Particle-state and effective-state arsenic-antimony synchronous solidification and stabilization material in heavy metal contaminated soil, preparation method and application

Abstract

The invention discloses a material for synchronously solidifying and stabilizing granular and effective arsenic and antimony in heavy metal contaminated soil as well as a preparation method and application of the material. The material comprises the following components in percentage by mass: 5-25% of polyacrylamide, 5-20% of nano silicon dioxide, 10-25% of fly ash, 20-60% of ferrihydrite and 5-20% of biochar. The material can efficiently improve the mechanical property of heavy metal contaminated soil and prevent water and soil loss, the granular arsenic / antimony solidification effect is 95% or above, the 28d unconfined compressive strength can be improved by 30-110%, and meanwhile the leaching rate of effective arsenic / antimony is reduced by 99% or above. The material is suitable for repairing arsenic / antimony combined polluted soil, improves the soil stability, and prevents heavy metals from diffusing to the surrounding through surface runoff and soil flow. The material is an environment-friendly material, does not cause damage and large disturbance to soil, and can also improve the soil and maintain the utilization value of the soil while solidifying and stabilizing arsenic / antimony.

Description

Technical Field

[0001] The present invention belongs to the field of heavy metal contaminated soil solidification, stabilization and restoration, and relates to a material for the simultaneous solidification and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil, a preparation method and application thereof. Background Art

[0002] Pollutants in the soil can migrate and spread in environmental media through water and soil erosion, and can enter the human body through the food chain or other pathways, thus causing harm, posing a great threat to the ecological environment and human health, and pollution control and risk reduction are needed. Among them, it is crucial to control the migration and diffusion of particulate and effective heavy metals in the soil.

[0003] There are three major aspects of soil arsenic / antimony pollution remediation technology: physical technology, chemical technology, and biological technology. Solidification / stabilization technology has been more widely used in site area remediation due to its relatively low cost, strong resistance to biodegradation, easy implementation, and quick results. Solidification and stabilization technology can improve soil stability and prevent arsenic / antimony from spreading to the surrounding areas through surface runoff and soil flow by means of physical encapsulation, adsorption and precipitation.

[0004] A large number of studies have been reported on the solidification / stabilization technology of heavy metal pollution in soil. The patent with publication number CN113337293A, an antifreeze-type solidification and stabilization agent for antimony-contaminated soil and its preparation method and application, has both high-efficiency complexation and anti-freeze-thaw capabilities, and can be used for the remediation of antimony-contaminated soil, but lacks the application of remediation of arsenic and other composite heavy metal-contaminated soil. The patent with publication number CN 110016345 A, a cadmium-reducing and arsenic-stabilizing soil passivator and its use method, has a good stabilization effect on the effective arsenic and cadmium in the soil, but does not consider the blocking effect on particulate heavy metals. The patent with publication number CN 108277017 A, a soil improver that can reduce the effective state of heavy metal arsenic and antimony in the soil and its use method, can stabilize the effective arsenic and antimony at the same time, but has no blocking effect on particulate arsenic and antimony that migrate through soil erosion and surface runoff. The patent with publication number CN 115074134 A, a soil solidifier and its preparation method, uses polyacrylamide and fly ash, among which calcium oxide can improve acidic soil, but it may make the soil too alkaline when used for neutral soil repair. This solidifier has a good effect on the repair of soil contaminated by cationic heavy metals such as cadmium and lead, but its repair effect on soil contaminated by arsenic and antimony in the form of anions needs further research and improvement.

[0005] At present, traditional soil solidification technology mainly tends to be used for solid waste storage and roadbed materials. For example, cement-based and geopolymer gel materials have problems of excessive alkalinity and easy disturbance and damage to the soil environment. At the same time, arsenic will also be activated and released in a high pH environment. Although stabilization agents such as iron-based materials have a good adsorption effect on arsenic and antimony, they have no fixation effect on particulate arsenic and antimony. Particulate arsenic and antimony will migrate and diffuse into the environment through soil erosion and surface runoff. In the study of the site soil pollution remediation process, there is little consideration of the soil erosion resistance of the solidified soil and the migration of particulate heavy metals.

[0006] The present invention takes into account the improvement of soil water and soil erosion resistance by the curing agent, based on the consideration of soil toxicity leaching and mechanical properties, and develops a material for the simultaneous curing and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil. This is crucial for the curing and stabilization of particulate arsenic / antimony, and is also a technical problem that urgently needs to be solved to improve traditional repair materials. Summary of the invention

[0007] The present invention aims to solve the problems that the traditional curing agent has a poor remediation effect on particulate heavy metal pollutants and the solidified soil has a poor ability to resist soil erosion. The purpose of the present invention is to provide a material for the simultaneous curing and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil and a method for use.

[0008] The technical solution of the present invention:

[0009] A material for synchronously solidifying and stabilizing particulate and effective arsenic and antimony in heavy metal polluted soil comprises the following parts in percentage by mass: 5-25% polyacrylamide, 5-20% nano silicon dioxide, 10-25% fly ash, 20-60% ferrihydrite and 5-20% biochar.

[0010] Furthermore, the solidification and stabilization material includes the following mass percentages: 10-20% polyacrylamide, 10-15% nano-silicon dioxide, 12-20% fly ash, 30-55% ferrihydrite, and 6-15% biochar.

[0011] A method for preparing a material for synchronously solidifying and stabilizing particulate and effective arsenic and antimony in heavy metal contaminated soil comprises the following steps: mixing polyacrylamide, nano silicon dioxide, fly ash, ferrihydrite and biochar according to mass percentage, and dry stirring for 10 to 30 minutes.

[0012] A material for simultaneously solidifying and stabilizing particulate and effective arsenic and antimony in heavy metal contaminated soil is used in the restoration of heavy metal contaminated soil.

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

[0014] The invention discloses an application of a synchronous solidification and stabilization material for particulate and effective arsenic and antimony in heavy metal contaminated soil in the restoration of contaminated soil, wherein the content of arsenic or antimony in the contaminated soil is 100-2000 mg / kg.

[0015] The dosage of the granular and effective arsenic and antimony synchronous 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 provided by the factory. The composition of fly ash is shown in Table 1, which is mainly composed of silica and alumina.

[0017] Table 1 Chemical composition of fly ash

[0018]

[0019] The preparation method of ferrihydrite comprises the following steps: dissolving Fe(NO3)3·9H2O in deionized water, adding a prepared NaOH solution, adjusting the pH value to 7.4-7.6, removing the supernatant after centrifugation, washing the solid part and centrifuging again, repeating the process 4 times and then drying, and grinding to obtain ferrihydrite powder.

[0020] A further object of the present invention is to provide an application of the solidified and stabilized material in the restoration of heavy metal-contaminated soil, wherein the restoration target is arsenic and its associated heavy metals in mining areas, such as arsenic, antimony, lead and cadmium.

[0021] The purpose of stirring in the present invention is to mix the components of the solidified stabilization material uniformly.

[0022] The purpose of tilling in the present invention is to mix the solidified stabilization material and the contaminated soil evenly.

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

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention provides a material for the simultaneous solidification and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil. The raw materials are easily available, and the arsenic in the soil is stabilized by the adsorption, coordination exchange, and coprecipitation of ferrihydrite and biochar. Gel materials such as polyacrylamide, nano-silicon dioxide, and fly ash can aggregate 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 of arsenic pollution in mining areas, such as arsenic, antimony, cadmium and lead. Components such as biochar and ferrihydrite 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 blocked.

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

[0028] (4) It breaks the problem of traditional soil solidifiers using gel materials with high alkalinity such as cement, and at the same time realizes resource utilization of industrial byproduct fly ash, and preserves the utilization value of polluted soil after solidification. The effective ingredient biochar can also improve the soil so that it can continue to grow plants and achieve the purpose of ecological restoration.

[0029] (5) The curing and stabilizing material of the present invention contains both inorganic gel materials such as ferrihydrite and nano-silica and organic gel materials such as polyacrylamide, so that it has both the strength and toughness of the curing and stabilizing material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the result of soil and water loss experiment;

[0031] Figure 2 is the unconfined compressive strength diagram;

[0032] Figure 3 The scanning electron microscope microscopic mechanism diagram of the solidified stabilization material before and after being added to the soil; wherein, (A) is before being added to the soil, and (B) is after being added to the soil. DETAILED DESCRIPTION

[0033] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0034] Example 1

[0035] The solidification and stabilization material is suitable for repairing soil contaminated by arsenic / antimony and its associated heavy metals in mining areas. The mass fraction of each component is: polyacrylamide 15%, nano silicon dioxide 15%, fly ash 18%, ferrihydrite 40%, and biochar 12%.

[0036] The types and contents of heavy metals in soil contaminated by arsenic and its associated heavy metals are: arsenic 950 mg / kg, antimony 544 mg / kg, cadmium 25 mg / kg, and lead 476 mg / kg.

[0037] The method for using the solidification and stabilization material suitable for repairing arsenic / antimony and its associated heavy metal contaminated soil in mining areas is: adding the solidification and stabilization material to the contaminated soil in a fixed proportion, tilling and mixing evenly, spraying an appropriate amount of water on the surface 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 soil contaminated with arsenic / antimony and its associated heavy metals in Example 1 was taken without adding any solidification and stabilization materials.

[0040] Example 2

[0041] The same as Example 1, except that the solidification and stabilization material includes the following parts by mass percentage: 20% polyacrylamide, 10% nano-silicon dioxide, 15% fly ash, 40% ferrihydrite, and 15% biochar.

[0042] The method for using the solidification and stabilization material suitable for repairing soil contaminated by arsenic / antimony and its associated heavy metals in mining areas is as follows: adding the solidification and stabilization material to the contaminated soil in a fixed proportion, tilling and mixing evenly, spraying an appropriate amount of water on the surface 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] The same as Example 1, except that the solidification and stabilization material includes the following parts by mass percentage: polyacrylamide 15%, nano-silicon dioxide 10%, fly ash 20%, ferrihydrite 45%, and biochar 10%.

[0045] The method for using the solidification and stabilization material suitable for repairing arsenic / antimony and its associated heavy metal contaminated soil in mining areas is: adding the solidification and stabilization material to the contaminated soil in a fixed proportion, tilling and mixing evenly, spraying an appropriate amount of water on the surface 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 curing for 3 days, the soils of Examples 1-3 and Comparative Example 1 were tested for soil erosion.

[0047] Experimental plan: The anti-soil and water loss test was carried out by a simulation device in the laboratory. The contaminated soil was placed in the experimental box. The rainfall intensity was 210 mm / h and the slope was 0.33.

[0048] The experimental results are shown in Figure 1Compared with comparative example 1, the soil erosion of example 1 was reduced from 37.98 g / L to 2.07 g / L, and the solidification effect on pollutants such as particulate arsenic and antimony was 94.55%. Similarly, the soil erosion of examples 2 and 3 was reduced to 0.30 g / L and 0.19 g / L, respectively, and the solidification effect on pollutants such as particulate arsenic and antimony was 99.21% and 99.50%.

[0049] The soil samples after application of Examples 1-3 and Comparative Example 1 were sealed with ziplock bags and cured at 23±2° C. and 95% relative humidity for 28 days, and the contaminated soil was subjected to unconfined compressive strength and toxicity leaching tests.

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

[0051] The experimental results are shown in Table 2 and Figure 2 . The toxic leaching results are shown in Table 2. In Comparative Example 1 without the addition of solidification and stabilization materials, the leaching concentrations of arsenic, antimony, cadmium and lead are far higher than the limit of Class III water in the Groundwater Environmental Quality Standard (GB / T14848-2017). Although the amount added in Example 1 is relatively small, it also achieves the solidification and stabilization effect on heavy metals. The effects of Examples 2 and 3 are the most significant, both lower than the limit of Class III water in the Groundwater Environmental Quality Standard (GB / T 14848-2017), and the four heavy metal elements can no longer be detected in the leachate. The unconfined compressive strength of soil solidified with different treatments for 28 days is shown in Figure 2. Figure 2 As shown, the 28d unconfined compressive strength of Examples 1-3 increased by 47.94%, 72.91% and 103.33% respectively compared with Comparative Example 1. The unconfined compressive strength here is not used as an indicator of solid waste landfill and roadbed materials, but only represents the effect of improving the mechanical strength and stability of the soil. The purpose of this patent is to in-situ repair arsenic / antimony and its associated heavy metal contaminated soil, and maintain the use value of the soil without causing damage and major disturbance.

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

[0053]

[0054] Note: --- means the sample is below the detection limit and not detected

[0055] To further explore the curing and stabilization mechanism of the curing and stabilization materials, the scanning electron microscope images of the soil before and after adding the curing and stabilization materials are shown in Figure 2. Figure 3 As shown in (A) and (B), it can be seen that after adding the solidification and stabilization material, the small soil particles are cross-linked together to form larger aggregates, which is beneficial to improving the mechanical strength and stability of the soil.

[0056] The above-described embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A material for the simultaneous solidification and stabilization of arsenic and antimony in particulate and effective states in heavy metal contaminated soil, characterized in that: The material for synchronously solidifying and stabilizing particulate and effective arsenic and antimony in heavy metal polluted soil comprises the following parts in percentage by mass: 5-25% polyacrylamide, 5-20% nano silicon dioxide, 10-25% fly ash, 20-60% ferrihydrite and 5-20% biochar.

2. The material for simultaneous solidification and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil according to claim 1, characterized in that: The material for synchronously solidifying and stabilizing particulate and effective arsenic and antimony in heavy metal-contaminated soil comprises the following percentages by mass: 10-20% polyacrylamide, 10-15% nano silicon dioxide, 12-20% fly ash, 30-55% ferrihydrite and 6-15% biochar.

3. A method for preparing a material for the simultaneous solidification and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil, characterized in that: The method comprises the following steps: polyacrylamide, nano silicon dioxide, fly ash, ferrihydrite and biochar are mixed according to mass percentage, and dry-stirred for 10 to 30 minutes.

4. Application of a material for simultaneous solidification and stabilization of particulate and effective arsenic and antimony in heavy metal contaminated soil in the remediation of heavy metal contaminated soil.

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

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

7. The use according to claim 4, characterized in that: The dosage of the granular and effective arsenic and antimony synchronous solidification and stabilization material in the heavy metal contaminated soil is 1-10% of the dry weight percentage of the soil.

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