Method for remediation of acid lead-zinc contaminated soil

Abstract

The application discloses a kind of acid lead-zinc contaminated soil remediation methods, belong to environmental geotechnical engineering technical field.The application includes that acid lead-zinc contaminated soil is mixed with solid component of solidifying agent uniformly, then mixture is sprayed with phosphoric acid solution, obtains solidified soil, completes acid lead-zinc contaminated soil remediation;The solid component of solidifying agent includes by mass fraction: fly ash: 90~100%, diatomite: 0~10%.The application can effectively construct physical adsorption-chemical fixation-structure locking triple solidification mechanism in the process of repair, to effectively strengthen the solidification and stabilization effect of heavy metal pollutants of acid lead-zinc composite contaminated soil, after repair, soil strength can be increased by about 6.59 times, lead, zinc fixation rate is more than 99.7% and 73.9% respectively, compared with traditional cement-based solidifying agent, carbon emission is reduced by about 40%, so that the soil body after repair can maintain stable morphology and heavy metal solidification effect under extreme conditions, realize contaminated soil resource utilization by waste disposal, with the characteristics of efficient and stable, environment-friendly, cost-saving.

Description

Technical Field

[0001] This invention belongs to the field of environmental geotechnical engineering technology, specifically relating to a method for remediating acidic lead-zinc contaminated soil. Background Technology

[0002] Mining, metallurgy, and agriculture are all prone to causing heavy metal pollution in soil. Heavy metal pollutants are insidious, persistent, and irreversible. They can accumulate through the food chain, threatening ecological security and human health, and significantly altering soil physical properties (such as increasing liquid limit and decreasing permeability), leading to engineering hazards such as soil swelling and reduced foundation bearing capacity. Therefore, it is urgent to carry out efficient treatment of heavy metal-contaminated soil to prevent further pollution and eliminate engineering hazards.

[0003] Solidification / stabilization (S / S) technology is an important means of treating soil contaminated with heavy metals. Currently, cement-based solidification agents are commonly used for solidification / stabilization of soil contaminated with heavy metals. However, the production of cement-based solidification agents is energy-intensive and highly polluting (accounting for 8% of global carbon emissions), which is not conducive to their practical use.

[0004] Lead and zinc are both heavy metal pollutants. Therefore, when soil is contaminated with lead or zinc, it needs to be treated. However, most solidification agents currently available are only effective against a single heavy metal pollutant and are not suitable for dealing with combined lead and zinc pollution. Furthermore, under acidic conditions, lead is more stable and easily forms stable compounds, while zinc is more reactive and difficult to solidify. These contrasting characteristics of lead and zinc significantly negatively impact the remediation of acidic lead-zinc contaminated soil, often resulting in inadequate zinc solidification and persistently excessive zinc leaching after treatment.

[0005] Therefore, it is necessary to provide a remediation method for acidic lead-zinc contaminated soil to weaken the negative impact of soil acidity on the solidification and stability of lead and zinc pollutants, and effectively improve the synergistic solidification and stability effect of lead and zinc in acidic lead-zinc co-contaminated soil. Summary of the Invention

[0006] To overcome the problems in the background technology, the present invention uses diatomaceous earth, fly ash and phosphoric acid to remediate acidic lead-zinc composite contaminated soil. By utilizing a triple solidification mechanism of physical adsorption-chemical fixation-structural locking, the synergistic solidification and stabilization effect of lead and zinc heavy metal pollutants can be effectively enhanced under acidic conditions.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention proposes a method for remediating acidic lead-zinc contaminated soil, the remediation method comprising the following steps: The acidic lead-zinc contaminated soil is mixed evenly with the solid components of the solidifying agent, and then the mixture is sprayed with phosphoric acid solution to obtain solidified soil, thus completing the remediation of acidic lead-zinc contaminated soil.

[0008] The solid components of the curing agent, by mass fraction, include: fly ash: 90%~100%, diatomaceous earth: 0~10%.

[0009] The preferred solid component of the curing agent is a mixture of fly ash and diatomaceous earth. When diatomaceous earth is not added to the solid component of the curing agent, the present invention does not produce a structural locking mechanism, and thus the curing effect will decrease slightly. However, it can still maintain a relatively good lead and zinc synergistic curing stability when facing acidic lead and zinc contaminated soil.

[0010] When mixing acidic lead-zinc contaminated soil with the solid components of the solidifying agent, conventional mixing methods such as mechanical mixing can be used to achieve uniform mixing.

[0011] In actual repair processes, if special weather conditions such as rainfall occur, the soil in the repaired area needs to be protected after repair to prevent the solidifying agent that was just added to the contaminated soil from being washed away by rainwater and losing its repair effect.

[0012] In the actual remediation process, it is only necessary to mix the solid components of the curing agent evenly with the contaminated soil, and then spray the phosphoric acid solution for in-situ remediation.

[0013] Preferably, the solid component of the curing agent is used at a mass of 5% to 10% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil.

[0014] Further optimization involves using a solid component of the curing agent at a mass of 5% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil.

[0015] Preferably, in step (1), the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of acidic lead-zinc contaminated soil and solid component of the curing agent is: phosphoric acid: acidic lead-zinc contaminated soil and solid component of curing agent = 0.23~0.3.

[0016] Further optimization of phosphoric acid: acidic lead-zinc contaminated soil and solidifying agent solid component = 0.25.

[0017] Preferably, in step (1), the mass concentration of the phosphoric acid solution is 30% to 60%.

[0018] Further optimization yields a phosphoric acid solution with a mass concentration of 50%.

[0019] Preferably, the fly ash is high-calcium fly ash, wherein the mass fraction of SiO2 is 35.3%, the mass fraction of Al2O3 is 21.5%, the mass fraction of CaO is 30.6%, the mass fraction of Fe2O3 is 6.2%, the mass fraction of MgO is 1.2%, the mass fraction of K2O is 0.6%, and the mass fraction of Na2O is 1.2%.

[0020] The remaining substances in fly ash are unavoidable impurities.

[0021] Preferably, the diatomite is industrial-grade diatomite, and the mass fraction of SiO2 in the diatomite is 60%~90%.

[0022] Further optimization revealed that the mass fraction of SiO2 in the diatomaceous earth was 87%.

[0023] In diatomaceous earth, the remaining substances are unavoidable impurities, such as soluble hydrochloric acid, soluble water, and non-silicon substances.

[0024] Preferably, the fly ash particle size is 0.83~104.7μm.

[0025] Preferably, the diatomaceous earth has a particle size of 0.14~3283.6μm.

[0026] Preferably, in step (1), the solid component of the curing agent is dried before it is mixed with the acidic lead-zinc contaminated soil.

[0027] Preferably, the drying temperature is 60~105℃ and the drying time is 8~10h.

[0028] The beneficial effects of this invention are: 1. This invention utilizes the porous structure of diatomaceous earth to achieve dual physical interception of lead and zinc ions, while simultaneously adsorbing some free water in the contaminated soil, laying the foundation for subsequent stabilization reactions. By spraying phosphoric acid solution, it promotes precise chemical reactions between phosphate ions and lead and zinc ions in the soil, generating insoluble salts such as lead phosphate and zinc phosphate, thereby achieving synergistic solidification and stabilization of lead and zinc at the chemical level. Under the activation effect of phosphoric acid solution, fly ash and diatomaceous earth form geopolymers, which promote the formation of a dense three-dimensional aluminosilicate network structure. This network simultaneously locks the physically adsorbed and intercepted lead and zinc ions and the chemically fixed insoluble salts within the network, blocking ion migration channels and preventing secondary leaching of lead and zinc in acidic environments or under conditions of varying humidity. This achieves efficient, high-quality, and long-lasting solidification and stabilization of lead and zinc in acidic lead-zinc contaminated soil.

[0029] 2. Soil treated by the method of this invention has an increase in strength of approximately 6.59 times, and the fixation rates of lead and zinc exceed 99.7% and 73.9%, respectively.

[0030] 3. Compared with the traditional cement-based curing agent repair process, the carbon emissions of the repair process of the present invention are reduced by about 40%.

[0031] 4. The soil repaired by the method of the present invention has excellent strength properties and excellent pollutant solidification and stabilization effect, which is conducive to the resource utilization of contaminated soil. Attached Figure Description

[0032] Figure 1 These are macroscopic morphology images of the soil after repair in Example 1 of the present invention, taken under different pH conditions and after different number of cycles. Figure 2 The diagrams show the unconfined compressive strength of soil after wet-dry cycles in Example 1 and the comparative example of the present invention, where (a) is the unconfined compressive strength diagram of the comparative example soil and (b) is the unconfined compressive strength diagram of the soil in Example 1. Figure 3 Zn in soil after wet-dry cycles in Example 1 of the present invention (comparative example) 2+ Leaching concentration diagram, where (a) represents the Zn concentration in the comparative soil sample. 2+ Leaching concentration diagram, (b) shows the Zn concentration of the soil in Example 1. 2+ Leaching concentration graph; Figure 4 Example 1 of the present invention: Pb of soil after wet-dry cycle in a comparative sample. 2+ Leaching concentration diagram, where (a) represents the Pb concentration of the comparative soil sample. 2+ Leaching concentration diagram, (b) shows the Pb concentration of the soil in Example 1. 2+ Leaching concentration graph; Figure 5 As described in Example 1 of the present invention, after a comparative example of soil wet-dry cycling, Pb is accelerated. 2+ Zn 2+ The graph shows the concentration of Zn over time, where (a) represents the accelerated leaching of Zn from the comparative soil sample. 2+ The concentration of Pb over time is shown in graph (b), which is a comparative example of accelerated leaching of Pb from soil. 2 + The concentration change over time is shown in graph (c), which shows the Zn accelerated leaching from the soil in Example 1. 2+ The concentration change over time graph, (d) shows the Pb concentration leached from the soil in Example 1 by accelerated leaching. 2+ Concentration versus time graph; Figure 6 The XRD pattern of the soil in Example 1 of this invention after undergoing 5 wet-dry cycles; Figure 7The images shown are scanning electron microscope (SEM) images of soil after undergoing 2, 3, and 4 wet-dry cycles in Example 1 of this invention. (a) is the SEM image of the soil after the second cycle at pH=3, (b) is the SEM image of the soil after the third cycle at pH=3, (c) is the SEM image of the soil after the fourth cycle at pH=3, (d) is the SEM image of the soil after the second cycle at pH=5, (e) is the SEM image of the soil after the third cycle at pH=5, (f) is the SEM image of the soil after the fourth cycle at pH=5, (g) is the SEM image of the soil after the second cycle at pH=7, (h) is the SEM image of the soil after the third cycle at pH=7, and (i) is the SEM image of the soil after the fourth cycle at pH=7. Figure 8 The image shows the scanning electron microscope-energy dispersive X-ray images of soil samples from Example 1 after cycling 0, 1, 3, and 5 times at pH=3. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0034] The contaminated soil in the embodiments and comparative examples of this invention was artificially prepared. The soil was collected from the foundation pit of a construction site, and the physicochemical properties of the collected soil are shown in Table 1.

[0035] Table 1 After air-drying and crushing the soil, it was sieved through a 2mm sieve to obtain clean soil. Pb(NO3)2 and Zn(NO3)2 were completely dissolved in deionized water. The Pb(NO3)2 solution and Zn(NO3)2 solution were added to the clean soil as pollution sources to make the mass content of Pb and Zn in the soil 1%. After standing for 7 days, the soil was placed in an oven at 60℃ for passivation to obtain contaminated soil.

[0036] Example 1 This embodiment uses the following method to remediate contaminated soil: (1) Place fly ash and diatomaceous earth (SiO2 mass fraction of 87%) in an oven and dry at 105℃ for 8 hours to remove moisture.

[0037] (2) The acidic lead-zinc contaminated soil and the solid component of the curing agent are mixed evenly by mechanical mixing, and then the mixture is sprayed with phosphoric acid solution to obtain the cured soil. Among them, the mass of the solid component of the curing agent accounts for 5% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil; the mass fraction of fly ash in the solid component of the curing agent is 94%, and the mass fraction of diatomaceous earth is 6%; the concentration of phosphoric acid solution is 50%, and the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of the contaminated soil and the solid component of the curing agent is 0.25; the particle size of fly ash is 0.83~104.7μm, and the particle size of diatomaceous earth is 0.14~3283.6μm.

[0038] In this embodiment, the composition of fly ash is shown in Table 2.

[0039] Table 2 Comparative Example This comparative example uses the same contaminated soil as Example 1, but does not remediate the contaminated soil in this comparative example; it only sprays the contaminated soil with deionized water.

[0040] Example 2 This embodiment uses the following method to remediate contaminated soil: (1) Place fly ash and diatomaceous earth (SiO2 mass fraction of 60%) in an oven and dry at 90℃ for 9h to remove moisture.

[0041] (2) The acidic lead-zinc contaminated soil and the solid component of the curing agent are mixed evenly by mechanical mixing, and then the mixture is sprayed with phosphoric acid solution to obtain the cured soil. Among them, the mass of the solid component of the curing agent accounts for 7% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil; the mass fraction of fly ash in the solid component of the curing agent is 90%, and the mass fraction of diatomaceous earth is 10%; the concentration of phosphoric acid solution is 30%, and the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of the contaminated soil and the solid component of the curing agent is 0.27; the particle size of fly ash is 0.83~104.7μm, and the particle size of diatomaceous earth is 0.14~3283.6μm.

[0042] The repair effect in this embodiment is similar to that in embodiment 1.

[0043] Example 3 (1) Place fly ash and diatomaceous earth (SiO2 mass fraction of 90%) in an oven and dry at 60℃ for 10h to remove moisture.

[0044] (2) The acidic lead-zinc contaminated soil and the solid component of the curing agent are mixed evenly by mechanical mixing, and then the mixture is sprayed with phosphoric acid solution to obtain the cured soil. Among them, the mass of the solid component of the curing agent accounts for 10% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil; the mass fraction of fly ash in the solid component of the curing agent is 99%, and the mass fraction of diatomaceous earth is 1%; the concentration of phosphoric acid solution is 60%, and the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of the contaminated soil and the solid component of the curing agent is 0.3; the particle size of fly ash is 0.83~104.7μm, and the particle size of diatomaceous earth is 0.14~3283.6μm.

[0045] The repair effect in this embodiment is similar to that in embodiment 1.

[0046] Example 4 This embodiment uses the following method to remediate contaminated soil: (1) Place the fly ash in an oven and dry it at 105°C for 7 hours to remove the moisture.

[0047] (2) The acidic lead-zinc contaminated soil and the solid component of the curing agent are mixed evenly by mechanical mixing, and then the mixture is sprayed with phosphoric acid solution to obtain the cured soil. Among them, the mass of the solid component of the curing agent accounts for 5% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil; the concentration of the phosphoric acid solution is 50%, and the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of the contaminated soil and the solid component of the curing agent is 0.25; the particle size of fly ash is 0.83~104.7μm, and the particle size of diatomaceous earth is 0.14~3283.6μm.

[0048] The repair effect in this embodiment is similar to that in embodiment 1.

[0049] Example of effect Performance tests were conducted on the soil remediated in Example 1 and the unremediated contaminated soil in the comparative example.

[0050] The soil from Example 1 and the contaminated soil from the comparative example were both compressed under a static pressure of 20 kN into cylindrical shapes with a diameter of 39.1 mm and a height of 80 mm (the density of the compressed soil from Example 1 was approximately 1.65 g / cm³). 3 Then, the cylindrical sample is sealed (using a plastic bag is sufficient) and transferred to a curing chamber with a relative humidity of 95% and a temperature of 25±2℃ for 28 days to obtain the experimental sample.

[0051] The experimental samples underwent a wet-dry cycle treatment: first, the experimental samples were dried in an oven at 40℃ for 24 hours; then, the sides of the experimental samples were wrapped with plastic wrap and placed in a triaxial saturator to induce axial wet cycling; after that, the experimental samples were placed in a vacuum environment for 2 hours and then immersed in a mixed solution of sulfuric acid and nitric acid at 25℃ for 22 hours. This constitutes one wet-dry cycle treatment process. By adjusting the concentration of the mixed solution to achieve pH values ​​of 3, 5, and 7, the experimental samples were subjected to 0-5 rounds of wet-dry cycles under different pH conditions, and the relevant properties of the experimental samples were measured.

[0052] pass Figure 1 As can be seen, after the wet-dry cycle, the macroscopic morphology of the soil repaired by the present invention still maintains the state after compression, and no obvious deformation or collapse occurs. This proves that after the soil is repaired using the repair method of the present invention, the soil structure has excellent stability, strong resistance to acid rain and other erosion, and the repaired soil has excellent potential for resource utilization.

[0053] The unconfined compressive strength (UCS) of the experimental samples was measured, and the results are as follows: Figure 2 As shown.

[0054] pass Figure 2 (a) and Figure 2 The comparison in (b) shows that the UCS of the soil in Example 1 reached 730 kPa, approximately 6.59 times that of the soil in the comparative example. After wet-dry cycles, the UCS enhancement of the soil in Example 1 was pH=3>pH=5>pH=7, while the UCS enhancement of the soil in the comparative example was pH=5>pH=3≈pH=7. This demonstrates that the remediation method of the present invention has excellent adaptability to acidic environments and can effectively remediate contaminated soil in acidic environments. Furthermore, the peak UCS of the soil in Example 1 reached 1575 kPa, further proving that the remediation method of the present invention has excellent remediation effects.

[0055] Basic toxicity tests were conducted on the experimental samples: The tests were performed according to the standard "Leaching Toxicity Method for Solid Waste," using a sulfuric acid / nitric acid mixed solution with a mass ratio of 2:1 as the leaching solution to simulate acid rain erosion. The toxicity leaching of the experimental samples was tested under different pH conditions and after different numbers of wet-dry cycles. The results are as follows: Figure 3-4 As shown.

[0056] pass Figure 3 (a) Figure 4 (a) It can be seen that the lead and zinc ion leaching concentrations in the soil of the comparative example were 778.7 mg / L and 773.2 mg / L, respectively. Figure 3 (b) Figure 4(b) It can be seen that the lead and zinc leaching concentrations of the soil in Example 1 are only 96.9 μg / L and 201.4 mg / L, respectively, and the curing rates reach 99.99% and 73.95%, respectively. This proves that the repair method of the present invention has excellent repair effect under long-term dry and wet cycle conditions, and has a good curing effect on lead and zinc. At the same time, the curing effect is relatively stable.

[0057] Accelerated leaching experiments were conducted on the experimental samples, and the results are as follows: Figure 5 As shown.

[0058] pass Figure 5 The comparison shows that the lead and zinc ion leaching concentration in the soil sample was seriously exceeded. However, the remediation method of this invention can effectively solidify and stabilize lead and zinc pollutants, resulting in a significant reduction in the lead and zinc ion leaching concentration. Furthermore, the solidification and stabilization effect has a strong resistance to environmental damage.

[0059] pass Figure 6 As can be seen, after the soil of this invention underwent a wet-dry cycle, some new diffraction peaks were observed. These newly appearing diffraction peaks had low intensity, and the corresponding crystalline compounds were mainly lead phosphate precipitates, zinc phosphate precipitates, lead sulfate, zinc sulfate, and Berlinite (AlPO4). The detected phosphates demonstrate that lead ions can be solidified / stabilized through chemical precipitation. The presence of Berlinite (AlPO4) plays a role in filling and improving the strength of the geopolymer structure. Lead sulfate and zinc sulfate demonstrate that the remediated soil can resist acid rain erosion, prevent secondary release of heavy metals, and has good durability.

[0060] pass Figure 7 , 8 It can be seen that, under extreme environmental conditions, only a very small amount of lead and zinc detached from the solidified soil after being repaired by the present invention, proving that the present invention has excellent solidification and stabilization effects on lead and zinc pollutants, and that the solidification and stabilization effect has strong resistance to extreme environments.

[0061] In summary, the remediation method of this invention can effectively construct a triple solidification mechanism of physical adsorption, chemical fixation, and structural locking. Under acidic conditions, it effectively enhances the synergistic solidification and stabilization effect of lead and zinc heavy metal pollutants, achieving long-term solidification and stabilization. Furthermore, the method of this invention is simple, convenient, and low-cost, possessing good economic value. It provides a new approach and technical path for the remediation of acidic lead and zinc composite contaminated soil, while also providing scientific basis and theoretical support for the resource utilization of hazardous solid waste.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for remediating acidic lead-zinc contaminated soil, characterized in that: The repair method includes the following steps: The acidic lead-zinc contaminated soil is mixed evenly with the solid components of the solidifying agent, and then the mixture is sprayed with phosphoric acid solution to obtain solidified soil, thus completing the remediation of acidic lead-zinc contaminated soil. The solid components of the curing agent, by mass fraction, include: fly ash: 90%~100%, diatomaceous earth: 0~10%.

2. The repair method according to claim 1, characterized in that: The solid component of the curing agent is used at a mass of 5% to 10% of the total mass of the solid component of the curing agent and the acidic lead-zinc contaminated soil.

3. The repair method according to claim 1, characterized in that: In step (1), the ratio of the mass of phosphoric acid in the phosphoric acid solution to the total mass of acidic lead-zinc contaminated soil and solid component of the curing agent is: phosphoric acid: acidic lead-zinc contaminated soil and solid component of curing agent = 0.23~0.

3.

4. The repair method according to claim 1, characterized in that: In step (1), the mass concentration of the phosphoric acid solution is 30%~60%.

5. The repair method according to claim 1, characterized in that: The fly ash is high-calcium fly ash, in which the mass fractions of SiO2 are 35.3%, Al2O3 are 21.5%, CaO is 30.6%, Fe2O3 is 6.2%, MgO is 1.2%, K2O is 0.6%, and Na2O is 1.2%.

6. The repair method according to claim 1, characterized in that: The diatomaceous earth is industrial grade diatomaceous earth, and the mass fraction of SiO2 in the diatomaceous earth is 60%~90%.

7. The repair method according to claim 1, characterized in that: The fly ash particle size is 0.83~104.7μm.

8. The repair method according to claim 1, characterized in that: The diatomaceous earth has a particle size of 0.14~3283.6μm.

9. The repair method according to claim 1, characterized in that: In step (1), the solid component of the curing agent is dried before it is mixed with the acidic lead-zinc contaminated soil.

10. The repair method according to claim 9, characterized in that: The drying temperature is 60~105℃, and the drying time is 8~10h.

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