Modified biomass charcoal material, preparation method thereof and application of modified biomass charcoal material in soil cadmium pollution treatment

Abstract

The invention discloses a modified biomass charcoal material as well as a preparation method and application thereof in soil cadmium pollution treatment, and relates to the technical field of heavy metal pollution treatment. The modified biomass charcoal material is prepared through camellia oleifera shell composting pretreatment, ultrasonic wave-enzymolysis synergistic treatment and Mn / Fe modification, and the modified biomass charcoal material can efficiently adsorb cadmium. When the modified biomass material is used for soil cadmium pollution treatment, the pH and C / N ratio of soil can be increased, the physical and chemical properties of the soil are improved, high cadmium adsorption efficiency is still kept after multiple times of cyclic adsorption-desorption, the remediation effect and regeneration capacity are achieved, and an efficient and sustainable solution is provided for cadmium pollution soil treatment.

Description

Technical Field

[0001] This invention relates to the field of heavy metal pollution control technology, and in particular to a modified biochar material, its preparation method, and its application in the control of cadmium pollution in soil. Background Technology

[0002] With the acceleration of industrialization and urbanization, heavy metal pollution has become a global environmental problem, among which cadmium (Cd) pollution is characterized by its high toxicity, bioaccumulation, and recalcitrant nature. Cadmium pollution mainly originates from industrial activities such as electroplating, battery manufacturing, mining, fertilizer use, and electronic waste disposal, entering the environment through wastewater discharge or soil infiltration. Once in water or soil, cadmium can accumulate through the food chain, causing irreversible harm to ecosystems and human health, such as inducing kidney damage, osteomalacia, and cancer. Therefore, the development of efficient, economical, and environmentally friendly cadmium pollution remediation technologies is urgently needed.

[0003] Existing cadmium pollution treatment technologies mainly include physicochemical methods (such as chemical precipitation, ion exchange, and membrane separation) and bioremediation methods (such as plant absorption and microbial adsorption). However, these methods have significant limitations: physicochemical methods often generate large amounts of secondary polluting sludge and have low removal efficiency for low concentrations of cadmium; while bioremediation is environmentally friendly, it relies on specific microorganisms or plants, has a long treatment cycle, and is difficult to scale up. In contrast, adsorption methods have attracted much attention due to their simplicity and wide applicability, but traditional adsorption materials (such as activated carbon and clay minerals) generally suffer from limited adsorption capacity and regeneration difficulties, making it difficult to meet practical engineering needs.

[0004] In recent years, biochar has received widespread attention as a green adsorbent material. Its raw materials are widely available (such as agricultural waste and forestry waste), its preparation process is low-carbon and environmentally friendly, and it possesses a porous structure and abundant oxygen-containing functional groups, enabling it to efficiently adsorb heavy metals. However, the cadmium adsorption capacity of ordinary biochar (typically below 30 mg / g) and the uneven distribution of surface functional groups limit its application potential. Furthermore, its selectivity for cadmium is insufficient, and it is easily affected by coexisting ions in complex polluted environments, leading to a decrease in adsorption efficiency. Therefore, how to improve the cadmium adsorption performance and regeneration capacity of biochar through structural regulation is a key issue that urgently needs to be addressed in the field of environmental remediation. Summary of the Invention

[0005] The purpose of this invention is to provide a modified biochar material, its preparation method, and its application in the remediation of cadmium-contaminated soil, so as to solve the problems existing in the prior art and achieve efficient remediation of cadmium-contaminated soil.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention is to provide a method for preparing modified biochar material, characterized by comprising the following steps:

[0008] (1) Composting pretreatment: Add fermenting agent and tea leaf extract to the tea oil shells, and compost ferment at 50-60℃. After fermentation, dry to obtain pretreated tea oil shells.

[0009] (2) Ultrasonic-enzymatic hydrolysis synergistic treatment: The pretreated camellia shells are added to an acetate buffer solution, then cellulase is added, and the enzymatic hydrolysis is carried out at 35-40℃ for 10-12h. The resulting enzymatic hydrolysate is then subjected to ultrasonic treatment at a power of 350-400W and a temperature of 35-40℃. The filtered residue is then dried to obtain a biochar precursor.

[0010] (3) Modification treatment: The biochar precursor is added to a mixed solution of MnSO4 and FeSO4, and the pH of the system is adjusted to 9.0 by adding alkali solution at 55-60℃ for modification treatment. After that, the precipitate is collected and washed until neutral, and then pyrolyzed at 500-600℃ under a protective atmosphere to obtain the modified biochar material.

[0011] As a further preferred embodiment of the present invention, the composting and fermentation time is 13-15 days.

[0012] As a further preferred embodiment of the present invention, the tea oil extract is obtained by reflux extraction of tea oil with ethanol. More preferably, it is ethanol with a volume concentration of 70%.

[0013] As a further preferred embodiment of the present invention, the camellia oil shells are pulverized to a particle size of <5mm; the moisture content of the camellia oil shells is 60±5%.

[0014] As a further preferred embodiment of the present invention, the amount of tea oil tea extract added is 3-4% of the mass of the tea oil tea shell.

[0015] As a further preferred embodiment of the present invention, the fermentation agent is a mixed fermentation agent of Bacillus subtilis and yeast.

[0016] As a further preferred embodiment of the present invention, the ultrasonic treatment time is 20-25 minutes.

[0017] As a further preferred embodiment of the present invention, the pyrolysis temperature is 500-600℃.

[0018] As a further preferred embodiment of the present invention, the concentration of MnSO4 in the mixed solution is 0.05-0.07 mol / L, and the concentration of FeSO4 is 0.05-0.07 mol / L.

[0019] The second technical solution of the present invention: providing modified biochar material prepared by the above preparation method.

[0020] The third technical solution of this invention is to provide the application of the above-mentioned modified biochar material in the remediation of cadmium pollution in soil.

[0021] This invention, by adding tea oil extract during the composting and fermentation process and controlling the compost temperature at 55-60℃, not only ensures the cadmium adsorption and removal effect of the final biochar material, but also achieves a shorter fermentation cycle in the composting process.

[0022] In this invention, the added Bacillus subtilis and yeast during the composting process secrete cellulase and ligninase, effectively decomposing the lignocellulose in the camellia oleifera shell. Simultaneously, the ethanol extract of the camellia oleifera significantly promotes microbial activity, accelerating the degradation of lignin into humic precursors, thereby generating more active groups such as carboxyl and phenolic hydroxyl groups on the surface of the biochar. Furthermore, the active components in the ethanol extract of the camellia oleifera can regulate the redox environment of the compost pile, creating favorable preconditions for subsequent modification of the biochar.

[0023] The metabolic products (such as organic acids) generated during the composting and fermentation process of this invention corrode the fiber structure of the camellia shell. This process provides a more easily broken structural basis for the subsequent ultrasonic-enzymatic hydrolysis treatment, fundamentally ensuring the adsorption effect of the product on cadmium.

[0024] The cavitation effect of ultrasound can generate a localized high-temperature and high-pressure environment. These unique physical conditions can disrupt the residual lignin microstructure after stacking, thus providing more physical adsorption sites for cadmium ions. Furthermore, the polysaccharides released during enzymatic hydrolysis can chemically react with the polyphenols in the tea oil extract, further enhancing the complexation ability with cadmium.

[0025] This invention fully utilizes the synergistic effect of bimetallic oxides to promote the combination of cadmium with iron and manganese oxides, thereby significantly reducing the bioavailability of cadmium and providing an efficient solution for the remediation of cadmium pollution in soil.

[0026] The present invention discloses the following technical effects:

[0027] This invention produces modified biochar material capable of efficiently adsorbing cadmium through steps including pretreatment with camellia oleifera shells, synergistic ultrasonic-enzymatic hydrolysis, and Mn / Fe modification. Adding a fermenting agent and camellia oleifera extract during composting promotes microbial decomposition of lignocellulose, generating more oxygen-containing functional groups and regulating the redox environment of the compost pile. The synergistic effect of ultrasonic and enzymatic hydrolysis enhances pore development, increasing adsorption sites. Bimetallic oxide modification, through redox and co-precipitation, converts cadmium into a stable state, reducing its bioavailability.

[0028] When the modified biomass material of this invention is used for the remediation of cadmium pollution in soil, it can increase the soil pH and C / N ratio, improve the soil physicochemical properties, and maintain a high cadmium adsorption efficiency after multiple cycles of adsorption-desorption. It has both remediation effect and regeneration capacity, providing an efficient and sustainable solution for the remediation of cadmium-polluted soil. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0035] Biochar is a carbon-rich solid material produced by the high-temperature pyrolysis of biomass (such as plant residues and agricultural waste) under anaerobic or oxygen-limited conditions. Its unique physicochemical properties—a highly aromatic carbon skeleton, abundant porous structure, oxygen-containing functional groups on the surface, and alkaline characteristics—have made it a research hotspot in the field of soil pollution remediation. Converting biomass waste into biochar can not only reduce the environmental pressure caused by waste accumulation but also provide a sustainable solution for soil remediation through resource utilization.

[0036] In the remediation of cadmium-contaminated soil, biochar plays a role through multiple mechanisms, including physical adsorption, chemical fixation, and ecological regulation. Its application significantly reduces the bioavailability and mobility of cadmium, thereby reducing the exposure risk to crops and humans. However, despite its widely recognized environmental friendliness, biochar still faces challenges in practical applications, such as insufficient adsorption capacity, poor selectivity, and weak adaptability to complex polluted environments. These limitations restrict its large-scale application in the remediation of heavily polluted soils.

[0037] Physical adsorption is the initial and crucial process for biochar removal of cadmium from soil, primarily relying on van der Waals forces and pore-filling effects. Chemical adsorption and complexation are the core mechanisms of cadmium fixation by biochar. The abundant oxygen-containing functional groups on the surface of biochar react chemically with cadmium ions to form stable complexes, achieving efficient cadmium fixation. For example, complexes formed by carboxyl groups and cadmium ions exhibit strong stability and can effectively reduce the migration and bioavailability of cadmium in the soil. Simultaneously, mineral components in biochar, such as iron and manganese oxides, can also co-precipitate with cadmium. Under certain conditions, active sites on the surface of iron and manganese oxides bind with cadmium ions, forming insoluble compound precipitates that fix cadmium in the soil.

[0038] When biochar is applied to soil, it can significantly improve the soil's physical and chemical properties, indirectly reducing the bioavailability of cadmium. Firstly, biochar is typically alkaline, which can neutralize acidic soils and increase soil pH. As soil pH rises, the chemical form of cadmium ions changes, forming hydroxides or carbonate precipitates, reducing their solubility and mobility in the soil. Secondly, biochar can increase soil organic matter content and improve soil structure. It can promote the formation of soil aggregates, making the pore distribution between soil particles more rational, and enhancing soil aeration and water retention. A good soil structure helps reduce the diffusion of cadmium ions in the soil, making them more difficult for plant roots to absorb. Furthermore, biochar can provide habitats and carbon sources for soil microorganisms, promoting their growth and metabolism, and altering the structure of the soil microbial community. Some microorganisms can convert cadmium ions into less toxic or non-toxic forms through their metabolic activities, further reducing the bioavailability of cadmium.

[0039] Biochar has a wide range of raw material sources, including agricultural waste (such as rice husks, corn stalks, and peanut shells), forestry waste (such as sawdust and bark), and urban organic waste. Biochar prepared from different raw materials exhibits varying performance in soil cadmium pollution remediation due to differences in their chemical composition and physical structure. Although biochar has a certain adsorption capacity for cadmium, its adsorption capacity is still insufficient compared to some high-performance synthetic adsorbents, especially when dealing with heavily cadmium-contaminated soil, making it difficult to meet the requirements for efficient remediation. Furthermore, in actual contaminated soil, cadmium often coexists with other heavy metals (such as lead, zinc, and copper) and various cations. Biochar has poor selectivity for cadmium and is easily interfered with by competitive adsorption of other ions. This significantly reduces the adsorption efficiency of biochar for cadmium in complex pollution environments, making it impossible to achieve precise removal and fixation of cadmium, thus limiting its application in practical soil remediation.

[0040] As research and practical applications deepen, the limitations of raw biochar have become increasingly apparent, such as insufficient adsorption capacity and poor selectivity for certain pollutants, making it difficult to meet the demands for efficient remediation in complex polluted environments. To overcome these bottlenecks, modified biochar has emerged, treating raw biochar through physical, chemical, or biological methods to endow it with superior performance to address increasingly complex environmental challenges. However, current modified biochar preparation processes, whether using expensive modifying reagents (such as specific metal salts and organic modifiers) or complex modification processes (such as high-temperature and high-pressure treatment and nanomaterial loading), result in high modification costs. This limits the widespread application of modified biochar, especially in large-scale soil remediation and large-scale wastewater treatment, due to economic constraints.

[0041] One objective of this invention is to provide a method for preparing modified biochar materials, comprising the following steps:

[0042] (1) Composting pretreatment: Add fermenting agent and tea leaf extract to the tea oil shells, and compost ferment at 50-60℃. After fermentation, dry to obtain pretreated tea oil shells.

[0043] (2) Ultrasonic-enzymatic hydrolysis synergistic treatment: The pretreated camellia shells are added to an acetate buffer solution, then cellulase is added, and the enzymatic hydrolysis is carried out at 35-40℃ for 10-12h. The resulting enzymatic hydrolysate is then subjected to ultrasonic treatment at a power of 350-400W and a temperature of 35-40℃. The filtered residue is then dried to obtain a biochar precursor.

[0044] (3) Modification treatment: The biochar precursor is added to a mixed solution of MnSO4 and FeSO4, and the pH of the system is adjusted to 9.0 by adding alkali solution at 55-60℃ for modification treatment. After that, the precipitate is collected and washed until neutral, and then pyrolyzed at 500-600℃ under a protective atmosphere to obtain the modified biochar material.

[0045] Preferably, the composting and fermentation time is 13-15 days.

[0046] Preferably, the tea oil extract is obtained by reflux extraction of tea oil with ethanol. More preferably, it is ethanol with a volume concentration of 70%.

[0047] Preferably, the camellia oleifera shells are pulverized to a particle size of <5mm; and the moisture content of the camellia oleifera shells is 60±5%.

[0048] Preferably, the amount of the tea oil tea extract added is 3-4% of the mass of the tea oil tea shell.

[0049] Preferably, the fermentation agent is a mixed fermentation agent of Bacillus subtilis and yeast.

[0050] Preferably, the ultrasonic treatment time is 20-25 minutes.

[0051] Preferably, the pyrolysis temperature is 500-600℃.

[0052] Preferably, in the mixed solution, the concentration of MnSO4 is 0.05-0.07 mol / L and the concentration of FeSO4 is 0.05-0.07 mol / L.

[0053] The second objective of this invention is to provide modified biochar materials prepared by the above-mentioned preparation method.

[0054] The third objective of this invention is to provide the application of the above-mentioned modified biochar materials in the remediation of cadmium pollution in soil.

[0055] Example 1

[0056] A method for preparing modified biochar material for cadmium pollution remediation in soil, comprising the following steps:

[0057] (1) Extraction of tea oil tea alcohol extract: The washed and dried tea oil tea leaves were extracted twice by reflux with 70% ethanol (volume concentration), concentrated under reduced pressure and freeze-dried into powder to obtain tea oil tea alcohol extract.

[0058] (2) Pre-treatment for composting: Crush the camellia oleifera shells to a particle size <5mm, adjust the moisture content to 60%, and add 0.5% composting agent (commercially available strains, a mixture of Bacillus subtilis and yeast in a mass ratio of 3:2, with a viable count ≥1×10⁻⁶) based on the weight of the camellia oleifera shells. 9The tea leaves were treated with CFU / g and 4% tea oil alcohol extract. The leaves were stacked in a windrow, with a height of 1.5m and a width of 2m. The pile was turned over every 2 days, and the pile temperature was controlled at 55℃. The fermentation cycle was 15 days. After fermentation, the leaves were dried at 60℃, crushed and passed through a 2mm sieve to obtain pretreated tea oil shells.

[0059] (3) Ultrasonic-enzymatic synergistic treatment:

[0060] The pretreated camellia shells obtained in step (2) were added to an acetate buffer solution with pH = 4.8 at a material-to-liquid ratio of 1:8, and 1.5% (w / w) of cellulase was added. The mixture was enzymatically hydrolyzed at 40°C for 10 h. The resulting hydrolysate was transferred to an ultrasonic reactor and treated at 350 W power and 38°C for 20 min. After filtration, the filter residue was dried at 80°C to obtain a biochar precursor.

[0061] (4) Modification treatment: Prepare a mixed solution containing 0.05 mol / L MnSO4 and 0.05 mol / L FeSO4. Add the biochar precursor to the mixed solution at a mass ratio of 1:10. Under magnetic stirring at 55℃, slowly add 1 mol / L NaOH solution until the pH = 9.0. Maintain the reaction for 1.5 h. After the reaction is completed, collect the precipitate, wash it with deionized water until neutral, dry it at 80℃, and then pyrolyze it at 550℃ for 1 h in a nitrogen atmosphere to obtain modified biochar material for soil cadmium pollution remediation.

[0062] Example 2

[0063] A method for preparing modified biochar material for cadmium pollution remediation in soil, comprising the following steps:

[0064] (1) Extraction of tea oil tea alcohol extract: The washed and dried tea oil tea leaves were extracted twice by reflux with 70% ethanol (volume concentration), concentrated under reduced pressure and freeze-dried into powder to obtain tea oil tea alcohol extract.

[0065] (2) Pre-treatment for composting: Crush the camellia oleifera shells to a particle size <5mm, adjust the moisture content to 60%, and add 0.5% composting agent (a mixture of Bacillus subtilis and yeast in a mass ratio of 3:2, with a viable count ≥1×10⁻⁶) according to the weight of the camellia oleifera shells. 9 The tea leaves were fermented with CFU / g and 3% tea oil tea alcohol extract. They were stacked in windrows with a height of 1.5m and a width of 2m. The piles were turned over every 2 days, and the temperature was controlled at 60℃. The fermentation cycle was 13 days. After fermentation, the leaves were dried at 60℃, crushed and passed through a 2mm sieve to obtain pretreated tea oil shells.

[0066] (3) Ultrasonic-enzymatic synergistic treatment:

[0067] The pretreated camellia shells obtained in step (2) were added to an acetate buffer solution with pH = 4.8 at a material-to-liquid ratio of 1:8, and 1.5% (w / w) of cellulase was added. The mixture was enzymatically hydrolyzed at 40°C for 12 h. The resulting hydrolysate was transferred to an ultrasonic reactor and treated at 400W power and 35°C for 20 min. After filtration, the filter residue was dried at 80°C to obtain a biochar precursor.

[0068] (4) Modification treatment: Prepare a mixed solution containing 0.07 mol / L MnSO4 and 0.05 mol / L FeSO4. Add the biochar precursor to the mixed solution at a mass ratio of 1:10. Under magnetic stirring at 55℃, slowly add 1 mol / L NaOH solution until the pH = 9.0. Maintain the reaction for 1.5 h. After the reaction is completed, collect the precipitate, wash it with deionized water until neutral, dry it at 80℃, and then pyrolyze it at 600℃ for 2 h in a nitrogen atmosphere to obtain modified biochar material for soil cadmium pollution remediation.

[0069] Example 3

[0070] A method for preparing modified biochar material for cadmium pollution remediation in soil, comprising the following steps:

[0071] (1) Extraction of tea oil tea alcohol extract: The washed and dried tea oil tea leaves were extracted twice by reflux with 70% ethanol (volume concentration), concentrated under reduced pressure and freeze-dried into powder to obtain tea oil tea alcohol extract.

[0072] (2) Pre-treatment for composting: Crush the camellia oleifera shells to a particle size <5mm, adjust the moisture content to 60%, and add 0.5% composting agent (a mixture of Bacillus subtilis and yeast in a mass ratio of 3:2, with a viable count ≥1×10⁻⁶) according to the weight of the camellia oleifera shells. 9 The tea leaves were fermented with CFU / g and 3% tea oil tea alcohol extract. They were stacked in windrows with a height of 1.5m and a width of 2m. The piles were turned over every 2 days, and the temperature was controlled at 60℃. The fermentation cycle was 13 days. After fermentation, the leaves were dried at 60℃, crushed and passed through a 2mm sieve to obtain pretreated tea oil shells.

[0073] (3) Ultrasonic-enzymatic synergistic treatment:

[0074] The pretreated camellia shells obtained in step (2) were added to an acetate buffer solution with pH = 4.8 at a material-to-liquid ratio of 1:8, and 1.5% (w / w) of cellulase was added. The mixture was enzymatically hydrolyzed at 40°C for 10 h. The resulting hydrolysate was transferred to an ultrasonic reactor and treated at 350 W power and 35°C for 25 min. After filtration, the filter residue was dried at 80°C to obtain a biochar precursor.

[0075] (4) Modification treatment: Prepare a mixed solution containing 0.05 mol / L MnSO4 and 0.05 mol / L FeSO4. Add the biochar precursor to the mixed solution at a mass ratio of 1:10. Under magnetic stirring at 60℃, slowly add 1 mol / L NaOH solution until the pH = 9.0. Maintain the reaction for 1.5 h. After the reaction is completed, collect the precipitate, wash it with deionized water until neutral, dry it at 80℃, and then pyrolyze it at 600℃ for 2 h in a nitrogen atmosphere to obtain modified biochar material for soil cadmium pollution remediation.

[0076] Example 4

[0077] A method for preparing modified biochar material for cadmium pollution remediation in soil, comprising the following steps:

[0078] (1) Extraction of tea oil tea alcohol extract: The washed and dried tea oil tea leaves were extracted twice by reflux with 70% ethanol (volume concentration), concentrated under reduced pressure and freeze-dried into powder to obtain tea oil tea alcohol extract.

[0079] (2) Pre-treatment for composting: Crush the camellia oleifera shells to a particle size <5mm, adjust the moisture content to 60%, and add 0.5% composting agent (a mixture of Bacillus subtilis and yeast in a mass ratio of 3:2, with a viable count ≥1×10⁻⁶) according to the weight of the camellia oleifera shells. 9 The tea leaves were fermented with CFU / g and 4% tea oil alcohol extract. They were stacked in windrows with a height of 1.5m and a width of 2m. The piles were turned over every 2 days, and the temperature was controlled at 50℃. The fermentation cycle was 15 days. After fermentation, the leaves were dried at 60℃, crushed and passed through a 2mm sieve to obtain pretreated tea oil shells.

[0080] (3) Ultrasonic-enzymatic synergistic treatment:

[0081] The pretreated camellia shells obtained in step (2) were added to an acetate buffer solution with pH=4.8 at a material-to-liquid ratio of 1:8, and 1.5% (w / w) of cellulase was added. The mixture was enzymatically hydrolyzed at 35°C for 12 h. The resulting hydrolysate was transferred to an ultrasonic reactor and treated at 400W power and 40°C for 25 min. After filtration, the filter residue was dried at 80°C to obtain a biochar precursor.

[0082] (4) Modification treatment: Prepare a mixed solution containing 0.07 mol / L MnSO4 and 0.07 mol / L FeSO4. Add the biochar precursor to the mixed solution at a mass ratio of 1:10. Under magnetic stirring at 60℃, slowly add 1 mol / L NaOH solution until the pH = 9.0. Maintain the reaction for 1.5 h. After the reaction is completed, collect the precipitate, wash it with deionized water until neutral, dry it at 80℃, and then pyrolyze it at 500℃ for 2 h in a nitrogen atmosphere to obtain modified biochar material for soil cadmium pollution remediation.

[0083] Comparative Example 1

[0084] The only difference from Example 1 is that no stacking process is performed; instead, the camellia shells are used directly as raw materials for the ultrasonic-enzymatic hydrolysis synergistic treatment in step (3).

[0085] Comparative Example 2

[0086] The only difference from Example 1 is that FeSO4 is replaced with an equimolar amount of MnSO4, that is, 0.1 mol / L MnSO4 is used as the soaking solution.

[0087] Comparative Example 3

[0088] The only difference from Example 1 is that the ultrasonic-enzymatic hydrolysis synergistic treatment in step (3) is not performed, and the pretreated camellia shells are directly subjected to the modification treatment in step (4).

[0089] Comparative Example 4

[0090] The only difference from Example 1 is that the tea oil extract is replaced with an equal amount of humic acid.

[0091] Example of effect verification:

[0092] 1. Cd in modified biochar materials 2+ Adsorption saturation experiment

[0093] The modified biochar material prepared in Example 1 was added to 50 mg / L of Cd. 2+ Samples were taken after shaking the solution (prepared by dissolving cadmium chloride in deionized water) at 180 rpm for 30 min, 60 min, 90 min, 120 min, 180 min and 240 min at 25 °C in a shaker.

[0094] The results showed that the modified biochar material prepared in Example 1 had a Cd content of 90 min. 2+ The adsorption capacity reached 46.7 mg / g, and the Cd at 120 min was... 2+ The adsorption increase of <1% indicates that the modified biochar material reaches Cd within 90 minutes.2+ Adsorption saturation.

[0095] The modified biochar materials of Examples 2-4 and Comparative Examples 1-4 were subjected to the same Cd treatment. 2+ Adsorption saturation test.

[0096] The results showed that the modified biochar materials in Examples 2-4 all reached adsorption saturation within 90 minutes, while the modified biochar materials in Comparative Examples 1-4 all reached adsorption saturation within 120 minutes.

[0097] 2. Modified biochar materials for Cd 2+ Adsorption capacity determination and recycling experiment

[0098] The modified biochar materials prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to Cd24 analysis. 2+ Static adsorption test.

[0099] The modified biochar material was added to 50 mg / L of Cd at a solid-liquid ratio of 1.0 g / L. 2+ The solution (prepared by dissolving cadmium chloride in deionized water) was reacted in a shaker at 25°C and 180 rpm for 150 min. After the reaction, the Cd concentration in the solution was determined by ICP-MS. 2+ The remaining concentration is used to calculate the adsorption capacity, where the adsorption capacity calculation formula is:

[0100] q e =(C0-C e )×V / m.

[0101] Where, q e For Cd 2+ Adsorption capacity, in mg / g;

[0102] C0 represents the Cd in the solution. 2+ Initial concentration, in mg / L;

[0103] C e The Cd in the solution after the reaction is complete 2+ The concentration is expressed in mg / L.

[0104] V is the volume of the solution, in L;

[0105] m represents the mass of the modified biochar material, in grams.

[0106] Cd in various modified biochar materials 2+ The maximum adsorption capacity is shown in Table 1.

[0107] Table 1

[0108] Maximum adsorption capacity (mg / g) Example 1 46.7±0.5 Example 2 46.5±0.3 Example 3 46.5±0.2 Example 4 46.9±0.7 Comparative Example 1 28.7±0.1 Comparative Example 2 35.2±1.2 Comparative Example 3 32.4±0.9 Comparative Example 4 38.6±1.1

[0109] Using 0.1 mol / L HCl solution as the desorption agent, the modified biochar material after adsorption was added to the desorption agent at a solid-liquid ratio of 1 g:10 mL. The mixture was shaken at 25°C for 3 hours, washed with deionized water until neutral, and dried to regenerate the modified biochar material. The adsorption-desorption process was repeated 5 times, and the Cd of the modified biochar material was calculated. 2+ The adsorption retention rate is shown in Table 2.

[0110] Among them: Cd 2+ Adsorption retention rate (%) = Adsorption amount of Nth adsorption / Adsorption amount of the first adsorption × 100%.

[0111] Table 2

[0112] <![CDATA[Cd after 5 cycles 2+ Adsorption retention rate (%)]]> Example 1 89.2±1.3 Example 2 90.3±1.1 Example 3 88.9±0.7 Example 4 88.7±1.2 Comparative Example 1 41.2±0.9 Comparative Example 2 55.6±2.5 Comparative Example 3 48.3±2.1 Comparative Example 4 62.5±1.9

[0113] 3. The effect of modified biochar materials on Cd in mixed ionic solutions 2+ Adsorption experiment

[0114] Preparation of Cu 2+ Pb 2+ Cd 2+ A mixed metal solution (prepared by dissolving copper sulfate, lead nitrate, and cadmium chloride in deionized water) with a concentration of 50 mg / L was used. Modified biochar material was added to the mixed metal solution at a solid-liquid ratio of 1.0 g / L, and the solution was shaken at 25°C for 24 h. The Cd concentration was calculated. 2+ The removal rate is shown in Table 3.

[0115] Table 3

[0116] <![CDATA[Cu 2+ Removal rate (%) <![CDATA[Pb 2+ Removal rate (%) <![CDATA[Cd 2+ Removal rate (%) Example 1 67.5±1.1 78.2±1.3 92.1±0.9 Example 2 66.9±0.8 77.9±1.5 91.3±1.1 Example 3 67.2±1.0 78.3±1.0 92.0±0.8 Example 4 67.1±1.1 78.0±0.8 91.2±1.9 Comparative Example 1 45.8±1.2 52.6±0.9 53.8±1.0 Comparative Example 2 53.2±2.3 61.8±1.4 68.3±2.1 Comparative Example 3 48.7±1.3 56.3±2.3 58.9±1.7 Comparative Example 4 57.6±2.0 65.4±1.8 76.2±2.1

[0117] 4. Verification Experiment for Soil Cadmium Pollution Remediation

[0118] (1) Test soil: The topsoil of acidic red soil cadmium-contaminated farmland from 0-20cm was selected (initial pH 4.8, total cadmium content 85mg / kg, available cadmium 28.6mg / kg).

[0119] (2) Experimental Groups:

[0120] Blank control group: No repair material was applied.

[0121] Experimental group 1: 5g of the modified biochar material from Example 1 was applied to every 1kg of soil;

[0122] Experimental group 2: 5g of the modified biochar material from Example 2 was applied to every 1kg of soil;

[0123] Experimental group 3: 5g of the modified biochar material from Example 3 was applied to every 1kg of soil;

[0124] Experimental group 4: 5g of the modified biochar material from Example 4 was applied to every 1kg of soil;

[0125] Control group 1: 5g of the modified biochar material from Comparative Example 1 was applied per 1kg of soil;

[0126] Control group 2: 5g of the modified biochar material from Comparative Example 2 was applied per 1kg of soil;

[0127] Control group 3: 5g of the modified biochar material from comparison example 3 was applied per 1kg of soil;

[0128] Control group 4: 5g of the modified biochar material from comparison example 4 was applied per 1kg of soil;

[0129] Each group was repeated 3 times, using plastic pots (3kg soil / pot), and incubated at a constant temperature (25±2℃) for 60 days. During the experiment, the soil moisture content was maintained at 60±5%.

[0130] After the experiment, soil pH and C / N ratio were measured, and the available cadmium content was determined using the 0.1 mol / L HCl extraction method. The results are shown in Table 4.

[0131] Table 4

[0132] Effective cadmium content (mg / kg) Soil pH C / N ratio Experimental group 1 9.7±0.3 6.2±0.1 13.8±0.3 Experimental group 2 9.7±0.8 6.1±0.2 13.7±0.2 Experimental group 3 9.8±1.0 6.2±0.1 13.8±0.1 Experimental group 4 9.6±0.7 6.1±0.1 13.8±0.2 Control group 1 16.8±1.8 5.4±0.2 12.1±0.1 Control group 2 14.3±2.4 5.7±0.1 12.8±0.3 Control group 3 15.5±1.9 5.5±0.2 12.3±0.1 Control group 4 13.9±2.0 5.7±0.8 12.7±0.5 Blank control group 28.6±1.7 4.8±0.3 10.6±0.3

[0133] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing modified biochar material, characterized in that, Includes the following steps: (1) Pretreatment of Camellia oleifera shells: Add fermenting agent and tea leaf extract to Camellia oleifera shells, and ferment them at 50-60℃. After fermentation, dry them to obtain pretreated Camellia oleifera shells. (2) Ultrasonic-enzymatic hydrolysis synergistic treatment: The pretreated camellia shells are added to an acetate buffer solution, then cellulase is added, and the enzymatic hydrolysis is carried out at 35-40℃ for 10-12h. The resulting enzymatic hydrolysate is then subjected to ultrasonic treatment at a power of 350-400W and a temperature of 35-40℃. The filtered residue is then dried to obtain a biochar precursor. (3) Modification treatment: The biochar precursor is added to a mixed solution of MnSO4 and FeSO4, and the pH of the system is adjusted to 9.0 by adding alkali solution at 55-60℃ for modification treatment. After that, the precipitate is collected and washed until neutral, and then pyrolyzed at 500-600℃ under a protective atmosphere to obtain the modified biochar material.

2. The preparation method according to claim 1, characterized in that, The composting and fermentation process takes 13-15 days.

3. The preparation method according to claim 1, characterized in that, The tea oil extract is obtained by reflux extraction of tea oil leaves with ethanol.

4. The preparation method according to claim 1, characterized in that, The amount of tea oil tea extract added is 3-4% of the mass of the tea oil tea shell.

5. The preparation method according to claim 1, characterized in that, The fermentation agent is a mixture of Bacillus subtilis and yeast.

6. The preparation method according to claim 1, characterized in that, The ultrasonic treatment time is 20-25 minutes.

7. The preparation method according to claim 1, characterized in that, The pyrolysis temperature is 500-600℃.

8. The preparation method according to claim 1, characterized in that, In the mixed solution, the concentration of MnSO4 is 0.05-0.07 mol / L and the concentration of FeSO4 is 0.05-0.07 mol / L.

9. Modified biochar material prepared by the preparation method according to any one of claims 1-8.

10. The application of the modified biochar material as described in claim 9 in the remediation of cadmium pollution in soil.