Remediation agent and method for arsenic-containing soil

Abstract

The present application belongs to the field of arsenic-containing soil remediation, and particularly relates to a remediation agent for arsenic-containing soil, which comprises steel slag, manganese ore, ferrous source and modified fly ash in a weight ratio of 1-3.5:1-3.5:3-7:1-5; the modified fly ash is a product obtained by subjecting fly ash to iron precipitation, aldehyde amine polycondensation and organic acid modification; and the present application also provides a method for remediation of arsenic-containing soil by using bidens pilosa in combination with the remediation agent. The present application can unexpectedly realize synergy based on the components and proportions of the remediation agent and the combination of bidens pilosa, and can significantly improve the effective arsenic content in soil.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology in environmental engineering, and specifically relates to a remediation material that reduces the bioavailability of cadmium and arsenic in soil. Background Technology

[0002] Currently, soil heavy metal pollution is becoming increasingly serious. Excessive levels of heavy metals accumulate in the food chain, severely threatening human health and safety. Arsenic is the most harmful heavy metal to humans; it is metabolized extremely slowly and can remain in the body for decades, damaging the liver and causing diseases such as cancer. Arsenic is highly toxic, causing significant damage to the gastrointestinal, respiratory, and nervous systems. Arsenic pollution is often released to varying degrees during the processing of non-ferrous metal mines. Soil degradation caused by arsenic heavy metal pollution has become a major global environmental problem, and the remediation of arsenic-contaminated soil is urgently needed.

[0003] Currently, the main methods for remediating arsenic pollution in soil include soil replacement, chemical remediation, solidification and stabilization, and phytoremediation. Soil replacement is effective, but its drawback is that the transferred contaminated soil is difficult to absorb, and the imported soil can disrupt the original soil ecosystem. Chemical remediation mainly involves chemical leaching, which uses chemical reagents to wash away and transfer pollutants from the soil to the leaching solution. Its drawback is that the addition of chemical reagents leads to a decrease in soil enzyme activity and microbial diversity, as well as mineral loss. Solidification and stabilization involves adding solidifying materials to the soil to fix heavy metals through adsorption, precipitation or co-precipitation, ion exchange, and enhanced soil cohesion, thereby reducing the mobility, availability, and leaching toxicity of heavy metals. Phytoremediation utilizes plant growth to extract and transfer pollutants, and is easy to implement in engineering projects. However, its drawback is that the active substances secreted by plants (such as organic acids) often activate heavy metals in the soil, causing pollution to worsen. As can be seen from the above, soil replacement and chemical remediation have significant drawbacks, while solidification and stabilization can reduce the toxicity of heavy metals in soil and is highly feasible, but it is difficult to completely remove heavy metals. Therefore, by combining solidification and stabilization methods with phytoremediation, heavy metals can be solidified in the soil before extraction, thus achieving safe reduction and remediation of heavy metals. Summary of the Invention

[0004] To address the unsatisfactory remediation effect of arsenic in soil, this invention provides a remediation agent for arsenic-containing soil, aiming to synergistically improve the remediation effect of arsenic in soil based on the combination of components.

[0005] The second objective of this invention is to provide a method for remediating arsenic-containing soil using the aforementioned remediation agent and Bidens pilosa in combination, aiming to synergistically improve the remediation effect of arsenic-containing soil based on the combination of the aforementioned remediation agent and Bidens pilosa.

[0006] A soil remediation agent containing arsenic comprises steel slag, manganese ore, ferrous iron source, and modified fly ash in a weight ratio of 1–3.5:1–3.5:3–7:1–5.

[0007] The modified fly ash is a product of fly ash after iron precipitation, aldehyde-amine polycondensation, and organic acid modification.

[0008] This invention demonstrates that by innovatively combining steel slag, manganese ore, ferrous iron source, and modified fly ash, and further coordinating the joint control of component ratios, a synergistic effect can be unexpectedly achieved, effectively reducing available arsenic in the soil.

[0009] In this invention, the preparation steps of the modified fly ash are as follows: fly ash and iron source are mixed for iron precipitation treatment, then mixed with aldehyde and amine for aldehyde-amine polycondensation modification, and then modified with organic acid to obtain the final product.

[0010] In this invention, the iron source is at least one of ferrous sulfate, ferrous oxide, ferrous succinate, ferrous lactate, ferrous gluconate, ferrous fumarate, ferrous pyrophosphate, and ferrous oxalate.

[0011] In this invention, the weight ratio of fly ash to iron source is 1:1 to 2;

[0012] In this invention, the temperature during the iron deposition stage is 40–60°C;

[0013] In this invention, the aldehyde is 3,4-dihydroxybenzaldehyde;

[0014] In this invention, the amine is melamine;

[0015] In this invention, the molar ratio of aldehyde to amine is 1 to 2:1.

[0016] In this invention, the weight ratio of aldehyde to fly ash is 1 to 3:100;

[0017] In this invention, the temperature of the aldehyde-amine polycondensation stage is 60–80°C;

[0018] In this invention, the organic acid is at least one selected from citric acid, lactic acid, acetic acid, oxalic acid, malic acid, and tartaric acid;

[0019] In this invention, the weight ratio of the organic acid to fly ash is 1-3:100;

[0020] In this invention, the temperature of the organic acid modification stage is 70–90°C.

[0021] In this invention, the ferrous source is at least one of ferrous sulfate, ferrous oxide, ferrous succinate, ferrous lactate, ferrous gluconate, ferrous fumarate, ferrous pyrophosphate, and ferrous oxalate.

[0022] In this invention, the manganese ore is pyrolusite.

[0023] In this invention, the weight ratio of steel slag, manganese ore, ferrous source, and modified fly ash is 1–2:1–1.5:6–7:2–4; preferably 1.4–1.6:1–1.2:6.4–6.6:2.8–3.2. Research in this invention shows that, under the aforementioned composition, further controlling the component ratios within the preferred range can further achieve synergistic effects and contribute to further improving the remediation effect of arsenic in soil.

[0024] The present invention also provides a method for remediating arsenic-containing soil, which involves mixing the arsenic-containing soil to be remediated with the aforementioned remediation agent and using Bidens pilosa for bioremediation.

[0025] This invention innovatively combines the remediation agent with Bidens pilosa for remediation. Based on the combination of the remediation agent's components, ratio, and Bidens pilosa type, an unexpected synergistic effect can be achieved, which can effectively reduce active arsenic in the soil.

[0026] In this invention, the arsenic-containing soil is also permitted to contain at least one pollutant selected from cadmium, lead, zinc, nickel, and copper. This invention has found that the preferred process effectively reduces active arsenic in the soil and simultaneously reduces harmful substances such as Cd, demonstrating excellent results.

[0027] In this invention, the amount of the remediation agent can be adjusted as needed. Considering the treatment effect and cost, preferably, the remediation agent is 1-20% of the soil weight, more preferably 8-16%, and even more preferably 11-13%.

[0028] In this invention, the Bidens pilosa is the white-flowered Bidens pilosa.

[0029] In this invention, the amount of Bidens pilosa sown can be adjusted according to conventional needs, for example, it can be 0.0001g to 0.001 / 1g of soil, and considering processing efficiency and cost, it can be further 0.0001g to 0.0005 / 1g of soil.

[0030] Beneficial effects

[0031] This invention demonstrates that the innovative combination of steel slag, manganese ore, ferrous iron source, and modified fly ash, along with the combined control of component ratios, can unexpectedly achieve synergistic effects, thereby synergistically reducing available arsenic in the soil and exhibiting excellent results.

[0032] This invention innovatively combines the remediation agent with Bidens pilosa for remediation. Based on the combination of the remediation agent's components, ratio, and Bidens pilosa type, an unexpected synergistic effect can be achieved, which can effectively reduce active arsenic in the soil. Detailed Implementation

[0033] In this invention, the steel slag is 100-200 mesh and was purchased from Hebei Shijiazhuang Yuanjing Mineral Products Co., Ltd.

[0034] The pyrolusite ore is 100-200 mesh and was purchased from Xingfa Manganese Industry Co., Ltd. in Leiyang City, Hengyang, Hunan Province.

[0035] The modified fly ash can be prepared by mixing fly ash and an iron source for iron precipitation treatment, then mixing with aldehydes and amines for aldehyde-amine polycondensation modification, and finally modifying with organic acids. The following example, as a typical demonstration, uses DTCH-MFA as an example. The preparation method is as follows: First, a mixture of fly ash and iron salt (specifically ferrous sulfate, where the weight ratio of fly ash to iron salt is 1:1.5) is ultrasonically stirred in a 50°C water bath to prepare magnetic fly ash (MFA) via iron salt co-precipitation. Then, MFA and 3,4-dihydroxybenzaldehyde (the weight ratio of aldehyde to fly ash is 2:100) are heated and stirred at 70°C in an ethanol system for 2 hours. After reacting, a hot DMSO solution of melamine (the molar ratio of aldehyde to amine is 1.5:1) is added, and the reaction is carried out for 1 hour. Finally, the ethanol in the previous system was evaporated using a rotary evaporator. The product was then stirred with a DMSO solution of citric acid (the weight ratio of citric acid to fly ash was 2:100) at 80°C for 1 hour. After washing, filtering, and drying, the final modified fly ash was obtained.

[0036] In this invention, the particle size ranges of steel slag, pyrolusite, and modified fly ash are 100-200 mesh, 100-200 mesh, and -200 mesh, respectively.

[0037] The soil described in this invention is arsenic-containing soil, wherein the initial arsenic content is not particularly required. For example, it can be 30 mg / kg to 500 mg / kg. Furthermore, the soil described in this invention can also be Cd-containing soil.

[0038] In the following cases, the scale of soil treatment can be adjusted as needed. For example, unless otherwise stated, the following cases are typical examples of laboratory scale of 300-500g.

[0039] In this invention, the repair agent and the repair method of Bidens pilosa can be achieved based on existing means, for example:

[0040] The planting method for the remediation plants is as follows: Mix the soil to be treated with the modifier, then sprinkle the extracted plant seeds on the soil surface and cover with 2mm of soil. Water once every 5 days and carry out regular maintenance. The remediation period is 1-2 months. It is necessary to ensure that the plants have sufficient water and light, and the optimal growth temperature is maintained between 18-25℃.

[0041] In the planting method, the amount of seeds sown is 0.04g, and the seed-to-soil ratio is 1:10000.

[0042] In the following remediation agents, the content refers to the weight percentage relative to the soil to be treated.

[0043] In this invention, the As content before and after soil remediation can be tested using industry-recognized standards.

[0044] For example, in the following case, the test method for available As is as follows: Weigh 5g of sample that has passed through a 2mm sieve into a 250mL Erlenmeyer flask, add 50mL of 0.5mol / L NaHCO3 solution, shake for 2h at 25℃ and 200r / min, filter with a 0.45μm microporous membrane, then dilute the sample to be tested by ICP-MS, and calculate the available As content based on the data.

[0045] Example 1

[0046] The experimental results were obtained for the treatment group where the plant used for extraction was Bidens pilosa and the remediation agent was added at a relative amount of 12% of the soil (containing steel slag, pyrolusite, ferrous sulfate, and modified fly ash in a weight ratio of 3:3:3:3).

[0047]

[0048] Example 2

[0049] The plant used for extraction was *Bidens pilosa*, and the remediation agent was added at a relative soil concentration of 12% (containing steel slag, pyrolusite, ferrous sulfate, and modified fly ash in a weight ratio of 1.5:1:6.5:3). The experimental results obtained were as follows:

[0050]

[0051] Example 3

[0052] Compared to Example 2, the only difference is that the soil also contains Cd, and the effective Cd was reduced by 90.36% after treatment.

[0053] Example 4

[0054] The plant used for extraction was *Bidens pilosa*, and the remediation agent was added at a relative soil concentration of 12% (containing steel slag, pyrolusite, ferrous sulfate, and modified fly ash in a weight ratio of 1.5:2.5:5:3). The experimental results were as follows:

[0055]

[0056] Example 5

[0057] Compared to Example 2, the only difference is that the content of the remediation agent relative to the soil is 8-16%.

[0058] The obtained experimental decibels are:

[0059]

[0060] Comparative Example 1

[0061] Compared with Example 1, the only difference is that the amount of remediation agent added relative to the soil is 12% (which contains steel slag, pyrolusite, and ferrous sulfate in a mass ratio of 3:3:3).

[0062] The experimental results obtained are as follows:

[0063]

[0064] Comparative Example 2

[0065] Compared with Example 1, the only difference is that the amount of remediation agent added relative to the soil is 12% (which contains steel slag, pyrolusite, and modified fly ash in a mass ratio of 3:3:3).

[0066] The experimental results obtained are as follows:

[0067]

[0068] Comparative Example 3

[0069] Compared with Example 1, the only difference is that the amount of remediation agent added relative to the soil is 12% (which contains steel slag, ferrous sulfate, and modified fly ash in a mass ratio of 3:3:3).

[0070] The experimental results obtained are as follows:

[0071]

[0072] Comparative Example 4

[0073] Compared with Example 1, the only difference is that the amount of remediation agent added relative to the soil is 12% (which contains pyrolusite, ferrous sulfate, and modified fly ash in a mass ratio of 3:3:3).

[0074] The experimental results obtained are as follows:

[0075]

[0076] Comparative Example 5

[0077] The only difference from Example 1 is that the plant used for extraction is ramie.

[0078] The experimental results obtained are as follows:

[0079]

[0080] Comparative Example 6

[0081] Compared to Example 1, the only difference is that the plant used for extraction is Bermuda grass.

[0082] The experimental results obtained are as follows:

[0083]

[0084] Comparative Example 7

[0085] Compared with Example 1, the only difference is that the amount of the remediation agent relative to the soil is 12%, and it contains steel slag, pyrolusite, ferrous sulfate, and modified fly ash in a weight ratio of 2:0.5:6.5:3.

[0086] The experimental results obtained are as follows:

[0087]

[0088] In summary, the innovative combination of steel slag, manganese ore, ferrous iron source, and modified fly ash, along with the coordinated control of component ratios, unexpectedly achieves synergistic effects, effectively reducing available arsenic in the soil. This invention also innovatively combines the aforementioned remediation agent with Bidens pilosa for remediation; based on the combination of the remediation agent's components, ratios, and the type of Bidens pilosa, an unexpected synergistic effect is achieved, effectively reducing reactive arsenic in the soil. Furthermore, this method can also simultaneously and effectively reduce the content of heavy metals such as Cd.

Claims

1. A method for remediating arsenic-containing soil, characterized in that, The arsenic-containing soil to be remediated was mixed with the remediation agent, and then bioremediation was carried out using Bidens pilosa. The arsenic-containing soil remediation agent comprises steel slag, manganese ore, ferrous iron source, and modified fly ash in a weight ratio of 1~3.5:1~3.5:3~7:1~5. The modified fly ash is a product of fly ash after iron precipitation, aldehyde-amine polycondensation, and organic acid modification. The preparation steps of the modified fly ash are as follows: Fly ash and iron source are mixed and subjected to iron precipitation treatment, then mixed with aldehydes and amines for aldehyde-amine polycondensation modification, and finally modified with organic acids to obtain the final product.

2. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The iron source is at least one of ferrous sulfate, ferrous oxide, ferrous succinate, ferrous lactate, ferrous gluconate, ferrous fumarate, ferrous pyrophosphate, and ferrous oxalate. The weight ratio of fly ash to iron source is 1:1~2; The temperature during the iron sinking stage is 40~60℃.

3. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The aldehyde mentioned is 3,4-dihydroxybenzaldehyde; The amine in question is melamine; The molar ratio of the aldehyde to the amine is 1~2:1; The weight ratio of the aldehyde to fly ash is 1~3:100; The temperature for the aldehyde-amine polycondensation stage is 60~80℃.

4. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The organic acid is at least one of citric acid, lactic acid, acetic acid, oxalic acid, malic acid, and tartaric acid; The weight ratio of the organic acid to fly ash is 1~3:100; The temperature for the organic acid modification stage is 70~90℃.

5. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The ferrous source is at least one of ferrous sulfate, ferrous oxide, ferrous succinate, ferrous lactate, ferrous gluconate, ferrous fumarate, ferrous pyrophosphate, and ferrous oxalate.

6. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The manganese ore mentioned is pyrolusite.

7. The method for remediating arsenic-containing soil as described in any one of claims 1 to 6, characterized in that, The weight ratio of steel slag, manganese ore, ferrous iron source and modified fly ash is 1~2:1~1.5:6~7:2~4.

8. The method for remediating arsenic-containing soil as described in claim 7, characterized in that, The weight ratios of steel slag, manganese ore, ferrous iron source, and modified fly ash are 1.4~1.6:1~1.2:6.4~6.6:2.8~3.

2.

9. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The arsenic-containing soil is also permitted to contain at least one of the following pollutants: cadmium, lead, zinc, nickel, and copper.

10. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The remediation agent is 1-20% of the soil weight.

11. The method for remediating arsenic-containing soil as described in claim 10, characterized in that, The remediation agent is 8-16% of the soil weight.

12. The method for remediating arsenic-containing soil as described in claim 11, characterized in that, The remediation agent is 11-13% of the soil weight.

13. The method for remediating arsenic-containing soil as described in claim 1, characterized in that, The Bidens pilosa mentioned is the white-flowered Bidens pilosa.

14. The method for remediating arsenic-containing soil as described in claim 13, characterized in that, The sowing rate of Bidens pilosa is 0.0001g to 0.001g of soil.

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