A chlorite and mg / al-lhds composite modified cow dung hydrothermal carbon and a preparation method and application thereof

Abstract

The present application relates to the field of agricultural waste resource utilization and soil improvement material technology, and particularly relates to a chlorite and Mg / Al-LDHs composite modified cow dung hydrothermal carbon and a preparation method and application thereof.A specific technical scheme is as follows: the present application takes cow dung as raw material, and after hydrothermal carbonization, is modified by chlorite co-hydrothermal modification and Mg / Al-LDHs post-treatment modification in sequence.The present application realizes the synergistic composite modification of natural layered silicate mineral and artificial synthesized layered double hydroxide, so that the specific surface area of the material is significantly increased, a rich multi-level pore network is formed, and the theoretical maximum adsorption capacity of the material to phosphorus reaches 1707.72 mg / kg.The material is applied to agricultural production as a soil improvement agent or a phosphorus slow-release material, can significantly promote crop growth, and has important application value in efficient recovery and utilization of livestock and poultry manure phosphorus resources.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste resource utilization and soil improvement materials technology, specifically to a hydrothermal char of cow manure modified with chlorite and Mg / Al-LDHs, its preparation method and application. Background Technology

[0002] Phosphorus is an essential nutrient for plants, but global phosphate rock resources are dwindling. my country produces over 4 billion tons of livestock and poultry waste annually, with cow manure accounting for over 30%, containing 1.5-3.0 g / kg of total phosphorus on a dry basis, indicating a considerable total phosphorus resource. However, current cow manure treatment primarily involves direct discharge and return to fields, with approximately 15% of farms discharging it directly, leading to phosphorus loss and severe eutrophication problems in water bodies. Therefore, developing technologies for phosphorus recovery from livestock and poultry manure is crucial for alleviating the phosphorus resource crisis and controlling agricultural non-point source pollution.

[0003] Hydrothermal carbonization technology has become a research hotspot in the resource utilization of livestock and poultry manure due to its advantages such as direct processing of high-moisture materials, low energy consumption, and high phosphorus recovery rate. After hydrothermal carbonization, the phosphorus recovery rate of cow manure can reach over 88%, and the amount of water-extractable phosphorus is reduced by more than 80%, with phosphorus mainly existing in the form of crystalline phosphate, significantly improving stability. However, in unmodified hydrothermal carbon of cow manure, phosphorus mainly exists in a poorly soluble form, with low bioavailability and difficulty in being directly absorbed and utilized by plants. Therefore, how to modify and control the occurrence form of phosphorus in hydrothermal carbon to convert poorly soluble phosphorus into bioavailable phosphorus is the key to achieving efficient utilization of phosphorus resources in livestock and poultry manure.

[0004] Layered hydrogen hydroxides (LDHs) are widely used in biochar modification to enhance phosphorus adsorption and fixation due to their unique interlayer anion exchange capacity, high specific surface area, and structural memory effect. Chinese patent CN112691634A discloses a method for preparing zirconium-doped layered double hydroxide (LDH) flower-shaped microspheres for highly efficient phosphorus adsorption. This material achieves a phosphate removal rate of 97.1% in water with an adsorption capacity of 12.09 mg / g. However, this material is mainly used for phosphorus removal from wastewater, and the synthesis process requires the introduction of precious metals such as zirconium, resulting in high costs and making it unsuitable for low-cost recovery of phosphorus resources from livestock and poultry manure. Chinese patent CN103274491A provides a method for removing vanadium from water using magnesium-aluminum LDHs. While demonstrating the ion exchange performance of LDHs, this patent focuses on the adsorption of heavy metal cations, rather than the targeted regulation of phosphorus speciation. The aforementioned LDHs modification technologies mainly focus on the adsorption and removal of phosphorus in water, and have limited effect on the regulation of the inherent phosphorus form in hydrothermal carbon. Furthermore, LDHs have insufficient structural stability under hydrothermal conditions, making them difficult to directly apply to the regulation of phosphorus form in hydrothermal carbon of livestock and poultry manure.

[0005] Natural layered silicate minerals (such as chlorite) are rich in magnesium, iron, and other metal ions. Their layered structure is stable and widely available. Their surface hydroxyl groups can form stable complexes with phosphorus, demonstrating potential for reducing phosphorus leaching in soil amendment. Chinese patent CN102380350A discloses a hydroxyapatite-modified eggshell adsorbent and its preparation method, achieving a phosphate removal rate of 92.1%. However, this adsorbent uses eggshells as a carrier, which differs from the modification mechanism of natural layered minerals, and its adsorption rate is relatively slow. While the aforementioned natural mineral modification technologies possess some phosphorus adsorption capacity, the phosphorus adsorption capacity of chlorite-modified adsorbents is limited, making it difficult to meet the demand for efficient utilization of phosphorus resources from livestock and poultry manure.

[0006] It is evident that existing patents mostly focus on single modifiers, and there is a lack of in-depth reporting on the synergistic effect mechanism of composite modification of cow manure hydrothermal carbon using natural layered minerals and artificially synthesized layered materials. Therefore, there is an urgent need to develop a composite modified cow manure hydrothermal carbon material that is simple to process, low in cost, has a significant effect on phosphorus speciation control, and is environmentally friendly. This material should achieve efficient recovery and utilization of phosphorus resources from livestock and poultry manure through the synergistic composite modification of natural layered silicate minerals and artificially synthesized layered double hydroxides. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a chlorite-Mg / Al-LDHs composite modified cow dung hydrothermal char, its preparation method, and its application. Through the synergistic composite modification of natural layered silicate minerals and artificially synthesized layered double hydroxides, the phosphorus speciation in cow dung hydrothermal char is effectively regulated, improving the bioavailability of phosphorus and enhancing the material's phosphorus retention capacity, thereby reducing the risk of environmental loss.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention discloses a method for preparing hydrothermal carbon of cow dung modified with chlorite and Mg / Al-LDHs, comprising the following steps:

[0010] (1) After air-drying and sieving cow dung, add chlorite powder and carry out hydrothermal reaction. After the reaction is completed, cool naturally to room temperature, filter and dry to obtain chlorite-modified hydrothermal carbon.

[0011] (2) The chlorite-modified hydrothermal carbon is mixed with Mg / Al-LDHs powder, deionized water is added, and the mixture is subjected to magnetic stirring and ultrasonic treatment in sequence. After filtration and drying, the composite modified cow dung hydrothermal carbon is obtained.

[0012] Preferably, in step (1), the amount of chlorite powder added is 5%-10% of the mass of cow dung; the temperature of the hydrothermal reaction is 220℃ and the time is 6h.

[0013] Preferably, in step (2), the amount of Mg / Al-LDHs powder added is 3%-15% of the mass of cow dung.

[0014] Preferably, in step (2), the magnetic stirring time is 30 min to 2 h and the ultrasonic treatment time is 5 to 30 min.

[0015] Preferably, the mass ratio of chlorite powder to Mg / Al-LDH powder is 4-1:1-4, and the total amount added is 15% of the mass of cow dung.

[0016] Preferably, in step (2), the specific process for preparing the Mg / Al-LDHs is as follows: magnesium chloride hexahydrate and aluminum chloride hexahydrate are mixed and ultrasonically treated. Under constant temperature water bath and stirring conditions, the pH value of the system is maintained at 10.0±0.5 for 2 hours. After the reaction is completed, the mixture is filtered and separated, washed with deionized water until neutral, and then dried to obtain the Mg / Al-LDHs.

[0017] Correspondingly, a hydrothermal carbon modified from cow dung by chlorite and Mg / Al-LDHs prepared by the aforementioned preparation method is also available.

[0018] Correspondingly, a composite modified cow manure hydrothermal carbon made of chlorite and Mg / Al-LDHs is used as a soil conditioner or phosphorus slow-release material in agricultural production.

[0019] Preferably, the amount of chlorite and Mg / Al-LDHs composite modified cow manure hydrothermal carbon added is 2% of the soil mass.

[0020] The present invention has the following beneficial effects:

[0021] 1. This invention uses cow dung as raw material, chlorite as a natural layered silicate mineral modifier, and Mg / Al-LDHs as a synthetic layered double hydroxide modifier. A combined hydrothermal process and post-treatment method are employed to obtain a chlorite-Mg / Al-LDHs composite modified cow dung hydrothermal carbon with excellent phosphorus speciation control properties. Hydrothermal carbonization is a simple, economical, and easy-to-implement livestock manure treatment technology. Cow dung hydrothermal carbon not only possesses a carbon-based structure similar to biochar but also exhibits good physicochemical properties and phosphorus recovery capacity due to its complex elemental composition. Furthermore, chlorite is a natural, harmless, and environmentally friendly material with high ion exchange capacity and surface complexation sites, forming relatively stable compounds with phosphorus. This chlorite-Mg / Al-LDHs composite modified hydrothermal carbon material is the first of its kind synthesized.

[0022] 2. This invention utilizes the controllability of chlorite layer elements to introduce Mg / Al-LDHs, resulting in an excess of positive charge in the layered structure, thus enabling easier exchange of interlayer anions. Compared to unmodified cow dung hydrothermal carbon, the composite-modified material features a richer multi-level porous network formed by the interpenetration and composite growth of chlorite particles and LDHs sheets. This results in a larger specific surface area for the modified hydrothermal carbon, significantly improving its phosphorus adsorption capacity, accelerating adsorption, enhancing phosphorus retention, and providing sustained-release properties.

[0023] 3. The composite modified cow manure hydrothermal char of this invention can also slowly release phosphorus, which not only achieves the purpose of fixing phosphorus and solves the environmental hazards caused by phosphorus loss from livestock and poultry manure, but also allows the recovered modified hydrothermal char to be used as a slow-release phosphorus fertilizer in the soil, which can promote the growth of different plants, thereby broadening the application of hydrothermal char in the field of fertilizer preparation technology. Attached Figure Description

[0024] Figure 1 Scanning electron microscope (SEM) images of unmodified cow dung hydrothermal char and composite modified cow dung hydrothermal char; where (a) is unmodified cow dung hydrothermal char and (b) is composite modified cow dung hydrothermal char.

[0025] Figure 2 X-ray diffraction patterns of cow dung raw material and composite modified cow dung hydrothermal carbon;

[0026] Figure 3 Adsorption isotherms of phosphates on different hydrothermal carbons;

[0027] Figure 4 The graph shows the desorption rate of phosphate by different hydrothermal carbons;

[0028] Figure 5 Comparison of the growth of Chinese cabbage after applying modified hydrothermal charcoal to the soil and before application;

[0029] Figure 6 This is a flowchart of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0032] like Figure 6As shown, this invention discloses a method for preparing hydrothermal carbon of cow dung modified with chlorite and Mg / Al-LDHs. The method uses cow dung as raw material, adds chlorite to carry out a co-hydrothermal carbonization reaction to prepare chlorite-modified hydrothermal carbon, and then performs composite modification by Mg / Al-LDHs post-treatment.

[0033] Specifically, the steps include:

[0034] (1) Pretreatment of cow dung: The cow dung was air-dried naturally, passed through a 100-mesh sieve, and stored for later use; Pretreatment of chlorite: The chlorite was dried in a 60℃ forced-air drying oven to constant weight, ground and passed through a 100-mesh sieve for later use; Preparation of Mg / Al-LDHs: Mg / Al-LDHs were prepared by co-precipitation method, and the Mg / Al molar ratio was controlled to be 2:1;

[0035] The specific process for preparing the Mg / Al-LDHs is as follows: a mixed metal salt solution containing magnesium chloride hexahydrate and aluminum chloride hexahydrate is prepared, with the Mg / Al molar ratio controlled at 2:1; after ultrasonic treatment for 0.5 h, a mixed alkaline solution of NaOH and Na2CO3 is added dropwise under constant temperature water bath at 60℃ and stirring at 500 r / min, maintaining the pH value of the system at 10.0±0.5, and the reaction is carried out for 2 h; after the reaction is completed, the mixture is separated by filtration and washed with deionized water until neutral; the solid product is dried at 60℃ for 24 h, ground and passed through a 100-mesh sieve to obtain the Mg / Al-LDHs.

[0036] (2) Weigh the cow dung raw material, add deionized water at a solid-liquid ratio of 1:12, place it in a hydrothermal synthesis reactor, react at 220℃ for 6 hours, after the reaction is completed, cool naturally to room temperature, filter to separate the solid product, dry at 60℃ to constant weight, grind through a 100-mesh sieve to obtain hydrothermal carbon.

[0037] (3) Chlorite hydrothermal modification: Chlorite powder is added to cow dung raw material, mixed evenly, and then prepared according to the hydrothermal conditions in step (4) to obtain chlorite modified hydrothermal carbon.

[0038] (4) Composite modification: The chlorite-modified hydrothermal carbon obtained in step (3) is mixed with Mg / Al-LDHs powder, an appropriate amount of deionized water is added, the mixture is magnetically stirred for 30 min-2 h, ultrasonicated for 5-30 min, filtered and dried to obtain composite modified cow dung hydrothermal carbon.

[0039] The amount of chlorite powder added is 5%-10% of the mass of cow dung raw material, and the amount of Mg / Al-LDHs powder added is 3%-15% of the mass of cow dung raw material.

[0040] Furthermore, the mass ratio of chlorite to Mg / Al-LDHs is 4-1:1-4, and the total amount added is 15% of the mass of cow dung raw material.

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] Example 1: A method for preparing hydrothermal carbon of cow dung modified with chlorite and Mg / Al-LDHs.

[0043] (1) Weigh 10.0g of cow dung raw material, add deionized water at a solid-liquid ratio of 1:12, place it in a 200mL hydrothermal synthesis reactor, react at 220℃ for 6h, after the reaction is completed, cool naturally to room temperature, filter and separate the solid product with a 0.45μm fiber membrane, dry at 60℃ to constant weight, grind through a 100-mesh sieve to obtain hydrothermal carbon (HC).

[0044] (2) Add 10% of the mass of chlorite powder (1.0g) to the cow dung raw material, mix evenly, and prepare according to the above hydrothermal conditions to obtain chlorite-modified hydrothermal carbon (Cli@HC).

[0045] (3) The prepared chlorite-modified hydrothermal carbon (2.0g) was mixed with 5% Mg / Al-LDHs powder (0.1g), and an appropriate amount of deionized water was added. The mixture was magnetically stirred for 2h, ultrasonicated for 30min, filtered and dried to obtain composite modified cow dung hydrothermal carbon (Cli-LDHs@HC).

[0046] The structural characterization and performance testing of the material are as follows:

[0047] 1. The morphology of unmodified cow dung hydrothermal char and composite modified cow dung hydrothermal char was observed using scanning electron microscopy. The results are as follows: Figure 1 As shown, unmodified cow dung hydrothermal char has a relatively smooth surface with visible fibrous structure and a small number of pores. After composite modification, the surface of the hydrothermal char exhibits a structure where chlorite particles and LDH sheets interweave and grow in a composite manner, forming a richer hierarchical porous network that exposes more active sites. Compared with unmodified cow dung hydrothermal char, this structure has better dispersibility, a higher specific surface area, and better phosphorus adsorption performance.

[0048] The X-ray diffraction (XRD) pattern of chlorite and Mg / Al-LDHs composite modified cow dung hydrothermal carbon is shown below. Figure 2As shown, for unmodified cow dung raw material, a broad amorphous organic composite diffuse peak is observed between 20° and 30°, while sharp diffraction peaks appear at 20.9°, 26.6°, and 36.5°, which are attributed to quartz (SiO2). A characteristic peak of calcite (CaCO3) and a crystalline peak of albite (NaAlSi3O8) are detected at 29.4°. After modification with chlorite and Mg / Al-LDHs, the modified hydrothermal carbon, while retaining the original framework minerals, shows a significant new (Fe,Mg)Al2(PO4)2(OH)2 diffraction peak near 28.0°, and an anorthite (CaAl2Si2O8) crystalline phase is formed near 31.8°. This indicates that the active metal elements such as iron, magnesium, and aluminum introduced by chlorite and LDHs modifiers achieve reconstruction of the physicochemical structure of hydrothermal carbon and composite loading of mineral phases during hydrothermal or subsequent processes.

[0049] 2. Analysis of phosphorus speciation distribution

[0050] Phosphorus speciation was performed on the hydrothermal char prepared in Example 1 using a modified Hedley sequential extraction method. The results showed that the phosphorus speciation in the cow dung raw material (CD) was relatively uniform, with soluble H₂O-P accounting for 22.14%, NaHCO₃-P for 25.38%, NaOH-P for 23.42%, HCl-P for 25.18%, and residual-P for 8.83%. After hydrothermal carbonization, the proportion of HCl-P (insoluble calcium-bound phosphorus) in HC increased sharply to 95.82%, while H₂O-P decreased to 0.35%, NaHCO₃-P to 0.66%, NaOH-P to 1.05%, and residual-P to 2.2%, indicating that the hydrothermal process promoted the mineralization of organic phosphorus. 2+ Phosphorus combines with phosphate to form stable calcium phosphate precipitates such as hydroxyapatite, which reduces the risk of loss but greatly weakens the bioavailability of phosphorus.

[0051] In the composite modified cow dung hydrothermal char (Cli-LDHs@HC), the content of H2O-P, a readily soluble phosphorus, was further reduced to 0.31%, a decrease of 11.4% compared to HC; the content of NaHCO3-P, a moderately active phosphorus, increased to 2.79%, and NaOH-P increased to 1.86%, with the total proportion of bioavailable phosphorus (NaHCO3-P + NaOH-P) reaching 4.96%, an increase of 140.8% compared to HC's 2.06%. This indicates that the composite modification, through the synergistic effect of Fe and Mg ions provided by chlorite and Mg and Al ions provided by LDHs, effectively controls the phosphorus speciation by converting some of the insoluble HCl-P into moderately active magnesium / aluminum / iron bound phosphorus.

[0052] 3. To test the phosphorus adsorption and fixation performance of the composite modified cow dung hydrothermal carbon, phosphate (potassium dihydrogen phosphate) was selected as a representative pollutant for adsorption experiments. A certain amount of adsorbent was weighed and dispersed in a phosphate solution of a certain initial concentration. The solution was shaken at a constant temperature, and samples were taken at regular intervals. After filtration, the concentration of residual phosphate was determined using the molybdenum-antimony spectrophotometric method, and the adsorption capacity was calculated.

[0053] The adsorption isotherm of phosphate by hydrothermal carbon modified with chlorite and Mg / Al-LDHs is as follows: Figure 3 As shown in the figure, the adsorption capacity of phosphate gradually increases with the initial phosphorus concentration, eventually approaching saturation. Calculations show that the theoretical maximum adsorption capacity of the composite modified cow dung hydrothermal char for phosphorus can reach 1707.72 mg / kg, which is 2.87 times that of the unmodified cow dung hydrothermal char. Compared with the unmodified hydrothermal char, the adsorption capacity is increased by 1.87 times. This indicates that the composite modified cow dung hydrothermal char has excellent phosphorus retention performance.

[0054] 4. Phosphorus adsorption performance test

[0055] Phosphorus adsorption isotherms were conducted on the composite modified cow dung hydrothermal char prepared in Example 1. The adsorption isotherm data were fitted using both the Langmuir model and the Freundlich model. The results are shown in Table 1.

[0056] Table 1. Fitting parameters of the adsorption isotherms of phosphorus under different treatments

[0057]

[0058] Table 1 shows that the theoretical maximum adsorption capacity (q) of the composite modified cow dung hydrothermal carbon (Cli-LDHs@HC) is... m The concentration was as high as 1707.72 mg / kg, which was 2.87 times and 2.15 times that of HC and Cli@HC, respectively; Langmuir model R 2 The highest value (0.9878) indicates that the adsorption is mainly monolayer chemisorption.

[0059] 5. Desorption performance test

[0060] Phosphorus desorption experiments were conducted on different hydrothermal carbons prepared in Example 1. For example... Figure 4As shown in the results, the desorption rate of each treatment generally decreased with increasing initial phosphorus concentration. The desorption rate of HC reached 115.1% at an initial phosphorus concentration of 20 mg / L, indicating that the adsorbed phosphorus was easily released. The desorption rate of Cli-LDHs@HC remained stable between 24.4% and 30.8% at initial phosphorus concentrations of 140-200 mg / L, significantly lower than that of HC. This indicates that the composite modification effectively enhanced the phosphorus fixation capacity and reduced the risk of re-release. Furthermore, the moderate desorption rate suggests that this material may exhibit good phosphorus slow-release performance in soil applications, meeting crop growth requirements while reducing the risk of environmental runoff.

[0061] Example 2: Optimization of Modifier Dosage

[0062] To determine the optimal addition amount of the modifier, single-factor experiments were conducted with mass fraction gradients of chlorite and Mg / Al-LDHs (5%, 7%, 10%, 12%, 15%), using NaHCO3-P and NaOH-P (bioavailable phosphorus) as evaluation indicators. Table 2 shows that the optimal addition amount of chlorite was 10%, and the optimal addition amount of Mg / Al-LDHs was 5%. Based on this, with the total addition amount fixed at 15%, composite modification optimization was carried out by setting mass ratios of chlorite to LDHs (4:1, 2:1, 1:1, 1:2, 1:4), and the optimal composite ratio was determined to be 1:2. Subsequent experiments all used the above optimal ratio.

[0063] Table 2. Phosphorus forms and bioavailable phosphorus content of modified hydrothermal char with different dosages (unit: mg / kg)

[0064]

[0065] Note: C(bioavailable phosphorus) = C(NaHCO3-P) + C(NaOH-P).

[0066] Example 3: Soil column leaching experiment to verify phosphorus fixation effect

[0067] Soil leaching experiments were conducted using an acrylic glass column (9 cm inner diameter, 50 cm height). Soil and the hydrothermal carbon sample prepared in Example 1 were thoroughly mixed at a 2% addition rate (approximately 25 cm high, total mass 1 kg) and then loaded into the soil column. Before the experiment, 900 mL of deionized water was added to saturate the soil. Leaching was performed every 3 days, with 100 mL added each time, for a total of 9 times.

[0068] The results showed that the original cow dung (CD) suffered the greatest phosphorus leaching loss, with a cumulative leaching amount of 3824.05 mg. Leaching significantly decreased after hydrothermal carbonization (HC: 1293.10 mg). The cumulative leaching amount of the composite modified cow dung hydrothermal carbon (Cli-LDHs@HC) was 1387.43 mg, lower than that of the single hydrothermally modified sample (Cli@HC: 1959.96 mg). Combined with phosphorus speciation analysis, although the proportion of bioavailable phosphorus increased after composite modification, leaching loss did not increase proportionally. This indicates that the multi-site fixation of phosphorus synergistically constructed by chlorite and Mg / Al-LDHs has a stronger phosphorus retention capacity, effectively controlling the risk of phosphorus loss to the environment while improving phosphorus availability.

[0069] Example 4: Experimental Verification of Application Effect of Potted Bok Choy

[0070] To further investigate the practical application effect of the composite modified cow dung hydrothermal charcoal, a potted bok choy experiment was conducted. 700g of soil was weighed and placed in a plastic pot (13.5cm high, 13.5cm top diameter, 10cm bottom diameter). The composite modified cow dung hydrothermal charcoal prepared in Example 1 was added at a rate of 2% and thoroughly mixed with the soil. Plump bok choy seeds were selected, soaked in 30℃ warm water for 6 hours, and then sown using the hole application method (approximately 2cm deep, 10 seeds evenly sown per pot). After sowing, the soil was thoroughly watered, covered with plastic wrap to retain moisture, and the wrap was removed after 3 days. Seedlings were thinned to 5 plants per pot 10 days after sowing, and to 1 plant per pot 20 days after sowing. Watering was done according to the "water when dry" principle during cultivation, and no other fertilizers were applied. The entire plant was harvested 45 days after sowing, and the growth status of the bok choy was measured.

[0071] The growth status of Chinese cabbage after applying compound modified cow manure hydrothermal charcoal is as follows: Figure 5 As shown in the figure, after 45 days of cultivation, compared with the blank control group, the pakchoi grown in the soil with added compound modified cow manure hydrothermal charcoal showed significantly better growth, with darker green leaves and stronger plants. Table 3 shows the growth status of the pakchoi; at a 2% addition level, compared with the blank control group (CK), the aboveground fresh weight of the pakchoi in the compound modified cow manure hydrothermal charcoal treatment group increased by 126.0%, root length increased by 56.9%, and underground biomass (after drying) increased by 190.0%; this material has good growth-promoting properties.

[0072] Table 3 Growth status of bok choy

[0073]

[0074] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing hydrothermal char of cow dung modified with chlorite and Mg / Al-LDHs, characterized in that: Includes the following steps: (1) After air-drying and sieving cow dung, add chlorite powder and carry out hydrothermal reaction. After the reaction is completed, cool naturally to room temperature, filter and dry to obtain chlorite-modified hydrothermal carbon. (2) The chlorite-modified hydrothermal carbon is mixed with Mg / Al-LDHs powder, deionized water is added, and the mixture is subjected to magnetic stirring and ultrasonic treatment in sequence. After filtration and drying, the composite modified cow dung hydrothermal carbon is obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the amount of chlorite powder added is 5%-10% of the mass of cow dung; the temperature of the hydrothermal reaction is 220℃ and the time is 6h.

3. The preparation method according to claim 2, characterized in that: In step (2), the amount of Mg / Al-LDHs powder added is 3%-15% of the mass of cow dung.

4. The preparation method according to claim 1, characterized in that: In step (2), the magnetic stirring time is 30 min to 2 h and the ultrasonic treatment time is 5 to 30 min.

5. The preparation method according to claim 3, characterized in that: The mass ratio of chlorite powder to Mg / Al-LDH powder is 4-1:1-4, and the total amount added is 15% of the mass of cow dung.

6. The preparation method according to claim 1, characterized in that: In step (2), the specific process for preparing the Mg / Al-LDHs is as follows: magnesium chloride hexahydrate and aluminum chloride hexahydrate are mixed and ultrasonically treated. Under constant temperature water bath and stirring conditions, the pH value of the system is maintained at 10.0±0.5 for 2 hours. After the reaction is completed, the mixture is separated by filtration and washed with deionized water until neutral. After drying, the Mg / Al-LDHs are obtained.

7. A hydrothermal carbon of cow dung prepared by the preparation method according to any one of claims 1-6.

8. The application of the chlorite and Mg / Al-LDHs composite modified cow manure hydrothermal biochar as described in claim 7 as a soil conditioner or phosphorus slow-release material in agricultural production.

9. The application according to claim 8, characterized in that: The amount of chlorite and Mg / Al-LDHs composite modified cow manure hydrothermal carbon added is 2% of the soil mass.

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