A carbon-based soil remediation material and a method for preparing the same

Abstract

The application discloses a carbon-based soil remediation material and a preparation method thereof. The method comprises the following steps: after wood cellulose biomass raw materials are pretreated by drying, crushing and screening, the pretreated wood cellulose biomass raw materials are mixed with iron salt and clay minerals to obtain compounded raw materials; short-range low-temperature co-pyrolysis is carried out under an oxygen isolation condition to obtain modified biochar and pyrolysis volatile products; wood vinegar is obtained by condensing and separating the pyrolysis volatile products, and the modified biochar is conditioned by using the wood vinegar; the conditioned modified biochar is contacted with an organic polymer modifier solution, impregnation loading is carried out under a low-temperature condition, and drying is carried out to obtain the carbon-based soil remediation material. The prepared material has good heavy metal fixation capacity, pore structure advantages and water and fertilizer retention performance, and can be used for remediation of heavy metal contaminated soil and saline-alkali soil.

Description

Technical Field

[0001] This invention relates to the field of soil remediation materials technology, and in particular to a carbon-based soil remediation material and its preparation method. Background Technology

[0002] Currently, biochar-based soil remediation materials have attracted widespread attention due to their wide availability, rich pore structure, large specific surface area, and certain regulatory effects on heavy metals and salinity. Existing technologies mainly focus on the application of biochar alone, iron-modified biochar, mineral / clay composite biochar, and the combination of biochar and microbial agents, aiming to improve pollutant adsorption and fixation capacity, improve soil physicochemical properties, or enhance fertilizer efficiency. However, ordinary biochar generally suffers from problems such as high pH, ​​strong surface free radical activity, unfavorable microbial colonization, and insufficient stability of functional component loading, which limits its remediation efficacy and adaptability in complex polluted soils.

[0003] While existing technologies employ individual methods such as wood vinegar conditioning, iron salt modification, clay mineral composites, and organic polymer loading, most are dispersed modifications or simple mixtures. They lack an integrated preparation pathway that synergistically regulates the bulk structure and surface chemistry of carbon materials. In particular, they lack a technical solution that organically combines short-range low-temperature co-pyrolysis, alkali control of pyrolysis byproduct wood vinegar, and low-temperature impregnation with loaded organic polymers. Therefore, it is necessary to provide a method for preparing carbon-based soil remediation materials to obtain materials with superior pH compatibility, contaminant immobilization capacity, and subsequent microbial friendliness. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a carbon-based soil remediation material and its preparation method. By performing short-range low-temperature co-pyrolysis of biomass with iron salts and clay minerals, and combining alkali control with pyrolysis byproduct wood vinegar and low-temperature impregnation loading of organic polymers, a carbon-based remediation material with pollution fixation, pH buffering, and interface compatibility is obtained.

[0005] This invention can be achieved through the following technical solutions: A method for preparing a carbon-based soil remediation material includes the following steps: S1. The lignocellulosic biomass raw materials are dried, crushed and screened for pretreatment, and then mixed with iron salts and clay minerals to obtain compound raw materials; S2. The compound raw materials are subjected to short-range low-temperature co-pyrolysis under oxygen-free conditions to obtain modified biochar and pyrolysis volatile products. The pyrolysis volatile products are condensed and separated to obtain wood vinegar. The modified biochar is alkali-controlled with the wood vinegar to adjust its pH to 5.5-7.5. The conditioned modified biochar is then contacted with an organic polymer modifier solution and impregnated and loaded under low-temperature conditions. It is then dried at 40-90℃ to obtain carbon-based soil remediation material.

[0006] Preferably, the biomass raw material is one or more of agricultural straw, wood waste, and garden waste; the pretreated biomass raw material has a moisture content of 10%-14% and a particle size of 0.5-20mm.

[0007] Preferably, the mass ratio of the biomass raw material, iron salt and clay mineral is 100:(2-20):(5-30).

[0008] Preferably, the iron salt is one or more of ferric chloride, ferric sulfate, ferrous sulfate, and ferric nitrate; and the clay mineral is one or more of montmorillonite, bentonite, attapulgite, sepiolite, and kaolinite.

[0009] Preferably, the pyrolysis temperature of the short-path low-temperature co-pyrolysis is 350-550℃, the heating rate is 2-20℃ / min, and the holding time is 10-120min.

[0010] Preferably, the solid-liquid ratio of the wood vinegar to the modified biochar is 1:(0.5-10), and the alkali control conditioning time is 0.5-24h.

[0011] Preferably, the organic polymer modifier is one or more of humic acid, lignin sulfonate, polyglutamic acid, alginate, and chitosan; the low-temperature impregnation loading temperature is 20-80℃, and the impregnation time is 0.5-8h.

[0012] The beneficial effects of this invention are: This invention firstly constructs iron-containing active sites and a mineral synergistic framework simultaneously during the formation of biochar materials through the co-pyrolysis of iron salts and clay minerals with biomass, thereby enhancing the material's pore structure, surface activity, and adsorption and fixation capacity for heavy metals. Secondly, it utilizes wood vinegar, a byproduct of pyrolysis, to condition the modified biochar, achieving not only the resource recycling of pyrolysis byproducts but also optimizing the surface chemical environment of the material and enhancing the synergistic effect between various functional components. Thirdly, it employs low-temperature impregnation and loading of organic polymers to form a more stable hydrophilic and water-retaining interface on the surface of the biochar material, improving the material's water retention and fertilizer retention performance and its adaptability to the soil environment. The resulting carbon-based soil remediation material possesses excellent heavy metal passivation capabilities, superior pore structure, excellent water retention and fertilizer retention performance, and strong interface regulation capabilities. It can improve the soil's physicochemical environment while reducing the content of available heavy metals in the soil. Furthermore, the preparation process involves a wide range of raw material sources, good process continuity, and is easy to scale up, demonstrating significant resource utilization value and promising application prospects. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The physical and chemical properties of soil remediation materials; Figure 2 The soil remediation performance of soil remediation materials. Detailed Implementation

[0014] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0015] Example 1: A method for preparing a carbon-based soil remediation material, comprising the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to a moisture content of 10% and a particle size of 0.5 mm. Then it is mixed with 2 kg of ferric chloride and 5 kg of bentonite to obtain a compound raw material. S2. Under oxygen-free conditions, the compound raw materials are pyrolyzed at a temperature controlled at 350℃, with a heating rate of 2℃ / min and a holding time of 120min to obtain modified biochar and pyrolysis volatile products. The pyrolysis volatile products are condensed and separated to obtain wood vinegar. The wood vinegar and modified biochar are contacted and conditioned at a solid-liquid ratio of 1:0.5 for 0.5h to adjust the pH of the resulting material to 5.5. The modified biochar after alkali-controlled conditioning is then contacted with a humic acid aqueous solution and impregnated at 20℃ for 8h. The impregnated material is then dried at 40℃ to obtain carbon-based soil remediation material.

[0016] Example 2: A method for preparing a carbon-based soil remediation material, comprising the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to a moisture content of 12% and a particle size of 10.25 mm. Then it is mixed with 11 kg of ferric sulfate and 17.5 kg of bentonite to obtain the compound raw material. S2. Under oxygen-free conditions, the compound raw materials are pyrolyzed at a temperature controlled at 450℃, a heating rate of 11℃ / min, and a holding time of 65min to obtain modified biochar and pyrolysis volatiles. The pyrolysis volatiles are condensed and separated to obtain wood vinegar. The wood vinegar and modified biochar are contacted and conditioned at a solid-liquid ratio of 1:5.25 for 12.25h to adjust the pH of the resulting material to 6.5. The alkali-controlled modified biochar is then contacted with a humic acid aqueous solution and impregnated at 50℃ for 4.25h. The impregnated material is then dried at 65℃ to obtain carbon-based soil remediation material.

[0017] Example 3: A method for preparing a carbon-based soil remediation material, comprising the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to a moisture content of 14% and a particle size of 20 mm. Then it is mixed with 20 kg of ferrous sulfate and 30 kg of bentonite to obtain the compound raw material. S2. Under oxygen-free conditions, the compound raw materials are pyrolyzed at a temperature controlled at 550℃, a heating rate of 20℃ / min, and a holding time of 10min to obtain modified biochar and pyrolysis volatile products. The pyrolysis volatile products are condensed and separated to obtain wood vinegar. The wood vinegar and modified biochar are contacted and conditioned at a solid-liquid ratio of 1:10 for 24 hours to adjust the pH of the resulting material to 7.5. The alkali-controlled modified biochar is then contacted with a humic acid aqueous solution and impregnated at 80℃ for 0.5 hours. The impregnated material is then dried at 90℃ to obtain carbon-based soil remediation material.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that the wood vinegar alkali control conditioning is not performed.

[0019] A method for preparing a carbon-based soil remediation material includes the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to a moisture content of 10% and a particle size of 0.5 mm. Then it is mixed with 2 kg of ferric chloride and 5 kg of bentonite to obtain a compound raw material. S2. Under oxygen-free conditions, the compound raw materials are pyrolyzed at a temperature of 350℃, a heating rate of 2℃ / min, and a holding time of 120min to obtain modified biochar. The modified biochar is then contacted with an aqueous solution of humic acid and impregnated at 20℃ for 8 hours. The impregnated material is then dried at 40℃ to obtain carbon-based soil remediation material.

[0020] Comparative Example 2: The difference between this comparative example and Example 1 is that ferric chloride and bentonite are not added.

[0021] A method for preparing a carbon-based soil remediation material includes the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to achieve a moisture content of 10% and a particle size of 0.5 mm. S2. The treated agricultural straw was pyrolyzed under oxygen-free conditions at a temperature of 350℃, a heating rate of 2℃ / min, and a holding time of 120min to obtain biochar and pyrolysis volatiles. The pyrolysis volatiles were condensed and separated to obtain wood vinegar. The wood vinegar and biochar were contacted and conditioned at a solid-liquid ratio of 1:0.5 for 0.5h to adjust the pH of the resulting material to 5.5. The alkali-controlled biochar was then contacted with a humic acid aqueous solution and impregnated at 20℃ for 8h. The impregnated material was dried at 40℃ to obtain carbon-based soil remediation material.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that it does not involve low-temperature impregnation and loading of organic polymer (humic acid).

[0023] A method for preparing a carbon-based soil remediation material includes the following steps: S1. 100 kg of agricultural straw is dried, crushed and screened to a moisture content of 10% and a particle size of 0.5 mm. Then it is mixed with 2 kg of ferric chloride and 5 kg of bentonite to obtain a compound raw material. S2. Under oxygen-free conditions, the compound raw materials are pyrolyzed at a temperature of 350℃, a heating rate of 2℃ / min, and a holding time of 120min to obtain modified biochar and pyrolysis volatile products. The pyrolysis volatile products are condensed and separated to obtain wood vinegar. The wood vinegar and modified biochar are contacted and conditioned at a solid-liquid ratio of 1:0.5 for 0.5h to adjust the pH of the resulting material to 5.5. The material is then dried at 40℃ to obtain carbon-based soil remediation material.

[0024] Performance testing 1 BET specific surface area The determination was carried out in accordance with the GB / T 19587-2017 standard.

[0025] 2 Saturated water holding capacity The soil remediation material sample was dried at 40℃ to constant weight. 1.0g of the sample was weighed and placed in a pre-weighed 300-mesh nylon mesh bag. The bag was immersed in deionized water for 24 hours, then removed and hung for 30 minutes until all free water dripped out. Its mass was then recorded as m1. The initial dry sample mass was recorded as m0. The saturated water holding capacity was calculated using the following formula: Saturated water holding capacity (%) = (m1 - m0) / m0 × 100% Each sample was measured in triplicate, and the average value was taken.

[0026] Table 1. Test results of the physicochemical properties of soil remediation materials

[0027] As shown in Table 1, the BET specific surface areas of the carbon-based soil remediation materials obtained in Examples 1-3 were 82.5 m² / g, 136.9 m² / g, and 188.7 m² / g, respectively, and the saturated water holding capacities were 158%, 203%, and 261%, respectively, all significantly higher than those of the comparative examples. This indicates that the integrated preparation path of "biomass-iron salt-clay mineral co-pyrolysis-wood vinegar alkali-low-temperature impregnation and loading" effectively promotes the development of pore structure in carbon materials and significantly increases the specific surface area as the amount of iron salt and clay minerals added increases and the pyrolysis conditions are strengthened. At the same time, the synergistic effect of wood vinegar conditioning and organic polymer loading improves the hydrophilicity and pore structure stability of the material surface, thereby significantly enhancing its water holding capacity.

[0028] In contrast, Comparative Example 1, without wood vinegar alkali conditioning, showed a decrease in saturated water holding capacity to 136%, indicating that while wood vinegar conditioning has a limited impact on pore structure, it can significantly improve the hydrophilicity of the material surface, thereby enhancing water retention. Comparative Example 2, without the addition of iron salts and clay minerals for co-pyrolysis, showed a decrease in BET specific surface area to 51.6 m² / g and a decrease in saturated water holding capacity to 122%, the largest decrease, indicating that iron salts and clay minerals play a crucial role in the pore structure construction and specific surface area improvement of the carbon material during pyrolysis. Comparative Example 3, without low-temperature impregnation loading of organic polymers, showed a decrease in saturated water holding capacity to 129%, indicating that organic polymer loading mainly works by improving the interfacial properties and water retention capacity of the material surface.

[0029] 3. Effect of reducing available Cd in soil Artificially simulated Cd-contaminated soil was collected, air-dried, impurities removed, and sieved through a 2mm sieve. A blank control (CK) was set up without remediation material. For the other treatments, 2.0% of the soil dry weight was added to each sample, and the mixture was thoroughly mixed. The moisture content was adjusted to 60% of the field capacity, and the soil was incubated at a constant temperature of 25℃ for 30 days. During this period, water was added every 2 days to maintain stable moisture content. After the incubation period, soil samples were collected, air-dried, and sieved through a 2mm sieve. The available Cd content in the soil was determined according to HJ 804-2016. The available Cd reduction rate (%) was calculated as follows: (available Cd in CK group - available Cd in treatment group) / available Cd in CK group × 100%.

[0030] Table 2. Test results of soil remediation performance of soil remediation materials

[0031] Table 2 shows that the carbon-based soil remediation materials prepared in Examples 1-3 all exhibited good heavy metal passivation effects. Compared with the blank control CK (available Cd content of 0.82 mg / kg), each example significantly reduced the available Cd content in the soil. Specifically, the available Cd in Examples 1, 2, and 3 decreased to 0.48 mg / kg, 0.37 mg / kg, and 0.28 mg / kg, respectively, with reduction rates of 41.5%, 54.9%, and 65.9%. With increasing amounts of iron salts and clay minerals, higher pyrolysis temperatures, and enhanced alkali control and organic polymer loading via wood vinegar, the remediation performance of the materials gradually improved. This indicates that the present invention, through the synergistic effect of "constructing a composite carbon framework through co-pyrolysis of iron salts / clay minerals—alkali control and loading via wood vinegar—low-temperature impregnation and loading of organic polymers," can effectively improve the material's ability to fix Cd in the soil. On the one hand, the iron components and clay minerals introduced during the co-pyrolysis process provide more adsorption and precipitation active sites; on the other hand, the wood vinegar solution controls the alkali, keeping the pH of the material within a suitable range and reducing the disturbance of the slightly alkaline biochar to the soil system; simultaneously, the organic polymer loading improves the interfacial properties and dispersibility of the material, thereby jointly promoting the reduction of the available heavy metals and demonstrating a good synergistic enhancement effect. Compared with Example 1, the soil remediation effects of Comparative Examples 1-3 were significantly reduced, with the reduction rates of available Cd in Comparative Examples 1, 2, and 3 being 24.4%, 18.3%, and 31.7%, respectively.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-based soil remediation material, characterized in that, Includes the following steps: S1. The lignocellulosic biomass raw materials are dried, crushed and screened for pretreatment, and then mixed with iron salts and clay minerals to obtain compound raw materials; S2. The compound raw materials are subjected to short-range low-temperature co-pyrolysis under oxygen-free conditions to obtain modified biochar and pyrolysis volatile products. The pyrolysis volatile products are condensed and separated to obtain wood vinegar. The modified biochar is alkali-controlled with the wood vinegar to adjust its pH to 5.5-7.

5. The conditioned modified biochar is then contacted with an organic polymer modifier solution and impregnated and loaded under low-temperature conditions. It is then dried at 40-90℃ to obtain carbon-based soil remediation material.

2. The preparation method of the carbon-based soil remediation material according to claim 1, characterized in that, The biomass raw material is one or more of agricultural straw, wood waste, and garden waste; the pretreated biomass raw material has a moisture content of 10%-14% and a particle size of 0.5-20mm.

3. The preparation method of the carbon-based soil remediation material according to claim 1, characterized in that, The mass ratio of the biomass raw material, iron salt and clay mineral is 100:(2-20):(5-30).

4. The preparation method of the carbon-based soil remediation material according to claim 1, characterized in that, The iron salt is one or more of ferric chloride, ferric sulfate, ferrous sulfate, and ferric nitrate; the clay mineral is one or more of montmorillonite, bentonite, attapulgite, sepiolite, and kaolinite.

5. The method for preparing carbon-based soil remediation material according to claim 1, characterized in that, The pyrolysis temperature of the short-path low-temperature co-pyrolysis is 350-550℃, the heating rate is 2-20℃ / min, and the holding time is 10-120min.

6. The method for preparing carbon-based soil remediation material according to claim 1, characterized in that, The solid-liquid ratio of the wood vinegar to the modified biochar is 1:(0.5-10), and the alkali control conditioning time is 0.5-24h.

7. The method for preparing carbon-based soil remediation material according to claim 1, characterized in that, The organic polymer modifier is one or more of humic acid, lignin sulfonate, polyglutamic acid, alginate, and chitosan; the low-temperature impregnation loading temperature is 20-80℃, and the impregnation time is 0.5-8h.

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