Broussonetia papyrifera biochar, a preparation method thereof and broussonetia papyrifera charcoal-based soil heavy metal mineralization agent and application thereof

Abstract

The present application provides a broussonetia papyrifera carbon material and a preparation method thereof and a broussonetia papyrifera carbon-based soil heavy metal mineralization agent and application thereof, and belongs to the technical field of soil remediation. The preparation method of the broussonetia papyrifera carbon material can effectively change the dense structure of the broussonetia papyrifera material in a short time by using steam explosion technology; after high-temperature carbonization, the internal porosity and specific surface area of the broussonetia papyrifera fiber are greatly increased, the surface functional groups are enriched, and the adsorption efficiency of the carbon material for heavy metal ions is improved; the broussonetia papyrifera material is impregnated with a reducing slurry, so that the prepared broussonetia papyrifera carbon material can reduce high-valence heavy metals in the soil to low-valence heavy metals with less toxicity, thereby reducing the harmful effect of heavy metals on the soil. The broussonetia papyrifera carbon material prepared by the present application is light and porous, has rich surface groups, has good adsorption capacity for various heavy metals, can efficiently repair heavy metal contaminated soil, and can significantly reduce the leaching toxicity of plants.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil remediation, and particularly relates to a broussonetia papyrifera carbon material, a preparation method thereof, and a broussonetia papyrifera carbon-based soil heavy metal mineralization agent and application thereof. BACKGROUND

[0002] Soil is an important environmental medium for plant growth and an important habitat for microorganisms, and is the primary link for the safety of grains, vegetables, oils, melons and fruits, and is a livelihood issue related to food safety. With the rapid development of industry and agriculture, soil heavy metal pollution is becoming increasingly serious. Long-term accumulation of heavy metals in soil will change the function of farmland soil and seriously affect the quality of crops, and ultimately affect human health through the food chain. However, how to repair farmland soil heavy metal pollution and ensure the safe production of food crops is an urgent task in the field of soil and environment.

[0003] At present, the repair of soil heavy metal pollution mainly transfers or passivates heavy metals through physical, chemical and biological methods to limit the migration of heavy metals to target plants. Among them, adding exogenous passivation materials to the adsorption substrate to change the chemical occurrence form of heavy metals in the soil is one of the effective and economical and practical means to quickly and efficiently reduce the ecological risk of soil.

[0004] Biomass carbon as a new type of soil ecological remediation material has attracted widespread attention from environmental workers. Adding single components or composite passivation materials such as clay minerals, fly ash, phosphorus-based fertilizer, humic acid, metal oxide, etc. to biomass carbon as an adsorption substrate can repair heavy metal contaminated soil, but the effect has not been very ideal, the main reasons are: 1. The adsorption capacity of biomass carbon material obtained by simple biomass carbonization treatment is low, and the stability and durability of the repair effect are not ideal; 2. The nutrient content of inorganic passivation agents is low, resulting in insufficient soil organic matter and low soil quality; some have poor biocompatibility and can easily cause secondary pollution. Therefore, developing an economical and efficient, green and environmentally friendly soil heavy metal repair agent to improve the repair effect and maintain soil fertility has become one of the problems to be solved in the field. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of broussonetia papyrifera carbon material, which can utilize broussonetia papyrifera resources and repair heavy metal contaminated soil.

[0006] In order to solve the above technical problems, the present application provides the following technical scheme:

[0007] The present application provides a preparation method of broussonetia papyrifera carbon material, comprising the following steps:

[0008] The broussonetia papyrifera branch and stem steam explosion product and / or broussonetia papyrifera bark is impregnated with a reducing slurry to obtain a broussonetia papyrifera loaded material;

[0009] The paper mulberry support material is carbonized at high temperature to obtain paper mulberry carbon material.

[0010] Preferably, the reducing slurry comprises a catalytically active sol; the catalytically active sol comprises the following components:

[0011] Nonionic surfactants, silica sol, and ferrous sulfate.

[0012] Preferably, the catalytically active sol further includes a modified solution; the modified solution includes one or more of triethylamine, ethylenediamine, ethylamine, urea, and ammonia.

[0013] Preferably, the impregnation includes a vacuum negative pressure stage and a positive pressure holding stage;

[0014] The vacuum degree during the vacuum negative pressure stage is 0.065–0.98 MPa; the duration of the vacuum negative pressure stage is 10–15 min.

[0015] The pressure during the positive pressure holding phase is 1–3 MPa; the positive pressure holding time is 5–10 min.

[0016] Preferably, the impregnation is performed twice; the metal loading of the resulting paper mulberry loading material is 2–12 wt.%.

[0017] Preferably, the high-temperature carbonization method is variable-temperature carbonization; the starting temperature of the variable-temperature carbonization is 24°C, which is increased to 150°C to 350°C at a rate of 3 to 5°C / min, and after being kept at a constant temperature for 5 to 15 minutes, it is increased to 450°C to 600°C at a rate of 18 to 22°C / min, and kept at a constant temperature for 1 hour, followed by natural cooling.

[0018] Preferably, the steam pressure for the steam explosion is 1.0 to 3.0 MPa; and the pressure holding time for the steam explosion is 30 to 240 s.

[0019] The present invention also provides a paper mulberry char material prepared by the preparation method described in the above technical solution.

[0020] The present invention also provides a mulberry charcoal-based soil heavy metal mineralizer, comprising the following components by weight: 1 part of the mulberry charcoal material described in the above technical solution, 0.05-0.15 parts of passivating agent, 0.05-0.2 parts of humic acid, and 0.08-0.3 parts of woody peat.

[0021] The present invention also provides the application of the paper mulberry charcoal material described in the above-mentioned technical solutions or the paper mulberry charcoal-based soil heavy metal mineralizer described in the above-mentioned technical solutions in soil remediation.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a method for preparing paper mulberry charcoal material, comprising: impregnating paper mulberry branches and / or paper mulberry bark with a reducing slurry to obtain a paper mulberry loaded material; and subjecting the paper mulberry loaded material to high-temperature carbonization to obtain paper mulberry charcoal material. The preparation method of paper mulberry charcoal material of this invention utilizes steam explosion technology to effectively alter the dense structure of paper mulberry material in a short time, further improving fiber quality; high-temperature carbonization significantly increases the internal porosity and specific surface area of ​​paper mulberry fibers and enriches surface functional groups, improving the adsorption efficiency of the charcoal material for heavy metal ions; impregnation of the paper mulberry material with a reducing slurry enables the prepared paper mulberry charcoal material to reduce high-valence heavy metals in the soil to low-valence heavy metals with lower toxicity, mitigating the harmful effects of heavy metals on the soil. The paper mulberry charcoal material prepared by the method of this invention is lightweight and porous, with abundant surface groups, exhibiting good adsorption capacity for various heavy metals, and can efficiently remediate heavy metal-contaminated soil while significantly reducing the leaching toxicity of plants. The preparation method and equipment for the paper mulberry charcoal material of this invention are mature, suitable for large-scale industrial production, easy to implement in engineering applications, easy to apply in agriculture, non-toxic to farmland soil environment, and have good ecological and environmental benefits. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A comparison of fiber lengths of paper mulberry bark carbon materials, paper mulberry charcoal materials, paulownia charcoal materials, and poplar charcoal materials.

[0026] Figure 2 The changes in the speciation and content of cadmium (Cd) in the soil after 90 days of treatment with the soil remediation agents prepared in Examples 1-9 and Comparative Examples 1-11;

[0027] Figure 3 This is an electron microscope image of the paper mulberry carbon material prepared in Example 3. Detailed Implementation

[0028] This invention provides a method for preparing paper mulberry charcoal material, comprising the following steps:

[0029] Paper mulberry branches and / or paper mulberry bark were impregnated with a reducing slurry to obtain paper mulberry load material;

[0030] The paper mulberry support material is carbonized at high temperature to obtain paper mulberry carbon material.

[0031] This invention uses a reducing slurry to impregnate the steam-exploded debris of paper mulberry branches and / or paper mulberry bark to obtain paper mulberry load material.

[0032] The present invention preferably involves steam explosion of paper mulberry branch powder to obtain paper mulberry branch steam explosion product.

[0033] In this invention, the paper mulberry branch powder is preferably obtained by crushing paper mulberry branches. The paper mulberry branches are preferably hybrid paper mulberry branches, more preferably branches of hybrid paper mulberry branches after debarking. Before debarking, the hybrid paper mulberry branches are preferably cut and soaked. The cutting method preferably includes cutting the paper mulberry branches into equal-length segments; the length of the segments is preferably 3-8 cm, more preferably 5 cm. After cutting the paper mulberry branches into segments, the segments are preferably soaked. The soaking time is preferably 0.5-3 hours, more preferably 2 hours. Soaking is preferably performed in water. Cutting and soaking the paper mulberry branches facilitates debarking. This invention does not specifically limit the debarking method; conventional debarking methods in the art are acceptable. After debarking, the paper mulberry branches are preferably dried. This invention does not specifically limit the drying method; conventional drying methods in the art are acceptable. Embodiments of this invention can use oven drying or natural drying. When using an oven for drying, the drying temperature is preferably 50℃~80℃, more preferably 60℃. The drying is preferably performed until the moisture content of the paper mulberry branches is 15%~20%. After drying, the paper mulberry branches are preferably pulverized to obtain paper mulberry branch powder. The method of pulverizing the paper mulberry branches is not particularly limited; conventional pulverization methods for branches in the art are acceptable. The paper mulberry branch powder is preferably sieved to obtain wood powder, which is the paper mulberry branch powder. The sieve aperture is preferably 4~100 mesh, more preferably 30~80 mesh, and more preferably 50~60 mesh. Pulverizing the paper mulberry branches is mainly beneficial for nitrogen doping and metal ion loading in the subsequent preparation of paper mulberry charcoal materials. The paper mulberry branches are preferably pulverized before steam explosion because pulverizing after steam explosion will change the surface properties of the raw material, thereby adversely affecting the performance of the paper mulberry charcoal material.

[0034] After obtaining the paper mulberry branch powder, the present invention performs steam explosion on the paper mulberry branch powder. In the present invention, the steam pressure of the steam explosion is preferably 1.0-3.0 MPa, more preferably 1.0-2.5 MPa, even more preferably 1.5-2.3 MPa, and more preferably 1.5-2.0 MPa; the holding time of the steam explosion is 30-240 s, more preferably 50 s-220 s, even more preferably 80 s-200 s, and more preferably 100 s-150 s. In the present invention, the steam explosion mainly degrades the hemicellulose of the biomass raw material. The steam explosion of the present invention is preferably carried out in a steam explosion equipment. The steam explosion equipment in the embodiment of the present invention is the QBS-80 steam explosion test bench produced by Henan Hebi Zhengdao Heavy Machinery Factory. After obtaining the steam-exploded product, the present invention preferably dries the steam-exploded product. The drying is preferably carried out under vacuum conditions; the drying temperature is preferably 80–120°C, more preferably 90–110°C, and even more preferably 95–100°C; the drying time is preferably 2–4 hours, and even more preferably 3 hours. The drying of the present invention is preferably carried out in a vacuum drying oven. The present invention preferably seals the dried steam-exploded product for later use.

[0035] This invention utilizes steam explosion to treat hybrid paper mulberry. The treated raw material's structure is broken down, releasing the bast fibers that are irregularly embedded in the cork tissue and parenchyma cell groups in the form of fiber bundles. The area of ​​the amorphous region is greatly increased, and the fragments mostly form fine particles or filaments. Simultaneously, the lignin is softened, the fiber structure becomes less compact, and irregular tears occur, resulting in a wrinkled, honeycomb-like surface. Figure 3 The specific surface area is greatly increased, and the surface functional groups are further enriched.

[0036] After obtaining the steam-exploded material of paper mulberry branches, the present invention uses a reducing slurry to impregnate the steam-exploded material of paper mulberry branches and / or paper mulberry bark to obtain paper mulberry load material.

[0037] In this invention, the bark of the paper mulberry tree can be directly impregnated; the steam-exploded product of the paper mulberry tree branches can be directly impregnated; or the steam-exploded product of the paper mulberry tree branches and the bark of the paper mulberry tree can be impregnated together.

[0038] In this invention, the reducing slurry is preferably a catalytically active sol; the catalytically active sol preferably comprises a nonionic surfactant, silica sol, and ferrous sulfate. The molar ratio of the nonionic surfactant, silica sol, and ferrous sulfate in the catalytically active sol of this invention is preferably (0.1–0.2):(0.5–1):(7.6–8.8), more preferably (0.15–0.2):(0.5–1):(7.8–8.2), and even more preferably (0.15–0.2):(0.5–1):8. In this invention, the nonionic surfactant is preferably one or more of citric acid, lactic acid, and lignovinic acid. In this invention, the nonionic surfactant functions to better disperse silica sol and ferrous ions, reduce the surface tension of the sol, and ensure uniform distribution and good stability of ferrous ions on the paper mulberry powder. This results in a coating with a large specific surface area, uniform pore size distribution, and high mechanical strength. The silica sol acts as a binder, firmly anchoring metal ions on the biomass. It also provides layered isolation for the biomass carbon after subsequent pyrolysis, preventing metal ion aggregation that could affect activity. The ferrous sulfate acts as a metal reduction center in the reducing slurry, providing transition electrons for the reduction of high-valence heavy metals. It also effectively improves soil pH, lowers the soil pH value, and promotes chlorophyll synthesis in plants. In this invention, the catalytic active center sol preferably uses ethanol as a solvent. The catalytic active center sol preferably also includes a modification solution; the modification solution is preferably one or more of triethylamine, ethylenediamine, ethylamine, urea, and ammonia water. The modification solution mainly adjusts the pH of the catalytic active center sol, performing alkaline modification.

[0039] The preferred method for preparing the catalytically active center sol of the present invention includes the following steps: mixing a nonionic surfactant, silica sol and ferrous sulfate and dissolving them in an ethanol solvent to obtain a mixed solution; adding a modified solution to the mixed solution to obtain an alkaline mixed solution; adjusting the viscosity of the alkaline mixed solution and allowing it to stand to obtain the catalytically active center sol.

[0040] In this invention, a nonionic surfactant, silica sol, and ferrous sulfate are mixed and dissolved in ethanol solvent, and then preferably subjected to high-speed stirring. The stirring speed is preferably 1500–2000 rpm, more preferably 1600–1800 rpm, and even more preferably 1700 rpm. The stirring time is preferably 0.5–3 h, more preferably 1–2.5 h, and even more preferably 1.5–2 h. In this invention, the high-speed stirring is mainly to ensure that the solute is thoroughly mixed in the solvent.

[0041] After obtaining the mixed solution, the present invention preferably adds the modified solution to the mixed solution to obtain an alkaline mixed solution. After adding the modified solution to the mixed solution, the present invention preferably performs high-speed stirring. The stirring speed is preferably 1500-2000 rpm, more preferably 1600-1800 rpm, and more preferably 1700 rpm; the high-speed stirring time is 20 min. In the present invention, the pH of the alkaline mixed solution is preferably 7.5-9, more preferably 8-8.5. After obtaining the alkaline mixed solution, the present invention preferably adjusts the viscosity of the alkaline mixed solution and then allows it to stand to obtain a catalytically active center sol. In the present invention, the viscosity of the catalytically active center sol is preferably 5-12 mPa·s, more preferably 7 mPa·s. The method for adjusting the viscosity of the alkaline solution is preferably evaporation concentration or the addition of deionized water. When the viscosity of the alkaline mixed solution is lower than 5-12 mPa·s, evaporation concentration is performed; when the viscosity is higher than 5-12 mPa·s, deionized water is added. In this invention, the settling time is preferably 6–12 hours, more preferably 7–10 hours, and even more preferably 8 hours. The settling process described in this invention yields a more stable sol containing catalytically active centers.

[0042] In this invention, the catalytically active sol, serving as a reduction center slurry, primarily functions to load ferrous salts onto biomass feedstocks. The catalytically active sol is crucial in determining the performance of mulberry charcoal materials in reducing the valence of high-valence heavy metals. The concentration, viscosity, pH, and / or preparation method of each component in the catalytically active sol significantly influence the internal structure and physicochemical properties of the mulberry charcoal-based adsorption substrate, determining its specific surface area and the bonding strength between the reduction centers and the support, thereby affecting the reactivity of the mulberry charcoal material.

[0043] In this invention, the impregnation preferably includes a vacuum negative pressure stage and a positive pressure holding stage. The vacuum degree of the vacuum negative pressure stage is preferably 0.065–0.98 MPa, more preferably 0.075–0.085 MPa; the vacuum negative pressure time is preferably 10–15 min, more preferably 12–14 min, more preferably 13 min; the pressure of the positive pressure holding stage is preferably 1–3 MPa, more preferably 2 MPa; the positive pressure holding time is preferably 5–10 min, more preferably 7–9 min, more preferably 8 min. The impregnation process of this invention, combining the vacuum negative pressure and positive pressure holding stages, is beneficial for improving the wettability of the high-viscosity catalytic active center sol on the biomass surface, achieving the corresponding metal loading. After the positive pressure holding stage is completed, this invention preferably dries the product, preferably by air drying, more preferably by natural air drying. After drying the impregnated product, this invention preferably repeats the impregnation and drying process to ensure that the metal loading of the paper mulberry loading material reaches the corresponding standard. The present invention relates to a paper mulberry loaded material obtained by impregnation, wherein the metal loading of the paper mulberry loaded material is preferably 2-12 wt.%, more preferably 2.5-4 wt.%, and even more preferably 3 wt.%. In this invention, the metal loading refers to the ratio of the mass of iron element calculated based on the amount of ferrous sulfate added to the mass of the total material after drying. The impregnation process of this invention is preferably carried out in a breathable vacuum pressure impregnation machine. The impregnation method of this invention, combining pressure impregnation and vacuum impregnation, is beneficial for improving the wettability of the high-viscosity sol on the biomass material.

[0044] After obtaining the steam-exploded biomass, this invention uses an alkaline-modified catalytic active center sol to perform biomimetic breathing impregnation on the biomass raw material. This removes the gas adsorbed inside the pores of the porous material, which is beneficial for the metal ions to be impregnated to enter the pores. This effectively solves the problems of micropore blockage and easy detachment of the loaded coating. In particular, the addition of triethylamine, ethylenediamine, ethylamine, urea, and ammonia water can enable the biomass raw material to form pyridine carbon catalytic active centers during carbonization, which promotes the reduction of high-valence heavy metals.

[0045] After obtaining the paper mulberry support material, the present invention performs high-temperature carbonization on the paper mulberry support material to obtain paper mulberry carbon material.

[0046] In this invention, the high-temperature carbonization method is preferably variable-temperature carbonization. The starting temperature of the variable-temperature carbonization is preferably 24°C. The variable-temperature carbonization preferably includes two heating stages, namely a first heating stage and a second heating stage. The temperature of the first heating stage is preferably increased at 3-5°C / min, more preferably at 4°C / min. The temperature of the first heating stage is preferably increased to 150°C-350°C, further preferably to 180°C-330°C, more preferably to 200°C-300°C, and most preferably to 250°C. After the first heating stage is completed, the invention preferably maintains a constant temperature for 5-15 minutes, more preferably 8-12 minutes, and more preferably 10 minutes. After the constant temperature treatment, the invention preferably performs a second heating stage. The temperature of the second heating stage is preferably increased at 18-22°C / min, more preferably at 20°C / min. The second heating stage preferably raises the temperature to 450℃~600℃, more preferably 480℃~580℃, even more preferably 500℃~550℃, and most preferably 520℃. After the second heating stage is completed, the present invention preferably maintains a constant temperature for 1 hour before cooling. The cooling is preferably natural cooling. In the present invention, the high-temperature carbonization is preferably carried out under the protection of an inert gas; the inert gas is preferably argon or nitrogen. The high-temperature carbonization of the present invention is preferably carried out in a tube furnace.

[0047] Carbonization temperature is crucial to the performance of carbon materials. Low temperatures hinder complete carbonization, while high temperatures increase graphitization and reduce activity. Both low and high carbonization temperatures are unfavorable for the adsorption of heavy metal ions. The carbonization temperature used in this invention promotes complete carbonization of the paper mulberry material while reducing the degree of graphitization. The variable-temperature high-temperature carbonization method described in this invention, employing two temperature-changing rates, facilitates the formation of more framework defects in the carbon skeleton, thus promoting the catalytic activity of the carbon material. The heating rate used in this invention helps prevent excessively high heating rates from causing N-doped molecules to volatilize too quickly and fail to participate effectively in the formation of the carbon framework.

[0048] This invention involves high-temperature carbonization and nitrogen doping reactions during the high-temperature carbonization process. The high-temperature carbonization significantly increases the porosity and specific surface area of ​​the paper mulberry fibers and enriches the surface functional groups, thereby improving the adsorption efficiency of the carbon material for heavy metal ions. In the nitrogen doping reaction, nitrogen participates in the formation of the carbon skeleton. During biomass pyrolysis, the long carbon chains of biomolecules undergo breakage and rearrangement. Exogenous nitrogen atoms, derived from urea, triethylamine, ethylenediamine, ethylamine, ammonia, or other nitrogen-containing molecules, are incorporated into the carbon skeleton, forming nitrogen atoms in different bonding states such as graphitic nitrogen, pyrrole nitrogen, and pyridine nitrogen, thus reducing the graphitization degree of the biochar. This invention, by subjecting paper mulberry materials to nitrogen doping, can improve the reduction capacity of biochar for high-valence heavy metals.

[0049] In the preparation method of paper mulberry char provided by this invention, hybrid paper mulberry is selected as the biochar source because the phloem fibers of hybrid paper mulberry are characterized by their slender length, with an average length of 7.45 mm, an average width of 18.86 μm, an aspect ratio of 395, and a fiber coarseness of 14.15 mg / (100 m). It is a high-quality quasi-one-dimensional char material, and after N doping, it exhibits excellent performance in catalyzing the reduction of high-valence heavy metals. The hybrid paper mulberry wood fibers are relatively short, with an average length of 0.58 mm, and the percentage of fine fibers below 0.2 mm is 43.31%. The fiber distribution frequency in the length range of 0.23–0.47 mm is 53.86%. The average fiber length is shorter than that of typical broadleaf woods. This structure results in higher porosity and abundant surface oxygen-containing functional groups in the carbonized biochar, promoting deprotonation and amorphous transformation of the material, thereby increasing the coordination binding of heavy metals to the biochar. The phloem and xylem fibers of hybrid paper mulberry complement each other, showing excellent results in the application of heavy metal reduction and passivation in soil.

[0050] This invention also provides a method for preparing paper mulberry charcoal material as described in the above-mentioned technical solution. In this invention, the paper mulberry charcoal material is characterized by its light weight, porous structure, large specific surface area, and abundant surface functional groups.

[0051] The present invention also provides a mulberry charcoal-based soil heavy metal mineralizer, comprising the following components by weight: 1 part of the mulberry charcoal material described in the above technical solution, 0.05-0.15 parts of passivating agent, 0.05-0.2 parts of humic acid, and 0.08-0.3 parts of woody peat.

[0052] Based on the mass fraction of mulberry charcoal material, the mulberry charcoal-based soil heavy metal mineralizing agent of the present invention includes 0.05 to 0.15 parts of passivating agent, preferably 0.1 to 0.15 parts, and more preferably 0.15 parts. The passivating agent is preferably one or more of ferrous sulfate, potassium carbonate, and hydroxyapatite.

[0053] Based on the mass fraction of mulberry charcoal material, the mulberry charcoal-based soil heavy metal mineralizer of the present invention includes 0.05-0.2 parts of humic acid, preferably 0.1-0.2 parts, and more preferably 0.2 parts. The humic acid not only promotes the formation of soil aggregates, improves the availability of nitrogen, phosphorus, and potassium in alkaline soils, and enhances the physicochemical and biochemical properties of the soil, but also strengthens crop resistance to disease, drought, and lodging, and improves crop quality.

[0054] Based on the mass fraction of mulberry charcoal material, the mulberry charcoal-based soil heavy metal mineralizer of this invention includes 0.08-0.3 parts of woody peat, preferably 0.2-0.3 parts, and more preferably 0.3 parts. The woody peat is a stable, non-decomposable organic matter accumulation layer formed by the long-term accumulation of woody plant remains in a swampy environment with excessive moisture, poor aeration, and low temperature. It is rich in organic matter, which can promote the growth and development of crop roots and above-ground parts, increase crop yield, improve agricultural product quality indicators, enhance crop resistance to stress and pests, improve the soil ecological environment, increase the organic matter and nutrient content in the soil, and improve soil fertility. In this embodiment of the invention, the woody peat was purchased from Shijiazhuang Beinong Mineral Products Co., Ltd.

[0055] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials mentioned above, and commercially available products well known to those skilled in the art can be used.

[0056] The present invention also provides the application of the paper mulberry charcoal material and / or paper mulberry charcoal-based soil heavy metal mineralizer described in the above technical solution in soil remediation.

[0057] The soil remediation method described in this invention preferably includes improving the heavy metal pollution status of the soil.

[0058] The paper mulberry charcoal material and / or paper mulberry charcoal-based soil heavy metal mineralizer of this invention are preferably capable of passivating heavy metals in soil. The passivation method is preferably to allow the heavy metals in the soil to exist in the form of carbonates, sulfates, or phosphates as precipitates. When heavy metals exist in the form of carbonates, sulfates, or phosphates, the resulting heavy metal compounds have good chemical stability, are difficult to dissolve again, and are less easily absorbed by crops. The paper mulberry charcoal material and / or paper mulberry charcoal-based soil heavy metal mineralizer provided by this invention can achieve a passivation rate of over 75% for Pb, Cd, or Cr in soil, with Cd passivation exceeding 90%.

[0059] The soil remediation method described in this invention preferably includes reducing soil heavy metals. The reduction of soil heavy metals preferably includes reducing high-valent cadmium ions. The paper mulberry charcoal material and / or paper mulberry charcoal-based soil heavy metal mineralizer described in this invention can reduce hexavalent cadmium to trivalent cadmium, thereby reducing the toxicity of heavy metal ions. Specifically, in the structure of the paper mulberry charcoal material, ferrous ions on pyridine nitrogen-containing active centers can reduce high-valent heavy metal particles into low-valent heavy metal ions with lower toxicity.

[0060] The soil remediation method described in this invention preferably also includes reducing phytoleaving toxicity. The paper mulberry charcoal material and / or paper mulberry charcoal-based soil heavy metal mineralizer described in this invention can reduce the accumulation of heavy metals in plants by 54% to 69%, significantly reducing the phytoleaving toxicity.

[0061] The soil remediation method described in this invention preferably also includes improving soil nutrients and promoting plant growth.

[0062] The beneficial effects of this invention are:

[0063] The main material of this invention is biomass raw material from agricultural and forestry waste, which can solve environmental problems, achieve waste recycling, and avoid secondary pollution, making it safe and reliable. This invention utilizes steam explosion technology to effectively change the dense structure of paper mulberry material in a short time, further improving fiber quality. After carbonization, the internal porosity and specific surface area increase significantly, and the surface functional groups are enriched, improving the adsorption efficiency of carbon materials for heavy metal ions. The soil passivation material prepared by this invention is lightweight and porous with abundant surface groups, achieving a passivation rate of over 75% for Pb, Cd, and Cr in the soil, with Cr passivation exceeding 90%. It reduces the accumulation of heavy metals in plants by 54%–69%, significantly reducing the leaching toxicity of plants and demonstrating good remediation effects on heavy metal-contaminated soil. This invention causes heavy metals in the soil to exist in the form of carbonates, sulfates, or phosphates, exhibiting good chemical stability, making them difficult to dissolve again and less easily absorbed by crops. The raw materials used in this invention are widely available, and the processing equipment is mature, making it suitable for large-scale industrial production and easy to implement in engineering applications. It is also easy to apply in agriculture, has no toxic effects on farmland soil, and provides good ecological and environmental benefits. Furthermore, this product has excellent adsorption capacity for various heavy metals, and ferrous and potassium ions can promote crop production.

[0064] To further illustrate the present invention, the paper mulberry charcoal material, its preparation method, and the paper mulberry charcoal-based soil heavy metal mineralizer provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0067] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them and peel off the bark. Then dry the peeled hybrid paper mulberry branches in a 60℃ oven and keep the peeled paper mulberry bark for later use.

[0068] The dried hybrid paper mulberry branches were crushed and sieved to obtain 100-mesh paper mulberry wood powder.

[0069] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 1.0 MPa for a holding time of 30 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 80°C for 2 hours before being removed, sealed, and stored for later use.

[0070] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.1:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at 2000 r / min for 0.5 h. Urea solution was added to adjust the pH to 7.5. After stirring for another 20 min, deionized water was added to adjust the viscosity to 5 mPa·s. The mixture was allowed to stand for 6 h to obtain the catalytically active center sol.

[0071] The dried steam-exploded material and paper mulberry bark were placed in a vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.065 MPa, the material was then held under positive pressure of 1 MPa for 5 minutes. After that, the material was removed and air-dried. The above impregnation and air-drying process was repeated to achieve a metal loading of 2.5 wt%, thus obtaining the paper mulberry loaded material.

[0072] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of N2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 150℃ at a rate of 5℃ / min, held for 5min, then increased to 450℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry char material.

[0073] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, humic acid, and woody peat in a mass ratio of 1:0.05:0.05:0.08 and stirring evenly to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0074] Example 2

[0075] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0076] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them and peel off the bark. Then dry the peeled hybrid paper mulberry branches in a 60℃ oven and keep the peeled paper mulberry bark for later use.

[0077] The dried hybrid paper mulberry branches were crushed and sieved to obtain 80-mesh paper mulberry wood powder.

[0078] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 1.5 MPa for a holding time of 100 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 95°C for 2 hours before being removed, sealed, and stored for later use.

[0079] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.15:1:7.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 1600 r / min for 1.5 h. Ethylenediamine solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 7 mPa·S. The mixture was allowed to stand for 8 h to obtain the catalytically active center sol.

[0080] The dried steam-exploded material and paper mulberry bark were placed in a vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.075 MPa, they were then held under positive pressure of 1 MPa for 5 minutes. After that, they were taken out and air-dried. The above impregnation and air-drying were repeated to make the metal loading reach 3 wt%, thus obtaining the paper mulberry loaded material.

[0081] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 200℃ at a rate of 3℃ / min, held for 10min, then increased to 500℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0082] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, humic acid, and woody peat in a mass ratio of 1:0.1:0.1:0.1 to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0083] Example 3

[0084] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0085] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them, peel off the bark, and let the peeled branches air dry naturally. Keep the paper mulberry bark for later use.

[0086] The dried hybrid paper mulberry branches were crushed and sieved to obtain 30-mesh paper mulberry wood powder.

[0087] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 2.0 MPa for a holding time of 200 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 100℃ for 4 hours before being removed, sealed, and stored for later use.

[0088] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:0.5:8.2 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 1800 r / min for 2 h. Urea solution was added to adjust the pH to 8.5. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·S. The mixture was allowed to stand for 6 h to obtain the catalytically active center sol.

[0089] The dried steam-exploded material and paper mulberry bark were placed in a vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 15 minutes under a vacuum degree of 0.085 MPa, the material was then held under positive pressure of 2 MPa for 5 minutes. After that, the material was removed and air-dried. The above impregnation and air-drying process was repeated to achieve a metal loading of 2.5 wt%, thus obtaining the paper mulberry loaded material.

[0090] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of N2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 300℃ at a rate of 5℃ / min, held for 15min, then increased to 550℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry char material.

[0091] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with hydroxyapatite, humic acid, and woody peat in a mass ratio of 1:0.15:0.2:0.2 to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0092] Example 4

[0093] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0094] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them, peel off the bark, and let the peeled branches air dry naturally. Keep the paper mulberry bark for later use.

[0095] The dried hybrid paper mulberry branches were crushed and sieved to obtain 4-mesh paper mulberry wood powder.

[0096] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 3.0 MPa for a holding time of 240 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 120℃ for 2 hours before being removed, sealed, and stored for later use.

[0097] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 2000 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 9. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·S. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0098] The dried steam-exploded material and paper mulberry bark were placed in a simulated breathing vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.98 MPa, it was then held under positive pressure of 3 MPa for 10 minutes, removed and air-dried. The above impregnation and air-drying were repeated to achieve a metal loading of 4 wt%, thus obtaining paper mulberry loaded material.

[0099] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0100] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with potassium carbonate, humic acid, and woody peat in a ratio of 1:0.15:0.2:0.3 and stirring evenly to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0101] Example 5

[0102] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0103] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them and peel off the bark. Then dry the peeled hybrid paper mulberry branches in a 60℃ oven and keep the peeled paper mulberry bark for later use.

[0104] The dried hybrid paper mulberry branches were crushed and sieved to obtain 4-mesh paper mulberry wood powder, thus obtaining paper mulberry branch powder.

[0105] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 3.0 MPa and a holding time of 240 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 120℃ for 2 hours before being removed, sealed, and stored for later use.

[0106] The catalytically active center sol was prepared by the following steps: lactic acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 1500 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·s. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0107] The dried steam-exploded material and paper mulberry bark were placed in a simulated breathing vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.98 MPa, it was then held under positive pressure of 3 MPa for 10 minutes, removed and air-dried. The above impregnation and air-drying were repeated to achieve a metal loading of 4 wt%, thus obtaining paper mulberry loaded material.

[0108] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0109] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, sodium humate, and woody peat in a mass ratio of 1:0.15:0.2:0.3 until homogeneous to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0110] Example 6

[0111] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0112] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them and peel off the bark. Then dry the peeled hybrid paper mulberry branches in a 60℃ oven and keep the peeled paper mulberry bark for later use.

[0113] The dried hybrid paper mulberry branches were crushed and sieved to obtain 4-mesh paper mulberry wood powder, thus obtaining paper mulberry branch powder.

[0114] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 3.0 MPa and a holding time of 240 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 120℃ for 2 hours before being removed, sealed, and stored for later use.

[0115] The catalytically active center sol was prepared by the following steps: wood acetic acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.1:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 1500 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·S. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0116] The dried steam-exploded material and paper mulberry bark were placed in a simulated breathing vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.98 MPa, it was then held under positive pressure of 3 MPa for 10 minutes, removed and air-dried. The above impregnation and air-drying were repeated to achieve a metal loading of 4 wt%, thus obtaining paper mulberry loaded material.

[0117] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0118] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, sodium humate, and woody peat in a mass ratio of 1:0.15:0.2:0.3 until homogeneous to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0119] Example 7

[0120] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0121] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them, peel off the bark, and let the peeled branches air dry naturally. Keep the paper mulberry bark for later use.

[0122] The dried hybrid paper mulberry branches were crushed and sieved to obtain 4-mesh paper mulberry wood powder, thus obtaining paper mulberry branch powder.

[0123] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 3.0 MPa for a holding time of 240 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 120℃ for 2 hours before being removed, sealed, and stored for later use.

[0124] The catalytically active center sol was prepared by the following steps: a mixture of lactic acid, vinaigrette, and citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:0.5:8 and dissolved in ethanol. The mixture was dispersed and stirred at 1500 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·s. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0125] The dried steam-exploded material and paper mulberry bark were placed in a simulated breathing vacuum pressure impregnation machine to impregnate the catalytic active center sol. After vacuum negative pressure for 10 minutes under a vacuum degree of 0.98 MPa, it was then held under positive pressure of 3 MPa for 10 minutes, removed and air-dried. The above impregnation and air-drying were repeated to achieve a metal loading of 4 wt%, thus obtaining paper mulberry loaded material.

[0126] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0127] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, sodium humate, and woody peat in a mass ratio of 1:0.15:0.2:0.3 and stirring evenly to obtain the mulberry charcoal-based soil heavy metal remediation agent.

[0128] Example 8

[0129] The preparation method of the paper mulberry charcoal material is the same as in Example 1, except that only the paper mulberry branch powder is impregnated during impregnation, without adding paper mulberry bark. The resulting paper mulberry charcoal material is the paper mulberry branch charcoal material.

[0130] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry twig charcoal material with ferrous sulfate, humic acid, and woody peat in a mass ratio of 1:0.05:0.05:0.08 until homogeneous to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0131] Example 9

[0132] The preparation method of paper mulberry charcoal material is the same as in Example 1, except that the paper mulberry bark is impregnated without adding paper mulberry branch decomposition products. The resulting paper mulberry charcoal material is paper mulberry bark charcoal material.

[0133] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry bark charcoal with ferrous sulfate, humic acid, and woody peat in a mass ratio of 1:0.05:0.05:0.08 until homogeneous to obtain a hybrid mulberry charcoal-based soil heavy metal remediation agent.

[0134] Comparative Example 1 (without steam explosion)

[0135] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0136] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them and peel off the bark. Then dry the peeled hybrid paper mulberry branches in a 60℃ oven and keep the peeled paper mulberry bark for later use.

[0137] The dried hybrid paper mulberry branches are crushed, sieved to obtain 4-mesh paper mulberry wood powder, and then naturally dried to obtain paper mulberry branch powder.

[0138] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 2000 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·s. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0139] The catalytic active center sol was impregnated in a vacuum pressure impregnation machine with the branch powder and bark of paper mulberry. After vacuum negative pressure for 10 minutes at a vacuum degree of 0.98 MPa, it was then held at a positive pressure of 3 MPa for 10 minutes. After that, it was taken out and air-dried. The above impregnation and air-drying were repeated to make the metal loading reach 4 wt%, thus obtaining the paper mulberry loaded material.

[0140] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0141] A mulberry charcoal-based soil heavy metal mineralizer is prepared by mixing mulberry charcoal material with ferrous sulfate, sodium humate, and woody peat in a mass ratio of 1:0.15:0.2:0.3 and stirring evenly to obtain the mulberry charcoal-based soil heavy metal remediation agent.

[0142] Comparative Example 2 (impregnation process using only atmospheric pressure impregnation)

[0143] A method for preparing paper mulberry charcoal material, comprising the following steps:

[0144] After cutting the hybrid paper mulberry branches into 5 cm sections, soak them in water for 2 hours, remove them, peel off the bark, and let the peeled branches air dry naturally. Keep the paper mulberry bark for later use.

[0145] The dried hybrid paper mulberry branches were crushed and sieved to obtain 4-mesh paper mulberry wood powder, thus obtaining paper mulberry branch powder.

[0146] The catalytically active center sol was prepared by the following steps: citric acid, silica sol, and ferrous sulfate were mixed in a molar ratio of 0.2:1:8.8 and dissolved in ethanol solvent. The mixture was dispersed and stirred at high speed at 2000 r / min for 0.5 h. Ammonia solution was added to adjust the pH to 8. After stirring for another 20 min, deionized water was added to adjust the viscosity to 12 mPa·s. The mixture was allowed to stand for 12 h to obtain the catalytically active center sol.

[0147] Paper mulberry branch powder was placed in a steam explosion device and subjected to gas explosion at a steam pressure of 3.0 MPa and a holding time of 240 s to obtain steam-exploded material. The steam-exploded material was placed in a vacuum drying oven and dried at 120℃ for 2 hours before being removed, sealed, and stored for later use.

[0148] The dried vapor explosion product and paper mulberry bark were placed in a catalytically active sol and impregnated at atmospheric pressure for 24 hours. The product was then removed and air-dried. The atmospheric pressure impregnation and air-drying were repeated to achieve a metal loading of 4 wt%, thus obtaining the paper mulberry loaded material.

[0149] The paper mulberry loading material was placed in a tube furnace and carbonized at high temperature under the protection of Ar2 gas. The carbonization conditions were as follows: the initial temperature was 24℃, the temperature was increased to 350℃ at a rate of 5℃ / min, held for 15min, then increased to 600℃ at a rate of 20℃ / min, held for 1h, and then cooled naturally to obtain paper mulberry carbon material.

[0150] A paper mulberry charcoal-based soil heavy metal mineralization agent is prepared by mixing paper mulberry charcoal material with ferrous sulfate, sodium humate and woody peat in a ratio of 1:0.15:0.2:0.3 and stirring evenly to obtain the paper mulberry charcoal-based soil heavy metal remediation agent.

[0151] Comparative Example 3

[0152] Paulownia branches were used to prepare paulownia charcoal material, and the preparation method was the same as in Example 1, resulting in paulownia charcoal material and paulownia carbon-based soil heavy metal remediation agent.

[0153] Comparative Example 4

[0154] Poplar branches were used to prepare poplar charcoal materials, using the same method as in Example 1, to obtain poplar charcoal materials and poplar carbon-based soil heavy metal remediation agents.

[0155] Comparative Example 5

[0156] The preparation method is the same as in Example 1, except that during the high-temperature carbonization process, the initial temperature is 24°C, and the temperature is directly increased to 450°C at a rate of 5°C / min. After holding for 1 hour, the temperature is naturally cooled to obtain the paper mulberry char material.

[0157] Comparative Example 6

[0158] The preparation method is the same as in Example 1, except that during the high-temperature carbonization process, the initial temperature is 24℃, and the temperature is directly increased to 450℃ at a rate of 20℃ / min. After maintaining this temperature for 1 hour, the temperature is allowed to drop naturally to obtain paper mulberry char material and paper mulberry char-based soil heavy metal remediation agent.

[0159] Comparative Example 7

[0160] The preparation method is the same as in Example 1, except that during the high-temperature carbonization process, the initial temperature is 24℃, which is increased to 150℃ at a rate of 5℃ / min, held for 5 minutes, and then increased to 700℃ at a rate of 20℃ / min. This yields mulberry charcoal material and mulberry charcoal-based soil heavy metal remediation agent.

[0161] Comparative Example 8

[0162] The preparation method is the same as in Example 1, except that impregnation is not performed. Paper mulberry charcoal material and paper mulberry charcoal-based soil heavy metal remediation agent were prepared.

[0163] Comparative Example 9

[0164] The preparation method is the same as in Example 1, except that the impregnation solution is an aqueous solution of urea-modified ferrous sulfate, ferrous nitrate, and ferrous chloride. Specifically, the molar concentration of ferrous particles in the impregnation solution is the same as in Example 3. The impregnation solution is prepared by adding urea solution to ferrous ion solution, so that the molar concentration ratio of urea to ferrous ion in the impregnation solution is 0.19:1. This yields paper mulberry charcoal material and paper mulberry carbon-based soil heavy metal remediation agent.

[0165] Comparative Example 10

[0166] The preparation method is the same as in Example 1, except that no modifying solution is added to the impregnation solution. Paper mulberry charcoal material and paper mulberry charcoal-based soil heavy metal remediation agent were prepared.

[0167] Comparative Example 11

[0168] Commercially available heavy metal soil remediation agents.

[0169] Application Example 1

[0170] The fiber lengths of the paper mulberry charcoal materials prepared in Example 8 and Example 9, the paulownia charcoal materials prepared in Comparative Example 3, and the poplar charcoal materials prepared in Comparative Example 4 were observed using scanning electron microscopy. The fiber lengths of the paper mulberry charcoal, paulownia charcoal, and poplar charcoal materials are shown below. Figure 1 As shown, where Figure 1 In Example 9, 'a' represents the fiber length of the paper mulberry bast carbon material. Figure 1 In Example 8, b represents the fiber length of the mulberry tree trunk carbon material. Figure 1 In the figure, 'c' represents the fiber length of the paulownia branch charcoal material. Figure 1 Fiber length of poplar tree branch charcoal material.

[0171] Depend on Figure 1 It can be seen that the phloem fibers of the hybrid paper mulberry are characterized by their slender length, with an average length of 7.45 mm, an average width of 18.86 μm, an aspect ratio of 395, and a fiber coarseness of 14.15 mg / (100 m), making them a high-quality quasi-one-dimensional carbon material. The wood fibers of the hybrid paper mulberry are relatively short, with an average length of 0.58 mm, and the percentage of fine fibers shorter than 0.2 mm is 43.31%. The fiber distribution frequency in the length range of 0.23–0.47 mm is 53.86%.

[0172] Application Example 2

[0173] In cadmium (Cd) contaminated soil (acid-soluble, reducible, oxidizable, and residual states: 28.12%, 16.52%, 8.93%, and 46.43%, respectively), the cadmium (Cd) content in the soil was 53 mg / kg. Passivation experiments were conducted by adding the soil remediation agents from Examples 1-9 and Comparative Examples 1-11 to the cadmium (Cd) contaminated soil, with an addition amount of 50 g of soil remediation agent per kilogram of soil. Soil samples were collected 90 days later. Cd was completely extracted from the samples using a hydrochloric acid-nitric acid-hydrofluoric acid-perchloric acid digestion method. Flame atomic absorption spectrometry was used at a wavelength of 228.8 nm, a slit of 0.70 nm, a lead lamp current of 8 mA, a negative voltage of 300 V, a carrier gas flow rate of 250 mL / min, and an air-acetylene flame. The instrument was zeroed with water, and 20 μL of sample was injected. The absorbance of cadmium was measured, and the absorbance of the accompanying blank solution was subtracted. The corresponding cadmium concentration was determined from the standard curve. The blank experiment was conducted on soil without any added soil remediation agent. The test results are shown in Table 1 and... Figure 2 As shown.

[0174] Table 1. Changes in the speciation and content of cadmium (Cd) in soil after 90 days of treatment with soil remediation agents prepared in Examples 1-7 and Comparative Examples 1-11.

[0175]

[0176]

[0177] From Table 1 and Figure 2 It was found that, compared with the blank experiment, all remediation agents altered the speciation of heavy metal ions in the soil. Steam explosion treatment, active sol impregnation, carbonization temperature control, and nitrogen-containing substance modification all had a beneficial effect on the experiment. Furthermore, the fiber length of the carbon source materials (mulberry branches, paulownia, poplar, and hybrid mulberry bark) was also an important factor affecting the heavy metal mineralization effect. Figure 1 It can be seen that the fiber length of several carbon source materials is greater than that of paper mulberry bark (a) > paper mulberry branches (b) > poplar branches (d) > paulownia branches (c). The heavy metal mineralization effect is greater in Example 9 (paper mulberry bark) than in Example 8 (paper mulberry bark + paper mulberry branches) > in Examples 1-7 (paper mulberry branches) > in Comparative Example 4 (poplar branches) > in Comparative Example 3 (paulownia branches). The overall heavy metal mineralization effect of all examples of this invention is better than that of the commercially available heavy metal soil remediation agent in Comparative Example 11.

[0178] In the comparison of Example 1 and Comparative Examples 5 and 6, it was found that, in the high-temperature carbonization stage, low-speed heating is more effective for the modification of heavy metals by mulberry charcoal materials for soil remediation than high-speed heating. The high-temperature carbonization method of the present invention, which first heats at a low speed and then at a high speed, can more effectively improve the remediation effect of mulberry charcoal materials on heavy metals in soil. This is because if the heating rate is too low, it is not conducive to the volatilization of tar produced by mulberry powder, which will block the pores of the charcoal material and affect its adsorption; while if the heating rate is too high, it will cause the nitrogen-containing modification solution to decompose and oxidize too quickly, which is not conducive to its entry into the carbon skeleton and affects the doping effect.

[0179] As can be seen from Example 1 and Comparative Example 7, in the high-temperature carbonization process of the present invention, the higher the temperature, the better the modification effect of the mulberry charcoal material on soil heavy metals. Excessive temperature will increase the graphitization degree of the charcoal material, which is not conducive to the adsorption of heavy metals.

[0180] Comparing Example 1 and Comparative Example 8, it was found that the simulated breathing vacuum pressure impregnation process during the preparation of paper mulberry char material significantly improved the effect of paper mulberry char material in repairing heavy metals. This is because the simulated breathing vacuum pressure impregnation can remove the gas adsorbed inside the porous structure of hybrid paper mulberry powder, which is conducive to the entry of metal ions into the cell cavity of hybrid paper mulberry and their alternating diffusion, so that the metal ions are evenly distributed and finally evenly embedded in the biomass skeleton of hybrid paper mulberry powder. They are not easy to fall off during carbonization, thus improving the reduction effect of the repair agent.

[0181] Comparing Example 1 and Comparative Example 9, it can be seen that the catalytic active center sol of the present invention can significantly improve the remediation capacity of mulberry charcoal materials for heavy metals compared with conventional heavy metal soil remediation agents. This is because the catalytic active center sol can effectively solve the problems of existing loaded coatings such as clogging micropores, easy cracking, and further reducing metal ion shedding.

[0182] The comparison between Example 1 and Comparative Example 10 shows that adding a modified solution during the impregnation process can significantly improve the ability of mulberry charcoal to repair heavy metals. This is because the addition of nitrogen-containing modified solution will cause nitrogen doping to form in the carbon material during carbonization. In nitrogen-doped carbon material, the carbon atoms adjacent to N heteroatoms have a high positive charge density. At the same time, there is a conjugation effect between the lone pair electrons of N atoms and the large π bonds of carbon atom lattice. This makes nitrogen-doped carbon material exhibit excellent catalytic performance.

[0183] Application Example 3

[0184] An experiment on the enrichment of maize plants in cadmium (Cd) contaminated soil.

[0185] Five whole maize plants were randomly collected from farmland with Cd-contaminated soil (acid-soluble, reducible, oxidizable, and residual states were 28.12%, 16.52%, 8.93%, and 46.43%, respectively) and soils treated with heavy metal remediation agents in Examples 1-9 and Comparative Examples 1-11. The plants were cut into sections, washed three times with deionized water, placed in an oven, blanched at 105°C for 30 minutes, and then dried at 65°C to constant weight. After pulverizing the sample using a grinder, take 0.5g of the pulverized sample and place it in an Erlenmeyer flask. Add 8mL of mixed acid (nitric acid to perchloric acid solution volume ratio of 3:1). Let it stand overnight, then digest at 110℃ on a hot plate for 1h, 170℃ for 30min, and finally at 210℃ to completely digest the sample. Rinse the sample with 10mL of deionized water along the flask wall. Remove the acid at 140℃ until about 3mL of solution remains. Repeat this process three times until the acid removal is complete. Dilute to volume in a 25mL volumetric flask, filter, and determine the Cd content in the filtrate using graphite furnace atomic absorption spectrophotometry. The blank experiment consisted of corn plants grown in soil without added soil remediation agents. The results are shown in Table 2 below.

[0186] Table 2. Results of enrichment test of maize plants in cadmium (Cd) contaminated soil, unit: mg / kg

[0187] Cd enrichment content Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Blank experiment 2.8 2.8 2.7 2.9 2.6 Example 1 1.3 1.2 1.2 1.1 1.2 Example 2 1.1 1 1.1 1.2 1 Example 3 1 0.9 1 0.9 0.9 Example 4 1.2 1.1 1.2 1 1.2 Example 5 1.1 1.2 1.3 1.2 1.4 Example 6 1 1.1 1.1 1.3 1.2 Example 7 1.3 1.2 1.1 1.3 1.3 Example 8 0.9 1 0.9 0.9 1.0 Example 9 0.8 0.7 0.7 0.6 0.8 Comparative Example 1 1.7 1.6 1.7 1.8 1.6 Comparative Example 2 1.8 1.8 1.8 1.7 1.8 Comparative Example 3 1.8 1.7 1.9 1.6 1.7 Comparative Example 4 1.6 1.5 1.6 1.7 1.5 Comparative Example 5 1.4 1.5 1.6 1.6 1.5 Comparative Example 6 1.7 1.6 1.6 1.7 1.8 Comparative Example 7 1.5 1.6 1.5 1.4 1.5 Comparative Example 8 1.9 1.8 1.9 1.8 2.0 Comparative Example 9 1.7 1.8 1.6 1.7 1.8 Comparative Example 10 1.6 1.7 1.7 1.6 1.7 Comparative Example 11 2.2 1.3 2.2 2.4 2.5

[0188] As shown in Table 2, all the remediation agents can effectively prevent the migration of heavy metal ions from the soil to the plants. The soil heavy metal remediation agents improved in Examples 1-7 of this invention have better prevention effects than those in Comparative Examples 1-11. A comparison between Examples 1-9 and Comparative Example 11 shows that the soil heavy metal remediation agents provided by this invention can significantly reduce Cd accumulation in maize plants compared to commercially available soil heavy metal remediation agents.

[0189] In summary, the paper mulberry char material prepared by the method of this invention is lightweight and porous with abundant surface groups, exhibiting good adsorption capacity for various heavy metals. It can efficiently remediate soil contaminated with heavy metals while significantly reducing the leaching toxicity of plants.

[0190] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A mulberry charcoal-based soil heavy metal mineralizer, characterized in that, The product comprises the following components by weight: 1 part of paper mulberry charcoal, 0.05-0.15 parts of passivating agent, 0.05-0.2 parts of humic acid, and 0.08-0.3 parts of woody peat; wherein the passivating agent is one or more of ferrous sulfate, potassium carbonate, and hydroxyapatite; The preparation method of the paper mulberry charcoal material includes the following steps: A paper mulberry branch and / or paper mulberry bark are impregnated with a reducing slurry to obtain a paper mulberry loaded material; the reducing slurry includes a catalytically active sol; the catalytically active sol includes the following components: a nonionic surfactant, silica sol, ferrous sulfate, and a modifying solution; the modifying solution is one or more of triethylamine, ethylenediamine, ethylamine, urea, and ammonia water; The paper mulberry support material is carbonized at high temperature to obtain paper mulberry carbon material; The high-temperature carbonization method includes variable-temperature carbonization; The variable-temperature carbonization starts at 24°C, increases to 150°C–350°C at a rate of 3–5°C / min, is kept at a constant temperature for 5–15 min, then increases to 450°C–600°C at a rate of 18–22°C / min, is kept at a constant temperature for 1 h, and then cools down naturally.

2. The paper mulberry carbon-based soil heavy metal mineralizer according to claim 1, characterized in that, The impregnation process includes a vacuum negative pressure stage and a positive pressure holding stage; The vacuum degree during the vacuum negative pressure stage is 0.075–0.085 MPa; the duration of the vacuum negative pressure stage is 10–15 min. The pressure during the positive pressure holding phase is 1–3 MPa; the positive pressure holding time is 5–10 min.

3. The paper mulberry carbon-based soil heavy metal mineralizer according to claim 2, characterized in that, The metal loading of the impregnated paper mulberry loaded material is 2–12 wt.%.

4. The paper mulberry carbon-based soil heavy metal mineralizer according to claim 1, characterized in that, The steam pressure for the steam explosion is 1.0–3.0 MPa; the pressure holding time for the steam explosion is 30–240 s.

5. The application of the mulberry charcoal-based soil heavy metal mineralizer according to any one of claims 1 to 4 in soil remediation.

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