A heavy metal contaminated soil particle state and available state arsenic antimony synchronous solidification stabilization material, preparation method and application

Abstract

A kind of heavy metal contaminated soil in particulate state and effective state arsenic antimony synchronous solidification and stabilization material, preparation method and application, including the following mass percentage of components: polyacrylamide 5~25%, nano silicon dioxide 5~20%, fly ash 10~25%, ferrihydrite 20~60%, biochar 5~20%.The material of the application can efficiently improve the mechanical properties of heavy metal contaminated soil and prevent water and soil erosion, the solidification effect of particulate state arsenic / antimony is more than 95%, the 28d unconfined compressive strength can be increased by 30~110%, while the leaching rate of effective state arsenic / antimony is reduced by more than 99%.The material is suitable for repairing arsenic / antimony composite contaminated soil, improving soil stability, and preventing heavy metals from spreading around through surface runoff and interflow.The material is an environmentally friendly material, which does not damage and greatly disturb the soil, and can improve the soil while solidifying and stabilizing arsenic / antimony, and maintain the soil utilization value.

Description

Technical Field

[0001] This invention belongs to the field of solidification and stabilization remediation of heavy metal contaminated soil, and relates to a material for the simultaneous solidification and stabilization of particulate and available arsenic and antimony in heavy metal contaminated soil, its preparation method, and its application. Background Technology

[0002] Arsenic and antimony soil pollution is currently quite serious. Pollutants in the soil can migrate and spread through environmental media via soil erosion and other pathways, and can enter the human body through the food chain or other routes, posing a significant threat to both the ecological environment and human health. Therefore, pollution control and risk reduction are necessary. Controlling the migration and diffusion of particulate and available heavy metals in the soil is of paramount importance.

[0003] Soil arsenic / antimony contamination remediation technologies encompass three main aspects: physical, chemical, and biological technologies. Solidification / stabilization technologies, due to their relatively low cost, strong resistance to biodegradation, ease of implementation, and rapid effectiveness, have found wider application in site remediation. Solidification and stabilization technologies can improve soil stability, preventing arsenic / antimony from diffusing into the surrounding environment through surface runoff and interstitial flow via physical encapsulation, adsorption, and precipitation.

[0004] Numerous studies have reported on soil heavy metal contamination solidification / stabilization technologies. Patent CN113337293 A discloses an antifreeze solidification and stabilization agent for antimony-contaminated soil, its preparation method, and application. This agent possesses both high-efficiency complexing and freeze-thaw resistance capabilities and can be used for antimony-contaminated soil remediation, but its application for remediating arsenic and other complex heavy metal contaminated soils is lacking. Patent CN110016345 A discloses a cadmium-reducing and arsenic-stabilizing soil passivating agent and its application method. This agent has a good stabilizing effect on available arsenic and cadmium in soil, but its effectiveness in controlling particulate heavy metals is not considered. Patent CN108277017 A discloses a soil conditioner that can reduce the available forms of arsenic and antimony in soil and its application method. This agent can simultaneously stabilize available arsenic and antimony, but it has no effect on controlling particulate arsenic and antimony migrating through soil erosion and surface runoff. The patent with publication number CN 115074134 A discloses a soil stabilizer and its preparation method, which uses polyacrylamide and fly ash, among other things. Calcium oxide can improve acidic soil, but when used for the remediation of neutral soil, it may make the soil too alkaline. This stabilizer has a good remediation effect on soil contaminated with cationic heavy metals such as cadmium and lead, but its remediation effect on soil contaminated with anionic substances such as arsenic and antimony needs further research and improvement.

[0005] Current traditional soil stabilization technologies primarily focus on solid waste storage and roadbed materials, such as cement-based and geopolymer-based gels. These technologies suffer from problems like excessive alkalinity and potential disturbance and damage to the soil environment. Furthermore, arsenic can be activated and released in high pH environments. While stabilizing agents like iron-based materials show good adsorption effects on arsenic and antimony, they do not stabilize particulate arsenic and antimony, which can migrate and diffuse into the environment through soil erosion and surface runoff. Studies on soil contamination remediation processes often neglect the post-stabilization soil's resistance to soil erosion and the migration of particulate heavy metals.

[0006] This invention, taking into account soil toxicity leaching and mechanical properties, incorporates the improvement of soil's resistance to water and soil erosion by the solidifying agent, and develops a material for the simultaneous solidification and stabilization of particulate and available arsenic / antimony in heavy metal contaminated soil. This is crucial for the solidification and stabilization of particulate arsenic / antimony and is also a technical problem that urgently needs to be solved to improve traditional remediation materials. Summary of the Invention

[0007] This invention addresses the problems of traditional solidifying agents' poor remediation effect on particulate heavy metal pollutants and the lack of effective soil erosion resistance after solidification. The objective of this invention is to provide a material for the simultaneous solidification and stabilization of particulate and available arsenic and antimony in heavy metal-contaminated soil, along with its application method.

[0008] The technical solution of the present invention:

[0009] A material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil comprises the following components by weight percentage: 5-25% polyacrylamide, 5-20% nano-silica, 10-25% fly ash, 20-60% ferrohydrate, and 5-20% biochar.

[0010] Furthermore, the curing and stabilizing material comprises the following mass percentages: 10-20% polyacrylamide, 10-15% nano silica, 12-20% fly ash, 30-55% ferrohydrate, and 6-15% biochar.

[0011] A method for preparing a material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil includes the following steps: mixing polyacrylamide, nano-silica, fly ash, ferrous sulfate and biochar by mass percentage, and dry stirring for 10-30 min.

[0012] Application of a material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil in the remediation of heavy metal contaminated soil.

[0013] The application of the solidified and stabilized material in the remediation of heavy metals in soil includes the following steps: adding the solidified and stabilized material to the contaminated soil in a fixed proportion, tilling and mixing it evenly, and spraying an appropriate amount of water on the surface to make the moisture content 15-35%.

[0014] Application of a material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil in the remediation of contaminated soil, wherein the content of arsenic or antimony in the contaminated soil is 100-2000 mg / kg.

[0015] The dosage of the particulate and available arsenic-antimony co-solidification and stabilization material in the heavy metal contaminated soil is 1-10% of the dry weight of the soil.

[0016] Both fly ash and biochar are supplied by the factory. The composition of fly ash is shown in Table 1, mainly consisting of silicon dioxide and alumina.

[0017] Table 1 Chemical composition of fly ash

[0018]

[0019] The preparation method of ferrohydrate involves dissolving Fe(NO3)3·9H2O in deionized water, adding a prepared NaOH solution, adjusting the pH to 7.4~7.6, centrifuging, removing the supernatant, washing the solid part, centrifuging again, repeating the process 4 times, drying, and grinding to obtain ferrohydrate powder.

[0020] A further objective of this invention is to provide the application of the solidification and stabilization material in the remediation of heavy metal contaminated soil, with the remediation target being arsenic and its associated heavy metals, such as arsenic, antimony, lead, and cadmium, in mining areas.

[0021] The purpose of stirring in this invention is to ensure that the components of the solidified and stabilized material are mixed evenly.

[0022] The purpose of tilling in this invention is to mix the solidified and stabilized materials with the contaminated soil evenly.

[0023] The purpose of spraying water in this invention is to allow the solidified and stabilized material to fully react in the soil and produce a cross-linking stabilization effect.

[0024] The beneficial effects of this invention are:

[0025] (1) This invention provides a material for the simultaneous solidification and stabilization of particulate and available arsenic and antimony in heavy metal contaminated soil. The raw materials are readily available. Arsenic in the soil is stabilized through adsorption, coordination exchange, and co-precipitation of ferrophosphate and biochar. Gel materials such as polyacrylamide, nano-silica, and fly ash can agglomerate soil particles to form stable aggregates, while improving the mechanical properties of the soil.

[0026] (2) The solidification and stabilization materials have a good effect on the associated heavy metals such as arsenic, antimony, cadmium and lead in the mining area. Components such as biochar and ferrophosphate can adsorb toxic heavy metal ions such as arsenic, antimony, cadmium and lead. At the same time, under the overall cross-linking effect of the solidification and stabilization materials, the stability of the soil is improved and the leaching of heavy metal ions is effectively controlled.

[0027] (3) This invention breaks through the limitation of traditional soil heavy metal remediation agents that can only reduce heavy metal leaching but cannot prevent the migration of particulate heavy metals. The solidification and stabilization material in this patent can simultaneously reduce the leaching of effective heavy metals and the migration of particulate arsenic / antimony through soil erosion.

[0028] (4) It breaks away from the problem of traditional soil stabilizers using excessively alkaline gel materials such as cement, while simultaneously realizing the resource utilization of industrial by-product fly ash, and preserving the utilization value of polluted soil after stabilization. The effective ingredient, biochar, can also improve the soil, allowing it to continue to grow plants, thus achieving the purpose of ecological restoration.

[0029] (5) The solidified and stabilized material of the present invention contains both inorganic gel materials such as ferrophosphate and nano silica, and organic gel materials such as polyacrylamide, so that it has both the strength and toughness of solidified and stabilized materials. Attached Figure Description

[0030] Figure 1 Figure showing the results of the soil and water conservation experiment;

[0031] Figure 2 This is a diagram of unconfined compressive strength.

[0032] Figure 3 Scanning electron microscopy (SEM) images of the solidification and stabilization material before and after the addition of soil; where (A) is before the addition of soil and (B) is after the addition of soil. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0034] Example 1

[0035] This solidification and stabilization material is suitable for remediating soils contaminated with arsenic / antimony and their associated heavy metals in mining areas. The mass fraction of each component is as follows: polyacrylamide 15%, nano silica 15%, fly ash 18%, ferrous ore 40%, and biochar 12%.

[0036] The heavy metal categories and contents in the soil contaminated with arsenic and its associated heavy metals are as follows: arsenic 950 mg / kg, antimony 544 mg / kg, cadmium 25 mg / kg, and lead 476 mg / kg.

[0037] The method of using the solidification and stabilization material for remediating arsenic / antimony and associated heavy metal contaminated soil in mining areas is as follows: add the solidification and stabilization material to the contaminated soil in a fixed proportion, till and mix evenly, spray the surface with an appropriate amount of water to make the moisture content 20%, wherein the added solidification and stabilization material accounts for 2% of the dry weight of the contaminated soil.

[0038] Comparative Example 1

[0039] Only the arsenic / antimony and its associated heavy metal contaminated soil from Example 1 was used, without adding any solidification or stabilization materials.

[0040] Example 2

[0041] Similar to Example 1, except that the curing and stabilizing material comprises the following components by mass percentage: 20% polyacrylamide, 10% nano silica, 15% fly ash, 40% ferrous sulfate, and 15% biochar.

[0042] The method of using the solidification and stabilization material for remediating arsenic / antimony and associated heavy metal contaminated soil in mining areas is as follows: add the solidification and stabilization material to the contaminated soil in a fixed proportion, till and mix evenly, spray the surface with an appropriate amount of water to make the moisture content 20%, wherein the added solidification and stabilization material accounts for 4% of the dry weight of the contaminated soil.

[0043] Example 3

[0044] Similar to Example 1, except that the curing and stabilizing material comprises the following components by mass percentage: 15% polyacrylamide, 10% nano silica, 20% fly ash, 45% ferrous sulfate, and 10% biochar.

[0045] The method of using the solidification and stabilization material for remediating arsenic / antimony and associated heavy metal contaminated soil in mining areas is as follows: add the solidification and stabilization material to the contaminated soil in a fixed proportion, till and mix evenly, spray the surface with an appropriate amount of water to make the moisture content 20%, wherein the added solidification and stabilization material accounts for 6% of the dry weight of the contaminated soil.

[0046] After 3 days of curing, soil samples from Examples 1-3 and Comparative Example 1 were used for soil erosion tests.

[0047] Experimental procedure: The soil erosion resistance test was conducted in a laboratory simulation device. The contaminated soil was placed in the experimental chamber, the rainfall intensity was 210 mm / h, and the slope was 0.33.

[0048] The experimental results are shown in Figure 1Compared to Comparative Example 1, the soil erosion rate in Example 1 decreased from 37.98 g / L to 2.07 g / L, with a solidification effect of 94.55% for particulate arsenic and antimony pollutants. Similarly, the soil erosion rates in Examples 2 and 3 decreased to 0.30 g / L and 0.19 g / L, respectively, with solidification effects of 99.21% and 99.50% for particulate arsenic and antimony pollutants.

[0049] Soil samples from Examples 1-3 and Comparative Example 1 were sealed in self-sealing bags and cured for 28 days at 23 ± 2℃ and 95% relative humidity. Unconfined compressive strength and toxicity leaching tests were then performed on the contaminated soil.

[0050] Experimental protocol: Refer to ASTM C109 / C109M-16a and "Solid Waste Leaching Toxicity Leaching Method Acetic Acid Buffer Solution Method" (HJ / T 300-2007).

[0051] The experimental results are shown in Table 2 and Figure 2 The toxicity leaching results are shown in Table 2. In Comparative Example 1 without added solidification and stabilization materials, the leaching concentrations of arsenic, antimony, cadmium, and lead were all far higher than the limits for Class III water in the Groundwater Environmental Quality Standard (GB / T 14848-2017). Although the amount added in Example 1 was small, it still achieved the effect of solidification and stabilization of heavy metals. The effects of Examples 2 and 3 were the most significant, both below the limits for Class III water in the Groundwater Environmental Quality Standard (GB / T 14848-2017), and the four heavy metal elements were no longer detectable in the leachate. The unconfined compressive strength of the soil after 28 days of solidification under different treatments is shown in Table 2. Figure 2 As shown, compared to Comparative Example 1, the 28-day unconfined compressive strength of Examples 1-3 increased by 47.94%, 72.91%, and 103.33%, respectively. Here, unconfined compressive strength is not used as an indicator for solid waste landfill or roadbed materials; it only represents the improvement in soil mechanical strength and stability. The purpose of this patent is to remediate arsenic / antimony and its associated heavy metal contaminated soils in situ while maintaining the soil's usability and avoiding damage and significant disturbance.

[0052] Table 2. Toxicity leaching results of contaminated soil (mg / L)

[0053]

[0054] Note: --- indicates that the sample was not detected below the detection limit.

[0055] Further investigation into the solidification and stabilization mechanism of the solidification and stabilization material was conducted, and scanning electron microscopy images of the soil before and after the addition of the solidification and stabilization material were obtained, as shown in the following figures. Figure 3As shown in (A) and (B), it can be seen that after adding solidification and stabilization materials, soil particles cross-link together, forming larger aggregates, which helps to improve the mechanical strength and stability of the soil.

[0056] The embodiments described above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil, characterized in that, The material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in the heavy metal contaminated soil comprises the following components by weight percentage: 5-25% polyacrylamide, 5-20% nano-silica, 10-25% fly ash, 20-60% ferrohydrate, and 5-20% biochar.

2. The material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil according to claim 1, characterized in that, The material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil comprises the following mass percentages: polyacrylamide 10-20%, nano-silica 10-15%, fly ash 12-20%, ferrous sulfate 30-55%, and biochar 6-15%.

3. A method for preparing a material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil, characterized in that, The process includes the following steps: mixing polyacrylamide, nano silica, fly ash, ferrous sulfate and biochar by mass percentage, and dry stirring for 10-30 minutes.

4. Application of a material for simultaneously solidifying and stabilizing particulate and available arsenic and antimony in heavy metal contaminated soil in the remediation of heavy metal contaminated soil.

5. The application according to claim 4, characterized in that, The application of the solidified and stabilized material for particulate and available arsenic and antimony in heavy metal contaminated soil in the remediation of heavy metals in soil includes the following steps: adding the solidified and stabilized material to the contaminated soil in a fixed proportion, tilling and mixing evenly, and spraying an appropriate amount of water on the surface to make the moisture content 15-35%.

6. The application according to claim 4, characterized in that, The arsenic or antimony content in the contaminated soil is 100–2000 mg / kg.

7. The application according to claim 4, characterized in that, The dosage of the particulate and available arsenic-antimony co-solidification and stabilization material in the heavy metal contaminated soil is 1-10% of the dry weight of the soil.

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