A nano zero-valent iron modified material and a method for repairing dechlorination pollution thereof

Abstract

The present invention discloses a biochar-supported rhamnolipid-coated nano-zero valent iron modified material, its preparation method and application. The modified nano-zero valent iron material includes biomass carbon, rhamnolipid and nano-zero valent iron. The rhamnolipid is modified on the surface of the nano-zero valent iron and loaded on the biomass carbon. The mass ratio of nano-zero valent iron, rhamnolipid and biochar is 1:0.05-0.2:0.5-2. The preparation method is to mix the rhamnolipid solution with the ferrous sulfate solution, then mix with the biomass carbon, and dropwise add the NaHB4 solution for reaction to obtain the modified nano-zero valent iron material. The biochar-supported rhamnolipid-coated nano-zero valent iron material of the present invention has the advantages of good stability, high reaction activity, strong dispersion performance, etc. It has good removal efficiency for the chlorinated flame retardant dechlorane in the environment and will not cause secondary pollution, and has potential good application value and broad application prospects in the field of organic polluted soil and water treatment.

Description

Technical Field

[0001] The present invention relates to the field of environmental pollution remediation research, and specifically to a preparation method and a remediation method of a nano zero-valent iron modified material for remediating dechlorane pollution in soil. Background Art

[0002] Soil is both a source and a sink of pollutants. With industrialization and urban expansion, a large amount of pollutants have accumulated in urban soil, posing a threat to ecological security and human health. It is crucial to develop environmentally friendly soil pollution remediation technologies to ensure the safety of urban soil. Dechlorane Plus (DP) is a chlorinated flame retardant that has been widely added to electronic and electrical products (such as TVs and computers), plastics, fibers, and wire and cable coatings. Since DP is an additive flame retardant and does not form chemical bonds with plastics or other products, it is extremely easy to detach from the product surface and be released into the environment. Moreover, DP has biological toxicity, long-distance transportability, and is difficult to degrade, posing a huge potential risk to the ecological environment and biological health. However, there are few reports on the treatment technology for DP. Based on this, this patent has prepared an environmentally friendly material for the removal of organic pollutants such as DP.

[0003] Nano zero-valent iron (NZVI) is regarded as an effective remediation material for removing heavy metals and organic pollutants due to its large specific surface area and strong reducibility. However, NZVI itself is prone to agglomeration, which will reduce its migration in soil and groundwater. NZVI is extremely easy to oxidize, forming a passivation film on its surface, which prevents NZVI from further reacting with pollutants during application. In addition, due to the extremely small particle size of NZVI, it is difficult to separate in practical applications and is easy to lose, which may cause new ecological environment problems. Therefore, in order to improve the limitations of NZVI, NZVI needs to be modified.

[0004] Surface modification and loading of NZVI are currently the two main modification methods. Among them, the use of surface stabilizers performs excellently in terms of steric stabilization or electrostatic repulsion. On this basis, it can be coated on the surface of NZVI to improve the mobility of NZVI and weaken aggregation. Rhamnolipid is a glycolipid anionic biosurfactant. It has been studied that it can effectively prevent the aggregation of NZVI, and at the same time has multifunctionality and environmental friendliness. In particular, it can desorb hydrophobic organic pollutants from the soil and enhance the effective removal of organic pollutants by NZVI. In addition, biochar loaded with NZVI can endow the adsorbent with characteristics such as a developed pore structure and a high specific surface area, as well as good mechanical strength and chemical stability, significantly enhancing the reduction performance and adsorption performance of NZVI. And biochar is low-cost, renewable and recyclable, meeting the current theme of "green development". Therefore, a biochar-supported rhamnolipid-coated nano zero-valent iron material was synthesized by a liquid-phase reduction method using rice straw biochar as a carrier and rhamnolipid as a coating. This material not only improves the drawback that nanomaterials may flow into the ecosystem due to their too small size and cause new environmental problems, but also improves the shedding problem caused by the insufficient stabilization of zero-valent iron by a single mechanical support. In summary, the present invention provides a new idea and method for the removal of organic pollutants by modified nano zero-valent iron. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a modified nano zero-valent iron material and repairing decabromodiphenyl ether (BDE-209)-contaminated soil, that is, using biochar-supported rhamnolipid-coated nano zero-valent iron for modification and applying it to the treatment of BDE-209-contaminated new pollutants.

[0006] The present invention is achieved by the following technical solutions:

[0007] Preparation of a biochar-supported rhamnolipid-coated nano zero-valent iron modified material and its application to the repair method of BDE-209 contamination. This method first selects biomass for the preparation of biochar, then coats rhamnolipid on nano zero-valent iron to modify nano zero-valent iron, and then loads the rhamnolipid-coated nano zero-valent iron material on biochar to prepare a biochar-supported rhamnolipid-coated nano zero-valent iron modified material. Then the material is applied to the repair of BDE-209-contaminated soil and water bodies.

[0008] The specific implementation steps of the method of the present invention are as follows:

[0009] 1. Wash the selected biomass, dry it, crush it, and then put it into a muffle furnace for pyrolysis. After completion, cool it down to room temperature to obtain the biochar;

[0010] 2. Mix absolute ethanol and deoxygenated deionized water in a volume ratio of 1:1 (v:v), put them into a three-necked flask, introduce nitrogen, and stir and mix evenly to obtain solution A;

[0011] 3. Add rhamnolipid to deoxygenated deionized water to prepare solution B;

[0012] 4. Pour solution B and FeSO4·7H20 into solution A, and perform electric stirring under nitrogen protection to obtain solution C;

[0013] 5. Put biochar into solution C and continuously stir to obtain solution D;

[0014] 6. Dropwise add NaBH4 solution to solution D, continue stirring under nitrogen protection, and centrifuge to separate precipitate E;

[0015] 7. Wash precipitate E repeatedly with absolute ethanol and deoxygenated deionized water, and freeze-dry to obtain the biochar-supported rhamnolipid-coated nano zero-valent iron material;

[0016] 8. Mix the dried biochar-supported rhamnolipid-coated nano zero-valent iron material with the soil contaminated by Dechlorane Plus (DP) in a certain proportion. After a certain period of time, DP in the contaminated soil can be removed until its environmental safety standard is reached.

[0017] The present invention has the following advantages and beneficial effects:

[0018] The present invention uses biochar, rhamnolipid, and FeSO4·7H20 as raw materials, and prepares the biochar-supported rhamnolipid-coated nano zero-valent iron material by the liquid-phase reduction method. Compared with the unmodified nano zero-valent iron, the oxidation rate and agglomeration phenomenon of the prepared material are significantly decreased.

[0019] Modify nano zero-valent iron with biochar and rhamnolipid. The obtained modified material combines the advantages of the three. It not only increases the size of the material, facilitating the recovery of the material after soil remediation. Also, due to the coating effect of rhamnolipid, the bioavailability of DP is improved, thus promoting the reaction activity of nano zero-valent iron and DP.

[0020] The biochar-supported rhamnolipid-coated nano zero-valent iron material prepared by the present invention can efficiently remove DP in the soil and effectively inhibit the accumulation of DP in the ecological environment. This method will also provide a reference for the remediation of other types of organic pollution. Description of the Drawings

[0021] Figure 1It is the removal rate of the biochar-supported rhamnolipid-coated nano-zero-valent iron material applied to the DP-contaminated soil (for 60 days), and the dechlorane concentrations in the contaminated soil are 1500 ng / g, 2000 ng / g, and 3000 ng / g, respectively. A total of five treatments are set: (1) control treatment without adding materials (CK); (2) 3% nano-zero-valent iron material (F); (3) 3% biochar-supported nano-zero-valent iron material (FC); (4) 3% rhamnolipid-coated nano-zero-valent iron material (FR); (5) 3% biochar-supported rhamnolipid-coated nano-zero-valent iron material (FRC);

[0022] Figure 2 It is the DP removal rate after different proportions of biochar-supported rhamnolipid-coated nano-zero-valent iron materials are put into the water with a DP contamination concentration of 1000 ng / L. Detailed implementation mode

[0023] Example 1: Simulation test for the remediation of dechlorane-contaminated soil

[0024] This experiment was carried out in the laboratory. A certain amount of DP pollutant was artificially added to the soil, and after equilibration for a period of time, remediation was carried out. The soil used was brown loam soil not contaminated by DP. First, a certain dose of DP pollutant was added to the soil, and then it was mixed evenly to obtain DP-contaminated soil. During this period, deionized water was regularly sprayed into the soil to keep the soil moisture content at about 30%, and stirring was carried out. A total of five treatments were done: (1) control treatment without adding materials (CK); (2) 3% nano-zero-valent iron material (F); (3) 3% biochar-supported nano-zero-valent iron material (FC); (4) 3% rhamnolipid-coated nano-zero-valent iron material (FR); (5) 3% biochar-supported rhamnolipid-coated nano-zero-valent iron material (FRC).

[0025] The specific implementation steps are as follows:

[0026] (1) First, the DP pollutant powder was evenly mixed with the soil to obtain DP-contaminated soil with concentrations of 1500 ng / g, 2000 ng / g, and 3000 ng / g, respectively; (2) Then, the nano-zero-valent iron (F), biochar-supported nano-zero-valent iron (FC), rhamnolipid-coated nano-zero-valent iron (FR), and biochar-supported rhamnolipid-coated nano-zero-valent iron (FRC) materials were added to the dechlorane-contaminated soil at different concentrations according to a ratio of 3% and mixed evenly, and a group of DP-contaminated soil without adding materials was prepared as a control group; (3) After 60 days, soil samples were collected, freeze-dried, extracted and purified through a 0.22 μm filter head, filtered into a 1 mL injection vial, and the residual amount of DP in the soil was measured by a gas chromatograph, and its removal rate was calculated.

[0027] This example can enable researchers and technicians in this field to understand the invention more intuitively and comprehensively, but does not limit the invention in any way.

[0028] Example 2: Simulation test of the removal effect of dechlorane plus in aqueous solution

[0029] This experiment was conducted in the laboratory. A certain amount of DP pollutant was artificially added to the aqueous solution to prepare a polluted water sample with an initial DP concentration of 1000 ng / L. Then, with the zero-valent iron ratio maintained at 1, modified materials with different mass ratios of rhamnolipid to biochar were added to the DP-polluted water sample and shaken in a constant-temperature shaker (25 °C) for 2 h. The modified materials with different mass ratios of nano zero-valent iron to rhamnolipid mainly included: (1) rhamnolipid:biochar = 0.05:0.5; (2) rhamnolipid:biochar = 0.05:1; (3) rhamnolipid:biochar = 0.05:2; (4) rhamnolipid:biochar = 0.1:0.5; (5) rhamnolipid:biochar = 0.1:1; (6) rhamnolipid:biochar = 0.1:20.5; (7) rhamnolipid:biochar = 0.2:0.5; (8) rhamnolipid:biochar = 0.2:1; (9) rhamnolipid:biochar = 0.2:2.

[0030] The specific implementation steps are as follows:

[0031] (1) First, the dechlorane plus pollutant powder was evenly mixed with deionized water to obtain a polluted water sample with a DP concentration of 1000 ng / L; (2) Then, the rhamnolipid-coated nano zero-valent iron material (FRC) loaded on biochar was added to the polluted water sample in a certain proportion and evenly mixed (the nano iron content was 1 g / L); (3) Then, the water sample was shaken in a constant-temperature shaker (25 °C) for 2 h. The removal samples were extracted and purified through a 0.45 μm filter head and filtered into a 1 mL injection vial, and the residual amount of DP in the water sample was measured by a gas chromatograph, and its removal rate was calculated.

[0032] This example can enable researchers and technicians in the field to understand the invention more intuitively and comprehensively, but does not limit the invention in any way.

Claims

1. A method for repairing clonal contamination using nano zero-valent iron modified materials, characterized in that The method modifies nano zero-valent iron by coating rhamnolipid on nano zero-valent iron, and then loads the rhamnolipid-coated nano zero-valent iron material on biochar to prepare a biochar-loaded rhamnolipid-coated nano zero-valent iron modified material, and applies the material to the remediation of Deklon contaminated soil. The specific implementation steps are as follows: (1) washing, drying, and crushing the selected biomass, and then placing it in a muffle furnace for pyrolysis. After completion, cooling it to room temperature to obtain the biochar; (2) Anhydrous ethanol and deoxygenated deionized water were mixed at a V:V ratio of 1:1, placed in a three-necked flask, introduced with nitrogen, and stirred to mix well to obtain a solution A; (3) Add rhamnolipid to deoxygenated deionized water to prepare solution B; put solution B and FeSO4·7H20 into solution A, and stir electrically under nitrogen protection to obtain solution C; put biochar into solution C and continue stirring to obtain solution D; (4) NaBH4 solution was added dropwise to solution D, stirring was continued under nitrogen protection, precipitate E was separated by centrifugation, precipitate E was repeatedly washed with anhydrous ethanol and deoxygenated deionized water, and freeze-dried to obtain the biochar-loaded rhamnolipid-coated nano zero-valent iron material; (5) The dried biochar-loaded rhamnolipid-coated nano-zero-valent iron material is mixed with the Deklon contaminated soil or aqueous solution in a certain proportion. After a certain period of time, the Deklon contaminated soil or water can be removed until its environmental safety standard is met.

2. The method for repairing clonal contamination by using a nanometer zero-valent iron modified material according to claim 1, characterized in that: The biochar in step (1) is obtained by pyrolysis of readily available biomass such as corn stalks, rice stalks, sorghum stalks and soapberry shells at a temperature of 400° C. to 700° C. in a muffle furnace for 4 hours.

3. The method for repairing clonal contamination by using a nano-zero-valent iron modified material according to claim 1, characterized in that: The concentration of rhamnolipid solution B in step (2) is 1.25 g / L, 2.5 g / L or 5 g / L.

4. The method for repairing clonal contamination using a nano-zero-valent iron modified material according to claim 1, characterized in that: In step (3), the molar concentration of FeSO4·7H20 in solution D is 0.15 mol / L; the biochar concentration is 4.16 g / L or 8.33 g / L or 16.67 g / L; and the mass ratio of nano-zero-valent iron, rhamnolipid and biochar is 1: 0.05~0.2: 0.5~2.

5. The method for repairing clonal contamination by using a nano-zero-valent iron modified material according to claim 1, characterized in that: The concentration of NaBH4 solution in step (4) is 0.18 g / mL; freeze drying is performed by pre-freezing for 2 h and freeze drying for 12 h.

6. The method for repairing clonal contamination by using nano-zero-valent iron modified materials according to claim 1, characterized in that: When used in the remediation of Deklon contaminated soil, the amount of the nano-zero-valent iron modified material added is 1%~5% of the soil mass, and the remediation time is 60 days; when used in the remediation of Deklon contaminated water, the nano-zero-valent iron modified material is added to the water body with a nano-iron content of 0.5g / L~2g / L. After the nano-zero-valent iron modified material is added to the soil or water body, it is shaken at 25°C for 2 hours.

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