Rice husk biochar modified Fe 3+ TiO2 composite materials and copper sulfide methods for acidic soil remediation

Abstract

This invention discloses a rice husk biochar modified Fe 3+ The method for remediating acidic soil using TiO2 composite materials and copper sulfide involves first mixing tetrabutyl titanate and anhydrous ethanol at a predetermined mass ratio of X1 to obtain reagent A; then mixing Fe(NO3)3·9H2O, acetic acid, and anhydrous ethanol at a predetermined mass ratio of X2 to obtain reagent B; next, adding acetic acid to reagent A and stirring, then adding reagent B dropwise while stirring, followed by adding acetic acid dropwise again while stirring continuously to obtain reagent C; further, aging reagent C, drying it, and finally calcining it to obtain Fe 3+ -TiO2; then Fe 3+ TiO2, rice husk biochar, deionized water, and ethanol were refluxed and stirred to obtain a homogeneous gray solution; finally, the gray solution was dried to obtain rice husk biochar-modified Fe. 3+ -TiO2 composite material; This invention provides a new and efficient functional material for the ecological remediation of acidic heavy metal contaminated soil in copper sulfide mines, and also provides a theoretical basis and technical reference for the synergistic remediation of soil acidification and heavy metal pollution in mining areas.

Description

Technical Field

[0001] This invention belongs to the field of soil pollution remediation and soil restoration technology, and relates to a biochar composite material and a method for remediating acidic soil, specifically involving a rice husk biochar-modified Fe... 3+ -TiO2 composite materials and copper sulfide methods for remediating acidic soils. Background Technology

[0002] In recent decades, with the acceleration of global industrialization, the demand for metals such as gold, silver, copper, and nickel has continued to grow, leading to a significant increase in various metal mining activities (Reference 1). However, large-scale mining of mineral resources, especially through unreasonable development methods, is often accompanied by serious ecological and environmental problems (Reference 2). During the mining of copper sulfide ores, sulfide minerals (mainly pyrite FeS2 and chalcopyrite CuFeS2), which were originally in a reduced state, are exposed to oxygen and water, undergoing violent oxidation under chemical and microbial catalysis, thereby producing sulfuric acid and releasing sulfates and dissolving metals (Reference 3). Under continuous acidic conditions, the physicochemical properties and mineral composition of the soil change, affecting the migration and transformation behavior of heavy metals in the soil and their ecological risks, thus posing a potential threat to regional ecosystem security and human health. Therefore, revealing the formation mechanism and ecological effects of soil acidification and heavy metal pollution in mining areas is a key issue that urgently needs to be addressed in the field of ecological restoration of mining areas (Reference 4).

[0003] Currently, the remediation of heavy metals in soil mainly involves physical, chemical, and biological remediation (Reference 5). Most physical remediation techniques are relatively simple and low-cost, with soil replacement and thermal desorption being the main methods (Reference 6). Soil replacement mainly involves whole soil exchange, topsoil and subsoil replacement, partial soil exchange, and covering with new soil (Reference 7). Chemical remediation can extract or dissolve heavy metals in the soil through chemical leaching or convert them into less toxic forms through stabilization (Reference 8). Bioremediation mainly includes phytoremediation and microbial remediation. Phytoremediation can absorb heavy metals in the soil through lignification, thereby storing them in plant tissues, or volatilize and mineralize them into carbon dioxide and water, thus converting the heavy metals into less toxic forms (Reference 9). Microbial remediation mainly involves introducing microorganisms into the soil and utilizing their metabolism to reduce the concentration of microorganisms in the soil, thereby improving soil quality. The main remediation mechanisms include biosorption, bioaccumulation, bioleaching, biovolatilization, and biomineralization (Reference 10).

[0004] Photocatalysis is a promising environmental pollution treatment technology that can completely oxidize organic molecules at a relatively low energy cost (Reference 11). Among them, titanium dioxide (TiO2) is one of the most promising photocatalysts. Due to its excellent electronic, optical properties and chemical stability, it is widely used in environmental purification and can be actively added to water or soil as an environmental purifier (References 12-13). Nano-titanium dioxide has been widely used in the remediation of heavy metal pollution in soil. Zhang et al. (Reference 14) found through pot experiments that TiO2NPs can reduce the phytotoxicity of Cd by changes in morphology and biochemical characteristics. The addition of TiO2NPs to the soil affected the physiological parameters of Oryza sliva L., leading to an increase in plant height, biomass, and chlorophyll content. During the heading stage, the addition of TiO2NPs resulted in a 15%–32% and 24%–48% reduction in malondialdehyde (MDA) content in the C2 and C3 groups, respectively, compared with the corresponding control treatment (T0), while also reducing the activity of antioxidant enzymes. Ali Daryabeigi Zand (Reference 15) found that adding TiO2 NPs to the soil significantly improved the accumulation capacity of Cd in poplar, with a maximum accumulation capacity of 1235 µg·pot in combination with plant growth-promoting rhizosphere bacteria (PGPR). -1 .

[0005] However, TiO2 also has obvious drawbacks in practical applications. Due to its large band gap (Reference 16), it can only be excited under ultraviolet or near-ultraviolet radiation. In addition, the photogenerated electrons (e) in the valence band (VB) and the holes (h) in the conduction band (CB) are also limited. +TiO2 is prone to rapid recombination, which leads to a significant decrease in photocatalytic efficiency (Reference 17). To improve these shortcomings and enhance its photocatalytic performance, the advantages of composite materials can be utilized to synthesize TiO2 composite materials with high specific surface area and good adsorption capacity. Doping TiO2 with different metals (References 18-20) or non-metal ions (References 21-23) is an effective means to improve the photocatalytic performance of TiO2. Among various transition metals, iron is considered a suitable choice. Choi et al. (Reference 24) studied the photocatalytic performance of TiO2 doped with 21 metal ions and found that Fe ion doping had the best performance. S. Arunmetha (Reference 25) synthesized TiO2 nanoparticles with different concentrations of Fe doping by thermal melting. As the doping concentration increased, the band gap gradually shortened, and the energy difference decreased from 3.2 eV to 2.9 eV. During this process, electron-hole recombination decreased, and photocatalytic activity was enhanced. Cátia Afonso (Reference 26) prepared Fe-doped TiO2 using a simple and low-cost method. During the doping process, the spectrum of TiO2 changed, showing a Ti-O-Fe vibrational relationship, and the band gap energy decreased from 3.16 eV to 2.06 eV. TiO2 with a 1:1.6 ratio exhibited the highest activity in the photocatalytic degradation of RhB, with an efficiency of 93.8% after 3 hours of irradiation. Photocatalysts doped with carbon materials, such as biochar, can improve the separation efficiency of photogenerated carriers due to their excellent conductivity and strong visible light absorption (Reference 27). Lignin biochar, as an amorphous material, has a microcrystalline graphite structure and a large number of adsorption active sites, which is beneficial to improving the photocatalytic efficiency of semiconductors (Reference 28). Biochar-modified TiO2 exhibits two significant advantages in photocatalytic degradation. The first advantage is the increased specific surface area of ​​the photocatalyst, which improves the absorption efficiency. The second advantage is the exhibiting of electron-hole pair recombination, which is caused by the high conductivity and well-crystallized structure of biochar (Reference 29).

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[29] Ahmad S, Tahir MS, Kamal GM, et al. TiO2 / activated carbon / 2Dselenides composite photocatalysts for industrial wastewater treatment[J]. Water, 2023, 15(9): 1788. Summary of the Invention To address the challenges of remediation technology for acidic soils from copper sulfide ore deposits, this invention utilizes rice husk biochar to modify Fe... 3+ -TiO2 composite materials provide a shell biochar modified Fe 3+ -TiO2 composite materials and copper sulfide acid soil remediation methods provide a new approach for the ecological restoration of mines.

[0007] This invention provides a rice husk biochar modified Fe 3+ -TiO2 composite material, which is a hierarchical porous core-shell heterojunction composite structure; wherein, the core layer is Fe 3+ Doped anatase TiO2 nanocrystals, Fe 3+It exists in a lattice-doped state, forming an internal lattice bond Fe–O–Ti structure with intermediate impurity energy levels, narrowing the band gap; the shell layer is a porous carbon layer of rice husk biochar; the interface between the core layer and the shell layer is connected by Ti–O–C covalent bonds, forming a continuous electron transport channel.

[0008] Preferably, the manufacturing process of the composite material includes the following steps: Step 1: Mix tetrabutyl titanate and anhydrous ethanol at a predetermined mass ratio of X1 to obtain reagent A; Step 2: Mix Fe(NO3)3·9H2O, acetic acid and anhydrous ethanol at a predetermined mass ratio of X2 to obtain reagent B; Step 3: Add the preset amount of Y1 acetic acid to reagent A and stir. Then add reagent B dropwise and stir for T1 hours. Then add acetic acid dropwise again and continue stirring for T2 hours to obtain reagent C. Wherein, T1 and T2 are preset values. Step 4: Aging reagent C for T3 hours, drying at C1 degree Celsius, and finally calcining at C2 degree Celsius for T4 hours and C3 degree Celsius for T5 hours to obtain Fe. 3+ -TiO2; where T3, T4, T5, C1, C2, and C3 are all preset values; Step 5: Add Fe 3+ TiO2, rice husk biochar, deionized water and ethanol were refluxed and stirred at a preset mass ratio of X3 at C4 for T6 hours to obtain a homogeneous gray solution; where C4 and T6 are preset values. Step 6: Dry the gray solution at C5 degrees Celsius to obtain rice husk biochar modified Fe. 3+ -TiO2 composite material; where C5 is a preset value.

[0009] Preferably, in step 1, the preset mass ratio X1 is set to a value range of 1:2.5 to 4.5.

[0010] Preferably, in step 2, the preset mass ratio X2 is set to a value range of 1:5.0~8.0:1.5~2.5.

[0011] Preferably, in step 3, the value range of reagent A:Y1 is 1:0.040~0.065; the value range of T1 is 3~10 minutes, and the value range of T2 is 1.5~3 hours.

[0012] Preferably, in step 4, the value range of T3 is 12~24h, the value range of T4 is 0.5~1.5h, and the value range of T5 is 1.5~2.5h.

[0013] Preferably, in step 4, the value range of C1 is 100~130℃, the value range of C2 is 150~250℃, and the value range of C3 is 450~500℃.

[0014] Preferably, in step 5, the value range of the preset quantity X3 is 0.01~0.05:2.0:500:197.25; the value of C4 is 80~120℃; and the value range of T6 is 0.5~2h.

[0015] Preferably, in step 6, the value of C5 is 50~70℃.

[0016] The present invention provides a method for remediating copper sulfide acidic soil, wherein the composite material is mixed with copper sulfide acidic soil at a mass ratio of 1:100 to 1:20, and the soil is incubated for T6 days with stable water holding capacity, without soil turning or ex-situ treatment; wherein the value range of T6 is 45 to 75 days.

[0017] The beneficial effects achieved by this invention compared to the prior art include: (1) In this invention, reagent B is added dropwise to reagent A, and co-doping is carried out dropwise during the sol formation stage, rather than by later impregnation doping, to ensure Fe 3+ Uniformly embedded in the TiO2 lattice to avoid agglomeration of iron oxides; (2) The present invention in Fe 3+ - The TiO2 preparation process adopts the "room temperature aging - low temperature drying - segmented calcination" process to precisely control the anatase crystal phase and grain size; (3) In this invention, Fe is loaded using a water-ethanol azeotropic system via wet interfacial bonding of rice husk biochar. 3+ - TiO2 and rice husk biochar are refluxed and stirred at 100°C to form Ti–O–C and Fe–O–C covalent bonds through hydroxyl dehydration, rather than simple physical coating, thus achieving strong interfacial bonding; (4) The composite material prepared by the present invention is a loose and porous three-dimensional skeleton with dispersed particles and no agglomeration. The specific surface area increases with the amount of biochar added, which can provide sufficient adsorption sites and reactive sites for heavy metal ions and accelerate the adsorption and interfacial catalytic reaction rate.

[0018] (5) This invention employs an in-situ synergistic passivation-photocatalytic coupling remediation process for acidic soils containing copper sulfide. Utilizing the visible light response characteristics of composite materials, it continuously generates reactive oxygen species under natural light, oxidizing reduced sulfides in the soil, reducing sulfuric acid production, and driving Cu from a weakly acidic extractable state to an oxidizable state, and further to a residual state in a directional transformation, rather than simple adsorption and retention. This achieves long-term stable acid and toxicity control; simultaneously, it improves soil pH, CEC, and organic matter, neutralizing acidity in situ and fixing Cu. 2+No stepwise application of modifiers and passivators is required.

[0019] (6) This invention uses rice husks, an agricultural waste, to prepare biochar, thereby realizing the resource utilization of solid waste. The raw materials are cheap and readily available, green and environmentally friendly, reducing the cost of preparing composite materials. At the same time, the inherent pores and surface functional groups of biochar can synergistically enhance the soil's water retention, fertilizer retention, and air permeability, improve the soil aggregate structure, and avoid soil compaction after remediation. (7) The present invention adopts a preparation process combining sol-gel combined segmented calcination and hydrothermal reflux. The process parameters are highly controllable and have good repeatability. The batch performance of the product is stable and easy to prepare on a large scale and promote its engineering application. Attached Figure Description

[0020] The technical solutions of the present invention will be further illustrated below using embodiments and specific implementation methods. In addition, some accompanying drawings are used in the description of the technical solutions. Those skilled in the art can obtain other drawings and the intent of the present invention from these drawings without any creative effort.

[0021] Figure 1 This is a schematic diagram of the composite material structure according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the preparation process of composite materials according to an embodiment of the present invention; Figure 3 The UV-Vis spectra corresponding to the characteristic wavelengths and band gaps of the materials in the experiments of this embodiment of the invention are shown. Figure 4 The following are the UV-vis DRS and BET analysis results in the experiments of the present invention: (a) is the UV-Vis spectrum (BF1-BF3) of the prepared photocatalyst; (b) is the BET specific surface area spectrum (T, FT, BF1-BF3) of the prepared photocatalyst. Figure 5 The images show the SEM analysis results from the experiments in this embodiment of the invention; (a) SEM TiO2; (b) Fe 3+ -TiO2; (ce)BF1–BF3; Figure 6 This is a graph showing the XRD analysis results from an experiment in an embodiment of the present invention. Figure 7 This is a graph showing the XPS analysis results from an experiment in an embodiment of the present invention; Figure 8 This is a schematic diagram illustrating the changes in soil pH and electrical conductivity during experiments in an embodiment of the present invention. Figure 9 This is a schematic diagram of soil cation exchange and organic matter analysis in an embodiment of the present invention. Figure 10This is a schematic diagram illustrating the analysis of total copper and available copper components in soil under different treatment conditions in the experiments of this invention. Figure 11 This is a diagram showing the proportional distribution of different forms of copper (Cu) in acidic soil during experiments in this embodiment of the invention. Figure 12 This is a schematic diagram of the Pearson correlation analysis between soil physicochemical properties and the total content of heavy metal copper in the soil in an experiment according to an embodiment of the present invention. Detailed Implementation

[0022] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] Please see Figure 1 This embodiment provides a rice husk biochar modified Fe 3+ -TiO2 composite material, which is a hierarchical porous core-shell heterojunction composite structure; the core layer is Fe. 3+ Doped anatase TiO2 nanocrystals, Fe 3+ It exists in a lattice-doped state, forming an internal lattice bond Fe–O–Ti structure with intermediate impurity energy levels, narrowing the band gap; the shell layer is a porous carbon layer of rice husk biochar; the interface between the core layer and the shell layer is connected by Ti–O–C covalent bonds, forming a continuous electron transport channel.

[0024] according to Figure 3 The UV-Vis image was used to calculate the band gap width using the formula Eg=1240 / λonset (λonset is the wavelength at which the absorption intensity is zero). The results are shown in Table 3. The characteristic wavelength of A1 redshifts to 423 nm, and the band gap decreases to 2.75 eV, indicating that Fe... 3+ Successfully entered the TiO2 lattice and introduced impurity energy levels into the band gap.

[0025] according to Figure 7 XPS image analysis revealed that the shell layer is a porous carbon layer of rice husk biochar. The interface between the core layer and the shell layer is firmly bonded by Ti–O–C covalent bonds, forming a continuous and interconnected electron transport channel, which effectively suppresses photogenerated electron-hole recombination and improves photocatalytic quantum efficiency.

[0026] Please see Figure 2 The rice husk biochar modified Fe provided in this embodiment according to claim 1 3+ -TiO2 composite material, the manufacturing process of which includes the following steps: Step 1: Mix tetrabutyl titanate and anhydrous ethanol at a predetermined mass ratio of X1 to obtain reagent A; In one embodiment, the value of X1 ranges from 1:2.5 to 4.5. Choosing the lower limit of 1:2.5 prevents the tetrabutyl titanate from dispersing unevenly when anhydrous ethanol is insufficient, leading to large agglomerates and localized high concentrations that can cause rapid hydrolysis. Choosing the upper limit of 1:4.5 prevents the tetrabutyl titanate from becoming too low when anhydrous ethanol is excessive, resulting in a decreased sol-gel reaction rate, prolonged gelation time, and negatively impacting subsequent crystallization. The optimal value for X1 is 1:3.2, which sufficiently dissolves the tetrabutyl titanate while preventing excessively low concentrations that could hinder subsequent reactions.

[0027] Step 2: Mix Fe(NO3)3·9H2O, acetic acid and anhydrous ethanol at a predetermined mass ratio of X2 to obtain reagent B; In one embodiment, the value range of X2 is 1:5.0~8.0:1.5~2.5; acetic acid is used as a chelating agent, hydrolysis inhibitor, and pH adjuster. Insufficient acetic acid can lead to Fe... 3+ Rapid hydrolysis and aggregation produce flocculent precipitates of ferric hydroxide, which cannot be uniformly dispersed. Excessive acetic acid leads to excessively high overall acidity, which is detrimental to the sol-gel process, and subsequent calcination leaves excessive organic residue, resulting in a decrease in specific surface area. Anhydrous ethanol primarily acts as a dispersant; however, when the concentration is too low, Fe... 3+ Uneven dispersion; excessively high concentrations result in slow sol-gel formation, poor aging and molding properties, prolonged preparation cycle, and increased costs. The optimal value for X2 is 1:6.28:1.97, allowing acetic acid to fully chelate Fe. 3+ Inhibit Fe 3+ Pre-hydrolysis of the precipitate, appropriate acidity, and matching ethanol dosage ensure complete dissolution of ferric nitrate.

[0028] Step 3: Add the preset amount of Y1 acetic acid to reagent A and stir. Then add reagent B dropwise and stir for T1 hours. Then add acetic acid dropwise again and continue stirring for T2 hours to obtain reagent C. Wherein, T1 and T2 are preset values. In one embodiment, the ratio of reagent A to Y1 ranges from 1:0.040 to 0.065; when acetic acid is insufficient, the chelation inhibition of hydrolysis is too weak, and subsequent addition of reagent B easily leads to rapid and violent hydrolysis, instantaneous agglomeration and clumping, resulting in an uneven sol and Fe. 3+ Doping leads to segregation and low specific surface area; excessive acetic acid results in excessively high acidity, slow gelation, and overly strong sol stability, making gelation difficult. After calcination, the residual carbon content decreases photocatalytic activity, and it also increases solvent costs and wastewater treatment pressure. The optimal ratio of reagent A to Y1 is 1:0.050 to control the hydrolysis rate of tetrabutyl titanate, preventing localized boiling or precipitation; it also provides an acidic environment to promote Fe... 3+Uniformly incorporate a Ti-O-Ti network; form a pH gradient with subsequently added reagent B to optimize the gel network structure.

[0029] In one implementation, T1 is taken as 3-10 minutes (if the time is too short, reagent B cannot fully diffuse and miscible with reagent A after being added, Fe...). 3+ The inability to rapidly coordinate with the titanium precursor easily leads to localized ion enrichment, resulting in uneven doping and large performance dispersion in the later stages of material preparation. Excessive time causes premature localized condensation, producing tiny agglomerates and disrupting sol homogeneity, while unnecessarily increasing preparation time and reducing experimental efficiency. Therefore, the optimal value for T1 is 5 minutes, which precisely satisfies the requirement for rapid mixing of reagent A and reagent B, and for Fe³⁺… + Ions are dispersed and coordinated instantaneously, without delay or over-dispersion; short-time constant-temperature stirring ensures system uniformity without causing premature hydrolysis and aggregation.

[0030] In one embodiment, T2 is set at 1.5–3 h. Below 1.5 h, the subsequent hydrolysis-gel polymerization reaction after adding acetic acid is insufficient, resulting in an incomplete sol-gel network structure. Above 3.0 h, prolonged vigorous stirring will destroy the initially formed network gel structure, leading to excessive grain growth, reduced specific surface area, and wasted energy and time. The optimal T2 value is 2 h, ensuring complete sol-gel polymerization and the formation of a structurally complete TiO2-based precursor network with uniform pore size distribution, providing an ideal structural basis for subsequent aging, calcination, and biochar composite formation.

[0031] Step 4: Aging reagent C for T3 hours, drying at C1 degree Celsius, and finally calcining at C2 degree Celsius for T4 hours and C3 degree Celsius for T5 hours to obtain Fe. 3+ -TiO2; where T3, T4, T5, C1, C2, and C3 are all preset values; In one implementation, T3 is taken as 12~24h; too short an aging time will result in insufficient cross-linking of the sol, Fe 3+ Insufficient ion pre-intercalation in the crystal lattice leads to numerous crystal defects during later calcination; excessively short aging time results in excessive sol aging, spontaneous particle agglomeration and growth, and a decrease in specific surface area; the preparation cycle is significantly prolonged, increasing time costs without any performance gain. The optimal value for T3 is 18h, for Fe... 3+ Uniformly embedded in ionic form to avoid gel cracking or excessive shrinkage.

[0032] In one embodiment, the value of T4 ranges from 0.5 to 1.5 hours. If the calcination holding time is too short, the bound water and residual organic matter will not be completely removed; if the holding time is too long, premature crystallization or grain growth will occur, causing the crystal phase to transform from anatase to rutile, resulting in a significant decrease in specific surface area, a decline in photocatalytic and adsorption performance, and wasted energy. The optimal value of T4 is 1 hour, which can completely remove the solvent, functional groups, and salts, allowing TiO2 to fully crystallize and stably retain the highly active anatase phase.

[0033] In one implementation, T5 ranges from 1.5 to 2.5 hours; when the secondary high-temperature holding time is insufficient, lattice defects cannot be adequately repaired, and Fe... 3+ The doping energy level is unstable; prolonged high-temperature holding causes severe grain coarsening and pore collapse, disrupting the biochar composite interface structure. The optimal value for T5 is 2h, which further regulates the TiO2 lattice structure and stabilizes the Fe... 3+ The doping sites maintain appropriate porosity and specific surface area, and the composite with rice husk biochar exhibits strong interfacial bonding, stable performance, and durability.

[0034] In one embodiment, the value of C1 ranges from 100 to 130°C. If the temperature is too low, ethanol, acetic acid, adsorbed water, and water of crystallization evaporate slowly, resulting in incomplete drying and residual solvent inside. If the temperature is too high, organic components carbonize prematurely, clogging pores and reducing the material's specific surface area and catalytic activity. The optimal value of C1 is 120°C, which completely removes free water, prevents rapid escape of water vapor during calcination that could cause material cracking, and ensures uniform drying both inside and out.

[0035] In one embodiment, the value of C2 ranges from 150 to 250°C. If the temperature is too low, the remaining hydroxyl groups and organic matter will carbonize during high-temperature calcination, producing impurity phases; if the temperature is too high, the rapid heating in the low-temperature stage may induce premature crystallization of TiO2. The optimal value of C2 is 200°C; this temperature rises gently, allowing for uniform removal of free water, alcohols, and acetic acid solvents, resulting in uniform drying both internally and externally, preventing crust formation, collapse, and hard agglomeration; and maximizing the preservation of the original porous precursor structure of the sol-gel, laying a good foundation for subsequent calcination and crystallization.

[0036] In one embodiment, the value of C3 ranges from 450 to 500°C; if the temperature is too low, the anatase crystallization is insufficient, resulting in a large amount of amorphous TiO2, low photocatalytic activity, and Fe... 3+ Insufficient doping into the crystal lattice results in poor doping performance; excessively high temperatures cause rapid TiO2 grain growth, leading to the transformation of anatase into the rutile phase and a sharp decrease in specific surface area. The optimal value for C3 is 500℃, ensuring complete crystallization and maintaining the anatase phase of TiO2. 2， Fe 3+ Uniform doping is incorporated into the crystal lattice, making it difficult for particles to precipitate. The grain size is moderate and the porosity is well-developed.

[0037] Step 5: Add Fe 3+ TiO2, rice husk biochar, deionized water and ethanol were refluxed and stirred at a preset mass ratio of X3 at C4 for T6 hours to obtain a homogeneous gray solution; where C4 and T6 are preset values. In one embodiment, the preset amount X3 ranges from 0.01 to 0.05: 2.0: 500: 197.25. If the amount of rice husk biochar added is too low, the proportion of porous framework carrier is insufficient, the overall specific surface area of ​​the composite material increases only slightly, and the number of adsorption active sites is limited. If the proportion of rice husk biochar is too high, excess carbon material is prone to stacking and agglomeration, clogging the pores, which reduces mass transfer efficiency and increases raw material costs. The optimal value is 0.04: 2.0: 500: 197.25, which is a balanced and reasonable ratio. Sufficient rice husk biochar is used to construct a multi-level porous three-dimensional framework, providing abundant adsorption sites and ion diffusion channels.

[0038] In one embodiment, the value of C4 is in the range of 80~120℃. If the temperature is too low, the reflux boiling of the ethanol-water system is insufficient, resulting in poor wetting and dispersion of the rice husk biochar in the liquid phase. If the temperature is too high, the system experiences violent boiling and severe material sloshing, leading to excessive ethanol evaporation and loss. This can easily cause localized overheating and agglomeration, damaging the pore structure of the biochar, while also increasing energy consumption and reducing experimental safety. The optimal value of C4 is 120℃, ensuring stable, slightly boiling reflux, which guarantees sufficient wetting of the biochar in the ethanol-water liquid phase while allowing Fe... 3+ -TiO2 particles are uniformly loaded on the surface and inside the pores of rice husk biochar.

[0039] In one implementation, the value of T6 ranges from 0.5 to 2 hours; if the reflux stirring time is too short, Fe... 3+ Insufficient mixing and impregnation of TiO2 with rice husk biochar and ethanol aqueous solution results in uneven loading, only simple surface adhesion, weak interfacial bonding, easy detachment during subsequent use, and poor cycle stability. Prolonged stirring damages the original pore structure of the rice husk biochar, while TiO2 particles collide and agglomerate, reducing specific surface area and increasing preparation time and energy consumption without performance gain. The optimal T6 value is 1 hour, ensuring thorough mixing and complete liquid phase impregnation of the materials, and reducing Fe... 3+ - TiO2 is uniformly loaded on the surface and pores of biochar to form a stable composite system; the time is moderate, it does not damage the structure of the carbon material, does not cause particle agglomeration, and the process is efficient and has good repeatability.

[0040] Step 6: Dry the gray solution at C5 degrees Celsius to obtain rice husk biochar modified Fe. 3+ -TiO2 composite material; where C5 is a preset value.

[0041] In one embodiment, the value of C5 ranges from 50 to 70°C. If the temperature is too low, the evaporation rate of ethanol and deionized water in the system is extremely slow, significantly increasing drying time and easily leading to residual solvent on the biochar surface, affecting the material's specific surface area and interfacial bonding stability. If the temperature is too high, the solvent evaporates too quickly, easily causing surface crusting and internal water trapping. Simultaneously, slightly high temperatures can cause micropore shrinkage and slight pore collapse in the rice husk biochar, damaging the original pore structure and reducing adsorption active sites. The optimal value of C5 is 60°C, employing gentle low-temperature constant-temperature drying, allowing the solvent to evaporate slowly and uniformly, preventing surface crusting, internal water trapping, and secondary particle agglomeration, thus preserving the original microporous structure of the rice husk biochar to the greatest extent possible.

[0042] This embodiment also provides a method for remediating copper sulfide acidic soil, wherein the composite material and copper sulfide acidic soil are mixed evenly at a mass ratio of 1:100 to 1:20, and the soil is incubated for T6 days with stable water holding capacity, without soil turning or ex-situ treatment; wherein the value range of T6 is 45 to 75 days.

[0043] In one implementation, the mass ratio range is 1:100 to 1:20; if the amount of remediation material added is too low, there will be insufficient active sites, which will affect the pH buffering and regulation of acidic soil and the heavy metal Cu. 2+ Solidification and improvement effects are not obvious; excessive dosage, although it has limited effect on remediation, significantly increases remediation costs; the optimal ratio is 1:50, which is moderate in dosage, can effectively neutralize the acidity of the soil in copper sulfide mining areas, passivate copper ions, and adsorb and fix heavy metals, without damaging the original physical and chemical properties and microbial environment of the soil. The remediation cost is controllable, the improvement effect is optimal, and it is suitable for large-scale in-situ application in mining areas.

[0044] In one implementation, the field water holding capacity (FBC) is 50%–70%. If the soil moisture content is too low, the migration rate of soil solid ions is slow, making it difficult for the remediation composite material to fully react with soil colloids, acidic ions, and heavy metal ions. This significantly slows down the acid-base neutralization and heavy metal passivation and solidification processes, prolonging the remediation cycle. If the soil moisture content is too high, the soil aeration pores are largely occupied, creating a moist anaerobic environment that inhibits the activity of aerobic soil microorganisms and is detrimental to soil microecological restoration. The optimal value is 60%, which provides a balanced and appropriate soil water-air ratio, ensuring that water serves as an ion transport medium while maintaining good soil aeration.

[0045] In one implementation, the value of T6 ranges from 45 to 75 days; insufficient cultivation time leads to problems with the composite material's ability to neutralize soil acidity and Cu. 2+The adsorption and solidification reaction had not reached equilibrium, and soil pH and the content of available heavy metals remained fluctuating, resulting in unstable remediation effects and a tendency for rebound acidification and heavy metal activation in the later stages. Excessive maintenance time led to a plateauing of remediation effects with no significant gains, increasing both economic and time costs. The optimal value for T6 was 60 days (within 60 days, the composite material fully interacts with the soil, significantly improving pH, CEC, and OM; weakly acid-extractable copper reaches its minimum, while residual copper reaches its peak; 60 days is a commonly used cycle for both laboratory cultivation and field remediation, balancing effectiveness and efficiency).

[0046] The invention will be further illustrated below through specific experiments.

[0047] The copper sulfide acidic soil samples used in this experiment were collected from a copper mine in Jiujiang City, Jiangxi Province. Soil samples were collected from a depth of 0-20 cm at the site, air-dried, and then processed. Surface roots were removed, and large particles were sieved to remove them. After processing, the samples were sealed and stored for subsequent experiments. The main physicochemical properties of the soil (including pH, electrical conductivity, cation exchange capacity, organic matter content, and metal concentration) were measured according to standard procedures. The results are shown in Table 1.

[0048] Table 1. Physicochemical properties of soil

[0049] This embodiment describes the preparation of Fe. 3+ In the TiO2 process, reagent B was added dropwise to reagent A. During the addition of reagent B, four different ratios were prepared, denoted as A1, A2, A3, and A4. These ratios, along with pure TiO2 (A0), were analyzed to determine the optimal doping ratio of reagent B. This was done to obtain Fe modified with rice husk biochar at different ratios. 3+ TiO2 composite material.

[0050] During the experiment, four different treatment groups were established: pure TiO2, Fe... 3+ -TiO2, rice husk biochar modified Fe 3+ - The TiO2 application rate was 2.0 wt%, with a blank control set up. Soil samples were sieved, weighed (30 g), and transferred to polyethylene containers. Each treatment was performed three times to ensure statistical robustness. Soil moisture levels were monitored daily by gravity analysis, and any evaporation loss was compensated by adding water to maintain a single environmental condition for all treatments for 60 days. After the remediation period, the soil samples were systematically processed for subsequent analysis: one portion was air-dried at room temperature and mechanically sieved, while parallel aliquots were stored at -80°C for further analysis. The variables for the soil culture experiment are shown in Table 2, where T is pure TiO2 and BF1-BF3 are 0.02-0.04 g of rice husk biochar modified Fe. 3+-TiO2.

[0051] Table 2 Variable settings for soil culture experiment

[0052] 1.1(1) Fe 3+ Characterization analysis of TiO2; Ultraviolet detection was used to determine the concentrations of pure TiO2 and Fe in different proportions. 3+ -Analyze the changes in wavelength and band gap of TiO2.

[0053] By performing ultraviolet (UV) detection on the material, the characteristic wavelength and bandgap of the material are respectively determined by the corresponding UV-Vis (UV-Vis) Figure 3 The spectrum was determined using formula E. g =1240 / λ onset (λ onset The band gap width was calculated using the wavelength at which the absorption intensity is zero, and the results are shown in Table 3.

[0054] Table 3 Characteristic wavelengths and band gaps of the materials

[0055] according to Figure 3 From Table 3, the following conclusions can be drawn. With Fe... 3+ With increasing doping concentration, the optical absorption characteristics of the TiO2 sample changed significantly. Iron promoted photocatalytic properties through charge transfer and narrowing the band gap of TiO2. Pure TiO2 (A0) has a characteristic absorption wavelength of 387 nm, corresponding to a band gap of 3.20 eV, and only exhibits a UV response; in Fe... 3+ After doping, the characteristic absorption wavelength of the material shifts significantly towards longer wavelengths, and the optical band gap gradually decreases. Specifically, the characteristic wavelength of Al redshifts to 423 nm, and the band gap decreases to 2.75 eV, indicating that Fe... 3+ Successfully entering the TiO2 lattice and introducing impurity energy levels into the band gap, thereby expanding the visible light absorption range. When Fe 3+ When the doping concentration was further increased to A2, the characteristic wavelength significantly redshifted to 509 nm, and the band gap decreased to 2.36 eV, exhibiting the strongest visible light response. However, further increasing the Fe concentration... 3+ When the doping levels reach A3 and A4, the characteristic wavelengths recede to 460 nm and 485 nm, respectively, with a slight increase in the band gap. This is attributed to the formation of Fe–O–Fe clusters or a second phase by excess Fe ions, which enhances the carrier recombination effect. These results indicate that Fe… 3+ Doping exhibits a significant nonlinear characteristic in regulating the bandgap structure of TiO2, with A2 showing the best bandgap structure and visible light absorption performance.

[0056] 1.1.1 (2) UV-vis DRS and BET analysis; like Figure 4 As shown in (a), further modification with biochar on the basis of Fe-modified TiO2 further enhances the absorption capacity of the composite material in the visible light region. Figure 4 As shown in (a), the absorption intensities of BF1, BF2, and BF3 in the 400-600 nm wavelength range are all higher than those of FT, indicating that the introduction of biochar is beneficial to improving the light absorption capacity of the material and promoting the migration of photogenerated electrons. As the amount of biochar added increases from 0.02 g to 0.04 g, the overall absorption curve of the composite material does not change significantly, but the absorption intensity in the visible light region slightly increases, indicating that the addition of biochar can promote the improvement of light absorption performance to a certain extent. This is mainly because biochar has a graphite-like structure and good electrical conductivity. Its surface π-conjugated structure can promote electron transport and form an effective interface between TiO2 and biochar, thereby improving the separation efficiency of photogenerated electrons and holes and enhancing the visible light response capability of the material. Specific surface area analysis results are as follows Figure 4 As shown in (b), the specific surface area of ​​pure TiO2 is approximately 18.067 m². 2 ·g -1 The specific surface area of ​​the Fe-doped FT increased significantly to approximately 31.599 m². 2 ·g -1 This indicates that the introduction of Fe inhibited the growth of TiO2 grains to some extent, making the particles more dispersed and thus increasing the specific surface area of ​​the material. When biochar was further introduced, the specific surface area of ​​the composite material continued to increase, with BF1, BF2, and BF3 having specific surface areas of approximately 34.0384 m². 2 ·g -1 35.8452 m 2 ·g -1 and 36.7675 m 2 ·g -1 As the amount of biochar added increases, the specific surface area gradually increases. This is mainly because biochar has a rich pore structure and a large intrinsic specific surface area, which can provide more surface active sites after being combined with TiO2. At the same time, it can also inhibit the aggregation of TiO2 nanoparticles, thereby forming a more loose and porous composite structure. The results of combining UV-Vis absorption spectroscopy and specific surface area analysis show that Fe doping mainly promotes the redshift of the TiO2 absorption edge and improves its visible light response, while the introduction of biochar further enhances the material's absorption capacity in the visible light region and significantly increases the specific surface area of ​​the composite material. A larger specific surface area provides more reactive sites, which is beneficial for the adsorption and reaction of pollutants on the catalyst surface, thus potentially further improving the photocatalytic performance of the composite material. With increasing biochar content, the structure and optical properties of the material are improved to some extent, with BF3 exhibiting the largest specific surface area and strong visible light absorption capacity, providing favorable conditions for its potential photocatalytic applications.

[0057] 1.1.2 (3) SEM analysis; The structure and surface morphology of the material were observed using scanning electron microscopy (SEM), and the results are as follows: Figure 5 As shown, all samples consist of irregularly shaped particles and exhibit varying degrees of agglomeration. However, when the proportion of biochar added is different, there are significant differences in particle size, surface roughness, and structural characteristics.

[0058] Microstructure of pure TiO2 sample as follows Figure 5 As shown in (a), the main body consists of micron-sized blocky and flaky particles with a diameter of 1-3 μm. The particle boundaries are clear and regular, the surface is relatively smooth, and there is significant agglomeration. The internal pore structure is scarce, and the specific surface area and dispersibility are both at a low level. 3+ After doping modification, Fe 3+ -TiO2 sample Figure 5 (b) The morphology underwent a significant change, Fe 3+ The introduction of biochar effectively suppressed the directional growth of TiO2 grains, causing the original regular blocky structure to break down, significantly reducing the overall particle size, and significantly improving surface roughness. It also alleviated the particle agglomeration problem and initially improved dispersibility. After synergistic modification with biochar, the composite material... Figure 5 (ce) Morphological characteristics were further optimized, and the microstructure control effect was more prominent. A large number of TiO2-based fine particles were uniformly attached to the surface of the biochar support, forming a loose and porous multi-level composite structure. The biochar provided sufficient attachment sites for particle loading, fundamentally optimizing the particle distribution. With the increase of the biochar doping ratio, the degree of particle agglomeration in the sample continuously decreased, the distribution uniformity gradually increased, the surface porosity and roughness intensified simultaneously, and the proportion of small-sized particles significantly increased, directly driving the increase in the specific surface area of ​​the material; when the biochar ratio was further increased... Figure 5(e) Although a small number of large blocky particles remain, their surfaces are covered by dense fine particles and microporous structures, forming a stable three-dimensional composite skeleton, which not only enhances the structural stability of the material, but also provides abundant active sites and efficient mass transfer channels for the reaction process.

[0059] 1.1.3 (4) XRD analysis; To investigate Fe 3+ The effects of doping and biochar modification on the crystal structure of TiO2, and on the original TiO2(T) and Fe... 3+ X-ray diffraction (XRD) analysis was performed on TiO2 (FT) and modified materials further incorporating biochar (BF1–BF3). Figure 6 As shown, the pure TiO2 sample exhibits distinct diffraction peaks at 2θ = 25.34°, 37.84°, 48.10°, 53.95°, and 62.77°, corresponding to the (101), (004), (200), (105), (211), and (204) crystal planes of the anatase phase TiO2, respectively. This is highly consistent with the JCPDS No. 21-1272 standard card, indicating that the original TiO2 is mainly composed of the highly crystalline anatase phase. No characteristic peaks of rutile or other impurities were observed within the test range, indicating that its crystal structure is relatively pure and stable.

[0060] Compared to pure TiO2 (sample T), Fe 3+ The XRD diffraction peak positions of the modified TiO2 (FT sample) remained basically stable with respect to the crystal phase composition. The characteristic diffraction peaks all corresponded to the standard diffraction angles of the anatase phase TiO2, confirming that Fe 3+ Doping did not disrupt the crystal framework structure of the TiO2 matrix. However, the characteristic peaks of the FT sample showed slight peak position shifts and intensity fluctuations compared to the T sample. The root cause is Fe... 3+ With Ti 4+ There are differences in ionic radius, Fe 3+ The incorporation of TiO2 into the crystal lattice induces local lattice distortion, resulting in subtle changes in diffraction characteristics; furthermore, the absence of characteristic peaks for iron oxides such as Fe2O3 and Fe3O4 in the diffraction pattern indicates that Fe... 3+ It is uniformly distributed in the TiO2 matrix in the form of lattice doping or highly dispersed morphology. The BF1–BF3 series samples, synergistically modified with biochar, showed a high degree of agreement between their XRD patterns and FT patterns, retaining the typical diffraction characteristics of anatase TiO2. No new diffraction peaks were generated, indicating that the introduction of biochar did not alter the main crystalline phase composition of TiO2. Biochar is predominantly amorphous, exhibiting weak diffraction signals that easily overlap with the TiO2 background peaks, making them difficult to identify clearly in the XRD patterns. With increasing biochar doping ratio, the intensity of the main TiO2 diffraction peak decreased slightly, while the peak shape gradually broadened. This is presumably due to the biochar coating effect inhibiting grain growth or increasing the disorder on the crystal surface. Overall, Fe 3+ Both single doping and iron-biochar synergistic modification retain the TiO2 anatase main crystal phase. The microstructure is precisely controlled through lattice distortion and interfacial interaction, laying a solid structural foundation for optimizing photocatalytic activity and improving interfacial charge transport efficiency.

[0061] 1.1.4 (5) XPS analysis; To clarify the effects of Fe doping and biochar synergistic modification on the surface chemical state and electronic structure of TiO2, XPS full spectra and high-resolution analyses of Ti 2p, Fe 2p, and C 1s were performed on samples T, FT, and BF3. The results are as follows: Figure 7 As shown.

[0062] like Figure 7 (a) shows the high-resolution XPS spectrum of Fe 2p, further confirming the successful introduction of Fe into the TiO2 system. For the FT sample, Fe 2p 3 / 2 and Fe 2p 1 / 2 The characteristic peaks are located at 710.00 eV and 724.13 eV, respectively, while distinct satellite peaks (Sat.) are observed at approximately 719–720 eV and in the high binding energy region, which are typical characteristics of iron oxides. Based on the peak positions and satellite peak characteristics, it can be determined that Fe in the FT sample is mainly in the form of Fe²⁺. 3+ Mainly composed of, with a small amount of Fe 2+ Coexistence. This mixed valence state indicates that Fe exhibits a certain degree of electron transfer behavior within the TiO2 lattice or on its surface, which is beneficial to the material's redox properties. In the BF3 sample, Fe 2p 3 / 2 and Fe 2p 1 / 2The peaks are located at 710.30 eV and 724.10 eV, respectively, shifting slightly towards higher binding energies compared to the FT sample. Meanwhile, the satellite peaks remain, but their relative intensities have changed, indicating that the introduction of biochar has a regulatory effect on the local chemical environment of Fe. This binding energy shift suggests that biochar affects the electronic structure of Fe through interfacial interactions, placing the Fe species in a more stable coordination environment.

[0063] like Figure 7 (b) In the high-resolution XPS spectrum of Ti 2p shown, the T sample exhibits two distinct characteristic peaks at approximately 459.00 eV and 464.69 eV, which are attributed to Ti 2p, respectively. 3 / 2 and Ti 2p 1 / 2 The spin-orbit splitting energy is approximately 5.7 eV, indicating that Ti mainly exists as Ti... 4+ The Ti 2p form exists and conforms to the characteristics of typical anatase TiO2. Compared with T, the FT sample contains Ti 2p 3 / 2 and Ti 2p 1 / 2 The peaks shift slightly towards higher binding energies (approximately 0.2 eV), indicating a decrease in electron density around Ti after Fe doping, with electrons transferring from Ti to adjacent Fe or O atoms. This positive shift in binding energy is usually closely related to the formation of Fe–O–Ti bonds, suggesting that Fe is not present in a simple physical adsorption form but has been successfully incorporated into the TiO2 structure. In the BF3 sample, the Ti 2p peak position shifts to a certain extent in the opposite direction compared to the FT sample, accompanied by peak broadening, indicating that the electronic environment around Ti is further modulated after the introduction of biochar. This may stem from the formation of Ti–O–C bonds and the electron supply effect of the carbon phase, leading to a redistribution of electron density at the interface, thereby enhancing the interfacial electronic coupling ability of the material.

[0064] like Figure 7As shown in (c), the C 1s spectrum can be decomposed into multiple characteristic peaks, indicating the presence of various carbon chemical environments on the material surface. For the pure TiO2(T) sample, the main peak at 284.80 eV in the C 1s spectrum is attributed to C–C bonds, primarily originating from adsorbed carbon on the sample surface or environmental carbon pollution. Furthermore, C–O and O–C=O bonds are observed at 286.08 eV and 288.50 eV, respectively, corresponding to oxygen-containing carbon species adsorbed on the surface. Notably, a weak peak near 284.30 eV is distinguishable, belonging to the Ti–O–C bond, indicating that some carbon species have undergone chemical coupling with the TiO2 surface, rather than simple physical adsorption. In the Fe-modified sample (FT), the Ti–O–C peak shifts to 284.40 eV, and the peak intensity is enhanced, due to the introduction of Fe promoting chemical bonding between carbon species and the TiO2 surface. For BF3, the Ti–O–C peak in the C 1s spectrum shifted to 284.70 eV, while the C–O and O–C=O peak intensities significantly increased. This indicates that the introduction of biochar significantly increased the number of oxygen-containing functional groups on the material surface and achieved strong interfacial coupling between biochar and Fe–TiO2 through the formation of stable Ti–O–C bonds. This chemical connection facilitates the construction of continuous electron transport channels, thereby optimizing the interfacial electronic structure of the material.

[0065] XPS analysis results of Ti 2p, Fe 2p, and C 1s confirm that Fe was successfully incorporated into the TiO2 lattice in a multivalent state and its electronic structure was regulated by Fe–O–Ti bonds; biochar, on the other hand, formed a stable interfacial coupling structure with Fe–TiO2 through Ti–O–C bonds. 3+ / Fe 2+ The coexistence of various oxygen-containing functional groups on the surface and the enhanced interfacial electronic interactions together optimize the surface chemical state and electron transport properties of the material, providing an important structural and electronic basis for its performance improvement.

[0066] 1.1.5 (6) Analysis of changes in soil pH and electrical conductivity; like Figure 8 As shown, the addition of rice husk biochar to modify Fe 3+After adding TiO2, the pH of the soil in the CK group was approximately 4.14, indicating a significantly acidic state. The addition of pure TiO2 (T) slightly increased the pH, but its effect on improving acidic soil was limited. After Fe-modified TiO2 (FT) treatment, the pH significantly increased to 4.79, indicating that the introduction of iron alleviated soil acidity to some extent. From BF1 to BF3, the pH continuously increased, reaching approximately 5.52, 5.72, and 6.03 respectively, showing a gradual increase with increasing biochar addition. This is mainly because biochar itself is alkaline and can neutralize H+ in the soil. + Its surface contains functional groups such as phenolic hydroxyl and carboxyl groups, which can regulate pH through proton exchange; at the same time, the oxidation process of Fe consumes H+. + (4Fe + 3O2 + 12H) + → 4Fe 3+ + 6H2O) together promote the increase of pH.

[0067] Soil electrical conductivity (EC), a key parameter reflecting soluble salt content, reached as high as 238.67 μS·cm in the CK group. 1 This indicates a high content of soluble salts in the soil. EC significantly decreased after T and FT treatments, with the CFT group dropping to 218.33 μS·cm⁻¹. 1 This indicates that the modified material has a certain adsorption or fixation effect on soil salinity. The EC content in the CBF3 group was slightly increased to 230.67 μS·cm. 1 However, it is still lower than the CK level, and the overall concentration initially decreased and then slightly increased. This is consistent with the reference mechanism: at low addition levels, biochar adsorbs ions through its porous structure and high specific surface area, reducing the salt concentration in the solution; while at high addition levels, some soluble substances may be introduced, causing a slight increase in EC, but overall it remains within a reasonable range, which is beneficial to soil nutrient supply.

[0068] 1.1.6 (7) Analysis of changes in soil organic matter and cation exchange capacity; like Figure 9 As shown, cation exchange capacity (CEC) is a key indicator for maintaining nutrient supply, from 12.83 cmol in the CK group. + ·kg 1 Increased to 15.13 cmol + ·kg 1 This indicates that the modified material enhanced the ion exchange capacity of the soil, mainly due to the negative charge on the surface of biochar, which can adsorb K+. + Ca 2+Mg 2+ The adsorption capacity is enhanced by the presence of isocations, and the introduction of Fe may alter the surface electronic structure, further strengthening the adsorption capacity. Furthermore, an increase in pH also promotes an increase in CEC, demonstrating a synergistic relationship between the two.

[0069] Organic matter (OM) content is a key indicator of soil fertility. In acidic soils, the content is extremely low, only 7.5%, but it significantly increases after the application of modifying materials, confirming that biochar is a key factor in improving soil organic matter. This is due, in part, to the fact that biochar itself is rich in carbon, directly increasing soil organic matter; and in part, its porous structure provides a habitat for microorganisms, promoting organic matter transformation and humus formation, thereby further increasing OM content.

[0070] Overall, after the addition of composite modifiers, soil pH, CEC, and OM all showed a continuous upward trend, while EC initially decreased and then slightly rebounded. These overall changes were beneficial to improving the physicochemical properties of acidic soils. Among these, the BF2 and BF3 treatments showed the most significant effects, indicating that appropriately increasing the amount of biochar added can significantly enhance the ability of the composite material to improve acidic soils.

[0071] 1.1.7 (8) Analysis of changes in total and available Cu content in soil; like Figure 10 As shown, in the study of passivation remediation of heavy metal contaminated soil, the application effect of composite materials indicates that each treatment has a limited impact on the total copper content of the soil. The total copper content of the CK to BF3 treatments decreased from 3319.37 mg·kg⁻¹. -1 Slightly reduced to 3025.00 mg·kg -1 The decrease was approximately 8.9%, mainly attributed to the dilution effect of the amendment; however, different treatments significantly affected the bioavailability of copper in the soil (characterized by DTPA-Cu). Compared with the blank control (CK, 198.67 mg·kg⁻¹), the decrease was... -1 Compared to pure TiO2 treatment (CT), the reduction effect on available copper was limited (181.67 mg·kg⁻¹). -1 Fe-modified TiO2 (CFT) treatment significantly reduced the available copper content (145.67 mg·kg⁻¹). -1 This is mainly attributed to the specific adsorption of iron oxides and the effect of their oxidation process on H₂. + The consumption of Cu increased soil pH and enhanced the soil colloid's ability to absorb Cu. 2+ The affinity of DTPA-Cu was further enhanced by the introduction of biochar (BF1, BF2, BF3), resulting in a continuous and significant decrease in DTPA-Cu content, which dropped to 131.33, 123.00, and 118.00 mg·kg, respectively. -1The reduction was as high as 40.6%. This significant effect is the result of the synergistic effect of multiple mechanisms: biochar not only directly adsorbs free Cu through its high specific surface area and porous structure, but also... 2+ The abundant oxygen-containing functional groups (such as carboxyl and phenolic hydroxyl groups) on the surface of biochar can convert active heavy metals into stable states through complexation reactions. Simultaneously, the alkalinity of biochar further increases soil pH, promoting the hydrolysis or precipitation of heavy metal ions, and forming a positive synergistic effect with the adsorption enhancement brought about by Fe modification. Among these, the BF2 treatment exhibited the best passivation efficiency, and further increasing the amount of biochar (BF3) reduced the marginal benefit of reducing available copper. In summary, Fe-modified TiO2-supported biochar composites, especially the BF2 treatment, can effectively reduce the bioavailability of copper in acidic soils through multiple pathways, including pH regulation, functional group complexation, and adsorption fixation, achieving efficient passivation and remediation of heavy metal pollution.

[0072] 1.1.8 (9) Analysis of the distribution and variation of Cu speciation in soil; like Figure 11 As shown in the figure, based on the distribution data of BCR speciation of copper in soil under different treatment groups (CK, T, FT, BF1, BF2, BF3), it can be divided into four speciations: weakly acid-extractable (F1), reducible (F2), oxidizable (F3), and residual (F4). This allows for a systematic analysis of the effects of composite materials on copper speciation and bioavailability. In the blank control (CK) group, F1 had the highest content, reaching 586 mg·kg⁻¹. -1 This indicates that copper in the soil is predominantly in a highly bioavailable form, posing a significant ecological risk. The F3 concentration remained stable at 640 mg / kg in all treatment groups. -1 Around 100 mg / kg, F2 was not detected in any of the treatments, indicating that the transformation of copper speciation in this soil mainly involved the migration between acid-soluble and residual forms. With the introduction of the amendment, the content of acid-soluble copper showed a continuous decreasing trend: in the CT group, it decreased to 504 mg / kg. -1 The CFT group further decreased to 469 mg·kg⁻¹. -1 The biochar composite material treatment groups (CBF1, CBF2, and CBF3) showed reductions of 465, 462, and 456 mg·kg, respectively. -1 The decrease was significant. Correspondingly, the F4 content decreased from 928 mg / kg in the CK group. -1 Gradually increased to 1438 mg·kg in the CBF3 group -1This indicates a continuous transformation of copper from an active to an inert form. This pattern is highly consistent with the mechanistic analysis that "biochar, with its abundant oxygen-containing functional groups and high specific surface area, achieves electrostatic adsorption and functional group chelation of copper ions, ultimately forming a stable organic-mineral complex." Simultaneously, the introduction of Fe-modified TiO2 further promoted pH increase and increased adsorption sites, forming a synergistic effect with biochar and accelerating the transformation of copper from an acid-soluble state to a residual state. Overall, the promoting effect of each treatment on copper stabilization was: BF series > FT > T > CK. Among these, BF2 and BF3 treatments showed the highest proportion of residual copper and the lowest proportion of acid-soluble copper, indicating that appropriately increasing the biochar loading can significantly enhance the copper fixation capacity of the composite material, effectively reducing the bioavailability of copper in acidic soils and its environmental risks.

[0073] 1.1.9 (10) Analysis of the relationship between soil physicochemical properties and soil Cu content; according to Figure 12 Pearson correlation analysis of soil physicochemical properties and total copper content revealed significant and complex interactions among the various indicators. Total copper (Cu) showed significant negative correlations with pH, ​​organic matter (OM), cation exchange capacity (CEC), and electrical conductivity (EC) (correlation coefficients approximately -0.92, p < 0.01). This indicates that with increasing soil pH, organic matter content, cation exchange capacity, and appropriate regulation of soluble salts, the soil's ability to fix copper significantly improves, thereby reducing copper mobility and bioavailability. This phenomenon can be attributed to the increased negative charge density on soil colloid surfaces due to higher pH, enhancing the fixation of Cu²⁺. + Electrostatic adsorption occurs; simultaneously, organic matter (especially humic substances), with its abundant oxygen-containing functional groups, complexes or chelates with copper ions to form stable organometallic complexes, further reducing the activity of copper. Furthermore, OM shows a significant positive correlation with CEC and pH (p<0.01), mainly because humic substances have a high negative charge density, which can retain Ca through electrostatic adsorption. 2+ K + Mg 2+ It contains cations, thereby directly enhancing the soil's cation exchange capacity, while simultaneously buffering soil pH fluctuations through proton exchange reactions. OM and EC also showed a positive correlation (p<0.05), possibly due to the release of soluble ions during microbial decomposition; while the positive correlation between CEC and pH and soil water saturation (SWC) (p<0.05) reflects that higher CEC can be absorbed by H+. +Adsorption-desorption stabilizes pH, while favorable moisture conditions help maintain ion exchange balance. In summary, a mutually reinforcing and synergistic relationship is formed among the various physicochemical indicators: the application of soil amendments drives the transformation of copper in the soil from an active to a stable state through multiple pathways, such as increasing pH, increasing organic matter content, and enhancing cation exchange capacity, thereby achieving efficient passivation and remediation of heavy metal pollution.

[0074] This invention targets acidic copper-contaminated soil from copper sulfide ore for remediation, and utilizes Fe... 3+ A novel TiO2 composite material was prepared by doping and modifying it with rice husk biochar. The structural characterization, soil physicochemical property improvement effect, and copper contamination passivation remediation mechanism of the material were systematically studied, and the remediation efficacy and mechanism of the composite material for acidic copper contaminated soil were clarified.

[0075] UV-Vis and BET analyses confirmed that after modification, the material's band gap narrowed and its specific surface area increased, which is beneficial for catalytic reactions. SEM showed reduced particle aggregation and dispersion, and an increased specific surface area, providing abundant active sites for the adsorption and passivation of heavy metals in the soil. XRD analysis confirmed that the TiO2 anatase main crystal phase was not destroyed. XPS analysis showed that Fe was successfully incorporated into the TiO2 lattice in a multivalent state, forming Fe–O–Ti bonds, and the biochar formed a stable interfacial coupling structure with Fe–TiO2 through Ti–O–C bonds.

[0076] In the soil culture experiment, it significantly improved the soil's physicochemical properties: pH increased from [value missing] to [value missing], CEC [value missing], OM [value missing], EC [value missing]. The total Cu content decreased most significantly when BF3 was applied, from 3319.37 mg·kg [value missing]. -1 Reduced to 3025 mg·kg -1 The total copper content decreased by 8.9%, the available copper content decreased by 40.6%, and the acid-soluble copper content decreased from 18.34% to 14.84%. These indicators collectively demonstrate the effective stabilization capacity of the composite material for copper. Pearson correlation analysis showed a significant negative correlation (p<0.01) between total copper content and soil pH, CEC, and organic matter. These physicochemical indicators mutually promoted and synergistically evolved, jointly enhancing the soil's adsorption and fixation capacity for copper ions, achieving synergistic remediation of soil acidification and heavy metal pollution. This provides a novel and efficient technical approach and material support for the ecological remediation of acidic heavy metal contaminated soils from copper sulfide mines.

[0077] It should be understood that the embodiments described above are only some, not all, of the embodiments of the present invention. Furthermore, the technical features of the various embodiments or individual embodiments provided by the present invention can be arbitrarily combined to form feasible technical solutions. Such combinations are not constrained by the order of steps and / or structural composition patterns, but must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0078] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A rice husk biochar modified Fe 3+ -TiO2 composite material, characterized in that: It is a hierarchical porous core-shell heterojunction composite structure; wherein, the core layer is Fe 3+ Doped anatase TiO2 nanocrystals, Fe 3+ It exists in a lattice-doped state, forming an internal lattice bond Fe–O–Ti structure with intermediate impurity energy levels, narrowing the band gap; the shell layer is a porous carbon layer of rice husk biochar; the interface between the core layer and the shell layer is connected by Ti–O–C covalent bonds, forming a continuous electron transport channel.

2. The rice husk biochar modified Fe according to claim 1 3+ -TiO2 composite material, characterized in that: The manufacturing process of the composite material includes the following steps: Step 1: Mix tetrabutyl titanate and anhydrous ethanol at a predetermined mass ratio of X1 to obtain reagent A; Step 2: Mix Fe(NO3)3·9H2O, acetic acid and anhydrous ethanol at a predetermined mass ratio of X2 to obtain reagent B; Step 3: Add the preset amount of Y1 acetic acid to reagent A and stir. Then add reagent B dropwise and stir for T1 hours. Then add acetic acid dropwise again and continue stirring for T2 hours to obtain reagent C. Where T1 and T2 are preset values. Step 4: Aging reagent C for T3 hours, drying at C1 degree Celsius, and finally calcining at C2 degree Celsius for T4 hours and C3 degree Celsius for T5 hours to obtain Fe. 3+ -TiO2; where T3, T4, T5, C1, C2, and C3 are all preset values; Step 5: Add Fe 3+ TiO2, rice husk biochar, deionized water and ethanol were refluxed and stirred at a preset mass ratio of X3 at C4 for T6 hours to obtain a homogeneous gray solution; where C4 and T6 are preset values. Step 6: Dry the gray solution at C5 degree Celsius to obtain rice husk biochar modified Fe. 3+ -TiO2 composite material; where C5 is a preset value.

3. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 1, the preset mass ratio X1 is in the range of 1:2.5 to 4.

5.

4. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 2, the preset mass ratio X2 is set to a range of 1:5.0~8.0:1.5~2.

5.

5. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 3, the value range of reagent A:Y1 is 1:0.040~0.065; the value range of T1 is 3~10 minutes, and the value range of T2 is 1.5~3 hours.

6. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 4, the value range of T3 is 12~24h, the value range of T4 is 0.5~1.5h, and the value range of T5 is 1.5~2.5h.

7. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 4, the value range of C1 is 100~130℃, the value range of C2 is 150~250℃, and the value range of C3 is 450~500℃.

8. The rice husk biochar modified Fe according to claim 2 3+ -TiO2 composite material, characterized in that: In step 5, the preset mass ratio X3 is in the range of 0.01~0.05:2.0:500:197.25; the value of C4 is 80~120℃; and the value of T6 is in the range of 0.5~2h.

9. The rice husk biochar modified Fe according to any one of claims 2-8 3+ -TiO2 composite material, characterized in that: In step 6, the value of C5 is 50~70℃.

10. A method for remediating copper sulfide acidic soil, comprising the composite material described in any one of claims 1-9; characterized in that: The composite material was mixed with copper sulfide acidic soil at a mass ratio of 1:100 to 1:20, and the soil was kept at a stable water content and cultured for T6 days without turning the soil or exposing the soil to a different location; the range of T6 was 45 to 75 days.

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