A soil-contaminating in-situ blocking material and a method for preparing the same

Abstract

The present application relates to the technical field of soil remediation, and more particularly to a polluted soil in-situ blocking material, which uses regional in-situ soil as a main matrix raw material, significantly reduces the construction cost of the blocking material, and cooperates with fly ash, cementing material and modified bentonite and other concrete raw materials to form a blocking material with stable structure, no loose structure and outstanding anti-seepage performance, which has a good application prospect in the application process of preparing a blocking wall and preventing soil pollution and underground water.

Description

Technical Field

[0001] This invention belongs to the field of soil pollution control, and in particular relates to an in-situ blocking material for contaminated soil and its preparation method. Background Technology

[0002] The quality of water resources not only affects human health but also plays a vital role in social stability and development. Therefore, the treatment and prevention of groundwater pollution is of paramount importance.

[0003] For soil sites already contaminated with heavy metals, taking appropriate anti-seepage measures to block the pathways of pollutants into the groundwater environment is the main measure for isolating pollution and preventing groundwater pollution. Currently, the most widely used method in the industry is to construct barrier walls. However, traditional cement barrier walls are very expensive to build and have poor anti-seepage performance. During use, they often experience problems such as failure of anti-seepage performance and degradation of adsorption performance, which limits the promotion of barrier walls.

[0004] Therefore, there is an urgent need to develop a barrier wall material with low construction cost and excellent seepage prevention performance. Summary of the Invention

[0005] To address the technical problems of high construction cost, weak seepage prevention and adsorption performance, and short effective period of traditional cement barrier walls in existing technologies, this invention provides an in-situ barrier material for contaminated soil. This material uses regional in-situ soil as the main raw material, combined with modified bentonite, fly ash, and other materials, to prepare a barrier wall with outstanding seepage prevention performance and low construction cost, showing great application prospects in the prevention and control of soil pollution and groundwater.

[0006] To achieve the above-mentioned objectives, the embodiments of the present invention employ the following technical solutions:

[0007] On the one hand, embodiments of the present invention provide an in-situ blocking material for contaminated soil, which specifically comprises the following substances in mass percentage: 40% to 60% regional in-situ soil, 5% to 10% modified bentonite, 10% to 20% fly ash, 20% to 30% cementing material, 2% to 5% calcium oxide and 2% to 5% potassium polycarboxylate.

[0008] Compared to existing technologies, the in-situ contaminated soil blocking material provided by this invention uses locally sourced soil as the main matrix material, which is readily available and reduces the construction cost of the barrier material. The concrete raw materials, such as fly ash, cementitious materials, and modified bentonite, can rapidly and stably adsorb heavy metals. Furthermore, with the synergistic effect of auxiliary materials such as calcium oxide and potassium polycarboxylate, they can combine with the locally sourced soil, significantly reducing the soil's permeability coefficient, thus forming a structurally stable and non-loose blocking material with excellent seepage prevention performance. The blocking material provided by this invention has excellent application prospects in the preparation of barrier walls and the prevention and control of soil-contaminated groundwater.

[0009] Preferably, the modified bentonite is cellulose-modified bentonite, and its preparation raw materials include the following components in mass percentage: sodium bentonite 75%–85%, carboxymethyl cellulose 2%–5%, hydroxypropyl methyl cellulose 5%–10%, and polyanionic cellulose 5%–10%.

[0010] Modifying sodium-based bentonite with specific amounts of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose can reduce the particle size of bentonite and improve its impermeability. Furthermore, it imbues the modified bentonite with a negative charge, which, combined with the hydroxyl groups in the cellulose structure, significantly enhances the bentonite's ability to chelate and adsorb heavy metal ions. Using cellulose-modified bentonite as a raw material for blocking materials significantly improves both the impermeability and heavy ion adsorption performance of these materials.

[0011] Preferably, the degree of substitution of carboxymethyl cellulose is ≥0.8, the degree of substitution of hydroxypropyl methyl cellulose is ≥1.5, and the molecular weight of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose is below 10. -6 -10 -4 between.

[0012] Carboxymethyl cellulose and hydroxypropyl cellulose with optimized substitution degrees exhibit superior mechanical properties. When modifying bentonite, they do not reduce the strength, toughness, or other mechanical properties of the bentonite material. Furthermore, using cellulose with optimized molecular weight can further enhance the modification effect on bentonite and allow for further control over the particle size of the bentonite, thereby improving the performance of the blocking material.

[0013] Preferably, the modified bentonite is prepared by taking each raw material according to the mass percentage, grinding sodium bentonite to ≤200 mesh, and grinding carboxymethyl cellulose, hydroxypropyl methyl cellulose and polyanionic cellulose to ≤100 mesh, and then adding them to a sealed container and stirring until they are mixed evenly to obtain the modified bentonite.

[0014] Preferably, the cementing material is one or a mixture of two or more of the following: sulfoaluminate cement, ferroaluminate cement, and phosphate cement.

[0015] The selected cement raw materials not only ensure that the barrier material forms a whole and has excellent mechanical properties, but also introduce elements such as aluminum, iron, and phosphorus into the barrier material that have a fixing effect on heavy metal elements, thereby further improving the barrier material's impermeability and heavy metal ion adsorption capacity.

[0016] Preferably, the preparation method of the in-situ soil blocking material specifically includes the following steps:

[0017] Step A: Prepare each raw material according to the mass percentage, and mix the modified bentonite, fly ash and cementitious material evenly to obtain premix a;

[0018] Step B: After the calcium oxide and potassium polycarboxylate are dissolved in water, they are added to the premix a and mixed evenly to obtain premix b;

[0019] Step C: After the premix b is mixed with the in-situ soil, water equivalent to 20% to 40% of the mass of the in-situ soil is added and stirred to obtain the soil in-situ blocking material.

[0020] On the other hand, the present invention also provides the application of the above-mentioned in-situ soil blocking materials in the process of contaminated soil management and remediation. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] In the following examples, the soil used was excavated in situ from a contaminated site surrounding a steel plant in northern China.

[0023] The soil at this site contains arsenic, cadmium, and lead levels exceeding the risk control values ​​for Class II land use in the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control" (GB36600-2018). Specifically, the arsenic content is 180 mg / kg, the cadmium content is 200 mg / kg, and the lead content is 2800 mg / kg.

[0024] The soil in areas with light or no pollution was selected for excavation. The excavated soil was subjected to leaching tests using the acetic acid buffer solution method (HJT300-2007) for leaching toxicity of solid waste. The content of heavy metals arsenic, cadmium, and lead in the leachate was tested, and all of them met the Class IV standard in the Surface Water Quality Standard (GB3838-2002). Therefore, this excavated soil can be used as regional in-situ soil in the in-situ barrier material for contaminated soil.

[0025] Example 1

[0026] This embodiment provides an in-situ containment material for contaminated soil, which comprises the following substances in mass percentage: 40% regional in-situ soil, 10% cellulose-modified bentonite, 20% fly ash, 25% sulfoaluminate cement, 3% calcium oxide, and 3% potassium polycarboxylate.

[0027] The cellulose-modified bentonite is made from sodium bentonite, carboxymethyl cellulose with a degree of substitution of 1.0–1.2, hydroxypropyl methyl cellulose with a degree of substitution of 1.5–1.8, and polyanionic cellulose. The mass percentage of each raw material is as follows: sodium bentonite 80%, carboxymethyl cellulose 5%, hydroxypropyl methyl cellulose 10%, and polyanionic cellulose 5%. The molecular weights of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose are all within 10. -6 -10 -4 between;

[0028] The specific preparation method of cellulose-modified bentonite is as follows:

[0029] Sodium-based bentonite was ground to ≤200 mesh, and carboxymethyl cellulose, hydroxypropyl methyl cellulose and polyanionic cellulose were ground to ≤100 mesh. All raw materials were then added to a dry powder mixer and stirred at 80 rpm for 30 minutes to obtain the cellulose-modified bentonite.

[0030] The preparation method of this soil-blocking material specifically includes the following steps:

[0031] Step A: Prepare each raw material according to the mass percentage, and mix the modified bentonite, fly ash and cementitious material evenly to obtain premix a;

[0032] Step B: After dissolving calcium oxide and potassium polycarboxylate in water, add them to premix a and mix evenly to obtain premix b;

[0033] Step C: After mixing premix b with the in-situ soil, add water equivalent to 30% of the mass of the in-situ soil, stir, and the in-situ blocking material of the soil is obtained.

[0034] This embodiment also provides the application of the soil in-situ barrier material in the process of soil management and remediation, that is, using conventional processes to make a barrier wall to isolate contaminated soil from groundwater.

[0035] Example 2

[0036] This embodiment provides an in-situ containment material for contaminated soil, which comprises the following substances in mass percentage: 50% regional in-situ soil, 8% cellulose-modified bentonite, 15% fly ash, 20% phosphate cement, 5% calcium oxide, and 2% potassium polycarboxylate.

[0037] The cellulose-modified bentonite is made from sodium bentonite, carboxymethyl cellulose with a degree of substitution of 0.8–1.2, hydroxypropyl methyl cellulose with a degree of substitution of 1.5–1.8, and polyanionic cellulose. The mass percentage of each raw material is as follows: sodium bentonite 78%, carboxymethyl cellulose 2%, hydroxypropyl methyl cellulose 10%, and polyanionic cellulose 10%. The molecular weights of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose are all within 10. -6 -10 -4 between;

[0038] The specific preparation method of cellulose-modified bentonite is as follows:

[0039] Sodium-based bentonite was ground to ≤200 mesh, and carboxymethyl cellulose, hydroxypropyl methyl cellulose and polyanionic cellulose were ground to ≤100 mesh. All raw materials were then added to a dry powder mixer and stirred at 80 rpm for 30 minutes to obtain the cellulose-modified bentonite.

[0040] The preparation method of this soil-blocking material specifically includes the following steps:

[0041] Step A: Prepare each raw material according to the mass percentage, and mix the modified bentonite, fly ash and cementitious material evenly to obtain premix a;

[0042] Step B: After dissolving calcium oxide and potassium polycarboxylate in water, add them to premix a and mix evenly to obtain premix b;

[0043] Step C: After mixing premix b with the in-situ soil, add water equivalent to 30% of the mass of the in-situ soil, stir, and the in-situ blocking material of the soil is obtained.

[0044] This embodiment also provides the application of the soil in-situ barrier material in the process of soil management and remediation, that is, using conventional processes to make a barrier wall to cut off the direct connection between contaminated soil and groundwater.

[0045] Example 3:

[0046] This embodiment provides an in-situ containment material for contaminated soil, which comprises the following substances in mass percentage: 55% regional in-situ soil, 5% cellulose-modified bentonite, 10% fly ash, 25% aluminoferrite cement, 2% calcium oxide, and 3% potassium polycarboxylate.

[0047] The cellulose-modified bentonite is made from sodium bentonite, carboxymethyl cellulose with a degree of substitution of 0.8–1.2, hydroxypropyl methyl cellulose with a degree of substitution of 1.5–1.8, and polyanionic cellulose. The mass percentage of each raw material is as follows: sodium bentonite 78%, carboxymethyl cellulose 2%, hydroxypropyl methyl cellulose 10%, and polyanionic cellulose 10%. The molecular weights of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose are all within 10. -6 -10 -4 between;

[0048] The specific preparation method of cellulose-modified bentonite is as follows:

[0049] Sodium-based bentonite was ground to ≤200 mesh, and carboxymethyl cellulose, hydroxypropyl methyl cellulose and polyanionic cellulose were ground to ≤100 mesh. All raw materials were then added to a dry powder mixer and stirred at 80 rpm for 30 minutes to obtain the cellulose-modified bentonite.

[0050] The preparation method of this soil-blocking material specifically includes the following steps:

[0051] Step A: Prepare each raw material according to the mass percentage, and mix the modified bentonite, fly ash and cementitious material evenly to obtain premix a;

[0052] Step B: After dissolving calcium oxide and potassium polycarboxylate in water, add them to premix a and mix evenly to obtain premix b;

[0053] Step C: After mixing premix b with the in-situ soil, add water equivalent to 30% of the mass of the in-situ soil, stir, and the in-situ blocking material of the soil is obtained.

[0054] This embodiment also provides the application of the soil in-situ barrier material in the process of soil management and remediation, that is, using conventional processes to make a barrier wall to cut off the direct connection between contaminated soil and groundwater.

[0055] Comparative Example 1:

[0056] This comparative example provides an in-situ blocking material for contaminated soil. Compared with Example 1, this material is identical to Example 1 except that the cellulose-modified bentonite used is replaced with an equal amount of sodium-based bentonite.

[0057] Comparative Example 2:

[0058] This comparative example provides an in-situ blocking material for contaminated soil. Compared with Example 1, this material differs in that, in the raw materials used to prepare the cellulose-modified bentonite, the degree of substitution of carboxymethyl cellulose is 0.4–0.6, the degree of substitution of hydroxypropyl methyl cellulose is 1.0–1.4, and the molecular weights of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose are greater than 10. -4 Except for the raw materials and preparation methods, the rest are consistent with those in Example 1.

[0059] Comparative Example 3:

[0060] This comparative example provides an in-situ blocking material for contaminated soil. Compared with Example 1, this material is identical in all raw materials and preparation methods except that the sulfoaluminate cement used is replaced with an equal amount of silicate cement.

[0061] Detection example

[0062] The in-situ barrier materials for contaminated soil prepared in Examples 1-3 and Comparative Examples 1-3 were used to fill identical cuboid molds. After the barrier materials solidified at room temperature, the molds were removed to obtain barrier wall samples of the same specifications. An improved filtration loss experiment was used to verify the barrier wall samples' ability to block heavy metal ions. The filtrate was an artificially prepared simulated heavy metal contamination solution with arsenic content of 80 mg / kg, cadmium content of 3 mg / kg, and lead content of 20 mg / kg. The permeability coefficient test results of each sample are shown in the table below:

[0063] project Permeability coefficient (m / s) Example 1 <![CDATA[4.8*10 -6 ]]> Example 2 <![CDATA[5.2*10 -6 ]]> Example 3 <![CDATA[6.2*10 -6 <!-- 4 -->]]> Comparative Example 1 <![CDATA[1.2*10 -5 ]]> Comparative Example 2 <![CDATA[9.8*10 -5 ]]> Comparative Example 3 <![CDATA[9.5*10 -5 ]]>

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A material for blocking in-situ contaminated soil, characterized by, The material specifically comprises the following mass percentage of substances: 40-60% of regional in-situ soil, 5-10% of modified bentonite, 10-20% of fly ash, 20-30% of cementing material, 2-5% of calcium oxide and 2-5% of potassium polycarboxylate; the cementing material is at least one of sulphoaluminate cement, ferroaluminate cement and phosphate cement; The modified bentonite is cellulose modified bentonite, and the preparation raw material comprises the following mass percentage of components: 75-85% of sodium-based bentonite, 2-5% of carboxymethyl cellulose, 5-10% of hydroxypropyl methyl cellulose and 5-10% of polyanionic cellulose; The degree of substitution of the carboxymethyl cellulose is ≥0.8, and the degree of substitution of the hydroxypropyl methyl cellulose is ≥1.

5.

2. The contaminated soil in situ barrier material of claim 1, wherein, The carboxymethyl cellulose, hydroxypropyl methyl cellulose, and polyanionic cellulose have a molecular weight of between 10 -6 -10 -4 thousand and 100 thousand.

3. The contaminated soil in situ barrier material of Claim 1, wherein, The preparation method of the modified bentonite is that, taking each raw material by mass percentage, grinding the sodium-based bentonite to ≤200 mesh, grinding the carboxymethyl cellulose, hydroxypropyl methyl cellulose and polyanionic cellulose to ≤100 mesh, then adding them into a sealed container to stir and mix uniformly to obtain the modified bentonite.

4. The contaminated soil in situ barrier material of Claim 1, wherein, The preparation method of the contaminated soil in-situ blocking material specifically comprises the following steps: Step A: preparing each raw material by mass percentage, mixing the modified bentonite, fly ash and cementing material uniformly to obtain premix a; Step B: dissolving the calcium oxide and potassium polycarboxylate in water, then adding them into the premix a to mix uniformly to obtain premix b; Step C: mixing the premix b with the regional in-situ soil, adding water equivalent to 20-40% of the mass of the regional in-situ soil to stir to obtain the contaminated soil in-situ blocking material.

5. Application of the contaminated soil in-situ blocking material according to any one of claims 1-4 in the process of contaminated soil control and remediation.