Preparation method and application of iron-modified malus micromalus crispus charcoal based on malus micromalus crispus waste

Abstract

The application discloses a preparation method of iron modified malus micromalus crabapple biochar based on malus micromalus crabapple waste and application thereof. The preparation method of the malus micromalus crabapple iron modified biochar comprises two steps of carbonization and modification. The malus micromalus crabapple litter waste is subjected to oxygen-limited heating carbonization to prepare carbonized materials, and then is subjected to acid pickling and iron modification to prepare the iron modified malus micromalus crabapple biochar. The prepared biochar has high adsorption capacity for selenium in water, has the function of holding selenium in selenium-rich soil, can simultaneously passivate harmful heavy metals in soil, and has the functions of controlling the release of selenium in water and improving soil quality. The application not only provides a new way for resource utilization of the malus micromalus crabapple litter, but also provides an efficient technology for water selenium pollution treatment, soil selenium holding and heavy metal soil fixation, and achieves the effect of turning waste into treasure.

Description

A method for preparing iron-modified prickly pear biochar based on prickly pear waste and its application Technical Field

[0001] This invention relates to the field of waste resource utilization and metal pollution control in the production process of economic crops, specifically to a method for preparing iron-modified prickly pear biochar based on prickly pear waste and its application in removing selenium from water, retaining selenium in soil and passivating heavy metals in soil. Background Technology

[0002] Selenium (Se) is an essential nutrient element that plays a vital role in human health and the growth and development of plants and animals. However, a daily selenium intake exceeding 400 μg can cause acute or chronic poisoning. The World Health Organization has set the reference level for Se in drinking water at 40 μg / L. -1 The most common form of selenium in environmental water is selenite (SeO3). 2- ) and selenate (SeO4) 2- Of these, Se(IV) has high bioavailability, but its toxicity is 10 times that of Se(VI). Due to human activities such as mining, metal smelting, and agricultural irrigation, large amounts of selenate and selenite are released into the environment. High concentrations of selenite (SeO3) are easily detected in water bodies near the plant area. 2- ) and selenate (SeO4) 2- Traditional technologies for removing selenium from water include ion exchange, biological methods, membrane separation, and adsorption. Ion exchange and membrane separation are highly efficient, but their high cost has limited their widespread adoption. Biological methods are low-cost but have a long cycle time. Adsorption has many advantages, such as low cost, repeatability, and ease of operation, and has become one of the most commonly used methods for removing selenium from water.

[0003] Biochar is a material produced by the pyrolysis of carbonaceous biomass under relatively low temperature and limited or anaerobic conditions. It possesses characteristics such as a large specific surface area, abundant oxygen-containing functional groups, well-developed pore structure, and good electrical conductivity. As a soil conditioner, biochar can improve soil properties, influence the abundance and activity of soil microorganisms, and reduce the bioavailability of various pollutants, including heavy metals. In recent years, it has been frequently used to remediate organic and inorganic pollutants in soil. However, with further research, some drawbacks of biochar have gradually become apparent. It does not meet expectations in binding and adsorbing various metal ions.

[0004] Rosa roxburghii Tratt, a perennial shrub of the Rosa genus, is rich in various nutrients beneficial to human health and is an important economic crop in Guizhou, China. In 2022, the planting area of ​​Rosa roxburghii in Guizhou reached 2.1 million mu (approximately 140,000 hectares), with a comprehensive output value exceeding 15 billion yuan, demonstrating significant economic benefits. However, the Rosa roxburghii industry in Guizhou still faces certain challenges. The main Rosa roxburghii planting areas in Guizhou primarily cultivate 5- to 7-year-old trees, but some trees are over 9 years old. The pruning of Rosa roxburghii orchards and the resulting fallen branches and leaves generate a huge amount of waste, causing significant resource waste.

[0005] Currently, research on the resource utilization of prickly pear planting waste is still limited, and no studies have focused on the high-value utilization of prickly pear branches and fallen leaves. Patent CN116235768A discloses a method for preparing a soil remediation matrix for rocky desertification areas using prickly pear waste and other agricultural waste as raw materials, and its application, but it does not involve the preparation of prickly pear biochar or the treatment of soil selenium and heavy metals. Patent CN115736090A discloses a method for preparing fermented prickly pear residue roughage and its application in TMR feed for beef buffalo, but it does not involve the preparation of prickly pear biochar or soil improvement and remediation. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned defects and deficiencies in the prior art and to provide a method for preparing iron-modified prickly pear biochar based on prickly pear waste.

[0007] Another object of the present invention is to provide iron-modified prickly pear biochar prepared by the above preparation method.

[0008] Another object of the present invention is to provide the application of the iron-modified prickly pear biochar in the removal of selenium from water, the retention of selenium in soil, and the passivation of heavy metals in soil.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] A method for preparing iron-modified prickly pear biochar based on prickly pear waste includes the following steps:

[0011] S1. Collect fallen branches and leaves of the prickly pear tree, separate and remove impurities, dry, crush and sieve;

[0012] S2. The raw material pretreated in step S1 is subjected to pyrolysis under anaerobic conditions to obtain carbonized material, which is then naturally cooled, pulverized again, and sieved; the pyrolysis temperature is 480-510℃ and the pyrolysis time is 1.8-2.2h.

[0013] S3. The carbonized material obtained in step S2 is acid-impregnated, and after the impurities are removed by filtration, drying and grinding.

[0014] S4. Place the carbonized material powder after acid washing in step S3 into Fe 3+ After adjusting the pH of the system to 7.5–8.5 in the solution, the system was aged, then filtered, dried, and ground to prepare iron-modified prickly pear biochar.

[0015] This invention takes into account the large amount of agricultural waste generated during the cultivation of prickly pear. The main components of the dead branches and fallen leaves produced during prickly pear pruning are cellulose and hemicellulose. After high-temperature, oxygen-limited pyrolysis, these substances produce various functional groups on their surface, which helps to enhance the adsorption and binding capacity of biochar. Therefore, carbonized materials are first prepared from prickly pear waste using an oxygen-limited heating method. Then, iron modification technology is used to improve the biochar's ability to retain selenium and passivate heavy metals in the soil. The resulting iron-modified prickly pear biochar can be used for selenium fixation and soil heavy metal passivation, providing a new approach for the resource utilization of agricultural waste from prickly pear plantations.

[0016] Furthermore, the acid immersion in step S3 is to soak in HCl solution for 0.8 to 1.2 hours.

[0017] Furthermore, the concentration of the HCl solution is 0.8–1.2 mol·L⁻¹. -1 The amount of carbonized material powder added is 100-135 g / L.

[0018] Further, the Fe described in step S4 3+ Fe in solution 3+ Concentration of 0.8–1.2 mol·L -1 The amount of material added after S3 treatment is 87-112 g / L.

[0019] Furthermore, in steps S2, S3, and S4, the pyrolysis temperature is 480–490℃, the pyrolysis time is 1.8–1.9 h, the hydrochloric acid soaking time is 0.8–0.9 h, the amount of carbonized material powder added is 100–112 g / L, and the amount of material added after treatment in S3 is 87–94 g / L. The prepared material is FeBBCI, which has a better and more efficient ability to adsorb Se(IV) from water.

[0020] Preferably, in steps S2, S3, and S4, the pyrolysis temperature is 485℃, the pyrolysis time is 1.85h, the hydrochloric acid soaking time is 0.85h, the amount of carbonized material powder added is 106g / L, and the amount of material added after treatment in S3 is 92g / L.

[0021] Furthermore, in steps S2, S3, and S4, the pyrolysis temperature is 490–500℃, the pyrolysis time is 1.9–2.0 h, the hydrochloric acid soaking time is 0.9–1.1 h, the amount of carbonized material powder added is 114–121 g / L, and the amount of material added after treatment in S3 is 95–103 g / L. The prepared material is FeBBCⅡ, which has a better ability to retain Se in the soil.

[0022] Preferably, in steps S2, S3, and S4, the pyrolysis temperature is 505℃, the pyrolysis time is 1.95h, the hydrochloric acid soaking time is 0.95h, the amount of carbonized material powder added is 118g / L, and the amount of material added after treatment in S3 is 98g / L.

[0023] Furthermore, in steps S2, S3, and S4, the pyrolysis temperature is 500–510℃, the pyrolysis time is 2.0–2.1 h, the hydrochloric acid soaking time is 1.1–1.2 h, the amount of carbonized material powder added is 121–135 g / L, and the amount of material added after treatment in S3 is 103–112 g / L. The prepared material is FeBBCⅢ, which has a better ability to passivate heavy metals in soil.

[0024] Preferably, in steps S2, S3, and S4, the pyrolysis temperature is 505℃, the pyrolysis time is 2.05h, the hydrochloric acid soaking time is 1.15h, the amount of carbonized material powder added is 127g / L, and the amount of material added after treatment in S3 is 108g / L.

[0025] The present invention also provides iron-modified prickly pear biochar prepared by any of the above-described preparation methods.

[0026] The iron-modified prickly pear biochar provided by this invention exhibits highly efficient adsorption and removal capacity for Se(IV) in water, can immobilize selenium in soil, and simultaneously has a passivation effect on various heavy metals in soil, effectively improving the quality of soils contaminated with multiple heavy metals. Therefore, this invention also provides the application of the iron-modified prickly pear biochar in remediating selenium pollution in environmental media, immobilizing selenium in soil, and / or passivating heavy metals in the soil environment.

[0027] Specifically, the selenium pollution in the remediation environmental medium is Se(IV) adsorbed in the water, and the heavy metals in the passivated soil environment are Mn, Zn, Fe and / or Cu.

[0028] The present invention also provides a method for remediating selenium-polluted water bodies, which involves adding the above-mentioned iron-modified prickly pear biochar to the selenium-polluted water bodies for treatment; the amount of biochar used is 3.8-4.2 g / L; the adsorption equilibrium time is 30 min-24 h; the initial concentration of Se(IV) in the polluted water body is 1-100 mg / L; and the selenium-polluted water bodies are all Se(IV) polluted water bodies.

[0029] Preferably, the prickly pear biochar is the above-mentioned FeBBCⅠ.

[0030] Preferably, the pH of the Se(IV) polluted water is 3-10 and the water temperature is 25.0±2℃.

[0031] This invention also provides a method for retaining selenium in soil, which involves treating the target soil with the aforementioned iron-modified prickly pear biochar; the amount of the iron-modified prickly pear biochar is 1.8% to 2.0%. This method can fix selenium in the soil and reduce the loss of selenium from the soil due to water leaching.

[0032] Preferably, the prickly pear biochar is the FeBBC II described above.

[0033] This invention also provides a method for passivating heavy metals in soil with complex contamination, which involves adding the aforementioned iron-modified prickly pear biochar to the target soil for treatment; the amount of iron-modified prickly pear biochar used is 2.0% to 2.2%. This method can passivate heavy metals Mn, Zn, Fe, and Cu in the soil.

[0034] Preferably, the iron-modified prickly pear biochar is the aforementioned FeBBC III.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention provides an iron-modified prickly pear biochar based on prickly pear waste. The process involves first carbonizing prickly pear litter with limited oxygen and elevated temperature to prepare carbonized material, followed by acid washing and iron modification to obtain the iron-modified prickly pear biochar. The prepared biochar exhibits high adsorption capacity for selenium in water and simultaneously retains selenium in selenium-rich soil. It can also passivate harmful heavy metals in the soil, thus controlling selenium release from water and improving soil quality. This invention not only provides a new approach for the resource utilization of prickly pear litter but also offers an efficient technology for water selenium pollution control, soil selenium retention, and heavy metal fixation in soil, achieving the effect of turning waste into treasure. Attached Figure Description

[0037] Figure 1 shows the Langmuir adsorption isotherm and the Freundlich adsorption isotherm of Se(IV) adsorbed by iron-modified prickly pear charcoal.

[0038] Figure 2 shows the adsorption kinetics curves of Fe-BBCⅠ and prickly pear biochar (BBC).

[0039] Figure 3 shows the SEM images (2 μm) of prickly pear biochar and iron-modified prickly pear biochar.

[0040] Figure 4 shows the X-ray diffraction patterns of prickly pear biochar (BBC) and iron-modified prickly pear biochar (FeBBC) before and after Se(IV) adsorption.

[0041] Figure 5 shows the FT-IR spectra of prickly pear biochar and iron-modified prickly pear biochar before and after Se(IV) adsorption.

[0042] Figure 6 shows the effect of Fe-BBC II on Se leaching in soil.

[0043] Figure 7 shows the difference in Se(Ⅳ) concentration in different soil layers after leaching under Fe-BBC II treatment.

[0044] Figure 8 shows the effect of Fe-BBC III on Mn leaching in soil.

[0045] Figure 9 shows the effect of Fe-BBC III on Zn leaching in soil.

[0046] Figure 10 shows the effect of Fe-BBC III on Cu leaching in soil.

[0047] Figure 11 shows the effect of Fe-BBC III on Fe leaching in soil. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0049] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0050] Example 1: Preparation of modified prickly pear biochar Fe-BBCⅠ, its removal effect on different concentrations of Se(IV) in water, and its adsorption kinetics of Se(IV) removal from water.

[0051] 1. Method

[0052] This embodiment investigates the removal effect of iron-modified prickly pear biochar on different concentrations of Se(IV) in water, specifically including:

[0053] (1) The raw material for prickly pear biochar (BBC) is prickly pear dead branches and leaves. The dead branches and leaves are washed with distilled water, dried and crushed, and then dried and stored through a 20-mesh sieve.

[0054] (2) The powder was loaded into the reactor and placed in the muffle furnace for oxygen-free high-temperature pyrolysis at 485°C for 1.85 hours. After the temperature of the muffle furnace dropped to room temperature, it was taken out and stored in an indoor desiccator for later use.

[0055] (3) Modified prickly pear (Fe-BBC) biochar was prepared by acid-base impregnation modification. A certain mass of prickly pear biochar was placed in a beaker, and 1.0 mol·L⁻¹ was added. -1After stirring with HCl, soak thoroughly for 1.85 hours. The amount of charcoal added to prickly pear biochar is 106 g / L. After soaking, filter, rinse and dry.

[0056] (4) Weigh the acid-washed prickly pear biochar obtained in the previous step and put it into a 1.0 mol·L⁻¹ solution. -1 In FeCl3·6H2O solution, the amount of acid-washed prickly pear biochar treated with hydrochloric acid was 92 g / L. The pH was adjusted to 8.0, and the mixture was shaken in a shaker at 25.0±2℃ for 1 h. After filtration, the mixture was rinsed with deionized water, dried, and Fe-BBCⅠ was obtained. The mixture was then ground through a 100-mesh sieve and stored in an indoor desiccator for later use.

[0057] (5) Add 0.1 g of BBC and Fe-BBCⅠ to 25 mL of Se(IV) solution, and set the concentrations to 1 mg·L⁻¹ respectively. -1 2.5 mg·L -1 5 mg·L -1 10 mg·L -1 20 mg·L -1 30 mg·L -1 50 mg·L -1 70 mg·L -1 100 mg·L -1 The temperature was set to 25±2℃, and the machine was placed on a shaker at a speed of approximately 180 rpm. -1 Under the condition of adsorption for 24 h, the isothermal adsorption data of the two biochars were fitted using the Langmuir (Equation 1) and Freundlich (Equation 2) models to explore the adsorption characteristics of prickly pear biochar for Se(IV).

[0058] Linear relationship of Langmuir isothermal adsorption model (1):

[0059]

[0060] Linear relationship of Freundlich isothermal adsorption model (2):

[0061]

[0062] Q e —The amount of Se(IV) adsorbed per unit mass of biochar in the adsorption solution (mg·g) -1 );

[0063] C e —Concentration at adsorption equilibrium (mg·L) -1 );

[0064] Q max—Maximum adsorption capacity of Langmuir monolayer (mg·g) -1 );

[0065] K L —Adsorption constant of Langmuir isotherm (L·mg) -1 );

[0066] K F The adsorption constant of n-Freundlich isothermal adsorption

[0067] (6) Add BBC and Fe-BBCⅠ to 2.5 mg·L -1 Se(IV) solution (0.1g·25ml) -1 ), 180 r·min -1 Sampling was performed after the shaking reaction. Fe-BBCⅠ treated solution was sampled at 1, 2, 3, 5, 10, 20, 30, 60, 90, 120, 180, 240, and 360 min; BBC treated solution was sampled at 5, 10, 20, 90, 120, 180, 360, 720, 1200, and 1440 min. The Se(IV) concentration in the equilibrium solution was determined by ICP-MS, and the adsorption capacity was calculated. The data were fitted using pseudo-first-order kinetic equations (Equation 3) and pseudo-second-order kinetic equations (Equation 4).

[0068] The pseudo-first-order dynamic equation:

[0069] ln(Q e -Q t )=lnQ e -k1t (3)

[0070] Pseudo-second-order dynamic equations:

[0071]

[0072] Q e —The amount of Se(IV) adsorbed per unit mass of biochar in the adsorption solution (mg·g) -1 );

[0073] Q t — represents the amount of Se(IV) adsorbed per unit mass of biochar in the adsorption solution at time t (mg·g). -1 );

[0074] t — adsorption time (min);

[0075] k1 — Pseudo-first-order adsorption rate constant (min) -1 );

[0076] k2 — pseudo-second-order adsorption rate constant (g·min·mg) -1)

[0077] (7) Characterization and determination of selenium adsorption before and after Fe-BBCⅠ:

[0078] Add BBC and Fe-BBCⅠ to 2.5 mg·L -1 Se(IV) solution (0.1g·25ml) -1 ), 180 r·min -1 Samples were collected after oscillation reactions for 360 min and 1440 min, respectively. The functional group structure distribution was analyzed and determined using Fourier transform infrared spectroscopy (Vertex 70). The crystal diffraction pattern of the material was determined using X-ray diffraction (Ulitma IV, Rigaku).

[0079] 2. Results

[0080] (1) The adsorption isotherms of Fe-BBCⅠ for Se(IV) were fitted using the Langmuir and Freundlich equations, and the results are shown in Figure 1. Table 1 shows the calculated adsorption isotherm parameters of iron-modified biochar for Se(IV), indicating that the adsorption equilibrium of iron-modified prickly pear biochar gradually increases with the increase of Se(IV) concentration. The fitted isotherm adsorption model parameters show that the Freundlich and Langmuir adsorption isotherm equations Ri and Ri are consistent. 2 The values ​​were 0.9763 and 0.8528, respectively, indicating that the adsorption of Se(IV) by Fe-BBCⅠ better conforms to the Freundlich adsorption equation. The fitted correlation parameters show that the adsorption of Se(IV) by Fe-BBCⅠ follows the Freundlich model, suggesting that the adsorption behavior of iron-modified prickly pear biochar is mainly characterized by multilayer chemisorption. This mechanism is related to the formation of complexes or surface precipitates between Se(IV) and iron atoms, indicating that iron modification alters the biochar's adsorption capacity for selenium in water.

[0081] Table 1 Fitting parameters of the isothermal adsorption model

[0082]

[0083] (2) Different adsorption times significantly affected the adsorption efficiency of BBC and Fe-BBCⅠ on Se(IV). As shown in Figure 2, Fe-BBCⅠ reached adsorption equilibrium for Se(IV) after 30 min, and after 3 h, Fe-BBCⅠ reached adsorption equilibrium for Se(IV). The results obtained all showed good fit to the pseudo-second-order kinetic equation, but poor correlation with the pseudo-first-order kinetic direction. The R values ​​of BBC and Fe-BBCⅠ were relatively stable. 2The values ​​were 0.9784 and 0.9285, respectively, both fitting the experimental data well. Table 2 shows the calculated adsorption kinetic parameters of Se(IV) for the two biochars, indicating that both biochars exhibit two adsorption stages for Se(IV): fast and slow. From 30 to 180 min, both biochars are in the fast adsorption stage for Se(IV), where abundant adsorption sites exist on the biochar surface, allowing Se(IV) ions to be rapidly adsorbed onto the material surface. As time progresses, the number of adsorption sites decreases, and both biochars enter the slow adsorption stage before reaching adsorption equilibrium. Both the prickly pear biochar and the iron-modified prickly pear biochar showed good correlation with pseudo-second-order kinetics, indicating that chemisorption is the dominant mechanism. Fe-BBCⅠ reached adsorption equilibrium in 30 min, while BBC took 3 h, indicating that Fe-BBCⅠ has more active adsorption sites than BBC, which significantly improves its adsorption efficiency for Se(IV).

[0084] Table 2 Fitting parameters for the pseudo-first-order and pseudo-second-order dynamic models

[0085]

[0086] (3) SEM results showed that iron modification affected the morphology of prickly pear biochar. As shown in Figure 3, the BBC structure exhibited a porous structure with honeycomb-like pores and hollow strips inside. The structure was relatively loose and contained more pores in the cross-section. The Fe-BBCⅠ structure showed a rough and irregular morphology and contained a large number of particulate attachments.

[0087] (4) Iron modification affected the crystal structure of prickly pear biochar. X-ray diffraction (XRD) was used to characterize the two biochars before and after adsorption. The results are shown in Figure 4. The XRD patterns of BBC showed sharp peaks at 23.05°, 29.4°, 31.44°, 35.97°, 39.4°, 43.16°, 47.5°, and 48.5°. No new mineral crystals appeared after BBC adsorbed Se. In the XRD patterns of Fe-BBCⅠ before and after Se(IV) adsorption, broad diffraction peaks were observed near 23.0°, 35.5°, and 62.9°. Comparing the XRD results of the prickly pear biochar before and after modification, the characteristic peak of carbon at 23.0° for Fe-BBCⅠ is mainly due to the presence of cellulose. The characteristic peaks at 35.5° and 62.9° are Fe3O4. 4 The characteristic peak of Fe-BBCⅠ is at 596 cm⁻¹. -1The absorption peak at 454 cm⁻¹ is a characteristic absorption peak of the Fe-O vibration, indicating that magnetite is the main crystal phase in Fe-BBC, which also confirms the X-ray diffraction pattern of Fe-BBCⅠ. Compared with BBC, Fe-BBCⅠ shows a peak at 454 cm⁻¹. -1 and 1067cm -1 The vibrational peaks representing hematite and Fe-OH in the vicinity indicate that iron is immobilized on the biochar. After adsorption, the functional groups representing -OH and CH weaken, indicating that the functional groups on the modified biochar surface participate in adsorption. In addition to pure adsorption, the incorporation of Se oxygen anions into Fe2O3 is also an important immobilization mechanism, which is consistent with the results obtained by SEM. A large number of particulate deposits appear on the surface of the modified biochar, with a rough surface and irregular shape, indicating that iron is successfully attached to the surface of the biochar, thereby improving the adsorption performance of biochar for Se(IV).

[0088] (5) Iron modification affected the functional groups of prickly pear biochar, and there were significant differences in the FT-IR spectra of BBC and Fe-BBCⅠ. As shown in Figure 5, the positions of several characteristic absorption peaks of the organic functional groups of the materials changed before and after modification. Fe modification treatment caused the BBC to reach a higher position at 3620 cm⁻¹. -1 The characteristic peak at 3397 cm⁻¹ disappears, and a new characteristic peak appears at 3397 cm⁻¹. -1 The presence of Fe modification treatment resulted in BBC at 1434 cm⁻¹. -1 The characteristic peaks disappeared, while the BBC at 1039 cm⁻¹ was enhanced. -1 The characteristic peak at 874 cm⁻¹. Meanwhile, Fe modification treatment resulted in BBC reaching a peak at 874 cm⁻¹. -1 The characteristic peaks weakened, and compared with BBC, a 596 cm⁻¹ peak was found in Fe-BBCⅠ. -1 and 466cm -1 Vibration peaks nearby.

[0089] Example 2: Preparation of iron-modified biochar Fe-BBC II and its selenium retention effect in selenium-rich soil

[0090] 1. Method

[0091] The specific steps in this embodiment to investigate the effect of Fe-BBC II on soil leachate element leaching are as follows:

[0092] (1) The raw material for prickly pear biochar (BBC) is the dead branches and leaves of the prickly pear tree. The dead branches and leaves are washed with distilled water, dried and crushed, and then dried and stored through a 20-mesh sieve.

[0093] (2) The powder was loaded into the reactor and placed in the muffle furnace for oxygen-free high-temperature pyrolysis at 495°C for 1.95 hours. After the temperature of the muffle furnace dropped to room temperature, it was taken out and stored in an indoor desiccator for later use.

[0094] (3) Modified prickly pear (Fe-BBC) biochar was prepared by acid-base impregnation modification. A certain mass of prickly pear biochar was placed in a beaker, and 1.0 mol·L⁻¹ was added. -1 After stirring evenly with HCl, soak thoroughly for 0.95 hours. The amount of carbonized material powder added is 118 g / L. After soaking, filter, rinse and dry.

[0095] (4) Weigh the acid-washed prickly pear biochar obtained in the previous step and put it into a 1.0 mol·L⁻¹ solution. -1 In FeCl3·6H2O solution, the amount of material added after hydrochloric acid treatment was 98 g / L, the pH was adjusted to 8.0, and the mixture was shaken in a shaker at 25.0±2℃ for 1 h. After filtration, it was rinsed with deionized water, dried, and Fe-BBC II was obtained. The mixture was then ground through a 100-mesh sieve and stored in an indoor desiccator for later use.

[0096] (5) Ash content determination of prickly pear biochar

[0097] Ash content was determined by differential gravimetric method. 1.0 g of prickly pear biochar was weighed and placed in a crucible. The crucible was heated to 800 °C in a muffle furnace and kept at that temperature for 4 h. After cooling, it was taken out and weighed. The ash content of the biochar was calculated using formula (1).

[0098]

[0099] In the formula: M - mass of biochar before combustion (g); M1 - mass of empty crucible before combustion (g); M2 - mass of empty crucible and ash after combustion (g)

[0100] (6) Determination of physicochemical characterization properties of biochar

[0101] The physicochemical properties of biochar were characterized, including pH, surface morphology, elemental analysis, functional groups, and crystal structure. Biochar and deionized water were added to centrifuge tubes at a mass ratio of 1:20, shaken on a shaker for 10 min, and allowed to stand for 0.5 h before pH measurement using a pH meter (Leici PHSJ4F, Shanghai). BBC and Fe-BBC were determined using scanning electron microscopy (EVO MA15, TESCAN MIRA4), and the C, H, O, N, and S contents of the biochar were determined using an elemental analyzer (Vario EL CUBE).

[0102] (7) Cut a PVC pipe (7.5cm in diameter, 44.15cm² in cross-sectional area). 2 The bottom of the cut PVC pipe is wrapped with nylon mesh.

[0103] (8) Load different treated soils into a soil column, and fill the bottom of the soil column with about 2cm thick quartz sand. Place a 300-mesh gauze between the quartz sand and the soil.

[0104] (9) Cover the bottom of the soil with a PVC cap, make a small hole with a diameter of 0.5cm at the bottom of the cap, and fix the drain pipe with a rubber stopper to facilitate the collection of leachate.

[0105] (10) Place the soil column upright on the frame. According to 1.1 g / cm³ 3 The dry soil mass required for a 20cm soil column was calculated based on the field soil bulk density level. The weighed soil was then placed into a PVC pipe to form a simulated soil column of about 20cm. The total length of the soil column was uniformly 30cm for all treatments.

[0106] (11) Place a filter paper on the surface of the soil column to ensure that the surface is flat when water is added. Mix the original biochar and iron-modified biochar with the test soil at a mass fraction of 1.95% to prepare a biochar-soil mixture. Use the soil without biochar as the control.

[0107] (12) Place a layer of filter paper on top to prevent water leaching from disturbing the surface soil. After the soil column is filled, add distilled water to make the soil in the column nearly saturated with water. After standing for 12 hours, add 100 mL of distilled water. This is the first leaching. Leach once every 48 hours, adding 100 mL of distilled water each time.

[0108] 2. Results

[0109] (1) Before and after iron modification, the element content of the two biochars was in the order of C>O>H>N>S. The prickly pear biochar had the highest C content, reaching about 74%, while the N, H, and S contents of both materials were relatively low. Among the two biochars, Fe-BBC II had the highest O / C ratio and was more hydrophilic. After modification, the C content of prickly pear biochar decreased by 33.78%, while the O content increased by 59.78%. Table 3 compares the pH, ash content, and main components of BBC and Fe-BBC II. In the table, the pH of biochar is BBC>Fe-BBC II, and the ash content is Fe-BBC II>BBC. H / C and O / C represent the aromaticity and hydrophilicity of biochar, respectively. The smaller the H / C value, the higher the aromaticity and the more complete the carbonization; the larger the O / C value, the greater the hydrophilicity. After iron modification, the O / C ratio on the surface of the biochar increased, which made Fe-BBC II have a stronger adsorption capacity for Se(IV).

[0110] Table 3 Elemental content and element ratio of biochar

[0111]

[0112]

[0113] (2) The effect of Fe-BBC II on Se leaching in soil is shown in Figure 6. The Se concentration in the leachate showed a trend of first decreasing and then increasing. The Se leaching concentration was the highest after the first leaching. The Se concentration in the CK leachate was 3.19 mg / L, and the Se concentration in the Fe-BBC II leachate was 2.39 mg / L. The Se concentration in the leachate of the Fe-BBC II treatment group was significantly lower than that of the CK group in all groups, indicating that the Fe-BBC II treatment significantly enhanced the soil's selenium retention effect. After 20 days of leaching, the Se content in different soil layers was measured, and the results are shown in Figure 7. D20 0-10cm and D20 10-20cm represent the selenium concentrations in the two soil layers after 20 days of leaching. Compared with the unleached soil (D0), the Se concentrations in the 0-10cm and 10-20cm soil layers of the CK group decreased by 27.57% and 23.61%, respectively. After leaching, the Se concentration in the 0-10cm soil layer of the Fe-BBC II treatment group decreased by 17.33%, while the Se concentration in the 10-20cm soil layer increased by 2.69%.

[0114] Example 3: Preparation of iron-modified biochar Fe-BBC III and its passivation effect on heavy metals in compound-contaminated soil.

[0115] 1. Method

[0116] The specific steps of this embodiment to investigate the effect of Fe-BBC III on the leaching of heavy metals in soil leachate are as follows:

[0117] (1) The raw material for prickly pear biochar (BBC) is the dead branches and fallen leaves of the prickly pear tree. The dead branches and fallen leaves are washed with distilled water, dried and crushed, and then dried and stored after passing through a 20-mesh sieve.

[0118] (2) The powder was loaded into the reactor and placed in the muffle furnace for oxygen-free high-temperature pyrolysis at 505℃ for 2.05h. After the temperature of the muffle furnace dropped to room temperature, it was taken out and stored in an indoor desiccator for later use.

[0119] (3) Modified prickly pear (Fe-BBC) biochar was prepared by acid-base impregnation modification. A certain mass of prickly pear biochar was placed in a beaker, and 1.0 mol·L⁻¹ was added. -1 After stirring evenly with HCl, soak thoroughly for 2.05 hours. The amount of carbonized material powder added is 127 g / L. After soaking, filter, rinse and dry.

[0120] (4) Weigh the acid-washed prickly pear biochar obtained in the previous step and put it into a 1.0 mol·L⁻¹ solution. -1In FeCl3·6H2O solution, the amount of material added after hydrochloric acid treatment was 108 g / L, the pH was adjusted to 8.0, and the mixture was shaken in a shaker at 25.0±2℃ for 1 h. After filtration, it was rinsed with deionized water, dried, and Fe-BBC III was obtained. The mixture was then ground through a 100-mesh sieve and stored in an indoor desiccator for later use.

[0121] (5) Cut a PVC pipe (7.5cm in diameter, 44.15cm² in cross-sectional area). 2 The bottom of the cut PVC pipe is wrapped with nylon mesh.

[0122] (6) Load different treated soils into a soil column, and fill the bottom of the soil column with about 2cm thick quartz sand. Place a 300-mesh gauze between the quartz sand and the soil.

[0123] (7) Cover the bottom of the soil with a PVC cap, make a small hole with a diameter of 0.5cm at the bottom of the cap, and fix the drain pipe with a rubber stopper to facilitate the collection of leachate.

[0124] (8) Place the soil column upright on the frame. According to 1.1 g / cm³ 3 The dry soil mass required for a 20cm soil column was calculated based on the field soil bulk density level. The weighed soil was then placed into a PVC pipe to form a simulated soil column of about 20cm. The total length of the soil column was uniformly 30cm for all treatments.

[0125] (9) Place a filter paper on the surface of the soil column to ensure that the surface is flat when water is added. Mix the original biochar and iron-modified biochar with the test soil at a mass fraction of 2.05% to prepare a biochar-soil mixture. Use the soil without biochar as the control.

[0126] (10) Place a layer of filter paper on top to prevent water leaching from disturbing the surface soil. After the soil column is filled, add distilled water to make the soil in the column nearly saturated with water. After standing for 12 hours, add 100 mL of distilled water. This is the first leaching. Leach once every 48 hours, adding 100 mL of distilled water each time.

[0127] 2. Results

[0128] (1) As shown in Figures 8-11, the retention effect of heavy metals in the soil treated with Fe-BBC III was significantly improved compared with the control. The concentrations of Mn, Cu, and Zn in the leaching solutions of the four groups of experiments showed a gradual decreasing trend with increasing time, and the leaching concentration gradually decreased and eventually stabilized. After all leaching was completed, the leaching of Mn was reduced by 53.45% compared with CK, and Mn tended to stabilize after the fourth leaching. The leaching concentration of Cu gradually decreased and tended to stabilize after the third leaching. It was not detected after the eighth leaching. The Cu leaching concentration was the highest in the first leaching. The first leaching concentration of CK group was 99.54 ug / g, and the first leaching concentration of Fe-BBCIII group was 25.61 ug / g. The leaching concentration of Zn gradually decreased and tended to stabilize after the third leaching. The Zn leaching concentration was the highest in the first leaching. The first leaching concentration of CK group was 253.72 ug / g, and the first leaching concentration of Fe-BBC III group was 299.06 ug / g.

[0129] The highest Fe concentration in the leachate of the CK treatment group was observed during the first leaching, at 17.03 ug / g. In contrast, the Fe concentration in the Fe-BBC III group showed a gradual increasing trend, reaching its peak at 2.99 ug / g during the eighth leaching. Compared to the control group without biochar, the concentration of heavy metals in the leachate of the Fe-BBC III treatment group was significantly lower. This indicates that Fe-BBC III effectively reduces the mobility of heavy metals in composite contaminated soils and has a good passivation effect on heavy metal elements in composite contaminated soils.

Claims

1. The application of iron-modified prickly pear biochar in the remediation of selenium pollution in environmental media and / or the retention of selenium in soil, characterized in that, The selenium pollution in the remediation medium is Se(IV) pollution in water bodies; the preparation method of the iron-modified prickly pear biochar includes the following steps: S1. Collect fallen branches and leaves of prickly pear, separate and remove impurities, dry, pulverize and sieve; S2. Pyrolyze the raw material pretreated in step S1 under anaerobic conditions to obtain carbonized material, cool naturally, pulverize again, and sieve; the pyrolysis temperature is 480-510℃, and the pyrolysis time is 1.8-2.2h; S3. Acid-impregnate the carbonized material obtained in step S2, and after impregnation, filter, dry, and grind to remove impurities from the carbonized material; S4. Place the carbonized material powder after acid washing in step S3 into Fe 3+ In the solution, after adjusting the pH to 7.5–8.5, the system undergoes aging treatment, followed by filtration, drying, and grinding to prepare iron-modified prickly pear biochar. Step S3 involves acid impregnation with an HCl solution for 0.8–1.2 hours; the concentration of the HCl solution is 0.8–1.2 mol / L. L -1 The amount of carbonized material powder added is 100-135 g / L; the Fe in step S4 3+ Fe in solution 3+ Concentration of 0.8–1.2 mol L -1 The addition amount of carbonized material powder after S3 treatment and pickling is 87-112 g / L.

2. A method for remediating selenium-polluted water bodies, characterized in that, Iron-modified prickly pear biochar was added to selenium-polluted water for treatment; the amount of biochar was 3.8–4.2 g / L; the adsorption equilibrium time was 30 min–24 h; the initial concentration of Se(IV) in the polluted water was 1–100 mg / L; the preparation method of the iron-modified prickly pear biochar included the following steps: S1. Collect fallen branches and leaves of prickly pear, separate and remove impurities, dry, pulverize and sieve; S2. Pyrolyze the raw material pretreated in step S1 under anaerobic conditions to obtain carbonized material, cool naturally, pulverize again, and sieve; the pyrolysis temperature was 480–510℃, and the pyrolysis time was 1.8–2.2 h; S3. Acid-impregnate the carbonized material obtained in step S2, and after impregnation, filter, dry, and grind to remove impurities from the carbonized material; S4. Place the carbonized material powder after acid washing in step S3 into Fe 3+ In the solution, after adjusting the pH to 7.5–8.5, the system undergoes aging treatment, followed by filtration, drying, and grinding to prepare iron-modified prickly pear biochar. Step S3 involves acid impregnation with an HCl solution for 0.8–1.2 hours; the concentration of the HCl solution is 0.8–1.2 mol / L. L -1 The amount of carbonized material powder added is 100-135 g / L; the Fe in step S4 3+ Fe in solution 3+ Concentration of 0.8–1.2 mol L -1 The addition amount of carbonized material powder after S3 treatment and pickling is 87-112 g / L.

3. A method for retaining selenium in soil, characterized in that, Iron-modified prickly pear biochar was added to the target soil for treatment; the amount of iron-modified prickly pear biochar was 1.8% to 2.0%; the preparation method of the iron-modified prickly pear biochar included the following steps: S1. Collect fallen branches and leaves of prickly pear, separate and remove impurities, dry and then crush and sieve; S2. The raw material pretreated in step S1 was subjected to pyrolysis reaction under anaerobic conditions to obtain carbonized material, naturally cooled, crushed again, and sieved; the pyrolysis temperature was 480 to 510℃, and the pyrolysis time was 1.8 to 2.2 h; S3. The carbonized material obtained in step S2 was acid-impregnated, and after the impregnation was completed, it was filtered, dried, and ground to remove impurities from the carbonized material; S4. The carbonized material powder after acid washing in step S3 was placed in Fe 3+ In the solution, after adjusting the pH to 7.5–8.5, the system undergoes aging treatment, followed by filtration, drying, and grinding to prepare iron-modified prickly pear biochar. Step S3 involves acid impregnation with an HCl solution for 0.8–1.2 hours; the concentration of the HCl solution is 0.8–1.2 mol / L. L -1 The amount of carbonized material powder added is 100-135 g / L; the Fe in step S4 3+ Fe in solution 3+ Concentration of 0.8–1.2 mol L -1 The addition amount of carbonized material powder after S3 treatment and pickling is 87-112 g / L.

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