CN116673031A

CN116673031A - Broussonetia papyrifera biochar, preparation method thereof, and Broussonetia papyrifera charcoal-based soil heavy metal mineralizer and application thereof

Info

Publication number: CN116673031A
Application number: CN202310636909.5A
Authority: CN
Inventors: 聂宁; 王品胜; 梁博; 高正龙; 陈红; 肖进彬
Original assignee: Henan Hi Tech Industry Co ltd; Henan Academy of Sciences
Current assignee: Henan Hi Tech Industry Co ltd; Henan Academy of Sciences
Priority date: 2023-06-01
Filing date: 2023-06-01
Publication date: 2023-09-01

Abstract

The invention provides a paper mulberry charcoal material and a preparation method thereof, and a paper mulberry charcoal-based soil heavy metal mineralizer and application thereof, belonging to the technical field of soil remediation. The preparation method of the paper mulberry carbon material can effectively change the compact structure of paper mulberry materials in a short time by utilizing the steam explosion technology; the internal porosity and the specific surface area of the paper mulberry fiber are greatly increased after high-temperature carbonization, the surface functional groups are enriched, and the efficiency of adsorbing heavy metal ions by the carbon material is improved; the paper mulberry carbon material is impregnated with the reducing slurry, so that the prepared paper mulberry carbon material can reduce high-valence heavy metals in soil to low-valence heavy metals with low toxicity, and the harm effect of the heavy metals on the soil is reduced. The paper mulberry carbon material prepared by the method is light and porous, has rich surface groups, has good adsorption capacity on various heavy metals, can efficiently repair heavy metal polluted soil, and simultaneously remarkably reduces leaching toxicity of plants.

Description

Broussonetia papyrifera biochar, preparation method thereof, and Broussonetia papyrifera charcoal-based soil heavy metal mineralizer and application thereof

Technical Field

The invention belongs to the technical field of soil remediation, and particularly relates to a paper mulberry carbon material, a preparation method thereof, a paper mulberry carbon-based soil heavy metal mineralizer and application thereof.

Background

Soil is an important environmental medium for plant growth and is also an important place for microorganisms to inhabit, and the primary link for determining the safety of grains, vegetables, oil and melons and fruits is a civil problem about food safety. With the rapid development of industry and agriculture, the heavy metal pollution of soil is more serious. The long-term accumulation of heavy metals in the soil will change the function of the agricultural soil and seriously affect the quality of the crops, ultimately affecting the physical health of humans through the food chain. However, how to repair heavy metal pollution of farmland soil and ensure safe production of grain crops is an unprecedented task in the current soil and environment fields.

At present, the remediation of heavy metal pollution in soil is mainly realized by transferring or passivating heavy metal through physical, chemical and biological methods, so that the migration of the heavy metal to target plants is limited. The chemical occurrence form of heavy metals in soil is changed by adding exogenous passivation materials into the adsorption substrate, so that the method is one of effective, economical and practical means for rapidly and efficiently reducing ecological risks of the soil.

Biomass charcoal is used as a novel soil ecological restoration material, which is widely paid attention to by environmental workers, biomass charcoal is used as an adsorption base material, and single components or composite passivation materials such as clay minerals, fly ash, phosphorus-based fertilizers, humic acid, metal oxides and the like are added to restore heavy metal contaminated soil, but the effect is not ideal all the time, and the main reasons are as follows: 1. the biomass charcoal material obtained by simple biomass carbonization treatment has low adsorption capacity, and the stability and durability of the repairing effect are not ideal; 2. the inorganic passivating agent has low nutrient content, so that organic matters in farmland soil are insufficient, and the soil quality is low; and the biocompatibility is poor, and secondary pollution is easy to cause. Therefore, the development of economic, efficient, green and environment-friendly soil heavy metal restoration agents, the improvement of restoration effect and the maintenance of soil fertilizer efficiency become one of the problems to be solved in the field.

Disclosure of Invention

The invention aims to provide a preparation method of a paper mulberry carbon material, which can comprehensively utilize paper mulberry resources and repair heavy metal polluted soil.

In order to solve the technical problems, the invention provides the following technical scheme:

the invention provides a preparation method of a paper mulberry charcoal material, which comprises the following steps:

Dipping the dry steam explosion products of the paper mulberry branches and/or paper mulberry bark by adopting reducing slurry to obtain a paper mulberry load material;

and (3) carbonizing the paper mulberry load material at high temperature to obtain the paper mulberry carbon material.

Preferably, the reducing slurry comprises a catalytically active centre sol; the catalytically active center sol comprises the following components:

nonionic surfactant, silica sol and ferrous sulfate.

Preferably, the catalytically active core sol further comprises a modifying solution; the modifying solution comprises one or more of triethylamine, ethylenediamine, ethylamine, urea and ammonia water.

Preferably, the impregnation comprises a vacuum negative pressure stage and a positive pressure maintenance stage;

the vacuum degree of the vacuum negative pressure stage is 0.065-0.98 MPa; the time of the vacuum negative pressure is 10-15 min;

the pressure in the positive pressure maintaining stage is 1-3 MPa; the positive pressure is maintained for 5-10 min.

Preferably, the number of times of impregnation is 2; the metal loading of the impregnated paper mulberry loading material is 2-12 wt.%.

Preferably, the high-temperature carbonization mode is variable-temperature carbonization; the initial temperature of the variable-temperature carbonization is 24 ℃, the temperature rises to 150-350 ℃ at the speed of 3-5 ℃/min, the constant temperature treatment is carried out for 5-15 min, the temperature rises to 450-600 ℃ at the speed of 18-22 ℃/min, the constant temperature treatment is carried out for 1h, and the temperature is naturally reduced.

Preferably, the steam pressure of the steam explosion is 1.0-3.0 MPa; the dwell time of the steam explosion is 30-240 s.

The invention also provides the paper mulberry charcoal material prepared by the preparation method.

The invention also provides a paper mulberry charcoal-based soil heavy metal mineralizer, which comprises the following components in parts by mass: the paper mulberry charcoal material comprises 1 part of paper mulberry charcoal material, 0.05-0.15 part of passivating agent, 0.05-0.2 part of humic acid and 0.08-0.3 part of woody peat.

The invention also provides application of the paper mulberry charcoal material according to the technical scheme or the paper mulberry charcoal-based soil heavy metal mineralizer according to the technical scheme in soil remediation.

The invention has the beneficial effects that:

the invention provides a preparation method of a paper mulberry charcoal material, which comprises the following steps: dipping the dry steam explosion products of the paper mulberry branches and/or paper mulberry bark by adopting reducing slurry to obtain a paper mulberry load material; and (3) carbonizing the paper mulberry load material at high temperature to obtain the paper mulberry carbon material. The preparation method of the paper mulberry carbon material can effectively change the compact structure of paper mulberry materials in a short time by utilizing the steam explosion technology, and the fiber quality is further improved; the internal porosity and the specific surface area of the paper mulberry fiber are greatly increased after high-temperature carbonization, the surface functional groups are enriched, and the efficiency of adsorbing heavy metal ions by the carbon material is improved; the paper mulberry carbon material is impregnated with the reducing slurry, so that the prepared paper mulberry carbon material can reduce high-valence heavy metals in soil to low-valence heavy metals with low toxicity, and the harm effect of the heavy metals on the soil is reduced. The paper mulberry carbon material prepared by the preparation method disclosed by the invention is light and porous, has abundant surface groups, has good adsorption capacity on various heavy metals, can efficiently repair heavy metal polluted soil, and simultaneously remarkably reduces leaching toxicity of plants. The preparation method of the paper mulberry carbon material has mature process equipment, is suitable for large-scale industrial production, is easy to realize engineering application, has low agricultural application difficulty, has no toxic effect on farmland soil environment and has good ecological environmental benefit.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a fiber length comparison of paper mulberry bark carbon material, paper mulberry carbon material, paulownia carbon material and poplar carbon material.

FIG. 2 shows the changes in the form and content of Cd in the soil after the soil 90d is treated with the soil restoration agents prepared in examples 1 to 9 and comparative examples 1 to 11;

FIG. 3 is an electron micrograph of the paper mulberry carbon material prepared in example 3.

Detailed Description

The method adopts the reductive slurry to impregnate the steam explosion products of the paper mulberry trunk and/or the paper mulberry bark, thus obtaining the paper mulberry load material.

The invention preferably carries out steam explosion on the dry powder of the branches to obtain a steam explosion product of the branches.

In the invention, the dry paper mulberry branch powder is preferably obtained by crushing paper mulberry branch. The branches are preferably hybrid branches, more preferably the branches of hybrid branches after peeling. The present invention preferably cuts and soaks the hybrid branches prior to decortication of the branches. The cutting mode preferably comprises the following steps: cutting the branches of the paper mulberry into equal-length small sections; the length of the small segments is preferably 3 to 8 cm, more preferably 5 cm. After the branches of the structure are cut into small sections, the present invention preferably soaks the sections of the branches of the structure. The soaking time is preferably 0.5 to 3 hours, more preferably 2 hours. The soaking according to the invention is preferably performed in water. The invention cuts and soaks the branches of the paper mulberry, which is beneficial to peeling the branches of the paper mulberry. The method for peeling the branches of the paper mulberry is not particularly limited, and the conventional branch peeling method in the field is adopted. After the branches of the paper mulberry are peeled, the invention preferably dries the peeled branches of the paper mulberry. The drying mode is not particularly limited, and a conventional drying mode in the field can be adopted. The embodiment of the invention can adopt oven drying or natural drying. When oven drying is employed, the temperature of the drying is preferably 50 ℃ to 80 ℃, more preferably 60 ℃. The drying is preferably carried out until the moisture content of the branches is 15% -20%. After the dry paper mulberry branch is dried, the dried paper mulberry branch is preferably crushed to obtain the dry paper mulberry branch powder. The method for crushing the branches of the structure is not particularly limited, and the conventional crushing method of the branches in the field can be adopted. The method is preferably to screen the dry powder of the branches to obtain the wood powder, namely the dry powder of the branches. The pore diameter of the sieve is preferably 4 to 100 mesh, more preferably 30 to 80 mesh, and even more preferably 50 to 60 mesh. The method is mainly beneficial to nitrogen doping and metal ion loading in the subsequent preparation process of the paper mulberry carbon material. The present invention preferably pulverizes the tree branches before the steam explosion is performed because the pulverizing after the steam explosion changes the surface properties of the raw materials, thereby adversely affecting the performance of the paper mulberry charcoal material.

After the dry powder of the branches is obtained, the invention carries out steam explosion on the dry powder of the branches. In the present invention, the steam pressure of the steam explosion is preferably 1.0 to 3.0MPa, more preferably 1.0 to 2.5MPa, still more preferably 1.5 to 2.3MPa, and still more preferably 1.5 to 2.0MPa; the dwell time of the steam explosion is 30 to 240s, more preferably 50 to 220s, still more preferably 80 to 200s, still more preferably 100 to 150s. In the present invention, the steam explosion is mainly to degrade hemicellulose of biomass raw materials. The steam explosion is preferably carried out in steam explosion equipment, and the steam explosion equipment in the embodiment of the invention is QBS-80 steam explosion experiment table produced by Henan crane wall standard heavy machinery factory. The steam explosion product is obtained, and the steam explosion product is preferably dried. The drying is preferably carried out under vacuum; the drying temperature is preferably 80 to 120 ℃, more preferably 90 to 110 ℃, and even more preferably 95 to 100 ℃; the drying time is preferably 2 to 4 hours, more preferably 3 hours. The drying according to the invention is preferably carried out in a vacuum drying oven. The invention preferably seals the steam explosion product for standby after drying.

The invention utilizes steam explosion to process the hybrid broussonetia papyrifera, the processed raw material structure is broken up, the bast fibers irregularly embedded in the wood plug tissue and the parenchyma cell group in the form of fiber bundles are released, the area of an amorphous area is greatly increased, fragments are formed into tiny particles or filaries, lignin is softened, the fiber structure is no longer compact, irregular tearing occurs, the surface is in a wrinkled honeycomb shape as shown in figure 3, the specific surface area is greatly increased, and the surface functional groups are further enriched.

After the paper mulberry branch steam explosion product is obtained, the paper mulberry branch steam explosion product and/or paper mulberry bark is impregnated with the reducing slurry to obtain the paper mulberry load material.

In the present invention, paper mulberry bark may be directly impregnated; the steam explosion products of the structural branches can be directly immersed; the paper mulberry branch dry steam explosion product and paper mulberry bark can be impregnated together.

In the present invention, the reducing slurry is preferably a catalytically active center sol; the catalytically active center sol preferably comprises a nonionic surfactant, a silica sol and ferrous sulfate. The molar ratio of the nonionic surfactant, the silica sol and the ferrous sulfate in the catalytic active center sol 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, still more preferably (0.15-0.2): 0.5-1): 8. In the present invention, the nonionic surfactant is preferably one or more of citric acid, lactic acid and pyroligneous acid. In the invention, the nonionic surfactant has the functions of better dispersing silica sol and ferrous ions, reducing the surface tension of the sol, enabling the ferrous ions to be uniformly distributed on the paper mulberry powder, and having good stability, larger specific surface area, uniform pore size distribution and higher mechanical strength of the obtained coating; the silica sol is used as a binder to firmly anchor metal ions on biomass, and can generate lamellar isolation effect on biomass carbon after subsequent pyrolysis to prevent metal ions from agglomerating to influence activity; the ferrous sulfate is used as a metal reduction center of the reducing slurry, provides transition electrons for reducing high-valence heavy metals, can effectively improve the pH value of soil, reduces the pH value of the soil, and can promote the synthesis of plant chlorophyll. In the present invention, the catalytically active center sol preferably uses ethanol as a solvent. In the present invention, the catalytically active center sol preferably further comprises a modifying solution; the modifying solution is preferably one or more of triethylamine, ethylenediamine, ethylamine, urea and ammonia water. The modifying solution mainly adjusts the pH value of the catalytic active center sol and alkaline modifies the catalytic active center sol.

The preparation method of the catalytic active center sol preferably comprises the following steps: mixing a nonionic surfactant, silica sol and ferrous sulfate, and then dissolving the mixture in an ethanol solvent to obtain a mixed solution; adding the modified solution into the mixed solution to obtain an alkaline mixed solution; and (3) regulating the viscosity of the alkaline mixed solution, and standing to obtain the catalytic active center sol.

The invention mixes the nonionic surfactant, the silica sol and the ferrous sulfate and then dissolves the mixture in the ethanol solvent, and then preferably carries out high-speed stirring; the rotation speed of the high-speed stirring is preferably 1500-2000 rpm, more preferably 1600-1800 rpm, and even more preferably 1700rpm; the time for the high-speed stirring is preferably 0.5 to 3 hours, more preferably 1 to 2.5 hours, and still more preferably 1.5 to 2 hours. In the invention, the high-speed stirring mainly ensures that solutes are fully and uniformly mixed in a solvent.

After the mixed solution is obtained, the modified solution is preferably added to the mixed solution to obtain an alkaline mixed solution. In the present invention, after the modified solution is added to the mixed solution, high-speed stirring is preferably performed. The rotation speed of the high-speed stirring is preferably 1500-2000 rpm, more preferably 1600-1800 rpm, and even more preferably 1700rpm; the high-speed stirring time is 20min. In the present invention, the pH of the alkaline mixed solution is preferably 7.5 to 9, more preferably 8 to 8.5. After the alkaline mixed solution is obtained, the invention preferably adjusts the viscosity of the alkaline mixed solution and then stands to obtain the catalytic active center sol. In the present invention, the viscosity of the catalytically active center sol is preferably 5 to 12 mPas, more preferably 7 mPas. The method for adjusting the viscosity of the alkaline solution is preferably evaporation concentration or deionized water addition. Evaporating and concentrating when the viscosity of the alkaline mixed solution is lower than 5-12 mPa.S; and adding deionized water when the viscosity is higher than 5-12 mPa.S. In the present invention, the time for the standing is preferably 6 to 12 hours, more preferably 7 to 10 hours, and still more preferably 8 hours. The invention can obtain more stable catalytic active center sol by standing.

In the invention, the catalytic active center sol is used as reduction center slurry to mainly load ferrous salt on biomass raw materials, and is a key for determining the price reduction performance of the broussonetia papyrifera carbon material on high-valence heavy metals. The concentration, viscosity, pH and/or preparation method of the materials of the catalytic active center sol can greatly influence the internal structure and physical and chemical properties of the paper mulberry carbon-based adsorption substrate, and the determined specific surface area and the bonding strength of the reduction center and the carrier can further influence the reactivity of the paper mulberry carbon material.

In the present invention, the impregnation preferably includes a vacuum negative pressure stage and a positive pressure maintenance 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 time of the vacuum negative pressure is preferably 10 to 15min, more preferably 12 to 14min, and even more preferably 13min; the pressure in the positive pressure maintaining stage is preferably 1 to 3MPa, more preferably 2MPa; the positive pressure is maintained for a period of time of preferably 5 to 10 minutes, more preferably 7 to 9 minutes, and still more preferably 8 minutes. The impregnation process of the invention combines vacuum negative pressure and positive pressure to improve the wettability of the high-viscosity catalytic active center sol on the surface of the biomass, thereby achieving corresponding metal loading. After the positive pressure maintenance stage is completed, the product is preferably dried, preferably by air drying, more preferably by natural air drying. The impregnation product is preferably repeatedly impregnated and dried after being dried, so that the metal loading capacity of the paper mulberry loading material reaches the corresponding standard. The metal loading of the paper mulberry loading material obtained by impregnation is preferably 2-12 wt.%, more preferably 2.5-4 wt.%, and even more preferably 3wt.%. In the invention, the metal loading is calculated according to the adding amount of ferrous sulfate, and then the ratio of the mass of the iron element to the mass of the total material after drying is calculated, namely the metal loading. The impregnation according to the invention is preferably carried out in a breath-imitating vacuum pressure impregnator. The method adopts a mode of combining pressure impregnation and vacuum impregnation, and is beneficial to improving the wettability of the high-viscosity sol on the biomass material.

After the steam explosion product is obtained, the biological raw material is subjected to bionic breathing impregnation by adopting the alkaline modified catalytic active center sol, so that the gas adsorbed in the porous material pore canal is removed, the metal ions to be impregnated can enter the pore canal, the problems of micropore blockage and easy falling off of carbonization of a load coating can be effectively solved, and particularly, the addition of triethylamine, ethylenediamine, ethylamine, urea and ammonia water can enable the biomass raw material to form a pyridine carbon catalytic active center during carbonization, and the effect of promoting reduction of high-valence heavy metals can be achieved.

After the paper mulberry load material is obtained, the paper mulberry load material is carbonized at high temperature to obtain the paper mulberry carbon material.

In the present invention, the high-temperature carbonization is preferably temperature-variable carbonization. The initiation temperature of the variable temperature carbonization is preferably 24 ℃. The variable-temperature carbonization preferably comprises 2 heating stages, namely a first heating stage and a second heating stage. The temperature in the first temperature increasing step is preferably increased at 3 to 5 ℃/min, more preferably at 4 ℃/min. The first temperature-increasing stage is preferably increased to 150 ℃ to 350 ℃, more preferably 180 ℃ to 330 ℃, still more preferably 200 ℃ to 300 ℃, most preferably 250 ℃. After the first temperature raising stage is completed, the temperature is kept at a constant temperature for preferably 5 to 15 minutes, more preferably 8 to 12 minutes, and still more preferably 10 minutes. After the constant temperature treatment, the present invention preferably performs a second temperature rising stage. The temperature in the second temperature increasing step is preferably increased at 18 to 22 ℃/min, more preferably at 20 ℃/min. The second temperature-raising stage is preferably raised to 450 to 600 ℃, more preferably 480 to 580 ℃, still more preferably 500 to 550 ℃, and most preferably 520 ℃. After the second temperature rising stage is completed, the temperature is preferably kept at a constant temperature for 1h and then reduced. The cooling is preferably natural cooling. In the present invention, the high-temperature carbonization is preferably performed under the protection of inert gas; the inert gas is preferably argon or nitrogen. The high temperature carbonization according to the invention is preferably carried out in a tube furnace.

Carbonization temperature is the key to influence the performance of the carbon material, low temperature is unfavorable for complete carbonization, high temperature leads to high graphitization degree and activity is reduced. The carbonization temperature is low and high, which is unfavorable for the adsorption of heavy metal ions. The carbonization temperature adopted by the invention is favorable for completely carbonizing the paper mulberry material, and simultaneously, the graphitization degree of the carbon material can be reduced. The variable-temperature high-temperature carbonization adopts two variable-temperature rates, which is beneficial to the formation of more frame defects of carbon bones and the promotion of the formation of the catalytic activity of carbon materials. The temperature rising rate adopted by the invention is beneficial to preventing N-doped molecules from volatilizing too fast due to the too high temperature rising rate, and the N-doped molecules cannot participate in the formation of a carbon skeleton well.

The invention generates high-temperature carbonization and nitrogen doping reaction in the high-temperature carbonization process. The high-temperature carbonization greatly increases the internal porosity and specific surface area of the paper mulberry fiber, enriches the surface functional groups and improves the efficiency of the carbon material in adsorbing heavy metal ions. In the nitrogen doping reaction, nitrogen element participates in the formation of a carbon skeleton; in the process of biomass pyrolysis, long carbon chains of biological macromolecules are subjected to processes such as fracture, rearrangement and the like, and exogenous nitrogen atoms which are taken as urea, triethylamine, ethylenediamine, ethylamine, ammonia water or other N-containing molecules are doped into a carbon atom framework to form nitrogen atoms in different bonding states such as graphite nitrogen, pyrrole nitrogen, pyridine nitrogen and the like, so that the graphitization degree of the biochar is reduced. The method can improve the reduction capability of biomass charcoal to high-valence heavy metals through nitrogen doping reaction of the paper mulberry material.

In the preparation method of the paper mulberry carbon material provided by the invention, the hybrid paper mulberry is selected as a biomass carbon source because the phloem fiber characteristics of the hybrid paper mulberry are that the fiber is slender, the average length is 7.45mm, the average width is 18.86 mu m, the length-width ratio is 395, the fiber thickness is 14.15 mg/(100 m), and the paper mulberry carbon material is a high-quality quasi-one-dimensional carbon material and has a unusual expression in catalyzing high-valence heavy metal reduction after N doping. The hybrid tree mass part fiber is short, the average length is 0.58mm, the fine fiber percentage content is 43.31% below 0.2mm, and the fiber distribution frequency is 53.86% in the length range of 0.23-0.47 mm. The average length of the fiber is lower than that of common broad-leaved wood, and the structure has higher porosity and rich activity of surface oxygen-containing functional groups in carbonized biomass carbon, and promotes deprotonation and amorphous conversion of the material, thereby increasing coordination combination of biochar on heavy metals. The phloem fiber and the xylem fiber of the hybrid broussonetia papyrifera complement each other, and the hybrid broussonetia papyrifera shows excellent effects on the application of reducing the price and passivating the heavy metals in soil.

The invention also provides the paper mulberry charcoal material prepared by the preparation method. In the invention, the paper mulberry carbon material has the characteristics of light weight, multiple pores, large specific surface area and rich surface groups.

The invention also provides a paper mulberry charcoal-based soil heavy metal mineralizer, which comprises the following components in parts by mass: according to the technical scheme, 1 part of paper mulberry carbon material, 0.05-0.15 part of passivating agent, 0.05-0.2 part of humic acid and 0.08-0.3 part of woody peat are adopted.

The paper mulberry charcoal-based soil heavy metal mineralizer comprises 0.05-0.15 part of passivating agent, preferably 0.1-0.15 part, and more preferably 0.15 part by mass of paper mulberry charcoal material. The passivating agent is preferably one or more of ferrous sulfate, potassium carbonate and hydroxyapatite.

The paper mulberry charcoal-based soil heavy metal mineralizer comprises 0.05-0.2 part of humic acid, preferably 0.1-0.2 part of humic acid, and more preferably 0.2 part of humic acid by taking the mass parts of paper mulberry charcoal material as a reference. The humic acid not only can promote the formation of granular structures in soil, improve the effectiveness of nitrogen, phosphorus and potassium in alkaline soil and improve the physicochemical and biochemical properties of soil, but also can enhance the disease resistance, drought resistance and lodging resistance of crops and improve the quality of crops.

The paper mulberry charcoal-based soil heavy metal mineralizer comprises, by mass, 0.08-0.3 part of woody peat, preferably 0.2-0.3 part of woody peat, and more preferably 0.3 part of paper mulberry charcoal material. The woody peat is a non-degradable and stable organic matter accumulation layer formed by long-term accumulation of woody plant residues in a marsh environment with excessive moisture, poor ventilation and low air temperature, and is rich in organic matters, so that the growth and development of crop roots and overground parts can be promoted, the crop yield can be improved, the quality index of agricultural products can be improved, the stress resistance and the pest resistance of crops can be improved, the ecological environment of soil can be improved, the organic matters and the nutrient content in the soil can be increased, and the soil fertility can be improved. In the present example, the woody peat was purchased from Shijia Bei Nong mineral products Inc.

The source of the above-mentioned raw materials is not particularly limited, and commercially available products known to those skilled in the art may be used in the present invention unless otherwise specified.

The invention also provides application of the paper mulberry carbon material and/or paper mulberry carbon-based soil heavy metal mineralizer in soil restoration.

The remediation of soil according to the present invention preferably includes improving heavy metal contamination of the soil.

The paper mulberry carbon material and/or paper mulberry carbon-based soil heavy metal mineralizer of the invention can be used for passivating soil heavy metals, and the passivating mode is preferably that the heavy metals in the soil exist in the form of carbonate, sulfate or phosphate precipitation. The heavy metal exists in the form of carbonate, sulfate or phosphate, and the formed heavy metal compound has the effects of good chemical stability, difficult re-dissolution and difficult absorption by crops. The passivation rate of the paper mulberry carbon material and/or paper mulberry carbon-based soil heavy metal mineralizer provided by the invention on Pb, cd or Cr and the like in soil can reach more than 75%, wherein the passivation rate of Cd exceeds 90%.

The remediation of soil according to the present invention preferably comprises reduction of soil heavy metals. The reduction of soil heavy metals preferably includes reduction of high valence cadmium ions. The paper mulberry carbon material and/or paper mulberry carbon-based soil heavy metal mineralizer can reduce hexavalent cadmium to trivalent cadmium, reduce the toxicity of heavy metal ions, and specifically comprises the following components: in the structure of the paper mulberry carbon material, ferrous ions are on the active center containing pyridine nitrogen, and can reduce high-valence heavy metal particles into low-valence heavy metal ions with low toxicity.

The restoration of soil according to the invention preferably further comprises reducing phytotoxicity. The paper mulberry carbon material and/or paper mulberry carbon-based soil heavy metal mineralizer can reduce the heavy metal enrichment of plants by 54% -69%, and remarkably reduce the leaching toxicity of the plants.

The soil restoration method preferably further comprises the steps of improving soil nutrients and promoting plant growth.

The invention has the beneficial effects that:

the main material of the invention is biomass raw materials discarded by agriculture and forestry, which not only can solve the environmental problem, but also can recycle the waste, does not produce secondary pollution, and is safe and reliable; the invention can effectively change the compact structure of the paper mulberry material in a short time by utilizing the steam explosion technology, further improves the fiber quality, greatly increases the internal porosity and the specific surface area after carbonization, enriches the surface functional groups and improves the efficiency of adsorbing heavy metal ions by the carbon material; the soil passivation material prepared by the invention is light and porous, has abundant surface groups, has passivation rate of more than 75 percent on Pb, cd, cr and the like in soil, wherein the passivation rate of Cr exceeds 90 percent, the heavy metal enrichment of plants is reduced by 54 to 69 percent, the leaching toxicity of the plants is obviously reduced, and the remediation effect on heavy metal contaminated soil is good; the invention ensures that heavy metals in the soil exist in the form of carbonate, sulfate or phosphate precipitation, has good chemical combination stability, is difficult to dissolve out again and is less easy to be absorbed by crops. The invention has the advantages of commonly available raw materials, mature process equipment, suitability for large-scale industrial production, easy realization of engineering application, low agricultural application difficulty, no toxic action on farmland soil environment and good ecological environmental benefit. The product has good adsorption capacity to various heavy metals, and in addition, ferrous ions and potassium ions can promote crop production.

For further explanation of the present invention, the paper mulberry charcoal material, the preparation method thereof and the paper mulberry charcoal-based soil heavy metal mineralizer provided by the present invention are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of the present invention.

Example 1

A preparation method of a paper mulberry charcoal material comprises the following steps:

cutting the hybrid paper mulberry branch into 5 cm sections, soaking in water for 2h, taking out, peeling, drying the peeled hybrid paper mulberry branch in a 60 ℃ oven, and leaving the peeled paper mulberry bark for later use.

Crushing the dried hybrid tree branches, and screening to obtain 100-mesh tree material powder, thus obtaining the tree branch dry powder.

And (3) placing the branch dry powder into steam explosion equipment, and performing gas explosion under the condition that the steam pressure is 1.0MPa and the pressure maintaining time is 30s to obtain a steam explosion product. And (3) putting the steam explosion product into a vacuum drying oven, drying for 2 hours at 80 ℃, and taking out and sealing for standby.

The catalytic active center sol is prepared by the following steps: citric acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.1:1:8.8, mixing, dissolving in an ethanol solvent, dispersing and stirring at a high speed of 2000r/min for 0.5h, adding urea solution to adjust the pH to 7.5, continuously stirring for 20min, adding deionized water to adjust the viscosity to 5 mPa.S, and standing for 6h to obtain the catalytic active center sol.

And (3) placing the dried steam explosion product and paper mulberry bark into a respiration-simulated vacuum pressure impregnator to impregnate catalytic active center sol, sucking the catalytic active center sol into the paper mulberry bark for 10min under vacuum negative pressure under the condition that the vacuum degree is 0.065MPa, keeping the vacuum negative pressure for 5min under 1MPa, taking out the paper mulberry bark, and air-drying the paper mulberry bark, and repeating the impregnation and the air-drying to ensure that the metal loading amount reaches 2.5 weight percent, thereby obtaining the paper mulberry loading material.

Placing the paper mulberry load material in a tube furnace at N ₂ High-temperature carbonization is carried out under the protection of gas, the carbonization condition is that the initial temperature is 24 ℃, the temperature is increased to 150 ℃ at the speed of 5 ℃/min, the temperature is kept for 5min, the temperature is increased to 450 ℃ at the speed of 20 ℃/min, the temperature is kept for 1h, and the paper mulberry carbon material is obtained after natural cooling.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, ferrous sulfate, humic acid and woody peat are mixed according to the mass ratio of 1:0.05:0.05: and 0.08, mixing and stirring uniformly to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 2

Crushing the dried hybrid tree branches, and screening to obtain 80-mesh tree material powder, thus obtaining the tree branch dry powder.

The dry powder of the branches is placed in a steam explosion device, and the steam pressure is 1.5MPa, and (5) performing gas explosion under the condition that the pressure maintaining time is 100s to obtain a steam explosion product. And (3) putting the steam explosion product into a vacuum drying oven, drying for 2 hours at 95 ℃, and taking out and sealing for standby.

The catalytic active center sol is prepared by the following steps: citric acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.15:1:7.8, mixing, dissolving in an ethanol solvent, dispersing at high speed under 1600r/min, stirring for 1.5h, adding an ethylenediamine solution to adjust the pH to 8, continuously stirring for 20min, adding deionized water to adjust the viscosity to 7 mPa.S, and standing for 8h to obtain the catalytic active center sol.

And (3) placing the dried steam explosion product and paper mulberry bark into a respiration-simulated vacuum pressure impregnator to impregnate catalytic active center sol, sucking the catalytic active center sol into the paper mulberry bark for 10min under vacuum negative pressure under the condition of the vacuum degree of 0.075MPa, keeping the vacuum negative pressure for 5min under the positive pressure of 1MPa, taking out the paper mulberry bark, air-drying the paper mulberry bark, and repeating the impregnation and the air-drying to ensure that the metal load reaches 3wt percent, thereby obtaining the paper mulberry load material.

Placing the paper mulberry load material in a tube furnace under Ar ₂ High-temperature carbonization is carried out under the protection of gas, the carbonization condition is that the initial temperature is 24 ℃, the temperature is increased to 200 ℃ at the speed of 3 ℃/min, the temperature is kept for 10min, the temperature is increased to 500 ℃ at the speed of 20 ℃/min, the temperature is kept for 1h, and the paper mulberry carbon material is obtained after natural cooling.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, ferrous sulfate, humic acid and woody peat are mixed according to the mass ratio of 1:0.1:0.1: and 0.1, uniformly mixing and stirring to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 3

cutting the hybrid paper mulberry branch into 5 cm sections, soaking in water for 2h, taking out, peeling, naturally air-drying the peeled hybrid paper mulberry branch, and leaving the peeled paper mulberry bark for later use.

Crushing the dried hybrid tree branches, and screening to obtain 30-mesh tree material powder, thus obtaining the tree branch dry powder.

And (3) placing the branch dry powder into steam explosion equipment, and performing gas explosion under the condition that the steam pressure is 2.0MPa and the pressure maintaining time is 200s to obtain a steam explosion product. And (3) putting the steam explosion product into a vacuum drying oven, drying for 4 hours at 100 ℃, and taking out and sealing for standby.

The catalytic active center sol is prepared by the following steps: citric acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.2:0.5:8.2, dissolving the mixture into an ethanol solvent, dispersing and stirring at a high speed under the condition of 1800r/min for 2 hours, adding urea solution to adjust the pH to 8.5, continuously stirring for 20 minutes, adding deionized water to adjust the viscosity to 12 mPa.S, and standing for 6 hours to obtain the catalytic active center sol.

And (3) placing the dried steam explosion product and paper mulberry bark into a respiration-simulated vacuum pressure impregnator to impregnate catalytic active center sol, sucking the catalytic active center sol into the paper mulberry bark for 15min under vacuum negative pressure under the condition of the vacuum degree of 0.085MPa, keeping the vacuum negative pressure for 5min under the positive pressure of 2MPa, taking out the paper mulberry bark, air-drying the paper mulberry bark, and repeating the impregnation and the air-drying to ensure that the metal loading amount reaches 2.5 weight percent, thereby obtaining the paper mulberry loading material.

Placing the paper mulberry load material in a tube furnace at N ₂ High-temperature carbonization is carried out under the protection of gas, the carbonization condition is that the initial temperature is 24 ℃, the temperature is increased to 300 ℃ at the speed of 5 ℃/min, the temperature is kept for 15min, the temperature is increased to 550 ℃ at the speed of 20 ℃/min, the temperature is kept for 1h, and the paper mulberry carbon material is obtained after natural cooling.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: mixing paper mulberry carbon material with hydroxyapatite, humic acid and woody peat according to the mass ratio of 1:0.15:0.2: and 0.2, uniformly mixing and stirring to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 4

Crushing the dried hybrid tree branches, and screening to obtain 4-mesh tree material powder, thus obtaining the tree branch dry powder.

And (3) placing the branch dry powder into steam explosion equipment, and performing gas explosion under the condition that the steam pressure is 3.0MPa and the dwell time is 240s to obtain a steam explosion product. And (3) putting the steam explosion product into a vacuum drying oven, drying for 2 hours at 120 ℃, and taking out and sealing for standby.

The catalytic active center sol is prepared by the following steps: citric acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.2:1:8.8, mixing, dissolving in ethanol solvent, dispersing at 2000r/min, stirring at high speed for 0.5h, adding ammonia water solution to adjust pH to 9, continuously stirring for 20min, adding deionized water to adjust viscosity to 12 mPa.S, and standing for 12h to obtain the catalytic active center sol.

And (3) placing the dried steam explosion product and the paper mulberry bark into a respiration-simulated vacuum pressure impregnator to impregnate catalytic active center sol, sucking the catalytic active center sol into the paper mulberry bark for 10min under vacuum negative pressure under the condition of the vacuum degree of 0.98MPa, keeping the vacuum negative pressure for 10min under the positive pressure of 3MPa, taking out the paper mulberry bark, air-drying the paper mulberry bark, and repeating the impregnation and the air-drying to ensure that the metal loading amount reaches 4wt percent to obtain the paper mulberry loading material.

Placing the paper mulberry load material in a tube furnace under Ar ₂ High-temperature carbonization is carried out under the protection of gas, the carbonization condition is that the initial temperature is 24 ℃, the temperature is increased to 350 ℃ at the speed of 5 ℃/min, the temperature is kept for 15min, then the temperature is increased to 600 ℃ at the speed of 20 ℃/min, the temperature is kept for 1h, and the paper mulberry carbon material is obtained after natural cooling.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, potassium carbonate, humic acid and woody peat are mixed according to the weight ratio of 1:0.15:0.2: and 0.3, mixing and stirring uniformly to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 5

Crushing the dried hybrid tree branches, and screening to obtain 4-mesh tree material powder, thereby obtaining the tree branch dry powder.

And (3) placing the branch dry powder into steam explosion equipment, and performing gas explosion under the condition that the steam pressure is 3.0MPa and the pressure maintaining time is 240s respectively to obtain a steam explosion product. And (3) putting the steam explosion product into a vacuum drying oven, drying for 2 hours at 120 ℃, and taking out and sealing for standby.

The catalytic active center sol is prepared by the following steps: lactic acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.2:1:8.8, dissolving the mixture in an ethanol solvent, dispersing and stirring at a high speed for 0.5h under the condition of 1500r/min, adding an ammonia water solution to adjust the pH value to 8, continuously stirring for 20min, adding deionized water to adjust the viscosity to 12 mPa.S, and standing for 12h to obtain the catalytic active center sol.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, ferrous sulfate, sodium humate and woody peat are mixed according to the mass ratio of 1:0.15:0.2: and 0.3, mixing and stirring uniformly to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 6

The catalytic active center sol is prepared by the following steps: wood vinegar, silica sol and ferrous sulfate are mixed according to the mole ratio of 0.1:1:8.8, dissolving the mixture in an ethanol solvent, dispersing and stirring at a high speed for 0.5h under the condition of 1500r/min, adding an ammonia water solution to adjust the pH value to 8, continuously stirring for 20min, adding deionized water to adjust the viscosity to 12 mPa.S, and standing for 12h to obtain the catalytic active center sol.

Example 7

The catalytic active center sol is prepared by the following steps: lactic acid, wood vinegar and citric acid are mixed, silica sol and ferrous sulfate are mixed according to a mole ratio of 0.2:0.5:8, mixing and dissolving in an ethanol solvent, dispersing and stirring at a high speed for 0.5h under the condition of 1500r/min, adding an ammonia water solution to adjust the pH value to 8, continuously stirring for 20min, adding deionized water to adjust the viscosity to 12 mPa.S, and standing for 12h to obtain the catalytic active center sol.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, ferrous sulfate, sodium humate and woody peat are mixed according to the mass ratio of 1:0.15:0.2: and 0.3, uniformly mixing and stirring to obtain the paper mulberry carbon-based soil heavy metal restoration agent.

Example 8

The preparation method of the paper mulberry carbon material is the same as in example 1, except that only the dry paper mulberry powder is impregnated during the impregnation, and no paper mulberry bark is added. The paper mulberry carbon material is the paper mulberry branch carbon material.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: mixing the tree branch carbon material with ferrous sulfate, humic acid and woody peat according to the mass ratio of 1:0.05:0.05: and 0.08, mixing and stirring uniformly to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Example 9

The preparation method of the paper mulberry carbon material is the same as in example 1, except that paper mulberry bark is impregnated without adding the blasting product of the paper mulberry tree trunk. The paper mulberry carbon material is prepared.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry bark carbon material, ferrous sulfate, humic acid and woody peat are mixed according to the mass ratio of 1:0.05:0.05: and 0.08, mixing and stirring uniformly to obtain the carbon-based soil heavy metal restoration agent of the hybrid broussonetia papyrifera.

Comparative example 1 (without steam explosion)

Crushing the dried hybrid paper mulberry tree trunks, screening to obtain 4-mesh paper mulberry tree wood powder, and naturally drying to obtain paper mulberry tree trunk powder.

The catalytic active center sol is prepared by the following steps: citric acid, silica sol and ferrous sulfate are mixed according to a molar ratio of 0.2:1:8.8, mixing and dissolving in an ethanol solvent, dispersing and stirring at a high speed under 2000r/min for 0.5h, adding an ammonia water solution to adjust the pH value to 8, continuously stirring for 20min, adding deionized water to adjust the viscosity to 12 mPa.S, and standing for 12h to obtain the catalytic active center sol.

And (3) immersing the paper mulberry branch dry powder and paper mulberry bark in a respiration-simulated vacuum pressure impregnator to obtain catalytic active center sol, sucking the catalytic active center sol into the paper mulberry branch dry powder and paper mulberry bark for 10min under vacuum negative pressure under the condition of the vacuum degree of 0.98MPa, keeping the vacuum negative pressure for 10min under the positive pressure of 3MPa, taking out the paper mulberry branch dry powder, and repeating the immersing and the air drying to ensure that the metal loading amount reaches 4wt percent to obtain the paper mulberry loading material.

Placing the paper mulberry load material in a tube furnace under Ar ₂ High-temperature carbonization is carried out under the protection of gas, the carbonization condition is that the initial temperature is 24 ℃, the temperature is increased to 350 ℃ at the speed of 5 ℃/min, the temperature is kept for 15min, the temperature is increased to 600 ℃ at the speed of 20 ℃/min,and after keeping for 1h, naturally cooling to obtain the paper mulberry charcoal material.

Comparative example 2 (impregnation process using only atmospheric impregnation)

And (3) placing the dried steam explosion product and the paper mulberry bark in catalytic active center sol, soaking for 24 hours at normal pressure, taking out and air-drying, and repeating the soaking and air-drying at normal pressure to enable the metal loading amount to reach 4wt% to obtain the paper mulberry loading material.

A paper mulberry charcoal-based soil heavy metal mineralizer comprises the following specific preparation methods: the paper mulberry carbon material, ferrous sulfate, sodium humate and woody peat are mixed according to the weight proportion of 1:0.15:0.2: and 0.3, mixing and uniformly stirring to obtain the paper mulberry carbon-based soil heavy metal restoration agent.

Comparative example 3

The paulownia branch is prepared into the paulownia carbon material by the same method as in example 1 to obtain the paulownia carbon material and the paulownia carbon-based soil heavy metal restoration agent respectively.

Comparative example 4

The poplar branch is subjected to preparation of a poplar carbon material, and the preparation method is the same as that of example 1, so that the poplar carbon material and the poplar carbon-based soil heavy metal restoration agent are respectively obtained.

Comparative example 5

The preparation method is similar to example 1, except that in the high-temperature carbonization process, the initial temperature is 24 ℃, the temperature is directly increased by 450 ℃ at the speed of 5 ℃/min, and the paper mulberry carbon material is obtained after the paper mulberry carbon material is naturally cooled after being kept for 1 h.

Comparative example 6

The preparation method is the same as in example 1, except that in the high-temperature carbonization process, the initial temperature is 24 ℃, the temperature is directly increased by 450 ℃ at the speed of 20 ℃/min, and after the temperature is maintained for 1 hour, the temperature is naturally reduced, so that the paper mulberry carbon material and paper mulberry carbon-based soil heavy metal restoration agent are obtained.

Comparative example 7

The preparation method is the same as in example 1, except that in the high-temperature carbonization process, the initial temperature is 24 ℃, the temperature is raised to 150 ℃ at a speed of 5 ℃/min, and after the temperature is maintained for 5min, the temperature is raised to 700 ℃ at a speed of 20 ℃/min. The paper mulberry carbon material and paper mulberry carbon-based soil heavy metal restoration agent are prepared.

Comparative example 8

The preparation was identical to example 1, except that no impregnation was carried out. The paper mulberry carbon material and paper mulberry carbon-based soil heavy metal restoration agent are prepared.

Comparative example 9

The preparation method is the same as in example 1, except that the impregnating solution is impregnated with urea modified aqueous solutions of ferrous sulfate, ferrous nitrate and ferrous chloride, specifically, the molar concentration of ferrous particles in the impregnating solution is the same as in example 3, and the preparation method of the impregnating solution is as follows: the urea solution was added to the ferrous ion solution so that the ratio of the molar concentration of urea to the molar concentration of ferrous ions in the impregnating solution was 0.19:1. The paper mulberry carbon material and paper mulberry carbon-based soil heavy metal restoration agent are prepared.

Comparative example 10

The preparation method is the same as in example 1, except that the impregnating solution is not added with a modifying solution. The paper mulberry carbon material and paper mulberry carbon-based soil heavy metal restoration agent are prepared.

Comparative example 11

Commercially available heavy metal soil restoration agents.

Application example 1

The fiber lengths of the paper mulberry carbon material prepared in example 8, the paper mulberry carbon material prepared in example 9, the paulownia carbon material prepared in comparative example 3 and the poplar carbon material prepared in comparative example 4 were observed by using a scanning electron microscope. The fiber lengths of the paper mulberry carbon material, the paulownia carbon material and the poplar carbon material are shown in fig. 1, wherein a in fig. 1 is the fiber length of the paper mulberry bast carbon material prepared in example 9, b in fig. 1 is the fiber length of the paper mulberry branch carbon material prepared in example 8, c in fig. 1 is the fiber length of the paulownia branch carbon material, and d in fig. 1 is the fiber length of the poplar branch carbon material.

As can be seen from FIG. 1, the phloem fiber of the hybrid broussonetia papyrifera has the characteristics of slender fiber, average length of 7.45mm, average width of 18.86 μm, length-width ratio of 395 and fiber thickness of 14.15 mg/(100 m), and is a high-quality quasi-one-dimensional carbon material. The hybrid tree mass part fiber is short, the average length is 0.58mm, the fine fiber percentage content is 43.31% below 0.2mm, and the fiber distribution frequency is 53.86% in the length range of 0.23-0.47 mm.

Application example 2

In the cadmium (Cd) polluted soil (28.12 percent of acid-soluble state, 16.52 percent of reducible state, 8.93 percent of oxidizable state and 46.43 percent of residue state respectively), the content of the cadmium (Cd) in the soil is 53mg/kg. The soil restoration agents of examples 1 to 9 and comparative examples 1 to 11 were added to cadmium (Cd) contaminated soil, respectively, and passivation experiments were performed in an amount of 50g of soil restoration agent per kg of soil. Taking a soil sample after 90 days, fully extracting Cd in the sample by adopting a hydrochloric acid-nitric acid-hydrofluoric acid-perchloric acid full digestion method, and detecting the corresponding cadmium concentration from a standard curve by adopting a flame atomic absorption spectrophotometry, wherein the wavelength of an atomic absorption spectrometer is 228.8mm, the slit is 0.70nm, the current of a lead lamp is 8mA, the negative high pressure is 300V, the carrier gas flow is 250mL/min, an air-acetylene flame is used, the water is used for zeroing, 20 mu L of sample injection is performed, the absorbance of cadmium is measured, the absorbance of a blank solution along with the sample is subtracted, and the corresponding cadmium concentration is detected from the standard curve, wherein the blank experiment is the soil without adding a soil restoration agent. The results of the detection are shown in Table 1 and FIG. 2.

TABLE 1 variation of cadmium Cd morphology and content in soil after 90d treatment of soil with soil restoration agents prepared in examples 1 to 7 and comparative examples 1 to 11

As can be seen from table 1 and fig. 2, compared with the blank experiment, all the repairing agents change the form of heavy metal ions in soil, and the steam explosion treatment, the active sol impregnation, the carbonization temperature control and the nitrogen-containing substance modification have gain effects on the experiment; in addition, the fiber length of carbon source materials (broussonetia papyrifera, poplar and hybrid broussonetia papyrifera) is also an important factor influencing the mineralization effect of heavy metals, and as can be seen from fig. 1, several carbon source materials have fiber lengths of broussonetia papyrifera (a) > broussonetia papyrifera (b) > poplar (d) > paulownia (c), heavy metal mineralization effect example 9 (broussonetia papyrifera) > example 8 (broussonetia papyrifera+broussonetia) to examples 1 to 7 (broussonetia papyrifera) to comparative example 4 (poplar) to comparative example 3 (paulownia); the mineralization effect of the heavy metal in the soil in all the embodiments of the invention is generally better than that of the commercial heavy metal soil restoration agent of comparative example 11.

In the comparison between the embodiment 1 and the comparison between the embodiment 5 and the comparison between the embodiment 6, the comparison between the embodiment 5 and the comparison between the embodiment 6 shows that the high-temperature carbonization stage has better modification effect on heavy metals when being used for modifying soil for the paper mulberry carbon material compared with the high-temperature heating, and the low-temperature heating has better modification effect on the heavy metals, but the repair effect of the paper mulberry carbon material on the heavy metals in soil can be more effectively improved by adopting the high-temperature carbonization mode of firstly heating at a low speed and then heating at a high speed, because tar generated by paper mulberry powder is not volatilized, the pore canal of the carbon material is blocked, and the adsorption is influenced when the heating rate is too low; and the too high heating rate can cause too fast decomposition and oxidation of the nitrogen-containing modified solution, which is unfavorable for the nitrogen-containing modified solution to enter a carbon skeleton and affects the doping effect.

As can be obtained from example 1 and comparative example 7, in the high-temperature carbonization process of the present invention, the higher the temperature is, the better the modification effect of the paper mulberry carbon material on the soil heavy metal is, and the higher the temperature is, the higher the graphitization degree of the carbon material becomes, which is unfavorable for heavy metal adsorption.

Compared with the comparative example 8, the embodiment 1 and the comparative example 8 show that the breathing-imitating vacuum pressure impregnation is carried out in the preparation process of the paper mulberry carbon material, so that the effect of repairing heavy metals by the paper mulberry carbon material is remarkably improved, because the breathing-imitating vacuum pressure impregnation can remove the gas adsorbed in the porous structure of the hybrid paper mulberry powder, the metal ions are facilitated to enter the cell cavities of the hybrid paper mulberry and are alternately diffused, the metal ions are uniformly distributed, finally, the metal ions are uniformly embedded into the biomass framework of the hybrid paper mulberry powder, the paper mulberry carbon material is not easy to fall off during carbonization, and the reduction effect of the repairing agent is improved.

Compared with the conventional heavy metal soil restoration agent, the catalytic activity center sol can obviously improve the restoration capability of the paper mulberry carbon material to heavy metal, and the problems of micropore blockage, easiness in cracking, further reduction of metal ion falling and the like of the existing load coating can be effectively solved.

As a result of comparing example 1 with comparative example 10, the addition of the modifying solution during the impregnation process significantly improves the repair capability of the paper mulberry carbon material for heavy metals, because the addition of the nitrogen-containing modifying solution causes the carbon material to form nitrogen doping during carbonization, the carbon atoms adjacent to the N heteroatoms in the nitrogen-doped carbon material possess a high positive charge density, and at the same time, conjugation exists between the lone pair electrons of the N atoms and the lattice large pi bonds of the carbon atoms, which makes the nitrogen-doped carbon material exhibit excellent catalytic performance.

Application example 3

Corn plants are enriched in cadmium (Cd) contaminated soil.

Randomly collecting 5 plants of complete corn plants planted in the soil treated by the heavy metal restoration agent of the soil in examples 1-9 and comparative examples 1-11 in farmland of Cd polluted soil (28.12%, 16.52%, 8.93% and 46.43% of acid soluble state, reducible state, oxidizable state and residue state respectively), cutting into segments, repeatedly cleaning with deionized water for 3 times, placing into an oven, deactivating enzyme at 105 ℃ for 30min, and drying at 65 ℃ until the weight is constant. Crushing by using a crusher, taking 0.5g, putting into a triangular flask, adding 8mL of mixed acid, mixing the mixed acid with a ratio of nitric acid to perchloric acid (the volume ratio of nitric acid to perchloric acid is 3:1), standing overnight, carrying out digestion on a 110 ℃ electric plate for 1h, carrying out digestion on the mixture at 170 ℃ for 30min, then carrying out complete digestion on the sample at 210 ℃, flushing the mixture along the periphery of the flask wall by using 10mL of deionized water, expelling the acid at 140 ℃ until about 3mL of solution remains, repeating the acid expelling operation for three times, fixing the volume by using a 25mL volumetric flask, filtering, and measuring the Cd content in the filtrate by using a graphite furnace atomic absorption spectrophotometry, wherein a blank experiment is corn plants planted in soil without adding a soil restoration agent. The results are shown in Table 2 below.

TABLE 2 enrichment test results of maize plants in cadmium (Cd) contaminated soil in mg/kg

Concentration of Cd	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

As can be seen from Table 2, all the restoration agents can effectively prevent heavy metal ions in soil from migrating to plants, and the prevention effect of the soil heavy metal restoration agents improved in the embodiments 1 to 7 of the invention is better than that of the comparative examples 1 to 11. Compared with the commercial soil heavy metal restoration agent, the soil heavy metal restoration agent provided by the invention can obviously reduce Cd enrichment in corn plants by comparing examples 1-9 with comparative example 11.

In conclusion, the paper mulberry carbon material prepared by the preparation method of the paper mulberry carbon material provided by the invention is light and porous, has abundant surface groups, has good adsorption capacity on various heavy metals, can efficiently repair heavy metal polluted soil, and simultaneously remarkably reduces leaching toxicity of plants.

Although the foregoing embodiments have been described in some, but not all, embodiments of the invention, it should be understood that other embodiments may be devised in accordance with the present embodiments without departing from the spirit and scope of the invention.

Claims

1. The preparation method of the paper mulberry charcoal material is characterized by comprising the following steps of:

2. The method of claim 1, wherein the reducing slurry comprises a catalytically active center sol; the catalytically active center sol comprises the following components:

nonionic surfactant, silica sol and ferrous sulfate.

3. The method of claim 2, wherein the catalytically active core sol further comprises a modifying solution; the modifying solution comprises one or more of triethylamine, ethylenediamine, ethylamine, urea and ammonia water.

4. The method of claim 1, wherein the impregnating comprises a vacuum negative pressure stage and a positive pressure holding stage;

5. The preparation method according to claim 4, wherein the metal loading of the impregnated paper mulberry loading material is 2-12 wt.%.

6. The method of claim 1, wherein the high temperature carbonization comprises temperature swing carbonization; the initial temperature of the variable-temperature carbonization is 24 ℃, the temperature rises to 150-350 ℃ at the speed of 3-5 ℃/min, the constant temperature treatment is carried out for 5-15 min, the temperature rises to 450-600 ℃ at the speed of 18-22 ℃/min, the constant temperature treatment is carried out for 1h, and the temperature is naturally reduced.

7. The method according to claim 1, wherein the steam pressure of the steam explosion is 1.0 to 3.0MPa; the dwell time of the steam explosion is 30-240 s.

8. A paper mulberry charcoal material prepared by the preparation method of any one of claims 1 to 7.

9. The paper mulberry charcoal-based soil heavy metal mineralizer is characterized by comprising the following components in parts by mass: 1 part of paper mulberry carbon material, 0.05 to 0.15 part of passivating agent, 0.05 to 0.2 part of humic acid and 0.08 to 0.3 part of woody peat according to claim 8.

10. Use of the paper mulberry charcoal material of claim 8 or the paper mulberry charcoal-based soil heavy metal mineralizer of claim 9 in restoring soil.