A temperature-sensitive salt-resistant iron-manganese material, a preparation method and application thereof

Abstract

This invention belongs to the field of in-situ remediation technology for contaminated soil and groundwater, specifically relating to a temperature-sensitive, salt-resistant iron-manganese material, its preparation method, and its application. The material comprises an iron-manganese binary active core, a temperature-sensitive, salt-resistant copolymer layer, and a polydopamine adhesion layer. The iron-manganese binary active core is used for As(III) oxidation and As fixation. The copolymer layer is preferentially distributed on the surface of the iron oxidation / hydroxide component, while the manganese oxidation sites are partially exposed. Before entering the geothermal zone, it maintains good dispersibility and migration ability. Upon reaching the high-temperature, high-chlorine pore water region, the polyN-vinylcaprolactam segments undergo dehydration and shrinkage, the active sites contact As, the sulfobetaine segments maintain the hydration layer and reduce particle aggregation, and the polydopamine adhesion layer enhances retention. The material of this invention can oxidize highly mobile As(III) into easily fixed As(V) in geothermal pore water and fix it through the iron oxidation / hydroxide component, reducing the arsenic concentration and arsenic migration risk in the pore water.

Description

Technical Field

[0001] This invention belongs to the field of in-situ remediation technology for contaminated soil and groundwater, specifically relating to a temperature-sensitive, salt-resistant iron-manganese material, its preparation method, and its application. Background Technology

[0002] The processes of tailwater storage, transportation, reinjection, and drilling operations during the development and utilization of geothermal resources not only cause significant physical disturbances but may also introduce or leak exogenous chemical substances, disrupting the original geochemical balance of the geothermal area. This anthropogenic disturbance can significantly activate pollutants under high geological background conditions, increasing their bioavailability and toxicity, leading to the deterioration of regional environmental quality. Arsenic (As) is a class of highly toxic, environmentally persistent, and widely present metalloid pollutants in natural soils. In underground reducing environments, trivalent arsenic (As(III)) is the dominant form of arsenic, exhibiting higher toxicological activity and stronger migration ability compared to pentavalent arsenic (As(V)). As(III) can strongly bind to sulfhydryl groups in proteins and enzyme molecules within organisms, interfering with cellular energy metabolism, redox balance, and DNA repair processes, and can induce oxidative stress, cell damage, and multi-organ toxicity. Long-term exposure to As(III)-containing water or soil environments can increase the risk of skin damage, nervous system damage, cardiovascular disease, and various cancers. Since As(III) typically has a stronger cellular uptake capacity and higher acute and chronic toxicity, its presence in soil pore water and groundwater in geothermal areas can significantly increase the health and ecological risks of contaminated sites.

[0003] Compared to conventional surface environments, groundwater in geothermal areas is characterized by higher temperatures, higher mineralization, alkaline pH, lower dissolved oxygen content, and higher concentrations of coexisting ions such as bicarbonate and silicate. These geochemical conditions are extremely sensitive to anthropogenic disturbances; changes in these conditions can weaken the stable binding of As (As) on soil mineral surfaces, promoting the release of As from the solid phase into pore water, thereby further exacerbating the migration and environmental risks of As in geothermal environments. Therefore, effective control of As(III) in soil and groundwater in geothermal areas is one of the key issues in this field.

[0004] Iron oxides / hydroxides are commonly used as As (As) immobilization materials in soil and groundwater remediation. However, under neutral to slightly alkaline conditions, As(III) has a weak affinity for the surface of iron oxides / hydroxides, making it difficult to rapidly reduce highly reactive As in geothermal pore water when using iron-based materials alone. Manganese oxides can oxidize As(III) to As(V), but their long-term As immobilization capacity is limited, making it difficult to achieve stable As control when used alone. Therefore, coupling the As(III) oxidation capacity of manganese oxide components with the As(V) immobilization capacity of iron oxide / hydroxide components is an important technical direction for improving the As(III) detoxification efficiency and long-term As stabilization effect.

[0005] For deep soil pollution, conventional ex-situ treatment methods are usually costly, highly disruptive, and difficult to adapt to the complex groundwater flow field and thermal anomaly conditions in geothermal areas. In contrast, in-situ injection technology has advantages such as less environmental disturbance, relatively lower engineering workload, and the ability of the agent to act directly on the target pollution area, making it more suitable for the remediation of As-contaminated soil and pore water in geothermal areas. However, existing iron-manganese binary materials still have significant shortcomings when applied in-situ in geothermal areas: (1) Geothermal pollution hotspots are usually located deep in the soil, in fracture channels, or in local thermal anomaly areas, and conventional particulate materials have limited migration ability in soil pores, making it difficult to effectively reach the target pollution area; (2) High temperature, high salinity, and high ionic strength conditions will enhance particle collision and aggregation, reducing the active sites of the material and shrinking the effective radius of action. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a temperature-sensitive, salt-resistant iron-manganese material, its preparation method, and its application. The temperature-sensitive, salt-resistant iron-manganese material provided by this invention is a composite material that maintains good migration ability before entering geothermal areas, reduces agglomeration in high-chloride ion pore water, and improves the accessibility of active sites after geothermal temperature triggering.

[0007] The present invention provides a temperature-sensitive salt-resistant iron-manganese material, comprising a polymer selectively coated iron-manganese material and an adhesion layer located on the outer surface of the polymer selectively coated iron-manganese material; The polymer selectively coated iron-manganese material includes an iron-manganese binary active core and a temperature-sensitive salt-resistant copolymer layer coated on a portion of the surface of the iron-manganese binary active core. The iron-manganese binary active core includes an iron oxide / hydrogen hydroxide component and a manganese oxide component; the temperature-sensitive and salt-resistant copolymer layer is selectively and preferentially distributed on the surface of the iron oxide / hydrogen hydroxide component, and the surface of the manganese oxide component retains exposed sites. The temperature-sensitive and salt-resistant copolymer layer is a poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer; The adhesive layer is a polydopamine layer.

[0008] Preferably, the particle size of the temperature-sensitive, salt-resistant iron-manganese material is 50~300 nm.

[0009] Preferably, the iron oxide / hydrogen hydroxide component includes one or more of low-crystallization iron hydroxide, iron oxide hydroxyl, and hydrated iron oxide; the manganese oxide component includes one or more of manganese dioxide, manganese oxide hydroxyl, and manganese oxide containing Mn(III) / Mn(IV).

[0010] Preferably, the molar ratio of iron to manganese in the iron-manganese binary active core is 1.5 to 4:1.

[0011] Preferably, the mass ratio of N-vinylcaprolactam to sulfobetaine methacrylate, the raw material for preparing the temperature-sensitive salt-resistant copolymer layer, is 60-90:10-40. The temperature-sensitive salt-resistant copolymer layer undergoes dehydration shrinkage within the range of 35-70°C to improve the accessibility of active sites in the iron-manganese binary active core; the sulfobetaine methacrylate segments form a hydration layer in chloride-containing porous water to reduce material aggregation in high-salt porous water.

[0012] Preferably, the mass of the polydopamine layer is 0.5-8% of the total mass of the temperature-sensitive, salt-resistant iron-manganese material. The polydopamine layer is used to enhance the adhesion of the temperature-sensitive, salt-resistant iron-manganese material to the iron-aluminum oxide coating on the surface of fine soil particles, the hydroxyl sites at the edges of clay minerals, and the mineral-organic composite interface.

[0013] This invention also provides a method for preparing the temperature-sensitive, salt-resistant iron-manganese material described above, comprising the following steps: The pH of the mixed solution containing iron and manganese metal salts was first adjusted to 7.2-7.8 before Fe... 3+ Hydrolysis forms iron oxide / hydrogen hydroxide precursor particles, which are then adjusted to 8.3~9.0, Mn 2+ The iron oxide / hydrogen hydroxide precursor particles were loaded onto the surface of the iron oxide / hydrogen hydroxide precursor particles; the resulting system was mixed with hydrogen peroxide solution and aged to obtain an iron-manganese binary active core. The iron-manganese binary active core, water, N-vinylcaprolactam and sulfobetaine methacrylate are mixed for pre-adsorption. The resulting system, crosslinking agent and initiator are mixed for copolymerization reaction to form a temperature-sensitive salt-resistant copolymer layer on the surface of the iron-manganese binary active core, thus obtaining a polymer selectively coated iron-manganese material. The polymer is selectively coated with iron-manganese material, dopamine and buffer solution are mixed and subjected to self-polymerization reaction to form an adhesion layer, thereby obtaining the temperature-sensitive salt-resistant iron-manganese material.

[0014] Preferably, the concentration of iron ions in the mixed solution of iron and manganese ions is 0.03~0.10 mol / L, and the concentration of manganese ions is 0.01~0.05 mol / L; the molar ratio of iron ions to manganese ions is 1.5~4:1.

[0015] Preferably, the hydrogen peroxide solution has a mass fraction of 1-5%, and the volume of the hydrogen peroxide solution is 1-8% of the volume of the metal salt mixed solution; the aging reaction temperature is 50-70℃, and the time is 1-4h.

[0016] Preferably, the mixture of the iron-manganese binary active core, water, N-vinylcaprolactam, and sulfobetaine methacrylate further includes: adjusting the pH of the system to 5.5-6.5; the pre-adsorption is carried out under stirring for 20-60 minutes; and the copolymerization reaction is carried out at a temperature of 65-75°C for 0.5-2 hours.

[0017] Preferably, the concentration of dopamine in the system after selectively coating the iron-manganese material with polymer, mixing dopamine and buffer solution is 0.2~1.0 g / L; the buffer solution is a Tris buffer solution with a pH of 8.0~8.8; and the self-polymerization reaction time is 0.5~3 h.

[0018] This invention also provides the application of the temperature-sensitive salt-resistant iron-manganese material described in the above technical solution or the temperature-sensitive salt-resistant iron-manganese material obtained by the above preparation method in the remediation of arsenic pollution in soil and groundwater in geothermal areas.

[0019] Compared with the prior art, the present invention has the following beneficial effects: To address the challenges of materials failing to reach the target contaminated area in in-situ remediation of As contaminated soil in geothermal regions, easily agglomerating and becoming unstable upon entering high-salt pore water, and experiencing reduced accessibility of active sites, this invention constructs a temperature-sensitive, salt-resistant iron-manganese material. Through the synergistic design of an iron-manganese binary active core, a temperature-sensitive, salt-resistant copolymer layer, and a polydopamine adhesion layer, this material exhibits good dispersion and migration capabilities before entering the geothermal area, strong anti-agglomeration ability in high-chloride pore water, and increased contact opportunities between iron-manganese active sites and As in the high-temperature geothermal region.

[0020] The iron-manganese binary active core is used for As(III) oxidation and As fixation. The copolymer layer is preferentially distributed on the surface of the iron oxide / hydroxide component, while the manganese oxidation sites retain some exposed surfaces. Before entering the geothermal area, it maintains good dispersibility and migration ability, reducing the problems of premature agglomeration and premature retention during injection and transportation. Upon reaching the high-temperature, high-chloride pore water area affected by geothermal water, the poly(N-vinylcaprolactam) segments undergo dehydration and shrinkage, increasing the contact opportunity between the iron-manganese active sites and As. The sulfobetaine segments maintain the hydration layer and weaken particle agglomeration under high chloride ion conditions. The polydopamine adhesion layer enhances the retention of the material on soil fine particles, clay mineral edge hydroxyl sites, and mineral-organic matter interfaces. The material of this invention can oxidize highly mobile As(III) into more easily fixed As(V) in geothermal pore water, and further adsorb, co-precipitate, or complex with the iron oxide / hydroxide component, thereby reducing the As concentration and migration risk in the pore water.

[0021] This invention also provides a method for preparing the temperature-sensitive, salt-resistant iron-manganese material described in the above technical solution. This invention uses an iron-manganese binary active core as the main reaction unit, and through stepwise alkalization and in-situ surface oxidation, forms manganese oxidation sites on or near the surface of iron oxide / hydrogen hydroxide precursor particles, constructing a reaction structure in which As(III) oxidation sites and As(V) fixation sites are closely coupled. This structure allows As(III) to be first oxidized by the manganese oxidation component to more easily fixed As(V), and then fixed by adsorption, co-precipitation, or surface complexation by the adjacent iron oxide / hydrogen hydroxide component, thereby improving the As(III) detoxication efficiency and As fixation stability.

[0022] The beneficial effects of this invention are also reflected in: (1) This invention uses the natural temperature of the geothermal area as the response condition, without the need for external field addition or additional heating equipment, and is suitable for in-situ remediation scenarios in geothermal areas, with relatively simple on-site operating conditions; (2) The present invention improves the dispersibility and migration of iron-manganese materials during the injection stage through a temperature-sensitive salt-resistant copolymer layer, reduces the risk of material agglomeration and premature retention before entering the geothermal pollution area, and increases the possibility of material reaching the target pollution area. (3) The sulfobetaine methacrylate segment in this invention can maintain the hydration layer in pore water with high chloride ion and high mineralization, reduce particle aggregation caused by high salt environment, and reduce the problem of active sites being blocked by particle aggregation. (4) The N-vinylcaprolactam segment in this invention can respond to the increase in temperature in the geothermal area, causing the polymer layer to change from a hydrated and extended state to a relatively contracted state, increasing the contact opportunity between the iron-manganese active sites and As, thereby improving the efficiency of the material in geothermal hot spots. (5) The present invention uses an iron-manganese binary active core to couple the As(III) oxidation capacity of the manganese oxidation component with the As(V) fixation capacity of the iron oxidation / hydrogenation component in the same particle system, overcoming the shortcomings of single iron-based materials being difficult to quickly process As(III) and single manganese-based materials being difficult to fix As for a long time. (6) By first forming iron oxide / hydrogen hydroxide precursor particles and then generating manganese oxide sites in situ on their surface or near-surface region, the present invention makes the As(III) oxidation and As(V) fixation processes spatially adjacent to each other, reducing intermediate product diffusion loss and improving oxidation-fixation synergistic efficiency. (7) The present invention improves the adhesion of the material to soil fine particles, clay mineral edge hydroxyl sites and mineral-organic composite interfaces through the polydopamine adhesion layer, making it easier for the material to stay at key soil interfaces and play a role after reaching the geothermal target area. (8) The preparation method of the material of the present invention has a clear process, and the raw materials such as iron salt, manganese salt, polymer monomer and dopamine are readily available. The reaction conditions are relatively mild, making it suitable for further scale-up preparation and in-situ remediation of As-contaminated soil in geothermal areas. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The effect of different preparation conditions on the oxidation rate of As(III) and the total As fixation rate at 25℃ and 60℃ is shown in the figure. Figure 2 Figures showing the percentage of retention within an independent soil column for ordinary Fe-Mn binary material and Material II under different temperatures and chloride ion concentrations. Figure 3 The graph shows the change of total As concentration in pore water with reaction time after pulsed material injection. Figure 4 The proportion of As(III) in total As after pulse-injected material and reaction for 14 days, and at 60℃ and 1000 mg / L Cl - Distribution map of As speciation in soil under the given conditions; Figure 5 This diagram illustrates the change in total As concentration in the leachate during geothermal pore water rinsing. Detailed Implementation

[0025] The present invention provides a temperature-sensitive salt-resistant iron-manganese material, comprising a polymer selectively coated iron-manganese material and an adhesion layer located on the outer surface of the polymer selectively coated iron-manganese material; The polymer selectively coated iron-manganese material includes an iron-manganese binary active core and a temperature-sensitive salt-resistant copolymer layer coated on a portion of the surface of the iron-manganese binary active core. The iron-manganese binary active core includes an iron oxide / hydrogen hydroxide component and a manganese oxide component; the temperature-sensitive and salt-resistant copolymer layer is selectively and preferentially distributed on the surface of the iron oxide / hydrogen hydroxide component, and the surface of the manganese oxide component retains exposed sites. The temperature-sensitive and salt-resistant copolymer layer is a poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer; The adhesive layer is a polydopamine layer.

[0026] In this invention, the particle size of the temperature-sensitive salt-resistant iron-manganese material is preferably 50~300nm, specifically 70~120nm, 120~180nm, 180~260nm or 200~300nm.

[0027] In this invention, the iron oxide / hydroxide component includes one or more of low-crystallization iron hydroxide, iron oxide hydroxyl, and hydrated iron oxide; the manganese oxide component includes one or more of manganese dioxide, manganese oxide hydroxyl, and manganese oxide containing Mn(III) / Mn(IV). The molar ratio of iron to manganese in the iron-manganese binary active core is preferably 1.5 to 4:1, specifically 1.5:1, 2:1, or 4:1; the particle size of the iron-manganese binary active core is preferably 50 to 300 nm.

[0028] In this invention, the temperature-sensitive salt-resistant copolymer layer is preferentially distributed on the surface of the iron oxide / hydroxide component, while the manganese oxide component retains some exposed sites. The preferred mass ratio of the raw material N-vinylcaprolactam to sulfobetaine methacrylate in the preparation of the temperature-sensitive salt-resistant copolymer layer is 60-90:10-40, specifically 60:40, 70:30, 75:25, or 90:10. The temperature-sensitive salt-resistant copolymer layer of this invention can undergo dehydration shrinkage within the range of 35-70°C, increasing the exposure of active sites and improving the accessibility of the active sites of the iron-manganese binary active core. The sulfobetaine methacrylate segments form a hydration layer in chloride-containing porous water to reduce material aggregation in high-salt porous water.

[0029] In this invention, the mass of the polydopamine layer is preferably 0.5-8% of the total mass of the temperature-sensitive, salt-resistant iron-manganese material, specifically 0.5%, 3.0%, 6.0%, or 8.0%. The polydopamine layer enables the material to adhere to the iron-aluminum oxide coating on the surface of fine soil particles, the hydroxyl sites at the edges of clay minerals, and the mineral-organic composite interface, thereby enhancing the material's adhesion.

[0030] This invention also provides a method for preparing the temperature-sensitive, salt-resistant iron-manganese material described above, comprising the following steps: The pH of the mixed solution containing iron and manganese metal salts was first adjusted to 7.2-7.8 before Fe... 3+ Hydrolysis forms iron oxide / hydrogen hydroxide precursor particles, which are then adjusted to 8.3~9.0, Mn 2+ The iron oxide / hydrogen hydroxide precursor particles were loaded onto the surface of the iron oxide / hydrogen hydroxide precursor particles; the resulting system was mixed with hydrogen peroxide solution and aged to obtain an iron-manganese binary active core. The iron-manganese binary active core, water, N-vinylcaprolactam and sulfobetaine methacrylate are mixed for pre-adsorption. The resulting system, crosslinking agent and initiator are mixed for copolymerization reaction to form a temperature-sensitive salt-resistant copolymer layer on the surface of the iron-manganese binary active core, thus obtaining a polymer selectively coated iron-manganese material. The polymer is selectively coated with iron-manganese material, dopamine and buffer solution are mixed and subjected to self-polymerization reaction to form an adhesion layer, thereby obtaining the temperature-sensitive salt-resistant iron-manganese material.

[0031] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0032] In this invention, the pH value of a mixed solution of iron and manganese metal salts is first adjusted to 7.2-7.8, and then Fe is carried out. 3+ Hydrolysis forms iron oxide / hydrogen hydroxide precursor particles, which are then adjusted to 8.3~9.0, Mn 2+ The iron oxide / hydrogen hydroxide precursor particles were loaded onto the surface of the particles; the resulting system was mixed with hydrogen peroxide solution and aged to obtain an iron-manganese binary active core.

[0033] This invention performs stepwise alkalization and in-situ surface oxidation, which preferentially hydrolyzes iron ions to form iron oxide / hydrogen hydroxide precursor particles containing surface hydroxyl groups, and then oxidizes manganese ions on or near the surface of the iron oxide / hydrogen hydroxide precursor particles to form manganese oxidation sites, thus obtaining an iron-manganese binary active core.

[0034] In this invention, the iron ions (Fe) in the mixed solution of metal salts containing iron ions and manganese ions are... 3+ The concentration of manganese ions (Mn) is preferably 0.03~0.10 mol / L, specifically 0.03 mol / L, 0.04 mol / L, 0.06 mol / L or 0.10 mol / L. 2+The concentration of the iron salt is preferably 0.01~0.05 mol / L, specifically 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, or 0.05 mol / L; the molar ratio of iron ions to manganese ions is preferably 1.5~4:1, specifically 1.5:1, 2:1, or 4:1. This invention mixes iron salts, manganese salts, and water to obtain a mixed solution of metal salts containing iron and manganese ions. In an embodiment of this invention, FeCl3∙6H2O and MnSO4∙H2O are added to deoxygenated and deionized water and stirred until completely dissolved to obtain a mixed solution of metal salts containing iron and manganese ions. Before use, the mixed solution is preferably purged with nitrogen or argon gas for 20~40 min to reduce the dissolved oxygen content in the system. The iron salt provides precursor ions for the subsequent formation of iron oxide / hydroxide components, and the manganese salt provides precursor ions for the subsequent formation of manganese oxide components. This invention, through pre-deoxygenation and inert gas protection, can reduce uncontrolled oxidation caused by dissolved oxygen, allowing subsequent Fe... 3+ Preferential hydrolysis and Mn 2+ The in-situ oxidation process is easier to perform in a set sequence.

[0035] In this invention, the pH adjustment process is preferably carried out under inert gas protection and stirring conditions, wherein the inert gas preferably includes nitrogen or argon. The pH adjuster used for the first and second adjustments is preferably a NaOH solution, and the concentration of the sodium hydroxide solution is preferably 0.1 mol / L; in this invention, the sodium hydroxide solution is preferably added dropwise to the metal salt mixed solution.

[0036] Preferably, the pH value of the system is first adjusted to 7.2, 7.5, 7.6, or 7.8, wherein the Fe... 3+ The hydrolysis time is preferably 10 to 40 minutes, specifically 10 minutes, 20 minutes, 30 minutes or 40 minutes.

[0037] In this invention, the pH value of the system is preferably adjusted to 8.3, 8.6, 8.8 or 9.0, so that some manganese ions are adsorbed or deposited on the surface of the iron oxide / hydrogen hydroxide precursor particles.

[0038] In this invention, the mass fraction of the hydrogen peroxide solution is preferably 1-5%, specifically 1%, 3%, 4%, or 5%; the volume of the hydrogen peroxide solution is preferably 1-8% of the volume of the metal salt mixed solution, specifically 1%, 3%, 5%, or 8%. The aging reaction temperature is preferably 50-70℃, specifically 50℃, 60℃, 65℃, or 70℃, and the time is preferably 1-4h, specifically 1h, 2h, 3h, or 4h; the aging process causes manganese ions on or near the surface of the iron oxide / hydrogen hydroxide precursor particles to be oxidized in situ to manganese oxide sites containing Mn(III) / Mn(IV).

[0039] In this invention, the aging process preferably further includes: centrifuging the aged system and washing the resulting solid. The washing preferably uses deoxygenated and deionized water, and is preferably performed 2-4 times. This washing removes unreacted salt ions and residual oxidants.

[0040] In this invention, Fe 3+ The preferential hydrolysis and in-situ formation process of manganese oxide sites on the surface are as follows: First, Fe is generated by alkalization. 3+ Mn is preferentially hydrolyzed to form iron oxide / hydrogen hydroxide precursor particles, and then oxidized on the surface or in the vicinity of these precursor particles. 2+ This allows for close coupling between manganese oxidation sites and iron oxidation / hydroxide components, resulting in an iron-manganese binary active core. Specifically, the metal salts (Fe...) are first mixed under inert gas protection and stirring conditions. 3+ +Mn 2+ The pH of the solution was adjusted to 7.2-7.8 and maintained for 10-40 minutes to allow Fe to... 3+ Preferential hydrolysis forms iron oxide / hydrogen hydroxide precursor particles containing surface hydroxyl groups. Subsequently, the pH of the system is adjusted to 8.3–9.0 to allow some Mn to... 2+ The iron oxide / hydrogen hydroxide precursor particles are adsorbed or deposited on their surface; then, a 1-5% (w / w) hydrogen peroxide solution is added dropwise, and the reaction is carried out at 50-70°C for 1-4 hours. This causes the manganese ions on or near the surface of the iron oxide / hydrogen hydroxide precursor particles to be oxidized in situ to manganese oxide sites containing Mn(III) / Mn(IV), resulting in an iron-manganese binary active core. The purpose of the first pH adjustment is to utilize Fe... 3+ The relatively easy hydrolysis of iron oxide / hydrogen hydroxide precursor particles allows for their initial formation, providing hydroxyl sites on their surface; the secondary pH adjustment aims to promote the formation of Mn. 2+ The iron oxide / hydroxide precursor particles are adsorbed or deposited onto the surface of the particles; subsequently, Mn located on or near the surface of the iron phase is subjected to hydrogen peroxide oxidation. 2+ In situ, it is converted into a manganese oxide site.

[0041] Unlike the common method of simultaneous precipitation or mechanical mixing of iron and manganese salts, this invention uses a stepwise nucleation method to form manganese oxidation sites in situ on the surface or near the surface of the iron oxidation / hydrogenation component. This allows the As(III) oxidation sites and As(V) fixation sites to maintain close coupling, thereby shortening the mass transfer distance between As(III) oxidation and As(V) fixation and improving the subsequent oxidation-fixation synergistic efficiency.

[0042] After obtaining the iron-manganese binary active core, the present invention mixes the iron-manganese binary active core, water, N-vinylcaprolactam and sulfobetaine methacrylate for pre-adsorption, and mixes the obtained system, crosslinking agent and initiator for copolymerization reaction to form a temperature-sensitive salt-resistant copolymer layer on the surface of the iron-manganese binary active core, thereby obtaining a polymer selectively coated iron-manganese material.

[0043] In this invention, the water is preferably deoxygenated water. The preferred method for mixing the iron-manganese binary active core, water, N-vinylcaprolactam, and sulfobetaine methacrylate is as follows: first, the iron-manganese binary active core is dispersed in water to obtain an iron-manganese binary active core dispersion; then, N-vinylcaprolactam and sulfobetaine methacrylate are added to the iron-manganese binary active core dispersion. The mixing of the iron-manganese binary active core, water, N-vinylcaprolactam, and sulfobetaine methacrylate preferably further includes: adjusting the pH of the system to 5.5~6.5, specifically 5.5, 6.0, 6.2, or 6.5; the pre-adsorption is preferably carried out under stirring, and the preferred time is 20~60 min, specifically 20 min, 30 min, 45 min, or 60 min. The pH value of the system described in this invention allows the monomer to preferentially adsorb onto the hydroxyl sites on the surface of the iron oxide / hydrogen hydroxide component.

[0044] In this invention, the mass ratio of N-vinylcaprolactam to sulfobetaine methacrylate is preferably 60~90:10~40, specifically 60:40, 70:30, 75:25 or 90:10.

[0045] In this invention, the crosslinking agent is preferably N,N'-methylenebisacrylamide, and the initiator is preferably potassium persulfate.

[0046] In this invention, the copolymerization reaction is preferably carried out under an inert gas atmosphere. The temperature of the copolymerization reaction is preferably 65~75℃, specifically 65℃, 70℃, or 75℃, and the time is preferably 0.5~2h, specifically 0.5h, 1h, 1.5h, or 2h. During the copolymerization reaction, N-vinylcaprolactam and sulfobetaine methacrylate copolymerize, preferentially forming a poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer on the surface of the iron oxide / hydrogen hydroxide component, while the surface of the manganese oxide component maintains an exposure ratio of 20~70%.

[0047] Because the iron oxide / hydroxide component has abundant hydroxyl groups on its surface, N-vinylcaprolactam and sulfobetaine methacrylate can preferentially accumulate on the surface of the iron oxide / hydroxide component through hydrogen bonding, electrostatic interaction, or coordination. This invention does not add the monomer, crosslinking agent, and initiator simultaneously, but instead adopts a feeding and reaction sequence of "monomer pre-adsorption followed by in-situ copolymerization." Specifically, the iron-manganese binary active core is first dispersed in deoxygenated water, and the pH of the system is adjusted to 5.5-6.5. Then, N-vinylcaprolactam and sulfobetaine methacrylate are added, with a mass ratio of 60-90:10-40, and pre-adsorbed under stirring for 20-60 min, so that the two monomers preferentially accumulate on the surface of the iron oxide / hydrogen hydroxide component. After pre-adsorption, N,N'-methylenebisacrylamide, a crosslinking agent, and potassium persulfate, an initiator, are added, and the reaction is carried out at 65-75℃ for 0.5-2 h, so that the two monomers already enriched on the surface of the iron oxide / hydrogen hydroxide component undergo in-situ copolymerization. As a result, the poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer is mainly formed on the surface of the iron oxide / hydrogen hydroxide component, rather than completely covering the manganese oxide sites. Thus, on the one hand, the polymer layer improves the dispersion and migration properties and salt agglomeration resistance of the material, and on the other hand, it maintains a certain exposed ratio of manganese oxide sites, ensuring that As(III) can contact the manganese oxide sites in time and be oxidized to As(V). For example, in Example 1, the washed iron-manganese binary active cores were completely dispersed in 80 mL of deoxygenated water. After adjusting the pH to 5.5, 0.12 g of N-vinylcaprolactam and 0.08 g of sulfobetaine methacrylate were added, and the mixture was stirred for pre-adsorption for 60 min. Subsequently, 0.006 g of N,N'-methylenebisacrylamide and 0.004 g of potassium persulfate were added, and the mixture was reacted at 65°C for 2 h. This sequence is "pre-adsorption followed by in-situ copolymerization".

[0048] After obtaining the polymer selectively coated iron-manganese material, the present invention mixes the polymer selectively coated iron-manganese material, dopamine and buffer solution to carry out a self-polymerization reaction to form an adhesion layer (polydopamine layer) to obtain a temperature-sensitive salt-resistant iron-manganese material.

[0049] In this invention, the dopamine is preferably used in the form of dopamine hydrochloride; the concentration of dopamine hydrochloride in the system after mixing the polymer selectively coated iron-manganese material, dopamine, and buffer solution is preferably 0.2~1.0 g / L, specifically 0.2 g / L, 0.5 g / L, 0.8 g / L, or 1.0 g / L. The buffer solution is preferably a Tris buffer solution with a pH of 8.0~8.8.

[0050] In this invention, the self-polymerization reaction is preferably carried out under stirring at room temperature for a time preferably of 0.5 to 3 hours, specifically 0.5 hours, 1 hour, 2 hours, or 3 hours. The self-polymerization reaction preferably further includes washing the resulting product. The polydopamine layer is located on the outer surface of the material and its purpose is not as a major As oxidation or fixation component, but rather as an interfacial adhesion layer. This adhesion layer can improve the adhesion of the material to iron and aluminum oxide coatings on the surface of fine soil particles, hydroxyl sites at the edges of clay minerals, and at mineral-organic composite interfaces.

[0051] This invention also provides the application of the temperature-sensitive salt-resistant iron-manganese material described in the above technical solution or the temperature-sensitive salt-resistant iron-manganese material obtained by the above preparation method in the remediation of arsenic pollution in soil and groundwater in geothermal areas.

[0052] The material of this invention can oxidize As(III) and fix As in soil and groundwater in geothermal areas.

[0053] This invention also provides a method for remediating As-contaminated soil in geothermal areas using the temperature-sensitive, salt-resistant iron-manganese material described above, comprising the following steps: The temperature-sensitive, salt-resistant iron-manganese material was formulated into a dispersion and applied to As-contaminated soil in geothermal areas by in-situ injection, mixing, or dosing.

[0054] In this invention, the preferred dosage of the temperature-sensitive and salt-resistant iron-manganese material is 0.05-3.0% of the dry weight of the soil, or 0.05-2.0 g / L based on the volume of pore water in the geothermal area; the temperature of the geothermal pore water area is 35-80℃, the pH value is 7.5-9.5, and the chloride ion concentration is 200-2000 mg / L.

[0055] The material of this invention maintains dispersed transport during the low-temperature, low-salt migration stage. After entering the geothermal pore water region with increased temperature and chloride ions, the poly-N-vinylcaprolactam segments undergo dehydration and shrinkage, increasing the accessibility of iron and manganese active sites. The sulfobetaine methacrylate segments maintain the anti-salinization layer. The manganese oxidation component oxidizes As(III) in the pore water to As(V), and the iron oxidation / hydrogenation component further fixes As(V). The polydopamine adhesion layer allows the material to adhere to the key interfaces of the soil, thereby achieving As(III) detoxification and As fixation.

[0056] The temperature-sensitive and salt-resistant iron-manganese material is kept dispersed and transported before entering the geothermal area to improve its migration ability in the soil pore medium. After entering the geothermal pore water area with increased temperature and chloride ions, the temperature-sensitive and salt-resistant copolymer layer responds to temperature and improves the accessibility of the active sites of the iron-manganese binary active core. The sulfobetaine methacrylate segment reduces the aggregation of the material in the high chloride ion pore water. The manganese oxidation component oxidizes As(III) in the pore water to As(V). The iron oxidation / hydrogenation component fixes As(V).

[0057] This invention can improve the migration capacity of in-situ remediation materials for As-contaminated soil in geothermal areas, reduce particle aggregation in high-salt pore water, reduce the concentration of As(III) in pore water, and reduce the migration of total As.

[0058] Although existing studies have attempted to improve the dispersibility and migration of particulate materials during soil injection through polymer coating, surface grafting, or carrier loading, current technologies typically only focus on transport performance under normal temperature and conventional groundwater conditions, without considering the combined effects of increased temperature, high salt ion strength, low oxygen reduction conditions, and complex coexisting ions on the number of active sites, anti-agglomeration ability, and retention behavior in the target area after the material enters the geothermal environment.

[0059] To address the problems of existing in-situ remediation materials for As contaminated soil, such as retention before entering geothermal areas, limited migration distance, and agglomeration in high-salt pore water leading to a reduction in active sites, this invention provides a temperature-sensitive, salt-resistant iron-manganese material for As contaminated soil remediation in geothermal areas, possessing migration, salt-resistant dispersion, and As reactive fixation functions. The material uses an iron-manganese binary active core as the main reaction unit. The manganese oxide component oxidizes the highly toxic and migratory As(III) into the more easily fixed As(V), while the iron oxide / hydrogen hydroxide component adsorbs, co-precipitates, or surface-complexes the generated As(V). Unlike conventional iron-manganese materials obtained through simultaneous precipitation or simple mechanical mixing of iron and manganese salts, this invention uses stepwise alkalization and in-situ surface oxidation to first form iron oxide / hydrogen hydroxide precursor particles, followed by the formation of manganese oxide sites on or near the surface of these precursor particles. This ensures close coupling between As(III) oxidation sites and As(V) fixation sites, improving the synergy of the As oxidation-fixation process.

[0060] Simultaneously, this invention constructs a poly(N-vinylcaprolactam) / sulfobetaine methacrylate thermosensitive and salt-resistant copolymer layer on the surface of the iron-manganese binary active core, and further forms a polydopamine adhesion layer. The poly(N-vinylcaprolactam) segments are used to respond to natural warming in geothermal areas, improving the accessibility of iron-manganese active sites after the material enters high-temperature geothermal contaminated areas; the sulfobetaine methacrylate segments are used to maintain the hydration layer in high-chloride, high-salinity pore water, reducing particle aggregation due to increased salinity; the polydopamine layer enhances the material's adhesion to fine soil particles, hydroxyl sites at clay mineral edges, and mineral-organic composite interfaces. This invention can improve the migration ability of iron-manganese remediation materials before entering geothermal areas, reduce aggregation and deactivation in high-salinity pore water, and achieve As(III) oxidation and As(V) fixation in the geothermal target area.

[0061] To further illustrate the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, describes the temperature-sensitive salt-resistant iron-manganese material, its preparation method, and its application, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0062] Example 1: Preparation of materials with low iron-manganese ratio, high salt-resistant monomer ratio, and high-temperature response Weigh 0.811 g FeCl3∙6H2O and 0.338 g MnSO4∙H2O and dissolve them in 100 mL of deoxygenated water to prepare Fe 3+ The concentration is 0.03 mol / L, Mn 2+ A 0.02 mol / L mixed solution of metal salts was prepared, with a Fe to Mn molar ratio of 1.5:1. Nitrogen gas was bubbled into the mixed solution for 20 min to reduce the dissolved oxygen content. Subsequently, 0.1 mol / L NaOH solution was added dropwise under stirring to adjust the pH to 7.2 and maintain this pH for 10 min, allowing Fe to... 3+ Preferential hydrolysis forms iron oxide / hydrogen hydroxide precursor particles containing surface hydroxyl groups.

[0063] Continue adding NaOH solution dropwise to adjust the pH of the system to 8.3, so that Mn 2+ Adsorption, coordination enrichment, and deposition occur on the surface of hydroxyl-rich iron oxide / hydroxide precursor particles; subsequently, 1 mL of 1% hydrogen peroxide solution is added, and the mixture is aged at 50 °C for 4 h to allow Mn to be loaded onto the surface of the iron oxide / hydroxide precursor particles. 2+ In-situ oxidation and heterogeneous nucleation growth resulted in manganese oxide sites containing Mn(III) / Mn(IV), yielding iron-manganese binary active nuclei with surface-loaded manganese oxide sites. After aging, the reaction system was centrifuged, and the resulting solid was washed three times with deoxygenated water to remove unreacted salt ions and residual oxidant.

[0064] The washed iron-manganese binary active cores were dispersed in 80 mL of deoxygenated water, and the pH was adjusted to 5.5. 0.12 g of N-vinylcaprolactam and 0.08 g of sulfobetaine methacrylate were added to the dispersion at a mass ratio of 60:40, and pre-adsorbed for 60 min. Then, 0.006 g of N,N'-methylenebisacrylamide and 0.004 g of potassium persulfate were added, and the reaction was carried out at 65 °C for 2 h. This allowed the poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer to preferentially form on the surface of the iron oxide / hydrogen hydroxide components, while maintaining a high proportion of exposed manganese oxide sites. After the reaction, the product was centrifuged and washed three times with deoxygenated water to obtain the polymer-selectively coated iron-manganese material.

[0065] The polymer selectively coated iron-manganese material was dispersed in 100 mL of Tris buffer with a concentration of 10 mmol / L and a pH of 8.0. 20 mg of dopamine hydrochloride was added to make the dopamine hydrochloride concentration 0.2 g / L. The mixture was stirred at room temperature for 0.5 h. After the reaction was completed, the mixture was centrifuged and washed three times with deoxygenated water to obtain temperature-sensitive salt-resistant iron-manganese material I.

[0066] In this embodiment, the lower limit of the Fe to Mn molar ratio was used, and the mass ratio of N-vinylcaprolactam to sulfobetaine methacrylate was 60:40. The resulting material had a particle size of approximately 70–120 nm, which was obtained through dynamic light scattering. The polydopamine layer accounted for approximately 0.5% of the total material mass, a proportion estimated through thermogravimetric analysis combined with a control of uncoated polydopamine samples. Due to the high proportion of sulfobetaine methacrylate, the material exhibited strong resistance to salt dispersion in chloride-containing water. This property was further verified by varying the concentration of different Cl-containing compounds. - The hydrated particle size and Zeta potential under different concentration conditions were evaluated. The material exhibited significant dehydration shrinkage and exposure of active sites in the range of approximately 65–70 °C. This temperature-sensitive response was determined by dynamic light scattering test under varying temperatures and verified by combining the As(III) oxidation rate and total As fixation rate at different temperatures.

[0067] Example 2: Preparation of materials with medium iron-manganese ratio, medium salt-resistant monomer ratio, and medium temperature response. Dissolve FeCl3∙6H2O and MnSO4∙H2O in 100 mL of deoxygenated water to prepare Fe 3+ The concentration is 0.06 mol / L, Mn 2+ A 0.03 mol / L mixed solution of metal salts, with a Fe to Mn molar ratio of 2:1, was prepared. After purging with nitrogen for 30 min, a 0.1 mol / L NaOH solution was added dropwise under stirring to adjust the pH of the system to 7.5 and maintain this pH for 20 min, allowing Fe to... 3+ Preferential hydrolysis forms iron oxide / hydrogen hydroxide precursor particles.

[0068] Continue adding NaOH solution dropwise to adjust the pH of the system to 8.6, so that Mn 2+ The manganese component is adsorbed or deposited on the surface of the iron oxide / hydrogen hydroxide precursor particles; then a 3% hydrogen peroxide solution is added dropwise, with the volume of the added solution being 3% of the volume of the metal salt mixture. The mixture is aged at 60°C for 2 h to allow the manganese component to be oxidized in situ on or near the surface of the iron oxide / hydrogen hydroxide precursor particles, thus obtaining an iron-manganese binary active core.

[0069] The obtained iron-manganese binary active core was centrifuged and washed three times with deoxygenated water, then dispersed completely in 80 mL of deoxygenated water, and the pH was adjusted to 6.0. 0.15 g of N-vinylcaprolactam and 0.05 g of sulfobetaine methacrylate were added to the dispersion at a mass ratio of 75:25, and pre-adsorbed for 30 min under stirring. After pre-adsorption, 0.006 g of N,N'-methylenebisacrylamide was added as a crosslinking agent, and 0.004 g of potassium persulfate was added as an initiator. The reaction was carried out at 70 °C for 1 h, allowing the two monomers to copolymerize in situ on the surface of the iron-manganese binary active core to form a temperature-sensitive, salt-resistant copolymer layer. After the reaction, the product was centrifuged and washed three times with deoxygenated water to obtain a polymer-selectively coated iron-manganese material.

[0070] Subsequently, the selectively coated iron-manganese material was dispersed in 100 mL of Tris buffer solution with a concentration of 10 mmol / L and a pH of 8.5. 50 mg of dopamine hydrochloride was added to make the dopamine hydrochloride concentration 0.5 g / L. The mixture was stirred and self-polymerized at room temperature for 1 h. After the reaction was completed, the mixture was centrifuged and washed three times with deoxygenated water to obtain temperature-sensitive salt-resistant iron-manganese material II.

[0071] The resulting material has a particle size of approximately 120-180 nm, and the polydopamine layer accounts for approximately 3.0% of the total material mass. This embodiment represents a preferred intermediate ratio, and the resulting copolymer layer exhibits significant dehydration shrinkage and site exposure within a temperature range of approximately 50-60°C. This allows it to maintain migration during the low-temperature injection stage while also exposing iron-manganese active sites in geothermal hotspot areas.

[0072] Example 3: Preparation of materials with high iron-manganese ratio, high temperature-sensitive monomer ratio, and low temperature response. Dissolve FeCl3∙6H2O and MnSO4∙H2O in 100 mL of deoxygenated water to prepare Fe 3+ The concentration is 0.04 mol / L, Mn 2+ A 0.01 mol / L mixed solution of metal salts, with a Fe to Mn molar ratio of 4:1 (Mn... 2+ Feed amount is Fe 3+The feed amount was 25 mol%, accounting for 20 mol% of the total metal ion feed amount. Argon gas was introduced into the metal salt mixture solution for 40 min; then the pH of the system was adjusted to 7.8 and maintained for 40 min, so that Fe 3+ Complete hydrolysis forms iron oxide / hydrogen hydroxide precursor particles.

[0073] Continue adding NaOH solution dropwise to adjust the pH of the system to 9.0, so that Mn 2+ Adsorption, coordination enrichment, and deposition occur on the surface of hydroxyl-rich iron oxide / hydroxide precursor particles; subsequently, a 5% (w / w) hydrogen peroxide solution is added dropwise, with the volume of the hydrogen peroxide solution being 8% of the volume of the metal salt mixed solution. The mixture is aged at 70°C for 1 h, allowing Mn to be loaded onto the surface of the iron oxide / hydroxide precursor particles. 2+ In-situ oxidation and heterogeneous nucleation growth into manganese oxide sites containing Mn(Ⅲ) / Mn(Ⅳ) yields an iron-manganese binary active core with surface-loaded manganese oxide sites.

[0074] The obtained iron-manganese binary active core was washed and dispersed in deoxygenated water. The pH was adjusted to 6.5, and 0.18 g of N-vinylcaprolactam and 0.02 g of sulfobetaine methacrylate were added to make a mass ratio of 90:10. Pre-adsorption was performed for 20 min. N,N'-methylenebisacrylamide and potassium persulfate were added, with N,N'-methylenebisacrylamide accounting for 3 wt% of the total monomer mass and potassium persulfate accounting for 2 wt% of the total monomer mass. The reaction was carried out at 75 °C for 0.5 h to form a copolymer layer.

[0075] Subsequently, the polymer selectively coated iron-manganese material obtained in the above steps was dispersed in 100 mL of Tris buffer with a concentration of 10 mmol / L and a pH of 8.8. 100 mg of dopamine hydrochloride was added to make the concentration of dopamine hydrochloride 1.0 g / L. The mixture was stirred and self-polymerized at room temperature for 3 h. After the reaction was completed, the mixture was centrifuged and washed three times with deoxygenated water to obtain temperature-sensitive salt-resistant iron-manganese material III.

[0076] In this embodiment, Fe 3+ With Mn 2+ With the upper limit of the molar ratio and the upper limit of the N-vinylcaprolactam ratio, the resulting material has a particle size of approximately 180~260 nm, and the mass of the polydopamine layer accounts for approximately 8.0% of the total mass of the material. The mass ratio of manganese oxide sites in the resulting material is 2~35%. The copolymer layer undergoes dehydration shrinkage and site exposure in the range of approximately 35~45℃, making it suitable for geothermal pollution transition zones where temperature rise occurs early.

[0077] Example 4: Preparation of materials with high precursor concentration, strong adhesion layer and moderate response temperature Weigh out FeCl3∙6H2O and MnSO4∙H2O and dissolve them in 100 mL of deoxygenated water to prepare Fe 3+ Concentration of 0.10 mol / L, Mn 2+ A 0.05 mol / L mixed solution of metal salts was prepared, with a Fe to Mn molar ratio of 2:1. After purging with nitrogen for 35 min, the pH of the system was adjusted to 7.6 and maintained for 30 min to allow the iron oxide / hydroxide precursor particles to form first.

[0078] Continue adding NaOH solution to adjust the pH of the system to 8.8, then add 4% hydrogen peroxide solution (volume 5% of the metal salt mixture), and age at 65℃ for 3 h to obtain the iron-manganese binary active core.

[0079] The obtained iron-manganese binary active core was washed and dispersed in deoxygenated water. The pH was adjusted to 6.2, and 0.14 g of N-vinylcaprolactam and 0.06 g of sulfobetaine methacrylate were added to make a mass ratio of 70:30. Pre-adsorption was performed for 45 min. Then, 0.006 g of N,N'-methylenebisacrylamide was added as a crosslinking agent, and 0.004 g of potassium persulfate was added as an initiator. The reaction was carried out at 70 °C for 1.5 h.

[0080] Subsequently, the polymer selectively coated iron-manganese material obtained in the above steps was dispersed in 100 mL of Tris buffer with a concentration of 10 mmol / L and a pH of 8.6. 80 mg of dopamine hydrochloride was added to make the dopamine hydrochloride concentration 0.8 g / L. The mixture was stirred and self-polymerized at room temperature for 2 h. After the reaction was completed, the mixture was centrifuged and washed three times with deoxygenated water to obtain temperature-sensitive salt-resistant iron-manganese material IV.

[0081] In this embodiment, Fe 3+ and Mn 2+ The concentration is taken at the upper limit, the particle size of the obtained material is about 200~300 nm, the mass of the polydopamine layer accounts for about 6.0% of the total mass of the material, and 35~50% of the manganese oxide sites are exposed. The obtained material undergoes dehydration and shrinkage in the range of about 45~55℃ and has a strong soil interface adhesion ability.

[0082] Comparative Example 1: Ordinary iron-manganese binary composite material Weigh out FeCl3·6H2O and MnSO4·H2O and dissolve them in deoxygenated water to prepare Fe 3+ The concentration is 0.06 mol / L, Mn 2+A 0.03 mol / L mixed solution of metal salts, with a Fe to Mn molar ratio of 2:1, was prepared. After purging with nitrogen for 30 min, a 0.1 mol / L NaOH solution was added dropwise under stirring to adjust the pH to 8.6, allowing iron and manganese ions to precipitate simultaneously. Subsequently, a 3% (w / w) hydrogen peroxide solution was added dropwise, accounting for 3% of the volume of the mixed metal salt solution. The mixture was aged at 60℃ for 2 h to oxidize the manganese component, forming a manganese oxide component containing Mn(III) / Mn(IV). After aging, the mixture was centrifuged and washed three times with deoxygenated water to obtain a common iron-manganese binary composite material.

[0083] This comparative example does not have an N-vinylcaprolactam / sulfobetaine methacrylate copolymer coating or a polydopamine layer modification. It is used to evaluate the effects of the temperature-sensitive salt-resistant copolymer layer and the polydopamine adhesive layer on material migration, salt resistance dispersion, temperature response, and As fixation properties.

[0084] Test Example 1: Screening of materials obtained under different preparation conditions and evaluation of geothermal temperature triggering effect Simulated geothermal pore water with an As(III) concentration of 1.0 mg / L was prepared using NaAsO2, and the pH was adjusted to 8.3. NaCl was then added to make Cl... - The concentration was 1000 mg / L. NaHCO3 was added to make the HCO3 concentration 500 mg / L, and Na2SiO3 was added to make the silicate concentration (calculated as SiO2) 50 mg / L. This was used to simulate the alkaline, high chloride ion, bicarbonate and silicate-containing pore water environment of a geothermal area. The simulated pore water-contaminated soil system consisted of 50 mL of the above-mentioned simulated geothermal pore water and 5.0 g of As(III) contaminated simulated soil. The As(III) contaminated simulated soil was obtained by mixing quartz sand, loam, bentonite, humic acid and iron-aluminum oxide sand in a mass ratio of 70:20:5:2:3, and then fully contacting and aging it with NaAsO2 solution. Materials I, II, III and IV prepared in Examples 1-4 were added to the simulated pore water-contaminated soil system at 0.5 g / L, and reacted at 25℃ and 60℃ for 24 h, respectively. The ordinary iron-manganese binary composite material prepared in Comparative Example 1 was used as a control.

[0085] Figure 1 The graph shows the effect of different preparation conditions on the oxidation rate of As(Ⅲ) and the total As fixation rate at 25℃ and 60℃.

[0086] like Figure 1As shown, at 25°C, the oxidation rates of As(III) by materials I, II, III, and IV were 24%, 28%, 31%, and 29%, respectively, with total As fixation rates of 20%, 18%, 16%, and 21%, respectively. The oxidation rate of As(III) by the ordinary iron-manganese binary composite material was 26%, and the total As fixation rate was 24%. These results indicate that during the low-temperature transport stage, the materials of this invention do not prematurely exhibit strong reactivity and retention characteristics, which is beneficial for the continued migration of the materials to deeper or thermally contaminated areas.

[0087] At 60°C, the oxidation rates of As(III) by materials I, II, III, and IV were 88%, 94%, 91%, and 92%, respectively, and the total As fixation rates were 86%, 92%, 88%, and 90%, respectively. The oxidation rate of As(III) by the ordinary iron-manganese binary composite material was 84%, and the total As fixation rate was 70%. Among them, the total As concentration in the pore water of material II decreased from 1.0 mg / L to 0.08 mg / L at 60°C, and both the As(III) oxidation rate and the total As fixation rate were at a relatively high level. Therefore, material II prepared in Example 2 was selected as the preferred material for subsequent examples.

[0088] Material II of this invention exhibits a significantly enhanced As reduction effect above 40°C, with the total As concentration in pore water decreasing to 0.08 mg / L and 0.07 mg / L at 60°C and 70°C, respectively. These results indicate that the material of this invention does not rely solely on room-temperature adsorption, but rather demonstrates stronger As(III) oxidation and total As fixation capabilities in high-temperature regions influenced by geothermal water.

[0089] Test Example 2: Evaluation of the retention performance of materials in independent soil columns under different temperature and salinity conditions Six independent temperature-controlled soil columns, each 10 cm in length, were used to investigate the effects of temperature and chloride ion concentration on material retention behavior. Each column was filled with a simulated geothermal soil medium, composed of quartz sand, loam, bentonite, humic acid, and iron-aluminum oxide-coated sand in a mass ratio of 70:20:5:2:3. Quartz sand provided the main pore framework, loam and bentonite provided hydroxyl sites at the edges of fine-grained and clay minerals, humic acid provided the mineral-organic matter interface, and iron-aluminum oxide-coated sand provided the iron-aluminum oxide coating on the surface of fine soil particles. This medium simulates the key interfaces at which materials may migrate, adhere, and remain in geothermal soils.

[0090] The experimental conditions for the six soil columns were as follows: the temperature of the first soil column was 25℃, Cl... - The concentration was 0 mg / L; the temperature of the second soil column was 35℃; Cl - The concentration was 0 mg / L; the temperature of the third soil column was 60℃; Cl- The concentration was 0 mg / L; the temperature of the fourth soil column was 25℃; Cl - The concentration was 1000 mg / L; the temperature of the fifth soil column was 35℃, Cl - The concentration was 1000 mg / L; the temperature of the sixth soil column was 60℃; Cl - The concentration is 1000 mg / L.

[0091] Material II obtained in Example 2 was prepared as a 0.5 g / L dispersion and injected into the six independent soil columns at a flow rate of 1.0 mL / min for 72 minutes. Elution was then carried out for 18 minutes using the corresponding background solution without the material. Parallel experiments were conducted under the same conditions using a common Fe-Mn binary material as a control. After the column experiments, the filling medium and effluent from each independent soil column were collected, and the Fe and Mn contents were determined. The retention percentage of the material within the column under different temperatures and chloride ion concentrations was calculated.

[0092] Figure 2 The graph shows the percentage of retention of ordinary Fe-Mn binary material and material II in an independent soil column under different temperatures and chloride ion concentrations.

[0093] like Figure 2 As shown, at 25℃, Cl - Under low temperature and low salinity conditions with a concentration of 0 mg / L, the retention percentage of material II in the column is relatively low, indicating that material II is not easily intercepted by the soil medium before entering the geothermal target area and has good transport capacity. In contrast, the retention percentage of ordinary Fe-Mn binary material in the column is relatively high under the same conditions, indicating that it is easily intercepted during the transport stage and has a limited migration distance.

[0094] At 35℃, Cl - Under the transition temperature condition with a concentration of 0 mg / L, the retention percentage of material II in the column increased compared to the 25℃ condition, but was much lower than that at 60℃, indicating that material II began to exhibit partial response and retention in the initial stage of temperature increase, while still retaining a certain migration capacity. The retention percentage of ordinary Fe-Mn binary materials showed little change under low-salt conditions at 25℃, 35℃, and 60℃, indicating that its retention behavior lacked a significant temperature response characteristic.

[0095] At 60℃, Cl - Under geothermal high-temperature conditions with a concentration of 0 mg / L, the retention percentage of material II within the column increased significantly, indicating that material II exhibits a temperature-sensitive response upon entering the high-temperature region and enhances its retention in the soil medium. This result demonstrates that the material of this invention can maintain migration at low temperatures while enhancing retention in the geothermal high-temperature target area, which is beneficial for improving material utilization in the target area.

[0096] At 25℃ and 35℃, 1000 mg / L Cl - Under the given conditions, the column retention percentage of ordinary Fe-Mn binary materials was significantly higher than that under the same low-salt conditions, indicating that increased chloride ion concentration exacerbates particle agglomeration and non-target retention in ordinary Fe-Mn, reducing its migration ability. In contrast, the column retention percentage of material II under high chloride conditions was only slightly higher than that under low-salt conditions, indicating that the sulfobetaine segments can mitigate particle instability caused by high-salt environments, endowing the material with better salt resistance and transport capabilities.

[0097] At 60℃ and 1000 mg / L Cl - Under high temperature and high salinity conditions, the retention percentage of Material II within the column remained at a high level, indicating that Material II can effectively retain material under geothermal target conditions. Simultaneously, compared to low salinity conditions at 60℃, its retention percentage changed less, suggesting that the high chloride ion environment did not cause uncontrollable aggregation of the material; rather, the material achieved retention in the target area through temperature-sensitive shrinkage and polydopamine interfacial adhesion. In summary, the material of this invention possesses migration-retention characteristics: it is mobile at low temperatures, can be retained in high-temperature target areas, and does not undergo uncontrollable aggregation under high chloride conditions. It is suitable for in-situ injection remediation of As-contaminated soils in geothermal areas.

[0098] Test Example 3: Evaluation of In-Column Oxidation Fixation in As-Containing Geothermal Target Section Two independent temperature-controlled soil columns, each 10 cm in length, were used to investigate the effect of temperature changes on the oxidation and fixation of materials in As-containing geothermal soil media under high chloride ion pore water conditions. The filling medium for each soil column was a simulated geothermal soil medium, composed of quartz sand, loam, bentonite, humic acid, and iron-aluminum oxide-coated sand in a mass ratio of 70:20:5:2:3. This medium was used to simulate the key interfaces for material migration, adhesion, retention, and As fixation in geothermal soil.

[0099] NaAsO2 solution was thoroughly mixed with the simulated geothermal soil medium at the target moisture content, allowing As(III) to first contact with fine soil particles, hydroxyl sites at the edges of clay minerals, the mineral-organic complex interface, and iron-aluminum oxide-coated sand. Subsequently, the mixture was sealed and aged under dark, low-oxygen conditions, allowing As to reach a relatively stable distribution state between the soil solid phase and pore water, thus preparing the As(III) contaminated soil medium. This As(III) contaminated soil medium was then filled into an independent temperature-controlled soil column and subjected to Cl... -Background pore water with a concentration of 1000 mg / L and a pH of 8.3 was pre-saturated and equilibrated until the total As concentration in the effluent stabilized. After equilibration, the initial As(III) concentration in the pore water of each soil column was 1.0 mg / L, and the initial total As concentration in the pore water was 1.20 mg / L. Therefore, the As in the column mainly originated from the continuous release of As from the contaminated soil under high-chlorine pore water conditions, rather than from a one-time addition of pore water followed by rapid flushing out with the water flow.

[0100] The experimental conditions for the first soil column were: temperature 25℃, Cl... - The concentration was 1000 mg / L; the experimental conditions for the second soil column were: temperature 60℃, Cl... - The concentration is 1000 mg / L.

[0101] Material II obtained in Example 2 was prepared as a 0.5 g / L dispersion and introduced into the two independent soil columns at a flow rate of 1.0 mL / min, allowing the material to migrate, remain, and react with the continuously released As(III) in the As-contaminated soil medium. A parallel experiment was conducted under the same conditions using a common Fe-Mn binary material as a control, with a geothermal blank group without material addition. During operation, the temperature and high-chlorine pore water conditions of each soil column were maintained. Soil column effluent or pore water samples were collected at 0, 1, 3, 7, and 14 days to determine the total As concentration. At 14 days, the proportion of As(III) in the total As was determined, and the soil column filling medium was collected. The speciation of As in the soil was determined using the Tessier continuous extraction method.

[0102] Figure 3 The graph shows the change in total As concentration in pore water over reaction time after pulsed material injection.

[0103] like Figure 3 As shown, at 1000 mg / L Cl - Under the given conditions, the total As concentration in pore water of the 25℃ geothermal control group increased from 1.20 mg / L to 1.34 mg / L, and further increased to 1.72 mg / L in the 60℃ geothermal control group, indicating that temperature increases under high chlorine conditions promote the release of As from the solid phase of contaminated soil into pore water. Ordinary Fe-Mn binary materials can reduce the total As concentration in pore water, but it remains at 0.55 mg / L after 14 days under high-temperature, high-chlorine conditions at 60℃, indicating limited control over the continuous release of As from high-temperature, high-chlorine geothermal soils. In contrast, material II can reduce the total As concentration in pore water to 0.38 mg / L under 25℃ high-chlorine conditions and to 0.09 mg / L under 60℃ high-temperature, high-chlorine conditions, indicating that material II, after short-range injection and retention in contaminated soil, can continuously reduce the As concentration in pore water under geothermal temperature triggering.

[0104] Figure 4The proportion of As(III) in total As after pulse-injected material and reaction for 14 days, and at 60℃ and 1000 mg / L Cl - Distribution of As species in soil under certain conditions.

[0105] like Figure 4 As shown, As(III) still accounts for the majority of total As in the geothermal blank group. Ordinary Fe-Mn binary materials can reduce the proportion of As(III), but under high temperature and high chlorine conditions at 60℃, the proportion of As(III) is still 38%. After treatment with material II, the proportion of As(III) is significantly reduced; specifically, under high chlorine conditions at 25℃, the proportion of As(III) is 27%, and under high temperature and high chlorine conditions at 60℃, it drops to 6%, indicating that material II can more fully expose the iron and manganese active sites under high geothermal conditions and promote the conversion of As(III) to As(V).

[0106] Figure 5 This diagram illustrates the change in total As concentration in the leachate during geothermal pore water rinsing.

[0107] like Figure 5 As shown, at 60℃ and 1000 mg / L Cl - Under the target geothermal conditions, the sum of exchangeable As (F1) and carbonate-bound As (F2) was high in the geothermal blank group, indicating a greater risk of As migration. After treatment with ordinary Fe-Mn binary material, the proportion of As in F3 iron-manganese oxide-bound state increased to 43%. After treatment with material II, the sum of F1 and F2 decreased to 6%, while the proportion of As in F3 iron-manganese oxide-bound state increased to 76%. These results indicate that the material of this invention can not only reduce the total As concentration in pore water in As-containing geothermal soil columns, but also oxidize highly mobile As(III) into more easily fixed As(V), and further transform it into a stable form dominated by iron-manganese oxide-bound state.

[0108] This invention utilizes a combination design of an iron-manganese binary active core, a polymer selectively coated temperature-sensitive salt-resistant copolymer layer, and a polydopamine adhesion layer to enable the material to migrate during the low-temperature, low-salt injection stage, retain and react in the geothermal high-temperature, high-chlorine target area, and ultimately achieve As(III) oxidation, As(V) fixation, and reduction of total As in pore water.

[0109] This invention develops a temperature-sensitive, salt-resistant iron-manganese composite material that maintains good migration ability before entering geothermal areas, reduces aggregation in high-chloride pore water, and improves the accessibility of active sites after geothermal temperature triggering. This material has significant theoretical value and promising engineering applications. The material improves target accessibility during in-situ injection, reduces the loss of active sites due to aggregation, and achieves As(III) oxidation and As(V) fixation in the geothermal target area, thereby enhancing the in-situ remediation efficiency of As-contaminated soil in geothermal areas.

[0110] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A temperature-sensitive, salt-resistant iron-manganese material, characterized in that, It includes a polymer selectively coated iron-manganese material and an adhesive layer located on the outer surface of the polymer selectively coated iron-manganese material; The polymer selectively coated iron-manganese material includes an iron-manganese binary active core and a temperature-sensitive salt-resistant copolymer layer coated on a portion of the surface of the iron-manganese binary active core. The iron-manganese binary active core includes an iron oxide / hydrogen hydroxide component and a manganese oxide component; the temperature-sensitive and salt-resistant copolymer layer is selectively and preferentially distributed on the surface of the iron oxide / hydrogen hydroxide component, and the surface of the manganese oxide component retains exposed sites. The temperature-sensitive and salt-resistant copolymer layer is a poly(N-vinylcaprolactam / sulfobetaine methacrylate) copolymer layer; The adhesive layer is a polydopamine layer.

2. The temperature-sensitive, salt-resistant iron-manganese material according to claim 1, characterized in that, The molar ratio of iron to manganese in the iron-manganese binary active core is 1.5 to 4:

1.

3. The temperature-sensitive, salt-resistant iron-manganese material according to claim 1, characterized in that, The mass ratio of N-vinylcaprolactam to sulfobetaine methacrylate, the raw material for preparing the temperature-sensitive and salt-resistant copolymer layer, is 60~90:10~40.

4. The temperature-sensitive, salt-resistant iron-manganese material according to claim 1, characterized in that, The mass of the polydopamine layer is 0.5 to 8% of the total mass of the temperature-sensitive and salt-resistant iron-manganese material.

5. The method for preparing the temperature-sensitive, salt-resistant iron-manganese material according to any one of claims 1 to 4, characterized in that, Includes the following steps: The pH of the mixed solution containing iron and manganese metal salts was first adjusted to 7.2-7.8 before Fe... 3+ Hydrolysis forms iron oxide / hydrogen hydroxide precursor particles, which are then adjusted to 8.3~9.0, Mn 2+ The iron oxide / hydrogen hydroxide precursor particles were loaded onto the surface of the iron oxide / hydrogen hydroxide precursor particles; the resulting system was mixed with hydrogen peroxide solution and aged to obtain an iron-manganese binary active core. The iron-manganese binary active core, water, N-vinylcaprolactam and sulfobetaine methacrylate are mixed for pre-adsorption. The resulting system, crosslinking agent and initiator are mixed for copolymerization reaction to form a temperature-sensitive salt-resistant copolymer layer on the surface of the iron-manganese binary active core, thus obtaining a polymer selectively coated iron-manganese material. The polymer is selectively coated with iron-manganese material, dopamine and buffer solution are mixed and subjected to self-polymerization reaction to form an adhesion layer, thereby obtaining the temperature-sensitive salt-resistant iron-manganese material.

6. The preparation method according to claim 5, characterized in that, The concentration of iron ions in the mixed solution of iron and manganese ions is 0.03~0.10 mol / L, and the concentration of manganese ions is 0.01~0.05 mol / L; the molar ratio of iron ions to manganese ions is 1.5~4:

1.

7. The preparation method according to claim 5, characterized in that, The hydrogen peroxide solution has a mass fraction of 1-5% and a volume of 1-8% of the volume of the metal salt mixed solution; the aging reaction temperature is 50-70℃ and the time is 1-4h.

8. The preparation method according to claim 5, characterized in that, The mixture of the iron-manganese binary active core, water, N-vinylcaprolactam, and sulfobetaine methacrylate further includes: adjusting the pH of the system to 5.5-6.5; the pre-adsorption is carried out under stirring for 20-60 minutes; and the copolymerization reaction is carried out at a temperature of 65-75°C for 0.5-2 hours.

9. The preparation method according to claim 5, characterized in that, The concentration of dopamine in the system after selectively coating the iron-manganese material with polymer, mixing dopamine and buffer solution is 0.2~1.0 g / L; the buffer solution is a Tris buffer solution with pH value of 8.0~8.8; the self-polymerization reaction time is 0.5~3 h.

10. The application of the temperature-sensitive salt-resistant iron-manganese material according to any one of claims 1 to 4 or the temperature-sensitive salt-resistant iron-manganese material obtained by the preparation method according to any one of claims 5 to 9 in the remediation of arsenic pollution in soil and groundwater in geothermal areas.

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