A method for remediating heavy metal contaminated soil based on biochar loading technology

Abstract

This invention relates to the field of heavy metal pollution remediation in soil, and discloses a method for remediating heavy metal contaminated soil based on biochar loading technology. The method involves constructing a helical chiral topological structure of biochar through femtosecond laser etching and loading a composite layer of CdS quantum dots and graphene oxide to enhance the selective adsorption and photocatalytic reduction capabilities of heavy metals. Combined with magnetic field-responsive microcapsules that dynamically release remediation agents, reinforcement learning algorithms are used to optimize multi-physics parameters, achieving precise control over the migration, transformation, and fixation of heavy metals. An ultraviolet light-triggered self-healing mechanism is introduced to repair microcapsule damage, and pyrolysis oxidation and acid leaching processes are simultaneously employed to recover heavy metals and regenerate biochar. This invention overcomes the shortcomings of traditional technologies, such as poor material selectivity, uncontrollable release, and non-recyclability, achieving efficient targeted remediation and resource recovery.

Description

Technical Field

[0001] This invention relates to the field of soil heavy metal pollution remediation technology, specifically a method for remediating heavy metal contaminated soil based on biochar loading technology. Background Technology

[0002] In heavy metal contaminated soil remediation technologies, biochar is widely used as an adsorption carrier due to its high porosity and abundant surface functional groups. However, the functional design of traditional biochar-based materials presents a fundamental contradiction: on the one hand, its non-directional adsorption characteristics lead to poor adsorption of highly toxic heavy metal ions (such as Cr). 6+ As 5+ The selectivity of remediation agents is insufficient, making it difficult to prioritize the removal of target pollutants in complex pollution scenarios. On the other hand, statically loaded remediation agents (such as zero-valent iron and sulfides) are prone to uncontrollable release in the soil environment, resulting in premature consumption of materials or passivation effects caused by excessively high local concentrations.

[0003] Existing research attempts to improve remediation efficiency through surface modification (such as graphene oxide coating) or external field assistance (such as electric field driving). However, modified biochar is still limited by the uneven spatial distribution of immobilization sites, and the static setting of external field parameters cannot adapt to dynamic changes in the soil environment, resulting in significant fluctuations in remediation effectiveness. In addition, regeneration technologies for spent biochar mostly focus on pyrolysis activation, neglecting the simultaneous recovery of loaded heavy metals, leading to both resource waste and environmental risks.

[0004] Therefore, this invention proposes a method for remediating heavy metal contaminated soil based on biochar loading technology to address the shortcomings of existing technologies. Summary of the Invention

[0005] This invention addresses the problems of poor material adsorption selectivity, uncontrollable release of remediation agents, disconnect between regeneration processes and heavy metal recovery in traditional biochar-based remediation technologies, as well as significant fluctuations in remediation efficiency under complex pollution scenarios. Through dynamic load control technology, a synergistic mechanism of selective adsorption and speciation transformation, and a closed-loop regeneration process, it achieves efficient targeted removal and resource recovery of heavy metals.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for remediating heavy metal contaminated soil based on biochar loading technology, comprising the following steps:

[0007] S1. Preparation of modified biochar matrix: The biomass raw material is pyrolyzed and acid-washed to obtain porous biochar, and loading sites are constructed on its surface;

[0008] S2. Constructing a dynamic loading system based on the biochar matrix: immobilizing microcapsules containing repair materials at the loading sites, and regulating the release behavior of the microcapsules through an external physical field;

[0009] S3. Dynamic regulation of the remediation process: Real-time monitoring of soil environmental parameters, adjustment of the physical field parameters based on monitoring data, driving the release of remediation materials and the migration-fixation of heavy metals;

[0010] S4. Regeneration and Recycling: After the repair is completed, the load system function is restored by triggering the self-repair mechanism, and heavy metals and biochar are recycled.

[0011] Preferably, in step S1:

[0012] The pyrolysis is carried out in an inert gas atmosphere at a temperature of 500-800℃ for 1-4 hours.

[0013] The pickling process uses nitric acid or hydrochloric acid solution with a concentration of 0.05-0.5 mol / L and a treatment time of 12-36 h.

[0014] Preferably, in step S1, a helical chiral topology is formed on the surface of biochar by laser etching, with a chiral index of (n,m)=(5,2)-(9,4), a trench depth of 50-500nm, and a spacing of 20-100nm.

[0015] Preferably, in step S2:

[0016] The microcapsule comprises a core and a shell, wherein the core is a mixture of FeS nanoparticles and a polymer, and the shell is a graphene oxide-humic acid composite film incorporating magnetic nanoparticles.

[0017] The release threshold of the microcapsule satisfies the formula:

[0018]

[0019] Where, M s σ is the saturation magnetization of the magnetic nanoparticles, H is the external magnetic field strength, μ0 is the free permeability, and σ is the magnetic nanoparticle saturation magnetization. s d is the yield stress of the outer shell, and d is the thickness of the outer shell.

[0020] Preferably, the microcapsules are fixed within the helical chiral grooves of biochar by ultraviolet light curing, with the ultraviolet light wavelength being 300-400 nm and the intensity being 30-100 mW / cm². 2 The curing time is 5-20 minutes.

[0021] Preferably, in step S3, the adjustment of the physical field parameters is achieved through a reinforcement learning model. The model takes real-time data of soil pH, redox potential, and heavy metal concentration as input, and outputs magnetic field strength and ultraviolet light intensity, wherein:

[0022] The reinforcement learning model is the Q-learning algorithm, and its action space is defined as the magnetic field strength range of 0-200 kA / m and the ultraviolet light intensity range of 0-100 mW / cm. 2 ;

[0023] The reward function of the model is the weighted difference between the amount of heavy metals removed and the amount of materials consumed.

[0024] Preferably, in step S3, the heavy metal migration is achieved through dielectric migration driven by a high-frequency alternating electric field, and its migration equation satisfies:

[0025]

[0026] Where C is the heavy metal concentration, D is the diffusion coefficient, ∈ m Let r be the dielectric constant of the medium, r be the particle radius, η be the viscosity, and f be the viscosity of the medium. CM It is the Clausius-Mossotti factor.

[0027] Preferably, in step S4, the self-repair mechanism is a UV-triggered thiol-alkene click chemistry reaction, and its reaction formula is:

[0028]

[0029] Preferably, in step S4, heavy metal recovery is achieved through pyrolysis oxidation and acid leaching, wherein the pyrolysis temperature is 500-800℃ and the acid leaching solution is 0.5-2 mol / L hydrochloric acid.

[0030] This invention provides a method for remediating heavy metal contaminated soil based on biochar loading technology. It has the following beneficial effects:

[0031] 1. This invention constructs a helical chiral topological structure on the surface of biochar through femtosecond laser etching, combined with heterojunction modification of quantum dots (CdS) and graphene oxide (GO). Utilizing the synergistic effect of geometric confinement and photocatalytic reduction capabilities, it overcomes the limitations of traditional biochar in terms of low adsorption capacity and poor selectivity for heavy metals, achieving adsorption of highly toxic heavy metals (such as Cr). 6 + As 5+ Targeted capture and speciation transformation of heavy metals are particularly suitable for the differentiated removal needs of multivalent heavy metals in complex polluted soils.

[0032] 2. This invention proposes a magnetic field-encoded microcapsule dynamic loading technology. By doping magnetic nanoparticles and controlling the rupture threshold formula, combined with ultraviolet light crosslinking and fixation process, the repair material (FeS-PEI) is precisely positioned and released on demand in the biochar trench. This overcomes the defects of uneven material dispersion and low utilization rate in traditional static loading technology. At the same time, through the synergy of dielectrophoretic migration and photocatalytic reaction, the spatial enrichment and chemical conversion efficiency of heavy metal ions are enhanced.

[0033] 3. This invention constructs an intelligent control model based on reinforcement learning algorithm. It uses real-time monitored soil pH, redox potential and heavy metal concentration gradient as input parameters to dynamically optimize physical field parameters such as magnetic field strength, electric field frequency and ultraviolet light intensity, forming a closed-loop control of "perception-decision-execution". This solves the problem of parameter lag or excessive consumption in experience-driven remediation technology and significantly improves the stability and adaptability of the remediation process under complex pollution scenarios.

[0034] 4. This invention introduces a UV-triggered thiol-ene click chemistry self-healing mechanism to extend the service life of the dynamic loading system by repairing microcapsule shell damage online; simultaneously, a pyrolysis-oxidation-acid leaching combined process is developed to convert heavy metals in spent biochar into recyclable forms (such as Cd). 2+ This enables the recycling and resource recovery of remediation materials, forming a full life-cycle technology path of "pollution remediation - material regeneration - resource recovery," which significantly reduces the long-term cost of environmental governance.

[0035] 5. This invention integrates multiple technologies, including quantum dot photocatalysis, dielectrophoretic migration, intelligent algorithm regulation, and self-healing chemistry, to construct a complete chain solution for heavy metal identification, migration, transformation, fixation, and recycling on biochar carriers. It systematically solves the problems that traditional single technologies cannot address, such as the complexity of heavy metal occurrence forms, irreversible loss of remediation materials, and delayed environmental response. It provides an efficient, low-consumption, and sustainable integrated strategy for the remediation of complex heavy metal pollution in soil. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for remediating heavy metal contaminated soil based on biochar loading technology. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Please see the appendix Figure 1This invention provides a method for remediating heavy metal contaminated soil based on biochar loading technology. The steps of the method are described in detail below.

[0039] S1. Preparation of modified biochar matrix: The biomass raw material is subjected to pyrolysis and acid washing to obtain porous biochar, and loading sites are constructed on its surface.

[0040] In this embodiment, step S1, the preparation of the modified biochar matrix, includes raw material pretreatment, quantum dot embedding and surface modification, and chiral topological structure etching. The technical features are described in detail below:

[0041] Agricultural waste is crushed to obtain biomass pellets with uniform particle size. Biomass includes raw materials rich in cellulose, such as rice husks, straw, or fruit shells. The crushed biomass is then subjected to pyrolysis in an inert gas atmosphere (nitrogen or argon), with the pyrolysis temperature range set between 500℃ and 800℃ and the isothermal time controlled between 1 and 4 hours. After pyrolysis, the resulting biochar is acid-washed using nitric acid or hydrochloric acid solution at a concentration range of 0.05 mol / L to 0.5 mol / L for 12 to 36 hours. Acid washing removes ash impurities from the biochar and activates surface functional groups, including hydroxyl, carboxyl, and phenolic hydroxyl groups, thereby enhancing the anchoring ability of subsequent quantum dot loading.

[0042] Quantum dot embedding and surface modification:

[0043] Cadmium sulfide quantum dots (CdSQDs) were synthesized using a solvothermal method. Cadmium salt and a sulfur source were dissolved in ethylene glycol or deionized water at a molar ratio of 1:2 to 1:3, and reacted at 120°C to 180°C for 2 to 6 hours. CdSQDs with uniform particle size distribution were obtained by centrifugation and washing. The CdSQDs were further dispersed in ethanol or water at a mass ratio of 1:3 to 1:8, and a homogeneous suspension was formed by ultrasonic treatment. The suspension was loaded into the pores of acid-washed biochar using a vacuum impregnation method at a vacuum degree of -0.1 MPa to -0.08 MPa for 2 to 6 hours. After loading, annealing was performed under inert gas protection at a temperature of 200°C to 400°C for 1 to 3 hours to form a stable heterojunction structure between the CdSQDs and GO. The crystal form and dispersion state of the quantum dots were confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM).

[0044] Chiral topology etching:

[0045] A femtosecond laser processing system was used to etch helical chiral topologies onto the surface of biochar. The femtosecond laser wavelength ranged from 800 nm to 1064 nm, with pulse widths of 100 fs to 500 fs, single-pulse energies of 10 μJ to 100 μJ, and repetition rates of 1 kHz to 10 kHz. The laser focus position was controlled by a three-dimensional motion platform to form helical grooves with depths of 50 nm to 500 nm and spacings of 20 nm to 100 nm on the biochar surface. The chiral indices (n, m) were selected from the range of (5, 2) to (9, 4). The chiral topologies modulated the diffusion paths of heavy metal ions through geometric confinement effects.

[0046] S2. Dynamic loading system based on biochar matrix: Microcapsules containing repair materials are fixed to the loading site, and the release behavior of the microcapsules is regulated by an external physical field.

[0047] In this embodiment, the construction of the dynamic loading system in step S2 includes the preparation of microcapsules, magnetic field encoding, and immobilization on a biochar matrix. The technical features are described in detail below:

[0048] Preparation of microcapsules:

[0049] First, ferrous sulfide (FeS) nanoparticles were synthesized via a chemical coprecipitation method. Iron salt and a sulfur source were dissolved in deionized water at a molar ratio of 1:1 to 1:1.5. The reaction was carried out under inert gas protection with stirring, the reaction temperature was controlled at 20℃ to 60℃, and the reaction time was 1 to 4 hours. After centrifugation and washing, FeS nanoparticles with uniform particle size distribution were obtained. The reducing properties of FeS nanoparticles can effectively remove high-valence heavy metal ions (such as Cr) 6+ As 5+ ) is converted into a low-toxicity form (such as Cr) 3+ As 3+ ).

[0050] FeS nanoparticles were further mixed with polyethyleneimine (PEI) at a mass ratio of 1:1 to 1:3 to form a chelate-reduction composite core. PEI has a molecular weight of 5 kDa to 20 kDa, and its amino functional groups can bind to heavy metal ions through coordination, enhancing its immobilization ability. The mixture was dispersed in a composite solution of graphene oxide (GO) and humic acid (HA), and core-shell structured microcapsules were generated using microfluidic technology. The mass ratio of GO to HA was 1:2 to 1:5; the layered structure of GO provided mechanical strength, while the carboxyl and phenolic hydroxyl groups of HA enhanced the hydrophilicity and environmental responsiveness of the shell.

[0051] Magnetic field coding and rupture threshold regulation:

[0052] Magnetic nanoparticles are incorporated into the shell of microcapsules to achieve magnetic field responsiveness. The magnetic nanoparticles are Fe3O4 or CoFe2O4, and the incorporation amount is 3% to 10% of the total mass of the shell. The rupture threshold of the microcapsules is controlled by an external magnetic field, and their mechanical equilibrium relationship satisfies the following formula:

[0053]

[0054] Among them, M s σ is the saturation magnetization of the magnetic particle, H is the applied magnetic field strength, μ0 is the free permeability, and σ is the magnetic particle saturation magnetization. s denoted as σy, where σ is the yield stress of the outer shell material and d is the shell thickness. By adjusting the magnetic field strength (HH), the timing of microcapsule rupture in the soil environment can be precisely controlled, thereby releasing the core remediation material as needed.

[0055] Microcapsules immobilized on a biochar matrix:

[0056] Microcapsules were dispersed within the helical chiral grooves on the surface of the biochar prepared in step S1. A cross-linking reaction was initiated using ultraviolet light to achieve stable immobilization of the microcapsules. Ultraviolet light irradiation triggered the photothermal effect on the graphene oxide surface, promoting the condensation reaction between the phenolic hydroxyl groups in humic acid and the epoxy groups in GO, forming a covalently cross-linked network. The ultraviolet light wavelength range was 300 nm to 400 nm, and the irradiation intensity was 20 mW / cm². 2 Up to 100mW / cm 2 The curing time is 5 to 30 minutes.

[0057] S3. Dynamic regulation of the remediation process: Real-time monitoring of soil environmental parameters, adjustment of physical field parameters based on monitoring data, driving the release of remediation materials and the migration and fixation of heavy metals.

[0058] In this embodiment, the dynamic regulation and remediation process in step S3 includes real-time monitoring of soil parameters, optimization of the reinforcement learning model, and regulation by field-chemical synergy. The technical features are described in detail below:

[0059] Real-time monitoring of soil parameters:

[0060] A sensor network was deployed in contaminated soil, comprising a pH electrode, a redox potential sensor, and a heavy metal ion selective electrode. The pH electrode employed a glass electrode structure with a detection range of pH 3 to pH 10; the redox potential sensor measured the potential difference between a platinum electrode and a reference electrode, covering a range of -1000 mV to +1000 mV; and the heavy metal ion selective electrode targeted specific heavy metals (such as Cd). 2+ Pb 2+ Cr 6+The design employs an ion-carrier-modified polymer membrane electrode, with a detection limit of 0.1 ppm to 10 ppm. A sensor network acquires data at a frequency of 1 to 10 times per minute and transmits real-time data to the control module via a wireless transmission module.

[0061] Reinforcement learning model optimization:

[0062] A reinforcement learning model based on the Q-learning algorithm is constructed to dynamically adjust the magnetic field strength and ultraviolet light intensity. The model's state space is defined as a three-dimensional vector. in The heavy metal concentration gradient is represented by the action space, which is defined as a two-dimensional vector a. t =[H,I UV ], corresponding to magnetic field strength and ultraviolet light intensity, respectively. The reward function is designed as follows:

[0063] R = w1·ΔC removal -w2·ΔC material ;

[0064] Where, ΔC removal ΔC represents the amount of heavy metals removed. material w1 and w2 are weighting coefficients, representing material consumption. The learning rate of the model is set to 0.05 to 0.2, and the discount factor is set to 0.8 to 0.95. Strategy optimization is achieved by iteratively updating the Q-value table.

[0065] Field-chemical synergistic regulation:

[0066] A high-frequency alternating electric field drives the directional migration of heavy metal ions through dielectric migration. The frequency of the electric field is set from 1 MHz to 10 MHz, and the field strength is from 10 V / m to 100 V / m, generated by a signal generator and a power amplifier. The dielectric migration process is described by the following partial differential equation.

[0067]

[0068] Where D is the diffusion coefficient of heavy metal ions, ∈ m Let η be the dielectric constant of the soil medium, r be the ion hydration radius, η be the viscosity of the soil pore fluid, and f be the dielectric constant of the soil medium. CM It is the Clausius-Mossotti factor.

[0069] When the Cr concentration exceeds a preset threshold, an ultraviolet light source is activated to drive the photocatalytic reduction reaction of CdS quantum dots. The ultraviolet light wavelength is set to 300 nm to 400 nm, and the light intensity is 10 mW / cm². 2 Up to 50mW / cm 2 Photogenerated electrons transfer from the conduction band of CdS to Cr. 6+ , triggers a reduction reaction:

[0070]

[0071] S4. Regeneration and Recycling: After the repair is completed, the load system function is restored by triggering the self-repair mechanism, and heavy metals and biochar are recycled.

[0072] In this embodiment, the regeneration and recycling process in step S4 includes activation of the self-repair mechanism, biochar regeneration, and heavy metal recovery. The technical features are described in detail below:

[0073] Self-repair mechanism activated:

[0074] When the sensor network detects that the oxidation rate of FeS nanoparticles in the dynamic loading system exceeds a preset threshold, it triggers ultraviolet light to irradiate the microcapsule shell. The ultraviolet light wavelength is selected from 250nm to 300nm, and the light intensity range covers 50mW / cm². 2 Up to 150mW / cm 2 Ultraviolet photons excite photosensitive groups in the graphene oxide-humic acid composite shell, initiating a click chemistry reaction between thiols (-SH) and alkenes (C=C):

[0075]

[0076] The reaction proceeds via a free radical chain mechanism, repairing microcapsule shell cracks caused by mechanical stress or chemical corrosion. The repaired microcapsules regain their controlled-release function of the loaded material and re-engage in the heavy metal repair process.

[0077] Biochar regeneration and heavy metal recovery:

[0078] The remediation-completed biochar matrix was removed from the soil and subjected to pyrolysis oxidation. The pyrolysis process was carried out in air at a temperature set between 500°C and 800°C for 0.5 to 2 hours. Under these high-temperature conditions, CdS quantum dots loaded in the biochar pores were oxidized to CdO. The reaction equation is as follows:

[0079]

[0080] After pyrolysis, the biochar is pulverized and then immersed in an acidic solution using 0.5 mol / L to 2 mol / L hydrochloric acid as the leaching agent. The solution is treated for 1 to 4 hours under stirring to convert CdO into soluble Cd. 2+ Ions. The leachate is separated by filtration, and Cd is recovered by electrolytic deposition or chemical precipitation. 2+ The regenerated biochar is washed with deionized water until neutral, dried, and then reintroduced into the modification process in step S1 to achieve recycling.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for remediating heavy metal contaminated soil based on biochar loading technology, characterized in that, Includes the following steps: S1. Preparation of modified biochar matrix: The biomass raw material is subjected to pyrolysis and acid washing to obtain porous biochar, and loading sites are constructed on its surface; S2. Constructing a dynamic loading system based on the biochar matrix: immobilizing microcapsules containing repair materials at the loading sites, and regulating the release behavior of the microcapsules through an external physical field; S3. Dynamic regulation of the remediation process: Real-time monitoring of soil environmental parameters, adjustment of physical field parameters based on monitoring data, driving the release of remediation materials and the migration and fixation of heavy metals; S4. Regeneration and Recycling: After the repair is completed, the load system function is restored by triggering the self-repair mechanism, and heavy metals and biochar are recycled. In step S1, a helical chiral topology is formed on the surface of biochar by laser etching, with a chiral index of (n,m)=(5,2)-(9,4), a trench depth of 50-500nm, and a spacing of 20-100nm. In step S2: The microcapsule comprises a core and a shell, wherein the core is a mixture of FeS nanoparticles and a polymer, and the shell is a graphene oxide-humic acid composite film incorporating magnetic nanoparticles. The release threshold of the microcapsule satisfies the formula: ； in, The saturation magnetization of the magnetic nanoparticles. The external magnetic field strength, The permeability of free space, For the shell yield stress, This refers to the thickness of the outer casing.

2. The method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, In step S1: The pyrolysis is carried out in an inert gas atmosphere at a temperature of 500-800℃ for 1-4 hours. The pickling process uses nitric acid or hydrochloric acid solution with a concentration of 0.05-0.5 mol / L and a treatment time of 12-36 h.

3. The method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, The microcapsules were fixed within the helical chiral grooves of biochar by ultraviolet light curing at a wavelength of 300-400 nm and an intensity of 30-100 mW / cm². 2 The curing time is 5-20 minutes.

4. The method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, In step S3, the adjustment of the physical field parameters is achieved through a reinforcement learning model. This model takes real-time data on soil pH, redox potential, and heavy metal concentration as input, and outputs magnetic field strength and ultraviolet light intensity, wherein: The reinforcement learning model is the Q-learning algorithm, and its action space is defined as the magnetic field strength range of 0-200 kA / m and the ultraviolet light intensity range of 0-100 mW / cm. 2 ; The reward function of the model is the weighted difference between the amount of heavy metals removed and the amount of materials consumed.

5. A method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, In step S3, the migration of heavy metals is achieved through dielectric migration driven by a high-frequency alternating electric field, and its migration equation satisfies: ； in, This refers to the concentration of heavy metals. Where is the diffusion coefficient. The dielectric constant of the medium, Where is the particle radius, Viscosity, It is the Clausius-Mossotti factor.

6. The method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, In step S4, the self-repair mechanism is a UV-triggered thiol-alkene click chemistry reaction, and its reaction formula is: 。 7. A method for remediating heavy metal contaminated soil based on biochar loading technology according to claim 1, characterized in that, In step S4, heavy metal recovery is achieved through pyrolysis oxidation and acid leaching, wherein the pyrolysis temperature is 500-800℃ and the acid leaching solution is 0.5-2 mol / L hydrochloric acid.

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