Remediation material for alkaline cadmium polluted soil and preparation device thereof

Abstract

The invention discloses a remediation material for alkaline cadmium contaminated soil and a preparation device thereof, and belongs to the field of soil remediation, the remediation material comprises a remediation material substrate prepared from biochar particles, hydroxyapatite particles are mineralized in situ in mesopores of the biochar particles, and a pH responsive polymer layer is grafted on the surface hydroxyl of the biochar particles. And a biological gel layer is adsorbed on the periphery of the pH responsive polymer layer. According to the invention, hydroxyapatite particles are generated in situ in mesopores on biochar, so that the specific surface area of chemical remediation of the remediation material is increased, and the pH value of local soil is reduced by using the pH-responsive polymer layer modified and connected on the outer layer, so that the solubility of cadmium in the soil is improved; the reaction of inner-layer hydroxyapatite particles and cadmium is promoted to generate thermodynamically stable minerals, so that the cadmium in the soil is efficiently fixed in a long-acting manner, and meanwhile, the preparation difficulty and cost of the remediation material are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of soil remediation, and in particular relates to a remediation material for alkaline cadmium-contaminated soil and a preparation device thereof. Background Art

[0002] With the development of industrialization and agricultural intensification, heavy metal pollution has become a global environmental problem. Cadmium (Cd), among other things, poses a serious threat to the ecological environment and human health due to its high toxicity, mobility, and bioaccumulation. In parts of my country, soil cadmium contamination is particularly prominent due to activities such as mining, smelting, chemical production, and wastewater irrigation. In alkaline soils (pH > 7.5), the solubility and bioavailability of cadmium are significantly affected by the soil's physical and chemical properties. Its presence is susceptible to transformation, making remediation more difficult. As soil salinity increases, cadmium hydroxide may form negatively charged coordination ions, which are easily reactivated by soil redox conditions or microbial activity.

[0003] Cadmium-contaminated soil not only directly inhibits plant growth and reduces crop yields, but also accumulates through the food chain, leading to food safety issues such as "cadmium rice" and "cadmium vegetables," and harming organs such as the kidneys and bones. Therefore, developing highly effective remediation materials and technologies for alkaline cadmium-contaminated soil is crucial for ensuring sustainable agricultural development and ecological and environmental safety.

[0004] Existing materials and technologies for remediating alkaline cadmium-contaminated soil primarily use chemical stabilizers to adsorb cadmium ions and shift the soil's pH away from the cadmium ion adsorption zone, reducing their bioavailability. However, single materials or remediation methods often disrupt the ionic and material balance within the soil, leading to even more serious problems. The modification process for existing remediation materials is not only costly but also requires the use of hazardous chemicals, which undoubtedly increases the difficulty of preparing the remediation materials, as shown in patent document CN107459992A.

[0005] To this end, it is necessary to propose a repair material and its preparation device for alkaline cadmium-contaminated soil that can efficiently passivate and fix cadmium in alkaline soil, synergize biological remediation and chemical remediation to improve soil cleanliness, improve soil structure, achieve efficient remediation of alkaline cadmium-contaminated soil and synergistic improvement of ecological functions, and reduce the large-scale production and application of repair materials. Summary of the Invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a remediation material for alkaline cadmium-contaminated soil and a preparation device thereof, which increases the specific surface area of ​​the remediation material for chemical remediation by in situ generating hydroxyapatite particles in the mesopores on biochar, and uses a pH-responsive polymer layer modified and connected to the outer layer to lower the pH value of the local soil, thereby increasing the solubility of cadmium in the soil, promoting the reaction between the inner layer hydroxyapatite particles and cadmium to form thermodynamically stable minerals, and efficiently and long-term fixing the cadmium in the soil, while reducing the difficulty and cost of preparing the remediation material.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: a remediation material for alkaline cadmium-contaminated soil, comprising a remediation material substrate made of biochar particles, hydroxyapatite particles in situ mineralized within the mesopores of the biochar particles, a pH-responsive polymer layer grafted onto the hydroxyl groups on the surface of the biochar particles, and a biogel layer adsorbed on the periphery of the pH-responsive polymer layer;

[0008] pH-responsive polymer layer, used to ionize in alkaline soil, forming a negatively charged double layer, which specifically adsorbs Cd in soil solution through electrostatic attraction 2+ , while releasing H + , so that the pH value of the micro-area at the interface between the repair material and the soil is reduced from alkaline to near neutral or form a local slightly acidic environment, thus promoting the adsorption of Cd on the soil colloid. 2+ Dissolution; Hydroxyapatite particles are used to bind dissolved Cd through surface hydroxyl groups. 2+ Coordination exchange occurs to form thermodynamically stable minerals; the biogel layer is used to secrete alkaline phosphatase and laccase, oxidatively degrade polycyclic aromatic hydrocarbons, and produce extracellular polymers to complex residual free Cd 2+ , forming Cd–EPS complexes and promoting soil particle aggregation.

[0009] The principle of the basic scheme is that the repair material uses biochar particles as the base, and uses its porous structure and high specific surface area characteristics to provide a basic platform for subsequent functional transformation. In alkaline soil environments, the pH-responsive polymer layer grafted on the surface of biochar becomes a key functional component. When the soil pH value is greater than 7, the acidic functional groups (such as carboxyl and sulfonic acid groups) in the polymer layer are ionized, releasing H + , making the polymer chain negatively charged and forming a double layer structure. This charged state gives the polymer layer electrostatic adsorption ability, which can specifically capture Cd in the soil solution. 2+ At the same time, H + The release of Cd leads to a decrease in the pH value of the micro-area at the interface between the material and the soil, forming a local slightly acidic environment. This slightly acidic environment has a dual effect: on the one hand, by lowering the pH value, it breaks the Cd adsorbed on the surface of the soil colloid. 2+ The electrostatic balance between Cd and soil particles 2+It desorbs from soil colloids and enters the soil solution phase; on the other hand, the slightly acidic environment provides favorable conditions for subsequent chemical fixation reactions.

[0010] Desorbed Cd 2+ After entering the soil solution, it immediately interacts with the in-situ mineralized hydroxyapatite particles in the biochar mesopores. Hydroxyapatite is a mineral with excellent ion exchange properties. The hydroxyl groups (-OH) on its surface can react with Cd 2+ Specifically, the Ca in the hydroxyapatite crystal structure 2+ Can be Cd 2+ Partial replacement forms thermodynamically more stable Cd-phosphate minerals. This chemical fixation is irreversible, and even if the soil environment fluctuates, the fixed heavy metals are unlikely to be released back into the environment.

[0011] The biogel layer, the outermost structure, further enhances the repair effect through the dual mechanisms of biodegradation and complex fixation. Enzymes such as alkaline phosphatase and laccase secreted by the gel layer can catalyze the oxidative degradation reaction of organic pollutants (such as polycyclic aromatic hydrocarbons) in the soil, destroy their stable structure, and realize the mineralization of organic pollutants. At the same time, the extracellular polymers (EPS) secreted by microorganisms contain a large number of oxygen-containing functional groups (such as carboxyl, hydroxyl, amino, etc.), which can react with residual Cd 2+ A complex reaction occurs to form a Cd-EPS complex. This complexation not only reduces the mobility of heavy metals, but the resulting polysaccharide-protein complex can also act as a binder, promoting the aggregation of soil particles to form a large particle structure, thereby improving the physical properties of the soil.

[0012] The beneficial effects of the basic scheme are: 1. The remediation material achieves efficient remediation of alkaline cadmium contaminated soil through a three-step progressive mechanism of electrostatic adsorption, chemical fixation and biological complexation. First, in terms of heavy metal fixation, the material directly reduces the free Cd in the soil solution through the electrostatic adsorption of the pH-responsive polymer layer. 2+ concentration; at the same time, by releasing H + Forming a local slightly acidic environment, promoting the adsorption of Cd on soil colloids 2+ Desorption further increases the Cd content in the soil solution 2+ The concentration of Cd2+ provides more target ions for subsequent chemical fixation. Hydroxyapatite particles transfer the desorbed Cd2+ to the ion matrix through coordination exchange reaction. 2+ The biogel layer further captures the residual Cd through complexation. 2+ , forming a multi-layered heavy metal fixation barrier.

[0013] 2. In terms of soil improvement, this material also shows significant advantages. The porous structure of biochar particles can improve the air permeability and water retention of the soil, which is conducive to the survival and reproduction of soil microorganisms. The H released by the pH-responsive polymer layer + It neutralizes soil alkalinity, lowering local pH and restoring normal soil physical and chemical properties. Enzymes secreted by the biogel layer accelerate the mineralization of organic pollutants, reducing toxic and harmful substances in the soil. Furthermore, the EPS produced by the gel layer promotes the aggregation of soil particles, forming a healthy soil structure and improving soil fertility and productivity.

[0014] 3. Furthermore, the material is environmentally friendly. Both the biochar and biogel layers are derived from natural substances or environmental microorganisms and will not cause secondary pollution to the soil ecosystem. The materials gradually degrade in the soil, ultimately transforming into beneficial substances such as humus, providing long-term nutrient support for the soil. Therefore, this remediation material not only effectively treats alkaline cadmium-contaminated soil but also improves soil quality and promotes the recovery and reconstruction of the soil ecosystem.

[0015] Furthermore, the pH-responsive polymer layer includes citric acid grafted onto the hydroxyl groups on the surface of the biochar particles, and the carboxyl functional groups of the citric acid are cross-linked with the amino groups of chitosan via a Schiff base reaction.

[0016] The beneficial effects of the basic scheme are: 1. The pH-responsive polymer layer enables the material to have the ability to intelligently respond to alkaline environments. Citric acid, as a natural organic acid, has a carboxyl functional group that is easily deprotonated under alkaline conditions and is negatively charged. Chitosan, as a natural polysaccharide, has an amino group that is easily protonated under acidic conditions and is positively charged. Through the Schiff base reaction, the carboxyl group of citric acid and the amino group of chitosan are cross-linked to form a covalent bond, constructing a pH-sensitive polymer network. In alkaline soil, the carboxyl group of citric acid in the polymer layer is deprotonated, while the amino group of chitosan remains deprotonated, making the polymer as a whole negatively charged. This charged state enables the polymer layer to specifically adsorb Cd in the soil solution through electrostatic attraction. 2+ , effectively reducing the mobility of heavy metal ions.

[0017] 2. The polymer layer adsorbs Cd 2+ At the same time, it can also release H + , neutralizing the soil alkalinity. The deprotonation of the carboxyl group of citric acid is accompanied by H + The release of these H + It can reduce the pH value of the micro-area at the interface between the material and the soil, forming a local slightly acidic environment. This slightly acidic environment helps to break down the Cd adsorbed on the surface of the soil colloid. 2+ The electrostatic balance between Cd and soil particles 2+ Desorbed from soil colloids and entered the soil solution phase.2+ It is then further fixed by a polymer layer or other repair components (such as hydroxyapatite particles), thereby achieving deep removal of heavy metals.

[0018] 3. The pH-responsive polymer layer can also synergize with other repair components to enhance the overall repair effect. For example, the H released by the polymer layer + It not only promotes Cd 2+ The desorption of Cd can also provide favorable conditions for the coordination exchange reaction of hydroxyapatite particles. In a slightly acidic environment, the hydroxyl groups on the surface of hydroxyapatite are more likely to react with Cd 2+ Coordination exchange occurs to form a more thermodynamically stable Cd-phosphate mineral. At the same time, the extracellular polymers (EPS) secreted by the biogel layer can better play a chelating role in a slightly acidic environment and capture residual Cd 2+ , forming a Cd-EPS complex.

[0019] 4. In addition to the fixation of heavy metals, the pH-responsive polymer layer also improves soil quality. Citric acid and chitosan are both natural organic substances, and their degradation products can provide organic matter to the soil, promoting the survival and reproduction of soil microorganisms. + It can neutralize soil alkalinity and help restore the normal physical and chemical properties of the soil.

[0020] Furthermore, the biogel layer includes a plurality of montmorillonite nanosheets electrostatically bonded to the cationic sites of the biochar particles. The outer sides of the montmorillonite nanosheets are each wrapped with a gelled sodium alginate protective layer, and a plurality of alkali-resistant bacterial strains are embedded in the sodium alginate protective layer.

[0021] The beneficial effects of the basic scheme are: 1. Montmorillonite nanosheets enhance the adsorption and fixation capacity of the biogel layer. Montmorillonite, as a natural layered silicate mineral, has a very high specific surface area and ion exchange capacity. Its nanosheet structure can significantly increase the adsorption of Cd in soil solution. 2+ The negative charge on the surface of montmorillonite can adsorb Cd through electrostatic attraction. 2+ At the same time, its interlayer domain can act as a "molecular container" to accommodate heavy metal ions, forming a stable inner layer complex. In addition, the layered structure of montmorillonite can provide a microenvironmental shelter for alkali-resistant strains, reducing the strains' exposure to harmful substances in the soil.

[0022] 2. The sodium alginate protective layer not only provides a physical barrier for alkali-resistant strains but also provides moisturizing and sustained-release properties. Sodium alginate is a natural polysaccharide. The three-dimensional network structure it forms after gelation effectively encapsulates montmorillonite nanosheets, preventing strain inactivation due to soil drying, pH fluctuations, or heavy metal toxicity.

[0023] 3. The montmorillonite and sodium alginate in the biogel layer interact synergistically with the alkali-resistant bacterial strain. The montmorillonite provides attachment sites and shelter for the bacterial strain, while the sodium alginate protective layer maintains bacterial activity. The bacterial strain's metabolic activity, in turn, promotes the fixation of heavy metals by the montmorillonite and the degradation of the sodium alginate. This bio-mineral composite system not only improves remediation efficiency but also enhances the material's stability and durability.

[0024] A device for preparing repair materials for alkaline cadmium-contaminated soil comprises a pyrolysis component, the pyrolysis component comprises an inclined pyrolysis furnace, the bottom wall of the pyrolysis furnace is fixedly connected to a bracket, the bracket is fixedly connected to a controller, the pyrolysis furnace comprises a hot air cylinder, a rotating cylinder is sleeved in the hot air cylinder, a collecting cylinder is sleeved in the rotating cylinder, both ends of the hot air cylinder are fixedly connected to sealing covers, the sealing covers and the rotating cylinder are slidably connected, the top of the rotating cylinder is connected to a feed pipe through the corresponding sealing cover, the feed pipe is connected to a feed hopper, the outer wall of the top of the rotating cylinder is coaxially fixedly connected to the output shaft of an annular motor, the outer wall of the annular motor is fixedly connected to the corresponding sealing cover, the bottom end of the collecting cylinder is connected to a charcoal outlet pipe through the corresponding sealing cover, the charcoal outlet pipe is connected to a first material moving assembly, the side wall of the hot air cylinder is connected to a hot steam boiler, and the annular motor and the hot steam boiler are both connected to the controller signal.

[0025] The basic solution offers the following benefits: 1. The pyrolysis furnace utilizes an inclined rotary drum design, coupled with a ring-shaped motor drive, enabling continuous biomass feedstock feeding, uniform pyrolysis, and rapid charcoal production. The synergistic effect of the tilt angle and rotation speed ensures thorough mixing of the materials during pyrolysis, preventing localized overheating and incomplete pyrolysis. Furthermore, the integration of the hot air drum and steam boiler provides a stable high-temperature environment for pyrolysis, significantly improving pyrolysis efficiency and shortening the production cycle.

[0026] 2. The controller's signal connection to the hot steam boiler and annular motor enables precise control of key parameters such as pyrolysis temperature and rotation speed. Preset process curves allow the device to automatically adapt to the pyrolysis characteristics of different feedstocks, ensuring consistent biochar product quality. Furthermore, automated control reduces manual intervention, eases operational complexity, and improves production safety.

[0027] 3. The pyrolysis furnace utilizes a three-layer sleeve structure (hot gas cylinder, rotary cylinder, and collection cylinder) to effectively separate pyrolysis gases, solid products, and unpyrolyzed raw materials. The hot gas cylinder provides the heat required for pyrolysis, the rotary cylinder completes the pyrolysis reaction, and the collection cylinder collects the biochar product. This structural design not only improves pyrolysis efficiency but also prevents cross-contamination of products, ensuring the purity and quality of the biochar.

[0028] Furthermore, a plurality of sieve holes are opened on the upper side of the bottom end of the collecting cylinder, and a plurality of inclined plates are vertically fixedly connected to the outer periphery of the lower side of the bottom end of the collecting cylinder.

[0029] The beneficial effects of the basic solution are: 1. The design of the sieve holes realizes the particle size classification and purification of biochar. During the pyrolysis process, the biomass raw materials are cracked at high temperature to produce biochar, pyrolysis gas and a small amount of tar. The sieve holes at the bottom of the collecting cylinder can dynamically screen the falling biochar: qualified biochar particles with smaller particle sizes pass through the sieve holes and enter the bottom of the collecting cylinder, while larger particles or incompletely pyrolyzed lumps are retained in the collecting cylinder and continue to participate in the pyrolysis reaction. This grading process ensures the uniformity of the particle size of the biochar product and improves its applicability as a soil remediation material. In addition, the sieve holes also reduce the maintenance cost of the device, because the sieve holes intercept most of the incompletely pyrolyzed materials, reducing the risk of clogging of the carbon outlet pipe.

[0030] 2. The inclined plate design optimizes the biochar discharge path and efficiency. The inclined plate is fixed vertically to the outer periphery of the lower end of the collection drum, forming a certain angle with the horizontal plane. As the biochar rotates with the drum, the inclined plate provides an inclined upward and downward path for it, allowing it to slide smoothly to the bottom under the action of gravity. This design prevents biochar accumulation and blockage at the bottom of the drum, ensuring continuous screening of biochar.

[0031] Furthermore, the first material moving component includes a first material moving tube, one end of the first material moving tube is fixedly connected to the first material moving motor, the output shaft of the first material moving motor extends into the first material moving tube and is coaxially fixedly connected to the first material moving screw, the other end of the first material moving tube is connected to a material collecting tank, the bottom of the material collecting tank is connected to a material collecting valve, a pressure sensor is provided on the material collecting valve, the other end of the material collecting valve is connected to a first material delivery pipe, the first material delivery pipe is connected to a modification component, an airtight valve is provided in the first material delivery pipe, the modification component includes a supercritical CO2 fluid modification cabin, the first material moving motor, the pressure sensor, the airtight valve, the material collecting valve and the supercritical CO2 fluid modification cabin are all connected to the controller signal.

[0032] The basic solution offers the following benefits: 1. The first material transfer assembly utilizes a screw conveyor mechanism, driven by a first material transfer motor, ensuring continuous and stable biochar transfer. A collection valve at the bottom of the collection tank works in conjunction with a pressure sensor to monitor the biochar accumulation within the tank in real time. When the biochar reaches a preset level, the pressure sensor triggers the collection valve to open, ensuring precise discharge. This design not only avoids the tediousness and errors of manual operation but also ensures a continuous and stable biochar supply, providing a reliable source of raw materials for subsequent modification processes.

[0033] 2. An airtight valve installed in the first feed pipe ensures the airtightness of the biochar during transportation, preventing the leakage of pyrolysis gases and dust, and improving the production environment. Furthermore, the opening and closing of the airtight valve can be linked to the operating status of the modification component, achieving a precise connection between biochar transportation and modification process. When the modification chamber is ready to receive material, the airtight valve automatically opens, and the biochar is transported to the supercritical CO2 fluid modification chamber, ensuring the continuity and efficiency of the process.

[0034] Furthermore, the bottom of the supercritical CO2 fluid modification chamber is connected to a second material moving assembly, the second material moving assembly includes a second material moving pipe, the second material moving pipe is connected to the bottom of the supercritical CO2 fluid modification chamber, the inner wall of the second material moving pipe is fixedly connected to the airtight valve, one side of the second material moving pipe is fixedly connected to a second material moving motor, the output shaft of the second material moving motor extends into the second material moving pipe and is coaxially fixedly connected to a second material moving screw, the other end of the second material moving pipe is connected to an adsorption assembly, and the second material moving motor is connected to the controller signal.

[0035] The basic solution offers the following benefits: the second material transfer assembly utilizes a similar screw conveyor structure to the first, driven by a second material transfer motor, enabling continuous and stable transfer of modified biochar. An airtight valve ensures airtightness during transfer, preventing leakage of the modifier or biochar. This design not only automates the modification and adsorption processes but also avoids the errors and contamination risks associated with manual operation, ensuring the continuity and efficiency of the preparation process.

[0036] Furthermore, the adsorption component includes an adsorption cabin, the top wall of the adsorption cabin is fixedly connected to a stirring motor, the output shaft of the stirring motor extends into the adsorption cabin and is coaxially fixedly connected to a number of stirring fans, a driving gear is coaxially fixedly connected to the output shaft of the stirring motor, a tooth groove is opened on the inner side wall of the top of the adsorption cabin, driven gears are symmetrically engaged on both sides of the driving gear, the driven gears are coaxially fixedly connected to the spray pipe, the driven gears are all engaged with the tooth groove, and the stirring motor is connected to the controller signal.

[0037] The basic solution offers the following benefits: 1. The adsorption assembly utilizes a stirring motor to drive the stirring fan, which, through the transmission of driving and driven gears, simultaneously drives the spray pipe to rotate synchronously. This achieves dynamic mixing of the biochar and biogel precursor solution. The rotation of the stirring fan promotes macroscopic material flow, while the rotation of the spray pipe achieves uniform spraying and microscopic mixing of the modifier. These two functions work synergistically to ensure sufficient contact and uniform reaction between the biochar and the modifier, improving the performance consistency of the repair material.

[0038] 2. The adsorption component ensures the stability of the repair material performance by precisely controlling the mixing and reaction conditions. The modified biochar gradually accumulates from top to bottom, and the pressure of the upper layer is lower than that of the lower layer, which is in line with the adsorption reaction law of the biogel precursor solution and the modified biochar. Initial adsorption is achieved in the low-pressure section, and the gel compression and solidification are completed in the high-pressure section to form microcapsules with a porosity gradient distribution. The uniform mixing and sufficient reaction make the surface functional modification of the biochar more thorough, improving its resistance to heavy metals (such as Cd 2+ ) adsorption capacity and selectivity.

[0039] Furthermore, the bottom end of the spray pipe is slidably connected to a rotating ring groove, and a number of nozzles are connected to the bottom wall of the rotating ring groove. The nozzles on the same rotating ring groove are all facing in the same direction along the arc of the rotating ring groove. A sliding ring groove is provided on the top wall of the adsorption cabin. The bottom wall of the sliding ring groove is rotatably connected to the top of the spray pipe. The top wall of the sliding ring groove is connected to a liquid inlet pipe, and the liquid inlet pipe passes through the top wall of the adsorption cabin and is connected to a liquid inlet pump. The liquid inlet pump is used to supply montmorillonite suspension and sodium alginate solution containing alkali-resistant strains, and the liquid inlet pump is connected to the controller signal.

[0040] The basic solution offers the following benefits: 1. The rotating ring groove and directional nozzle design at the bottom of the spray pipe allows the solution to be sprayed tangentially under the influence of centrifugal force. Because the nozzles on the same rotating ring groove all face the same arc, the solution spreads in a spiral as the spray pipe rotates, creating a dynamic spray pattern. This design not only expands the solution's coverage but also, through the shear force generated by the rotation, evenly spreads the montmorillonite suspension and sodium alginate solution across the biochar surface, avoiding localized accumulation or incomplete coverage.

[0041] 2. The directional arrangement of the nozzles, combined with the rotary spraying, creates a laminar coupling effect within the adsorption chamber. During the spraying process, the montmorillonite suspension and the sodium alginate solution undergo microscopic mixing, with the montmorillonite nanosheets encapsulated by the sodium alginate molecules to form "mineral-polymer" composite particles. When these composite particles are deposited on the biochar surface, the gelation reaction of the sodium alginate and the layered structure of the montmorillonite work synergistically: the sodium alginate gel network cross-links the montmorillonite nanosheets into a three-dimensional skeleton, while the interlayer domains of the montmorillonite serve as "molecular anchors" to stabilize the gel network.

[0042] 3. Precise control of the spray system enables functional modification of the biochar surface. By adjusting the rotation speed of the spray pipe, the spray pressure of the nozzle, and the solution supply ratio, the thickness, porosity, and functional group density of the biogel layer can be controlled. For example, increasing the spray volume of the montmorillonite suspension increases the mineral content of the gel layer and enhances its adsorption capacity for heavy metals; while increasing the spray volume of the sodium alginate solution increases the crosslinking density of the gel network and improves its degradation efficiency for organic pollutants. This ability to customize performance enables the remediation material to adapt to the needs of different pollution scenarios, expanding its application range.

[0043] Furthermore, an electrostatic field generator is fixedly connected to the inner wall of the adsorption cabin on the opposite side of the second material transfer tube, the bottom wall of the adsorption cabin is connected to a discharge pipe, a discharge motor is fixedly connected to the side wall of the discharge pipe, the output shaft of the discharge motor extends into the discharge pipe and is coaxially fixedly connected to a discharge spiral, the discharge spiral extends into the adsorption cabin, and the discharge motor and the electrostatic field generator are both connected to the controller signal.

[0044] The beneficial effects of the basic scheme are: 1. The directional electric field generated by the electrostatic field generator exerts Coulomb force on the charged particles, strengthening the directional migration and adsorption of montmorillonite nanosheets and biochar particles, and significantly improving the loading amount and distribution uniformity of functional components.

[0045] 2. The electrostatic field and the original stirring flow field in the adsorption chamber produce a synergistic effect, further strengthening the micro-mixing, promoting the collision and aggregation between particles, accelerating the formation of montmorillonite-sodium alginate composite gel, and at the same time enhancing the electrostatic adsorption between the biochar surface and functional components, improving the interfacial bonding strength, and making the repair material have a longer effective action time in the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the structure of the repair material in an embodiment of the present invention.

[0047] Figure 2 Schematic diagram of the preparation process and action process of the repair material in an embodiment of the present invention.

[0048] Figure 3 This is an axonometric view of a pyrolysis furnace in an embodiment of the present invention.

[0049] Figure 4 It is a side cross-sectional view of a pyrolysis furnace in an embodiment of the present invention.

[0050] Figure 5 This is an axonometric view of the adsorption cabin in an embodiment of the present invention.

[0051] Figure 6 It is a side cross-sectional view of the adsorption cabin in an embodiment of the present invention.

[0052] Figure 7 It is a cross-sectional view from above of the adsorption cabin in the embodiment of the present invention.

[0053] The reference numerals in the drawings of the specification include: 1. biochar particles; 2. hydroxyapatite particles; 3. pH-responsive polymer layer; 4. montmorillonite nanosheets; 5. sodium alginate protective layer; 6. alkali-resistant strain; 7. pyrolysis furnace; 8. steam boiler; 9. annular motor; 10. feed hopper; 11. charcoal outlet pipe; 12. first material transfer motor; 13. first material transfer pipe; 14. collecting tank; 15. first material delivery pipe; 16. sealing cover; 17. hot air cylinder; 18. feed pipe ; 19. Rotating drum; 20. Collecting drum; 21. Sieve hole; 22. Inclined plate; 23. First material transfer screw; 24. Collecting valve; 25. Adsorption cabin; 26. Second material transfer pipe; 27. Liquid inlet pipe; 28. Stirring motor; 29. ​​Discharge pipe; 30. Stirring fan; 31. Nozzle; 32. Rotating ring groove; 33. Spray pipe; 34. Driving gear; 35. Driven gear; 36. Slip ring groove; 37. Electrostatic field generator; 38. Discharge motor; 39. Discharge screw. DETAILED DESCRIPTION

[0054] The following is further described in detail through specific implementation methods:

[0055] Example 1

[0056] Basically as attached Figure 1 and Figure 2 As shown: A remediation material for alkaline cadmium contaminated soil, including a remediation material base made of biochar particles 1, hydroxyapatite particles 2 are in situ mineralized in the mesopores of the biochar particles 1, a pH-responsive polymer layer 3 is grafted onto the hydroxyl groups on the surface of the biochar particles 1, and a biogel layer is adsorbed on the periphery of the pH-responsive polymer layer 3.

[0057] The pH-responsive polymer layer 3 is used to ionize in alkaline soil, forming a negatively charged double layer, and specifically adsorbing Cd in the soil solution through electrostatic attraction. 2+ , while releasing H + , so that the pH value of the micro-area at the interface between the repair material and the soil is reduced from alkaline to near neutral or form a local slightly acidic environment, thus promoting the adsorption of Cd on the soil colloid. 2+ Dissolution, pH responsive polymer layer 3, including citric acid grafted to the surface hydroxyl groups of biochar particles 1, the carboxyl functional groups of citric acid are cross-linked with chitosan amino groups through Schiff base reaction.

[0058] Hydroxyapatite particles 2, used to bind dissolved Cd through surface hydroxyl groups 2+ Coordination exchange occurs, forming thermodynamically stable minerals.

[0059] Biogel layer, used to secrete alkaline phosphatase and laccase, oxidatively degrade PAHs, and generate extracellular polymeric substances to complex residual free Cd 2+, forming a Cd–EPS complex, promoting soil particle aggregation. The biogel layer includes several montmorillonite nanosheets 4 electrostatically bonded to the cationic sites of the biochar particles 1. The outside of the montmorillonite nanosheets 4 are wrapped with a gelled sodium alginate protective layer 5, and several alkali-resistant bacterial strains 6 are embedded in the sodium alginate protective layer 5.

[0060] The specific implementation process is as follows:

[0061] 1. The action process of repair materials after spreading in alkaline soil.

[0062] 1. Within 24 hours

[0063] (1) Sustained release and activation of functional bacteria

[0064] After soil water penetrates into the sodium alginate-montmorillonite microcapsules, the Ca 2+ Upon gradual release, the gel network swells and ruptures, releasing the embedded alkali-resistant bacteria.

[0065] (2) Activation of pH-responsive polymer layer 3

[0066] The citric acid-chitosan copolymer on the surface of the repair material is ionized in alkaline soil, and the carboxyl group (-COO-) and amino group (-NH2) form a negatively charged double layer, which specifically adsorbs Cd in the soil solution through electrostatic attraction. 2+ During the adsorption process, the copolymer releases H + , so that the pH value of the micro-area at the material-soil interface drops from >7 to 6.5-7.0, forming a local "slightly acidic environment".

[0067] (3) Coordination reaction of hydroxyapatite particles 2 (nHAP)

[0068] After the interfacial pH decreases, the surface hydroxyl groups (≡P–OH) of nHAP in the biochar mesopores interact with the adsorbed Cd 2+ Coordination exchange occurs, and the chemical formula is as follows:

[0069] ≡P–OH+Cd 2+ →≡P–OCd + +H +

[0070] ≡P–OCd generated by the reaction + It further combines with the surrounding phosphate and hydroxyl groups to gradually form the thermodynamically stable Cd5(PO4)3OH mineral - cadmium hydroxyapatite, whose solubility product (Ksp = 10 -67.5 ) is much lower than Cd(OH)2(Ksp=10 -14.2 ), achieving irreversible fixation of cadmium.

[0071] The rapid adsorption of the copolymer and the mineralization reaction of nHAP form a synergistic effect, reducing the exchangeable cadmium by more than 70% within 24 hours, and local pH regulation avoids the problem of passivation failure of traditional materials under high alkalinity.

[0072] 2. Day 2-Day 15

[0073] (1) Alkali-resistant strain 6 secretes alkaline phosphatase and laccase in an alkaline environment, initiating the oxidative degradation of polycyclic aromatic hydrocarbons (PAHs). The degradation process is as follows:

[0074] PAHs+O2→quinone intermediates→carboxylic acid small molecules (such as oxalic acid, acetic acid)

[0075] (2) Synergistic passivation of extracellular polymers (EPS)

[0076] The EPS produced by bacterial metabolism contains a large number of sulfhydryl (-SH) and carboxyl (-COOH) groups, which further complex the residual free Cd 2 + , forming a Cd–EPS complex (binding constant LogK = 8.2), supplementing the chemical passivation effect.

[0077] The alkali-resistant strain 6 not only degrades organic matter but also secretes EPS, which enhances cadmium fixation through molecular chelation, while also avoiding the drawbacks of traditional single-use remediation materials that often overlook complex contamination. EPS interacts with montmorillonite gel through hydrogen bonding and cationic bridging, promoting the aggregation of soil particles. This increases the proportion of large aggregates (>0.25 mm) from 35% to 50%, improving air permeability and water retention.

[0078] 3. Day 15-Day 120

[0079] (1) Mineral aging and anti-desorption enhancement

[0080] The initially generated Cd5(PO4)3OH undergoes an "aging" process in the soil, and the crystal structure transforms from an amorphous state to a crystalline state (the XRD characteristic peaks 2θ=31.8° and 49.5° gradually become sharper), and its resistance to acid decomposition increases by 3 times.

[0081] (2) Microbial-plant synergistic remediation

[0082] Alkali-resistant bacteria continuously secrete auxin (IAA) and siderophores, stimulating the development of herbaceous plant roots. Plant root secretions (such as malic acid) further activate insoluble phosphates in the soil, releasing PO4 3 -Reacts with residual cadmium, creating a secondary passivation effect. Plant photosynthesis absorbs CO2, which, together with microbial respiration, regulates the soil microenvironment, causing the overall soil pH to naturally decrease from >7 to near neutrality.

[0083] 2. Experiment on application of restoration materials in alkaline soil

[0084] 1. Experimental group settings:

[0085] Control group: alkaline cadmium-contaminated soil without adding remediation materials; experimental group: adding 2% by mass of remediation materials (composite biochar containing montmorillonite-alkali-resistant bacteria microcapsules).

[0086] 2. Soil preparation:

[0087] Artificially prepared alkaline cadmium-contaminated soil (pH = 8.5): the basic soil is clay: sand = 3:1, with an organic matter content of 1.5%; cadmium pollution: Cd(NO3)2 solution is added to a total cadmium concentration of 50 mg / kg; PAHs pollution: 100 mg / kg each of phenanthrene and pyrene are added.

[0088] 3. Material application:

[0089] The remediation materials were evenly mixed with the contaminated soil, placed in a constant temperature and humidity incubator (25°C, 70% humidity), and watered daily (maintaining 60% of the field water holding capacity) to simulate the natural light cycle.

[0090] 4. Sampling and analysis time points:

[0091] On day 0 (initial), day 1, day 15, day 60, and day 120, three parallel samples were collected for testing each time.

[0092] 5. Testing process:

[0093] Initial state measurement (0 day): Determination of soil pH, available cadmium, PAHs content, microbial activity, and aggregate distribution.

[0094] Dynamic monitoring and sampling:

[0095] After 1 day: the surface adsorbed cadmium content and interfacial pH changes were detected; after 15 days: the microbial activity and PAHs degradation rate were evaluated; after 60 days: the soil aggregate structure and mineral aging degree were analyzed; after 120 days: a plant planting (ryegrass) test was carried out and the leaching stability was determined.

[0096] Detection methods: Cadmium form detection uses the TCLP method (toxic leaching) and BCR continuous extraction method; PAHs detection uses GC-MS determination; microbial activity detection uses the FDA hydrolase method; aggregate distribution detection uses the wet screening method; plant planting indicators detect biomass and seed cadmium content (ICP-MS).

[0097] 6. Experimental Results

[0098] As shown in Table 1 below:

[0099] Table 1. Results of remediation tests on alkaline cadmium-contaminated soil

[0100]

[0101]

[0102] The test results showed that the effective cadmium in the control group only decreased naturally by 8.9% within 120 days, and the leaching and absorption rate was as high as 34.7%, indicating that cadmium in untreated soil continues to pose an environmental risk. Relying solely on the degradation of indigenous microorganisms, the total PAHs degradation rate was only 12.4% after 120 days, far lower than the 91.5% of the experimental group. The proportion of large aggregates dropped from 35% to 30%, soil compaction intensified, porosity decreased, and plant growth was inhibited. There was no significant increase in dehydrogenase activity, the microbial community was inhibited by cadmium toxicity, and the cadmium content of plant seeds (2.8 mg / kg) far exceeded the food safety standard (0.2 mg / kg).

[0103] In the experimental group, the available cadmium content decreased by 71.5% within one day and stabilized at 5.2 mg / kg after 120 days. The leaching and absorption rate was less than 3.1%, which was much lower than that of the control group. The PAHs degradation rate reached 68.9% 15 days after microbial activation and 91.5% after 120 days. The degradation products were mainly low-toxic carboxylic acids. After 120 days, the dehydrogenase activity increased by 9 times, the improved aggregate structure promoted plant growth, and the cadmium content of ryegrass seeds met the food safety standards. Mineral aging and microbial-plant synergy ensured that the remediation effect continued to increase after 120 days, without the risk of secondary pollution. The control experiment verified the high efficiency and ecological safety of the remediation material in alkaline cadmium-organic composite contaminated soil.

[0104] Example 2

[0105] The difference from the above embodiment is that, as shown in the attached Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7As shown, a device for preparing a repair material for alkaline cadmium contaminated soil. Since the preparation of the above-mentioned repair material at least includes the pyrolysis of biochar, the grafting modification of the surface of the biochar particles 1, and the adsorption of the montmorillonite nanosheets 4 on the surface of the biochar, a corresponding pyrolysis furnace 7, a superfluid modification chamber, and an adsorption tower are required. Therefore, the device for preparing a repair material for alkaline cadmium contaminated soil includes a pyrolysis component, which includes a pyrolysis furnace 7 placed obliquely, a bracket welded to the bottom wall of the pyrolysis furnace 7, a controller welded to the bracket, the pyrolysis furnace 7 includes a hot air cylinder 17, a rotary cylinder 19 is sheathed in the hot air cylinder 17, and a rotary cylinder 19 is sheathed in the rotary cylinder 19. The collecting cylinder 20 and the hot air cylinder 17 are both welded with sealing covers 16 at both ends, and the sealing covers 16 and the rotary cylinder 19 are both slidably connected. The top of the rotary cylinder 19 is connected to the feed pipe 18 through the corresponding sealing cover 16, and the feed pipe 18 is connected to the feed hopper 10. The output shaft of the annular motor 9 is coaxially welded to the outer wall of the top of the rotary cylinder 19, and the outer wall of the annular motor 9 is welded to the corresponding sealing cover 16. The bottom end of the collecting cylinder 20 is connected to the charcoal outlet pipe 11 through the corresponding sealing cover 16, and the charcoal outlet pipe 11 is connected to the first material moving assembly. The side wall of the hot air cylinder 17 is connected to the hot steam boiler 8, and the annular motor 9 and the hot steam boiler 8 are both connected to the controller signal.

[0106] A plurality of sieve holes 21 are formed on the upper side of the bottom end of the collecting cylinder 20 , and a plurality of inclined plates 22 are vertically welded to the outer periphery of the lower side of the bottom end of the collecting cylinder 20 .

[0107] The first material moving assembly includes a first material moving tube 13, one end of which is welded with a first material moving motor 12, the output shaft of the first material moving motor 12 extends into the first material moving tube 13 and is coaxially welded with a first material moving screw 23, the other end of the first material moving tube 13 is connected to a collecting tank 14, the bottom of the collecting tank 14 is connected to a collecting valve 24, a pressure sensor is provided on the collecting valve 24, the other end of the collecting valve 24 is connected to a first material delivery pipe 15, the first material delivery pipe 15 is connected to a modification assembly, an airtight valve is installed in the first material delivery pipe 15, the modification assembly includes a supercritical CO2 fluid modification cabin, the first material moving motor 12, the pressure sensor, the airtight valve, the collecting valve 24 and the supercritical CO2 fluid modification cabin are all connected to the controller signal.

[0108] The bottom of the supercritical CO2 fluid modification chamber is connected to a second material moving assembly, which includes a second material moving pipe 26. The second material moving pipe 26 is connected to the bottom of the supercritical CO2 fluid modification chamber, the inner wall of the second material moving pipe 26 is welded to the airtight valve, a second material moving motor is welded to one side of the second material moving pipe 26, the output shaft of the second material moving motor extends into the second material moving pipe 26 and is coaxially welded with a second material moving spiral, the other end of the second material moving pipe 26 is connected to an adsorption assembly, and the second material moving motor is connected to the controller signal.

[0109] The adsorption assembly includes an adsorption cabin 25, the top wall of which is welded with a stirring motor 28, the output shaft of the stirring motor 28 extends into the adsorption cabin 25 and is coaxially welded with a number of stirring fans 30, a driving gear 34 is coaxially welded on the output shaft of the stirring motor 28, a tooth groove is provided on the top side wall of the adsorption cabin 25, and driven gears 35 are symmetrically engaged on both sides of the driving gear 34, the driven gears 35 are coaxially welded with a spray pipe 33, and the driven gears 35 are all engaged with the tooth groove, and the stirring motor 28 is connected to the controller signal.

[0110] The bottom end of the spray pipe 33 is slidably connected to a rotating ring groove 32, and a number of nozzles 31 are connected to the bottom wall of the rotating ring groove 32. The nozzles 31 on the same rotating ring groove 32 are all facing in the same direction along the arc of the rotating ring groove 32. A sliding ring groove 36 is installed on the top wall of the adsorption cabin 25. The bottom wall of the sliding ring groove 36 is rotatably connected to the top of the spray pipe 33. The top wall of the sliding ring groove 36 is connected to the liquid inlet pipe 27. The liquid inlet pipe 27 passes through the top wall of the adsorption cabin 25 and is connected to a liquid inlet pump. The liquid inlet pump is used to supply montmorillonite suspension and sodium alginate solution containing alkali-resistant strain 6. The liquid inlet pump is connected to the controller signal.

[0111] An electrostatic field generator 37 is fixedly connected to the inner wall of the adsorption cabin 25 on the opposite side of the second material transfer tube 26. The bottom wall of the adsorption cabin 25 is connected to a discharge pipe 29. A discharge motor 38 is welded to the side wall of the discharge pipe 29. The output shaft of the discharge motor 38 extends into the discharge pipe 29 and is coaxially welded with a discharge screw 39. The discharge screw 39 extends into the adsorption cabin 25. The discharge motor 38 and the electrostatic field generator 37 are both connected to the controller signal.

[0112] The specific implementation process is as follows: During the preparation of the repair material,

[0113] 1. First, it is necessary to prepare biochar particles 1, using agricultural straw as raw material. After being crushed to a particle size of ≤2mm, it is added to the pyrolysis furnace 7 through the feed hopper 10. The controller turns on the steam boiler 8, raises the temperature to 550-600℃ at a rate of 20℃ / min, and pyrolyzes at a constant temperature for 30 minutes. The raw materials enter between the rotary drum 19 and the collecting drum 20 and accumulate at the bottom due to the inclined arrangement of the pyrolysis furnace 7. The controller turns on the rotary motor to rotate the rotary drum 19, stirring and shaking the pyrolysis raw materials inside to promote heating uniformity. The inclined plate 22 at the bottom of the collecting drum 20 guides the pyrolysis raw materials to rise above the sieve hole 21 for screening, and on the other hand, it can also crush the pyrolysis raw materials to improve the fineness of the raw materials, facilitate uniform pyrolysis and ensure screening quality. Pyrolysis promotes rapid devolatilization inside the straw, generating a high specific surface area (>400m 2 / g) of porous biochar, whose surface is rich in carboxyl and phenolic hydroxyl functional groups, while retaining plant-derived minerals such as calcium and magnesium.

[0114] 2. The pyrolyzed biochar particles 1 enter the collection tube 20 and follow the first material transfer pipe 13. The first material transfer screw 23 driven by the first material transfer motor 12 pushes them into the collection tank 14 and accumulates on the collection valve 24. After the pressure sensor on the collection valve 24 senses that the biochar particles 1 have accumulated to a certain amount, the controller controls the collection valve 24 and the airtight valve in the first feed pipe 15 to open and pass the biochar particles 1 into the supercritical CO2 fluid modification chamber. Under the automatic control of the controller, the supercritical CO2 fluid modification chamber is introduced into the precursor solution of ammonium dihydrogen phosphate (NH4H2PO4) and citric acid. Under the conditions of 60°C and 15MPa, the high diffusivity and low surface tension of supercritical CO2 drive the precursor to penetrate into the mesopores of the biochar particles 1. At this time, the endogenous calcium ions (derived from straw ash) in the biochar react with phosphate in the confined space. The chemical formula is as follows:

[0115] 5Ca 2+ +3PO4 3 -+OH-→Ca5(PO4)3OH↓

[0116] The reaction generates hydroxyapatite (nHAP) with a size of less than 20 nm. The mesoporous structure of biochar particles 1 inhibits particle agglomeration and increases the specific surface area to 550 m 2 / g. Simultaneously, citric acid carried by supercritical CO2 undergoes an esterification reaction with the biochar surface hydroxyl groups in the acidic microenvironment, grafting carboxyl functional groups. Chitosan acetic acid solution is then introduced. In the local turbulence created by the decompression of CO2, the chitosan amino groups cross-link with the citric acid carboxyl groups via a Schiff base reaction, forming a pH-responsive polymer layer 3. Biochar particles 1, now coated with the pH-responsive polymer layer 3, enter the second transfer tube 26 through an airtight valve within the tube and are propelled into the adsorption chamber 25 by a second transfer screw driven by a second transfer motor.

[0117] 3. Prepare the alkali-resistant strain 6 (OD 600=1.2) mixed with a 2% sodium alginate solution, injected through the sliding ring groove 36 and the spray pipe 33 at a pressure of 0.3 MPa, driving the atomized montmorillonite suspension (5% w / v) (particle size 50-100 μm) into the adsorption chamber 25 to contact the biochar. The stirring motor 28 drives the stirring fan 30 to rotate and stir the biochar particles 1, while the driving gear 34 and the driven gear 35 drive the spray pipe 33 to rotate around the stirring fan 30. The nozzles 31 on the same rotating ring groove 32 all face the same direction along the arc. When the spray pipe 33 rotates, the solution spreads in a spiral shape, forming a dynamic spray pattern. This not only expands the coverage of the solution, but also, through the shear force generated by the rotation, evenly spreads the montmorillonite suspension and sodium alginate solution on the surface of the biochar. Due to the negative surface charge of the montmorillonite nanosheets 4, they electrostatically bond with the cationic sites of the biochar to form a porous mineralized protective layer. The electrostatic field maintained by the electrostatic field generator 37 can enhance this electrostatic adsorption effect. At the same time, the Ca inside the droplets 2+ Released from the montmorillonite interlayers, the sodium alginate gelation triggers, encapsulating the bacteria within a three-dimensional network. The biochar particles 1 accumulate at the bottom of the adsorption chamber 25, where they experience increasing pressure, accelerating the formation of a montmorillonite-alginate composite gel. This process is completed at 25°C and 70% humidity, with a microbial survival rate exceeding 90%, ensuring structural stability under mechanical stress.

[0118] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0119] The above is only an embodiment of the present invention. Common knowledge such as the known specific structures and characteristics in the scheme is not described in detail here. Ordinary technicians in the field are aware of all common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all existing technologies in the field, and have the ability to apply conventional experimental means before that date. Ordinary technicians in the field can improve and implement this scheme in combination with their own abilities under the inspiration given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A repair material for alkaline cadmium-contaminated soil, comprising a repair material substrate made of biochar particles (1), characterized in that: Hydroxyapatite particles (2) are in situ mineralized in the mesopores of the biochar particles (1), a pH-responsive polymer layer (3) is grafted onto the hydroxyl groups on the surface of the biochar particles (1), and a biogel layer is adsorbed on the periphery of the pH-responsive polymer layer (3); The pH-responsive polymer layer (3) is used to ionize in alkaline soil to form a negatively charged double layer, which specifically adsorbs Cd in the soil solution through electrostatic attraction. 2+ , while releasing H + , so that the pH value of the micro-area at the interface between the repair material and the soil is reduced from alkaline to near neutral or form a local slightly acidic environment, thus promoting the adsorption of Cd on the soil colloid. 2+ Dissolution; Hydroxyapatite particles (2) are used to bind the dissolved Cd through the surface hydroxyl groups. 2+ Coordination exchange occurs to form thermodynamically stable minerals; the biogel layer is used to secrete alkaline phosphatase and laccase, oxidatively degrade polycyclic aromatic hydrocarbons, and produce extracellular polymers to complex residual free Cd 2+ , forming Cd–EPS complexes and promoting soil particle aggregation.

2. The repair material for alkaline cadmium contaminated soil according to claim 1, characterized in that: The pH-responsive polymer layer (3) comprises citric acid grafted onto the hydroxyl groups on the surface of the biochar particles (1), wherein the carboxyl functional groups of the citric acid are cross-linked with the amino groups of chitosan via a Schiff base reaction.

3. The repair material for alkaline cadmium contaminated soil according to claim 1, characterized in that: The biogel layer includes a plurality of montmorillonite nanosheets (4) electrostatically bonded to the cationic sites of the biochar particles (1); the outer sides of the montmorillonite nanosheets (4) are each wrapped with a gelled sodium alginate protective layer (5); and a plurality of alkali-resistant bacterial strains (6) are each embedded in the sodium alginate protective layer (5).

4. A device for preparing a repair material for alkaline cadmium-contaminated soil, based on any one of the repair materials for alkaline cadmium-contaminated soil described in claims 1-3, comprising a pyrolysis component, characterized in that: The pyrolysis assembly includes a pyrolysis furnace (7) placed obliquely, a bracket fixedly connected to the bottom wall of the pyrolysis furnace (7), a controller fixedly connected to the bracket, the pyrolysis furnace (7) includes a hot air cylinder (17), a rotary cylinder (19) is sleeved inside the hot air cylinder (17), a collecting cylinder (20) is sleeved inside the rotary cylinder (19), both ends of the hot air cylinder (17) are fixedly connected to a sealing cover (16), the sealing cover (16) and the rotary cylinder (19) are both slidably connected, and the top of the rotary cylinder (19) passes through the corresponding sealing cover (16) and is connected to a feed pipe (18), the feed pipe (18) is connected to the feed hopper (10), the outer wall of the top of the rotary cylinder (19) is coaxially fixedly connected to the output shaft of the annular motor (9), the outer wall of the annular motor (9) is fixedly connected to the corresponding sealing cover (16), the bottom end of the collecting cylinder (20) passes through the corresponding sealing cover (16) and is connected to the charcoal outlet pipe (11), the charcoal outlet pipe (11) is connected to the first material moving assembly, the side wall of the hot air cylinder (17) is connected to the hot steam boiler (8), and the annular motor (9) and the hot steam boiler (8) are both connected to the controller signal.

5. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 4, characterized in that: A plurality of sieve holes (21) are provided on the upper side of the bottom end of the collecting cylinder (20), and a plurality of inclined plates (22) are vertically fixedly connected to the outer periphery of the lower side of the bottom end of the collecting cylinder (20).

6. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 4, characterized in that: The first material moving component comprises a first material moving pipe (13), one end of the first material moving pipe (13) is fixedly connected to a first material moving motor (12), an output shaft of the first material moving motor (12) extends into the first material moving pipe (13) and is coaxially fixedly connected to a first material moving screw (23), the other end of the first material moving pipe (13) is connected to a material collecting tank (14), the bottom of the material collecting tank (14) is connected to a material collecting valve (24), a pressure sensor is laid on the material collecting valve (24), the other end of the material collecting valve (24) is connected to a first material delivery pipe (15), the first material delivery pipe (15) is connected to a modification component, an airtight valve is provided in the first material delivery pipe (15), the modification component comprises a supercritical CO2 fluid modification chamber, the first material moving motor (12), the pressure sensor, the airtight valve, the material collecting valve (24) and the supercritical CO2 fluid modification chamber are all connected to the controller signal.

7. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 6, characterized in that: The bottom of the supercritical CO2 fluid modification chamber is connected to a second material moving assembly, the second material moving assembly includes a second material moving pipe (26), the second material moving pipe (26) is connected to the bottom of the supercritical CO2 fluid modification chamber, the inner wall of the second material moving pipe (26) is fixedly connected to the airtight valve, one side of the second material moving pipe (26) is fixedly connected to a second material moving motor, the output shaft of the second material moving motor extends into the second material moving pipe (26) and is coaxially fixedly connected to a second material moving screw, the other end of the second material moving pipe (26) is connected to an adsorption assembly, and the second material moving motor is connected to a controller signal.

8. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 7, characterized in that: The adsorption assembly includes an adsorption cabin (25), a top wall of the adsorption cabin (25) is fixedly connected to a stirring motor (28), an output shaft of the stirring motor (28) extends into the adsorption cabin (25) and is coaxially fixedly connected to a plurality of stirring fans (30), a driving gear (34) is coaxially fixedly connected to the output shaft of the stirring motor (28), a tooth groove is opened on the top side wall of the adsorption cabin (25), and driven gears (35) are symmetrically meshed on both sides of the driving gear (34), and the driven gears (35) are coaxially fixedly connected to the spray pipe (33), and the driven gears (35) are all meshed with the tooth groove. The stirring motor (28) is connected to the controller signal.

9. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 8, characterized in that: The bottom ends of the spray pipes (33) are all slidably connected to the rotating ring grooves (32), and the bottom walls of the rotating ring grooves (32) are all connected to a plurality of nozzles (31). The nozzles (31) on the same rotating ring groove (32) are all oriented in the same direction along the arc of the rotating ring groove (32). The top wall of the adsorption cabin (25) is provided with a sliding ring groove (36). The bottom wall of the sliding ring groove (36) is rotatably connected to the top of the spray pipe (33). The top wall of the sliding ring groove (36) is connected to a liquid inlet pipe (27). The liquid inlet pipe (27) passes through the top wall of the adsorption cabin (25) and is connected to a liquid inlet pump. The liquid inlet pump is used to supply a montmorillonite suspension and a sodium alginate solution containing an alkali-resistant strain (6). The liquid inlet pump is connected to a controller signal.

10. The device for preparing a repair material for alkaline cadmium-contaminated soil according to claim 9, characterized in that: An electrostatic field generator (37) is fixedly connected to the inner wall of the adsorption cabin (25) on the opposite side of the second material transfer tube (26); a discharge pipe (29) is connected to the bottom wall of the adsorption cabin (25); a discharge motor (38) is fixedly connected to the side wall of the discharge pipe (29); an output shaft of the discharge motor (38) extends into the discharge pipe (29) and is coaxially fixedly connected to a discharge screw (39); the discharge screw (39) extends into the adsorption cabin (25); and both the discharge motor (38) and the electrostatic field generator (37) are connected to controller signals.

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