Modified apple branch nano biochar as well as preparation method and application thereof

Abstract

The invention relates to the field of resource utilization of agricultural and forestry wastes, in particular to modified apple branch nano biochar as well as a preparation method and application thereof. The preparation method of the modified apple branch nano biochar comprises the following steps: drying and crushing apple branches to obtain apple branch particles; impregnating the apple branch particles in a modifier solution, and then drying to obtain modifier-loaded apple branch particles; pyrolyzing the modifier-loaded apple branch particles under the protection of an inert gas atmosphere to obtain modified apple branch biochar; freezing the modified apple branch biochar, and performing ball milling to obtain modified apple branch nano biochar with nano-scale particle size; the modified apple branch nano biochar has efficient nitrogen and / or phosphorus adsorption performance, and has multiple benefits of realizing waste resource utilization, improving soil structure, enhancing nutrient storage and preventing and controlling underground water pollution.

Description

Technical Field

[0001] The invention relates to the field of resource utilization of agricultural and forestry wastes, and in particular to a modified apple branch nano biochar and a preparation method and application thereof. Background Art

[0002] Nanobiochar is a good remediation material and is widely used in agriculture and the environment. Nanobiochar has a good adsorption effect on both nutrients and pollutants, and its adsorption capacity depends on the source of the material and the pyrolysis temperature. Studies have shown that the adsorption of ammonium nitrogen in water by nanobiochar prepared from rice straw as biomass raw material can reach twice that of the original biochar. The use of nanobiochar has a certain adsorption effect on ammonium nitrogen in the soil and can reduce the loss of ammonium nitrogen in the soil. The use of nanobiochar in slopes can reduce the leaching of effective phosphorus in the soil. The combined application of nanobiochar and alfalfa can reduce the leaching of effective phosphorus by 43.01% compared with the control. The interaction between nanobiochar and soil minerals significantly increases the adsorption of phosphorus, which is mainly attributed to the surface oxygen-containing functional groups of nanobiochar. However, the research on nanobiochar is still in its infancy, and its product characteristics and soil improvement effects still need to be systematically studied.

[0003] With the rapid development of the apple industry in Shaanxi, waste fruit tree branches are generated in the mass production of apples. The consumption of fruit tree branches in natural degradation and reuse is limited. At the same time, in order to increase apple production, environmental problems such as groundwater pollution caused by excessive nitrogen and phosphorus application have emerged. As a soil conditioner, biochar has a good application effect in carbon fixation and emission reduction, water and fertilizer conservation, and pollutant removal. As a plant material with high lignin content, apple branches have a high carbon yield, but the adsorption performance of the original product and the main biochar is poor, and it needs to be modified to improve its adsorption performance. Summary of the invention

[0004] The purpose of the present invention is to provide a modified apple branch nano-biochar and a preparation method and application thereof to solve the above-mentioned technical problems.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing modified apple branch nano-biochar, comprising the following steps:

[0007] After drying and crushing the apple branches, apple branch particles are obtained;

[0008] The apple branch particles are immersed in a modifier solution, and then dried to obtain the modifier-loaded apple branch particles;

[0009] Pyrolyzing the apple branch particles carrying the modifier under the protection of an inert gas atmosphere to obtain modified apple branch biochar;

[0010] The modified apple branch biochar is frozen and then ball-milled to obtain modified apple branch nano-biochar with a particle size of nanometers;

[0011] Wherein, the modifier solution is a KOH solution with a concentration of 0.28 to 0.32 g / mL, an AlCl3 solution with a concentration of 0.09 to 0.11 g / mL, or a MgCl2 solution with a concentration of 0.28 to 0.32 g / mL.

[0012] The present invention uses apple branches as raw materials to burn bulk biochar, and combines chemical modification (KOH, AlCl3, MgCl2 soaking) and physical modification (ball milling) to prepare nano biochar. The physicochemical properties of bulk biochar and nano biochar obtained by different chemical modifications, as well as the adsorption performance for ammonium nitrogen, nitrate nitrogen and phosphate are systematically compared, the structure-activity relationship between the modified preparation method and the size and properties of biochar is clarified, and a basis is provided for the directional preparation of nano biochar with target characteristics from apple branches.

[0013] Furthermore, the particle size of the apple branch particles is less than 1 mm.

[0014] Furthermore, the inert gas is N2.

[0015] Furthermore, when the modifier solution is a KOH solution with a concentration of 0.28 to 0.32 g / mL, the immersion time is 10 to 12 h, and when the modifier solution is an AlCl3 solution with a concentration of 0.09 to 0.11 g / mL or a MgCl2 solution with a concentration of 0.28 to 0.32 g / mL, the immersion time is 6 h.

[0016] Furthermore, the pyrolysis time is 1.5 to 2.5 hours, and the pyrolysis temperature is 550 to 560°C.

[0017] Furthermore, the freezing temperature is -80 to -75°C, and the freezing time is 22 to 24 hours.

[0018] Furthermore, the ball-to-powder ratio of the ball mill is 18-20:1, the rotation speed is 350-400 r / min, and the time is 2-3 h.

[0019] In a second aspect, the present invention provides modified apple branch nano-biochar prepared by the preparation method.

[0020] In a third aspect, the present invention provides the use of the modified apple branch nano-biochar in the adsorption of nitrogen and / or phosphorus.

[0021] In a fifth aspect, the present invention provides the use of the modified apple branch nano-biochar in improving soil structure, enhancing nutrient retention and / or preventing groundwater pollution.

[0022] 1. The present invention has advanced concepts and novel technologies. It uses apple branches as raw materials, which not only solves the problem of difficult treatment of discarded apple branches, but also realizes the resource utilization of solid waste in the rapid development of the apple industry, and also provides a new idea for resource utilization in other fields.

[0023] 2. The biochar prepared by the present invention is very different from traditional biochar. The pore structure of traditional biochar is underdeveloped and the surface adsorption characteristics are weak. Compared with the bulk biochar, the average diameter of the modified apple branch nano-biochar of the present invention is significantly reduced, the number of micropores is increased, and the specific surface area is significantly increased; the number of oxygen-containing functional groups on the surface is increased; the number of negative charges on the surface is increased, and the water stability is enhanced. It has a higher adsorption affinity for nutrient elements and pollutants including phosphorus in orchard groundwater and downstream water bodies.

[0024] 3. The preparation method of the present invention is low in cost, simple in operation, easy to control, and pollution-free. It has great application prospects and multiple benefits of realizing waste resource utilization, improving soil structure, enhancing nutrient conservation, and preventing groundwater pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the SEM and EDS images of modified apple branch nano-biochar, a is the SEM image of AB, b is the SEM image of MAB, c is the SEM image of K-MAB, d is the EDS image of K-MAB, e is the SEM image of 0.1Mg-MAB, f is the EDS image of 0.1Mg-MAB, g is the SEM image of 0.3Mg-MAB, h is the EDS image of 0.3Mg-MAB, i is the SEM image of 0.1Al-MAB, j is the EDS image of 0.1Al-MAB, k is the SEM image of 0.3Al-MAB, and l is the EDS image of 0.3Al-MAB.

[0026] Figure 2 This is the XRD pattern of modified apple branch nano-biochar.

[0027] Figure 3 Zeta potential of modified apple branch nanobiochar.

[0028] Figure 4 This is the FTIR spectrum of modified apple branch nanobiochar.

[0029] Figure 5 This is the adsorption effect of modified apple branch nano-biochar on different ions, a is ammonium nitrogen, b is nitrate nitrogen, and c is phosphate.

[0030] Figure 6 is the adsorption performance of K-MAB for ammonium nitrogen, a is the adsorption amount of ammonium nitrogen at different pH values, b is the adsorption kinetics diagram, c is the intra-particle diffusion model fitting diagram, d is the adsorption isotherm curve model fitting diagram based on the Langmuir model and the Freundlich model, and e is the adsorption isotherm curve model fitting diagram based on the Temkin model.

[0031] Figure 7 This is the desorption kinetics of K-MAB in KCl solution.

[0032] Figure 8 is the adsorption performance of 0.1Al-MAB for nitrate nitrogen, a is the adsorption amount of nitrate nitrogen at different pH values, b is the adsorption kinetics diagram, c is the intra-particle diffusion model fitting diagram, d is the adsorption isotherm curve model fitting diagram based on the Langmuir model and the Freundlich model, and e is the adsorption isotherm curve model fitting diagram based on the Temkin model and the Spis model.

[0033] Fig. 9 is the desorption capacity of 0.1Al-MAB in KCl solution.

[0034] Fig.10 is the adsorption performance of 0.3Mg-MAB for phosphate, a is the adsorption amount of phosphate at different pH values, b is the adsorption kinetics, c is the fitting diagram of the intra-particle diffusion model, d is the fitting diagram of the adsorption isotherm model based on the Langmuir model and the Freundlich model, and e is the fitting diagram of the adsorption isotherm model based on the Temkin model.

[0035] Fig.11 The desorption kinetics of phosphate by 0.3Mg-MAB in different solutions, a is KCl solution, b is citric acid solution.

[0036] Fig.12 SEM image of 0.3Mg-MAB saturated with phosphate.

[0037] Fig.13 The schematic diagram and actual picture of soil column leaching, a is the schematic diagram and b is the actual picture.

[0038] Fig.14 This is the effect of the addition of nano-biochar from modified apple branches on the properties of the leachate from the soil column test. a is the volume of the leachate, b is the total volume of the leachate, c is the pH of the leachate, d is the turbidity of the leachate, and e is the conductivity of the leachate.

[0039] Fig.15This is the effect of adding nano-biochar to modified apple branches on the nutrient leaching loss of the soil column test. a is the ammonium nitrogen leaching loss, b is the nitrate nitrogen leaching loss, c is the total nitrogen leaching loss, and d is the soluble nitrogen leaching loss.

[0040] Fig.16 This is the effect of leaching of nano-biochar suspension from modified apple branches on the physical and chemical properties of soil, a is the soil organic carbon content, b is the soil ammonium nitrogen content, and c is the soil nitrate nitrogen content.

[0041] Fig.17 This is the effect of adding nano-biochar from modified apple branches on the total phosphorus and available phosphorus contents in soil at different soil depths. a is the total phosphorus content in soil, and b is the available phosphorus content in soil. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0043] Example 1: Preparation and characterization of modified apple branch nanobiochar

[0044] 1. Experimental methods

[0045] (1) Preparation of modified apple branch nanobiochar

[0046] The preparation method of modified apple branch nano biochar in this example comprises the following steps:

[0047] Apple branches were collected at the Baishui Apple Experimental Station of Northwest Agriculture and Forestry University as raw materials for biochar burning. The apple branches were dried and crushed at 60°C and then passed through a 1mm sieve. Pyrolysis was performed under N2 atmosphere for 2h, and the preparation temperature was set to 550°C to obtain apple branch biochar, which was recorded as AB.

[0048] Before firing, the apple branch raw material was passed through a 1 mm sieve, immersed in a 0.3 g / mL KOH solution for 12 h, dried overnight, and then fired and pyrolyzed under the above conditions to obtain potassium-modified apple branch bulk biochar.

[0049] Before firing, the apple branches were immersed in 0.1 g / mL and 0.3 g / mL MgCl2 for 6 hours respectively. After drying, they were fired and pyrolyzed under the above conditions to obtain magnesium-modified apple branch biochar.

[0050] Before firing, the apple branches were immersed in 0.1 g / mL and 0.3 g / mL AlCl3 solutions for 6 hours respectively. After drying, they were fired and pyrolyzed under the above conditions to obtain aluminum-modified apple branch biochar.

[0051] Each bulk biochar was crushed through a 100 mesh sieve, frozen at -80 °C for 24 hours, and then ground at 350 r / min for 2 hours using a planetary ball mill (grinding ball diameters were 3, 5, and 8 mm, and the ball-to-powder ratio was 20:1) to obtain ball-milled biochar. Ball-milled apple branch bulk biochar, ball-milled potassium-modified apple branch biochar, ball-milled magnesium-modified apple branch biochar, and ball-milled aluminum-modified apple branch biochar were recorded as MAB, K-MAB, 0.1Mg-MAB, 0.3Mg-MAB, 0.1Al-MAB, and 0.3Al-MAB, respectively. A total of 1 bulk biochar and 6 modified apple branch nano-biochars were obtained. The yield of bulk biochar and modified apple branch nano-biochar is the ratio of the final biochar product mass to the original apple branch mass.

[0052] (2) Characterization of modified apple branch nanobiochar

[0053] The morphology of biochar was determined by high-definition transmission electron microscopy (SEM), and the types and contents of surface elements were tested by energy dispersive X-ray spectrometer (EDS). The test mode was secondary electrons, and the position of the dot energy spectrum was 1 μm. The diameter distribution of biochar was determined by dynamic light scattering (DLS). The colloid concentration of biochar suspension was 0.25 g / L, the supporting electrolyte was 0.1 mmol / L NaCl solution, and the particle diameter was intensity-weighted diameter. The pH value of biochar was determined by pH meter, and the solid-liquid ratio was 1:20. The C, H, N, S and O element contents of biochar were determined by elemental analyzer (EA). The specific surface area and total pore size of biochar were determined by fully automatic specific surface area and porosity analyzer. The mineral components of biochar were determined by X-ray diffractometer (XRD). The surface functional groups were determined by Fourier transform infrared spectrometer (FTIR). The potential was measured using a high-sensitivity zeta potential analyzer. The biochar suspension colloid was 0.25 g / L, the supporting electrolyte was 0.1 mmol / L NaCl solution, and the biochar zeta potential was measured at pH 3-11. The specific results are shown in the figure. Figure 1-Figure 4 shown.

[0054] 2. Experimental results

[0055] Seven types of biochar were prepared from apple branches by physical (ball milling) and chemical modification (soaking in potassium, magnesium, and aluminum salt solutions). They were apple branch bulk biochar (AB) directly fired at 550°C, ball milled biochar (MAB), ball milled potassium-modified biochar (K-MAB), ball milled magnesium-modified biochar (0.1Mg-MAB and 0.3Mg-MAB), and ball milled aluminum-modified biochar (0.1Al-MAB and 0.3Al-MAB). Dynamic light scattering analysis showed that the average diameter of the modified biochars was 152-438nm. Compared with AB, MAB had more small and medium particles. A large number of long flocculent structures were observed on the surface and pores of Mg-MAB, and the surface of 0.3Al-MAB was rough. Compared with bulk biochar, the carbon content of the modified nano-biochar was reduced, while the oxygen content was increased. AB and MAB are rich in calcium carbonate, K-MAB contains potassium-rich carbonate and potassium chloride, 0.3Al-MAB generates amorphous aluminum hydroxide, and Mg exists in the form of nitrate, oxide and hydroxide in Mg-MAB. Zeta potential analysis shows that AB, MAB and K-MAB are negatively charged, and the charge zero points of 0.1Mg-MAB, 0.3Mg-MAB, 0.1Al-MAB and 0.3Al-MAB are 4.0, 5.7, 9.2 and 9.0, respectively. The above results show that the newly generated positively charged minerals in the modification process reduce the negative charge on the surface of Mg-MAB and Al-MAB, and the reduction effect of aluminum modification is stronger than that of magnesium modification.

[0056] Example 2: Adsorption performance of modified apple branch nano-biochar on ammonium nitrogen, nitrate nitrogen and phosphate

[0057] 1. Experimental methods

[0058] Preliminary adsorption effect determination:

[0059] The batch balance method was used to determine the adsorption capacity of phosphate by different nano-biochars.

[0060] Effects of environmental conditions on the adsorption performance of different nano-biochars:

[0061] (1) Effect of pH

[0062] The initial concentration of phosphate ions was set to 1000 mg / L. At 25 °C, the pH of the phosphate solution was adjusted to 5, 6, 7, 8, 9, and 10 with 0.01 mol / L NaOH or HCl solution, 100 mg of nano-biochar was added, and the adsorption amount was calculated after reacting in a shaker at 210 r / min for 12 h.

[0063] (2) Adsorption kinetics

[0064] At 25°C, the initial concentration of phosphate ions was set to 1000 mg / L, and the initial pH of the phosphate solution was set to 7, and a batch adsorption test was performed. Samples were taken at the 1st, 5th, 10th, 30th, 60th, 90th, 120th, 150th, 180th, 240th, 300th, 360th, 420th, 480th, 540th, 600th, 660th, and 720th minutes of reaction time to obtain the reaction equilibrium time and calculate the adsorption amount. The pseudo-first-order kinetic model, pseudo-second-order kinetic model, and intraparticle diffusion model were used to fit and analyze the obtained data.

[0065] (3) Adsorption isotherm

[0066] At 25°C, the initial concentrations of phosphate ions were set to 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, and 100 mg / L, respectively. The initial pH of the phosphate solution was 7, and the adsorption amount was measured at a reaction equilibrium time of 12 h. The Langmuir model, Freundlich model, and Temkin model were used to fit and analyze the adsorption phosphate data.

[0067] (4) Adsorption thermodynamics

[0068] When the reaction temperatures were 25°C, 35°C, and 45°C, the initial pH of the phosphate solution was 7, and the adsorption amount was measured at a reaction equilibrium time of 12 h.

[0069] (5) Desorption characteristics

[0070] 1) Desorption of ammonium nitrogen and nitrate nitrogen

[0071] First, biochar saturated with ammonium nitrogen and nitrate nitrogen was obtained. The experimental conditions were set as follows: the reaction temperature was set at 25°C, 50 mg of K-MAB was weighed each time and added to an ammonium nitrogen solution with a volume of 100 mL, a pH of 10, and an initial concentration of ammonium nitrogen ions of 50 mg / L, and the adsorption time was 12 hours to obtain biochar saturated with ammonium nitrogen adsorption. 50 mg of 0.1Al-MAB was weighed each time and adsorbed in a nitrate nitrogen solution with a volume of 100 mL, a pH of 5, and an initial concentration of nitrate nitrogen ions of 50 mg / L for 12 hours to obtain biochar saturated with nitrate nitrogen adsorption.

[0072] The saturated adsorption suspension was centrifuged at 3500r / min for 20min, and the supernatant was filtered through 0.22μm filter paper. The precipitate was rinsed three times with anhydrous ethanol and dried. 100mL of 0.01mol / L KCl solution was added. The pH of the saturated biochar suspension adsorbed by ammonium nitrogen was adjusted to 10, and the pH of the saturated biochar suspension adsorbed by nitrate nitrogen was adjusted to 5. Samples were taken at different time points (5min, 10min, 30min, 60min, 90min, 120min, 240min, 360min, 480min, 720min), and the desorption of ammonium nitrogen and nitrate nitrogen by K-MAB and 0.1Al-MAB in KCl solution after saturated adsorption was calculated.

[0073] 2) Phosphate desorption

[0074] 50mg 0.3Mg-MAB was adsorbed in a phosphate solution with a volume of 100mL and an initial phosphate concentration of 1000mg / L at a pH of 7 for 12h to make the biochar reach a saturated adsorption state. The saturated adsorption suspension was centrifuged at 3500r / min for 20min, and the supernatant was filtered through a 0.22μm filter paper. The precipitate was washed three times with anhydrous ethanol and dried. Two parallel tests were performed. 100mL 0.01mol / L KCl solution was added to parallel 1 to adjust the pH to 7. 100mL 0.01mol / L citric acid solution was added to parallel 2 to adjust the pH to 7. The parallel groups were sampled at different time points (5min, 10min, 30min, 60min, 90min, 120min, 240min, 360min, 480min, 720min), and the desorption of phosphate by 0.3Mg-MAB in KCl solution and citric acid solution after saturated adsorption was calculated.

[0075] 2. Experimental results

[0076] The results are as follows Figure 5-Figure 12 As shown, the results show that:

[0077] (1) K-MAB has the strongest adsorption capacity for ammonium nitrogen. The adsorption of ammonium nitrogen by K-MAB increases with the increase of pH value and temperature; at pH = 10 and 298K, the maximum adsorption of ammonium nitrogen by K-MAB is 9.24 mg / g. The fitting results of adsorption kinetics and adsorption isotherm model show that ammonium nitrogen on the K-MAB surface is a non-uniform multilayer adsorption dominated by electrostatic adsorption and chemical adsorption.

[0078] (2) The adsorption of nitrate nitrogen by 0.1Al-MAB decreases with the increase of solution pH. At 298K, the maximum adsorption of nitrate nitrogen by 0.1Al-MAB is 43.70 mg / g. The fitting results of adsorption kinetics and adsorption isotherm model show that the adsorption of nitrate nitrogen on the surface of 0.1Al-MAB is mainly single-molecule adsorption dominated by chemical action.

[0079] (3) 0.3Mg-MAB exhibited the highest phosphate adsorption capacity, and its adsorption capacity first increased and then decreased with the increase of pH. The maximum adsorption capacity of phosphate by 0.3Mg-MAB was as high as 349.29 mg / g at pH = 7 and 298 K, which was mainly monolayer adsorption dominated by chemical adsorption precipitation and was also regulated by electrostatic adsorption.

[0080] Example 3: Soil column leaching test

[0081] 1. Experimental methods

[0082] The soil column leaching test was used to simulate the effect of nano-biochar on phosphorus control. Fig.13 As shown, the outer shell is a PVC pipe with a height of 1m and an inner diameter of 10cm. The soil column is filled in layers, and each layer of the soil column is compacted evenly. The soil layer is filled according to the actual bulk density in the field. When filling the soil column, apply vaseline on the inner wall to increase the density of the soil and prevent the leaching solution from flowing down the wall during leaching. Starting from the top, from top to bottom, there are 8cm quartz sand at the top, 80cm soil in the middle, and 7cm quartz sand at the bottom. The top 8cm quartz sand is 5cm coarse sand and 3cm fine sand from top to bottom, and the 80cm soil is the soil of the 0-20cm, 20-40cm, 40-60cm and 60-80cm soil layers at the sampling points from top to bottom. The 7cm quartz sand at the bottom is 2cm fine sand and 5cm coarse sand from top to bottom. The role of coarse sand is to make the water distribution uniform. In addition to making the water distribution uniform, the role of fine sand can also effectively prevent the soil from entering the coarse sand during leaching, causing soil disturbance. The top of the soil column is sealed with plastic wrap to prevent water evaporation. The top of the soil column is about 1.3g / cm 3 The soil is loaded into the soil column with a bulk density of 2.56 kg. A sampling port is set at the bottom of the soil column to extract the naturally flowing leachate.

[0083] Add 4.73g potassium dihydrogen phosphate to the 0-20cm soil layer and mix well, which is equivalent to applying 402kg / hm 2Potassium dihydrogen phosphate fertilizer. 0.3Mg-MAB was applied to the soil column to store phosphorus fertilizer in the area with the highest root distribution density. Apple branch nano-biochar was added and mixed at the 0-20cm soil layer. A total of 5 treatments were set up, including CK (no biochar), 1% biochar (20.41g), 3% biochar (61.23g), 5% biochar (102.05g) and 10% biochar (204.10g).

[0084] Before the leaching test, distilled water was added from the bottom with a peristaltic pump in batches to saturate the soil column. After stabilization for 3 days, the soil was ensured to be in a relatively stable environment. Before sampling each leaching test, 150 mL (equivalent to 20 mm rainfall) of distilled water was added from the top of each soil column at a uniform speed to simulate leaching. From the 1st to the 13th day of the test, leaching was carried out every 3 days and the naturally flowing leaching liquid was collected from the soil column, which was carried out on the 1st, 4th, 7th, 10th, and 13th days, for a total of 5 times; from the following 14th to 41st days, sampling was carried out every 7 days, on the 20th, 27th, 34th, and 41st days, for a total of 4 times; from 42th to 61st days, sampling was carried out once every 10 days, on the 51st and 61st days, for a total of 2 times. A total of 11 samples were collected for the leaching test. All sampling ports were kept closed when no sampling was performed.

[0085] After the leachate is collected, it is placed in a 4°C refrigerator for testing. First, the volume of the leachate is measured with a measuring cylinder, and then the turbidity is measured with a turbidimeter (GB13200-1991), the unit is scattered turbidity (NTU). The higher the NTU value, the more turbid the leachate. At the same time, the pH, conductivity and total phosphorus content of the leachate are measured. After the leaching is completed, the soil column is dismantled, and the soil of each treatment layer is taken out and air-dried. The basic physical and chemical properties of the soil, including total phosphorus and available phosphorus in the soil, are measured, and the nutrient distribution of the profile is analyzed.

[0086] 2. Experimental results

[0087] The results are as follows Figure 14-17 As shown in the figure, after adding 0.3Mg-MAB to the orchard soil, the volume of the leachate decreased, the turbidity increased, and the conductivity decreased. This is because the biochar is loose and porous, which improves the soil's water holding capacity. The biochar ash and small particles of biochar are leached out with the leachate, which increases the turbidity. In the 20-40cm soil, the addition of biochar has a certain inhibitory effect on soil nitrification. Biochar has a good storage effect on soil phosphorus. The total phosphorus content of the leachate was not detected using a flow analyzer and molybdenum antimony anti-spectrophotometry. In the 20-40cm soil, the effective phosphorus content was the highest when 3% biochar was added. Considering the soil nutrient content of each soil layer, adding 3% biochar to the orchard soil has the best effect.

[0088] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0089] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing modified apple branch nano-biochar, characterized in that: The following steps are involved: After drying and crushing the apple branches, apple branch particles are obtained; The apple branch particles are immersed in a modifier solution, and then dried to obtain the modifier-loaded apple branch particles; Pyrolyzing the apple branch particles carrying the modifier under the protection of an inert gas atmosphere to obtain modified apple branch biochar; The modified apple branch biochar is frozen and then ball-milled to obtain modified apple branch nano-biochar with a particle size of nanometers; Wherein, the modifier solution is a KOH solution with a concentration of 0.28 to 0.32 g / mL, an AlCl3 solution with a concentration of 0.09 to 0.11 g / mL, or a MgCl2 solution with a concentration of 0.28 to 0.32 g / mL.

2. The preparation method according to claim 1, characterized in that: The particle size of the apple branch particles is less than 1 mm.

3. The preparation method according to claim 1, characterized in that: The inert gas is N2.

4. The preparation method according to claim 1, characterized in that: When the modifier solution is a KOH solution with a concentration of 0.28 to 0.32 g / mL, the immersion time is 10 to 12 hours. When the modifier solution is an AlCl3 solution with a concentration of 0.09 to 0.11 g / mL or a MgCl2 solution with a concentration of 0.28 to 0.32 g / mL, the immersion time is 6 hours.

5. The preparation method according to claim 1, characterized in that: The pyrolysis time is 1.5 to 2.5 hours, and the pyrolysis temperature is 550 to 560°C.

6. The preparation method according to claim 1, characterized in that: The freezing temperature is -80 to -75°C and the freezing time is 22 to 24 hours.

7. The preparation method according to claim 1, characterized in that: The ball-to-powder ratio of the ball mill is 18-20:1, the rotation speed is 350-400 r / min, and the time is 2-3 h.

8. Modified apple branch nano-biochar prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the modified apple branch nano-biochar according to claim 8 in the adsorption of nitrogen and / or phosphorus.

10. Use of the modified apple branch nano-biochar according to claim 8 in improving soil structure, enhancing nutrient retention and / or preventing groundwater pollution.

Images