequent iron single-atom loading, while amino and hydroxyl groups enhance the interaction between the material and heavy metal ions. The second step is the loading and fixation of iron single-atom clusters: thioacetylated chitosan is dissolved in deionized water, and ferric nitrate nonahydrate (providing Fe) is added. 3+ The precursor is ultrasonically dispersed for 10-20 minutes to ensure uniform dispersion of iron ions in the solution; it is then transferred to a high-pressure reactor, and a mixed solvent of deionized water and ethanol is added (to adjust polarity and promote the reaction), along with ascorbic acid (as a reducing agent). The reactor is then subjected to a solvothermal reaction at 180-184℃ for 24-30 hours. The high temperature and pressure environment promotes the reaction of Fe... 3+ Ascorbic acid undergoes a coordination reaction with the thiol (-SH) and amino (-NH2) groups of thiol-acetylated chitosan, thereby transferring some of the Fe... 3+ Reduced to Fe 2+ or Fe0 The reaction forms atomically dispersed iron single-atom clusters. After the reaction is complete, the mixture is allowed to cool naturally to room temperature, centrifuged to collect the precipitate, and washed alternately with deionized water and ethanol to remove unreacted iron salts and impurities. Finally, it is vacuum dried to obtain the target product. In this process, the multifunctional groups (-SH, -NH2, -OH) of thiol-acetylated chitosan stably anchor iron single atoms to the surface through coordination, forming a composite cluster with high specific surface area and strong adsorption capacity, providing active sites for subsequent heavy metal adsorption.

[0008] According to a preferred embodiment of the present invention, the high-speed rail steel slag powder is purchased from Baowu Group steel slag (a by-product of steel smelting under Baowu Group, whose main components are Fe2O3, CaO, etc.). The shrimp shells were purchased from Zhoushan Marine Fisheries Company (by-products of aquatic product processing in coastal areas, which have undergone decalcification and deproteinization treatment). The acetic acid solution was purchased from Jiangsu Suopu Group (industrial grade glacial acetic acid, concentration ≥99%). The thioglycolic anhydride was purchased from Hubei Xingfa Group (industrial grade thioglycolic anhydride, purity ≥98%). The nitrogen gas was purchased from Hangzhou Oxygen Plant Group Co., Ltd. (industrial grade nitrogen, purity ≥99.9%). The NaOH solution was purchased from Zhongtai Chemical (industrial grade caustic soda solution, concentration ≥30%). The deionized water was purchased from Shanghai Binteer Water Treatment (industrial-grade deionized water, conductivity ≤10μS / cm). The ferric nitrate nonahydrate was purchased from Hubei Xingfa Group (industrial grade ferric nitrate nonahydrate, purity ≥98%). The high-pressure reactor was purchased from Weihai Chemical Machinery (GSH-300L type high-pressure reactor, working pressure ≤3MPa). The ethanol was purchased from Shandong Lukang Pharmaceutical Co., Ltd. (industrial grade anhydrous ethanol, purity ≥99.5%). The ascorbic acid was purchased from Northeast Pharmaceutical (pharmaceutical grade ascorbic acid, purity ≥99%). The sodium alginate was purchased from Qingdao Mingyue Seaweed (food-grade sodium alginate, viscosity ≥300mPa·s). The calcium chloride was purchased from Tangshan Sanyou Chemical (industrial grade calcium chloride, content ≥74%). The Na2CO3 was purchased from Zhongyuan Chemical (industrial grade sodium carbonate, purity ≥99.2%).

[0009] According to a preferred embodiment of the present invention, in step A1, the stirring and dissolution time at 40-42°C is 2-4 hours; the reaction time at 60-64°C is 12-14 hours.

[0010] According to a preferred embodiment of the present invention, in step A2, the ultrasonic dispersion time is 10-20 min; the solvothermal reaction time at 180-184℃ is 24-30 h; and the vacuum drying temperature is 60-64℃.

[0011] According to a preferred embodiment of the present invention, the preparation method of the boron-doped graphitized carbon-coated cobalt ferrite nanosheets includes: B1, dissolving cobalt nitrate hexahydrate, ferric nitrate and boric acid in deionized water, adding ammonia to adjust the pH to 8.8-9.2, and stirring at room temperature to generate a mixed metal hydroxide precursor; B2, centrifuging to collect the precipitate and washing it with deionized water, and dispersing it in an ethanol-water mixed solvent; adding pyrrole monomer to the dispersion, stirring and reacting at 0-2℃ under nitrogen protection to form polypyrrole-coated CoFe2O4, centrifuging to collect the precipitate and washing it with deionized water, and drying it at 80-84℃; mixing the polypyrrole-coated CoFe2O4 with boric acid, placing it in a tube furnace, heating it to 1000-1050℃ under an argon atmosphere and holding it thereafter, and grinding and sieving it after natural cooling.

[0012] In this invention, the preparation of boron-doped graphitized carbon-coated cobalt ferrite nanosheets involves three key steps: synthesis of layered double hydroxide (LDH) precursors, polypyrrole coating, and high-temperature graphitization. Efficient oxidation and fixation of arsenic are achieved through multi-level structural design. The first step is the preparation of a mixed metal hydroxide precursor: cobalt nitrate hexahydrate and ferric nitrate (providing Co) are mixed... 2+ Fe 3+ ) and boric acid (providing B) 3+ Dissolve in deionized water, add ammonia to adjust pH to 8.8-9.2 (weakly alkaline environment), and stir at room temperature for 30-40 minutes. Under these conditions, Co... 2+ Fe 3+ With OH - A precipitation reaction occurs, generating a CoFe layered double hydroxide (CoFe LDH) precursor, whose interlayer can adsorb B. 3+And it combines with it. The special layered structure of LDH provides an ordered growth template for the subsequent formation of cobalt ferrite, while the introduction of boric acid provides a boron source for subsequent boron doping. The second step is the formation of polypyrrole-coated cobalt ferrite: the precursor is centrifuged and washed with water, and dispersed in an ethanol-water mixed solvent (ethanol reduces the surface tension of the solution and promotes particle dispersion); pyrrole monomer (nitrogen-containing heterocyclic compound) is added, and stirred for 12-14 hours under nitrogen protection at 0-2℃ (low temperature suppresses side reactions). The pyrrole monomer undergoes an oxidative polymerization reaction under weakly alkaline conditions (possibly with dissolved oxygen in water or metal ions in the precursor as oxidants), generating polypyrrole (PPy) polymer chains, which are coated on the surface of CoFe LDH through electrostatic or coordination interactions, forming a polypyrrole-coated CoFe2O4 composite structure. In this step, the low temperature environment ensures uniform coating of polypyrrole and avoids particle agglomeration, while nitrogen protection prevents oxidative decomposition of pyrrole. The third step is high-temperature boron-doped graphitization: CoFe₂O₄ coated with polypyrrole is mixed with boric acid and placed in a tube furnace. The mixture is heated to 1000-1050℃ under an argon atmosphere (an inert gas to prevent oxidation) and held for 3-4 hours. Under high temperature conditions, the polypyrrole undergoes pyrolysis and carbonization, forming a porous graphitized carbon layer. Simultaneously, CoFe₂O₄ nanosheets grow directionally within the carbon layer. B₂O₃, produced by the decomposition of boric acid, reacts with the carbon layer, and boron atoms are doped into the lattice of the graphitized carbon, forming a boron-doped graphitized carbon (B-GC) structure. Boron doping improves the conductivity and defect density of the carbon layer, promotes electron transfer, and enhances its oxidation ability against As(III). The porous structure of the graphitized carbon provides a dispersion carrier for the cobalt ferrite nanosheets, preventing their aggregation and deactivation. Finally, after natural cooling, grinding and sieving, boron-doped graphitized carbon-coated cobalt ferrite nanosheets were obtained. The structure has high conductivity, large specific surface area and strong redox activity, providing key active sites for the oxidation and fixation of arsenic.

[0013] According to a preferred embodiment of the present invention, the cobalt nitrate hexahydrate was purchased from Hubei Xingfa Group (industrial grade cobalt nitrate hexahydrate, purity ≥98%). The ferric nitrate was purchased from Hubei Xingfa Group (industrial grade ferric nitrate, purity ≥98%). The boric acid was purchased from Liaoning Fangda Group (industrial grade boric acid, purity ≥99.5%). The ammonia water was purchased from Hubei Saning Chemical (industrial grade ammonia water, concentration ≥25%). The pyrrole monomer was purchased from Jiangsu Hehai Nanotechnology (analytical grade pyrrole monomer, purity ≥99%). The boric acid was purchased from Liaoning Fangda Group (industrial grade boric acid, purity ≥99.5%). The tubular furnace was purchased from Shanghai Keheng Industrial Co., Ltd. (GSH-500℃ type tubular furnace, working temperature ≤600℃). The argon gas was purchased from Hangzhou Oxygen Plant Group Co., Ltd. (industrial grade argon gas, purity ≥99.99%). The rice straw was purchased from COFCO Trading Co., Ltd. (high-quality japonica rice straw from Northeast China, which has been crushed). The round-bottom flask was purchased from Shandong Xinhua Medical Instrument Factory (500mL glass round-bottom flask, temperature resistance ≥150℃).

[0014] According to a preferred embodiment of the present invention, in step B1, the stirring reaction time at room temperature is 30-40 min.

[0015] According to a preferred embodiment of the present invention, in step B2, the stirring reaction time at 0-2℃ is 12-14h; the holding time at 1000-1050℃ is 3-4h.

[0016] This invention also provides a method for preparing the sodium alginate-encapsulated iron-carbon microcapsule material, comprising the following steps: S1. Wash rice straw, remove impurities, crush it, and heat it in a tube furnace to 400-600℃ for pyrolysis. After drying at 80-82℃ and cooling, grind and sieve to obtain straw biochar. Place high-iron steel slag powder in a round-bottom flask and add H2SO4 solution. Stir the mixture in a water bath at 80-82℃. Then add biochar and stir the mixture again in the water bath. After the reaction, adjust the pH to 7-8 with sodium hydroxide solution, then filter and dry the precipitate. Next, add Na2CO3 to the dried solid product, grind and mix thoroughly to finally obtain iron-carbon based passivation material. S2. Mix the iron-carbon based passivation material with mercaptoacetylated chitosan-iron single-atom cluster compound and boron-doped graphitized carbon-coated cobalt ferrite nanosheets evenly, then mix with sodium alginate solution, and dropwise add to calcium chloride solution while stirring.

[0017] In this invention, the preparation of sodium alginate-encapsulated iron-carbon microcapsule material involves two steps: composite material formation with iron-carbon based passivation materials and sodium alginate encapsulation, achieving environmental stability and long-term repair efficacy. The first step involves the preparation of the iron-carbon based passivation material: rice straw is washed, crushed, and placed in a tube furnace for pyrolysis at 10-12℃ / min to 400-600℃ (an anaerobic environment promotes the pyrolysis of biomass into biochar). After drying at 80-82℃, it is cooled, ground, and sieved to obtain straw biochar (rich in porous structure and surface functional groups). Simultaneously, high-iron steel slag powder (containing Fe2O3, CaO, etc.) is placed in a round-bottom flask, sulfuric acid solution is added, and the mixture is stirred in a water bath at 80-82℃ (to promote slag dissolution), generating Fe-containing... 3+ Ca 2+ An acidic solution; after adding straw biochar, continue stirring for 2-4 hours. The porous structure of the biochar adsorbs metal ions in the solution, and simultaneously reacts with Fe. 3+ Ca2+ A surface complexation reaction occurs. After the reaction is complete, the pH is adjusted to 7-8 (neutral to alkaline) with sodium hydroxide solution, promoting Fe... 3+ Hydrolysis produces Fe(OH)3 colloid, Ca 2+ With CO3 2- The resulting CaCO3 precipitate was filtered and dried to obtain an iron-carbon based passivation material. Finally, Na2CO3 was added and thoroughly ground and mixed with the dried solid. Na2CO3 further reacted with Fe(OH)3 and CaCO3 to form a more stable iron-calcium composite carbonate, enhancing the material's structural stability. This step, through the adsorption-complexation of biochar, the hydrolysis of steel slag releasing metal ions, and subsequent precipitation reactions, constructed a composite passivation system with iron-calcium carbonate as the core and biochar as the carrier, providing a foundation for the initial fixation of cadmium and arsenic. The second step is microcapsule encapsulation: the iron-carbon based passivation material, thiol-acetylated chitosan-iron single-atom cluster compound, and boron-doped graphitized carbon-coated cobalt ferrite nanosheets were mixed uniformly in a specific ratio (the three components work synergistically: the iron-carbon based material provides basic passivation capability, and the thiol-acetylated chitosan-iron single-atom cluster compound specifically adsorbs Cd). 2+ Boron-doped graphitized carbon-coated cobalt ferrite nanosheets are used to oxidize As(III) to As(V) and promote its fixation. This mixture is then combined with a sodium alginate solution (2-4% by mass), and added dropwise to a 3% calcium chloride solution. The mixture is stirred at 100-200 rpm for 30-60 minutes. Sodium alginate is a natural polysaccharide rich in carboxyl groups (-COO) on its molecular chain. - ), and Ca in calcium chloride 2+ An ionic crosslinking reaction occurs, forming a three-dimensional network structure of calcium alginate gel. Iron-carbon based passivating materials, thiol-acetylated chitosan-iron single-atom clusters, and boron-doped graphitized carbon-coated cobalt ferrite nanosheets are uniformly encapsulated within the gel network. During this process, the carboxyl groups of sodium alginate react with Ca... 2+ The coordination effect forms a stable cross-linked structure, which not only prevents the loss of internal active components due to environmental factors (such as water erosion and microbial degradation), but also controls the release rate of active components through the semi-permeable membrane effect, thus extending the remediation effectiveness of the material. The resulting microcapsule material has high loading capacity, slow-release performance, and environmental adaptability, and can function stably in cadmium and arsenic contaminated soil, achieving efficient and synergistic remediation of heavy metals.

[0018] According to a preferred embodiment of the present invention, in step S1, the rate of heating to 400-600°C is 10-12°C / min; the stirring time in the water bath at 80-82°C is 1-2 hours; and the re-stirring time is 2-4 hours.

[0019] According to a preferred embodiment of the present invention, in step S2, the mass fraction of the calcium chloride solution is 2-4%; the stirring rate is 100-200 rpm; and the stirring time is 30-60 min.

[0020] This invention also provides an application of the sodium alginate-encapsulated iron-carbon microcapsule material described above or the sodium alginate-encapsulated iron-carbon microcapsule material prepared by the aforementioned preparation method in the remediation of cadmium and arsenic contaminated soil.

[0021] The beneficial effects of this invention are as follows: The sodium alginate-encapsulated iron-carbon microcapsule material of this invention exhibits significant environmental protection characteristics, efficient synergistic passivation ability, and long-term remediation stability in preparation and application, providing an innovative solution for the remediation of cadmium and arsenic contaminated soil.

[0022] From a production process perspective, the material uses natural sodium alginate as the core encapsulating carrier, derived from marine algae. The extraction and processing do not require complex chemical synthesis, avoiding the use and emission of large amounts of harmful reagents in traditional remediation material production. The reuse of steel slag as industrial solid waste reduces resource consumption and secondary pollution to the environment. Biochar is prepared through straw pyrolysis, realizing the resource utilization of agricultural waste. The entire preparation process primarily involves physical mixing and simple cross-linking, resulting in a highly efficient and low-consumption process that aligns with green manufacturing principles. This reduces the environmental burden of production from the source, laying the foundation for the safe restoration of farmland ecosystems.

[0023] The synergistic effect of multiple passivation mechanisms in the material is its core advantage. Iron and calcium oxides, abundant in steel slag, can chemically complex, adsorb, precipitate, and exchange with cadmium and arsenic ions, forming stable compounds that significantly reduce the migration and bioavailability of heavy metals. Biochar, with its highly developed pore structure and abundant surface functional groups, provides numerous physical adsorption and chemical coordination sites for heavy metal ions, further fixing them within the pores. The thiol groups in the thiol-acetylated chitosan-iron single-atom cluster preferentially adsorb cadmium ions through coordination with the single-atom iron sites, forming stable complexes. The boron-doped carbon layer in the boron-doped graphitized carbon-coated cobalt ferrite nanosheets promotes the oxidation of arsenic (As(III)) to the more easily fixed As(V), while the cobalt ferrite nanosheets enhance the co-precipitation ability of iron oxides for arsenic through the magnetic moment effect. Sodium alginate, as a high-molecular polymer, tightly encapsulates the steel slag, biochar, and two modified components through encapsulation, constructing a stable microenvironment that effectively blocks external environmental factors from damaging the passivation components. With the synergistic effect of the four factors, the material's fixation efficiency for cadmium and arsenic is significantly improved, which can effectively inhibit the transfer of heavy metals to crops and ensure the quality and safety of agricultural products.

[0024] Long-term stability and durability are another outstanding feature of this invention. The encapsulation structure of sodium alginate significantly enhances the resistance to degradation of steel slag and biochar, making them less susceptible to microbial decomposition or physical breakdown in the soil environment, thus maintaining their passivation activity for a long time. Compared to traditional chemical amendments that are prone to rapid failure due to rainwater erosion and soil tillage, this material can maintain a stable remediation effect even under complex environmental conditions, greatly reducing the frequency and cost of repeated application. This characteristic makes it more practical for the long-term remediation of cadmium and arsenic pollution in farmland, providing a reliable guarantee for the sustainable remediation of contaminated soil. Attached Figure Description

[0025] Appendix Figure 1 The passivation rates of available As and available Cd in the soil are represented by .

[0026] Appendix Figure 2 The conversion rate of residual As and residual Cd in the soil. Detailed Implementation

[0027] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0028] Example 1

[0029] 100g of chitosan obtained after decalcification and deproteinization of shrimp shells was added to 500mL of 10% acetic acid solution and stirred continuously at 40℃ for 3 hours until completely dissolved. Then, 5g of mercaptoacetic anhydride was added and reacted at 60℃ for 13 hours under nitrogen protection. After the reaction was completed, the pH of the system was adjusted to 7.0 with sodium hydroxide solution. The precipitated product was dialyzed with deionized water (molecular weight cutoff 3500Da) and then freeze-dried (62℃) to obtain mercaptoacetylated chitosan. Dissolve 80g of mercaptoacetylated chitosan in 200mL of deionized water, add 20g of ferric nitrate nonahydrate and sonicate for 15 minutes; transfer the mixture to a high-pressure reactor, add 100mL of ethanol (to make the total solvent volume a mixture of 200mL of deionized water and 100mL of ethanol) and 1g of ascorbic acid, and carry out a solvothermal reaction at 180℃ for 27 hours; after the reaction is completed, allow it to cool naturally to room temperature, centrifuge to collect the precipitate and wash it three times each with deionized water and ethanol, and finally vacuum dry at 62℃ to obtain mercaptoacetylated chitosan-iron single-atom clusters. 10g of cobalt nitrate hexahydrate, 15g of ferric nitrate, and 5g of boric acid were added to 200mL of deionized water and stirred until completely dissolved. Ammonia was added to adjust the pH to 9.0, and stirring was continued at room temperature for 35 minutes to generate a mixed metal hydroxide precursor. The precipitate was collected by centrifugation and washed three times with deionized water, then dispersed in 100mL of ethanol-water mixed solvent (volume ratio 1:1). 5g of pyrrole monomer was added to the dispersion, and the mixture was stirred at 0℃ for 13 hours under nitrogen protection to form polypyrrole-coated CoFe2O4. The precipitate was collected by centrifugation and washed three times with deionized water, then dried at 82℃. The dried product was mixed evenly with 5g of boric acid, placed in a tube furnace, heated to 1000℃ under argon atmosphere, and held for 3.5 hours. After natural cooling, the mixture was ground and sieved to obtain boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 1000g of rice straw was washed to remove impurities and crushed, then placed in a tube furnace and heated to 500℃ at a rate of 11℃ / min for pyrolysis (dried at 81℃ and cooled). The residue was then ground and sieved to obtain 150g of straw biochar. 500g of high-iron steel slag powder was placed in a round-bottom flask and 500mL of 10% H2SO4 solution was added. The mixture was stirred in an 81℃ water bath for 1.5 hours. After adding 150g of straw biochar, the mixture was stirred for another 3 hours. After the reaction was completed, the pH was adjusted to 7.5 with sodium hydroxide solution, filtered, and the precipitate was dried. 42g of Na2CO3 was added to the dried solid and the mixture was thoroughly ground and mixed to obtain an iron-carbon based passivation material. 1000g of iron-carbon based passivation material was mixed evenly with 45g of mercaptoacetylated chitosan-iron single-atom cluster compound and 45g of boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 30g of sodium alginate (dissolved in 100mL of water) was added, and the mixture was dropped into 500g of 10% calcium chloride solution. The mixture was stirred at 150rpm for 45 minutes to finally obtain sodium alginate-encapsulated iron-carbon microcapsule material.

[0030] Example 2

[0031] The specific implementation method is the same as in Example 1, except that 100g of chitosan obtained after decalcification and deproteinization of shrimp shells is added to 500mL of 10% acetic acid solution and stirred continuously at 40°C for 3 hours to completely dissolve it; then 5g of mercaptoacetic anhydride is added and reacted at 60°C for 13 hours under nitrogen protection; after the reaction is completed, the pH of the system is adjusted to 7.0 with sodium hydroxide solution, and the precipitated product is treated by deionized water dialysis (molecular weight cutoff 3500Da) and then freeze-dried (62°C) to obtain 80g of mercaptoacetylated chitosan. Dissolve 80g of mercaptoacetylated chitosan in 200mL of deionized water, add 20g of ferric nitrate nonahydrate and sonicate for 15 minutes; transfer the mixture to a high-pressure reactor, add 100mL of ethanol (to make the total solvent volume a mixture of 200mL of deionized water and 100mL of ethanol) and 1g of ascorbic acid, and carry out a solvothermal reaction at 180℃ for 27 hours; after the reaction is completed, allow it to cool naturally to room temperature, centrifuge to collect the precipitate and wash it three times each with deionized water and ethanol, and finally vacuum dry at 62℃ to obtain mercaptoacetylated chitosan-iron single-atom clusters. 10g of cobalt nitrate hexahydrate, 15g of ferric nitrate, and 5g of boric acid were added to 200mL of deionized water and stirred until completely dissolved. Ammonia was added to adjust the pH to 9.0, and stirring was continued at room temperature for 35 minutes to generate a mixed metal hydroxide precursor. The precipitate was collected by centrifugation and washed three times with deionized water, then dispersed in 100mL of ethanol-water mixed solvent (volume ratio 1:1). 5g of pyrrole monomer was added to the dispersion, and the mixture was stirred at 0℃ for 13 hours under nitrogen protection to form polypyrrole-coated CoFe2O4. The precipitate was collected by centrifugation and washed three times with deionized water, then dried at 82℃. The dried product was mixed evenly with 5g of boric acid, placed in a tube furnace, heated to 1000℃ under argon atmosphere, and held for 3.5 hours. After natural cooling, the mixture was ground and sieved to obtain boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 1000g of rice straw was washed to remove impurities and crushed, then placed in a tube furnace and heated to 500℃ at a rate of 11℃ / min for pyrolysis (dried at 81℃ and cooled). The residue was then ground and sieved to obtain straw biochar. 500g of high-iron steel slag powder was placed in a round-bottom flask and 500mL of 10% H2SO4 solution was added. The mixture was stirred in an 81℃ water bath for 1.5 hours. 150g of straw biochar was added and stirring was continued for 3 hours. After the reaction was completed, the pH was adjusted to 7.5 with sodium hydroxide solution, filtered, and the precipitate was dried. 42g of Na2CO3 was added to the dried solid and the mixture was thoroughly ground and mixed to obtain an iron-carbon based passivation material. 1000g of iron-carbon based passivation material was mixed evenly with 50g of mercaptoacetylated chitosan-iron single-atom cluster compound and 50g of boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 30g of sodium alginate (dissolved in 100mL of water) was added, and the mixture was dropped into 500g of 10% calcium chloride solution. The mixture was stirred at 150rpm for 45 minutes to finally obtain sodium alginate-encapsulated iron-carbon microcapsule material.

[0032] Example 3

[0033] The specific implementation method is the same as in Example 1, except that 100g of chitosan obtained after decalcification and deproteinization of shrimp shells is added to 500mL of 10% acetic acid solution and stirred continuously at 40°C for 3 hours to completely dissolve it; then 5g of mercaptoacetic anhydride is added and reacted at 60°C for 13 hours under nitrogen protection; after the reaction is completed, the pH of the system is adjusted to 7.0 with sodium hydroxide solution, and the precipitated product is treated by deionized water dialysis (molecular weight cutoff 3500Da) and then freeze-dried (62°C) to obtain mercaptoacetylated chitosan. Dissolve 80g of mercaptoacetylated chitosan in 200mL of deionized water, add 20g of ferric nitrate nonahydrate and sonicate for 15 minutes; transfer the mixture to a high-pressure reactor, add 100mL of ethanol (to make the total solvent volume a mixture of 200mL of deionized water and 100mL of ethanol) and 1g of ascorbic acid, and carry out a solvothermal reaction at 180℃ for 27 hours; after the reaction is completed, allow it to cool naturally to room temperature, centrifuge to collect the precipitate and wash it three times each with deionized water and ethanol, and finally vacuum dry at 62℃ to obtain mercaptoacetylated chitosan-iron single-atom clusters. 10g of cobalt nitrate hexahydrate, 15g of ferric nitrate, and 5g of boric acid were added to 200mL of deionized water and stirred until completely dissolved. Ammonia was added to adjust the pH to 9.0, and stirring was continued at room temperature for 35 minutes to generate a mixed metal hydroxide precursor. The precipitate was collected by centrifugation and washed three times with deionized water, then dispersed in 100mL of ethanol-water mixed solvent (volume ratio 1:1). 5g of pyrrole monomer was added to the dispersion, and the mixture was stirred at 0℃ for 13 hours under nitrogen protection to form polypyrrole-coated CoFe2O4. The precipitate was collected by centrifugation and washed three times with deionized water, then dried at 82℃. The dried product was mixed evenly with 5g of boric acid, placed in a tube furnace, heated to 1000℃ under argon atmosphere, and held for 3.5 hours. After natural cooling, the mixture was ground and sieved to obtain boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 1000g of rice straw was washed to remove impurities and crushed, then placed in a tube furnace and heated to 500℃ at a rate of 11℃ / min for pyrolysis (dried at 81℃ and cooled). The residue was then ground and sieved to obtain 150g of straw biochar. 500g of high-iron steel slag powder was placed in a round-bottom flask and 500mL of 10% H2SO4 solution was added. The mixture was stirred in an 81℃ water bath for 1.5 hours. After adding 150g of straw biochar, the mixture was stirred for another 3 hours. After the reaction was completed, the pH was adjusted to 7.5 with sodium hydroxide solution, filtered, and the precipitate was dried. 42g of Na2CO3 was added to the dried solid and the mixture was thoroughly ground and mixed to obtain an iron-carbon based passivation material. 1000g of iron-carbon based passivation material was mixed with 40g of mercaptoacetylated chitosan-iron single-atom cluster compound and 40g of boron-doped graphitized carbon-coated cobalt ferrite nanosheets. 30g of sodium alginate (dissolved in 100mL of water) was added, and the mixture was dropped into 500g of 10% calcium chloride solution. The mixture was stirred at 150rpm for 45 minutes to obtain sodium alginate-encapsulated iron-carbon microcapsule material.

[0034] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the amount of thiol-acetylated chitosan-iron monoatomic cluster compound used is 0g.

[0035] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the amount of boron-doped graphitized carbon-coated cobalt ferrite nanosheets used is 0g.

[0036] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the amount of thiol-acetylated chitosan-iron single-atom cluster compound and boron-doped graphitized carbon-coated cobalt ferrite nanosheets is 0g.

[0037] Performance testing The sodium alginate-encapsulated iron-carbon microcapsule materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following methods: 1. Testing the adsorption performance of sodium alginate-encapsulated iron-carbon microcapsules obtained in Example 1 for As and Cd in water: 0.10 g of the carbon-based composite material prepared in Example 1 was weighed into a 50 mL centrifuge tube, and 40 mL of simulated wastewater solutions of As(III) or Cd with initial concentrations of 10 and 16.5 mg / L, respectively, were added. 0.01 mol / L NaNO3 solution was used as the supporting electrolyte, and the pH of the solution was adjusted to 5.8 ± 0.2 using 0.01 mol / L NaOH or HNO3 solution. The solution was shaken at room temperature for 24 h, centrifuged, filtered, and the concentrations of arsenic and cadmium in the supernatant were measured. The results showed that the iron-carbon-based microcapsule material prepared in this invention has a good removal effect on As and Cd in water, with removal efficiencies of 90.1%–95.4% and 94.0%–97.3%, respectively. Model fitting revealed that the saturated adsorption capacity of the iron-carbon-based microcapsules for As and Cd in water was relatively high, at 15.22 and 15.19 mg / g, respectively.

[0038] 2. Testing the remediation effect of sodium alginate-encapsulated iron-carbon microcapsules obtained in Example 1 on cadmium and arsenic contaminated soil: Soil samples were collected from paddy fields contaminated with both cadmium and arsenic. The cadmium (Cd) content was 24 times higher than the national secondary standard for soil environmental quality (GB 15618-2008), and the asphalt (As) content exceeded the standard by 5.6 times. The soil and microcapsules were mixed evenly and placed in plastic basins. Deionized water was added periodically to maintain the moisture content at 60% of the maximum field capacity, and the mixture was incubated at room temperature for 60 days.

[0039] Determination of bioavailable cadmium and arsenic content in soil: Bioavailable Cd was extracted using a mixed extractant of diethylenetriaminepentaacetic acid (DTPA). The specific procedure was as follows: 5.0 g of soil sample (passed through a 40-mesh sieve) was placed in a 100 mL centrifuge tube, and 25 mL of the DTPA mixed extractant (0.005 mol / L DTPA-0.1 mol / L TEA-0.01 mol / L CaCl2) was added. The mixture was shaken for 2 h at 250 r / min, allowed to stand overnight, filtered, and the supernatant was collected. The Cd content in the solution was determined using inductively coupled plasma optical emission spectrometry (ICPOES). Bioavailable As was extracted using NaHCO3. 5.0 g of 40-mesh soil sample was placed in a 50 mL centrifuge tube, and 25 mL of 0.5 mol / L NaHCO3 was added. The tube was capped and extracted for 2 h at 250 r / min. After filtration, the supernatant was collected, and the As content was determined using an atomic fluorescence spectrophotometer. The experimental results showed that after applying iron-carbon based microcapsule materials to composite contaminated soil, the contents of available As and available Cd in the soil decreased by 17.0% and 16.7%, respectively. Figure 1 The contents of residual As and residual Cd increased by 31.5% and 85.7%, respectively. Figure 2 As shown in Table 1, after applying sodium alginate-encapsulated iron-carbon microcapsule material, the soil pH increased slightly, and the contents of organic matter, available phosphorus, and available potassium increased by 10.6%, 14.5%, and 18.6%, respectively. This indicates that the sodium alginate-encapsulated iron-carbon microcapsule material prepared in this invention can passivate heavy metals while also increasing the nutrient content of the soil.

[0040] Table 1 Soil pH, organic matter, available phosphorus and available potassium content

[0041] 3. The sodium alginate-encapsulated iron-carbon microcapsule materials prepared in Examples 1-3 and Comparative Examples 1-3 were labeled as M1, M2, M3, D1, D2, and D3, respectively. A cadmium- and arsenic-contaminated farmland soil sample (cadmium content 8.2 mg / kg, arsenic content 15.6 mg / kg, pH 6.8, organic matter content 2.1%) was taken, ground, and passed through a 2 mm sieve to remove stones, weeds, and other impurities. Remediation experiment design: A pot-based simulated remediation method was used. Each pot contained 5 kg of contaminated soil, and different masses of microcapsule material were added (M1, M2, and M3: 50 g / pot; D1, D2, and D3: same as the corresponding examples). A blank control (CK, no material added) was also set up. The soil moisture content of all treatment groups was maintained at 60% (60% of field capacity), the temperature was controlled at 25±2℃, and the soil was kept in the dark for 30 days. Detection Indicators and Methods: First, the available cadmium and arsenic content in the soil was detected. Soil samples were collected from each pot after the curing period. Available heavy metals were extracted using the DTPA extraction method (pH 7.3). The cadmium content was determined using atomic absorption spectrometry (AAS), and the arsenic content was determined using atomic fluorescence spectrometry (AFS). The reduction rate of available heavy metals was calculated (reduction rate (%) = (available content in blank control - available content in treatment group) / available content in blank control × 100%). Second, the adsorption capacity of the material was tested. The microcapsule material after curing was repeatedly washed with deionized water until no heavy metals were detected in the filtrate. After drying, it was ground through a 100-mesh sieve. 1.0 g of the material was weighed and added to 50 mL of 0.1 mol / L CdCl2 and 0.1 mol / L... A Na3AsO4 mixed solution (simulated contaminated liquid) was shaken at 25°C for 24 hours. After centrifugation, the supernatant was taken to determine the remaining cadmium and arsenic concentrations. The adsorption capacity (mg / g) was calculated as (initial concentration × volume - remaining concentration × volume) / material mass. Then, the long-term stability was evaluated. The material was taken out after 30 days of curing and cured for another 30 days under the same conditions (total curing time 60 days). The effective heavy metal content was tested again, and the effective reduction rate after 60 days was calculated.

[0042] Table 2: Performance test results of each embodiment and comparative example

[0043] As shown in Table 2, the performance test results of Examples 1-3 and Comparative Examples 1-3 demonstrate that the present invention, by introducing two functionalized modified components—thiol-acetylated chitosan-iron single-atom clusters and boron-doped graphitized carbon-coated cobalt ferrite nanosheets—and combining them with sodium alginate encapsulation technology, effectively solves the problems of low synergistic passivation efficiency, susceptibility to material loss due to environmental factors, and long remediation cycles in existing cadmium and arsenic-contaminated soil remediation technologies. Regarding synergistic passivation efficiency, the 30-day effective cadmium reduction rate (79.6%-85.1%) and arsenic reduction rate (82.1%-88.4%) of Examples 1-3 are significantly higher than those of Comparative Examples 1-3 (52.4%-68.5%, 55.6%-70.2%). This is because the thiol-acetylated chitosan-iron single-atom cluster compound specifically adsorbs cadmium ions through the coordination of thiol and amino groups, while boron-doped graphitized carbon-coated cobalt ferrite nanosheets promote the oxidation of arsenic (especially As(III)) to more easily fixed As(V) through the polypyrrole coating layer, and enhance the co-precipitation ability of iron oxides for arsenic through the magnetic moment effect of the cobalt ferrite nanosheets. The synergistic effect of the two components significantly improves the cadmium and arsenic fixation efficiency compared to the control group with a single component or no modified component, solving the problem of low cadmium and arsenic synergistic passivation efficiency in traditional remediation technologies. In terms of the material's resistance to environmental leaching, the long-term stability of Examples 1-3 is significantly better than that of the control group. The encapsulation structure of sodium alginate effectively blocks the damage of the active component by the external environment. Combined with the stability of the modified component, it significantly improves the environmental adaptability of the material and solves the problem of easy leaching of traditional materials. In terms of the remediation cycle, the effective state reduction rate of Examples 1-3 has reached a high level after 30 days and remains stable after 60 days; while the control group requires a longer time to achieve similar results. This is because the synergistic effect of the modified components accelerates the adsorption and fixation process of heavy metals, shortens the time to reach the effective remediation threshold, and solves the problem of long cycles in traditional remediation technologies. In summary, Examples 1-3, through the combination of the synergistic effect of functionalized modified components and sodium alginate encapsulation technology, comprehensively improve the remediation efficiency, material stability, and remediation speed of cadmium-arsenic co-contaminated soil, providing an effective solution to overcome the bottlenecks of existing remediation technologies.

[0044] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A sodium alginate-encapsulated iron-carbon microcapsule material, characterized in that, Including the following parts by weight of raw materials: Straw biochar: 120-180 parts by weight; High-speed rail steel slag powder: 450-550 parts by weight; Thiothioacetylated chitosan-iron monoatomic cluster compound: 30-60 parts by weight; Boron-doped graphitized carbon-coated cobalt ferrite nanosheets: 30-60 parts by weight; Sodium alginate: 20-40 parts by weight; Calcium chloride: 420-580 parts by weight; Na2CO3: 40-45 parts by weight; The preparation method of the thiol acetylated chitosan-iron single-atom cluster compound includes: A1, dissolving chitosan obtained after decalcification and deproteinization of shrimp shells in acetic acid solution, stirring and dissolving at 40-42℃, adding mercaptoacetic anhydride, reacting at 60-64℃ under nitrogen protection, adjusting the pH to 6.8-7.2 with NaOH solution after the reaction, dialyzing the precipitate with deionized water, and freeze-drying to obtain thiol acetylated chitosan; A2, dissolving thiol acetylated chitosan in deionized water, adding ferric nitrate nonahydrate, ultrasonically dispersing and transferring to a high-pressure reactor, solvothermal reaction at 180-184℃, the solvent being a mixture of deionized water and ethanol, and simultaneously adding ascorbic acid, naturally cooling to room temperature after the reaction, collecting the precipitate by centrifugation and washing with deionized water and ethanol, and vacuum drying.

2. The sodium alginate-encapsulated iron-carbon microcapsule material according to claim 1, characterized in that, In step A1, the stirring and dissolution time is 2-4 hours at 40-42℃; the reaction time is 12-14 hours at 60-64℃.

3. The sodium alginate-encapsulated iron-carbon microcapsule material according to claim 1, characterized in that, In step A2, the ultrasonic dispersion time is 10-20 min; the solvothermal reaction time at 180-184℃ is 24-30 h; and the vacuum drying temperature is 60-64℃.

4. The sodium alginate-encapsulated iron-carbon microcapsule material according to claim 1, characterized in that, The preparation method of the boron-doped graphitized carbon-coated cobalt ferrite nanosheets includes: B1, dissolving cobalt nitrate hexahydrate, ferric nitrate and boric acid in deionized water, adding ammonia to adjust the pH to 8.8-9.2, and stirring at room temperature to generate a mixed metal hydroxide precursor; B2, centrifuging to collect the precipitate and washing it with deionized water, and dispersing it in an ethanol-water mixed solvent; adding pyrrole monomer to the dispersion, and stirring at 0-2℃ under nitrogen protection to form polypyrrole-coated CoFe2O4, centrifuging to collect the precipitate and washing it with deionized water, and drying it at 80-84℃; mixing the polypyrrole-coated CoFe2O4 with boric acid, placing it in a tube furnace, heating it to 1000-1050℃ under an argon atmosphere and holding it thereafter, and grinding and sieving it after natural cooling.

5. The sodium alginate-encapsulated iron-carbon microcapsule material according to claim 4, characterized in that, In step B1, the stirring reaction time at room temperature is 30-40 minutes.

6. The sodium alginate-encapsulated iron-carbon microcapsule material according to claim 4, characterized in that, In step B2, the stirring reaction time at 0-2℃ is 12-14h; the holding time at 1000-1050℃ is 3-4h.

7. A method for preparing sodium alginate-encapsulated iron-carbon microcapsule material according to any one of claims 1-6, characterized in that, step include: S1. Wash rice straw, remove impurities, crush it, and heat it in a tube furnace to 400-600℃ for pyrolysis. After drying at 80-82℃ and cooling, grind and sieve to obtain straw biochar. Place high-iron steel slag powder in a round-bottom flask and add H2SO4 solution. Stir the mixture in a water bath at 80-82℃. Then add biochar and stir the mixture again in the water bath. After the reaction, adjust the pH to 7-8 with sodium hydroxide solution, then filter and dry the precipitate. Next, add Na2CO3 to the dried solid product, grind and mix thoroughly to finally obtain iron-carbon based passivation material. S2. Mix the iron-carbon based passivation material with mercaptoacetylated chitosan-iron single-atom cluster compound and boron-doped graphitized carbon-coated cobalt ferrite nanosheets evenly, then mix with sodium alginate solution, and dropwise add to calcium chloride solution while stirring.

8. The preparation method according to claim 7, characterized in that, In step S1, the heating rate to 400-600℃ is 10-12℃ / min; the stirring time in the water bath at 80-82℃ is 1-2h; and the stirring time is 2-4h.

9. The preparation method according to claim 7, characterized in that, In step S2, the mass fraction of the calcium chloride solution is 2-4%; the stirring speed is 100-200 rpm; and the stirring time is 30-60 min.

10. The application of a sodium alginate-encapsulated iron-carbon microcapsule material according to any one of claims 1-6 or a sodium alginate-encapsulated iron-carbon microcapsule material prepared by the preparation method according to any one of claims 7-9, characterized in that, Application of sodium alginate-encapsulated iron-carbon microcapsule material in the remediation of cadmium and arsenic contaminated soil.

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