Calcium carbonate slag-corn cob-based caal-layers modified biochar composite material and preparation method and application thereof

Abstract

This invention discloses a CaAl-LDH modified biochar composite material based on calcium carbonate slag and corn cob, its preparation method, and its applications. The preparation method uses industrial solid waste calcium carbonate slag as the calcium source for synthesizing CaAl-LDH. First, a mixed salt suspension containing calcium source and aluminum salt is prepared. Then, a co-precipitation method, ball milling, and hydrothermal reaction process are used to thoroughly mix the mixed salt suspension with agricultural waste corn cob particles, followed by a hydrothermal reaction. After filtration and freeze-drying of the filter residue, the CaAl-LDH modified biochar composite material is finally obtained. This invention simultaneously realizes the resource utilization of industrial solid waste and agricultural waste, is green and environmentally friendly, and has low cost. In addition, the ball milling method effectively avoids the consumption of large amounts of alkali solution in traditional processes. Through one-step hydrothermal composite, CaAl-LDH and biochar are more tightly bound, resulting in a composite material with significant synergistic effects in the fields of acidic soil improvement and heavy metal contaminated soil remediation.

Description

Technical Field

[0001] This invention relates to the field of soil remediation materials, and in particular to a CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, its preparation method, and its application. Background Technology

[0002] Acidic soils are widely distributed in southern my country and the Yangtze-Huaihe River basin, with pH values ​​consistently ranging from 4.0 to 5.5. Continuous acidification not only leads to the activation and toxicity of inert metals such as aluminum (Al) and manganese (Mn) in the soil, causing crop black root disease, hindered water and nutrient absorption, and reduced yields, but also disrupts the balance of soil microbial communities. The acidic environment inhibits the activity of beneficial microorganisms such as nitrogen-fixing bacteria, inducing the spread of soil-borne diseases such as root rot. Furthermore, acidic conditions further enhance the mobility and bioavailability of heavy metal ions such as lead (Pb), cadmium (Cd), and mercury (Hg) in the soil, seriously threatening the quality and safety of agricultural products.

[0003] Currently, applying lime, industrial calcium slag, or biochar alone are common methods for improving acidic soils. However, traditional slag-based amendments tend to deteriorate the soil's physical structure and cause compaction, and their stabilization effect on heavy metals is not long-lasting. While biochar alone can increase organic matter content, its acid buffering capacity is limited, making it difficult to effectively remediate acidic soils.

[0004] Layered double hydroxides (LDHs), as a type of layered anionic clay mineral material, have shown excellent performance in heavy metal passivation and acid neutralization. However, pure LDH powder is prone to agglomeration and difficult to recycle, and the conventional preparation cost is high, which limits its large-scale agricultural application. Summary of the Invention

[0005] The purpose of this invention is to propose a CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob and its preparation method, so as to solve the problem of easy agglomeration and difficulty in dispersion of pure LDH powder.

[0006] The present invention also aims to propose an application of CaAl-LDH modified biochar composite material to address the problems of soil acidity and heavy metal pollution.

[0007] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, including steps A and B, wherein step A includes one of step A1 or step A2. Step A1 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; The calcium oxide powder obtained by calcination was dispersed in deionized water to obtain a calcium oxide suspension; Aluminum chloride hexahydrate is dispersed in deionized water and dissolved evenly to obtain an aluminum chloride solution. The above calcium oxide suspension was mixed with aluminum chloride solution, stirred evenly, and the pH value was adjusted to 11.8-12.1 to obtain a mixed salt suspension. Step A2 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; Calcination of aluminum hydroxide yields aluminum oxide powder; The calcium oxide powder obtained by calcination and the alumina powder obtained by calcination are thoroughly mixed and ball-milled. After ball milling, deionized water is added to obtain a mixed salt suspension. Step B includes the following steps: mixing the mixed salt suspension with corn cob particles, and then placing it at 195-205℃ for a hydrothermal reaction for 23-24.5h to obtain a biochar composite material suspension; The biochar composite material suspension was filtered, and the filter residue was freeze-dried to obtain the CaAl-LDH modified biochar composite material.

[0008] In the preparation method of the CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, in step A1, the calcination temperature of the calcium carbonate slag is 940-960℃ and the calcination time is 1.5-2.5h.

[0009] In the method for preparing the CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, in step A1, the concentration of the calcium oxide suspension is 11.1-11.5 g / L, and the concentration of the aluminum chloride solution is 53.2-53.4 g / L.

[0010] In the preparation method of the CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, in step A2, the calcination temperature of the calcium carbonate slag is 940-960℃ and the calcination time is 1.5-2.5h; the calcination temperature of the aluminum hydroxide is 540-560℃ and the calcination time is 3.0-3.5h.

[0011] In the preparation method of CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, in step A2, the ball milling ball ratio is 8mm:5mm:2mm=1:2:3, the ball-to-material ratio is 45-50; the ball milling speed is 400-500rpm, and the ball milling time is 4-6h; the ball milling method is intermittent ball milling in both forward and reverse directions, wherein forward ball milling is performed for 10min, paused for 5min, and then reverse ball milling is performed for the same time.

[0012] In the preparation method of CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, in step A2, the calcium-aluminum ratio in the mixed salt suspension is 2:1 to 1:4.

[0013] In the preparation method of the CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, the mass ratio of the mixed salt suspension to corn cob particles is (3.8-4.5):(4.8-5.2).

[0014] The present invention also provides a CaAl-LDH modified biochar composite material, which is prepared by the method described above for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob.

[0015] The present invention also provides an application of the above-mentioned CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob in soil remediation.

[0016] One of the technical solutions in this invention can have the following beneficial effects: The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob involves a hydrothermal reaction between a mixed salt suspension and corn cob particles. The corn cob particles undergo hydrolysis, dehydration, and aromatization, transforming into biochar with abundant oxygen-containing functional groups (such as -OH and -COOH) and a porous structure. Simultaneously, the calcium and aluminum sources in the mixed salt suspension co-precipitate and crystallize under alkaline hydrothermal conditions to form CaAl-LDH. The oxygen-containing functional groups on the surface of the biochar formed from the corn cob particles adsorb metal cations from the solution through electrostatic attraction, coordination bonds, or hydrogen bonds, resulting in a stronger bond between CaAl-LDH and biochar. This synergistic effect leverages the high specific surface area of ​​biochar and the adsorption and ion exchange properties imparted by the layered structure of CaAl-LDH, leading to a synergistic effect on acidic soil improvement and heavy metal pollution remediation. Attached Figure Description

[0017] Figure 1 This is a material composition analysis diagram from Example 1; wherein, Figure 1 (a) is the XRD pattern of LDH-A. Figure 1 (b) shows the FTIR spectrum of LDH-A. Figure 1 (c) is the EDS image of LDH-A. Figure 1 (d) is the SEM image of LDH-A; Figure 2 This is a material composition analysis diagram from Example 2; wherein, Figure 2 (a) is the XRD pattern of LDH-A. Figure 2(b) shows the FTIR spectrum of LDH-A. Figure 2 (c) is the EDS image of LDH-A. Figure 2 (d) is the SEM image of LDH-A; Figure 3 This is a graph showing the changes in soil pH in Example 3; Figure 4 This is a graph showing the soil organic carbon content of Example 3; Figure 5 This is the overall growth diagram of Example 4; Figure 6 This is a diagram showing the overall plant growth in Example 4. Detailed Implementation

[0018] The technical solution of the present invention will be further illustrated below through specific embodiments. To facilitate understanding of the present invention, a more comprehensive description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0019] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] This invention provides a method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, including steps A and B, wherein step A includes one of step A1 or step A2. Step A1 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; The calcium oxide powder obtained by calcination was dispersed in deionized water to obtain a calcium oxide suspension; Aluminum chloride hexahydrate is dispersed in deionized water and dissolved evenly to obtain an aluminum chloride solution. The above calcium oxide suspension was mixed with aluminum chloride solution, stirred evenly, and the pH value was adjusted to 11.8-12.1 to obtain a mixed salt suspension. Step A2 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; Calcination of aluminum hydroxide yields aluminum oxide powder; The calcium oxide powder obtained by calcination and the alumina powder obtained by calcination are thoroughly mixed and ball-milled. After ball milling, deionized water is added to obtain a mixed salt suspension. Step B includes the following steps: mixing the mixed salt suspension with corn cob particles, and then placing it at 195-205℃ for a hydrothermal reaction for 23-24.5h to obtain a biochar composite material suspension; The biochar composite material suspension was filtered, and the filter residue was freeze-dried to obtain the CaAl-LDH modified biochar composite material.

[0022] The preparation method uses calcium carbonate slag as the calcium source for synthesizing CaAl-LDH. First, a mixed salt suspension containing calcium and aluminum salts is prepared. Then, a ball milling method combined with a hydrothermal reaction process is used to thoroughly mix the mixed salt suspension with corn cob particles from agricultural waste and carry out a hydrothermal reaction to obtain a biochar composite material suspension. Subsequently, after filtration and freeze-drying of the filter residue, the CaAl-LDH modified biochar composite material is finally obtained.

[0023] This invention uses industrial solid waste calcium carbonate slag as the calcium source and agricultural waste corn cobs as the carbon source. By employing ball milling, it effectively avoids the consumption of large amounts of alkaline solution in traditional processes. Furthermore, through direct hydrothermal composite method, the bond between CaAl-LDH and the biochar matrix is ​​made stronger. On the one hand, it realizes the efficient resource utilization of industrial solid waste and agricultural waste, taking into account both environmental and economic benefits. On the other hand, it can synergistically leverage the structural advantages of biochar's high specific surface area and the excellent adsorption and ion exchange properties endowed by the layered structure of CaAl-LDH. This makes the composite material have a significant synergistic effect in the fields of acid soil improvement and heavy metal contaminated soil remediation, with broad application prospects.

[0024] In a specific embodiment of the present invention, a 0.10 mol / L sodium hydroxide solution is used to adjust the pH value to avoid introducing other metal ions that may affect the subsequent hydrothermal reaction.

[0025] The preparation method includes steps A and B. Step A is to prepare a mixed salt suspension for calcium and aluminum salts, which includes one of steps A1 and A2. Step B includes mixing the mixed salt suspension with corn cob particles and then carrying out a hydrothermal reaction to obtain a biochar composite material suspension. The biochar composite material suspension is filtered, and the filter residue is freeze-dried to obtain a CaAl-LDH modified biochar composite material.

[0026] Steps A1 and B are specifically coprecipitation-hydrothermal methods. Through steps A1 and B, CaAl-LDH modified biochar composite material is obtained, hereinafter referred to as LDH-A.

[0027] Step A2 involves ball milling, a process that consumes alkaline substances, resulting in a stronger pH-raising ability, more significant plant growth promotion, and more stable increase in organic carbon in the subsequently prepared CaAl-LDH modified biochar composite. Furthermore, LDH exhibits higher crystallinity, but the conversion is incomplete, resulting in residual peaks of Ca-Al composite oxides and CaO, classifying it as a multiphase composite. Steps A2 and B specifically employ a ball milling-hydrothermal method. The CaAl-LDH modified biochar composite prepared through steps A2 and B is hereinafter referred to as LDH-B. In addition to the characteristic peaks of CaAl-LDH, LDH-B also contains some characteristic peaks of CaO2 and Al2O3. In comparison, the LDH phase in LDH-A is purer.

[0028] Specifically, in step A1, the calcination temperature of the calcium carbonate slag is 940–960°C, and the calcination time is 1.5–2.5 h.

[0029] The complete decomposition temperature of calcium carbonate is approximately 900℃. Below this temperature, decomposition is incomplete, resulting in low calcium oxide yield, the presence of undecomposed phases, insufficient CaO active components, and poor activity. Excessively high temperatures (>1000℃) can lead to severe sintering of calcium oxide. 950℃, located in the middle of this range, is the preferred temperature to ensure rapid and complete decomposition with high product activity.

[0030] The calcium oxide powder obtained after calcining calcium carbonate slag contains common inert impurities that remain stable in subsequent reactions, do not participate in the synthesis reaction of LDH, and do not affect the formation of the target product CaAl-LDH. Therefore, no special chemical or physical impurity removal treatment is required.

[0031] Specifically, in step A1, the concentration of the calcium oxide suspension is 11.1–11.5 g / L, and the concentration of the aluminum chloride solution is 53.2–53.4 g / L.

[0032] By using the above concentration, the calcium and aluminum ions in the reaction system are controlled at a suitable stoichiometric ratio for the formation of CaAl-LDH, resulting in a more complete LDH crystal structure.

[0033] Specifically, in step A2, the calcination temperature of the calcium carbonate slag is 940–960°C, and the calcination time is 1.5–2.5 h; the calcination temperature of the aluminum hydroxide is 540–560°C, and the calcination time is 3.0–3.5 h.

[0034] In a preferred embodiment of the present invention, the calcination temperature of calcium carbonate slag is 950°C and the calcination time is 2 hours; the calcination temperature of aluminum hydroxide is 550°C and the calcination time is 3.5 hours.

[0035] Specifically, in step A2, the ball-to-ball ratio is 8mm:5mm:2mm=1:2:3, the ball-to-material ratio is 45-50, the ball-milling speed is 400-500rpm, the ball-milling time is 4-6h, and the ball-milling method is intermittent ball milling in both forward and reverse directions, wherein the forward ball milling is 10min, paused for 5min, and then the reverse ball milling is performed for the same amount of time.

[0036] A single forward and reverse cycle consists of 10 minutes of forward ball milling, a 5-minute pause, 10 minutes of reverse ball milling, and a 5-minute pause. The 5-minute pause is to prevent overheating inside the tank.

[0037] In a preferred embodiment of the present invention, the ball-to-material ratio is 49. If the ball-to-material ratio is too high, the collisions between the balls increase, which can lead to overheating of the mill jar and severe wear of the milling media; while if the ball-to-material ratio is too low, the grinding balls cannot fully impact the material, resulting in low efficiency.

[0038] In a preferred embodiment of the invention, the ball milling speed is 450 rpm. Higher rotational speeds result in greater energy, but can also easily lead to material overheating, agglomeration, or unwanted phase changes.

[0039] In a preferred embodiment of the present invention, the ball milling time is 5 hours. Longer ball milling time is not necessarily better; once the material reaches a certain fineness, it will enter a grinding equilibrium, and continuing ball milling will only increase impurity contamination.

[0040] Specifically, in step A2, the calcium-to-aluminum ratio in the mixed salt suspension is 2:1 to 1:4.

[0041] By adopting the above calcium-aluminum ratio, the calcium and aluminum ions in the reaction system are controlled at a stoichiometric ratio suitable for the formation of CaAl-LDH, resulting in a more complete LDH crystal structure.

[0042] Specifically, the mass ratio of the mixed salt suspension to corn cob particles is (3.8–4.5):(4.8–5.2).

[0043] If too little corn cob granules are added, the yield will be insufficient, indirectly increasing costs; if too much corn cob granules are added, the CaAL-LDH loading will be insufficient, resulting in inadequate ability to regulate soil pH in the later stages.

[0044] The method for preparing corn cob pellets is as follows: dry the corn cobs in the sun, and then crush them into 5mm pellets for later use.

[0045] The present invention also provides a CaAl-LDH modified biochar composite material, which is prepared by the above-described method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob.

[0046] The CaAl-LDH modified biochar composite material was prepared by the above method, which enabled CaAl-LDH to be generated in situ on the surface of corn cob-derived biochar, achieving uniform loading. The LDH and biochar in the composite material were tightly bound together, and the interfacial bonding strength was high, effectively avoiding the problems of easy agglomeration and difficulty in dispersion of pure LDH powder.

[0047] There are two methods for preparing mixed salt suspensions. Comparatively, the mixed salt suspension prepared by co-precipitation, after being mixed with corn cob particles and subjected to a hydrothermal reaction, results in a purer LDH phase. Calcium and aluminum ions can form organic and inorganic complexes through coordination complexation and electrostatic adsorption, enhancing the chemical stability of the soil and significantly increasing the soil's organic carbon content. Conversely, the mixed salt suspension prepared by ball milling, after being mixed with corn cob particles and subjected to a hydrothermal reaction, exhibits higher LDH crystallinity. The CaAl-LDH modified biochar composite material demonstrates stronger pH-raising ability, more significant plant growth promotion effects, and a more stable increase in organic carbon.

[0048] The present invention also provides an application of the above-mentioned CaAl-LDH modified biochar composite material in soil remediation.

[0049] When the CaAl-LDH modified biochar composite material is used in acidic soil, it can neutralize soil acidity, alleviate aluminum and manganese toxicity, and efficiently passivate heavy metal ions such as lead, cadmium, and mercury, reducing their bioavailability. At the same time, it improves the soil microbial community structure, thus having the dual functions of soil improvement and pollution remediation.

[0050] Example 1 A method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob includes the following steps: Calcium carbonate slag was calcined in a muffle furnace at 950℃ for 2 hours to obtain calcium oxide powder. Weigh 0.28g of calcium oxide powder, disperse it in deionized water, and make up to 25mL. Stir well to obtain a calcium oxide suspension with a concentration of 11.2g / L. Weigh 2.408 g of aluminum chloride hexahydrate and disperse it in 25 mL of deionized water. After dissolving evenly, an aluminum chloride solution with a concentration of 53.26 g / L is obtained. The above calcium oxide suspension was mixed with aluminum chloride solution and stirred until homogeneous. The pH of the solution was adjusted to 12.0 with 0.10 mol / L sodium hydroxide solution to obtain a mixed salt suspension. The mixed salt suspension was placed in a 100ml hydrothermal reactor, 5g of corn cob particles were added, and the mixture was placed in a 200℃ electric heating drying oven for hydrothermal reaction for 24h to obtain a biochar composite material suspension. The biochar composite material suspension was filtered, and the filter residue was freeze-dried to obtain the CaAl-LDH modified biochar composite material.

[0051] Example 2 A method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob includes the following steps: Weigh out calcium carbonate slag and calcine it in a muffle furnace at 950℃ for 2 hours to obtain calcium oxide powder; Weigh aluminum hydroxide and calcine it in a muffle furnace at 550℃ for 3.5 hours to obtain aluminum oxide powder; Weigh out 2.8g of calcium oxide powder and 1.25g of alumina powder and mix thoroughly, then ball mill. The ball ratio is 8mm:5mm:2mm = 1:2:3, and the ball-to-material ratio is 49. Place the mixture in a ball mill and ball mill at 450rpm for 5 hours. The ball milling method is intermittent ball milling in both forward and reverse directions. Forward ball milling is performed for 10 minutes, paused for 5 minutes, and then reverse ball milling is performed for the same amount of time. Subsequently, 100ml of deionized water is added to obtain a mixed salt suspension. The calcium-to-aluminum ratio in the mixed salt suspension is [missing information]. Add 5g of corn cob to the mixed salt suspension and place it in a 200℃ electric heating drying oven for 24h. The biochar composite material suspension was filtered, and the filter residue was freeze-dried to obtain the CaAl-LDH modified biochar composite material.

[0052] The CaAl-LDH modified biochar composite material obtained in Example 1 was named LDH-A, and the CaAl-LDH modified biochar composite material obtained in Example 2 was named LDH-B. Hereinafter, they will be referred to as LDH-A and LDH-B, respectively. The material composition of LDH-A and LDH-B was analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive spectroscopy (EDS), and scanning electron microscopy. The results are shown in [Figure number missing]. Figure 1 and Figure 2 .

[0053] Figure 1 (a) is the XRD pattern of LDH-A, from Figure 1 (a) It can be seen that the characteristic diffraction peaks at 2θ = 14.9°, 22.56°, 31.62° and 45.35° correspond to the (003), (006), (110) and (018) crystal planes of CaAl-LDH, respectively. The appearance of these peaks indicates the formation of a typical LDH layered bimetallic hydroxide structure, indicating that CaAl-LDH was formed in situ on the surface of biochar during the hydrothermal formation of biochar from corn cobs.

[0054] Figure 1 (b) shows the FTIR spectrum of LDH-A. Figure 1 (b) It can be seen that at 3339cm -1The characteristic peak appearing at 2932 cm⁻¹ belongs to the stretching vibration peak of the hydroxyl groups in the aluminum-oxygen octahedral structure. -1 and 1598cm -1 The characteristic peaks appearing at 1060 cm⁻¹ correspond to the stretching and bending vibrations of water molecules in the hydrogen bond network structure, indicating a strong hydrogen bond interaction between water molecules and the interlayer environment. -1 The characteristic peaks appearing at this point are attributed to the bending vibration peaks of hydrogen bonds in the interlayer water.

[0055] Figure 1 (c) EDS image of LDH-A. EDS scanning of the prepared corn cob biochar-supported CaAl-LDH composite material revealed a continuous substrate-like distribution of carbon elements within the observed area. This spatial distribution was highly consistent with the morphology of the corn cob biochar support. The combination of spherical nanosheets and irregular corn cob biochar indicates that the corn cob biochar, as a carbonaceous framework, was fully preserved in the composite material. The enrichment characteristics of oxygen correspond to the lamellar structure of CaAl-LDH—the lamellar structure of CaAl-LDH consists of Ca²⁺. + Al³ + Composed of hydroxyl groups (-OH) and oxygen ligands, it contains a high amount of oxygen. This distribution characteristic further confirms the successful loading of the CaAl-LDH phase onto the surface of biochar.

[0056] Figure 1 (d) is a SEM image of LDH-A. The porous structure of corn cob biochar provides loading sites for CaAl-LDH. CaAl-LDH nanosheets are stacked on the surface of corn cob biochar, indicating that LDH is successfully loaded on the surface of biochar.

[0057] Figure 2 (a) shows the XRD pattern of LDH-B. As can be seen from the figure, the prepared LDH-B has high crystallinity. The diffraction peaks at 2θ=17.27° and 19.97° correspond to the (003) and (006) crystal planes of LDH, respectively. The peaks at 2θ=26.51°, 31.82°, and 39.22° belong to the residual phases of Ca-Al composite oxide or CaO, indicating that the ball milling method has not yet achieved complete transformation, but the main crystalline phase of LDH has been successfully formed.

[0058] Figure 2 (b) is the FTIR plot of LDH-B at 3663 cm⁻¹. -1 The characteristic peak that appears is the oxygen-hydrogen bond stretching vibration peak in calcium aluminum hydrotalcite, at 1583 cm⁻¹. -1 The characteristic peak that appears is the HOH bending vibration peak of interlayer water molecules, at 1425 cm⁻¹. -1 The characteristic peak that appears is attributed to the antisymmetric tensile vibration of CO, at 533 cm⁻¹.-1 The characteristic peaks that appear are caused by MO or M-OH (M represents Ca or Al) lattice vibrations. This further confirms the formation of metal-oxygen bonds in LDH.

[0059] Figure 2 (c) is the EDS image of LDH-B. The prepared corn cob biochar-supported CaAl-LDH composite material was analyzed by EDS scanning. The Ca enrichment region was completely embedded in the carbon matrix, and no obvious element segregation phenomenon was observed.

[0060] Figure 2 (d) is a SEM image of LDH-B, showing a large number of plate-like calcium aluminum hydrotalcite (CaAl-LDH) stacked on the surface of corn cob biochar, indicating a good interfacial bond between CaAl-LDH and corn cob biochar. This tight interfacial bond helps to synergistically leverage the advantages of the high specific surface area of ​​biochar and the adsorption and ion exchange properties conferred by the layered structure of CaAl-LDH.

[0061] Example 3 The steps for testing the effects of LDH-A and LDH-B on soil pH and organic carbon include: (1) Typical acidic soils were collected from Foshan, Guangdong. After removing stones and plant residues, the soils were air-dried and ground, and then passed through a 2mm standard sieve to obtain background soil. The initial pH value of the background soil was 5.56 and the organic carbon content was 35.92g / kg. (2) Seven treatment groups were set up. 400g of background soil was taken from each group and placed in a mixing container. The seven treatment groups included: a blank control group (CK), three LDH-A treatment groups and three LDH-B treatment groups. Blank control group (CK): No conditioner was added. LDH-A treatment group: LDH-A was added at a mass addition ratio of 0.5%, 1.0%, and 2.0% (w / w), respectively, with corresponding addition amounts of 2g, 4g, and 8g, and numbered A2, A4, and A8. LDH-B treatment group prepared in Example 2: LDH-B was added at a mass addition ratio of 0.5%, 1.0%, and 2.0% (w / w), respectively, with corresponding addition amounts of 2g, 4g, and 8g, and numbered B2, B4, and B8. (3) Place the quantitative amendment material and soil in a container, and use mechanical vibration or multi-dimensional mixing to ensure that the conditioner and soil particles are fully in contact and mixed; (4) Moisture adjustment: 80 mL of tap water was added to each group to make the soil moisture content reach 20% of the field capacity, simulating a natural moist state; (5) Potted plant aging: Transfer the well-mixed soil sample to uniformly sized flowerpots. Aging is carried out in a constant temperature and humidity environment at 25℃, away from light; (6) Sampling and testing: Core soil samples from the middle layer of each basin were collected on the 7th and 14th days after aging, and their physicochemical properties were measured. After the experiment, the pH value and soil organic carbon (SOC) content of each treatment group were measured. The results are shown in Table 1. Figure 3 and Figure 4 .

[0062] Table 1 - Effects of different gradients of LDH-modified biochar addition on soil pH and organic carbon two weeks later.

[0063] Figure 3 This study demonstrates the changes in soil pH under different treatment systems. Soil pH was measured in the first and second weeks according to the determination methods specified in China's National Environmental Protection Standard (HJ962-2018). Figure 3 It was found that two weeks after the application of the soil conditioner, the soil pH increased significantly. The pH of the control group without conditioner was 5.56, while the pH of the treatment group with 8g of LDH-B conditioner reached a maximum of 6.88. In a neutral soil environment (pH=6.5~7.5), the availability of nitrogen, phosphorus, potassium, and various trace elements is usually at a high level, which is conducive to microbial activity and plant growth.

[0064] Figure 4 The dynamic changes in soil organic carbon content under different treatment systems were demonstrated. Organic carbon content was determined strictly according to the HJ615-2011 standard method. Compared to the control group (35.9 g / kg) without conditioner, all treatment groups treated with LDH-A or LDH-B showed varying degrees of organic carbon accumulation, with significant increases, fully demonstrating the effectiveness and potential of the soil conditioner developed in this invention in carbon sequestration and enrichment.

[0065] Example 4 The steps for testing the effects of LDH-A and LDH-B on plant germination and overall growth include: (1) Select water spinach seeds that are plump and uniform in size, soak them in tap water at 25℃ for 24 hours to promote germination, and change the water twice during the process. After the seeds absorb water and swell, they are ready for use. (2) Using the typical acidic soil of Foshan described in Example 3, a total of 7 treatment groups (CK, A2, A4, A8, B2, B4, B8) were set up, and 400g of soil was taken from each group. According to the method of steps (2) to (4) in Example 3, the corresponding dose of LDH-A or LDH-B was thoroughly mixed with the soil, the moisture was adjusted to 20% of the field water holding capacity, and the mixture was put into planting pots of uniform size; (3) Sow seeds on the soil surface of each pot using the spot sowing method, digging planting holes 1 cm deep at the corners (leaving a 1 cm margin) and center of a regular hexagon. Sow 3 treated seeds in each hole; (4) After sowing, cover with a thin layer of soil and water appropriately to keep the surface moist. During the experiment, the plants were placed in an artificial climate chamber at 25°C and watered once a day at regular intervals to ensure that the moisture conditions of each group were consistent. (5) Observe the germination of water spinach in each group daily, and count the final germination rate on the 4th day. The results are shown in the table below. Figure 5 .

[0066] (6) Regularly measure the plant height (bud height) of water spinach seedlings and observe the apparent growth of the plants, such as leaf color and root development. The results are shown in the table below. Figure 6 .

[0067] like Figure 5 As shown, the treatment groups with added LDH-A and LDH-B exhibited significantly higher germination rates than the control group, demonstrating a remarkable promoting effect. This phenomenon fully demonstrates that the composite material not only efficiently neutralizes soil acidity but also effectively alleviates the toxic stress caused by aluminum ions on seed germination, thereby reconstructing and optimizing the micro-ecological environment required for seed germination.

[0068] Figure 6 The graph shows the overall growth status and plant height changes of water spinach in different treatment groups. As shown in the figure, after 14 days of continuous observation, the water spinach in each group showed significant differences in growth performance and distinct morphological development levels. Among them, the 8g LDH-B treatment group showed the most vigorous growth, with an average plant height of 12.1cm, ranking first among all groups; followed by the 4g LDH-B treatment group, which also showed good plant height at 10.7cm, demonstrating a good promoting effect; while the blank control group (CK) was limited by the acidic stress environment, and its growth was inhibited, with a plant height of only 9.9cm, which was significantly lagging behind, highlighting the key role of the improvement measures in plant growth.

[0069] Comparative analysis revealed that the LDH-B composite conditioner prepared in this invention exhibits excellent growth-promoting efficacy. LDH-B, with its unique layered crystal structure, can achieve slow-release regulation of alkalinity, thereby synergistically working with the highly developed porous network of biochar to significantly optimize soil physicochemical properties and comprehensively improve soil fertility. This synergistic mechanism effectively neutralizes acid stress and alleviates its inhibitory effect on water spinach root development, thus promoting plant growth at the physiological level and significantly increasing crop biomass accumulation, demonstrating broad application prospects.

[0070] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, characterized in that, It includes steps A and B, where step A includes either step A1 or step A2; Step A1 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; The calcium oxide powder obtained by calcination was dispersed in deionized water to obtain a calcium oxide suspension; Aluminum chloride hexahydrate is dispersed in deionized water and dissolved evenly to obtain an aluminum chloride solution. The above calcium oxide suspension was mixed with aluminum chloride solution, stirred evenly, and the pH value was adjusted to 11.8-12.1 to obtain a mixed salt suspension. Step A2 includes the following steps: Calcium carbonate slag is calcined to obtain calcium oxide powder; Calcination of aluminum hydroxide yields aluminum oxide powder; The calcium oxide powder obtained by calcination and the alumina powder obtained by calcination are thoroughly mixed and ball-milled. After ball milling, deionized water is added to obtain a mixed salt suspension. Step B includes the following steps: mixing the mixed salt suspension with corn cob particles, and then placing it at 195-205℃ for a hydrothermal reaction for 23-24.5h to obtain a biochar composite material suspension; The biochar composite material suspension was filtered, and the filter residue was freeze-dried to obtain the CaAl-LDH modified biochar composite material.

2. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 1, characterized in that, In step A1, the calcination temperature of the calcium carbonate slag is 940–960°C, and the calcination time is 1.5–2.5 h.

3. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 2, characterized in that, In step A1, the concentration of the calcium oxide suspension is 11.1–11.5 g / L, and the concentration of the aluminum chloride solution is 53.2–53.4 g / L.

4. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 1, characterized in that, In step A2, the calcination temperature of the calcium carbonate slag is 940–960℃, and the calcination time is 1.5–2.5 h; the calcination temperature of the aluminum hydroxide is 540–560℃, and the calcination time is 3.0–3.5 h.

5. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 1, characterized in that, In step A2, the ball-to-ball ratio is 8mm:5mm:2mm=1:2:3, the ball-to-material ratio is 45-50, the ball-milling speed is 400-500rpm, the ball-milling time is 4-6h, and the ball-milling method is intermittent ball milling in both forward and reverse directions, wherein the forward ball milling is 10min, paused for 5min, and then the reverse ball milling is performed for the same time.

6. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 1, characterized in that, In step A2, the calcium-to-aluminum ratio in the mixed salt suspension is 2:1 to 1:

4.

7. The method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob according to claim 1, characterized in that, The mass ratio of the mixed salt suspension to corn cob particles was (3.8–4.5):(4.8–5.2).

8. A CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob, characterized in that, The CaAl-LDH modified biochar composite material is prepared by the method for preparing CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob as described in any one of claims 1 to 7.

9. The application of a CaAl-LDH modified biochar composite material based on calcium carbonate slag-corn cob as described in claim 8 in soil remediation.

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