L-cysteine-based soil lead pollution eluent and preparation method thereof

Abstract

The application discloses an L-cysteine-based soil lead pollution leaching agent and a preparation method thereof, and belongs to the technical field of soil heavy metal pollution remediation. The L-cysteine-based soil lead pollution leaching agent comprises the following raw materials: an L-cysteine solution, a pH buffer and a polyvinylpyrrolidone solution; the concentration of the L-cysteine solution is 0.3-0.5 mmol / L, the concentration of the pH buffer is 1 mmol / L, and the mass fraction of the polyvinylpyrrolidone solution is 0.003%-0.005%; the volume ratio of the L-cysteine solution, the pH buffer and the polyvinylpyrrolidone solution is 1:1:0.15-0.4. The leaching agent has a remarkable leaching effect on soil lead, and the removal rate of the leaching agent on the contaminated soil with a Pb content of more than 500 mg / kg can reach more than 85%, so that the leaching agent can effectively prevent lead from migrating through the soil into a food chain or a water environment, and is much stronger than a traditional carboxyl-based leaching agent.

Description

Technical Field

[0001] This invention belongs to the field of soil heavy metal pollution remediation technology, specifically relating to an L-cysteine-based soil lead pollution leaching agent and its preparation method. Background Technology

[0002] Lead pollution in soil is a pressing global environmental problem with widespread and far-reaching consequences. Its sources are diverse: Pb-containing wastewater / residue seepage from industry, cumulative input from agriculture, and historical residues from transportation have resulted in varying degrees of Pb contamination across over 160 million hectares of soil worldwide (according to the Global Soil Pollution Status Report). As a non-essential heavy metal, Pb can accumulate in the human body through the soil-crop-food chain or be inhaled through dust, causing irreversible damage to the nervous, digestive, and hematopoietic systems. Furthermore, its half-life in soil exceeds 2000 years, making it difficult to degrade naturally. Therefore, the efficient solidification and remediation of Pb-contaminated soil has become a core requirement for ensuring food security and human health. Currently, soil phosphorus (Pb) remediation technologies are mainly divided into three categories: physical remediation, chemical remediation (immobilization / leaching), and bioremediation. Physical remediation technologies (such as topsoil replacement and deep tillage) can rapidly reduce the Pb content in topsoil, but require large-scale replacement with high-quality soil, resulting in high costs and damage to soil aggregate structure and microbial communities, leading to decreased soil fertility. Bioremediation technologies have lower efficiency, greater environmental dependence, and potential for secondary pollution, limiting their application in the remediation of large-scale, high-concentration, and urgently needed redevelopment sites. Chemical immobilization technologies (such as applying phosphates and hydroxyapatite) immobilize Pb by generating low-soluble Pb phosphate precipitates, but the immobilization effect is significantly affected by environmental factors such as soil pH and organic matter. Furthermore, in the long term, immobilized Pb may be reactivated due to environmental changes, posing a risk of secondary release.

[0003] Traditional chemical leaching technology is currently the mainstream method for efficiently removing Pb from soil, but existing leaching agents have core defects: (1) insufficient complexing ability, such as carboxyl leaching agents like citric acid, which have insufficient complexing ability with Pb². + The complexation constant is only 10. 6.5 -10 8 (1) It is difficult to efficiently remove bound Pb from the soil. (2) It poses a high environmental risk. For example, artificial chelating agents such as EDTA have strong complexing ability but poor biodegradability. They are easy to remain in the soil and cause secondary activation of other heavy metals. (3) It damages the soil ecology. Most traditional leaching agents are acidic. After leaching, the soil pH decreases, leading to soil acidification and nutrient loss. Additional neutralizing agents are required, increasing the cost of remediation.

[0004] L-cysteine, as a natural amino acid derivative, has a sulfhydryl group (-SH) in its molecule that interacts with Pb.2+ The complexation constant is as high as 10. 19.2 It is far superior to traditional leaching agents and has good biodegradability, theoretically making it an ideal active ingredient for Pb leaching. However, in existing technologies, L-cysteine ​​is mostly used for Pb pollution control in water bodies. In soil Pb leaching, it cannot adapt to the complex environment of soil, such as high concentrations of Ca in the soil. 2+ Mg 2+ Colloidal particles compete for the binding of L-cysteine ​​sulfhydryl groups, reducing their affinity for Pb. 2 + The selectivity of L-cysteine; the thiol activity of L-cysteine ​​is pH sensitive, and large fluctuations in soil pH can easily lead to a sharp drop in its complexing ability.

[0005] Based on the above background, a method with L-cysteine ​​as the core and high efficiency in Pb complexation was developed. 2+ Environmentally friendly, adaptable to complex soil environments, and recyclable leaching agents have become key to solving the problem of soil Pb pollution remediation. Summary of the Invention

[0006] To address or partially address the problems existing in related technologies, this invention provides an L-cysteine-based soil lead-contaminated leaching agent and its preparation method.

[0007] This invention provides an L-cysteine-based soil lead contamination leaching agent, comprising the following raw materials: L-cysteine ​​solution, pH buffer, and polyvinylpyrrolidone solution; the concentration of the L-cysteine ​​solution is 0.3-0.5 mmol / L, the concentration of the pH buffer is 1 mmol / L, and the mass fraction of the polyvinylpyrrolidone solution is 0.003%-0.005%; the volume ratio of the L-cysteine ​​solution, pH buffer, and polyvinylpyrrolidone solution is 1:1:0.15-0.4.

[0008] Preferably, the pH buffer is a sodium phosphate buffer solution, specifically a Na₂HPO₄-NaH₂PO₄ buffer solution, wherein the molar ratio of Na₂HPO₄ to NaH₂PO₄ is 1-1.5:1, and the concentration of the Na₂HPO₄-NaH₂PO₄ buffer solution is the total concentration of the conjugate acid-base pair, where the conjugate acid-base pair refers to HPO₄. 2- With H2PO4 - .

[0009] Preferably, the average molecular weight of the polyvinylpyrrolidone is 2000-4000.

[0010] Preferably, the pH value of the L-cysteine-based soil lead contamination leaching agent is 6.8-7.2.

[0011] This invention also claims a method for preparing the L-cysteine-based soil lead-contaminated leaching agent, comprising the following steps: (1) Prepare L-cysteine ​​solution, pH buffer and polyvinylpyrrolidone solution respectively; (2) Add the pH buffer to the L-cysteine ​​solution and stir until homogeneous, then adjust the pH to 6.8-7.2 to obtain mixture A; (3) Add the polyvinylpyrrolidone solution to mixture A and stir to obtain crude eluent; (4) Test the pH value of the crude leaching agent. If the pH value is not in the range of 6.8-7.2, adjust it to 6.8-7.2 with HNO3 solution or NaOH solution to obtain L-cysteine-based soil lead pollution leaching agent.

[0012] The technical solution provided by this invention has the following beneficial effects: (1) The leaching agent of the present invention has a significant effect on the leaching of lead in soil. The removal rate of polluted soil with a Pb content of more than 500 mg / kg can reach more than 85%. It can effectively prevent lead from migrating into the food chain or water environment through the soil, which is far superior to traditional carboxyl leaching agents.

[0013] (2) This invention improves leaching performance through the multi-component synergistic effect of L-cysteine, Na2HPO4-NaH2PO4 buffer system and ultra-low molecular weight PVP, which in turn complexes Pb 2+ Maintaining soil pH at 6.8–7.2 ensures stable thiol activity and prevents protonation or interaction with other cations such as Ca. 2+ Mg 2+ Competition from Pb²⁺, while ultra-low molecular weight PVP disperses L-cysteine ​​through steric hindrance, preventing its adsorption by soil colloids and enhancing its affinity for Pb²⁺. + This improves contact efficiency, forming a highly efficient collaborative system of "complexation-stability-dispersion".

[0014] (3) The leaching agent of the present invention has outstanding environmental friendliness: L-cysteine ​​is a natural amino acid derivative with good biodegradability and no risk of residue; the buffer system can maintain the soil pH at 6.5~7.5, avoid soil acidification or alkalization caused by traditional leaching agents, protect soil aggregate structure and microbial activity, and is suitable for various scenarios such as farmland and industrial sites.

[0015] (4) The leaching agent and preparation process of the present invention are sustainable: Pb in the leaching liquid can be recovered by Na2S precipitation, and L-cysteine ​​can be concentrated and regenerated to achieve resource recycling, which has both remediation efficiency and economic feasibility. Detailed Implementation

[0016] Example 1 A method for preparing an L-cysteine-based soil lead-contaminated leaching agent, comprising the following specific steps: (1) Prepare 0.3 mmol / L L-cysteine ​​solution: Weigh 0.0363 g L-cysteine, add 1000 mL of deionized water, place on a magnetic stirrer and stir at room temperature at 120 rpm until completely dissolved to obtain 0.3 mmol / L L-cysteine ​​solution.

[0017] (2) Preparation of Na2HPO4-NaH2PO4 buffer solution: Weigh 0.0852g Na2HPO4 (0.6mmol) and 0.0480g NaH2PO4 (0.4mmol), add 1000mL of deionized water, stir until dissolved, and obtain a 1mmol / L buffer solution (molar ratio of Na2HPO4:NaH2PO4 = 1.5:1). The initial pH of the solution is 7.02.

[0018] (3) Prepare ultra-low molecular weight PVP solution: Weigh 0.03g PVP (average molecular weight is 2000-4000), add 1000mL of deionized water, stir at room temperature and speed 100rpm until completely dissolved to obtain 0.003% (mass fraction) PVP solution.

[0019] (4) Mixing and pH adjustment: Measure 500 mL of the prepared L-cysteine ​​solution into a 1000 mL beaker, add 500 mL of Na2HPO4-NaH2PO4 buffer solution, adjust the magnetic stirrer to 150 rpm and stir for 20 minutes; use a pH meter with an accuracy of 0.01 to detect the pH of the mixture, the reading is 6.98, no additional adjustment is required, and the mixture A is obtained.

[0020] (5) Add dispersant: Use a pipette to slowly add 150 mL of PVP solution to mixture A at a rate of 1.5 mL / min, and continue stirring for 25 minutes; the solution is uniform and transparent, with no visible particles, and crude eluent is obtained.

[0021] (6) Test the pH value of the crude leaching agent again. The reading should be between 6.8 and 7.2. If it is not in this range, add 0.1 mol / L HNO3 or 0.1 mol / L NaOH solution dropwise. After standing for 3 minutes, test again. If the pH fluctuation is ≤ ±0.05, it meets the requirements and the finished product L-cysteine-based soil lead pollution leaching agent is obtained.

[0022] Example 2: The difference from Example 1 is that a 0.5 mmol / L L-cysteine ​​solution was prepared, while all other conditions and preparation methods were the same as in Example 1.

[0023] Example 3: The difference from Example 1 is that a 0.005% mass fraction of PVP solution dispersant was prepared, while all other conditions and preparation methods were the same as in Example 1.

[0024] Example 4 The difference from Example 1 is that in step (2), the molar ratio of Na2HPO4 to NaH2PO4 is 1:1; in step (5), the amount of PVP solution added is 200 mL; and other conditions and preparation methods are the same as in Example 1.

[0025] Comparative Example 1: The difference from Example 1 is that the Na2HPO4-NaH2PO4 buffer solution is not added to the rinsing agent, while the other conditions and preparation methods are the same as in Example 1.

[0026] Comparative Example 2: The difference from Example 1 is that the rinsing agent does not contain ultra-low molecular weight PVP solution, while the other conditions and preparation methods are the same as in Example 1.

[0027] Comparative Example 3: The difference from Example 1 is that PVP was replaced with xanthan gum of the same mass in the rinsing agent, while the other conditions and preparation methods are the same as in Example 1.

[0028] Comparative Example 4: The difference from Example 1 is that an L-cysteine ​​solution with a concentration of 0.1 mmol / L was prepared, while other conditions and preparation methods were the same as in Example 1.

[0029] Comparative Example 5: The difference from Example 1 is that a 0.001% mass fraction of PVP solution dispersant was prepared, while all other conditions and preparation methods were the same as in Example 1.

[0030] Comparative Example 6 The difference from Example 1 is that the average molecular weight of PVP is 8000, while the other conditions and preparation methods are the same as in Example 1.

[0031] Example of effect The leaching effect of the leaching agent of this invention on simulated Pb-contaminated soil was verified, and the repeatability of the preparation process and the synergistic effect of each component were clarified. Topsoil from farmland (particle size ≤2mm, naturally air-dried and passed through a 100-mesh sieve) was taken and mixed with a Pb(NO3)2 aqueous solution to achieve a Pb content of 1000mg / kg. The soil was aged at room temperature in the dark for 7 days, with stirring once daily to ensure uniform Pb distribution. The pH of the soil was 6.9.

[0032] The test samples were: Examples 1-3 and Comparative Examples 1-5, 0.3 mmol / L citric acid, and deionized water.

[0033] The application of test samples for soil Pb contamination remediation includes the following steps: (1) A glass chromatography column with an inner diameter of 5 cm was used, with the bottom filled with quartz sand. 200.0 g of the above-mentioned contaminated soil was accurately weighed and subjected to chromatography at a concentration of 1.3 g / cm³. 3 The density is uniformly filled into the column.

[0034] (2) Elute the test sample from the top of the column at a constant flow rate of 5 mL / min. Continue rinsing until the total volume of eluent added is 800 mL (i.e., the liquid-to-solid ratio is 4:1 L / kg).

[0035] (3) After leaching, the combined leachate was filtered through a 0.22 μm filter membrane. 10 mL of the filtrate was diluted to 100 mL with 1% HNO3. The Pb concentration was determined by ICP-OES. The total amount of Pb leached out was determined, the Pb removal rate was calculated, and the soil pH was determined. The results are shown in Table 1.

[0036] Table 1 Table 1 shows that, compared with Examples 1-3, Comparative Examples 4 and 5 exhibit poor Pb removal efficiency when the concentration of L-cysteine ​​or the PVP content is low. Examples 1, 2, and 3 show good Pb removal efficiency, and the soil pH change after leaching is within the range of 6.8-7.2. Therefore, the optimal leaching agent is selected with an L-cysteine ​​concentration of 0.3-0.5 mmol / L and a PVP content of 0.003%-0.005%.

[0037] Compared with Comparative Examples 1 and 2, Example 1 demonstrates that the combination of L-cysteine, PVP, and the Na2HPO4-NaH2PO4 buffer system exhibits a synergistic effect, achieving efficient removal of Pb from soil and maintaining a neutral pH environment. The Na2HPO4-NaH2PO4 buffer system selected in this invention not only stabilizes the pH to maintain thiol activity but also facilitates the removal of Pb from the soil through the PO4 buffer system. 3- (and HPO4) 2- With H2PO4 - To reduce the amount of Ca in the soil 2+ Mg 2+ The competitive adsorption of cations and Pb enhances the removal efficiency of the eluent for Pb.

[0038] Compared with Comparative Example 3, Example 1 shows that the present invention uses ultra-low molecular weight PVP to block Ca. 2+ Mg2+ Approaching the thiol active site reduces the concentration of other cations such as Ca. 2+ Mg 2+ Competition from other cations enhances the removal efficiency of the eluent for Pb. However, using xanthan gum instead of PVP results in poor Pb removal because it cannot synergize with L-cysteine ​​and cannot reduce the competitive adsorption of other cations.

[0039] Compared with Comparative Example 6, the PVP molecular chain with a molecular weight of 8000 in Example 1 is longer. Although the steric hindrance effect is enhanced, it cannot achieve a better synergistic effect with L-cysteine. The eluent prepared in this case has a poor removal effect on Pb.

[0040] This invention also explored leaching soil with deionized water or 0.3 mmol / L citric acid. Deionized water showed poor removal efficiency for Pb, only removing Pb adsorbed on the soil surface. At the same concentration of 0.3 mmol / L, citric acid showed extremely poor removal efficiency for Pb, and the soil pH decreased slightly.

[0041] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An L-cysteine-based soil lead-contaminated leaching agent, characterized in that: The raw materials include: L-cysteine ​​solution, pH buffer, and polyvinylpyrrolidone solution; the concentration of L-cysteine ​​solution is 0.3-0.5 mmol / L, the concentration of pH buffer is 1 mmol / L, and the mass fraction of polyvinylpyrrolidone solution is 0.003%-0.005%; the volume ratio of L-cysteine ​​solution, pH buffer, and polyvinylpyrrolidone solution is 1:1:0.15-0.

4.

2. The L-cysteine-based soil lead-contaminated leaching agent according to claim 1, characterized in that: The pH buffer is a Na2HPO4-NaH2PO4 buffer solution, wherein the molar ratio of Na2HPO4 to NaH2PO4 is 1-1.5:

1.

3. The L-cysteine-based soil lead-contaminated leaching agent according to claim 1, characterized in that: The average molecular weight of the polyvinylpyrrolidone is 2000-4000.

4. The L-cysteine-based soil lead-contaminated leaching agent according to claim 1, characterized in that: The pH value of the L-cysteine-based soil lead contamination leaching agent is 6.8-7.

2.

5. The method for preparing the L-cysteine-based soil lead-contaminated leaching agent according to any one of claims 1-4, characterized in that: Includes the following steps: (1) Prepare L-cysteine ​​solution, pH buffer and polyvinylpyrrolidone solution respectively; (2) Add the pH buffer to the L-cysteine ​​solution and stir until homogeneous, then adjust the pH to 6.8-7.2 to obtain mixture A; (3) Add the polyvinylpyrrolidone solution to the mixture A and stir to obtain the crude eluent; (4) Test the pH value of the crude leaching agent. If the pH value is not in the range of 6.8-7.2, adjust it to 6.8-7.2 with HNO3 solution or NaOH solution to obtain L-cysteine-based soil lead pollution leaching agent.

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