Preparation method and application of agriculture and forestry biomass-based hydrothermal carbon

Abstract

The invention provides a preparation method and application of agriculture and forestry biomass-based hydrothermal carbon, and belongs to the field of rural and urban organic solid waste resourceful treatment. The method comprises the following steps: (1) uniformly mixing agricultural straws and / or garden wastes with water; (2) carbonizing the mixture in a hydrothermal reaction kettle to generate a porous structure and organic matters; (3) carrying out solid-liquid separation on the product to obtain a solid product and a lysate; (4) uniformly mixing the solid product with an activating agent, and activating in the hydrothermal reaction kettle again to form hydrothermal carbon with a microporous structure capable of immobilizing Cr < 6 + > and functional groups; and (5) drying the product to obtain the Fe modified hydrothermal carbon. The method disclosed by the invention is simple in production process, can be used in the fields of treatment of acidic Cr < 6 + >-containing wastewater and environment-friendly basic building materials, and provides a new thought for reduction treatment of rural and urban organic solid wastes, and a novel cement tank prepared by pressing the hydrothermal carbon disclosed by the invention has the effects of water permeation, sewage interception and the like.

Description

Technical Field

[0001] The invention relates to the field of resource treatment of rural and urban organic solid waste, and in particular to a preparation method of agricultural and forestry biomass-based hydrothermal charcoal and application thereof. Background Art

[0002] With the continuous advancement of industrialization and the continuous growth of population, the output of industrial wastewater is increasing, especially acidic wastewater, which not only contains high concentrations of heavy metal ions and organic pollutants, but also exhibits strong corrosiveness. Cr in acidic wastewater mostly exists in the form of hexavalent anions, which are highly toxic and carcinogenic. High-concentration Cr-containing wastewater will seriously pollute the ecological environment, threaten the safety of agricultural products, and ultimately cause irreparable damage to human health.

[0003] At the same time, the development of agriculture and the acceleration of urbanization are accompanied by the generation of more and more solid waste, the most typical of which include various crop straws and abandoned dead branches and leaves formed by garden pruning, which are usually abandoned, piled up or burned, not only occupying land resources, but also causing environmental pollution and other problems. Studies have shown that such wastes can be hydrothermally carbonized into hydrothermal charcoal and activated to make it have the function of adsorbing pollutants. Among them, the preparation and application process of hydrothermal charcoal is bound to be accompanied by the generation and release of organic matter, further regulating the migration and transportation of substances in the ecological environment.

[0004] However, the current research on hydrothermal char mainly focuses on changing its microscopic morphology such as specific surface area, pore structure, surface functional groups, etc., in order to improve the biochar's Cr 6+ For example, CN112547009A provides a modified grapefruit peel hydrothermal carbon adsorption of Cr 6+ The method adopts potassium permanganate and phosphoric acid as modifiers. Its main functions are reflected in two aspects: first, potassium permanganate is a commonly used oxidant, which can effectively increase the number of functional groups on the surface of hydrothermal carbon (especially -COOH), and can enhance the adsorption capacity of hydrothermal carbon for metal cations; second, phosphoric acid, as a strong acid, can react chemically with some minerals in hydrothermal carbon, and can effectively improve the pore structure, such as pore size and specific surface area, to promote the increase of adsorption capacity for metal cations.

[0005] The above method has not taken into account that more than 70% of chromium in the actual environment exists in the form of hexavalent anions, making it difficult to adsorb. At the same time, it also ignores the fact that Cr(VI) in the environment will be reduced to Cr(III) in the presence of abundant organic matter and Fe, making it easy to deposit and reducing its toxicity. Therefore, it is necessary to explore new principles and methods for the adsorption of chromium ions by hydrothermal carbon. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention provides a method for preparing agricultural and forestry biomass-based hydrothermal charcoal and its application. The method of the present invention has a simple production process and can be used for acidic Cr-containing 6+ In the field of wastewater treatment and environmentally friendly basic building materials, a new idea is provided for the reduction of rural and urban organic solid waste. The new cement tank pressed by the hydrothermal carbon of the present invention has the functions of water permeability and sewage interception.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention first provides a method for preparing agricultural and forestry biomass-based hydrothermal charcoal, the method comprising the following steps:

[0009] (1) uniformly mixing agricultural straw and / or garden waste with water;

[0010] (2) carbonizing the mixture obtained in step (1) in a hydrothermal reactor to produce a porous structure and organic matter;

[0011] (3) performing solid-liquid separation on the product obtained in step (2) to obtain a solid product and a pyrolysis solution;

[0012] (4) The solid product obtained in step (3) is uniformly mixed with an activator, and activated again in a hydrothermal reactor to form a solid product capable of retaining Cr. 6+ The microporous structure and functional groups of hydrothermal carbon;

[0013] (5) Drying the product obtained in step (4) to obtain Fe-modified hydrothermal carbon.

[0014] Preferably, the agricultural straw and / or garden waste described in step (1) is pretreated by sun exposure or drying, and the crop straw and / or garden waste is broken into particles with a size of less than 0.35 mm, and the solid-liquid ratio with water is 1:6.25 g / mL.

[0015] Preferably, the hydrothermal reaction kettle described in step (2) is placed in an oven at 210-230° C., and the hydrothermal reaction is maintained for more than 4 hours.

[0016] Preferably, the activator in step (4) is Fe 2+ or Fe 3+ Solution.

[0017] Preferably, the solid product described in step (4): activator = 1: 6.25 g / mL, the hydrothermal reaction kettle is placed in an oven at 210-230° C., and the reaction is maintained for more than 4 hours.

[0018] Further, in step (4), Fe 2+ or Fe 3+Solutions include but are not limited to FeCl recycled by industrial enterprises 3 、FeSO 4 , or soluble Fe such as steel slag 2+ or Fe 3+ wait.

[0019] Preferably, the drying temperature in step (5) is 50-70°C.

[0020] The present invention secondly provides agricultural and forestry biomass-based hydrothermal charcoal obtained by the above-mentioned preparation method.

[0021] The present invention thirdly provides the agricultural and forestry biomass-based hydrothermal charcoal in an acidic Cr-containing 6+ Application in wastewater treatment.

[0022] The present invention fourthly provides the use of the agricultural and forestry biomass-based hydrothermal charcoal in environmentally friendly basic building materials, and the environmentally friendly basic building materials include but are not limited to water-permeable or sewage-intercepting building materials.

[0023] 10. The application of the agricultural and forestry biomass-based hydrothermal charcoal in the new cement trough for mine drainage ditch according to claim 7 is characterized in that the preparation method of the new cement trough for mine drainage ditch comprises the following steps:

[0024] S1. Mix the agricultural and forestry biomass-based hydrothermal charcoal with a binder, gravel, sand and water and stir them evenly; the mass ratio of each raw material is hydrothermal charcoal: binder: gravel: sand: water = 0.5:1:3:1:0.6;

[0025] S2, placing the stirred product obtained in step S1 into a mold for compression molding. Furthermore, the lysate in step (3) can be stored in a 4° C. refrigerator away from light.

[0026] Furthermore, the main component of the adhesive in step S1 is 3CaO·SiO 2 ,2CaO·SiO 2 、3CaO·Al 2 O 3 、4CaO·Al 2 O 3 ·Fe 2 O 3 .

[0027] Furthermore, the pressure in step S2 is specifically a standard 150 tons / m 2 , the mold shape is U-shaped.

[0028] The beneficial technical effects of the present invention are:

[0029] 1. The present invention utilizes waste straw to undergo complex carbonization, cracking, condensation, polymerization, oxidation and reduction reactions under hydrothermal conditions with subcritical water as the medium, including decarboxylation, dehydration, decarbonylation, demethoxylation, intramolecular condensation and aromatization. The reaction produces a small amount of CO 2 The main gas and a large amount of liquid and solid hydrothermal charcoal. Add Fe 3+ Then, Fe 3+ Hydrolysis to form amorphous Fe(OH) 3 , FeO(OH), and then further to Fe 2 O 3 The aldehyde groups generated during the hydrothermal carbonization process can convert Fe 2+ , Fe 3+ Reduced to nano-Fe, Fe is dispersed in the hydrothermal carbon to produce more active sites for heavy metals to bind. Due to the loading of nano-Fe, the modified hydrothermal carbon also has the function of reducing Cr 6+ The ability of the filter can achieve the effect of efficiently intercepting heavy metals in practical applications.

[0030] 2. The inventors' previous research found that the wastewater in the actual environment is strongly acidic and exists in the form of Cr(VI) anions, including Cr 2 O 7 2- (pH < 1), HCrO 4 - (pH 1-6.4), CrO 4 2- (pH ≥ 6.4), making the adsorption capacity of Cr(VI) very weak. Since Cr in actual wastewater or surface water exists in Cr(III) and Cr(VI) valence states, Cr(VI) is the main one, accounting for more than 70%, while Cr(III) is less toxic, has low mobility in a wide pH range, and is easy to precipitate (such as Cr(OH) 3 ) or adsorbed on the surface of minerals. Therefore, the present invention uses the function of the dissolved organic matter electron shuttle released by hydrothermal carbon and the reducing ability of Fe(II) to reduce Cr(VI) to Cr(III). On the one hand, the toxicity of Cr(VI) can be reduced, and on the other hand, the ability of Cr(III) to easily precipitate and be easily adsorbed can be used to remove or detoxify Cr(VI) in the system. Therefore, the principle of adsorbing chromium ions in the present invention is to first reduce Cr(VI) to Cr(III) and then adsorb it. This reaction path can adapt to the actual wastewater environment and can significantly reduce the toxicity of the actual wastewater.

[0031] 3. The hydrothermal carbon obtained by the present invention can adsorb Cr in acidic wastewater 6+ , under strong acid conditions, its effect on the environmental concentration of Cr 6+The retention rate of (2mg / L) can reach 79.38-100.00%; the resulting pyrolysis solution is rich in organic matter. Hydrochar can also release dissolved organic matter in an acidic environment (DOC content is 9.09-11.80mg / L), and the dissolved organic matter can reduce Cr 6+ , under strong acid conditions, its effect on the environmental concentration of Cr 6+ The contribution rate of reduction of (2mg / L) can reach 22.20-29.74%.

[0032] 4. The hydrothermal charcoal prepared by the present invention has high adsorption capacity and high specific surface area, and can fix Cr(VI) in acidic wastewater and alleviate the ecotoxicity of Cr(VI). The hydrothermal charcoal of the present invention can also release abundant soluble organic matter, providing abundant soluble organic matter for environments lacking nutrients (such as poor soil). The preparation process of the present invention is simple, the effect is significant and stable, and it provides a new solution for the reduction and resource treatment of agricultural and garden waste straw, and provides a necessary reference basis for subsequent research on improving the performance of hydrothermal charcoal based on waste straw. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 From left to right are the actual pictures of the garden waste hydrothermal charcoal, the pyrolysis solution prepared in Example 1, and the waste cotton straw hydrothermal charcoal obtained in Example 2.

[0034] Figure 2 This is a three-dimensional fluorescence spectrum profile of the release of dissolved organic matter from the hydrothermal carbon in Example 3.

[0035] Figure 3 This is the dimension diagram of the new cement tank obtained in Example 6. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Embodiment 1:

[0038] This embodiment provides a Cr-fixing 6+ , supplementing organic matter functional hydrothermal charcoal, prepared by the following steps:

[0039] (1) The garden waste that has been pre-treated by exposure and crushing (particle size less than 0.35 mm) is uniformly mixed with water at a solid-liquid ratio of 1:6.25.

[0040] (2) The mixture in (1) was placed in a hydrothermal reactor and placed in an oven and heated to 220°C for 4 h.

[0041] (3) The product obtained in (2) is subjected to solid-liquid separation, wherein the solid product is garden waste hydrothermal charcoal, and the pyrolysis liquid needs to be stored in a 4°C refrigerator away from light.

[0042] (4) The garden waste hydrothermal charcoal obtained in (3) was mixed with FeCl 3 The solution was mixed evenly at a solid-liquid ratio of 1:6.25, and the mixture was then placed in a hydrothermal reactor and placed in an oven to heat to 220°C for 4 hours.

[0043] (5) Drying the solid product of step (4) at 60° C. to obtain Fe-modified garden waste hydrothermal charcoal.

[0044] (6) The BET specific surface areas of the garden waste hydrothermal charcoal and Fe-modified garden waste hydrothermal charcoal obtained in this example are 2.18 m 2 / g, 9.13m 2 / g. Figure 1 The two pictures on the left are actual pictures of the garden waste hydrothermal charcoal and pyrolysis liquid prepared in Example 1.

[0045] Embodiment 2:

[0046] This embodiment provides a Cr-retaining 6+ , hydrothermal charcoal with the function of supplementing organic matter is prepared by the following steps:

[0047] (1) The waste cotton straw that has been pre-treated by exposure and crushing (particle size less than 0.35 mm) is uniformly mixed with water at a solid-liquid ratio of 1:6.25.

[0048] (2) The mixture in (1) was placed in a hydrothermal reactor and placed in an oven and heated to 220°C for 4 h.

[0049] (3) The product obtained in (2) is subjected to solid-liquid separation, wherein the solid product is waste cotton straw hydrothermal charcoal, and the pyrolysis liquid needs to be stored in a 4°C refrigerator away from light.

[0050] (4) The waste cotton straw hydrochar obtained in (3) was mixed with FeCl 3 The solution was mixed evenly at a solid-liquid ratio of 1:6.25, and the mixture was then placed in a hydrothermal reactor and placed in an oven to heat to 220°C for 4 hours.

[0051] (5) Drying the solid product of step (4) to obtain Fe-modified waste cotton straw hydrothermal charcoal.

[0052] (6) The BET specific surface areas of the waste cotton straw hydrothermal charcoal and Fe-modified waste cotton straw hydrothermal charcoal obtained in this example are 15.48 m 2 / g, 30.32m 2 / g. Figure 1 The picture on the right is a real picture of the waste cotton straw hydrothermal charcoal prepared in Example 2. The hydrothermal charcoal after Fe modification has a similar appearance to the hydrothermal charcoal before Fe modification.

[0053] Embodiment 3:

[0054] This embodiment provides a Cr adsorption material prepared from garden waste and waste cotton straw. 6+ Removal of Cr from acidic wastewater by hydrothermal carbon 6+ The application is completed using the following steps:

[0055] (1) Prepare several 500mL 2mg / L Cr 6+ The solution was placed in a beaker and diluted with H 2 SO 4 Solution Adjustment Cr 6+ The pH of the solution was 2.0 ± 0.1.

[0056] (2) To the solution in (1), 0.15 g of the garden waste hydrochar obtained in step (3) of Example 1, the Fe-modified garden waste hydrochar obtained in step (5) of Example 1, the waste cotton stalk hydrochar obtained in step (3) of Example 2, and the Fe-modified waste cotton stalk hydrochar obtained in step (5) of Example 2 were added respectively.

[0057] (3) The beaker in (2) was kept on a magnetic stirrer at 25°C and 180 rpm for continuous reaction. Samples were taken at 0, 10, 30, 60, 120, 240, 480, 720, 960, and 1440 min of reaction and filtered through a 0.45 μm filter membrane. Cr was determined using a UV-visible spectrophotometer. 6+ concentration and calculate the adsorption amount.

[0058] (4) The results showed that hydrothermal charcoal from garden waste, Fe-modified hydrothermal charcoal from garden waste, hydrothermal charcoal from waste cotton straw, and hydrothermal charcoal from Fe-modified hydrothermal charcoal from waste cotton straw had a significant effect on the degradation of Cr 6+ The equilibrium adsorption capacity (Q e ) were 5.08mg / g, 7.20mg / g, 7.66mg / g, and 7.48mg / g, respectively. Effect of hydrothermal carbon on Cr in acidic wastewater before and after modification 6+ The adsorption kinetics of the hydrothermal carbon of garden waste were consistent with the pseudo-second-order kinetic model (as shown in Table 1). Fe modification increased the equilibrium adsorption capacity of garden waste hydrothermal carbon (Q e), Fe modification accelerated the adsorption rate of waste cotton straw hydrothermal carbon (k).

[0059] Table 1 Adsorption of Cr on hydrothermal carbon based on pseudo-first-order and pseudo-second-order kinetic model fitting 6+ Kinetic related parameters

[0060]

[0061] The three-dimensional fluorescence spectrum profile of the release of dissolved organic matter from the hydrothermal charcoal of garden waste and the hydrothermal charcoal of waste cotton straw in Example 3 is as follows: Figure 2 As shown in the figure, it can be seen that during use, hydrothermal carbon will release aromatic protein-rich Ar-P components, which have abundant unsaturated oxygen-containing groups and can promote Cr 6+ The ability to restore.

[0062] Embodiment 4:

[0063] This embodiment provides an application of Fe-modified hydrothermal charcoal prepared from garden waste and waste cotton straw in an acidic environment lacking nutrients, which is completed by the following steps:

[0064] (1) Prepare several 500 mL portions of an aqueous solution with a pH of 2.0 ± 0.1 and place them in a beaker.

[0065] (2) Add 0.15 g of Fe-modified garden waste hydrochar and Fe-modified waste cotton straw hydrochar to the solution in (1).

[0066] (3) The beaker in (2) was kept on a magnetic stirrer at 25°C and 180 rpm for continuous reaction. Samples were taken at 0, 20, 40, 60, 90, 120, 240, 360, 480, 600, 720, and 1440 min of the reaction and filtered through a 0.45 μm filter membrane. The DOC content was determined using a total organic carbon analyzer, and the fluorescence spectral characteristics were determined using a three-dimensional fluorescence spectrophotometer.

[0067] (4) The results showed that after 24 hours, Fe-modified garden waste hydrochar and Fe-modified waste cotton straw hydrochar released 9.09 mg / L and 11.80 mg / L of dissolved organic matter, respectively. The results of three-dimensional fluorescence spectroscopy combined with regional integration method showed that the dissolved organic matter released by hydrochar contained four fluorescent components, namely, aromatic protein-like component Ar-P, fulvic acid-like component Fa-L, microbial metabolite SMP and humic acid-like component Ha-L.

[0068] Embodiment 5:

[0069] This embodiment provides a method for reducing Cr by hydrothermal charcoal release from garden waste and waste cotton straw. 6+Functional dissolved organic matter in reducing Cr in acidic wastewater 6+ The application is completed using the following steps:

[0070] (1) Prepare several 450 mL 2 mg / L Cr 6+ The solution was placed in an anaerobic bottle and diluted with H 2 SO 4 Solution Adjustment Cr 6+ The pH of the solution was 2.0 ± 0.1, and the solution was exposed to N 2 Anaerobic treatment.

[0071] (2) Add 50 mL of dissolved organic matter released from hydrochar of garden waste and dissolved organic matter released from hydrochar of waste cotton straw to the solution in (1) respectively, so that the DOC concentration of the lysate in the anaerobic bottle is 10 mg / L. The dissolved organic matter released refers to the substances released during the use of hydrochar.

[0072] (3) The anaerobic bottle in (2) was kept on a magnetic stirrer at 25°C and 180 rpm for continuous reaction. Samples were taken at 0, 20, 40, 60, 90, 120, 240, 360, 480, 600, 720, and 1440 min of reaction, respectively, and filtered through a 0.45 μm filter membrane. Cr was determined using a UV-visible spectrophotometer. 6+ The reduction rate was calculated and the results are shown in Table 2.

[0073] (4) The results show that the above dissolved organic matter has an effect on Cr in acidic wastewater. 6+ The reduction kinetics of the Cr 6+ The equilibrium reduction rates were 29.74% and 22.20% respectively.

[0074] Table 2 Reduction of Cr by dissolved organic matter based on the single exponential function model 6+ Process kinetic parameters

[0075]

[0076] Embodiment 6:

[0077] This embodiment provides a method for preparing a new type of cement tank by using hydrothermal charcoal made from garden waste, which is prepared by the following steps:

[0078] (1) The Fe-modified garden waste hydrothermal charcoal obtained in Example 1 was mixed with a binder: gravel: sand: water in a mass ratio of 0.5:1:3:1:0.6 and stirred evenly.

[0079] (2) Pour the mixture in (1) into a U-shaped metal mold with a bottom width of 30 cm, a top width of 50 cm, a length of 100 cm, and a depth of 30 cm. The specific shape is as follows: Figure 3 shown.

[0080] (3) Apply 150 tons / m2 of pressure to the mixture in the mold. 2 The pressure is applied and demoulding is performed after solidification.

[0081] The test results show that the new cement tank with a certain amount of Fe-modified hydrothermal carbon added has a higher water permeability. Under normal pressure conditions, the water permeability is increased by 15%-23%; compared with ordinary cement tanks, it also has a certain effect of intercepting heavy metals, and the retention rate of Cr is increased by 75%-81%.

[0082] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes, and can be fully applicable to various fields suitable for the present invention. For those familiar with the art, for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing agricultural and forestry biomass-based hydrothermal charcoal, characterized in that: The method comprises the following steps: (1) uniformly mixing agricultural straw and / or garden waste with water; (2) carbonizing the mixture obtained in step (1) in a hydrothermal reactor to produce a porous structure and organic matter; (3) performing solid-liquid separation on the product obtained in step (2) to obtain a solid product and a pyrolysis solution; (4) The solid product obtained in step (3) is uniformly mixed with an activator, and activated again in a hydrothermal reactor to form a solid product capable of retaining Cr. 6+ The microporous structure and functional groups of hydrothermal carbon; (5) Drying the product obtained in step (4) to obtain Fe-modified hydrothermal carbon.

2. The preparation method according to claim 1, characterized in that: The agricultural straw and / or garden waste described in step (1) is pretreated by sun exposure or drying, and the crop straw and / or garden waste is broken into particles with a size of less than 0.35 mm, and the solid-liquid ratio with water is 1:6.25 g / mL.

3. The preparation method according to claim 1, characterized in that: The hydrothermal reaction kettle described in step (2) is placed in an oven at 210-230° C. and the hydrothermal reaction is maintained for more than 4 hours.

4. The preparation method according to claim 1, characterized in that: The activator described in step (4) is Fe 2+ or Fe 3+ Solution.

5. The preparation method according to claim 1, characterized in that: The solid product described in step (4): activator = 1: 6.25 g / mL, the hydrothermal reaction kettle is placed in an oven at 210-230° C., and the reaction is maintained for more than 4 hours.

6. The preparation method according to claim 1, characterized in that: The drying temperature in step (5) is 50-70°C.

7. The agricultural and forestry biomass-based hydrothermal charcoal obtained by the preparation method according to any one of claims 1 to 6.

8. The agricultural and forestry biomass-based hydrothermal charcoal according to claim 7 is used in an acidic Cr-containing 6+ Application in wastewater treatment.

9. The use of the agricultural and forestry biomass-based hydrothermal charcoal in environmentally friendly basic building materials according to claim 7, characterized in that: The environmentally friendly basic building materials include but are not limited to water-permeable or sewage-intercepting building materials.

10. The application of the agricultural and forestry biomass-based hydrothermal charcoal in a new cement trough for mine drainage ditches as claimed in claim 7, characterized in that: The preparation method of the novel cement trough for mine drainage ditch comprises the following steps: S1. Mix the agricultural and forestry biomass-based hydrothermal charcoal with a binder, gravel, sand and water and stir them evenly; the mass ratio of each raw material is hydrothermal charcoal: binder: gravel: sand: water = 0.5:1:3:1:0.6; S2, placing the stirred product obtained in step S1 into a mold for compression molding.

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