Biochar soil heavy metal repairing agent and preparation method thereof

Abstract

The invention discloses a biochar soil heavy metal remediation agent and a preparation method thereof, and relates to the technical field of soil remediation, and the biochar soil heavy metal remediation agent comprises, by weight, 15 parts of plant straw; 20 to 25 parts of sludge; 8-12 parts of a functional filler; 1.2 to 2.5 parts of a synergist; the synergist is prepared from hydrazine hydrate and sodium sulfide in a molar ratio of 1: 1. Under the synergistic effect of sodium sulfide and hydrazine hydrate, high-valence heavy metal is reduced into low-valence heavy metal which is easy to precipitate, permanent fixation is realized by generating extremely indissolvable metal sulfide, a'sulfur chain network structure 'is formed, sulfide is physically encapsulated, additional adsorption sites are provided, and the adsorption efficiency is improved. The long-term stabilization capability and the environmental disturbance resistance of the sludge biochar to various heavy metals are greatly improved, and the method is a core step for preparing the high-performance'sulfur chain enhanced sludge biochar '.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a biochar soil heavy metal remediation agent and its preparation method. Background Technology

[0002] Soil remediation refers to the use of physical, chemical, and biological methods to transfer, absorb, degrade, and transform pollutants in soil, reducing their concentration to acceptable levels, or converting toxic and harmful pollutants into harmless substances. Fundamentally, the technical principles of contaminated soil remediation can include: (1) changing the form of pollutants in the soil or their binding with the soil, reducing their mobility and bioavailability in the environment; and (2) reducing the concentration of harmful substances in the soil.

[0003] Biochar is an aromatic solid material produced by the pyrolysis and carbonization of biomass materials in an anaerobic or oxygen-deficient environment. It has a large specific surface area and contains abundant functional groups (carboxyl, carbonyl, lactone, hydroxyl). It has strong adsorption, oxidation and cation exchange capabilities. It has been applied to the passivation and remediation of heavy metal pollutants in soil, including copper, zinc, lead, cadmium, mercury and arsenic, and has great application potential in soil heavy metal remediation.

[0004] However, due to the chelation and blocking effect of humic acid, the large number of carboxyl and phenolic hydroxyl groups it contains form chelate bonds with heavy metal ions, leading to solidification failure. The humic acid also volatilizes and escapes during the pyrolysis of biochar, making it difficult to stably fix heavy metals in high organic matter sludge, resulting in a significant reduction in the effectiveness of biochar remediation agents. Summary of the Invention

[0005] This application provides a biochar soil heavy metal remediation agent and its preparation method, which solves the problem that heavy metals in high organic matter sludge are difficult to stabilize and fix in the prior art, and achieves a significant improvement in the soil remediation effect of biochar.

[0006] This application provides a biochar soil heavy metal remediation agent, comprising, by weight: 15 parts plant straw; 20-25 parts sludge; 8-12 parts functional filler; and 1.2-2.5 parts synergist. The synergist consists of hydrazine hydrate and sodium sulfide in a 1:1 molar ratio.

[0007] Furthermore, the plant straw is made by mixing wheat straw and corn straw in a 1:1 mass ratio.

[0008] Furthermore, the functional filler is composed of zinc oxide and ferric oxide in a mass ratio of 2:1.

[0009] The method for preparing the above-mentioned biochar soil heavy metal remediation agent includes the following steps: S1. Dissolve hydrazine hydrate and sodium sulfide in deionized water to form a 10% solution and preheat to 50°C. Inject the solution into sludge with a water content of 80% and stir at 120 rpm for 15 minutes. Control the oxidation-reduction potential to -250 mV and then let it stand for 30 minutes to obtain sulfur network sludge. S2. Add 0.5 mol / L zinc oxide solution to the sulfur network sludge, wherein the ratio of zinc ions to sludge dry weight is 1:20; stir at low speed at 100 rpm for 3 hours at 60°C, then dry at 70°C for 3 hours and then dry at 105°C to obtain sulfur chain enhanced sludge biochar. S3. Soak the plant straw in 30% hydrogen peroxide at 40°C for 12 hours, then wash and dry it. Ball mill it with functional filler and citric acid at a total mass ratio of 1.5% for 6.5 hours at a ball mill speed of 280 rpm. Then, pyrolyze it in a tube furnace at 450°C for 25 minutes in an acetylene atmosphere to generate magnetic iron oxide-doped biochar. S4. Sulfur-chain reinforced sludge biochar and magnetic Fe3O4-doped biochar were added to a styrene-butadiene copolymer methyl ethyl ketone solution; ultrasonically dispersed for 25 minutes, and treated with ethanol vapor at 95°C for 13 minutes to remove the solvent; microwave irradiated at 300W for 9 minutes under nitrogen atmosphere; then soaked in 0.5 mol / L sodium hydroxide solution at 65°C for 0.8 hours to dissolve impurities; washed with 0.1 mol / L sodium thiosulfate solution at 40°C for 20 minutes to remove surface elemental sulfur; washed with water and dried to obtain the final product.

[0010] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: The synergistic effect of sodium sulfide and hydrazine hydrate is used to reduce high-valence heavy metals to easily precipitated low-valence states, achieving permanent fixation by generating extremely insoluble metal sulfides. This forms a "sulfur chain network structure," physically encapsulating the sulfides and providing additional adsorption sites, greatly enhancing the long-term stabilization capacity of sludge biochar for various heavy metals (especially cadmium, lead, chromium, and mercury) and its resistance to environmental disturbances (such as pH changes and oxidation). This is the core step in preparing high-performance "sulfur chain-enhanced sludge biochar." Detailed Implementation

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0012] Example 1: A biochar soil heavy metal remediation agent, comprising, by weight: 15 parts plant straw; 20-25 parts sludge; 8-12 parts functional filler; and 1.2-2.5 parts synergist; The plant straw is made by mixing wheat straw and corn straw in a 1:1 mass ratio; The functional filler is zinc oxide:ferric oxide in a mass ratio of 2:1; The synergists include hydrazine hydrate and sodium sulfide, which are prepared by combining the two in a 1:1 molar ratio; The preparation method of the above-mentioned biochar soil heavy metal remediation agent is as follows: S1. Dissolve hydrazine hydrate and Na2S in deionized water (concentration 10%) and preheat to 50℃±2℃; inject into sludge with 80% water content and stir at 120 rpm for 15 minutes; control the oxidation-reduction potential Eh=-250 mV, and then let it stand for 30 minutes to obtain sulfur network sludge. S2. Add 0.5 mol / L zinc oxide solution (Zn2+: sludge dry weight = 1:20) to sulfur network sludge; stir at low speed (100 rpm) at 60℃ for 3 hours, then dry at 70℃ for 3 hours and then dry at 105℃ to obtain sulfur chain enhanced sludge biochar. S3. Plant straw is soaked in hydrogen peroxide (30%, 40℃) for 12 hours, washed and dried; ball-milled with functional filler and citric acid (1.5% by mass) for 6.5 hours (280 rpm); pyrolyzed with acetylene in a tubular furnace (450℃, 25 minutes) to produce magnetic Fe3O4-doped biochar. S4. Sulfur-chain reinforced sludge biochar and magnetic Fe3O4-doped biochar were added to a styrene-butadiene copolymer (SBS) methyl ethyl ketone solution; ultrasonically dispersed for 25 minutes, and treated with ethanol vapor (95℃, 13 minutes) to remove the solvent; microwave irradiated at 300W for 9 minutes under nitrogen atmosphere; then soaked in 0.5 mol / L NaOH solution for 0.8 hours (65℃) to dissolve impurities; washed with 0.1 mol / L Na2S2O3 for 20 minutes (40℃) to remove surface elemental sulfur; washed with water and dried to obtain the final product.

[0013] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages: Sodium sulfide provides S2- ions, which react with heavy metal ions in sludge (such as Cd2+, Pb2+, Cu2+, Zn2+, Hg2+, etc.) to form extremely insoluble metal sulfide precipitates (with very small solubility products Ksp); for example, the solubility product Ksp of CdS and PbS is ≈10-28. Under reducing conditions, excess S2- can further react to form polysulfides (Sn2-) or elemental sulfur. These sulfur species are linked by sulfur bonds (SS) to form a "sulfur chain network structure" in sludge biochar. This network can physically encapsulate heavy metal sulfides and serve as adsorption sites for heavy metal ions. Sodium sulfide hydrolyzes into hydrogen hyposulfide and hydroxide ions, creating an alkaline environment that promotes the precipitation of benign metals (such as aluminum ions) into insoluble salts, reducing competition with sulfur ions. In an alkaline environment, the carboxyl groups in humic acid ionize, reducing their chelation ability with heavy metals, causing non-toxic heavy metal ions (such as aluminum ions) to precipitate, thus reducing competition with the target heavy metal. Sodium sulfide readily hydrolyzes to produce a large amount of hydrogen sulfide, but the large amount of hydroxide ions produced by the decomposition of hydrazine hydrate results in a pH greater than 10, maintaining the sulfide ions in a stable ionic state and inhibiting the formation of hydrogen sulfide. The low redox potential (Eh = -250mV) prevents S²⁻ from being oxidized to elemental sulfur or SO₄²⁻. In an alkaline reducing environment, excess S²⁻ is converted into polysulfide ions (SO₄²⁻, S₆²⁻), which then polymerize through S₂S bonds to form a "sulfide chain network." Polysulfides are chemically stable, do not produce H₂S, and serve as immobilization carriers for heavy metals. Furthermore, they promote the recycling of sulfide ions in the reaction and prevent hydrazine hydrate from forming polysulfide heavy metal products with polysulfide bonds. For example, with lead: SH−+S2−→S2H−+H+; SnH−+S2−→Sn+1H−+H+; Pd2++Sn+H−→CdSn+H+; When n≥2, the polysulfide bonds generated are more likely to form network aggregations and form a more stable fixed structure compared to CdS. Polysulfide bonds preferentially bind to heavy metals compared to the carboxyl / phenolic hydroxyl groups of humic acids, thus blocking the chelation pathway. The synergistic effect of sodium sulfide and hydrazine hydrate is used to reduce high-valence heavy metals to easily precipitated low-valence states, achieving permanent fixation by generating extremely insoluble metal sulfides and forming a "sulfur chain network structure". This physically encapsulates the sulfides and provides additional adsorption sites, greatly enhancing the long-term stabilization ability of sludge biochar for various heavy metals (especially cadmium, lead, chromium, mercury, etc.) and its resistance to environmental disturbances (such as pH changes and oxidation). This is the core step in preparing high-performance "sulfur chain enhanced sludge biochar".

[0014] To verify the above technical solution and technical principle, experiments were conducted, including determination of the reduction rate of available heavy metals (GB / T 23739-2009), detection of leaching concentration (US EPA 1311), and detection of sulfur chain stability (heavy metal leaching rate was detected after curing in an oxidizing environment containing 0.1 mol / L H2O2). The experimental site was artificially prepared simulated contaminated soil containing Cd2+ (50 mg / kg), Pb2+ (300 mg / kg), and humic acid (200 g / kg). The remediation agent was added to the contaminated soil at a mass ratio of 5%, and the soil was cured for 28 days. The results are shown in Table 1. Table 1. Results of the formulation experiment

[0015] Then, a principle experiment was conducted, building upon Experiment 5, including S. 2- (Methylene blue spectrophotometry), S n 2- (Cyanide decomposition method + methylene blue method), S 0 Content detection (HPLC detection after toluene extraction), H2S release detection (GB / T 16157), pH detection, grouped as G1: the only difference from Experiment 5 is the absence of hydrazine hydrate; G2: the only difference from Experiment 5 is the absence of sodium sulfide; G3: Experiment 5; results are shown in Table 2. Table 2 Principle Experiment Results

[0016] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biochar soil heavy metal remediation agent, characterized in that, By weight, it includes: 15 parts plant straw; 20-25 parts sludge; 8-12 parts functional filler; and 1.2-2.5 parts synergist. The synergist consists of hydrazine hydrate and sodium sulfide in a 1:1 molar ratio.

2. The biochar soil heavy metal remediation agent according to claim 1, characterized in that, The plant straw mentioned therein is made by mixing wheat straw and corn straw in a 1:1 mass ratio.

3. The biochar soil heavy metal remediation agent according to claim 1, characterized in that, The functional filler is composed of zinc oxide and ferric oxide in a mass ratio of 2:

1.

4. A method for preparing the biochar soil heavy metal remediation agent as described in claim 1, characterized in that, Includes the following steps: S1. Dissolve hydrazine hydrate and sodium sulfide in deionized water to form a 10% solution and preheat to 50°C. Inject the solution into sludge with a water content of 80% and stir at 120 rpm for 15 minutes. Control the oxidation-reduction potential to -250 mV and then let it stand for 30 minutes to obtain sulfur network sludge. S2. Add 0.5 mol / L zinc oxide solution to the sulfur network sludge, wherein the ratio of zinc ions to sludge dry weight is 1:20; stir at low speed at 100 rpm for 3 hours at 60°C, then dry at 70°C for 3 hours and then dry at 105°C to obtain sulfur chain enhanced sludge biochar. S3. Soak the plant straw in 30% hydrogen peroxide at 40°C for 12 hours, then wash and dry it. Ball mill it with functional filler and citric acid at a total mass ratio of 1.5% for 6.5 hours at a ball mill speed of 280 rpm. Then, pyrolyze it in a tube furnace at 450°C for 25 minutes in an acetylene atmosphere to generate magnetic iron oxide-doped biochar. S4. Sulfur-chain reinforced sludge biochar and magnetic Fe3O4-doped biochar were added to a styrene-butadiene copolymer methyl ethyl ketone solution; ultrasonically dispersed for 25 minutes, and treated with ethanol vapor at 95°C for 13 minutes to remove the solvent; microwave irradiated at 300W for 9 minutes under nitrogen atmosphere; then soaked in 0.5 mol / L sodium hydroxide solution at 65°C for 0.8 hours to dissolve impurities; washed with 0.1 mol / L sodium thiosulfate solution at 40°C for 20 minutes to remove surface elemental sulfur; washed with water and dried to obtain the final product.

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