A modified biochar material, a preparation method thereof and application thereof in treating soil pollution

Abstract

This invention discloses a modified biochar material, its preparation method, and its application in soil pollution remediation. The preparation method includes: carbonizing melon or bean vines to obtain biochar; stirring the biochar and concentrated nitric acid in an ice bath, then adding distilled water and stirring while maintaining the temperature, followed by adding the biochar to an ammonium persulfate solution and stirring again while maintaining the temperature, to obtain a first modified biochar; adding the biochar to a calcium or iron solution, and then adding sodium selenite solution to react, to obtain a second modified biochar; dispersing the first and second modified biochar in distilled water, adding sodium tetrapolybenzenesulfonate and carboxymethyl cellulose to react, to obtain the modified biochar material. The biochar material of this invention has good physical / chemical stability and can specifically adsorb heavy metals including cadmium, lead, and arsenic, significantly improving the adsorption performance of heavy metal ions, and enhancing the adsorption capacity and efficiency, making it suitable for the remediation of heavy metal pollution in mine soils.

Description

Technical Field

[0001] This invention relates to the field of soil pollution remediation technology, and in particular to a modified biochar material, its preparation method, and its application in soil pollution remediation. Background Technology

[0002] Mine soil pollution prevention and control refers to technical measures to control or mitigate soil environmental pollution caused by mining operations. Pollutants generated during mining operations enter the soil and accumulate continuously through processes such as physical and mechanical absorption, retention, colloidal physicochemical adsorption, chemical precipitation, and biological absorption. When these pollutants reach a certain level, they cause deterioration of soil composition, texture, properties, and functions. Heavy metals are difficult to degrade in soil and exhibit strong cumulative and biotoxic properties. They can be absorbed by plants and transferred through the food chain, ultimately harming human health and causing various diseases.

[0003] Biochar is a novel environmental functional material. It is a type of insoluble, stable, highly aromatic, carbon-rich solid substance produced by the high-temperature pyrolysis of biological residues under anaerobic conditions. It possesses a well-developed porous structure, a large specific surface area, and a large number of functional groups and negative charges on its surface, exhibiting a strong adsorption capacity for heavy metal ions. It can serve as an excellent adsorbent material and shows potential in soil pollution remediation. However, in actual mine soil remediation, the area of ​​soil pollution is large, the remediation cost is high, and the soil pollution factors in mines are complex, including not only heavy metal pollution but also organic pollution, acid and alkali pollution, and even pollution containing some radioactive elements. Under the various complex pollution factors in mines, the ability of traditional biochar to remediate heavy metals in soil is very limited.

[0004] Therefore, exploring ways to modify biochar to improve its ability to stably adsorb, fixate, and degrade heavy metal pollutants in soil is of great practical significance for the remediation of soil pollution in mines. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a modified biochar material, its preparation method, and its application in soil pollution remediation. The biochar material of this invention exhibits excellent physical / chemical stability and can specifically adsorb heavy metals, including cadmium, lead, and arsenic, significantly improving the adsorption performance for heavy metal ions. The adsorption capacity and efficiency are enhanced, making it suitable for the remediation of heavy metal pollution in large-scale mine soils. The specific technical solution is as follows:

[0006] A method for preparing a modified biochar material includes the following steps:

[0007] S1. Preparation of biochar: After drying the melon vines or bean vines, crush them and sieve them, then carbonize them at high temperature, and take them out after naturally cooling to room temperature to obtain biochar for later use.

[0008] S2. Preparation of the first modified biochar: Take a certain amount of biochar, stir the biochar and concentrated nitric acid in an ice bath, and react at 0-3℃ for 3-6 hours to obtain the first reaction solution; heat the first reaction solution, add distilled water to keep warm and stir, and then add it to ammonium persulfate solution and keep warm and stir again to obtain the second reaction solution; filter the obtained second reaction solution, wash the filter residue with ethanol and water alternately, and dry it to obtain the first modified biochar;

[0009] S3. Preparation of the second modified biochar: Take a certain amount of biochar, add it to calcium solution or iron solution, adjust the pH to 11-13, mix and let stand, add sodium selenite solution, perform ultrasonic treatment, then heat and stir at 80-90℃, dry, and then wash with distilled water until pH=7 to obtain the second modified biochar.

[0010] S4. Preparation of modified biochar material: The first modified biochar and the second modified biochar are dispersed in distilled water and mixed evenly to obtain a dispersion. Sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose are added to the dispersion, stirred evenly, and dried to obtain the modified biochar material.

[0011] Preferably, in step S2, the reaction step of the second reaction solution specifically involves adding distilled water, maintaining the temperature at 50-60°C and stirring for 30 min-1 h, and then adding it to an ammonium persulfate solution, heating it to 70-80°C, and stirring for 3-6 h.

[0012] Preferably, in step S2, the concentration of concentrated nitric acid is 4-7 mol / L, and the mass ratio of concentrated nitric acid to biochar is 10-20:1; the concentration of ammonium persulfate solution is 10-30%, and the mass ratio of ammonium persulfate solution to biochar is 30-50:1.

[0013] Preferably, in step S3, the concentration of calcium ions or iron ions in the calcium solution or iron solution is 0.1-2 mol / L, and the concentration of biochar in the calcium solution or iron solution is 10-20 g / L.

[0014] Preferably, in step S4, the mass ratio of the first modified biochar, the second modified biochar, and distilled water is 1.5-2:1:10-15.

[0015] Preferably, in step S4, the stirring temperature is 40-60℃ and the stirring time is 1-3h.

[0016] Preferably, in step S4, the mass ratio of the dispersion to sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose is 15-20:1-3:0.5-1.

[0017] Preferably, in step S3, the mass ratio of the second modified biochar to sodium selenite is 2-3:0.5-1.

[0018] This invention provides a modified biochar material, characterized in that it is prepared by the above-described preparation method.

[0019] The present invention also provides an application of the modified biochar material as described above in the remediation of heavy metal contaminated soil in mines.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The modified biochar material prepared by the method of this invention has good physical / chemical stability. The dual modification treatment, involving functional oxidation and loading of calcium, iron, and selenium active components, introduces various oxygen-containing functional groups (carboxyl, carbonyl, and phenolic functional groups) onto the biochar surface, resulting in rich modification. The first modified biochar is obtained by oxidative functionalization of the biochar using concentrated nitric acid and ammonium persulfate, endowing it with abundant heavy metal anchoring active sites. It also exhibits stronger interactions with sodium tetrapoly(propylene benzenesulfonate) (ABS) and carboxymethyl cellulose, making its adsorption properties more stable. The second modified biochar provides numerous non-uniform and coarse-grained morphologies. The porous structure, formed by the adhesion of smaller, rougher particles, offers a larger specific surface area and a more prominent microporous structure. This allows the material to load iron and calcium ions within its micropores and to replace these ions with heavy metal ions, including cadmium (Cd), lead (Pb), and arsenic (As), thus reducing their concentration in the soil. This dual modification significantly enhances the material's adsorption performance for heavy metal ions, improving both adsorption capacity and efficiency. Furthermore, it maintains stable adsorption even under complex mine pollution conditions involving organic matter, acid / alkali, and radioactive elements, making it suitable for large-scale remediation of heavy metal pollution in mine soils.

[0022] 2. The applicant discovered that the introduction of sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose endows the material with good stability, making the biochar material unaffected by complex environments such as organic pollution, excessive acidity or alkalinity, enabling it to more effectively adsorb heavy metals in the soil, and giving the biochar material a stable binding and adsorption effect.

[0023] 3. During the harvest season, vines of melons and beans are often discarded or burned, resulting in resource waste and environmental pollution. Using them as raw materials for biochar has great potential. This invention utilizes these common biological wastes, such as vines of melons and beans, offering advantages of environmental friendliness and low cost. Furthermore, the reagents used are non-toxic and will not pollute the environment. Moreover, the biochar material can be directly added to soil contaminated with the heavy metals without requiring additional conditions, making it convenient and easy to operate. Detailed Implementation

[0024] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0025] Example 1

[0026] The method for preparing a modified biochar material according to this embodiment includes the following steps:

[0027] S1. Preparation of biochar: After drying the watermelon vines, crush them through a 100-mesh sieve, then carbonize them at a high temperature of 800℃, and take them out after naturally cooling to room temperature to obtain biochar for later use.

[0028] S2. Preparation of the first modified biochar: Biochar and 5 mol / L concentrated nitric acid (10 times the mass of biochar) were stirred in an ice bath and reacted at 0°C for 3 h to obtain the first reaction solution; the first reaction solution was heated, distilled water was added, and the mixture was kept at 50°C and stirred for 30 min, then ammonium persulfate solution (30 times the mass of biochar) was added, the temperature was raised to 80°C, and the mixture was kept at 80°C and stirred for 3 h to obtain the second reaction solution; the second reaction solution was filtered, and the filter residue was washed alternately with ethanol and water and dried to obtain the first modified biochar;

[0029] S3. Preparation of the second modified biochar: Biochar was added to a 0.5 mol / L ferric chloride solution, the concentration of biochar in the ferric chloride solution was 12 g / L, the pH was adjusted to 11 with ammonia water, the mixture was mixed and allowed to stand, sodium selenite solution was added, and the mixture was ultrasonically treated at 500 W for 1 h, then heated and stirred at 80 °C for 4 h, dried, and then washed with distilled water until pH = 7 to obtain the second modified biochar; the mass ratio of the second modified biochar to sodium selenite was 2:0.5.

[0030] S4. Preparation of modified biochar material: First modified biochar and second modified biochar are dispersed in distilled water at a mass ratio of 1.5:1:10. After mixing evenly, a dispersion is obtained. Sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose are added to the dispersion at a mass ratio of 15:1:0.5. The mixture is stirred at 50°C for 1 hour and then dried to obtain the modified biochar material.

[0031] Example 2

[0032] The method for preparing a modified biochar material according to this embodiment includes the following steps:

[0033] S1. Preparation of biochar: After drying the watermelon vines, crush them through a 100-mesh sieve, then carbonize them at a high temperature of 800℃, and take them out after naturally cooling to room temperature to obtain biochar for later use.

[0034] S2. Preparation of the first modified biochar: Biochar and 7 mol / L concentrated nitric acid (15 times the mass of biochar) were stirred in an ice bath and reacted at 0°C for 6 h to obtain the first reaction solution; the first reaction solution was heated, distilled water was added, and the mixture was kept at 60°C and stirred for 1 h, then ammonium persulfate solution (40 times the mass of biochar) was added, the temperature was raised to 80°C, and the mixture was kept at 80°C and stirred for 3 h to obtain the second reaction solution; the second reaction solution was filtered, and the filter residue was washed alternately with ethanol and water and dried to obtain the first modified biochar;

[0035] S3. Preparation of the second modified biochar: Biochar was added to a 2 mol / L calcium chloride solution, and the concentration of the second modified biochar in the calcium chloride solution was 20 g / L. The pH was adjusted to 12 using ammonia water. After mixing and standing, sodium selenite solution was added, and the mixture was ultrasonically treated at 500 W for 1 h. Then, it was heated and stirred at 90 °C for 4 h, dried, and then washed with distilled water until the pH was 7 to obtain the second modified biochar. The mass ratio of the second modified biochar to sodium selenite was 3:1.

[0036] S4. Preparation of modified biochar material: First modified biochar and second modified biochar are dispersed in distilled water at a mass ratio of 2:1:15. After mixing evenly, a dispersion is obtained. Sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose are added to the dispersion at a mass ratio of 20:3:1. The mixture is stirred at 60°C for 1 hour and then dried to obtain the modified biochar material.

[0037] Example 3

[0038] The method for preparing a modified biochar material according to this embodiment includes the following steps:

[0039] S1. Preparation of biochar: After drying the mung bean vines, they were crushed and passed through a 100-mesh sieve, then carbonized at a high temperature of 800℃. After naturally cooling to room temperature, the biochar was obtained and set aside for later use.

[0040] S2. Preparation of the first modified biochar: Biochar and 4 mol / L concentrated nitric acid (20 times the mass of biochar) were stirred in an ice bath and reacted at 0℃ for 3 h to obtain the first reaction solution; the first reaction solution was heated, distilled water was added, and the mixture was kept at 55℃ and stirred for 1.50 min, then ammonium persulfate solution (30 times the mass of biochar) was added, the temperature was raised to 80℃, and the mixture was kept at 80℃ and stirred for 3 h to obtain the second reaction solution; the second reaction solution was washed alternately with ethanol and water and dried to obtain the first modified biochar;

[0041] S3. Preparation of the second modified biochar: Biochar was added to a 0.5 mol / L ferric chloride solution, and the concentration of the second modified biochar in the ferric chloride solution was 12 g / L. The pH was adjusted to 11 using ammonia water. After mixing and standing, sodium selenite solution was added, and the mixture was subjected to ultrasonic treatment at 500 W. Then, it was heated and stirred at 80 °C for 4 h, dried, and then washed with distilled water until the pH was 7 to obtain the second modified biochar. The mass ratio of the second modified biochar to sodium selenite was 2:0.5.

[0042] S4. Preparation of modified biochar material: First modified biochar and second modified biochar are dispersed in distilled water at a mass ratio of 1.5:1:10. After mixing evenly, a dispersion is obtained. Sodium tetrapolybenzenesulfonate (ABS) and carboxymethyl cellulose are added to the dispersion at a mass ratio of 15:1:0.5. The mixture is stirred at 50°C for 1 hour and then dried to obtain the modified biochar material.

[0043] Comparative Example 1

[0044] This comparative example does not contain the first modified biochar, and the rest of the preparation methods are the same as in Example 1.

[0045] Comparative Example 2

[0046] This comparative example does not contain the second modified biochar, and the rest of the preparation methods are the same as in Example 1.

[0047] Comparative Example 3

[0048] The preparation method of the first modified biochar in this comparative example is as follows: biochar and 5 mol / L concentrated nitric acid (10 times the mass of biochar) are stirred at 50°C for 5 hours, then washed alternately with ethanol and water, and dried to obtain the first modified biochar. The remaining preparation methods are the same as in Example 1.

[0049] Comparative Example 4

[0050] The preparation method of the second modified biochar in this comparative example is as follows: biochar is added to a 0.5 mol / L ferric chloride solution, the concentration of the second modified biochar in the ferric chloride solution is 12 g / L, the pH is adjusted to 11 using ammonia water, then heated and stirred at 80℃ for 4 h, dried, and then washed with distilled water until pH=7 to obtain the second modified biochar.

[0051] Comparative Example 5

[0052] The preparation method of the biochar material in this comparative example is as follows: the first modified biochar and the second modified biochar are directly mixed evenly at a ratio of 1.5:1. The remaining preparation methods are the same as in Example 1.

[0053] The applicant conducted an experiment in a mining area in Nandan County, Hechi City, Guangxi Zhuang Autonomous Region. The soil pH value of the experimental area was 4-4.5, which is acidic soil. The main heavy metals detected were cadmium (Cd), lead (Pb) and arsenic (As). The cadmium content was 5.62 mg / kg, the lead content was 79.8 mg / kg, and the arsenic content was 36.9 mg / kg, all of which exceeded the standard.

[0054] The biochar materials prepared by the methods of Examples 1-2 and Comparative Examples 1-5 of this invention were tested. The experiment was divided into 7 groups, with each group having a test area of ​​50m². 2 Till the soil to a depth of 40cm, using a soil density of 0.5kg / m³. 2 The biochar material was mixed evenly with the tilled soil, and the removal rates of cadmium, lead and arsenic in the soil were tested after 90 days and 180 days, respectively. The test results are shown in Table 1 and Table 2 below.

[0055] Table 1. Removal rates of cadmium, lead, and arsenic in soil after 90 days.

[0056] Group Cadmium removal rate (%) Lead removal rate (%) Arsenic removal rate (%) Example 1 53.2 50.6 60.2 Example 2 54.9 51.5 61.9 Example 3 54.5 51.3 61.0 Comparative Example 1 39.2 35.7 50.8 Comparative Example 2 41.1 36.3 45.4 Comparative Example 3 44.5 40.6 41.0 Comparative Example 4 42.8 39.2 49.2 Comparative Example 5 47.1 44.3 53.9

[0057] Table 2. Removal rates of cadmium, lead, and arsenic in soil after 180 days.

[0058]

[0059]

[0060] The biochar materials prepared by the preparation methods of Example 1 and Comparative Example 5 were tested. 0.2g of biochar sample was taken from each sample and mixed with a solution containing 50mg / L cadmium and 20mg / L rhodamine B dye. The mixture was shaken intermittently at room temperature, with an interval of 6 hours between each shake and a shaking time of 1min. The removal effect after 96h is shown in Table 3 below.

[0061] Table 3

[0062] Group Cadmium removal rate (%) Rhodamine B removal rate (%) Example 1 45.9 61.2 Comparative Example 3 36.8 40.5 Comparative Example 5 30.8 29.3

[0063] As shown in the table above, the biochar material of Example 1 of the present invention can still achieve good adsorption effect under the interference of organic matter compared with that of Comparative Example 1, and also has a certain removal rate of organic matter.

[0064] In summary, the modified biochar material prepared by the method of this invention exhibits excellent physical / chemical stability. The dual modification treatment, involving functional oxidation and loading with calcium, iron, and selenium active components, introduces various oxygen-containing functional groups (carboxyl, carbonyl, and phenolic functional groups) onto the biochar surface, resulting in rich modification and the creation of numerous non-uniform pores with small, coarsely shaped aggregates. These unique adsorption pore structures facilitate the targeted adsorption of heavy metals, including cadmium (Cd), lead (Pb), and arsenic (As), significantly improving the material's adsorption performance for heavy metal ions. This enhances the adsorption capacity and efficiency, making it suitable for large-scale remediation of heavy metal pollution in mine soils. The introduction of sodium tetrapoly(propylene benzenesulfonate) (ABS) and carboxymethyl cellulose imparts excellent stability to the material, protecting it from complex environments such as organic pollution, excessive acidity, or excessive alkalinity. This allows for more effective adsorption of heavy metals in the soil, resulting in a stable binding and adsorption effect.

[0065] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a modified biochar material, characterized in that, Includes the following steps: S1. Preparation of biochar: After drying the melon vines or bean vines, crush and sieve them, and then carbonize them at high temperature to obtain biochar for later use. S2. Preparation of the first modified biochar: Take a certain amount of biochar, stir the biochar and concentrated nitric acid in an ice bath, and react at 0~3℃ for 3-6 h to obtain the first reaction solution; heat the first reaction solution, add distilled water, keep warm at 50-60℃ and stir for 30 min-1 h, then add it to ammonium persulfate solution, heat to 70-80℃ and keep warm and stir for 3-6 h to obtain the second reaction solution; filter the obtained second reaction solution, wash the filter residue alternately with ethanol and water, and dry to obtain the first modified biochar; S3. Preparation of the second modified biochar: Take a certain amount of biochar, add it to calcium solution or iron solution, adjust the pH to 11-13, mix and let stand, add sodium selenite solution, perform ultrasonic treatment, then heat and stir at 80-90℃, dry, and then wash with distilled water until pH=7 to obtain the second modified biochar. S4. Preparation of modified biochar material: The first and second modified biochars are dispersed in distilled water and mixed evenly to obtain a dispersion. Sodium tetrapolybenzenesulfonate and carboxymethyl cellulose are added to the dispersion. The mass ratio of the dispersion to sodium tetrapolybenzenesulfonate and carboxymethyl cellulose is 15-20:1-3:0.5-1. The mixture is stirred evenly and dried to obtain the modified biochar material.

2. The method for preparing a modified biochar material according to claim 1, characterized in that, In step S2, the concentration of concentrated nitric acid is 4-7 mol / L, and the mass ratio of concentrated nitric acid solution to biochar is 10-20:1; the concentration of ammonium persulfate solution is 10-30%, and the mass ratio of ammonium persulfate solution to biochar is 30-50:

1.

3. The method for preparing modified biochar according to claim 1, characterized in that, In step S3, the concentration of calcium ions or iron ions in the calcium solution or iron solution is 0.1-2 mol / L, and the concentration of biochar in the calcium solution or iron solution is 10-20 g / L.

4. The method for preparing modified biochar according to claim 1, characterized in that, In step S4, the mass ratio of the first modified biochar, the second modified biochar, and distilled water is 1.5-2:1:10-15.

5. The method for preparing modified biochar according to claim 1, characterized in that, In step S4, the stirring temperature is 40-60℃ and the stirring time is 1-3h.

6. The method for preparing modified biochar according to claim 1, characterized in that, In step S3, the mass ratio of the second modified biochar to sodium selenite is 2-3:0.5-1.

7. A modified biochar material, characterized in that, It is prepared by the preparation method of any one of claims 1-6.

8. The application of the modified biochar material as described in claim 7 in the remediation of heavy metal contaminated soil in mines.

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