Heavy metal contaminated soil remediation agent and use method thereof

Abstract

The present invention belongs to the field of heavy metal contaminated soil remediation technology and provides a heavy metal contaminated soil remediation agent and its use method. The remediation agent is composed of the following substances in parts by weight: 35-45 parts red mud, 25-30 parts white mud, 15-20 parts iron sulfate, 2.5-7 parts calcium oxide, and 2.5-8 parts lime. The heavy metal contaminated soil remediation agent of the present invention is mainly based on red mud and white mud, solving the problem of resource utilization of red mud and white mud, turning waste into treasure; it has low cost, simple and easy use method, and great economic benefits; and can effectively repair soil contaminated by arsenic, cadmium, lead and their composite heavy metals.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal contaminated soil remediation, and in particular relates to a heavy metal contaminated soil remediation agent and a method of using the agent. Background Art

[0002] Heavy metal pollution in soils primarily involves pollutants such as cadmium, nickel, copper, arsenic, mercury, lead, chromium, and zinc. With the development of urbanization and industrialization, heavy metal pollution in soils caused by human factors is an increasingly serious environmental issue worldwide. Heavy metals, mostly non-ferrous metals, are widely used in all aspects of human production and daily life, but this also leads to serious soil heavy metal pollution.

[0003] Once a large amount of heavy metals enter the soil, they cannot be degraded and are difficult to migrate out of the soil. They will accumulate more and more, and their content will gradually increase, which will have obvious adverse effects on the physical and chemical properties of the soil, the biological characteristics of the soil, and the structure of the microbial community, and destroy the ecological structure and function of the soil. In addition, if the degree of heavy metal pollution in the soil is further aggravated, it will also pose a serious threat to the survival of the biological communities in the soil.

[0004] Excessive heavy metal levels in soil can directly harm crops and lead to plant death. Excessive heavy metal levels in soil can impair crop absorption of nutrients like nitrogen, phosphorus, and potassium, inhibiting growth and causing a decrease in agricultural yields. Furthermore, heavy metal contamination in soil can increase heavy metal levels in crops, leading to agricultural product contamination and threatening agricultural product quality and safety.

[0005] Pollutants such as heavy metals in the soil will pass through various food chains, accumulate in organisms step by step, and eventually cause harm to human health. They can also indirectly threaten human health by affecting the quality of water bodies and the atmospheric environment.

[0006] Due to inappropriate development and utilization in society, land pollution and ecological damage are becoming increasingly serious, seriously threatening human life, property, and the safety of the human living environment. Remediation of heavy metal contaminated soil is urgent. Therefore, the search for a remediation agent for heavy metal-contaminated soil with good remediation effects and low application costs is of great research value and practical significance. Summary of the Invention

[0007] The present invention provides a heavy metal contaminated soil remediation agent and a method for using the agent. The agent can effectively remediate soil contaminated with heavy metals, mainly arsenic, cadmium, and lead, and effectively reduce the effective content of heavy metals in the soil.

[0008] The invention provides a heavy metal contaminated soil remediation agent. The remediation agent is composed of the following substances in parts by mass: 35-45 parts of red mud, 25-30 parts of white mud, 15-20 parts of polyferric sulfate, 2.5-7 parts of calcium oxide, and 2.5-8 parts of lime.

[0009] Optionally, the red mud is Bayer red mud, which comes from an alumina plant, has a pH of 12-13, a calcium oxide content of 3.25%, an aluminum oxide content of 14.93%, a ferric oxide content of 46.78%, a silicon dioxide content of 3.64%, and a sodium oxide content of 2.8%; and the red mud particle size is 1-10 μm.

[0010] Optionally, the white mud comes from the alkali recovery section of a paper mill, the pH of the white mud is 10-11, the calcium carbonate content is 85%, the sodium carbonate content is 3.69%, the sodium chloride content is 0.45%, and the sodium hydroxide content is 0.8%.

[0011] Optionally, the polyferric sulfate comes from a steel plant and is polyferric sulfate prepared from pickling waste liquid of the steel plant.

[0012] Optionally, the heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 40 parts red mud, 28 parts white mud, 5 parts calcium oxide, 6 parts lime; and 18 parts polyferric sulfate.

[0013] The present invention also provides a method for using the heavy metal contaminated soil remediation agent, which comprises the following steps:

[0014] S1. Pre-treat the heavy metal contaminated soil to make its particle size less than 5 cm;

[0015] S2. Mix the heavy metal contaminated soil remediation agent (polyferric sulfate) with the pretreated heavy metal pollution and stir them thoroughly; after the reaction is complete, mix the heavy metal contaminated soil remediation agent (other component agents) with them and stir them, add water in small amounts to the obtained mixed solid several times, and the total amount of water added is 35-45% of the mass of the mixed solid, and stir them thoroughly;

[0016] S3. Compact, flatten and shape the fully stirred mixture, and transfer it to a dry, naturally ventilated and rainproof environment for curing for 10-15 days;

[0017] S4. Sample the mixture that has expired and send it for inspection to test the heavy metal leaching index. If it meets the standard, it can be used for terminal landfill, greening soil, and mine filling material.

[0018] Optionally, the heavy metal contaminated soil is slightly contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil at a mass ratio of 0.01-0.03:1, and the total amount of water added is 35% of the mixed solid mass.

[0019] Optionally, the heavy metal contaminated soil is lightly contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil at a mass ratio of 0.03-0.05:1, and the total amount of water added is 35% of the mixed solid mass.

[0020] Optionally, the heavy metal contaminated soil is moderately contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil in a mass ratio of 0.05-0.15:1, and the total amount of water added is 40% of the mixed solid mass.

[0021] Optionally, the heavy metal contaminated soil is severely contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil in a mass ratio of 0.15-0.6:1, and the total amount of water added is 40-45% of the mixed solid mass.

[0022] Red mud is a polluting industrial solid waste generated by the alumina industry. It's named for its rich iron oxide content and its resemblance to reddish earth. The main hazard of red mud comes from its high alkalinity. The large amount of alkaline substances in the leachate causes the pH value of the leachate to reach as high as 12-13. Current disposal methods rely on open-air accumulation, deep pit landfill, and the construction of red mud dams. These not only occupy large amounts of land and farmland, posing significant environmental risks, but also impose high maintenance and management costs on companies, leading to increased aluminum production costs. Therefore, there is an urgent need to address the red mud problem through resource utilization.

[0023] Papermaking white mud comes from the alkali recovery section, so it is also called causticized white mud. Its main component is calcium carbonate.

[0024] The present invention utilizes alkaline solid waste (red mud, white mud, etc.) to provide an alkaline environment for heavy metals in soil, which can form a gel state in the hydration reaction and is conducive to the conversion of heavy metals into hydroxides or carbonate precipitates or complexes with lower solubility.

[0025] Red mud and white mud can create an alkaline environment for contaminated soils, raising soil pH and increasing ion exchange, which can directly lead to or induce the precipitation of heavy metal hydroxides. Iron-based materials such as ferrous sulfate are widely available and inexpensive, and can interact with heavy metals like arsenic.

[0026] Red mud and white mud contain more Al, Si, Fe, and Mg oxides. Metal cations form hydroxyl states, which enhance their affinity with soil adsorption sites. Oxides such as Ca and Mg and aluminosilicate substances promote the transformation of heavy metals into silicate precipitation, increasing the soil's specific adsorption of heavy metals.

[0027] The present invention mainly uses red mud, white mud and iron sulfate as the main materials, providing a practical method for the resource utilization of bulk solid waste and the disposal of heavy metal contaminated soil. Its beneficial technical effects are as follows:

[0028] 1. The heavy metal contaminated soil remediation agent of the present invention is mainly composed of red mud, white mud and iron sulfate, which solves the problem of resource utilization of red mud and white mud and turns waste into treasure.

[0029] 2. The heavy metal contaminated soil remediation agent of the present invention has low cost, simple and easy use method, and great economic benefits.

[0030] 3. The present invention can effectively repair soil contaminated by arsenic, cadmium, lead and their combined heavy metals. DETAILED DESCRIPTION

[0031] The following will describe the embodiments of the present invention in detail with reference to examples, thereby illustrating how the present invention applies technical means to solve technical problems, achieve technical effects, and be implemented accordingly.

[0032] Example 1

[0033] A heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 45 parts red mud, 25 parts white mud, 2.5 parts calcium oxide, 8 parts lime, and 20 parts polyferric sulfate.

[0034] Example 2

[0035] A heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 35 parts red mud, 30 parts white mud, 7 parts calcium oxide, 2.5 parts lime, and 15 parts polyferric sulfate.

[0036] Example 3

[0037] A heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 40 parts red mud, 28 parts white mud, 18 parts polyferric sulfate, 5 parts calcium oxide, and 6 parts lime.

[0038] Example 4

[0039] A heavy metal contaminated soil remediation agent is composed of the following substances in parts by weight: 38 parts red mud, 26 parts white mud, 4 parts calcium oxide, 5 parts lime, and 17 parts polyferric sulfate.

[0040] Example 5

[0041] A heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 42 parts red mud, 32 parts white mud, 6 parts calcium oxide, 4 parts lime, and 19 parts polyferric sulfate.

[0042] In Examples 1-5, the red mud is Bayer red mud, which is derived from an alumina plant, has a pH of 12-13, a calcium oxide content of 3.25%, an aluminum oxide content of 14.93%, a ferric oxide content of 46.78%, a silicon dioxide content of 3.64%, and a sodium oxide content of 2.8%. The red mud particle size is 1-10 μm, and the internal and external radiation indicators of the Bayer red mud are 0.14 and 0.17, respectively (both lower than the control indicator 1), meeting the national standard for Class A building materials (Limits of Radioactive Nuclides in Building Materials (GB656 6-2010), and its production, sales and use are not restricted; the white mud comes from the alkali recovery section of the paper mill, the pH of the white mud is 10-11, the calcium carbonate content is 85%, the sodium carbonate content is 3.69%, the sodium chloride content is 0.45%, and the sodium hydroxide content is 0.8%. The internal and external radiation indicators of the papermaking white mud are 0.3 and 0.53 respectively (both lower than the control indicator 1), meeting the national standard for Class A building materials (Limits of Radioactive Nuclides in Building Materials (GB6566-2010)), and its production, sales and use are not restricted.

[0043] The usage of Example 1-5 is:

[0044] S1. Pre-treat the heavy metal contaminated soil to make its particle size less than 5 cm;

[0045] S2. Mix the heavy metal contaminated soil remediation agent (polyferric sulfate) with the pretreated heavy metal pollution and stir them thoroughly; after the reaction is complete, mix the heavy metal contaminated soil remediation agent (other component agents) with them and stir them, add water in small amounts to the obtained mixed solid several times, and the total amount of water added is 35-45% of the mass of the mixed solid, and stir them thoroughly;

[0046] S3. Compact, flatten and shape the fully stirred mixture, and transfer it to a dry, naturally ventilated and rainproof environment for curing for 10-15 days;

[0047] S4. Sample the mixture that has expired and send it for inspection to test the heavy metal leaching index. If it meets the standard, it can be used for terminal landfill, greening soil, and mine filling material.

[0048] In Examples 1-5, the heavy metal contaminated soil is soil contaminated by arsenic, cadmium, and lead alone or in combination.

[0049] If the pollutant content does not exceed the assessment standard, it is considered non-polluting; if it is between 1 and 2 times (inclusive), it is considered slightly polluted; if it is between 2 and 3 times (inclusive), it is considered lightly polluted; if it is between 3 and 5 times (inclusive), it is considered moderately polluted; if it is more than 5 times, it is considered severely polluted.

[0050] Heavy metal content testing standards:

[0051] The heavy metal leaching concentration is monitored using the Horizontal Oscillation Method for Leaching Toxicity of Solid Waste (HJ557-2010). The leaching toxicity of the treated soil is no higher than the maximum allowable emission concentration in the Integrated Sewage Discharge Standard (GB8978-1996) (arsenic < 0.5 mg / L, cadmium < 0.1 mg / L, lead < 1 mg / L).

[0052] Examples 1-5 were used to remediate different heavy metal contaminated soils. After 15 days of curing, the heavy metal leaching content was tested. The test results are as follows:

[0053]

[0054] Note: “ND” means not detected

[0055] The above test results show that the heavy metal contaminated soil remediation agent of the present invention can effectively remediate single or composite contaminated soil of arsenic, cadmium and lead. It has low cost and simple and easy use method. It solves the problem of resource utilization of red mud, white mud and iron sulfate, turning waste into treasure, has great economic and environmental benefits, and has great market prospects.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A heavy metal contaminated soil remediation agent, the remediation agent is composed of the following substances in parts by weight: Red mud 35-45, white mud 25-30, polyferric sulfate 15-20, calcium oxide 2.5-7, lime 2.5-8; The red mud is Bayer red mud, which comes from an alumina plant, has a pH of 12-13, a calcium oxide content of 3.25%, an aluminum oxide content of 14.93%, a ferric oxide content of 46.78%, a silicon dioxide content of 3.64%, and a sodium oxide content of 2.8%; and a red mud particle size of 1-10 μm. The white mud comes from the alkali recovery section of a paper mill. The pH of the white mud is 10-11, and the calcium carbonate content is 85%, the sodium carbonate content is 3.69%, the sodium chloride content is 0.45%, and the sodium hydroxide content is 0.8%.

2. The heavy metal contaminated soil remediation agent according to claim 1, characterized in that: The polyferric sulfate comes from a steel plant and is prepared from the pickling waste liquid of the steel plant.

3. The heavy metal contaminated soil remediation agent according to claim 1, characterized in that The heavy metal contaminated soil remediation agent is composed of the following substances in parts by mass: 40 parts red mud, 28 parts white mud, 18 parts polyferric sulfate, 5 parts calcium oxide, and 6 parts lime.

4. A method for using the heavy metal contaminated soil remediation agent according to any one of claims 1 to 3, comprising the following steps: S1. Pre-treat the heavy metal contaminated soil to make its particle size less than 5 cm; S2. Mix the polyferric sulfate in the heavy metal contaminated soil remediation agent with the pretreated heavy metal pollution and stir them thoroughly; after the reaction is complete, mix and stir the other components of the heavy metal contaminated soil remediation agent with them, and add water in small amounts to the obtained mixed solid several times, with the total amount of water added being 35-45% of the mass of the mixed solid, and stir thoroughly; S3. Compact, flatten and shape the fully stirred mixture, and transfer it to a dry, naturally ventilated and rainproof environment for curing for 10-15 days; S4. Sample the mixture that has expired and send it for inspection to test the heavy metal leaching index. If it meets the standard, it can be used for terminal landfill, greening soil, and mine filling material.

5. The method for using the heavy metal contaminated soil remediation agent according to claim 4, characterized in that: The heavy metal contaminated soil is slightly contaminated soil. The heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil in a mass ratio of 0.01-0.03:1, and the total amount of water added is 35% of the mixed solid mass.

6. The method for using the heavy metal contaminated soil remediation agent according to claim 4, characterized in that: The heavy metal contaminated soil is lightly contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil at a mass ratio of 0.03-0.05:1, and the total amount of water added is 35% of the mixed solid mass.

7. The method for using the heavy metal contaminated soil remediation agent according to claim 4, characterized in that: The heavy metal contaminated soil is moderately contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil at a mass ratio of 0.05-0.15:1, and the total amount of water added is 40% of the mixed solid mass.

8. The method for using the heavy metal contaminated soil remediation agent according to claim 4, characterized in that: The heavy metal contaminated soil is severely contaminated soil, and the heavy metal contaminated soil remediation agent is mixed with the pretreated heavy metal contaminated soil in a mass ratio of 0.15-0.6:1, and the total amount of water added is 40-45% of the mixed solid mass.

Images