Method for preparing soil remediation matrix through synergistic activation of coal-based solid waste

Abstract

The invention discloses a preparation method for preparing a soil remediation matrix through coal-based solid waste synergistic activation, and belongs to the technical field of coal chemical industry solid waste recycling and soil remediation. The functional biomass charcoal is prepared by constructing a fly ash-coal gangue-desulfurized gypsum-biomass charcoal quaternary synergistic system and combining a coal gangue gradient thermal activation technology, a fly ash mechanochemical modification technology, a desulfurized gypsum carbonate chemical conversion technology and agricultural wastes. And the soil remediation matrix with double functions of heavy metal resistance and control and nutrient regulation and control is constructed. The method is stable in process, and the prepared matrix can remarkably increase the pH value of acid soil, effectively reduce the bioavailability of heavy metal, increase the organic matter content of soil and provide nutrients and is suitable for repairing and improving large-area polluted soil.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical solid waste resource utilization and soil remediation technology, and more specifically, it relates to a method for preparing soil remediation matrix by synergistic activation of coal-based solid waste. Background Technology

[0002] Coal chemical processes generate large amounts of solid waste such as fly ash, coal gangue, and desulfurization gypsum. Traditional stockpiling methods occupy land and easily cause environmental pollution. In addition, existing soil remediation materials mostly rely on natural minerals or chemical products, which are costly, have limited functions, and lack long-term stability against heavy metals and nutrient retention capabilities.

[0003] Based on this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing soil remediation matrix through the synergistic activation of coal-based solid waste, thereby solving the problems existing in the prior art. This invention uses coal-based solid waste and agricultural waste as main raw materials, and employs a multi-process synergistic activation method to prepare a soil remediation matrix, achieving the dual goals of solid waste resource utilization and soil remediation. The prepared matrix simultaneously possesses the functions of heavy metal biomass control and nutrient regulation, and the process is stable and cost-effective.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a method for preparing soil remediation matrix through synergistic activation of coal-based solid waste, comprising the following steps: Agricultural waste is pyrolyzed and carbonized, then impregnated with a chemical activation and modifier solution and subjected to activation heat treatment to obtain functionalized biochar, which provides phosphorus and nitrogen sources. After thermal activation, coal gangue is leached with an organic acid solution to obtain activated coal gangue rich in active aluminum ions. Fly ash is mixed with alkaline solution and then subjected to mechanical chemical modification by vibration, stirring or ultrasound to obtain chemically modified fly ash with improved specific surface area and surface activity. The desulfurized gypsum is chemically converted with a carbonate solution to produce a desulfurized gypsum conversion product mainly composed of calcium carbonate. The obtained functionalized biochar, activated coal gangue, chemically modified fly ash and desulfurized gypsum conversion products are mixed evenly, granulated and dried to obtain the soil remediation matrix.

[0006] Preferably, the specific preparation steps of the functionalized biochar are as follows: agricultural waste is pyrolyzed at 500-700℃ for 60-120 min under an inert atmosphere to obtain crude biochar; the crude biochar is impregnated in a chemical activator and modifier solution with a mass concentration of 10-15% for 12-24 h, and after impregnation, the solid and liquid are separated, and the obtained solid is activated and heat-treated at 450-550℃ for 30-60 min under an inert atmosphere; finally, after washing, drying and pulverizing, functionalized biochar is obtained; the chemical activator and modifier is diammonium hydrogen phosphate or diammonium dihydrogen phosphate.

[0007] Preferably, the mass ratio of the crude biochar and the chemical activator and modifier is 1:(8~12).

[0008] Preferably, the temperature for thermal activation is 650~850℃.

[0009] Preferably, the organic acid solution includes a solution of citric acid, oxalic acid, or tartaric acid; the concentration of the organic acid solution is 0.2~1 mol / L; the mass ratio of coal gangue to organic acid solution is 1:5; and the leaching treatment time is 2~6 hours.

[0010] Preferably, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a mass concentration of 1-10%; the mass ratio of fly ash to alkaline solution is 1:3; and the mechanochemical modification time is 45 min.

[0011] Preferably, the carbonate solution is a sodium carbonate solution or an ammonium carbonate solution, and the carbonate solution concentration is 0.8~1.2 mol / L; the mass ratio of the desulfurized gypsum to the carbonate solution is 1:(8~12); the temperature of the chemical conversion reaction is 50~70℃, and the time is 2~4h.

[0012] Preferably, the mass ratio of the chemically modified fly ash, activated coal gangue, desulfurized gypsum conversion product and functionalized biochar is (4~5):(3~4):(1~1.5):(0.5~1).

[0013] The second technical solution of the present invention provides a soil remediation matrix prepared by the above method.

[0014] The third technical solution of the present invention is to provide the application of the above-mentioned soil remediation matrix in the remediation and improvement of acidic and heavy metal contaminated soils.

[0015] Preferably, the soil remediation matrix of the present invention mainly plays the following roles: (1) to adjust the pH value of acidic soil and stabilize the available heavy metals in the soil; (2) to increase the organic matter content of soil and improve the physical structure of soil; (3) as a nutrient carrier to provide nitrogen, phosphorus, potassium and other nutrients to the soil.

[0016] The present invention discloses the following technical effects: This invention utilizes coal-based solid waste and agricultural waste as raw materials, achieving highly efficient resource utilization and significantly reducing remediation costs compared to commercial products. The biochar preparation process, through diammonium hydrogen phosphate chemical activation, simultaneously optimizes pore structure and nitrogen and phosphorus nutrient loading, enhancing its nutrient regulation and heavy metal adsorption capacity. The process is stable and controllable, avoiding uncertainties such as strain cultivation and condition sensitivity in biotransformation technologies. At a substrate application rate of 4 t / mu, it can significantly increase the pH value of acidic soils, reduce the content of available heavy metals, and increase the organic matter content. The quaternary components work synergistically, combining heavy metal chemical stabilization, soil structure improvement, and nutrient regulation functions. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation process of the soil remediation matrix of the present invention. Detailed Implementation

[0018] This invention provides a method for preparing a soil remediation matrix through synergistic activation of coal-based solid waste. The preparation steps are as follows: 1. Raw material ratio: By mass, 40-50 parts of chemically modified fly ash, 30-40 parts of activated coal gangue, 10-15 parts of desulfurized gypsum conversion products, and 5-10 parts of functionalized biochar constitute a quaternary synergistic system.

[0019] 2. Preparation of functionalized biochar: a) Raw material pretreatment: Agricultural waste (such as corn stalks, rice husks, etc.) is crushed to a particle size of 1-3 cm and dried at 80℃ until the moisture content is less than 10%.

[0020] b) Pyrolysis carbonization: The dried raw material is placed in a tubular furnace or rotary kiln and heated to 500-700°C at a heating rate of 10-15°C / min under nitrogen or argon protection. The temperature is maintained at this temperature for 60-120 min to obtain crude biochar.

[0021] c) Chemical activation and modification: After the crude biochar has cooled to room temperature, it is impregnated in a chemical activation and modification agent solution with a concentration of 10-15 wt%, with a solid-liquid mass ratio of 1:(8-12), for 12-24 hours. Then, it is filtered, and the filter cake is reheated to 450-550℃ under an inert atmosphere using the same heating program, and held for 30-60 minutes for activation.

[0022] d) Post-processing: The activated product was washed with deionized water until the pH value was 6.5~7.5, then dried at 105℃, and ground through a 100-mesh sieve to obtain functionalized biochar rich in nitrogen and phosphorus functional groups and well-developed pore structure.

[0023] 3. Coal gangue activation treatment: The coal gangue is crushed to a particle size ≤2mm, thermally activated at 850℃ for 2h, cooled, and then leached with 0.5mol / L citric acid solution at a solid-liquid ratio of 1:5 for 4h. After filtration and washing, activated coal gangue enriched with active aluminum ions is obtained.

[0024] 4. Mechanochemical modification of fly ash: Fly ash is subjected to mechanochemical modification through vibration, stirring, or ultrasound to increase its specific surface area to 18-22 m². 2 / g, enhancing surface activity and adsorption capacity.

[0025] 5. Chemical conversion of desulfurized gypsum: Desulfurized gypsum powder is mixed with carbonate solution with a concentration of 0.8~1.2mol / L at a solid-liquid mass ratio of 1:(8~12), and reacted in a water bath at 50~70℃ for 2~4h. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a conversion product with calcium carbonate as the main component.

[0026] 6. Matrix preparation and compounding: The above-mentioned chemically modified fly ash, activated coal gangue, desulfurized gypsum conversion products and functionalized biochar are mixed evenly in proportion, granulated (particle size 2~4mm), and dried to obtain the soil remediation matrix.

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0031] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0032] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0033] The preparation process of the soil remediation matrix described in this invention is as follows: Figure 1 As shown.

[0034] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0035] The untreated fly ash used in the following comparative examples needs to be ground in a vibratory mill for 45 minutes and then set aside. The untreated coal gangue needs to be crushed to a particle size ≤2mm.

[0036] Example 1 Preparation of functionalized biochar: Corn stalks were crushed to a particle size of 1-3 cm and dried at 80℃ until the moisture content was below 10%. The dried corn stalk particles were pyrolyzed at 600℃ for 90 min under nitrogen protection at a rate of 12℃ / min. After cooling, the pyrolyzed particles were immersed in a 12wt% diammonium hydrogen phosphate solution (solid-liquid mass ratio 1:10) for 18 h. After filtration, the pyrolyzed particles were activated again at 500℃ for 45 min under nitrogen protection at the same rate. The activated product was washed with deionized water until the pH value was 6.5-7.5, then dried at 105℃, ground through a 100-mesh sieve, and then set aside for use.

[0037] Coal-based solid waste treatment: The coal gangue is crushed to a particle size ≤2mm, thermally activated at 850℃ for 2h, cooled, and then leached with 0.5mol / L citric acid solution at a solid-liquid ratio of 1:5 for 4h. After filtration and washing, coal gangue material enriched with active aluminum ions is obtained. Mechanochemical modification of fly ash: Place fly ash in a vibratory mill, add 5wt% NaOH solution (solid-liquid mass ratio 1:3), grind for 45 minutes, and then set aside for use.

[0038] Chemical conversion of desulfurized gypsum: Desulfurized gypsum powder and 1 mol / L sodium carbonate solution were mixed at a solid-liquid mass ratio of 1:10 and reacted in a water bath at 60℃ for 3 hours. The conversion product was obtained by filtration, washing and drying.

[0039] Matrix preparation: Take 45 parts of the above-treated fly ash, 35 parts of coal gangue, 12 parts of desulfurized gypsum conversion product, and 8 parts of functionalized biochar, mix them evenly in proportion, granulate (particle size 2~4mm), and dry to obtain the soil remediation matrix.

[0040] Example 2 Preparation of functionalized biochar: Rice husks were crushed to a particle size of 1-3 cm and dried at 80℃ until the moisture content was less than 10%. The dried rice husk particles were pyrolyzed at 550℃ for 70 min under nitrogen protection at a rate of 12℃ / min. After cooling, the pyrolyzed particles were immersed in a 15wt% diammonium hydrogen phosphate solution (solid-liquid mass ratio 1:9) for 20 h. After filtration, the pyrolyzed particles were activated again at 480℃ for 50 min under nitrogen protection at the same rate. The activated product was washed with deionized water until the pH value was 6.5-7.5, then dried at 105℃, ground through a 100-mesh sieve, and then ready for use.

[0041] Coal-based solid waste treatment: The coal gangue is crushed to a particle size ≤2mm, thermally activated at 850℃ for 2h, cooled, and then leached with 0.5mol / L citric acid solution at a solid-liquid ratio of 1:5 for 4h. After filtration and washing, coal gangue material enriched with active aluminum ions is obtained. Mechanochemical modification of fly ash: Place fly ash in a vibratory mill, add 5wt% NaOH solution (solid-liquid mass ratio 1:3), grind for 45 minutes, and then set aside for use.

[0042] Chemical conversion of desulfurized gypsum: Desulfurized gypsum powder and 0.9 mol / L sodium carbonate solution were mixed at a solid-liquid mass ratio of 1:9 and reacted in a water bath at 55℃ for 3.5 h. The conversion product was obtained by filtration, washing and drying.

[0043] Matrix preparation: Take 50 parts of the above-treated fly ash, 30 parts of coal gangue, 15 parts of desulfurized gypsum conversion product, and 5 parts of functionalized biochar, mix them evenly in proportion, granulate (particle size 2~4mm), and dry to obtain the soil remediation matrix.

[0044] Comparative Example 1 Mechanochemically modified fly ash was used as the soil remediation matrix, and the steps for mechanochemical modification of fly ash were the same as in Example 1.

[0045] Comparative Example 2 Activated coal gangue was used as the soil remediation matrix, and the preparation steps of activated coal gangue were the same as in Example 1.

[0046] Comparative Example 3 Using only the chemical conversion product of desulfurized gypsum as the soil remediation matrix, the preparation steps of the chemical conversion product of desulfurized gypsum are the same as in Example 1.

[0047] Comparative Example 4 Functionalized biochar was used as the soil remediation matrix, and the preparation steps of functionalized biochar were the same as in Example 1.

[0048] Comparative Example 5 Untreated fly ash, coal gangue, desulfurized gypsum, and corn straw charcoal were uniformly mixed in the proportions of Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix.

[0049] The steps for preparing corn stalk charcoal are as follows: crush corn stalks to a particle size of 1-3 cm, dry them at 80℃ until the moisture content is less than 10%; take the dried corn stalk particles, pyrolyze them at 600℃ for 90 min under nitrogen protection at a temperature of 12℃ / min, grind them through a 100-mesh sieve, and then set them aside for use.

[0050] Comparative Example 6 Untreated coal gangue was uniformly mixed with desulfurized gypsum chemical conversion products, functionalized biochar, and mechanochemically modified fly ash in the proportions of Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix. The preparation steps of desulfurized gypsum chemical conversion products, functionalized biochar, and mechanochemically modified fly ash were the same as in Example 1.

[0051] Comparative Example 7 Untreated fly ash, desulfurized gypsum chemical conversion products, functionalized biochar, and activated coal gangue were uniformly mixed according to the proportions in Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix. The preparation steps of desulfurized gypsum chemical conversion products, functionalized biochar, and activated coal gangue were the same as in Example 1.

[0052] Comparative Example 8 Untreated fly ash, coal gangue, desulfurized gypsum chemical conversion products, and functionalized biochar were uniformly mixed according to the proportions in Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix. The preparation steps of the desulfurized gypsum chemical conversion products and functionalized biochar were the same as in Example 1.

[0053] Comparative Example 9 Untreated desulfurized gypsum, functionalized biochar, mechanochemically modified fly ash, and activated coal gangue were uniformly mixed according to the proportions in Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix. The preparation steps of functionalized biochar, mechanochemically modified fly ash, and activated coal gangue were the same as in Example 1.

[0054] Comparative Example 10 Corn straw charcoal, desulfurized gypsum chemical conversion products, mechanochemically modified fly ash, and activated coal gangue were uniformly mixed according to the proportions in Example 1, granulated (particle size 2-4 mm), and dried to obtain the soil remediation matrix. The preparation steps of the desulfurized gypsum chemical conversion products, mechanochemically modified fly ash, and activated coal gangue were the same as in Example 1. The preparation steps of the corn straw charcoal were the same as in Comparative Example 5.

[0055] Experimental examples verify the remediation capacity of the above-mentioned soil remediation matrix. The soil remediation substrates prepared in the above embodiments and comparative examples were applied to an acid-contaminated farmland (application rate of 4 t / mu). The initial characteristics of the acid-contaminated farmland were: pH=5.5, available Cd and Pb contents of 0.7 mg / kg and 370 mg / kg, respectively, organic matter content of 8.7 g / kg, and contents of available nitrogen, available phosphorus, and available potassium of 32.3 mg / kg, 7.8 mg / kg, and 45.6 mg / kg, respectively. After even spreading, the 10 cm thick soil was tilled to ensure uniform mixing between the soil and the substrate. The soil properties after 60 days of treatment are shown in Table 1.

[0056] The detection methods for each indicator are as follows: pH: pH meter method; Cd and Pb available content: acid digestion-plasma spectrometry; organic matter content: potassium dichromate oxidation-external heating method; alkaline nitrogen, available phosphorus and available potassium content: extraction spectrophotometry.

[0057] Table 1. Remediation capacity of soil remediation matrices prepared in each embodiment and comparative example. As shown in Table 1, Examples 1 and 2 (synergistic compounding of four types of treated solid waste) exhibited the most comprehensive and balanced superior effects in regulating soil acidity, passivating heavy metals (Cd and Pb), and improving soil fertility (organic matter and nitrogen, phosphorus, and potassium). While individual use of any one of the treated solid waste materials (Comparative Examples 1-4) showed outstanding performance in certain indicators (e.g., Comparative Example 2 showed good Cd reduction, and Comparative Example 4 showed strong organic matter enhancement), it failed to achieve a balanced and good effect across all remediation targets and may even have negative effects (e.g., Comparative Example 1 resulted in excessively high pH, ​​and Comparative Example 3 exacerbated acidification). Furthermore, the remediation effect of directly compounding untreated raw solid waste (Comparative Example 5) was far lower than that of the examples where all components underwent targeted pretreatment. The lack of pretreatment for any component (Comparative Examples 6-10) resulted in significant shortcomings in specific aspects of the remediation effect, demonstrating that each pretreatment process is indispensable for enhancing the specific remediation function of that component.

[0058] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing soil remediation matrix through synergistic activation of coal-based solid waste, characterized in that, Includes the following steps: Agricultural waste is pyrolyzed and carbonized, then impregnated with a chemical activation and modifier solution and subjected to activation heat treatment to obtain functionalized biochar. After thermal activation, coal gangue is leached with an organic acid solution to obtain activated coal gangue rich in active aluminum ions. Fly ash is mixed with alkaline solution and then subjected to mechanical chemical modification by vibration, stirring or ultrasound to obtain chemically modified fly ash with improved specific surface area and surface activity. The desulfurized gypsum is chemically converted with a carbonate solution to produce a desulfurized gypsum conversion product mainly composed of calcium carbonate. The functionalized biochar, activated coal gangue, chemically modified fly ash, and desulfurized gypsum conversion products are mixed evenly, granulated, and dried to obtain the soil remediation matrix.

2. The method according to claim 1, characterized in that, The specific preparation steps of the functionalized biochar are as follows: agricultural waste is pyrolyzed at 500-700℃ for 60-120 min under an inert atmosphere to obtain crude biochar; the crude biochar is impregnated in a chemical activator and modifier solution with a mass concentration of 10-15% for 12-24 h, and after impregnation, the solid and liquid are separated. The obtained solid is activated and heat-treated at 450-550℃ for 30-60 min under an inert atmosphere; finally, after washing, drying, and pulverizing, functionalized biochar is obtained; the chemical activator and modifier is diammonium hydrogen phosphate or diammonium dihydrogen phosphate.

3. The method according to claim 2, characterized in that, The mass ratio of the crude biochar to the chemical activator and modifier is 1:(8~12).

4. The method according to claim 1, characterized in that, The temperature for thermal activation is 650~850℃.

5. The method according to claim 1, characterized in that, The organic acid solution includes a solution of citric acid, oxalic acid, or tartaric acid; the concentration of the organic acid solution is 0.2~1 mol / L; the mass ratio of coal gangue to organic acid solution is 1:5; and the leaching treatment time is 2~6 hours.

6. The method according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide or potassium hydroxide solution with a mass concentration of 1-10%; the mass ratio of fly ash to alkaline solution is 1:3; and the mechanochemical modification time is 45 min.

7. The method according to claim 1, characterized in that, The carbonate solution is a sodium carbonate solution or an ammonium carbonate solution, and the carbonate solution concentration is 0.8~1.2 mol / L; the mass ratio of the desulfurized gypsum to the carbonate solution is 1:(8~12); the temperature of the chemical conversion reaction is 50~70℃, and the time is 2~4h.

8. The method according to claim 1, characterized in that, The mass ratio of the chemically modified fly ash, activated coal gangue, desulfurized gypsum conversion product and functionalized biochar is (4~5):(3~4):(1~1.5):(0.5~1).

9. The soil remediation matrix prepared by the method according to any one of claims 1 to 8.

10. The application of the soil remediation matrix according to claim 9 in the remediation and improvement of acidic and heavy metal contaminated soils.

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