Preparation method and application of iron modified roxburgh rose biochar based on roxburgh rose waste

Abstract

The invention discloses a preparation method and application of iron modified rosa roxburghii tratt charcoal based on rosa roxburghii tratt waste. The preparation method of the rosa roxburghii tratt iron-modified biochar comprises two steps of carbonization and modification, firstly, rosa roxburghii tratt litter waste is subjected to oxygen-limited heating carbonization to prepare a carbonized material, then acid pickling and iron modification are performed to prepare the iron-modified rosa roxburghii tratt biochar, and the prepared biochar has efficient adsorption capacity on selenium in a water body; meanwhile, selenium in the selenium-rich soil is immobilized, harmful heavy metal in the soil can be passivated, and the functions of controlling selenium release of a water body and improving the soil quality are achieved. The invention not only provides a new way for resource utilization of rosa roxburghii tratt litter, but also provides an efficient technology for water selenium pollution treatment, soil selenium immobilization and heavy metal soil immobilization, and achieves the effect of turning waste into wealth.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource utilization and metal pollution control in the process of cash crop production, and specifically to a preparation method of iron-modified roxburghii biochar based on roxburghii waste and its application in removing selenium from water, fixing selenium in soil and passivating heavy metal in soil. Background Art

[0002] Selenium (Se) is an essential nutrient that plays an important role in human health and the growth and development of plants and animals. However, if the daily intake of Se in the human body exceeds 400 μg, it will cause acute or chronic poisoning. The World Health Organization has set the reference amount of Se in drinking water as 40 μg·L -1 The most common form of selenium in environmental waters is selenite (SeO3 2- ) and selenate (SeO4 2- ), among which Se(IV) has a high bioavailability and its toxicity is 10 times that of Se(VI). Due to human activities such as mining, metal smelting and agricultural irrigation, a large amount of selenate and selenite are released into the environment. High concentrations of selenite (SeO3 2- ) and selenate (SeO4 2- ). Traditional removal technologies for selenium-containing water include ion exchange, biological method, membrane separation and adsorption. Ion exchange and membrane separation are highly efficient, but they are not widely used due to their high cost. Biological method is low-cost but has a long cycle. Adsorption has many advantages such as low cost, repeatability and easy operation, and has become one of the most commonly used methods for removing Se from water.

[0003] Biochar is a material produced by the pyrolysis of carbon-containing biomass at relatively low temperatures and in an oxygen-limited or oxygen-free environment. It has the characteristics of large specific surface area, rich oxygen-containing functional groups, developed pore structure, and good electrical conductivity. As a soil conditioner, biochar can not only improve soil properties, affect the abundance and activity of soil microorganisms, but also reduce the bioavailability of various pollutants including heavy metals. In recent years, it has been commonly used to treat organic and inorganic pollutants in the soil. As research deepens, some disadvantages of biochar have gradually emerged. It does not meet expectations in terms of binding and adsorption of various metal ions.

[0004] Rosa roxburghii Tratt is a perennial shrub of the genus Rosa. Its fruit is rich in a variety of nutrients that are beneficial to the human body. It is an important economic crop in Guizhou, China. In 2022, the planting area of ​​​​Rosa roxburghii in Guizhou has reached 2.1 million mu, and the comprehensive output value has exceeded 15 billion yuan. The rosa roxburghii industry has significant economic benefits. At present, there are still certain problems in the rosa roxburghii industry in Guizhou, my country. The main rosa roxburghii planting areas in Guizhou, my country are mainly 5 to 7 years old rosa roxburghii. There are also some rosa roxburghii plants that are more than 9 years old. The pruning of rosa roxburghii plantations and dead branches and leaves have produced a huge amount of waste, resulting in obvious waste of resources.

[0005] At present, there are still few studies on the resource utilization of sea buckthorn planting waste, and no research has focused on the high-value utilization of sea buckthorn dead branches and leaves. Patent CN116235768A discloses a preparation method and application of sea buckthorn waste and other agricultural waste as raw materials for preparing soil remediation matrix in rocky desertification areas, but does not involve the preparation of sea buckthorn biochar and the treatment of soil selenium and heavy metal elements. Patent CN115736090A discloses a method for preparing fermented sea buckthorn residue roughage and its application in beef buffalo TMR feed, but does not involve the preparation of sea buckthorn biochar and soil improvement and remediation. Summary of the invention

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

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

[0008] Another object of the present invention is to provide the use of the iron-modified roxburghii biochar in removing selenium from water, fixing selenium in soil and passivating heavy metal in soil.

[0009] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0010] A method for preparing iron-modified roxburghii biochar based on roxburghii waste comprises the following steps:

[0011] S1. Collect fallen branches and leaves of Rosa roxburghii, separate and remove impurities, dry and crush and sieve;

[0012] S2. The raw material pretreated in step S1 is subjected to pyrolysis reaction in an oxygen-free state to obtain a carbonized material, which is naturally cooled, crushed again, and sieved; the pyrolysis temperature is 480 to 510° C., and the pyrolysis time is 1.8 to 2.2 h;

[0013] S3. The carbonized material obtained in step S2 is acid-impregnated, and after the immersion is completed, it is filtered, dried, and ground to remove impurities in the carbonized material;

[0014] S4. Place the carbonized material powder after pickling in step S3 on Fe 3+ In the solution, the pH value of the system is adjusted to 7.5-8.5, and then an aging treatment is performed, followed by suction filtration, drying and grinding to prepare iron-modified roxburghii biochar.

[0015] The present invention takes into account a large amount of agricultural waste generated during the planting process of roxburghii, and the main components of the dead branches and leaves generated by pruning roxburghii are cellulose and hemicellulose. After high-temperature oxygen-limited cracking, such substances will produce a variety of different functional groups on the surface, which is helpful to enhance the adsorption and binding ability of biochar. Therefore, the carbonized material is first prepared by the oxygen-limited heating method using roxburghii waste, and then the biochar is improved by iron modification technology to improve the selenium fixation ability and soil heavy metal passivation ability. The prepared iron-modified roxburghii biochar can be used for selenium fixation and soil heavy metal passivation, which provides a new way for the resource utilization of agricultural waste in roxburghii plantations.

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

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

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

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

[0020] Preferably, in steps S2, S3 and S4, the pyrolysis temperature is 485°C, 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 S3 treatment is 92g / L.

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

[0022] Preferably, in steps S2, S3 and S4, the pyrolysis temperature is 505°C, 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 S3 treatment is 98g / L.

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

[0024] Preferably, in steps S2, S3 and S4, the pyrolysis temperature is 505°C, 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 S3 treatment is 108g / L.

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

[0026] The iron-modified roxburghii biochar provided by the present invention has a highly efficient adsorption and removal capability for Se(IV) in water, can fix selenium in soil, and has a passivation effect on a variety of soil heavy metals, effectively improving the quality of soil contaminated by heavy metal complexes. Therefore, the present invention also provides the use of the iron-modified roxburghii biochar in repairing selenium pollution in environmental media, fixing selenium in soil, and / or passivating heavy metals in soil environments.

[0027] Specifically, the method for repairing selenium pollution in environmental media is to adsorb Se(IV) in water bodies, and passivate heavy metals in the soil environment are specifically Mn, Zn, Fe and / or Cu.

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

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

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

[0031] The present invention also provides a method for fixing soil selenium, which is to add the iron-modified roxburghii biochar to the target soil for treatment; the amount of the iron-modified roxburghii biochar is 1.8% to 2.0%. The method can fix the selenium element in the soil and reduce the loss of selenium in the soil under water leaching.

[0032] Preferably, the roxburghii biochar is the above-mentioned FeBBC II.

[0033] The present invention also provides a method for passivating heavy metals in composite contaminated soil, which is to add the iron-modified roxburghii biochar to the target soil for treatment; the amount of the iron-modified roxburghii biochar is 2.0% to 2.2%. The method can passivate heavy metals Mn, Zn, Fe, and Cu in the soil.

[0034] Preferably, the iron-modified Rosa roxburghii biochar is the above-mentioned FeBBC III.

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

[0036] The invention provides an iron-modified roxburghii biochar based on roxburghii waste, which is to first perform oxygen-limited temperature carbonization on roxburghii litter waste to prepare a carbonized material, then perform acid washing and iron modification to prepare the iron-modified roxburghii biochar, and the prepared biochar has a high-efficiency adsorption capacity for selenium in water bodies, and has a fixation effect on selenium in selenium-rich soil, can simultaneously passivate harmful heavy metals in the soil, and has the function of controlling the release of selenium in water bodies and improving soil quality. The invention not only provides a new way for the resource utilization of roxburghii litter, but also provides an efficient technology for water body selenium pollution control, soil selenium fixation, and heavy metal soil fixation, achieving the effect of turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Langmuir adsorption isotherm and Freundlich adsorption isotherm of Se(IV) on iron-modified sea buckthorn charcoal.

[0038] Figure 2 This is the adsorption kinetic curve of Fe-BBCⅠ and Rosa roxburghii biochar (BBC).

[0039] Figure 3 These are the SEM (2μm) of sea buckthorn biochar and the SEM (2μm) of iron-modified sea buckthorn biochar.

[0040] Figure 4These are the X-ray diffraction patterns of sea buckthorn biochar (BBC) and iron-modified sea buckthorn charcoal (FeBBC) before and after adsorption of Se(IV).

[0041] Figure 5 FT-IR spectra of sea buckthorn biochar and iron-modified sea buckthorn charcoal before and after adsorption of Se(IV).

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

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

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

[0045] Fig. 9 The effect of Fe-BBC III on Zn leaching in soil.

[0046] Fig.10 The effect of Fe-BBC III on Cu leaching in soil.

[0047] Fig.11 This is a diagram showing the effect of Fe-BBC III on Fe leaching in soil. DETAILED DESCRIPTION

[0048] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

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

[0050] Example 1 Preparation of modified Rosa roxburghii biochar Fe-BBCⅠ and its removal effect on Se(IV) at different concentrations in water and its adsorption kinetic characteristics for removing Se(IV) from water

[0051] 1. Methods

[0052] This example explores the removal effect of iron-modified roxburghii biochar on different concentrations of Se(IV) in water, specifically including:

[0053] (1) The raw materials of roxburghii biochar (BBC) are dead branches and leaves of roxburghii. The dead branches and leaves are washed with distilled water, dried and crushed, and dried and stored after being sieved through a 20-mesh sieve.

[0054] (2) The powder is loaded into a reactor and placed in a muffle furnace for pyrolysis at 485°C without oxygen for 1.85 h. After the temperature of the muffle furnace drops to room temperature, the powder is taken out and placed in an indoor desiccator for storage.

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

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

[0057] (5) 0.1 g BBC and Fe-BBCⅠ were added to 25 mL Se(IV) solution, and the concentrations were set to 1 mg·L -1 , 2.5mg·L -1 , 5mg·L -1 、10mg·L -1 , 20mg·L -1 、30mg·L -1 , 50mg·L -1 、70mg·L -1 、100mg·L -1 , the temperature was set to 25±2℃, and the speed was about 180r min after being placed on a shaker. -1 The adsorption was carried out for 24 h under the conditions of , and the isothermal adsorption data of the two biochars were fitted using the Langmuir (Formula 1) and Freundlich models (Formula 2) to explore the adsorption characteristics of Rosa roxburghii biochar for Se(IV).

[0058] Langmuir isotherm adsorption model linear relationship (1):

[0059]

[0060] Freundlich isotherm adsorption model linear relationship (2):

[0061]

[0062] Q e —The amount of Se(IV) adsorbed per unit mass of biochar 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 ,n—adsorption constant of Freundlich isotherm

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

[0068] Pseudo-first-order kinetic equation:

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

[0070] Pseudo-second-order kinetic equation:

[0071]

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

[0073] Q t — is the amount of Se(IV) adsorbed per unit mass of biochar 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—quasi-secondary adsorption rate constant (g·min·mg -1 )

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

[0078] BBC and Fe-BBCⅠ were added to 2.5 mg·L -1 Se(IV) solution (0.1 g·25 ml -1 ), 180r·min -1 The samples were collected after oscillating reaction for 360 min and 1440 min respectively. The functional group structure distribution was analyzed and determined by Fourier transform infrared spectrometer (Vertex70). The crystal diffraction pattern of the material was determined by X-ray diffractometer (Ulitma IV, Rigaku).

[0079] 2. Results

[0080] (1) The adsorption isotherm of Fe-BBCⅠ for Se(IV) was fitted by Langmuir equation and Freundlich equation. The results are shown in Figure 1 Table 1 gives the calculated adsorption isotherm parameters of Se(IV) by iron-modified biochar, which shows that the adsorption equilibrium amount of iron-modified roxburghii charcoal gradually increases with the increase of Se(IV) concentration. The fitting isotherm adsorption model parameters show that the Freundlich and Langmuir adsorption isotherm equations R 2 The adsorption of Se(IV) by Fe-BBCⅠ is more consistent with the Freundlich adsorption equation. The fitting correlation parameters show that the adsorption of Se(IV) by Fe-BBCⅠ conforms to the Freundlich model, which indicates that the adsorption behavior of iron-modified roxburghii charcoal is mainly based on multi-molecular layer chemical adsorption. This mechanism is related to the complex or surface precipitation formed between Se(IV) and iron atoms, which indicates that iron modification changes the adsorption capacity of biochar for selenium in water.

[0081] Table 1 Isotherm adsorption model fitting parameters

[0082]

[0083] (2) Different adsorption times have a significant effect on the adsorption of Se(IV) by BBC and Fe-BBCⅠ. Figure 2As shown in the figure, after 30 minutes, Fe-BBCⅠ reached adsorption equilibrium for Se(IV), and after 3 hours, Fe-BBCⅠ reached adsorption equilibrium for Se(IV). The obtained results were well fitted with the pseudo-second-order kinetic equation, but poorly correlated with the pseudo-first-order kinetic direction. The R 2 are 0.9784 and 0.9285, respectively, which fit the experimental data well. Table 2 gives the calculated adsorption kinetic parameters of the two biochars for Se(IV), showing that the two biochars have two stages of fast adsorption and slow adsorption for Se(IV). From 30 to 180 min, the two biochars are in the fast adsorption stage for Se(IV). At this time, there are abundant adsorption sites on the surface of biochar, and Se(IV) ions are quickly adsorbed to the surface of the material. As time goes by, the adsorption sites become fewer, and the two biochars enter the slow adsorption stage and then reach adsorption equilibrium; both the sea buckthorn biochar and the iron-modified sea buckthorn biochar have a good correlation with the pseudo-secondary kinetics, indicating that chemical adsorption is the dominant mechanism. Fe-BBCⅠ reaches adsorption equilibrium at 30 min, while BBC reaches adsorption equilibrium at 3 h, indicating that Fe-BBCⅠ has more active adsorption sites than BBC, which greatly improves its adsorption efficiency for Se(IV).

[0084] Table 2 Fitting parameters of pseudo-first-order kinetic model and pseudo-second-order kinetic model

[0085]

[0086] (3) SEM results showed that iron modification had an impact on the morphology of the biochar, such as Figure 3 As shown in the figure, the BBC structure shows a porous structure with honeycomb-shaped pores and hollow strips inside. The structure is relatively loose and contains more pores on the cross section. The structure of Fe-BBCⅠ shows a rough and irregular morphology and contains a large number of granular attachments.

[0087] (4) Iron modification has an impact on the crystal structure of the Rosa roxburghii biochar. The two biochars were characterized by X-ray diffraction (XRD) before and after adsorption. The results are as follows: Figure 4As shown in the figure, the XRD patterns of BBC all showed sharp peaks, with diffraction 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 adsorption of Se(IV), it can be found that broad diffraction peaks appeared near 23.0°, 35.5°, and 62.9°, respectively. Comparing the X-ray diffraction results of the Rosa roxburghii biochar before and after modification, Fe-BBCⅠ showed a characteristic peak of carbon at 23.0°, which was mainly due to the presence of cellulose. The characteristic peaks at 35.5° and 62.9° are Fe3O 4 The characteristic peak of Fe-BBCⅠ is at 596cm -1 The absorption peak at 454 cm is the characteristic absorption peak of Fe-O vibration, which also shows that magnetite is the main crystal phase structure in Fe-BBC. This also confirms the X-ray diffraction pattern of Fe-BBCⅠ. -1 and 1067cm -1 The vibration peaks representing hematite and Fe-OH nearby indicate that iron is fixed on the biochar. After adsorption, the functional groups representing -OH and CH weaken, indicating that the functional groups on the surface of the modified biochar participate in the 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 particle attachments 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 has an effect on the functional groups of the roxburghii biochar, and there are obvious differences in the FT-IR spectra of BBC and Fe-BBCⅠ. Figure 5 As shown in the figure, the positions of several characteristic absorption peaks of the organic functional groups of the material changed before and after the modification. Fe modification treatment resulted in a BBC peak at 3620 cm -1 The characteristic peak at 3397cm -1 The Fe modification treatment resulted in the BBC at 1434 cm -1 The characteristic peak of BBC at 1039cm disappears, while the peak of BBC at 1039cm is enhanced. -1 At the same time, Fe modification treatment leads to a BBC peak at 874 cm -1 The characteristic peak of Fe-BBCⅠwas weakened. Compared with BBCⅠ, the peak at 596cm -1 and 466cm -1 near the vibration peak.

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

[0090] 1. Methods

[0091] This example explores the effect of Fe-BBC II on the leaching loss of soil leaching solution elements. The specific steps are as follows:

[0092] (1) The raw materials of roxburghii biochar (BBC) are the dead branches and leaves of roxburghii trees. The dead branches and leaves are washed with distilled water, dried and crushed, and dried and stored through a 20-mesh sieve.

[0093] (2) The powder is loaded into a reactor and placed in a muffle furnace for high-temperature pyrolysis at 495°C without oxygen for 1.95 h. After the temperature of the muffle furnace drops to room temperature, the powder is taken out and placed in an indoor desiccator for storage.

[0094] (3) Modified Rosa roxburghii (Fe-BBC) biochar was prepared by acid-base impregnation modification. A certain amount of Rosa roxburghii biochar was placed in a beaker and 1.0 mol·L -1 HCl, stir evenly and soak for 0.95h, the amount of carbonized material powder added is 118g / L, after soaking, filter, rinse and dry.

[0095] (4) Weigh the acid-washed roxburghii biochar obtained in the previous step and place it in a 1.0 mol·L -1 In the FeCl3·6H2O solution, the material treated with hydrochloric acid was added in an amount of 98 g / L, the pH was adjusted to 8.0, and the solution was shaken in a shaker at 25.0±2℃ for 1 h. After filtration, it was rinsed with deionized water and dried to obtain Fe-BBC II, which was ground through a 100-mesh sieve and placed in an indoor desiccator for storage.

[0096] (5) Ash content determination of roxburghii biochar

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

[0098]

[0099] Where: M-mass of biochar before burning (g); M1 mass of empty crucible before burning (g); M2 mass of empty crucible and ash after burning (g)

[0100] (6) Determination of physical and chemical properties of biochar

[0101] The characterization of the physical and chemical properties of biochar included pH, surface morphology, elemental analysis, functional groups and crystal structure. Biochar and deionized water were added to the centrifuge tube at a mass ratio of 1:20, shaken on a shaker for 10 minutes, and left to stand for 0.5 hours before being measured using a pH meter (Leci PHSJ4F, Shanghai). BBC and Fe-BBC were measured using a scanning electron microscope (EVO MA15, TESCAN MIRA4), respectively, and the C, H, O, N and S contents of biochar were measured using an elemental analyzer (Vario EL CUBE);

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

[0103] (8) The soils from different treatments were placed into soil columns. The bottom of the soil column was filled with quartz sand about 2 cm thick, and a 300-mesh gauze was placed 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 0.5 cm at the bottom of the cap, and fix the drain pipe with a rubber stopper to collect the leaked liquid.

[0105] (10) Place the soil column upright on a rack. 3 The dry soil mass required for a 20-cm soil column was calculated based on the field soil bulk density level. The weighed soil was placed into a PVC tube to form a simulated soil column of approximately 20 cm. The total length of the soil column was unified to 30 cm for all treatments.

[0106] (11) A piece of filter paper was placed on the surface of the soil column to ensure a smooth surface when water was added. The original biochar and iron-modified biochar were mixed with the test soil at a mass fraction of 1.95% to prepare a charcoal-soil mixture, and the soil without charcoal was used as a control.

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

[0108] 2. Results

[0109] (1) Before and after iron modification, the order of element content in the two biochars was C>O>H>N>S. The C content of the sea buckthorn biochar was the highest, reaching about 74%. The N, H, and S contents of the two materials were all low. Among the two biochars, Fe-BBC II had the highest O / C and was highly hydrophilic. After modification, the C content of the sea buckthorn biochar decreased by 33.78%, and the O content increased by 59.78%. Table 3 compares the pH, ash content, and main components of BBC and Fe-BBC II. The pH of the biochar in the table is: BBC>Fe-BBC II, and the ash content of Fe-BBC II>BBC. H / C and O / C represent the aromaticity and hydrophilicity of the 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 on the surface of the biochar increased, making Fe-BBC II have a stronger adsorption capacity for Se(IV).

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

[0111]

[0112]

[0113] (2) Effect of Fe-BBC II on Se leaching in soil Figure 6 As shown in the figure, 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 seepage liquid was 3.19 mg / L, and the Se concentration in the Fe-BBCII seepage liquid was 2.39 mg / L. The Se concentration in the Fe-BBC II treatment group was significantly lower than that in 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 were as follows: Figure 7 As shown in the figure, D20 0-10cm and D20 10-20cm are the selenium concentrations in the two soil layers after leaching for 20 days. 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%; after leaching, the Se concentration in the 0-10cm soil layer of the Fe-BBC II treatment group decreased by 17.33%, and 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 composite contaminated soil

[0115] 1. Methods

[0116] This example explores the effect of Fe-BBC III on the leaching loss of heavy metal elements in soil leaching solution. The specific steps are as follows:

[0117] (1) The raw materials of roxburghii biochar (BBC) are dead branches and leaves of roxburghii trees. The dead branches and leaves are washed with distilled water, dried and crushed, and dried and stored after being sieved through a 20-mesh sieve.

[0118] (2) The powder is loaded into a reactor and placed in a muffle furnace for pyrolysis at 505°C without oxygen for 2.05 h. After the temperature of the muffle furnace drops to room temperature, the powder is taken out and placed in an indoor desiccator for storage.

[0119] (3) Modified Rosa roxburghii (Fe-BBC) biochar was prepared by acid-base impregnation modification. A certain amount of Rosa roxburghii biochar was placed in a beaker and 1.0 mol·L -1 HCl, stir evenly and soak for 2.05h, the amount of carbonized material powder added is 127g / L, after soaking, filter, rinse and dry.

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

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

[0122] (6) The soils from different treatments were placed into soil columns. The bottom of the soil column was filled with quartz sand about 2 cm thick, and a 300-mesh gauze was placed 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 0.5 cm at the bottom of the cap, and fix the drain pipe with a rubber stopper to collect the leaked liquid.

[0124] (8) Place the soil column upright on a rack. 3 The dry soil mass required for a 20-cm soil column was calculated based on the field soil bulk density level. The weighed soil was placed into a PVC tube to form a simulated soil column of approximately 20 cm. The total length of the soil column was unified to 30 cm for all treatments.

[0125] (9) A piece of filter paper was placed on the surface of the soil column to ensure that the surface was flat when water was added. The original biochar and iron-modified biochar were mixed with the test soil at a mass fraction of 2.05% to prepare a charcoal-soil mixture, and the soil without charcoal was used as a control.

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

[0127] 2. Results

[0128] (1) By Figures 8 to 11 It can be seen that the immobilization 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 experimental groups showed a gradual downward trend with the increase of time, and the leaching concentration gradually decreased and finally stabilized. After all the leaching was completed, the leaching loss of Mn element decreased by 53.45% compared with CK, and Mn tended to be stable after the fourth leaching; the leaching concentration of Cu element gradually decreased, tended to be stable after the third leaching, and was not detected after the eighth leaching. The leaching concentration of Cu was the highest in the first time, and the first leaching concentration of CK group was 99.54ug / g, and the first leaching concentration of Fe-BBCIII group was 25.61ug / g; the leaching concentration of Zn element gradually decreased, and tended to be stable after the third leaching. The leaching concentration of Zn was the highest in the first time, and the first leaching concentration of CK group was 253.72ug / g, and the first leaching concentration of Fe-BBC III group was 299.06ug / g.

[0129] The Fe concentration in the seepage solution of the CK treatment group was the highest at the first leaching loss, which was 17.03ug / g, while the Fe concentration in the seepage solution of the Fe-BBC III group showed a gradual increase, reaching the highest point at the eighth time, which was 2.99ug / g. Compared with the control group without adding biochar, the concentration of heavy metals in the seepage solution of the Fe-BBC III treatment group decreased significantly, indicating that Fe-BBC III effectively reduced the mobility of heavy metals in the composite contaminated soil and had a good passivation effect on the heavy metal elements in the composite contaminated soil.

Claims

1. A method for preparing iron-modified roxburghii biochar based on roxburghii waste, characterized in that: The following steps are involved: S1. Collect fallen branches and leaves of Rosa roxburghii, separate and remove impurities, dry and crush and sieve; S2. The raw material pretreated in step S1 is subjected to pyrolysis reaction in an oxygen-free state to obtain a carbonized material, which is naturally cooled, crushed again, and sieved; the pyrolysis temperature is 480 to 510° C., and the pyrolysis time is 1.8 to 2.2 h; S3. The carbonized material obtained in step S2 is acid-impregnated, and after the immersion is completed, it is filtered, dried, and ground to remove impurities in the carbonized material; S4. Place the carbonized material powder after pickling in step S3 on Fe 3+ In the solution, the pH of the system is adjusted to 7.5-8.5, and then an aging treatment is performed, followed by suction filtration, drying, and grinding to prepare iron-modified roxburghii biochar.

2. The preparation method according to claim 1, characterized in that: The acid immersion in step S3 is performed by fully immersing in HCl solution for 0.8 to 1.2 hours.

3. The preparation method according to claim 2, characterized in that: The concentration of the HCl solution is 0.8 to 1.2 mol·L -1 The addition amount of carbonized material powder is 100-135g / L.

4. The preparation method according to claim 1, characterized in that: Step S4: Fe 3+ Fe in solution 3+ Concentration: 0.8~1.2mol·L -1 , the addition amount of the material after S3 treatment is 87~112g / L.

5. Iron-modified roxburghii biochar prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the iron-modified roxburghii biochar according to claim 5 in repairing selenium pollution in environmental media, fixing selenium in soil and / or passivating heavy metals in soil environment.

7. The use according to claim 6, characterized in that: The selenium pollution in the remediation environmental medium is Se(IV) in water; the heavy metals are Mn, Zn, Fe and / or Cu.

8. A method for repairing selenium-contaminated water, characterized in that: Add the iron-modified roxburghii biochar described in claim 5 to selenium-contaminated water for treatment; the amount of the biochar is 3.8-4.2 g / L; the adsorption equilibrium time is 30 min-24 h; the initial concentration of Se(IV) in the contaminated water is 1-100 mg / L.

9. A method for retaining selenium in soil, characterized in that: The iron-modified roxburghii biochar according to claim 5 is added to the target soil for treatment; the amount of the iron-modified roxburghii biochar is 1.8% to 2.0%.

10. A method for passivating heavy metals in composite contaminated soil, characterized in that: The iron-modified roxburghii biochar according to claim 5 is added to the target soil for treatment; the amount of the iron-modified roxburghii biochar is 2.0% to 2.2%.

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