A method for remediating antimony and arsenic contaminated soil

Abstract

This invention provides a method for remediating antimony and arsenic contaminated soil, relating to the field of soil remediation technology. The method includes: S1, covering the surface of the antimony and arsenic contaminated soil with a composite barrier layer; the thickness of the composite barrier layer is 20cm to 40cm, and the composite barrier layer is composed of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer from bottom to top; S2, spraying a mixed functional bacterial solution onto the surface of the antimony and arsenic contaminated soil with the composite barrier layer to remediate the antimony and arsenic contaminated soil; the mixed functional bacterial solution contains sulfate-reducing bacteria and iron-reducing bacteria. This invention constructs a surface barrier for antimony and arsenic contaminated soil by combining a composite barrier layer and microbial barrier, thereby significantly reducing the leaching of heavy metals in moderately to mildly contaminated soil. It can better achieve long-term, efficient, and stable control and blocking of typical pollutants such as antimony and arsenic, not only reducing the risk of heavy metal pollutant migration, but also realizing deep remediation of contaminated soil.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a method for remediating antimony and arsenic contaminated soil. Background Technology

[0002] Arsenic and antimony are amphoteric metals in Group 5 of the periodic table, possessing similar chemical properties and toxicity. Arsenic, a toxic heavy metal found on Earth, was once used as a wood preservative and antibiotic in medicine, and is currently widely used in alloys, such as in the electronics industry. The widespread use of arsenic compounds has led to the release and accumulation of large amounts of arsenic into the soil environment, gradually endangering human health. Long-term exposure to high arsenic levels can cause a range of health problems, including skin diseases, cardiovascular diseases, neurological disorders, immune disorders, and even cancer. Antimony is widely used in industrial semiconductors, diodes, glass, and flame retardant materials. Furthermore, with the large-scale mining and smelting of antimony ore, increasing amounts of antimony are released into the environment. Therefore, antimony is a very typical pollutant in mining areas, possessing potential toxicity and carcinogenicity. As the world's largest producer of antimony, China faces a far more severe risk of antimony and arsenic pollution than other countries. For example, in Xikuangshan, Hunan, known as the "Antimony Capital of the World," the antimony content in agricultural soil and well water ranges from 141.92 mg / kg to 8733.26 mg / kg and 131 μg / L to 22980 μg / L, respectively, far exceeding the values ​​set by the World Health Organization.

[0003] With the mining of antimony, tin, and other non-ferrous metal minerals, heavy metal pollution has gradually attracted widespread attention, and the coexistence of antimony and arsenic has increased the difficulty of soil remediation. Large quantities of stibnite (Sb₂S₃), stibnite (Sb₂O₃), and polymetallic complex minerals (stable stibnite) generate large amounts of smelting slag and arsenic-alkali slag after mining and smelting. These are piled up around mines and smelters, polluting the soil around the mining areas through flue gas deposition, dust diffusion, and leaching of waste residue, resulting in antimony and arsenic pollution in large areas of farmland. In an aerobic environment, antimony and arsenic undergo a series of transformations, mainly existing in the form of oxidized pentavalent antimony and pentavalent arsenic. Pentavalent arsenic has low toxicity and mobility, while pentavalent antimony, although low in toxicity, has high mobility. Rainfall and rising groundwater levels can cause soil to transition from an aerobic to an anaerobic state. In the anaerobic state, the reduction and dissolution of iron and manganese oxides in the soil, as well as the metabolic processes of antimony and arsenic-reducing bacteria, lead to the reduction and dissolution of antimony and arsenic in the soil. The dissolved antimony and arsenic migrate with rainwater and surface runoff, polluting groundwater and farmland soil around mining areas. On the other hand, the dissolution of antimony and arsenic increases their bioavailability, thereby exacerbating their ecological and environmental risks.

[0004] Therefore, in the field of soil remediation technology, how to effectively control antimony and arsenic in antimony-contaminated soil and prevent their migration into plants has become an urgent technical problem to be solved. Summary of the Invention

[0005] To address the above problems, in a first aspect, the present invention provides a method for remediating antimony and arsenic-contaminated soil, the method comprising:

[0006] S1, a composite barrier layer is covered on the surface of antimony and arsenic contaminated soil; the thickness of the composite barrier layer is 20cm to 40cm, and the composite barrier layer is composed of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer from bottom to top.

[0007] S2, spray a mixed functional bacterial solution onto the surface of the antimony and arsenic contaminated soil having the composite barrier layer to remediate the antimony and arsenic contaminated soil; the mixed functional bacterial solution contains sulfate-reducing bacteria and iron-reducing bacteria.

[0008] Preferably, the composite barrier layer covering the surface of the antimony and arsenic contaminated soil includes:

[0009] Iron-modified montmorillonite is applied to the surface of the antimony and arsenic contaminated soil to form the iron-modified montmorillonite layer;

[0010] Then, a biochar-manganese slag composite material is applied to the iron-modified montmorillonite layer to form the biochar-manganese slag composite material layer.

[0011] Preferably, the thickness of the iron-modified montmorillonite layer is 10cm to 20cm, and the thickness of the biochar-manganese slag composite material layer is 10cm to 20cm.

[0012] Preferably, the preparation method of the biochar-manganese slag composite material includes:

[0013] Solid waste manganese slag and waste wheat straw with a mass ratio of 1:2 were placed in a vacuum tube furnace for heat preservation. After heat preservation for 2 hours, the mixture was naturally cooled to room temperature, then ground and passed through a 100-mesh sieve to obtain the biochar-manganese slag composite material.

[0014] Preferably, the amount of the biochar-manganese slag composite material applied is 5% to 10% of the antimony-arsenic contaminated soil.

[0015] Preferably, the heat preservation inside the vacuum tube furnace includes:

[0016] The inlet flow rate is 50 mL·min -1 After purging with N2 for 20 minutes, the temperature is increased to 700℃ at a rate of 10℃ / min and then held at that temperature. The gas pressure inside the vacuum tube furnace is maintained at ≤0.02Mpa.

[0017] Preferably, the method for preparing the iron-modified montmorillonite includes:

[0018] Montmorillonite was dried in an oven at 80°C and passed through a 100-mesh sieve to obtain pretreated montmorillonite.

[0019] The pretreated montmorillonite was added to the ferrous ion solution and mixed evenly to form a montmorillonite-ferrous chloride mixed suspension.

[0020] A constant pressure funnel was used to add 60 mL of 1 mol / L NaBH4 solution dropwise to the montmorillonite-ferrous chloride mixed suspension at a rate of 3 mL / min. After the addition was completed, the mixture was stirred continuously for 45 min to allow it to react fully and obtain the composite material.

[0021] The composite material was first rinsed with deionized water after being filtered through a 25 μm filter membrane under vacuum, then washed three times with anhydrous ethanol, and then pre-frozen in a refrigerator for 12 hours. Finally, it was freeze-dried in a vacuum freeze dryer at -55°C for 24 hours. After drying, the iron-modified montmorillonite was obtained.

[0022] Preferably, the amount of iron-modified montmorillonite applied is 1% to 2% of the antimony-arsenic contaminated soil.

[0023] Preferably, the method for preparing the mixed functional bacterial solution includes:

[0024] The mixed functional bacteria were inoculated into the culture medium at a total inoculation rate of 10% in the anaerobic bottle. After purging with pure nitrogen gas for 5 minutes, the anaerobic bottle was sealed and incubated at 30°C for 3-5 days until the mixed functional bacteria reached the logarithmic growth phase. The mixed functional bacteria were a mixture of sulfate-reducing bacteria and iron-reducing bacteria.

[0025] The mixed functional bacteria, which have grown to the logarithmic growth phase, are inoculated into the culture medium at a rate of 10%. Then, three different concentrations of antimony-arsenic mixed solutions are added to the culture medium in sequence for acclimatization culture to obtain the mixed functional bacterial solution.

[0026] Preferably, the culture medium is formulated as follows: yeast extract 1.2 g / L, Ca(NO3)2 0.01 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, KCl 0.1 g / L, sodium lactate 1 ml / L; the pH of the culture medium is adjusted to 6.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention provides a method for remediating antimony and arsenic contaminated soil, relating to the field of soil remediation technology. The method includes: S1, covering the surface of the antimony and arsenic contaminated soil with a composite barrier layer; the thickness of the composite barrier layer is 20cm to 40cm, and the composite barrier layer is composed of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer from bottom to top; S2, spraying a mixed functional bacterial solution onto the surface of the antimony and arsenic contaminated soil with the composite barrier layer to remediate the antimony and arsenic contaminated soil; the mixed functional bacterial solution contains sulfate-reducing bacteria and iron-reducing bacteria. This invention constructs a surface barrier for antimony and arsenic contaminated soil by combining a composite barrier layer and microbial barrier, thereby significantly reducing the leaching of heavy metals in moderately to mildly contaminated soil. It can better achieve long-term, efficient, and stable control and blocking of typical pollutants such as antimony and arsenic, not only reducing the risk of heavy metal pollutant migration, but also realizing deep remediation of contaminated soil.

[0029] In this embodiment of the invention, a surface barrier technology for antimony and arsenic contaminated soil is constructed by combining a composite barrier layer and microbial barrier. On the one hand, the iron-modified montmorillonite layer and the biochar-manganese slag composite material layer in the composite barrier layer synergistically passivate antimony and arsenic, and enrich the heavy metal pollutants. The passivated and enriched antimony and arsenic are then rapidly reduced and solidified into stable sulfide mineral precipitates by mixed functional bacteria, thereby achieving long-term control of heavy metal contaminated soil and reducing the risk of heavy metal pollutant migration. On the other hand, the composite barrier layer and microorganisms work synergistically. The microorganisms enhance the passivation effect of the composite barrier layer, and the composite barrier layer provides an anaerobic environment and strong reducing conditions for deep microbial reduction, thereby enhancing the effect of in-situ microbial reduction and mineralization. This significantly reduces the leaching of heavy metals in moderately to mildly contaminated antimony and arsenic soil, and better achieves efficient, long-term, and stable control and blocking of typical pollutants such as antimony and arsenic. In addition, the method provided by this invention is also characterized by high efficiency, environmental friendliness, and low cost. Attached Figure Description

[0030] 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 these drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating a method for remediating antimony and arsenic contaminated soil according to an embodiment of the present invention;

[0032] Figure 2 This refers to the solidification rate of antimony in the soil after remediation of antimony-arsenic contaminated soil in Example 1 of the present invention.

[0033] Figure 3 This refers to the arsenic solidification rate in the soil after remediation of antimony-arsenic contaminated soil in Example 1 of the present invention. Detailed Implementation

[0034] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0035] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0036] Firstly, the present invention provides a method for remediating antimony and arsenic contaminated soil, such as... Figure 1 As shown, the method includes:

[0037] S1, a composite barrier layer is covered on the surface of antimony and arsenic contaminated soil; the thickness of the composite barrier layer is 20cm to 40cm, and the composite barrier layer is composed of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer from bottom to top.

[0038] In this embodiment, by constructing a composite barrier layer consisting of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer, the antimony and arsenic in the antimony and arsenic contaminated soil can be passivated, thus passivating the antimony and arsenic in the soil.

[0039] Specifically, the iron-modified montmorillonite layer passivates antimony and arsenic in contaminated soil through strong adsorption, thereby reducing the bioavailability of antimony and arsenic. The biochar-manganese slag composite material layer has a strong passivation effect on antimony and arsenic. It can not only electrostatically adsorb antimony and arsenic, reducing their solubility in the soil to a certain extent, but also has various organic functional groups on its surface, such as carboxyl groups and hydroxyl groups. These organic functional groups can complex with heavy metals, thereby reducing their bioavailability.

[0040] In this embodiment, on the one hand, an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer are simultaneously set. The iron-modified montmorillonite layer and the biochar-manganese slag composite material layer synergistically passivate antimony and arsenic, which can enhance the passivation effect of antimony and arsenic. Moreover, the synergy of the two can better enrich the heavy metal pollutant antimony and arsenic, thereby facilitating the reduction and solidification of heavy metal pollutant antimony and arsenic by mixed functional bacteria. Specifically, the passivated antimony and arsenic can be more easily reduced and solidified, and the enriched mixed functional bacteria can reduce and solidify the heavy metal pollutant antimony and arsenic more quickly. On the other hand, the biochar-manganese slag composite material layer can improve soil fertility and reshape the soil ecology. More importantly, the outermost biochar-manganese slag composite material layer is a surface barrier with high sealing performance, which can provide an anaerobic environment and strong reduction conditions for the deep mixed functional bacteria to reduce and solidify, thereby ensuring that the mixed functional bacteria can solidify antimony and arsenic.

[0041] S2, spray a mixed functional bacterial solution onto the surface of the antimony and arsenic contaminated soil having the composite barrier layer to remediate the antimony and arsenic contaminated soil; the mixed functional bacterial solution contains sulfate-reducing bacteria and iron-reducing bacteria.

[0042] In this embodiment, by spraying a mixed functional bacterial solution containing sulfate-reducing bacteria and iron-reducing bacteria onto the surface of antimony and arsenic-contaminated soil, it is not necessary to excavate the contaminated soil, thus achieving in-situ remediation of antimony and arsenic-contaminated soil. The mixed functional bacteria can reduce and solidify antimony and arsenic in the soil into stable sulfide mineral precipitates, such as antimony sulfide and arsenic sulfide, which greatly reduces the leaching of antimony and arsenic, reduces the risk of pollutant migration, and achieves the barrier against antimony and arsenic pollution in the soil.

[0043] Specifically, iron-reducing bacteria can reduce iron ions present in the soil; sulfate-reducing bacteria can produce sulfides by using sulfate as the terminal electron acceptor during organic matter metabolism. These sulfides can not only combine with the iron ions reduced by iron-reducing bacteria to form iron sulfide, which can then be used to adsorb heavy metal pollutants such as antimony and arsenic, but also directly form insoluble metal sulfide mineral precipitates with antimony and arsenic to achieve the remediation of antimony and arsenic in the soil.

[0044] In this embodiment, when the mixed functional bacterial solution is sprayed onto the surface of antimony and arsenic contaminated soil with a composite barrier layer, the powdery material of the composite barrier layer mixes with the antimony and arsenic contaminated soil as the bacterial solution seeps down. Thus, the mixed functional bacteria and the composite barrier layer work together to remediate the antimony and arsenic contaminated soil, which can enhance the fixation effect on antimony and arsenic.

[0045] Specifically, on the one hand, both sulfate-reducing bacteria and iron-reducing bacteria form clay mineral-microorganism complexes with iron-modified montmorillonite layer materials. This complex can increase the surface active sites of sulfate-reducing bacteria, iron-reducing bacteria, and iron-modified montmorillonite layer materials, thereby significantly enhancing the adsorption and fixation of antimony and arsenic by the clay mineral-microorganism complex. On the other hand, iron-reducing bacteria can reduce ferric iron in iron-modified montmorillonite layer materials to ferrous iron, thereby increasing the reactivity of iron-modified montmorillonite layer materials. The iron-modified montmorillonite layer with increased reactivity not only enhances its passivation effect on antimony and arsenic, but can also directly reduce antimony and arsenic. The reduced antimony and arsenic form aggregates with iron-modified montmorillonite layer materials, thereby directly weakening the migration process of antimony and arsenic in the soil environment. Therefore, the iron-modified montmorillonite layer is set closer to the soil, thus eliminating the need to use mixed functional bacteria to reduce and solidify the passivated antimony and arsenic into stable sulfide mineral precipitates.

[0046] Specifically, the outermost layer of biochar-manganese slag composite material in antimony-arsenic contaminated soil serves two main purposes. First, the highly sealing biochar-manganese slag composite material provides a dense environment, thereby enhancing the barrier effect against antimony and arsenic. Second, the highly sealing biochar-manganese slag composite material provides an anaerobic environment and strong reducing conditions for the reduction and solidification of mixed functional bacteria in the antimony-arsenic contaminated soil. In an anaerobic environment, the mixed functional bacteria not only grow better but also have a lower redox potential, significantly enhancing their reduction and solidification capabilities and ensuring their long-term control over antimony-arsenic contamination. Furthermore, the highly sealing biochar-manganese slag composite material layer also enhances the synergistic effect between iron-reducing bacteria and the iron-modified montmorillonite layer, further improving the reactivity of the iron-modified montmorillonite layer. Therefore, the method provided in this embodiment can effectively control the release of antimony and arsenic in an anaerobic iron-reducing environment, thus avoiding the problem of "a large amount of antimony and arsenic being released from the soil when it enters an anaerobic iron-reducing environment but the reduction degree does not reach that of a sulfate-reducing environment."

[0047] In this embodiment of the invention, a surface barrier technology for antimony and arsenic contaminated soil is constructed by combining a composite barrier layer and microbial barrier. On the one hand, the iron-modified montmorillonite layer and the biochar-manganese slag composite material layer in the composite barrier layer synergistically passivate antimony and arsenic, and enrich the heavy metal pollutants. The passivated and enriched antimony and arsenic are then rapidly reduced and solidified into stable sulfide mineral precipitates by mixed functional bacteria, thereby achieving long-term control of heavy metal contaminated soil and reducing the risk of heavy metal pollutant migration. On the other hand, the composite barrier layer and microorganisms work synergistically. The microorganisms enhance the passivation effect of the composite barrier layer, and the composite barrier layer provides an anaerobic environment and strong reducing conditions for deep microbial reduction, thereby enhancing the effect of in-situ microbial reduction and mineralization. This significantly reduces the leaching of heavy metals in moderately to mildly contaminated antimony and arsenic soil, and better achieves efficient, long-term, and stable control and blocking of typical pollutants such as antimony and arsenic. In addition, the method provided by this invention is also characterized by high efficiency, environmental friendliness, and low cost.

[0048] The method provided in this embodiment is particularly effective in solidifying and remediating antimony and arsenic in deep soil, thereby achieving deep remediation of contaminated soil. Specifically, through multiple sprays of mixed functional bacterial solution, the method of combining the composite barrier layer and microbial barrier provided by this invention can remediate antimony and arsenic contaminated soil down to the bedrock at the very bottom of the soil. By utilizing the high fluidity of the bacterial solution, it naturally seeps into the deep soil to reduce and solidify antimony and arsenic, thus expanding the remediation range. If only a composite barrier layer is used to remediate antimony and arsenic contaminated soil, not only is it necessary to increase the thickness of the composite barrier layer, but it is also impossible to achieve long-term, efficient, and stable control and blocking of heavy metal pollutants such as antimony and arsenic. Specifically, in order for the composite barrier layer to better passivate antimony and arsenic in the soil, the thickness of the composite barrier layer needs to be increased, that is, the amount of composite barrier layer material applied needs to be increased. Over time, the composite barrier layer will slowly mix with deeper layers of soil to passivate antimony and arsenic in deeper soil layers, which will lead to excessive costs. Simply using the composite barrier layer to passivate antimony and arsenic in antimony and arsenic contaminated soil cannot effectively reduce the migration of antimony and arsenic. The passivated antimony and arsenic are unstable and may still dissolve back into the soil, leading to remediation failure. Therefore, using the composite barrier layer alone cannot achieve long-term control of heavy metal contaminated soil.

[0049] In some embodiments of the present invention, covering the surface of antimony-arsenic contaminated soil with a composite barrier layer includes:

[0050] Iron-modified montmorillonite is applied to the surface of the antimony and arsenic contaminated soil to form the iron-modified montmorillonite layer;

[0051] Then, a biochar-manganese slag composite material is applied to the iron-modified montmorillonite layer to form the biochar-manganese slag composite material layer.

[0052] In some embodiments of the present invention, the thickness of the iron-modified montmorillonite layer is 10cm to 20cm, and the thickness of the biochar-manganese slag composite material layer is 10cm to 20cm.

[0053] In some embodiments of the present invention, the preparation method of the biochar-manganese slag composite material includes:

[0054] Solid waste manganese slag and waste wheat straw with a mass ratio of 1:2 were placed in a vacuum tube furnace for heat preservation. After heat preservation for 2 hours, the mixture was naturally cooled to room temperature, then ground and passed through a 100-mesh sieve to obtain the biochar-manganese slag composite material.

[0055] Solid waste manganese slag and waste wheat straw underwent pretreatment before being placed in a vacuum tube furnace. Specifically, the manganese slag was washed multiple times to remove impurities such as sulfate and ammonium ions. Washing ensures the manganese slag is safe for use and prevents the release of its own pollutants. After air-drying, the washed manganese slag was ground and passed through a 200-mesh sieve, completing the pretreatment. Wheat straw was washed with deionized water until neutral, soaked for 12 hours, dried to constant weight, and then crushed and screened, completing the pretreatment.

[0056] In this embodiment, wheat straw undergoes thermal decomposition at a certain temperature to form porous biochar, and manganese slag enters the pores during the thermal decomposition process, thereby obtaining a biochar-manganese slag composite material.

[0057] The biochar-manganese slag composite material obtained in this embodiment achieves passivation of heavy metals through adsorption and complexation. After passivation, the heavy metals are transformed into more stable oxidizable and residual states, reducing the migration ability of antimony and arsenic in the soil and significantly decreasing their activity. Furthermore, the large amount of manganese ions loaded on the surface and pores of the biochar exhibits a strong affinity for heavy metals, especially for antimony and arsenic, with a particularly strong passivation effect. Specifically, antimony and arsenic can be adsorbed through Mn-O-Sb / As bonds, thus significantly enhancing the passivation effect on antimony and arsenic by the manganese ions loaded in the pores of the biochar-manganese slag composite material. In particular, the biochar-manganese slag composite material electrostatically adsorbs heavy metals, reducing their solubility after adsorption. The surface of the biochar-manganese slag composite material contains various organic functional groups, such as carboxyl and hydroxyl groups, which can complex with heavy metals, thereby reducing their bioavailability.

[0058] In this embodiment, waste manganese slag and waste wheat straw are used as raw materials for the composite material, making full use of agricultural waste resources. In addition, biochar itself contains alkaline substances and has a high organic matter content. Therefore, covering the soil with biochar-manganese slag composite material can improve soil fertility and soil physicochemical properties, thereby reshaping the soil ecology.

[0059] In some embodiments of the present invention, the amount of the biochar-manganese slag composite material applied is 5% to 10% of the antimony-arsenic contaminated soil.

[0060] In this embodiment, since the biochar-manganese slag composite material has a stronger passivation effect on antimony and arsenic, the amount of biochar-manganese slag composite material applied can be reduced, thereby reducing the remediation cost of contaminated soil.

[0061] In some embodiments of the present invention, the heat preservation inside the vacuum tube furnace includes:

[0062] The inlet flow rate is 50 mL·min -1 After purging with N2 for 20 minutes, the temperature is increased to 700℃ at a rate of 10℃ / min and then held at that temperature. The gas pressure inside the vacuum tube furnace is maintained at ≤0.02Mpa.

[0063] In this embodiment, wheat straw undergoes thermal decomposition at 700°C to form porous biochar, and manganese slag enters the pores at this temperature, thereby obtaining a biochar-manganese slag composite material.

[0064] In some embodiments of the present invention, the method for preparing the iron-modified montmorillonite includes:

[0065] Montmorillonite was dried in an oven at 80°C and passed through a 100-mesh sieve to obtain pretreated montmorillonite.

[0066] The pretreated montmorillonite was added to the ferrous ion solution and mixed evenly to form a montmorillonite-ferrous chloride mixed suspension.

[0067] A constant pressure funnel was used to add 60 mL of 1 mol / L NaBH4 solution dropwise to the montmorillonite-ferrous chloride mixed suspension at a rate of 3 mL / min. After the addition was completed, the mixture was stirred continuously for 45 min to allow it to react fully and obtain the composite material.

[0068] The composite material was first rinsed with deionized water after being filtered through a 25 μm filter membrane under vacuum, then washed three times with anhydrous ethanol, and then pre-frozen in a refrigerator for 12 hours. Finally, it was freeze-dried in a vacuum freeze dryer at -55°C for 24 hours. After drying, the iron-modified montmorillonite was obtained.

[0069] The preparation process of the ferrous ion solution is as follows: 2.5074g of FeCl2·4H2O is dissolved in 100mL of ethanol-water solution to form a 0.126mol / L ferrous ion solution; during the process of mixing the montmorillonite-ferrous chloride mixed suspension evenly, the rotation speed is controlled at 600r / min and the stirring is continued for 60min; after vacuum filtration, the mixture is rinsed with deionized water to remove residual sodium borohydride on the surface of the particles;

[0070] In this embodiment, the passivation of antimony and arsenic by the iron-modified montmorillonite layer is mainly achieved through adsorption. Its huge specific surface area and strong exchange capacity can adsorb antimony and arsenic in the soil, making the antimony and arsenic tend to be stable.

[0071] In this embodiment, iron modification not only increases the specific surface area of ​​montmorillonite by 30% to 80% compared to the unmodified form, thereby enhancing its adsorption capacity, but more importantly, compared to the unmodified montmorillonite, which has a certain adsorption effect on most metals (such as heavy metals such as copper, lead, zinc, and cadmium), the iron-modified montmorillonite has stronger adsorption and passivation properties for arsenic, thus greatly reducing the effectiveness of arsenic.

[0072] In some embodiments of the present invention, the amount of iron-modified montmorillonite applied is 1% to 2% of the antimony-arsenic contaminated soil.

[0073] In this embodiment, since iron-modified montmorillonite has a strong adsorption capacity, especially for arsenic, the amount of iron-modified montmorillonite applied can be reduced for antimony and arsenic contaminated soil, thereby reducing the remediation cost of the contaminated soil.

[0074] In some embodiments of the present invention, the method for preparing the mixed functional bacterial solution includes:

[0075] The mixed functional bacteria were inoculated into the culture medium at a total inoculation rate of 10% in the anaerobic bottle. After purging with pure nitrogen gas for 5 minutes, the anaerobic bottle was sealed and incubated at 30°C for 3-5 days until the mixed functional bacteria reached the logarithmic growth phase. The mixed functional bacteria were a mixture of sulfate-reducing bacteria and iron-reducing bacteria.

[0076] The mixed functional bacteria, which have grown to the logarithmic growth phase, are inoculated into the culture medium at a rate of 10%. Then, three different concentrations of antimony-arsenic mixed solutions are added to the culture medium in sequence for acclimatization culture to obtain the mixed functional bacterial solution.

[0077] The antimony-arsenic mixed solutions added sequentially were: an antimony-arsenic mixed solution with an antimony concentration of 5 mg / L and an arsenic concentration of 5 mg / L; an antimony-arsenic mixed solution with an antimony concentration of 10 mg / L and an arsenic concentration of 10 mg / L; and an antimony-arsenic mixed solution with an antimony concentration of 20 mg / L and an arsenic concentration of 20 mg / L.

[0078] In this embodiment, the cultivation and domestication of the mixed functional bacteria were carried out in an anaerobic operating chamber. In this embodiment, iron-reducing bacteria and sulfate-reducing bacteria with high tolerance and adaptability to antimony and arsenic were obtained through cultivation and domestication. The resulting mixed functional bacteria are suitable for mild to moderate antimony and arsenic pollution.

[0079] In some embodiments of the present invention, the culture medium is formulated as follows: yeast extract 1.2 g / L, Ca(NO3)2 0.01 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, KCl 0.1 g / L, sodium lactate 1 ml / L; the pH of the culture medium is adjusted to 6.

[0080] To enable those skilled in the art to better understand the present invention, the preparation method provided by the present invention will be described below through several specific embodiments.

[0081] Example 1

[0082] This embodiment selects antimony and arsenic contaminated soil from the Qinglong antimony mining area in Guizhou Province. The total antimony and arsenic concentrations in the soil of this area are 5447 mg / kg and 472 mg / kg, respectively, with toxic leaching concentrations of 11.2 mg / L and 0.17 mg / L, respectively. The total thickness of the remediation soil layer is 60 cm. Surface barrier technology is adopted for remediation according to the following steps.

[0083] 2% iron-modified montmorillonite was applied to the surface of antimony and arsenic contaminated soil to form an iron-modified montmorillonite layer; then 5% biochar-manganese slag composite material was applied on the iron-modified montmorillonite layer to form a biochar-manganese slag composite material layer; the thickness of the iron-modified montmorillonite layer was 20cm, and the thickness of the biochar-manganese slag composite material layer was 20cm.

[0084] Spray a mixed functional bacterial solution containing sulfate-reducing and iron-reducing bacteria onto the surface of antimony-arsenic contaminated soil with a composite barrier layer, at a rate of 2 L / m² per spray. 2 Spray bacteria every 2-3 days within the first week, then spray bacteria weekly for a month. The iron-modified montmorillonite layer, biochar-manganese slag composite material and mixed functional bacteria can reach the bedrock at the bottom of the soil to remediate the soil, thus remediating antimony and arsenic contaminated soil and constructing a deep biomineralization layer.

[0085] Long-term monitoring of contaminated soil after remediation was conducted, with soil samples collected to detect the toxic leaching concentrations of antimony and arsenic. Continuous monitoring of surface barriers (composite barrier layer and microbial barrier) for up to 4 months was performed, with the control group (CK) lacking both composite and microbial barriers. The antimony and arsenic immobilization rates in the soil were as follows: Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that the surface barrier technology has a stable curing rate (resistance rate) of about 95% for antimony and arsenic. The monitoring results show that the method provided by this invention can effectively control the diffusion risk of heavy metals.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that 5% biochar was applied to the iron-modified montmorillonite layer. Specifically, the biochar was prepared by washing wheat straw with deionized water until neutral, soaking for 12 hours, drying to constant weight, and then crushing and sieving. The crushed and sieved wheat straw was placed in a vacuum tube furnace and introduced at a flow rate of 50 mL / min. -1 After purging with N2 for 20 min, the temperature was increased to 700℃ at a rate of 10℃ / min and then held at that temperature. The pressure inside the vacuum tube furnace was maintained at ≤0.02Mpa. After holding at that temperature for 2 h, the temperature was naturally cooled to room temperature, then ground and passed through a 100-mesh sieve to obtain biochar.

[0088] Using the method provided in this comparative example, the solidification rate (resistance rate) of antimony was 40%, and the solidification rate (resistance rate) of arsenic was 35%. It can be seen that when biochar is applied to the soil, it will accelerate the release of antimony and arsenic under anaerobic conditions because biochar accelerates the reduction of iron ore in the soil. In addition, biochar can effectively remediate heavy metal cation pollution, but it has no adsorption and fixation capacity for antimony and arsenic.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that 2% montmorillonite was applied to the surface of the antimony and arsenic contaminated soil; wherein the montmorillonite was commercially available.

[0091] Using the method provided in this comparative example, the curing rate (resistance control rate) of antimony is 60%, and the curing rate (resistance control rate) of arsenic is 65%.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 1 is that 2% montmorillonite was applied to the surface of the antimony and arsenic contaminated soil, and then 5% biochar was applied to the iron-modified montmorillonite layer. Specifically, the montmorillonite was commercially available, and the biochar was prepared using the same method as in Comparative Example 1. Using the method provided in this comparative example, the solidification rate (resistance rate) of antimony was 20%, and the solidification rate (resistance rate) of arsenic was 5%.

[0094] As can be seen from Comparative Examples 1-3, compared with the unmodified montmorillonite layer, the iron-modified montmorillonite layer provided by the present invention has a stronger passivation effect and a stronger ability to enrich antimony and arsenic, and can work synergistically with the biochar-manganese slag composite material layer and mixed functional bacteria to remediate antimony and arsenic contaminated soil; compared with biochar not combined with manganese slag, the biochar-manganese slag composite material layer provided by the present invention has a stronger passivation effect and a stronger ability to enrich antimony and arsenic, and can work synergistically with the iron-modified montmorillonite layer and mixed functional bacteria to remediate antimony and arsenic contaminated soil.

[0095] Comparative Example 4

[0096] The only difference between this comparative example and Example 1 is that solid waste manganese slag and waste wheat straw in a mass ratio of 1:20, 1:28, or 1:40 are used to make a biochar-manganese slag composite material, which constitutes a biochar-manganese slag composite material layer. After using the method provided in this comparative example, the antimony curing rate (resistance rate) of the biochar-manganese slag composite material layer composed of a mass ratio of 1:20 is 70%, and the arsenic curing rate (resistance rate) is 70%; the antimony curing rate (resistance rate) of the biochar-manganese slag composite material layer composed of a mass ratio of 1:28 is 55%, and the arsenic curing rate (resistance rate) is 40%; and the antimony curing rate (resistance rate) of the biochar-manganese slag composite material layer composed of a mass ratio of 1:40 is 45%, and the arsenic curing rate (resistance rate) is 38%.

[0097] This shows that as the proportion of wheat straw in waste increases, the solidification rate of antimony and arsenic gradually decreases.

[0098] In this comparative example, the proportion of manganese in the biochar-manganese slag composite material layer is extremely small, resulting in poor passivation effect and further reduction in the solidification rate of antimony and arsenic. In addition, the biochar-manganese slag composite material layer obtained in this comparative example cannot effectively improve the reactivity of the iron-modified montmorillonite layer. More importantly, the biochar-manganese slag composite material layer has poor sealing performance and cannot provide a good anaerobic environment and strong reducing conditions for the reduction and solidification of mixed functional bacteria, thus failing to achieve long-term control of antimony and arsenic contaminated soil.

[0099] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0100] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0101] The above provides a detailed description of a method for remediating antimony and arsenic contaminated soil. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the invention. At the same time, those skilled in the art will recognize that, based on the ideas of the invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A method for remediating antimony and arsenic contaminated soil, characterized in that, The method includes: S1, a composite barrier layer is covered on the surface of antimony and arsenic contaminated soil; the thickness of the composite barrier layer is 20 cm to 40 cm, and the composite barrier layer is composed of an iron-modified montmorillonite layer and a biochar-manganese slag composite material layer from bottom to top. S2, spray a mixed functional bacterial solution onto the surface of the antimony and arsenic contaminated soil having the composite barrier layer to remediate the antimony and arsenic contaminated soil; the mixed functional bacterial solution contains sulfate-reducing bacteria and iron-reducing bacteria; The composite barrier layer covering the surface of antimony and arsenic contaminated soil includes: Iron-modified montmorillonite is applied to the surface of the antimony and arsenic contaminated soil to form the iron-modified montmorillonite layer; Then, biochar-manganese slag composite material is applied to the iron-modified montmorillonite layer to form the biochar-manganese slag composite material layer; The thickness of the iron-modified montmorillonite layer is 10 cm to 20 cm, and the thickness of the biochar-manganese slag composite material layer is 10 cm to 20 cm. The iron-modified montmorillonite layer, biochar-manganese slag composite material, and mixed functional bacteria can reach the bedrock at the bottom of the soil to remediate the soil, thereby remediating antimony and arsenic contaminated soil and constructing a deep biomineralization layer. The preparation method of the biochar-manganese slag composite material includes: Solid waste manganese slag and waste wheat straw with a mass ratio of 1:2 were placed in a vacuum tube furnace for heat preservation. After heat preservation for 2 hours, the mixture was naturally cooled to room temperature, then ground and passed through a 100-mesh sieve to obtain the biochar-manganese slag composite material. The heat preservation inside the vacuum tube furnace includes: The inlet flow rate is 50 mL·min -1 After purging with N2 for 20 min, the temperature is increased to 700 ℃ at a heating rate of 10 ℃ / min and then held at that temperature. The gas pressure inside the vacuum tube furnace is maintained at ≤0.02 MPa.

2. The method according to claim 1, characterized in that, The amount of the biochar-manganese slag composite material applied is 5% to 10% of the antimony and arsenic contaminated soil.

3. The method according to claim 1, characterized in that, The preparation method of the iron-modified montmorillonite includes: Montmorillonite was dried in an oven at 80 °C and passed through a 100-mesh sieve to obtain pretreated montmorillonite. The pretreated montmorillonite was added to the ferrous ion solution and mixed evenly to form a montmorillonite-ferrous chloride mixed suspension. A constant pressure funnel was used to add 60 mL of 1 mol / L NaBH4 solution dropwise to the montmorillonite-ferrous chloride mixed suspension at a rate of 3 mL / min. After the addition was complete, the mixture was stirred for 45 min to allow it to react fully and obtain the composite material. The composite material was first filtered through a 25 µm filter membrane under vacuum, then rinsed with deionized water, then washed three times with anhydrous ethanol, and then pre-frozen in a refrigerator for 12 h. Finally, it was freeze-dried in a vacuum freeze dryer at -55 ℃ for 24 h. After drying, the iron-modified montmorillonite was obtained.

4. The method according to claim 1, characterized in that, The amount of iron-modified montmorillonite applied is 1% to 2% of the antimony and arsenic contaminated soil.

5. The method according to claim 1, characterized in that, The method for preparing the mixed functional bacterial solution includes: The mixed functional bacteria were inoculated into the culture medium at a total inoculation rate of 10% in the anaerobic bottle. After purging with pure nitrogen gas for 5 minutes, the anaerobic bottle was sealed and incubated at 30 °C for 3-5 days until the mixed functional bacteria grew to the logarithmic growth phase. The mixed functional bacteria were a mixture of sulfate-reducing bacteria and iron-reducing bacteria. The mixed functional bacteria, which have grown to the logarithmic growth phase, are inoculated into the culture medium at a rate of 10%. Then, three different concentrations of antimony-arsenic mixed solutions are added to the culture medium in sequence for acclimatization culture to obtain the mixed functional bacterial solution.

6. The method according to claim 5, characterized in that, The culture medium is formulated as follows: yeast extract 1.2 g / L, Ca(NO3)2 0.01 g / L, K2HPO4 0.5 g / L, MgSO4·7H2O 0.5 g / L, KCl 0.1 g / L, sodium lactate 1 ml / L; the pH of the culture medium is adjusted to 6.

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