Method for remediating arsenic contaminated soil by using biochar reinforced pteris vittata

Abstract

The present application belongs to the technical field of soil remediation, and relates to a method for remediation of arsenic contaminated soil by Pteridium aquilinum Linn. with biochar. The present application uses biochar, including one of straw biochar, iron modified biochar, aluminum modified biochar and iron-aluminum modified biochar; 1% to 2% of biochar is applied to the arsenic contaminated soil in terms of mass ratio, which strengthens the arsenic remediation capacity of Pteridium aquilinum Linn. to the soil, and improves the efficiency of Pteridium aquilinum Linn. in remediation of arsenic in the soil to 19.25% to 26.24%. The boundary use conditions of the technology for remediation of heavy metal contaminated soil by biochar strengthened plant are not clear, and the present application eliminates the prejudice or misunderstanding of ordinary technical personnel in the field, including researchers in the field, that the modified biochar is superior to the biochar for remediation of arsenic contaminated soil. The present application enables the practitioners in the field to have a more comprehensive understanding of the biochar, especially the metal modified biochar, for remediation of arsenic contaminated soil.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology and relates to a method for remediating arsenic-contaminated soil using biochar-enhanced Centipede Grass. Background Technology

[0002] During the mining and utilization of arsenic-containing mineral resources, the leakage and emission of arsenic-containing substances are inevitable, polluting the regional ecological environment. Arsenic accumulates in the soil and water environment through atmospheric deposition, runoff, and biological absorption, ultimately affecting human health through the food chain. Soil arsenic pollution is characterized by its strong concealment, delayed effects, and bioaccumulation, making it difficult to achieve rapid remediation through soil self-purification capabilities or single biological / chemical / physical remediation technologies. Therefore, current research employs a combination of methods and technologies to remediate soil arsenic pollution.

[0003] Common porous materials for heavy metal adsorption and passivation, such as biochar, are readily available, inexpensive, and environmentally friendly materials with a large specific surface area and abundant surface functional groups, effectively reducing the bioavailability of pollutants. Further research into porous materials has revealed that the adsorption capacity of simple porous materials is limited. Therefore, research has proposed improvement schemes to enhance their adsorption performance, primarily through modification with metals, minerals, or organic matter. Current technology generally believes that metal modification of porous materials to optimize their structure and adsorption properties can improve their remediation efficiency for heavy metals. For example, iron salt-modified porous materials have a large specific surface area, strong mechanical properties, can provide iron ions, and are rich in functional groups, significantly improving the adsorption efficiency of heavy metals (arsenic, cadmium, lead, etc.).

[0004] Centipede grass ( Pteris vittata L. As a hyperaccumulator of arsenic, *Pteris vittata* exhibits superior arsenic accumulation / tolerance compared to non-accumulator plants. It can rapidly transport As from the soil to the aboveground parts via its roots and is widely used in the remediation of arsenic-contaminated soils. However, blindly selecting the type and dosage of metal-modified biochar can actually reduce or diminish the ability of *Pteris vittata* to remediate As pollution in soil. Therefore, it is necessary to investigate the impact of biochar on the availability of As in soil and clarify the interaction mechanism between biochar and hyperaccumulator plants.

[0005] Methods for remediating arsenic-contaminated soil using Centipede Grass include: (1) using Centipede Grass alone to remediate arsenic-contaminated soil; (2) using Centipede Grass in combination with other plants to remediate heavy metal-contaminated soil; (3) using Centipede Grass intercropped with other crops to remediate heavy metal-contaminated soil and reduce the accumulation of heavy metals in agricultural products. For example, intercropping Centipede Grass with corn can reduce the arsenic content in the soil and reduce the accumulation of arsenic in corn, but the remediation cycle is too long and the arsenic content in corn is still high; (4) enhancing the remediation capacity of Centipede Grass for heavy metal-contaminated soil through materials, reagents, microorganisms, etc. For example, CN108636995A and CN110918638A disclose methods for remediating heavy metals by using chemical barrier agents in combination with Centipede Grass, but there are problems such as contradictory effects of barrier agents, large dosage and high cost, and unclear quantitative remediation effect. For example, CN111389904A uses Centipede Grass, oxalic acid and Sedum aizoon to remediate heavy metal-contaminated soil through a unique planting method, which has a good effect, but the implementation method is complicated and not easy to promote. As research into the mechanism of biochar in porous materials for the remediation of arsenic-contaminated soil deepens, the understanding of the use of centipede grass in the remediation of arsenic-contaminated soil has also become more objective and clear. However, the boundary conditions for the combined use of biochar and centipede grass in arsenic-contaminated soil remain unclear. Summary of the Invention

[0006] The purpose of this invention is to enhance the remediation of arsenic-contaminated soils by utilizing the properties of biochar. However, blindly selecting the type of biochar modification and the dosage can lead to a decrease or insignificant improvement in the ability of the accumulating plant *Pteris vittata* to remediate arsenic pollution in soil. Therefore, it is necessary to explore the impact of biochar on the availability of arsenic in soil, clarify the interaction mechanism between biochar and accumulating plants, and define the boundary conditions for the combined use of biochar and *Pteris vittata* in arsenic-contaminated soils (biochar type, response dose, application timing, pollution level, application method, and different parent soils). It is generally recognized in the art that modifying biochar with metals, minerals, or organic matter can improve its application effect in soil remediation. The underlying principle is that modifying porous materials can enhance their adsorption capacity.

[0007] This invention provides a method for remediating arsenic-contaminated soil by biochar-enhanced Pteris vittata, comprising: applying 1% to 2% biochar to the arsenic-contaminated soil by mass ratio, and planting an equal amount of uncontaminated Pteris vittata spores in the arsenic-contaminated soil.

[0008] When the leaves of the centipede grass grow to more than 40cm, they should be harvested. The arsenic content of the arsenic-contaminated soil was 37 mg / kg to 50 mg / kg; The pH value of the arsenic-contaminated soil is 8.8-9.2. Optionally, for long-term reuse, the centipede grass should be harvested when the leaves grow to more than 40cm, leaving a stubble of 5cm. The biochar promotes the enrichment of arsenic in the soil by Centipede Grass.

[0009] Furthermore, in the method for remediating arsenic-contaminated soil using biochar-enhanced Centipede Grass provided by the present invention, the biochar is selected from one of the following: straw biochar, iron-modified biochar, aluminum-modified biochar, and iron-aluminum-modified biochar.

[0010] Furthermore, in the method for remediating arsenic-contaminated soil with biochar-enhanced Centipede Grass provided by the present invention, the raw material for preparing the straw biochar is corn straw, with a yield of 23.40% and a total organic carbon content of 453.2 g / kg.

[0011] Furthermore, in the method for remediating arsenic-contaminated soil with biochar-enhanced Centipede Grass provided by the present invention, the preparation method of the iron-modified biochar includes: adding biochar to FeCl3 solution, stirring and adjusting the pH to 7.0 and maintaining for 2 hours, letting it stand at 25°C for 48 hours, separating the solid and liquid by centrifugation, washing twice with deionized water, and then washing with ethanol until no Cl is found. - Dry at 75℃ until constant weight and pass through a 1mm sieve.

[0012] Furthermore, in the method for remediating arsenic-contaminated soil with biochar-enhanced Centipede Grass provided by the present invention, the preparation method of the aluminum-modified biochar includes: adding biochar to an AlCl3 solution, stirring and adjusting the pH to 7.0 and maintaining this for 2 hours, allowing it to stand at 25°C for 48 hours, centrifuging to separate the solid and liquid, washing twice with deionized water, and then washing with ethanol until no Cl is found. - Dry at 75℃ until constant weight and pass through a 1mm sieve.

[0013] Furthermore, in the method for remediating arsenic-contaminated soil with biochar-enhanced Centipede Grass provided by the present invention, the preparation method of the iron-aluminum modified biochar includes: mixing FeCl3 solution and AlCl3 solution, adding biochar, stirring, adjusting the pH to 7.0 and maintaining for 2 hours, letting it stand at 25°C for 48 hours, centrifuging to separate the solid and liquid, washing twice with deionized water, and then washing with ethanol until no Cl is found. - Dry at 75℃ until constant weight and pass through a 1mm sieve.

[0014] Furthermore, in the biochar-enhanced method for remediating arsenic-contaminated soil using Centipede Grass provided by this invention, the iron-aluminum modified porous material, by mass ratio, contains 2.34% iron ions, 1.27% aluminum ions, has a CEC of 36.7~37.6, and a specific surface area of ​​5.86~12.46 m². 2 / g.

[0015] For example, in the method for remediating arsenic-contaminated soil with biochar-enhanced centipede grass provided by the present invention, 1% biochar is applied to the arsenic-contaminated soil by mass ratio, wherein the biochar is selected from straw biochar and iron-aluminum modified biochar.

[0016] For example, in the method for remediating arsenic-contaminated soil with biochar-enhanced centipede grass provided by the present invention, 2% biochar is applied to the arsenic-contaminated soil by mass ratio, wherein the biochar is iron-aluminum modified biochar.

[0017] In the preparation of iron-modified porous materials, aluminum-modified porous materials, and iron-aluminum-modified porous materials, this invention does not limit the method of solid-liquid separation. For example, a centrifuge at 4000 r / min can be used to separate the solid and liquid.

[0018] On the other hand, the present invention relates to the application of the above-mentioned method in the remediation of arsenic-contaminated soil.

[0019] Compared with the prior art, the present invention has the following beneficial effects or advantages: (1) This invention clarifies that both biochar and metal-modified biochar have a positive promoting effect on the remediation of As in lightly contaminated soil by Pteris vittata. This invention provides a method for biochar-enhanced Pteris vittata remediation of arsenic-contaminated soil. By applying biochar or metal-modified biochar at different mass ratios, both Pteris vittata have a positive promoting effect on the remediation of As in lightly contaminated soil by Pteris vittata, further increasing the efficiency of As enrichment by Pteris vittata to 19.25%~26.24%.

[0020] (2) This invention clarifies the mechanism by which biochar or metal-modified biochar positively promotes the remediation of As in lightly polluted soil by Centipede Grass. This invention provides a method for enhancing the remediation of arsenic-contaminated soil with biochar-enhanced Centipede Grass. Applying a certain amount of modified biochar can effectively reduce the content of available As in lightly polluted soil. Among them, aluminum-modified biochar and iron-aluminum-modified biochar with a mass ratio of 1% showed the best passivation effect on As in lightly polluted soil. The distribution of As forms in soil is as follows: residual form > calcium-bound form > iron-bound form, aluminum-bound form > water-soluble form, exchangeable form. For heavily polluted soil, modified biochar promotes the conversion of available As in the soil to less bioavailable bound forms and non-directly usable residual forms to varying degrees.

[0021] (3) This invention clarifies that, under different application ratios, metal-modified biochar is not necessarily superior to biochar, and that increasing the mass ratio of biochar or modified biochar does not necessarily increase the effect of *Pteris vittata* on improving the soil As remediation efficiency. This invention clarifies that the mechanism by which biochar promotes the soil As remediation efficiency of *Pteris vittata* is different from the passivation effect of biochar on soil As, therefore, the application of metal modification of biochar in soil remediation cannot inspire the use of metal-modified biochar to enhance the remediation of arsenic-contaminated soil by *Pteris vittata*. This invention eliminates the prejudice or misunderstanding of those skilled in the art, including researchers in the art, regarding the use of metal-modified biochar relative to biochar for soil pollution remediation, namely, that modified biochar is superior to biochar for soil remediation. This invention provides a method for remediating arsenic-contaminated soil using Pteris vittata (a type of wild herb) enhanced with biochar. As the mass ratio of biochar application increases (1%→2%), the remediation efficiency of Pteris vittata for arsenic in soil decreases from 15.31% to 11.62% under biochar conditions; while under iron-modified biochar, aluminum-modified biochar, and iron-aluminum-modified biochar conditions, the remediation efficiency of Pteris vittata for arsenic in soil increases from 11.07%, 15.00%, and 21.93% to 19.97%, 19.25%, and 26.24%, respectively. Attached Figure Description

[0022] Figure 1 The surface structural characteristics of different biochars.

[0023] Figure 2 The adsorption kinetics curves of As in different biochars are shown.

[0024] Figure 3 Isothermal adsorption curves for different biochars.

[0025] Figure 4 The influence of environmental conditions on the adsorption capacity of modified biochar for As.

[0026] Figure 5 The effect of biochar on the available As content in soil.

[0027] Figure 6 Distribution of As speciation in moderately polluted soil under 1% biochar application.

[0028] Figure 7 Distribution of As speciation in moderately polluted soil under 2% biochar application.

[0029] Figure 8 Distribution of As speciation in heavily polluted soil under 1% biochar application.

[0030] Figure 9 Distribution of As speciation in heavily polluted soil under 1% biochar application.

[0031] Figure 10 Potted experiment to enhance the remediation of aspergillus spp. with biochar in centipede grass.

[0032] Figure 11 Comparison of the efficiency of different biochar-enhanced centipede grass in remediating aspergillus oryzae.

[0033] Among them, CK is the blank control group, BC is corn straw biochar, Fe-BC is iron-modified biochar, Al-BC is aluminum-modified biochar, and Fe-Al-BC is iron-aluminum modified biochar. Detailed Implementation

[0034] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0035] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0036] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0037] Example 1 This embodiment provides experiments on the preparation of different biochars and their differences in properties.

[0038] In the following embodiments, BC is corn straw biochar, Fe-BC is iron-modified biochar, Al-BC is aluminum-modified biochar, and Fe-Al-BC is iron-aluminum modified biochar.

[0039] (1) Preparation of biochar Biochar was prepared using corn stalks from farmland free from heavy metal contamination as raw material via a muffle furnace. The stalks were cut to appropriate sizes and filled into a covered ceramic crucible. The crucible was sealed and placed in a muffle furnace for pyrolysis. The pyrolysis temperature was increased to 350℃ at a rate of 20℃ / min and maintained for 4 hours. The resulting material (BC) was cooled to room temperature, crushed, sieved through a 1mm sieve, and then sealed for later use. The biochar yield was 23.40% (biochar dry weight / original straw dry weight), and the total organic carbon (TOC) was 453.2 g / kg.

[0040] This study prepared iron-modified (Fe-BC), aluminum-modified (Al-BC), and iron-aluminum-modified (Fe-Al-BC) biochar using an impregnation method. 0.3 mol / L FeCl3, AlCl3, and FeCl3&AlCl3 solutions were used at a ratio of 1:10 (kg:L). While magnetically stirring, the pH of the suspensions was adjusted to 7.0 with 0.5 mol / L NaOH and maintained for 2 h. After standing at 25℃ for 48 h, the biochars were centrifuged at 4000 r / min (r / g × (g × 2π / 60)). 2 Centrifuge to separate the solid and liquid, wash twice with deionized water, and then wash with ethanol until no Cl- is visible. - Dry at 75℃ to constant weight, pass through a 1mm sieve, and seal for later use.

[0041] (2) Characterization analysis of biochar The physicochemical properties of biochar are shown in Table 1. The pH values ​​of all modified biochars decreased to varying degrees, becoming acidic. Modification had the most significant effect on the zeta potential of the materials; the zeta potentials of the Fe and Fe-Al modified materials became positive. The cation exchange capacity (CEC) and specific surface area of ​​the modified biochars both increased, with Fe-BC having the largest specific surface area, 2.88 times that of BC; and Fe-Al-BC having a specific surface area 2.51 times that of BC.

[0042] Table 1. Basic Physicochemical Properties of Biochar

[0043] (3) Comparison of surface structure of modified biochar before and after modification like Figure 1 As shown, compared to the unmodified state, the surface structure of the modified biochar has changed significantly, with noticeable deposits, leading to changes in properties such as the specific surface area. The biochar surface is primarily composed of a distinct carbon skeleton structure; after modification, the surface of the material is covered with numerous functional groups containing elements such as iron and aluminum.

[0044] Example 2 This embodiment provides experiments on the arsenic adsorption characteristics of different biochars.

[0045] (1) Adsorption kinetics Depend on Figure 2It can be seen that the absorption of As in solution gradually increases before and after biochar modification. The adsorption capacity of iron-modified biochar (Fe-BC) for As after 24 hours is approximately 1.71 mg / g, which is 53% higher than that of BC. Among all materials, Fe-Al modified biochar starts adsorption earliest, and the As concentration in water decreases significantly after 15 minutes. The adsorption capacity of biochar for As in solution is: Fe-Al-BC > Al-BC > Fe-BC > Unmodified (BC). The adsorption capacity of Fe-Al-BC for As is approximately 5 times that of BC, Al-BC for As is approximately 4.2 times that of BC, and Fe-BC for As is approximately 1.6 times that of BC.

[0046] (2) Isothermal adsorption characteristics Isothermal adsorption tests were conducted on the three types of modified biochar, such as... Figure 3 As shown, under conditions of 20±0.5℃, the adsorption capacity of modified biochar for As showed a trend of first increasing and then decreasing with the increase of As concentration in the solution. The adsorption capacity for As reached its highest value in a solution with an As concentration of 25 mg / L.

[0047] Example 3 This embodiment provides an experiment on the effect of environmental conditions on the arsenic adsorption efficiency of biochar.

[0048] Three conditions—As concentration, pH, and ambient temperature—were selected, and three levels were set for each condition. An orthogonal experiment was conducted to study the suitable adsorption environment for Fe-Al-BC and Al-BC.

[0049] like Figure 4 As shown, the factors affecting the adsorption capacity of Al-BC for As are concentration > temperature > pH, with the optimal adsorption conditions being an As concentration of 50 mg / L, pH = 7, and a temperature of 40℃. The factors affecting the adsorption capacity of Fe-Al-BC for As are concentration > pH > temperature, with the optimal adsorption conditions being an As concentration of 100 mg / L, pH = 10, and a temperature of 40℃.

[0050] Example 4 (1) The effect of biochar on available As in soil Using no biochar as a control, 1% and 2% biochar were applied to moderately arsenic-contaminated (40 mg / kg) and heavily arsenic-contaminated (150 mg / kg) soils, respectively, and cultured at room temperature for 150 days, maintaining a soil moisture content of 30%.

[0051] like Figure 5As shown, different biochars exhibit varying passivation effects on arsenic in soil. For moderately contaminated soil (40 mg / kg), using BC as a control, the application of 1%–2% (by mass) of Fe-BC, Al-BC, and Fe-Al-BC significantly reduced the content of available As in the soil. Specifically, with 1% biochar application, the Fe-BC treatment resulted in the lowest available As content of 0.48 mg / kg, increasing to 0.68 mg / kg when the application rate increased to 2%. Similarly, with BC and Fe-Al-BC at a mass ratio of 1%, the available As content in the soil was 0.944 mg / kg and 0.50 mg / kg, respectively; increasing the application rate to 2% also resulted in varying degrees of increase in available As content. Conversely, with Al-BC, the available As content in the soil decreased from 0.73 mg / kg to 0.58 mg / kg with increasing application rate; the higher the application rate, the better the passivation effect. Overall, the application of Al-BC and Fe-Al-BC at a mass ratio of 1% showed the best passivation effect on As in moderately polluted (40 mg / kg) soil, with the lowest content of available As.

[0052] like Figure 5 As shown, for heavily polluted soil (150 mg / kg), with BC as the control, the application of 1%–2% (by mass ratio) of Fe-BC, Al-BC, and Fe-Al-BC all increased the content of available As in the soil to varying degrees. When 1% and 2% of Al-BC were applied, the available As content was 37.69 mg / kg and 37.82 mg / kg, respectively, with no significant difference. Furthermore, with the increase of the application mass ratio (1%→2%), the available As content in the soil decreased from 101.41 mg / kg and 32.68 mg / kg to 88.46 mg / kg and 28.65 mg / kg, respectively, for Fe-BC and Fe-Al-BC. This indicates that Fe-BC had the best passivation effect on available As in the soil at a mass ratio of 1%, and was superior to Fe-Al-BC. Overall, for heavily polluted soil, the application of biochar at a certain mass ratio (1%–2%) can reduce the content of available As in the soil to varying degrees.

[0053] (2) Analysis of the passivation effect of different biochars on soil As Table 2 shows that applying biochar at different mass ratios significantly passivated As in moderately As-contaminated soil (40 mg / kg). Compared with soil without biochar application, after 150 days of natural aging, a significant portion of the available As was converted into a less bioavailable bound state (29.96 mg / kg). When 1% and 2% biochar were applied to the soil, the content of available As decreased significantly, converting into a residual state that cannot be directly utilized by organisms. The passivation efficiencies of Al-BC, Fe-BC, and Fe-Al-BC for As were 83.83–86.88%, 82.45–87.77%, 81.97–91.09%, and 84.42–87.03%, respectively. The results indicate that applying 1% Fe-BC can maximize the conversion of available As in the soil into a stable state (residual state) that cannot be directly utilized by organisms, with a passivation efficiency as high as 91.09%. Overall, the passivation efficiency of 1% Al-BC and 2% Fe-Al-BC in moderately polluted soil can reach over 86%.

[0054] Table 2. As passivation efficiency of biochar in moderately polluted soil

[0055] Table 3 shows that applying biochar at different mass ratios significantly passivated As in heavily contaminated As soil (150 mg / kg). Compared with soil without biochar application, the content of available As decreased significantly when 1% and 2% biochar were applied, with more As being converted into bioavailable bound forms and less efficient conversion into unusable residues. The passivation efficiencies of Al-BC, Fe-BC, and Fe-Al-BC in converting available As into residues were 8.06–45.30%, 6.48–17.46%, 26.42–32.45%, and 20.96–29.38%, respectively. Biochar converted more available As into bioavailable bound forms, but compared with the natural aging results of the control group (without material application), the passivation effects of 1% and 2% biochar on As in heavily contaminated soil were not significant.

[0056] Table 3. Passivation efficiency of biochar on As in heavily polluted soil

[0057] (3) Effects of different biochar on the distribution of As speciation in soil Depend on Figure 6 and Figure 7It was found that adding biochar at different mass ratios significantly affected the ascorbate (As) speciation in moderately polluted soil (40 mg / kg). Applying 1% biochar (Al-BC, Fe-BC, and Fe-Al-BC) significantly passedivated As, with As in the soil primarily existing in residual form, followed by calcium-bound form. Applying 2% biochar also significantly affected As speciation, with As remaining in the soil as residual form. However, compared to the 1% treatment, Fe-Al-BC and BC showed little change, while the proportion of residual As decreased and the proportion of calcium-bound As slightly increased under the Fe-BC and Al-BC treatments.

[0058] Depend on Figure 8 and Figure 9 It was found that different biochars significantly affected the distribution and transformation of As speciation in heavily polluted (150 mg / kg) soil. The passivation efficiency of As in soil was not significantly different among Al-BC, Fe-BC, and Fe-Al-BC at different application rates, and the distribution and transformation patterns of As speciation were basically consistent. Application of 1% and 2% biochar by mass ratio both promoted the transformation of available As in soil into stable forms with low / difficult bioavailability. Under the 1% treatment, the transformation to residual and calcium-bound forms was predominant, while the transformation efficiency to residual, calcium-bound, and aluminum-bound forms was lower under the 2% treatment compared to the 1% treatment.

[0059] Example 5 This embodiment provides an experimental study on the effect of biochar on the remediation of soil aspergillus by Centipede Grass.

[0060] like Figure 10 As shown, modified biochar was applied to moderately contaminated (40 mg / kg) and heavily contaminated (150 mg / kg) As soils at mass ratios of 1% and 2%, respectively. *Pteris vittata*, an As hyperaccumulator, was used as the remediation plant. Each pot contained 3.5 kg of soil (dry weight) and three plants were planted. Water and light conditions were kept consistent throughout the pot cultivation process, which lasted for six months. The results showed that soil As concentration directly affected the growth of *Pteris vittata* and its efficiency in arsenic remediation. *Pteris vittata* grew better overall in moderately contaminated soils, while its growth was poor in heavily contaminated soils.

[0061] like Figure 11The effects of different biochar types on the remediation of As (As) in soil by *Pteris vittata* vary. When the biochar mass ratio is 1%, the efficiency of *Pteris vittata* in remediating As ranges from 11.07% to 21.93%, with the order being Fe-Al-BC > Fe-BC > Al-BC. The highest efficiency of As remediation by *Pteris vittata* is 23.93% when Fe-Al-BC is applied. As the biochar mass ratio increases (1%→2%), the remediation efficiency of *Pteris vittata* for As in soil increases from 11.07%, 15.00%, and 21.93% under Al-BC, Fe-BC, and Fe-Al-BC conditions to 19.97%, 19.25%, and 26.24%, respectively. Overall, when remediating soils with a certain degree of As contamination by *Pteris vittata*, applying biochar at a mass ratio of 1%–2% helps to enrich and accumulate As in the soil, thereby accelerating the remediation of As-contaminated soil. However, for unmodified biochar, i.e., the BC group experiment, the remediation efficiency of Centipede Grass on soil As decreased as the biochar application mass ratio increased.

[0062] In conclusion, the following conclusions can be drawn: (1) The modification of Fe, Al and Fe-Al significantly changed the material properties. The pH value of the material decreased, changing from alkaline to acidic or weakly acidic; the specific surface area increased, with the specific surface area of ​​Fe-BC being 2.88 times that of BC; the CEC increased significantly, and the surface structure characteristics of the material changed significantly.

[0063] (2) The adsorption capacity of biochar for As in solution is Fe-Al-BC>Al-BC>Fe-BC>BC. Among them, the adsorption capacity of Fe-Al-BC for As is about 5 times that of BC. The influence of environmental conditions on the adsorption capacity of Fe-Al-BC for As is as follows: initial As concentration>pH>temperature. The relatively optimal adsorption conditions are As concentration of 100mg / L, pH=10, and temperature of 40℃.

[0064] (3) Different types of biochar all promoted the passivation of soil arsenic, but the effect was affected by the type of material and its dosage. Applying biochar at a mass ratio of 1% and 2% could effectively reduce the content of available As in moderately polluted soil. At a mass ratio of 1%, porous materials had a relatively better overall passivation effect on moderately polluted As, with little difference in passivation efficiency. The As form distribution was residual > calcium-bound > iron-bound, aluminum-bound > water-soluble, and exchangeable. For heavily polluted (150 mg / kg) soil, modified biochar increased the content of available As in the soil to varying degrees. At a mass ratio of 1%, the passivation efficiency of As in the soil was relatively the highest. The content of each As form was in the order of residual > calcium-bound > exchangeable > water-soluble > aluminum-bound > iron-bound. Overall, the application of biochar promoted the conversion of available As in the soil into bound forms with low bioavailability and residual forms that could not be directly utilized, that is, it had different degrees of passivation effect on As in the soil.

[0065] (4) The application of biochar at different mass ratios all had a positive promoting effect on the remediation of moderately As-contaminated soil by Centipede Grass. When the biochar mass ratio was 1%, the efficiency of Centipede Grass in remediating As was Fe-Al-BC > Fe-BC > Al-BC, with the highest efficiency of Centipede Grass in remediating As being 23.93% when Fe-Al-BC was applied. As the biochar mass ratio increased (1%→2%), the efficiency of Centipede Grass in enriching As further increased to 19.25~26.24%, which was significantly higher than that of BC or low mass ratio (1%).

[0066] As described above, the present invention can be effectively implemented. The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for remediating arsenic-contaminated soil using biochar-enhanced Centipede Grass, characterized in that, include: Biochar was applied to arsenic-contaminated soil by weight ratio, and an equal amount of uncontaminated centipede spores were planted in the arsenic-contaminated soil. When the leaves of the centipede grass grow to more than 40cm, they should be harvested. The arsenic content of the arsenic-contaminated soil was 37 mg / kg to 50 mg / kg; The pH value of the arsenic-contaminated soil was 8.8~9.2; The biochar application reduces the content of available arsenic in the arsenic-contaminated soil and promotes the enrichment of arsenic in the soil by Centipede Grass. 1% biochar was applied to the arsenic-contaminated soil by mass ratio, wherein the biochar was selected from straw biochar or iron-aluminum modified biochar. Alternatively, 2% biochar may be applied to the arsenic-contaminated soil by weight, wherein the biochar is iron-aluminum modified biochar.

2. The method according to claim 1, characterized in that, The raw material for preparing the straw biochar is corn straw, with a yield of 23.40% and a total organic carbon content of 453.2 g / kg; The preparation method of the iron-aluminum modified biochar includes: mixing FeCl3 solution and AlCl3 solution, adding the straw biochar, stirring, adjusting the pH to 7.0 and maintaining this for 2 hours, letting it stand at 25℃ for 48 hours, centrifuging to separate the solid and liquid, washing twice with deionized water, and then washing with ethanol until no Cl is found. - Dry at 75℃ until constant weight and pass through a 1mm sieve.

3. The method according to claim 2, characterized in that, By mass ratio, the iron-aluminum modified biochar contains 2.34% iron ions, 1.27% aluminum ions, has a CEC of 36.7~37.6, and a specific surface area of ​​5.86~12.46 m². 2 / g.

4. The application of the biochar-enhanced Centipede Grass method for remediating arsenic-contaminated soil according to any one of claims 1 to 3 in the remediation of arsenic-contaminated soil.

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