Biochemical composite soil heavy metal pollution fixing and repairing material and preparation method thereof

Abstract

The invention provides a biochemical composite soil heavy metal pollution fixing and repairing material and a preparation method thereof.The preparation method comprises the steps that biochar is subjected to acid treatment, and activated biochar is obtained; uniformly mixing calcium salt, ferric salt, aluminum salt and deionized water to obtain a mixed salt solution, adding urea to obtain a precursor solution, dipping the activated charcoal in the precursor solution, and then performing hydrothermal reaction to obtain loaded charcoal; mixing and grinding the oyster shell powder and dipotassium phosphate, and calcining at high temperature to obtain activated oyster shell powder; mixing the bacillus subtilis liquid, the activated oyster shell powder and trehalose, oscillating, centrifugally separating, and freeze-drying to obtain the biological composite material. Uniformly mixing the loaded biochar, the biological composite material and a carboxymethyl cellulose solution, granulating, and drying wet granules to obtain the biochemical compound type soil heavy metal pollution fixing and repairing material. According to the prepared fixing and repairing material, the fixing efficiency and adaptability to various heavy metals in soil are improved.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology and relates to a biochemical composite soil heavy metal pollution fixation and remediation material and its preparation method. Background Technology

[0002] With the rapid development of industry and agriculture, soil heavy metal pollution has become a severe global environmental challenge. Currently, technologies for remediating heavy metal-contaminated soil mainly rely on two strategies: one is to separate and remove heavy metals from the soil, and the other is to alter their form in the soil, reducing their bioavailability and mobility. Among various remediation methods, in-situ passivation remediation technology is considered to have good application prospects due to its relatively low cost, ease of operation, and high efficiency in remediating moderately to lightly contaminated soils.

[0003] The core of this technology lies in adding passivating materials to the soil to fix heavy metals through adsorption, precipitation, and complexation. Traditionally used soil amendments are diverse, including inorganic materials such as lime, zeolite, and bentonite, as well as organic materials such as compost. However, each of these materials has its limitations: for example, lime-based passivating agents remediate pollution by increasing soil pH, but the effect may be difficult to sustain due to the soil's self-purification capacity, posing a risk of reactivation; while some organic solidifying agents may have limited remediation effects or even cause secondary pollution.

[0004] In recent years, biochar has attracted widespread attention due to its wide availability of raw materials and good environmental compatibility. However, biochar prepared by simple pyrolysis often has limited adsorption and fixation capacity for heavy metals in terms of pore structure and surface chemical properties. Meanwhile, biochemical composite materials that combine chemical passivation with bioremediation have shown great potential. These materials aim to comprehensively utilize the stability of inorganic materials, the modifying properties of organic materials, and the degradation and transformation capabilities of microorganisms to achieve synergistic remediation.

[0005] Therefore, there is an urgent need to develop a remediation material that is efficient, stable, free of secondary pollution, and suitable for sites with complex contamination. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a biochemical composite soil heavy metal pollution fixation and remediation material and its preparation method.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a biochemically composite soil heavy metal pollution immobilization and remediation material, the preparation method comprising:

[0009] (I) Acid treatment of biochar to obtain activated biochar; calcium salt, iron salt, aluminum salt and deionized water are mixed evenly to obtain a mixed salt solution, urea is added to the mixed salt solution to obtain a precursor solution, the activated biochar is impregnated in the precursor solution, and then a hydrothermal reaction is carried out. After the reaction is completed, the biochar is obtained by filtration, washing and drying.

[0010] (II) Oyster shell powder is mixed and ground with dipotassium hydrogen phosphate and then calcined at high temperature to obtain activated oyster shell powder; Bacillus subtilis bacterial solution, the activated oyster shell powder and trehalose are mixed and shaken, and then centrifuged and freeze-dried to obtain a biocomposite material;

[0011] (III) The loaded biochar, the biocomposite material and the carboxymethyl cellulose solution are mixed evenly and then granulated to obtain wet granules. The wet granules are then dried to obtain the biochemical composite soil heavy metal pollution fixation and remediation material.

[0012] This invention first involves acid activation and hydrothermal reaction of biochar, then loading layered calcium, iron, and aluminum hydroxide (LDH) onto the activated biochar. Subsequently, oyster shell powder is calcined and activated, then combined with Bacillus subtilis to prepare a biocomposite material. Finally, both are mixed with carboxymethyl cellulose solution and granulated, achieving multiple effects of physical adsorption, chemical precipitation, and bioremediation. The loaded biochar utilizes its well-developed porous structure and the ion exchange capacity of LDH to rapidly capture heavy metal ions. The biocomposite material provides long-term stabilization through microbial metabolism and phosphate precipitation, thereby significantly improving the fixation efficiency and adaptability of various heavy metals (such as lead, cadmium, and arsenic) in soil. This solves the problems of the short-lasting effects of traditional materials, the limited remediation capacity of organic materials, and the potential for secondary pollution.

[0013] First, this invention involves acid treatment of biochar to obtain activated biochar, followed by a hydrothermal reaction with a mixed salt solution (calcium, iron, and aluminum salts) and urea to finally obtain loaded biochar. Biochar itself has a porous structure and can capture heavy metal ions through physical adsorption; however, the surface functional groups of simply pyrolyzed biochar are limited, resulting in insufficient affinity for heavy metals. Therefore, this invention uses a mixed acid solution composed of nitric acid and phosphoric acid to microwave-activate the biochar, eroding its surface, increasing its specific surface area and porosity, and simultaneously introducing oxygen-containing functional groups, carboxyl and hydroxyl groups. These functional groups can directly adsorb heavy metal ions through complexation reactions, increasing the initial adsorption capacity of the biochar. However, the fixation effect of the activated biochar is unstable due to environmental changes. This invention utilizes calcium, iron, and aluminum salts to form a layered metal hydroxide (LDH) structure with urea under hydrothermal conditions, which is then in situ loaded into the pores of activated biochar. LDH is a layered material whose layers are composed of metal hydroxides, and the interlayers can accommodate anions. This structure gives it a strong adsorption and ion exchange capacity for heavy metal ions. In soil environments, heavy metals such as lead and cadmium often exist in the form of cations or complexed anions. LDH can fix heavy metals in its layered structure through interlayer anion exchange, thereby reducing the mobility and bioavailability of heavy metals and providing more durable chemical fixation. Activated biochar, as a porous carrier of LDH, provides support for the nucleation and growth of LDH and prevents LDH particle aggregation. At the same time, LDH can be embedded in the pores of activated biochar, utilizing its high charge density and buffering capacity to compensate for the insufficient functional group activity of activated biochar in low pH environments, thereby enhancing the adsorption of various heavy metals.

[0014] Subsequently, this invention involves calcining oyster shell powder with dipotassium hydrogen phosphate to obtain activated oyster shell powder, which is then mixed with Bacillus subtilis bacterial solution and trehalose and freeze-dried. The main component of oyster shell powder is calcium carbonate, which, upon calcination, generates calcium oxide and reacts with dipotassium hydrogen phosphate to form calcium phosphate compounds. These components can react with heavy metal ions (cadmium, zinc) through precipitation reactions to form insoluble phosphates or carbonates, thereby reducing their bioavailability. Furthermore, the activated oyster shell powder after calcination possesses a rich porous structure and a large specific surface area, providing an ideal carrier for the adsorption and colonization of Bacillus subtilis. When the Bacillus subtilis bacterial solution is mixed and shaken with the activated oyster shell powder, bacterial cells can be effectively loaded onto the particle surface and pores of the activated oyster shell powder, prolonging the retention time of the bacterial agent in the soil and preventing the loss of free bacteria through erosion. Bacillus subtilis is a common probiotic that produces extracellular polymers and organic acids through its metabolic activities. These substances can chelate heavy metals, reducing high-valence heavy metals to low-valence states and decreasing their toxicity. Simultaneously, the bacteria's life activities may promote the dissolution and release of phosphates in activated oyster shell powder. Phosphate ions form phosphate precipitates with lower solubility with heavy metals (such as lead and cadmium), thus achieving a synergistic effect of biological action and chemical precipitation.

[0015] Finally, this invention involves mixing and granulating loaded biochar and biocomposite materials with a carboxymethyl cellulose solution to obtain a soil heavy metal pollution fixation and remediation material. Carboxymethyl cellulose, acting as a binder, not only enhances the mechanical strength of the particles, making them less prone to breakage during transportation and application, but also possesses certain water solubility and biodegradability, enabling the slow release of active ingredients and extending remediation time. Loaded biochar is used for rapid adsorption and chemical fixation, while the biocomposite materials are used for long-term bioremediation and precipitation. The combination of loaded biochar and biocomposite materials can address the diverse heavy metal problems in complexly contaminated sites, simultaneously treating both cationic (e.g., lead, cadmium) and anionic (e.g., arsenic) heavy metals.

[0016] As a preferred technical solution of the present invention, in step (I), the activated biochar is prepared by the following method:

[0017] (1) Bamboo powder and calcium carbonate are mixed evenly and subjected to gradient pyrolysis under nitrogen atmosphere. Then, bamboo-based biochar is obtained by crushing, sieving and acid washing.

[0018] (2) The bamboo-based biochar was dispersed in a mixed acid solution composed of nitric acid solution and phosphoric acid solution and then activated by microwave. After filtration, washing and drying, the activated biochar was obtained.

[0019] First, bamboo powder and calcium carbonate are mixed under nitrogen protection and subjected to gradient pyrolysis. This gradient pyrolysis gradually carbonizes the organic matter in the bamboo powder, forming a stable carbon skeleton structure. Calcium carbonate decomposes at high temperatures to produce carbon dioxide gas. As this gas escapes from the biochar, it erodes and creates numerous pores, significantly increasing the material's specific surface area and pore volume, providing more attachment sites and diffusion channels for subsequent reactions.

[0020] The bamboo-based biochar was then placed in a mixed acid solution composed of nitric acid and phosphoric acid and activated under microwave radiation. Microwave heating ensures uniform heating throughout the solution, resulting in high energy transfer efficiency and avoiding the problem of excessive surface reaction and insufficient internal activation that may occur with traditional heating methods. The nitric acid and phosphoric acid in the mixed acid solution have strong oxidizing properties, capable of corroding the biochar surface and etching out finer nanoscale pores. Simultaneously, they introduce a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the surface. These functional groups can specifically bind to heavy metal ions in the soil through ion exchange and surface complexation, significantly enhancing the biochar's chemical adsorption capacity. Furthermore, the addition of phosphoric acid helps form phospho groups in the carbon framework, further improving the material's fixation effect on heavy metals such as lead and cadmium.

[0021] The resulting activated biochar serves as a carrier for subsequent loading of layered hydrogen hydroxide (LDH). Its rich porous structure provides ample growth space for LDH generation, preventing particle agglomeration. Furthermore, the functional groups on its surface can chemically bond with LDH to form a more stable composite structure, thereby jointly enhancing the load-bearing biochar's ability to fix heavy metals and its environmental adaptability.

[0022] As a preferred technical solution of the present invention, in step (1), the mass ratio of bamboo powder to calcium carbonate is 1:(0.8~1.2), for example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] This invention specifically defines the mass ratio of bamboo powder to calcium carbonate as 1:(0.8~1.2). During the gradient pyrolysis process, calcium carbonate decomposes upon heating to produce carbon dioxide gas. This gas escapes from the carbon skeleton formed by the carbonization of bamboo powder, effectively eroding pores and increasing the specific surface area and pore volume of the biochar. When the amount of calcium carbonate is within this range, it is sufficient to provide an appropriate amount of carbon dioxide, promoting uniform pore formation and ensuring that the biochar has a suitable pore size distribution. This is beneficial for subsequent acid activation and LDH loading, while also maintaining the mechanical strength of the biochar.

[0024] When the amount of calcium carbonate used is below the lower limit of the range defined in this invention, the amount of carbon dioxide gas produced is too small, making it difficult to effectively create pores. As a result, the pore structure of the biochar obtained is not fully developed, the specific surface area is small, and the number of surface functional group sites is limited, which reduces the physical adsorption capacity of the biochar.

[0025] When the amount of calcium carbonate used exceeds the upper limit of the range defined in this invention, excessive carbon dioxide gas will be generated. During the pyrolysis process, the gas escapes too violently, eroding and forming excessively large or interconnected pores, and even destroying the integrity of the carbon skeleton, resulting in biochar with excessively large pores but low strength.

[0026] In some optional instances, the gradient pyrolysis operation steps include sequential low-temperature pyrolysis and high-temperature pyrolysis.

[0027] In some optional instances, the heating rate of the low-temperature pyrolysis is 3~5℃ / min, for example, it can be 3.0℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4.0℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min or 5.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In some optional instances, the pyrolysis temperature of the low-temperature pyrolysis is 300~400℃, for example, it can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some optional instances, the holding time for the low-temperature pyrolysis is 60 to 90 minutes, for example, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In some optional instances, the heating rate of the high-temperature pyrolysis is 5~10℃ / min, for example, it can be 5.0℃ / min, 5.5℃ / min, 6.0℃ / min, 6.5℃ / min, 7.0℃ / min, 7.5℃ / min, 8.0℃ / min, 8.5℃ / min, 9.0℃ / min, 9.5℃ / min or 10.0℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional instances, the pyrolysis temperature of the high-temperature pyrolysis is 600~700℃, for example, it can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃ or 700℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] In some optional instances, the holding time for the high-temperature pyrolysis is 60 to 90 minutes, for example, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In the gradient pyrolysis process, the initial low-temperature pyrolysis stage aims to stably decompose components such as hemicellulose and cellulose in bamboo powder, forming the initial pore structure. The pyrolysis temperature is set at 300–400℃ to effectively remove volatile organic compounds and moisture, while preventing biochar pore collapse due to sudden temperature increases, thus contributing to the formation of a preliminary carbon skeleton structure with a certain mechanical strength. The subsequent high-temperature pyrolysis stage raises the temperature to 600–700℃. Within this temperature range, recalcitrant components such as lignin in the bamboo powder are fully carbonized, the carbon skeleton undergoes further aromatic reorganization, and the graphitization degree of the biochar increases. This leads to the construction of a more developed pore network on the already formed preliminary skeleton, promoting the formation of micropores and mesopores, and significantly increasing the specific surface area of ​​the biochar.

[0034] By using a stepped pyrolysis method, the pore blockage and structural defects caused by single high-temperature pyrolysis are avoided. The resulting bamboo-based biochar has a more developed and interconnected three-dimensional pore structure, which not only provides a more effective reaction interface for subsequent acid washing and microwave activation, but also creates an ideal and sufficient growth space for the formation and loading of LDH.

[0035] In some optional instances, the mesh size of the sieve used for crushing and sieving is 100 to 120 mesh, for example, 100 mesh, 102 mesh, 104 mesh, 106 mesh, 108 mesh, 110 mesh, 112 mesh, 114 mesh, 116 mesh, 118 mesh or 120 mesh, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] In some optional instances, the pickling process includes:

[0037] The pulverized and sieved biochar powder is added to a 2-3 wt% dilute hydrochloric acid solution, for example, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%. The mixture is stirred and washed at 60-80°C for 1-2 hours. The stirring temperature can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, or 80°C, and the stirring time can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, or 2.0 h. The mixture is then filtered, washed with deionized water until neutral, and dried to obtain the bamboo-based biochar. However, the values ​​are not limited to those listed; other unlisted values ​​within this range are also applicable.

[0038] As a preferred technical solution of the present invention, in step (2), the solid-liquid ratio of the bamboo-based biochar to the mixed acid solution is 1g:(12~15)mL, for example, it can be 1g:12mL, 1g:12.5mL, 1g:13mL, 1g:13.5mL, 1g:14mL, 1g:14.5mL or 1g:15mL, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] In some selected examples, the mixed acid solution is a homogeneous mixture of phosphoric acid solution and nitric acid solution in a volume ratio of (2~3):1, for example, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0040] In the preparation of activated biochar, a mixed acid solution consisting of phosphoric acid and nitric acid was selected, with the volume ratio of phosphoric acid to nitric acid controlled within the range of (2~3):1. Nitric acid is a strong oxidizing acid, and its main function is to rapidly erode the carbon skeleton of biochar, etching a large number of pores on the surface of biochar through oxidation, thereby significantly increasing its specific surface area. Simultaneously, the oxidizing effect of nitric acid can introduce oxygen-containing functional groups, especially carboxyl and hydroxyl groups, onto the surface of the carbon material. These functional groups can directly bind to heavy metal ions through ion exchange and surface complexation, enhancing the chemical adsorption capacity of biochar. However, if nitric acid is used alone or in excessive amounts, its strong oxidizing properties can lead to excessive corrosion of the carbon skeleton of biochar, destroying or even collapsing the microporous structure, which is detrimental to the formation of a stable and well-developed pore structure.

[0041] Phosphoric acid solution has a weaker oxidizing power than nitric acid solution, thus its erosion of the carbon skeleton is more gentle, which helps to form and retain a more stable mesoporous and macroporous structure. Furthermore, under heating conditions, phosphoric acid solution can undergo a deeper chemical reaction with the carbon matrix in biochar. Phosphoric acid molecules can intercalate into the carbon skeleton and react with hydroxyl groups and other groups on carbon atoms to form carbon-phosphorus-oxygen (COP) phosphate esters or polyphosphates. These phosphorus-containing functional groups have a strong affinity for heavy metals such as lead and cadmium, forming stable phosphate precipitates. Simultaneously, it can enhance the cross-linking degree of the biochar skeleton, making the activated biochar structure more stable and less prone to structural collapse during subsequent use.

[0042] In some alternative instances, the phosphoric acid solution has a mass fraction of 10 to 15 wt%, for example, 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt%, or 15 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] In some alternative instances, the nitric acid solution has a mass fraction of 10 to 15 wt%, for example, 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt%, or 15 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0044] In some optional instances, the microwave power for microwave activation is 300 to 400 W, for example, 300 W, 310 W, 320 W, 330 W, 340 W, 350 W, 360 W, 370 W, 380 W, 390 W or 400 W, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0045] In some optional instances, the microwave activation treatment time is 10 to 15 minutes, for example, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes, or 15 minutes, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0046] In some optional instances, the drying temperature is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] In some optional instances, the drying time is 6 to 8 hours, for example, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0048] As a preferred technical solution of the present invention, in step (I), the calcium salt includes calcium nitrate.

[0049] In some alternative instances, the iron salt includes ferric nitrate.

[0050] In some optional instances, the aluminum salt includes aluminum nitrate.

[0051] The LDH prepared by this invention has a main layer composed of positively charged calcium, iron, and aluminum hydroxides, while the spaces between the layers are filled with exchangeable anions and water molecules. The relatively large radius of calcium ions helps to form and stabilize the overall layered structure. Simultaneously, the introduction of calcium provides a certain degree of alkalinity to the material, enabling the slow release of hydroxide ions in the soil, gently regulating soil pH and mitigating the activity of heavy metals in acidic soil environments. Iron and aluminum ions, due to their high charge density, significantly enhance the positive charge of the layers, resulting in a strong electrostatic attraction and adsorption capacity of LDH for negatively charged anionic heavy metals such as arsenate in the soil.

[0052] For anionic heavy metals such as arsenate, LDH materials primarily capture and immobilize them within their layered structures through interlayer anion exchange. For cationic heavy metals such as lead and cadmium, the metal hydroxyl sites on the surface of LDH materials can firmly adsorb them onto the surface through complexation. Furthermore, the alkaline substances slowly released by the LDH materials themselves can moderately increase the soil pH, promoting the formation of hydroxide or carbonate precipitates for some heavy metals, thereby reducing their solubility and bioavailability. LDH materials composed of metal elements with different valence states and ionic radii can effectively address heavy metal pollution in multiple chemical forms simultaneously, overcoming the limitation of single-component materials that are often only effective against a specific type of heavy metal.

[0053] In some optional instances, the Ca in the mixed salt solution 2+ Fe 3+ And Al 3+The molar ratio is 3:(0.3~0.5):(0.5~0.7), for example, it can be 3:0.3:0.7, 3:0.32:0.68, 3:0.34:0.66, 3:0.36:0.64, 3:0.38:0.62, 3:0.4:0.6, 3:0.42:0.58, 3:0.44:0.56, 3:0.46:0.54, 3:0.48:0.52 or 3:0.5:0.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] This invention specifically limits the Ca in mixed salt solutions. 2+ Fe 3+ And Al 3+ The molar ratio is 3:(0.3~0.5):(0.5~0.7). LDH materials are usually composed of divalent and trivalent metal ions in a specific ratio, Fe 3+ The introduction of Fe can enhance the material's adsorption capacity for anionic heavy metals (such as arsenate) because Fe 3+ Providing a high positive charge density in the laminate promotes electrostatic attraction; while Al 3+ This helps maintain the alkaline environment and structural stability of the layers. The combination of two trivalent metal ions avoids the crystallization defects caused by an excess of a single trivalent ion, resulting in a well-developed specific surface area and uniform interlayer channels in the final LDH, which is beneficial for immobilizing multiple heavy metals through ion exchange and surface complexation.

[0055] When Fe 3+ Excessive Fe content can lead to an excessively high positive charge density in the LDH layers, increasing the exchange capacity of anions between layers. However, it can also cause the layered structure to become too dense, reducing porosity and affecting the diffusion and adsorption of heavy metal ions. Furthermore, excessive Fe... 3+ It also promotes the formation of amorphous phases, reducing the crystallinity of LDH and weakening its long-term stability; in soil environments, Fe... 3+ Excessive amounts of LDH materials make them more susceptible to dissolution under acidic conditions, releasing iron ions and causing secondary soil pollution. Conversely, when Fe... 3+ When the dosage is too low, it will lead to a decrease in the number of adsorption sites for anionic heavy metals in the LDH material, Fe 3+ It is a key component for fixing elements such as arsenic. If its dosage is too low, the fixation effect of LDH on these heavy metals will decrease. In addition, a low total amount of trivalent ions will affect the structural integrity of LDH, resulting in insufficient strength of the layer and making it susceptible to degradation by environmental factors in the soil.

[0056] When Al 3+Excessive use of Al can lead to an excessively high positive charge density in the LDH layer, making the layered structure too dense. This reduces the number of adsorption sites for heavy metals, decreasing ion exchange capacity. Furthermore, it can cause uneven charge distribution in the LDH layer, affecting ion exchange efficiency. 3+ It is easily soluble in soil, especially under acidic conditions, and can be toxic to plants and microorganisms, leading to secondary soil pollution. Conversely, when Al... 3+ When the dosage is too low, due to Al 3+ It can effectively promote the orderly arrangement of LDH layers. Insufficient dosage will lead to a decrease in the crystallinity of LDH, a loose layered structure, a smaller specific surface area, a decrease in the physical adsorption capacity of LDH material, a reduction in surface hydroxyl sites, and an impact on the complexation of cationic heavy metals.

[0057] In some optional instances, the Ca in the mixed salt solution 2+ Fe 3+ And Al 3+ The total concentration is 0.4~0.6 mol / L, for example, it can be 0.4 mol / L, 0.42 mol / L, 0.44 mol / L, 0.46 mol / L, 0.48 mol / L, 0.5 mol / L, 0.52 mol / L, 0.54 mol / L, 0.56 mol / L, 0.58 mol / L or 0.6 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] This invention specifically limits the Ca in mixed salt solutions. 2+ Fe 3+ And Al 3+ The total concentration is 0.4~0.6 mol / L. Within this concentration range, sufficient hydrolysis and precipitation reactions can be ensured on the pore surface and inside of the activated biochar, promoting the formation and stable growth of LDH crystal nuclei, achieving uniform LDH loading, and avoiding LDH particle agglomeration caused by insufficient LDH loading due to excessively low concentration or excessively high local concentration. In addition, urea decomposes under hydrothermal conditions to release ammonia and carbon dioxide, which can slowly increase the pH value of the reaction system, guiding the orderly precipitation of metal ions to form a regular layered structure, rather than rapidly forming amorphous precipitates. The addition of urea helps to form LDH with good crystallinity and a large specific surface area, thereby enhancing its adsorption and fixation capacity for heavy metal ions.

[0059] When the total concentration is below 0.4 mol / L, the low ion concentration slows down the nucleation rate, resulting in fewer LDH nuclei and incomplete crystal growth. Consequently, the amount of LDH loaded is limited, and the specific surface area of ​​biochar cannot be fully utilized. In subsequent hydrothermal reactions, due to the low reactant concentration, the crystallinity of LDH is poor, and the layered structure is not fully developed, weakening its ion exchange and surface complexation capabilities.

[0060] When the total concentration exceeds 0.6 mol / L, excessive ions in the solution cause metal ions to precipitate rapidly in the early stages of the hydrothermal reaction, easily forming amorphous hydroxide aggregates rather than ordered LDH crystals. This results in coarse LDH particles that clog the pores of the biochar, reducing the number of effective adsorption sites. Furthermore, excessively high ion concentrations increase the viscosity of the mixed salt solution, hindering the diffusion of metal ions within the biochar and causing LDH to be primarily loaded on the surface of the biochar rather than within it.

[0061] In some alternative examples, the urea and the Ca in the mixed salt solution 2+ Fe 3+ And Al 3+ The total molar ratio is (3~5):1, for example, it can be 3.0:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4.0:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1 or 5.0:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0062] In some optional instances, the solid-liquid ratio of the activated biochar to the precursor solution is 1 g:(15~20) mL, for example, it can be 1 g:15 mL, 1 g:15.5 mL, 1 g:16 mL, 1 g:16.5 mL, 1 g:17 mL, 1 g:17.5 mL, 1 g:18 mL, 1 g:18.5 mL, 1 g:19 mL, 1 g:19.5 mL or 1 g:20 mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0063] In some optional instances, the immersion time of the activated biochar in the precursor solution is 3 to 5 hours, for example, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, or 5.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0064] In some alternative instances, the temperature of the hydrothermal reaction is 100~150°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0065] In some optional instances, the hydrothermal reaction time is 10 to 15 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, or 15 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0066] In some optional instances, the drying temperature is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0067] In some optional instances, the drying time is 6 to 8 hours, for example, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0068] As a preferred technical solution of the present invention, in step (II), the mass ratio of the oyster shell powder to the dipotassium hydrogen phosphate is 1:(0.1~0.2), for example, it can be 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19 or 1:0.2, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] This invention specifically limits the mass ratio of oyster shell powder to dipotassium hydrogen phosphate to 1:(0.1~0.2). Within this range, high-temperature calcination is carried out. The main component of oyster shell powder, calcium carbonate, can react with dipotassium hydrogen phosphate to form calcium phosphate and pyrophosphate on the surface of oyster shell powder particles. These phosphorus-containing groups have a strong affinity for heavy metal ions such as lead and cadmium in the soil and can form stable phosphates through precipitation reactions, thereby enhancing the chemical fixation ability of the material.

[0070] When the amount of dipotassium hydrogen phosphate is too low, the number of phosphate active sites introduced is limited, which restricts its ability to precipitate and fix heavy metals. When the amount of dipotassium hydrogen phosphate is too high, excessive phosphate will coat the surface of oyster shell powder during high-temperature calcination, blocking the pore structure of the oyster shell powder, reducing its specific surface area, and hindering the subsequent attachment and reproduction of Bacillus subtilis.

[0071] In some optional instances, the high-temperature calcination temperature of the oyster shell powder and the dipotassium hydrogen phosphate is 180~200℃, for example, it can be 180℃, 182℃, 184℃, 186℃, 188℃, 190℃, 192℃, 194℃, 196℃, 198℃ or 200℃, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0072] In some optional instances, the high-temperature calcination time of the oyster shell powder and the dipotassium hydrogen phosphate is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0073] As a preferred embodiment of the present invention, in step (II), the viable count of the Bacillus subtilis bacterial solution is ≥10. 9 CFU / mL.

[0074] In some alternative examples, the solid-liquid ratio of the activated oyster shell powder to the Bacillus subtilis culture is 1g:(2~3)mL, for example, it can be 1g:2.0mL, 1g:2.1mL, 1g:2.2mL, 1g:2.3mL, 1g:2.4mL, 1g:2.5mL, 1g:2.6mL, 1g:2.7mL, 1g:2.8mL, 1g:2.9mL or 1g:3.0mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0075] In some optional instances, the amount of trehalose used is 1.5 to 2 wt% of the mass of the Bacillus subtilis bacterial solution, for example, it can be 1.5 wt%, 1.55 wt%, 1.6 wt%, 1.65 wt%, 1.7 wt%, 1.75 wt%, 1.8 wt%, 1.85 wt%, 1.9 wt%, 1.95 wt%, or 2.0 wt%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0076] In some optional instances, the mixing and oscillation of the Bacillus subtilis culture, the activated oyster shell powder, and trehalose is performed at a speed of 150-200 rpm, for example, 150 rpm, 155 rpm, 160 rpm, 165 rpm, 170 rpm, 175 rpm, 180 rpm, 185 rpm, 190 rpm, 195 rpm, or 200 rpm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0077] In some optional instances, the mixing and agitation temperature of the Bacillus subtilis culture, the activated oyster shell powder, and trehalose is 30-40°C, for example, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, or 40°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0078] In some optional instances, the mixing and shaking time of the Bacillus subtilis culture, the activated oyster shell powder, and trehalose is 2 to 3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0079] As a preferred technical solution of the present invention, in step (II), the centrifugal separation speed is 4000~6000rpm, for example, it can be 4000rpm, 4200rpm, 4400rpm, 4600rpm, 4800rpm, 5000rpm, 5200rpm, 5400rpm, 5600rpm, 5800rpm or 6000rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] In some optional instances, the centrifugation time is 10 to 15 minutes, for example, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes, or 15 minutes, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0081] In some optional instances, the freeze-drying process includes sequential pre-cooling and deep cooling.

[0082] In some optional instances, the precooling temperature is 0~5°C, for example, it can be 0°C, 0.5°C, 1°C, 1.5°C, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C or 5°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0083] In some optional instances, the precooling time is 4 to 6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0084] In some optional instances, the cryogenic temperature is -30 to -40°C, for example, it can be -30°C, -31°C, -32°C, -33°C, -34°C, -35°C, -36°C, -37°C, -38°C, -39°C or -40°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, the cryogenic time is 12 to 24 hours, for example, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, or 24 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0086] As a preferred technical solution of the present invention, in step (III), the mass ratio of the supported biochar to the biocomposite material is 1:(1~1.5), for example, it can be 1:1.0, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45 or 1:1.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] In some alternative examples, the carboxymethyl cellulose solution has a mass fraction of 5 to 8 wt%, for example, 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, or 8.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0088] In some optional instances, the mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 1 to 3 wt% of the total mass of the supported biochar and the biocomposite material, for example, it may be 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0089] In some alternative instances, the particle size of the wet aggregate is 3 to 5 mm, for example, it can be 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4.0 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm or 5 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0090] In some optional examples, the drying process of the wet aggregate includes: hot air drying at 35~40℃ for 1~2 hours, followed by air drying in a ventilated and cool place. The hot air drying temperature can be 35℃, 35.5℃, 36℃, 36.5℃, 37℃, 37.5℃, 38℃, 38.5℃, 39℃, 39.5℃ or 40℃, and the hot air drying time can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0091] Secondly, the present invention provides a biochemical composite soil heavy metal pollution fixation and remediation material prepared by the preparation method described in the first aspect.

[0092] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0093] This invention first involves acid activation and hydrothermal reaction of biochar, then loading layered calcium, iron, and aluminum hydroxide (LDH) onto the activated biochar. Subsequently, oyster shell powder is calcined and activated, then combined with Bacillus subtilis to prepare a biocomposite material. Finally, both are mixed with carboxymethyl cellulose solution and granulated, achieving multiple effects of physical adsorption, chemical precipitation, and bioremediation. The loaded biochar utilizes its well-developed porous structure and the ion exchange capacity of LDH to rapidly capture heavy metal ions. The biocomposite material provides long-term stabilization through microbial metabolism and phosphate precipitation, thereby significantly improving the fixation efficiency and adaptability of various heavy metals (such as lead, cadmium, and arsenic) in soil. This solves the problems of the short-lasting effects of traditional materials, the limited remediation capacity of organic materials, and the potential for secondary pollution. Attached Figure Description

[0094] Figure 1 The following is a process flow diagram of the preparation of soil heavy metal pollution fixation and remediation materials provided in Examples 1-5 of the present invention;

[0095] Figure 2 This is a scanning electron microscope image of the supported biochar prepared in Example 1 of the present invention;

[0096] Figure 3 The infrared spectrum of the supported biochar prepared in Example 1 of this invention is shown. Detailed Implementation

[0097] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0098] Example 1

[0099] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0100] (1) Bamboo powder and calcium carbonate were mixed evenly at a mass ratio of 1:0.8. Under a nitrogen atmosphere, the temperature was raised to 300℃ at a heating rate of 3℃ / min and held for 90min to complete low-temperature pyrolysis. Then, the temperature was raised to 600℃ at a heating rate of 5℃ / min and held for 90min to complete high-temperature pyrolysis. After cooling to room temperature in the furnace, the mixture was pulverized and passed through a 100-mesh sieve to obtain biochar powder. The biochar powder was dispersed in a 2wt% dilute hydrochloric acid solution and stirred and washed at 60℃ for 2h. Then, it was filtered, washed with deionized water until neutral, and dried to obtain bamboo-based biochar.

[0101] (2) The bamboo-based biochar obtained in step (1) was dispersed in a mixed acid solution composed of nitric acid and phosphoric acid. The mixed acid solution was obtained by mixing 10 wt% phosphoric acid solution and 10 wt% nitric acid solution in a volume ratio of 2:1. The solid-liquid ratio of bamboo-based biochar to mixed acid solution was 1 g: 12 mL. Then, it was microwave activated for 15 min at a microwave power of 300 W. After microwave activation, it was filtered, and the residue was washed with deionized water until neutral. It was then dried at 100 °C for 8 h to obtain activated biochar.

[0102] (3) Mix calcium nitrate, ferric nitrate, aluminum nitrate, and deionized water thoroughly to obtain a mixed salt solution. The Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio is 3:0.3:0.7, and the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration is 0.4 mol / L. Urea is added to the mixed salt solution. The urea reacts with the Ca in the mixed salt solution. 2+ Fe 3+ And Al 3+ The total molar ratio is 3:1, and after mixing evenly, a precursor solution is obtained.

[0103] The activated biochar obtained in step (2) was immersed in the precursor solution for 3 hours. The solid-liquid ratio of the activated biochar to the precursor solution was 1 g: 15 mL. Then, a hydrothermal reaction was carried out at 100 °C for 15 hours. After the reaction was completed, the mixture was filtered, and the residue was washed with deionized water until neutral. The residue was then dried at 100 °C for 8 hours to obtain the loaded biochar.

[0104] (4) After crushing the oyster shells, pass them through a 150-mesh sieve to obtain oyster shell powder. Mix the oyster shell powder with dipotassium hydrogen phosphate at a mass ratio of 1:0.1 and grind them. Then, calcine them at 180°C for 3 hours to obtain activated oyster shell powder. The live bacteria count is 10 9 CFU / mL Bacillus subtilis bacterial suspension, activated oyster shell powder, and trehalose were mixed. The solid-liquid ratio of activated oyster shell powder to Bacillus subtilis bacterial suspension was 1g:2mL. The amount of trehalose used was 1.5wt% of the mass of Bacillus subtilis bacterial suspension. After mixing evenly, the mixture was shaken at 30℃ and 150rpm for 3h. Then, it was centrifuged at 4000rpm for 15min. The precipitate was pre-cooled at 0℃ for 4h and then freeze-dried at -30℃ for 24h to obtain the biocomposite material.

[0105] (5) The loaded biochar obtained in step (3), the biocomposite material obtained in step (4) and the carboxymethyl cellulose solution are mixed. The mass ratio of the loaded biochar and the biocomposite material is 1:1. The mass fraction of the carboxymethyl cellulose solution is 5wt%. The mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 1wt% of the total mass of the loaded biochar and the biocomposite material. After mixing evenly, the mixture is fed into a granulator for extrusion granulation to obtain wet granules with a particle size of 3mm. The wet granules are dried with hot air at 35℃ for 2h. Finally, they are placed in a ventilated and cool place to dry, thus obtaining the biochemical composite soil heavy metal pollution fixation and remediation material.

[0106] Figure 2This is a scanning electron microscope (SEM) image of the supported biochar prepared in this embodiment. As can be seen from the image, the surface of the supported biochar is uniformly covered with and grows an interlaced, stacked lamellar structure. This is a typical microstructure of layered double hydroxides (LDHs) synthesized via a hydrothermal method, indicating that Ca... 2+ Fe 3+ Al 3+ Metal ions were co-precipitated under alkaline hydrothermal conditions and then in situ loaded onto the surface of biochar in the morphology of LDH nanosheets.

[0107] Figure 3 The image shows the infrared spectrum of the supported biochar prepared in this embodiment. As can be seen from the image, at 3500 cm⁻¹... -1 The broad peak at 1040 cm⁻¹ is attributed to the OH stretching vibration, originating from the hydroxyl groups between the biochar and LDH layers. -1 The strong peak at that point is from phosphate (PO4). 3- The characteristic absorption peak of 875 cm⁻¹ is due to the successful introduction of phosphate groups onto the surface of the activated biochar through microwave activation with a mixed acid solution containing phosphoric acid. -1 and 605~568cm -1 The absorption peaks appearing in the region correspond to carbonate (CO3) ions intercalated in the LDH layers. 2- Vibrations of metal-oxygen or metal-hydroxy bonds (such as Fe-O, Al-O or M-OH) are typical characteristic peaks of LDH.

[0108] Example 2

[0109] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0110] (1) Bamboo powder and calcium carbonate were mixed evenly at a mass ratio of 1:0.9. Under a nitrogen atmosphere, the temperature was raised to 320°C at a heating rate of 3.5°C / min and held for 80 min to complete low-temperature pyrolysis. Then, the temperature was raised to 620°C at a heating rate of 6°C / min and held for 80 min to complete high-temperature pyrolysis. After cooling to room temperature in the furnace, the mixture was pulverized and passed through a 100-mesh sieve to obtain biochar powder. The biochar powder was dispersed in a 2.2wt% dilute hydrochloric acid solution and stirred and washed at 65°C for 1.8 h. Then, it was filtered, washed with deionized water until neutral, and dried to obtain bamboo-based biochar.

[0111] (2) The bamboo-based biochar obtained in step (1) was dispersed in a mixed acid solution composed of nitric acid and phosphoric acid. The mixed acid solution was obtained by mixing 11 wt% phosphoric acid solution and 11 wt% nitric acid solution in a volume ratio of 2.2:1. The solid-liquid ratio of bamboo-based biochar to mixed acid solution was 1 g: 13 mL. Then, it was microwave activated for 13 min at a microwave power of 320 W. After microwave activation, it was filtered, and the residue was washed with deionized water until neutral. It was then dried at 102 °C for 7.5 h to obtain activated biochar.

[0112] (3) Mix calcium nitrate, ferric nitrate, aluminum nitrate, and deionized water thoroughly to obtain a mixed salt solution. The Ca in the mixed salt solution... 2+ Fe 3+ and Al 3+ The molar ratio is 3:0.35:0.65, and the Ca in the mixed salt solution... 2+ Fe 3+ and Al 3+ The total concentration is 0.45 mol / L. Urea is added to the mixed salt solution. The urea reacts with the Ca in the mixed salt solution. 2+ Fe 3+ and Al 3+ The total molar ratio is 3.5:1, and after thorough mixing, a precursor solution is obtained.

[0113] The activated biochar obtained in step (2) was impregnated in the precursor solution for 3.5 h. The solid-liquid ratio of activated biochar to precursor solution was 1 g: 16 mL. Then, a hydrothermal reaction was carried out at 110 °C for 13 h. After the reaction was completed, the mixture was filtered, and the residue was washed with deionized water until neutral. The residue was then dried at 102 °C for 7.5 h to obtain loaded biochar.

[0114] (4) After crushing the oyster shells, pass them through a 160-mesh sieve to obtain oyster shell powder. Mix the oyster shell powder with dipotassium hydrogen phosphate at a mass ratio of 1:0.12 and grind them. Then, calcine them at 185°C for 2.8 hours to obtain activated oyster shell powder. The live bacteria count is 10 9 CFU / mL Bacillus subtilis bacterial suspension, activated oyster shell powder, and trehalose were mixed. The solid-liquid ratio of activated oyster shell powder to Bacillus subtilis bacterial suspension was 1g:2.2mL. The amount of trehalose used was 1.6wt% of the mass of Bacillus subtilis bacterial suspension. After mixing evenly, the mixture was shaken at 32℃ and 160rpm for 2.8h. Then, it was centrifuged at 4500rpm for 13min. The precipitate was pre-cooled at 1℃ for 4.5h and then freeze-dried at -32℃ for 21h to obtain the biocomposite material.

[0115] (5) The loaded biochar obtained in step (3), the biocomposite material obtained in step (4), and the carboxymethyl cellulose solution are mixed. The mass ratio of the loaded biochar to the biocomposite material is 1:1.1, the mass fraction of the carboxymethyl cellulose solution is 6wt%, and the mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 1.5wt% of the total mass of the loaded biochar and the biocomposite material. After mixing evenly, the mixture is fed into a granulator for extrusion granulation to obtain wet granules with a particle size of 3.5mm. The wet granules are dried with hot air at 36℃ for 1.8h, and finally placed in a ventilated and cool place to dry, thus obtaining the biochemical composite soil heavy metal pollution fixation and remediation material.

[0116] Example 3

[0117] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0118] (1) Bamboo powder and calcium carbonate were mixed evenly at a mass ratio of 1:1. Under a nitrogen atmosphere, the temperature was raised to 350°C at a heating rate of 4°C / min and held for 70 min to complete low-temperature pyrolysis. Then, the temperature was raised to 650°C at a heating rate of 7°C / min and held for 70 min to complete high-temperature pyrolysis. After cooling to room temperature in the furnace, the mixture was pulverized and passed through a 120-mesh sieve to obtain biochar powder. The biochar powder was dispersed in a 2.5wt% dilute hydrochloric acid solution and stirred and washed at 70°C for 1.5 h. Then, it was filtered, washed with deionized water until neutral, and dried to obtain bamboo-based biochar.

[0119] (2) The bamboo-based biochar obtained in step (1) was dispersed in a mixed acid solution composed of nitric acid and phosphoric acid. The mixed acid solution was obtained by mixing 12wt% phosphoric acid solution and 12wt% nitric acid solution in a volume ratio of 2.5:1. The solid-liquid ratio of bamboo-based biochar to mixed acid solution was 1g:13mL. Then, it was microwave activated for 12min at a microwave power of 350W. After microwave activation, it was filtered, and the residue was washed with deionized water until neutral. It was then dried at 105℃ for 7h to obtain activated biochar.

[0120] (3) Mix calcium nitrate, ferric nitrate, aluminum nitrate, and deionized water thoroughly to obtain a mixed salt solution. The Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio is 3:0.4:0.6, and the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration is 0.5 mol / L. Urea is added to the mixed salt solution. The urea reacts with the Ca in the mixed salt solution. 2+ Fe3+ And Al 3+ The total molar ratio is 4:1, and after mixing evenly, a precursor solution is obtained.

[0121] The activated biochar obtained in step (2) was impregnated in the precursor solution for 4 hours. The solid-liquid ratio of the activated biochar to the precursor solution was 1 g: 17 mL. Then, a hydrothermal reaction was carried out at 120 °C for 12 hours. After the reaction was completed, the mixture was filtered, and the residue was washed with deionized water until neutral. The residue was then dried at 105 °C for 7 hours to obtain the loaded biochar.

[0122] (4) After crushing the oyster shells, pass them through a 170-mesh sieve to obtain oyster shell powder. Mix the oyster shell powder with dipotassium hydrogen phosphate at a mass ratio of 1:0.15 and grind them. Then, calcine them at 190°C for 2.5 hours to obtain activated oyster shell powder. The live bacteria count is 10 9 CFU / mL Bacillus subtilis bacterial suspension, activated oyster shell powder, and trehalose were mixed. The solid-liquid ratio of activated oyster shell powder to Bacillus subtilis bacterial suspension was 1g:2.5mL. The amount of trehalose used was 1.7wt% of the mass of Bacillus subtilis bacterial suspension. After mixing evenly, the mixture was shaken at 35℃ and 170rpm for 2.5h. Then, it was centrifuged at 5000rpm for 12min. The precipitate was pre-cooled at 2℃ for 5h and then freeze-dried at -35℃ for 18h to obtain the biocomposite material.

[0123] (5) The loaded biochar obtained in step (3), the biocomposite material obtained in step (4), and the carboxymethyl cellulose solution are mixed. The mass ratio of the loaded biochar to the biocomposite material is 1:1.2, the mass fraction of the carboxymethyl cellulose solution is 6wt%, and the mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 2wt% of the total mass of the loaded biochar and the biocomposite material. After mixing evenly, the mixture is fed into a granulator for extrusion granulation to obtain wet granules with a particle size of 4mm. The wet granules are dried with hot air at 37℃ for 1.5h, and finally placed in a ventilated and cool place to dry, thus obtaining the biochemical composite soil heavy metal pollution fixation and remediation material.

[0124] Example 4

[0125] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0126] (1) Bamboo powder and calcium carbonate were mixed evenly at a mass ratio of 1:1.1. Under a nitrogen atmosphere, the temperature was raised to 380℃ at a heating rate of 4.5℃ / min and held for 70min to complete low-temperature pyrolysis. Then, the temperature was raised to 680℃ at a heating rate of 8℃ / min and held for 70min to complete high-temperature pyrolysis. After cooling to room temperature in the furnace, the mixture was pulverized and passed through a 120-mesh sieve to obtain biochar powder. The biochar powder was dispersed in a 2.8wt% dilute hydrochloric acid solution and stirred and washed at 75℃ for 1.2h. Then, it was filtered, washed with deionized water until neutral, and dried to obtain bamboo-based biochar.

[0127] (2) The bamboo-based biochar obtained in step (1) was dispersed in a mixed acid solution composed of nitric acid and phosphoric acid. The mixed acid solution was obtained by mixing 13wt% phosphoric acid solution and 13wt% nitric acid solution at a volume ratio of 2.8:1. The solid-liquid ratio of bamboo-based biochar to mixed acid solution was 1g:14mL. Then, it was microwave activated at a microwave power of 380W for 11min. After microwave activation, it was filtered, and the residue was washed with deionized water until neutral. It was then dried at 108℃ for 6.5h to obtain activated biochar.

[0128] (3) Mix calcium nitrate, ferric nitrate, aluminum nitrate, and deionized water thoroughly to obtain a mixed salt solution. The Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio is 3:0.45:0.55, and the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration is 0.55 mol / L. Urea is added to the mixed salt solution. The urea reacts with the Ca in the mixed salt solution. 2+ Fe 3+ And Al 3+ The total molar ratio is 4.5:1, and after thorough mixing, a precursor solution is obtained.

[0129] The activated biochar obtained in step (2) was impregnated in the precursor solution for 4.5 h. The solid-liquid ratio of the activated biochar to the precursor solution was 1 g: 18 mL. Then, a hydrothermal reaction was carried out at 130 °C for 11 h. After the reaction was completed, the mixture was filtered, and the residue was washed with deionized water until neutral. The residue was then dried at 108 °C for 6.5 h to obtain the loaded biochar.

[0130] (4) After crushing the oyster shells, pass them through an 180-mesh sieve to obtain oyster shell powder. Mix the oyster shell powder with dipotassium hydrogen phosphate at a mass ratio of 1:0.18 and grind them. Then, calcine them at 195°C for 2.2 hours to obtain activated oyster shell powder. The live bacteria count is 10 9CFU / mL Bacillus subtilis bacterial suspension, activated oyster shell powder, and trehalose were mixed. The solid-liquid ratio of activated oyster shell powder to Bacillus subtilis bacterial suspension was 1g:2.8mL. The amount of trehalose used was 1.8wt% of the mass of Bacillus subtilis bacterial suspension. After mixing evenly, the mixture was shaken at 38℃ and 180rpm for 2.2h. Then, it was centrifuged at 5500rpm for 11min. The precipitate was pre-cooled at 3℃ for 5.5h and then freeze-dried at -38℃ for 15h to obtain the biocomposite material.

[0131] (5) The loaded biochar obtained in step (3), the biocomposite material obtained in step (4), and the carboxymethyl cellulose solution are mixed. The mass ratio of the loaded biochar to the biocomposite material is 1:1.3, the mass fraction of the carboxymethyl cellulose solution is 7wt%, and the mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 2.5wt% of the total mass of the loaded biochar and the biocomposite material. After mixing evenly, the mixture is fed into a granulator for extrusion granulation to obtain wet granules with a particle size of 4.5mm. The wet granules are dried with hot air at 38℃ for 1.2h, and finally placed in a ventilated and cool place to dry, thus obtaining the biochemical composite soil heavy metal pollution fixation and remediation material.

[0132] Example 5

[0133] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, such as... Figure 1 As shown, the preparation method specifically includes the following steps:

[0134] (1) Bamboo powder and calcium carbonate were mixed evenly at a mass ratio of 1:1.2. Under a nitrogen atmosphere, the temperature was raised to 400℃ at a heating rate of 5℃ / min and held for 60min to complete low-temperature pyrolysis. Then, the temperature was raised to 700℃ at a heating rate of 10℃ / min and held for 60min to complete high-temperature pyrolysis. After cooling to room temperature in the furnace, the mixture was pulverized and passed through a 120-mesh sieve to obtain biochar powder. The biochar powder was dispersed in a 3wt% dilute hydrochloric acid solution and stirred and washed at 80℃ for 1h. Then, it was filtered, washed with deionized water until neutral, and dried to obtain bamboo-based biochar.

[0135] (2) The bamboo-based biochar obtained in step (1) was dispersed in a mixed acid solution composed of nitric acid and phosphoric acid. The mixed acid solution was obtained by mixing 15wt% phosphoric acid solution and 15wt% nitric acid solution in a volume ratio of 3:1. The solid-liquid ratio of bamboo-based biochar to mixed acid solution was 1g:15mL. Then, it was microwave activated for 10min at a microwave power of 400W. After microwave activation, it was filtered, and the residue was washed with deionized water until neutral. It was then dried at 110℃ for 6h to obtain activated biochar.

[0136] (3) Mix calcium nitrate, ferric nitrate, aluminum nitrate, and deionized water thoroughly to obtain a mixed salt solution. The Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio is 3:0.5:0.5, and the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration is 0.6 mol / L. Urea is added to the mixed salt solution. The urea reacts with the Ca in the mixed salt solution. 2+ Fe 3+ And Al 3+ The total molar ratio is 5:1, and after mixing evenly, a precursor solution is obtained.

[0137] The activated biochar obtained in step (2) was impregnated in the precursor solution for 5 hours. The solid-liquid ratio of the activated biochar to the precursor solution was 1 g: 20 mL. Then, a hydrothermal reaction was carried out at 150 °C for 10 hours. After the reaction was completed, the mixture was filtered, and the residue was washed with deionized water until neutral. The residue was then dried at 110 °C for 6 hours to obtain the loaded biochar.

[0138] (4) After crushing the oyster shells, pass them through a 200-mesh sieve to obtain oyster shell powder. Mix the oyster shell powder with dipotassium hydrogen phosphate at a mass ratio of 1:0.2 and grind them. Then, calcine them at 200°C for 2 hours to obtain activated oyster shell powder. The live bacteria count is 10 9 CFU / mL Bacillus subtilis bacterial suspension, activated oyster shell powder, and trehalose were mixed. The solid-liquid ratio of activated oyster shell powder to Bacillus subtilis bacterial suspension was 1g:3mL. The amount of trehalose used was 2wt% of the mass of Bacillus subtilis bacterial suspension. After mixing evenly, the mixture was shaken at 40℃ and 200rpm for 2h. Then, it was centrifuged at 6000rpm for 10min. The precipitate was pre-cooled at 5℃ for 6h and then freeze-dried at -40℃ for 12h to obtain the biocomposite material.

[0139] (5) The loaded biochar obtained in step (3), the biocomposite material obtained in step (4), and the carboxymethyl cellulose solution are mixed. The mass ratio of the loaded biochar to the biocomposite material is 1:1.5, the mass fraction of the carboxymethyl cellulose solution is 8wt%, and the mass of the carboxymethyl cellulose in the carboxymethyl cellulose solution is 3wt% of the total mass of the loaded biochar and the biocomposite material. After mixing evenly, the mixture is fed into a granulator for extrusion granulation to obtain wet granules with a particle size of 5mm. The wet granules are dried with hot air at 40℃ for 1h, and finally placed in a ventilated and cool place to dry, thus obtaining the biochemical composite soil heavy metal pollution fixation and remediation material.

[0140] Example 6

[0141] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (1), the mass ratio of bamboo powder to calcium carbonate is adjusted to 1:0.5, while other operation steps and process parameters are exactly the same as in Embodiment 1.

[0142] Example 7

[0143] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (1), the mass ratio of bamboo powder to calcium carbonate is adjusted to 1:1.5, while other operation steps and process parameters are exactly the same as in Embodiment 1.

[0144] Example 8

[0145] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio was adjusted to 3:0.1:0.7, and the other operating steps and process parameters were exactly the same as in Example 1.

[0146] Example 9

[0147] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio was adjusted to 3:0.8:0.7, and the other operating steps and process parameters were exactly the same as in Example 1.

[0148] Example 10

[0149] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The molar ratio was adjusted to 3:0.3:0.1, and the other operating steps and process parameters were exactly the same as in Example 1.

[0150] Example 11

[0151] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al3+ The molar ratio was adjusted to 3:0.3:1, and the other operating steps and process parameters were exactly the same as in Example 1.

[0152] Example 12

[0153] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration was adjusted to 0.1 mol / L, and the other operating steps and process parameters were exactly the same as in Example 1.

[0154] Example 13

[0155] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (3), the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ The total concentration was adjusted to 1 mol / L, and the other operating steps and process parameters were exactly the same as in Example 1.

[0156] Example 14

[0157] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (4), the mass ratio of oyster shell powder to dipotassium hydrogen phosphate is adjusted to 1:0.05. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0158] Example 15

[0159] This embodiment provides a method for preparing a biochemical composite soil heavy metal pollution fixation and remediation material. The difference from Embodiment 1 is that in step (4), the mass ratio of oyster shell powder to dipotassium hydrogen phosphate is adjusted to 1:0.3. Other operation steps and process parameters are exactly the same as in Embodiment 1.

[0160] The saturated adsorption capacity, heavy metal removal rate, and leaching concentration of the soil heavy metal contamination immobilization and remediation materials prepared in Examples 1-15 were tested. The specific test steps included:

[0161] (1) Saturated adsorption capacity of heavy metal ions

[0162] Prepare the target heavy metal (Cd) separately 2+ Pb 2+ and AsO4 3-The standard stock solution (1000 mg / L, source solution of Cd(NO3)2·4H2O, Pb(NO3)2 and Na3AsO4) was diluted with deionized water to prepare initial solutions of different concentrations (50 mg / L, 100 mg / L, 200 mg / L, 500 mg / L, 800 mg / L and 1000 mg / L). 2+ Standard stock solution and Pb 2+ The pH of the standard stock solution was adjusted to 5.0 ± 0.1 using dilute HNO3 or NaOH solution, and AsO4 was added. 3- The pH of the standard stock solution was adjusted to 7 using dilute HNO3 or NaOH solution.

[0163] The soil heavy metal pollution fixation and remediation material prepared in the examples was ground and passed through a 100-mesh sieve, then dried at 105℃ to constant weight. 50 mg of the dried sample was placed in an Erlenmeyer flask, and 50 mL of initial solutions of different concentrations (solid-liquid ratio 1:1000) were added to each flask. The flasks were sealed and placed in a constant-temperature shaker at 25±1℃ and 150 rpm for 24 h. Immediately after shaking, the solution was filtered through a 0.45 μm microporous membrane. The residual concentration of heavy metal ions in the filtrate was determined by inductively coupled plasma mass spectrometry (ICP-MS). The equilibrium adsorption capacity of heavy metal ions for different initial solutions was calculated using the following formula:

[0164]

[0165] Among them: Q e To determine the equilibrium adsorption capacity (mg / g), C0 represents the initial concentration of heavy metal ions in the solution (mg / L). e V represents the residual concentration of heavy metal ions in the filtrate (mg / L), V represents the initial solution volume (L), and m represents the sample mass (g).

[0166] Summarize different initial concentrations of C e The corresponding equilibrium adsorption amount Q e A series of (C) were obtained e Q e Data points were collected, adsorption isotherms were plotted, and the saturated adsorption capacity Q was fitted using the Langmuir model. max :

[0167]

[0168] Among them, K L is the Langmuir constant (L / mg).

[0169] (2) Heavy metal removal rate

[0170] Take clean soil (pH=6.5±0.5, organic matter content 2.5%), crush it and pass it through a 2mm sieve, add Pb(NO3)2 solution, Cd(NO3)2 solution and Na3AsO4 solution to adjust the Pb content in the soil. 2+ Concentration up to 800±50 mg / kg, Cd 2+ The concentration was increased to 50±5 mg / kg, and the arsenic (as As) concentration was increased to 100±10 mg / kg. The mixture was aged at 25℃ for 30 days to age the heavy metals.

[0171] The soil heavy metal pollution immobilization remediation material prepared in the example was crushed into particles with a diameter of 5-10 mm. The crushed remediation material particles were added at 5 wt% of the soil mass. The soil moisture content was adjusted to 60% of field capacity with deionized water and incubated in a constant temperature incubator (25±1℃, protected from light). On the 7th day, soil samples from a depth of 0-15 cm were collected, freeze-dried, and ground through a 100-mesh sieve. Digestion was performed using the EPA 3052 method (HCl-HNO3-HF microwave digestion). The concentrations of total Pb, total Cd, and total As in the soil were determined by ICP-MS. The heavy metal removal rate was calculated using the following formula:

[0172]

[0173] Where C0 is the initial concentration of heavy metals in the soil, C t The concentration of heavy metals in the soil after 7 days of treatment.

[0174] (3) Leaching toxicity

[0175] Take clean soil (pH=6.5±0.5, organic matter content 2.5%), crush it and pass it through a 2mm sieve, add Pb(NO3)2 solution, Cd(NO3)2 solution and Na3AsO4 solution to adjust the Pb content in the soil. 2+ Concentration up to 800±50 mg / kg, Cd 2+ The concentration was increased to 50±5 mg / kg, and the arsenic (as As) concentration was increased to 100±10 mg / kg. The mixture was aged at 25℃ for 30 days to age the heavy metals.

[0176] The soil heavy metal pollution fixation and remediation material prepared in the example was crushed into particles with a particle size of 5-10 mm. The crushed remediation material particles were added at 5 wt% of the soil mass. The soil moisture content was adjusted to 60% of the field capacity with deionized water and kept in a constant temperature incubator (25±1℃, protected from light). On the 7th day, soil samples were taken from a depth of 0-15 cm.

[0177] Dissolve 5.7 mL of glacial acetic acid in 500 mL of deionized water, add 64.3 mL of NaOH solution (1 mol / L), and bring the volume to 1 L. Adjust the pH to 2.88 ± 0.05 to obtain the extractant. Place 5.0 g of soil sample in a centrifuge tube, add 100 mL of the extractant, place the tube on a shaker, and shake continuously at 30 ± 2 rpm for 18 h. After shaking, let stand for 10 min, filter under vacuum using a 0.45 μm microporous membrane, collect the filtrate, acidify the filtrate with 5 wt% dilute nitric acid, and determine the total Pb leaching concentration, total Cd leaching concentration, and total As leaching concentration in the filtrate using inductively coupled plasma mass spectrometry.

[0178] The test results are shown in Table 1.

[0179] Table 1

[0180] <![CDATA[Pb 2+ Saturated adsorption capacity (mg / g) <![CDATA[Cd 2+ Saturated adsorption capacity (mg / g) <![CDATA[AsO4 3- Saturated adsorption capacity (mg / g) Total Pb removal rate (%) Total Cd removal rate (%) Total As removal rate (%) Total Pb leaching concentration (mg / L) Total Cd leaching concentration (mg / L) Total As leaching concentration (mg / L) Example 1 258.3 205.4 160.5 93.45 90.23 85.67 0.73 0.34 1.23 Example 2 259.7 206.8 161.9 94.12 90.89 86.34 0.81 0.43 1.31 Example 3 261.2 208.3 163.4 94.78 91.54 87.02 0.69 0.38 1.27 Example 4 260.8 207.9 162.8 94.33 91.12 86.58 0.77 0.45 1.35 Example 5 262.1 209.2 164.1 95.10 91.87 87.25 0.85 0.41 1.29 Example 6 230.6 180.2 140.3 85.34 80.45 75.12 1.52 0.89 2.14 Example 7 210.4 165.8 125.7 78.91 72.68 68.93 2.31 1.27 3.05 Example 8 245.7 195.6 135.8 90.12 88.34 72.45 1.24 0.64 2.87 Example 9 235.9 185.3 145.2 87.56 85.67 78.91 1.68 0.92 2.45 Example 10 242.8 192.4 130.6 89.78 87.12 70.34 1.34 0.73 3.12 Example 11 228.3 178.9 148.7 84.67 82.45 76.89 1.76 0.98 2.67 Example 12 225.4 175.6 142.5 82.34 78.91 73.45 1.89 1.05 2.98 Example 13 218.7 170.2 138.9 80.12 75.68 71.23 2.14 1.18 3.24 Example 14 240.5 165.3 155.8 88.45 75.34 80.12 1.45 1.42 2.31 Example 15 222.6 160.7 142.6 83.78 70.89 77.45 1.97 1.63 2.56

[0181] The test data from Examples 1, 6, and 7 show that in Example 6, the amount of calcium carbonate used was too low, resulting in insufficient carbon dioxide gas production during the pyrolysis of biochar, inadequate pore structure development, small specific surface area, and limited surface functional group sites, which reduced the physical adsorption capacity. Therefore, the saturated adsorption capacity and removal rate both decreased, while the leaching concentration increased. In Example 7, the amount of calcium carbonate used was too high, resulting in excessive gas escape during pyrolysis, forming excessively large or interconnected pores, which damaged the integrity of the carbon skeleton, reduced the strength of the biochar, caused the pore structure to fail, reduced the adsorption capacity, and significantly increased the leaching concentration.

[0182] The test data from Examples 1, 8, and 9 show that the Fe in the mixed salt solution in Example 8... 3+ If the amount of AsO4 added is too low, the positive charge density of the LDH layer will be insufficient, weakening its electrostatic attraction and ion exchange capacity for anionic heavy metals (such as arsenate). 3- The saturated adsorption capacity and total As removal rate decreased significantly, while the total As leaching concentration increased; Fe in the mixed salt solution in Example 9 3+ Excessive addition of certain substances leads to an excessively high positive charge density in the LDH layer, resulting in an overly dense structure and reduced porosity. This affects the diffusion and adsorption of heavy metal ions, causing a decrease in the saturated adsorption capacity and removal rate of all heavy metals, and an increase in the leaching concentration.

[0183] The test data from Examples 1, 10, and 11 show that the Al in the mixed salt solution of Example 10... 3+ Insufficient addition of LDH leads to decreased crystallinity, a looser layered structure, reduced specific surface area, and fewer surface hydroxyl sites, weakening its complexation effect on cationic heavy metals, particularly affecting its ability to fix As; Al in the mixed salt solution of Example 113+ Excessive addition of Al caused uneven charge distribution in the LDH layers, resulting in decreased ion exchange efficiency. 3+ It is easily soluble in soil and produces toxicity, which reduces the adsorption and fixation of all heavy metals and increases the leaching concentration.

[0184] The test data from Examples 1, 12, and 13 show that the Ca in the mixed salt solution in Example 12... 2+ Fe 3+ And Al 3+ The total concentration was too low, resulting in a slow LDH nucleation rate, insufficient loading, incomplete crystal growth, and failure to fully utilize the specific surface area of ​​biochar, thus reducing the saturated adsorption capacity and removal rate; In Example 13, the Ca in the mixed salt solution... 2+ Fe 3+ And Al 3+ Excessive total concentration causes metal ions to precipitate rapidly, forming amorphous aggregates that clog the pores of biochar. Uneven LDH distribution reduces adsorption sites, leading to decreased adsorption capacity and increased leaching concentration.

[0185] The test data from Examples 1, 14, and 15 show that in Example 14, the amount of dipotassium hydrogen phosphate was too low, resulting in insufficient phosphate active sites formed after calcination of oyster shell powder. This reduced the precipitation and fixation capacity for heavy metals such as Cd, thus significantly decreasing the total Cd removal rate and increasing the total Cd leaching concentration. In Example 15, the amount of dipotassium hydrogen phosphate was too high, leading to excessive phosphate coating on the surface of oyster shell powder, clogging the pores of the oyster shell powder, reducing the specific surface area of ​​the oyster shell powder, affecting the adhesion of Bacillus subtilis and the release of phosphate, resulting in a decrease in the adsorption and fixation effect of heavy metals and an increase in the leaching concentration.

[0186] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a biochemical composite soil heavy metal pollution immobilization and remediation material, characterized in that, The preparation method includes: (I) Acid treatment of biochar to obtain activated biochar; calcium salt, iron salt, aluminum salt and deionized water are mixed evenly to obtain a mixed salt solution, urea is added to the mixed salt solution to obtain a precursor solution, the activated biochar is impregnated in the precursor solution, and then a hydrothermal reaction is carried out. After the reaction is completed, the biochar is obtained by filtration, washing and drying. (II) Oyster shell powder is mixed and ground with dipotassium hydrogen phosphate and then calcined at high temperature to obtain activated oyster shell powder; Bacillus subtilis bacterial solution, the activated oyster shell powder and trehalose are mixed and shaken, and then centrifuged and freeze-dried to obtain a biocomposite material; (III) The loaded biochar, the biocomposite material and the carboxymethyl cellulose solution are mixed evenly and then granulated to obtain wet granules. The wet granules are then dried to obtain the biochemical composite soil heavy metal pollution fixation and remediation material.

2. The preparation method according to claim 1, characterized in that, In step (I), the activated biochar is prepared by the following method: (1) Bamboo powder and calcium carbonate are mixed evenly and subjected to gradient pyrolysis under nitrogen atmosphere. Then, bamboo-based biochar is obtained by crushing, sieving and acid washing. (2) The bamboo-based biochar was dispersed in a mixed acid solution composed of nitric acid solution and phosphoric acid solution and then activated by microwave. After filtration, washing and drying, the activated biochar was obtained.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of bamboo powder to calcium carbonate is 1:(0.8~1.2); The gradient pyrolysis operation steps include sequential low-temperature pyrolysis and high-temperature pyrolysis; The heating rate of the low-temperature pyrolysis is 3~5℃ / min; The pyrolysis temperature of the low-temperature pyrolysis is 300~400℃; The holding time for the low-temperature pyrolysis is 60~90 min; The heating rate of the high-temperature pyrolysis is 5~10℃ / min; The pyrolysis temperature of the high-temperature pyrolysis is 600~700℃; The holding time for the high-temperature pyrolysis is 60~90 min; The sieve mesh size for pulverizing and sieving is 100-120 mesh; The pickling process includes: The pulverized and sieved biochar powder is added to a 2-3 wt% dilute hydrochloric acid solution and stirred and washed at 60-80℃ for 1-2 hours. Then it is filtered, washed with deionized water until neutral, and dried to obtain the bamboo-based biochar.

4. The preparation method according to claim 2, characterized in that, In step (2), the solid-liquid ratio of the bamboo-based biochar to the mixed acid solution is 1g:(12~15)mL; The mixed acid solution is made by uniformly mixing phosphoric acid solution and nitric acid solution in a volume ratio of (2~3):1; The phosphoric acid solution has a mass fraction of 10-15 wt%. The nitric acid solution has a mass fraction of 10-15 wt%. The microwave power for microwave activation is 300~400W; The microwave activation process takes 10-15 minutes. The drying temperature is 100~110℃; The drying time is 6-8 hours.

5. The preparation method according to claim 1, characterized in that, In step (I), the calcium salt includes calcium nitrate; The iron salt includes ferric nitrate; The aluminum salt includes aluminum nitrate; The Ca in the mixed salt solution 2+ Fe 3+ And Al 3+ The molar ratio is 3:(0.3~0.5):(0.5~0.7); The Ca in the mixed salt solution 2+ Fe 3+ And Al 3+ The total concentration was 0.4~0.6 mol / L; The urea and the Ca in the mixed salt solution 2+ Fe 3+ And Al 3+ The total molar ratio is (3~5):1; The solid-liquid ratio of the activated biochar to the precursor solution is 1 g:(15~20) mL; The activated biochar was impregnated in the precursor solution for 3-5 hours. The temperature of the hydrothermal reaction is 100~150℃; The hydrothermal reaction time is 10-15 hours; The drying temperature is 100~110℃; The drying time is 6-8 hours.

6. The preparation method according to claim 1, characterized in that, In step (II), the mass ratio of the oyster shell powder to the dipotassium hydrogen phosphate is 1:(0.1~0.2); The calcination temperature of the oyster shell powder and the dipotassium hydrogen phosphate is 180~200℃; The oyster shell powder and the dipotassium hydrogen phosphate are calcined at high temperature for 2-3 hours.

7. The preparation method according to claim 1, characterized in that, In step (II), the viable count of the Bacillus subtilis bacterial solution is ≥10. 9 CFU / mL; The solid-liquid ratio of the activated oyster shell powder to the Bacillus subtilis bacterial solution is 1g:(2~3)mL; The amount of trehalose used is 1.5~2 wt% of the mass of the Bacillus subtilis bacterial solution; The mixing and oscillation of the Bacillus subtilis bacterial solution, the activated oyster shell powder, and trehalose is performed at a speed of 150-200 rpm. The temperature for mixing and shaking the Bacillus subtilis bacterial solution, the activated oyster shell powder, and trehalose is 30~40℃. The mixing and shaking time of the Bacillus subtilis culture, the activated oyster shell powder and trehalose is 2-3 hours.

8. The preparation method according to claim 1, characterized in that, In step (II), the centrifugal separation speed is 4000~6000 rpm; The centrifugation time is 10-15 minutes; The freeze-drying process includes pre-cooling and deep cooling performed sequentially; The pre-cooling temperature is 0~5℃; The precooling time is 4-6 hours; The cryogenic temperature is -30~-40℃; The cryogenic treatment time is 12-24 hours.

9. The preparation method according to claim 1, characterized in that, In step (III), the mass ratio of the supported biochar to the biocomposite material is 1:(1~1.5); The carboxymethyl cellulose solution has a mass fraction of 5-8 wt%. The mass of carboxymethyl cellulose in the carboxymethyl cellulose solution is 1-3 wt% of the total mass of the supported biochar and the biocomposite material. The particle size of the wet granules is 3~5mm; The drying process of the wet granules includes: hot air drying at 35~40℃ for 1~2 hours, followed by air drying in a ventilated and cool place.

10. A biochemical composite soil heavy metal pollution fixation and remediation material prepared by the preparation method according to any one of claims 1 to 9.

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