Preparation method of lanthanum oxide modified biochar fertilizer

Abstract

The invention provides a preparation method of a lanthanum oxide modified biochar fertilizer, which belongs to the technical field of agricultural fertilizers. The method comprises the following steps: 1. microwave activation of biochar: placing corn straw biochar in a microwave reactor for radiation to obtain porous activated biochar; 2. potassium ion loading: immersing the porous activated biochar in a saturated KOH solution to obtain a solid precipitate, drying the solid precipitate, and preparing potassium-loaded biochar; 3. preparation of a lanthanum-organic complex: mixing lanthanum oxide with citric acid, adding deionized water to form a suspension, and evaporating and crystallizing the suspension to obtain a lanthanum-citric acid complex; 4. modified biochar compounding: mixing the obtained lanthanum-citric acid complex with potassium-loaded biochar to obtain slow-release lanthanum oxide modified biochar; and 5. phosphate fertilizer compounding to obtain a slow-release composite biochar fertilizer. According to the invention, the biochar is modified by lanthanum oxide so that the modified biochar has a larger specific surface area, better improves the problem of saline-alkali soil compaction, and improves the oxygen content of the soil.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural fertilizers, and specifically relates to a method for preparing lanthanum oxide-modified biochar fertilizer. Background Art

[0002] Rare earth elements, as a strategic resource, are highly valued worldwide. They are particularly widely used in agriculture, particularly in improving saline-alkali soils. Lanthanum, at low concentrations, promotes the growth of soil microorganisms (such as bacteria and actinomycetes), potentially enhancing organic matter decomposition and nutrient cycling. This process helps increase soil organic matter content, indirectly improving the aggregate structure of saline-alkali soils, enhancing permeability, and accelerating salt leaching. Lanthanum oxide can chemically react with soil components to promote the cohesion of soil particles, increasing soil aggregation and improving soil structure. This helps alleviate soil compaction and improves soil aeration and water permeability.

[0003] Soil salinization is a global ecological problem, affecting nearly 932 million hectares of land worldwide. my country's saline-alkali land area ranks third in the world, accounting for 10% of the global saline-alkali land area. Soil salinization has become a major obstacle to the efficient use of national land resources, sustainable agricultural development, and ecological and environmental quality. Salinized soils have high soluble salt ion content, leading to poor aggregate stability, manifested as soil compaction and poor water retention. Saline-alkali environments are often accompanied by reduced nutrient availability. Salt inhibits plant absorption of nutrients, and high pH environments produce alkaline stress, affecting plant cell stability and causing physiological and metabolic disturbances.

[0004] As an effective soil conditioner, biochar can improve the structure of saline-alkali land through its unique physical and chemical properties. The rare earth fertilizer obtained by modifying biochar with lanthanum oxide can effectively improve the germination rate of saline-alkali soil, which is helpful for the growth of crops. It can also change the form and content of heavy metals in the soil.

[0005] In the existing technology, biochar is mostly used directly for water adsorption, and is rarely used in saline-alkali land. At the same time, most of the existing lanthanum fertilizers use lanthanum nitrate. However, the nitrate ion of lanthanum nitrate can easily cause eutrophication of the land and quickly release lanthanum elements. It is only suitable for quickly supplementing lanthanum and cannot provide nutrients to the land for a long time. Summary of the Invention

[0006] Based on the existing modified biochar technology, the present invention invents a slow-release composite biochar fertilizer. An appropriate amount of lanthanum oxide can promote the growth and development of plant roots, leaves, and stems, enhance the plant's ability to absorb nutrients, thereby improving the plant's resistance to lodging, helping plants grow better in saline-alkali soil, improving the agglomeration phenomenon of saline-alkali soil, and achieving the purpose of improving salinized soil.

[0007] The details are as follows:

[0008] A method for preparing lanthanum oxide modified biochar fertilizer, characterized by comprising the following steps:

[0009] (1) Microwave activated biochar: Place corn straw biochar in a microwave reactor and irradiate it at a power of 200-300W for 2-5 minutes to obtain porous activated biochar;

[0010] (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 4-6 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 80-105°C to constant weight to obtain potassium-loaded biochar;

[0011] (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 50-70 ° C for 1.5-2.5 h, and evaporated and crystallized to obtain lanthanum-citric acid complex;

[0012] (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:4.5-5.5, and humic acid was added at 1-2% of the mass of the biochar to simultaneously improve soil agglomeration. The mixture was magnetically stirred at 400-600 r / min for 25-35 min to obtain a slow-release lanthanum oxide modified biochar;

[0013] (5) Compounding of phosphate fertilizer: The slow-release lanthanum oxide-modified biochar obtained in step (4) is mixed with monoammonium phosphate or diammonium hydrogen phosphate in a mass ratio of 4.5-5.5:1, and magnetically stirred at 400-600 r / min for 8-12 min to obtain a slow-release composite biochar fertilizer.

[0014] Furthermore, a method for preparing lanthanum oxide modified biochar fertilizer comprises the following steps:

[0015] (1) Microwave activated biochar: Place corn straw biochar in a microwave reactor and irradiate it at a power of 200-300W for 2-5 minutes to obtain porous activated biochar;

[0016] (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 5 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 80-105°C to constant weight to obtain potassium-loaded biochar;

[0017] (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 50-70 ° C for 2 h, and evaporated and crystallized to obtain lanthanum-citric acid complex;

[0018] (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:5, and then humic acid was added at 1.5% of the mass of the biochar, and magnetic stirring was carried out at 500 r / min for 25-35 min to obtain a slow-release lanthanum oxide modified biochar;

[0019] (5) Phosphate fertilizer compounding: The slow-release lanthanum oxide modified biochar obtained in step (4) was mixed with monoammonium phosphate or diammonium hydrogen phosphate in a mass ratio of 5:1, and magnetically stirred at 500 r / min for 10 min to obtain a slow-release composite biochar fertilizer.

[0020] Moreover, during the microwave activation process in step (1), the moisture content of the biochar is controlled at 5-10%.

[0021] Furthermore, in step (2), 90-110 ml of KOH solution was added per 10 g of porous activated biochar.

[0022] Moreover, in step (3), during the preparation of the lanthanum-citric acid complex, the evaporation crystallization temperature is 80° C., and the crystallized product is ground to a particle size of ≤50 μm.

[0023] At the same time, the present invention provides a slow-release composite biochar fertilizer prepared by the above method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention optimizes the pore structure of biochar through microwave activation, providing a high-specific-surface-area carrier for loading. KOH solution impregnation is then used to efficiently load potassium, which neutralizes soil acidity, promotes nutrient absorption, and enhances the cation exchange capacity of the biochar.

[0026] 2. The present invention uses lanthanum oxide as the source of lanthanum element, and prepares a lanthanum-citrate complex with citric acid to avoid nitrate contamination, effectively solving the problem that traditional lanthanum nitrate is prone to eutrophication, achieving a slow-release supply of lanthanum element, and also avoiding soil agglomeration.

[0027] 3. Compared with lanthanum nitrate fertilizer, the present invention modifies biochar by lanthanum oxide, so that the modified biochar has a larger specific surface area, better improves the problem of saline-alkali soil compaction, and increases the oxygen content of the soil. At the same time, the slow-release composite biochar fertilizer not only has a certain promoting effect on the germination rate of crops and the growth of roots, stems and leaves, increases the lodging resistance of crops, and promotes the absorption of nitrogen and phosphorus in the soil by crops, but also can selectively adsorb Na+ ions in saline-alkali soil, improve the alkaline environment of saline-alkali soil, reduce soil pH, and reduce the heavy metal content in the soil, thereby obtaining a new rare earth fertilizer for saline-alkali soil.

[0028] 4. The slow-release composite biochar fertilizer provided by the present invention compounds the lanthanum-citric acid complex with potassium-loaded biochar in a mass ratio of 1:5, and adds humic acid, monoammonium phosphate or diammonium hydrogen phosphate to achieve potassium-lanthanum-phosphorus synergistic modification of saline-alkali soil, thereby enhancing agglomeration and nutrient supply.

[0029] 5. The present invention provides a slow-release composite biochar fertilizer for the research and application of saline-alkali soil. The preparation method of the new rare earth fertilizer for saline-alkali soil is simple, the investment cost is low, and it has a good effect in the actual crop growth application in saline-alkali soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an electron microscope scan of the soil around the roots of the water control group;

[0031] Figure 2 This is an electron microscope scan of the soil around the root system of Example 3;

[0032] Figure 3 XRD patterns of pure biochar, KOH biochar compound fertilizer and slow-release compound biochar;

[0033] Figure 4 The growth conditions of alfalfa in each group;

[0034] Figure 5 is the chlorophyll content in the soil;

[0035] Figure 6 Scanning electron microscope energy spectrum analysis was performed on the water control group and the soil of Example 3 group;

[0036] Figure 7 The adsorption-desorption curve and pore size distribution diagram of the soil in the water control group;

[0037] Figure 8 The adsorption-desorption curve and pore size distribution diagram of the soil in Example 3;

[0038] Figure 9 This is the thermogravimetric analysis diagram of biochar and the slow-release composite biochar prepared in Example 3. DETAILED DESCRIPTION

[0039] Example 1

[0040] A method for preparing lanthanum oxide modified biochar fertilizer comprises the following steps:

[0041] (1) Microwave activated biochar: corn straw biochar was placed in a microwave reactor and irradiated at a power of 200 W for 2 minutes to obtain porous activated biochar;

[0042] (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 4 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 80°C to constant weight to obtain potassium-loaded biochar;

[0043] (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 50 °C for 1.5 h, and evaporated and crystallized to obtain lanthanum-citric acid complex;

[0044] (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:4.5, and then humic acid was added at 1% of the mass of the biochar, and magnetic stirring was carried out at 400 r / min for 25 min to obtain a slow-release lanthanum oxide modified biochar;

[0045] (5) Phosphate fertilizer compounding: The slow-release lanthanum oxide modified biochar obtained in step (4) was mixed with monoammonium phosphate or diammonium hydrogen phosphate at a mass ratio of 4.5:1, and magnetically stirred at 400 r / min for 8 min to obtain a slow-release composite biochar fertilizer.

[0046] Furthermore, during the microwave activation process in step (1), the moisture content of the biochar is controlled at 5%.

[0047] Furthermore, in step (2), 90 ml of KOH solution was added to every 10 g of porous activated biochar.

[0048] Furthermore, in step (3), during the preparation of the lanthanum-citric acid complex, the evaporation crystallization temperature is 80° C., and the crystallized product is ground to a particle size of ≤50 μm.

[0049] Furthermore, in step (4), humic acid is added in an amount of 1-2% by mass of the biochar during the mixing process.

[0050] Example 2

[0051] A method for preparing lanthanum oxide modified biochar fertilizer comprises the following steps:

[0052] (1) Microwave activated biochar: corn straw biochar was placed in a microwave reactor and irradiated at a power of 300 W for 5 minutes to obtain porous activated biochar;

[0053] (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 6 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 105°C to constant weight to obtain potassium-loaded biochar;

[0054] (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 70 °C for 2.5 h, and evaporated and crystallized to obtain lanthanum-citric acid complex;

[0055] (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:5.5, and then humic acid was added at 2% of the mass of the biochar, and magnetic stirring was carried out at 600 r / min for 5 min to obtain a slow-release lanthanum oxide modified biochar;

[0056] (5) Phosphate fertilizer compounding: The slow-release lanthanum oxide modified biochar obtained in step (4) was mixed with monoammonium phosphate or diammonium hydrogen phosphate at a mass ratio of 5.5:1, and magnetically stirred at 600 r / min for 12 min to obtain a slow-release composite biochar fertilizer.

[0057] Furthermore, during the microwave activation process in step (1), the moisture content of the biochar is controlled at 10%.

[0058] Furthermore, in step (2), 110 ml of KOH solution was added to every 10 g of porous activated biochar.

[0059] Furthermore, in step (3), during the preparation of the lanthanum-citric acid complex, the evaporation crystallization temperature is 80° C., and the crystallized product is ground to a particle size of ≤50 μm.

[0060] Furthermore, in step (4), humic acid is added in an amount of 1-2% by mass of the biochar during the mixing process.

[0061] Example 3

[0062] A method for preparing lanthanum oxide modified biochar fertilizer comprises the following steps:

[0063] (1) Microwave activated biochar: corn straw biochar was placed in a microwave reactor and irradiated at a power of 250 W for 3 minutes to obtain porous activated biochar;

[0064] (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 5 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 90°C to constant weight to obtain potassium-loaded biochar;

[0065] (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 60 °C for 2 h, and evaporated and crystallized to obtain lanthanum-citric acid complex;

[0066] (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:5, and then humic acid was added at 1-2% of the mass of the biochar, and magnetic stirring was carried out at 500 r / min for 30 min to obtain a slow-release lanthanum oxide modified biochar;

[0067] (5) Phosphate fertilizer compounding: The slow-release lanthanum oxide-modified biochar obtained in step (4) was mixed with diammonium hydrogen phosphate in a mass ratio of 5:1, and magnetically stirred at 500 r / min for 10 min to obtain a slow-release composite biochar fertilizer.

[0068] Moreover, during the microwave activation process in step (1), the moisture content of the biochar is controlled at 8%.

[0069] Moreover, in step (2), 100 ml of KOH solution was added per 10 g of porous activated biochar.

[0070] Moreover, in step (3), during the preparation of the lanthanum-citric acid complex, the evaporation crystallization temperature is 80° C., and the crystallized product is ground to a particle size of ≤50 μm.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 3 is that step (1) of microwave activation of biochar to prepare the slow-release compound fertilizer is not performed.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 3 is that step (3) of preparing the lanthanum-organic complex is not performed, and step (4) is performed directly using lanthanum oxide: lanthanum oxide and potassium-loaded biochar are mixed in a mass ratio of 1:5, and magnetic stirring is performed at 500 r / min for 30 min to prepare a slow-release compound fertilizer.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 3 is that lanthanum oxide is replaced by lanthanum nitrate to prepare compound fertilizer.

[0077] Comparative Example 4

[0078] The difference between this comparative example and Example 3 is that steps (3) and (4) are not performed, and the potassium-loaded biochar is directly compounded with the phosphate fertilizer to prepare the KOH biochar compound fertilizer.

[0079] Comparative Example 5

[0080] The difference between this comparative example and Example 3 is that step (2) is not performed, and the porous activated biochar is directly compounded with the lanthanum-organic complex to prepare a slow-release compound fertilizer.

[0081] Experimental part

[0082] Alfalfa seeds were planted in the same soil at the same time, and the fertilizers of Example 3 and Comparative Examples 1-5 were applied respectively. A water control group was also provided.

[0083] Experiment 1

[0084] After one week, the seed germination rates of the six fertilizers and the clear water control group were statistically analyzed, as shown in Table 1. As can be seen from Table 1, Example 3 had the best effect: Example 3 had the highest germination rate, reaching 85.6%, significantly higher than the other comparative examples and the clear water control group, indicating that the slow-release composite biochar fertilizer preparation method prepared by the present invention can most effectively promote the germination of alfalfa seeds. Comparative Example 1 did not perform the microwave activation biochar step, and its germination rate was lower than that of Example 3. This is because microwave activation of biochar helps increase the porosity and surface area of ​​biochar, thereby better loading and releasing nutrients. Comparative Example 2 did not perform lanthanum-organic complex preparation and directly used lanthanum oxide. Its germination rate was also lower than that of Example 3, indicating that forming a complex with citric acid helps to improve the slow-release effect and bioavailability of the fertilizer. Comparative Example 3 replaced lanthanum oxide with lanthanum nitrate, and its germination rate was lower than that of Example 3, indicating that lanthanum oxide is more effective than lanthanum nitrate in promoting seed germination as a modifier. Comparative Example 4, in which potassium-loaded biochar was directly compounded with phosphate fertilizer without the lanthanum-organic complex preparation and modified biochar compounding steps, yielded a lower germination rate. This suggests that the synergistic effects of loading, lanthanum modification, and phosphate fertilizer compounding significantly enhance fertilizer effectiveness. Comparative Example 5, in which porous activated biochar was directly compounded with the lanthanum-organic complex without the potassium ion loading step, also yielded a lower germination rate than Example 3, demonstrating that potassium ion loading enhances the biochar's nutrient retention and slow-release properties.

[0085] Table 1 Comparison of germination rates of alfalfa seeds in 6 fertilizers and water

[0086]

[0087] Experiment 2

[0088] Two weeks later, the soil around the roots of the water control group and Example 3 group was scanned by electron microscope. Figure 1-2 As can be seen from the figure, compared with the water control group, the soil material morphology after adding slow-release compound biochar fertilizer is loose, porous and rich in impurities, while the soil material morphology without slow-release compound biochar fertilizer is compacted, effectively improving the original soil compaction, thereby improving the saline-alkali soil. The soil surface of the water control group is flat and smooth, with a small pore structure. After adding slow-release compound biochar fertilizer, the soil surface becomes unusually rough, with a large number of irregular particles of different sizes. Compared with the original state, the surface pores of the modified biochar are significantly increased.

[0089] The two groups of soil were further analyzed by scanning electron microscope energy spectrum. The results are shown in Figure 6 After applying slow-release compound biochar fertilizer, the soil removes heavy metal aluminum. Aluminum inhibits the growth and development of plant roots. It mainly acts on the root tip, hindering the elongation and division of cells, making the roots shorter and thicker, and reducing the number of root hairs, thereby affecting the plant's absorption of water and nutrients.

[0090] Experiment 3

[0091] The BET (Between-Emitting Diode) surface area (BET) is a core parameter for characterizing a material's surface properties. Defined as the total surface area per unit mass or volume (unit: m² / g), it comprehensively reflects a material's pore structure, active site distribution, and surface physicochemical properties. Its value directly influences a material's adsorption capacity, catalytic activity, and electrochemical performance, making it a key indicator in materials science and industrial applications. Figure 7 The adsorption-desorption curve and pore size distribution diagram of the soil in the clear water control group in Experiment 2. Figure 8 The adsorption-desorption curves and pore size distribution diagrams of the soil of Example 3 in Experiment 2 are shown in Table 2. The specific surface areas and pore structures of the two groups of samples are shown in Table 2.

[0092] Table 2 Specific surface area and pore structure of samples

[0093]

[0094] By comparison Figure 7 and 8 It can be seen from the adsorption-desorption curve that in the low relative pressure (P / P0) region (about 0-0.2), the adsorption amount increases slowly, indicating that it is mainly monolayer molecular adsorption at this time. As the relative pressure increases, the adsorption amount gradually increases. In the high relative pressure region (0.8-1.0), the adsorption amount rises rapidly, indicating the presence of capillary condensation. There are a certain amount of mesopores and macropore structures in the soil of Example 3. The adsorption curve and desorption curve have obvious hysteresis loops in the high relative pressure region, which is a typical feature of mesoporous materials, indicating that the soil of Example 3 has more mesoporous structures. The adsorption-desorption curve of the clear water control group also increases slowly in the low relative pressure region, which is the monolayer adsorption stage. In the entire relative pressure range, the adsorption amount is generally low. Although the adsorption amount also rises rapidly in the high relative pressure region, the amplitude is smaller than that of Example 3, and the hysteresis loop is relatively small, indicating that the mesoporous structure of the clear water control group may be relatively small.

[0095] contrast Figure 7 and 8From the pore size distribution diagram, it can be seen that the pore size distribution of the clear water control group shows an obvious peak in the smaller pore size region (close to 0nm), indicating that the soil of the clear water control group has a large number of pore structures with smaller pore sizes, which may be micropores or small mesopores. As the pore size increases, the pore volume decreases rapidly, and the overall pore size distribution is relatively concentrated in the smaller pore size range, indicating that the pore structure of the soil of the clear water control group is mainly small pore size. The pore size of the soil in Example 3 group is the largest in the range of 0-25nm, and the pore size distribution is relatively dispersed thereafter, with peaks appearing in multiple pore size ranges. Unlike the clear water control group, there is no single obvious main peak at the small pore size, indicating that the pore structure of the soil in Example 3 group is more complex and diverse, and the pore size distribution is wider. Combined with the morphological analysis of the scanning electron microscope, since the addition of rare earth lanthanum changes the original pore structure of the soil, the soil with the amendment is more loose and porous than the soil without the amendment, which is more conducive to the growth of alfalfa, increases the air permeability of the soil, and improves the compaction problem of saline-alkali soil.

[0096] Depend on Figure 7 and 8 It can be seen that the adsorption-desorption isotherms are all type IV, indicating that the biochar has significant mesoporous properties. Table 2 shows that the average pore diameters of the water control group and Example 3 group are 15.004nm and 17.133nm respectively, while the average pore diameter of the mesoporous material is 2-50nm, which once again verifies that Example 3 group is a mesoporous adsorption material. The specific surface area of ​​Example 3 group is much higher than that of the water control group, from 0.282m 2 / g increased to 3.393 m2 / g, which was due to the loading of metallic La making the biochar surface rough, thereby increasing the specific surface area, which was consistent with the SEM analysis results.

[0097] Experiment 4

[0098] Pure biochar, the KOH biochar compound fertilizer prepared in Comparative Example 4, and the slow-release compound biochar fertilizer prepared in Example 3 of the present invention were subjected to XRD (X-Ray Diffraction) analysis. The results are shown in FIG. Figure 3 .Depend on Figure 3 Pure biochar, with its weak and broadened diffraction peaks, is generally amorphous, primarily composed of complex organic polymers and amorphous carbon, including pyrolysis residues such as cellulose, hemicellulose, and lignin, and possibly small amounts of natural minerals. The sharp, intense peaks observed in KOH biochar fertilizers indicate the formation of new crystalline phases, likely potassium carbonates, potassium silicates, and potassium aluminates. Slow-release composite biochar exhibits characteristic peaks of lanthanum oxide (La2O3). During the loading process, lanthanum oxide may react with KOH biochar surface groups or generated potassium compounds to form lanthanum-potassium composite oxides or oxyacid salts.

[0099] Experiment 5

[0100] Thermogravimetry (TG or TGA) is a thermal analysis method based on programmed temperature control technology that continuously measures the mass change of a substance to study its thermal stability, decomposition process, and composition. Its core is to reveal the thermal behavior and reaction mechanism of the material by accurately recording the mass change of the sample at different temperatures or time. The TG curve is used to determine the initial decomposition temperature (T0) and the temperature corresponding to the maximum weight loss rate (T0) of the light-converting film. ), evaluate its thermal stability in high temperature environment, verify the effect of improving thermal stability after adding rare earth lanthanum based on the residual mass percentage in the medium and low temperature stages, and infer the proportion of inorganic components (such as rare earth oxides) in the material. The thermogravimetric analysis of biochar and the slow-release composite biochar prepared in Example 3 is shown in Figure 9 Comparison of the two samples reveals good thermal stability at low temperatures (0-100°C), with their weight remaining largely stable and no significant weight loss due to thermal decomposition or volatilization. This indicates a similar thermal stability difference between the two samples at this stage. However, at medium temperatures (100-200°C), both samples experienced rapid weight loss, with sharp negative peaks appearing in their DTG curves. This indicates that a large amount of unstable components in the samples rapidly decomposed or volatilized within this temperature range, representing the worst thermal stability. This indicates that both samples exhibit poor thermal stability within this temperature range. In the range of (200 - 800℃), the TG curve of the slow-release composite biochar continues to decline slowly, and the DTG curve fluctuates less in the negative area, indicating that the sample continues to lose weight at high temperature, but the weight loss rate gradually decreases, showing a certain high-temperature stability. The TG curve of biochar also shows a trend of continuing to decline slowly, and the DTG curve fluctuates less, indicating that there are still components decomposing at high temperature, but the weight loss rate is decreasing, and the thermal stability is improved, but there are still certain thermal stability problems. In comprehensive comparison, the DTG curve of the slow-release composite biochar fluctuates less in the range of (200 - 800℃), which means that its weight change rate in the high-temperature stage is more stable and its thermal stability is slightly better.

[0101] Experiment 6

[0102] Three weeks after planting, the soil pH change, the salt content in the soil, the heavy metal content in the soil, the organic matter content in the soil, and the chlorophyll content in the soil were detected. The results of the soil pH change are shown in Table 3. As can be seen from Table 3, the slow-release composite biochar fertilizer prepared by the present invention can reduce the pH value of the soil and improve the alkalinity of saline-alkali soil.

[0103] Table 3 Soil pH changes

[0104]

[0105] The results of the change of salt content in the soil are shown in Table 4. It can be seen from Table 4 that the slow-release composite biochar fertilizer prepared by the present invention can effectively reduce the salt content in the soil and improve the soil environment.

[0106] Table 4 Changes in soil salt content

[0107]

[0108] Table 5 shows the results of heavy metal content in soil. As can be seen from Table 5, the slow-release composite biochar fertilizer prepared by the present invention can effectively reduce the content of heavy metals such as mercury, chromium, and arsenic in soil. This is because lanthanum oxide is alkaline, and its application to soil lowers the soil pH. As the pH decreases, the forms of heavy metal ions in the soil change. For example, mercury ions may form precipitates such as mercuric hydroxide under alkaline conditions, reducing their solubility and availability in the soil. Arsenic and chromium ions also undergo hydrolysis under alkaline conditions, forming hydroxide precipitates or other poorly soluble compounds. This reduces the exchangeable and water-soluble arsenic and chromium content in the soil, thereby reducing the activity of these heavy metals in the soil and their toxicity to plants.

[0109] Table 5 Changes in soil heavy metals

[0110]

[0111] The organic matter content in the soil is shown in Table 6. It can be seen from Table 6 that the slow-release composite biochar fertilizer prepared by the present invention can effectively increase the organic matter content in the soil and improve the soil environment.

[0112] Table 6 Changes in soil organic matter content

[0113]

[0114] The chlorophyll content in the soil is Figure 5 As can be seen from the figure, the chlorophyll content in the soil of the water control group is 21.9 mg / cm 2 , Comparative Example 1: 26.4 mg / cm 2 , Comparative Example 2: 26.5 mg / cm 2 , Comparative Example 3: 30.3 mg / cm 2 , Comparative Example 4 is 29.4 mg / cm 2 , Comparative Example 5: 26.7 mg / cm 2 , Example 3 is 38.2 mg / cm 2 , which proves that the slow-release composite biochar fertilizer prepared by the present invention can effectively increase the chlorophyll content in the soil and improve the soil environment.

[0115] One month later, the growth of each group of alfalfa was recorded. Figure 4 As can be seen from the figure, the growth of alfalfa after applying fertilizer is better than that of the water control group, and Example 3 is the best.

Claims

1. A method for preparing lanthanum oxide modified biochar fertilizer, characterized in that: The following steps are involved: (1) Microwave activated biochar: Place corn straw biochar in a microwave reactor and irradiate it at a power of 200-300W for 2-5 minutes to obtain porous activated biochar; (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 4-6 hours, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 80-105°C to constant weight to obtain potassium-loaded biochar; 90-110 ml of saturated KOH solution was added to every 10 g of porous activated biochar; (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 50-70 ° C for 1.5-2.5 h, and evaporated and crystallized to obtain lanthanum-citric acid complex; (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) are mixed in a mass ratio of 1:4.5-5.5, and then humic acid is added at 1-2% of the mass of the biochar, and magnetic stirring is carried out at 400-600 r / min for 25-35 minutes to obtain a slow-release lanthanum oxide modified biochar; (5) Compounding of phosphate fertilizer: The slow-release lanthanum oxide-modified biochar obtained in step (4) is mixed with monoammonium phosphate or diammonium hydrogen phosphate in a mass ratio of 4.5-5.5:1, and magnetically stirred at 400-600 r / min for 8-12 min to obtain a slow-release composite biochar fertilizer.

2. The method for preparing a lanthanum oxide modified biochar fertilizer according to claim 1, wherein: The following steps are involved: (1) Microwave activated biochar: Place corn straw biochar in a microwave reactor and irradiate it at a power of 200-300W for 2-5 minutes to obtain porous activated biochar; (2) Potassium ion loading: The porous activated biochar obtained in step (1) was immersed in a saturated KOH solution, magnetically stirred for 5 h, and then filtered to separate the solid precipitate, washed with deionized water, and dried at 80-105°C to constant weight to obtain potassium-loaded biochar; 100 ml of saturated KOH solution was added to every 10 g of porous activated biochar; (3) Preparation of lanthanum-organic complex: lanthanum oxide and citric acid were mixed in a mass ratio of 1:2, deionized water was added to form a suspension, stirred at 50-70 ° C for 2 h, and evaporated and crystallized to obtain lanthanum-citric acid complex; (4) Modified biochar composite: the lanthanum-citric acid complex obtained in step (3) and the potassium-loaded biochar obtained in step (2) were mixed in a mass ratio of 1:5, and magnetically stirred at 500 r / min for 30 min to obtain a slow-release lanthanum oxide modified biochar; (5) Phosphate fertilizer compounding: The slow-release lanthanum oxide modified biochar obtained in step (4) was mixed with monoammonium phosphate or diammonium hydrogen phosphate in a mass ratio of 5:1, and magnetically stirred at 500 r / min for 10 min to obtain a slow-release composite biochar fertilizer.

3. The method for preparing a lanthanum oxide modified biochar fertilizer according to claim 1, wherein: During the microwave activation process in step (1), the moisture content of the biochar is controlled at 5-10%.

4. The method for preparing a lanthanum oxide modified biochar fertilizer according to claim 1, characterized in that: In step (3), during the preparation of the lanthanum-citric acid complex, the evaporation crystallization temperature is 80° C., and the crystallized product is ground to a particle size of ≤50 μm.

5. A slow-release composite biochar fertilizer obtained by the preparation method of lanthanum oxide modified biochar fertilizer according to any one of claims 1 to 4.

Images