Method for preparing humus soil heavy metal stabilizer by using mixed carbonized modified fly ash

Abstract

The invention relates to a heavy metal pollution treatment technology, and aims to provide a method for preparing a humus soil heavy metal stabilizer by using mixed carbonized modified fly ash. Comprising the following steps: adding phosphate and charcoal into fly ash, uniformly mixing, putting into a closed tubular furnace, and carbonizing in a nitrogen atmosphere to obtain modified fly ash; adding the modified fly ash and humic acid into a proper amount of water, uniformly stirring and mixing, and drying and sieving the mixture to obtain the humus soil heavy metal stabilizer product. The porosity and the specific surface area of the fly ash are improved in a mixed modification mode, and the types and the number of active groups on the surface of the fly ash are increased; the stabilizing effect of heavy metal pollutants is remarkably improved, and the stabilizing agent is suitable for treating soil and waste subjected to multi-metal combined pollution. The stabilizer product is relatively low in preparation cost and has the characteristic of keeping a stable effect for a long time; the cost effectiveness is remarkable, the preparation process is simple and convenient, large-scale production is easy, and the method has wide application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal pollution control, and in particular to a method for preparing a humus heavy metal stabilizer by using mixed carbonized modified fly ash, wherein the stabilizer is used to solidify / stabilize heavy metal pollution components in humus of landfill. Background Art

[0002] With the rapid development of industrialization and urbanization, a large amount of waste containing heavy metals has been landfilled, resulting in a sharp increase in the content of heavy metals in humus soil, posing a serious threat to the ecological environment and human health. Heavy metals such as Pb, Zn, Cd, etc. are highly biotoxic and cumulative, and can enter the human body through the food chain, causing a variety of diseases. Their harm should not be underestimated. Therefore, in the field of environmental pollution control, the problem of remediation of humus soil in landfills contaminated by heavy metals has become increasingly prominent and has become a major challenge that needs to be overcome urgently.

[0003] Traditional soil remediation technologies, such as physical separation and biological remediation, often face limitations such as low efficiency, high cost, and long cycle when dealing with humus soil contaminated by heavy metals.

[0004] As an industrial byproduct, fly ash is not only rich in mineral components such as silicates, which can adjust the pH of humus soil, but also can fix heavy metals through physical adsorption and chemical precipitation mechanisms. The main components of fly ash include silicon dioxide (SiO 2 ) and aluminum oxide (Al 2 O 3 ), its structure is similar to kaolinite, and it has the basis of modified substances. At present, the modification methods of fly ash mainly include mechanical grinding, acid modification and alkali modification. However, mechanical grinding has limited improvement on the performance of fly ash; while acid modification and alkali modification require the introduction of irritating and harmful chemical reagents. The use and discharge of these chemical reagents may bring about secondary pollution problems and have a negative impact on the environment. In addition, factors such as the properties of fly ash, the types and concentrations of heavy metals, the physical and chemical properties of the soil, and environmental conditions may affect the stability and consistency of the solidification and stabilization effect. Therefore, selecting suitable raw material types, optimizing preparation conditions, exploring new methods for fly ash modification, and developing low-cost, simplified, and green fly ash modification processes are of great practical significance for achieving long-term stability and stabilization of multi-metal composite-contaminated humus soils.

[0005] Therefore, it has become an urgent task to explore an efficient, economical and environmentally friendly heavy metal contaminated humus soil remediation technology. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a humus soil heavy metal stabilizer by using mixed carbonized modified fly ash.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] A method for preparing a humus soil heavy metal stabilizer by using mixed carbonized modified fly ash is provided, comprising the following steps:

[0009] (1) First, weigh phosphate, humic acid and biochar in a weight ratio of 1-5:1-5:1-5, and then weigh fly ash equal to the total amount of the three raw materials;

[0010] (2) adding phosphate and biochar to fly ash, mixing evenly, placing in a closed tube furnace, and carbonizing for 2 to 4 hours under a nitrogen atmosphere at 600 to 800° C. to obtain modified fly ash;

[0011] (3) Adding the modified fly ash and humic acid into a proper amount of water, stirring and mixing evenly, drying and sieving the mixture to obtain a humus soil heavy metal stabilizer product.

[0012] As a preferred embodiment of the present invention, the phosphate is one or more of calcium dihydrogen phosphate, potassium dihydrogen phosphate, superphosphate, and dipotassium hydrogen phosphate.

[0013] As a preferred embodiment of the present invention, the biochar is prepared in the following manner: granular corn and / or wheat straw is placed in a closed tubular furnace and maintained in a nitrogen atmosphere, the temperature is raised to 500-600°C at a rate of 10°C / min and then maintained for 2-4 hours, and the biochar is obtained by high-temperature decomposition and carbonization treatment.

[0014] As a preferred embodiment of the present invention, the fly ash is fly ash waste discharged from a coal-fired power plant, and its SiO2 content is 41-66%, Al 2 O 3 The content is 20-43%.

[0015] As a preferred embodiment of the present invention, the particle size of the biochar is 20-50 meshes, and the particle size of the fly ash is 50-100 meshes.

[0016] As a preferred embodiment of the present invention, in the step (2), the stirring rate is controlled to be 20 to 100 rpm / min and the stirring time is 0.5 to 2 hours during mixing.

[0017] As a preferred embodiment of the present invention, in step (2), the heating rate during the carbonization treatment is 5°C / min; after heating to the target temperature, the temperature is kept for a predetermined time, and then naturally cooled to room temperature.

[0018] As a preferred embodiment of the present invention, in the step (3), the stirring rate is controlled at 20 to 100 rpm / min and the stirring time is 5 to 8 hours during mixing; the temperature is controlled at 60 to 80°C during drying, and a 150 to 200 mesh sieve is selected during sieving.

[0019] The present invention further provides a method for using the stabilizer prepared by the aforementioned method for the treatment of heavy metal pollution in humus soil, comprising the steps of uniformly mixing the stabilizer with humus soil containing heavy metal components, wherein the weight ratio of the stabilizer to the humus soil is 6:100; then covering the surface of the soil layer with a perforated plastic film, and allowing the film to stand for 3 to 56 days at room temperature and in a semi-sealed state, thereby achieving solidification / stabilization of the heavy metal components in the humus soil.

[0020] Description of the invention principle:

[0021] (1) The present invention utilizes phosphate, biochar and humic acid to mix and modify fly ash, which can improve the pore structure characteristics of fly ash, specifically, increasing the number of pores in the fly ash particles in the stabilizer product and optimizing the pore size.

[0022] Biochar and humic acid have large specific surface areas. They can adhere to the surface of fly ash during carbonization and subsequent mixing, further increasing the specific surface area of ​​fly ash particles. In addition, the carbonization process can also promote the formation of porous structures. Higher treatment temperatures can increase porosity and specific surface area, while nitrogen atmosphere can prevent excessive oxidation, thereby obtaining a more developed porous structure. At the same time, SiO 2 、Al 2 O 3 , CaO, TiO 2 The components such as carbonyl and thiocyanate act as a solid skeleton, which prevents the collapse of the carbonaceous structure to a certain extent during the carbonization process, forming a stable and efficient porous structure for heavy metal adsorption.

[0023] (2) The present invention utilizes phosphate, biochar, and humic acid to mix and modify fly ash, which can not only improve the physical structure of the fly ash particles in the stabilizer product, but also improve its surface chemical properties.

[0024] Among them, phosphate can react chemically with the hydroxyl groups on the surface of fly ash, biochar, and humic acid to form phosphate bonds; this change greatly enriches the types of active groups on the surface of fly ash and increases their number, thereby significantly enhancing the interaction ability of fly ash with other substances, and can greatly improve the application performance of fly ash in adsorption, catalysis and other fields.

[0025] (3) The present invention utilizes phosphate, biochar, and humic acid to perform mixed modification on fly ash, thereby achieving a double improvement in the adsorption performance and stability of the fly ash particles in the stabilizer product.

[0026] Phosphate, biochar, humic acid and fly ash have certain adsorption capacity, and the modification process further enhances its adsorption potential by changing the chemical environment of fly ash surface. + The combination of the two not only strengthens the adsorption effect, but also improves the overall stability of fly ash through the stability of chemical bonds. This comprehensive modification method provides strong technical support for the wide application of fly ash in the fields of environmental governance, material science, etc.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention improves the porosity and specific surface area of ​​fly ash by mixed modification, and increases the types and quantities of surface active groups of fly ash; thereby, in the process of landfill management, the stabilization effect of heavy metal pollutants can be significantly improved, and the stabilizer is suitable for the treatment of soil and waste contaminated by multiple metals.

[0029] 2. Compared with other heavy metal pollutant treatment technologies, the preparation cost of the stabilizer product of the present invention is relatively low. Fly ash and biochar are both products based on waste recycling; by using them for mixed modification, not only the pollution of waste to the environment is reduced, but also the effective recycling of resources is achieved.

[0030] 3. The stabilizer product of the present invention has the characteristic of maintaining a long-term stabilization effect. Since the fly ash particles in the stabilizer have a very stable structure, they will not quickly become ineffective due to changes in environmental factors, which is of great significance for the long-term treatment of polluted soil and waste.

[0031] 4. The product of the present invention is used to stabilize heavy metal ions in humus soil, which can effectively prevent the leaching of heavy metals under acid rain and groundwater erosion, thereby protecting groundwater resources and avoiding further spread of heavy metal pollution.

[0032] 5. The present invention uses industrial solid waste as the main raw material, and converts industrial byproducts fly ash and biochar into effective tools for treating heavy metal pollution, which not only reduces the treatment cost, but also promotes the resource utilization of these materials, and realizes the environmental protection concept of "treating waste with waste". Due to its significant cost-effectiveness, simple preparation process, and easy large-scale production, it has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 SEM images of unmodified fly ash and mixed modified fly ash.

[0034] Figure 2 FTIR graphs of unmodified fly ash and mixed modified fly ash.

[0035] Figure 3 To investigate the effect of stabilization time on the toxicity of heavy metal leaching from humus soil.

[0036] Figure 4 To study the effect of stabilization time on the storage form of Cd.

[0037] Figure 5 To study the effect of stabilization time on the storage form of Zn.

[0038] Figure 6 To study the effect of stabilization time on the occurrence form of Pb.

[0039] Figure 7 The effect of stabilization time on the pH of humus soil. DETAILED DESCRIPTION

[0040] In order to clarify the implementation objectives, technical solutions and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation modes. It should be pointed out that for ordinary method personnel in this field, several modifications and improvements can be made without departing from the principles of the present invention, and these are also considered to belong to the protection scope of the present invention.

[0041] Part I Implementation of the Invention

[0042] The method for preparing a humus soil heavy metal stabilizer by using mixed carbonized modified fly ash provided by the present invention comprises the following steps:

[0043] (1) First, weigh phosphate, humic acid and biochar in a weight ratio of 1-5:1-5:1-5, and then weigh fly ash equal to the total amount of the three raw materials.

[0044] Among them, phosphate and humic acid can be directly used as commercial reagents, and the present invention does not limit their specific manufacturers. Phosphate can be selected from one or more of calcium dihydrogen phosphate, potassium dihydrogen phosphate, superphosphate, and dipotassium hydrogen phosphate. Fly ash is fly ash waste discharged from coal-fired power plants, and its SiO 2 The content is 41-66%, Al 2 O 3 The content is 20-43%, and the fly ash particle size is 50-100 mesh.

[0045] The biochar is prepared in the following manner: granular corn and / or wheat straw is placed in a closed tubular furnace and maintained in a nitrogen atmosphere, the temperature is raised to 500-600°C at a rate of 10°C / min and then maintained for 2-4 hours, and the biochar is obtained by high-temperature decomposition and carbonization treatment, and the particle size of the biochar is 20-50 meshes.

[0046] (2) Phosphate and biochar are added to fly ash, mixed evenly and placed in a closed tube furnace; during mixing, the stirring rate is controlled to be 20-100 rpm / min and the stirring time is 0.5-2 hours. Then, carbonization treatment is carried out in a nitrogen atmosphere at 600-800°C for 2-4 hours to obtain modified fly ash. The heating rate during carbonization treatment is 5°C / min; after heating to the target temperature, the temperature is kept for a predetermined time, and then naturally cooled to room temperature.

[0047] (3) Add the modified fly ash and humic acid to an appropriate amount of water, stir and mix evenly, dry and sieve the mixture to obtain a humus heavy metal stabilizer product. When mixing, control the stirring rate to 20-100 rpm / min and the stirring time to 5-8 hours; when drying, control the temperature to 60-80°C, and select a 150-200 mesh sieve when sieving.

[0048] The stabilizer prepared by the present invention can be used for the treatment of heavy metal pollution in humus soil. The specific method of use includes: uniformly mixing the stabilizer with humus soil containing heavy metal components, with the weight ratio of the stabilizer to the humus soil being 6:100; then covering the surface of the soil layer with a perforated plastic film, and continuously standing at room temperature and in a semi-sealed state for 7 to 56 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil. The purpose of the film coating is to provide a relatively stable environment for the humus soil and the stabilizer, and reduce the influence of external climate conditions (such as temperature, humidity, wind force, etc.) on the reaction.

[0049] Part II Specific Examples and Comparative Examples

[0050] Among the various reagents used in the embodiments of the present invention, phosphate, hydrochloric acid, and NaOH are conventional commercial reagents, and humic acid is a commercially available product of Tianjin Guangfu Technology Development Co., Ltd.; there are multiple portions of fly ash, which are taken from fly ash waste discharged at different production stages of the Huaneng Shangan Coal-fired Power Plant in Hebei Province, and its SiO 2 The content is rounded to 41-66%, Al 2 O 3 The content is rounded to 20-43%.

[0051] Example 1

[0052] In this example, the method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash includes the following steps:

[0053] 1. Preparation of biochar:

[0054] The corn stalks were crushed and passed through a 10-mesh sieve, and the obtained pellets were placed in a closed tubular furnace; heating was started at room temperature under a nitrogen atmosphere at a heating rate of 10°C / min; after the temperature reached 550°C, the temperature was maintained and continued to heat for 3 hours. The corn stalks were finally subjected to high-temperature decomposition and carbonization treatment to obtain biochar particles, which were passed through a 20-mesh sieve.

[0055] 2. Preparation of heavy metal stabilizer

[0056] (1) Weigh 5g of potassium dihydrogen phosphate, 1g of humic acid, 3g of biochar and 9g of fly ash respectively, that is, the weight ratio of potassium dihydrogen phosphate: humic acid: biochar is 5:1:3, and the total weight of these three raw materials is equal to the weight of fly ash. 2 The content is 52.1%, Al 2 O 3 The content is 30.1%, and has passed through a 100-mesh sieve.

[0057] (2) Add all the weighed potassium dihydrogen phosphate, biochar and fly ash into the stirrer, control the stirring rate to 100 rpm / min, and stir for 0.5 hours. Move the mixture into a closed tube furnace and heat it from room temperature under a nitrogen atmosphere at a heating rate of 5°C / min; after heating to 700°C, maintain the temperature and continue heating for 3 hours. After the mixture is carbonized, it is naturally cooled to room temperature to obtain modified fly ash.

[0058] (3) Add the prepared modified fly ash and weighed humic acid into an appropriate amount of water, stir and mix them evenly at a stirring rate of 100 rpm / min for 5 hours. Dry the mixture at 60°C and pass it through a 200-mesh sieve to finally obtain a humus soil heavy metal stabilizer product.

[0059] Example 2

[0060] In this example, the method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash includes the following steps:

[0061] 1. Preparation of biochar:

[0062] The wheat straw was crushed and passed through a 10-mesh sieve, and the obtained granular material was placed in a closed tubular furnace; heating was started at room temperature under a nitrogen atmosphere at a heating rate of 10°C / min; after the temperature reached 550°C, the temperature was maintained and heating was continued for 3 hours. The corn straw was subjected to high-temperature decomposition and carbonization treatment to finally produce biochar particles with a particle size of 40 mesh.

[0063] 2. Preparation of heavy metal stabilizer

[0064] (1) Weigh 1g of potassium dihydrogen phosphate, 5g of humic acid, 3g of biochar and 9g of fly ash respectively, that is, the weight ratio of potassium dihydrogen phosphate: humic acid: biochar is 1:5:3, and the total amount of these three raw materials is equal to the weight of fly ash. 2 The content is 60.5%, Al 2 O 3 The content is 29.8%, and has passed 80 mesh sieve.

[0065] (2) Add all the weighed potassium hydrogen phosphate, biochar and fly ash into the stirrer, control the stirring rate to 80 rpm / min, and stir for 1 hour. Move the mixture into a closed tube furnace and heat it from room temperature under a nitrogen atmosphere at a heating rate of 5°C / min; after heating to 700°C, maintain the temperature and continue heating for 3 hours. After the mixture is carbonized, it is naturally cooled to room temperature to obtain modified fly ash.

[0066] (3) Add the prepared modified fly ash and weighed humic acid into an appropriate amount of water and mix them evenly by stirring at a stirring rate of 80 rpm / min for 6 hours. Dry the mixture at 80°C and pass it through a 180-mesh sieve to finally obtain a humus soil heavy metal stabilizer product.

[0067] Example 3

[0068] In this example, the method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash includes the following steps:

[0069] 1. Preparation of biochar:

[0070] The corn stalks were crushed and passed through a 10-mesh sieve, and the obtained pellets were placed in a closed tubular furnace; heating was started at room temperature under a nitrogen atmosphere at a heating rate of 10°C / min; after the temperature reached 600°C, the temperature was maintained and heating was continued for 2 hours. The corn stalks were subjected to high-temperature decomposition and carbonization treatment to finally produce biochar particles with a particle size of 30 mesh.

[0071] 2. Preparation of heavy metal stabilizer

[0072] (1) Weigh 1g of calcium dihydrogen phosphate, 3g of humic acid, 5g of biochar and 9g of fly ash respectively, that is, the weight ratio of calcium dihydrogen phosphate: humic acid: biochar is 1:3:5, and the total amount of these three raw materials is equal to the weight of fly ash. 2 The content is 65.9%, Al 2 O 3 The content is 19.0%, and has passed through a 60-mesh sieve.

[0073] (2) Add all the weighed calcium dihydrogen phosphate, biochar and fly ash into the stirrer, control the stirring rate to 60 rpm / min, and stir for 1.5 hours. Move the mixture into a closed tube furnace and heat it from room temperature under a nitrogen atmosphere at a heating rate of 5°C / min; after heating to 800°C, maintain the temperature and continue heating for 2 hours. After the mixture is carbonized, it is naturally cooled to room temperature to obtain modified fly ash.

[0074] (3) Add the prepared modified fly ash and weighed humic acid into an appropriate amount of water and mix them evenly by stirring at a stirring rate of 60 rpm / min for 7 hours. Dry the mixture at 70°C and pass it through a 160-mesh sieve to finally obtain a humus soil heavy metal stabilizer product.

[0075] Example 4

[0076] In this example, the method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash includes the following steps:

[0077] 1. Preparation of biochar:

[0078] The wheat straw was crushed and passed through a 10-mesh sieve, and the obtained granular material was placed in a closed tubular furnace; heating was started at room temperature under a nitrogen atmosphere at a heating rate of 10°C / min; after the temperature was raised to 500°C, the temperature was maintained and heating was continued for 4 hours. The corn straw was subjected to high-temperature decomposition and carbonization treatment to finally produce biochar particles with a particle size of 50 mesh.

[0079] 2. Preparation of heavy metal stabilizer

[0080] (1) Weigh 5g superphosphate, 3g humic acid, 1g biochar and 9g fly ash respectively, that is, the weight ratio of superphosphate: humic acid: biochar is 5:3:1, and the total amount of these three raw materials is equal to the weight of fly ash. 2 The content is 41.3%, Al 2 O 3 The content is 42.5%, and has passed through a 50-mesh sieve.

[0081] (2) Add all the weighed superphosphate, biochar and fly ash into the stirrer, control the stirring rate to 20 rpm / min, and stir for 2 hours. Move the mixture into a closed tube furnace and heat it from room temperature under a nitrogen atmosphere at a heating rate of 5°C / min; after heating to 600°C, maintain the temperature and continue heating for 4 hours. After the mixture is carbonized, it is naturally cooled to room temperature to obtain modified fly ash.

[0082] (3) Add the prepared modified fly ash and weighed humic acid into an appropriate amount of water and mix them evenly by stirring at a stirring rate of 20 rpm / min for 8 hours. Dry the mixture at 60°C and pass it through a 150-mesh sieve to finally obtain a humus soil heavy metal stabilizer product.

[0083] Example 5

[0084] In this example, the method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash includes the following steps:

[0085] 1. Preparation of biochar:

[0086] The corn stalks were crushed and passed through a 10-mesh sieve, and the obtained pellets were placed in a closed tubular furnace; heating was started at room temperature under a nitrogen atmosphere at a heating rate of 10°C / min; after the temperature reached 550°C, the temperature was maintained and continued to heat for 3 hours. The corn stalks were finally subjected to high-temperature decomposition and carbonization treatment to obtain biochar particles, which were passed through a 20-mesh sieve.

[0087] 2. Preparation of heavy metal stabilizer

[0088] (1) Weigh 3g of potassium dihydrogen phosphate, 3g of humic acid, 3g of biochar and 9g of fly ash respectively, that is, the weight ratio of potassium dihydrogen phosphate: humic acid: biochar is 3:3:3, and the total weight of these three raw materials is equal to the weight of fly ash. 2 The content is 52.1%, Al 2 O 3 The content is 30.1%, and has passed through a 100-mesh sieve.

[0089] (2) Add all the weighed potassium dihydrogen phosphate, biochar and fly ash into the stirrer, control the stirring rate to 100 rpm / min, and stir for 0.5 hours. Move the mixture into a closed tube furnace and heat it from room temperature under a nitrogen atmosphere at a heating rate of 5°C / min; after heating to 700°C, maintain the temperature and continue heating for 3 hours. After the mixture is carbonized, it is naturally cooled to room temperature to obtain modified fly ash.

[0090] (3) Add the prepared modified fly ash and weighed humic acid into an appropriate amount of water, stir and mix them evenly at a stirring rate of 100 rpm / min for 5 hours. Dry the mixture at 60°C and pass it through a 200-mesh sieve to finally obtain a humus soil heavy metal stabilizer product.

[0091] Application Example 1

[0092] Take the stabilizer product prepared in Example 1 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the moisture content of the mixture is 35%. Cover the cup mouth with a perforated plastic film, and continue to stand at room temperature and semi-sealed state for 28 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the heavy metals in the humus soil.

[0093] Application Example 2

[0094] Take the stabilizer product prepared in Example 2 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the water content of the mixture is 35%. Cover the cup mouth with a perforated plastic film, and continue to stand at room temperature and semi-sealed state for 28 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the heavy metal leaching toxicity of the humus soil.

[0095] Application Example 3

[0096] Take the stabilizer product prepared in Example 3 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the water content of the mixture is 35%. Cover the cup mouth with a perforated plastic film, and continue to stand at room temperature and semi-sealed state for 28 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the heavy metal leaching toxicity of the humus soil.

[0097] Application Example 4

[0098] Take the stabilizer product prepared in Example 4 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the water content of the mixture is 35%. Cover the cup mouth with a perforated plastic film, and continue to stand at room temperature and semi-sealed state for 28 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the heavy metal leaching toxicity of the humus soil.

[0099] Application Example 5

[0100] Take the stabilizer product prepared in Example 5 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the water content of the mixture is 35%. Cover the mouth of the cup with a perforated plastic film, and continue to stand at room temperature and semi-sealed state for 28 days to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the leaching toxicity of heavy metals in the humus soil.

[0101] Application Example 6

[0102] Take the stabilizer product prepared in Example 1 and the humus soil sample containing heavy metal components; mix them evenly at a weight ratio of 6:100, and transfer them to a 500mL beaker, the water content of the mixture is 35%. Cover the cup mouth with a perforated plastic film, and let it stand at room temperature and in a semi-sealed state for 3, 7, 10, 14, 28, 42, and 56 days respectively to achieve the solidification / stabilization treatment of the heavy metal components in the humus soil, and record the pH of the humus soil and the leaching toxicity and occurrence form of the heavy metals.

[0103] Comparative Example 1

[0104] Refer to the operation contents of Example 2, except that only fly ash is added without mixed carbonization modification treatment.

[0105] Fly ash was mixed into heavy metal contaminated humus soil at a weight ratio of 6:100, and the water content of the mixture was 35%. It was placed in a 500mL beaker, and the beaker mouth was sealed with a perforated plastic wrap. It was stabilized in a semi-sealed state for 28 days, and the pH of the humus soil and the leaching toxicity and occurrence form of heavy metals were recorded.

[0106] Comparative Example 2

[0107] 50 g of unmodified fly ash was mixed with 250 mL of 11% hydrochloric acid solution and shaken for 18 h, washed with water until neutral, filtered, and dried (105° C., 2 h) to obtain acid-modified fly ash.

[0108] Refer to the operation content of Example 2 of the present invention, except that the acid-modified fly ash is mixed with heavy metal-contaminated humus soil at a weight ratio of 6:100, and the moisture content of the mixture is set to 35%. Place it in a 500mL beaker, seal the beaker mouth with a perforated plastic wrap, and stabilize it in a semi-sealed state for 28 days, and record the pH of the humus soil and the leaching toxicity and occurrence form of heavy metals.

[0109] Comparative Example 3

[0110] 50 g of unmodified fly ash was mixed with 50 mL of 2 mol / L NaOH solution and shaken for 18 h, washed with water until pH = 9.0-10, filtered, and dried (105° C., 2 h) to obtain alkali-modified fly ash.

[0111] Refer to the operation content of Example 2 of the present invention, except that the alkali-modified fly ash is mixed with heavy metal-contaminated humus soil at a weight ratio of 6:100, and the moisture content of the mixture is set to 35%. Place it in a 500mL beaker, seal the beaker mouth with a perforated plastic wrap, and stabilize it in a semi-sealed state for 28 days, and record the pH of the humus soil and the leaching toxicity and occurrence form of heavy metals.

[0112] Part III Product Testing and Result Analysis

[0113] 1. The specific surface area tests were carried out on the products in the embodiments of the present invention and the comparative examples, and the test results are shown in Table 1.

[0114] Table 1 Specific surface area of ​​various stabilized materials

[0115]

[0116] The specific surface area of ​​acid-modified fly ash is 8.6 times higher than that of unmodified fly ash, the specific surface area of ​​alkali-modified fly ash is 11.1 times higher than that of unmodified fly ash, and the specific surface area of ​​mixed modified fly ash is 62.1 times higher. It can be seen that the mixed modification method is more conducive to increasing the specific surface area of ​​fly ash than single acid modification or alkali modification. The reason may be that the carbonization process promotes the formation of porous structure, and higher temperature increases porosity and specific surface area. The selection of nitrogen atmosphere can prevent excessive oxidation during the carbonization process, thereby obtaining a more developed pore structure.

[0117] 2. The product and unmodified fly ash in Example 1 of the present invention were tested by SEM, XRF and FTIR respectively. The test results are shown in Table 2 and Figure 1-2 shown.

[0118] Table 2 Chemical composition of unmodified fly ash and mixed modified fly ash (%)

[0119]

[0120] Figure 1 Figures 2 and 3 are scanning electron microscope images of fly ash at different magnifications before and after modification. In the figure, a and c are unmodified fly ash in Example 1, and b and d are mixed modified fly ash in Example 1. Before modification, the fly ash has a clear structure and a smooth and dense particle surface. It is mainly composed of some spherical particles, some larger unformed particles and aggregates of some small particles. The surface of the fly ash after mixed modification shows a rougher and more complex morphology, with more cracks, protrusions and particles intertwined on the surface. This change is mainly caused by the chemical and physical interaction between humic acid, biochar and phosphate and fly ash, which destroys its regular glassy structure and complicates the surface structure, thereby increasing the adsorption capacity and reactivity of the material. The XRF test results of the fly ash after modification (see Table 2) show that P 2 O 5 The content increased significantly, and this change provided a strong chemical basis for the formation of phosphate heavy metal precipitation in fly ash, thereby enhancing the efficiency of fly ash in the heavy metal stabilization process.

[0121] Figure 2 FTIR images of the unmodified fly ash in Comparative Example 1 and the mixed modified fly ash in Example 1, 3440 cm -1 The OH peak intensity of the carboxyl group in the mixed modified fly ash increased significantly; the unmodified fly ash 2580cm -1 2919cm -1 The peak at 1149-1085cm disappears, which may be due to the disappearance of CH due to high temperature carbonization; -1 and 555cm -1The peak intensity at the position is significantly enhanced, which may indicate that the modification process has an impact on the silicate structure or introduces a new silicate phase; 450-1100cm -1 Multiple vibration peaks in the range of PO 4 3- The tetrahedral groups are associated, which is consistent with the XRF test results.

[0122] 3. The samples in Application Examples 1-4 and Comparative Examples 1-3 of the present invention were tested respectively. The heavy metal leaching toxicity test scheme was based on the provisions of "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T299-2007). The test results are shown in Table 3.

[0123] Table 3 Effect of heavy metal stabilization in humus soil of each project

[0124]

[0125] From the above data, it can be seen that the combined modification of fly ash with phosphate, biochar and humic acid significantly improves the efficiency of heavy metal solidification and stabilization of fly ash in humus soil, and its effect is better than that of using acid-modified or alkali-modified fly ash alone. This is because the porosity and specific surface area of ​​the mixed modified fly ash increase, and the number and types of surface active groups increase, which enhances its adsorption capacity for heavy metals and can form hydroxide, phosphate and silicate precipitation with heavy metals, thereby greatly improving the solidification and stabilization effect, especially suitable for humus soil contaminated with multiple metals such as Cd, Zn, and Pb.

[0126] 4. The products in Application Example 6 of the present invention were tested for heavy metal leaching toxicity, occurrence form and pH. Figure 3 The experimental results show that the concentration of heavy metal leaching decreases first and then stabilizes with the increase of solidification time, indicating that the mixed modified fly ash stabilizer has a certain long-term stability. The reason is that the structure of the stabilizer is stable and will not fail quickly due to changes in environmental factors. Figure 4-6 The experimental results show that the exchangeable form of Cd, Zn, and Pb decreased, while the organic binding form and residual form increased, especially the form change of Pb was the most significant, resulting in the reduction of the bioavailability of these heavy metals. Compared with other forms, exchangeable heavy metals are more susceptible to soil environmental conditions, easy to migrate and transform, poor stability, and easily leached by groundwater or acid rain, thus causing heavy metal pollution. Figure 7 The experimental results show that the mixed modified fly ash stabilizer for heavy metal pollution in humus soil can adjust the pH of humus soil. The alkalinity of the mixed modified fly ash reduces the acidity of humus soil because CaO and other substances in the mixed modified fly ash can react with H under acidic conditions. + The reaction consumes H +, the pH of the humus soil can be adjusted to a neutral environment of about 6 to 8. Based on the above results, the preferred conditions for the stabilizer in the present invention during use are: standing still for 3 to 56 days at room temperature and in a semi-sealed state.

[0127] Description of the application based on actual scenarios:

[0128] Since a large number of comparative tests are required for the performance of stabilizers obtained under different preparation conditions, in order to improve work efficiency, in each embodiment and comparative example of the present invention, the product preparation and application test operations are all carried out under laboratory conditions. In actual application scenarios, the corresponding scale can be enlarged and the corresponding treatment can be performed according to the corresponding weight ratio. After repeated verification tests by the applicant at a landfill in Zhejiang Province, the relevant test results are basically matched with the results shown in Application Examples 1-5 of the present invention, and meet the actual application performance requirements.

[0129] In summary, the present invention utilizes phosphate and biochar to carbonize fly ash at high temperature and then prepares a mixed modified fly ash stabilizer with humic acid. By increasing the porosity, specific surface area, and the number and types of surface active functional groups of fly ash, the stabilization effect on heavy metal contaminated humus soil can be significantly improved. This stabilization technology can effectively prevent the migration and transformation of heavy metals in humus soil, reduce its bioavailability, and thus achieve efficient remediation of heavy metal contaminated humus soil. Although the present invention has been represented and described with reference to specific preferred embodiments, it shall not be interpreted as a limitation on the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for preparing a humus soil heavy metal stabilizer using mixed carbonized modified fly ash, characterized in that: The following steps are involved: (1) First, weigh phosphate, humic acid and biochar in a weight ratio of 1-5:1-5:1-5, and then weigh fly ash equal to the total amount of the three raw materials; (2) adding phosphate and biochar to fly ash, mixing evenly, placing in a closed tube furnace, and carbonizing for 2 to 4 hours under a nitrogen atmosphere at 600 to 800° C. to obtain modified fly ash; (3) Adding the modified fly ash and humic acid into a proper amount of water, stirring and mixing evenly, drying and sieving the mixture to obtain a humus soil heavy metal stabilizer product.

2. The method according to claim 1, characterized in that The phosphate is one or more of calcium dihydrogen phosphate, potassium dihydrogen phosphate, superphosphate, and dipotassium hydrogen phosphate.

3. The method according to claim 1, characterized in that The biochar is prepared by placing granular corn and / or wheat straw in a closed tubular furnace and maintaining a nitrogen atmosphere, heating the furnace to 500-600°C at a rate of 10°C / min and maintaining the temperature for 2-4 hours, and obtaining the biochar through high-temperature decomposition and carbonization.

4. The method according to claim 1, characterized in that: The fly ash is fly ash waste discharged from a coal-fired power plant, and has a SiO2 content of 41-66% and an Al2O3 content of 20-43%.

5. The method according to claim 1, characterized in that The particle size of the biochar is 20-50 meshes, and the particle size of the fly ash is 50-100 meshes.

6. The method according to claim 1, characterized in that In the step (2), the stirring rate is controlled to be 20 to 100 rpm / min and the stirring time is 0.5 to 2 hours during mixing.

7. The method according to claim 1, characterized in that In the step (2), the heating rate during the carbonization treatment is 5°C / min; after heating to the target temperature, the temperature is kept for a predetermined time, and then naturally cooled to room temperature.

8. The method according to claim 1, characterized in that: In the step (3), the stirring rate is controlled to be 20-100 rpm / min and the stirring time is 5-8 hours during mixing; the temperature is controlled to be 60-80° C. during drying, and a 150-200 mesh sieve is selected during sieving.

9. A method for treating heavy metal pollution in humus soil by using the stabilizer prepared by the method of claim 1, characterized in that: The stabilizer is mixed evenly with humus containing heavy metal components, with the weight ratio of the stabilizer to the humus being 6:100; then a perforated plastic film is covered on the surface of the soil layer, and the film is left standing for 3 to 56 days at room temperature and in a semi-sealed state, so as to achieve solidification / stabilization of the heavy metal components in the humus.

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