A hexavalent chromium contaminated soil remediation agent

Abstract

This application relates to the field of hexavalent chromium contaminated soil remediation, specifically disclosing a hexavalent chromium contaminated soil remediation agent. Taking 100 kg of hexavalent chromium contaminated soil as an example, it comprises the following raw materials in the following amounts: molasses: 10-50 kg; vinegar residue wastewater: 10-50 kg; modified nano-iron: 5-15 kg; the pH value of the vinegar residue wastewater is 2-3. The remediation agent of this application can more quickly and thoroughly reduce hexavalent chromium in the soil, improving the remediation effect.

Description

Technical Field

[0001] This application relates to the field of hexavalent chromium contaminated soil remediation, and in particular to a hexavalent chromium contaminated soil remediation agent. Background Technology

[0002] In the industrial production processes of chromium ore mining and smelting, electroplating, metal processing, leather making, pigment production, and printing and dyeing, the discharge of wastewater, waste residue, and waste has caused serious chromium pollution to the surrounding soil and groundwater. This has greatly harmed the lives of residents and the ecological environment.

[0003] Chromium in contaminated soil and groundwater exists primarily in two valence states: hexavalent chromium and trivalent chromium. Trivalent chromium has low toxicity and high stability, while hexavalent chromium is highly toxic, has poor stability, and strong migration ability. The key to remediating chromium pollution lies in reducing hexavalent chromium to trivalent chromium, thereby reducing its toxicity and migration ability.

[0004] Molasses is a commonly used soil chromium pollution remediation agent. It contains abundant sugars (mainly sucrose), colloids, and other reducing substances, which can act as electron donors for hexavalent chromium, reducing it to trivalent chromium. Simultaneously, it significantly promotes the growth of soil microorganisms and reduces soil oxygen content, thereby gradually lowering the soil's redox potential and maintaining a reducing environment. This further promotes the reduction of hexavalent chromium to trivalent chromium, which then reacts with organic matter to form stable chelates, achieving a more efficient reduction of hexavalent chromium. However, molasses has limited reducing capacity and exhibits poor remediation effects and low efficiency for medium-to-high chromium contaminated soils (>1000 mg / kg), requiring a long remediation time. Summary of the Invention

[0005] This application provides a hexavalent chromium contaminated soil remediation agent, which can significantly improve the remediation effect and efficiency of medium- and high-concentration hexavalent chromium contaminated soil.

[0006] This application provides a hexavalent chromium contaminated soil remediation agent. Taking 100 kg of hexavalent chromium contaminated soil as an example, it includes the following raw materials in the following amounts:

[0007] Molasses: 10-50 kg;

[0008] Vinegar residue wastewater: 10-50 kg;

[0009] Modified nano-iron: 5-15 kg;

[0010] The pH value of the vinegar residue wastewater is 2 to 3.

[0011] Preferably, the particle size of the nano-iron is 10-100 nm, more preferably 20-60 nm.

[0012] A remediation agent derived from the compounding of molasses, vinegar residue wastewater, and modified nano-iron significantly improves the remediation effect and rate for soils contaminated with medium to high concentrations of chromium. Firstly, vinegar residue wastewater contains abundant Bacillus, Escherichia coli, Abnormal cocci, Micromonas, Methylobacterium, Massébacterium, Acidobacterium, Trichophyton, Rhizobium, and Arthrobacter. These microorganisms utilize vinegar residue wastewater and molasses as carbon sources and nutrients, enabling rapid reproduction and growth, and reducing hexavalent chromium to trivalent chromium, thus improving reduction efficiency and effectiveness. Nano-iron possesses high reducing activity and high migration capacity. In the acidic environment provided by vinegar residue wastewater, its activity is further enhanced, allowing it to rapidly react with hexavalent chromium in the soil, thereby improving the remediation effect and rate.

[0013] Secondly, molasses is relatively viscous and has poor migration ability. Vinegar residue wastewater can dilute molasses, promoting its migration and reaction, effectively saving water resources; it also reduces energy consumption in treating vinegar residue wastewater. Furthermore, vinegar residue wastewater can provide an acidic environment for molasses, further enhancing its reducing activity and improving remediation efficiency.

[0014] Finally, the remediated soil not only shows a significant reduction in pollutant concentration but also a marked improvement in soil fertility, preventing soil compaction and salinization, which is beneficial for agricultural production.

[0015] The vinegar residue in this application is a byproduct of the vinegar-making process. In production, wheat bran, sorghum, broken rice, etc. are used as raw materials. After fermentation and brewing, the residue left after extracting vinegar is the vinegar residue. The vinegar residue wastewater is a mixture of vinegar residue and water.

[0016] Preferably, the modified nano-iron is prepared by surface modification of nano-iron and a modifier in a mass ratio of 10:(0.2-0.5); the modifier includes an anionic surfactant and hexamethylsilazane in a mass ratio of (1-2):1; the anionic surfactant contains long-chain alkyl groups in its molecular chain.

[0017] Using anionic surfactants and hexamethylsilazane as surface modifiers for nano-iron can inhibit its aggregation and sedimentation tendency while ensuring its migration and reduction capabilities, thus enabling it to be fully dispersed and exert a reduction and repair effect. Specifically, after the anionic surfactant adheres to the surface of the nano-iron, it can form a steric hindrance through long-chain alkyl groups, which can repel oxidizing macromolecular organic matter and reduce the loss of nano-iron. At the same time, the anionic surfactant adsorbs hexavalent chromium through electrostatic interaction, promoting its reduction and transformation.

[0018] However, excessive anionic surfactants can reduce the migration ability of nano-iron in soil and inhibit its remediation effect. Therefore, the modifier in this application incorporates a portion of hexamethyldisilazane, which, after hydrolysis to form silanol groups, adsorbs onto the surface of nano-iron. This inhibits aggregation while maintaining a high degree of migration ability of the nano-iron, ensuring remediation efficiency.

[0019] In summary, using anionic surfactants and hexamethylsilazane as surface modifiers for nano-iron is beneficial for achieving a balance between the steric hindrance and migration capabilities of nano-iron, thereby improving the repair effect and rate of hexavalent chromium.

[0020] Preferably, the anionic surfactant is selected from one or more of alkylbenzene sulfonates, alkyl glycerol ether sulfonates, alkyl phosphate salts, sodium alkyl ether sulfates, fatty alcohol sulfates, and fatty alcohol polyoxyethylene ether sulfates.

[0021] The above-mentioned anionic surfactants all contain long-chain alkyl groups, which have good steric hindrance and anti-agglomeration effects, inhibit the agglomeration and sedimentation of nano-iron, and block the reaction between oxidizing macromolecular organic matter and nano-iron.

[0022] Preferably, the long-chain alkyl group has 12 to 18 carbon atoms.

[0023] Preferably, the repair agent further includes 3-10 kg of molasses hydrolysate.

[0024] Due to factors such as soil viscosity and charged particles, soil particles easily aggregate to form dense flocs. The hexavalent chromium encapsulated within these flocs is difficult to reduce, leading to a decrease in reduction efficiency and rate. To overcome this problem, this application adds enzymatically hydrolyzed molasses products. These products contain small-molecule reducing substances and natural small-molecule dispersants. The small-molecule dispersants can insert into and adsorb onto the soil particles in the flocs, acting as a dispersant and promoting the penetration reaction of the small-molecule reducing substances. They can even break down the aggregates and release the encapsulated hexavalent chromium, thereby improving remediation efficiency and hexavalent chromium removal rate.

[0025] Preferably, the molasses enzymatic hydrolysis product amine is prepared according to the following method:

[0026] Pretreatment: Mix molasses with water to prepare a molasses aqueous solution, adjust the pH of the solution to 4.5-5.5, and obtain the reaction solution; Enzymatic hydrolysis: Heat the reaction solution to 50-60℃, add enzyme solution, mix well, and carry out enzymatic hydrolysis under microwave to obtain molasses enzymatic hydrolysate;

[0027] Preferably, the concentration of the molasses aqueous solution is 50–150 g / L;

[0028] Preferably, the concentration of the enzyme solution is 0.05–0.1 U / mL;

[0029] Preferably, the mass ratio of the molasses aqueous solution to the enzyme solution is 1 to 3:1;

[0030] Preferably, the enzymatic hydrolysis time is 3 to 6 hours.

[0031] Preferably, the microwave power is 500-1000W.

[0032] Preferably, the enzymes used in the molasses hydrolysate include fructosyltransferase and / or cellulase.

[0033] Preferably, the enzymes used in the molasses hydrolysate are fructosyltransferase and cellulase in a mass ratio of (5-10):1.

[0034] Fructosyltransferases primarily function to break down sucrose in molasses into smaller, reducing glucose or fructose molecules. Cellulases can break down flavonoids and other substances in molasses into smaller, reducing molecules.

[0035] It should be noted that the cellulase in this application is a complex enzyme composed of exo-β-glucanase, endo-β-glucanase, and β-glucosidase.

[0036] Preferably, the vinegar residue content in the vinegar residue wastewater is 10-60 wt%.

[0037] This application does not have special requirements for the vinegar residue content in the vinegar residue wastewater, but preferably uses wastewater with a content of 10-60 wt% to improve the remediation efficiency.

[0038] Preferably, the molasses is selected from at least one of sugarcane molasses and beet molasses.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. This application utilizes molasses, vinegar residue wastewater, and nano-iron oxide in combination to significantly improve the remediation rate and hexavalent chromium ion removal rate of soils contaminated with medium to high concentrations of chromium; at the same time, it improves soil fertility.

[0041] 2. This application uses anionic surfactants and hexamethylsilazane as modifiers for nano-iron particles, which can effectively balance the steric hindrance and migration ability of nano-iron, thereby improving the repair effect and rate of hexavalent chromium.

[0042] 3. By adding molasses hydrolysate, this application can penetrate and destroy flocculent aggregates in the soil, thereby improving the remediation effect and rate of hexavalent chromium. Detailed Implementation

[0043] Example of preparation of modified nano-iron

[0044] Preparation Example 1-1: A modified nano-iron was prepared according to the following method:

[0045] 10 kg of nano-iron was added to a mixed solution of 2 kg ethanol and 0.5 kg water and dispersed evenly. Then, 0.24 kg of sodium dodecyl ether sulfate and 0.12 kg of hexamethyldisilazane were added, and the mixture was heated to 55 °C and stirred for 1.5 h. After the reaction was completed, the material was released, dried to remove ethanol and water, and modified nano-iron was obtained.

[0046] Preparation Examples 1-2: A modified nano-iron was prepared according to the following method:

[0047] 10 kg of nano-iron was added to a mixed solution of 2 kg ethanol and 0.5 kg water and dispersed evenly. Then, 0.1 kg of sodium dodecylbenzenesulfonate and 0.1 kg of hexamethyldisilazane were added, and the mixture was heated to 55 °C and stirred for 1.5 h. After the reaction was completed, the material was released, dried to remove ethanol and water, and modified nano-iron was obtained.

[0048] Preparation Examples 1-3: A modified nano-iron was prepared according to the following method:

[0049] 10 kg of nano-iron was added to a mixed solution of 2 kg ethanol and 0.5 kg water and dispersed evenly. Then, 0.25 kg of sodium dodecyl ether sulfate and 0.2 kg of hexamethyldisilazane were added, and the mixture was heated to 60 °C and stirred for 2 h. After the reaction was completed, the material was released, dried to remove ethanol and water, and modified nano-iron was obtained.

[0050] Preparation Examples 1-4, a modified nano-iron, differs from Preparation Example 1-1 in that an equal amount of sodium dodecyl ether sulfate is used instead of hexamethyldisilazane.

[0051] Preparation Examples 1-5, a modified nano-iron, differ from Preparation Example 1-1 in that an equal amount of hexamethyldisilazane is used instead of sodium dodecyl ether sulfate.

[0052] Preparation Examples 1-6, a modified nano-iron, differ from Preparation Example 1-1 in that an equal amount of octadecyltrimethylammonium chloride is used instead of sodium dodecyl ether sulfate.

[0053] Example of molasses degradation solution preparation

[0054] Preparation Example 2-1: A molasses enzymatic hydrolysate was prepared according to the following method:

[0055] Pretreatment: Mix molasses with water to prepare a molasses aqueous solution of 100 g / L, adjust the pH of the solution to 4.5-5.5, and obtain the reaction solution.

[0056] Enzymatic hydrolysis: Take 26 kg of reaction solution, heat it to 60°C, add 10 kg of enzyme solution with a concentration of 0.1 U / mL, stir evenly, and carry out enzymatic hydrolysis under microwave with a microwave power of 1000 W. After 5 h, molasses hydrolysate is obtained.

[0057] The enzyme solution contains fructosyltransferase and cellulase in a mass ratio of 8:1. Both fructosyltransferase and cellulase are commercially available products.

[0058] Preparation Example 2-2: A molasses enzymatic hydrolysate was prepared according to the following method:

[0059] Pretreatment: Mix molasses with water to prepare a molasses aqueous solution of 50 g / L, adjust the pH of the solution to 4.5-5.5, and obtain the reaction solution.

[0060] Enzymatic hydrolysis: Take 30 kg of reaction solution, heat it to 60°C, add 10 kg of enzyme solution with a concentration of 0.06 U / mL, stir evenly, and carry out enzymatic hydrolysis under microwave with a microwave power of 1000 W. After 4 hours, molasses hydrolysate is obtained.

[0061] The enzyme solution contains fructosyltransferase and cellulase in a mass ratio of 5:1. Both fructosyltransferase and cellulase are commercially available products.

[0062] Preparation Example 2-3: A molasses enzymatic hydrolysate was prepared according to the following method:

[0063] Pretreatment: Mix molasses with water to prepare a molasses aqueous solution of 150 g / L, adjust the pH of the solution to 4.5-5.5, and obtain the reaction solution.

[0064] Enzymatic hydrolysis: Take 22 kg of reaction solution, heat it to 60°C, add 10 kg of enzyme solution with a concentration of 0.08 U / mL, stir evenly, and carry out enzymatic hydrolysis under microwave with a microwave power of 1000 W. After 6 h, molasses hydrolysate is obtained.

[0065] The enzyme solution contains fructosyltransferase and cellulase in a mass ratio of 7:1. Both fructosyltransferase and cellulase are commercially available products.

[0066] Preparation Example 2-4, a molasses enzymatic hydrolysate, differs from Preparation Example 2-1 in that an equal amount of fructosyltransferase is used instead of cellulase in the enzyme solution.

[0067] Preparation Example 2-5, a molasses enzymatic hydrolysate, differs from Preparation Example 2-1 in that an equal amount of cellulase is used instead of fructosyltransferase in the enzyme solution.

[0068] Example

[0069] Example 1: A hexavalent chromium contaminated soil remediation agent, the raw material composition of which is shown in Table 1.

[0070] Examples 2-4 describe a hexavalent chromium contaminated soil remediation agent, which differs from Example 1 in that the raw material ratios are different and are shown in Table 1.

[0071] Table 1. Raw material ratios for Examples 1-4

[0072]

[0073]

[0074] Example 5, a hexavalent chromium contaminated soil remediation agent, differs from Example 2 in that the modified nano-iron is obtained from Preparation Examples 1-4.

[0075] Example 6, a hexavalent chromium contaminated soil remediation agent, differs from Example 2 in that the modified nano-iron is obtained from Preparation Examples 1-5.

[0076] Example 7, a hexavalent chromium contaminated soil remediation agent, differs from Example 2 in that the modified nano-iron is obtained from Preparation Examples 1-6.

[0077] Example 8, a soil remediation agent for hexavalent chromium contaminated soil, differs from Example 2 in that the molasses hydrolysate is obtained from Preparation Examples 2-4.

[0078] Example 9, a soil remediation agent for hexavalent chromium contaminated soil, differs from Example 2 in that the molasses hydrolysate is obtained from Preparation Examples 2-5.

[0079] Example 10, a soil remediation agent for hexavalent chromium contaminated soil, differs from Example 2 in that an equal amount of molasses is used to replace the molasses hydrolysate prepared in Example 2-1.

[0080] Comparative Example

[0081] Comparative Example 1, a hexavalent chromium contaminated soil remediation agent, differs from Example 1 in that it uses an equal amount of molasses instead of modified nano-iron.

[0082] Comparative Example 2, a hexavalent chromium contaminated soil remediation agent, differs from Example 1 in that it uses an equal amount of unmodified nano-iron instead of modified nano-iron.

[0083] Comparative Example 3, a hexavalent chromium contaminated soil remediation agent, differs from Example 1 in that it uses an equal amount of molasses instead of vinegar residue wastewater.

[0084] Comparative Example 4, a hexavalent chromium contaminated soil remediation agent, differs from Example 1 in that an equal amount of vinegar residue wastewater is used instead of molasses.

[0085] Performance testing

[0086] Repair agent repair performance test:

[0087] (1) Sample preparation: The hexavalent chromium contaminated soil was taken from a chromium-contaminated site in Inner Mongolia. The soil texture was clayey sandy soil and the hexavalent chromium content was 8090 mg / kg. 1 kg of the remediation agent obtained in the above examples or comparative examples was added to 1 kg of hexavalent chromium contaminated soil as a test sample; 1 kg of deionized water was added to 1 kg of hexavalent chromium contaminated soil as a blank control; the soil was cured for 30 days in a test environment of 23℃±2℃. Every day, the soil was taken out and placed on a constant temperature shaker and shaken for 1 hour.

[0088] (2) Periodic sampling and testing: The content of hexavalent chromium in the soil of the system was determined by the method of "Determination of hexavalent chromium in soil and sediment by alkaline extraction-flame atomic absorption spectrophotometry (HJ 1082-2019)" and the content of hexavalent chromium in the supernatant of the system was determined by the method of "Determination of hexavalent chromium in water by diphenylcarbazide spectrophotometry (GB / T7467-1987)". The experimental results are shown in Table 2.

[0089] Table 2. Experimental Results

[0090]

[0091] (1) As can be seen from Examples 1-10 and Comparative Examples 1-4 and Table 2, this application can significantly improve the remediation effect and remediation rate of hexavalent chromium contaminated soil by using vinegar residue wastewater, molasses and modified nano iron together.

[0092] (2) As can be seen from Example 1 and Example 2 and Table 2, the addition of molasses hydrolysate in this application is beneficial to improving the remediation effect of hexavalent chromium contaminated soil and the reduction of hexavalent chromium in the soil is more thorough.

[0093] (3) As can be seen from Examples 2 and 5-7 and Table 2, this application improves the remediation rate (hexavalent chromium removal rate) and reduction rate of hexavalent chromium soil by using anionic surfactants containing long-chain alkyl groups and hexamethyldisilazane to modify the surface of nano-iron. The reason may be that the combination of the two substances can inhibit the tendency of agglomeration and sedimentation while ensuring the migration ability of nano-iron, and promote its uniform dispersion, thereby helping to ensure the reduction effect of nano-iron.

[0094] (4) As can be seen from Examples 2 and 8-10 and Table 2, the enzymatic hydrolysate of this application uses a combination of cellulase and fructosyltransferase, which is beneficial to improving the removal rate of hexavalent chromium in the soil. The reason may be that the combination of the two enzymes is conducive to obtaining higher content and more types of small molecule reducing substances.

[0095] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A soil remediation agent for hexavalent chromium contaminated soil, characterized in that, Taking 100 kg of hexavalent chromium-contaminated soil as an example, the remediation agent comprises the following raw materials in parts by weight: Molasses: 10-50 kg; Vinegar residue wastewater: 10-50 kg; Modified nano-iron: 5-15 kg; The pH value of the vinegar residue wastewater is 2-3; The modified nano-iron is prepared by surface modification of nano-iron and a modifier in a mass ratio of 10:(0.2-0.5); the modifier includes an anionic surfactant and hexamethylsilazane in a mass ratio of (1-2):1; the anionic surfactant contains long-chain alkyl groups in its molecular chain; The repair agent also includes 3-10 kg of molasses enzymatic hydrolysate; The molasses enzymatic hydrolysis product was prepared according to the following method: Pretreatment: Mix molasses with water to prepare a molasses aqueous solution, adjust the pH of the solution to 4.5-5.5, and obtain the reaction solution; Enzymatic hydrolysis: Heat the reaction solution to 50-60℃, add enzyme solution, mix well, and carry out enzymatic hydrolysis under microwave to obtain molasses hydrolysate; The concentration of the molasses aqueous solution is 50–150 g / L; The concentration of the enzyme solution is 0.05–0.1 U / mL; The mass ratio of the molasses aqueous solution to the enzyme solution is 1 to 3:1; The enzymatic hydrolysis time is 3 to 6 hours.

2. The hexavalent chromium contaminated soil remediation agent according to claim 1, characterized in that, The anionic surfactant is selected from one or more of alkylbenzene sulfonates, alkyl glycerol ether sulfonates, alkyl phosphate salts, sodium alkyl ether sulfates, fatty alcohol sulfates, and fatty alcohol polyoxyethylene ether sulfates.

3. A hexavalent chromium contaminated soil remediation agent according to claim 1 or 2, characterized in that, The long-chain alkyl group has 12 to 18 carbon atoms.

4. The hexavalent chromium contaminated soil remediation agent according to claim 1, characterized in that, The enzymes used in the molasses hydrolysate include fructosyltransferase and / or cellulase.

5. The hexavalent chromium contaminated soil remediation agent according to claim 4, characterized in that, The enzymes used in the molasses hydrolysate are fructosyltransferase and cellulase in a mass ratio of (5-10):

1.

6. The hexavalent chromium contaminated soil remediation agent according to claim 1, characterized in that, The vinegar residue content in the vinegar residue wastewater is 10-60 wt%.

7. The hexavalent chromium contaminated soil remediation agent according to claim 1, characterized in that, The molasses is selected from at least one of sugarcane molasses and beet molasses.

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