Recyclable magnetic stabilizer for arsenic and antimony combined polluted soil as well as preparation method and application of recoverable magnetic stabilizer

Abstract

The invention relates to a preparation method of a recoverable magnetic stabilizer for arsenic and antimony polluted soil, which comprises the following steps: step 1, adding ferroferric oxide solid particles and ferrous sulfate heptahydrate particles into 200-400ml of deionized water, mixing, introducing nitrogen, and stirring for 20-30 minutes at the same time; and 2, preparing a sodium borohydride solution, introducing the sodium borohydride solution into the mixed solution of the ferroferric oxide solid particles and the ferrous sulfate heptahydrate particles in the step 1 under the condition of nitrogen, stirring for 10-20 minutes, and separating and drying the solid to obtain a zero-valent iron loaded ferroferric oxide magnetic material, namely the recoverable magnetic stabilizer for the arsenic and antimony polluted soil. The magnetic stabilizer has good magnetism all the time in the remediation period, dry magnetic separation of an external magnetic field is facilitated, the recovery rates of arsenic and antimony can reach 30% and 60% or above respectively, physicochemical properties such as soil moisture content do not need to be changed, waste liquid is reduced, and damage to basic substances such as soluble organic matter in soil is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal contaminated soil remediation, and more specifically, relates to a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil, a preparation method thereof, and an application thereof. Background Art

[0002] Abandoned industrial sites in China are severely polluted, and the problem of heavy metal pollution is prominent. In 2016, the State Council issued the "Soil Pollution Prevention and Control Action Plan", requiring the implementation of pollution treatment and remediation to improve the regional soil environmental quality. In 2018, the "Soil Environmental Quality Risk Control Standards for Construction Land Soil Pollution" (GB 36600-2018) came into force. In the same year, the number of domestic polluted sites repaired / regulated reached the peak in the past 10 years, exceeding 130. Arsenic and antimony are common heavy metals in industry. Among them, antimony, as an important military industrial metal, is commonly found in the soil of shooting ranges, mineral mining, and industrial smelting sites. Arsenic and antimony often occur as associated elements in ore deposits, so they often appear synchronously in the soil and have similar geochemical behaviors.

[0003] The stabilization technology is a commonly used technical means for remediating heavy metal contaminated soil. This technology is simple to operate and has high remediation efficiency. The stabilization technology was listed as a recommended technology in the "2014 Pollution Site Remediation Technology Catalog (First Batch)" issued by China. The stabilizer is the core of the stabilization technology. It reacts with heavy metals in the soil through precipitation, adsorption, complexation, redox and other reactions, weakening the mobility of heavy metals and achieving the purpose of passivation. However, this technology can only reduce the leaching risk of heavy metals in the soil and cannot completely remove heavy metals. In the long-term natural environment, it is difficult for the stabilizer to maintain a long-term stabilization effect, and there is a risk of secondary pollution. To overcome the failure of the stabilizer under long-term natural conditions, methods can be taken to separate the stabilizer from the soil.

[0004] To achieve the removal of heavy metals from the soil, in the prior art, CN110976496A developed a soil remediation plate. By applying water to the soil, heavy metals are migrated to the surface of the plate for removal. The temperature and pressure must be strictly controlled during the molding process of the composite plate; CN105709699B developed a light floating core loaded with nano-inorganic compounds and an organic polymer adsorbent with chelating groups. The preparation method is complex and the recovery process requires the soil to be in a water-containing condition, generating waste liquid and causing secondary pollution; CN104609684A directly added zero-valent iron or magnetite to the contaminated soil or sediment, and only 3.45% of arsenic in the soil can be recovered.

[0005] According to the above, aiming at the problems of long-term failure of the stabilizer, complex preparation of recyclable materials, secondary pollution in the recovery process, and low recovery efficiency in the current technology, it is necessary to design a simple and feasible preparation method of magnetic stabilizer, simplify the recovery process, reduce pollution, and achieve the complete removal of heavy metals in the soil. Summary of the Invention

[0006] The object of the present invention is to address the problems existing in the above-mentioned prior art and propose a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil and a preparation method thereof.

[0007] A preparation method of a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to the present invention includes the following steps:

[0008] Step 1: Add solid particles of iron tetroxide and ferrous sulfate heptahydrate particles to 200 - 400 ml of deionized water for mixing, introduce nitrogen, and stir for 20 - 30 minutes simultaneously;

[0009] Step 2: Prepare a sodium borohydride solution, introduce it into the mixed solution of the solid particles of iron tetroxide and ferrous sulfate heptahydrate described in Step 1 under nitrogen conditions, stir for 10 - 20 minutes, then separate and dry the solid to obtain a magnetic stabilizer with zero-valent iron loaded on iron tetroxide.

[0010] Further, in Step 1, the raw material for preparing zero-valent iron is solid ferrous sulfate heptahydrate.

[0011] Further, in Step 1, the mass ratio of the solid ferrous sulfate heptahydrate to the solid iron tetroxide is (0.99 - 24.85):1; in Step 2, the mass ratio of zero-valent iron to iron tetroxide is (0.2 - 5.0):1.

[0012] Further, the mass ratio of the solid ferrous sulfate heptahydrate to the solid iron tetroxide is 4.97:1 or 19.88:1; in Step 2, the mass ratio of zero-valent iron to iron tetroxide is 1:1 or 4:1.

[0013] Further, in Step 2, the concentration of the sodium borohydride solution is 0.05 - 0.5 mol / L, and a peristaltic pump is used to constantly introduce it into the mixed solution of ferrous sulfate and iron tetroxide at a constant speed.

[0014] Further, in Step 2, the magnetic stabilizer is a mixture of spherical zero-valent iron and square iron tetroxide, with a size of nanoscale or micron-scale and a mesoporous network structure under microscopic conditions.

[0015] The present invention also relates to a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil, which is prepared by the above method.

[0016] The present invention also relates to a method for stabilizing and recovering heavy metals in contaminated soil. The method uses the above magnetic stabilizer, and the dosage of the magnetic stabilizer is 1% - 5% of the mass of the soil to be repaired.

[0017] Furthermore, in the process of recovering the magnetic stabilizer from the soil, a permanent magnet or an electromagnet is used to provide an external magnetic field, and after the remediation is completed, it is directly recovered from the soil particles through dry magnetic separation.

[0018] Furthermore, the heavy metal is one or more of arsenic and antimony.

[0019] Beneficial effects

[0020] The magnetic stabilizer provided by the present invention has the following outstanding features and excellent effects compared with the prior art:

[0021] The magnetic stabilizer of the present invention is prepared in one step by the aqueous phase reduction method. The raw materials selected are ferrous sulfate heptahydrate solid, magnetite solid and sodium borohydride solid. The raw materials are easily available and the preparation method is simple. The magnetic stabilizer appears as black solid particles and has good magnetism.

[0022] The magnetic stabilizer of the present invention can synchronously stabilize arsenic and antimony in the soil. When used to repair the contaminated soil of a certain site at a dosing ratio of 5:100, after 50 days of remediation, according to the "Horizontal Oscillation Method for Toxicity Leaching of Solid Wastes" (HJ / T 557-2010), the leaching concentrations of arsenic and antimony are lower than the groundwater Class Ⅳ standard limits in the "Groundwater Quality Standard" (GB / T 14848-2017) (arsenic: 0.05 mg / L, antimony: 0.01 mg / L).

[0023] The magnetic stabilizer of the present invention forms stable compounds with arsenic and antimony in the soil through adsorption, precipitation and complexation, converts the arsenic and antimony present in the adsorbed state in the soil into arsenic and antimony present in the more stable amorphous iron-bound state and crystalline iron-bound state, improves the stability of the existence of arsenic and antimony in the soil, effectively reduces the leaching of arsenic and antimony during the remediation period, and after the remediation is completed, it is attracted by the external magnetic field and separated from the soil, achieving the complete removal of heavy metals;

[0024] The magnetic stabilizer of the present invention always has good magnetism during the remediation period, which is conducive to dry magnetic separation by the external magnetic field. The recovery rates of arsenic and antimony can reach more than 30% and 60% respectively, without changing the physical and chemical properties such as the soil moisture content, reducing the generation of waste liquid, and avoiding the destruction of basic substances such as soluble organic matter in the soil. Description of the drawings

[0025] Figure 1 It is a process flow chart of the preparation of the magnetic stabilizer in the present invention.

[0026] Figure 2 It is a flow chart of the magnetic stabilizer in the present invention for repairing contaminated soil and recovery.

[0027] Figure 3 It is a magnetization curve diagram of the magnetic stabilizer in the present invention with different ratios.

[0028] Figure 4 It is a schematic diagram of the leaching concentration of the magnetic stabilizer for repairing contaminated soil in the present invention. Detailed implementation mode

[0029] The following is combined with Figures 1 to 4 to specifically describe this implementation mode.

[0030] As shown in the appendix Figure 1 A method for preparing a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to the present invention includes the following steps:

[0031] Step 1: Add solid particles of magnetite and ferrous sulfate heptahydrate particles to 200 - 400 ml of deionized water for mixing. The ferrous sulfate heptahydrate particles are used to reduce and synthesize zero-valent iron. Nitrogen is introduced while stirring for 20 - 30 minutes. The mass ratio of ferrous sulfate heptahydrate solid to magnetite solid is (0.99 - 24.85):1;

[0032] Step 2: Prepare a sodium borohydride solution with a concentration of 0.05 - 0.5 mol / L. Under nitrogen conditions, use a peristaltic pump to constantly introduce the mixed solution of ferrous sulfate and magnetite at a constant speed. After stirring for 10 - 20 minutes, separate and dry the solid to obtain a zero-valent iron-loaded magnetite magnetic material, that is, a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil. The mass ratio of zero-valent iron to magnetite is (0.2 - 5.0):1.

[0033] Preferably, the mass ratio of ferrous sulfate heptahydrate solid to magnetite solid is 4.97:1 or 19.88:1; the mass ratio of zero-valent iron to magnetite is 1:1 or 4:1.

[0034] The magnetic stabilizer is a mixture of spherical zero-valent iron and square magnetite, with a size of nanoscale or micron-scale and a mesoporous network structure under microscopic conditions.

[0035] As shown in the appendix Figure 2 The present invention also relates to a method for stabilizing and recovering heavy metals in contaminated soil. The method uses the above magnetic stabilizer, and the dosage of the magnetic stabilizer is 1% - 5% of the mass of the soil to be repaired. The process of recovering the magnetic stabilizer in the soil uses a permanent magnet or an electromagnet to provide an external magnetic field, and it is directly recovered from the soil particles by dry magnetic separation after the repair is completed. The heavy metal is one or more of arsenic and antimony.

[0036] Example 1

[0037] 1 g of iron tetroxide and 4.965 g of ferrous sulfate were added to 300 ml of deionized water to prepare a mixed solution. Nitrogen was continuously introduced into the mixed solution while mechanically stirring for 30 minutes to fully wet the surface of the solid particles.

[0038] According to the following reaction process of sodium borohydride and ferrous sulfate, the mass of sodium borohydride added to the reaction was selected based on the molar ratio:

[0039] 2Fe 2+ + 3NaBH4 + 8H2O → 2Fe 3+ + NaBO2 + 8H2 (1)

[0040] 2.72 g of sodium borohydride was dissolved in 100 ml of deionized water, and the sodium borohydride solution was introduced into the mixed solution using a peristaltic pump. Nitrogen was continuously introduced and stirred for 10 minutes. After the reaction was completed, the mixed solution was transferred to a centrifuge tube, centrifuged, and freeze-dried to obtain a magnetic stabilizer with a mass ratio of zero-valent iron to iron tetroxide of 1:1. The saturation magnetization intensity of the prepared magnetic stabilizer was 86 emu / g (as Figure 3 shown).

[0041] According to the degree of soil pollution, the concentrations of arsenic and antimony in the contaminated soil of an abandoned industrial site were 60 - 100 mg / kg, and the original moisture content was approximately 12%. A magnetic stabilizer was added to the contaminated soil, and the dosage was 5% of the mass of the contaminated soil. The magnetic stabilizer and the contaminated soil were mixed evenly using mechanical agitation and left to stand for remediation. After standing for 28 days, soil samples were taken to measure the heavy metal leaching concentration. According to the "Horizontal Oscillation Method for the Leaching Toxicity of Solid Wastes" (HJ / T 557 - 2010), the leaching concentrations of arsenic and antimony were 0.005 mg / L and 0.007 mg / L respectively, which were lower than the groundwater class IV standard limits in the "Groundwater Quality Standard" (GB / T 14848 - 2017) (arsenic: 0.05 mg / L, antimony: 0.01 mg / L), meeting the remediation requirements (as Figure 4 shown). After 28 days of remediation, a permanent magnet was used as an external magnetic field to recover the magnetic substances in the soil. The permanent magnet can be an N52 permanent magnet. After covering the magnet with a transparent film and directly contacting the soil to attract the magnetic particles, the transparent film and the magnetic particles were removed together. As determined by ICP-OES, 99.24% of arsenic and 97.79% of antimony in the soil were removed.

[0042] Example 2

[0043] 1 g of iron tetroxide and 19.88 g of ferrous sulfate were added to 300 ml of deionized water to prepare a mixed solution. Nitrogen was continuously introduced into the mixed solution while mechanically stirring for 30 minutes to fully wet the surface of the solid particles. 5.4 g of sodium borohydride was dissolved in 200 ml of deionized water, and the sodium borohydride solution was introduced into the mixed solution using a peristaltic pump. Nitrogen was continuously introduced and stirred for 10 minutes. After the reaction was completed, the mixed solution was transferred to a centrifuge tube, centrifuged, and freeze-dried to obtain a magnetic stabilizer with a mass ratio of zero-valent iron to iron tetroxide of 4:1.

[0044] According to the degree of soil pollution, the concentrations of arsenic and antimony in a contaminated soil were 100 - 150 mg / kg, and the original moisture content was approximately 60%. A magnetic stabilizer was added to the contaminated soil, and the dosage was 5% of the mass of the contaminated soil. Mechanical agitation was used to mix the magnetic stabilizer and the contaminated soil evenly, and then static remediation was carried out. After standing for 50 days, soil samples were taken to measure the leaching concentration of heavy metals. According to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Wastes" (HJ / T 557 - 2010), the leaching concentrations of arsenic and antimony were 0.007 mg / L and 0.009 mg / L respectively, which were lower than the groundwater class IV standard limits in the "Groundwater Quality Standard" (GB / T 14848 - 2017) (arsenic: 0.05 mg / L, antimony: 0.01 mg / L), meeting the remediation requirements, as Figure 4 shown.

[0045] After 50 days of remediation, a permanent magnet was used as an external magnetic field to recover the magnetic substances in the soil. The recovery process was the same as in Example 1. The permanent magnet can be an N52 permanent magnet. After covering the magnet with a transparent film and directly contacting the soil to attract the magnetic particles, the transparent film and the magnetic particles were removed together to achieve the complete removal of heavy metals from the soil.

[0046] Example 3

[0047] 0.5 g of iron tetroxide and 9.94 g of ferrous sulfate were added to 200 ml of deionized water to prepare a mixed solution. Nitrogen was continuously introduced into the mixed solution while mechanically stirring for 20 minutes to fully wet the surface of the solid particles. 2.7 g of sodium borohydride was dissolved in 400 ml of deionized water, and the sodium borohydride solution was introduced into the mixed solution using a peristaltic pump. Nitrogen was continuously introduced and stirred for 15 minutes. After the reaction was completed, the mixed solution was transferred to a centrifuge tube, centrifuged, and freeze-dried to obtain a magnetic stabilizer with a mass ratio of zero-valent iron to iron tetroxide of 4:1. The saturation magnetization intensity of the prepared magnetic stabilizer was 87 emu / g (as Figure 3 shown), meeting the conditions for magnetic separation.

[0048] Soil remediation effect

[0049] According to the degree of soil pollution, the concentrations of arsenic and antimony in the contaminated soil of a certain abandoned industrial site are 100 - 150 mg / kg, and the original moisture content is about 12%. A magnetic stabilizer is added to the contaminated soil, and the dosage is 5% of the mass of the contaminated soil. Mechanical agitation is used to mix the magnetic stabilizer and the contaminated soil evenly, and then static remediation is carried out. After 28 days of static settlement, soil samples are taken to measure the leaching concentrations of heavy metals. According to the "Solid Waste Leaching Toxicity Leaching Method - Acetic Acid Buffer Solution Method" (HJ / T 300 - 2007), the leaching concentrations of arsenic and antimony are 0.001 mg / L and 0.009 mg / L respectively, which are far lower than the pollutant control limits in the leachate of the "Pollution Control Standard for Domestic Waste Landfills" (GB 16889 - 2024) (total arsenic: 0.3 mg / L) (as Figure 4 shown), and the "Pollution Control Standard for Domestic Waste Landfills" (GB 16889 - 2024) does not set a limit requirement for the leaching concentration of antimony.

[0050] After 28 days of remediation, an electromagnet is used as an external magnetic field to recover the magnetic substances in the soil. The electromagnet can be a DC circular or square electromagnet. After being energized, it comes into contact with the remediated soil to attract the magnetic particles therein. After the adsorption is completed, the electromagnet is moved to the collection area and the power is cut off to make the electromagnet lose its magnetism, realizing the complete removal of heavy metals from the soil.

[0051] Table 1 Leaching Concentration Results of Contaminated Soil Before Treatment and After Curing

[0052]

[0053] The zero-valent iron in the material undergoes oxidative corrosion in the soil environment and becomes iron oxides such as iron oxyhydroxide, providing a large number of adsorption sites for arsenic and antimony in the soil. The process of the transformation of zero-valent iron into amorphous iron oxides and crystalline iron oxides in the soil is accompanied by the combination with arsenic and antimony, making the arsenic and antimony existing in the adsorbed form in the soil transform into more stable amorphous iron-bound and crystalline iron-bound forms. Magnetite not only provides strong magnetism for the stabilizer, but also separates the zero-valent iron particles from each other, reducing the aggregation of effective components. The semiconductor property of magnetite promotes the corrosion process of zero-valent iron, overcomes the disadvantage of the rapid formation of a surface passivation layer of zero-valent iron in the soil, and improves the performance.

[0054] The above content of the present invention is only the preferred embodiment of the present invention and is not used to limit the implementation scheme of the present invention. Those of ordinary skill in the art can easily make corresponding changes or modifications according to the main idea and spirit of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope required by the claims.

Claims

1. A preparation method of a recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil, characterized in that, It includes the following steps: Step 1: Add solid particles of iron tetroxide and ferrous sulfate heptahydrate particles into deionized water for mixing, and introduce nitrogen and stir. Step 2: Prepare a sodium borohydride solution, and under the condition of nitrogen, introduce it into the mixed solution of the solid particles of iron tetroxide and ferrous sulfate heptahydrate described in Step 1. After stirring, separate the solid and dry it to obtain a magnetic stabilizer with zero-valent iron loaded on iron tetroxide.

2. The preparation method of the recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to claim 1, characterized in that, In Step 1, the raw material for preparing zero-valent iron is solid ferrous sulfate heptahydrate.

3. The preparation method of the recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to claim 2, characterized in that, In Step 1, the mass ratio of the solid ferrous sulfate heptahydrate and the solid iron tetroxide is (0.99 - 24.85):1; in Step 2, the mass ratio of zero-valent iron to iron tetroxide is (0.2 - 5.0):

1.

4. The preparation method of the recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to claim 3, wherein, The mass ratio of the solid ferrous sulfate heptahydrate and the solid iron tetroxide is 4.97:1 or 19.88:1; in Step 2, the mass ratio of zero-valent iron to iron tetroxide is 1:1 or 4:

1.

5. The preparation method of the recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to claim 1, characterized in that, In Step 2, the concentration of the sodium borohydride solution is 0.05 - 0.5 mol / L, and a peristaltic pump is used to constantly introduce it into the mixed solution of ferrous sulfate and iron tetroxide.

6. The preparation method of the recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil according to claim 1, characterized in that, In Step 2, the magnetic stabilizer is a mixture of spherical zero-valent iron and square iron tetroxide, with a size of nanoscale or microscale, and a mesoporous network structure under microscopic conditions.

7. A recyclable magnetic stabilizer for arsenic- and antimony-contaminated soil, characterized in that, Prepared by the method according to any one of claims 1 to 6 above.

8. A method for stabilizing and recovering heavy metals in contaminated soil, characterized in that, The method uses the magnetic stabilizer described in claim 7, and the dosage of the magnetic stabilizer is 1% - 5% of the mass of the soil to be repaired.

9. The method for stabilizing and recovering heavy metals in contaminated soil according to claim 8, characterized in that, In the process of recovering the magnetic stabilizer in the soil, a permanent magnet or an electromagnet is used to provide an external magnetic field, and it is directly recovered from the soil particles by dry magnetic separation after the repair is completed.

10. The method for stabilizing and recovering heavy metals in contaminated soil according to claim 8, characterized in that, The heavy metal is one or more of arsenic and antimony.

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