Soil heavy metal curing composition and application method thereof
By using a combination of legume urease-urea solution and chitosan within a specific pH range, along with inorganic acid treatment, the problems of heavy metal migration and increased soil moisture content caused by high pH values were solved, achieving efficient solidification of heavy metals and cost control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2026-04-10
- Publication Date
- 2026-05-12
AI Technical Summary
When treating contaminated soil rich in organic matter, existing technologies suffer from high pH values that lead to the migration of heavy metal complexes. Furthermore, traditional methods require the addition of exogenous calcium salts, which carries the risk of secondary activation. Additionally, the increased soil moisture content raises engineering costs.
The pH was adjusted to 7.5-8.3 using a soybean urease-urea solution, and combined with chitosan. Through specific ratios and the use of inorganic acids, high pH values and exogenous calcium salts were avoided, thereby achieving the precipitation and fixation of heavy metals and controlling soil moisture content.
It effectively immobilizes heavy metals, prevents the activation of amphoteric heavy metals, reduces soil moisture content, reduces engineering costs, and improves remediation results.
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Abstract
Description
Technical Field
[0001] This invention application belongs to the field of geotechnical engineering technology, especially the field of soil remediation technology, and specifically relates to a soil heavy metal solidification composition and its application method. Background Technology
[0002] With the acceleration of urbanization and the increasing environmental protection requirements, a large number of simple landfills in my country urgently need to be excavated, screened, and reused. After excavation and screening, humus, as the main fine-grained component, accounts for more than 50% of the total excavated waste. Humus has an organic matter content exceeding 10%, mainly containing humus-like organic matter and lignin, with a moisture content of approximately 20-25% and a pH of 7.5-8.0. The composition of humus is similar to fertile loam, meeting the requirements of GB8172-87, the standard for controlling the use of urban waste in agriculture. The total nitrogen and total phosphorus contents are 0.41-0.76% and 1.02-1.18%, respectively, higher than conventional loam, indicating good ecological functions. It can be used as an ecological restoration covering material for slope greening and vegetation restoration. However, humus contains serious pollution from multiple heavy metals such as Cu, Zn, Cd, and Pb, with leachate concentrations generally exceeding the Class III limits of the "Surface Water Environmental Quality Standard" (GB3838-2002). Under the influence of rainfall and leachate, heavy metals in humus soil may migrate into surrounding soil and groundwater, posing risks to the ecological and water environment.
[0003] Enzyme-induced carbonate precipitation (EICP), as a mild and controllable biomineralization method, is widely used in soil heavy metal remediation. This technology utilizes urease to catalyze the hydrolysis of urea to produce carbonate ions (CO3-). 2- ) and ammonium ions (NH4) + Carbonate ions reduce the bioavailability of heavy metals by combining with them to form insoluble carbonate precipitates. Traditional EICP technology also introduces calcium chloride solutions of varying concentrations. Calcium ions react with carbonate ions to form calcium carbonate precipitates, further immobilizing the heavy metals through co-precipitation of calcium carbonate with heavy metal cations and the adsorption and complexation capabilities of calcium carbonate.
[0004] However, in practical applications, especially when treating contaminated soil rich in organic matter or of certain types (such as humus), EICP technology still faces the following insurmountable technical problems: (1) When urease and urea are mixed, the hydrolysis of urea will produce a large amount of ammonia / ammonium ions, which will eventually cause the pH value of the reaction system to rise rapidly to 9.0 or above (Bian Y, Chen Y, Zhan L, et al. Effects of enzyme-induced carbonate precipitation technique on multiple heavy metal simmobilization and unconfined compressive strength improvement of contaminated sand[J]. Science of The Total Environment, 2024, 947(000):18.). Although an alkaline environment is conducive to carbonate precipitation, for amphoteric metals (such as Cu, Zn, Cd), excessively high pH value and high concentration of NH4 are detrimental. + This induces the formation of soluble copper / zinc / cadmium-ammonia complexes, which are extremely stable and easily migrate, severely weakening the remediation effect (CN114605046B). To ensure the mineralization effect of heavy metals, traditional EICP formulations usually require multiple injections of large amounts of treatment solution (typically one injection volume equal to the pore volume of the soil), resulting in a significant increase in soil moisture content, approaching saturation. The treated soil is in a fluid state, significantly increasing the cost of desiccation in engineering projects and hindering subsequent resource recovery pathways such as drying, screening, and preparation of ecological cover materials.
[0005] (2) Traditional EICP technology usually requires the addition of high concentrations of exogenous calcium salts to generate calcium carbonate precipitates to encapsulate heavy metals or cemented soil particles (Science of The Total Environment, 2024, 947(000):18). At the same time, the addition of calcium ions can effectively alleviate the problem of rapid pH rise caused by urea decomposition. However, exogenous calcium ions will compete with some heavy metals (such as Cu, Zn, Cd) adsorbed on the soil or organic matter for ion exchange, resulting in the displacement and desorption of inherent heavy metals, which will increase the bioavailability and migration risk of heavy metals, and may lead to soil salinization and compaction (Adaptability and improvement of EICP technology for stabilizing and remediating cadmium-contaminated calcareous soils [D]. Lanzhou University). Therefore, although the addition of exogenous calcium salts consumes the calcium carbonate precipitates formed by carbonate ions and further reduces the pH of the system, it increases the risk of "secondary activation" of amphoteric heavy metals.
[0006] Therefore, how to achieve efficient mineralization of heavy metals without adding exogenous calcium salts is a major challenge at present. Summary of the Invention
[0007] This invention provides a soil heavy metal immobilization composition and its application method, aiming to solve the problem of heavy metal complexation and migration caused by high pH in heavy metal-contaminated soil without adding exogenous calcium salts. Existing technologies exhibit a technical bias that high pH (defined in this invention as pH ≥ 9) is more conducive to carbonate precipitation. Therefore, exogenous calcium salts are typically added to immobilize heavy metals through co-precipitation of calcium carbonate and heavy metal cations, as well as the adsorption and complexation capabilities of calcium carbonate. This invention overcomes this technical bias by using exogenous inorganic acid to control the pH of the legume urease-urea solution within a specific pH range, 7.5-8.3. Within this pH range, the solution and specific components of the composition exert a synergistic effect. This allows carbonate ions to precipitate and immobilize heavy metals while avoiding the risk of reactivation of amphoteric heavy metals. Through a specific formulation, this invention controls the total amount of added liquid at a low level, further controlling the soil moisture content and solving the problem of near-saturation of soil moisture during remediation.
[0008] This invention resolves a contradiction inherent in traditional EICP technology: the conflict between high pH (defined in this invention as pH ≥ 9) which favors heavy metal precipitation but leads to the activation of amphoteric heavy metals, and low pH which inhibits amphoteric heavy metal activation but results in low precipitation efficiency. This invention employs a combination of adjusting a urease-urea aqueous solution to a specific pH and specific components to achieve a synergistic effect in heavy metal fixation, effectively reducing available heavy metals in the soil while simultaneously preventing the activation of amphoteric heavy metals.
[0009] Existing technologies include compositions and methods for the remediation of heavy metals in water. However, the remediation of heavy metals in water is guided by the goal of achieving emission standards for heavy metal concentrations, while soil remediation focuses on reducing the bioavailability of heavy metals and ensuring soil ecological functions. The difference in technical objectives further determines that the remediation methods for heavy metals in water are not feasible for migration to soil remediation scenarios.
[0010] This invention addresses the problem of rapid pH increases to above 9.0 in soil heavy metal remediation by directly adding exogenous inorganic acids, which generates large amounts of ammonia / ammonium ions during urea hydrolysis. This is achieved through a synergistic effect between specific pH values and specific components of the composition. It also avoids secondary activation of amphoteric heavy metals (forming soluble copper / zinc / cadmium-ammonia complexes). Existing technologies suggest that alkaline conditions are beneficial for maintaining the catalytic activity of urease and for CO32-. 2-The presence of this form also facilitates the adsorption, complexation, and fixation of other non-ampholyte heavy metals by calcium carbonate. However, for amphoteric heavy metals, a continuous rise in pH (generally greater than or equal to 9) can lead to their activation. Current technologies do not employ the addition of inorganic acids; instead, they use the addition of exogenous calcium ions to consume carbonate ions, forming carbonate precipitates and thus mitigating the problem of a rapid pH increase.
[0011] In existing technologies for soil heavy metal remediation, the pH adjustment method of directly adding inorganic acids is usually avoided, mainly for the following reasons: Firstly, this method tends to inhibit the catalytic activity of urease and reduce the effective proportion of carbonate ions in the system, thus adversely affecting the smooth progress of the mineralization precipitation reaction; (Zhang Qiucai. Effects of pH-regulated urease conformation on the efficiency of microbial-induced carbonate precipitation and simulation study [J]. Chinese Journal of Biochemistry and Molecular Biology, 2025, 41(6):879-894.) Secondly, in porous media systems, the direct addition of inorganic acids can easily trigger local acidification, causing heavy metals present in the environment to dissolve and migrate in a short period of time, thus increasing environmental risks. Third, the introduction of inorganic acids can lead to the entry of other anions into the target system, potentially causing additional environmental safety hazards. Due to these constraints, existing technologies have failed to fundamentally address the issue of pH elevation during urea hydrolysis, and often overlook the potential risk of secondary activation and migration of amphoteric heavy metal ions forming soluble hydroxyl complexes under high pH conditions.
[0012] This invention overcomes the technical biases of existing technologies. In soil heavy metal remediation, without adding an external calcium source, it employs the method of adding exogenous inorganic acids. By controlling the pH of the legume urease-urea solution at 7.5-8.3, it can both allow carbonate ions to precipitate and fix heavy metals, thus avoiding the risk of reactivation of amphoteric heavy metals. Through a specific formulation, this invention controls the total amount of added liquid at a low level, further controlling the soil moisture content and solving the problem of near-saturation of soil moisture during the remediation process.
[0013] In the soil heavy metal remediation of this invention, chitosan, as a linear polycationic polymer, can directly chelate free heavy metal ions in the soil. At the same time, the active groups on its colloidal surface can adsorb heavy metal ions, reduce the content of exchangeable heavy metals, and reduce the toxicity to urease.
[0014] The specific technical solution of the present invention is as follows: In a first aspect, the present invention provides a soil heavy metal solidification composition, which is prepared from raw materials comprising the following components: a urease aqueous solution of legumes, a chitosan aqueous solution, urea, and inorganic acids.
[0015] In some embodiments of the present invention, 1000 parts by weight of heavy metal-contaminated soil, the soil heavy metal solidification composition is prepared from raw materials comprising the following components: 100-150 parts by weight of legume urease aqueous solution, 20-50 parts by weight of chitosan aqueous solution, 20-40 parts by weight of urea, and 5-100 parts by weight of inorganic acid; or 1000 parts by weight of heavy metal-contaminated soil, the soil heavy metal solidification composition is prepared from raw materials comprising the following components: 120-130 parts by weight of legume urease aqueous solution, 35-45 parts by weight of chitosan aqueous solution, 25-35 parts by weight of urea, and 50-60 parts by weight of inorganic acid.
[0016] In some embodiments of the present invention, the concentration of the soybean urease aqueous solution is 1-6%, the concentration of the chitosan aqueous solution is 1-6%, and the concentration of the inorganic acid is 3-10% (w / v).
[0017] Preferably, the concentration of the soybean urease aqueous solution is 2-4%, the concentration of the chitosan aqueous solution is 1-2%, and the concentration of the inorganic acid is 8-10% (w / v); more preferably, the concentration of the soybean urease aqueous solution is 2.5-3.5%, the concentration of the chitosan aqueous solution is 1.5-2%, and the concentration of the inorganic acid is 8-10% (w / v).
[0018] In some embodiments of the present invention, the pH of the mixed solution of soybean urease aqueous solution, urea, and inorganic acid is controlled at 7.5-8.3; preferably, the pH of the mixed solution of soybean urease aqueous solution, urea, and inorganic acid is controlled at 7.5-8.2; more preferably, the pH of the mixed solution of soybean urease aqueous solution, urea, and inorganic acid is controlled at 7.8-8.0.
[0019] In some embodiments of the present invention, the soil is soil contaminated with multiple heavy metals.
[0020] In some embodiments of the present invention, the soil is humus soil; preferably, the humus soil meets one or more of the following conditions: (1) the water content is 20-25%; (2) the total organic matter content is greater than or equal to 10%; (3) the soil pH is 7.5-8.0.
[0021] In some embodiments of the present invention, the humus soil comes from a sanitary landfill for municipal solid waste or a municipal solid waste landfill; preferably, the humus soil is fine-grained sand.
[0022] In some embodiments of the present invention, the inorganic acid is any one or more of sulfuric acid and hydrochloric acid.
[0023] In some embodiments of the present invention, the water is deionized water.
[0024] Secondly, the present invention provides a method for solidifying heavy metals in soil, the steps of which are as follows: S100: Grind legume seeds into legume flour, add water, and prepare a legume urease aqueous solution; S200: Add urea to the soybean urease aqueous solution in S100, stir thoroughly and react for 12-72 hours, add inorganic acid to adjust the pH of the mixed solution to obtain soybean urease-urea solution; S300: Dissolve chitosan powder in water to obtain a chitosan aqueous solution, and mix it evenly with heavy metal contaminated soil in a certain proportion and let it stand. S400: Mix the heavy metal contaminated soil containing chitosan from S300 with the soybean urease-urea mixed solution from S200 in a certain proportion and let it stand for 12-72 hours.
[0025] In some embodiments of the present invention, in step S100, the legume seeds are selected from any one or more of the following: soybean, sword bean, pigeon pea, chickpea, sword bean.
[0026] In some embodiments of the present invention, in step S200, the pH value of the soybean urease-urea solution is adjusted to be no more than 0.5 different from the pH value of the heavy metal contaminated soil; preferably, the pH value of the soybean urease-urea solution is adjusted to be no more than 0.3 different from the pH value of the heavy metal contaminated soil. In some embodiments of the present invention, in step S300, chitosan powder is dissolved in water to obtain a chitosan aqueous solution, and then mixed evenly and allowed to stand in a ratio of 20-50 parts of chitosan aqueous solution to 1000 parts of heavy metal contaminated soil.
[0027] In some embodiments of the present invention, in step S300, the settling time is 0.5-6 hours.
[0028] In some embodiments of the present invention, in step S100, the ratio of soybean flour to water in the soybean urease aqueous solution is 30-60g soybean flour : 1000mL water.
[0029] In some embodiments of the present invention, in step S200, the ratio of urea to soybean urease aqueous solution is 30-60g soybean flour : 1000mL soybean urease aqueous solution.
[0030] In some embodiments of the present invention, in step S200, an inorganic acid is added to adjust the pH of the mixed solution, and the pH of the resulting soybean urease-urea solution is 7.5-8.3; preferably, the pH of the soybean urease-urea solution is 7.5-8.0.
[0031] In some embodiments of the present invention, in step S200, an inorganic acid is added to adjust the pH of the mixed solution, and the pH difference between the obtained soybean urease-urea solution and the pH of the heavy metal contaminated soil is less than or equal to 0.5; preferably, in step S200, an inorganic acid is added to adjust the pH of the mixed solution, and the pH difference between the obtained soybean urease-urea solution and the pH of the heavy metal contaminated soil is less than or equal to 0.3. In some embodiments of the present invention, in step S300, the ratio of chitosan to water in the heavy metal contaminated soil and the chitosan aqueous solution is 1000g soil : 0.32~0.64g chitosan : 40mL water.
[0032] In some embodiments of the present invention, in step S400, the ratio between heavy metal contaminated soil and soybean urease-urea solution is 1000g soil : 100~150mL soybean urease-urea mixed solution.
[0033] In some embodiments of the present invention, in step S300, the heavy metal contaminated soil is soil contaminated with multiple heavy metals.
[0034] In some embodiments of the present invention, in step S300, the heavy metal contaminated soil is humus soil; preferably, the humus soil meets one or more of the following conditions: (1) the water content is 20~25%; (2) the total organic matter content is greater than or equal to 10%; (3) the soil pH is 7.5~8.0.
[0035] In some embodiments of the present invention, in step S300, the heavy metal contaminated soil is humus soil; further, the humus soil comes from a sanitary landfill for municipal solid waste or a municipal solid waste landfill; preferably, the humus soil is fine-grained sand.
[0036] In some embodiments of the present invention, the water is deionized water.
[0037] In some embodiments of the present invention, chitosan, as a colloidal substance, can encapsulate soil particles, fill micropores, and disperse aggregates when mixed with soil, thus preventing excessive local compaction of the soil. This treatment makes the subsequent addition of urease-urea solution more uniformly mixed with the soil.
[0038] Thirdly, the present invention provides the application of the soil heavy metal solidification composition or the method described above in the remediation of heavy metal contaminated soil.
[0039] This invention utilizes the overall synergistic effect of adjusting the urease-urea aqueous solution to a specific pH and specific components in the composition to effectively reduce available heavy metals in the soil while avoiding the activation of amphoteric heavy metals.
[0040] Compared with the prior art, the beneficial effects of this invention application are as follows: (1) The innovative introduction of inorganic acids effectively lowered the pH of the system, thereby solving the problem of NH4 under high pH conditions. + The problem of forming soluble complexes with amphoteric heavy metals (Cu, Zn) can be addressed through specific pH and the overall synergistic effect of specific components in the composition.
[0041] (2) No exogenous calcium ions were introduced, effectively avoiding the introduction of Ca. 2+ Cu adsorbed on the surface of mineral particles in the soil 2+ Zn 2+ Competitive ion exchange between heavy metal cations reduces the desorption of heavy metals from the surface of soil particles, thus solving the problem of "secondary activation" of amphoteric heavy metals.
[0042] (3) To ensure the mineralization effect of heavy metals, traditional EICP formulations typically require multiple injections of large amounts of treatment solution (usually one injection volume equal to the soil pore volume), leading to a significant increase in soil moisture content, approaching saturation. This invention solves the problem of "secondary activation" of amphoteric heavy metals under high pH conditions by adding inorganic acids. This further improves the mineralization effect and effectively reduces the amount of treatment solution used. This invention, through a specific ratio, controls the total amount of added liquid at a low level, further controlling the soil moisture content, solving the problem of soil moisture content approaching saturation, improving the physical state of the soil, eliminating the need for subsequent dehydration, and reducing engineering costs. Detailed Implementation
[0043] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0044] Unless otherwise specified, all percentage contents in this invention are expressed as mass fractions.
[0045] The terms "heavy metal fixation", "fixed heavy metals", and "soil heavy metal removal" used in this invention refer to reducing the available forms (migratory forms) of heavy metals in the soil.
[0046] The heavy metals described in this invention exist primarily in fixed and mobile states in soil. Fixed states refer to heavy metals that are fixed in the soil, existing in an unusable form, and therefore cannot be detected in soil leachate. Mobile states refer to heavy metals that are fixed in the soil, existing in a usable form, and therefore can be detected in soil leachate.
[0047] In this invention, "activation" and "secondary activation" refer to the transformation of a fixed state that was originally fixed in the soil and could not be detected into a migratory state.
[0048] Example 1 The humus soil in landfills S1 and A is characterized by fine-grained sand, based on its particle size distribution curve.
[0049] The humus soil in this landfill was classified as fine-grained sand according to national standards. Its composition and physical properties were determined according to the national standard "Standard for Geotechnical Testing Methods" (GB / T 50123-1999). The liquid and plastic limits were determined using a digital liquid and plastic limit tester.
[0050] The basic physical properties of the selected humus soil are shown in Table 1, and the particle size distribution is shown in Table 2.
[0051] Table 1A Basic Physical Properties of Humus Table 2A Particle size distribution of humus soil 100g of the humic soil was quartered to prepare 1000ml of humic soil leachate. Following the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ 557—2010), the oscillation frequency was set to 110±10 times / min and the amplitude to 40mm. The mixture was oscillated at room temperature for 8 hours and then allowed to stand for 16 hours. The liquid in the bottle was then filtered through a 0.45µm filter membrane to obtain the leachate.
[0052] S2. The heavy metal concentrations of the leachate were measured using the inductively coupled plasma mass spectrometry method for the determination of 65 elements in water (HJ700-2-14). Among them, Pb and Cd exceeded the Class III standard in the Surface Water Environmental Quality Standard (GB 3838-2002), and their concentrations are shown in Table 3. Zn, As, Cr and Cu were also measured, and none of them exceeded the Class III standard for surface water.
[0053] S3. Grind the sword beans into bean flour, and prepare a bean urease solution with deionized water at a ratio of 3.6g bean flour: 120g water; or a 2.9% bean urease solution.
[0054] S4. Add 30g of urea to the soybean urease solution in S3, stir thoroughly and react for 24 hours. Then add about 45g of 1M dilute sulfuric acid to adjust the pH to 8.0.
[0055] S5. Dissolve 16g of chitosan powder in 1L of water to obtain a chitosan solution. Take 40g of the chitosan solution and mix it with 1000g of humus soil, then let it stand.
[0056] S6. Mix the humus soil mixed with chitosan in S5 with the soybean urease-urea mixed solution in S4 for 10 minutes and then let it stand for 48 hours.
[0057] According to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ700-2-14), the concentrations of heavy metal ions in the leachate after the reaction were measured. The concentrations of Pb and Cd are shown in Table 3. The concentrations of these two heavy metals meet the requirements of Class III standards in the "Environmental Quality Standard for Surface Water" (GB 3838-2002). Furthermore, the concentrations of Zn, As, Cr, and Cu all decreased to varying degrees.
[0058] Table 3: Concentration of heavy metal ions in leachate before and after humus treatment As shown in Table 3, this embodiment has a good effect on removing heavy metal ions and can significantly reduce the heavy metal content in a short time, making it suitable as a method for removing heavy metals from landfill humus.
[0059] Example 2 The humus soil in landfills S1 and B is characterized by fine-grained sand, based on its particle size distribution curve.
[0060] The humus soil in this landfill was classified as fine-grained sand according to national standards. Its composition and physical properties were determined according to the national standard "Standard for Geotechnical Testing Methods" (GB / T 50123-1999). The liquid and plastic limits were determined using a digital liquid and plastic limit tester.
[0061] The basic physical properties of the selected humus soil are shown in Table 4, and the particle size distribution is shown in Table 5.
[0062] Table 4B Basic Physical Properties of Humus Table 5B Particle size distribution of humus soil 100g of the humic soil was quartered to prepare 1000ml of humic soil leachate. Following the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ 557—2010), the oscillation frequency was set to 110±10 times / min and the amplitude to 40mm. The mixture was oscillated at room temperature for 8 hours and then allowed to stand for 16 hours. The liquid in the bottle was then filtered through a 0.45µm filter membrane to obtain the leachate.
[0063] S2. The heavy metal concentrations of the leachate were measured using the inductively coupled plasma mass spectrometry method for the determination of 65 elements in water (HJ700-2-14). Among them, Pb and Cd exceeded the Class III standard in the Surface Water Environmental Quality Standard (GB 3838-2002), and their concentrations are shown in Table 6. Zn, As, Cr and Cu were also measured, and none of them exceeded the Class III standard for surface water.
[0064] S3. Grind the sword beans into bean flour and prepare a bean urease solution with deionized water at a ratio of 3.6g bean flour: 120g water. S4. Add 30g of urea to the soybean urease solution in S3, stir thoroughly and react for 24 hours, then add about 46g of 1M dilute sulfuric acid to adjust the pH to 8.0. S5. Dissolve 16g of chitosan powder in 1L of water to obtain a chitosan solution. Take 40g of the chitosan solution and mix it with 1000g of humus soil, then let it stand. S6. Mix the humus soil mixed with chitosan in S5 with the soybean urease-urea mixed solution in S4 for 10 minutes and then let it stand for 48 hours.
[0065] According to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ700-2-14), the concentration of heavy metal ions in the leachate after the reaction was measured respectively, and the results are shown in Table 6. As can be seen from the table, the concentrations of all heavy metals after treatment meet the requirements of Class III standards in "Environmental Quality Standard for Surface Water" (GB 3838-2002); and all kinds of heavy metals have been reduced to varying degrees.
[0066] Table 6: Concentration of heavy metal ions in leachate before and after humus treatment As shown in Table 6, this embodiment has a good effect on removing heavy metal ions and can significantly reduce the heavy metal content in a short time, making it suitable as a method for removing heavy metals from landfill humus.
[0067] Example 3 The same method as in Example 1 was used for the treatment, except that in step S4, the pH was adjusted to 8.2, and the results are shown in the table below.
[0068] Table 7: Concentration of heavy metal ions in leachate before and after humus treatment As shown in Table 7, this embodiment has a good effect on removing heavy metal ions and can significantly reduce the heavy metal content in a short time, making it suitable as a method for removing heavy metals from landfill humus.
[0069] Example 4 The same method as in Example 1 was used for processing, except that in step S4, the pH was adjusted to 7.9, and the results are shown in the table below.
[0070] Table 8: Concentration of heavy metal ions in leachate before and after humus treatment As shown in Table 8, this embodiment has a good effect on removing heavy metal ions and can significantly reduce the heavy metal content in a short time, making it suitable as a method for removing heavy metals from landfill humus.
[0071] Comparative Example 1 Results of pH adjustments on humus soil from landfill B The humus soil used in landfills S1 and B is the same as that used in Example 2, and its particle size distribution curve indicates that it contains fine-grained sand.
[0072] 100g of the humic soil was quartered to prepare 1000ml of humic soil leachate. Following the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ 557—2010), the oscillation frequency was set to 110±10 times / min and the amplitude to 40mm. The mixture was oscillated at room temperature for 8 hours and then allowed to stand for 16 hours. The liquid in the bottle was then filtered through a 0.45µm filter membrane to obtain the leachate.
[0073] S2. The heavy metal concentrations of the leachate were measured using the inductively coupled plasma mass spectrometry method for the determination of 65 elements in water (HJ700-2-14). Among them, Pb and Cd exceeded the Class III standard in the surface water environmental quality standard (GB 3838-2002), and their concentrations are shown in Table 5-1. Zn, As, Cr and Cu were also measured, and none of them exceeded the Class III standard for surface water.
[0074] S3. Grind the sword beans into bean flour and prepare a bean urease solution with deionized water at a ratio of 3.6g bean flour: 120g water. S4. Add 30g of urea to the soybean urease solution in S3, stir thoroughly and react for 24 hours. The pH was measured to be ≈9.4. Take the same four groups of solutions and add 1M dilute sulfuric acid to adjust the pH to 8.0, 8.5 and 9.0 respectively. There is one group without pH adjustment. S5. Dissolve 16g of chitosan powder in 1L of water to obtain a chitosan solution. Take 40g of the chitosan solution and mix it with 1000g of humus soil, then let it stand. S6. Mix the humus soil mixed with chitosan in S5 with the soybean urease-urea mixed solution in S4 for 10 minutes and then let it stand for 48 hours.
[0075] According to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ700-2-14), the concentration of heavy metal ions in the leachate after the reaction was measured, and the results are shown in Table 5-1.
[0076] Table 5-1: Concentration of heavy metal ions in leachate before and after humus treatment Table 5-1: Concentration of heavy metal ions in leachate before and after humus treatment Table 5-1 shows that the closer the pH of the treatment solution is to the pH of the soil itself, the lower the leaching concentration of heavy metals. Conversely, a higher pH in the treatment solution can cause a reversal in the concentration of some heavy metals (especially Cu and Zn). This is because in a more alkaline environment, ammonium ions more readily form complexes with heavy metals, making them more mobile and thus increasing the concentration of the leachate. The comparative examples further demonstrate that adjusting the pH of the treatment solution to 8.0 is more effective in this method. This invention promotes the conversion of heavy metals to a stationary state through the overall synergy of a specific pH and specific components of the composition, thereby reducing the detection concentration.
[0077] Comparative Example 2 pH adjustment of humus soil in landfill B - results of calcium chloride addition The humus soil used in landfills S1 and B is the same as that used in Example 2, and its particle size distribution curve indicates that it contains fine-grained sand.
[0078] 100g of the humic soil was quartered to prepare 1000ml of humic soil leachate. Following the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ 557—2010), the oscillation frequency was set to 110±10 times / min and the amplitude to 40mm. The mixture was oscillated at room temperature for 8 hours and then allowed to stand for 16 hours. The liquid in the bottle was then filtered through a 0.45µm filter membrane to obtain the leachate.
[0079] S2. The heavy metal concentrations of the leachate were determined using the inductively coupled plasma mass spectrometry method for the determination of 65 elements in water (HJ700-2-14). Among them, Pb and Cd exceeded the Class III standard in the Surface Water Environmental Quality Standard (GB 3838-2002), and their concentrations are shown in Table 6-1. Zn, As, Cr and Cu were also measured, and none of them exceeded the Class III standard for surface water.
[0080] S3. Grind the sword beans into bean flour and prepare a bean urease solution with deionized water at a ratio of 3.6g bean flour: 120g water. S4. Add 30g of urea to the soybean urease solution in 1L of S3. Take two portions of the solution, add 55.5g of calcium chloride to one portion and add a blank control group to the other portion. Stir the mixture thoroughly and react for 24 hours. Add 1M dilute sulfuric acid to adjust the pH to 8.0 and continue the reaction for 24 hours. S5. Dissolve 16g of chitosan powder in 1L of water to obtain a chitosan solution. Take 40g of the chitosan solution and mix it with 1000g of humus soil, then let it stand. S6. Mix the humus soil mixed with chitosan in S5 with the mixed solution of legume urease-urea-calcium chloride in S4 for 10 minutes and let it stand for 48 hours.
[0081] According to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ700-2-14), the concentration of heavy metal ions in the leachate after the reaction was measured, and the results are shown in Table 6-1.
[0082] Table 6-1: Concentration of heavy metal ions in leachate before and after humus treatment As shown in Table 6-1, the treatment effect of exogenous calcium addition was poor. Cd was not detected before treatment, and heavy metals changed from a fixed state to a mobile state after treatment. However, after treatment with specific pH range and specific components using this method, the concentration of various heavy metal ions was reduced. In particular, it solved the activation problem of amphoteric heavy metals, and made heavy metals fixed in the soil.
[0083] Those skilled in the art will understand that the steps, measures, and schemes in the various operations, methods, and processes discussed in this application can be alternated, modified, combined, or deleted; furthermore, other steps, measures, and schemes in the various operations, methods, and processes discussed in this application can also be alternated, modified, rearranged, decomposed, combined, or deleted; furthermore, the steps, measures, and schemes in the prior art that are similar to those disclosed in this application can also be alternated, modified, rearranged, decomposed, combined, or deleted. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above-described embodiments are merely illustrative of several implementation methods of this disclosure, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the patent for the embodiments of this disclosure. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the embodiments of this disclosure, and these all fall within the protection scope of the embodiments of this disclosure. Therefore, the protection scope of the embodiments of this disclosure should be determined by the appended claims. As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes in form and detail can be made without departing from the spirit and scope of the present invention as defined in the appended claims.
[0084] The present invention and its embodiments have been described above. This description is not restrictive, and what is shown is only one embodiment of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.
Claims
1. A soil heavy metal solidification composition, characterized in that, The soil heavy metal solidification composition is prepared from raw materials including the following components: a urease aqueous solution from legumes, a chitosan aqueous solution, urea, and inorganic acids; By weight, 1000 parts of heavy metal contaminated soil, the soil heavy metal solidification composition is prepared from raw materials including the following components: 100-150 parts of urease aqueous solution of legumes, 20-50 parts of chitosan aqueous solution, 20-40 parts of urea, and 5-100 parts of inorganic acid.
2. The soil heavy metal solidification composition according to claim 1, characterized in that, The pH of the mixed solution of soybean urease aqueous solution, urea, and inorganic acid is controlled at 7.5-8.
3.
3. The soil heavy metal solidification composition according to claim 1, characterized in that, The concentration of the urease aqueous solution from legumes is 1-6%, the concentration of the chitosan aqueous solution is 1-6%, and the concentration of the inorganic acid is 3-10% (w / v).
4. The soil heavy metal solidification composition according to claim 1, characterized in that, The inorganic acid is any one or more of sulfuric acid and hydrochloric acid.
5. The soil heavy metal solidification composition according to claim 1, characterized in that, 120-130 parts of soybean urease aqueous solution, 35-45 parts of chitosan aqueous solution, 25-35 parts of urea, and 50-60 parts of inorganic acid.
6. A method for solidifying heavy metals in soil, characterized in that, The steps are as follows: S100: Grind legume seeds into legume flour, add water, and prepare a legume urease aqueous solution; S200: Add urea to the soybean urease aqueous solution in S100, stir thoroughly and react for 12-72 hours, add inorganic acid to adjust the pH of the mixed solution to obtain soybean urease-urea solution; S300: Dissolve chitosan powder in water to obtain a chitosan aqueous solution, and mix it evenly with heavy metal contaminated soil in a certain proportion and let it stand. S400: Mix the heavy metal contaminated soil containing chitosan from S300 with the soybean urease-urea mixed solution from S200 in a certain proportion and let it stand for 12-72 hours.
7. The method according to claim 6, characterized in that, In step S100, the legume seeds are selected from any one or more of the following: soybean, sword bean, pigeon pea, chickpea, sword bean.
8. The method according to claim 6, characterized in that, In step S200, the pH value of the soybean urease-urea solution is adjusted to be no more than 0.5 different from the pH value of the heavy metal contaminated soil.
9. The method according to claim 6, characterized in that, In step S300, the settling time is 0.5-6 hours.
10. The application of the soil heavy metal solidification composition according to any one of claims 1-5 or the method according to any one of claims 6-9 in the remediation of heavy metal contaminated soil.