Biochar-based slow-release oxygen material for gleying soil improvement as well as preparation method and application of biochar-based slow-release oxygen material

Abstract

The invention belongs to the technical field of biochar oxygen-releasing materials, and particularly relates to a biochar-based oxygen-releasing material for gleying soil improvement as well as a preparation method and application of the biochar-based oxygen-releasing material. The biochar-based oxygen release material is a CaO2 at phosphorus-rich biochar material obtained by taking modified phosphorus-rich biochar as a carrier and combining with calcium peroxide, and has remarkable beneficial effects in the field of gleying rice field improvement. According to the biochar-based oxygen release material, the mass fraction of calcium peroxide is remarkably increased, so that the oxygen release function of the material is enhanced, and the biochar-based oxygen release material has important significance for improving the ventilation condition of a rice field and promoting the growth of a rice root system. In the preparation process, raw materials such as dimethylbenzene and polyethylene which may cause soil pollution and ecological problems are avoided, and the environment-friendly concept is embodied. Meanwhile, the modified biochar not only serves as a carrier to improve the loading capacity of calcium peroxide, but also has the function of releasing a phosphate fertilizer, and is beneficial to improvement of the soil fertility of the rice field and increase of the rice yield.

Description

Technical Field

[0001] The invention belongs to the technical field of biochar oxygen-releasing materials, and in particular relates to a biochar-based slow-release oxygen material for fertilized soil improvement, and a preparation method and application thereof. Background Art

[0002] Incubated rice fields are widely distributed in southern my country, accounting for about one-third of the total area of ​​rice fields, especially in provinces such as Hunan, Hubei and Guangdong. Although the soil of these rice fields is rich in organic matter and nutrients, the long-term accumulation of water has led to a decrease in the oxygen content in the soil and a decrease in the redox potential, which has led to the accumulation of a large number of harmful reducing substances. These substances not only destroy the biological activity of the soil and reduce the effectiveness of nutrients, but also inhibit the growth of rice and seriously idle the rice yield. Traditional improvement measures, such as water conservancy project construction and land use adjustment, can solve the problem, but they are often costly and short-lived. Emerging improvement methods, such as applying oxygen-releasing materials with calcium peroxide as the core to increase the dissolved oxygen content of incubated rice fields, can accurately control the oxygen supply in the soil, but their preparation process is complicated, the cost is high, and it may have adverse effects on the soil environment. Therefore, it is necessary to find an improvement method that is both economical and environmentally friendly to improve the soil quality and rice yield of incubated rice fields.

[0003] my country produces a large amount of agricultural waste 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 anti-microbial degradation ability, biochar has been widely used in agriculture and environmental protection. Recent studies have found that biochar can be used as a carrier of calcium peroxide. Its good chemical stability and large specific surface area help solve the agglomeration problem of calcium peroxide, thereby increasing its oxygen release. At the same time, the hydrophobicity and porosity of biochar may 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 amount of oxygen released by calcium peroxide, but its effective utilization rate is not high. In particular, the calcium hydroxide generated by the reaction of calcium peroxide with water will form a covering layer on its surface, hindering further reactions inside the calcium peroxide, thereby reducing its utilization efficiency. Therefore, it has become an important topic to study how to effectively combine biochar with calcium peroxide to enhance the oxygen release performance of calcium peroxide and improve its utilization efficiency.

[0004] The interaction between biochar and calcium peroxide involves multiple mechanisms, including chemical adsorption, physical adsorption, surface charge 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 prior art, in the production process of the oxidant release agent, the granulation and coating steps will result in 8.3% loss of calcium peroxide, mainly due to its decomposition in water and high temperature treatment. Large-scale industrial production may further increase the loss. In addition, the xylene solvent used in production is toxic and carcinogenic, and the non-degradability of polyethylene may cause soil pollution and ecological problems. And although the modification of biochar significantly increases the mass fraction of calcium peroxide in the carbon-based calcium peroxide material, the oxygen release rate of the carbon-based calcium peroxide material prepared by the modified biochar is too fast compared with the oxygen-releasing material prepared by pure calcium peroxide and original biochar, which limits its oxygen release capacity. Based on this, this study aims to use phosphorus-loaded biochar as a carrier, combined with calcium peroxide, to prepare a new type of calcium peroxide@biochar oxygen-releasing material. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a biochar-based slow-release oxygen material for fertilized soil improvement and a preparation method and application thereof.

[0006] The technical contents of the present invention are as follows:

[0007] The present invention provides a method for preparing a biochar-based slow-release oxygen material for fertilization soil improvement, comprising the following steps:

[0008] 1) Preparation of biochar

[0009] Select agricultural and forestry wastes for calcination to prepare biochar, and pass through a 60-100 mesh sieve;

[0010] The agricultural and forestry wastes include one or more of rice husks, rice leaves, rice straw, reeds, switchgrass, miscanthus, bamboo poles, and sugarcane bagasse;

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

[0012] 2) Preparation of phosphorus-rich biochar

[0013] The biochar and phosphate particles are mixed, deionized water is added, stirred evenly into a slurry, and allowed to stand at room temperature;

[0014] After the slurry is dried to constant weight, it is calcined to obtain biochar material, cooled to room temperature, deionized water is added, stirred evenly, and then filtered until the conductivity of the filtrate remains basically unchanged, the solid matter is collected, dried, and passed 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°C, and the heating rate is 10-30°C / min;

[0018] The conductivity being substantially unchanged is determined as a relative deviation of the measured value being less than 1%, the same below;

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

[0020] The phosphorus-rich biochar was mixed with CaO2, anhydrous ethanol was added, and the mixture was stirred evenly into a slurry, and then dried to a constant weight after shaking on a shaker;

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

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

[0023] The calcination temperature is 150-300° C., and the heating rate is 10-30° C. / min.

[0024] The present invention also provides a biochar-based slow-release oxygen material for improving fertilized soil obtained by the above-mentioned preparation method, which is a material obtained by calcining CaO2 and phosphorus-rich biochar, namely CaO2@phosphorus-rich biochar.

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

[0026] The beneficial effects of the present invention are as follows:

[0027] The biochar-based oxygen-releasing material and preparation method thereof of the present invention are CaO2@phosphorus-rich biochar materials obtained by combining modified phosphorus-rich biochar as a carrier and calcium peroxide, which show significant beneficial effects in the field of latent rice field improvement. First, 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 the ventilation of rice fields and promoting the growth of rice roots. In addition, the material also realizes the effective utilization of agricultural wastes such as straw, and converts these wastes into biochar through pyrolysis reaction, which not only solves the problem of agricultural waste treatment, but also gives it new value. More importantly, the invention avoids the use of raw materials such as xylene and polyethylene that may cause soil pollution and ecological problems during the preparation process, reflecting the concept of environmental protection. At the same time, the modified biochar not only increases the loading amount of calcium peroxide as a carrier, but also has the function of releasing phosphorus fertilizer, which helps to improve the fertility of paddy field soil and increase rice yield. The biochar-based oxygen-releasing material prepared by the present invention can not only slow down the oxygen release rate of calcium peroxide in water, but also improve its use efficiency. The calcium element in biochar can combine with phosphate in the solution to form a stable calcium-phosphorus complex. This not only enhances the biochar's ability to adsorb phosphorus, but also provides a new idea for regulating the oxygen-release characteristics of calcium peroxide. Phosphorus-loaded biochar can form a stable phosphorus-calcium complex on the surface, which not only increases the loading amount of calcium peroxide, but also helps to reduce its oxygen release rate. This strategy is expected to improve the utilization efficiency of calcium peroxide and show application potential in areas such as latent rice field improvement. The invented biochar-based oxygen-releasing material has shown significant advantages and beneficial effects in environmental protection, resource utilization and agricultural production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the result diagram of the mass fraction of CaO2 in CaO2@biochar;

[0029] Figure 2 is the XRD pattern of CaO2@biochar;

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

[0031] Figure 3 It is the oxygen release kinetic curve of CaO2@biochar, and the solid line represents the fitting value of the data;

[0032] Figure 4 It is the first-order kinetic curve of dissolved oxygen concentration changing with time, and the solid line represents the fitting value of the data. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below through specific implementation cases and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art are all within the scope of the claims attached to this application.

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

[0035] Example 1

[0036] A method for preparing biochar-based slow-release oxygen material for fertilization soil improvement

[0037] 1) Preparation of biochar

[0038] The washed, dried and crushed rice husk was passed through a 50-mesh sieve for later use, and the rice husk was placed in a 300 mL ceramic crucible and transferred to a muffle furnace. The temperature was raised to 500 °C at 20 °C / min and maintained for 120 min. After cooling naturally to room temperature, the husk was taken out and passed through a 60-mesh sieve for later use, which 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 masses 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 homogenous slurry, and the mixture was allowed to stand at room temperature for 30 min, during which it was stirred 3 to 4 times. After drying to constant weight at 60 °C, the mixture was transferred to a 300 mL ceramic crucible, placed in a muffle furnace, heated to 250 °C at 20 °C / min, and kept for 120 min for calcination.

[0041] After cooling to room temperature, deionized water (100 mL / time) was added, stirred evenly and filtered until the conductivity of the filtrate remained basically unchanged (the relative deviation of the two measured values ​​was less than 1%), and the solids were collected, dried at 60°C overnight, and passed through a 60-mesh sieve, and recorded as BP1, BP2, and BP3 respectively;

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

[0043] Put 2g BP0 (or BP1, BP2 and BP3) in a 100mL beaker and add 1g CaO2. Add an appropriate amount of anhydrous ethanol to the mixture to form a homogenate. After shaking on a shaker for 30min (200rpm), dry at 60℃ to constant weight. The above mixture is placed in a 25mL ceramic crucible, transferred to a muffle furnace, and heated to 250℃ at 20℃ / min, and kept for 120min for calcination. Take it out after cooling to room temperature. Filter with cold (about 4℃) deionized water (100mL / time) until the filtrate conductivity remains basically unchanged (the relative deviation of the two measured values ​​is less than 1%). Filter with 50mL anhydrous ethanol for 3 times as above to remove residual H2O. Collect the solid and dry it at 60℃ to constant weight. Grind it through a 60-mesh sieve and record it as CaO2@BP0 (or CaO2@BP1, CaO2@BP2 and CaO2@BP3).

[0044] Example 2

[0045] A method for preparing biochar-based slow-release oxygen material for soil improvement

[0046] 1) Preparation of biochar

[0047] The cleaned, dried and crushed reeds were sieved through a 20-mesh sieve for later use, and the reeds were placed in a 300 mL ceramic crucible and transferred to a muffle furnace, heated to 400°C at a rate of 15°C / min, maintained for 120 min, naturally cooled to room temperature, taken out, sieved through a 100-mesh sieve for later use, and reed charcoal was obtained;

[0048] 2) Preparation of phosphorus-rich biochar

[0049] 10 g of reed charcoal was placed in a 200 mL beaker, KH2PO4 particles were added, and the mass ratio of KH2PO4 to biochar was set to 0.4:1. An appropriate amount of deionized water was added to the mixture to form a homogenous slurry, and the mixture was allowed to stand at room temperature for 30 min, during which it was stirred 3 to 4 times; after drying to constant weight at 60 °C, the mixture was transferred to a 300 mL ceramic crucible, placed in a muffle furnace, heated to 200 °C at 20 °C / min, and kept for 120 min for calcination;

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

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

[0052] Place 4g of phosphorus-rich biochar in a 100mL beaker and add 2g of CaO2. Add an appropriate amount of anhydrous ethanol to the mixture to form a homogenate. After shaking on a shaker for 30min (200rpm), dry at 60℃ to constant weight. The above mixture is loaded into a 25mL ceramic crucible, transferred to a muffle furnace, heated to 200℃ at 15℃ / min, and maintained for 100min for calcination. Take it out after cooling to room temperature. Filter with cold (about 4℃) deionized water (100mL / time) until the filtrate conductivity remains basically unchanged (the relative deviation of the two measured values ​​is less than 1%). Filter with 50mL of anhydrous ethanol three times as above to remove residual H2O. Collect the solids and dry them at 60℃ to constant weight. Crush through a 100-mesh sieve and record it as CaO2@phosphorus-rich biochar.

[0053] Example 3

[0054] A method for preparing biochar-based slow-release oxygen material for fertilization soil improvement

[0055] 1) Preparation of biochar

[0056] The washed, dried and crushed switchgrass was passed through a 18-mesh sieve for later use, the switchgrass was placed in a 300 mL ceramic crucible, and transferred to a muffle furnace, heated to 600° C. at a rate of 10° C. / min, maintained for 120 min, naturally cooled to room temperature, taken out, passed through a 100-mesh sieve for later use, and switchgrass charcoal was obtained;

[0057] 2) Preparation of phosphorus-rich biochar

[0058] 10 g of switchgrass charcoal was placed in a 200 mL beaker, K2HPO4 particles were added, and 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, and the mixture was allowed to stand at room temperature for 30 min, during which it was stirred 3 to 4 times; after drying to constant weight at 60 °C, it was transferred to a 300 mL ceramic crucible, placed in a muffle furnace, and heated to 150 °C at 10 °C / min, and maintained for 120 min for calcination;

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

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

[0061] Place 5g of phosphorus-rich biochar in a 100mL beaker and add 2.5g of CaO2. Add an appropriate amount of anhydrous ethanol to the mixture to form a homogenate. After shaking on a shaker for 30min (200rpm), dry at 60°C to constant weight. The above mixture is loaded into a 25mL ceramic crucible, transferred to a muffle furnace, heated to 150°C at 10°C / min, and maintained for 100min for calcination. Take it out after cooling to room temperature. Filter with cold (about 4°C) deionized water (100mL / time) until the filtrate conductivity remains basically unchanged (the relative deviation of the two measured values ​​is less than 1%). Filter with 50mL of anhydrous ethanol three times as above to remove residual H2O. Collect the solids and dry them at 60°C to constant weight. Crush through a 60-mesh sieve and record it as CaO2@phosphorus-rich biochar.

[0062] Example 4

[0063] A method for preparing biochar-based slow-release oxygen material for fertilization soil improvement

[0064] 1) Preparation of biochar

[0065] The washed, dried and crushed bamboo poles were passed through a 20-mesh sieve for later use, and the bamboo poles were placed in a 300 mL ceramic crucible and transferred to a muffle furnace, heated to 700°C at 20°C / min, maintained for 120 min, naturally cooled to room temperature, taken out, and passed through a 100-mesh sieve for later use to obtain bamboo pole charcoal;

[0066] 2) Preparation of phosphorus-rich biochar

[0067] 10 g of bamboo charcoal was placed in a 200 mL beaker, K2HPO4 particles were added, and 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 homogenous slurry, and the mixture was allowed to stand at room temperature for 30 min, during which it was stirred 3 to 4 times; after drying to constant weight at 60 °C, it was transferred to a 300 mL ceramic crucible, placed in a muffle furnace, heated to 200 °C at 15 °C / min, and kept for 100 min for calcination;

[0068] After cooling to room temperature, deionized water (100 mL / time) was added, stirred evenly and filtered until the conductivity of the filtrate remained basically unchanged (the relative deviation of the two measured values ​​was less than 1%), the solid matter was collected, dried at 60°C overnight, and passed through a 100-mesh sieve to obtain phosphorus-rich biochar;

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

[0070] Put 6g of phosphorus-rich biochar in a 100mL beaker and add 2g of CaO2. Add an appropriate amount of anhydrous ethanol to the mixture to form a homogenate. After shaking on a shaker for 30min (200rpm), dry at 60℃ to constant weight. The above mixture is loaded into a 25mL ceramic crucible, transferred to a muffle furnace, heated to 150℃ at 10℃ / min, and kept for 100min for calcination. Take it out after cooling to room temperature. Filter with cold (about 4℃) deionized water (100mL / time) until the filtrate conductivity remains basically unchanged (the relative deviation of the two measured values ​​is less than 1%). Filter with 50mL of anhydrous ethanol three times as above to remove residual H2O. Collect the solids and dry them at 60℃ to constant weight. Crush and pass through a 100-mesh sieve and record it as CaO2@phosphorus-rich biochar.

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

[0072] 1. Test the element content of biochar

[0073] Table 1 Element content of phosphorus-rich biochar

[0074]

[0075]

[0076] The results are shown in Table 1. The phosphorus content of phosphorus-rich biochar is significantly higher than that of BP0, and the P content of phosphorus-rich biochar increases significantly with the increase of the ratio of phosphate (KH2PO4) to biochar. The carbon and hydrogen content of phosphorus-rich biochar is significantly lower than that of BP0, probably due to the separation and dissolution of some soluble hydrocarbons during the stirring and filtration process in the preparation of phosphorus-rich biochar.

[0077] 2. Biochar’s ability to load CaO2

[0078] The ability of biochar to load CaO2 was evaluated by potassium permanganate titration, that is, 0.10g of CaO2@biochar was weighed and placed in a 100mL Erlenmeyer flask, 20mL of deionized water was added, and the mixture was stirred thoroughly to disperse. 10mL of 2mol / L sulfuric acid and 1mL of 0.05mol / L manganese sulfate solution were added, and the mixture was stirred at 100rpm for 5min. Filtered with a 0.45um filter membrane. The filtrate was titrated with a 0.02mol / 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] in, 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 are as follows Figure 1 As shown in the figure, with the increase of phosphorus content in biochar, the mass fraction of CaO2 in CaO2@biochar material also increases. It is proved that the loading amount of CaO2 depends on the phosphorus content of biochar. There are a series of phosphorus-containing compounds and functional groups on phosphorus-rich biochar, which can form P-Ca complexes with calcium, thereby enhancing the loading capacity of CaO2. However, when the phosphorus content of biochar increases to a certain extent, its ability to load CaO2 no longer increases. There is no significant difference in the mass fraction of CaO2 between CaO2@BP2 and CaO2@BP3. The reason may be that the complex formed by the phosphorus element on the biochar and CaO2 reaches a saturated state on the surface of the biochar. At this time, even if the phosphorus content continues to increase, no more complexes can be formed, resulting in the biochar's ability to load CaO2 no longer increasing.

[0086] 3. Structure of CaO2@biochar

[0087] The X-ray diffraction test of CaO2@biochar was carried out, and the results were as follows Figure 2 As shown in the figure, 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 the carbon material, respectively. Compared with the PDF card, the phase and intensity of some main peaks are consistent with the PDF card of CaO2 (JCPDS card number 03-0865), and there are 4 main peaks at 2θ = 30.2°, 35.6°, 47.3° and 53.2°. This shows that CaO2 was successfully synthesized and loaded on biochar. The phase and intensity of the other peaks correspond to CaCO3 (JCPDS card number 05-0586) and β-Ca3(PO4)2 (JCPDS card number 09-0169), respectively. CaCO3 and β-Ca3(PO4)2 may be formed by the reaction of CaO2 with CO2 in the air or phosphate loaded on biochar during the preparation process.

[0088] 4. Oxygen release kinetics of CaO2@biochar

[0089] The oxygen release kinetic characteristics of oxygen-releasing materials in latent acidification paddy field soil were determined by simulating latent acidification conditions. Weigh 0.33g CaCl2 in a conical flask, add 300mL deionized water to dissolve, and adjust the pH to 4.5 with 1% acetic acid. Pass N2 (0.75L / min, 20min) to reduce the dissolved oxygen concentration to 0.5mg / L. Quickly add 10mg pure CaO2 or CaO2@phosphorus-rich biochar with the same CaO2 content to the medium. Seal the bottle mouth to avoid the top space and place it in a dark incubator at 25℃ for oxygen release kinetic test. Within 12h after the start of the test, measure the dissolved oxygen concentration every 4h. From 12 to 36h, measure the dissolved oxygen concentration every 8h. When the relative deviation of the two measured values ​​is less than 1%, the oxygen release process is considered to be over. If the test exceeds 36h, change it to once every 12h.

[0090] The results are as follows Figure 3 As shown in the figure, according to the trend of dissolved oxygen concentration over time, it can be seen that the curve shows the characteristics of exponential growth. Therefore, the exponential growth model (Formula 1) in the following formula is selected to fit the data:

[0091] Formula 1:

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

[0093] Formula 3:

[0094] By deduction, Formula 1 is converted into Formula 2 which is consistent with the first-order reaction kinetic form, where A0 is the initial concentration, A is the dissolved oxygen concentration at a specific time t, and k is the rate constant. Figure 3 And formula 3 is drawn Figure 4 , and a linear fit was performed, and the results are shown in Table 2. Where A1 is the initial concentration, y-y0 is 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 fitting curve in the figure represents the oxygen release rate constant of the material, that is, how fast it releases oxygen in an environment simulating latent acid-reversing paddy field soil. From the perspective of the phosphorus content of the carbon material, except for CaO2@BP3, the rate constant of the oxygen-releasing material gradually decreases with the increase of phosphorus content. That is, the rate constant of CaO2@BP0 is the largest, followed by CaO2@BP1, and the smallest is CaO2@BP2. The reason may be that the phosphorus element on the biochar forms a complex with CaO2, which hinders 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 rate constant of CaO2@BP3 may be higher than that of CaO2@BP2 because the more phosphorus on CaO2@BP3 changes the oxygen release medium conditions.

[0098] Except for CaO2@BP2, whose rate constant is lower than that of CaO2, the rate constants of other CaO2@biochars are higher than that of CaO2. The reason may be that the larger specific surface area of ​​biochar significantly increases the contact area between CaO2 and water, resulting in its oxygen release rate being higher than that of CaO2.

[0099] Table 3. Medium pH and efficiency of CaO2 conversion into dissolved oxygen after oxygen release

[0100]

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

[0102]

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

[0104] DO1 is the dissolved oxygen concentration of the medium after the oxygen release is completed (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 theoretical amount of O2 produced by complete reaction of CaO2 and water (mg).

[0108] As can be seen from Table 3, after the oxygen release, there was no significant difference in the pH of each treatment medium. From the perspective of the efficiency of converting CaO2 into dissolved oxygen, the conversion efficiency of CaO2@biochar is significantly higher than that of CaO2, and except for CaO2@BP2 and CaO2@BP3, which have no significant difference, the conversion efficiency of CaO2@biochar increases with the increase of biochar phosphorus content. 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 a decrease in the conversion efficiency of CaO2. The CaO2@biochar material has a large specific surface area, and the CaO2 on it can fully 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 efficiency of CaO2 conversion into solution oxygen. It can be seen that CaO2@phosphorus-rich biochar material can be used to improve latent soil.

Claims

1. A method for preparing a biochar-based slow-release oxygen material for soil improvement, characterized in that: The steps include: 1) Preparation of biochar Select agricultural and forestry wastes and calcine them to prepare biochar; 2) Preparation of phosphorus-rich biochar The biochar and phosphate particles are mixed, deionized water is added, stirred evenly into a slurry, and allowed to stand at room temperature; After the slurry is dried to constant weight, it is calcined to obtain a biochar material, cooled to room temperature, added with deionized water, stirred evenly, and then filtered until the conductivity of the filtrate remains substantially unchanged, and the solid matter is collected and dried to obtain phosphorus-rich biochar; 3) Preparation of CaO2@phosphorus-rich biochar The phosphorus-rich biochar was mixed with CaO2, anhydrous ethanol was added, and the mixture was stirred evenly into a slurry, and then dried to a constant weight after shaking on a shaker; The dried mixture is calcined, cooled to room temperature, taken out, and filtered with cold water until the conductivity of the filtrate remains basically unchanged. It is then filtered with anhydrous ethanol, the solid is collected, and dried to constant weight to obtain CaO2@phosphorus-rich biochar.

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

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

4. The method for preparing the biochar-based slow-release oxygen material according to claim 1, characterized in that: Step 2) The mass ratio of the biochar to the phosphate particles is (0.2-0.6):

1.

5. The method for preparing the biochar-based slow-release oxygen material according to claim 4, characterized in that: The phosphates include KH2PO4 and K2HPO4.

6. The method for preparing the biochar-based slow-release oxygen material according to claim 1, characterized in that: Step 3) The mass ratio of the phosphorus-rich biochar to CaO2 is (2-3):

1.

7. The method for preparing the biochar-based slow-release oxygen material according to claim 1, characterized in that: In step 2) and step 3), the calcination temperature is 150-300°C, and the heating rate is 10-30°C / min.

8. The method for preparing the biochar-based slow-release oxygen material according to claim 1, characterized in that: The electrical conductivity being substantially constant is determined as a relative deviation of the measured value being less than 1%.

9. A biochar-based slow-release oxygen material for fertilized soil improvement obtained by the preparation method according to any one of claims 1 to 8, characterized in that: It is a material obtained by combining CaO2 and phosphorus-rich biochar through calcination, namely CaO2@phosphorus-rich biochar.

10. Use of the biochar-based slow-release oxygen material according to claim 9 in improving eutrophic soil.

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