Soil stabilizer for repairing lead-cadmium-arsenic combined pollution and preparation and application thereof

Abstract

The application provides a soil stabilizer for repairing lead, cadmium and arsenic composite pollution, which is an amorphous nano zero-valent iron-manganese serpentine composite material; wherein the amorphous nano zero-valent iron-manganese serpentine composite material has a distribution of scattered multilevel structures with small particles attached. Compared with the prior art, the soil stabilizer for repairing lead, cadmium and arsenic composite pollution realizes the common stabilization of anions and cations in the soil polluted by lead, cadmium and arsenic; the soil stabilizer has magnetism and can be recycled for secondary use, realizes the effective separation of the material from the repaired soil for repeated use, reduces the residual heavy metal pollutants in the soil, and greatly improves the environmental protection and economy of the treatment process. The preparation method of the soil stabilizer is simple, the reaction conditions are controllable, and the amorphization of iron and manganese in the soil stabilizer can be stably realized.

Description

Technical Field

[0001] This invention relates to the field of heavy metal contaminated soil remediation, and more particularly to a soil stabilizer for remediating lead, cadmium, and arsenic combined pollution, its preparation, and its application. Background Technology

[0002] Heavy metal pollution of soil is a globally recognized environmental problem. Numerous studies have shown that excessive accumulation of heavy metals in soil often threatens human health, food safety, and soil ecology. Due to rapid industrial and agricultural development, as well as the disruption of natural ecosystems caused by the massive growth of the world's population, heavy metal pollution has become a serious threat to the environment and food security. Unlike organic pollutants, heavy metal pollution is insidious, persistent, and irreversible. It not only reduces the quality of water, air, and crops, but also poses a significant threat to human health and well-being. Therefore, research on the remediation and treatment of soils contaminated with lead, cadmium, and arsenic in combination is urgently needed.

[0003] Existing methods for remediating heavy metal contaminated soil can be broadly categorized into three types based on their technological principles: physical remediation, chemical remediation, and bioremediation. Among these, stabilization in chemical remediation has proven to be an effective, convenient, and low-cost method. Currently, commonly used chemical passivating agents for soils with multiple contaminants include alkaline substances, phosphate compounds, metals and their oxides, and clay minerals. Lead, cadmium, and arsenic exhibit completely opposite chemical behaviors in soil, and trivalent arsenic is far more toxic than pentavalent arsenic. In soils with multiple contaminants, a single passivating agent is insufficient to meet remediation requirements, making the simultaneous stabilization of lead, cadmium, and arsenic extremely challenging.

[0004] Currently, in the remediation of soil contaminated with lead, cadmium, and arsenic, the simultaneous stabilization effect on heavy metals lead, cadmium, and arsenic is poor, meaning the stabilization efficiency for these heavy metals is low. In particular, during the simultaneous stabilization process, the stabilization efficiency for lead is even less than 40%.

[0005] Moreover, in existing technologies, it is difficult to achieve complete amorphization of amorphous nano-zero-valent iron, and it is prone to agglomeration and instability.

[0006] In view of this, it is necessary to provide a soil stabilizer for remediating lead-cadmium-arsenic contaminated soil, as well as its preparation and application, to address the above-mentioned problems in the remediation process of lead-cadmium-arsenic contaminated soil. The aim is to achieve simultaneous, stable and efficient treatment of lead, cadmium and arsenic in lead-cadmium-arsenic contaminated soil, reduce soil toxicity, and avoid secondary pollution. Summary of the Invention

[0007] The main objective of this invention is to provide a soil stabilizer for remediating combined lead, cadmium, and arsenic pollution, as well as its preparation and application. This invention aims to address the problems of existing soil stabilizers in remediating heavy metal pollution of a single type, the easy re-release of fixed heavy metals and low stabilization efficiency, and the introduction of new pollution sources into the soil by adding soil stabilizers.

[0008] To achieve the above objectives, the present invention provides a soil stabilizer for remediating lead-cadmium-arsenic combined pollution. The soil stabilizer for remediating lead-cadmium-arsenic combined pollution is an amorphous nano-zero-valent iron-manganese serpentine composite material; wherein the amorphous nano-zero-valent iron-manganese serpentine composite material has a multi-level structure with randomly distributed attached small particles.

[0009] This invention also provides a method for preparing a soil stabilizer for remediating lead, cadmium, and arsenic combined pollution, comprising the following steps:

[0010] S1, obtained by thermally activated serpentine.

[0011] S2, after mixing the thermally activated serpentine with an iron salt solution, an organic amine solution is added to obtain a first mixture.

[0012] S3, after adding manganese salt solution to the first mixture and mixing, a second mixture is obtained.

[0013] S4, add borohydride solution dropwise to the second mixture, and react under the action of protective gas to obtain the soil stabilizer for remediating lead, cadmium and arsenic complex pollution.

[0014] Further, in step S1, the method for obtaining thermally activated serpentine is to calcine and grind and sieve the serpentine to obtain the thermally activated serpentine; wherein, the calcination temperature is 600-800℃; and the particle size after grinding and sieving is <2.5μm.

[0015] Further, in step S2, the mass ratio of the thermally activated serpentine to the iron salt is 1:3 to 5; the molar concentration ratio of the organic amine solution to the iron salt solution is 1:1 to 3.

[0016] Furthermore, the solute in the iron salt solution is one or more of ferric chloride or ferric nitrate; the organic amine solution includes diethylenetriamine solution.

[0017] Furthermore, the molar concentration ratio of the manganese salt solution to the iron salt solution is 1:1 to 3; wherein the manganese salt solution includes a manganese chloride solution.

[0018] Further, the molar ratio of the borohydride solution to the iron salt solution is 3 to 5:1; wherein the borohydride solution includes a potassium borohydride solution or a sodium borohydride solution.

[0019] Furthermore, both steps S2 and S3 are performed under the protection of a protective gas.

[0020] In step S4, after the addition of the borohydride solution, the process further includes solid-liquid separation, washing, and freeze-drying to obtain the soil stabilizer for remediating lead, cadmium, and arsenic compound pollution.

[0021] This invention also provides a method for remediating lead-cadmium-arsenic co-contaminated soil, comprising:

[0022] The soil contaminated with lead, cadmium, and arsenic is remediated using the soil stabilizer for remediation of lead, cadmium, and arsenic combined pollution as described above, or the soil stabilizer for remediation of lead, cadmium, and arsenic combined pollution prepared by any of the methods described above.

[0023] Furthermore, the remediation process includes maintaining the soil moisture content of the lead-cadmium-arsenic contaminated soil at >40%; and the remediation duration is 7 days.

[0024] The beneficial effects achieved by this invention are as follows:

[0025] This invention provides an amorphous nano-zero-valent iron-manganese serpentine composite material as a soil stabilizer for remediating lead, cadmium, and arsenic combined pollution; wherein the amorphous nano-zero-valent iron-manganese serpentine composite material has a multi-level structure with randomly distributed small particles attached.

[0026] 1. Achieved co-stabilization of cations and anions.

[0027] Serpentine has a negatively charged surface and can dissolve Mg. 2+ and OH - Mg 2+ It can be used as a trace element fertilizer for soil, OH - It can coprecipitate with cations. The amorphous nano-zero-valent iron and manganese oxide products exist as fluffy γ-FeOOH, which can coprecipitate with lead, cadmium and arsenic and coordinate with the core. The two work together to achieve the co-stabilization of anions and cations.

[0028] 2. The soil stabilizer is magnetic and recyclable for reuse, achieving effective separation and reuse of the material and the remediated soil, reducing the residual heavy metal pollutants in the soil, and greatly improving the environmental friendliness and economy of the treatment process.

[0029] The present invention provides a method for preparing a soil stabilizer for remediating lead, cadmium, and arsenic combined pollution. This method involves mixing thermally activated serpentine, iron salt solution, organic amine solution, manganese salt solution, and potassium borohydride solution. This method overcomes the technical difficulties in existing technologies, such as the difficulty in achieving complete amorphization of nano-zero-valent iron and its tendency to agglomerate.

[0030] The method for preparing the soil stabilizer is simple, the reaction conditions are controllable, and the resulting soil stabilizer has a good long-term stabilization effect and a stable remediation effect.

[0031] Firstly, amorphous nano-zero-valent iron-manganese is fixed on the surface of thermally activated serpentine, which is conducive to the complete amorphization of nano-zero-valent iron, forming amorphous nano-zero-valent iron-manganese with excellent adsorption performance. Secondly, primary amine groups (-NH2) complex with silicon in serpentine, making its layered structure loose, giving amorphous nano-zero-valent iron-manganese ultra-high dispersibility, forming a multi-level structure with the advantages of dense adsorption pores and stable adsorption binding. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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 the structures shown in these drawings without creative effort.

[0033] Figure 1 The images show X-ray diffraction (XRD) patterns of the materials prepared in Comparative Example 1 and Example 1.

[0034] Figure 2 The images are scanning electron microscope (SEM) images of the materials prepared in Comparative Example 1, Comparative Example 2 and Example 1; where (a) is an SEM image of thermally activated serpentine material (Srp), (b) is an SEM image of amorphous nano-zero valent iron manganese (A-nZVIM), and (c) is an SEM image of soil stabilizer (Srp / A-nZVIM) for remediating lead, cadmium and arsenic combined pollution.

[0035] Figure 3 Infrared spectrum comparison of the thermally activated serpentine material (Srp) prepared in Comparative Example 1 and the soil stabilizer (Srp / A-nZVIM) prepared in Example 1 for remediating lead, cadmium and arsenic combined pollution.

[0036] Figure 4 The available content of heavy metals in the soil after the soil remediation agent prepared in Examples 1-3 was used to remediate lead-cadmium-arsenic contaminated soil in Example 4;

[0037] Figure 5 The available content of heavy metals in the soil after remediation of lead-cadmium-arsenic composite contaminated soil using the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 in Example 4;

[0038] Figure 6The images show a comparison of the speciation of lead, cadmium, and arsenic in the soil after remediation of lead-cadmium-arsenic contaminated soil using the soil stabilizer (Srp / A-nZVIM) prepared in Example 1, as described in Example 4. (a) shows the speciation of lead and cadmium in the remediated soil compared to the original lead-cadmium-arsenic contaminated soil, and (b) shows the speciation of arsenic in the remediated soil compared to the original lead-cadmium-arsenic contaminated soil.

[0039] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of this invention is for describing specific implementations and not for limiting the scope of protection of this invention.

[0042] Unless otherwise defined, all technical and scientific terms used in this invention are consistent with the prior art known to those skilled in the art and the description of this invention. This invention may also be implemented using any prior art methods, devices and materials similar to or equivalent to those described, used or made by means of methods, devices and materials in the embodiments of this invention.Those skilled in the art should understand that, as an explanation of this application, without affecting the actual understanding of the technical solution of this application, "Srp" can represent thermally activated serpentine material, "A-nZVIM" can represent amorphous nano-zero-valent iron-manganese material, "Srp / A-nZVIM" can represent a soil stabilizer for remediating lead, cadmium, and arsenic composite pollution, Intensity (au) can represent strength, 2θ (degree) can represent the angle between the extension of the incident X-ray and the reflected X-ray, XRD can represent X-ray diffraction technology, HJ 804-2016 can represent diethylenetriaminepentaacetic acid extraction-inductively coupled plasma atomic emission spectrometry, ICP-OES can represent inductively coupled plasma atomic emission spectrometry, SEM can represent scanning electron microscopy, Transmittance (%) can represent conversion rate (%), immobilization rate (%) can represent stabilization efficiency (%), Residual can represent residual state, Organic bound can represent organically bound state, Fe-Mn Oxide bound can be represented as an iron-manganese oxide bound state; carbonate bound can be represented as a carbonic acid bound state; exchangeable can be represented as an exchangeable state; crystalline iron-aluminum hydration oxide binding can be represented as a well-crystallized iron-manganese or iron-aluminum hydration oxide bound state; amorphous and weakly crystalline Fe-Al oxide binding can be represented as an amorphous or weakly crystalline iron-manganese or iron-aluminum hydration oxide bound state; special absorption can be represented as a specific adsorption state; non-specific... Absorption can be represented as non-specific adsorption state. CK(Pb) can represent the speciation of lead in the original lead-cadmium-arsenic co-contaminated soil. CK(Cd) can represent the speciation of cadmium in the original lead-cadmium-arsenic co-contaminated soil. CK(As) can represent the speciation of arsenic in the original lead-cadmium-arsenic co-contaminated soil. Srp / A-nZVIM+Pb can represent the speciation of lead in the soil after remediation of lead-cadmium-arsenic co-contaminated soil using the soil stabilizer prepared in Example 1. Srp / A-nZVIM+Cd can represent the speciation of cadmium in the soil after remediation of lead-cadmium-arsenic co-contaminated soil using the soil stabilizer prepared in Example 1. Srp / A-nZVIM+As can represent the speciation of arsenic in the soil after remediation of lead-cadmium-arsenic co-contaminated soil using the soil stabilizer prepared in Example 1.

[0043] When numerical ranges are given in the examples, it should be understood that, unless otherwise stated in the invention, both endpoints of each range and any value between the two endpoints may be used. Test methods in the following examples that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers. Unless otherwise specified, all materials or reagents required in the following examples are commercially available.

[0044] To address the problems of existing soil stabilizers for remediating heavy metal pollution, such as the limited range of types of heavy metals, the easy re-release of fixed heavy metals, low stabilization efficiency, and the introduction of new pollution sources into the soil, this invention provides a soil stabilizer for remediating lead-cadmium-arsenic complex pollution. The soil stabilizer for remediating lead-cadmium-arsenic complex pollution is an amorphous nano-zero-valent iron-manganese serpentine composite material; wherein, the amorphous nano-zero-valent iron-manganese serpentine composite material has a multi-level structure with randomly distributed attached small particles.

[0045] This invention also provides a method for preparing a soil stabilizer for remediating lead, cadmium, and arsenic combined pollution, comprising the following steps:

[0046] S1, obtaining thermally activated serpentine. Serpentine can provide a layered porous structure substrate for materials. After thermal activation, the serpentine crystal structure is destroyed, exhibiting a layered porous structure, and Mg is also added. 2+ and OH - The dissolution of OH. - It can co-precipitate with cations, forming precipitates such as Pb(OH)₂ and Cd(OH)₂, and has a certain adsorption effect on cations. Mg 2+ It can be used as a trace element fertilizer for soil.

[0047] S2, after mixing thermally activated serpentine with an iron salt solution, an organic amine solution is added to obtain the first mixture. Thermally activated serpentine has a stable layered structure. The primary amine groups (-NH2) in the added organic amine solution can complex with silicon in the serpentine, promoting Si-O tetrahedral distortion and disrupting the ordered six-membered ring structure in the serpentine crystal. This loosens the layered structure, enhancing the dispersibility of amorphous nano-zero-valent iron-manganese, solving the problems of dense nanosheet stacking and amorphous nano-zero-valent iron-manganese agglomeration, significantly increasing the specific surface area and improving adsorption performance.

[0048] The addition of organic amine solutions transforms the iron in the system into amorphous nano-zero-valent iron. This amorphous nano-zero-valent iron is fixed on the serpentine surface, thus reducing the number of seed crystals formed during liquid-phase reduction and inhibiting the growth of zero-valent iron crystals. This slows down the reduction to iron atoms, facilitating the complete amorphization of zero-valent iron. The iron oxides can form Fe-O-As bonds, synergistically adsorbing arsenic, enabling efficient and simultaneous remediation of cations and anions in the soil.

[0049] S3. After adding a manganese salt solution to the first mixture and mixing, a second mixture is obtained. The manganese salt solution interacts with the organic amine solution and amorphous nano-zero-valent iron in the system to form amorphous nano-zero-valent iron-manganese. The amorphous nano-zero-valent iron-manganese is fixed on the surface of thermally activated serpentine, forming a multi-level structure with dense adsorption pores and excellent adsorption performance. The formed amorphous nano-zero-valent iron-manganese oxide product exists as a loose γ-FeOOH, which can co-precipitate and coordinate with lead, cadmium, and arsenic through core complexation, and synergistically achieve co-stabilization of anions and cations with thermally activated serpentine. Moreover, the binding of amorphous nano-zero-valent iron-manganese can increase adsorption sites and enrich the functional groups on the material surface, achieving the complete and simultaneous separation of unstable exchangeable state and carbonate-bound state lead and cadmium, as well as non-specifically adsorbed arsenic from the soil.

[0050] S4, add borohydride solution dropwise to the second mixture, and react under the action of protective gas to obtain a soil stabilizer for remediating lead, cadmium and arsenic compound pollution.

[0051] The above preparation method is simple and the reaction conditions are controllable, solving the technical difficulties of complete amorphization and easy agglomeration of nano-zero valent iron in existing technologies. It has good long-term stabilization effect and stable remediation effect. Moreover, the prepared soil stabilizer achieves co-stabilization of anions and cations in the soil; the soil stabilizer is magnetic and recyclable for secondary use, realizing effective separation and reuse of the material and the remediated soil, reducing residual heavy metal pollutants in the soil, and greatly improving the environmental protection and economy of the treatment process.

[0052] Further, in step S1, the method for obtaining thermally activated serpentine involves calcining and grinding the serpentine, followed by sieving to obtain thermally activated serpentine; wherein the calcination temperature is 600–800℃; and the particle size after grinding and sieving is <2.5μm. Serpentine generally undergoes dehydration at 600–800℃, its crystal lattice is destroyed, and it exhibits a layered porous structure with a strong endothermic effect, which is beneficial for the fixation of amorphous nano-zero-valent iron-manganese on the surface of the thermally activated serpentine. A particle size <2.5μm increases the specific surface area of ​​the serpentine, maximizing the fixation of amorphous nano-zero-valent iron-manganese.

[0053] Furthermore, in step S2, the mass ratio of thermally activated serpentine to iron salt is 1:3 to 5. If the proportion of thermally activated serpentine is too high, it will affect the effect of amorphous nano-zero-valent iron-manganese, thereby reducing the remediation effect on lead-cadmium-arsenic composite contaminated soil. The molar concentration ratio of organic amine solution to iron salt solution is 1:1 to 3; only materials synthesized within this molar concentration ratio range are considered amorphous.

[0054] Furthermore, the solute in the iron salt solution is one or more of ferric chloride or ferric nitrate; the organic amine solution includes diethylenetriamine solution.

[0055] Furthermore, the molar concentration ratio of the manganese salt solution to the iron salt solution is 1:1 to 3; wherein, the manganese salt solution includes manganese chloride solution.

[0056] Furthermore, the molar ratio of borohydride solution to iron salt solution is 3–5:1; wherein the borohydride solution includes potassium borohydride solution or sodium borohydride solution. Zero-valent iron can only be synthesized under conditions of excess borohydride, i.e., when the molar ratio of borohydride solution to iron salt solution is >3. However, excessive amounts of borohydride will affect subsequent separation and other operations.

[0057] Furthermore, steps S2 and S3 are both performed under a protective gas atmosphere. Specifically, in step S2, before mixing the thermally activated serpentine with the iron salt solution, the iron salt solution is prepared using deoxygenated water, and nitrogen or inert gas is continuously introduced into the liquid until the potassium borohydride solution is completely added, thus obtaining a soil stabilizer for remediating lead, cadmium, and arsenic compound pollution. This ensures that iron is not oxidized throughout the preparation process, resulting in amorphous nano-zero-valent iron in the obtained soil stabilizer.

[0058] In step S4, after adding the borohydride solution, the process further includes sequential solid-liquid separation, washing, and freeze-drying to obtain a soil stabilizer for remediating lead, cadmium, and arsenic compound pollution. The solid-liquid separation can be achieved by centrifuging the resulting solid-liquid mixture.

[0059] This invention also provides a method for remediating lead-cadmium-arsenic co-contaminated soil, comprising:

[0060] The soil contaminated with lead, cadmium, and arsenic is remediated using the soil stabilizer for remediation of lead, cadmium, and arsenic combined pollution as described above, or the soil stabilizer for remediation of lead, cadmium, and arsenic combined pollution prepared by any of the methods described above.

[0061] Furthermore, the remediation process includes maintaining the soil moisture content of the lead-cadmium-arsenic co-contaminated soil at >40% and a remediation duration of 7 days. The soil stabilizer for remediating lead-cadmium-arsenic co-contaminated soil interacts with the heavy metals in the contaminated soil through a water-provided contact interface to achieve co-stabilization of the heavy metals. Specifically, maintaining the soil moisture content of the lead-cadmium-arsenic co-contaminated soil at >40% can be achieved by applying deionized water to the soil every 3 days.

[0062] To further illustrate the present invention, the following examples are provided:

[0063] Examples 1-3 and Comparative Examples 1-2 all used the following process to prepare thermally activated serpentine:

[0064] Place 10g of serpentine powder in a crucible and calcine it in a muffle furnace at 800℃ for 30min. Grind and sieve the calcined product to obtain thermally activated serpentine with a particle size of less than 2.5um.

[0065] Example 1

[0066] (1) Weigh 1.6218g of thermally activated serpentine into 150ml of deoxygenated water, wherein nitrogen gas is continuously passed through the deoxygenated water. Weigh 4.8654g of ferric chloride hexahydrate and add it to the above solution. Add 3.2ml of diethylenetriamine solution (0.45mol / L) to the solution and stir magnetically for 5min at a speed of 360rpm to obtain the first mixed solution.

[0067] (2) Weigh 3.5624g of manganese sulfate tetrahydrate and dissolve it in 150ml of deoxygenated water to obtain a manganese salt solution. Add the manganese salt solution to the first mixed solution obtained in step (1). The entire process is carried out under the protection of nitrogen gas and magnetically stirred for 15min. The stirring speed is maintained at 600rpm to obtain the second mixed solution.

[0068] (3) Weigh 3.881g of potassium borohydride and dissolve it in 75ml of deoxygenated water to obtain a potassium borohydride solution. Add the potassium borohydride solution dropwise to the second mixed solution obtained in step (2) at a rate of 3ml / min. The entire process is carried out under the protection of nitrogen and magnetic stirring for 30min at a stirring speed of 400rpm. The reaction continues until no significant bubbles are generated in the system to obtain the reaction slurry. After centrifugation, washing, and freeze-drying, the soil stabilizer (Srp / A-nZVIM) for remediating lead, cadmium, and arsenic composite pollution is obtained.

[0069] Example 2

[0070] (1) Weigh 1.2164g of thermally activated serpentine into 150ml of deoxygenated water, wherein nitrogen gas is continuously passed through the deoxygenated water. Weigh 4.8654g of ferric chloride hexahydrate and add it to the above solution. Add 4.8ml of diethylenetriamine solution (0.9mol / L) to the solution and stir magnetically for 5min at a speed of 360rpm to obtain the first mixed solution.

[0071] (2) Weigh 1.7812g of manganese sulfate tetrahydrate and dissolve it in 150ml of deoxygenated water to obtain a manganese salt solution. Add the manganese salt solution to the first mixed solution obtained in step (1). The entire process is carried out under the protection of nitrogen gas and magnetically stirred for 15min. The stirring speed is maintained at 600rpm to obtain the second mixed solution.

[0072] (3) Weigh 5.381g of potassium borohydride and dissolve it in 75ml of deoxygenated water to obtain a potassium borohydride solution. Add the potassium borohydride solution dropwise to the second mixed solution obtained in step (2) at a rate of 3ml / min. The entire process is carried out under the protection of nitrogen and magnetic stirring for 30min at a stirring speed of 400rpm. The reaction continues until no significant bubbles are generated in the system to obtain the reaction slurry. After centrifugation, washing, and freeze-drying, the soil stabilizer (Srp / A-nZVIM) for remediating lead, cadmium, and arsenic composite pollution is obtained.

[0073] Example 3

[0074] (1) Weigh 0.9731g of thermally activated serpentine into 150ml of deoxygenated water, wherein nitrogen gas is continuously passed through the deoxygenated water. Weigh 4.8654g of ferric chloride hexahydrate and add it to the above solution. Add 1.6ml of diethylenetriamine solution (0.3mol / L) to the solution and stir magnetically for 5min at a speed of 360rpm to obtain the first mixed solution.

[0075] (2) Weigh 1.1875g of manganese sulfate tetrahydrate and dissolve it in 150ml of deoxygenated water to obtain a manganese salt solution. Add the manganese salt solution to the first mixed solution obtained in step (1). The entire process is carried out under the protection of nitrogen gas and magnetic stirring for 15min. The stirring speed is maintained at 600rpm to obtain the second mixed solution.

[0076] (3) Weigh 2.910g of potassium borohydride and dissolve it in 75ml of deoxygenated water to obtain a potassium borohydride solution. Add the potassium borohydride solution dropwise to the second mixed solution obtained in step (2) at a rate of 3ml / min. The entire process is carried out under the protection of nitrogen and magnetic stirring for 30min at a stirring speed of 400rpm. The reaction continues until no significant bubbles are generated in the system to obtain the reaction slurry. After centrifugation, washing, and freeze-drying, the soil stabilizer (Srp / A-nZVIM) for remediating lead, cadmium, and arsenic composite pollution is obtained.

[0077] Comparative Example 1

[0078] Compared to Example 1, only 1.6218g of thermally activated serpentine was weighed into 150ml of deoxygenated water, wherein nitrogen gas was continuously passed through the deoxygenated water to obtain thermally activated serpentine material (Srp).

[0079] Comparative Example 2

[0080] Compared to Example 1, no thermally activated serpentine was added, i.e.:

[0081] (1) Weigh 4.8654 g of ferric chloride hexahydrate and add it to 150 ml of deoxygenated water, while continuously purging nitrogen gas into the deoxygenated water. Add 3.2 ml of diethylenetriamine solution (0.45 mol / L) to the solution, and stir magnetically for 5 min at a speed of 360 rpm to obtain the first mixed solution.

[0082] (2) Weigh 3.5624g of manganese sulfate tetrahydrate and dissolve it in 150ml of deoxygenated water to obtain a manganese salt solution. Add the manganese salt solution to the first mixed solution obtained in step (1). The entire process is carried out under the protection of nitrogen gas and magnetically stirred for 15min. The stirring speed is maintained at 600rpm to obtain the second mixed solution.

[0083] (3) Weigh 3.881g of potassium borohydride and dissolve it in 75ml of deoxygenated water to obtain a potassium borohydride solution. Add the potassium borohydride solution dropwise to the second mixed solution obtained in step (2) at 3ml / min. The whole process is carried out under the protection of nitrogen and magnetic stirring for 30min. The stirring speed is maintained at 400rpm. The reaction is continued until no significant bubbles are generated in the system to obtain the reaction slurry. After centrifugation, washing and freeze drying, amorphous nano zero-valent iron-manganese material (A-nZVIM) is obtained.

[0084] Analysis example 1

[0085] 1. Qualitative Analysis

[0086] The materials prepared in Comparative Example 1 and Example 1 were analyzed using X-ray diffraction (XRD) to examine their phase structures. The XRD test results for the thermally activated serpentine material (Srp) from Comparative Example 1 and the soil stabilizer (Srp / A-nZVIM) from Example 1 for remediating lead, cadmium, and arsenic combined pollution are shown below. Figure 1 As shown.

[0087] according to Figure 1 Observations show that the diffraction peaks of the thermally activated serpentine at diffraction angles of 17.45°, 22.9°, and 26.1° are consistent with the characteristic peaks of forsterite. After loading amorphous zero-valent iron and manganese, only the diffraction peak at 22.9° appears, and no crystallization peak corresponding to crystallization appears. This indicates that the zero-valent iron and manganese loaded on the thermally activated serpentine is amorphous, and the zero-valent iron and manganese has been successfully loaded onto the surface.

[0088] 2. Material morphology and structure analysis

[0089] The materials prepared in Comparative Example 1, Comparative Example 2, and Example 1 were observed using a scanning electron microscope (SEM) as follows: Figure 2 As shown in (a), (b), and (c).

[0090] according to Figure 2Observations show that (a) the spherical particles of thermally activated serpentine material (Srp) are clustered together, with a large number of spherical particles showing severe aggregation. (b) shows that the surface of amorphous nano-zero-valent iron-manganese material (A-nZVIM) is relatively flat with regular edges and the scale structures are stacked on each other. (c) shows the soil stabilizer (Srp / A-nZVIM) obtained after adding thermally activated serpentine to remediate lead, cadmium and arsenic composite pollution. It is non-uniformly distributed on the sheet material, with enhanced dispersion and a multi-level structure. In addition, the sheet structure is more scattered than before, and some sheet structures collapse and break into more irregular small pieces, which greatly increases its specific surface area and reduces the aggregation of amorphous zero-valent iron-manganese, thus improving the adsorption performance of the soil remediation agent.

[0091] 3. Infrared spectroscopy analysis of materials

[0092] The infrared spectra of Srp obtained in Comparative Example 1 and Srp / A-nZVIM obtained in Example 1 are as follows: Figure 3 As shown.

[0093] according to Figure 3 Observations revealed that 950–1100 cm -1 The region at 1630 cm⁻¹ represents the Si-O tetrahedral stretching and bending vibration bands. The stretching vibration peaks are significantly weakened after loading amorphous zero-valent iron-manganese. This is because the primary amine groups (-NH₂) in the added organic amine complex with silicon in the serpentine, disrupting the ordered six-membered ring structure in the serpentine crystal. -1 and 3363cm -1 The nearby peaks are formed by the elastic vibrations of hydroxyl groups. The strong intensity of the Srp / A-nZVIM material at this point indicates that its surface contains abundant OH groups, as seen at 1530 cm⁻¹. -1 The medium-intensity peaks that appear are mainly caused by lattice vibrations generated by manganese oxides, and the abundant functional groups on the surface can further enhance the adsorption performance of soil remediation agents.

[0094] Example 4

[0095] Soil remediation agents prepared in Examples 1-3, thermally activated serpentine material prepared in Comparative Example 1, and amorphous nano-zero-valent iron-manganese material prepared in Comparative Example 2 were used to remediate lead-cadmium-arsenic contaminated soil.

[0096] Table 1 Physicochemical properties of soil contaminated with lead, cadmium, and arsenic

[0097]

[0098]

[0099] (1) Weigh 200g of the above-mentioned lead-cadmium-arsenic composite contaminated soil, grind it, and pass it through a 20-mesh sieve.

[0100] (2) During the remediation of lead-cadmium-arsenic composite contaminated soil using the soil remediation agents prepared in Examples 1 to 3, three parallel samples were set up, namely groups 1, 2, and 3;

[0101] In the process of remediating lead-cadmium-arsenic composite contaminated soil using materials prepared in Comparative Examples 1 and 2, three parallel samples were set up, namely groups 4 and 5.

[0102] (3) 10g of ground lead-cadmium-arsenic composite contaminated soil was added to each of the above groups, and the corresponding materials were added to obtain samples Srp / A-nZVIM1-1, Srp / A-nZVIM1-2, Srp / A-nZVIM1-3, Srp / A-nZVIM2-1, Srp / A-nZVIM2-2, Srp / A-nZVIM2-3, Srp / A-nZVIM3-1, Srp / A-nZVIM3-2, and Srp / A-nZVIM3-3;

[0103] Srp4-1, Srp4-2, Srp4-3, A-nZVIM5-1, A-nZVIM5-2, A-nZVIM5-3.

[0104] (4) Mix all the above samples thoroughly and add 4 mL of deionized water to each sample. Continue to mix thoroughly. Place the samples after adding deionized water and mixing thoroughly in a ventilated place for repair. The repair time is 7 days. During this period, add deionized water to all samples every 3 days to ensure that the soil moisture content of all samples is >40%.

[0105] (5) Seven days after remediation, all samples were taken out and sequentially air-dried, ground, and then extracted with diethylenetriaminepentaacetic acid (DITA) using inductively coupled plasma atomic emission spectrometry (ICP-OES). The heavy metal content in the extract was detected using ICP-OES to obtain the available heavy metal content data for all samples. The data of parallel samples were processed to obtain the available heavy metal content in the soil remediated with the soil remediation agents prepared in Examples 1, 2, and 3, as shown below. Figure 4 As shown in the marks “1:3”, “1:4” and “1:5”;

[0106] The bioavailable content of heavy metals in soil remediated using materials prepared in Comparative Example 1, Comparative Example 2, and Example 1 is as follows: Figure 5 The markings “Srp”, “A-nZVIM”, and “Srp / A-nZVIM” are shown in the text.

[0107] Analysis example 2

[0108] 1. Analysis of the repair effect under different raw material ratios

[0109] according to Figure 4 Observations show that in Example 4, the available contents of lead, cadmium, and arsenic in the soil after remediation using the methods described in Examples 1-3 were significantly reduced, indicating good remediation effects. Furthermore, in the simultaneous remediation of lead, cadmium, and arsenic, the stabilization efficiency of lead remained consistently >80%. When the material prepared in Example 1 was added, the stabilization efficiencies for lead, cadmium, and arsenic were 99.19%, 84.72%, and 89.40%, respectively; when the material prepared in Example 2 was added, the stabilization efficiencies for lead, cadmium, and arsenic were 96.20%, 64.72%, and 78.74%, respectively; and when the material prepared in Example 3 was added, the stabilization efficiencies for lead, cadmium, and arsenic were 89.46%, 54.63%, and 73.31%, respectively.

[0110] Example 1 showed the best results, suggesting that the non-zero valent iron and manganese were most dispersed when using the raw material ratio of Example 1, resulting in a large specific surface area and numerous adsorption sites.

[0111] 2. Comparative analysis of the repair effects of different materials

[0112] according to Figure 5 Observations show that, in Example 4, the soil remediation agent (Srp / A-nZVIM) prepared in Example 1, the thermally activated serpentine (Srp) in Comparative Example 1, and the amorphous nano-zero-valent iron-manganese material (A-nZVIM) in Comparative Example 2 were used to remediate the same mass of lead-cadmium-arsenic composite contaminated soil. Srp / A-nZVIM showed better stabilization efficiency for the available forms of lead, cadmium, and arsenic than both Srp and the amorphous nano-zero-valent iron-manganese material A-nZVIM. The Srp / A-nZVIM prepared in Example 1 achieved a stabilization efficiency of 84.7% for cadmium, 99.2% for lead, and 78.74% for arsenic, thus achieving simultaneous and efficient stabilization and remediation of lead-cadmium-arsenic composite contaminated soil.

[0113] 3. Comparative analysis of the speciation of lead, cadmium, and arsenic in soil after remediation with soil remediation agent (Srp / A-nZVIM)

[0114] The soil remediated using the soil remediation agent (Srp / A-nZVIM) prepared in Example 1 in Example 4 was analyzed for the speciation of lead and cadmium in the soil using the Tessier five-step extraction method. The results are as follows: Figure 6 As shown in (a); the Wenzel method was used to determine the speciation of arsenic in the soil, and the results are as follows. Figure 6 As shown in (b).

[0115] according to Figure 6Observations show that in soil contaminated with lead, cadmium, and arsenic, exchangeable and carbonate-bound lead were transformed into stable iron-manganese oxide and residual forms, and the proportion of exchangeable and carbonate-bound lead decreased to 0.

[0116] The vast majority of exchangeable and carbonate-bound cadmium was transformed into stable residual, organically bound, and iron-manganese oxidized forms. Non-specifically adsorbed arsenic was significantly reduced, and its stability was significantly enhanced. After remediation with Srp / A-nZVIM, the bioavailability and soil migration capacity of lead, cadmium, and arsenic in the soil were significantly reduced, and they were transformed into more stable forms. This indicates that the modified remediation agent has good long-term stabilization effect and stable remediation effect, and has broad prospects for application in the remediation of lead-cadmium-arsenic combined contaminated soils.

[0117] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a soil stabilizer for remediation of lead, cadmium and arsenic complex contamination, characterized by, Including the following steps: S1, obtaining thermally activated serpentine; the method for obtaining thermally activated serpentine is to calcine the serpentine and grind and sieve it to obtain the thermally activated serpentine; wherein, the calcination temperature is 600~800℃; and the particle size after grinding and sieving is <2.5μm; S2, after mixing the thermally activated serpentine with the iron salt solution, an organic amine solution is added to obtain a first mixture; the mass ratio of the thermally activated serpentine to the iron salt is 1:3~5; the molar concentration ratio of the organic amine solution to the iron salt solution is 1:1~3; The solute in the iron salt solution is selected from at least one of ferric chloride or ferric nitrate; the organic amine solution is selected from diethylenetriamine solution. S3, after adding manganese salt solution to the first mixture and mixing, a second mixture is obtained; the molar ratio of manganese salt solution to iron salt solution is 1:1~3; wherein, the manganese salt solution is selected from manganese chloride solution; S4, add borohydride solution dropwise to the second mixture, and react under the action of protective gas to obtain the soil stabilizer for remediating lead, cadmium and arsenic complex pollution; the molar ratio of the borohydride solution to the iron salt solution is 3~5:1; The borohydride solution is selected from potassium borohydride solution or sodium borohydride solution.

2. The method for preparing the soil stabilizer for repairing lead-cadmium-arsenic combined pollution according to claim 1, characterized in that, Both steps S2 and S3 are performed under the protection of a protective gas. In step S4, after the addition of the borohydride solution, the process further includes solid-liquid separation, washing, and freeze-drying to obtain the soil stabilizer for remediating lead, cadmium, and arsenic compound pollution.

3. A method for remediation of soil contaminated with lead, cadmium and arsenic, characterized in that, include: The soil stabilizer for remediating lead-cadmium-arsenic composite pollution obtained by the preparation method described in claim 1 is mixed with lead-cadmium-arsenic composite polluted soil for remediation.

4. The method for remediating lead-cadmium-arsenic co-contaminated soil according to claim 3, characterized in that, The remediation process includes maintaining the soil moisture content of the lead-cadmium-arsenic contaminated soil at >40% and a remediation duration of 7 days.

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