A biological carbon-based slow-release oxygen material for improving gley soil and a preparation method and application thereof

Abstract

The present application belongs to the technical field of biochar oxygen-releasing materials, and particularly relates to a biochar-based slow-release oxygen material for gleization soil improvement and a preparation method and application thereof. The biochar-based oxygen-releasing material is a CaO2@ phosphorus-rich biochar material obtained by using modified phosphorus-rich biochar as a carrier and combining calcium peroxide, which exhibits significant beneficial effects in the field of gleization paddy field improvement. The biochar-based oxygen-releasing material significantly improves the mass fraction of calcium peroxide, thereby enhancing the oxygen-releasing function of the material, which is of great significance for improving the aeration condition of the paddy field and promoting the growth of rice root system. In the preparation process, raw materials such as dimethylbenzene and polyethylene that may cause soil pollution and ecological problems are avoided, embodying the environmental protection concept. At the same time, the modified biochar not only improves the loading capacity of calcium peroxide as a carrier, but also has the function of releasing phosphorus fertilizer by itself, which is helpful to the improvement of soil fertility of the paddy field and the increase of rice yield.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biochar oxygen-releasing materials, and particularly relates to a biochar-based slow-release oxygen material for improving gleyed soil and a preparation method and application thereof. BACKGROUND

[0002] Gleyed paddy fields are widely distributed in southern China, accounting for about one-third of the total paddy field area, especially in provinces such as Hunan, Hubei and Guangdong. Although the soil of these paddy fields is rich in organic matter and nutrients, the oxygen content in the soil is reduced due to long-term waterlogging, resulting in a decrease in the oxidation-reduction potential and accumulation of a large amount of harmful reducing substances. These substances not only destroy the biological activity of the soil and reduce the availability of nutrients, but also inhibit the growth of rice and seriously reduce the yield of rice. Traditional improvement measures, such as water conservancy engineering construction and land use mode adjustment, can solve the problem, but are often costly and short-lived. Emerging improvement methods, such as applying calcium peroxide-based oxygen-releasing materials to increase the dissolved oxygen content in gleyed paddy fields, can accurately control the oxygen supply in the soil, but the preparation process is complex, the cost is high, and it may have adverse effects on the soil environment. Therefore, it is necessary to find an economical and environmentally friendly improvement method to improve the soil quality and rice yield of gleyed paddy fields.

[0003] A large amount of agricultural waste is generated in China every year, which can be converted into biochar with environmental benefits and economic value through pyrolysis technology. Due to its large specific surface area, low density, high stability, strong adsorption capacity, excellent chemical stability and resistance to microbial degradation, biochar has been widely used in agriculture and environmental protection. Recent studies have found that biochar can be used as a carrier for calcium peroxide, and its good chemical stability and large specific surface area can help solve the problem of calcium peroxide agglomeration, thereby increasing its oxygen release capacity. At the same time, the hydrophobicity and porosity of biochar can also reduce the mass transfer efficiency of water and prolong the oxygen release time of calcium peroxide. Although mixing biochar with calcium peroxide or using biochar as a coating material can improve the oxygen release performance, this method may result in a large oxygen release capacity of calcium peroxide, but its effective utilization rate is not high. In particular, calcium hydroxide generated by the reaction of calcium peroxide with water can form a covering layer on the surface of calcium peroxide, hindering further reaction inside calcium peroxide, thereby reducing its utilization efficiency. Therefore, how to effectively combine biochar with calcium peroxide to enhance the oxygen release performance of calcium peroxide and improve its utilization efficiency has become an important topic.

[0004] The interaction between biochar and calcium peroxide involves multiple mechanisms, including chemical adsorption, physical adsorption, surface charge interaction, and hydrogen bonding. By optimizing the chemical composition and physical structure of biochar, its adsorption capacity for calcium peroxide can be effectively improved, thereby changing the interaction between the two. In the production process of oxygen release agents, the granulation and coating steps result in a loss of 8.3% of calcium peroxide, mainly due to its decomposition upon exposure to water and high-temperature treatment. Large-scale industrial production can further increase the loss. In addition, the use of xylene solvent in production is toxic and carcinogenic, while the non-degradability of polyethylene can lead to soil pollution and ecological problems. Furthermore, although the modification of biochar significantly increases the mass fraction of calcium peroxide in carbon-based calcium peroxide materials, the oxygen release rate of carbon-based calcium peroxide materials prepared from modified biochar is too fast compared to pure calcium peroxide and original biochar prepared oxygen release materials, which limits its oxygen release capacity. Based on this, the present study aims to use phosphorus-loaded biochar as a carrier to combine with calcium peroxide to prepare a new type of calcium peroxide@biochar oxygen release material. SUMMARY

[0005] To solve the above problems, the purpose of the present application is to provide a gley soil improvement biochar-based slow-release oxygen material and its preparation method and application.

[0006] The technical content of the present application is as follows:

[0007] The present application provides a preparation method of a gley soil improvement biochar-based slow-release oxygen material, comprising the following steps:

[0008] 1) Preparation of biochar

[0009] Selecting agricultural and forestry waste to prepare biochar by calcination, and passing through a 60-100 mesh sieve;

[0010] The agricultural and forestry waste includes one or more of rice husk, rice leaves, rice straw, reed, switchgrass, miscanthus, bamboo, and sugarcane residue;

[0011] The calcination temperature is 300-700℃, and the heating rate is 20-30℃ / min;

[0012] 2) Preparation of phosphorus-rich biochar

[0013] Mixing the biochar with phosphate particles, adding deionized water, and stirring uniformly to form a slurry, and standing at room temperature;

[0014] After drying the slurry to a constant weight, calcining to obtain a biochar material, cooling to room temperature, adding deionized water, stirring uniformly, and then filtering until the conductivity of the filtrate is essentially unchanged, collecting the solid, drying, and passing through a 60-100 mesh sieve to obtain phosphorus-rich biochar;

[0015] The mass ratio of the biochar to the phosphate particles is (0.2-0.6):1;

[0016] The phosphate includes KH2PO4 and K2HPO4.

[0017] The calcination temperature is 150-300 DEG C, and the temperature rising speed is 10-30 DEG C / min.

[0018] The conductivity is basically unchanged, and the relative deviation of the measured value is less than 1%, and the same below.

[0019] 3) Preparation of CaO2@ phosphorus-rich biochar

[0020] The phosphorus-rich biochar and CaO2 are mixed, anhydrous ethanol is added, and the mixture is stirred uniformly into a slurry, and then dried to constant weight after shaking bed oscillation.

[0021] The mass ratio of the phosphorus-rich biochar to CaO2 is (2-3):1.

[0022] The dried mixture is calcined, and then cooled to room temperature, and then taken out, filtered with cold water until the conductivity of the filtrate is basically unchanged, and then filtered with anhydrous ethanol, and then collected the solid, dried to constant weight, and then sieved through a 60-100 mesh sieve, to obtain CaO2@ phosphorus-rich biochar.

[0023] The calcination temperature is 150-300 DEG C, and the temperature rising speed is 10-30 DEG C / min.

[0024] The application further provides a biochar-based slow-release oxygen material for improving gley soil, which is a material obtained by calcining CaO2 and phosphorus-rich biochar, and is CaO2@ phosphorus-rich biochar.

[0025] The application further provides an application of the biochar-based slow-release oxygen material in improving gley soil, which not only has the effect of slowly releasing oxygen, but also can significantly improve the efficiency of converting CaO2 into solution oxygen.

[0026] The application has the following beneficial effects:

[0027] This invention relates to a biochar-based oxygen-releasing material and its preparation method. The material uses modified phosphorus-rich biochar as a carrier, combined with calcium peroxide to obtain CaO2@phosphorus-rich biochar, which exhibits significant beneficial effects in the field of gleyed paddy field improvement. Firstly, it significantly increases the mass fraction of calcium peroxide, thereby enhancing the oxygen-releasing function of the material, which is of great significance for improving paddy field aeration and promoting rice root growth. Furthermore, this material also achieves the effective utilization of agricultural waste such as straw, converting these wastes into biochar through pyrolysis, not only solving the problem of agricultural waste disposal but also giving them new value. More importantly, this invention avoids the use of raw materials such as xylene and polyethylene, which may cause soil pollution and ecological problems, reflecting an environmental protection concept. Simultaneously, the modified biochar not only increases the calcium peroxide loading as a carrier but also has the function of releasing phosphate fertilizer, contributing to the improvement of paddy field soil fertility and the increase of rice yield. The biochar-based oxygen-releasing material prepared by this invention not only slows down the oxygen release rate of calcium peroxide in water but also improves its utilization efficiency. Calcium in biochar can combine with phosphates in solution to form stable calcium-phosphorus complexes. This not only enhances the adsorption capacity of biochar for phosphorus but also provides a new approach to regulating the oxygen release characteristics of calcium peroxide. Phosphorus-loaded biochar can form stable phosphorus-calcium complexes on its surface, which not only increases the calcium peroxide loading but also helps to reduce its oxygen release rate. This strategy is expected to improve the utilization efficiency of calcium peroxide and shows application potential in areas such as gleyed paddy field improvement. The biochar-based oxygen-releasing material of this invention exhibits significant advantages and beneficial effects in environmental protection, resource utilization, and agricultural production. Attached Figure Description

[0028] Figure 1 The graph shows the mass fraction of CaO2 in CaO2@biochar.

[0029] Figure 2 XRD images of CaO2@biochar;

[0030] Note: Figure 2 The height of the green column does not indicate the level of the compound.

[0031] Figure 3 This is a graph showing the oxygen release kinetics of CaO2@biochar, with the solid line representing the fitted values ​​of the data.

[0032] Figure 4 This is a first-order kinetic curve of dissolved oxygen concentration changing over time, with the solid line representing the fitted values ​​of the data. Detailed Implementation

[0033] The application will be further described in detail below with specific examples and drawings. It should be understood that these examples are only used to illustrate the application and not to limit the protection scope of the application. After reading the application, those skilled in the art can make various equivalent modifications of the application, which fall within the scope defined by the appended claims.

[0034] Unless otherwise specified, all raw materials and reagents of the application are conventional market raw materials and reagents.

[0035] Example 1

[0036] A preparation method of a biochar-based slow-release oxygen material for gley soil improvement

[0037] 1) Preparation of biochar

[0038] The washed, dried and crushed rice husks were passed through a 50-mesh sieve for use. The rice husks were loaded into a 300-mL ceramic crucible and transferred to a muffle furnace, which was heated to 500℃ at a rate of 20℃ / min and maintained for 120 min. After natural cooling to room temperature, the sample was removed and passed through a 60-mesh sieve for use, and was recorded as BP0.

[0039] 2) Preparation of phosphorus-rich biochar

[0040] 10 g of rice husk charcoal was placed in a 200-mL beaker, and different amounts of KH2PO4 particles were added. The mass ratio of KH2PO4 to biochar was set to 0.2:1, 0.4:1 and 0.6:1. An appropriate amount of deionized water was added to the mixture to form a homogenate, which was left to stand at room temperature for 30 min, with stirring 3-4 times during this period. After drying to constant weight at 60℃, the mixture was transferred to a 300-mL ceramic crucible and placed in a muffle furnace, which was heated to 250℃ at a rate of 20℃ / min and maintained for 120 min for calcination.

[0041] After cooling to room temperature, deionized water (100 mL each time) was added, and the mixture was stirred uniformly and then filtered until the conductivity of the filtrate remained essentially unchanged (the relative deviation of two measured values was less than 1%). The solid was collected and dried overnight at 60℃, and then passed through a 60-mesh sieve. The resulting products were recorded as BP1, BP2 and BP3, respectively.

[0042] 3) Preparation of CaO2@phosphorus-rich biochar

[0043] The mixture was added with appropriate amount of anhydrous ethanol to form a homogenate. After shaking for 30 min (200 rpm), it was dried at 60 °C to constant weight. The mixture was loaded into a 25 mL ceramic crucible and transferred to a muffle furnace, and heated to 250 °C at a rate of 20 °C / min and kept for 120 min for calcination. After cooling to room temperature, it was taken out. Filtration was performed with cold (about 4 °C) deionized water (100 mL / time) until the conductivity of the filtrate was essentially unchanged (relative deviation of two measured values was less than 1 %). Then, 50 mL of anhydrous ethanol was used for filtration for three times as above to remove residual H2O. The solid was collected and dried at 60 °C to constant weight. It was crushed through a 60 mesh sieve and recorded as CaO2@BP0 (or CaO2@BP1, CaO2@BP2 and CaO2@BP3).

[0044] Example 2

[0045] A preparation method of a biochar-based slow-release oxygen material for gley soil improvement

[0046] 1) Preparation of biochar

[0047] The washed, dried and crushed reed was prepared through a 20 mesh sieve. The reed was loaded into a 300 mL ceramic crucible and transferred to a muffle furnace, and heated to 400 °C at a rate of 15 °C / min and kept for 120 min. After natural cooling to room temperature, it was taken out and crushed through a 100 mesh sieve to obtain reed charcoal.

[0048] 2) Preparation of phosphorus-rich biochar

[0049] The mixture was added with appropriate amount of anhydrous ethanol to form a homogenate. After shaking for 30 min (200 rpm), it was dried at 60 °C to constant weight. The mixture was loaded into a 25 mL ceramic crucible and transferred to a muffle furnace, and heated to 250 °C at a rate of 20 °C / min and kept for 120 min for calcination. After cooling to room temperature, it was taken out. Filtration was performed with cold (about 4 °C) deionized water (100 mL / time) until the conductivity of the filtrate was essentially unchanged (relative deviation of two measured values was less than 1 %). Then, 50 mL of anhydrous ethanol was used for filtration for three times as above to remove residual H2O. The solid was collected and dried at 60 °C to constant weight. It was crushed through a 60 mesh sieve and recorded as CaO2@BP0 (or CaO2@BP1, CaO2@BP2 and CaO2@BP3).

[0050] After cooling to room temperature, deionized water (100 mL / time) was added, stirred uniformly and then filtered until the conductivity of the filtrate was essentially unchanged (relative deviation of two measured values was less than 1 %). The solid was collected and dried at 60 °C overnight, and crushed through a 100 mesh sieve to obtain phosphorus-rich biochar.

[0051] 3) Preparation of CaO2@phosphorus-rich biochar

[0052] The 4 g of phosphorus-rich biochar was placed in a 100 mL beaker, and 2 g of CaO2 was added. An appropriate amount of anhydrous ethanol was added to the mixture to form a homogenate. After shaking for 30 min (200 rpm), it was dried at 60°C to constant weight. The mixture was loaded into a 25 mL ceramic crucible and transferred to a muffle furnace, and the temperature was raised to 200°C at a rate of 15°C / min and maintained for 100 min for calcination. After cooling to room temperature, it was removed. Filtration was performed with cold (about 4°C) deionized water (100 mL / time) until the conductivity of the filtrate was essentially unchanged (relative deviation of two measured values was less than 1%). Then, 50 mL of anhydrous ethanol was used to perform the same filtration three times to remove residual H2O. The solid was collected and dried at 60°C to constant weight. It was ground through a 100-mesh sieve and recorded as CaO2@phosphorus-rich biochar.

[0053] Example 3

[0054] A method for preparing a biochar-based slow-release oxygen material for improving gley soil

[0055] 1) Preparation of biochar

[0056] The washed, dried and crushed switchgrass was passed through an 18-mesh sieve for use. The switchgrass was loaded into a 300 mL ceramic crucible and transferred to a muffle furnace, and the temperature was raised to 600°C at a rate of 10°C / min and maintained for 120 min. After natural cooling to room temperature, it was removed and passed through a 100-mesh sieve for use, obtaining switchgrass charcoal.

[0057] 2) Preparation of phosphorus-rich biochar

[0058] 10 g of switchgrass charcoal was placed in a 200 mL beaker, and K2HPO4 particles were added. The mass ratio of K2HPO4 to biochar was set to 0.6:1. An appropriate amount of deionized water was added to the mixture to form a homogenate, which was left to stand at room temperature for 30 min, with stirring 3-4 times during this period. After drying to constant weight at 60°C, it was transferred to a 300 mL ceramic crucible and placed in a muffle furnace, and the temperature was raised to 150°C at a rate of 10°C / min and maintained for 120 min for calcination.

[0059] After cooling to room temperature, deionized water (100 mL / time) was added, and after stirring evenly, it was filtered until the conductivity of the filtrate was essentially unchanged (relative deviation of two measured values was less than 1%). The solid was collected and dried at 60°C overnight, and then passed through a 100-mesh sieve to obtain phosphorus-rich biochar.

[0060] 3) Preparation of CaO2@phosphorus-rich biochar

[0061] The 5 g of phosphorus-rich biochar was placed in a 100 mL beaker, and 2.5 g of CaO2 was added. An appropriate amount of anhydrous ethanol was added to the mixture to form a homogenate. After shaking for 30 min (200 rpm), the mixture was dried at 60°C until the weight was constant. The mixture was loaded into a 25 mL ceramic crucible and transferred to a muffle furnace, and the temperature was raised to 150°C at a rate of 10°C / min and maintained for 100 min for calcination. After cooling to room temperature, it was removed. Filtration was performed with cold (about 4°C) deionized water (100 mL / time) until the conductivity of the filtrate was essentially unchanged (the relative deviation of two measured values was less than 1%). Then, 50 mL of anhydrous ethanol was used to perform the same filtration three times to remove residual H2O. The solid was collected and dried at 60°C until the weight was constant. It was crushed through a 60-mesh sieve and labeled as CaO2@phosphorus-rich biochar.

[0062] Example 4

[0063] A method for preparing a biochar-based slow-release oxygen material for improving gley soil

[0064] 1) Preparation of biochar

[0065] The washed, dried and crushed bamboo was passed through a 20-mesh sieve and was loaded into a 300 mL ceramic crucible and transferred to a muffle furnace, and the temperature was raised to 700°C at a rate of 20°C / min and maintained for 120 min. After natural cooling to room temperature, it was removed and passed through a 100-mesh sieve to obtain bamboo charcoal.

[0066] 2) Preparation of phosphorus-rich biochar

[0067] 10 g of bamboo charcoal was placed in a 200 mL beaker, and K2HPO4 particles were added. The mass ratio of K2HPO4 to biochar was set to 0.4:1. An appropriate amount of deionized water was added to the mixture to form a homogenate, which was left to stand at room temperature for 30 min, with stirring 3-4 times during this period. After drying at 60°C until the weight was constant, it was transferred to a 300 mL ceramic crucible and placed in a muffle furnace, and the temperature was raised to 200°C at a rate of 15°C / min and maintained for 100 min for calcination.

[0068] After cooling to room temperature, deionized water (100 mL / time) was added, and after stirring evenly, filtration was performed until the conductivity of the filtrate was essentially unchanged (the relative deviation of two measured values was less than 1%). The solid was collected and dried at 60°C overnight, and then passed through a 100-mesh sieve to obtain phosphorus-rich biochar.

[0069] 3) Preparation of CaO2@phosphorus-rich biochar

[0070] In a 100 mL beaker, 6 g of the phosphorus-rich biochar was mixed with 2 g of CaO2. An appropriate amount of anhydrous ethanol was added to the mixture to form a homogenate. After shaking for 30 min (200 rpm), the mixture was dried at 60 °C until a constant weight was obtained. The mixture was then loaded into a 25 mL ceramic crucible and transferred to a muffle furnace, which was heated to 150 °C at a rate of 10 °C / min and maintained for 100 min. After cooling to room temperature, the mixture was removed. The mixture was filtered with cold (about 4 °C) deionized water (100 mL each time) until the conductivity of the filtrate was essentially unchanged (the relative deviation of two measured values was less than 1%). Then, the mixture was filtered with 50 mL of anhydrous ethanol three times to remove residual H2O. The solid was collected and dried at 60 °C until a constant weight was obtained. The powder was ground through a 100-mesh sieve and labeled as CaO2@phosphorus-rich biochar.

[0071] The biochar-based slow-release oxygen material prepared in Example 1 was tested as follows:

[0072] 1. Test of elemental content of biochar

[0073] Table 1. Elemental content of phosphorus-rich biochar

[0074]

[0075]

[0076] The results are shown in Table 1. The phosphorus content of the phosphorus-rich biochar was significantly higher than that of BP0, and the P content of the phosphorus-rich biochar increased significantly with the increase of the ratio of phosphate (KH2PO4) to biochar. It is possible that during the preparation of the phosphorus-rich biochar, some soluble hydrocarbons were separated and dissolved during the stirring and filtration process, resulting in a significant decrease in the carbon and hydrogen content of the phosphorus-rich biochar compared to BP0.

[0077] 2. Capacity of biochar to load CaO2

[0078] The capacity of biochar to load CaO2 was evaluated by potassium permanganate titration. Specifically, 0.10 g of CaO2@biochar was weighed into a 100 mL triangular flask, 20 mL of deionized water was added, and the mixture was stirred to disperse. Then, 10 mL of 2 mol / L sulfuric acid and 1 mL of 0.05 mol / L manganese sulfate solution were added, and the mixture was stirred at 100 rpm for 5 min. The mixture was filtered through a 0.45 um filter membrane. The filtrate was titrated with 0.02 mol / L potassium permanganate standard solution, and the volume of potassium permanganate solution consumed was recorded.

[0079] The formula for calculating the mass fraction of CaO2 is as follows:

[0080]

[0081] wherein, is the mass fraction of CaO2 (%);

[0082] and are the molar concentration (mol / L) and volume (L) of KMnO4, respectively;

[0083] is the molar mass of CaO2(72.08 g / mol);

[0084] m is the mass of CaO2@phosphorus-rich biochar (g).

[0085] The results, as shown in Figure 1 , show that the mass fraction of CaO2in CaO2@biochar materials increases with the increase of the phosphorus content of biochar. It is proved that the loading capacity of CaO2depends on the phosphorus content of biochar. There are a series of phosphorus-containing compounds and functional groups on the phosphorus-rich biochar, which can form P-Ca complexes with calcium elements, thereby enhancing the loading capacity of CaO2. However, when the phosphorus content of biochar increases to a certain extent, its loading capacity of CaO2no longer increases. There is no significant difference in the mass fraction of CaO2between CaO2@BP2and CaO2@BP3. The reason may be that the complexes formed by phosphorus elements on the biochar and CaO2reach a saturation state on the surface of the biochar. At this time, even if the phosphorus content continues to increase, more complexes cannot be formed, resulting in that the loading capacity of CaO2of biochar no longer increases.

[0086] 3. Structure of CaO2@biochar

[0087] The CaO2@biochar was subjected to X-ray diffraction test. The results, as shown in Figure 2 , show that all samples have a strong broad peak at 2θ = 23.8° and a weak broad peak at 2θ = 43.8°, which correspond to the (100) and (002) crystal planes of carbon materials, respectively. Compared with the PDF card, the phase and intensity of some main peaks are consistent with the PDF card (JCPDS card No. 03-0865) of CaO2, and there are four main peaks at 2θ = 30.2°, 35.6°, 47.3° and 53.2°. This indicates that CaO2is successfully synthesized and loaded on the biochar. The phase and intensity of other peaks correspond to CaCO3(JCPDS card No. 05-0586) and β-Ca3(PO4)2(JCPDS card No. 09-0169), respectively. CaCO3and β-Ca3(PO4)2may be formed by the reaction of CaO2with CO2in the air or phosphate loaded on the biochar during the preparation process.

[0088] 4. Oxygen release kinetic characteristics of CaO2@biochar

[0089] The oxygen release kinetics of oxygen-releasing materials in latent acidification paddy soil were determined under simulated latent acidification conditions. 0.33 g of CaCl2 was weighed into an Erlenmeyer flask, dissolved in 300 mL of deionized water, and the pH was adjusted to 4.5 with 1% acetic acid. N2 was bubbled through (0.75 L / min, 20 min) to lower the dissolved oxygen concentration to 0.5 mg / L. 10 mg of pure CaO2 or CaO2@phosphorus-rich biochar with equal CaO2 content was added to the rapid release medium. The flask was sealed to avoid headspace, and placed in a 25℃ dark incubator for the oxygen release kinetics experiment. Dissolved oxygen concentration was measured every 4 hours for the first 12 hours of the experiment. From 12 to 36 hours, dissolved oxygen concentration was measured every 8 hours. The oxygen release process was considered complete when the relative deviation between two measurements was less than 1%. If the experiment exceeded 36 hours, measurements were taken every 12 hours.

[0090] The results are as follows Figure 3 As shown, based on the trend of dissolved oxygen concentration over time, the curve exhibits an exponential growth characteristic. Therefore, the exponential growth model (Formula 1) is selected from the following formulas to fit the data:

[0091] Formula 1:

[0092] Formula 2: In(A / A0)=-kt;

[0093] Formula 3:

[0094] Through derivation, Equation 1 is transformed into Equation 2, which conforms to the form of first-order reaction kinetics, where A0 is the initial concentration, A is the dissolved oxygen concentration at a specific time t, and k is the rate constant. Based on... Figure 3 Plotting with Formula 3 Figure 4 The results of linear fitting are shown in Table 2. Here, A1 represents the initial concentration, y-y0 represents the dissolved oxygen concentration at a specific time x, and 1 / b1 is the negative value of the rate constant.

[0095] Table 2 Statistical data and rate constants of oxygen release curves of oxygen-releasing materials

[0096]

[0097] Figure 4The slope of the fitted curve represents the oxygen release rate constant of the material, i.e. how fast it releases oxygen in the simulated environment of the acid subsiding paddy soil. In terms of the phosphorus content of the carbon material, except for CaO2@BP3, the oxygen release rate constant of the material gradually decreases with the increase of the phosphorus content. That is, the rate constant of CaO2@BP0 is the largest, followed by CaO2@BP1, and CaO2@BP2 is the smallest. The reason may be that the phosphorus element on the biochar forms a complex with CaO2, hindering the reaction of CaO2 with water to generate O2. Although there is no significant difference in the CaO2 content between CaO2@BP3 and CaO2@BP2, the relatively high phosphorus content on CaO2@BP3 may change the oxygen release medium conditions, resulting in a higher rate constant of CaO2@BP3 than that of CaO2@BP2.

[0098] Except for CaO2@BP2, the rate constant of other CaO2@biochar is higher than that of CaO2. The reason may be that the large specific surface area of biochar significantly increases the contact area of CaO2 and water, resulting in a higher oxygen release rate than that of CaO2.

[0099] Table 3 pH of the medium after oxygen release and efficiency of CaO2 conversion to dissolved oxygen

[0100]

[0101] Table 3 is the pH of the medium after oxygen release and the efficiency of CaO2 conversion to dissolved oxygen, and the calculation formula is as follows:

[0102]

[0103] Wherein, η is the efficiency of CaO2 conversion to dissolved oxygen (%);

[0104] DO1 is the dissolved oxygen concentration of the medium after oxygen release (mg / L);

[0105] DO0 is the original dissolved oxygen concentration of the medium (mg / L);

[0106] V is the volume of the medium (L);

[0107] DO is the amount of O2 theoretically generated by the complete reaction of CaO2 with water (mg).

[0108] As shown in Table 3, there was no significant difference in pH of each treatment medium after the oxygen release ended. In terms of the conversion efficiency of CaO2 to dissolved oxygen, the conversion efficiency of CaO2@biochar was significantly higher than that of CaO2, and except for CaO2@BP2 and CaO2@BP3, the conversion efficiency of CaO2@biochar increased with the increase of phosphorus content of biochar. The reason may be that CaO2 reacts with water to generate Ca(OH)2, and the insoluble Ca(OH)2 covering the surface of CaO2 will hinder the further reaction of the internal CaO2, resulting in the decrease of the conversion efficiency of CaO2. While the CaO2@biochar material has a larger specific surface area, the CaO2 on it can be in full contact with water, resulting in a higher conversion efficiency.

[0109] In summary, CaO2@BP2 not only has the effect of slow oxygen release, but also can significantly improve the conversion efficiency of CaO2 to dissolved oxygen. It can be seen that CaO2@phosphorus-rich biochar material can be used for the improvement of gley soil.

Claims

1. A method for preparing a biochar-based slow-release oxygen material for gleying soil improvement, characterized in that, Includes the following steps: 1) Preparation of biochar Agricultural and forestry waste is selected and calcined to prepare biochar; 2) Preparation of phosphorus-rich biochar Mix biochar and phosphate granules, add deionized water, stir until homogeneous to form a slurry, and let stand at room temperature. The mass ratio of biochar to phosphate particles is (0.2~0.6):1; The phosphates include KH2PO4 and K2HPO4; After drying the slurry to constant weight, it was calcined to obtain biochar material. After cooling to room temperature, deionized water was added, and the mixture was stirred evenly and then filtered until the conductivity of the filtrate remained basically unchanged. The solid was collected, dried, and phosphorus-rich biochar was obtained. 3) Preparation of CaO2@phosphorus-rich biochar Phosphorus-rich biochar was mixed with CaO2, anhydrous ethanol was added, and the mixture was stirred evenly to form a slurry. After shaking on a shaker, the slurry was dried to constant weight. The mass ratio of the phosphorus-rich biochar to CaO2 is (2~3):1; The dried mixture was calcined, cooled to room temperature, and then filtered with cold water until the conductivity of the filtrate remained essentially unchanged. The solid was then collected by filtration with anhydrous ethanol and dried to constant weight to obtain CaO2@phosphorus-rich biochar.

2. The method for preparing biochar-based slow-release oxygen material according to claim 1, characterized in that, Step 1) The agricultural and forestry waste includes one or more of the following: rice husks, rice leaves, rice straw, reeds, willow branches, miscanthus, bamboo poles, and sugarcane bagasse.

3. The method for preparing biochar-based slow-release oxygen material according to claim 1, characterized in that, Step 1) The calcination temperature is 300~700℃, and the heating rate is 20~30℃ / min.

4. The method for preparing biochar-based slow-release oxygen material according to claim 1, characterized in that, The calcination temperature in steps 2) and 3) is 150~300℃, and the heating rate is 10~30℃ / min.

5. The method for preparing biochar-based slow-release oxygen material according to claim 1, characterized in that, The determination that the conductivity remains essentially unchanged is that the relative deviation of the measured value is less than 1%.

6. A biochar-based slow-release oxygen material for improving gley soil obtained by the preparation method according to any one of claims 1-5, characterized in that, It is a material obtained by combining CaO2 and phosphorus-rich biochar through calcination, namely CaO2@phosphorus-rich biochar.

7. The application of the biochar-based slow-release oxygen material of claim 6 in improving gley soil.

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