Preparation method of roadbed material and roadbed material
By mixing heavy metal contaminated clay with crushed stone, cement, and impermeable agents to form roadbed materials, the problem of insufficient compressive strength of heavy metal contaminated clay is solved, the resource utilization and disposal of soil are realized, and the performance of roadbed materials is improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI SHENGLONG ENVIRONMET REMEDIATION TECH CO LTD
- Filing Date
- 2024-10-18
- Publication Date
- 2026-04-21
AI Technical Summary
When heavy metal contaminated clay is solidified and used as roadbed material, its compressive strength is poor, which makes highway construction difficult and the soil after remediation difficult to dispose of.
The contaminated clay after heavy metal solidification treatment is mixed with crushed stone, cement and impermeable agent, and the moisture content is controlled at 8-20 wt%. The mixture is then maintained and treated. The mass ratio of the mixture is 10:(1-10):(0.5-5):(0.01-0.1). The mixture is then compacted to form the roadbed material.
It improves the compressive strength and permeability coefficient of the subgrade material, meets the requirements of the subgrade material, solves the problem of soil disposal after remediation, and realizes the resource utilization of the soil, which has economic benefits.
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of environmental protection and soil utilization, specifically to a method for preparing roadbed materials and the roadbed materials themselves. Background Technology
[0002] Heavy metal pollution is particularly prominent in industrial sites, involving major heavy metals such as cadmium, lead, copper, arsenic, zinc, mercury, and chromium. Currently, common remediation technologies for heavy metal-contaminated soil include solidification and stabilization, leaching, and cement kiln co-processing. Each technology has its own advantages and disadvantages. For example, solidification and stabilization is widely applicable but cannot remove heavy metals from the soil, and the disposal of remediated soil remains a major challenge for the industry. Leaching can remove heavy metals from soil, but it is less effective on heavy metal-contaminated clay, significantly limiting its application. Cement kiln co-processing can address both heavy metal contamination and different soil types, but it is not suitable for volatile heavy metals such as mercury. Furthermore, cement kiln co-processing is costly and constrained by factors such as the production capacity and distance of surrounding cement kilns.
[0003] Currently, after heavy metal contaminated soil is remediated using solidification and stabilization technology, the disposal pathways of the remediated qualified soil are greatly limited because the heavy metals in the soil cannot be removed. Generally, it can only be used as roadbed material, green land substrate, garden soil, landfill cover soil, or directly buried in solid waste landfills or municipal solid waste landfills.
[0004] Although the heavy metal leachate in soil may meet the remediation requirements after metal solidification treatment, the compressive strength of heavy metal-contaminated clay is poor when used as a roadbed material, causing difficulties in highway construction. Therefore, there is still a need to develop methods that can better utilize heavy metal-contaminated clay as roadbed materials. Summary of the Invention
[0005] The purpose of this invention is to overcome the problem of poor compressive strength when heavy metal contaminated clay is used as roadbed material after solidification treatment in the prior art, and to provide a method for preparing roadbed material and roadbed material.
[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing roadbed material, comprising: first mixing contaminated clay after heavy metal solidification treatment with crushed stone, cement and anti-permeability agent, and maintaining the mixture for a first time, such that the moisture content of the material obtained from the first mixture is 8-20 wt%; wherein the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent is 10:(1-10):(0.5-5):(0.01-0.1).
[0007] The second aspect of the present invention provides a roadbed material obtained by the method described in the first aspect.
[0008] Through the above technical solution, the present invention proposes a method for preparing roadbed material and a roadbed material, which has the following technical effects:
[0009] (1) The resulting subgrade material has high strength and meets the requirements for water content and permeability coefficient of subgrade material. It can be used stably as subgrade material. In addition, the heavy metal solidification treatment can reduce the environmental risk of heavy metal contamination of clay.
[0010] (2) By improving the compressive strength of the mixture, clay can be used as a roadbed material, thus solving the problem of soil disposal after remediation.
[0011] (3) The present invention uses the repaired clay as a raw material for roadbed material, which is also an effective resource utilization of soil, reduces the use of other building materials, and has good economic benefits. Detailed Implementation
[0012] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0013] The first aspect of the present invention provides a method for preparing roadbed material, comprising: first mixing contaminated clay after heavy metal solidification treatment with crushed stone, cement and anti-permeability agent, and maintaining the mixture for a first time, such that the moisture content of the material obtained from the first mixture is 8-20 wt%; wherein the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent is 10:(1-10):(0.5-5):(0.01-0.1).
[0014] In this invention, by adding crushed stone, cement and impermeable agent to contaminated clay after heavy metal solidification treatment, the resulting roadbed material has high compressive strength and also meets the requirements for roadbed material moisture content and permeability coefficient. This allows contaminated clay to be used as roadbed material, solves the problem of soil disposal after remediation, and enables effective resource utilization of soil.
[0015] In some specific embodiments of the present invention, the first mixing operation can be stirring, and during this process, methods such as turning, crushing, and forced stirring can also be used to appropriately remove moisture from the material. The engineering machinery used in the stirring process can be an ALLU crushing and screening bucket, a soil remediation integrated machine, or a complete set of mixing equipment.
[0016] In some specific embodiments of the present invention, the average diameter of the crushed stone is 5-10 cm; the average diameter refers to the diameter of the long axis of the crushed stone being within 5-10 cm.
[0017] In some specific embodiments of the present invention, the cement is silicate cement; the silicate cement can be ordinary silicate cement, and more preferably P.O42.5 or P.O52.5.
[0018] In some specific embodiments of the present invention, the concentration of heavy metal leachate in the contaminated clay after heavy metal solidification treatment is 0-0.1 mg / L.
[0019] In some specific embodiments of the present invention, the antipermeable agent is selected from one or more of organosilicon resin antipermeable agents, silicate antipermeable agents, or polyurethane antipermeable agents, and preferably from one or more of sodium silicate antipermeable agents and polyurethane antipermeable agents.
[0020] In some specific embodiments of the present invention, preferably, the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement, and anti-permeability agent is 10:(3-8):(0.8-2):(0.03-0.08). This mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement, and anti-permeability agent within this range further ensures high strength of the resulting roadbed material, enabling the contaminated clay to be used more effectively as a roadbed material.
[0021] In some specific embodiments of the present invention, the first maintenance time is 2-5 days; and / or, during the first maintenance process, water is sprayed appropriately to keep the mixture moist, avoid exposure to sunlight, and maintain the moisture content of the mixture at 8-20%.
[0022] During the first maintenance process, waterproof covering should be applied to isolate the air as much as possible. This can be done by covering the first mixed material with tarpaulin, HDPE film, or rainproof cloth. This also makes it easier to control the moisture content.
[0023] In some specific embodiments of the present invention, after the first maintenance is performed, the mixture is compacted to a degree of compaction of not less than 90%, and the compacted mixture is used as a roadbed material.
[0024] In some specific embodiments of the present invention, after the first maintenance, the mixture is compacted; the moisture content, compressive strength, and permeability coefficient of the compacted material are tested, and it is found that the compacted material meets the requirements for roadbed materials. Specifically, the roadbed material obtained in this application meets the following requirements: moisture content of 8%-20%; compressive strength of not less than 3 MPa; and permeability coefficient of not more than 10. -5 cm / s.
[0025] In some specific embodiments of the present invention, the heavy metal solidification treatment includes: mixing contaminated clay and a heavy metal solidification agent in a second mixing process to obtain a second mixture, and maintaining the mixture in a second state such that the moisture content of the second mixture is 30-40 wt%. The solidification can be achieved by using a metal complexing agent to complex the heavy metals, thereby solidifying them and preventing their migration and diffusion in the environment, thus reducing the toxicity of the heavy metals. This application uses different heavy metal solidification agents for different heavy metals, and these are heavy metal solidification agents that are conventionally achievable in the art.
[0026] In some specific embodiments of the present invention, the second mixture is covered during the second maintenance process, and the soil moisture content is controlled by detection and watering. The heavy metal leachate concentration of the material after the second maintenance is tested, and it is found to meet the requirements for heavy metal leachate concentration of roadbed materials.
[0027] In some specific embodiments of the present invention, the contaminated clay is heavy metal contaminated clay, and the heavy metal contained in the contaminated clay is selected from one or more of arsenic, lead, cadmium, chromium, or nickel. In the environmental field, because arsenic exhibits properties similar to heavy metals, although arsenic is generally considered a nonmetal, it can be considered a heavy metal pollutant in this field.
[0028] For example, when the heavy metal in the contaminated clay contains arsenic, the heavy metal solidification agent can be zero-valent iron, iron salts, iron oxides, aluminum oxides, ferrous sulfide, high-alumina slag, etc.; when the heavy metal is hexavalent chromium, the heavy metal solidification agent can be zero-valent iron, ferrous sulfate, ferrous chloride, sodium metabisulfite, calcium polysulfide, reducing sugar, etc.; when the heavy metal is lead, copper, zinc, cadmium, nickel, the heavy metal solidification agent can be calcium oxide, magnesium oxide, phosphate, montmorillonite, zeolite, activated carbon, biochar, etc.
[0029] In some specific embodiments of the present invention, the second maintenance time is 5-7 days;
[0030] In some specific embodiments of the present invention, similar to the first maintenance, appropriate water is sprayed to keep it moist and avoid exposure to sunlight; a waterproof cover is applied to isolate the air as much as possible, so that the moisture content of the second mixture is 30-40 wt%.
[0031] In some specific embodiments of the present invention, the mass of the heavy metal solidification agent added is 0.5-3 wt% of the mass of the contaminated clay.
[0032] In some specific embodiments of the present invention, the heavy metal content in the contaminated clay is 60-5500 mg / kg.
[0033] In some specific embodiments of the present invention, in the second mixture, the proportion of fine soil particles with a diameter of less than 0.075 mm in the contaminated clay is not less than 30%. Before solidifying the heavy metals, the contaminated clay can be pretreated to remove stones, buildings, and other debris from the contaminated soil, or the material after impurity removal can be sieved.
[0034] The second aspect of the present invention provides a roadbed material obtained by the method described in the first aspect.
[0035] In some specific embodiments of the present invention, the compressive strength of the roadbed material is not less than 3 MPa, preferably not less than 4 MPa.
[0036] According to a particularly preferred embodiment of the present invention, a method for preparing roadbed material is provided, comprising: first mixing contaminated clay treated with heavy metal solidification with crushed stone, cement, and an anti-permeability agent, and performing a first maintenance, such that the moisture content of the material obtained from the first mixture is 8-20 wt%; wherein the mass ratio of the contaminated clay treated with heavy metal solidification to crushed stone, cement, and anti-permeability agent is 10:(3-8):(0.8-2):(0.03-0.08); wherein the heavy metal solidification treatment includes: second mixing the contaminated clay and a heavy metal solidification agent to obtain a second mixture, and performing a second maintenance, such that the moisture content of the second mixture is 30-40 wt%; the average block diameter of the crushed stone is 5-10 cm; the cement is silicate cement; the anti-permeability agent is selected from one or more of organosilicon resin anti-permeability agents, silicate anti-permeability agents, or polyurethane anti-permeability agents; the first maintenance time is 2-5 days; and the second maintenance time is 5-7 days.
[0037] The present invention will be described in detail below through embodiments.
[0038] The method for detecting heavy metal content in contaminated clay is the soil pollutant analysis method in Table 3 of the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control (Trial)" (GB36600-2018).
[0039] The compaction degree was tested using the "Specifications for Testing Geotechnical Engineering of Highways" (JTG3430-2020).
[0040] The method for detecting the leaching concentration of heavy metals shown is the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ557-2010).
[0041] The moisture content was determined using the gravimetric method for the determination of dry matter and moisture in soil (HJ613-2011).
[0042] The compressive strength and permeability coefficient were tested using the "Geotechnical Testing Procedures" (SL237-1999).
[0043] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.
[0044] Example 1
[0045] In this embodiment, the contaminated clay is arsenic-contaminated clay with an arsenic concentration of 120 mg / kg. The proportion of fine soil particles with a diameter of less than 0.075 mm in the contaminated clay is not less than 40%.
[0046] (1) The arsenic-contaminated clay was pretreated by using an ALLU screening and crushing bucket to remove stones, buildings and other debris from the arsenic-contaminated clay and obtain contaminated clay with relatively uniform particle size.
[0047] (2) The pretreated contaminated clay and the heavy metal solidification agent were mixed according to the addition mass of heavy metal solidification agent (iron salt) being 0.8 wt% of the mass of contaminated clay. The stabilizing agent and the contaminated clay were thoroughly stirred to obtain a mixture, which was maintained for 5 days. During this maintenance process, the material was covered with tarpaulin, and the moisture content was controlled to be 35 wt% by detection and water spraying.
[0048] (3) The concentration of arsenic in the clay after maintenance was tested and the result was 0.003 mg / L, which meets the requirements of Class IV water quality standard in the "Groundwater Quality Standard" (GB14848-2017). The pH of the clay after maintenance was 7.5.
[0049] (4) According to the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent of 10:5:1:0.05, the contaminated clay after heavy metal solidification treatment is mixed with crushed stone, cement and anti-permeability agent. The average block diameter of crushed stone is 6.4cm, the cement is ordinary Portland cement P.O42.5, and the anti-permeability agent is sodium silicate anti-permeability agent. The mixture is thoroughly stirred and turned over 3 times by excavator.
[0050] (5) Maintain the mixed material for 3 days, sprinkling water appropriately during the maintenance process, avoiding exposure to the sun, and maintaining a moisture content of 18%;
[0051] (6) After the maintenance is completed, the material obtained from the maintenance is compacted to a compaction degree of 91.4%, and the subgrade material is obtained.
[0052] Example 2
[0053] In this embodiment, the contaminated clay is lead-contaminated clay with a lead concentration of 4250 mg / kg, and the proportion of fine soil particles with a diameter of less than 0.075 mm in the contaminated clay is not less than 38%.
[0054] (1) The lead-contaminated clay was pretreated by using an ALLU screening and crushing bucket to remove stones, buildings and other debris from the lead-contaminated clay, resulting in contaminated clay with relatively uniform particle size.
[0055] (2) The pretreated contaminated clay and the heavy metal solidification agent were mixed according to the addition mass of heavy metal solidification agent (iron salt and phosphate) being 2wt% of the mass of contaminated clay. The stabilizing agent and the contaminated clay were thoroughly stirred to obtain a mixture, which was maintained for 5 days. During this maintenance process, the material was covered with tarpaulin, and the moisture content was controlled to be 38% by detection and water spraying.
[0056] (3) The lead leaching solution concentration of the clay after maintenance was tested and the result was 0.008 mg / L, which meets the requirements of Class IV water quality standard in the "Groundwater Quality Standard" (GB14848-2017). The pH value of the clay after maintenance was 7.8.
[0057] (4) According to the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent of 10:6:1.3:0.06, the contaminated clay after heavy metal solidification treatment is mixed with crushed stone, cement and anti-permeability agent. The crushed stone has a particle size of 7cm, the cement is ordinary Portland cement P.O42.5, and the anti-permeability agent is sodium silicate anti-permeability agent. The mixture is thoroughly stirred and then turned over 4 times by an excavator.
[0058] (5) The mixed material is kept for 4 days. During the keeping process, water is sprinkled appropriately and exposure to the sun is avoided to keep the moisture content at 18.2%.
[0059] (6) After the maintenance is completed, the material obtained from the maintenance is compacted to a compaction degree of 93% to obtain the subgrade material.
[0060] Example 3
[0061] In this embodiment, the contaminated clay is chromium-contaminated clay, with a hexavalent chromium concentration of 98.6 mg / kg, and the proportion of fine soil particles with a diameter of less than 0.075 mm in the contaminated clay is not less than 35%.
[0062] (1) The chromium-contaminated clay was pretreated by using an ALLU screening and crushing bucket to remove stones, buildings and other debris from the chromium-contaminated clay, resulting in contaminated clay with a relatively uniform particle size.
[0063] (2) The pretreated contaminated clay and the heavy metal solidification agent were mixed according to the addition mass of the heavy metal solidification agent (sodium metabisulfite) being 2.4 wt% of the mass of the contaminated clay. The stabilizing agent and the contaminated clay were thoroughly stirred to obtain a mixture, which was maintained for 7 days. During this maintenance process, the material was covered with tarpaulin, and the moisture content was controlled to be 34% by detection and water spraying.
[0064] (3) The concentration of hexavalent chromium leaching solution in the maintained clay was tested, and the result was 0.002 mg / L of hexavalent chromium, which meets the requirements of Class IV water quality standard in the "Groundwater Quality Standard" (GB14848-2017). The pH value of the maintained clay was 7.6.
[0065] (4) According to the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent of 10:4:1.5:0.04, the contaminated clay after heavy metal solidification treatment is mixed with crushed stone, cement and anti-permeability agent. The crushed stone has a particle size of 9.2cm, the cement is ordinary Portland cement P.O52.5, and the anti-permeability agent is polyurethane anti-permeability agent. The mixture is thoroughly stirred and then turned over 4 times by an excavator.
[0066] (5) The mixed material is kept for 4 days. During the keeping process, water is sprinkled appropriately, and exposure to direct sunlight is avoided to keep the moisture content at 18.5%.
[0067] (6) After the maintenance is completed, the material obtained from the maintenance is compacted to a compaction degree of 92.3%, and the subgrade material is obtained.
[0068] Example 4
[0069] The method described in Example 1 is used with the soil from Example 1, except that the mass ratio of the contaminated clay after heavy metal solidification treatment to gravel, cement and impermeable agent is 10:2:0.7:0.02.
[0070] Example 5
[0071] The method in Example 1 was used with the soil from Example 1, except that in step (2), a second maintenance period of 2 days was performed and the moisture content in step (2) was 45%.
[0072] Example 6
[0073] The soil from Example 1 was used in accordance with the method in Example 1, except that in step (3), the pH of the clay was maintained at 9.5.
[0074] Example 7
[0075] The method described in Example 1 is used with the soil from Example 1, except that the average diameter of the crushed stone is 3.5 cm.
[0076] Example 8
[0077] The method described in Example 1 was used with the soil from Example 1, except that the proportion of the impermeable agent added was different, and the mass ratio of the contaminated clay after heavy metal solidification treatment to gravel, cement and impermeable agent was 10:5:1:0.01.
[0078] Example 9
[0079] The soil from Example 1 was used in accordance with the method described in Example 1, except that the contaminated clay contained 25% fine soil particles with a diameter of less than 0.075 mm.
[0080] Comparative Example 1
[0081] The soil from Example 1 was used in accordance with the method in Example 1, except that in step (5), the mixed material was maintained for 3 days to keep the moisture content at 27.5%.
[0082] Comparative Example 2
[0083] The method described in Example 1 was used with the soil from Example 1, except that the mass ratio of the contaminated clay after heavy metal solidification treatment to gravel, cement and impermeable agent was 10:0.5:0.3:0.007.
[0084] Comparative Example 3
[0085] The method of this comparative example follows the method in Example 1 using the soil in Example 1, except that the contaminated clay after heavy metal solidification treatment is first mixed with gravel and anti-seepage agent in a mass ratio of 10:1:0.05.
[0086] Comparative Example 4
[0087] The soil from Example 1 is used in accordance with the method in Example 1, except that no maintenance is performed in step (5), and compaction is carried out directly.
[0088] The moisture content, compressive strength, and permeability coefficient of the compacted test blocks were tested, and the test results are shown in Table 1.
[0089] Table 1
[0090]
[0091] As can be seen from the results in Table 1, the roadbed materials obtained by using the method described in this invention have significantly better compressive strength, permeability coefficient, and heavy metal leachate concentration.
[0092] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for preparing a roadbed material, characterized in that, include: The contaminated clay after heavy metal solidification treatment is first mixed with crushed stone, cement and anti-permeability agent, and then maintained for a first time, so that the moisture content of the material obtained from the first mixture is 8-20 wt%; wherein, the mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and anti-permeability agent is 10:(1-10):(0.5-5):(0.01-0.1).
2. The method according to claim 1, wherein, The average diameter of the crushed stone is 5-10 cm; And / or, the cement is silicate cement; And / or, in the contaminated clay after heavy metal solidification treatment, the concentration of heavy metal leachate is 0-0.1 mg / L; And / or, the pH of the contaminated clay after heavy metal solidification treatment is 6-9.
3. The method according to claim 1 or 2, wherein, The antipermeable agent is selected from one or more of organosilicon resin antipermeable agents, silicate antipermeable agents, or polyurethane antipermeable agents, preferably selected from one or more of sodium silicate antipermeable agents and polyurethane antipermeable agents.
4. The method according to claim 1 or 2, wherein, The mass ratio of the contaminated clay after heavy metal solidification treatment to crushed stone, cement and impermeable agent is 10:(3-8):(0.8-2):(0.03-0.08).
5. The method according to claim 1, wherein, The first maintenance period is 2-5 days; And / or, after the first maintenance, the mixture is compacted to a compaction degree of not less than 90%.
6. The method according to claim 1 or 5, wherein, The heavy metal solidification treatment method includes: mixing the contaminated clay and the heavy metal solidification agent in a second mixing process to obtain a second mixture, and maintaining the mixture in a second maintenance process to ensure that the moisture content of the second mixture is 30-40 wt%. The contaminated clay is heavy metal contaminated clay, and the heavy metal contained in the contaminated clay is selected from one or more of arsenic, lead, cadmium, chromium or nickel.
7. The method according to claim 6, wherein, The second maintenance period is 5-7 days.
8. The method according to claim 6 or 7, wherein, The mass of the heavy metal solidification agent added is 0.5-3 wt% of the mass of the contaminated clay.
9. The method according to claim 6 or 7, wherein, The heavy metal content in the contaminated clay ranges from 60 to 5500 mg / kg; And / or, in the second mixture, the proportion of fine soil particles with a diameter of less than 0.075 mm in the contaminated clay is not less than 30%.
10. The roadbed material obtained by the method according to any one of claims 1-9; Preferably, the compressive strength of the roadbed material is not less than 3 MPa, and more preferably not less than 4 MPa.