Pb-polluted soil curing agent and preparation method thereof

Abstract

The invention discloses a Pb-polluted soil curing agent and a preparation method thereof, and belongs to the technical field of environmental remediation materials. The method comprises the following steps: carrying out glutaraldehyde crosslinking and phosphorylation treatment on lysine to prepare functionalized natural lysine powder; mixing and grinding calcium magnesium phosphate and magnesium oxide to prepare a composite phosphate matrix; carrying out load reaction on the functionalized lysine powder and a composite phosphate matrix aqueous solution, and treating to obtain a precursor; and mixing the precursor, starch and sodium carboxymethyl cellulose, granulating and drying to finally prepare the spherical soil stabilizer. The natural lysine is used as a functional source, organic solvents or toxic chemicals are not needed, the preparation process is simple and convenient, large-scale production is easy, the environmental remediation requirements of greenization, low carbonization and recycling are met, and the Pb content in the polluted soil can be remarkably reduced when the prepared curing agent is used for remediation of the Pb-polluted soil.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation materials technology, specifically to a Pb-contaminated soil stabilizer and its preparation method. Background Technology

[0002] Lead (Pb), a typical heavy metal pollutant, is emitted in large quantities during mining, smelting, battery manufacturing, paint production, and traffic exhaust, leading to a general increase in lead content in soil. Lead is highly toxic, persistent, and bioaccumulative in the environment, and can enter the human body through the food chain, causing serious harm to the nervous system, blood system, and children's intellectual development. Therefore, how to efficiently, economically, and environmentally friendly immobilize and stabilize mobile Pb in soil is a current research hotspot and technical challenge in the field of soil remediation.

[0003] Existing solidification / stabilization technologies for Pb-contaminated soil mainly include inorganic solidification, organic adsorption, and composite solidification. Single phosphate systems often suffer from slow reaction rates, poor solidification layer density, and insufficient long-term stability in actual soils, and are prone to secondary leaching in low pH or complex ionic environments. On the other hand, while conventional organic solidification materials (such as humic acid and amino acids) possess metal ion complexing capabilities, they are easily degraded in soil, have poor durability, and are difficult to maintain solidification effects over long periods. However, in most studies on organic-inorganic composite solidification materials, the organic modifiers used typically suffer from cumbersome synthesis steps, high costs, or poor environmental compatibility, which greatly limits the engineering application and promotion of this technology.

[0004] Therefore, it is of great significance to develop a material that is simple to prepare, low in cost, environmentally friendly, and has both efficient adsorption and stable precipitation functions as a curing agent. Summary of the Invention

[0005] To address the problems of insufficient stability and easy re-dissolution in existing methods, easy degradation and difficulty in long-term use in organic methods, and high cost and complex process in composite methods, which restrict engineering applications, the purpose of this invention is to provide a method for preparing a Pb-contaminated soil stabilizer. This invention uses cross-linking modification and phosphorylation of lysine to enhance its complexation and fixation ability with lead ions, then loads it onto the treated calcium-phosphorus matrix (calcium-magnesium composite phosphate), and finally granulates the intermediate product into spheres.

[0006] The method described in this invention specifically includes the following steps: S1. Preparation of functionalized natural lysine: ① Cross-linking treatment: Add glutaraldehyde aqueous solution to lysine aqueous solution, adjust pH, stir reaction to obtain cross-linked lysine solution.

[0007] ② Phosphorylation treatment: Add NaH2PO4·2H2O solid powder to the cross-linked lysine solution, adjust the pH, heat the reaction, filter after the reaction is completed, wash, and vacuum dry to obtain functionalized natural lysine powder.

[0008] S2. Preparation of phosphate matrix: Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O were mixed, ground and sieved to obtain calcium magnesium phosphate matrix. Magnesium oxide was added to the calcium magnesium phosphate matrix and mixed and ground evenly to obtain composite phosphate matrix, which was then sealed and stored.

[0009] S3. Loading of functionalized lysine: The complex phosphate matrix was prepared into an aqueous solution, and then functionalized natural lysine powder was added to the aqueous solution. The pH was adjusted, and the loading reaction was carried out. After the reaction was completed, the mixture was filtered, vacuum dried, ground and sieved to obtain the precursor powder.

[0010] S4. Preparation of granule solidifying agent: The precursor powder, starch and sodium carboxymethyl cellulose are mixed evenly to obtain a dry mixture. Water is added to the dry mixture and stirred to form a wet mixture. The wet mixture is granulated to obtain wet granules. The wet granules are dried to obtain Pb contaminated soil solidifying agent granules.

[0011] Preferably, the mass percentage concentration of the lysine aqueous solution in the crosslinking treatment of step S1 of the present invention is 8%-12%.

[0012] Preferably, the mass percentage concentration of the glutaraldehyde aqueous solution in the crosslinking treatment of step S1 of the present invention is 20%-30%.

[0013] Preferably, the volume ratio of lysine aqueous solution to glutaraldehyde aqueous solution in the crosslinking treatment of step S1 of the present invention is 20:1.

[0014] Preferably, the pH adjustment condition in step S1 of the present invention is as follows: the pH is adjusted to 8.0 using an aqueous solution of NaH2PO4 with a mass percentage concentration of 8-10%.

[0015] Preferably, the conditions for the stirring reaction in step S1 of the crosslinking treatment of the present invention are: stirring reaction at 40-60℃ for 2 hours.

[0016] Preferably, in step S1 of the present invention, the mass ratio of NaH2PO4·2H2O solid powder to lysine in the crosslinked lysine solution is 1:5-10.

[0017] Preferably, the pH adjustment conditions in step S1 of the present invention are as follows: the pH is adjusted to 6.5-7.0 using an aqueous solution of NaH2PO4 with a mass percentage concentration of 8%-12%.

[0018] Preferably, the heating reaction conditions in step S1 of the present invention are: reaction at 50-70°C for 2-3 hours.

[0019] Preferably, the washing conditions in step S1 of the phosphorylation treatment of the present invention are: washing with deionized water 3 to 5 times.

[0020] Preferably, the vacuum drying conditions in step S1 of the present invention are: vacuum drying for 10-12 hours at a vacuum degree of 0.006-0.015 MPa and a temperature of 50-70°C.

[0021] Preferably, in step S2 of the present invention, the mass ratio of Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O is 2:2:1.

[0022] Preferably, in step S2 of the present invention, the mass ratio of calcium magnesium phosphate matrix to magnesium oxide is 5:1.

[0023] Preferably, the particle size of the calcium magnesium phosphate matrix in step S2 of the present invention is 100-300 mesh.

[0024] Preferably, the mass percentage concentration of the composite phosphate matrix aqueous solution in step S3 of the present invention is 20%-30%.

[0025] Preferably, in step S3 of the present invention, the mass ratio of functionalized natural lysine powder to the composite phosphate matrix in the aqueous solution of the composite phosphate matrix is ​​20:1-3.

[0026] Preferably, the pH adjustment condition in step S3 of the present invention is as follows: the pH is adjusted to 6.5-7.5 using an aqueous solution of NaH2PO4 with a mass percentage concentration of 8%-12%.

[0027] Preferably, the loading reaction conditions in step S3 of the present invention are: stirring at 50-70°C for 2 hours, and then standing at 50°C for 1 hour.

[0028] Preferably, the vacuum drying conditions in step S3 of the present invention are: vacuum drying for 6-10 hours at a vacuum degree of 0.006-0.015 MPa and a temperature of 50-70°C.

[0029] Preferably, in step S4 of the present invention, the mass ratio of lysine-loaded phosphate curing agent precursor powder, starch, and sodium carboxymethyl cellulose is 20:2:1.

[0030] Preferably, the moisture content of the wet material in step S4 of the present invention is 20-35 wt%.

[0031] Preferably, the granulation conditions in step S4 of the present invention are: granulation is carried out at a rotation speed of 15-20 rpm and an inclination angle of 45°.

[0032] Preferably, the diameter of the wet pellet in step S4 of the present invention is 2.0-3.0 mm.

[0033] Preferably, the drying conditions in step S4 of the present invention are: drying at 80-120°C for 6 hours.

[0034] Another objective of this invention is to provide a soil stabilizer for Pb-contaminated soil.

[0035] Unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade.

[0036] Mechanism of the invention: The excellent solidification performance of the Pb-contaminated soil stabilizer prepared by this invention stems from the multiple synergistic effects of raw material composition and preparation process. During the preparation process, natural lysine undergoes phosphorylation-crosslinking dual modification, introducing active functional groups such as phosphate groups (–PO4H2), amino groups (–NH2), and carboxyl groups (-COOH) onto the molecule, enabling it to possess both Pb²⁺ and other properties. + The ability to complex, and can also interact with Ca² + PO4³ - When inorganic ions undergo a bridging reaction, and functionalized lysine is blended with a calcium-phosphorus complex matrix, the organic coordination sites of lysine and Ca²⁺ in the matrix interact. + Chemical bonds are formed, enabling stable loading of organic molecules on the inorganic phase surface and creating an organic-inorganic interface layer. Simultaneously, magnesium oxide, acting as a pH buffer and crystal phase regulator, synergistically interacts with Ca–P salts in the system, slowly releasing Mg²⁺. + To maintain a weakly alkaline environment in the system, the formation and crystallization of Ca–P–Pb precipitate are promoted; the generated Mg–P phase can further fill the pores, improving the compactness and mechanical stability of the solidified particles; during granulation and drying, corn starch, as a natural biodegradable granulation binder, works synergistically with sodium carboxymethyl cellulose as a polymeric additive, significantly improving the bonding force and formability between powders, improving the flowability and spheroidization uniformity of wet materials, preventing granules from breaking during drying, and significantly improving the granule forming rate and crushing strength, ensuring the mechanical stability of the curing agent during storage, transportation, and on-site application; functionalized lysine, calcium phosphate, and Mg–P phase gradually construct a stable Ca–P–N–Mg composite network structure through interfacial chemical bonding and physical interpenetrating crosslinking; this invention achieves simultaneous fixation of organic complexation and inorganic precipitation through the synergistic effect of multi-component and multi-stage processes: functionalized lysine provides Pb² +With selective complexation and capture capabilities, the calcium-phosphorus matrix provides an environment for the formation of insoluble precipitates, while magnesium oxide maintains the reaction balance and structural densification of the system. The synergistic effect of these three components enables the curing agent to maintain a highly efficient and stable Pb fixation effect under complex environments such as acid rain, freeze-thaw cycles, and long-term leaching, significantly improving the curing efficiency and environmental durability of lead in contaminated soil.

[0037] Compared with the prior art, the present invention provides a soil stabilizer for Pb-contaminated soil and its preparation method, which has the following beneficial effects: (1) This invention combines functionalized lysine with calcium phosphate to prepare an organic-inorganic synergistic Pb-contaminated soil stabilizer. This stabilizer significantly improves the lead fixation efficiency and more effectively overcomes the problem of performance degradation of traditional materials under complex environments such as acid rain, freeze-thaw, and leaching, thus providing a durable and reliable stabilization solution for lead-contaminated soil.

[0038] (2) This invention uses natural amino acids (lysine) as the functional source, without the need for organic solvents or toxic chemicals. The preparation process only includes functionalization reaction, mixing, granulation and drying. The process is simple and easy to scale up, which meets the environmental remediation requirements of greening, low carbonization and resource utilization.

[0039] (3) The curing agent prepared by the present invention is in the form of spherical particles with uniform particle size and high mechanical strength. It is easy to store, transport and spread on site, and can be mixed evenly with soil, thereby improving the operability and reaction efficiency in the actual remediation process.

[0040] (4) The optimal curing effect of the material of the present invention is reflected in the significant reduction of Pb leaching concentration in the soil after curing, and the Pb concentration in the soil leachate is far lower than the "Hazardous Waste Identification Standard" (≤5 mg / L). Attached Figure Description

[0041] Figure 1 This is a fitting diagram of the adsorption isotherm curve of the Langmuir EXT1 model of the Pb-contaminated soil stabilizer prepared in Example 1 of this invention.

[0042] Figure 2 It refers to the Pb leaching concentration in the soil after the curing agent prepared in Examples 1-3 and Comparative Examples 1-7 of this invention is cured. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1 The method for preparing a soil stabilizer for Pb-contaminated soil specifically includes the following steps: S1. Preparation of functionalized natural lysine: ① Cross-linking treatment: Add glutaraldehyde aqueous solution (glutaraldehyde aqueous solution has a mass percentage concentration of 25%) to lysine aqueous solution (lysine aqueous solution has a mass percentage concentration of 10%), wherein the volume ratio of lysine aqueous solution to glutaraldehyde aqueous solution is 20:1. Adjust the pH to 8.0 using NaH2PO4 aqueous solution with a mass percentage concentration of 10%, and stir the reaction at 50℃ for 2 hours to obtain cross-linked lysine solution.

[0045] ② Phosphorylation treatment: Add NaH2PO4·2H2O solid powder (mass ratio of NaH2PO4·2H2O solid powder to lysine in cross-linked lysine solution is 1:7) to the cross-linked lysine solution, adjust the pH to 6.5 with 10% NaH2PO4 aqueous solution, react at 60℃ for 2.5h, filter after reaction, wash with water 3 times, and vacuum dry at 0.010MPa and 60℃ for 12h to obtain functionalized natural lysine powder.

[0046] S2. Preparation of phosphate matrix: Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O were mixed and ground in a mass ratio of 2:2:1, and sieved to obtain a calcium magnesium phosphate matrix (200 mesh). Magnesium oxide was added to the calcium magnesium phosphate matrix and mixed and ground evenly (the mass ratio of calcium magnesium phosphate matrix to magnesium oxide was 5:1) to obtain a composite phosphate matrix. The matrix was sealed and stored to avoid moisture.

[0047] S3. Loading of functionalized lysine: A 25% (w / w) aqueous solution of the composite phosphate matrix was prepared. Then, functionalized natural lysine powder (the mass ratio of functionalized natural lysine powder to the composite phosphate matrix in the aqueous solution was 10:1) was added to the aqueous solution of the composite phosphate matrix. The pH was adjusted to 6.5 using a 10% (w / w) NaH2PO4 aqueous solution. The loading reaction was carried out by stirring at 50°C for 2 hours and then standing at 50°C for 1 hour. After the reaction was completed, the mixture was filtered and vacuum dried at 0.010 MPa and 60°C for 8 hours. The mixture was then ground and sieved to obtain the lysine-loaded phosphate curing agent precursor powder.

[0048] S4. Preparation of granulated solidifying agent: Lysine-loaded phosphate solidifying agent precursor powder, starch and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 20:2:1 to obtain a mixed dry material. Deionized water at a mass of 38% of the mixed dry material is added to the mixed dry material and stirred to form a wet material with a moisture content of 27.5 wt%. The wet material is then granulated at a rotation speed of 15 rpm and an inclination angle of 45° to obtain wet granules (diameter of 2.0-3.0 mm). The wet granules are dried at 100℃ for 6 h to obtain Pb contaminated soil solidifying agent granules.

[0049] Example 2 The method for preparing a soil stabilizer for Pb-contaminated soil includes the following steps: S1. Preparation of functionalized natural lysine: ① Cross-linking treatment: Add glutaraldehyde aqueous solution (glutaraldehyde aqueous solution has a mass percentage concentration of 20%) to lysine aqueous solution (lysine aqueous solution has a mass percentage concentration of 8%), wherein the volume ratio of lysine aqueous solution to glutaraldehyde aqueous solution is 20:1. Adjust the pH to 8.0 using NaH2PO4 aqueous solution with a mass percentage concentration of 8%, and stir the reaction at 40℃ for 2 hours to obtain cross-linked lysine solution.

[0050] ② Phosphorylation treatment: Add NaH2PO4·2H2O solid powder (mass ratio of NaH2PO4·2H2O solid powder to lysine in cross-linked lysine solution is 1:7.5) to the cross-linked lysine solution, adjust the pH to 6.7 with 8% NaH2PO4 aqueous solution, react at 50℃ for 3h, filter after the reaction, wash with water 4 times, and vacuum dry at 50℃ for 11h under vacuum of 0.006MPa to obtain functionalized natural lysine powder.

[0051] S2. Preparation of phosphate matrix: Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O were mixed and ground in a mass ratio of 2:2:1, and sieved to obtain a calcium magnesium phosphate matrix (100 mesh). Magnesium oxide was added to the calcium magnesium phosphate matrix and mixed and ground evenly (the mass ratio of calcium magnesium phosphate matrix to magnesium oxide was 5:1) to obtain a composite phosphate matrix. The matrix was sealed and stored to avoid moisture.

[0052] S3. Loading of functionalized lysine: A 20% (w / w) aqueous solution of the composite phosphate matrix was prepared. Then, functionalized natural lysine powder (the mass ratio of functionalized natural lysine powder to the composite phosphate matrix in the aqueous solution was 20:1) was added to the aqueous solution of the composite phosphate matrix. The pH was adjusted to 7.0 using an 8% (w / w) NaH2PO4 aqueous solution, and the loading reaction was carried out. The mixture was stirred at 60°C for 2 hours and then allowed to stand at 50°C for 1 hour. After the reaction was completed, the mixture was filtered and vacuum dried at 50°C for 10 hours under a vacuum of 0.006 MPa. The mixture was then ground and sieved to obtain the lysine-loaded phosphate curing agent precursor powder.

[0053] S4. Preparation of granulated solidifying agent: Lysine-loaded phosphate solidifying agent precursor powder, starch and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 20:2:1 to obtain a mixed dry material. Deionized water at a mass of 25% of the mixed dry material is added to the mixed dry material and stirred to form a wet material with a moisture content of 20wt%. The wet material is then granulated at a rotation speed of 17rpm and an inclination angle of 45° to obtain wet granules (diameter of 2.0-3.0mm). The wet granules are dried at 80℃ for 6h to obtain Pb contaminated soil solidifying agent granules.

[0054] Example 3 The method for preparing a soil stabilizer for Pb-contaminated soil includes the following steps: S1. Preparation of functionalized natural lysine: ① Cross-linking treatment: Add glutaraldehyde aqueous solution (glutaraldehyde aqueous solution has a mass percentage concentration of 30%) to lysine aqueous solution (lysine aqueous solution has a mass percentage concentration of 12%), wherein the volume ratio of lysine aqueous solution to glutaraldehyde aqueous solution is 20:1. Adjust the pH to 8.0 using NaH2PO4 aqueous solution with a mass percentage concentration of 12%, and stir the reaction at 60℃ for 2 hours to obtain cross-linked lysine solution.

[0055] ② Phosphorylation treatment: Add NaH2PO4·2H2O solid powder (the mass ratio of NaH2PO4·2H2O solid powder to lysine in the cross-linked lysine solution is 1:10) to the cross-linked lysine solution, adjust the pH to 7.0 with a 12% NaH2PO4 aqueous solution, react at 70℃ for 2 hours, filter after the reaction, wash with water 5 times, and vacuum dry at 0.015 MPa and 70℃ for 11 hours to obtain functionalized natural lysine powder.

[0056] S2. Preparation of phosphate matrix: Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O were mixed and ground in a mass ratio of 2:2:1, and sieved to obtain a calcium magnesium phosphate matrix (300 mesh). Magnesium oxide was added to the calcium magnesium phosphate matrix and mixed and ground evenly (the mass ratio of calcium magnesium phosphate matrix to magnesium oxide was 5:1) to obtain a composite phosphate matrix. The matrix was sealed and stored to avoid moisture.

[0057] S3. Loading of functionalized lysine: A 30% (w / w) aqueous solution of the composite phosphate matrix was prepared. Then, functionalized natural lysine powder (the mass ratio of functionalized natural lysine powder to the composite phosphate matrix in the aqueous solution was 20:3) was added to the aqueous solution of the composite phosphate matrix. The pH was adjusted to 7.5 using a 12% (w / w) NaH2PO4 aqueous solution. The loading reaction was carried out by stirring at 70°C for 2 hours and then standing at 50°C for 1 hour. After the reaction was completed, the mixture was filtered and vacuum dried at 70°C for 6 hours under a vacuum of 0.015 MPa. The mixture was then ground and sieved to obtain the lysine-loaded phosphate curing agent precursor powder.

[0058] S4. Preparation of granulated solidifying agent: Lysine-loaded phosphate solidifying agent precursor powder, starch and sodium carboxymethyl cellulose are mixed evenly in a mass ratio of 20:2:1 to obtain a mixed dry material. Deionized water at a mass of 54% of the mixed dry material is added to the mixed dry material and stirred to form a wet material with a moisture content of 35wt%. The wet material is then granulated at a rotation speed of 20rpm and an inclination angle of 45° to obtain wet granules (diameter of 2.0-3.0mm). The wet granules are placed in an oven and dried at 120℃ for 6h to obtain Pb contaminated soil solidifying agent granules.

[0059] Comparative Example 1 The difference between this comparative example and Example 1 is that no functionalized natural lysine is added; the other steps are the same.

[0060] In this comparative example, without the addition of functionalized lysine, the curing agent relies solely on the calcium phosphate system and Pb². + Inorganic precipitation reactions occur, resulting in slow interfacial reaction rates, non-dense precipitates, and poor long-term stability. In contrast, the functionalized lysine molecules in this invention contain multiple functional groups, including amino, carboxyl, and phosphate groups, and can react with Pb²⁺. + Forming stable complex bonds, while also reacting with Ca² + PO4³ - An organic-inorganic composite layer is constructed on the substrate surface, which significantly enhances the reactivity and structural density of the cured body, thereby effectively reducing the leaching of Pb and improving the curing efficiency.

[0061] Comparative Example 2 The difference between this comparative example and Example 1 is that no cross-linking treatment is performed, while the other steps are the same.

[0062] In this comparative example, when lysine was phosphorylated without crosslinking modification, the resulting organic component exhibited weak bonding in the matrix, and the curing effect was not optimal. While phosphorylated lysine alone can introduce phosphate groups onto the molecule, it also contributes to the bonding of Pb²⁺ with other components. + Coordination or formation of Pb-PO4 precipitate occurs, but its molecular chain is short, its thermal stability is poor, and it lacks a multi-point cross-linking structure with the inorganic matrix. It is easy to migrate and desorb during preparation or curing, resulting in weak organic-inorganic interface bonding, uneven distribution of functional layer in the cured body, discontinuous Pb fixed layer, and decreased compactness and long-term stability of the cured body.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that phosphorylation is not performed; the other steps are the same.

[0064] In this comparative example, only lysine was cross-linked during the functionalization process without phosphorylation modification. While the resulting organic component exhibited some structural stability, it lacked the ability to interact with metal ions (especially Pb²⁺). + The effective complexation sites for lysine are not readily available. Cross-linking reactions primarily form –C=N– or –C–O–C– bonds between lysine molecules, enhancing the molecular backbone strength, but failing to introduce negatively charged phosphate groups (-PO4H2) onto the molecule, thus preventing the formation of effective complexation sites with Pb²⁺. + Strong coordination or formation of insoluble Pb-PO4 precipitates can occur. Furthermore, unphosphorylated lysine has poor surface hydrophilicity, making it difficult to chemically bond with the Ca-P matrix. It relies solely on physical adsorption to disperse on the particle surface, resulting in weak organic-inorganic interfacial bonding, low Pb adsorption, and a non-dense solidified layer, making Pb easily migrate and leach again. Conversely, phosphorylated lysine introduces highly active -PO4 groups into the molecule, enabling it to bind with Pb²⁺. + It forms a stable complex and can also interact with Ca²⁺. + PO4³ - This forms a chemically bridged structure, thereby significantly improving the curing agent's ability to fix Pb and its long-term stability.

[0065] Comparative Example 4 The difference between this comparative example and Example 1 is that unfunctionalized natural lysine is directly added; the other steps are the same.

[0066] In this comparative example, the curing effect was poor when unfunctionalized natural lysine was directly added without further treatment. This is because natural lysine molecules have short chains, strong hydrophilicity, and weak binding force with the inorganic matrix. Although they possess amino and carboxyl groups that can bind with Pb²⁺, the curing effect is still poor. +While some weak coordination occurs, this coordination lacks selectivity and is easily dissociated by competition with other ions in the aquatic environment. During granulation, drying, and on-site curing, uncrosslinked / unphosphorylated lysine is prone to migration, dissolution, or degradation by microorganisms, resulting in the loss of its active sites. In addition, natural lysine lacks phosphate groups and cannot directly promote the formation of insoluble lead phosphate precipitates. Therefore, it is difficult to precipitate large amounts of Pb in a short period of time and stably encapsulate it in the long term. As a result, the adsorption capacity is low, the solidified layer is not dense, and the resistance to re-leaching is poor.

[0067] Comparative Example 5 The difference between this comparative example and Example 1 is that the drying temperature and drying time are reduced. Specifically, in step S4, the wet pellets are placed in an oven and dried at 80°C for 2 hours, while the other steps are the same.

[0068] Comparative Example 6 The difference between this comparative example and Example 1 is that the drying temperature and drying time are increased. Specifically, in step S4, the wet pellets are placed in an oven and dried at 120°C for 8 hours. The other steps are the same.

[0069] Comparative Examples 5 and 6 show that when the drying temperature decreases or the drying time is insufficient, the moisture and unreacted components inside the curing agent cannot fully evaporate, leading to the reaction of lysine with phosphate and Ca²⁺. + or Mg² + Incomplete condensation, complexation, and phosphorylation reactions between particles reduce the amount of chemical bonds formed and precipitates. Simultaneously, residual moisture loosens the internal structure of the particles, increases porosity, and decreases particle density and strength. This makes the particles more prone to absorbing water and swelling later, leading to Pb²⁺ degradation. + Furthermore, insufficiently dried organic components are prone to dissolution or biodegradation, disrupting the stability of the curing system. The phase transformation of the Ca-P matrix is ​​also incomplete, making it difficult to form a stable hydroxyapatite structure. Under these combined effects, the organic-inorganic composite degree and structural integrity of the curing agent are significantly reduced, thus worsening the fixation ability of Pb and the long-term curing effect. When the drying temperature increases or the drying time becomes longer, the active functional groups (–NH2, –COOH, –PO4H2) in functionalized lysine are prone to thermal degradation, leading to their interaction with Pb²⁺. + The fixation capacity is significantly reduced; simultaneously, CaHPO4·2H2O and Ca(H2PO4)2·H2O in the calcium phosphate matrix undergo dehydration phase transformation, generating inert, low-solubility phases, resulting in incomplete Pb fixation reaction. Furthermore, excessively rapid or excessive drying can cause densification of the spheroid surface and the formation of microcracks, weakening ion diffusion and long-term stability. Under these combined effects, the material's curing efficiency and leaching resistance are significantly reduced.

[0070] Comparative Example 7 The difference between this comparative example and Example 1 is that no magnesium oxide additive was added to the phosphate matrix; the other steps are the same.

[0071] In this comparative example, the absence of magnesium oxide as an additive in the phosphate matrix significantly impacts the reaction environment and the resulting phase, leading to a poorer curing effect in the final curing agent. Magnesium oxide plays a crucial role in pH buffering, promoting precipitation reactions, and enhancing structural density. Without magnesium oxide, the reaction system becomes generally acidic, resulting in lower Pb² content. + With PO4³ - The reaction rate decreases, making it difficult to fully generate insoluble Pb3(PO4)2 or hydroxyapatite-type precipitates. At the same time, the lack of acidic products released by the magnesium oxide neutralization reaction leads to large pH fluctuations in the system, resulting in unstable ionization states of organic lysine functional groups (-NH2, -COOH) and decreased complexation efficiency. Magnesium oxide can also react with phosphates during the curing process to generate MgHPO4 or Mg2P2O7, which fill pores, enhance the compactness of the spherical structure, and improve leaching resistance. Therefore, without the addition of magnesium oxide, the internal structure of the material is loose, the reaction is incomplete, and the Pb fixation layer is discontinuous, ultimately resulting in a significant decrease in curing efficiency and long-term stability.

[0072] I. Curing effect test 1. To verify the effect of the functionalized natural lysine-supported calcium-phosphorus composite matrix of the present invention on lead (Pb²⁺) contaminated soil stabilizer (hereinafter referred to as "stabilizer"), this invention aims to improve the soil's ability to stabilize lead (Pb²⁺). + The adsorption capacity of the α-phosphorus compound and its fixation effect on Pb in contaminated soil were investigated, and the solidification performance was tested as follows: (1) The curing agent pellets prepared in this invention are crushed and passed through a 200-mesh sieve and dried for later use.

[0073] (2) Add 50.0 mL of the set concentration of Pb² to a 50 mL centrifuge tube. + The solutions had initial Pb concentrations (C0) of 10 mg / L, 25 mg / L, 50 mg / L, 100 mg / L, and 200 mg / L, respectively.

[0074] (3) Add 0.100g of curing agent powder, cover tightly and place in a constant temperature shaking box at 25℃ for 24h. Initial pH: 5.5 (adjust with dilute HNO3 or NaOH).

[0075] (4) After shaking, centrifuge at 3000 rpm for 10 min, and filter the supernatant through a 0.45 μm filter membrane.

[0076] (5) Take 10 mL of the filtrate, add 1 mL of concentrated nitric acid to acidify it, and store it for testing.

[0077] (6) ICP-OES determination of equilibrium Pb concentration C e.

[0078] 2. The instruments and reagents used are as follows: ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer, model: Agilent 5110, for quantitative Pb analysis); constant temperature shaker (25±1℃, 150rpm); pH meter (accuracy 0.01); 0.45μm filter membrane, centrifuge, oven; Pb(NO3)2 analytical grade, prepared with deionized water. + Standard solution (1000 mg / L stock solution, serially diluted to the required concentration); concentrated nitric acid (HNO3) and sodium hydroxide (NaOH) are used for pH adjustment of the solution.

[0079] 3. Calculation method Removal rate (%) = (C0) C e ) / C0×100% Adsorption capacity q e (mg / g)=(C0 C e )×V / m 4. Results The experimental results are shown in Table 1.

[0080] Table 1 Adsorption effect test From Table 1 and Figure 1 It can be seen that this curing agent is effective against Pb². + It exhibits extremely strong curing ability; according to Langmuir fitting, its maximum equilibrium adsorption capacity (q) max The concentration is approximately 140.14 mg / g.

[0081] II. Curing Effect Testing 1. Soil sample preparation A soil sample contaminated with Pb was collected, air-dried, ground, and passed through a 200-mesh sieve. The total Pb concentration was determined to be 985 mg / kg after acid digestion.

[0082] 2. Curing treatment The curing agents prepared in Examples 1-3 and Comparative Examples 1-7 were uniformly mixed with soil, and a group without curing agent was set up to determine the initial leaching concentration. The mixed samples were placed in polypropylene bottles and cured at 25°C for 7 days.

[0083] 3. The leaching test (TCLP method) is as follows: (1) Take 20g of soil sample after curing and add 400mL of acetic acid buffer solution (pH 4.93) with a liquid-solid ratio of 20:1.

[0084] (2) Place it in a rotating oscillator at 30 rpm and oscillate for 18 hours.

[0085] (3) Filtration (0.45μm filter membrane), and determination of Pb concentration C in the filtrate. l .

[0086] 4. Leaching rate calculation Leaching rate (%) = (C l ×V) / (total Pb mass)×100% 5. Results The experimental results are shown in Table 2.

[0087] Table 2. Analysis of curing effect in the examples. From Table 2 and Figure 2 It can be known that: The Pb leaching concentration in the soil after curing with the curing agent prepared in this invention is significantly lower than that in the comparative example, and the Pb concentration in the soil leachate is far lower than that in the "Hazardous Waste Identification Standard" (≤5 mg / L). This indicates that the introduction of functionalized lysine can enhance the complexation and fixation capacity of Pb, and the synergistic alkalization effect of magnesium oxide helps to generate Pb phosphate precipitation, thereby achieving efficient stabilization of Pb.

[0088] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a soil stabilizer for Pb-contaminated soil, characterized in that, Specifically, the following steps are included: S1. Preparation of functionalized natural lysine: ① Cross-linking treatment: Add glutaraldehyde aqueous solution to lysine aqueous solution, adjust pH, stir reaction to obtain cross-linked lysine solution; ② Phosphorylation treatment: Add NaH2PO4·2H2O solid powder to the cross-linked lysine solution, adjust the pH, heat the reaction, filter after the reaction is completed, wash, and vacuum dry to obtain functionalized natural lysine powder. S2. Preparation of phosphate matrix: Ca(H2PO4)2·H2O, CaHPO4·2H2O and MgHPO4·3H2O were mixed, ground and sieved to obtain calcium magnesium phosphate matrix. Magnesium oxide was added to the calcium magnesium phosphate matrix and mixed and ground evenly to obtain composite phosphate matrix, which was then sealed and stored. S3. Loading of functionalized lysine: The complex phosphate matrix was prepared into an aqueous solution, and then functionalized natural lysine powder was added to the aqueous solution. The pH was adjusted and the loading reaction was carried out. After the reaction was completed, the mixture was filtered and vacuum dried to obtain the precursor powder. S4. Preparation of granule solidifying agent: The precursor powder, starch and sodium carboxymethyl cellulose are mixed evenly to obtain a dry mixture. Water is added to the dry mixture and stirred to form a wet mixture. The wet mixture is granulated to obtain wet granules. The wet granules are dried to obtain Pb contaminated soil solidifying agent granules.

2. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, In step S1, the mass percentage concentration of the lysine aqueous solution in the crosslinking treatment is 8%-12%; the mass percentage concentration of the glutaraldehyde aqueous solution is 20%-30%; and the volume ratio of the lysine aqueous solution to the glutaraldehyde aqueous solution is 20:

1.

3. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, The pH adjustment conditions in step S1 crosslinking treatment are as follows: adjust the pH to 8.0 using an aqueous solution of NaH2PO4 with a mass percentage concentration of 8-12%; the stirring reaction conditions are as follows: stir the reaction at 40-60℃ for 2 hours.

4. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, In step S1, the mass ratio of NaH2PO4·2H2O solid powder to lysine in the cross-linked lysine solution is 1:5-10.

5. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, The pH adjustment conditions in step S1 phosphorylation are as follows: adjust the pH to 6.5-7.0 using an 8%-12% NaH2PO4 aqueous solution; the heating reaction conditions are as follows: react at 50-70℃ for 2-3 hours; the washing conditions are as follows: wash 3-5 times with deionized water; the vacuum drying conditions are as follows: vacuum dry at 0.006-0.015MPa and 50-70℃ for 10-12 hours.

6. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, In step S2, the mass ratio of Ca(H2PO4)2·H2O, CaHPO4·2H2O, and MgHPO4·3H2O is 2:2:1; the mass ratio of the calcium magnesium phosphate matrix to magnesium oxide is 5:1; and the particle size of the calcium magnesium phosphate matrix is ​​100-300 mesh.

7. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, The mass percentage concentration of the composite phosphate matrix aqueous solution in step S3 is 20%-30%; the mass ratio of the functionalized natural lysine powder to the composite phosphate matrix in the composite phosphate matrix aqueous solution is 20:1-3.

8. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, The pH adjustment conditions in step S3 are as follows: adjust the pH to 6.5-7.5 using an 8%-12% NaH2PO4 aqueous solution; the loading reaction conditions are as follows: stir at 50-70℃ for 2 hours, and then let stand at 50℃ for 1 hour; the vacuum drying conditions are as follows: vacuum dry at 50-70℃ for 6-10 hours under a vacuum of 0.006-0.015MPa.

9. The method for preparing the Pb-contaminated soil stabilizer according to claim 1, characterized in that, In step S4, the mass ratio of the lysine-supported phosphate curing agent precursor powder, starch, and sodium carboxymethyl cellulose is 20:2:1; the moisture content of the wet material is 20-35 wt%; the granulation conditions are: granulation is carried out at a rotation speed of 15-20 rpm and an inclination angle of 45°; the diameter of the wet pellets is 2.0-3.0 mm; and the drying conditions are: drying at 80-120℃ for 6 hours.

10. The Pb-contaminated soil stabilizer prepared by the method according to any one of claims 1 to 9.

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