Preparation method of selenium-rich biochar capable of reducing cadmium bioavailability in soil and application thereof

Abstract

The application belongs to the field of soil remediation, and discloses a preparation method of selenium-rich biochar capable of reducing soil cadmium bioavailability and application of the selenium-rich biochar, the preparation method of the selenium-rich biochar comprising the following steps: taking biomass grown in a selenium-rich area, air-drying and grinding, and then calcining at 400-800 DEG C for 1-3 hours to obtain the selenium-rich biochar; and application of the selenium-rich biochar in soil cadmium pollution treatment is disclosed.The preparation method of the selenium-rich biochar is simple, the reaction is mild, the safety is high, the environmental pollution is small, and the selenium-rich biochar contains a certain amount of selenium and can reduce soil cadmium bioavailability to a certain extent.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, and in particular relates to a method for preparing selenium-enriched biochar that can reduce the bioavailability of cadmium in soil and its application. Background Technology

[0002] Cadmium pollution is a type of heavy metal pollution, characterized by its bioaccumulation and difficulty in natural degradation, making it highly harmful to organisms. Because of its difficulty in degradation, it easily accumulates in plants and can enter the human body through the food chain, seriously impacting human health. Unlike organic soil pollution, heavy metal pollution cannot degrade naturally. If it enters the human body through the food chain, it can affect the kidneys, liver, nervous system, and brain, and may even pose risks of birth defects, cancer, and mutations.

[0003] Currently, phytoremediation is a type of soil heavy metal remediation technology. It utilizes plants with high accumulation rates, such as wheat and corn, planted in heavy metal-contaminated soil, and harvested when mature to facilitate the migration of heavy metals from the contaminated site. Due to its ease of operation, it is widely used in soil pollution remediation. However, this also raises some issues: while it accumulates large amounts of heavy metals in the plants, it increases the risk of these heavy metals entering the food chain. Furthermore, it generates large amounts of contaminated biomass that cannot be degraded, thus potentially causing secondary pollution to soil and groundwater.

[0004] Studies have shown that selenium can form selenium-cadmium complexes with cadmium. As an antagonist, selenium can bind to cadmium ions in the soil, reducing the impact of cadmium on in vivo mechanisms. Simultaneously, the formation of selenium-cadmium complexes can inhibit the transformation, absorption, and distribution of cadmium ions in the soil, thereby reducing cadmium toxicity. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and further study the preparation of biochar materials that reduce the environmental risk of heavy metals. This invention provides a method for preparing selenium-enriched biochar that can reduce the bioavailability of cadmium in soil, and its application. This selenium-enriched biochar is prepared by selecting biomass from selenium-rich areas and calcining it at a specific temperature. Based on biochar characterization results and soil testing results, it is concluded that selenium-enriched biochar has a better effect on reducing the bioavailability of cadmium in soil than ordinary biochar. The preparation method of the selenium-enriched biochar of this invention is simple, the reaction is mild, it is highly safe, and it causes minimal environmental pollution. Furthermore, it contains a certain amount of selenium, which can reduce the bioavailability of cadmium in soil to a certain extent.

[0006] The technical solution of the present invention is as follows: A method for preparing selenium-enriched biochar that can reduce the bioavailability of cadmium in soil includes the following steps: taking biomass grown in selenium-rich areas, air-drying and grinding it, and then calcining it at 400~800℃ for 1~3 hours to obtain the product.

[0007] Preferably, the biomass is derived from agricultural and forestry waste, such as straw, rice husks, bamboo, leaves, bark, peanut shells, pineapple peels, walnut shells, etc. More preferably, the agricultural and forestry waste is wheat straw.

[0008] The specific air-drying time can be determined according to the degree of dryness of the biomass material, with complete drying as the primary goal. Preferably, the air-drying time is 7 to 10 days.

[0009] Preferably, the grinding time is 4 to 10 minutes. More preferably, the grinding time is 5 to 10 minutes.

[0010] Preferably, the material is passed through a 20-100 mesh sieve after grinding. More preferably, it is passed through a 40-100 mesh sieve after grinding.

[0011] Preferably, calcination is carried out in an oxygen-isolated environment. More preferably, calcination is carried out in a nitrogen atmosphere.

[0012] Preferably, the calcination heating rate is 3~8℃ / min, and the calcination temperature is 500~700℃. More preferably, the calcination heating rate is 5~8℃ / min, and the calcination temperature is 700℃.

[0013] The present invention also provides an application of the selenium-enriched biochar prepared by the above method in the remediation of cadmium pollution in soil.

[0014] Preferably, the application includes reducing the bioavailability of cadmium in soil.

[0015] Preferably, the available cadmium content in the soil is 0.3~0.5 mg / kg.

[0016] Preferably, the amount of selenium-enriched biochar added to the soil is 0.5-2.0% by mass, and the soil treatment time is 5-10 days.

[0017] More preferably, the amount of selenium-enriched biochar prepared at a calcination temperature of 700℃ added to the soil is 1.0% by mass, and the soil remediation time is 5 days. Alternatively, the amount of selenium-enriched biochar prepared by calcination at 700℃ added to the soil is 2.0% by mass, and the soil treatment time is 10 days.

[0018] Technical effects of the present invention: 1. This invention selects biomass from selenium-rich areas and prepares selenium-rich biochar at a certain calcination temperature. Then, it is used to treat cadmium-contaminated soil at a certain addition ratio. According to the biochar characterization results and soil test results, it is found that the selenium-rich biochar has a better effect on reducing the bioavailability of cadmium in the soil than ordinary biochar. It can effectively reduce the bioavailability of cadmium in the soil and is relatively stable.

[0019] 2. The preparation method of the present invention has simple operation steps, mild reaction, high safety and low environmental pollution. Attached Figure Description

[0020] Figure 1 SEM images at 300x magnification of selenium-enriched biochar (Se-BC) and ordinary biochar (BC) (a, b, c, d, e, and f are the selenium-enriched biochar obtained in Examples 1-3 and the ordinary biochar obtained in Comparative Examples 1-3, respectively). Figure 2 XRD patterns of selenium-enriched biochar (Se-BC) and ordinary biochar (BC) are shown (a is the selenium-enriched biochar obtained in Example 1 and the ordinary biochar obtained in Comparative Example 1; b is the selenium-enriched biochar obtained in Example 2 and the ordinary biochar obtained in Comparative Example 2; c is the selenium-enriched biochar obtained in Example 3 and the ordinary biochar obtained in Comparative Example 3). Figure 3 The effects of ordinary biochar (BC) and selenium-enriched biochar (Se-BC) on the available cadmium content in soil under different soil remediation times (soil remediation time for a is 5 days, and soil remediation time for b is 10 days). Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified in the following examples, the implementation conditions are generally those of routine experiments, and the raw materials are all commercially available or prepared by conventional methods in the art.

[0023] Example 1: Preparation of selenium-enriched biochar (Se-BC-500℃) This embodiment provides a method for preparing selenium-enriched biochar that can reduce the bioavailability of cadmium in soil, including the following steps: (1) Preparation of biochar raw materials: Selenium-rich wheat straw grown in farmland in selenium-rich areas is taken and placed in a cool and ventilated place for air drying. The air drying time is 7 days. The specific time should be determined according to the degree of dryness of the sample. The selenium-rich wheat straw used in this example has been completely dried after 7 days of air drying. The dried straw is crushed and ground for 5 minutes and passed through a 40-mesh sieve to obtain biochar raw materials.

[0024] (2) Preparation of selenium-enriched biochar: Place the biochar raw material obtained in step (1) into a clean ceramic boat. To ensure the cleanliness of the ceramic boat, it can be placed in a non-ventilated tubular furnace in advance and heated to 900℃ for 2 hours. Then, spread the biochar raw material in the ceramic boat and place it into the tubular furnace. Seal the tubular furnace and introduce nitrogen. After confirming that it is sealed, set the heating program and heat at a heating rate of 5℃ / min. Set the temperature to 500℃ and hold for 2 hours. After the tubular furnace cools down to 50℃, take it out to obtain selenium-enriched biochar.

[0025] Example 2: Preparation of selenium-enriched biochar (Se-BC-600℃) The difference between this embodiment and Embodiment 1 is that the calcination temperature is 600℃.

[0026] Example 3: Preparation of selenium-enriched biochar (Se-BC-700℃) The difference between this embodiment and Embodiment 1 is that the calcination temperature is 700℃.

[0027] Comparative Example 1: Preparation of ordinary biochar (Se-BC-500℃) The difference between this comparative example and Example 1 is that ordinary biochar was prepared from wheat straw grown in ordinary farmland.

[0028] Comparative Example 2: Preparation of ordinary biochar (Se-BC-600℃) The difference between this comparative example and Example 2 is that ordinary biochar was prepared from wheat straw grown in ordinary farmland.

[0029] Comparative Example 3: Preparation of ordinary biochar (Se-BC-700℃) The difference between this comparative example and Example 3 is that ordinary biochar was prepared from wheat straw grown in ordinary farmland.

[0030] I. Structural Characterization of Different Biochars 1. Scanning Electron Microscopy (SEM) Experiment SEM analysis was performed on the selenium-enriched biochar (Se-BC) obtained in Examples 1-3 and the ordinary biochar (BC) obtained in Comparative Examples 1-3, respectively, and the results were as follows: Figure 1 The SEM image shown.

[0031] Comparing Se-BC-500℃ in Example 1 and BC-500℃ in Comparative Example 1, it can be seen that the structure of ordinary biochar is mainly in the form of small segments and sheets, while selenium-enriched biochar has more pores and a rougher surface than ordinary biochar.

[0032] The Se-BC-600℃ obtained in Example 2 has smaller particles and a distinctly strip-like shape compared to the Se-BC-500℃ obtained in Example 1. The BC-600℃ obtained in Comparative Example 2 also has significantly smaller particles compared to the BC-500℃ obtained in Comparative Example 1.

[0033] The Se-BC-700℃ obtained in Example 3 has denser particles compared to Se-BC-500℃ and Se-BC-600℃. The BC-700℃ obtained in Comparative Example 3 has a more regular shape, resembling strips, compared to BC-500℃ and BC-600℃.

[0034] 2. X-ray diffraction (XRD) test X-ray diffraction experiments were performed on the selenium-enriched biochar (Se-BC) obtained in Examples 1-3 and the ordinary biochar (BC) obtained in Comparative Examples 1-3, respectively, and the results were as follows: Figure 2 The X-ray diffraction pattern shown.

[0035] By comparing the XRD patterns and observing the small peaks, it can be seen that the selenium content of selenium-enriched biochar is higher than that of ordinary biochar.

[0036] II. Cadmium-contaminated soil remediation experiment 1. Test Methods 20g of cadmium-contaminated soil was weighed and placed in centrifuge tubes. Selenium-enriched biochar (Se-BC) obtained in Examples 1-3 and ordinary biochar (BC) obtained in Comparative Examples 1-3 were added to the centrifuge tubes containing cadmium-contaminated soil at different mass addition ratios (0.5%, 1.0%, and 2.0%), i.e., 0.1g, 0.2g, and 0.4g of different biochars were added respectively. Cadmium-contaminated soil without any added substances (blank contaminated soil) was used as the control group (CK). The samples were mixed using a vortex mixer to ensure that the cadmium-contaminated soil and biochar were fully mixed. The samples were then placed in a constant temperature incubator for incubation. The soil was kept moist during the incubation process. Soil samples were taken on the 5th and 10th days of incubation. The soil samples were extracted for available cadmium using the DTPA extraction method. The available cadmium content was measured using ICP-MS. The reduction effect of biochar on available cadmium was calculated based on the change in available cadmium concentration before and after the addition of biochar.

[0037] 2. Test Results The results of available cadmium content in soil on the 5th and 10th days of cultivation for the selenium-enriched biochar obtained in Examples 1-3 and the ordinary biochar obtained in Comparative Examples 1-3 are shown in the figure. Figure 3 As can be seen, compared with the blank contaminated soil, the content of available cadmium decreased after adding different types of biochar, and the reduction effect changed with the amount added. Compared with ordinary biochar, it can be found that under the same experimental conditions, selenium-enriched biochar has a better effect on reducing available cadmium in soil.

[0038] On day 5 of cultivation, the selenium-enriched biochar Se-BC-500℃ prepared in Example 1, with different addition ratios (0.5%, 1.0%, and 2.0%), reduced the available cadmium by 28.01%, 44.27%, and 38.20%, respectively, while the ordinary biochar BC-500℃ prepared in Comparative Example 1 reduced it by 31.46%, 29.10%, and 29.49%, respectively. Figure 3 (a) In the culture, on day 10, different addition ratios of Se-BC-500℃ (0.5%, 1.0%, and 2.0%) reduced the available cadmium by 25.09%, 36.83%, and 45.06%, respectively, while BC-500℃ reduced it by 36.58%, 33.56%, and 30.23%, respectively. Figure 3 (b) in the middle.

[0039] On day 5 of cultivation, the selenium-enriched biochar Se-BC-600℃ prepared in Example 2, with different addition ratios (0.5%, 1.0%, and 2.0%), reduced the available cadmium by 31.02%, 27.37%, and 31.17%, respectively, while the ordinary biochar BC-600℃ prepared in Comparative Example 1 reduced it by 27.72%, 27.05%, and 28.66%, respectively. Figure 3 (a) In the culture, on day 10, different addition ratios of Se-BC-600℃ (0.5%, 1.0%, and 2.0%) reduced the available cadmium by 39.68%, 36.66%, and 28.10%, respectively, while BC-600℃ reduced it by 22.25%, 27.31%, and 27.73%, respectively. Figure 3 (b) in the middle.

[0040] On day 5 of cultivation, the selenium-enriched biochar Se-BC-700℃ prepared in Example 3, with different addition ratios (0.5%, 1.0%, and 2.0%), reduced the available cadmium by 40.65%, 58.40%, and 36.17%, respectively, while the ordinary biochar BC-700℃ prepared in Comparative Example 1 reduced it by 27.42%, 39.08%, and 28.68%, respectively. Figure 3 (a) In the culture, on day 10, different addition ratios of Se-BC-700℃ (0.5%, 1.0%, and 2.0%) reduced the available cadmium by 54.42%, 51.99%, and 62.37%, respectively, while BC-700℃ reduced it by 39.09%, 30.58%, and 45.49%, respectively. Figure 3 (b) in the middle.

[0041] Comparing Examples 1 to 3, it can be seen that the selenium-enriched biochar of the present invention has a better effect on reducing the bioavailability of cadmium in soil than ordinary biochar. Among them, the treatment effect of selenium-enriched biochar with a calcination temperature of 700°C and an addition amount of 1.0% is better on the 5th day of cultivation; and the treatment effect of selenium-enriched biochar with a calcination temperature of 700°C and an addition amount of 2.0% is better on the 10th day of cultivation.

[0042] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of selenium-enriched biochar in the remediation of cadmium pollution in soil, characterized in that: The preparation method of the selenium-enriched biochar includes the following steps: taking biomass grown in selenium-rich areas, air-drying and grinding it, and then calcining it at 400~800℃ for 1~3 hours to obtain the product.

2. The application according to claim 1, characterized in that: The applications include reducing the bioavailability of cadmium in soil.

3. The application according to claim 1, characterized in that: The amount of selenium-enriched biochar added to the soil is 0.5-2.0% by mass, and the soil treatment time is 5-10 days.

4. The application according to claim 1, characterized in that: The biomass is derived from agricultural and forestry waste.

5. The application according to claim 1, characterized in that: The air-drying time is 7 to 10 days, and the grinding time is 4 to 10 minutes.

6. The application according to claim 1, characterized in that: After grinding, pass through a 20-100 mesh sieve.

7. The application according to claim 1, characterized in that: Calcination is carried out in an oxygen-isolated environment, with a heating rate of 3~8℃ / min and a calcination temperature of 500~700℃.

8. The application according to claim 2, characterized in that: The available cadmium content in the soil is 0.3~0.5 mg / kg.

9. The application according to claim 3, characterized in that: The amount of selenium-enriched biochar prepared by calcination at 700℃ added to the soil was 1.0% by mass, and the soil treatment time was 5 days. Alternatively, the amount of selenium-enriched biochar prepared by calcination at 700℃ added to the soil is 2.0% by mass, and the soil treatment time is 10 days.

10. The application according to claim 4, characterized in that: The agricultural and forestry waste mentioned is wheat straw.

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