A soil remediation agent, a preparation method and application thereof

Abstract

The present application relates to the field of soil treatment, in particular to a soil remediation agent, a preparation method and application thereof.The present application provides a soil remediation agent, raw materials of which include: iron filings, carbon powder, activated sludge, organic nitrogen source solution, zero-valent iron powder and carbon source.The soil remediation agent provided by the present application can remove hexavalent chromium in soil stably and for a long time.

Description

Technical Field

[0001] This invention relates to the field of soil remediation, specifically to a soil remediation agent, its preparation method, and its application. Background Technology

[0002] Chromium (Cr) is a toxic pollutant, mainly originating from industries such as electroplating and leather. Cr(VI) is the most toxic and mobile heavy metal pollutant due to its high solubility in water; therefore, most remediation technologies involve converting Cr(VI) into Cr(III), which is relatively insoluble, non-mobile, and less hazardous.

[0003] Existing methods for remediating hexavalent chromium-contaminated soil mainly include chemical leaching, bioremediation, solidification / stabilization, and chemical reduction. Chemical leaching requires the leaching agent to fully contact and elute Cr(VI) from the soil, consumes a large amount of water, and is only suitable for soils with high permeability, such as sandy loam. Furthermore, the leaching liquid must be properly treated to avoid secondary pollution. Bioremediation mainly refers to microbial remediation and phytoremediation. Microbial remediation utilizes the biochemical action of microorganisms in the soil to reduce Cr(VI) to Cr(III) and stabilize Cr(III) in the soil. Currently, microbial remediation technology still requires extensive basic research, and microorganisms have stringent requirements regarding environmental temperature and pH. Phytoremediation technology includes phytoextraction, phytofixation, and phytovolatilization techniques. This method has a long remediation cycle, making rapid remediation difficult in the short term, and it is also difficult to remediate soils with high contamination concentrations. Solidification / stabilization methods cannot change the form of hexavalent chromium, resulting in unstable remediation effects. Chemical reduction is an effective method for remediating Cr(VI) contaminated soil. This method typically uses strong reducing agents such as ferrous sulfate, iron-containing minerals, and sulfur-based materials (such as hydrogen sulfide and sulfites) as basic reagents to reduce Cr(VI) to Cr(III). Chemical reduction stabilization technology has the advantages of high treatment efficiency and strong operability, but it consumes a lot of reagents, is prone to secondary pollution, and significantly alters the physical and chemical properties of the soil.

[0004] Furthermore, in chemical reduction methods, chemical reagents are prone to degradation, and reduction products are easily re-oxidized, thus affecting the long-term effectiveness of chromium reduction stabilization in soil. While microorganisms can participate in the reduction of hexavalent chromium, their low environmental tolerance also hinders long-term chromium reduction stabilization. Zero-valent iron (ZVFe) is an environmentally friendly material that can be used for the remediation of chromium-contaminated soil and groundwater; however, related studies have shown that ZVFe particles are prone to agglomeration and surface oxidation, and chromium-iron precipitates adhering to the particle surface hinder the reduction of hexavalent chromium, significantly reducing the reactivity of ZVFe.

[0005] In summary, existing technologies urgently require a soil remediation agent that can effectively and stably remove hexavalent chromium metal pollutants in the treatment of hexavalent chromium-contaminated soil. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the need in the prior art for a soil remediation agent that can effectively and stably remove hexavalent chromium metal pollutants, thereby providing a soil remediation agent, its preparation method and application.

[0007] This invention provides a soil remediation agent, the raw materials of which include: iron filings, carbon powder, activated sludge, organic nitrogen source solution, zero-valent iron powder and carbon source.

[0008] Preferably, by weight, it includes 3-5 parts iron filings, 1 part carbon powder, 3-5 parts activated sludge, 90-110 parts organic nitrogen source solution, 10-15 parts zero-valent iron powder, and 10-20 parts carbon source.

[0009] Optionally, the iron filings are scrap iron filings, which are generated during the production process of an iron foundry and are washed and dried.

[0010] Optionally, the activated sludge can be derived from concentrated sludge from municipal wastewater treatment plants.

[0011] Preferably, the activated sludge includes Proteobacteria, Bacteroides, and Nitrifying Spiralellar.

[0012] Among them, the abundance of Proteobacteria was 45-53%, the abundance of Bacteroides was 30-40%, and the abundance of Nitrifying Spiral was 2%-5%.

[0013] Preferably, the charcoal powder includes biomass charcoal powder.

[0014] Preferably, the biochar powder includes corn stalk charcoal powder;

[0015] Preferably, the raw material for the corn stalk carbon powder is selected from corn stalks.

[0016] Preferably, the nitrogen content in the organic nitrogen source solution is 6-7 wt%;

[0017] Preferably, the water content in the organic nitrogen source solution is 80-90 wt%.

[0018] Optionally, the organic nitrogen source solution is protein waste liquid; the protein waste liquid comes from the waste liquid produced by a soy product processing plant.

[0019] Preferably, the particle size of the zero-valent iron powder is 150-250 mesh.

[0020] Preferably, the carbon source includes molasses.

[0021] The present invention also provides a method for preparing the soil remediation agent described above, comprising the following steps: first mixing iron filings, carbon powder, activated sludge and organic nitrogen source solution, then adding zero-valent iron powder for a second mixing, and then adding carbon source and mixing evenly to obtain the soil remediation agent.

[0022] Iron filings and carbon powder, when immersed in an organic nitrogen source solution, form countless tiny galvanic cells, and the Fe produced in the reaction... 2+ It has strong reducing properties and high chemical reactivity [·H]. The reactions in a micro galvanic cell include:

[0023] Anode (Fe): Fe - 2e → Fe 2+

[0024] Cathode (C): 2H + +2e→2[H]→H2.

[0025] Preferably, the first mixing process involves oscillating at 150-250 rpm for 4-6 hours at 25-40°C;

[0026] And / or, the second mixing process is to oscillate at 150-250 rpm at 25-30°C for 0.5-1.5 hours.

[0027] Preferably, the charcoal powder includes biomass charcoal powder, and the preparation steps of the biomass charcoal powder include: grinding biomass and passing it through a sieve with a pore size of 1.5-2.5 mm, drying the sieved material at 100-110℃ for 1-3 h, and then calcining it at 500-700℃ for 1-3 h at a heating rate of 5-15℃ / min to obtain the biomass charcoal powder.

[0028] This invention also provides an application of the above-described soil remediation agent in the treatment of hexavalent chromium contaminated soil.

[0029] The technical solution of this invention has the following advantages:

[0030] This invention provides a soil remediation agent comprising: iron filings, carbon powder, activated sludge, an organic nitrogen source solution, zero-valent iron powder, and a carbon source. The activated sludge and organic nitrogen source solution can undergo anaerobic fermentation, promoting the proliferation of microorganisms in the activated sludge. These proliferating microorganisms can effectively remove hexavalent chromium from the soil. During the anaerobic fermentation process, the iron filings and carbon powder establish a micro-electrolysis reaction in the system. The ferrous ions generated by this micro-electrolysis reaction can effectively remove hexavalent chromium from the soil. Furthermore, the micro-electrolysis reaction can promote the production of volatile fatty acids in the anaerobic fermentation system, thereby creating a weakly acidic environment. This weakly acidic environment allows the zero-valent iron powder to maintain its long-term reducing activity during the removal of hexavalent chromium. Additionally, the carbon source in the remediation agent provides nutrients for the growth of microorganisms, ensuring their long-term activity. In summary, the soil remediation agent provided by this invention can effectively and stably remove hexavalent chromium from the soil. Detailed Implementation

[0031] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0032] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] The organic nitrogen source solution is a waste liquid from a soy product processing plant, with a nitrogen content of 6.5 wt% and a water content of 85 wt%.

[0034] The activated sludge comes from the concentrated sludge of the municipal wastewater treatment plant. The concentrated sludge includes Proteobacteria, Bacteroides, and Nitrifying Spiralellar, with the abundance of Proteobacteria being 50%, Bacteroides 40%, and Nitrifying Spiralellar 5%.

[0035] Example 1

[0036] This embodiment provides a soil remediation agent comprising: 3 kg of iron filings, 1 kg of biochar powder, 3 kg of activated sludge, 100 kg of protein waste liquid, 10 kg of 200-mesh zero-valent iron powder, and 10 kg of molasses.

[0037] The preparation method of the above-mentioned soil remediation agent includes the following steps.

[0038] 1) Grind 10 kg of corn stalks and pass them through a sieve with a 2 mm aperture. Dry the sieve material at 105 °C for 1 h and then calcine it in a muffle furnace at a heating rate of 10 °C / min to 600 °C for 2 h to obtain biochar powder.

[0039] 2) Add 3 kg of iron filings, 1 kg of biochar powder prepared in step 1), and 3 kg of activated sludge to 100 kg of protein waste liquid, and shake at 180 rpm for 4 hours at 30°C to obtain iron-carbon waste liquid.

[0040] 3) Add 10 kg of 200 mesh zero-valent iron powder to the iron-carbon waste liquid prepared in step 2), and shake at 180 rpm for 0.5 h at 25 °C to obtain a reduced iron powder-microorganism mixture.

[0041] 4) Add 10 kg of molasses to the reduced iron powder-microorganism mixture prepared in step 3) and stir evenly to obtain the soil remediation agent.

[0042] Example 2

[0043] This embodiment provides a soil remediation agent comprising: 5 kg of waste iron filings, 1 kg of biochar powder, 5 kg of activated sludge, 90 kg of protein waste liquid, 15 kg of 200-mesh zero-valent iron powder, and 20 kg of molasses.

[0044] The preparation method of the above-mentioned soil remediation agent includes the following steps.

[0045] 1) Grind 10 kg of corn stalks and pass them through a sieve with a mesh size of 1.5 mm. Dry the sieve material at 105 °C for 1 h and then calcine it in a muffle furnace at a heating rate of 15 °C / min to 700 °C for 3 h to obtain biochar powder.

[0046] 2) Add 5 kg of iron filings, 1 kg of biochar powder prepared in step 1), and 5 kg of activated sludge to 90 kg of protein waste liquid, and shake at 250 rpm for 6 hours at 40°C to obtain iron-carbon waste liquid.

[0047] 3) Add 15 kg of 200 mesh zero-valent iron powder to the iron-carbon waste liquid prepared in step 2), and shake at 180 rpm for 1.5 h at 30 °C to obtain a reduced iron powder-microorganism mixture.

[0048] 4) Add 20 kg of molasses to the reduced iron powder-microorganism mixture prepared in step 3) and stir evenly to obtain the soil remediation agent.

[0049] Example 3

[0050] This embodiment provides a soil remediation agent comprising: 5 kg of waste iron filings, 1 kg of biochar powder, 3 kg of activated sludge, 110 kg of protein waste liquid, 15 kg of 200-mesh zero-valent iron powder, and 15 kg of molasses.

[0051] The preparation method of the above-mentioned soil remediation agent includes the following steps:

[0052] 1) Grind 10 kg of corn stalks and pass them through a sieve with a mesh size of 2.5 mm. Dry the sieve material at 110℃ for 1 h and then calcine it in a muffle furnace at a heating rate of 5℃ / min to 500℃ for 3 h to obtain biochar powder.

[0053] 2) Add 5 kg of iron filings, 1 kg of biochar powder prepared in step 1), and 3 kg of activated sludge to 110 kg of protein waste liquid, and shake at 250 rpm for 6 hours at 25°C to obtain iron-carbon waste liquid.

[0054] 3) Add 15 kg of 200 mesh zero-valent iron powder to the iron-carbon waste liquid prepared in step 2), and shake at 180 rpm for 1.5 h at 25 °C to obtain a reduced iron powder-microorganism mixture.

[0055] 4) Add 15 kg of molasses to the reduced iron powder-microorganism mixture prepared in step 3), stir evenly, and the soil remediation agent is obtained.

[0056] Comparative Example 1

[0057] This comparative example provides a soil remediation agent comprising: 3 kg of iron filings, 3 kg of activated sludge, 100 kg of protein waste liquid, 10 kg of 200-mesh zero-valent iron powder, and 10 kg of molasses.

[0058] The preparation method of the above-mentioned soil remediation agent includes the following steps.

[0059] 1) Add 3 kg of iron filings and 3 kg of activated sludge to 100 kg of protein waste liquid, and shake at 180 rpm for 4 hours at 30°C to obtain iron-carbon waste liquid.

[0060] 2) Add 10 kg of 200 mesh zero-valent iron powder to the iron-carbon waste liquid prepared in step 1), and shake at 180 rpm for 0.5 h at 25 °C to obtain a reduced iron powder-microorganism mixture.

[0061] 3) Add 10 kg of molasses to the reduced iron powder-microorganism mixture prepared in step 2) and stir evenly to obtain the soil remediation agent.

[0062] Comparative Example 2

[0063] This comparative example provides a soil remediation agent comprising: 3 kg of iron filings, 1 kg of biochar powder, 100 kg of protein waste liquid, 10 kg of 200-mesh zero-valent iron powder, and 10 kg of molasses.

[0064] The preparation method of the above-mentioned soil remediation agent includes the following steps.

[0065] 1) Grind 10 kg of corn stalks and pass them through a sieve with a 2 mm aperture. Dry the sieve material at 105 °C for 1 h and then calcine it in a muffle furnace at a heating rate of 10 °C / min to 600 °C for 2 h to obtain biochar powder.

[0066] 2) Add 3 kg of iron filings and 1 kg of biochar powder prepared in step 1) to 100 kg of protein waste liquid, and shake at 180 rpm for 4 hours at 30°C to obtain iron-carbon waste liquid.

[0067] 3) Add 10 kg of 200 mesh zero-valent iron powder to the iron-carbon waste liquid prepared in step 2), and shake at 180 rpm for 0.5 h at 25 °C to obtain a reduced iron powder-microorganism mixture.

[0068] 4) Add 10 kg of molasses to the reduced iron powder-microorganism mixture prepared in step 3) and stir evenly to obtain the soil remediation agent.

[0069] Test case

[0070] The soil remediation agents prepared in each embodiment and comparative example were subjected to performance tests for contaminated soil remediation. The specific test methods were as follows:

[0071] A soil incubation experiment was designed. Four 20g portions of chromium-contaminated soil (hexavalent chromium concentration 153.44 mg / kg) were placed in separate 50ml centrifuge tubes, and 10ml of deionized water was added to each tube. Soil remediation agent was added sequentially to the centrifuge tubes at concentrations of 0.4g, 0.6g, 0.8g, and 1g, respectively. After incubation for 14 and 60 days, samples were taken to determine the hexavalent chromium concentration in the soil (GBT15555.4-1995). According to the requirements of the Hazardous Waste Landfill Pollution Control Standard (GB 18598-2019), the hexavalent chromium stabilization control limit is 6 mg / L. The results after incubation are shown in Table 1.

[0072] Table 1. Leaching concentration of hexavalent chromium in soil after 14 and 60 days of curing.

[0073]

[0074]

[0075] As shown in the table above, the soil remediation agent provided by this invention significantly improves the stabilization effect of chromium when used to remediate heavy metal contaminated soil. It effectively solves the problem of long-term stable remediation of hexavalent chromium reduction using existing technologies. The remediation agent of this invention can achieve efficient reduction of hexavalent chromium, meeting the requirements of the Hazardous Waste Landfill Pollution Control Standard (GB 18598-2019). Furthermore, this technology has a short remediation cycle, low cost, and simple operation, making it suitable for the remediation of large-area heavy metal contaminated soil.

[0076] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A soil remediation agent, characterized in that, By weight, the raw materials include 3-5 parts iron filings, 1 part carbon powder, 3-5 parts activated sludge, 90-110 parts organic nitrogen source solution, 10-15 parts zero-valent iron powder, and 10-20 parts carbon source. The preparation method of the soil remediation agent includes the following steps: iron filings, carbon powder, activated sludge and organic nitrogen source solution are first mixed, zero-valent iron powder is added for a second mixing, and then carbon source is added and mixed evenly to obtain the soil remediation agent. The nitrogen content in the organic nitrogen source solution is 6-7 wt%.

2. The soil remediation agent according to claim 1, characterized in that, Charcoal powder includes biomass charcoal powder.

3. The soil remediation agent according to claim 1, characterized in that, The particle size of zero-valent iron powder is 150-250 mesh.

4. The soil remediation agent according to claim 1, characterized in that, Carbon sources include molasses.

5. A method for preparing the soil remediation agent according to any one of claims 1-4, characterized in that, The process includes the following steps: first mixing iron filings, carbon powder, activated sludge, and organic nitrogen source solution; then adding zero-valent iron powder for a second mixing; and finally adding carbon source and mixing evenly to obtain the soil remediation agent.

6. The preparation method according to claim 5, characterized in that, The first mixing process involves oscillating at 150-250 rpm for 4-6 hours at 25-40℃. And / or, the second mixing process is to oscillate at 150-250 rpm at 25-30°C for 0.5-1.5 hours.

7. The preparation method according to claim 6, characterized in that, The charcoal powder includes biomass charcoal powder. The preparation steps of the biomass charcoal powder include: grinding biomass and passing it through a sieve with a pore size of 1.5-2.5 mm, drying the sieved material at 100-110℃ for 1-3 h, and then calcining it at 500-700℃ for 1-3 h at a heating rate of 5-15℃ / min to obtain the biomass charcoal powder.

8. The application of the soil remediation agent according to any one of claims 1-4 in the remediation of hexavalent chromium contaminated soil.

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